284 / 2022-03-15 02:34:58

Research on characteristics and suppression method of DC-side power oscillation of VSC-HVDC system

VSC-HVDC；,DC-side power oscillatio,harmonic source,harmonic impedance,oscillation suppression method

The transmission technology of Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) has the advantages of independent control of active and reactive power, and has high controllability and flexibility. It is an important development direction of power grid in the future. However, actual project experience shows that the DC-side power oscillation (DCPO) frequently happens in VSC-HVDC system, and will easily result in equipment damage and system blocking. For example, during the commissioning of a VSC-HVDC project in China, serious DCPO happened when DC power is at low and medium Levels. At present, many researches have been done on the control methods and system dynamic characteristics of VSC-HVDC in relevant literature. However, there is still a lack of study on the characteristics and suppression method of DCOP of VSC-HVDC system. Thus, to study the characteristics of DCOP, the harmonic equivalent circuit of VSC-HVDC system is firstly established in this paper. Considering that the DC-side harmonic source and harmonic impedance are the key parameters determining whether DCPO will happen in VSC-HVDC system, a simulation calculation method of DC-side harmonic source and harmonic impedance are proposed based on the equivalent circuit. In the proposed calculation method, a small signal source is introduced into the electromagnetic transient simulation model of actual VSC-HVDC system, and the simulation results under different value of the small signal source are brought into the circuit equations of VSC-HVDC system to solve the amplitude of harmonic source and harmonic impedance. Next, by calculating the harmonic source and impedance using the proposed method, the influences of VSC-HVDC system parameters, such as DC power P and harmonic frequency F, on the DC-side harmonic impedance and harmonic source are analyzed, so that the characteristics of DCPO are revealed. On this bases, a consistency method of DCPO is proposed. In the proposed consistency method, the sub-module capacitance voltage and bridge arm current feeds back to modify the reference wave of bridge arm voltage in the Inner loop controller, in order to decrease the control deviation of VSC valve and increase the equivalent impedance of VSC valve at the same time, so that the DC-side harmonic source is reduced and the harmonic impedance is increased. As a result, the DCPO can be suppressed. A VSC-HVDC system with actual system parameters and control and protection strategies is modeled and simulated based on PSCAD/EMTDC platform to study and verify the characteristics and consistency method of DCOP proposed in this paper. The simulation results show that the proposed consistency method can reduce the harmonic source amplitude and increase the harmonic impedance amplitude on DC-side of VSC-HVDC system, so as to effectively suppress DCPO. The application effect in actual VSC-HVDC project of the proposed method is consistent with the simulation analysis results of this paper. The result of this study can help analyzing and understanding the DCPO characteristics and can be used to suppress the DCPO of actual VSC-HVDC project.