Control method for calculating optimum DC bus voltage to improve drive system efficiency in variable DC bus drive systems

In this paper, an online method to calculate the optimum DC bus voltage in variable DC bus voltage drive system is proposed. The required DC bus voltage in the low speed region is much lower than for the rated speed region. As a result, the machine drive system efficiency can be improved with lower DC bus voltage since the switching losses in the inverter are reduced. To achieve both desired machine output torque and minimized losses simultaneously, an optimum DC bus voltage is required. However, machine parameter estimation errors and spatial harmonics in the machine result in calculation errors for the required DC bus voltage. A voltage disturbance state filter (VDSF), which is formed by a Luenburger-style closed-loop stator current vector observer with voltage command feedforward, is used to mitigate the calculation errors. Voltage errors caused by the parameter deviations and machine spatial harmonics will inherently be estimated by the observer´s state feedback controller. Therefore, calculation voltage error can be corrected by the VDSF´s disturbance voltage, so that the optimum DC bus voltage can be obtained.