A sensorless algorithm is developed on the basis of a rotor flux observer in the stationary frame. In particular, it involves a parameter adaptive algorithm for an initial rotor flux like the observer, which was recently proposed by Bobtsov et al. (Automatica, vol. 61, Nov. 2015). In the proposed method, the flux observer is linked to the parameter estimator via a compensating term that results from parameter error. This method has a robust property against dc bias errors, i.e., it cures the inherent weakness of the pure integrator (flux observer) to dc offsets that frequently occur in current measurements and voltage estimates. The robust performance is demonstrated through simulations and experimental results.

A position sensorless algorithm is developed for IPMSM, while reflecting the saliency in an extended EMF term. Active flux is converted into a new linear regression form, and a high-pass filter was applied. Then, the gradient algorithm is applied to derive an estimate of the active flux in the stationary frame. The proposed observer is an inherently sensorless type because it does not require the rotor speed or position information. It is practically attractive since it does not require the use of pure integrator which is marginally stable. In addition, the observer can be constructed without the PM flux linkage constant. It is basically a model-based method. However, it is easily extended to a signal injection method which is robust in the low-speed region. Ultimate boundedness is established using the persistency of excitation condition. Validity of the algorithm is demonstrated experimentally via torque and speed control with a full load in the low-speed range.

An overmodulation (OVM) technique is proposed based on Fourier analysis. The OVM trajectory is a mixture of 6 arc segments of the inscribed circle and 6 vertices of the voltage hexagon. By adjusting the holding angle at each vertex, the modulation index is determined. The fundamental component is expressed as a function of the holding angle, and the linearity with the modulation index is obtained by the inverse relation. This algorithm guarantees seamless transitions from the space vector PWM (SVPWM) to OVM and finally to the six-step. Apart from the VVVF control, the proposed algorithm works well with the interior permanent magnet synchronous motor (IPMSM) current controller. By computer simulation and experimental evidences, the effectiveness is demonstrated.

A sensorless position scheme was developed for wound synchronous machines. The demodulation process is fundamentally the same as the conventional signal-injection method. The scheme is different from techniques for permanent-magnet synchronous machines, in that it injects a carrier signal into the field (rotor) winding. The relationship between the high-frequency current responses and the angle estimation error was derived with cross-coupling inductances. Furthermore, we develop a compensation method for the cross-coupling effect, and present several advantages of the proposed method in comparison with signal injection into the stator winding. This method is very robust against magnetic saturation because it does not depend on the saliency of the rotor. Furthermore, the proposed method does not need to check the polarity at a standstill. Experiments were performed to demonstrate the improvement in the compensation of cross-coupling, and the robustness against magnetic saturation with full-load operation.

Copper loss minimization schemes are widely used to control interior permanent magnet synchronous motors. In the field-weakening region, the maximum torque per ampere cannot be used due to the voltage limit set by the inverter DC-link voltage. It can be avoided when a high-voltage battery or a boost converter is used in the upstream of the inverter. In such cases, copper loss decreases as the current magnitude decreases. However, higher voltages may increase iron losses. In this article, a control method is investigated to minimize the sum of copper and iron losses. The loss sum is derived as a second-order function of a single flux variable, and the local minimum is determined analytically using the proposed approximation method. The proposed method offers several advantages, including high computational efficiency through analytical determination of the optimal operating point, reliable performance with acceptable approximation errors across various torque and speed conditions, and cost-effectiveness by eliminating the need for extensive dynamometer-based testing. Finally, the study is extended with an application to electric vehicle traction motors. Through simulation and experimental results, the benefits of the proposed control scheme are verified.

A new linear regression form is derived for a flux observer and a position observer is designed. In general, the observability of the permanent-magnet synchronous motor is lost at zero speed. In this work, the proposed regressor vector contains current derivative terms in both directions ($dq$-axis), and it gives the chance for the model-based flux observer to operate at zero speed. When an excitation signal is injected into d and q axes with the proposed flux observer, it helps to satisfy the persistent excitation condition in the low-speed range. Therefore, the sensorless performance of the model-based is improved greatly, even at zero speed. However, it appears with a disturbance term, which depends on the derivative of the d-axis current. Thus, the disturbance does not vanish when an excitation signal is injected. In this work, the disturbance term is also taken care of in constructing an observer. It results in an observer which allows signal injection. Thus, high frequency signal can be injected in the low speed region and turned off when it is unnecessary as the speed increases. This model-based approach utilizes the signal injection directly without recurring to a separate high frequency model. In other words, it provides a seamless transition without switching to the other algorithm. The validity is demonstrated by simulation and experimental results under various load conditions near zero speed.