Instantaneous voltage measurement technique for PWM voltage source inverters

The pulse width modulated (PWM) voltage source inverter (VSI) is almost universally used in industrial motor drives. Although measurement of the VSI output voltage is required in many applications, accurate measurement is problematic due to the high frequency inverter switching. Many commonly used inverter output voltage measurement methods, such as indirect and direct voltage measurement, produce inaccurate results under a variety of operating conditions. In this paper, the common sources of voltage measurement error are identified and an instantaneous voltage measurement technique is presented that significantly reduces inaccuracies introduced by common voltage measurement strategies. Implementation details of the proposed strategy are outlined and experimental results are used to compare the proposed technique with other methods of inverter output voltage measurement. The results demonstrate the opportunity for improvements to any inverter-driven motor control system that requires precise terminal voltage measurements to carry out the intended control objective.