This paper introduces the design and implementation method of all-digital single-phase inverter based on DSP chip TMS320LF2407A and using SPWM control technology. Finally, the experimental waveform is given.
1 Introduction to TMS320LF2407A chip
The TMS320LF2407A is a monolithic DSP controller designed by TI for motor control. It has a high-performance C2XLP core, improved Harvard architecture, and four-stage pipeline operation. It not only has powerful high-speed computing power, but also integrates a wealth of motor control peripheral components, such as event manager EVA and EVB. Independent bidirectional timer; supports programmable dead-time control PWM output; 2 of the 4 capture ports can directly connect quadrature-encoded pulses from the opto-electronic encoder; 2 independent 10-bit 8-channel A/D converters The conversion of two analog inputs can be completed in parallel at the same time; the on-chip serial communication interface can be used to communicate with the host computer; the on-chip serial peripheral port is used for communication with the peripheral; 40 independently programmable multiplexing I The /O port can be selected as an input/output port for keyboard input and oscilloscope display. These provide great convenience for realizing variable frequency speed control of AC motors.
2 system overall scheme and hardware circuit
Figure 1 shows the hardware block diagram of the system. In this system, TMS320LF2407A is the main control chip, and the inverter adopts SPWM modulation control method to realize the frequency conversion control algorithm. The system hardware consists of main circuit, display circuit, keyboard input circuit and detection and protection circuit. The DSP first collects the required frequency signal from the keyboard, and then generates a corresponding SPWM signal through the operation, transmits the optical tube to the driving circuit through the optical coupling, and then controls the power tube in the inverter bridge to be turned on and off, and simultaneously acquires relevant signals in the main circuit. Determine if there is a fault output. If there is a fault, turn off the SPWM output of the DSP, thus turning off the main circuit.
2.1 main circuit composition
Figure 2 shows the main circuit of the system, which consists of a rectifier circuit, a filter circuit and an inverter circuit. The rectifier circuit is a three-phase uncontrolled rectifier bridge, which converts 380 V, 50 Hz AC power into pulsating DC power. Filtering capacitors are used in the circuit to filter out the voltage ripple, and the filter capacitor is also decoupled between the rectifier circuit and the inverter to eliminate mutual interference. The average value of the rectified DC voltage is UO=1.35U2≈1.4U2=540 V. U2 is the rms voltage of the AC side. Considering that the input three-phase power has a 10% fluctuation, UO = 500 ~ 560 V. The power devices G1, G2, G3, and G4 in the main circuit diagram indicate IGBT devices, the model number is MG50Q2YS40, the withstand voltage is 1 200 V, the control voltage is 20 V for earth, and the current is 50 A. R1 is a current limiting resistor to prevent damage to the IGBT caused by the inrush current. L1 and L3 are common mode filters, and HL1 and HL2 are current Hall elements, which function to detect the current value of the main circuit as an input signal of the protection circuit. In addition, a voltage Hall element is used to detect the voltage value as a protection. The input signal of the circuit and the voltage feedback signal form a voltage negative feedback. Four IGBTs controlled by SPWM technology are used for inverter, and the output AC power is transformed by a transformer, and then filtered by an LC filter to output an AC power having a variable frequency of 220 V.
2.2 drive and protection circuit
Figure 3 shows the principle of the drive circuit. The power device of the inverter circuit of this system adopts IGBT chip, so the drive circuit selects four drive modules M57962L produced by Mitsubishi. The driver module is a hybrid integrated circuit that integrates the driving and overcurrent protection of the IGBT. In Figure 3, the 13th pin of M57962L is connected to the PWM1 of DSP (the other three M57962L are connected to PWM2, PWM3, PWM4 respectively), 14 feet are grounded, and the 1st and 6th pins are respectively connected to the power supply. In addition, the M57962L uses a low-voltage drive, which means that the M57962L can be driven only when the 13-pin input is negative. The advantage of this is to prevent interference. When an interference waveform occurs, the M57962L with low-level drive cannot be driven. In addition, during the turn-off process, if the voltage changes too much, the holding phenomenon will occur, and the IGBT will be out of control, causing the upper and lower arms to pass through. Therefore, the RC snubber circuit is used to suppress the overvoltage and voltage change rate du/dt.
　　
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