When the converter level count gets higher, the space vector pulse width modulation (SVPWM) will suffer from the calculation burden for synthesizing the voltage vectors and the redundant vector selection, which can be overcome by using the carrier-based PWM, as long as the carrier signal and modulation signal can be properly selected. This paper proposes a new carrier-based PWM method to achieve some important control objectives in multilevel converters by adding the optimized zero-sequence signal to the reference voltage. The control objective as well as the control method for balancing the dc-link neutral point (NP) potential is presented in the paper. Meanwhile, the relationship between the NP potential and zero-sequence voltage is comprehensively analyzed and an algorithm for injecting the optimized zero-sequence signal is derived. This paper also investigates how to use the zero-sequence voltage to achieve the "two-phase" mode operation for reducing the converter switching losses. A common mode (CM) voltage mitigation method is then proposed which effectively mitigates the CM voltage within 1/6 of the dc-link voltage. Furthermore, this paper gives a simple method to directly mapping the reference voltage to the converter switches by using the concept of voltage level. Experimental results with a scaled 1kW system validate the proposed NP potential control method and CM voltage mitigation method.

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