Accurate measurement of instantaneous voltage for power electronics circuits

For power electronics circuits such as inverter circuits, the measurement of the instantaneous average value of the output voltage is rather troublesome and has never been undertaken in a rigorous sense. However, it becomes important, when the inner states of the load connected to the inverter has to be calculated using the quantities of the load terminal voltages and currents, such as in the case of vector control of the induction motor without speed sensor. This paper tries to give an accurate measuring method for it. The voltage cluster from the inverter is integrated every half period of the switching. Then the output of the integrator will be reset to zero after its volt-second value has been detected digitally. Two groups of the circuit take the alternative operation. High accuracy and linearity of the measurement can be achieved. The measurement of the instantaneous current has also been discussed.