Innovative standstill position detection combined with sensorless control of synchronous motors

Sensorless control of PMSM's (Permanent Magnet Synchronous Motors) has occupied scientists for a long time. The result of this research is becoming widely accepted by the industry due to its low cost and reliability. However, the majority of today's motor drives are still equipped with some kind of position sensor. The reason is that sensorless control still have several limitations and is usually more complex than a traditional motor control. A new method to estimate the standstill position of PMSM's is presented. The method is based on the anisotropic properties of permanent magnets and is therefore referred to as MAM (Magnetic Anisotropy Method). The proposed method is independent of any ferromagnetic material and can therefore be used in many types of ironless PMSM's where standard methods fail. The MAM method is tested on a linear ironless motor, and measurement results from a "stripped" rotative motor without any supporting ferromagnetic material are also presented. Furthermore, it is shown in this thesis how Extended Kalman filters can be used to estimate the rotor position, and especially how the robustness and dynamic response of the overall control algorithm can be improved by using identification experiments and optimization algorithms. Some basic modelling of PMSM's are also presented. The modelling process is focused on techniques which are suitable for observers such as Extended Kalman filters. To show the versatility of the method, experimental results from two different motor types are presented. The first is a linear ironless motor while the second is a Hybrid Stepper Motor (HSM). Amongst other things it will be shown how the HSM can be transformed into a highly dynamic brushless DC motor without the drawbacks that is usually associated with HSM's. The linear ironless motor is used to demonstrate that it is possible to achieve good and robust position control without using a direct position sensor. Many different simulation and experimental results are presented for both the HSM and the linear ironless motor. The experiments are deliberately chosen to show both steady-state and dynamic operation of the proposed algorithm. The robustness of the overall algorithm is also analysed, considering unknown external load torque and motor parameters.

An Optimized Extended Kalman Filter Algorithm for Hybrid Stepper Motors

Yves Perriard, Jan Persson

In this article a high performance Extended Kalman filter algorithm is used to estimate rotor speed, rotor position and load torque in a Hybrid Stepper Motor (HSM). Together with a PI speed controller, the Kalman filter forms a very robust sensorless closed loop system. During acceleration the motor is capable of running in closed loop from 0-100% of the nominal speed. The controller can handle charge steps of over 50% of the maximum load torque, and acceleration up to 13 [krad/s 2]. To achieve theses good dynamic capabilities, the Kalman filter is optimized by an off-line identification process. This gives a very good match between the model and the real system. The standstill position at start-up is estimated by a current injection method. Due to the optimized Kalman filter the experimental results show very good precision and closed loop robustness for a 10.5 [W] HSM. The algorithm is implemented on a floating point DSP. The driver consists of two H-bridges with MOSFET transistors. The currents are measured with one shunt resistor for each phase.

2003

Steady state Kalman filtering for sensorless control of hybrid stepper motors

Yves Perriard, Jan Persson

Extended Kalman filtering techniques have been successfully used as sensorless control schemes on many different types of synchronous motors. One big disadvantage of the extended Kalman filtering technique is the large computational cost. Even with today's powerful DSPs, it is difficult to achieve effective real-time implementations. It is especially problematic for high speed motors or motors with many pole pairs such as hybrid stepper motors. In this article, it is shown how a steady-state version of the Kalman filter can be used to calculate the rotor position and speed for a hybrid stepper motor. By using a steady-state Kalman filter the computational effort can be drastically reduced. The proposed method is verified by a closed loop simulation of a hybrid stepper motor with additional current and speed regulators

IEEE2003

Analyse et conception de moteurs synchrones chemisés à commutation électronique

The number of brushless DC (BLDC) motor applications has increased significantly, essentially due to reduced costs of semiconductors and permanent magnets, but also because of the emergence of new control strategies, such as closed-loop and sensorless control. Among the different electric drives, the heating circulation pump is a typical application which could greatly benefits from new BLDC technologies. Nowadays, the majority of low power heating circulation pumps is driven by AC induction motors. Despite of its low efficiency (< 20% for a single phase motor and < 50% for a three phase motor), this kind of motor is still used widely, because of its inherent simplicity since no electronic driver is needed. When a regulation is necessary (for example pressure, flow regulation), this advantage disappears. The aim of this work is a systematic analysis of the circulating pump motor. One solution is investigated in particular: the pump with a sealed BLDC motor. The following points are analysed in details: An analytical method to calculate the flux density distribution is tailored for motors with an important gap, as the sealed motors or slotless motors. The analysis of the electromagnetic characteristics for brushless DC motors shows the similarity of the various brushless DC motors. The calculation of tube losses determines their influence on the energetic balance of the motor. The determination of the acoustical motor noise shows the influence of the different modes of phases switching. The thermal aspects which take into account the motor environment are examined from the theoretical and practical point of view. The synthesis of these points results in a concept for the design and optimisation of BLDC motors; a series of pump prototype have been designed. For the heating circulation pump, the replacement of the AC induction motor with a brushless DC motor makes it possible to double the global installation efficiency. This solution is very promising from an energising aspect as well as an economical one and contributes to electrical energy savings, essential in this end of century.

EPFL1998

Analyse et conception de moteurs synchrones chemisés à commutation électronique

EPFL1998