Control of a Three-Phase Power Converter Connected to Unbalanced Power Grid in a Non-Cartesian Oblique Frame

ABSTRACT:

The paper presents a new approach to positive and negative sequence current vector control of a grid connected three-phase three-wire power electronic converter operating under grid voltage imbalance conditions. The concept utilizes representation of unbalanced converter current in the new coordinates frame in which the current vector components are constant. The nonlinear trigonometric transformation of two-dimensional current vector components from the stationary frame to the new frame is found on-line depending on the reference current asymmetry. The presented concept of new coordinates utilization allows implementation of proportional-integral terms as current regulators without the use of resonant terms and without the use of the measured current symmetrical sequences decomposition. The paper presents the theoretical approach, simulation results, as well as laboratory tests results.

KEYWORDS:

  1. AC–DC power conversion
  2. Current control
  3. Clarke’s transformation
  4.  Park’s transformation

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Scheme of the power circuit of a three-phase power electronic converter operating with unbalanced grid voltage.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results showing the new trigonometric transformation properties in the case in which the asymmetry factor is out of the dead-zone.

Fig. 3. Simulation results showing the new trigonometric transformation properties in the case in which the asymmetry factor crosses the dead-zone

Fig. 4. Simulation results showing the reference vector hodograph in the case in which the asymmetry factor crosses the dead-zone.

Fig. 5. Simulation results presenting three-phase grid voltage (a), and three-phase unbalanced current for DSFR control with notch filters (b), DSFR control with positive and negative sequence decoupling (c), oscillatory terms based current controllers (d), and proposed current control method (e) during reference step change of the converter current imbalance.

Fig. 6. Simulation results presenting operation of the grid power converter with the new transformations application for the case of grid voltage imbalance compensation and fundamental positive sequence component sag compensation (0-0.05s – initial state, 0.05-0.3s – no load operation with imbalance and sag compensation, 0.3-0.5s – imbalance and sag compensation with simultaneous dc bus feeding from external source by 26kW of power (inverter operation mode).

CONCLUSION:

The paper presents a new transformation of unbalanced three-phase signals to the oblique non-Cartesian frame in which the obtained signals in the new frame have equal amplitudes and are shifted by despite three-phase signals imbalance. Thus in a new frame the vector is seen as balanced. Transformed next to the rotating frame using Park’s transformation the vector components are constant. The proposed transformation from stationary to new frame and next from to the frame was used in the voltage oriented vector control of a three-phase grid converter.

The new transformation parameters can be relatively simply found based on reference positive and negative sequence current vector components, making it possible to obtain any imbalance of converter current depending on the outer control loops referencing current vector components.

The method has a limitation in a narrow range of current asymmetries, where the magnitude of positive sequence vector is close to the magnitude of the negative sequence vector, therefore a dead-zone is implemented to avoid converter operation in this narrow range. Simulation and experimental results show that the method works in a stable manner even when crossing the dead-zone. Simulation and experimental tests were done with disabled outer control loops of dc and ac voltage (so with arbitrarily referenced positive and negative sequence components) and with enabled outer control loops. In both cases the results are satisfactory.

REFERENCES:

[1] VDE–AR–N 4120: Technical requirements for the connection and operation of customer installations to the high–voltage network VDE, Jan. 2015, Germany.

[2] M. M. Baggu, B. H. Chowdhury and J. W. Kimball, “Comparison of Advanced Control Techniques for Grid Side Converter of Doubly-Fed Induction Generator Back-to-Back Converters to Improve Power Quality Performance During Unbalanced Voltage Dips,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 3, no. 2, June 2015, pp. 516-524.

[3] W. Liu, F. Blaabjerg, D. Zhou and S. Chou, “Modified Instantaneous Power Control with Phase Compensation and Current-limited Function under Unbalanced Grid Faults,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 9, no. 3, June 2021, pp. 2896 – 2906.

[4] Y. Du, X. Lu, H. Tu, J. Wang and S. Lukic, “Dynamic Microgrids With Self-Organized Grid-Forming Inverters in Unbalanced Distribution Feeders,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 8, no. 2, June 2020, pp. 1097-1107.

[5] A. Mora, R. Cárdenas, M. Urrutia, M. Espinoza and M. Díaz, “A Vector Control Strategy to Eliminate Active Power Oscillations in Four-Leg Grid-Connected Converters Under Unbalanced Voltages,” IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 8, no. 2, June 2020, pp. 1728-1738.

Analysis of Fractional Order Sliding Mode Control in a D-STATCOM Integrated Power Distribution System

ABSTRACT:

At present, the disturbances like the voltage fluctuations, resulting from the grid’s complexities and unbalanced load conditions, create severe power quality concerns like total harmonic distortion (THD) and voltage unbalance factor (VUF) of the grid voltage. Though the custom power devices such as distribution-static compensators (D-STATCOMs) improve these power quality concerns, however, the accompanying controller plays the substantial role. Therefore, this paper proposes a fractional-order sliding mode control (FOSMC) for a D-STATCOM to compensate the low power distribution system by injecting/absorbing a specific extent of the reactive power under disturbances. FOSMC is a non-linear robust control in which the sliding surface is designed by using the Riemann-Liouville (RL) function and the chattering phenomenon is minimized by using the exponential reaching law. The stability of FOSMC is evidenced by employing the Lyapunov stability criteria. Moreover, the performance of the proposed FOSMC is further accessed while doing its parametric variations. The complete system is demonstrated with a model of 400V, 180kVA radial distributor along with D-STATCOM under two test scenarios in MATLAB/Simulink environment. The results of the proposed controller are compared with the fixed frequency sliding mode control (FFSMC) and conventional proportional-integral (PI) control. The results validate the superiority of the proposed controller in terms of rapid tracking, fast convergence, and overall damping with very low THD and VUF.

KEYWORDS:

  1. Power quality
  2. Custom power devices
  3. Distribution static compensator
  4. Fractional order
  5. Sliding mode control
  6. Total harmonic distortion
  7. Voltage unbalance factor

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Figure 1. Simplified Model Of D-Statcom Configuration.

EXPECTED SIMULATION RESULTS:

Figure 2. (A) Three-Phase Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid (B) Rms Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid (C) Load Active And Reactive Power Under Voltage Sag/Swell Of Main Grid.

Figure 3. (A) Three-Phase Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Pi Control (B) Rms Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Pi Control (C) Three-Phase Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Ffsmc (D) Rms Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Ffsmc (E) Three-Phase Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Fosmc (F) Rms Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Fosmc.

Figure 4. (A) Load Active And Reactive Power Under Voltage Sag/Swell With D-Statcom While Employing Pi Control (B) Load Active And Reactive Power Under Voltage Sag/Swell With D-Statcom While Employing Ffsmc (C) Load Active And Reactive Power Under Voltage Sag/Swell With D-Statcom While Employing Fosmc.

Figure 5. (A) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Pi Control (B) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Ffsmc.

Figure 6. (A) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Fosmc With _ D 0:2 And Kd , Kq D 5 _ 106 (B) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Fosmc With _ D 0:5 And Kd ; Kq D 5 _ 106 (C) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Fosmc With _ D 0:8 And Kd , Kq D 5 _ 106 (D) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Fosmc With _ D 0:5 And Kd , Kq D 3 _ 104:

CONCLUSION:

In this paper, the authors have proposed a FOSMC based DSTATCOM to compensate the low power distribution system under disturbances such as voltage sag/swell and unbalanced load conditions. Besides, the performance of the FOSMC under its parametric variations is discussed as well. The complete system is demonstrated with a model of 400V, 180kVA radial distributor along with D-STATCOM under two test scenarios in MATLAB/Simulink environment. In the first test scenario, the grid transients (voltage sag/swell) are considered at the LV AC bus. Likewise, in the second test scenario, the unbalanced load conditions are considered at the LV AC bus. D-STATCOM sustains the voltage at LV AC bus by injecting/absorbing a certain extent of reactive power under voltage sag/swell and unbalanced load conditions. The results of the proposed controller are compared with fixed frequency sliding mode control (FFSMC) and conventional proportional-integral (PI) control. The results validate the superiority of the proposed controller in terms of rapid tracking, fast convergence, and overall damping with very low THD, and VUF. In the first test scenario, the voltage THD of proposed FOSMC during voltage sag/swell results in 0.52% in contrast to FFSMC and PI control which have THD of 0.84% and 2.17% respectively. In the second test scenario, the voltage THD of proposed FOSMC during unbalanced load conditions results in 0.97% in contrast to FFSMC and PI control which have THD of 1.96% and 3.63%. Likewise, the VUF under unbalanced load conditions with proposed FOSMC is 0.0014% in contrast to FFSMC and PI control which have VUF of 0.02% and 0.71%. In terms of assessment with existing SMC schemes, the proposed FOSMC has a very high response time, very high accuracy, very high robustness, lowest chattering along with low THD and VUF. The proposed model could be realized on the hardware platform for real-time verification purposes in future applications.

REFERENCES:

[1] A. Q. Al-Shetwi, M. A. Hannan, K. P. Jern, A. A. Alkahtani, and A. E. P. Abas, “Power quality assessment of grid-connected PV system in compliance with the recent integration requirements,” Electronics, vol. 9, no. 2, p. 366, Feb. 2020.

[2] A. D. J. C. Leal, C. L. T. Rodríguez, and F. Santamaria, “Comparative of power calculation methods for single-phase systems under sinusoidal and non-sinusoidal operation,” Energies, vol. 13, no. 17, p. 4322, Aug. 2020.

[3] E. Hossain, M. R. Tür, S. Padmanaban, S. Ay, and I. Khan, “Analysis and mitigation of power quality issues in distributed generation systems using custom power devices,” IEEE Access, vol. 6, pp. 16816_16833, 2018.

[4] F. R. Islam, K. Prakash, K. A. Mamun, A. Lallu, and H. R. Pota, “Aromatic network: A novel structure for power distribution system,” IEEE Access, vol. 5, pp. 25236_25257, 2017.

[5] A. A. Alkahtani, S. T. Y. Alfalahi, A. A. Athamneh, A. Q. Al-Shetwi, M. B. Mansor, M. A. Hannan, and V. G. Agelidis, “Power quality in microgrids including supraharmonics: Issues, standards, and mitigations,” IEEE Access, vol. 8, pp. 127104_127122, 2020.

Analysis and Design of Hybrid Harmonic Suppression Scheme for VSG Considering Nonlinear Loads and Distorted Grid

ABSTRACT:

 The power quality of virtual synchronous generator (VSG) inevitably deteriorates in the presence of local nonlinear loads and distorted grid. In this paper, the conflict involved in the simultaneous elimination of distortion for both the inverter local load voltage and the grid exchanged current is first described. A unified control structure is presented that enables a tunable tradeoff between the two constrained harmonic sources. Then, a hybrid harmonic suppression scheme is proposed to enable the further improvement of the adaptability of VSG, which mainly consists of a local voltage harmonic control loop and an adaptive grid current-controlled loop. The local voltage harmonic control loop aims to scale down the inverter output impedance via a negative feedback loop, while the grid current-controlled compensator is intended to counteract the adverse effects from a weak grid via an additional voltage, which leads to substantially lower total harmonic distortion for both the local load voltage and the grid current at the same time. Small-signal modelling is performed to investigate the system stability and its robustness to parameter perturbations. The effectiveness of the proposed methodology is verified using hardware-in-the-loop simulations.

KEYWORDS:

  1. Distorted grid
  2. Harmonic suppression
  3. Harmonic observer
  4. Nonlinear load
  5. Virtual synchronous generator

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Structural diagram of grid-connected DG

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of voltage and current harmonics suppression. (a) Results without harmonic suppression. (b) Results with proposed voltage control loop only. (c)Results with proposed hybrid harmonic suppression method.

Fig. 3 Simulation results of the robustness against Lg variation. (a) Results without harmonic suppression. (b) Results with proposed voltage control loop only. (c)Results with proposed hybrid harmonic suppression method.

Fig. 4 Simulation results of the robustness to load variation of the proposed method. (a) Before load increases. (b) With increased linear load. (c) With increased nonlinear load. (d) Linear load current.

Fig. 5 Simulation results of the robustness to load variation of the comparison method. (a) Before load increases. (b) With increased linear load. (c) With increased nonlinear load. (d) Linear load current.

CONCLUSION:

In view of the inherent contradiction involved in attenuating adverse effects in the presence of nonlinear loads and distorted grid, this paper presents tunable tradeoff between constrained harmonic sources. A hybrid harmonic suppression scheme is then proposed and consists of a local voltage harmonic control loop and an adaptive grid current-controlled loop, with a concurrent distortion inhibition capability. Compared with the existing approaches, the proposed methodology provides high-quality power supplies for both the grid and local loads.

REFERENCES:

[1] Q. Zhong, and G. Weiss, “Synchronverters: inverters that mimic synchronous generators,” IEEE Trans. Ind. Electron., vol. 58, no. 4, pp. 1259-1267, Apr. 2011.

[2] J. Ailpoor, Y. Miura, and T. Ise, “Power system stabilization using virtual synchronous generator with alternating moment of inertia,” IEEE Journal Emerg. Sel. Topics Power Electron., vol. 3, no. 2, pp. 451-458, June 2014.

[3] J. Liu, Y. Miura, and T. Ise, “Comparison of dynamic characteristics between virtual synchronous generator and droop control in inverter-based distributed generators,” IEEE Trans. Power Electron., vol. 31, no. 5, pp. 3600-3611, May 2016.

[4] D. Arricibita, P. Sanchis, and L. Marroyo, “Virtual synchronous generators classification and common trends”, in Proc. IECON, 2016, pp. 2433-2438.

[5] J. Fang, Y. Tang, H. Li, and X. Li, “A battery/ultra-capacitor hybrid energy storage system for implementing the power management of virtual synchronous generators,” IEEE Trans. Power Electron., vol. 33, no. 4, pp. 2820-2824, Apr. 2018.

An Uninterruptable PV Array-Battery Based System Operating in Different Power Modes with Enhanced Power Quality

ABSTRACT:

 This work aims to develop a solar- battery energy storage (BES) based system, which ensures an uninterruptable supply to loads irrespective of availability of the grid. This system comprises of a solar photovoltaic (PV) array, a BES, the grid and local residential loads. A new control is implemented such that the active power demand of residential loads, is fed from the PV array, a BES unit and the utility grid. In this system, the power control operates in different power modes, which delivers the benefits to the end users with an integration of BES and an excess of PV array power, which is sold back to the grid. For this, an effective control logic is developed for the grid tied voltage source converter (VSC). Moreover, this system deals with the issue of an integrating power quality enhancement along with the power generation from the solar PV source. The cascaded delayed signal cancellation (CDSC) based phase locked loop (PLL) is implemented for grid synchronization during the grid voltage distortion. The developed control is easily implemented in a real time controller (dSPACE-1202). Test results validate the performance of the implemented control in different operating conditions such as varying solar power generation, load variations and unavailability of the grid.

KEYWORDS:

  1. Energy Storage
  2. Power Quality
  3. Quadrature Signal Generation
  4. Solar PV Generation
  5. Synchronization
  6. Voltage Control Mode

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1 System configuration

EXPECTED SIMULATION RESULTS:

Fig.2 Dynamic performance at different operating modes during PV hour

Fig. 3 Dynamic performance of the grid interfaced PV-BES system during SVPM

Fig. 4 Performance of PV-BES system under SVPM (a) IPV and VPV (b) ig and vg (c) iL and vg(d) ivsc and vvsc (e) load power (PL), (f) grid power Pg (g) Ibat and Vbat, (h) Pbat, (i) harmonic spectral of iL (j) harmonic spectral of ig (k) harmonic spectral of vg and (l) grid voltage and grid current phasors diagram

Fig 5 Dynamic response of the system under CGPM (a) vg, VDC, ig, IPV (b)VPV, iL, Ibat, iVSC and (c) Pg, PL, PPV and IPV

Fig. 6 Dynamic performance of the system during non-PV hours (a) vg, VDC, ig, iVSC (b) ig, IPV, iL, Pg and (c) IPVFF, ID, ILoss and isα

CONCLUSION:

The main contributions of this work are on the robustness of the system operating in different operating modes. The performance of a grid interfaced PV-BES system is validated through experimental results where the worst case of PV array insolation, load variation and grid unavailability are used for transition between modes. In addition, the system is operating in constant and variable power modes to provide power smoothening and a decrease the burden on the distribution grid during peak demand. This system is also found capable to work in an islanding mode to deliver the uninterruptable power to the load. The CDSC-PLL provides synchronization to the grid and MNSOGI-QSG-DQ control uses for current harmonics elimination and power quality improvement. The THD of ig and vL are achieved within limits of an IEEE-519-2014 standard.

REFERENCES:

[1] J. T. Bialasiewicz, “Renewable Energy Systems with Photovoltaic Power Generators: Operation and Modeling,” IEEE Trans. Industrial Electronics, vol. 55, no. 7, pp. 2752-2758, July 2008,

[2] R. Panigrahi, S. Mishra, S. C. Srivastava, A. K. Srivastava and N. Schulz, “Grid Integration of Small-Scale Photovoltaic Systems in Secondary Distribution Network- A Review,” IEEE Trans. Industry Applications, Early Access, 2020

[3] J. Krata and T. K. Saha, “Real-Time Coordinated Voltage Support with Battery Energy Storage in a Distribution Grid Equipped with Medium-Scale PV Generation,” IEEE Trans. Smart Grid, vol. 10, no. 3, pp. 3486-3497, May 2019.

[4] N. Liu, Q. Chen, X. Lu, J. Liu and J. Zhang, “A Charging Strategy for PV-Based Battery Switch Stations Considering Service Availability and Self-Consumption of PV Energy,” IEEE Trans. Ind. Elect., vol. 62, no. 8, pp. 4878-4889, Aug. 2015.

[5] Y. Shan, J. Hu, K. W. Chan, Q. Fu and J. M. Guerrero, “Model Predictive Control of Bidirectional DC-DC Converters and AC/DC Interlinking Converters – A New Control Method for PV-Wind-Battery Microgrids,” IEEE Trans. Sust. Energy, Early Excess 2018.

An MPC Based Algorithm for a Multipurpose Grid Integrated Solar PV System With Enhanced Power Quality and PCC Voltage Assist

ABSTRACT:

The continuously fluctuating energy output and varying power demands in the renewable energy systems have led to the degradation of power quality. This work presents a model predictive based control for a solar PV system integrated to the grid for optimal management and control of the power transfer. The double stage three-phase configuration is controlled using model predictive control (MPC) strategy, which considers the power converters’ switching states to predict the next control variable. The control uses a modified-dual second-order generalized-integrator for estimation of the power requirements based on the continuously varying system parameters. The PCC voltages assist and the ride through operation are performed based on the drops in voltage levels and optimum switching state is selected based on the minimization of the cost function to deliver the required active and reactive powers to the grid. The performance of the controller is validated through simulation and is also shown using hardware implementation. The IEEE-519 standard is followed throughout and a comparative analysis shows the remarkable performance of the presented grid controller.

KEYWORDS:

  1. MDSOGI
  2. Model predictive control
  3. PCC voltage assist
  4. Ride through, solar photovoltaic
  5. Voltage source converter

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Circuit diagram of system.

EXPECTED SIMULATION RESULTS:

Fig. 2. Steady State UPF operation. (a) vg_abiinv_a (b) Inverter Power (c) THD of inverter current (d) vg_abig_a (e) Grid Power (f) Grid voltage THD (g) Grid Current THD (h) Load Power (i) Load Current THD.

Fig. 3. Load current unbalance (a)-(c): (a) Phase ‘a’ PCC line voltage, Grid current, Load Current and VSC current (b) Phase ‘b’ PCC line voltage, Grid current, Load Current and VSC current (c) Internal Components Φloss, Φpvg, Φload and Φnet. (d) Grid current THD in steady state, (e) Load Current THD in steady state. (f) Solar Irradiation variation: PV current (IPV ), PV Voltage (V PV ) and DC link Voltage (V dc).

Fig. 4. Waveforms during grid voltage variations (a) Overvoltage: iL_a, V dc, vg_ab, ig_a (b)Undervoltage: iL_a, V dc, vg_ab, ig_a. (c) Grid current THD after overvoltage, (d) Load current THD after overvoltage, (e) Grid current THD after undervoltage, (f) Load current THD after undervoltage.

Fig. 5. High grid distortion (a) extracted fundamental voltage, highly distorted grid voltage, load current, current in the grid, (b) THD in voltage in the grid, (c) grid currentTHDfor Damped SOGI control based on [24] (d)LCS-MPC [25] (e) Presented MDSOGI-MPC control.

CONCLUSION:

A modified dual second order generalized integrator based model predictive control (MDSOGI-MPC) is presented in this work for the control of two stage three phase grid tied solar PV system. Various adverse grid variations are performed to highlight the performance of the control technique. The robustness and simple configuration as well as the implementation of the control make its performance superior to present control methods based on MPC. Themodified-dual second order generalized integrator has estimated the power requirements based on system parameters. The performance during the sag in the voltage is shown while the controller demonstrates the PCC voltage assist operation as well as the ride through performance. Optimum switching states are predicted based on the minimization of the cost function. The performance is tested on simulation as well as hardware setup and the results show that the implementation of this control is advantageous. The harmonic spectrum of the current in the grid network is maintained within the prescribed limits of IEEE-519 std. limits. A generic comparison is made with the current modern control strategies, which shows that it works well as compared to other techniques.

REFERENCES:

[1] Y. Chen et al., “From laboratory to production: Learning models of efficiency and manufacturing cost of industrial crystalline silicon and thin-film photovoltaic technologies,” IEEE J. Photovoltaic, vol. 8, no. 6, pp. 1531–1538, Nov. 2018.

[2] V. Saxena, N. Kumar, B. Singh, and B. K. Panigrahi, “A rapid circle centre-line concept-based MPPT algorithm for solar photovoltaic energy conversion systems,” IEEE Trans. Circuits Syst. I: Regular Papers, vol. 68, no. 2, pp. 940–949, Feb. 2021.

[3] A. Tazay and Z. Miao, “Control of a three-phase hybrid converter for a PV charging station,” IEEE Trans. Energy Convers., vol. 33, no. 3, pp. 1002–1014, Sep. 2018.

[4] IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems – Amendment 1. IEEE Standard 1547a-2014 (Amendment to IEEE Standard 1547-2003), pp. 4–16, May 21, 2014, doi: 10.1109/IEEESTD.2014.6818982.

[5] V. L. Srinivas, B. Singh, and S. Mishra, “Fault ride-through strategy for two-stage grid-connected photovoltaic system enabling load compensation capabilities,” IEEE Trans. Ind. Electron., vol. 66, no. 11, pp. 8913–8924, Nov. 2019.

An Improved Deadbeat Control Strategy Based on Repetitive Prediction Against Grid Frequency Fluctuation for Active Power Filter

ABSTRACT:

In order to improve the harmonic compensation performance of active power filter (APF) in distribution network, based on deadbeat control theory, the command current prediction algorithm and current tracking control strategy are optimized in this article. Firstly, the command current repetitive prediction in abc coordinate system is transferred to dq for improving its accuracy in lead compensation, and the equivalent for fractional delay beat is achieved by Lagrange Interpolation Polynomial to solve the problem of inaccurate prediction caused by grid frequency fluctuation. Then, considering the inherent half-sampling-period delay of sinusoidal PWM (SPWM), an improved deadbeat control strategy for current tracking is proposed by estimating the output current of next sampling period. Because the output current in next sampling period is replaced by that in current sampling period with traditional deadbeat control strategy, this estimation could make up for the defect of low control precision caused by that replacement. After that, adding error repetitive correction into the improved deadbeat control channel to reduce the periodic tracking error of output current. Finally, the stability and accuracy of the improved control system are analyzed theoretically, and its feasibility and effectiveness are verified by the simulation and hardware-in-the-loop (HIL) experiments.

KEYWORDS:

  1. Deadbeat control
  2. Frequency fluctuation
  3. Harmonic compensation
  4. Lagrange interpolation polynomial
  5. Error repetitive correction

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. Three-Phase Apf Topology And Overall Control Structure.

EXPECTED SIMULATION REUSLTS:

Figure 2. Predicted Command Current With Traditional Or Proposed Prediction Algorithm At Different Grid Frequency. (A) Grid Frequency of 50hz. (B) Grid Frequency Of 50.5hz. (C) Grid Frequency Of 49.5hz.

Figure 3. Simulation Results For The Improved Deadbeat Control Strategy With Traditional Or Proposed Repetitive Prediction. (A) With Traditional Prediction At Grid Frequency Of 50.5hz. (B) With Proposed Prediction At Grid Frequency Of 50.5hz (C) With Traditional Prediction At Grid Frequency Of 49.5hz. (D) With Proposed Prediction At Grid Frequency Of 49.5hz.

Figure 4. Power Grid Voltage And Nonlinear Load Current. (A) Power Grid

Voltage. (B) Nonlinear Load Current.

Figure 5. Grid-Side Current And Output Current Of Phase A With Traditional Or Improved Deadbeat Control Strategy. (A) Traditional Deadbeat. (B) Improved Deadbeat (Krc D 0).

Figure 6. Grid-Side Current And Output Current Of Phase A With Different Value Of Krc. (A) Krc D 0:15. (B) Krc D 0:30. (C) Krc D 0:45.

CONCLUSION:

In order to improve the harmonic compensation performance of APF, command current prediction algorithm and dead-beat control strategy for current tracking are optimized in this article. The feasibility and effectiveness of the proposed method are verified by theoretical analysis, simulation, and experiment. The conclusions are as follows:

(1) The accuracy of command current prediction is the pre- requisite for optimizing the current tracking control strategy. Compared with the traditional command current repetitive prediction algorithm, the proposed one exhibits higher prediction accuracy and stronger adaptability to the fluctuation of grid frequency.

(2) Compared with the traditional deadbeat control, because the APF output current in the next sampling period has been estimated, the effective controlled frequency band of the control system is enlarged on the premise of ensuring system stability.

(3) When current tracking error repetitive correction is added into the improved deadbeat control channel, the periodic tracking error could be reduced to some extent, and the control accuracy is increased as well.

(4) The simulation and experiment results demonstrate that the proposed control method has a fine steady-state performance to grid frequency fluctuation and a satisfactory dynamic response to the sudden change of load current.

REFERENCES:

[1] Y. Fang, J. Fei, and T. Wang, “Adaptive backstepping fuzzy neural controller based on fuzzy sliding mode of active power filter,” IEEE Access, vol. 8, pp. 96027_96035, Jun. 2020.

[2] J. Chen, H. Shao, Y. Cheng, X. Wang, G. Li, and C. Sun, “Harmonic circulation and DC voltage instability mechanism of parallel-SVG system,” IET Renew. Power Gener., vol. 14, no. 5, pp. 793_802, Apr. 2020.

[3] J. Fei and Y. Chu, “Double hidden layer output feedback neural adaptive global sliding mode control of active power filter,” IEEE Trans. Power Electron., vol. 35, no. 3, pp. 3069_3084, Mar. 2020.

[4] W. U. K. Tareen and S. Mekhielf, “Three-phase transformerless shunt active power filter with reduced switch count for harmonic compensation in grid-connected applications,” IEEE Trans. Power Electron., vol. 33, no. 6, pp. 4868_4881, Jun. 2018.

[5] Z.-X. Zou, K. Zhou, Z. Wang, and M. Cheng, “Frequency-adaptive fractional-order repetitive control of shunt active power filters,” IEEE Trans. Ind. Electron., vol. 62, no. 3, pp. 1659_1668, Mar. 2015.

An Enhanced EPP-MPPT Algorithm With Modified Control Technique in Solar-Based Inverter Applications: Analysis and Experimentation

ABSTRACT:

In this paper, an optimized adaptive perturb-perturb (PP) based algorithm is presented. The modified algorithm has a predictive variable step size calculated through the Newton-Raphson procedure, making its programming effort simple. This combination merits fewer calculations, faster response time and can simply be applied effectively in both bright and shady conditions. The algorithm is developed as a C language code linked to the PSIM simulation representing a typical photovoltaic module system. The proposed algorithm’s simulation results proved faster tracking time response with a reduced error than the standard system. The tracking time is ten times faster than the MPPT method and reduced by 10 seconds in a 100 kHz converter. The measured error is less than 0.03% at steady state. A modified control modulation scheme is blended with the algorithm as well. Experimental results are provided using a 10Wprototype for telecom applications and another 300W practical micro inverter as a proof of concept, and in agreement with both modelling and simulation results. In addition, the results validate the viability of the proposed algorithm in the cases of linear (resistor) and non-linear (brushless motor) loads. The PSIM and experimental setups are provided to prove the concept of the proposed methodology, which is critical for universal solar-inverter applications.

KEYWORDS:

  1. DC-DC converters
  2. MPPT improved algorithms
  3. Rural water pump applications
  4. Solar energy
  5. Standalone rural inverters
  6. Telecom distribution

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. Block Diagram For The Complete System.

EXPECTED SIMULATION RESULTS:

Figure 2. The Output Power With The Conventional P&O Method.

Figure 3. (A) Power Tracking For A Resistive Data Chip Load. (B) The Optimum Power Versus The Output Tracking Power For Load And Light Intensity Of 1000 W/M2 And Varying The Temperature From 20 _C To 30 _C.

Figure 4. The Optimum Power Versus The Output Tracking Power At Resistive Inductive (Motor) Load And Varying Light Intensity From 800 W/M2 To 1000 W/M2 And Temperature Of 25 _C.

Figure 5. (A) The Traditional Mppt Algorithm Has A Slow Tracking Time. (B) The Epp-Mppt Tracking Time For The Proposed Algorithm. (C) Curve Translating The Voltage Across The Dc-Link In A Pv-Ev-Grid System For A Variable Irradiation.

CONCLUSION:

This paper provided a (i) novel adaptive numerical EEP-MPPT algorithm with a new EPP modified algorithm and a predictive variable step size calculated using Newton-Raphson method, (ii) This combination gives outstanding results; the steady-state error has been reduced from 8% in MPPT and 1.2% in incremental conductance to 0.063 % with a tracking time of 1 _s instead of 10 _s, (iii) The system proves to have the ability to adjust itself in a very short period of time to track the new operating point for maximum power, within acceptable error, (iv) The new control proves excellent results under normal and shaded conditions as well. This will optimize the overall output power and add to the reliability, which is paramount for this industry, (v) PSIM simulation and experimental measurements are presented using different linear/non-linear loads; pure resistive load, and a brushless DC motor, (vi) Experimental results have verified the proof of concept, ensuring that the proposed numerical and control algorithms are working efficiently and precisely under motor loading conditions, (vii) In addition, the controller’s ability to recover the output voltage waveform under faulty conditions, proves compliant to the IEEE 519 standard. These advantages prove a reliable solution for this research problem.

REFERENCES:

[1] M. A. A. M. Zainuri, M. A. M. Radzi, A. C. Soh, and N. A. Rahim, “Development of adaptive perturb and observe-fuzzy control maximum power point tracking for photovoltaic boost DC_DC converter,” IET Renew. Power Gener., vol. 8, no. 2, pp. 183_194, Mar. 2014.

[2] C. R. Sullivan and M. J. Powers, “A high-ef_ciency maximum power point tracker for photovoltaic arrays in a solar-powered race vehicle,” in Proc. IEEE Power Electron. Spec. Conf., Jun. 1993, pp. 574_580.

[3] K. Hussein, I. Muta, T. Hoshino, and M. Osakada, “Maximum photovoltaic power tracking: An algorithm for rapidly changing atmospheric conditions,” IEE Proc. Gener., Transmiss. Distrib., vol. 142, no. 1, pp. 59_64, 1995.

[4] S. H. Hosseini, A. Farakhor, and S. K. Haghighian, “Novel algorithm of MPPT for PV array based on variable step Newton-Raphson method through model predictive control,” in Proc. 13th Int. Conf. Control, Autom. Syst. (ICCAS). Gwangju, South Korea: Kimdaejung Convention Center, Oct. 2013, pp. 1577_1582.

[5] Y. Chen, Y. Kang, S. Nie, and X. Pei, “The multiple-output DC_DC converter with shared ZCS lagging leg,” IEEE Trans. Power Electron., vol. 26, no. 8, pp. 2278_2294, Aug. 2011.

Resistive Load.

Figure 13. Pwm SignalVersus The Motor Input Voltage From The Pv

Module.

CONCLUSION:

This paper provided a (i) novel adaptive numerical EEP-MPPT algorithm with a new EPP modified algorithm and a predictive variable step size calculated using Newton-Raphson method, (ii) This combination gives outstan.

An Efficient Fuzzy-Logic Based Variable-Step Incremental Conductance MPPT Method For Grid-Connected PV Systems

ABSTRACT:

Recently, solar energy has been intensively employed in power systems, especially using the photovoltaic (PV) generation units. In this regard, this paper proposes a novel design of a fuzzy logic based algorithm for varying the step size of the incremental conductance (INC) maximum power point tracking (MPPT) method for PV. In the proposed method, a variable voltage step size is estimated according to the degree of ascent or descent of the power-voltage relation. For this purpose, a novel unique treatment is proposed based on introducing five effective regions around the point of maximum PV power. To vary the step size of the duty cycle, a fuzzy logic system is developed according to the locations of the fuzzy inputs regarding the five regions. The developed fuzzy inputs are inspired from the slope of the power-voltage relation, namely the current-voltage ratio and its derivatives whereas appropriate membership functions and fuzzy rules are designed. The benefit of the proposed method is that the MPPT efficiency is improved for varying the step size of the incremental conductance method, thanks to the effective coordination between the proposed fuzzy logic based algorithm and the INC method. The output DC power of the PV array and the tracking speed are presented as indices for illustrating the improvement achieved in MPPT. The proposed method is verified and tested through the simulation of a grid-connected PV system model. The simulation results reveal a valuable improvement in static and dynamic responses over that of the traditional INC method with the variation of the environmental conditions. Further, it enhances the output dc power and reduce the convergence time to reach the steady state condition with intermittent environmental conditions.

KEYWORDS:

  1. Maximum power point tracking
  2. Fuzzy logic
  3.  Incremental conductance
  4. PV system
  5. Dynamic responses

 SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1. An Overview Of The Grid-Connected Pv Array With The

Proposed Flc Based Variable Step Inc Mppt Method.

EXPECTED SIMULATION RESULTS:

Figure 2. Testing The Flc Based Algorithm Through The Step Variations

Of (A) The Solar Irradiance (G) (B) The Cell Temperature (Tc ).

Figure 3. Comparisons Of Flc Based And Fixed Duty Cycle Of The Inc

Mppt Method (Fixed Step=0.0003 S) For Step Variations Of G And Tc :

  • For The Step Change At 0.8 S; (B) For The Step Change At 1 S.

Figure 4. The Output Dc Power Comparison When Applying The

Conventional Fixed Step Inc Method, The Fixed Step P&O Method And The

  • Flc Based Variable Step Inc Method For Mppt.

Figure 5. The Difference Between The Output Dc Power When Applying

The Flc Based Algorithm And These Of The Conventional Fixed Step Inc And

  • P&O Methods For Mppt.

Figure 6. Proximate Views Of The Output Dc Power Comparison When

Applying The Flc Based Algorithm And These Of The Conventional Fixed

Step Inc And P&O Methods For Mppt: (A) From 0.2 To 0.5 S; (B) From

  • 0.7 To 0.95 S; (C) From 1.2 To 1.4 S; (D) From 1.4 To 1.5 S.

Figure 7. Testing The Flc Based Algorithm Through The Ramp Variations

  • Of: (A) The Solar Irradiance (G); (B) The Cell Temperature (Tc ).

CONCLUSION:

The PV system efficiency is a crucial index to evaluate the performance of grid-connected PV systems where the MPPT performance is a keynote. The conventional fixed step INC method for MPPT is widely used but it lacks some accuracy and speed of convergence. To tackle this issue, the proposed improvement of the INC method is introduced to employ a fuzzy logic algorithm to generate a variable step voltage increment or decrement, which is executed through decrement or increment of the duty cycle of the dc-dc boost converter. The voltage (duty cycle) step has five different sizes according to proposed five regions of the fuzzy inputs. The simulation results demonstrate that the proposed FLC based variable step INC method for MPPT enhances the output dc power and reduce the time of convergence to reach the steady state when switching of the environmental conditions. To illustrate the efficacy of the proposed MPPT method, it is compared to two conventional methods. The first one is the INC method with fixed step sizes of 0.0003 s and 0.001 s. The second method is the conventional P&O method with fixed step of 0.0003 s. In future work, the experimental application of the proposed FLC variable step method will be studied in a grid-connected PV systems.

REFERENCES:

[1] N. Priyadarshi, F. Azam, A. K. Bhoi, and A. K. Sharma, “Dynamic operation of grid-connected photovoltaic power system,” in Advances in Greener Energy Technologies. Singapore: Springer, 2020, pp. 211_218.

[2] H. Rezk, M. Aly, M. Al-Dhaifallah, and M. Shoyama, “Design and hardware implementation of new adaptive fuzzy logic-based MPPT control method for photovoltaic applications,” IEEE Access, vol. 7, pp. 106427_106438, 2019.

[3] A. S. Bayoumi, R. A. El-Sehiemy, K. Mahmoud, M. Lehtonen, and M. M. F. Darwish, “Assessment of an improved three-diode against modified two-diode patterns of MCS solar cells associated with soft parameter estimation paradigms,” Appl. Sci., vol. 11, no. 3, p. 1055, Jan. 2021, doi: 10.3390/app11031055.

[4] B. Subudhi and R. Pradhan, “A comparative study on maximum power point tracking techniques for photovoltaic power systems,” IEEE Trans. Sustain. Energy, vol. 4, no. 1, pp. 89_98, Jan. 2013.

[5] D. Sera, L. Mathe, T. Kerekes, S. V. Spataru, and R. Teodorescu, “On the Perturb-and-Observe and incremental conductance MPPT methods for PV systems,” IEEE J. Photovolt., vol. 3, no. 3, pp. 1070_1078, Jul. 2013.

Adaptive Hybrid Generalized Integrator Based SMO for Solar PV Array fed Encoderless PMSM Driven Water Pump

ABSTRACT:

The encoder influences reliability and cost of permanent magnet synchronous motor (PMSM) operated solar water pump (WP). It is even sensitive to electromagnetic noise and temperature, which thereby reduces its accuracy. To overcome these problems, an encoderless PMSM control by using adaptive hybrid generalized integrator (AHGI) based sliding mode observer (SMO) for the solar WP system is presented in this paper. The widely used low pass filter based SMO produces phase-shift, attenuation and dominant lower order harmonics (DLOH). This decreases the position estimation accuracy. Besides, the need for tracking dynamic system frequency further exacerbates its performance. The developed AHGI structure eliminates these drawbacks and provides an accurate estimate of position over a wide speed range. A harmonic decoupling network, a hybrid generalized integrator and an adaptive frequency tracker constitute AHGI, which respectively performs dominant harmonic signal generation, DLOH elimination and frequency tracking. The improvement in behavior of AHGI over the existing methods is analyzed by transfer functions, Bode plots and back electromotive force helices. Meanwhile an incremental conductance algorithm for PV array maximum power control is used. The developed structure is experimentally validated on a laboratory prototype and a comparison with the existing methods is also made.

KEYWORDS:

  1. Solar water pump
  2. Solar photovoltaic (PV) array
  3. Encoderless control
  4. PMSM
  5. Adaptive hybrid generalized integrator (AHGI)
  6. Adaptive frequency tracker (AFT)

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1 Encoderless PMSM driven solar WP system with developed AHGI based

SMO for rotor position estimation

EXPECTED SIMULATION RESULTS:

Fig. 2 Experimental performance of the solar WP system with the developed AHGI based SMO (a) Starting at 1000 W/m2, (b) Starting at 500 W/m2, (c),(d) continuous running at 1000 W/m2, (e),(f) continuous running at 500 W/m2

Fig. 3 Experimental dynamic performance of solar WP system with the developed AHGI based SMO for irradiation variation from (a),(b),(c) 500 W/m2 to 1000 W/m2; (d),(e),(f) 1000 W/m2 to 500 W/m2

CONCLUSION:

An adaptive hybrid generalized integrator (AHGI) based SMO for encoderless operation of PMSM driving a solar WP has been presented here. It has been found that the developed AHGI structure has produced a satisfactory estimate of both the speed and rotor position through selective elimination of DLOH along with the removal of phase-shift and fundamental attenuation. The improved performance of AHGI structure over the LPF, SOGI and FOGI has been demonstrated by the transfer function and the frequency response. Besides, the superiority of AHGI has also been shown through both the simulated and experimental performances of back EMF and rotor position. Even the detailed experimental performance of system with the AHGI at continuous running and starting under dynamics of solar irradiation have been obtained. It has been found that the developed AHGI structure has produced a satisfactory estimate of αβ-components of back-EMF even under dynamics. It has also been shown experimentally that the developed AHGI successfully tracks the variations in the speed. A stable and reasonably satisfying performance of the system has been observed under all operating conditions. The developed AHGI structure can be used with any PMSM system for rotor position and speed estimation.

REFERENCES:

[1] M. Rezkallah, A. Chandra, M. Tremblay and H. Ibrahim, “Experimental Implementation of an APC With Enhanced MPPT for Standalone Solar Photovoltaic Based Water Pumping Station,” IEEE Trans. Sustain. Energy, vol. 10, no. 1, pp. 181-191, Jan. 2019.

[2] M. E. Haque, Y. C. Saw and M. M. Chowdhury, “Advanced Control Scheme for an IPM Synchronous Generator-Based Gearless Variable Speed Wind Turbine,” IEEE Trans. Sustain. Energy, vol. 5, no. 2, pp. 354- 362, April 2014.

[3] C. Lascu and G. Andreescu, “PLL Position and Speed Observer With Integrated Current Observer for Sensorless PMSM Drives,” IEEE Trans. Ind. Electron., vol. 67, no. 7, pp. 5990-5999, July 2020.

[4] S. Shukla and B. Singh, “Reduced Current Sensor Based Solar PV Fed Motion Sensorless Induction Motor Drive for Water Pumping,” IEEE Trans. Ind. Informat., vol. 15, no. 7, pp. 3973-3986, July 2019.

[5] A. Andersson and T. Thiringer, “Motion Sensorless IPMSM Control Using Linear Moving Horizon Estimation With Luenberger Observer State Feedback,” IEEE Trans. Transport. Electrific., vol. 4, no. 2, pp. 464- 473, June 2018.

Active Fault Current Limitation for Low-Voltage Ride-Through of Networked Microgrids

ABSTRACT:

With the continuously increasing penetration of networked microgrids (MGs) on the local utility grid (UG), MGs face the challenge to avoid increasing system fault currents during low-voltage ride-through (LVRT). To solve this challenge, an active fault current limitation (AFCL) method is proposed with three parts: 1) a novel phase angle adjustment (PAA) strategy is conducted to relieve the impact of MGs output fault current on system fault current; 2) the current injection (CI) strategy for LVRT is formulated to fit the function of PAA; 3) a novel converter current generation (CCG) strategy is developed to achieve a better voltage support ability by considering network impedance characteristics. The proposed AFCL method is applied to the back-to-back converter, as a connection interface between MGs and UG. Extensive tests and pertinent results have verified the improvements of proposed AFCL method with better LVRT performance, while the networked MGs output fault current does not increase the amplitude of system fault current.

KEYWORDS:

  1. Networked microgrids
  2. Back-to-back converter
  3. Low-voltage ride-through
  4. Fault current limitation

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1. Structure of networked MGs and the corresponding fault current flow.

EXPECTED SIMULATION RESULTS:

Fig. 2. The PCC voltage of MG#1 and MG#2 with existing FCL method in [23]-[25].

Fig. 3. The PCC voltage of MG#1 and MG#2 with proposed AFCL method.

Fig. 4. The MG#1 and MG#2 fault current with existing FCL method in [23]-[25].

Fig. 5. The MG#1 and MG#2 fault current with proposed AFCL method.

Fig. 6. The MG#1 and MG#2 power injected by existing method in [23]-[25].

Fig. 7. The MG#1 and MG#2 power injected by proposed AFCL method.

Fig. 8. DC voltage of BTB converter with proposed/existing FCL in [23]-[25].

Fig. 9. The UG fault current with proposed/existing FCL in [23]-[25].

Fig. 10. The system fault current with existing FCL method in [23]-[25].

Fig. 11. The system fault current with proposed AFCL method.

CONCLUSION:

Under the UG fault condition, in view of the high-level system fault current during the LVRT of networked MGs, an AFCL method is proposed to avoid monotonically increasing system fault currents during the LVRT of networked MGs. In this method, in order to improve the voltage control ability of LVRT, the CCG strategy is proposed by embedding the network impedance characteristics. Then, in order to achieve a better fault current limitation by relieving the impact of MGs fault current, the PAA strategy is proposed with considering voltage’s phase angle difference from UG and MGs to fault branch. Meanwhile, the CI strategy is conducted to fit the feature of PAA. Numerous simulation results have validated the improvements of the proposed AFCL method with a successful LVRT, meanwhile, the networked MGs fault current does not increase the system fault current amplitude. Considering the fields with a high proportion of sensitive load, the BTB converter is widely used for the PCC connection point of DGs and MGs to provide high power quality. To reduce the fault current level, the AFCL method can be applied to the BTB converter, and can be also used to the other inverter products, such as wind and photovoltaic inverter, AC/DC microgrids, and HVDC transmission system.

REFERENCES:

[1] Q. Zhou, M. Shahidehpour, et al, “ Distributed Control and Communication Strategies in Networked Microgrids,” IEEE Communications Surveys & Tutorials, vol. 22, no. 4, pp. 2586-2633, Fourth quarter 2020.

[2] X. Zhao, J. M. Guerrero, et al, “Low-Voltage Ride-Through Operation of Power Converters in Grid-Interactive Microgrids by Using Negative-Sequence Droop Control,” IEEE Trans. Power Electron., vol. 32, no. 4, pp. 3128–3142, April 2017.

[3] I. Sadeghkhani, M. E. H. Golshan, A. Mehrizi-Sani, J. M. Guerrero, “Low-voltage ride-through of a droop-based three-phase four-wire grid-connected microgrid,” IET Gener. Transm. Distrib., vol. 12, no. 8, pp. 1906–1914, 2018.

[4] Y. He, M. Wang and Z. Xu, “Coordinative Low-Voltage-Ride-Through Control for the Wind-Photovoltaic Hybrid Generation System,” IEEE Journal of Emerging & Selected Topics in Power Electronics, vol. 8, no. 2, pp. 1503–1514, Jun. 2020.

[5] Y. Yang, F. Blaabjerg, and Z. Zou, “Benchmarking of grid fault modes in single-phase grid-connected photovoltaic systems,” IEEE Trans. Ind. Appl., vol. 49, no. 5, pp. 2167–2176, Sep./Oct. 2013.