Abstract
CHB is a suitable type of topology for synchronous rectifier application which has two or more independent DC loads. Focusing on the individual DC-link capacitor voltage balancing problems caused by asymmetric parameters of independent DC loads, this paper developed a new dual modulation signals based phase disposition pulse width modulation (PD-PWM) strategy using dynamic carrier bias allocation method. Its main idea is to allocate the bias of the carrier wave dynamically according to the balance situation of the system. Compared with the traditional modulation strategies, this method is more easily to be realized and has much stronger dynamic regulation ability. This modulation strategy is widely applicable to various types of CHB structures. A detailed analysis of the DC-link capacitor charge-discharge profile is performed, and an operation condition based dynamic bias allocation method is described using the cascaded H-bridge rectifier (CHBR) structure of five sub-modules as an example. A simulation model and an experiment platform are developed, and the feasibility and effectiveness of the modulation strategy are verified by simulation and experiment results.
Highlights
It is well established that the cascaded H-bridge (CHB) is the most suitable choice for many medium-voltage high power applications [1,2,3], especially for synchronous rectifier application which have two or more independent DC loads, but one of the most extensively addressed drawbacks of CHB rectifiers is the DC voltage balancing across all DC-link of the H-bridge sub-modules (SMs) with asymmetric parameters of independent DC loads [4]
A variety of methods have been proposed to maintain the voltage balancing across the capacitors of cascaded modular structure, including carrier phase-shift pulse width modulation (PS-PWM), nearest level modulation (NLM), predictive control strategy, phase disposition-pulse width modulation (PD-PWM)
A comprehensive comparison between the proposed PD-PWM, conventional PD-PWM, PS-PWM, NLM, predictive control method is summarized in Table
Summary
It is well established that the cascaded H-bridge (CHB) is the most suitable choice for many medium-voltage high power applications [1,2,3], especially for synchronous rectifier application which have two or more independent DC loads, but one of the most extensively addressed drawbacks of CHB rectifiers is the DC voltage balancing across all DC-link of the H-bridge sub-modules (SMs) with asymmetric parameters of independent DC loads [4]. NLM has been widely used in a large-scale sub-module scenario, such as a voltage source converter high-voltage direct current (VSC-HVDC) converter station [5,6]. NLM normally requires an additional filtering device when the number of sub-modules is insufficient for medium-voltage applications, because the output is a step waveform that contains a large proportion of harmonic waves. As in a medium-voltage scenario when there are fewer sub-modules, phase shift PWM (PS-PWM). In order to balance the DC-link voltage, an extra proportional-integral module can be added to the control unit of each SM to adjust
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