2n Pseudo-Random Coding Square-Wave Signal Injection Scheme for Sensorless Control of PMSM Drives

Permanent magnet synchronous motors (PMSMs) are widely used in various fields due to their advantages. However, mechanical position sensor failures will cause various serious safety issues. High-frequency square-wave injection (HF-SWI) enables sensorless control of PMSMs at low speeds; yet, the fixed-frequency nature of conventional methods results in narrow current power spectral density (PSD), causing harsh noise and limiting the widespread application of sensorless control, especially in household appliances. To address this, this paper proposes a pseudo-random coding (PRC) injection strategy. First, a 23 PRC-injection method (23 PRC-IN) is introduced, which disrupts the signal periodicity by varying the injection frequency and amplitude, thereby significantly expanding the current PSD. To further suppress residual peaks in the 23 PRC-IN, an improved 2(3&1) PRC-IN method is developed. By optimizing the code transition logic, this approach can completely eliminate the sharp noise. Experiments on a 5.5 kW PMSM platform validate that the proposed methods effectively broaden the current PSD and reduce the noise without compromising position observation accuracy.