A Novel SVPWM Technique for Leakage Current Reduction and Neutral-Point Voltage Balance in Transformerless Three-Level Inverters

In photovoltaic (PV) systems, transformerless three-level inverters have been widely used because of the simple structure and high efficiency. However, in addition to the inherent neutral-point voltage unbalance problem in three-level inverters, leakage current issues also should be carefully regulated in transformerless systems. But conventional common-mode voltage (CMV) reduction methods cannot well deal with the two problems. According to the principle of generation of leakage current, an improved large-medium-small-vector modulation (ILMSVM) method is proposed in this paper based on the LMP/NSVM method. Unlike conventional CMV suppression method, small vectors with high CMV are also used in the proposed method to control the neutral-point voltage while leakage current is well suppressed. Variation of CMV is kept within 1/6Udc in each switching cycle. And leakage current spikes are also avoided between the switching sequences. Compared with LMP/NSVM method, the neutralpoint voltage is adjusted faster and leakage current spikes is avoided in applying the ILMSVM method. Compared with conventional SVPWM method, ILMSVM method has little disadvantages in neutral point voltage control but can well suppress the leakage current. Effectiveness of the proposed method is verified by comparing the results with conventional SVPMW method and LMP/NSMV method in simulation.