01-08-2012, 04:34 PM
Phase-Control Alternatives for Single-Phase AC Motors
Offer Smart, Low-Cost, Solutions
Phase-Control Alternatives for Single-Phase AC Motors.pdf (Size: 216.64 KB / Downloads: 505)
Abstract
Single Phase AC motors continue to be the primary solution for air-movement,
pumping and compressor applications. Their low cost and availability make them ideal for lowperformance
systems. DC Brushless platforms attempt to address these applications but their
higher cost and complexity continue to form impenetrable barriers of entry. They are viewed as
overkill for most applications. Single-Phase Inverter Drives have come on the scene, making
headway, but remain complex and costly. Phase-Control solutions are being revisited and
upgraded to fill the void. This paper explores the performance limitations and trade-offs of the
Phase-Control solution and clarifies the boundaries under which the TRIAC Phase-control is a
preferred method of speed control and the improvements provided by smart phase-control.
INTRODUCTION
Variable speed motor controls have been available for many years. As technology
progresses, major innovations and improvements have been made in sophisticated
systems improving the motor drive performance and reducing cost and complexity of the
available solutions. Thus, improvements in the performance and availability of AC
inverter (Inverters) solutions as well as DC brushless drives (BLDC) and motors have
brought these solution options into the market in greater numbers.
There are many articles and technical papers that address the improvements and
innovations in brushless dc drives as well as improvements in AC drives. What we see
little of is the improvements in the existing low-cost control techniques focusing on phase
control or other low-cost AC control techniques that don’t require the AC power to be
converter to twice. This paper revisits the single-phase AC motor control and outlines
improvements and value added features now available that make phase-control drives a
viable alternative for speed control in most applications.
Of greatest interest is going back to revisit the Phase-control platform that has
been around for many years and look at the innovations and improvements that are
available. Comparisons will be made to the single-phase inverter designs but we will not
directly cover Inverter design innovations here. Most single-phase motors are not
designed to work well with high frequency inventers resulting in bearing pitting and
motor performance degradation.
The results demonstrate that with careful attention to the application requirements
and applying state-of-the-art technology to the basic TRIAC topology a good costperformance
solution can be provided that will allow variable speed to be incorporated
into numerous applications that were not viable for the manual controlled TRIAC or the
expensive Inverter solution. Upgrading the TRIAC control results in smart, performance
competitive solutions at a lower cost.
Power Systems World 2003 Phase Control Alternatives for Single Phase AC Motors
Page 2 of 8 H. Abramowitz
SINGLE- PHASE AC MOTOR SPEED CONTROLS
The two primary ways to control the speed of a single-phase AC motor is to either change the
frequency of the line voltage the motor sees or by changing the voltage seen by the motor,
thereby changing the rotational speed of the motor. An Inverter will convert the AC
waveform into a DC Voltage and them create a PWM signal output that will filter into a
waveform with a predetermined voltage (controlling torque) and frequency (controlling
speed). Figure 1 has a block diagram of the Inverter design and the various speed waveforms
are shown in Figure 2.
Key Benefits: Voltage / Frequency control