Analysis of Current Sampling Errors in PWM VSI Drives

Current measurement and pulsewidth modulation (PWM) are critical components of modern current-controlled voltage source inverters. Current measurements enable accurate and robust closed-loop control of current, while PWM enables the efficient high-bandwidth regulation of the voltage. These two components do not operate independently, however. The synthesized voltage from PWM, a sequential series of discrete voltage levels, from a predefined finite set of possible levels, is only equivalent to the desired voltage on an average basis. As a result, the response of the electrical current to this synthesized voltage deviates from the response to the desired voltage. This deviation from the desired response, when combined with the standard synchronous sampling method, results in current measurement errors. This paper will present an analytical derivation of this current response deviation. This can be used to model the current measurement errors. A better understanding of this phenomenon will result in better design and control of power converter systems. The analytical work will be evaluated and verified using simulations and experimental measurements.