LTC391AE01 HIEE401782R0001 DCS system card of ABB high speed counting module
The magnetic field of HIEE401782R0001 LTC391AE01 synchronous motor adopts DC excitation, and the power factor can lead, lag or unit power factor, and the reactive power can be fed to the power grid during operation to improve the power factor of the power grid, and has the characteristics of good operation stability, speed does not change with the load and high operation efficiency. Therefore, it is widely used in coal mines and other industrial sites. The excitation of synchronous motor plays an important role in the operation of synchronous motor. The traditional excitation system uses thyristor phase-shifting full bridge circuit to realize excitation. The excitation system needs to use synchronous transformer phasing, involves many devices, and the maintenance is complicated, which affects the safe operation of the excitation system. Moreover, the traditional embedded design adopts the single task sequence mechanism in software management, so the stability and real-time performance of the system are poor.
In this paper, the digital signal processor chip TMS320LF2812 of Texas Instruments (TI) is used as the control core, and the real-time operating system DSP+μC/OS-II is applied to the programming of DSP. With ZVZCS DC/DC phase-shift conversion full bridge circuit as the main circuit, DSP+μC/OS-II performs multiple core tasks in parallel to complete the closed-loop control of 3 kinds of excitation currents, which provides an ideal design scheme for the embedded design of synchronous excitation system.
1 Overall Structure
HIEE401782R0001 LTC391AE01 excitation system overall structure block diagram is shown in 1. Including zero voltage zero current switch (ZVZCS)DC/DC phase-shift conversion full bridge circuit, drive circuit, magnetic circuit, excitation voltage, current conditioning circuit, DSP control circuit, keyboard and display circuit, trip protection circuit, etc.
The three-phase AC power supply is added to the three-phase rectifier module through the contactor to become DC. The DC main circuit power supply adds 400 ms soft start to prevent high voltage shock, Ci is the input filter capacitor, and plays a role in improving the power factor. After the main circuit is switched on, the DSP outputs the specified excitation voltage according to an adjustment mode set by the keyboard after receiving the excitation instruction, and realizes the closed-loop control of the excitation current through the measurement of the excitation parameters by DSP. Design input overvoltage protection, undervoltage protection, overcurrent protection and overheating protection in the protection circuit.
2 Working principle of the main circuit
Figure 2 is the main circuit diagram of the ZVZCS converter. The parallel capacitors C1, C2 and the leakage sensing Lk of the transformer together realize the ZVS of the leading arm switching tube VQ1 and VQ2. By controlling the active clamp switch VQC, the ZCS of the lagging arm switch tube VQ3 and VQ4 are realized.
Figure 3 shows the main operating waveform of a switching cycle of the ZVZCS converter. VQ1 and VQ2 achieve ZVS under the action of C1, C2 and Lk. At T1, the primary voltage Vab of the transformer drops to zero. At this time, the VQC is switched on, so that the voltage Vcc on the clamping capacitor is reflected to the primary Lk, which is opposite to the direction of the electromotive force generated by the reduction of current. Therefore, the primary current ILk is rapidly reduced to zero. VD2 makes the transformer do not form a circulation in the opposite direction when the primary current is continued, so that the lagging arm switch tube VQ3 and VQ4 can realize zero current on and off.
3 Drive signal implementation
HIEE401782R0001 LTC391AE01 Driver signal generation can be generated by the DSP’s event management module EVA or EVB. The duty cycle of the four PWM signal drivers is set to 50%. There is a phase difference between the two groups of bridge arms. The phase advance signal is used as the advance bridge arm signal, and the phase lag signal is used as the driving signal of the lagging bridge arm. The duty cycle is adjusted by the phase shift of the leading bridge arm and the lagging bridge arm. Set the timer to the continuous increase and decrease count mode, set the value of the comparison register in the timer underflow interrupt and period interrupt respectively, and ensure that the sum of the parameters set in the same comparison register in the timer underflow interrupt and period interrupt is equal to the value T of the period register, so that the generated PWM pulse can be 50% of the duty cycle. Let the value of the comparison register corresponding to the phase shift Angle adjusted by the system be x(integer), and the value of the period register be T. Set one of the comparison registers to be assigned 0 on underflow interrupts and T on cycle interrupts; Another comparison register is assigned x on underflow interrupts and T-x on cycle interrupts, as shown in Figure 4. It can be seen that the phase of the first register is relatively 180°x/T ahead of the second register. One set of drive signals generates a drive signal when the count register is 0, and the other set of drive signals moves relatively between 0 and T.
LTC391AE01 HIEE401782R0001 DCS system card of ABB high speed counting module
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