New Drive System Using V/f Controlled Inverter and Current Controlled Inverter Suitable for High-Power Drives

Abstract

In large capacity drives such as blower, pump, linear railway and steel rolling mill drives, AC motors rated more than several thousands kW are used. In such cases, even though semiconductor switching devices of maximum capacity are used, the realizable capacity of the drive inverters are insufficient. Hence usually, for such drives, two or more inverters which operate with suitable phase differences have been combined using transformers or two inverters have been combined using inter-phase reactors. However, transformers and reactors have problems of acoustic noise and high losses, and in addition they are bulky and expensive.
To overcome these problems, in this paper, a new configuration for high-power drives using a wound rotor induction motor and two inverters, is proposed. In this configuration, the outputs of the two inverters are combined electro-mechanically in the machine, and hence the motor speed correspond to the sum or difference of the inverter frequency, and novel features can be obtained.