An Improved Multimode Synchronized Space Vector Modulation Strategy for High-Power Medium-Voltage Three-Level Inverter

The switching frequency of high-power medium-voltage three-level inverters is relatively low due to the limitation of switching loss. Thus, the output performance of the inverter will be deteriorated if the fundamental frequency is increased (in other words, the pulse number is decreased). To solve the aforementioned issue, synchronized modulation strategies are necessary to be adopted to ensure the synchronization and symmetry of the output waveform. However, the output waveform of the inverter will be still rich in low-order harmonics. In this article, the amplitude of the average current ripple vector is introduced as the evaluation index of the output waveform quality. And output performances of different synchronized switching sequences (continuous switching sequence and discontinuous switching sequences) are calculated and compared quantitatively. On this basis, the optimal synchronized switching sequence for each specific pulse number is determined and an improved multimode synchronized modulation strategy for three-level inverters is proposed. Experimental results show that the harmonic distortion of the output waveform is effectively reduced by the proposed strategy.