High performance controller design with PD feedback inner loop for three-phase four-leg inverter

Three-phase four-leg inverter has powerful ability to effectively treat unbalance and nonlinear loads, which outputs three phase symmetrical voltages. A novel control scheme with PD output voltage instantaneous-value feedback inner loop for voltage PID is proposed based on the model of three-phase four-leg inverter. The inner loop is designed to improve dynamic performance and the voltage external loop can ensure stable performance. The design methods of inner loop PD controller and external loop PID controller are discussed in detail. The control system is very simple and only the output voltage needs to be sampled. The PD inner and PID external controller are both easy to design and analyze. Simulation results are given to validate that the control scheme for the inverter proposed has not only excellence dynamic and static performances but also strong robustness. The control scheme proposed has advantage of controller structure, cost, robustness and this method is simple to implement and the design is convenient compared with voltage and current dual-loop control inverter scheme.