Abstract When the cascaded H-bridge (CHB) converter with an isolated DC-link is used as a power supply in parallel through the current-sharing reactor, the distributed controller will form an unstable circulating current between the parallel branches due to the parameter difference. However, when the output power is unbalanced, the conventional linear controller cannot actively suppress the circulating current, resulting in degraded reference tracking performances. Recent studies have proposed parallel methods based on improved master-slave predictive control. However, the problems of more stable circulating current observation and a large amount of computation still exist. Therefore, this paper proposes a parallel method of carrier-based model predictive control (MPC) and improved master-slave control. When the output power is unbalanced, the reference tracking and a circulating current suppression are realized by optimizing the global control value through the proposed prediction model. Firstly, the master controller reconstructs the branch current into the common load inductor current and the branch circulating current through the Luenberger observer. Secondly, a global cost function is established to optimize the reference tracking and the circulating current suppression. Finally, the globally optimized control values are sent to the slave controllers, and the interleaved H-bridges are managed by the respective carrier phase shifted pulse width modulation (CPSPWM) modulator. The master and slave controllers have similar optimized timing based on the carrier, and slave controllers only communicate with the master controller. In the proposed method, the Luenberger outputs stable state observations, the MPC solves the global optimal control values, the CPSPWM modulator fixes the switching frequency of the interleaved H-bridge, and the improved master-slave control reduces the communication resource. Therefore, the proposed method can realize stable reference tracking and the circulating current suppression in the parallel CHB power supply. The results show that when the current-sharing reactor is 2 mH or 1mH and the current reference difference reaches 50 %, the proposed method quickly tracks the steady-state reference after a small overshoot. The steady-state deviation is much smaller than the conventional linear controller. It is shown that the proposed method has a more stable dynamic tracking performance, with the reference suddenly changing when the amplitude step mutation of the reference signal is added. A 5 % mismatching of the current-sharing reactor is operated in the simulated test. The results show that the proposed method can effectively suppress the circulating current caused by the difference in hardware parameters. Observation errors of the proposed Luenberger observer are measured in simulation. The maximum deviation of the branch current is 0.83 A, almost following the sampling current. The program time of the proposed method is about 23 μs in DSP28335, which is less than the sampling period of 20 kHz. The analysis of the results leads to the conclusion that: (1) Compared with the parallel scheme of the conventional linear controller, the branch's current reference tracking performance is improved. Specifically in terms of high steady-state tracking accuracy and short dynamic adjustment time. (2) The circulating current caused by the unbalanced output power is effectively suppressed. (3) The proposed algorithm can be extended to any number of the multi-parallel CHB branches if the sampling period is sufficient to operate the program.
Huang Haihong,Yan Bichen,Wang Haixin. Model Predictive Control of Current Tracking Optimization and Circulating Current Suppression for Multi-Parallel Cascaded H-Bridge Power Supplies[J]. Transactions of China Electrotechnical Society, 2023, 38(16): 4376-4390.
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2023, Vol. 38 
