Method and system for ride-through of an adjustable speed drive for voltage sags and short-term power interruption

An adjustable speed drive for ride-through of voltage sags comprising:

• an adjustable speed drive comprising:
• a three phase electric utility;
• a diode rectifier coupled to the three-phase utility;
• a dc-link coupled to the diode rectifier and having a dc-link capacitor;
• an inverter coupled to the dc-link;
• a motor coupled to the inverter;
• and
• a ride-through circuit coupled to the adjustable speed drive comprising:
• a control unit having a first input, the first input operable to receive the voltage from each phase of the three phase electric utility and determine if there is a voltage sag;
• an IGBT coupled to an output of the control unit and operable to switch on and off at variable duty cycle which is dependent on voltage sag and remain off if there is no voltage sag;
• ride-through diodes operable to be forward biased when the IGBT is on, one ride-through diode associated with each phase of the three phase electric utility;
• a ride-through inductor coupled to the ride-through diodes and associated with the IGBT, the ride-through inductor operable to store energy when the IGBT is switched on and to transfer energy to the dc-link capacitor when the IGBT is off in order to maintain the dc-link voltage to continuously operate the adjustable speed drive.