Active Energy Filter for Compensation of Harmonic Distortion in Motor Soft Starter

For more than half a century of the exploitation of controlled electric drive systems built on semiconductor elements thyristor converter devices proved to be the most reliable and cost-effective systems. Thyristor voltage converters (TVC) are used as soft starters (MSS) for powerful asynchronous electric drives and are promising in terms of their use as systems with an economizer and for the development of devices to control the drive speed. However, the use of TVC causes significant harmonic distortion of the shape of the current consumed. The excessively consumed reactive power, direct current consumption, current pulses lead to the emergence of additional losses of electrical energy in the elements of the power-supply system, accelerate the aging of insulation of current-carrying parts of equipment and negatively influence its electromagnetic compatibility. While for a soft starter with rare starts of the drive these effects can be neglected, due to the shunting of the TVC after acceleration of the engine, for a soft starter with frequent starts and systems where the TVC remains in the operation after acceleration, they must be taken into account. In this paper, the authors describe a solution directed at compensating the harmonic distortion of the consumable current in systems with a TVC. The main element of the proposed device is an active energy filter (AEF) performed on IGBT-switches controlled by a relay current regulator. The paper contains an analytical overview of compensation process for the harmonic distortion of the current with the help of AEF and considers its structure and selected components. The TVC and the compensation device operation was investigated by mathematical simulation in the software MATLAB Simulink.