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PWM Voltage

PWM Voltage

PWM Voltage

Pulse Width Modulation Voltage

Variable frequency motor drives and inverters form distributed generation equipment, produce Pulse Width Modulated (PWM) voltage, not a true sine wave. PWM voltage can consist of hundreds of pulses per cycle or thousands of pulses per second. The magnitude of these pulses can be amplified in applications involving long motor leads causing possible damage to motor windings. The fast rise time (dv/dt or rate of voltage change over time) associated with these pulses can cause premature failure of electrical insulation for electrical equipment and conductors. Electrical equipment such as motors, experience higher power losses and temperature rise when supplied with PWM voltage as compared with sine wave voltage.

PWM Voltage Sine Wave Voltage

APQ offers Sine Wave dv/dt Filters and Load Reactors to improve the quality of voltage produced by a Pulse Width Modulated (PWM) inverter and to protect and extend the life of motors supplied by AC variable frequency drives. Voltage is restored to a near sine wave, dv/dt concerns are eliminated and voltage pulse amplification is eliminated.


  • Sine Wave dv/dt Filter (Type SWF)

    Use APQ Sine Wave dv/dt Filters (Type SWF) for best motor performance and life expectancy or to improve voltage quality for alternative energy inverter applications. Type SWF filters convert PWM voltage to a sine wave, eliminate all dv/dt concerns and also enable all three motor phase currents to be balanced within 0.20% of each other.

  • Load Reactor (Type SRT & HRT)

    Use APQ Load Reactors (Type SRT) rated 5% impedance to protect motors from excess peak voltage due to reflected voltage waves and high dv/dt when the cable lengths are short to medium in length (typically 500 feet/ 152 meters).

Improved voltage quality means longer life and lower power losses. PWM voltage by itself, results in higher motor temperature than sinusoidal voltage, and higher temperature typically means lower life expectancy. In applications where long cables are used, reflected waves can cause the peak voltage at the motor terminals to increase by up to 100% which can cause premature motor winding failure. The following chart demonstrates the effectiveness of several alternatives.

Motor Protection Alternatives
Filter OptionWaveform measured at motor terminals
300 meter (1000 feet) motor cable length
Results for Motor Life
APQ Type SWF
Sine-Wave dv/dt filter
BEST Motor Protection
dv/dt filter only Marginal Protection
Load reactor only Marginal Protection
No filter Not Good
Motor Life in Jeopardy