Design of permanent magnet brushless motor based on VB 6.0 programming language

1 Basic Principles of Brushless DC Motor

The brushless DC motor system shown in Figure 1 is used to illustrate the basic working principle of the brushless DC motor. The stator winding of the motor is a three-phase star connection. The position sensor is coaxial with the motor rotor. The control circuit generates a drive signal after performing a logical transformation on the position signal. The drive signal is amplified by the drive circuit and controls the power switch tube of the inverter, so that each phase winding of the motor works in a certain order. When the rotor rotates to the position shown in Figure 2 (a), the signal output by the rotor position sensor drives the inverter after the control circuit logic transformation, so that VI1 and VI6 (see Figure 1) are turned on, and the A and B two-phase windings are energized. The current flows out from the positive pole of the power supply, flows into the A phase winding through VI1, and then flows out from the B phase winding and returns to the negative pole of the power supply through VI6.

The magnetomotive force Fa generated by the armature winding in space is shown in Figure 2(a). At this time, the stator and rotor magnetic fields interact with each other, causing the rotor of the motor to rotate clockwise.

When the rotor rotates 60° electrical angle in space and reaches the position shown in Figure 2(b), VI1 and VI2 are turned on, causing the rotor of the motor to continue to rotate clockwise.

Every time the rotor rotates 60° in space, the inverter switch switches once, and the conduction logic of the power switch tube is VI1, VI6→VI1, VI2→VI3, VI2→VI3, VI4→VI5, VI4→VI5, VI6→VI1, VI6. In this cycle, the rotor is always subjected to the clockwise electromagnetic torque and rotates continuously in the clockwise direction.

In the 60° electrical angle range from Figure 2(a) to Figure 2(b), the rotor magnetic field rotates continuously in the clockwise direction, while the stator composite magnetic field does not rotate continuously in space, but is a jumping rotating magnetic field with a step of 60° electrical angle. Every time the rotor rotates 60° electrical angle in space, the stator winding undergoes a commutation, and the state of the stator composite magnetic field changes. It can be seen that the motor has six states, each state has two phases turned on, and the conduction time of each phase winding is the time for the rotor to rotate 120° electrical angle. This working mode is called two-phase conduction star three-phase six-state.

As long as the controllable transistors connected to the output terminals of each phase are turned on and off in an appropriate order according to the different positions of the magnetic poles, and the magnetic motive force generated by the rotor coil is always kept ahead of the magnetic motive force of the magnetic poles by a certain electrical angle, the motor can generate electromagnetic torque in a certain direction and run stably. It can be seen that the forward and reverse rotation of the motor can be achieved by changing the conduction order of the power transistors with the help of logic circuits.

2 Software Design

2.1 Main program flow chart

In the process of motor design, the most important thing is to solve the problem of a large number of curves and charts. This routine uses interpolation and fitting methods to process a large number of formulas and curves. Although it will produce a small error, it is convenient and fast to use and saves time. The main program flow chart is shown in Figure 3.

2.2 Programming Design Interface

The VB 6.0 programming language is used to implement the motor design visualization interface, which can quickly and accurately obtain the required data, save time and improve work efficiency, as shown in Figure 4.

2.3 Programming

In addition to the calculation formula, some charts and curves used in motor design need to be calculated by interpolation method if there is no original formula. In essence, the straight line segment between two points near the interpolation point x is used to replace the curve segment, and the function on the curve corresponding to x is approximately replaced by the corresponding function on this straight line segment. Some program codes are as follows:

3 Experimental Results

This example is a three-phase brushless DC motor with a power of 4 kW, a rated voltage of 208 V, a rated frequency of 26.5 Hz, and a pole pair number of 3. The motor operating characteristics are shown in Table 1 based on the calculation.

4 Conclusion

This paper uses modern motor design methods to design a prototype of a vehicle retarder motor. The performance indicators meet the technical requirements. Through the comparative analysis of experimental data and design results, it is concluded that the feasibility and efficiency of using brushless DC motors on retarders are achieved. The purpose of lightweight and miniaturization of automotive retarders is achieved, which shows that the application of brushless DC motors in automotive retarders is a future development trend.