Research on the Unbalanced Compensation of Delta-connected Cascaded H-bridge Multilevel SVG

ABSTRACT:

The paper presents the application of Delta- connected cascaded H-bridge multilevel SVG under unbalanced compensation currents or unbalanced supply voltages. Clustered balancing control for delta-connected SVG can be realized by injecting a zero-sequence current to the delta-loop. But zero-sequence current injection may cause the high peak phase current which may break converter switches. The aim of this paper is to analyze the key factors that affect the maximum output current of the SVG with injecting zero-sequence current and acquire the  quantitative relationship between unbalance compensation capability, the unbalance degree of the supply voltage, the initial phase of negative-sequence voltage, the unbalance degree of the compensation current and the initial phase of negative-sequence current. On this foundation, the valid compensation range of delta-connected SVG under unbalanced conditions is obtained. Furthermore, the compensation characteristic of the negative-sequence current is deduced with the certain supply voltage and the influence of supply voltage variation on the maximum output current for SVG is also considered with the certain compensation current. Finally, the correctness of the relevant theoretical analysis is verified by simulation and experiment.

 

KEYWORDS:

  1. Delta-connected cascaded H-bridge multilevel SVG
  2. Zero-sequence current
  3. Unbalance degree

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig.1. Delta-connected cascaded H-bridge multilevel SVG system configuration

EXPECTED SIMULATION RESULTS: 

 (a) Ki increased from 0 to 20%

(b) Ki increased from 20% to 50%

(c) Ki decreased from 50% to 20% and Ku increased from 0 to 10%

(d) Ku increased from 10% to 40%

Fig.2 Partial enlargement waveforms during sudden change of unbalance degree

 

CONCLUSION:

In this paper, the effect of unbalanced supply voltage and compensation current on the delta-connected SVG has been analyzed. Injecting zero-sequence current into the delta-loop allows maintaining cluster voltage balancing for the SVG. However, it has been shown that zero-sequence current injection may cause the high peak phase current which may break converter switches. In order to guarantee safe and reliable operation of the delta-connected SVG, whose maximum output current level Imax/Ip is chosen as the standard to measured its unbalance compensation capability and the valid compensation range under unbalanced conditions can also be obtained. The unbalance compensation range of the delta-connected structure is limited by the unbalance degree of the supply voltage, the initial phase of negative-sequence voltage, the unbalance degree of the compensation current and the initial phase of negative-sequence current. The quantitative relationship between unbalance compensation capability and other influence factors derived in this paper can provide a good theoretical basis for the parameter design and device selection of the delta-connected cascaded H-bridge multilevel SVG. In addition, the delta-connected SVG is more sensitive to the unbalance degree of the supply voltage than the unbalance degree of the compensation current, and it will be better way for industrial applications aiming at improving the power quality. The simulation and experimental results further verified the rationality and accuracy of the analysis.

  

REFERENCES:

  • Akagi, “Classification, Terminology, and Application of the Modular Multilevel Cascade Converter (MMCC),” IEEE Transactions on Power Electronics, vol. 26, no. 11, pp. 3119-3130, Nov. 2011.
  • Z. Peng and Jih-Sheng Lai, “Dynamic performance and control of a static VAr generator using cascade multilevel inverters,” IEEE Transactions on Industry Applications, vol. 33, no. 3, pp. 748-755, May/Jun 1997.
  • K. Lee, J. S. K. Leung, S. Y. R. Hui and H. S. H. Chung, “Circuit-level comparison of STATCOM technologies,” Power Electronics Specialist Conference, 2003. PESC ’03. 2003 IEEE 34th Annual, 2003, pp. 1777-1784 vol.4.
  • Z. Peng and Jin Wang, “A universal STATCOM with delta-connected cascade multilevel inverter,” 2004 IEEE 35th Annual Power Electronics Specialists Conference (IEEE Cat. No.04CH37551), 2004, pp. 3529-3533 Vol.5.
  • Maharjan, S. Inoue, H. Akagi and J. Asakura, “A transformerless battery energy storage system based on a multilevel cascade PWM converter,” 2008 IEEE Power Electronics Specialists Conference, Rhodes, 2008, pp. 4798-4804.

Single-phase hybrid cascaded H-bridge and diode-clamped multilevel inverter with capacitor voltage balancing

ABSTRACT:

Diode-clamped and cascaded H-bridge multilevel inverters are two of the main multilevel inverter topologies; each has its distinct advantages and drawbacks. Regarding the latter, cascaded H-bridge inverters require multiple separate dc sources, whereas (semi-active) diode-clamped inverters contain capacitors that require a means to balance their voltages. This paper investigates a hybrid-topology inverter, comprising a single-phase five-level semi-active diode-clamped inverter and a single-phase cascaded H-bridge inverter with their outputs connected in series, as one way to mitigate the drawbacks of each topology. The proposed control scheme for this inverter operates the switches at fundamental frequency to achieve capacitor voltage-balancing while keeping the switching losses low. Moreover, the step-angles are designed for the 13-level and 11-level output voltage waveform cases (as examples) for a fixed modulation index to achieve optimal total harmonic distortion. Furthermore, the scheme also achieves capacitor voltage-balancing for modulation indices that are close to the optimal modulation index, and for a wide range of load power factors, albeit at the cost of increased output voltage distortion. Simulation results are presented to help explain the processes of capacitor recharging and voltage-balancing, while experimental results are shown as verification of the expected behaviour of this inverter and the proposed control scheme.

 

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

 

Fig. 1. Five-level 1ϕ-DCMLI with semi-active front end

  

EXPECTED SIMULATION RESULTS:

Fig. 2 Simulated 13-level hybrid inverter output Vload (with waveform alternating between RM and DM cycle patterns), and capacitor voltages vc1, vc2, vc3 and vc4

Fig. 3. Simulated 13-level hybrid inverter output Vload (with waveform always in DM cycle pattern), and capacitor voltages vc1, vc2, vc3 and vc4

Fig. 4. Normalised harmonic spectra of the Vload waveforms obtained for the ideal, simulated and measured cases For RM operation, (b) For DM operation

Fig. 5: Simulation and test results for the 13-level hybrid inverter with various load PFs (a) 0 PF leading, (b) 0.1 PF lagging, (c) 0.95 PF leading

Fig. 6: Simulation and test results for the 13-level hybrid inverter with 0.95 lagging PF load (a) Simulated transition from RM to DM, and back to RM, (b) Measured transition from RM to DM, and back to RM

 

CONCLUSION:

This paper has described the operation of a hybrid inverter comprised of a five-level 1ϕ-DCMLI with a semi-active front end connected in series with either a nine-level 1ϕ-CHBMLI or a seven-level 1ϕ-CHBMLI to produce a staircase waveform with either 13-levels or 11-levels, respectively. The key contribution is a novel fundamental-frequency modulation scheme for the DCMLI’s switches so as to charge up its inner dc-link capacitors from the CHBMLI’s dc sources, and thereby achieve capacitor voltage balancing via an alternation between a RM and a DM based on capacitor voltage feedback with a hysteresis band. Both simulation and experimental results have been presented herein to substantiate this hybrid-topology inverter’s good performance when operated using the proposed modulation and feedback control schemes at an optimal modulation index with unity PF loads. Furthermore, the scheme also achieves capacitor voltage balancing for modulation indices that span at least 10% above and below the optimal modulation index, and for a wide range of load PFs, albeit at the cost of increased output voltage distortion. While (fundamental-frequency) staircase modulation of the DCMLI has the advantage of lower switching losses and higher power efficiency compared with (high-frequency) pulse-width modulation, the accompanying drawback is it requires large capacitances to prevent overcharging, and also too-rapid discharging, of the capacitors due to the long charging and discharging durations. Future work will consider pulse-width modulation of the hybrid inverter, especially for variable instead of fixed modulation index applications, and for supplying lagging PF loads.

 

REFERENCES:

  • Hayden, C.L.: ‘Peak shaving via emergency generator’. Proc. Int. Telecom. Energy Conf., 1979, pp. 316–318
  • ‘Non-Road mobile machinery emissions – European Commission’. Available at https://ec.europa.eu/growth/sectors/automotive/environment-protection/ non-road-mobile-machinery_en, accessed 9 August 2017
  • ‘FACT SHEET: Final Amendments to Emission Standards | U.S. EPA’. Available at https://www.epa.gov/stationary-engines/fact-sheet-finalamendments- emission-standards, accessed 9 August 2017
  • Baker, R.H., Bannister, L.H.: ‘Electric power converter’. U.S. Patent 3867643, February 1975
  • Nabae, A., Takahashi, I., Akagi, H.: ‘A new neutral-point clamped PWM inverter’, IEEE Trans. Ind. Appl.., 1981, IA-17, (Sept./Oct.), pp. 518–523

Control of a Three-Phase Hybrid Converter for a PV Charging Station

ABSTRACT:

Hybrid boost converter (HBC) has been proposed to replace a dc/dc boost converter and a dc/ac converter to reduce conversion stages and switching loss. In this paper, control of a three-phase HBC in a PV charging station is designed and tested. This HBC interfaces a PV system, a dc system with hybrid plugin electrical vehicles (HPEVs) and a three-phase ac grid. The control of the HBC is designed to realize maximum power point tracking (MPPT) for PV, dc bus voltage regulation, and ac voltage or reactive power regulation. A test bed with power electronics switching details is built in MATLAB/SimPowersystems for validation. Simulation results demonstrate the feasibility of the designed control architecture. Finally, lab experimental testing is conducted to demonstrate HBC’s control performance.

 

KEYWORDS:

  1. Plug-in hybrid vehicle (PHEV)
  2. Vector Control
  3. Grid-connected Photovoltaic (PV)
  4. Three-phase Hybrid Boost Converter
  5. Maximum Power Point Tracking (MPPT)
  6. Charging Station.

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig.1 Architecture configurations of a PV charging station. The conventional topology includes a dc/dc converter and a dc/ac VSC. These two converters will be replaced by a three-phase HBC.

 

EXPECTED SIMULATION RESULTS

 

Fig.2 Performance of CC-CV algorithm

Fig.3. Performance of a modified IC-PI MPPT algorithm when solar irradiance variation is applied.

Fig. 4. Performance of the dc voltage control in the vector control. The solid lines represent the system responses when the dc voltage control is enabled. The dashed lines represent the system responses when the dc voltage control is disabled.

Fig. 5. Performance of a proposed vector control to supply or absorb reactive power independently.

Fig. 6. Power management of PV charging station.

Fig. 7. Dst, Md and Mq for case 4.

Fig. 8.  System performance under 70% grid’s voltage drop.

 

CONCLUSION:

Control of three-phase HBC in a PV charging station is proposed in this paper. The three-phase HBC can save switching loss by integration a dc/dc booster and a dc/ac converter converter into a single converter structure. A new control for the three-phase HBC is designed to achieve MPPT, dc voltage regulation and reactive power tracking. The MPPT control utilizes modified incremental conductance-PI based MPPT method. The dc voltage regulation and reactive power tracking are realized using vector control. Five case studies are conducted in computer simulation to demonstrate the performance of MPPT, dc voltage regulator, reactive power tracking and overall power management of the PV charging station. Experimental results verify the operation of the PHEV charging station using HBC topology. The simulation and experimental results demonstrate the effectiveness and robustness of the proposed control for PV charging station to maintain continuous dc power supply using both PV power and ac grid power.

 

REFERENCES:

  • Ehsani, Y. Gao, and A. Emadi, Modern electric, hybrid electric, and fuel cell vehicles: fundamentals, theory, and design. CRC press, 2009.
  • Sikes, T. Gross, Z. Lin, J. Sullivan, T. Cleary, and J. Ward, “Plugin hybrid electric vehicle market introduction study: final report,” Oak Ridge National Laboratory (ORNL), Tech. Rep., 2010.
  • Khaligh and S. Dusmez, “Comprehensive topological analysis of conductive and inductive charging solutions for plug-in electric vehicles,” IEEE Transactions on Vehicular Technology, vol. 61, no. 8, pp. 3475–3489, 2012.
  • Anegawa, “Development of quick charging system for electric vehicle,” Tokyo Electric Power Company, 2010.
  • Musavi, M. Edington, W. Eberle, and W. G. Dunford, “Evaluation and efficiency comparison of front end ac-dc plug-in hybrid charger topologies,” IEEE Transactions on Smart grid, vol. 3, no. 1, pp. 413–421, 2012.

 

Standalone Photovoltaic Water Pumping System Using Induction Motor Drive with Reduced Sensors

ABSTRACT

A simple and efficient solar photovoltaic (PV) water pumping system utilizing an induction motor drive (IMD) is presented in this paper. This solar PV water pumping system comprises of two stages of power conversion. The first stage extracts the maximum power from a solar PV array by controlling the duty ratio of a DC-DC boost converter. The DC bus voltage is maintained by the controlling the motor speed. This regulation helps in reduction of motor losses because of reduction in motor currents at higher voltage for same power injection. To control the duty ratio, an incremental conductance (INC) based maximum power point tracking (MPPT) control technique is utilized. A scalar controlled voltage source inverter (VSI) serves the purpose of operating an IMD. The stator frequency reference of IMD is generated by the proposed control scheme. The proposed system is modeled and its performance is simulated in detail. The scalar control eliminates the requirement of speed sensor/encoder. Precisely, the need of motor current sensor is also eliminated. Moreover, the dynamics are improved by an additional speed feedforward term in the control scheme. The proposed control scheme makes the system inherently immune to the pump’s constant variation. The prototype of PV powered IMD emulating the pump characteristics, is developed in the laboratory to examine the performance under different operating conditions.

 

KEYWORDS:

  1. Photovoltaic cells
  2. MPPT
  3. Water pumping
  4. Scalar control
  5. Induction motor drives

SOFTWARE:MATLAB/SIMULINK

 

SYSTEM ARCHITECTURE:

System architechure for the standalone solar water pumping system

Fig. 1 System architechure for the standalone solar water pumping system

  

EXPECTED SIMULATION RESULTS:

Fig.2 Starting performance of the proposed system

Steady state and transient behavior of proposed system

Fig.3 Steady state and transient behavior of proposed system

Influence of the wrong estimation of pump’s constant

Fig.4 Influence of the wrong estimation of pump’s constant

A brief cost estimation of the proposed solar water pumping system

Fig. 5 A brief cost estimation of the proposed solar water pumping system

 

CONCLUSION

The standalone photovoltaic water pumping system with reduced sensor, has been proposed. It utilizes only three sensors. The reference speed generation for V/f control scheme has been proposed based on the available power the regulating the active power at DC bus. The PWM frequency and pump affinity law have been used to control the speed of an induction motor drive. Its feasibility of operation has been verified through simulation and experimental validation. Various performance conditions such as starting, variation in radiation and steady state have been experimentally verified and found to be satisfactory. The main contribution of the proposed control scheme is that it is inherently, immune to the error in estimation of pump’s constant. The system tracks the MPP with acceptable tolerance even at varying radiation.

 

REFERENCES

  • Drury, T. Jenkin, D. Jordan, and R. Margolis, “Photovoltaic investment risk and uncertainty for residential customers,” IEEE J. Photovoltaics, vol. 4, no. 1, pp. 278–284, Jan. 2014.
  • Muljadi, “PV water pumping with a peak-power tracker using a simple six-step square-wave inverter,” IEEE Trans. on Ind. Appl., vol. 33, no. 3, pp. 714-721, May-Jun 1997.
  • Sharma, S. Kumar and B. Singh, “Solar array fed water pumping system using induction motor drive,” 1st IEEE Intern. Conf. on Power Electronics, Intelligent Control and Energy Systems (ICPEICES), Delhi, 2016.
  • Franklin, J. Cerqueira and E. de Santana, “Fuzzy and PI controllers in pumping water system using photovoltaic electric generation,” IEEE Trans. Latin America, vol. 12, no. 6, pp. 1049-1054, Sept. 2014.
  • Kumar and B. Singh, “BLDC Motor-Driven Solar PV Array-Fed Water Pumping System Employing Zeta Converter,” IEEE Trans. Ind. Appl., vol. 52, no. 3, pp. 2315-2322, May-June 2016.

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Control and Performance Analysis of a Single-Stage Utility-Scale Grid-Connected PV System

IEEE SYSTEMS JOURNAL, VOL. 11, NO. 3, SEPTEMBER 2015

ABSTRACT:

For utility-scale photovoltaic (PV) systems, the control objectives, such as maximum power point tracking, synchronization with grid, current control, and harmonic reduction in output current, are realized in single stage for high efficiency and simple power converter topology. This paper considers a highpower three-phase single-stage PV system, which is connected to a distribution network, with a modified control strategy, which includes compensation for grid voltage dip and reactive power injection capability. To regulate the dc-link voltage, a modified voltage controller using feedback linearization scheme with feedforward PV current signal is presented. The real and reactive powers are controlled by using dq components of the grid current. A small-signal stability/eigenvalue analysis of a grid-connected PV system with the complete linearized model is performed to assess the robustness of the controller and the decoupling character of the grid-connected PV system. The dynamic performance is evaluated on a real-time digital simulator.

 

KEYWORDS:

  1. DC-link voltage control
  2. Feedback linearization (FBL)
  3. Photovoltaic (PV) systems
  4. Reactive power control
  5. Small signal stability analysis
  6. Voltage dip.

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

One of the four 375-kW subsystems.

Fig. 1. One of the four 375-kW subsystems.

  

EXPECTED SIMULATION RESULTS:

(a) PV array voltage for MPPT. (b) PV array (PPV) and grid injected real power (Pg). (c) Grid injected reactive power (Qg).

Fig. 2. (a) PV array voltage for MPPT. (b) PV array (PPV) and grid injected real power (Pg). (c) Grid injected reactive power (Qg).

Grid injected currents and THD.

Fig. 3. Grid injected currents and THD.

PV system response to voltage dip in grid.

Fig. 4 PV system response to voltage dip in grid.

PV system response to a three-phase fault at bus 3.

Fig. 5. PV system response to a three-phase fault at bus 3.

PV system response to an LG fault.

Fig. 6. PV system response to an LG fault.

Pg  response of the whole 1.5-MW PV system.

Fig. 7. Pg  response of the whole 1.5-MW PV system.

 

CONCLUSION:

The proposed modified dc-link voltage controller with FBL technique, using INC MPPT, and real and reactive power controls with enhanced filter for compensation for grid voltage dips has been tested at different insolation levels on a real-time digital simulator (RTDS). Small-signal analysis of a PV system connected to an IEEE 33-bus distributed system is performed. The results from simulation and eigenvalue analysis demonstrate the effectiveness of the FBL controller compared with the controller without FBL. It is found that the FBL controller  outperforms the controllerwithout FBL, as the FBL controller’s  performance is linear at different operating conditions. With grid voltage dip compensator filter, the dynamic performance is much improved in terms of less oscillations and distortion in waveforms. In addition, the eigenvalue analysis shows that the effect of the disturbance in distribution system is negligible on PV system stability as the eigenmodes of the PV system are almost independent of the distribution system. This has been also confirmed by three-phase fault analysis of distribution system in RTDS model. The controller performance is also validated on 4×375 kW PV units connected to the distribution system.

 

REFERENCES:

  • Oprisan and S. Pneumaticos, “Potential for electricity generation from emerging renewable sources in Canada,” in Proc. IEEE EIC Climate Change Technol. Conf., May 2006, pp. 1–10.
  • Petrone, G. Spagnuolo, R. Teodorescu, M. Veerachary, and M. Vitelli, “Reliability issues in photovoltaic power processing systems,” IEEE Trans. Ind. Electron., vol. 55, no. 7, pp. 2569–2580, Jul. 2008.
  • Jain and V. Agarwal, “A single-stage grid connected inverter topology for solar PV systems with maximum power point tracking,” IEEE Trans. Power Electron., vol. 22, no. 5, pp. 1928–1940, Jul. 2007.
  • Katiraei and J. Aguero, “Solar PV integration challenges,” IEEE Power Energy Mag., vol. 9, no. 3, pp. 62–71, May-Jun. 2011.
  • H. Ko, S. Lee, H. Dehbonei, and C. Nayar, “Application of voltageand current-controlled voltage source inverters for distributed generation systems,” IEEE Trans. Energy Convers., vol. 21, no. 3, pp. 782–792, Sep. 2006.

Three-phase grid connected PV inverters using the proportional resonance controller

2016 IEEE

ABSTRACT

The development in grid connected three phase inverter has increased the importance of achieving low distortion and high quality current waveform. This paper describes a method of reducing current ripple in a three phase grid connected inverter utilizing Proportional Resonance (PR) controller. The effectiveness of the PR current controller is demonstrated by comparing its performance with that of the Proportional Integral (PI) controller. Simulation and experimental results show that Proportional Resonance (PR) controller achieves better reduction in total harmonic distortion (THD) in the current signal spectrum.

 

KEYWORDS

  1. Grid-connected inverter
  2. LCL filter
  3. PI controller
  4. PR controller.

 

SOFTWARE:MATLAB/SIMULINK

  

BLOCK DIAGRAM:

block diagram

Fig.1. PI controller in synchronous reference scheme.

Fig. 2 PR controller in stationary reference control

SIMULATION RESULTS

Fig.3. The phase grid voltage

Fig.4. The phase current waveform using PI controller

 

Fig.5 The phase current waveform using Proportional resonance  controller

Fig.6. The FFT of the phase current waveform using PI controller

Fig.7. The FFT of the phase current waveform using Proportional Resonance controller

 

CONCLUSION

This paper has considered the impact of the current control scheme of a three-phase grid-connected inverter under normal and abnormal grid conditions using PI and PR controllers. In particular, this work has compared the performance of the industrially accepted PI controller, and the emerging PR controller which is popular in grid connected renewable energy applications. In keeping with the claims of other literature, simulation studies have confirmed that the PR controller shows better performance under normal operating conditions. There is no steady state error output, and the harmonic content of the current waveform is very low. Moreover, in this paper, the effect of grid voltage dips on the performance of the grid connected inverter was considered. Whilst the PI controller demonstrates very good performance, the Proportional Resonance controller offers superior output power regulation, and improved power quality performance. Overall, it suggests that the PR controller is better suited in the event of grid faults, or operation in weak grid environments.

 

REFERENCES

  1. Wuhua and H. Xiangning, “Review of Nonisolated High-Step-Up DC/DC Converters in Photovoltaic Grid-Connected Applications,” IEEE Trans. Ind Electron., vol. 58, pp. 1239-1250, 2011.
  2. Atkinson, G. Pannell, C. Wenping, B. Zahawi, T. Abeyasekera, and M. Jovanovic, “A doubly-fed induction generator test facility for grid fault ride-through analysis,” Instrumentation & Measurement Magazine, IEEE, vol. 15, pp. 20-27, 2012.
  3. Cecati, A. Dell’Aquila, M. Liserre, and V. G. Monopoli, “Design of H-bridge multilevel active rectifier for traction systems,” Industry Applications, IEEE Transactions on, vol. 39, pp. 1541-1550, 2003.
  4. Hassaine, E. Olias, J. Quintero, and V. Salas, “Overview of power inverter topologies and control structures for grid connected photovoltaic systems,” Renewable and Sustainable Energy Reviews, vol. 30, pp. 796-807, 2014.
  5. Nicastri and A. Nagliero, “Comparison and evaluation of the PLL techniques for the design of the grid-connected inverter systems,” in Industrial Electronics (ISIE), 2010 IEEE International Symposium on, 2010, pp. 3865-3870.

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Automatic droop control for a low voltage DC Microgrid

ABSTRACT

A DC microgrid (DC-MG) provides an effective mean to integrate various sources, energy storage units and loads at a common dc-side. The droop-based, in the context of a decentralized control, has been widely used for the control of the DC-MG. However, the conventional droop control cannot achieve both accurate current sharing and desired voltage regulation. This study proposes a new adaptive control method for DC-MG applications which satisfies both accurate current sharing and acceptable voltage regulation depending on the loading condition. At light load conditions where the output currents of the DG units are well below the maximum limits, the accuracy of the current sharing process is not an issue. As the load increases, the output currents of the DG units increase and under heavy load conditions accurate current sharing is necessary. The proposed control method increases the equivalent droop gains as the load level increases and achieves accurate current sharing. This study evaluates the performance and stability of the proposed method based on a linearised model and verifies the results by digital time-domain simulation and hardware-based experiments.

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig. 1 Simplified DC-MG with two DG units

 

EXPECTED SIMULATION RESULTS:

 

Fig. 2 Output currents of the DG units obtained in Simulation Results

a Conventional droop control method with small droop gains

b Conventional droop control method with large droop gains

c Proposed method

 

 

Fig. 3 Output voltages of the DG units obtained in Simulation Results

a Conventional droop control method with small droop gains

b Conventional droop control method with large droop gains

c Proposed method

 

CONCLUSION

This paper presents a new control scheme for DC-MG without using any communication links. In the conventional droop control, small droop gains result in good voltage regulation but inaccurate current sharing, and large droop gains result in accurate current sharing but unacceptable voltage regulation. To overcome this drawback, a new control method is proposed in which the equivalent droop gains automatically change based on the loading condition. The simulation results show and the experimental results verify that by adaptively changing the droop gains according to the load size, both accurate current sharing and desirable voltage regulation are achieved.

REFERENCES

  • Guerrero, J., Loh, P.C., Lee, T.-L., et al.: ‘Advanced control architectures for intelligent microgrids; part ii: Power quality, energy storage, and ac/dc microgrids’, IEEE Trans. Ind Electron., 2013, 60, (4), pp. 1263–1270
  • Vandoorn, T., De Kooning, J., Meersman, B., et al.: ‘Automatic power-sharing modification of p/v droop controllers in low-voltage resistive microgrids’, IEEE Trans. Power Deliv., 2012, 27, (4), pp. 2318–2325
  • Khorsandi, A., Ashourloo, M., Mokhtari, H.: ‘An adaptive droop control method for low voltage dc microgrids’. 2014 Fifth Power Electronics, Drive Systems and Technologies Conf. (PEDSTC), 2014, pp. 84–89
  • Loh, P.C., Li, D., Chai, Y.K., et al.: ‘Hybrid ac-dc microgrids with energy storages and progressive energy flow tuning’, IEEE Trans. Power Electron., 2013, 28, (4), pp. 1533–1543
  • Loh, P., Li, D., Chai, Y.K., et al.: ‘Autonomous operation of hybrid microgrid with ac and dc subgrids’, IEEE Trans. Power Electron., 2013, 28, (5), pp. 2214–2223

Control Strategy of Three-Phase Battery Energy Storage Systems for Frequency Support in Microgrids and with Uninterrupted Supply of Local Loads

 

ABSTRACT

Frequency control in autonomous microgrids (MG) with high penetration of renewable energy sources represents a great concern to ensure the system stability. In this regard, this paper presents an enhanced control method for battery energy storage systems (BESS) to support the frequency of MG and with the ability of disconnecting from the MG to supplying in the island mode a local consumer. A frequency controller, combining a conventional droop control with an inertia emulation function, governs the BESS active power transfer during the primary frequency control level. The BESS may also provide voltage support in the point of common coupling with the MG. Moreover, the proposed BESS may compensate, partially or totally, the power absorbed by the local loads in order to improve the MG frequency response. When the MG power quality worsens below a certain level, in terms of voltage and frequency, the BESS detaches from the MG and continues to operate islanded.

The reconnection is accomplished following a smoothly resynchronization of the local voltage with the MG, without disturbing the local loads supply. Additionally, this paper also discusses about the aspects related to the BESS management and its integration within the proposed system. The simulation and experimental results assess the feasibility of the proposed control solutions. Frequency control in autonomous microgrids (MG) with high penetration of renewable energy sources represents a great concern to ensure the system stability. In this regard, this paper presents an enhanced control method for battery energy storage systems (BESS) to support the frequency of MG and with the ability of disconnecting from the MG to supplying in the island mode a local consumer. A frequency controller, combining a conventional droop control with an inertia emulation function, governs the BESS active power transfer during the primary frequency control level. The BESS may also provide voltage support in the point of common coupling with the MG.

Moreover, the proposed BESS may compensate, partially or totally, the power absorbed by the local loads in order to improve the MG frequency response. When the MG power quality worsens below a certain level, in terms of voltage and frequency, the BESS detaches from the MG and continues to operate islanded. The reconnection is accomplished following a smoothly resynchronization of the local voltage with the MG, without disturbing the local loads supply. Additionally, this paper also discusses about the aspects related to the BESS management and its integration within the proposed system. The simulation and experimental results assess the feasibility of the proposed control solutions.

 

KEYWORDS

  1. Battery energy storage systems (BESS)
  2. Frequency control
  3. Inverter, microgrid (MG)
  4. Seamless transfer

 

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

 

 

 

 

 

Fig. 1 BESS Structure

 

EXPECTED SIMULATION RESULTS:

 

 

 

 

 

Fig. 2. MG frequency (Top) and BESS active power (Bottom) for different operating conditions (simulation results).

 

 

 

 

 

Fig. 3 MG frequency (Top) and BESS active power (Bottom) for different levels of the local load compensation

 

CONCLUSION

This paper presented a Battery Energy Storage Systems BESS mainly designed to provide frequency support in MG, but having special control features. The BESS can operate both connected to the MG (G-mode) or in (I-mode), whereas the transition between the two states is seamlessly coordinated by an original control method. The BESS may serve local sensitive consumers connected on the local bus, by including special control functions to protect them in adverse MG operating conditions. The BESS management is also taking into discussion from the perspective of its influence upon the proposed controller performance. Simulations and experimental results were provided to validate the proposed BESS. An improved frequency controller, with conventional droop and virtual inertia was proposed and in the simulation results, it proved to be an efficient solution, resulting in faster damping of the MG frequency oscillations. Moreover, by partially or totally compensating the local loads, the MG is relieved by the corresponding power disturbance produced by their stochastic operation and thus the MG frequency deviation can be diminished.

By this approach, the BESS along with the local loads may be considered as a sort of smart load. The transition between G-mode to I-mode took place when the PCC power quality worsened and the experimental results showed a clean transfer without important voltage and frequency variations. The transition between I-mode to G-mode included a smoothly synchronization period of the local voltage with the MG voltage, after which the switching to G-mode did not disturb either the local loads or the MG. During I-mode, the local loads are supplied directly by the BESS and the presented experimental results including a comprehensive operating case, proved that the voltage control quality falls into the required standards. Future studies are intended to be carried out on the system availability to contribute to the MG power quality improvement.

 

REFERENCES

  • European Commission, Energy Roadmap 2050, 2011. [Online].Available: http://ec.europa.eu/energy/energy2020/roadmap/index_en.htm
  • Bevrani, A. Ghosh, and G. Ledwich, “Renewable energy sources and frequency regulation: Survey and new perspectives,” IET Renew. Power Gen., vol. 4, no. 5, pp. 438–457, Sep. 2010.
  • Tan, Q. Li, and H. Wang, “Advances and trends of energy storage technology in Microgrid,” Int. J. Elect. Power Energy Syst., vol. 44, no. 1, pp. 179–191, Jan. 2013.
  • Bottrell, M. Prodanovic, and T. C. Green, “Dynamic stability of a microgrid with an active load,” IEEE Trans. Power Electron., vol. 28, no. 11, pp. 5107–5119, Nov. 2013.
  • A. P. Lopes, F. J. Soares, and P. M. R. Almeida, “Integration of electric vehicles in the electric power system,” Proc. IEEE, vol. 99, no. 1, pp. 168–183, Jan. 2011.

Speed Control of Induction Motor Using New Sliding Mode Control Technique

ABSTRACT

Induction Motors have been used as the workhorse in the industry for a long time due to its easy build, high robustness, and generally satisfactory efficiency. However, they are significantly more difficult to control than DC motors. One of the problems which might cause unsuccessful attempts for designing a proper controller would be the time varying nature of parameters and variables which might be changed while working with the motion systems. One of the best suggested solutions to solve this problem would be the use of Sliding Mode Control (SMC). This paper presents the design of a new controller for a vector control induction motor drive that employs an outer loop speed controller using SMC. Several tests were performed to evaluate the performance of the new controller method, and two other sliding mode controller techniques. From the comparative simulation results, one can conclude that the new controller law provides high performance dynamic characteristics and is robust with regard to plant parameter variations.

 

KEYWORDS:

  1. Induction Motor
  2. Sliding Mode Control
  3. DC Motors
  4. PI Controller

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Induction motor drive system with sliding mode controller

Fig. 1 Induction motor drive system with sliding mode controller

EXPECTED SIMULATION RESULTS:

                           Rotor speed tracking performance (b)Rotor speed tracking error (c)Control effort Rotor speed tracking performance (b)Rotor speed tracking error (c)Control effort Rotor speed tracking performance (b)Rotor speed tracking error (c)Control effort

Fig.2 (a)Rotor speed tracking performance  (b)Rotor speed tracking error   (c)Control effort

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Fig.3 (a)Rotor speed tracking performance  (b)Rotor speed tracking error   (c)Control effort

image008 image009 image010

Fig.4 (a)Rotor speed tracking performance  (b)Rotor speed tracking error   (c)Control effort

 

CONCLUSION

In this paper, new technique to reduced chattering for sliding mode control is submitted to design the rotor speed control of induction motor. To validate the performances of the new proposed control law, we provided a series of simulations and a comparative study between the performances of the new proposed sliding mode controller strategy and those of the Pseudo and Saturation sliding mode controller techniques. The sliding mode controller algorithms are capable of high precision rotor speed tracking. From the comparative simulation results, one can conclude that the three sliding mode controller techniques demonstrate nearly the same dynamic behavior under nominal condition. Also, from the simulation results, it can be seen obviously that the control performance of the new sliding mode controller strategy in the rotor speed tracking, robustness to parameter variations is superior to that of the other sliding mode controller techniques.

 

REFERENCES

  1. Wade, M.W.Dunnigan, B.W.Williams, X.Yu, ‘Position control of a vector controlled induction machine using slotine’s sliding mode control’, IEE Proceeding Electronics Power Application, Vol. 145, No.3, pp.231-238, 1998.
  2. I.Utkin, ‘Sliding mode control design principles and applications to electric drives’, IEEE Transactions on Industrial Electronics, Vol.40, No.1, pp. 23-36, February 1993.
  3. K.Namdam, P.C.Sen, ‘Accessible states based sliding mode control of a variable speed drive system’, IEEE Transactions Industry Application, Vol.30, August 1995, pp.373-381.
  4. Krishnan, ‘Electric motor drives: modelling, analysis, and control’, Prentice-Hall, New-Jersey, 2001.
  5. J.Wai, K.H.Su, C.Y.Tu, ‘Implementation of adaptive enhanced fuzzy sliding mode control for indirect field oriented induction motor drive’, IEEE International Conference on Fuzzy Systems, pp.1440-1445, 2003.

 

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Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics, and electro magnetism. This field first became an identifiable occupation in the later half of the 19th century after commercialization of the electric telegraph, the telephone, and electric power distribution and use. Subsequently, broad casting and recording media made electronics part of daily life. The invention of the transistor, and later the integrated circuit, brought down the cost of electronics to the point they can be used in almost any household object.

Electrical engineering has now subdivided into a wide range of sub fields including electronics, digital computers, power engineering, tele communications, control systems, radio-frequency engineering, signal processing, instrumentation, and microelectronics. Many of these sub disciplines overlap and also overlap with other engineering branches, spanning a huge number of specializations such as hardware engineering, power electronics, electro magnetics & waves, microwave engineering, nanotechnology, electro chemistry, renewable energies, mechatronics, electrical materials science, and many more.

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