Bandwidth Extending Approach for Sensorless Control of Synchronous Reluctance Machines Using an HF Square-Wave-Shaped-Voltage-Injection-Based Method for Low Speed Range

For many industrial applications, sensorless control of synchronous reluctance machines (SynRMs) is beneficial. Additional sinusoidal high-frequency (HF) test signals are often injected for sensorless control at standstill and in the low speed range. However, they have a number of drawbacks for SynRMs combined with a standard industrial inverter and without current oversampling. Hence, this paper presents an approach tailored to SynRMs using square-wave-shaped voltage test signals. They simultaneously increase the bandwidth, because they enable a higher HF frequency. The paper takes into account the highly nonlinear machine behaviour by using adaptive HF voltage levels. It compensates for the electrical angle error caused by cross-coupling effects and for that caused by load steps or dynamic behaviour during demodulation of the HF current amplitude. Only a special regular-update current sampling method is sufficient. A two-degree-of-freedom (2DoF) current and speed control is implemented. The theoretical background of the method is explained, and the control concept is validated on the basis of experimental results.