Auxiliary voltage sag ride-through system for adjustable-speed drives

Voltage sags and harmonics are two very important power quality problems. Adjustable-speed drives (ASD) trip due to voltage sags, interfering with production and resulting into financial losses. Harmonics can cause, among others, overheating and noise in the motors. In order to improve performance and reliability of ASD, this paper presents an auxiliary system that combines two sub-circuits that provide ride-through capabilities to critical ASD loads during balanced and unbalanced voltage sags and line current total harmonic distortion (THD) improvement using a third harmonic injection method. A supervised Adaline algorithm is used for voltage sag detection to activate a thyristor controlled rectifier to keep the DC-bus voltage within acceptable limits. A detailed description of the operating principle is presented. The theoretical analysis is verified by digital simulation using PSIM software. Implementation details and experimental results on a 12.5 kW prototype are also presented