Offline parameter identification of permanent magnet synchronous machines (PMSMs) is of great importance for general-purpose drives with sensorless control. This paper proposes an amplitude-auto-adjusting signal injection (ASI) method for the parameter self-learning of PMSMs at standstill considering inverter nonlinearities and the digital time-delay effect. The ASI method achieves the inductance identification process under various dq-axis currents and at the same time prevents the unexpected rotor rotation during the self-commissioning process. For the test PMSM, the spatial inductance maps of dq-axes and abc-phases concerning the magnetic saturation and cross-coupling effects are identified along with the stator resistance. To enhance the estimation accuracy, an error model of the inverter nonlinearities in dq-axes is established, and a compensation method independent of inverter parameters is proposed based on the Hermite interpolation. In addition, the influence of the digital time-delay effect is analyzed and compensated based on the transient model of the circuits. The effectiveness of the proposed parameter self-learning scheme is confirmed on a 2.2-kW PMSM drive. The accuracy of the experimental results is validated by finite element analysis (FEA) on the test machine.

This paper proposes a new sensorless control scheme of interior permanent magnet synchronous motors (IPMSM) using high-frequency (HF) orthogonal square-wave voltage injection into stationary reference frame (SRF). This scheme is an improvement on the conventional HF rotating sinusoidal voltage injection into SRF. Firstly, discrete sequences of HF currents are applied to establish the whole signal process. Then, a position estimation method without using low-pass filters is proposed and the phase shift caused by high-pass filter is also reduced. Therefore, the proposed sensorless control method would not be adversely affected by digital filters, which can solve the common drawbacks of the current SRF-based injection methods. Furthermore, digital delay in drive systems is considered and its negative influence can be eliminated effectively as well. The sensorless control method is verified by experiments on a 2.2-kW IPMSM drive platform.

The extra acoustic noise caused by the high-frequency (HF) signal injection imposes restrictions on its extensive applications for sensorless synchronous reluctance motor (SynRM) drives. To attenuate the undesired acoustic noise further, a hybrid pseudorandom (PR) signal injection scheme is proposed in this article. The hybrid PR signal injection is implemented by injecting square wave signals chosen in a random manner from a set of signals having either different frequencies or phases from each other. The optimal assembly of hybrid PR signals is designed via current power spectral density (PSD) analysis, aiming at reducing acoustic noise as much as possible. In this way, the proposed scheme achieves success in a massive acoustic noise reduction by means of completely eliminating the discrete harmonics of the current PSD and distributing the current PSD to a wider range. Besides, the low-pass filters used to separate the fundamental frequency component from injected HF components of currents could be eliminated because no discrete harmonics at injected frequencies exist with the proposed hybrid PR signal injection. The validity and superiority of the proposed sensorless control scheme are verified on a 3-kW position sensorless SynRM drive platform.

The conventional high-frequency (HF) voltage injection method can accurately extract rotor position for interior permanent magnet synchronous motor (IPMSM) drives at low and zero speed ranges. However, the fixed injection frequency will produce a loud audible noise. To solve this problem, a pseudo-random phase-switching fixed-frequency (PRPSFF) signal injection method is proposed in this paper. Based on the principle of phase selection for the PRPSFF injection scheme, the dc bias problem in the induced HF current can be diminished by setting a limitation in the injected voltage. Then a corresponding signal processing method is investigated to deal with the signal delay in the HF current extraction. Besides, the current power spectra density (PSD) for PRPSFF injection is analyzed, and a comparison between PRPSFF and the pseudo-random frequency-switching fixed-phase (PRFSFP) injection schemes is also introduced. The results show that the discrete harmonic spectrum in current PSD can be offset, and the continuous spectrum is smoother than that of PRFSFP injection. Finally, the effectiveness of the sensorless control method is verified by experiments on a 2.2-kW IPMSM drive platform.

Pulsating high-frequency (HF) signal injection is a common saliency-based sensorless control method applied for synchronous reluctance motor (SynRM) drives. However, the accuracy of the rotor position estimation deteriorates due to severe cross-coupling effect and voltage fluctuations. To solve this problem, a measured reference frame HF voltage injection (MHFVI) method is proposed in this paper. A total of two discontinuous pulsating square-wave voltage signals are injected along with two measured axes, and position information is extracted with a cross-coupling factor (CCF) introduced, which can inherently account for the estimation error caused by the cross-coupling effect. The signal processing scheme of the proposed MHFVI method is further developed to be robust to voltage errors, meanwhile has less fluctuation in the position estimation error. The position estimation error is investigated and analyzed based on the finite element analysis results and the introduced CCF is calculated based on the SynRM current-flux characteristics models. Finally, the proposed method is verified by experiments on a 3-kW SynRM drive platform.

The remarkable inductance nonlinearities of synchronous reluctance motors (SynRMs) could result in operating-point-dependent high frequency (HF) current responses, and more HF losses with audible noises with conventional constant amplitude high frequency signal injection (HFSI) methods applied. This paper proposes an adaptive pseudo-random high frequency square-wave voltage injection (AP-HFSVI) based sensorless control method for SynRM drives at low-speed operation. An adaptive high frequency current control strategy is applied using pseudo-random injection patterns to adapt with the nonlinear characteristic of SynRM inductances. The magnitude of the injected HF voltage signals can be adjusted adaptively with the load variation online via HF current adaptive control scheme, which processes and regulates the HF current components to be constant. Hence the HF losses and audible noises can be effectively suppressed due to the decreasing magnitude of injected signals. The current power spectra density of AP-HFSVI method is analyzed and compared with the conventional HFSI method. The effectiveness and superiority of the proposed sensorless control method is verified with experiments on a 3 kW SynRM drive platform.