Current Derivative Measurement Using Isolated Delta-Sigma Modulator

Most of the control systems operate with the current references which is needed to be realized. The current control strategies are based on conventional proportionalintegral regulators or model predictive control. Both control strategies require knowledge of the motor parameters in the operating point. The easiest way to predict current is to know its instantaneous derivative which can be obtained by the current derivative measurement. This approach is used in the model-free predictive control methods. The current derivative measurement can be performed using existing current sensers and calculating current difference for the specified increment of time or by the hardware solution. The software implementation is much more convenient due to smaller cost of the hardware. This paper is focused on the current measurement using isolated delta-sigma modulator and the data processing of its bitstream to evaluate the current derivative for proper operation of the control system. Several options for differentiating the delta-sigma modulated bitstream was introduced. The proposed measurement system was examined using a model with variable sampling period. The results show that the estimation of the current derivative can be obtained with 10% accuracy in 13 us approximately.