S2PC 2015, Chungju, Korea A Switching Method of Common Mode Noise Reduction of Single Phase PWM Inverter Seung Ju Lee ＊ , Chang Pyo Hong ＊ ,Hag wone Kim ＊ ,Kwan Yuhl Cho ＊ Korea National University of Transportation An PWM method for common mode noise reduction of single phase grid connected PWM inverter is proposed in this paper. Conventional general used switching method may have common mode voltage problem which is generates current leakge, EMI problem. A proposed switching method is that neutral point of output voltage is always fixed at input voltage both end to reduce common mode noise. The validity of the proposed method is proven by simulation and experimental result. Keywords Single Phase PWM Inverter, Common Mode Voltage, Common Mode Current, EMI 1. Introduction A PWM single-phase inverter is used with the purpose of AC power output in UPS (Uninterruptible Power Supply) and ESS (Energy Storage System). It made AC power through full-bridge circuit. Electric potential difference generated between input ground and ac voltage neutral point from previous switching method. It define CMV(Common Mode Voltage). EMI(Electro Magnetic Interference) is generated by CMV. It have a bad influence in total system. [1] It have a method for improvement of CMV, In order to reduce for leakage current. A paper[2] proposed that Unipolar PWM switching method to Bipolar PWM switching method. But, Bipolar PWM method switching loss is bigger than Unipolar PWM method. Further, voltage THD is increased. To solve this problem, A paper[3] is Common Mode Noise reduction method proposed a return current interval switch additionally in previous full bridge circuit and using Unipolar PWM method. But, It generated extra costs. To solve this problem in this paper, switching method maintain the previous Unipolar PWM switching method without special switch additional. And CMV is maintained by –Vdc and 0V as hardground method. It is a switching method of Common Mode Noise Reduction. It is validated by noise cause and reduction effect through simulation and experimental. 2. Proposed PWM Switching Method 2.1 Previous PWM Switching Method Unipolar PWM inverter switching method is in the table 1. Switching pulse is determined depending on condition of Reference voltage, supply of current and return of current. According to table 1 in positive voltage Table 1. Previous Switching Method Inverter Mode  ଵ  ଶ  ଷ  ସ  ௨௧ ∗ > 0 PWM 1 (60 Hz) PWM 2 (20k Hz) Power Supply 0 1 1 0 Recovery 0 1 0 1  ௨௧ ∗ < 0 PWM 1 (20k Hz) PWM 2 (60 Hz) Power Supply 1 0 0 1 Recovery 0 1 0 1 interval,  ଶ is always on as ͳ (60Hz), switch  ଷ ,  ସ is operated by complementary switching as ʹ . Common Mode Voltage is always maintained as 0V like figure 1(b). According to table 1 in negative voltage interval, ʹ is always ON during negative voltage interval. So,  ଵ and  ଶ is operated as complementary switching. When  ଵ ON,  ௖ hold -  ௗ௖ like figure. 2(a). When  ଶ ON,  ௖ hold 0V like figure 2(a). So,  ௖ is changed as a) Correspondence to: Hag wone Kim E-mail: khw@ut.ac.kr, ＊ The research was supported by the grant from National Research Foundation of the Education Ministry and Korea Institute of Energy Technology(KETEP) of Ministry of Trade in 2015. (a) (b) Fig. 1. (a) Previous inverter circuit of positive phase (b) Previous inverter voltage of positive phase