Transient Voltage Support Strategy for Hybrid Multi-Converter of Controlled Voltage/Current Source Converter
Yang Ming1, Cao Wu1, Zhao Jianfeng1, Zhu Lingzhi2, Wang Baoji3
1. School of Electrical Engineering Southeast University Nanjing 210096 China; 2. China Electric Power Research Institute (Nanjing) Nanjing 210003 China; 3. Sungrow Power Supply Co. Ltd Hefei 230009 China
Abstract The increasing proportion of renewable energy makes the power system have obvious power electronic characteristics. The converters used for renewable energy is more sensitive to system voltage due to its weak high-low voltage ride-through capability. Under the condition of large disturbance of transient voltage condition, the renewable energy converter is very easy to be locked and cut off. The stable operation of high voltage direct current transmission also highly depends on the transient voltage stability. Therefore, the transient voltage problem of new type power grid with high proportion of renewable energy is the key to the safe and stable operation of the system. Currently, the transient active support capability of the converter is not available due to synchronization problems and reactive power output ability under transient voltage conditions. To solve the problems existing in active support of renewable energy station, controlled voltage/current source converters are connected in parallel to form a hybrid multi-converter system. The controlled voltage source converter realizes power angle control through power control. The synchronization control is not affected by system transient voltage. Therefore, stable synchronization conditions are provided by controlled voltage source converters. The controlled current source converter can output fast and accurate reactive power support. Based on the analysis and summary of active transient voltage support requirements of renewable energy station, a hybrid multi-converter transient voltage support strategy of controlled voltage/current source converter is proposed to improve the transient voltage stability of renewable energy station and enable it to support transient voltage actively. Controlled voltage source converters are prone to lose voltage source characteristics and reduce reactive power output capabilities because of the large power fluctuations under transient conditions. The overcurrent degree of the converter is flexibly limited by virtual impedance to improve the adaptability of the controlled voltage source converter to transient conditions. By suppressing the response to voltage fluctuations in the active power control of the converter, the effect of increasing the active power fluctuation damping can be achieved. The reactive power output capability of the controlled voltage source converter can also be guaranteed while promoting the stable operation of the converter. The flexible limiting of transient current combined with transient active power damping control ensures the voltage control stability and reactive power output capability of the controlled voltage source converter under transient conditions. The steady state of the controlled current source converter is mainly output active power. In the transient state, it is necessary to adjust its power output target according to the voltage change. The reactive power compensation demand is calculated under the current condition. The compensation demand is superimposed on the current reactive power control target. And the active power control target is accordingly reduced. So the adaptive compensation control of the controlled current source converter is realized. The transient voltage reactive power support of the controlled current source converter can be realized under the limitation of the converter capacity. The following conclusions can be drawn from the simulation and experimental results: the proposed strategy can fully combine the advantages of the controlled voltage source converter and the controlled current source converter. The controlled voltage source converter can ensure the control voltage stability in the transient process and the output capability of the hybrid multi-converter system. Under the stable condition of phase locking, the controlled current source converter can take into account the stable and reliable reactive power output of its own operation. The hybrid multi-converter system based on controlled voltage/current source converter can meet the key requirements of transient voltage support and improve the voltage stable level under transient conditions. The hybrid multi-machine system with proposed strategy can be taken as the basis of further research on transient voltage support. The coordinated control of converters and other reactive power compensation equipment in renewable energy stations can be studied to further improve the transient voltage active support capability of renewable energy station.
Yang Ming,Cao Wu,Zhao Jianfeng等. Transient Voltage Support Strategy for Hybrid Multi-Converter of Controlled Voltage/Current Source Converter[J]. Transactions of China Electrotechnical Society, 2023, 38(19): 5207-5223.
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2023, Vol. 38 
