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The conventional control strategy for active power filters (APFs) is essentially a nested structure, where the output of the outer voltage loop will affect the command current of the inner loop, inevitably impairing the performance in harmonic compensation. In this article, to enhance the harmonic-compensation performance, the output of the dc-link voltage loop has been modified and added as a disturbance to the current loop, which forms a paralleled structure. Thus, the pure command current can be achieved and not affected by the output of the voltage loop. Parameters of the proposed paralleled strategy are designed considering both stability and dynamic responses, and larger phase and gain margins are achieved. In addition, a compound PI controller has been designed to avoid the integral overflow problem. Finally, experimental results verify that, though with a relatively slow the dc-link voltage response, the proposed paralleled strategy can achieve a faster and more precious current control, and a better performance in harmonic compensation compared with the conventional nested strategy.

A cascade H-bridge (CHB) stands out for its modular structure and high output voltage among various power converter schemes for battery energy storage systems. While space vector pulsewidth modulation (SVPWM) offers better utilization of the dc-link voltage, it is seldom employed in CHB designs due to the substantial computational burden associated with an increasing number of voltage levels in the converter. This article introduces a novel hybrid SVPWM approach in a multilevel CHB for battery energy storage systems. In this proposed system, the reference vector is decomposed into a low-frequency vector and a high-frequency vector. The low-frequency vector is generated by the low-frequency modules operating at the line frequency, while the high-frequency vector is produced by the high-frequency module working in the pulsewidth modulation mode. It compensates for the disparity between the low-frequency vector and the reference vector. To determine the low-frequency vector, an algorithm based on coordinate transformation is introduced. This significantly reduces the computational complexity, making it independent of the output voltage levels. The switching losses decrease as most power devices operate at the fundamental frequency. An experimental platform of the CHB is constructed to validate the advantages of the proposed modulation algorithm.