Low Frequency Harmonics Reduction Discontinuous PWM Strategy With Active Neutral Point Voltage Control for Neutral Point Clamped Three-Level Inverter

Weidong Jiang,Ma Mingna,Qingyan Zhang,Xinmei Huang

doi:10.1109/access.2020.3026668

Abstract

The traditional discontinuous pulse width modulation (DPWM) strategy is very suitable for reducing the switching losses of three-level inverter (TLI). However, large neutral point voltage (NPV) fluctuation is usually caused, which results in low frequency harmonics (LFHs) in the output line voltage. Therefore, a DPWM modulation strategy that can suppress LFHs is presented in this paper, and it is recorded as low frequency harmonic reduction DPWM (LFHRDPWM). The proposed LFHRDPWM can be seen as an improvement of traditional DPWM, which modifies the duty ratios according to voltages of the two DC-link capacitors. For LFHRDPWM, due to the suppressed LFHs, the self-balancing ability of NPV is thus lost, and gradually increased DC offset on NPV is caused. To overcome that, an active neutral point voltage control (ANPVC) method is also proposed. The proposed methods not only can achieve switching loss (SL) reduction almost as the same as traditional DPWM strategy, but also can realize NPV control and LFHs reduction. The effectiveness of the proposed method is verified by experiments.

Highlights

Multi-level inverters have been proposed to enhance the equipment power and efficiency and reduce production costs
The performance of three-level inverter (TLI) can usually be evaluated by the voltage offset on neutral point (NP), The associate editor coordinating the review of this manuscript and approving it for publication was Md
LFHRDPWM can not be directly applied without any active neutral point voltage control (ANPVC) control

Summary

INTRODUCTION

Multi-level inverters have been proposed to enhance the equipment power and efficiency and reduce production costs. W. Jiang et al.: LFHs Reduction Discontinuous PWM Strategy With ANPVC for NPC TLI problem is called DC offset. In [13], an algorithm that belongs to differentialmode harmonic current injection is proposed, which balances the NPV by modulating the input current amplitude This algorithm can obtain good results under all working conditions. Without any ANPVC, sometimes NPV change is zero over a period of time This NPV self-equilibrium ability is sometimes strong and sometimes weak and may only appear in a specific operating area. Compared with the use of continuous pulse width modulation (CPWM), the use of DPWM can reduce switching losses, and can obtain better harmonic characteristics at high modulation index [17]–[19]. The active power outputted by TLI can be expressed as: p mudc 2

REVIEW OF DPWM FOR TLI

THE ODD ORDER LFHs FORMED BY AC RIPPLE

THE INFLUENCE OF LFHs ON TLI

ANPVC FOR LFHRDPWM

CONCLUSION