A Flexible Multimode Control Scheme With Variable Switching Frequency for Parallel Interleaved Three-Phase Inverters

In this paper, a flexible multi-mode control scheme with variable switching frequency is proposed for parallel interleaved three-phase inverters. Three working modes are designed based on different operation sequence of inverters, corresponding to low, medium and high power conditions. Since number of alternately controlled inverters is changed according to the load conditions, the principle of current transition is derived by establishing equivalent circuit model. Based on this, current balance strategy is realized by estimating duration of switches. Further, the flexible mode-switching channel (FMSC) based mode-switching strategy is proposed to achieve fast and smooth transition among different modes. In the proposed scheme, only one field-oriented control (FOC) loop is configured while the drive pulses generated from FOC loop are reallocated to parallel legs for power distribution, thus greatly simplifying the control structure of the parallel inverters. The effectiveness of proposed method is verified on three parallel inverters with three current sensors. Experimental results show that the proposed scheme can achieve both good dynamic and steady state performances over wide range of switching frequency and output power.