Pseudorandom Frequency Sinusoidal Injection for MTPA Detection of PMa-SynRM Drives Considering Current Sampling Frequency

The traditional Constant Frequency Signal Injection (CFSI) based Maximum Torque per Ampere (MTPA) detection control scheme introduces significant three-phase current harmonics, which negatively impact the efficiency and stability of Permanent Magnet assisted Synchronous Reluctance Machines (PMa-SynRMs). This harmonic interference limits the accuracy of MTPA angle detection, making it unsuitable for high-performance applications. To address these issues, a Pseudorandom Frequency Sinusoidal Injection (PRFSI) MTPA detection scheme is proposed in this paper, in which the inductance variation, self-saturation and cross-saturation are considered. By optimizing the frequency spectrum and power spectral density (PSD) distribution of the injected high-frequency (HF) signals, PRFSI reduces MTPA angle detection errors. This improvement is achieved through the continuous and dispersed nature of the PRFSI frequency spectrum, which minimizes the concentration of harmonic energy in any specific frequency band. The proposed scheme significantly lowers steady-state current angle errors. The effectiveness of the proposed PRFSI-based method is validated through simulations and experimental tests conducted on a 0.54 kW PMa-SynRM. The proposed PRFSI approach effectively reduced the maximum detection angle error from 0.04 rad to 0.022 rad in rated load and 0.016 rad to 0.012 rad in half rated load for the MTPA control, resulting in a reduced current angle error.