With the development of power electronics and computer technology, high performance asynchronous motor speed control system has been widely used. The High-Performance AC speed control system is inseparable from the digital signal processor. In the past, the speed of digital signal processing is very fast, but the control function is poor. The new f24x / c24x series DSP is a digital motor speed controller specially developed by TI company for three-phase AC speed regulation. It not only has the rapidity of general DSP, but also has the control function of three-phase AC speed regulation. According to the direct torque control principle of asynchronous motor, a high performance AC speed control system based on TMS320F240 DSP is developed. The experimental results show that the control system based on TMS320F240 DSP has the characteristics of simple hardware circuit and excellent performance.

1 system structure and principle

The principle of direct torque control system uses the space vector analysis method, adopts the stator magnetic field orientation, and transforms the stator current and voltage by 3 / 2, so as to realize the direct torque control in the static state α-β The torque and flux of the AC motor are calculated in the coordinate system, and then compared with the given torque and flux respectively. According to the comparison results, the optimal switch table is found to generate PWM signal, which directly controls the switching state of the inverter. The basic block diagram is shown in Figure 1.

The following space vector expressions of stator voltage and current can be obtained by 3-phase / 2-phase coordinate transformation

According to the U-I model, the stator flux is expressed as follows:

φ s=∫(us-Rsis)dt(3)

The electromagnetic torque equation is as follows:

T=np( φ s α is β-φ s β is α)( 4)

The stator flux and electromagnetic torque are obtained and compared with the given value θ Determine the appropriate switching state, generate PWM inverter signal, control the working state of the main circuit inverter, so as to control the motor torque in real time.

2. Hardware system design

The AC speed control system is based on TMS320F240 DSP, which is composed of rectifier, voltage source main circuit and control circuit. The whole system is modularized by power circuit board, DPS control board, 15V switching power supply, etc.

2.1 power circuit

The power circuit consists of EMS, uncontrollable rectifier module and IGBT inverter module IPM,

At the same time, it has over-current, over-voltage and other protection functions. Through the reactance coil, EMS can eliminate the electromagnetic interference from the power grid and improve the anti-interference ability of the whole system. The intelligent IGBT inverter module IPM (pm10rsh120) of Mitsubishi company is selected as the driving circuit. It not only integrates the power switch device and driving circuit, but also has over-current, over-voltage, under voltage, temperature protection circuit. It can not only protect the IPM module, but also simplify the off chip driving circuit and reduce the failure rate of the system. The fault output signal fo of IPM is connected to the pdpint port of DSP through optocoupler. When IPM fails, DSP can set all output pins of event manager to high resistance state in time to prohibit PWM signal output and protect the system. HP hcpl4504 is selected as the PWM driving circuit in the driving circuit, and isolated to avoid the strong current in series into the DSP control circuit. Figure 2 shows a drive circuit.

The inverter requires that the upper and lower switches of the same bridge arm always have one on and the other off, and must be interlocked. Therefore, the PWM signal must have a certain dead time, otherwise it will cause the upper and lower switches of the same bridge arm to conduct at the same time, resulting in IGBT module burn out. TMS320F240 integrated dead time adjustment circuit, dead time can be 0 ~ 102 μ It can be adjusted within seconds. The dead time of the system is set by software, and the dead time of the system is 4.5 μ s。

Two magnetic balance Hall current sensors are used to detect the two-phase stator current, which are directly installed on the power board. Through the connector, the detected signal is sent to the TMS320F240 control board, and the on-chip ADC is used to obtain the real-time stator current signal.

2.2 DSP control board

DPS control consists of TMS320F240 DSP, JTAG, 128kwords external SRAM, 10m crystal oscillator, hardware reset circuit and so on. Its core is TMS320F240 DSP chip. It is a digital motor speed controller specially developed by TI company for three-phase AC speed regulation. The powerful processing ability of TMS320F240 makes the motor control oriented control algorithms such as vector control and direct torque control can be realized quickly. DSP control board mainly completes algorithm processing, PWM output, a / D conversion, communication with upper computer and display. In order to accomplish the above tasks, the system is expanded on the basis of the minimum system of DSP. The 16 channel 10 bit ADC interface is used to connect the current and other feedback signals; RS232 serial port is used to communicate with upper computer and display data and waveform; 16v8gal is used to combine control signals. In addition, LCD display circuit, keyboard input circuit, three 34 pin peripheral interfaces (connected with power board, sensor, keyboard, etc.) and circuit module are added.

2.3 switching power supply module

IPM has a high requirement for driving power supply. Each IGBT unit of upper bridge arm needs a separate 15 V voltage power supply to enhance anti-interference ability and reduce power noise; All units of the lower bridge arm are powered by a common 15V power supply. Therefore, the power module includes four isolated 15V power supplies to provide energy for the IPM module drive circuit. The core of switching power supply is top227, which integrates all functions of PWM control system into three terminal chip, including PWM, power switching FET, self bias circuit, protection circuit, high voltage starting circuit and loop compensation circuit.

3. System software design

The software of the whole system is written in c2000dps assembly language. TMS320F240 starts ADC through event manager to obtain current and voltage signals to control flux and torque. The whole software includes three parts: initialization, fault diagnosis, gptimer1 interrupt service program. The software module flow chart of the system is shown in Figure 3. Among them, the initialization module mainly completes the setting of motor parameters, variable initial value, timer time and timer service subroutine address. The initialization flow chart is shown in Figure 4.

Interrupt service program is the core of software design, it completes almost all the control algorithms, such as ADC detection, 3 / 2 conversion, calculation of flux and torque, angle θ The process includes the acquisition of voltage vector, the selection of voltage vector, the calculation and setting of action time and dead time, the generation of PWM, etc μ s) It will be finished in two weeks. The flow chart of interrupt service subroutine is shown in Figure 5.

The generation of PWM signal is completed by the time manager through the configuration of special registers

SPLK#2840H,T1CON; up/downcounTIn50nssteps

SPLK#PWM_ PERIOD,T1PR; PWMcarrierfrequency

; fpwm=50ns*2*

PWM_ PERIOD

SPLK#1207H,COMCON; CMPRx,T1PRreloadatTimer1

; ACTRreloadatTimer1=0

; enablePWM1-6outputs

SPLK#0207H,COMCON; SYMMETRICALPWM

SPLK#0666H,ACTR; PWM1,3,5activehigh

; PWM2,4,6activelow

SPLK#32E0H,DBTCON; deadband=2.5 μ s*/

SPLK#8000,COMCON; enablecompareunit*/

4 experimental results

The experiment of direct torque control system adopts 4-pole asynchronous motor: 2.2kW; 380V; 2.5A; 1500r/min。 DC generator is used as the load of asynchronous motor. Figure 6 shows the step response curve of torque and stator flux waveform. The experimental results show that the system has good performance.

The high performance direct torque control system based on TMS320F240 makes full use of TMS320F240’s high-speed computing function and abundant on-chip and off chip resources, which makes the AC speed control system simple in structure and high in reliability. The experimental results show that the proposed system has high control precision, fast dynamic response and is a high performance AC speed control system.

Editor in charge: GT

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