Design of a SRF Based MC UPQC Used for Load Voltage Control in Parallel Distribution Systems

ABSTRACT:

This paper deals with a new design dynamic model of synchronous-reference- frame (SRF)-based control in three phase system under different load considerations to improve power quality by using power conditioner with multi converters. The proposed MCUPQC system can regulate the load voltages/bus voltages on Parallel power distribution systems under balanced and distorted load conditions and obtain the state space model for MC-UPQC. The simulation results to support the SRF-based control method presented in this paper is done using Matlab/Simulink.

 

KEYWORDS:

  1. Power quality (PQ)
  2. Active power filter (APF)
  3. Synchronous reference frame (SRF) and multi converter
  4. Unified power-quality conditioner (MC-UPQC)

  

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

Fig.1.The single line diagram of conventional MC-UPQC

 

 EXPECTED SIMULATION RESULTS:

Fig. 2.a and b. the phase bus voltage, VS1 and load voltage VL1

Fig. 3.c and d. the phase bus voltage, VS2 and load voltage VL2

Fig.4.a & b. the phase Source Current, IS1 and Load CurrentIL1

Fig. 5 and 6 .a, b and c. The phase bus voltage, injected voltage and load Voltages

Fig. 7.a, b and c. The phase Source Currents (IS1), load Currents (IL1) and DC Capacitor Voltage(VDC).

Fig. 8.a, b, c, d, e and f. the phase bus voltage (VS1), load Voltages (VL1), load Voltages (VL2), the phase source currents (IS1), load Currents (IL1) and DC Capacitor Voltage (VDC).

  

CONCLUSION:

In this paper the SRF Based control MC-UPQC for regulates of load voltage and load current in adjacent parallel feeder has been proposed and compared to a conventional MC-UPQC, the proposed control topology is capable of fully protecting critical and sensitive loads against sudden changing loads, voltage sag/ swells, and fault interruption in two-feeder distribution systems. The performance of the SRF based MC-UPQC is tested under various disturbance conditions.

 

REFERENCES:

  • G. Hingorani “Introducing custom power,” IEEE spectrum, vol.32, June 1995, pp. 41-48.
  • Ray Arnold “Solutions to Power Quality Problems” power engineering Journal, Volume 15; Issue: 2 April 2001, pp: 65-73.
  • John Stones and Alan Collision “Introduction to Power Quality” power engineering journal, Volume 15; Issue 2, April 2001, pp: 58- 64.
  • Fujita and H. Akagi, “The unified power quality conditioner: The integration of series and shunt active filter,” IEEE Trans. Power Electron. , vol. 13, no. 2, pp. 315–322, Mar. 1998..
  • Gyugyi, C. D. Schauder, S. L. Williams, T. R. Rietman, D. R. To rjerson, and A. Edris, “The unified power flow controller: A new approach to power transmission control,” IEEE Trans. Power Del. , vol. 10, no. 2, pp. 1085–1097, Apr. 1995.

Multiconverter Unified Power Quality Conditioning System Using Artificial Neural Network Technique

ABSTRACT:

This paper presents a new unified power-quality conditioning system (MC-UPQC), capable of simultaneous compensation for voltage and current in multibus/multifeeder systems. In this configuration, one shunt voltage-source converter (shunt VSC) and two or more series VSCs exist. The system can be applied to adjacent feeders to compensate for supply-voltage and load current imperfections on the main feeder and full compensation of supply voltage imperfections on the other feeders. In the proposed configuration, all converters are connected back to back on the dc side and share a common dc-link capacitor. Therefore, power can be transferred from one feeder to adjacent feeders to compensate for sag/swell and interruption. The performance of the MC-UPQC as well as the adopted control algorithm is illustrated by simulation. The present work study the compensation principle and different control strategies used here are based on PI & ANN Controller of the MC-UPQC in detail. The results obtained in MATLAB/PSCAD on a two-bus/two-feeder system show the effectiveness of the proposed configuration.

KEYWORDS:

  1. power quality (PQ) unified power-quality conditioner (UPQC)
  2. voltage-source converter (VSC)
  3. Aritifical neural network- ANN

  

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig.1.Block diagram of MC_UPQC with STATCOM

  

EXPECTED SIMULATION RESULTS:

Fig2. BUS1 voltage,series compensating voltage, and load voltage in feeder1

Fig3.BUS2 voltage,series compensating voltage, and load voltage in feeder2

Fig4.nonlinear load current,compensating current,feeder1 current and capacitor voltage

Fig5.Bus1 loadcurrent,Bus2 load current,Bus1 load voltage,Bus2 load voltage wave forms using ANN controller in Mc- UPQC

Fig 6. Three phase source voltage(Va,Vb,Vc) wave form

Fig.7. load current with ANN controller

Fig.8 Load Voltage with ANN Controller

CONCLUSION:

The present topology illustrates the operation and control of Multi Converter Unified Power Quality Conditioner (MCUPQC). The system is extended by adding a series VSC in an adjacent feeder. A suitable mathematical have been described which establishes the fact that in both the cases the compensation is done but the response of ANN controller is faster and the THD is minimum for the both the voltage and current in sensitive/critical load. The device is connected between two or more feeders coming from different substations. A non-linear/sensitive load L-1 is supplied by Feeder-1 while a sensitive/critical load L-2 is supplied through Feeder-2. The performance of the MC-UPQC has been evaluated under various disturbance conditions such as voltage sag/swell in either feeder, fault and load change in one of the feeders. In case of voltage sag, the phase angle of the bus voltage in which the shunt VSC (VSC2) is connected plays an important role as it gives the measure of the real power required by the load. The MC-UPQC can mitigate voltage sag in Feeder-1 and in Feeder-2 for long duration.

 

REFERENCES:

  • Hamid Reza Mohammadi, Ali Yazdian Varjani, and Hossein Mokhtari,“Multiconverter Unified Power-Quality Conditioning System: MC- UPQC” IEEE RANSACTIONS ON POWER DELIVERY, VOL. 24,NO. 3, JULY 2009.
  • Rezaeipour and A.Kazemi, “Review of Novel control strategies for UPQC” Internal Journal of Electric and power Engineering 2(4) 241-247, 2008.
  • Ravi Kumar and S.Siva Nagaraju“Simulation of DSTATCOM and DVR in power systems” Vol. 2, No. 3, June 2007 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences.
  • V.Kasuni Perera” Control of a Dynamic Voltage Restorer to compensate single phase voltage sags” Master of Science Thesis, Stockholm, Sweden 2007.
  • Basu, S. P. Das, and G. K. Dubey, “Comparative evaluation of two models of UPQC for suitable interface to enhance power quality,” Elect.Power Syst. Res., pp. 821–830, 2007.

Synchronization and Reactive Current Support of PMSG based Wind Farm during Severe Grid Fault

ABSTRACT:

Grid codes require wind farm to remain on-grid and inject specific reactive current when grid fault occurs. To satisfy the requirements, reactive power devices such as the static synchronous compensator (STATCOM) are usually used in modern wind farms. In order to produce reactive currents, the wind energy generation system (WECS) and the STATCOM are normally controlled with the phase locked loop (PLL)-oriented vector control methods. Due to the active power imbalance between the generation and consumption, the wind farm has the risk of losing synchronization with the grid under severe fault conditions. This paper analyzes the dynamic synchronization mechanism and stability criteria of the wind farm and proposes a coordinated current control scheme for the WECS and the STATCOM during severe grid fault period. The synchronization stability of both the WECS and the STATCOM is remained by the active power balancing control of the wind farm. The control objectives of the generator- and grid-side converters for the WECS are swapped to avoid the interaction between the dc-link voltage control loop and the synchronization loop. The synchronized STATCOM produces additional reactive currents to help the wind farm meet the requirements of the grid code. Effectiveness of the theoretical analyses and the proposed control method are verified by simulations.

 

KEYWORDS:

  1. Low voltage ride through (LVRT)
  2. Permanent magnet synchronous generator (PMSG)
  3. Wind farm
  4. Coordinated current control

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig. 1. Configuration of the PMSG-based wind farm

  

EXPECTED SIMULATION RESULTS:

Fig. 2. System response of the PMSG-based wind farm with conventional control strategy during severe fault

Fig. 3. System response of the PMSG-based wind farm with proposed strategy during severe fault

 

CONCLUSION:

This paper studied the LOS mechanism and the coordinating LVRT scheme of the PMSG based wind farm when severe grid voltage dip occurs. The following conclusions can be derived from the theoretical analyses and simulation verification:

(1) Variable-speed wind turbines and STATCOM both have the LOS risk when the grid voltage dip is severe.

(2) The proposed active power balancing control scheme which relies on the frequency dynamic of the PLL can achieve the synchronization stability of the WECS. However, reactive current capability of the WECS would be sacrificed to implement such scheme.

(3) The coordinated current control between the PMSG based WECS and the STATCOM can achieve both the synchronization stability and the reactive current support according to the grid code under severe grid fault. The analysis results and proposed scheme are also available for the LVRT of other renewable energy conversion systems.

(4) It should be pointed out that this paper focuses on the symmetrical fault conditions. In practical applications, unsymmetrical faults occur more often than symmetrical ones. Some Europe grid codes, such as “VDE-AR-N 4120” code in Germany, are requiring the WECS to provide negative sequence current compensation during unsymmetrical fault period. In such cases, the advanced PLL, such as the second order generalized integrator (SOGI) PLL [31], should be employed to separate the positive and negative sequence components from the grid voltage. The advanced PLLs have much more complicated structures and models compared with the conventional one as indicated in this paper. Also the synchronization stability should be discussed in both positive and negative sequences. By further considering the coupling of the PLL and control loops during grid faults similarly with the case discussed in this paper, the synchronization issue would be more complicated. More studies are expected in this issue and would be our future work.

 

REFERENCES:

  • BDEW Technical Guideline, Generating Plants Connected to the Medium- Voltage Network [EB/OL], June 2008 issue.
  • Grid code-high and extra high voltage, E. ON Netz GmbH, 2006. Tech. Rep., [EB/OL].
  • Geng, C. Liu and G. Yang. LVRT Capability of DFIG-Based WECS Under Asymmetrical Grid Fault Condition [J]. IEEE Transactions on Industrial Electronics, vol. 60, no. 6, pp. 2495-2509, June 2013.
  • Chinchilla M., Arnaltes S., Burgos J. C. Control of permanent-magnet generators applied to variable-speed wind-energy systems connected to the grid [J]. IEEE Transactions on Energy Conversion, 2006, 21(1): 130-5.
  • Conroy J. F., Watson R. Frequency Response Capability of Full Converter Wind Turbine Generators in Comparison to Conventional Generation [J]. IEEE Transactions on Power Systems, 2008, 23(2): 649-56.

Control of permanent magnet synchronous generator-based stand-alone wind energy conversion system

ABSTRACT:

This study deals with an implementation of a constant speed permanent magnet synchronous generator (PMSG)-based three-phase stand-alone wind energy conversion system (SWECS). The voltage and frequency controller is realised using only a single voltage source converter (VSC) and a battery energy storage system (BESS). The BESS is used to provide load leveling under varying wind speeds and to control frequency of SWECS. The voltage of PMSG is regulated under varying wind speeds and loads by supplying the reactive power from VSC. The performance of SWECS is demonstrated as a load leveller, a load balancer, a harmonic compensator and a voltage and frequency controller.

 

SOFTWARE: MATLAB/SIMULINK

  

CIRCUIT DIAGRAM:

Fig. 1 Proposed system configurations of VFC for PMSG-based SWECS

a System configuration of VFC for PMSG-based 3P3W SWECS

b System configuration of VFC for PMSG-based 3P4W SWECS

  

EXPECTED SIMULATION RESULTS:

Fig. 2 Simulated performance of VFC under fall in wind speed (12 –10 m/s) at fixed balanced linear loads

Fig. 3 Simulated performance of VFC under rise in wind speed (10 –12 m/s) at balanced linear loads

 

CONCLUSION:

A VFC for a PMSG in stand-alone WECS has been designed, modelled and developed for feeding three-phase consumer loads. The VFC has been realised using a VSC and a battery energy storage system. A new control strategy for VFC has been realised using IcosF algorithm and implemented for PMSG-based SWECS. The performance of VFC has been found satisfactory under varying wind speeds and loads. The VFC has performed the functions of load leveller, load balancer and a harmonic eliminator along with VFC.

REFERENCES:

  • Patel, M.R.: ‘Wind and solar power systems’ (CRC Press, Washington, DC, 2006, 2nd edn.)
  • David, S.B., Jenkins, N., Bossanyi, E.: ‘Wind energy handbook’ (John Wiley & Sons. Ltd., 2001)
  • Simoes, M.G., Farret, F.A.: ‘Renewable energy systems’ (CRC Press, Florida, 2004)
  • Lai, L.L., Chan, T.F.: ‘Distributed generation -induction and permanent magnet generators’ (John Wiley and Sons Ltd., 2007
  • Heier, S.: ‘Grid integration of wind energy conversion systems’ (Wiley, New York, 1998)

Control of a Stand Alone Variable Speed Wind Turbine with a Permanent Magnet Synchronous Generator

ABSTRACT:

A novel control strategy for the operation of a permanent magnet synchronous generator (PMSG) based stand alone variable speed wind turbine is presented in this paper,. The direct drive PMSG is connected to the load through a switch mode rectifier and a vector controlled pulse width modulated (PWM) IGBT-inverter. The generator side switch mode rectifier is controlled to achieve maximum power from the wind. The load side PWM inverter is using a relatively complex vector control scheme to control the amplitude and frequency of the inverter output voltage. As there is no grid in a stand-alone system, the output voltage has to be controlled in terms of amplitude and frequency. The stand alone control is featured with output voltage and frequency controller capable of handling variable load. A damp resistor controller is used to dissipate excess power during fault or over-generation. The potential excess of power will be dissipated in the damp resistor with the chopper control and the dc link voltage will be maintained. Extensive simulations have been performed using Matlab/Simpower. Simulation results show that the controllers can extract maximum power and regulate the voltage and frequency under varying load condition. The controller performs very well during dynamic and steady state condition.

  

KEYWORDS:

  1. Permanent magnet synchronous generator
  2. Maximum power extraction
  3. Switch-mode rectifier
  4. Stand alone variable
  5. Speed wind turbine
  6. Voltage and frequency control

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Figure 1.Control Structure of a PMSG based standalone variable speed wind turbine.

 

EXPECTED SIMULATION RESULTS:

 

Figure 2. Response of the system for a step change of wind speed from 10 m/s to 12 m/s to 9 m/s to 10 m/s.

Figure 3. Voltage and current responses at a constant load.

Figure 4. Frequency response, DC link voltage and modulation index at a constant load.

Figure 5. Voltage and current responses when load is reduced by 50%.

Figure.6. Frequency response, DC link voltage and modulation index when load is reduced by 50%.

 

CONCLUSION:

Control strategy for a standalone variable speed wind turbine with a PMSG is presented in this paper. A simple control strategy for the generator side converter to extract maximum power is discussed and implemented using Simpower dynamic system simulation software. The controller is capable to maximize output of the variable speed wind turbine under fluctuating wind. The load side PWM inverter is controlled using vector control scheme to maintain the amplitude and frequency of the inverter output voltage. It is seen that the controller can maintain the load voltage and frequency quite well at constant load and under varying load condition. The generating system with the proposed control strategy is suitable for a small scale standalone variable speed wind turbine installation for remote area power supply. The simulation results demonstrate that the controller works very well and shows very good dynamic and steady state performance

 

REFERENCES:

  • Müller, S., Deicke, M., and De Doncker, Rik W.: ‘Doubly fed induction genertaor system for wind turbines’, IEEE Industry Applications Magazine, May/June, 2002, pp. 26-33.
  • Polinder, F. F. A. van der Pijl, G. J. de Vilder, P. J. Tavner, “Comparison of direct-drive and geared generator concepts for wind turbines,” IEEE Trans. On energy conversion, vol . 21, no. 3, pp. 725-733, Sept. 2006.
  • F. Chan, L. L. Lai, “Permanenet-magnet machines for distributed generation: a review,” in proc. 2007 IEEE power engineering annual meeting, pp. 1-6.
  • De Broe, S. Drouilhet, and V. Gevorgian, “A peak power tracker for small wind turbines in battery charging applications,” IEEE Trans. Energy Convers., vol. 14, no. 4, pp. 1630–1635, Dec. 1999.

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Grid Connected Wind- Photovoltaic hybrid System

ABSTRACT

 This paper presents a modeling and control strategies of a grid connected Wind-Photovoltaic hybrid system. This proposed system consists of two renewable energy sources in order to increase the system efficiency. The Maximum Power Point Tracking (MPPT) algorithm is applied to the PV system and the wind system to obtain the maximum power for any given external weather conditions. The generator side converter is controlled by the Field Oriented Control (FOC). This approach is used to control independently the flux and the torque by applying the d- and q-components of the current motor. The utility grid side converter is controlled by the Voltage Oriented Control (VOC) strategy which is adopted to adjust the DC-link at the desired voltage. The simulation results using PSIM software environment prove the good performance of these used techniques to generate sinusoidal current waveforms. This current is synchronized with the grid voltage. Moreover, the DC bus voltage is perfectly constant because only the active power is injected into the grid. Simulations are carried out to validate the effectiveness of the proposed system methods.

KEYWORDS

  1. Converter
  2. FOC
  3. Grid
  4. hybrid system
  5. MPPT control
  6. photovoltaic system
  7. SCIG
  8. VOC
  9. Wind turbine

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM

 

Fig. l.The proposed PV -wind hybrid system

 EXPECTED SIMULATION RESULTS

Fig. 2 Solar irradiance changes

Fig. 3 The variation of PY arrays current

Fig. 4 The PY arrays voltage

Fig. 5 The PY arrays power and reference

Fig. 6 Duty cycle

Fig. 7 Wind speed profile

Fig. 8 Electrical angular speed of the SCIG and its reference

Fig. 9 The active power injected into the grid

Fig. 10 The Reactive power injected into the grid

Fig. 11 The waveforms of the current

Fig. 12 The three phase current and voltage waveforms

Fig. 13. DC link voltage.

CONCLUSION

In this paper, Wind-Photo voltaic hybrid system control has been investigated. An MPPT method has been studied. It has been simulated with different solar irradiation and wind speed environments in order to maximize the output power of the proposed system . Two control techniques have been employed to improve the hybrid system usefulness . The controlled rectifier connected to the squirrel-cage induction generator (SCIG) has been controlled by the Field Oriented Control (FOC) to reach the optimal rotational speed, The grid-side inverter has been controlled by the Voltage Oriented Control (VOC) method to keep the dc-link voltage at the desired value. The hybrid system simulation has been implemented in PSIM software and its performances were proved when the solar irradiance change or the wind speed occurs.

REFERENCES

 [1] Liyuan Chen, Yun Liu “Scheduling Strategy of Hybrid Wind Photovoltaic- Hydro Power Generation System” International Conference on Sustainable Power Generation and Supply (SUPERGEN 2012), Sept. 2012.

[2] Akhilesh P. Pati!, Rambabu A. Vatti and Anuja S. Morankar,” Simulation of Wind Solar Hybrid Systems Using PSIM ” International Journal of Emerging Trends in Electrical and Electronics (lJETEE), Vol. 10, Issue. 3, April-2014.

[3] Rabeh Abbassi, Manel Hammami, Souad Chebbi. “Improvement of the integration of a grid connected wind-photovoltaic hybrid system” Electrical Engineering and Software Applications (lCEESA), International Conference , 2013

[4] Harini M., Ramaprabha R. and Mathur B. L. “Modeling of grid connected hybrid windlPV generation system using matlab, Vol. 7,no. 9, September 2012.

[5] Nabil A. Ahmed “On-Grid Hybrid Wind/Photovoltaic/Fuel Cell Energy System” Conference on Power & Energy ( IPEC), December 2012.

 

 

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Novel Family of Single-Stage Buck-Boost Inverters Based on Unfolding Circuit

ABSTRACT:

This paper describes a novel family of single-phase single-stage buck-boost inverters using output unfolding circuits. Operation principles, component design guidelines along with modulation techniques are presented and discussed. The simulation results confirm all theoretical statements. Experimental setup of the most promising solution is assembled and tested, where the efficiency for different operation modes is analyzed. Finally, the pros and cons along with applications of the proposed solutions are discussed in the conclusions.

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Family of the single-phase single-stage buck-boost inverters with unfolding circuits: single-inductor unfolding buck-boost inverter (a), tappedinductor unfolding buck-boost inverter (b), single-inductor twisted unfolding buck-boost inverter (c).

EXPECTED SIMULATION RESULTS:

Fig. 2..Simulation results of proposed circuits for boost case: the output voltage and the inductor`s current ((a) for circuit in Fig. 2a, (d) for circuit in Fig. 2b, (g) for circuit in Fig. 2c); the input voltage and the input current ((b) for circuit in Fig. 2a, (e) for circuit in Fig. 2b, (h) for circuit in Fig. 2c ); ripples of the output voltage and of the inductor`s current ((c) for circuit in Fig. 2a, (f) for circuit in Fig. 2b, (e) for circuit in Fig. 2c).

Fig. 3. Simulation results of proposed circuits for buck case: the output voltage and the inductor`s current ((a) for circuit in Fig. 2a, (d) for circuit in Fig. 2b, (g) for circuit in Fig. 2c); the input voltage and the input current ((b) for circuit in Fig. 2a, (e) for circuit in Fig. 2b, (h) for circuit in Fig. 2c); ripples of the output voltage and of the inductor`s current ((c) for circuit in Fig. 2a, (f) for circuit in Fig. 2b, (e) for circuit in Fig. 2c.

  

CONCLUSION:

This paper has presented a novel family of buck-boost inverters using output unfolding circuit. Component design guidelines along with modulation techniques are given. Simulation and experimental results confirmed the theoretical analysis. It is demonstrated that the main advantage of these solutions is the reduced size of passive elements in a wide range of input voltage regulation. It is achieved due to the direct dc to ac energy conversion without any dc-link stage. Despite the increased amount of semiconductors, the overall efficiency can be very high because only two semiconductors are involved in high switching performance in any period of operation. The solutions proposed can be recommended for PV applications where high power corresponds to high voltage. In advance, it gives reduced EMI compared to any other competitive solutions. At the same time, a continuous input current is achieved. The proposed modifications of the buck-boost inverters provide high selection flexibility. The buck-boost inverter with a tap-inductor and output unfolding circuit may provide very high step-up solutions. Another valuable advantage is the common voltage shape, which contains no high switching frequency components. As a result, leakage current problem does not exist for PV application.

 

REFERENCES:

  • Bortis, D. Neumayr, J. W. Kolar, “ηρ-Pareto optimization and comparative evaluation of inverter concepts considered for the GOOGLE Little Box Challenge”, in Proc. of IEEE 17th Workshop on Control and Modeling for Power Electronics (COMPEL), 2016, pp. 1–5.
  • Ghosh; Miao-xin Wang; S. Mudiyula; U. Mhaskar; R. Mitova, D. Reilly; D. Klikic, “Industrial Approach to Design a 2-kVa Inverter for Google Little Box Challenge”, IEEE Trans. Ind. Electron., vol. 65, no. 7, pp. 5539-5549, July 2018.
  • Morsy, P. Enjeti, “Comparison of Active Power Decoupling Methods for High-Power-Density Single-Phase Inverters Using Wide- Bandgap FETs for GoogleLittle Box Challenge”, in IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 4, N 3, 2016, pp. 790–798.
  • Kaminski, O. Hilt, “SiC and GaN Devices – Competition or Coexistence,” in Proc. of Integrated Power Electronics Systems (CIPS), 7th International Conference on, 2012, pp. 1-11.
  • Chub, M. Zdanowski, A. Blinov, J. Rabkowski “Evaluation of GaN HEMTs for high-voltage stage of isolated DC-DC converters” in proc. of 10th International Conference on Compatibility.

An Improved H8 Topology for Common-mode Voltage Reduction

ABSTRACT:

This paper presents an improved H8 power converter for common-mode voltage reduction and electromagnetic interference suppression. The proposed H8 converter can realize zero common-mode voltage variation when entering and leaving the zero state, which is mainly achieved by both the improvement of the structure and the control strategy. For the system structure, two switches are added on the DC bus to float the AC part of the three phase converter in the zero state. Besides, additional capacitors are used to realize controllable common-mode voltage. For the control strategy, a simple control strategy is proposed for the H8 converter. It can automatically adapt to the flowing orientation of the load current to realize synchronous switching of the power switches, which effectively eliminates the impact of the dead time. Through analysis, simulations and experiment, a comparison between the proposed H8 converter and the conventional H6 converter is performed. Results validates the effectiveness of the H8 topology.

 

KEYWORDS:

  1. H8 topology
  2. Common-mode voltage reduction
  3. Electromagnetic interference source suppression.

 SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. The topology of the proposed H8 converter.

 

EXPECTED SIMULATION RESULTS:

(a) Waveform of CMV in a fundamental circle.

(b) Waveform of CMV in a carrier circle.

(c) Waveform of CMV distortion.

Fig. 2. Comparison of the CMV of the proposed topology and conventional H6 topology

(a) 0 pF.

(b) 500 pF.

(c) 2.2 nF.

Fig. 3. Comparison of the CMV of the H8 converter with different additional capacitor.

 

CONCLUSION:

To reduce the CMV of the two level three phase power converter, an improved H8 converter is proposed in this study. The H8 topology disconnects the power supply and the AC output circuit in the zero state, and zero CMV variation is achieved though applying connection capacitors and specific control strategies. The performance of the proposed H8 converter is evaluated through theoretical analysis, simulations and experiments. Compared with the conventional H6 three phase topology, the proposed H8 much reduces the CMV in the zero state, which would be advantageous for the CMV-sensitive applications such as motor and photovoltaic systems. The suppressed CMV also results in the reduction of the common-mode EMI for a three phase converter. Besides, the proposed H8 topology precedes the previous H8 works by realizing zero CMV variation when entering and leaving zero state. Future work will be dedicated to the CMV suppression for other topologies.

 

REFERENCES:

  • Podrzaj, G. Gabic and M. Podhraski, “Introduction of some design aspects for improved performance of the DC/AC induction motor converter,” in Information and Communication Technology, Electronics and Microelectronics (MIPRO), 2014 37th International Convention on, May. 2014.
  • Lorenzani, G. Migliazza, F. Bianchini, and G. Buticchi, “Ground Leakage Current in PV Three-phase Current Source Inverter Topologies,” in Industrial Electronics Society, IECON 2017 – 43rd Annual Conference of the IEEE, Nov. 2017.
  • Alhasheem, T. Dragicevic, and F. Blaabjerg, “Evaluation of multi predictive controllers for a two-level three-phase stand-alone voltage source converter,” in Power Electronics Conference (SPEC), 2017 IEEE Southern, Dec. 2017.
  • H. Akagi, and S. Tamura, “A Passive EMI Filter for Eliminating Both Bearing Current and Ground Leakage Current From an Inverter-Driven Motor,” IEEE Trans. Power Electron., vol. 21, no. 5, pp. 1459-1469, 2006.
  • Gubia, P. Sanchis, A. Ursua, J. Lopez, and L. Marroyo, “Ground currents in single-phase transformerless photovoltaic systems,” Prog. Photovolt.: Res. Appl., vol. 15, no. 7, pp. 629–650, May. 2007.

ZSI for PV systems with LVRT capability

ABSTRACT:

This study proposes a power electronics interface (PEI) for photovoltaic (PV) applications with a wide range of ancillary services. As the penetration of distributed generation systems is booming, the PEI for renewable energy sources should be capable of providing ancillary services such as reactive power compensation and low-voltage ride through (LVRT). This study proposes a robust model predictive-based control strategy for grid-tied Z-source inverters (ZSIs) for PV applications with LVRT capability. The proposed system has two operation modes: normal grid condition and grid fault condition modes. In normal grid condition mode, the maximum available power from the PV panels is injected into the grid. In this mode, the system can provide reactive power compensation as a power conditioning unit for ancillary services from DG systems to main ac grid. In case of grid faults, the proposed system changes the behavior of reactive power injection into the grid for LVRT operation according to the grid requirements. Thus, the proposed controller for ZSI is taking into account both the power quality issues and reactive power injection under abnormal grid conditions. The proposed system operation is verified experimentally, the results demonstrate fast dynamic response, small tracking error in steady-state, and simple control scheme.

 

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

Fig. 1 General schematic representation of the proposed PEI based on the ZSI for grid-tied PV application with LVRT capability 

  

EXPECTED SIMULATION RESULTS

Fig. 2 System performance evaluation in steady-state MPPT mode and transition between LVRT and MPPT modes (a) Grid voltage (vg), grid current (ig), inductor L1 current (IL1), and pulsating dc-link voltage (Vdc) when the system is operating in MPPT mode and unit power factor in normal grid condition, (b) Grid voltage (vg), grid current (ig), inductor L1 current (IL1), and pulsating dc-link voltage (Vdc) when the system is operating in MPPT mode and unit power factor in normal grid condition with distorted grid voltage, (c) Grid voltage (vg), grid current (ig), inductor L1 current (IL1), and pulsating dc-link voltage (Vdc) when the 25% gridvoltage sag  occurs at t1 and the system changes its mode of operation from MPPT to LVRT with reactive current injection, (d) Grid voltage (vg), grid current (ig), inductor L1 current (IL1), and pulsating dc-link voltage (Vdc) when the grid goes back to normal condition at t2 and the system changes its mode from LVRT to MPPT with unity power factor

Fig. 3 System performance evaluation to changes in solar irradiance in MPPT and LVRT modes (a) Grid voltage (vg), grid current (ig), inductor L1 current (IL1), and pulsating dc-link voltage (Vdc) with a step change in solar irradiance level from 1000 to 700 W/m2 at time t3 when the system is operating in MPPT mode under normal grid condition, (b) Grid voltage (vg), grid current (ig), inductor L1 current (IL1), and pulsating dc-link voltage (Vdc) with step change in solar irradiance level from 700 to 1000 W/m2 at time t4 when the system is operating in LVRT mode and 25% grid voltage sag

Fig. 4 Active and reactive powers when the grid voltage sag of 25% occurs for time intervals t1–t2. The system is operating in normal grid condition before t1 and after t2

 

CONCLUSION:

This paper proposes a single-stage PEI based on impedance-source inverter for PV applications with LVRT capability during the grid voltage sag according to grid standards. By using the MPC framework, a simple control strategy is proposed with an adaptive cost function to seamlessly operate under normal and faulty grid conditions. The proposed system eliminates the requirements of multi–nested-loop of classical controller. Owing to the predictive nature of the controller, the proposed system has fast dynamic response to change in solar irradiance or grid reactive power requirement according to LVRT operation. The system is switching between LVRT and MPPT modes of operations seamlessly. The proposed system can be extended for overnight operation of PV sources in DGs with reactive power compensation capability as ancillary service from DG to main grid. Several experiments have been conducted to verify the performance of the proposed system. The results demonstrate robust operation, MPP operation during the healthy grid condition, high-power quality injection during steady-state condition, negligible overshoot/undershoot in grid current injection due to change in solar irradiance or reactive power reference, no observation of inrush current during dynamic change in MPC cost function references for LVRT operation, and maintaining constant peak grid current during the LVRT mode.

 

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