Model predictive direct power control strategy for leakage current suppression on a grid‐connected three‐level inverter

Abstract

The nonisolated grid‐connected photovoltaic inverter system suffers from the problem of leakage current. Therefore, a leakage current suppression control strategy based on the model predictive direct power control is proposed for the three‐level four‐leg grid‐connected inverter. At first, the system model is established to analyze the factors that affect the leakage current and the potential of the neutral point. Second, the first three legs, inverting part, use model predictive direct power control, and the fourth leg of the inverter is used to maintain a constant common‐mode voltage to achieve the suppression of the leakage current. The fourth leg is indirectly controlled by the switch state of the first three legs; thus, the number of optimization times is reduced. Finally, by simulation, the leakage current is compared and analyzed with the three‐level three‐leg inverter under conditions with different parasitic capacitance values. The results show that the proposed strategy suppresses the leakage current by more than 60% without affecting the neutral point potential and has a fast optimization speed.

Topology Optimization Analysis of Leakage Current Suppression in Three-Level Four-Leg Photovoltaic Grid-Connected Inverter

“…The inverter control strategy is adopted from [19] for suppression of the leakage current. The fourth leg is used to constant the common mode voltage to achieve the leakage current suppression.…”

“…The Figure shows that the excitation sources are 4u cm and e. There are two ideas to suppress the leakage current i cm without changing the component parameters. First, by excitation, the leakage current is indirectly suppressed by reducing the common mode voltage variation rate through the control strategy, as in [19]; second, by the principles of the hardware circuit, optimize the circuit topology to suppress the leakage current.…”

“…four-leg inverter to reduce leakage current, but discard part of the voltage vectors, which increases the fluctuation of the neutral point potential on the DC-side, weakening the stability of the system. In [19], for a three-phase four-leg inverter, the neutral point of filter capacitors is connected to the neutral point on the grid-side, a model predictive direct power control strategy is proposed to control the fluctuation of the common mode voltage to achieve the suppression of leakage current, but it increases the Total Harmonic Distortion (THD) of the grid-connected current.…”

Model predictive sliding mode control of six‐phase induction motor using nine‐switch converter

“…The control goal error terms are usually involved in the cost function, and an exhaustive search is employed to decide the optimum control actuation. The control sequence that offers the minimum cost value is recorded as an optimum input 18–20 . Fundamentally, the traditional MPC evaluates only the penalization terms, the error between the reference signals and the predictions, and no closed‐loop stability investigation is performed 21–24 .…”

“…The control sequence that offers the minimum cost value is recorded as an optimum input. [18][19][20] Fundamentally, the traditional MPC evaluates only the penalization terms, the error between the reference signals and the predictions, and no closed-loop stability investigation is performed. [21][22][23][24] Due to the lack of stability assessment in the optimization procedure, the traditional MPC formulation may agonize over the system instability in case of deviation from the nominal operating points.…”