Fault Tolerant And Grid-Connected Techniques For Input-Series-Output-Parallel Connected Inverter System

Input-Series-Output-Parallel(ISOP) inverter system is very suitable for high input voltage and high output current power conversion applications. Distributed control and redundancy are needed to improve system reliability, which is a crucial point of the topology. In addition, If we apply this inverter system topology into grid-connected application, we can built a large volume grid-connected-inverter-system using multiple standard inverter module with small volume, which can improve system reliability and convenience the designers.This paper firstly researches on redundancy techniques of ISOP inverter system under individual load condition. A power balance strategy for ISOP inverter system under distributed control architecture, with control loops dispersed into each module is shown. And modules communicate with buses. Relationships between control loops are analyzed and the design methods are given. Then an detailed implementation to fulfill redundancy is proposed, which bypasses the fault module using power relays. Precise operation sequences are needed to realize smooth switching. The operation sequences are proposed and verified by simulation. Then the proposed redundancy solution is tested on a three-module ISOP inverter system prototype.Next, the paper investigates on ISOP grid-connected system. Each module adopts LCL filter in order to achieve better harmonics attenuation. Then the paper proposes a topological optimization method with each module sharing the grid inductance L2, which can cut the number of inductance and reduce system volume. In order to meet multiple control targets, ie damping resonant peak, high power factor of the grid current, power balance between modules, we need to choose proper control variables. In this paper, the current of L1 is chosen and the power balance strategy is proposed using compound control method to realize power balance. The capacitive current contained in L1 can help damping resonance peak. And the proposed control method can obtain good power factor of the grid current. Simulation result is shown to verify the effectiveness of the strategy. At last, an ISOP grid-connected inverter system which consists of two modules is fabricated, experimental results are presented to prove the effectiveness of the proposed topology, control strategy and the design.