Predictive Current Control in Motor Drives Operating at Steady Low Switching Frequency

Despite advances in multilevel inverters and wide bandgap switches, it is still very beneficial to operate high power inverters at low switching frequencies to reduce switching losses, which are critical to improving efficiency and extending the life of the systems. Much research has been done on the problem of controlling electrical drives at low switching frequencies, and in particular predictive methods offer very good approaches. This article deals with a classical method of predictive current control, namely the boundary-circle predictive scheme, and proposes its improvement by keeping the switching frequency close to a predefined level. This is achieved by controlling the radius of the boundary circuit. After deriving a linear relationship from the non-linear interaction between the boundary circle and the switching frequency, the proposed scheme dynamically adjusts the boundary circle to keep the inverter operation near the preset low frequency, thereby reducing switching losses while maximizing power device performance. The range of the switching frequency to be adjusted is determined according to the application, taking into account the trade-off between the quality of the current and the switching frequency. Experimental results from a laboratory setup confirm the effectiveness of the proposed method.