DC Chopper control vs Phase Angle control

Posted on Feb 7, 2014

The two most common motor-control methods are: DC Chopper control and Phase Angle control. This article explores the differences between the two methods, identifying some of the key trade-offs that can be useful for motor-control designers when determining which is the best control method to use for their specific application. Shown in Figures 1 and 6, respectively, the triac control

DC Chopper control vs  Phase Angle control
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and chopper control circuits used to drive the universal motor can be used in a very simple household appliance. The main difference is that the triac and Gate Drive Transistor in the Phase Angle control circuit are replaced by an IGBT. The chopper circuit also introduces in a full-wave rectifier to the AC line circuit because the IGBT only conducts current in one direction. The main principle behind the Phase Angle control circuit is that the microcontroller (MCU) is used to vary the firing angle to the triac. By adjusting the firing angle to the triac, i. e. , the point in the AC voltage waveform where the triac turns on, the voltage applied to the motor can be modulated and the speed of the motor can be regulated. The firing angle of the triac is referenced to the zero crossing of the AC waveform, which is sensed using a zero crossing detect circuit on the line voltage. The MCU uses a special timer that emits a series of one-shot pulses into the gate of the triac to turn it on. A series of pulses are recommended as opposed to just a single pulse per cycle, because the motor is an inductive load, and a pulse train ensures the triac conducts current in both positive and negative directions. An illustration of this principle can be seen in Figures 2 and 3. In Figure 2, the gate pulses to the triac are for roughly one third of the duty cycle of the voltage waveform. The triac is conducting during this time. In the...

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