Operation of Series and Shunt Converters with 48-pulse Series Connected three-level NPC Converter for UPFC

ABSTRACT:

The 48-pulse series connected 3-level Neutral Point Clamped (NPC) converter approach has been used in Unified Power Flow Controller (UPFC) application due to its near sinusoidal voltage quality. This paper investigates the control and operation of series and shunt converters with 48-pulse Voltage Source Converters (VSC) for UPFC application. A novel controller for series converter is designed based on the “angle control” of the 48-pulse voltage source converter. The complete simulation model of shunt and series converters for UPFC application is implemented in Matlab/Simulink. The practical real and reactive power operation boundary of UPFC in a 3-bus power system is specifically investigated. The performance of UPFC connected to the 500-kV grid with the proposed controller is evaluated. The simulation results validate the proposed control scheme under both steady state and dynamic operating conditions.

KEYWORDS:

1.      48-pulse converter

2.      Neutral Point Clamped (NPC) converter

3.      Angle control

4.      Unified Power Flow Controller (UPFC)

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. 48-pulse VSC based +100 MVA UPFC in a 3-bus power system

EXPECTED SIMULATION RESULTS:

Fig.2 Line real power (top) and reactive power (bottom) references (MVA)

Fig. 3 Measured real and reactive power, DC link voltage and converter angles (Top trace: measured line real power (MW); second top trace: measured line reactive power, (MVar); third top trace: DC bus voltage; fourth top trace: shunt converter angle α ; fifth top trace: series converter angle α ; bottom trace: series converter angle σ ).

Fig.4 Shunt converter output voltage (blue), Line voltage (green) and shunt

converter current (red) (5.42s-5.48s)

Fig.5 Shunt converter real power (blue, p.u.), reactive power (green, p.u.).

Fig.6 Current (p.u.) of transmission line L1.

Fig.7 Series converter 48 pulse converter voltage (blue, p.u.) and current

(black, p.u.) during time 2~2.03s (when real power reference is increased)

Fig. 8 Series converter angle σ vs. DC bus voltage (Top trace: line real

power and reactive power; second top trace: shunt converter injected reactive

power; third top trace: DC bus voltage; bottom trace: series converter

angle σ )

CONCLUSION:

In this paper, the control and operation of series and shunt converters with 48-pulse series connected 3-level NPC converter for UPFC application are investigated. A new angle controller for 48-pulse series converter is proposed to control the series injection voltage, and therefore the real and reactive power flow on the compensated line. The practical UPFC real and reactive power operation boundary in a 3-bus system is investigated; this provides a benchmark to set the system P and Q references. The simulation of UPFC connected to the 500-kV grid verifies the proposed controller and the independent real power and reactive power control of UPFC with series connected transformer based 48-pulse converter.

REFERENCES:

[1] N. G. Hingorani, "Power electronics in electric utilities: role of power electronics in future power systems," Proceedings of the IEEE, vol. 76, pp. 481, 1988.

[2] N. G. Hingorani and L. Gyugyi, Understanding FACTS: concepts and technology of flexible AC transmission systems: IEEE Press, 2000.

[3] L. Gyugyi, "Dynamic compensation of AC transmission lines by solid-state synchronous voltage sources," IEEE Transactions on Power Delivery, vol. 9, pp. 904, 1994.

[4] C. D. Schauder, L. Gyugyi etc. “Operation of the unified power flow controller (UPFC) under practical constraints,” IEEE Transactions on Power Delivery, vol. 13, pp. 630-639, April 1998.

[5] L. Gyugyi. “Unified power-flow control concept for flexible AC transmission systems,” IEE Proceedings - Generation, Transmission and Distribution, vo. 139, pp. 323-331, July 1992.

A Novel Control Method for Transformerless H-Bridge Cascaded STATCOM With Star Configuration

ABSTRACT:

This paper presents a transformerless static synchronous compensator (STATCOM) system based on multilevel H-bridge converter with star configuration. This proposed control methods devote themselves not only to the current loop control but also to the dc capacitor voltage control. With regards to the current loop control, a nonlinear controller based on the passivity-based control (PBC) theory is used in this cascaded structure STATCOM for the first time. As to the dc capacitor voltage control, overall voltage control is realized by adopting a proportional resonant controller. Clustered balancing control is obtained by using an active disturbances rejection controller. Individual balancing control is achieved by shifting the modulation wave vertically which can be easily implemented in a field-programmable gate array. Two actual H-bridge cascaded STATCOMs rated at 10 kV 2 MVA are constructed and a series of verification tests are executed. The experimental results prove that H-bridge cascaded STATCOM with the proposed control methods has excellent dynamic performance and strong robustness. The dc capacitor voltage can be maintained at the given value effectively.

KEYWORDS

1.      Active disturbances rejection controller (ADRC)

2.      H-bridge cascaded

3.      Passivity-based control (PBC)

4.       Proportional resonant (PR) controller

5.      Shifting modulation wave

6.       Static synchronous compensator (STATCOM).

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig 1.Configuration of the experimental system.

EXPECTED SIMULATION RESULTS:

Fig. 2. Experimental results verify the effect of PBC in steady-state process. (a) Ch1: reactive current; Ch2: compensating current; Ch3: residual current of grid. (b) Ch1: reactive current; Ch2: compensating current; Ch3: residual current of grid.

Fig. 3. Experimental results show the dynamic performance of STATCOM in the dynamic process. Ch1: reactive current; Ch2: compensating current; Ch3: residual current of grid.

Fig. 4. Experimental results in the startup process and stopping process. (a) Ch1: reactive current; Ch2: compensating current; Ch3: residual current of grid. (b) Ch1: reactive current; Ch2: compensating current; Ch3: residual current of grid.

Fig. 5. Experimental waveforms for testing overall voltage control in the

startup process.

CONCLUSION:

This paper has analyzed the fundamentals of STATCOM based on multilevel H-bridge converter with star configuration. And then, the actual H-bridge cascaded STATCOM rated at 10 kV 2 MVA is constructed and the novel control methods are also proposed in detail. The proposed methods has the following characteristics.

1) A PBC theory-based nonlinear controller is first used in STATCOM with this cascaded structure for the current loop control, and the viability is verified by the experimental results.

2) The PR controller is designed for overall voltage control and the experimental result proves that it has better performance in terms of response time and damping profile compared with the PI controller.

3) The ADRC is first used in H-bridge cascaded STATCOM for clustered balancing control and the experimental results verify that it can realize excellent dynamic compensation for the outside disturbance.

4) The individual balancing control method which is realized by shifting the modulation wave vertically can be easily implemented in the FPGA.

The experimental results have confirmed that the proposed methods are feasible and effective. In addition, the findings of this study can be extended to the control of any multilevel voltage source converter, especially those with H-bridge cascaded structure.

 REFERENCES:

[1] B. Gultekin and M. Ermis, “Cascaded multilevel converter-based transmission STATCOM: System design methodology and development of a 12 kV ±12 MVAr power stage,” IEEE Trans. Power Electron., vol. 28, no. 11, pp. 4930–4950, Nov. 2013.

[2] B. Gultekin, C. O. Gerc¸ek, T. Atalik, M. Deniz, N. Bic¸er, M. Ermis, K. Kose, C. Ermis, E. Koc¸, I. C¸ adirci, A. Ac¸ik, Y. Akkaya, H. Toygar, and S. Bideci, “Design and implementation of a 154-kV±50-Mvar transmission STATCOM based on 21-level cascaded multilevel converter,” IEEE Trans. Ind. Appl., vol. 48, no. 3, pp. 1030–1045, May/Jun. 2012.

[3] S. Kouro, M. Malinowski, K. Gopakumar, L. G. Franquelo, J. Pou, J. Rodriguez, B.Wu,M. A. Perez, and J. I. Leon, “Recent advances and industrial applications of multilevel converters,” IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 2553–2580, Aug. 2010.

[4] F. Z. Peng, J.-S. Lai, J. W. McKeever, and J. VanCoevering, “A multilevel voltage-source inverter with separate DC sources for static var generation,” IEEE Trans. Ind. Appl., vol. 32, no. 5, pp. 1130–1138, Sep./Oct. 1996.

[5] Y. S. Lai and F. S. Shyu, “Topology for hybrid multilevel inverter,” Proc. Inst. Elect. Eng.—Elect. Power Appl., vol. 149, no. 6, pp. 449–458, Nov. 2002.

A Simple Design and Simulation of Full Bridge LLC Resonant DC-DC Converter for PV Applications

 ABSTRACT:

This paper deals with the design and simulation of full bridge LLC resonant converter suitable for photovoltaic applications. LLC converter has several desired features such as high efficiency, low electromagnetic interference (EMI) and high power density. This paper provides a detailed practical design aspect of full bridge LLC resonant converter. The LLC converter is implemented with a full-bridge on the primary side and a fu l-bridge rectifier on the secondary side. It includes designing the transformer turns ratio and selecting the components such as resonant inductor, resonant capacitor and magnetizing inductor. Also performance parameters such as voltage gain and output voltage ripple are calculated. Simulation of LLC resonant converter is carried out using MATLAB / SIMULINK and the results are verified.

KEYWORDS:

1.      LLC resonant converter

2.       Output voltage ripple

3.      Voltage gain

SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:

Fig. 1: Simulink diagram of full bridge LLC resonant converter

EXPECTED SIMULATION RESULTS:

 Fig. 2: Driving pulse of MOSFET Q1&Q3, current and voltage waveforms

Fig. 3: Driving pulse of MOSFET Q2&Q4, current and voltage waveforms

 Fig. 4: Output voltage of inverter & current through resonant components

                                              

 Fig. 5: Transformer primary and secondary voltages

                             Fig. 6: Output current, output voltage and output power of LLC resonant converter

Fig. 7: Output ripple voltage waveform

CONCLUSION:

The design procedure of Full Bridge LLC Resonant Converter is presented for photovoltaic application. Theoretical values of resonant component values are calculated using the design equations. Simulation results are provided for LLC Resonant converter for an input voltage of 33V. The voltage gain and output voltage ripple of LLC resonant converter is calculated which shows that the ripple is less in the proposed converter.

REFERENCES:

1. Abramovitz, A. and S. Bronshtein, 2011. A design methodology ofresonant LLC DC-DC converter’ Power Electronics and Applications (EPE2011), Proceedings of the European Conference, pp: 1-10.

2. Bing Lu, Wenduo Liu, Yan Liang, F.C. Lee and J.D. Van Wyk, 2006.Optimal design methodology for LLC resonant converter’, Applied Power Electronics Conference and Exposition. Twenty-First Annual IEEE, 6: 19-23.

3. Choi, H.S., 2007. Design consideration of half bridge LLC resonant converter, Journal of Power Electronics, 7(1): 13-20.

4. Gopiyani, A. and V. Patel, 2011. A closed-loop control of high power LLC Resonant Converter for DC-DC applications, Nirma University International Conference, pp: 1-6.

5. Senthamil, L.S., P. Ponvasanth and V. Rajasekaran, 2012. Design and implementation of LLC resonant half bridge converter’ Advances in Engineering, Science and Management (ICAESM), International Conference, pp: 84-87.

Performance Improvement of Single-Phase Grid–Connected PWM Inverter Using PI with Hysteresis Current Controller

ABSTRACT:

Now a day’s distributed generation (DG) system uses current regulated PWM voltage-source inverters (VSI) for synchronizing the utility grid with DG source in order to meet the following objectives: 1) To ensure grid stability 2) active and reactive power control through voltage and frequency control 3) power quality improvement (i.e. harmonic elimination) etc. In this paper the comparative study between hysteresis and proportional integral (PI) with hysteresis current controller is presented for 1-Φ grid connected inverter system. The main advantage of hysteresis+PI current controller is low total harmonic distortion (THD) at the point of common coupling (PCC) at a higher band width of the hysteresis band. The studied system is modeled and simulated in the MATLAB Simulink environment.

KEYWORDS:

1.      Hysteresis current controller

2.       PI controller

3.       Point of common coupling (PCC)

4.       DG

5.       Utility grid

6.      THD

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig.1. Block diagram for hysteresis current control of single-phase grid connected VSI

EXPECTED SIMULATION RESULTS:

Fig.2. Simulation result of the hysteresis current controller for fixed band (a) grid voltage (Vg) and grid current (Io) (b) reference current, actual current and current error(c) switching frequency

Fig.3. Simulation result of the hysteresis+PI current controller for fixed band (a) grid voltage (Vg) and grid current (Io) (b) reference current, actual current and current error(c) switching frequency

Fig.4. Simulation result of hysteresis current controller for change in band (a) grid current (b) switching frequency(c) current error

Fig.5. Simulation result of hysteresis+PI current controller for change in band (a) grid current (b) switching frequency(c) current error

Fig.6. THD of grid current for hysteresis current controller (a) HB=1(b)HB=3(c)HB=5

Fig.7. THD of grid current for hysteresis+PI current controller (a) HB=1(b) HB=3(c) HB=5

CONCLUSION:

From the study we observed that, hysteresis+PI current controller can enable to reduce switching frequency even if the band width increased without any significant increase in the current error. Hence it provides considerably less THD at higher band width as compared to conventional hysteresis current controller.

REFERENCES:

[1] Blaabjerg, F.; Teodorescu, R.; Liserre, M.; Timbus, A.V., “Overview of Control and Grid Synchronization for Distributed Power Generation Systems” IEEE Transactions on Industrial Electronics,Vol.:53 , Issue:5, Page(s): 1398 – 1409, 2006

[2] F.Blaabjerg, Zhe Chen, and S.B. Kjaer. “Power Electronics as Efficient Interface in Dispersed Power Generation Systems”, IEEE Transactions on Power Electronics, 19(5):1184–1194, Sept. 2004.

[3] Ho, C.N.-M.,Cheung, V.S.P.,Chung, H.S.-H.” Constant-Frequency Hysteresis Current Control of Grid-Connected VSI without Bandwidth Control”,IEEE Trans. on Power Electronics, TPEL 2009,Volume: 24, no. 11 ,, Pp:2484 – 2495, 2009

[4] Rahman, M.A.; Radwan, T.S.; Osheiba, A.M.; Lashine, A.E.; “Analysis of Current Controllers for Voltage-Source Inverter” IEEE Trans. On Industrial Electronics, Volume: 44 , no. 4 , Pp. 477 – 485, ,1997

[5] Tekwani, P.N, Kanchan, R.S., Gopakumar, K.; “Current-error spacevector- based hysteresis PWM controller for three-level voltage source inverter fed drives” Proceedings of Electric Power Applications, IEE Volume: 152 , Issue: 5, Pp: 1283 – 1295,2005