Buck-boost transformer and PWM topology help OEMs operate equipment in countries with mains fluctuating outside design limits

How the Technologies Compare



The Electromechanical Servo AVR

An electro-mechanical regulator uses a servo motor to turn the crank of an internal variable transformer to change the input voltage to the primary of a series connected buck-boost transformer. The servo receives its control voltage from the output of a feedback and control system that monitors the output voltage of the secondary winding of the buck-boost. The supply voltage is connected to the other end of the buck-boost and load current returns via the system neutral.



The Electronic Tap-switching AVR

An electronic regulator uses either an isolation or auto transformer with regulation taps on secondary winding. The typical number of taps range from three (3) to seven (7) which translates into the same number of regulation steps—the more steps the more precise the regulated output voltage. The taps are switched either using mechanical relays or SCRs (for higher-current systems). The switches are controlled by a voltage output from a feedback and control system comparator, which compares input voltage against a reference value—the error output causes the switches to change to the appropriate tap.



Dual Conversion AVR AC input is connected to a full-bridge rectifier that feeds a high-frequency boost converter circuit. The secondary of the boost converter forms the DC link that feeds the input of the DC-AC power inverter. The inverter output voltage and frequency can be the same as input or be set to a different voltage and frequency.