An Improved H8 Topology for Common-mode Voltage Reduction


This paper presents an improved H8 power converter for common-mode voltage reduction and electromagnetic interference suppression. The proposed H8 converter can realize zero common-mode voltage variation when entering and leaving the zero state, which is mainly achieved by both the improvement of the structure and the control strategy. For the system structure, two switches are added on the DC bus to float the AC part of the three phase converter in the zero state. Besides, additional capacitors are used to realize controllable common-mode voltage. For the control strategy, a simple control strategy is proposed for the H8 converter. It can automatically adapt to the flowing orientation of the load current to realize synchronous switching of the power switches, which effectively eliminates the impact of the dead time. Through analysis, simulations and experiment, a comparison between the proposed H8 converter and the conventional H6 converter is performed. Results validates the effectiveness of the H8 topology.



  1. H8 topology
  2. Common-mode voltage reduction
  3. Electromagnetic interference source suppression.



Fig. 1. The topology of the proposed H8 converter.



(a) Waveform of CMV in a fundamental circle.

(b) Waveform of CMV in a carrier circle.

(c) Waveform of CMV distortion.

Fig. 2. Comparison of the CMV of the proposed topology and conventional H6 topology

(a) 0 pF.

(b) 500 pF.

(c) 2.2 nF.

Fig. 3. Comparison of the CMV of the H8 converter with different additional capacitor.



To reduce the CMV of the two level three phase power converter, an improved H8 converter is proposed in this study. The H8 topology disconnects the power supply and the AC output circuit in the zero state, and zero CMV variation is achieved though applying connection capacitors and specific control strategies. The performance of the proposed H8 converter is evaluated through theoretical analysis, simulations and experiments. Compared with the conventional H6 three phase topology, the proposed H8 much reduces the CMV in the zero state, which would be advantageous for the CMV-sensitive applications such as motor and photovoltaic systems. The suppressed CMV also results in the reduction of the common-mode EMI for a three phase converter. Besides, the proposed H8 topology precedes the previous H8 works by realizing zero CMV variation when entering and leaving zero state. Future work will be dedicated to the CMV suppression for other topologies.



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