A new voltage-balancing controller in cascaded multilevel converters

Abstract

Voltage-balancing controller in cascaded multilevel converters has been discussed extensively in previous literatures where several effective methods have been proposed. The coupling effect between a voltage-balancing controller and the original system controller is however not addressed comprehensively. This paper proposes a new voltage-balancing controller for single-phase cascaded multilevel converters in a dq coordinate. The theoretical finding shows that the proposed method can effectively eliminate the coupling between two controllers in both steady and dynamic state. Simulation and experimental results validate the proposed method.

The Voltage Balance Control Strategy of Static Var Generators DC-Side Capacitors Based on Fuzzy-PI Adaptive Cascaded H-Bridge

“…Simulation conditions 1 as shown in Figure 10a, when the equivalent load on the DC-side is unbalanced, the DC-side voltage balance cannot be maintained only based on the DQ decoupling dual closed-loop control. Moreover, it can be seen from the Figure 10a that the ratio of the DC side voltage of the three H-bridge modules is proportional to the resistance, which is consistent with the results of the theoretical analysis of Equation (6), so an external voltage balance controller is required to balance the DC side voltage. The simulation condition is changed in Figure 10b to 100 Ω for all three H-bridge modules.…”

“…However, the most commonly used method is the additional hardware circuit method [5][6][7][8][9][10][11][12][13][14][15]. The relationship between the modulation ratio increment of the rectifier and the output voltage is proposed in [5].…”

“…On this basis, the modulation ratio is reconfigured by the fed DC voltage to adjust the DC voltage to balance. A new voltage-balancing controller is introduced in [6] for single-phase cascaded multilevel converters in a DQ coordinate. In [7], the power input from the H-bridge AC side to the DC side of the H-bridge is redistributed.…”

“…Through a voltage balance controller, a duty cycle adjustment amount is added in the public duty cycle to achieve the purpose of the DC side voltage balance. Due to the inappropriate setting of duty cycle adjustment in [5][6][7], these methods can keep the DC side voltage constant. The coupling effect of the additional voltage balance controller and the double closed-loop control system is not conducive to the overall stability of system.…”