Jorma Luomi

Analysis of an Adaptive Observer for Sensorless Control of Interior Permanent Magnet Synchronous Motors

This paper deals with a speed and position estimation method for the sensorless control of permanent magnet synchronous motors. The method is based on a speed-adaptive observer. The dynamics of the system are analyzed by linearizing both the motor model and the observer, and the observer gain is selected to give improved damping and noise suppression. At low speeds, the observer is augmented with a signal injection technique, providing stable operation down to zero speed. The experimental results, obtained using a 2.2-kW interior magnet motor, are in agreement with the results of the analysis.

Reduced-order flux observers with stator-resistance adaptation for speed-sensorless induction motor drives

This paper deals with reduced-order flux observers with stator-resistance adaptation for speed-sensorless induction motor drives. A general analytical solution for the stabilizing observer gain is given. The gain has two free positive parameters (which may depend on the operating point), whose selection significantly affects the damping, convergence rate, robustness, and other properties of the observer. The general stability conditions for the stator-resistance adaptation are derived. An observer design is proposed that yields a robust and well-damped system and requires a minimal amount of tuning work. The proposed observer design is experimentally tested using a 45-kW induction motor drive; stable operation at very low speeds under different loading conditions is demonstrated.

Stabilization of regenerating-mode operation in sensorless induction motor drives by full-order flux observer design

This paper deals with the full-order flux observer design for speed-sensorless induction motor drives. An unstable region encountered in the regenerating mode at low speeds is well known. To remedy the problem, a modified speed-adaptation law is proposed. Instead of using only the current estimation error perpendicular to the estimated flux, the parallel component is also exploited in the regenerating mode. Using current estimation error loci in steady state, a linearized model, simulations, and experiments, it is shown that the observer using the proposed speed-adaptation law does not have the unstable region. It is also shown that the effect of erroneous parameter estimates on the accuracy of the observer is comparatively small.

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.

Sensorless control of PMSM drives using a combination of voltage model and HF signal injection

This paper presents a method for the rotor speed and position estimation of permanent magnet synchronous motors in a wide speed range including standstill. The proposed method is based on a modified voltage model at high speeds, and combines the modified voltage model with a high-frequency signal injection technique at low speeds. The fast dynamic response of the voltage model is thus augmented with the steady-state accuracy of the high-frequency signal injection technique. The stability and robustness of the combined observer are confirmed by simulations and experiments.

Efficiency Optimization of a 100-W 500 000-r/min Permanent-Magnet Machine Including Air-Friction Losses

This paper proposes a method for the efficiency optimization of ultrahigh-speed permanent-magnet machines. Analytical methods are applied for the modeling of the machine that is equipped with a diametrically magnetized rotor and a slotless stator. The outer dimensions of the machine are design constraints, and the internal dimensioning is optimized for minimum losses. The air-friction losses are taken into account in addition to the usual iron, copper, and eddy-current losses. Laminated silicon-iron or laminated amorphous iron is used as the stator core material. The results show that air-friction losses influence the optimum design considerably, leading to a small rotor diameter at high speeds. The loss minimization and the amorphous iron core make it possible to reduce the calculated losses by 63% as compared to a machine design not considering air-friction losses. The resulting efficiency is 95% for a 100-W 500 000-r/min machine excluding bearing losses. Experimental results are shown to illustrate the validity of the method.

Sensorless Control of Induction Motor Drives Equipped With Inverter Output Filter

This paper deals with the speed sensorless vector control of an induction motor in a special case where the output voltage of the PWM inverter is filtered by an LC filter. The system states are estimated by means of an adaptive full-order observer, and no additional voltage, current or speed measurements are needed. The rotor speed adaptation is based on the estimation error of the inverter output current. Dynamic analysis is used to find an observer gain that enables a wide operation region, including very low and very high speeds. A torque-maximizing control method is applied in the field-weakening region. Simulation and experimental results show that the performance is comparable to that of a drive without the LC filter

Induction Motor Drives Equipped With Diode Rectifier and Small DC-Link Capacitance

This paper deals with sensorless vector-controlled induction motor drives that are fed by a frequency converter that is equipped with a diode front-end rectifier. A small dc-link capacitance is used, which makes it possible to replace the electrolytic capacitors with film capacitors. The natural frequency of the dc link is chosen to be considerably higher than six times the mains frequency but lower than the switching frequency. A recently proposed sensorless controller can be exploited; only minor modifications for small capacitances are needed. The simulation and experimental results of a 2.2-kW drive that is equipped with a capacitance of only 24 demonstrate operation in a wide speed range.

Loss-Minimizing Flux Level Control of Induction Motor Drives

This paper applies a dynamic space-vector model to loss-minimizing control in induction motor drives. The induction motor model, which takes hysteresis losses and eddy-current losses as well as the magnetic saturation into account, improves the flux estimation and rotor-flux-oriented control. Based on the corresponding steady-state loss function, a method is proposed for solving the loss-minimizing flux reference at each sampling period. A flux controller augmented with a voltage feedback algorithm is applied for improving the dynamic operation and field weakening. Both the steady-state and dynamic performance of the proposed method is investigated using laboratory experiments with a 2.2-kW induction motor drive. The method improves the accuracy of the loss minimization and torque production, it does not require excessive computational resources, and it shows fast convergence to the optimum flux level.

Signal Injection in Sensorless PMSM Drives Equipped With Inverter Output Filter

This paper proposes a hybrid observer for sensorless control of permanent-magnet synchronous motor drives equipped with an inverter output LC filter. An adaptive full-order observer is augmented with a high-frequency signal injection method at low speeds. The only measured quantities are the inverter phase currents and the dc-link voltage. The effects of the LC filter on the signal injection are investigated, and it is shown that the filter is not an obstacle to using signal injection methods. The proposed method allows sensorless operation in a wide speed range down to zero speed. Experimental results are given to confirm the effectiveness of the proposed method.