Figure 4.20 shows a snap for the oscilloscope screen in the “MATLAB/Simulink” environment. This oscilloscope was used to display the three injected pulses and the motor terminal voltages responses.
Fig. 4. 20, The injected pulses and the corresponding voltage responses in the modelling system
101 Figures 4.21(a) and 4.21(b) illustrate the modelling graphical results, which were obtained through a “MATLAB/Simulink” environment dynamic models, for both types of motors IPMSM and SM-PMSM respectively. The plots give the estimated rotor position against the actual position. The ramp straight lines is for the correct estimations, while the peaks, e1, e2 … etc., are the errors in the estimation process. It is noticeable
that the interior type has five estimating errors, out of 360 total estimations, against 8 for the SM-PMSM. Therefore the IPMSM has a lower rate of error than the surface mounted due to the improvement in the estimator performance under the influence of higher rotor saliency in IPMSM. This higher saliency makes the stator inductances to be more affected by the variation in rotor position. This leads to a higher voltage oscillation at the rotor terminals and a corresponding improvement in the estimating process.
Fig. 4. 21, Results of modelling the ZSRPE for (a) IPMSM (b) SM_PMSM
Figure 4.22 shows an example for rotor position according to the arithmetic model. The figure shows portions of the; theta matrix, current matrix, sector column vector and binary indicator of the current column. The estimation was achieved when the setting rotor position was 25o. The estimator successfully estimated the rotor position at 25o by applying the equation (4.28).
102 Fig. 4. 22, Outputs of the Mathematical model when estimating the rotor position 25o
4.9 Summary
This chapter explores firstly the importance of arithmetic modelling techniques and their impact on optimizing the real world systems. It also presents an arithmetic modelling simulation view to represent the permanent magnet synchronous motor. This modelling scheme comes in the environment of the “MATLAB/Simulink” programming for analysis and simulation the dynamic systems. The major part in this chapter is for modelling the PMSM itself and modelling the estimation process of the RPZSE for PMSM. The proposed simulations are based on detection and tracking the rotor saliency through monitoring its effect on the inductances of the stator windings. This is achieved by measuring the motor terminal voltages, which has been mathematically proved to be a time variant with rotor position. The measured values of the motor terminal voltages are employed to create two dimensions whose values are related to the rotor position of
103 the under test motor. These dimensions are exploited to access a memory structure, or a 2D-lookup table, where the corresponding values of the rotor positions are stored. This chapter also presents a mathematical simulation model for the rotor position estimation. This based on creating row and column vectors related to rotor position. A matrix, which represents the all-possible measured values of the terminal voltages or currents, at different rotor positions, is also created. Then multiplication of the row vector, column vector and the matrix gives the predicted value for the rotor position of permanent magnet synchronous motor.
The proposed “MATLAB” models were applied on two types of the permanent magnet motors, the interior magnet, IPMSM, and the surface mounted, SM-PMSM. Although it was found there is no large difference in the accuracy of the rotor position estimation in both cases, however, the estimation approach for interior motor was more accurate and softer. The reason is attributed to the fact that this type of motor, inherently, has larger amount of saliency, which the models were built according to its value, comparing to the surface mounted type.
104
CHAPTER FIVE
PRACTICAL SET-UP AND VERIFICATION FOR ZERO-
SPEED ROTOR POSITION ESTIMATION
5.1 Introduction
The work, in this chapter, illustrates the details of designing and implementing a platform, which should be employed to achieve the practical estimation for rotor position of a surface mounted permanent magnet synchronous motor, SM-PMSM. The strategy of performing this estimation was built on injection of three high frequency pulses in the stator windings and exploiting the voltage responses at the motor terminals. The setting- up of the platform is based on two main parts. First is a microcontroller type “ATmega328” which is supported by a C language programming software. Second is a three-phase voltage inverter, which has been built in the Cardiff University School of Engineering laboratory. The platform also includes some analogue components, such as operational amplifiers, have been involved to support the operation of the microcontroller and the inverter. In addition, the platform includes a pointer for the indication of standstill rotor position. Two commercial permanent magnet motors, types “M0200-104-4-000” and “ACM2n320-4/2-3”, have been tested, by the designated platform, to estimate their zero speed rotor position.
This chapter is going to be organized into seven main sections. Section 1 presents an introduction to the chapter subject. Section 2 introduces the main in the practical platform and gives a discussion for each of them. Section 3 describes the real world implementations for the modelling of the zero-speed rotor position estimation in addition to the principle of operation. Section 4 highlights the strategy, which was adopted in the work in exciting the motor windings. Section five demonstrates exciting the motor winding by the injected pulses and formation of the voltage responses. Section six presents the obtained results for zero-speed rotor position estimation and gives
105 comparisons with both the modelling results of chapter four and the results, which were obtained by applying different rotor position strategies. Eventually, section seven summarizes the chapter contents