Toni Tuovinen

A Combined Position and Stator-Resistance Observer for Salient PMSM Drives: Design and Stability Analysis

A reduced-order position observer with stator-resistance adaptation is proposed for motion-sensorless permanent-magnet synchronous motor drives. A general analytical solution for the stabilizing observer gain and stability conditions for the stator-resistance adaptation are derived. Under these conditions, the local stability of the position and stator-resistance estimation is guaranteed at every operating point except the zero frequency, if other motor parameters are known. Furthermore, the effect of inaccurate model parameters on the local stability of the position estimation is studied, and an observer gain design that makes the observer robust is proposed. The proposed observer is experimentally tested using a 2.2-kW motor drive; stable operation at very low speeds under different loading conditions is demonstrated.

Comparison of a Reduced-Order Observer and a Full-Order Observer for Sensorless Synchronous Motor Drives

Two back-electromotive-force-based position observers are compared for motion-sensorless synchronous motor drives: the reduced-order observer and the adaptive full-order observer. A stabilizing gain is proposed for the adaptive full-order observer, which guarantees the local stability of the closed-loop system, if the motor parameters are known. Equations for the steady-state position error and for the linearized estimation-error dynamics under erroneous parameters are derived, and the robustness of the two observers against parameter errors is analyzed and compared. The observers are experimentally evaluated using a 6.7-kW synchronous reluctance motor drive in low-speed operation and under parameter errors. The gain selection of the reduced-order observer is easier, but the adaptive full-order observer can be made more robust against parameter variations and noise.

Adaptive Full-Order Observer With High-Frequency Signal Injection for Synchronous Reluctance Motor Drives

A back-EMF-based position observer for motion-sensorless synchronous reluctance motor drives is augmented with high-frequency signal-injection method for improved low-speed operation. Previously proposed observer structure is further improved to account for the cross saturation in the motor. The combined observer is experimentally evaluated using a 6.7kW synchronous reluctance motor drive in low-speed operation and under various load conditions. The resulting position error at low speeds and standstill is small.

Current Control for Synchronous Motor Drives: Direct Discrete-Time Pole-Placement Design

This paper deals with discrete-time models and current control methods for synchronous motors with a magnetically salient rotor structure, such as interior permanent-magnet synchronous motors and synchronous reluctance motors (SyRMs). The dynamic performance of current controllers based on the continuous-time motor model is limited, particularly if the ratio of the sampling frequency to the fundamental frequency is low. An exact closed-form hold-equivalent discrete motor model is derived. The zero-order hold of the stator-voltage input is modeled in stationary coordinates, where it physically is. An analytical discrete-time pole-placement design method for two-degrees-of-freedom proportional-integral current control is proposed. The proposed method is easy to apply: only the desired closed-loop bandwidth and the three motor parameters (Rs, Ld, Lq) are required. The robustness of the proposed current control design against parameter errors is analyzed. The controller is experimentally verified using a 6.7-kW SyRM drive.

Discrete-Time Observer Design for Sensorless Synchronous Motor Drives

This paper deals with the speed and position estimation of interior permanent-magnet synchronous motor (IPMSM) and synchronous reluctance motor (SyRM) drives. A speed-adaptive full-order observer is designed and analyzed in the discrete-time domain. The observer design is based on the exact discrete-time motor model, which inherently takes the delays in the control system into account. The proposed observer is experimentally evaluated using a 6.7-kW SyRM drive. The analysis and experimental results indicate that drastic performance improvements can be obtained with the direct discrete-time design, especially if the sampling frequency is relatively low compared to the fundamental frequency.

Signal-Injection-Assisted Full-Order Observer With Parameter Adaptation for Synchronous Reluctance Motor Drives

A back-electromotive-force-based position observer for motion-sensorless synchronous reluctance motor (SyRM) drives is augmented with parameter adaptation laws for improved operation at all speeds, including standstill. The augmented observer is theoretically analyzed under various operating conditions. The analysis indicates that the stator-resistance adaptation should be enabled only at low speeds, the d-axis inductance adaptation should be enabled only at medium and high speeds near no load, and the q-axis inductance adaptation should be enabled only at high speeds under high load. The augmented observer is experimentally evaluated using a 6.7-kW SyRM drive.

Analysis and Design of a Position Observer With Resistance Adaptation for Synchronous Reluctance Motor Drives

A back-EMF-based reduced-order position observer with stator-resistance adaptation is analyzed for motion-sensorless synchronous reluctance motor drives. Analytical equations for steady-state estimation errors and stability conditions are derived (with and without resistance adaptation), taking into account errors in the parameter estimates. The effect of the observer gain on the noise reduction is studied by means of eigenvector analysis. A robust gain selection is proposed, which maximizes the allowed uncertainties in the parameter estimates. The proposed observer design is experimentally evaluated using a 6.7-kW synchronous reluctance motor drive; stable operation is demonstrated at low speeds under various parameter errors.

Analysis and design of a position observer with resistance adaptation for synchronous reluctance motor drives

A back-EMF-based reduced-order position observer with stator-resistance adaptation is analyzed for motion-sensorless synchronous reluctance motor drives. Analytical equations for steady-state estimation errors and stability conditions are derived (with and without resistance adaptation), taking into account errors in the parameter estimates. The effect of the observer gain on the noise reduction is studied by means of eigenvector analysis. A robust gain selection is proposed, which maximizes the allowed uncertainties in the parameter estimates. The proposed observer design is experimentally evaluated using a 6.7-kW synchronous reluctance motor drive; stable operation is demonstrated at low speeds under various parameter errors.

Current control for IPMSM drives: Direct discrete-time pole-placement design

This paper deals with discrete-time models and current control methods for synchronous motors with a magnetically anisotropic rotor structure, such as interior permanent-magnet synchronous motors (IPMSMs) and synchronous reluctance motors (SyRMs). Dynamic performance of current controllers based on continuous-time models is limited, especially if the ratio of the sampling frequency to the fundamental frequency is low. An exact closed-form hold-equivalent discrete motor model is derived. The zero-order hold of the stator-voltage input is modeled in stationary coordinates, where it physically is. An analytical discrete-time pole-placement design method for a two-degree-of-freedom state-space current controller with an integral action is proposed. The proposed method is easy to apply: only the desired closed-loop bandwidth and the three motor parameters (Rs, Ld, Lq) are required. The robustness of the proposed current control design against parameter errors is analyzed. The controller is experimentally verified using a 6.7-kW SyRM drive.

Minimizing losses of a synchronous reluctance motor drive taking into account core losses and magnetic saturation

This paper proposes a loss-minimizing controller for synchronous reluctance motor drives. The proposed method takes core losses and magnetic saturation effects into account. The core-loss model consists of hysteresis losses and eddy-current losses. Magnetic saturation is modeled using two-dimensional power functions considering cross coupling between the d- and q-axes. The efficiency optimal d-axis current is calculated offline using the loss model and motor parameters. Instead of generating a look-up table, an approximate function was fitted to the loss-minimizing results. The loss-minimizing method is applied in a motion-sensorless drive and the results are validated by measurements.