Parallel operation of series-connectedPWM voltage regulators without control interconnection

A novel current-sharing control scheme is presented that can parallel operate multiple series-connected pulse-width modulation (PWM) voltage regulators (VRs) directly with no control interconnection. The current-sharing control is dedicated for both fundamental and harmonic components. The fundamental current-sharing is controlled by the Q-V droop and P-δ shift scheme, while the harmonic current sharing is controlled by the resistive droop scheme. Both schemes have the feature of no real impedance connection between the VR and the load. Instead, the required impedance for executing both schemes is simulated in the control circuits. As a result, the VRs are tightly connected and thus have a lower output impedance. Other features include accurate voltage regulation, low voltage distortion and tolerance for parameter mismatch. Two 1 kV prototype capacitor current-controlled single-phase VRs with three-arms rectifier-inverter topology are designed and implemented. The effectiveness is demonstrated by some experimental results.