Speed Control of Induction Motor Using Matrix Converter

Speed Control of Induction Motor Using Matrix Converter

Matrix Converter

Matrix Converter (MC) is a new type of direct AC/AC converter which converts input line voltage into variable voltage with unrestricted frequency without using an intermediate DC link circuit. MC is an array of controlled semiconductor switches that connects directly the three-phase source to three-phase load. A three-phase MC consists of nine bi-directional voltage-blocking switches, arranged in three groups of three each group being associated with an output line (Bose, 2002). This arrangement of bi-directional switches connects any of the input line A, B or C to any of the output line a, b or c as schematically represented in Fig.1. In order to provide safe operation of the converter when operating with bi-directional switches two basic rules must be followed. The input terminals should not be short circuited. Furthermore, the load has typically an inductive nature and for this reason an output phase must never be opened. An input filter is necessary to the high frequency ripple from the input current because the matrix converter is capable to connect the load to the grid directly (Faiz, 2001).

Fig.1

Induction motor drives with full power control on the stator side are commonly used in industrial applications. Although either a cage-type or wound rotor induction machine can be used in the drive, the former is always preferred in terms of low weight, low cost, low rotor inertia, speed limitation, maintenance and reliability. One feature of the latter is that the slip power becomes easily available from the slip rings, which can be either mechanically or electronically controlled for motor speed adjustment. However, for limited range speed control applications, where the slip power is only a fraction of the total power rating of machine, power rating of the converter is reduced, hence reduction in cost. The wound rotor induction motor takes this advantage (Kim, 2004). Slip power for adjusting motor speed can be recovered through static converters instead of useless dissipation on resistors. Slip power recovery drives have been used in some applications such as large capacity pumps and fan drives, variable-speed wind energy systems, shipboard variable-speed/constant-frequency systems, variable-speed hydro pumps/generators and utility system ?ywheel energy storage systems.

Fig. 2

Motor current, electromagnetic torque and stator ?ux magnitude are obtained at rated torque and 2000 r/min, and shown in Figs. 2 a, respectively. This Figs. show the above quantities for DTC of SPIM by conventional VSI. Also, in Fig. 2 the input side line-to-neutral voltage and line current of matrix converter drive are shown. Figs. 2 emphasize the good performance of the drive system with regard to the implementation of the DTC technique. In fact, the motor current shows a sinusoidal waveform and the ?ux magnitude and the electromagnetic torque follow their references (Bose, 2002). Fig. 2 shows the un?ltered input line current waveform and the corresponding line-to-neutral voltage. As can be seen, the line current is in phase with voltage, con?rming the validity of the control strategy ...