Oct 23, 2020
Design of General Inverter Control System
In the past 20 years, with the introduction of new power electronic devices and microprocessors and the development of AC motor control theory, AC frequency conversion technology has made great technological progress. The emergence of variable frequency speed control technology makes AC speed control systems have a tendency to replace DC speed control systems. However, the rapid development of the national economy requires the AC variable frequency speed regulation system to have higher speed regulation accuracy, larger speed regulation range and faster response speed. It is difficult for general general purpose inverters to meet the needs of industrial applications, while AC motors The vector control speed regulation system can well meet this requirement. As a control method of AC asynchronous motors, vector control technology has become the first choice for high-performance variable frequency speed regulation systems. Compared with v/f control technology, vector control technology has the advantages of high control accuracy, excellent low frequency characteristics, and fast torque response. Compared with traditional spwm modulation, svpwm modulation has the advantages of small torque ripple, low noise, and high DC voltage utilization. It has been widely used in inverter products. This system uses TI’s motor control chip tms320lf2407 as the core, and adopts the direct vector control strategy and svpwm control technology with closed loop speed and flux linkage. The whole system has a simple structure and is easy to implement. The simulation results show that the vector control system has excellent control performance and precision.
2 Overview of vector control
If the two-phase dq coordinate system and the rotor flux linkage are rotated synchronously, and the d axis is further taken in the direction of the rotor flux linkage, the rotor flux linkage and torque are independently controlled by the excitation component isd and torque component isq of the stator current. When the amplitude of the rotor flux is kept constant, the system can realize the decoupling control of the torque and the rotor flux. The position angle of the rotor flux linkage used by the vector control system for orientation is estimated by the current speed flux linkage observer model.
3 System hardware design
The general frequency converter studied in this paper adopts AC-DC-AC voltage source main circuit structure, with ti's tms320lf2407 dsp as the control core. The hardware circuit is divided into: main circuit part, control circuit part, detection and protection circuit part.
4 System software design
The software of this system is composed of main program and interrupt service subroutine. The main program mainly completes system initialization, module initialization, and interrupt system settings. Interrupt service subroutine is the core part of the system, including serial interrupt service subroutine, pwm interrupt service subroutine, keyboard display interrupt service subroutine and fault protection interrupt service subroutine. The serial interrupt subroutine is responsible for the reception of motor parameters and the setting of the upper computer speed. The pwm interrupt subroutine is responsible for a/d conversion, speed calculation, coordinate transformation, svpwm waveform generation, etc.
4.1 dsp implementation of svpwm
The tms320lf2407 of ti company is very suitable for generating svpwm. This is because in addition to the common characteristics of fast dsp computing speed, it also has the following characteristics: There are two built-in event management modules (eva and evb), and each module has its own hardware circuit for generating svpwm. Each event management module can generate up to 8 pwm waveforms at the same time. There are 3 independent pairs (6 channels) generated by 3 full comparison units with programmable dead zone control, and 2 independent PWM outputs generated by gp timer comparison.
The generation of pwm is controlled by the registers of the event manager module: actr determines the current main vector, whose value is obtained by checking the conversion mode table according to the position of the output voltage; t1con determines whether the generated pwm wave is a symmetrical or asymmetrical waveform; The dead time is set by dbtcona, the setting range is 0～16us; comcona is the space vector mode selection bit; comcona is the comparison output enable bit, 0 means high impedance state (that is, output disabled), 1 means output enable can. The value of the three comparison registers cmprx (x=1,2,3) is determined by the action time (t1, t2 and t0) of the main, auxiliary and zero vectors. When the count value of the timer is equal to cmprx(x=1,2 ,3) value, it will change the control signal output of the space vector.
5 Experimental simulation
The simulation motor parameters are as follows:
p=3kw, np=2, nn=1420r/min, ten=21.45n·m, r1=1.898ω, r2=1.45ω, l1=196mh, l2=196mh, lm=187mh, j=0.0067kgm2, t2= 135.2ms.
The DC side voltage of the inverter is vdc=540v, the period of the pwm wave is t=0.0001s, and the given value of the rotor flux is 1wb. The ode23t algorithm is used in the simulation, and the simulation time is 1s.
(1) The motor starts without load, the initial speed is set to 1400r/min, and the set speed is reduced to 500r/min at 0.5s
(2) With a given speed of 1400r/min, the motor starts at a standstill with a load of 10n·m, and suddenly increases to the rated load at 0.5s. its
It can be seen from the simulation waveform that the motor speed is stable at about 0.12s, the speed overshoot is less than 8.5%, and there is no static error in the steady state; when the motor is suddenly loaded with load disturbance, the speed can quickly return to the steady state, and the overshoot is small. The torque response is fast.
The vector control system designed in this article makes full use of the dsp's high-speed computing capabilities and abundant on-chip peripheral resources, resulting in fewer peripheral circuits, compact structure and high reliability. The simulation results show that the vector control system has high control accuracy, good real-time performance and fast dynamic response.