Research on the cluster current control of delta-connected cascade multilevel STATCOM

The three phase of Delta-Connected STATCOM are independent, so its cluster current can be controlled individual. The cluster current controller is very important for the system performance when using individual phase instantaneous current control strategy. A novel current controller is proposed in this paper, which is composed by proportional controller and resonance controller (PR controller). First the current loop using P controller and PR controller is compared and the parameter of PR controller is designed. Then the dc voltage fluctuation of module is analyzed. In order to restrain the third order zero sequence circulating current, a resonance controller which center frequency is 150Hz is used in the control loop. Simulation results show that the STATCOM cluster current using PR controller obtain much better performance than using P controller. The cluster current can be controlled very accurately. The system response time is lower than 5 milliseconds and the overshoot is smaller than 15% Meanwhile the third order zero sequence current is suppressed within 1% rated current when STATCOM outputting rated reactive current.