Abstract
The three-phase H7 inverter topology installs an additional power semiconductor switch to the positive or negative node of the DC-link for reducing the common-mode voltage (CMV) by disconnecting the inverter from the DC source during the zero-voltage vectors. The conventional CMV reduction method for the three-phase H7 inverter uses modified discontinuous pulse width modulation (MDPWM) and generates a switching signal for the additional switch using logical operations. However, the conventional method is unable to eliminate the CMV for the entire dwell time of the zero-voltage vectors. It only has the effect of reducing the CMV in a limited area of the space vector where the V7 zero voltage vector is applied. Therefore, this paper proposes an optimized modulation method that can reduce the CMV during the entire dwell time of zero-voltage vectors. The proposed method moves the switching patterns by adding an offset voltage to guarantee that only one kind of zero-voltage vector, V7, is applied in the system. It then turns off the seventh switch only during the zero-voltage vector to disconnect the inverter from the DC source. As a result, the CMV and the leakage current are attenuated for the entire dwell time of the zero-voltage vector. Simulation and experimental results confirm the validity of the proposed method.
Highlights
The modified discontinuous pulse width modulation (MDPWM) uses a logical operation that generates a turn-off signal for the seventh switch (S7 ) during only the dwell time of the V7 zero-voltage vector to disconnect the motor from the DC source
The proposed algorithm attenuates the leakage current by 73% and 40% compared to the SVPM and MDPWM methods, respectively
In the H7 inverter topology, the SVPWM method does not use the off state of the seventh switch and generates a Common-mode voltage (CMV)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The design of the filter varies according to the applications because the parameters of the equivalent circuit for the common-mode voltage vary with switching frequency, length of the electric line, grounding technique, and motor parameters This approach increases the cost and size of the overall system [15]. The MDPWM uses a logical operation that generates a turn-off signal for the seventh switch (S7 ) during only the dwell time of the V7 zero-voltage vector to disconnect the motor from the DC source. It reduces the CMV magnitude from Vdc /2 to Vdc /4 only in the regions where the V7 zero-voltage vector is applied. Since the basic idea of the proposed modulation strategy is similar for both H7 inverter topologies in Figure 1a,b, most of the analysis in this paper is based on the circuit configuration of Figure 1a
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