Improved modulation of two-stage matrix converter for EMA in aircraft applications

This paper presents the improved modulation strategy of Two-Stage Matrix Converter (TSMC) for applications in aircraft Electro-Mechanical Actuator (EMA) system. In the modulation of rectifier stage, Phase Locked Loop (PLL) is employed to track the instantaneous value of both the angle and the frequency of the input voltage vector. The frequency is then taken into calculation to compensate the angle sample delay, as a result of the un-ignorable angle alternation in each Pulse Width Modulation (PWM) cycle at input frequency of 360∼800Hz. The drawbacks of the sample delay are discussed, which lie in the incorrect input power factor control, fluctuation of voltage transfer ratio and possibility of short circuit in inverter stage. In the modulation of inverter stage, a 4-time commutation PWM pattern is presented, which reduces the number of commutations from 6 to 4 in each PWM cycle. Therefore, increasing the PWM frequency by 50% remains the same number of commutations thus the same switching loss per time interval. The sample delay and the output current harmonic could be reduced thereafter at the increased PWM frequency. Simulation and experiment results verify the improved performance of the proposed modulation.