Model-based control structure for high-speed permanent magnet synchronous drives

Electrical fundamental frequencies of high-speed drives typically range between 1 and 2 kHz. In order to ensure low-loss operation of the drive, the switching frequency has to be kept as low as possible, resulting in pulse numbers smaller than 15. To avoid subharmonics of the modulated voltages, it is highly recommended to synchronize the PWM with the fundamental voltage. In addition to that, the application of optimized pulse patterns of quarter-or half-wave symmetry increases the efficiency even more. The disadvantage with these optimized patterns is that they are not suited to the standard field-oriented drive control structure. To overcome this problem, a modelbased current control structure which is based on the field-oriented control was established for PM-synchronous machines. If an additional LC-filter is required, the proposed control structure also manages to control the more complex drive system without the excitation of its resonance. A simulated drive model demonstrates the smooth and non-critical behavior of the presented model-based current control structure. Experimental results of a 35 kW test motor confirm its practical feasibility.