Application of commutation controller based on AT89C51 in periodic commutation power supply

O Introduction
In many actual production processes, control components with automatic reversing functions are often used. For example, the reciprocating operation (displacement) in mechanical processing, the forward and reverse output of the DC power supply, the forward and reverse operation of the motor, etc., are all repetitive processes in which the forward (or reverse) operation automatically switches to the reverse (or forward) operation when the forward (or reverse) operation reaches a certain time or a certain position. To realize the automation of this process, a set of control circuits must be designed, and then equipped with a displacement sensor or a time relay. Although the existing time relays on the market can be used in multiple combinations to meet the requirements of some use occasions, there are still shortcomings such as large repeated timing errors, low stable and reliable operation, and inconvenient and flexible use. For this reason, we have developed a time/displacement reversing controller SWHX-1 with a single-chip microcomputer as the core component, which has the advantages of low cost, high precision, stable and reliable operation, etc.

1 Circuit composition and working principle
The internal circuit of SWHX-1 is shown in Figure 1, which is divided into three parts: input and output electrical signal conversion, CPU software programming control and timing delay setting. There are 14 lead wires in total, of which pins 2, 3, and 4 are the common terminal VGND of the DC ground wire. The device can work in both AC and DC power supply modes. When powered by AC, 12V AC is input through pins 13 and 14, and after bridge rectification and voltage stabilization, it is supplied to the internal circuit constant voltage reference power supply, and the rectified DC 12V is sent out through pin 1 and VGND for other external circuits; when powered by DC, pins 1 and 2, 3, and 4 are input terminals, and the input 12V DC is supplied to the internal circuit after voltage stabilization. This method can save the AC power supply, but it should be noted that pins 14 and 13 should be placed in a suspended state.

The internal circuit design of SWHX-1 has 1-way commutation delay and 2-way timing output function. The commutation delay time refers to the time after the forward (or reverse) output group is turned off and then the reverse (or forward) group is turned on after a delay of a period of time. The user can set it arbitrarily between 0.5 and 2 seconds. The 2-way timing time refers to the working time of the forward and reverse group outputs, respectively. The user can set it arbitrarily between 60 seconds and 7 hours and 31 minutes. If the timing time of 60 seconds to 7 hours and 31 minutes cannot meet the use requirements, there are 4 ports P1 to P4, which can be connected to 4 time relays or 4 travel switches to compensate. P1 and P3 are the forward group, and P2 and P4 are the reverse group. 1.1 Delay and timing time setting (1) Delay time setting method In Figure 1, t0~t4 are short-circuit switches for setting the commutation delay time. t0 is the common terminal to the ground. t1~t4 correspond to 0.5s, 1s, 1.5s, and 2s respectively. When the two are short-circuited, the corresponding commutation delay is realized through CPU software programming. For example, when t0 and t1 are short-circuited, the delay is 0.5s, and when t0 and t3 are short-circuited, the delay is 1.5s. (2) Timing time setting method In Figure 1, S1 and S2 are two 8-bit timing time setting dial switches. The first three digits of each switch are the hour digits, and the last 5 digits are the minute digits. Binary coding is used. When the 8-bit dial code is selected, it is sent through the P1 and P2 ports of the CPU and controlled by software programming to realize the corresponding timing function. Therefore, the timing time of each channel can be set arbitrarily between 60s and 7h31min.

1.2 Working principle of timing commutator
When SWHX-1 is used as timing commutation control, the CPU first reads the timing setting value of the dial switch S, which is recognized by software programming and implemented through the CPU internal timer and software delay. When the timing time is up, a timing pulse is sent through the P0 port via pin 12 and pin 11. When pin 12 and pin 11 are short-circuited with pin 5 and pin 7 respectively, the timing pulse generates an interrupt request signal to the CPU. When the CPU receives this interrupt request, it outputs a blocking potential signal through the pin VS1 port to stop the current working group. After a delay of 0.5 to 2s, a start signal is output through the pin VS2 port to start the other group to start working, completing a commutation work cycle. Vice versa, repeating over and over again. 1.3 Working principle of displacement commutator When SWHX-1 is used for displacement commutation control, the timing function mentioned above does not work. Instead, the "displacement reached" signal sent by the displacement detection sensor (usually a travel switch) sends an interrupt request to the CPU through pins 5 and 7. When the CPU receives the interrupt request signal, the above commutation process is completed. In addition, pins 6 and 8 are used for displacement limitation. Because the displacement is limited in most actual production processes, the signal sent by the limit sensor is sent through ports 6 and 8. After the CPU receives the request signal, it immediately sends a limit blocking signal through pins 9 and 10 to stop the displacement work.

2 Software Design
The software program of SWHX-1 is divided into three parts: initialization, timing identification and delay processing, and interrupt commutation processing. The program flow is shown in Figure 2.

3 Application in periodic commutation power supply
Periodic commutation power supply devices are used in many production processes. Here, only one of the common electroplating power supplies is used as an example to illustrate its use. Figure 3 shows an example of the circuit schematic diagram of a three-phase double reverse star bidirectional 6-pulse periodic commutation power supply. The power supply uses two sets of thyristor controlled rectifier circuits, but under the control of SWHX-1, only one set can work at the same time, and the other set is blocked and cut off. The working time of the two sets of rectifier circuits is set by S1 and S2 in Figure 1 respectively. The CF97088B in Figure 3 is a double reverse star 6-pulse thyristor trigger dedicated device. In addition to generating 6 synchronous trigger pulses, it also has the current and voltage dual PI negative feedback regulation function inside, and can also automatically identify the phase loss, overvoltage protection, overcurrent limitation and other functions in the input three-phase power. When these phenomena occur, the output of the trigger pulse is automatically blocked to achieve the purpose of protection and limitation. W1 and W3 are the forward and reverse output voltage setting value adjustment knobs respectively; W2 and W4 are the forward and reverse output voltage feedback adjustment knobs.

The advantages of this power circuit are simple and clear structure, easy assembly, debugging and on-site maintenance. Since CF97088 and SWHX-1 are fully sealed devices, they are more suitable for electroplating, electrolysis and chemical industries, with anti-corrosion effect.

4 Conclusion
The future development direction is to realize timing control based on single chip microcomputer to replace the current timer and time relay. The SWHX-1 device introduced in this paper is an attempt, and the application results in the periodic commutation power supply show that the timing is accurate, the operation is reliable, and the effect is good.