Control analysis and validation of a high dynamic motor starter

Abstract

Connecting a motor directly to the supply can lead to an inrush current equal to 5-8 times the rated current of motor during starting. This can negatively affect the power source the motor is connected to and other equipment connected to the same power source. Hence, dedicated motor starters are employed for motors exceeding a certain size. One such motor starter is the soft starter, which reduces the voltage applied to the motor during starting. The novel High Dynamic Motor Starter (HDMS) is a soft starter for single-phase induction motors based on the Buck converter principle. It reduces the inrush supply current during starting, while still supplying a sufficiently high motor current in order to start the motor. The HDMS contains an input LC filter in order to reduce the ripple on the supply current, which may cause stability issues due to its natural resonance frequency. This dissertation carries out a stability analysis of the novel HDMS prototype. For this analysis, the HDMS is modelled in state space form and a component-level simulation model is established. A state feedback regulator is proposed as an alternative current control system and the performance of both current control systems is compared. The performance is based on locked rotor tests and motor soft-starts. During the locked rotor tests, the supply and motor winding currents and the resulting starting torque are recorded. Flicker tests are carried out for both locked rotor and motor soft-starting tests in order to investigate the current controllers’ effect on the power source. Based on these performance tests, a current controller is chosen and finally tested for robustness towards variations in the motor winding and grid impedance parameters.