Single Phase PWM Controlled Voltage Converter for Pumps and Fans without DC Link Electrolytic Capacitors

Single-phase induction motors are widely-used to drive pumps and fans up to several kilowatts. To satisfy the increased requirements in various application areas like modern air conditioning systems, speed-variable drives have become inevitable. Furthermore installations in homes, shops and offices make high demands on the running smoothness of the drive. With basic concepts like a phase-controlled single-phase AC voltage controller it is difficult to settle these claims. Moreover the indicated application areas are very cost sensitive. Advanced solutions including frequency converters often do not have a competitive position. This paper shows a novel concept to cope with these difficulties. The introduced converter is controlled by a high frequency pulsewidth modulation (PWM) signal. This allows an almost sinusoidal motor current with small distortions and therefore low noise emissions of the drive. The proposed circuit topology introduces low harmonics in the line current. This circumstance permits to comply with the relevant regulations without the need of bulky inductors or an active front end. The converter has a high efficiency even at high PWM frequencies. The absence of DC link electrolytic capacitors allows a space-saving design without drawbacks concerning reliability and lifetime at higher ambient temperatures.