Multi-loop voltage control strategy of half-bridge voltage balancers with current sensorless scheme

This paper proposes a multi-loop voltage balancing strategy for half-bridge voltage balancers. The proposed multi-loop scheme consists of a voltage controller and a current variation controller without current sensors. The proposed current variation controller (CVC) aims to regulate the derivative of the average inductor current to be zero at the steady-states as well as to increase the damping of the entire control loop. Furthermore, the CVC is implemented based on a current sensorless scheme. For this purpose, a simple method for detecting current variation by using dc-link voltages and a control model is also proposed. To secure the stability of the proposed CVC with the current sensorless method, a well-known type II regulator is adopted, and its design procedure is detailed. The proposed multi-loop strategy is applied to a 2.4-kW half-bridge voltage balancer. Both simulation and experimental results show good agreements with the theoretical analyses.