★ Electromechanical Control Technology Application of Switched Reluctance Motor Control System in Electric Vehicles Yang Yuefeng, Sun Jiming, and Zhang Haohuang (College of Electrical Engineering, Beijing Jiaotong University, Beijing 100044) Comparison and focus on the discussion! This kind of switch reluctance motor control system is suitable for traction and adopts a new generation of DSP products of TMS320LF2407 on the basis of single-chip microcomputer AT89C51, making the controller more reliable and faster. ) is a battery-powered car, with a significant difference from the fuel car. Electric vehicles are high-tech products that involve various disciplines such as machinery, electric power, electronics, and computer control. Electric vehicles will certainly become the main means of transportation to replace fuel vehicles in the 21st century.
1 A new type of drive device in which the characteristics of a switched reluctance motor has gradually developed. It can realize high-precision, fast response, high efficiency, and high output performance. The research and development of SRM has attracted extensive attention from the international electrician community.
The typical SRM principle, as shown, is a 12/8 pole three-phase switched reluctance motor. S1 and S2 are electronic switches, D1 and D2 are diodes, and E is a DC power supply. The reluctance of the motor changes with the centerlines of the rotor poles and the stator poles being aligned or staggered, because the inductance is inversely proportional to the magnetoresistance. When the rotor poles are in the centerline position of the stator poles, the phase windings have the largest inductance, when the centerline between the rotor poles When aligning the center line of the stator pole, the phase winding has the smallest inductance.
When stator A-phase magnetic pole axis OA does not coincide with rotor magnetic pole axis Oa, switches S1 and S2 close, and A-phase winding energizes, the radial magnetic field with OA axis is established in the motor, and the magnetic flux passes through the stator y, stator pole, Air gap, rotor pole, rotor pole, etc. are closed. When the magnetic flux through the air gap is curved, the magnetic path of the magnetic circuit is smaller than the magnetic flux at the time when the magnetic axes of the stator and the rotor coincide. Therefore, the rotor will be subjected to the torque generated by the tangential magnetic tension of the bending magnetic lines in the air gap. By rotating the rotor in the counterclockwise direction, the axis Oa of the rotor pole approaches the magnetic pole axis OA of the stator A phase. When the Oa and OA axes coincide, the rotor has reached an equilibrium position. At this time, the A-phase switches S1 and S2 are turned on, and the B-phase switch is closed, that is, the B-phase is energized while the A-phase is de-energized, a magnetic field is established with the stator poles of the B-phase as the axis, the magnetic field in the motor rotates clockwise, and the rotor is The magnetic field continues to rotate in a counterclockwise direction due to the magnetic force. It can be seen that continuously pressing the A line moves in the direction of A-B-C-A, and the rotor rotates counterclockwise in the direction of A-C-B-A. If A-C-B-A is used to give power to stator windings of each phase, the magnetic field rotates in the direction of A-C-B-A, and the rotor follows the opposite A-B-C-A direction. clockwise rotation. Based on the above analysis, the system uses a switched reluctance motor control system.
2 Electric vehicle motors and controllers Switched reluctance motor speed control system 2.1 Switched reluctance motor (SRM) SRM is a component of the SRD in the realization of the mechanical and electrical energy conversion, is a double salient pole variable reluctance motor, its stator, rotor salient pole All are made of ordinary silicon steel laminated. The rotor has no windings or permanent magnets. There are concentrated windings on the stator poles. Two diametrically opposed windings can be connected in series to form a two-pole magnetic pole, called "one phase". SRM can be designed into a variety of different phase number structures, and there are many different combinations of stator and rotor pole numbers.
For a driving situation with self-starting, four-quadrant operation requirements, the stator and rotor poles should have a reasonable combination of options. The SRM structure is as shown in the figure.
2.2 The power converter The function of the power converter is to provide the energy supplied by the power supply to the SRM after appropriate conversion, and the DC power obtained by the battery or the rectified AC power supply. Because the SRM winding current is unidirectional, the main circuit of the power converter is not only simpler in structure, but also the phase winding and the main switching device are in series, so short-circuit faults can be prevented.
2.3 Controller uses TMS320LF2407 from Texas Instruments (TI), which combines real-time signal processing and controller peripheral functions into one device and has the following features.
Based on high-performance static CMOS technology, the power supply voltage is reduced to 3.3V, reducing the controller's power consumption; 0MIPS execution speed makes the instruction cycle shortened to 33ns (frequency 30MHz), which improves the controller's real-time control capability.
The TMS320LF240X series DSP code is compatible with the TMS320 series DSP code.
Two event manager modules, EVA and EVB, each include: two 16-bit general-purpose timers; 16-bit pulse width modulation (PWM) channels. They can implement: three-phase inverter control; PWM symmetrical and asymmetrical waveforms; when the external pin PDPINTX appears low level, the PWM channel can be quickly turned off; programmable PWM dead-band control can prevent the upper and lower arms from simultaneously outputting the trigger pulse; 3 capture units.
The structure of the SRM power converter main circuit, as shown in the blish converter event management module, is suitable for an AC induction motor without an on-chip photoelectric encoder interface circuit; a notable feature of the 16-channel A/D electric vehicle It is the regular advancement, braking and reversing. Therefore, the electric motor drive motor needs to be constantly switched between electric and braking states. This requires the electric vehicle to drive 2) brushless DC motors, switched reluctance motors, stepper motors, multi-stage motors and inverters during freewheeling.
The scalable external memory (LF2407) has a total of 64 KB of subroutine memory; 64 KB of data memory; 64 KB of data memory; and 4 KBI/O address space.
Phase-locked loop based clock generator.
(13) Up to 40 general-purpose input/output pins (GPIOs) that can be individually programmed or multiplexed.
Five external interrupts (motor drive protection, reset, and two maskable interrupts).
Power management includes 3 low-power modes and can independently transfer peripheral devices to low-power modes.
These features make the TMSLF2407 DSP particularly suitable for controlling SRM motors and facilitates communication with other controllers.
3 control system design Switched reluctance motor as an electric vehicle drive motor, its control system compared with the general speed control system is much more complex. System hardware block diagram, as shown.
The controller design of a switched reluctance speed-regulating motor is quite different from a general-purpose speed-regulating system. Usually it drives the motor vehicle forward, when it needs to decelerate or brake, from the electric state to the braking state, while returning part of the energy back to the battery. For example, when a vehicle is going downhill, it is best to use its potential energy to feed back the battery through braking. This regenerative power generation performance is of great significance to improving the range of electric vehicles. If it can not achieve renewable power generation, the performance of electric vehicles is not perfect. The switched reluctance speed-regulating motor can easily realize braking power generation and has a good braking effect. Three-phase 12/8-phase SR motors only need to change the conduction angle of each phase to achieve braking.
Three pulse signals with mechanical angles of 15° are used in the system to feed back the position signal. The real-time detection of the three-way pulse signal by the capture unit (CAP1~3) of the F2407 realizes detection of the rotor position signal. The CAP unit not only detects changes in the signal, but also records the time interval between two signal changes. This determines the position of the motor rotor, calculates the actual operating speed of the motor, and precisely controls the on and off of each phase. In order to achieve the level of matching and improve the system's anti-jamming performance, the coded pulse signal is shaped through optocoupler isolation input.
3.2 PWM speed control strategy Using PWM control technology, the DC voltage source Us is implemented by chopping, and adjusting the power supply voltage U can realize the voltage regulation and speed control of the SRD system. Among the numerous speed regulation schemes of SR motor, the PWM voltage regulation speed regulation has the advantages of being simple and easy to realize, and at the same time, the speed regulation performance is better. The motor adopts a three-phase 6 control converter main circuit and is suitable for PWM control. We introduce the PWM signal in the phase winding conducting area. After the PWM signal and the phase conduction signal pass through an AND gate, a PWM-controlled composite conduction signal is formed, where ft is the opening angle and 02 is the turn-off angle. There are two kinds of current chopping modes of PWM complex modulation: æ–© single-tube mode and æ–© double-tube mode. In the case of a single turn, the composite turn-on signal is only introduced into the control terminal of the main switch of each phase (eg, V1) and the down tube (eg, V2) directly introduces the turn-on signal. The upper tube acts as a current chopping action, and the winding current only flows through the diode freewheeling during chopping.
3.2.1 Characteristics of single-tube mode (1) During free-wheeling, the voltage across the winding is approximately 0 and thus the current ripple is small, and the vibration noise and efficiency are satisfactory. In the single-loop PWM regulator, the average voltage applied to the main circuit: Therefore, the duty cycle can be controlled to control the average voltage on the main circuit, in order to achieve the purpose of voltage regulation and speed regulation.
Clear energy feedback power supply 3.2.2 æ–© double-pipe mode features æ–© double-pipe, composite conduction signal at the same time into the upper and lower two tubes (such as V1, V2) control terminal. When the wave is chopped, the winding current continues to flow through the power supply. The characteristic of this chopping mode is that during freewheeling, the voltage across the winding is approximately Us, so the current ripple is large, and the vibration noise and efficiency are both poor.
There is energy feedback power during freewheeling.
The use of single-channel PWM voltage regulation and speed control technology is simple and clear in theory, and it is also very convenient to implement. This has certain advantages over traditional angle control schemes and is easy to implement with simple hardware circuits. This control system uses this method.
After repeated debugging, the PID regulator used in this prototype selects suitable parameters to obtain good dynamic and static performance. PWM control strategy is generally used in the electric state. In the braking state of the switched reluctance motor, we also use PWM technology to control the braking current and braking torque. Brake current feedback combined with the PI regulator and the PWM loop form a current loop that controls the motor to brake with a constant braking current.
4 test results (1) voltage waveform, as shown. It can be known from the waveform diagram that the length of the conduction interval and the interruption interval of the motor winding decreases with the increase of the rotation speed. When the switch is on, the output voltage of the rectifier bridge is positively applied to the two ends of the motor winding; during the freewheeling of the voltage after switching off, two switches connected to the motor winding are only turned off, and the winding is freewheeling when the voltage is zero. When the two switches connected to the winding are turned off, the power supply voltage acts in opposite directions on both ends of the motor winding.
5 Conclusion In the electric car, the drive system design is very flexible. In addition to the different motor and control technologies that can be selected for this discussion, single-motor or multi-motor systems can be selected, with or without a reducer, a transmission or without a transmission, an ordinary motor, or an electric wheel. With the deepening of research and the adoption of new technologies, new materials, and new technologies, the performance of electric vehicles will be further improved, and it may become the ideal means of transportation in the next century.
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