As any other rotating motor, the function of permanent magnet motors is to convert the supplied electrical power into revolving mechanical torque. A permanent magnet (PM) is provided to the rotor to replace the rotor windings in producing an effectively strong magnetic field in the motor airgap sufficient to start the rotor spinning action. Accordingly, when this motor is running, a rotating magnetic field emerges in a synchronous speed to that of the field generated by the stator windings. So they have their name as permanent magnetic synchronous motors (PMSMs). They have started as competitive motors in industrial process since the 70s of the last century under the influence of cheap production of magnetic materials and the development in power electronic theories and applications.
2 Detection of the actual rotor position, with respect to stator windings, has a significant effect on the motor soft running; high performance speed control and torque ripple reduction. The literature review has showed that while the rotor position estimation is well solved at medium and high speeds, the topic is still need more improvements at zero and low speed.
As given in table 5.4, the zero-speed position estimation has verified an angle resolution of 22.5o, according to the impulse response method, while the low speed position estimation has predicted the position with high resolution but it still suffering from the problems of signals filtering and the acoustic noise. Therefore, this thesis aims to raise the resolution of the rotor position estimation of PMSM at zero speed and to verify a new strategy for rotor position estimation at low speed.
To achieve these goals, the thesis works focused on constructing a closed-loop microcontroller based system to achieve the estimation process and to control the operation of permanent magnet machine. The system involves a PC monitoring for the design performance. The thesis goals were primarily satisfied by simulated models based on “MATLAB/Simulink” environment models. Accordingly, real-time controllers were built to achieve an advance estimation for rotor position and, correspondingly, advance control on machine running. The works are designed to be fully sensorless through adopting only the voltage measurements as base to detect the rotor position. Finally, the performance of the proposed and verified controllers were tested practically and modified repeatedly to reach the optimum condition.
The thesis is introduced with two sections, zero-speed and low-speed rotor position estimations. In both sections, the inherent machine magnetic saliency feature was adopted as a base in detection the rotor position. Moreover, the thesis also considers addressing some problems related to operation of PMSM such as filter process and noise.
1.2.1 Zero-speed rotor position estimation
This thesis section aims to implement a high-resolution estimation system to estimate the rotor position of permanent magnet synchronous motors PMSMs at zero- speed condition. To achieve this goal, a system is built based on exploiting the impulse
3 responses to an injection of high frequency pulses, 3 kHz, into the motor stator windings. The responses are sensorlessly measured at the motor terminals. This section is primarily implemented through simulated models for surface mounted and salient pole permanent magnet motors. Then a practical system is setup depending on a microcontroller, type “ATMega328”. Its duty is limited into achieving three tasks, generating the high frequency pulses, measuring, manipulating and analysing the motor responses and finally displaying and monitoring the estimation progress. Three key points were taken into consideration in implementing the zero-speed rotor position estimations:
To reduce the sector gap in rotor position estimation. This means not to determine the rotor location between points x and y where the gap between these two points is wide enough.
To adopt only the motor terminal voltage variations, no current measurements contribution. This allows making the proposed approach fully sensorless. To be as cost effective as possible.
1.2.2 Low-speed machine driving and rotor position estimation
In this section, a variable speed drive servo system is built to run two types of surface mounted permanent magnet motors with high performance specifications. The system forward path drives the motors through a sensorless space vector control strategy. The system forward path drives the motors through a proposed method to modulate the space vector. It bases on inserting a virtual voltage, which causes in generating the optimum patterns in the space vector analysis. Whereas, the feedback path includes a sensorless rotor position estimator, which exploits the sinusoidal variations at the motor terminal voltages to calculate the rotor position angle. This system is firstly designated by the aid of mathematical modelling and then simulated by the “MATLAB/Simulink” environment. Accordingly, a practical representation is verified to obtain a real time low-speed implementation.
Advanced control algorithms were employed to meet the high implementation requirements of such systems Therefore, two high specifications microcontrollers are exploited to effectively manage the controlling process and to achieve data analysis and manipulation. One of the microcontrollers, type “ATMega2560”, controlled the forward
4 path operations, whereas the other, type “ATmega328”, was employed to manage the feedback path operations. Software programming of the microcontrollers is achieved through the C-language codes. These microcontrollers are effectively exploited to generate the required frequencies and to display and monitor the system performance and rotor position estimation progress in conjunction with a host personal computer.