Improvement of Phase-Voltage Measurement with Voltage-to-Frequency Converters via Residual-Voltage Sensing

Measurement of phase voltage is a common solution to deal with disturbances introduced by voltage source inverters in drive systems. Aside from classical sample-based measurement techniques, analog-integration-based approaches offer especially easy handling of the steep voltage transitions of pulse width modulation (PWM). One such integration-based approach is the utilization of voltage-to-frequency converters (VFCs). They overcome the challenge of integrator reset by performing charge balancing on the integrator capacitor instead of fully discharging it. Simulations and experiments indicate that measurement of disturbed phase voltage with VFCs leaves residual voltage on the integrator capacitor during this charge balancing procedure between PWM periods. This residual voltage is the physical explanation of quantization error. A new method is proposed and implemented to sense this residual voltage, compensate the quantization error and significantly increase instantaneous accuracy.