Phase-shifted Pulse Width Modulation Scheme Research Articles

Novel Level Shifted PWM Technique for Unequal and Equal Power Sharing in Quasi Z-Source Cascaded Multilevel Inverter for PV Systems

Conventional phase-shifted pulsewidth modulation (PS-PWM) is a usual switching technique for Z-source/quasi-Z-Source (qZS)-based cascaded multilevel inverters (CMIs) (qZS-CMIs). The PS-PWM scheme causes higher switching losses and creates an electromagnetic interference (EMI) problem for higher number of cascaded modules. To address these issues, a novel, modified level-shifted PWM (LS-PWM) technique is proposed with the aim of obtaining equal power from cascaded modules under abnormal conditions. The direct use of the alternate phase-opposed disposed PWM (APOD-PWM) results in unequal power sharing between the qZSI modules, under all operating conditions. An effective carrier rotation is incorporated in the conventional APOD-PWM to make equal power sharing between the qZSI modules. The proposed scheme is an excellent solution for photovoltaic (PV) systems to address the problem of partial or complete shading, temperature variation, PV module failure, and dust accumulation on the PV panels. Furthermore, the relationship between PS-PWM and APOD-PWM is geometrically obtained, which indicates that the proposed modulation scheme gives higher voltage gain over LS-PWM and PS-PWM techniques. In addition, detailed switching loss analysis for the proposed PWM methods is added to validate low-switching losses, and thus high efficiency. The MATLAB Simulink simulations are presented to verify the proposed modulation. An experimental prototype is developed, and the experimental outcomes validate the improved performance of the multilevel qZSI with proposed modulation.

Modified Phase-Shifted PWM Scheme for Reliability Improvement in Cascaded H-Bridge Multilevel Inverters

The cascaded H-bridge multilevel inverter (CHMI) is a modular structure that consists of many power semiconductor switches. With this increase in the number of power semiconductor switches, it is hard to predict and handle the failure of the devices, and hence reliability of CHMI decreases. The major cause of power semiconductor switch failure is junction temperature that is produced by power losses. The study proposes a multi-carrier pulse-width modulation (PWM) scheme for reduction in switching losses of CHMI. In the proposed modulation scheme, the two legs conduct switching operation at different frequencies for switching reduction. One leg conducts switching operation with high frequency, while the other leg conducts switching operation with fundamental frequency. The switching operations with different frequencies cause unbalanced switching loss to each leg. Therefore, the junction temperature that is based on power losses leads to different life-times for the power semiconductor switch. Additionally, the switching frequency of the two legs is alternated to evenly distribute switching losses and junction temperature. Simulation and experimental results verify the performance of the proposed PWM scheme.

Hybrid Modulation Concept for Five-Level Active-Neutral-Point-Clamped Converter

In this letter, a hybrid modulation concept consisting of three-level space vector modulation (3L-SVM) and phase-shifted pulse width modulation (PS-PWM) is proposed for five-level active-neutral-point-clamped (5L-ANPC) converter. Under this concept, a simpler 3L-SVM plus PS-PWM scheme is applied to realize 5L modulation, instead of using complex 5L-SVM. The control of neutral voltage, flying capacitor voltage, and the improved dc voltage utilization are all implemented. With the help of the proposed concept, well-developed 3L-SVM schemes can be directly applied to the 5L-ANPC converter, which significantly simplify the gating signal generation. This concept can also be applied to other hybrid clamped 5L converters with two dc-link capacitors. It provides a unique solution, which utilize lower level SVM scheme to control higher level multilevel converters.

A Novel Modulation Scheme and Voltage Balancing Algorithm for Modular Multilevel Converter

The control complexity of modular multilevel converter (MMC) increases with the number of submodules per arm. In particular, the implementation of a pulsewidth modulation (PWM) scheme and a voltage balancing approach for MMC is a major challenge. This paper proposes a generalized low-cost less computational decoupled sampled average PWM scheme for MMC. In this approach, the reference output voltage is generated by averaging the two nearest voltage levels from the top and bottom arms in each sampling interval. In addition, a simplified voltage balancing approach is proposed for MMC. The proposed approach does not require a sorting technique to select the submodules. Instead, the relative comparison logic is presented. The effectiveness of the proposed modulation scheme and voltage balancing approach is evaluated on a single-phase MMC system with three-level flying capacitor submodules. The proposed approach is extended to a three-phase system, which results in dynamic balancing of the zero-sequence voltage. Hence, the zero-sequence current is minimized. The performance of the proposed three-phase approach is compared with that of the conventional phase-shifted carrier PWM scheme. The simulation and experimental studies show successful voltage balancing among submodule capacitor voltage, low harmonic distortion, and less ripple in output current.

Improved Natural Balancing With Modified Phase-Shifted PWM for Single-Leg Five-Level Flying-Capacitor Converters

Flying-capacitor converters (FCCs), like most multilevel converter topologies, require a balancing mechanism of the capacitor voltages. FCCs feature natural voltage balancing when a special modulation technique is used. The classic methods, such as phase-shifted pulse width modulation (PS-PWM), result in very slow balancing for some duty-ratio ranges. Previous work has shown that for a single-leg five-level FCC, one time constant is infinite for a zero desired output voltage. In this paper, a modified PS-PWM scheme for a single-leg five-level FCC is presented, which results in faster balancing over the total duty-ratio range. The modified PS-PWM scheme is studied, resulting in an averaged voltage-balancing model. This model is verified using simulations and experiments. The modified PS-PWM scheme solves the slow-balancing problems of the normal PS-PWM method for odd-level FCCs, while maintaining the passive control property, and it provides a self-precharge capability.