Power and Voltage Control for Single-Phase Cascaded H-Bridge Multilevel Converters under Unbalanced Loads

Abstract

The conventional control method for a single-phase cascaded H-bridge (CHB) multilevel converter is vector (dq) control; however, dq control requires complicated calculations and additional time delays. This paper presents a novel power control strategy for the CHB multilevel converter. A power-based dc-link voltage balance control is also proposed for unbalanced load conditions. The new control method is designed in a virtual αβ stationary reference frame without coordinate transformation or phase-locked loop (PLL) to avoid the potential issues related to computational complexity. Because only imaginary voltage construction is needed in the proposed control method, the time delay from conventional imaginary current construction can be eliminated. The proposed method can obtain a sinusoidal grid current waveform with unity power factor. Compared with the conventional dq control method, the power control strategy possesses the advantage of a fast dynamic response. The stability of the closed-loop system with the dc-link voltage balance controller is evaluated. Simulation and experimental results are presented to verify the accuracy of the proposed power and voltage control method.

Voltage Jump Suppression and Capacitor Voltage Fluctuation Analysis for a Four-Level Hybrid Flying Capacitor T-Type Converter

“…Thanks to lower harmonic distortion, switching stress and electromagnetic interference (EMI), multilevel converters are widely used in medium-voltage high-power applications, such as motor drives, renewable power generations and microgrids, etc. [1][2][3]. Meanwhile, due to lower switching losses and reduced cooling and filter requirements, multilevel converters are also becoming more and more popular in low voltage application (e.g., 380 V) where high-density design is required, such as aerospace, electric vehicles and renewable energy [4,5].…”

“…The CHB converter has a modular structure, and is easier to expand to higher voltage levels. However, a phase-shifted transformer is required to provide multiple separated power sources, which increases the system volume and cost [1][2][3][4].…”

Simple DC-Link Voltage Balancing Approach for Cascaded H-Bridge Rectifier with Asymmetric Parameters of Independent DC Loads

“…Nowadays, 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).…”

“…As in a medium-voltage scenario when there are fewer sub-modules, phase shift PWM (PS-PWM) have proved to be a viable candidate for implementation [4,[7][8][9]. 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 voltage.…”

A Full-bridge Director Switches based Multilevel Converter with DC Fault Blocking Capability and Its Predictive Control Strategy

“…The modular multilevel converter (MMC) has been accepted as a suitable solution for high-voltage and high-power application fields due to several inherent features [1][2][3][4][5][6][7][8]. However, blocking the DC fault current becomes a difficult problem because the anti-parallel diodes are still conducting after the insulated-gate bipolar transistors (IGBTs) of HBSM are turned off [9].…”