Difference between revisions of "PWM"
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==Usage in GD products== | ==Usage in GD products== | ||
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| − | All GD motor drives produce PWM signal to motor. I.e. if drive supply voltage is 48VDC, then motor output pins will be driven either to 0V or 48V at switching rate of 15-20kHz. | + | All GD motor drives produce PWM signal to motor. I.e. if drive supply voltage is 48VDC, then motor output pins will be driven either to 0V or 48V at switching rate of 15-20kHz. VSD drives use MOSFET or IGBT based [http://en.wikipedia.org/wiki/H-Bridge half-bridge] circuits to produce the power PWM output. |
Inductance of motor coils will average the PWM pulses to equivalent DC. If motor inductance is very low, additional inductor is needed between drive and motor phases. | Inductance of motor coils will average the PWM pulses to equivalent DC. If motor inductance is very low, additional inductor is needed between drive and motor phases. | ||
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===As reference signal=== | ===As reference signal=== | ||
In some drive models, PWM signal can be used also as reference signal to replace analog signal (the +/- 10V control). In this case PWM voltage is typically 3-5V and the duty cycle of signal determines the amplitude. | In some drive models, PWM signal can be used also as reference signal to replace analog signal (the +/- 10V control). In this case PWM voltage is typically 3-5V and the duty cycle of signal determines the amplitude. | ||
Revision as of 13:43, 26 March 2012
PWM a.k.a. pulse-width modulation is a voltage waveform usually seen in power electronics such as motor drives and power supplies.
The main idea in PWM is to switch input voltage either fully on or off so rapidly that output device "feels" only the average voltage caused by pulsed voltage.
Contents
Pros and cons in power applications
Pros
- Very high efficiency due to low losses in electronics
- Usually very little heat sinking needed
- Easy to produce in digital circuits
- Robust
Cons
- Increased EMI noise compared to linear voltage
Usage in GD products
As motor output
All GD motor drives produce PWM signal to motor. I.e. if drive supply voltage is 48VDC, then motor output pins will be driven either to 0V or 48V at switching rate of 15-20kHz. VSD drives use MOSFET or IGBT based half-bridge circuits to produce the power PWM output.
Inductance of motor coils will average the PWM pulses to equivalent DC. If motor inductance is very low, additional inductor is needed between drive and motor phases.
As reference signal
In some drive models, PWM signal can be used also as reference signal to replace analog signal (the +/- 10V control). In this case PWM voltage is typically 3-5V and the duty cycle of signal determines the amplitude.
Compared to analog input in VSD products 0% PWM duty cycle equals -10V, 50% equals 0V and 100% equals +10V. Benefits of using PWM instead of analog reference:
- EMI noise tolerant
- Easy to galvanically isolate
- Easy to generate from digital circuits
