Current Ripple Analysis of New Double-Stator AC Drive Systems

Abstract

IntroductionMany studies have been conducted to improve the performance of AC drive system. With advanced progress of the power semiconductor switches, inverters can widely applied as AC drive with high-frequency switching and various levels of power requirements [1]- [4]. Various kinds of AC drive system topology by using an inverter has been researched and developed for a wide variety of applications, such as locomotive traction, electric ship propulsion, more-electric aircraft, and high-power industrial applications. For higher power requirements, multiphase and multilevel inverter is the most commonly used. The multiphase inverter basically consists of conventional n-half bridge inverter connected in parallel corresponding to the load supplies. It provides lower pulsating torque, better tolerance and the possibility of splitting motor current across a higher number of phases, thus reducing the converter rating [3], [5]- [7]. For high voltage applications, multilevel inverter is more suitable because the inverter output voltage is obtained through a few steps of voltage levels, although it also has some drawbacks. Multilevel system requires a lot of switches and has capacitor voltage unbalanced problem [8]- [11].In order to develop better performance of the AC drive system as Figure 1 [22]. On the input side of the inverter, the current ripple determines the size of the DC link capacitor of the inverter. It has been reported that the DC link capacitor is the most vulnerable component in an inverter. Furthermore, on the output side of the inverter, the higher current ripple could cause the motor to heat faster.In this paper, a new topology of double-stator AC drive system is proposed to combine the benefits of both multiphase and multilevel system. In the proposed system, as shown in Figure 2, two conventional two-level three-phase inverters are connected in series on the DC sides. Each three-phase output of these two inverters is supplying three-phase stator winding set of double-stator AC motor. By using the proposed topology, the advantages of simple twolevel inverter topology and high reliability and power density of multiphase AC motors can be combined. Analytical expressions of input and output current ripples of the proposed system are then derived. It is shown that under the same DC input voltages, the output current ripple of the proposed system is lower than the conventional topology. Under the same output voltage, the proposed system has lower input current and therefore, fewer losses on the DC power supply