Diode-Clamped Multilevel Statcom Study Based On Voltage Balancing Auxiliary Circuit

With large-scale application of no-linear loads in traction power, industry and agriculture devices, the reactive power and harmonics would increase. Therefore, it is significant to apply multilevel inverters such as active power filter and STATCOM for improving the reliability, controllability, and quality in power system.First of all, the paper has introduced three structure of multi-level inverter. Their operating principles and control strategies have been analyzed. The five-level STATCOM based on Diode-Clamped Circuit is used as an example to analyze its voltage output principle by using the carrier disposition PWM method.Secondly, the paper has analyzed the principle why the dc-link capacitors voltages fail to keep balance. If the voltages are unbalanced, the whole system would be out of control and even destroys the switching devices due to over-voltage. Therefore, it is necessary to solve the problem of voltage unbalance of multi-level diode-clamped circuit based STATCOM. And some capacitors’voltage stabilization circuits have been discussed, what’s more, their operating principles and simulation results are also analyzed.Thirdly, the paper has studied the decoupling control of reactive power current and active power current of STATCOM based on ip-iq algorithm. The control strategy and the capacitors’voltage stabilization circuits have been applied to the multi-level diode-clamped circuit based STATCOM.Finally, an experiment system of five-level STATCOM with three capacitors’voltage stabilization circuits has been designed. The experiment results have verified that the voltage stabilization circuits could keep voltage stabilization and balance for dc-link capacitors. And the experiment STATCOM can generate the reactive power currents.