Ask for advice from the experts! Design of soft start circuit based on single chip microcomputer

电工新手求指导

Ask for advice from the experts! Design of soft start circuit based on single chip microcomputer [Copy link]

 

Recently, I want to design a three-phase soft start circuit based on a single-chip microcomputer. The basic components required are:

1.IGBT tube

2. Single chip microcomputer

3. Relay

4. Motor

5. LCD display

6. Other auxiliary components

The basic structure of the circuit is:

1. Zero-crossing detection circuit

2. Phase loss detection circuit

3. Main control circuit

4. Protection circuit

5. Display circuit

The following are the basic functional requirements :

When the microcontroller receives the switch switching signal, when the voltage passes through zero, a pulse is sent out to trigger the IGBT tube to turn on, making the motor run. After a delay, the relay connected in parallel with the IGBT tube is triggered to turn on, and then the IGBT tube is turned off, allowing the relay to maintain the motor running. When it needs to be shut down, the IGBT tube is turned on first, then the relay is turned off, and then the IBGT tube is turned off. In addition, the circuit also has the function of detecting and displaying phase loss.

The above are the basic design requirements. Has any expert made a similar circuit, or has any guidance or suggestions? I hope the experts can give them to me so that I can learn and make progress together. I also hope the experts passing by can give me some advice. I will be very grateful!

maychang

"When the microcontroller receives the switch switching signal, when the voltage passes through zero..."

Your requirement is not to soft start the motor, but to use IGBT first when starting the motor, and then use relay contacts to replace IGBT. When shutting down the motor, first turn on the IGBT, then turn off the relay, and finally turn off the IGBT. The purpose of doing this is to prevent the relay contacts from generating sparks or arcs, but there is no voltage drop loss of the IGBT when the motor continues to run.

The relay used here can be a relay whose contacts can pass enough current but cannot withstand "on" and "off", and the IGBT does not need a large heat sink.

As for the phase loss detection and display function, that is another issue, but it can be completed with the same microcontroller.

maychang

You didn't say whether the motor is a DC motor, an AC single-phase motor, or something else. Judging from the use of IGBTs, it is most likely a DC motor.

电工新手求指导

maychang posted on 2020-4-2 12:49 "When the microcontroller receives the switch switching signal, when the voltage passes through zero..." Your requirement is not electric...

Awesome! You are worthy of being a master. This is the same project as another problem you guided me before. It is indeed not a soft start circuit, but it is similar. It is also similar to a composite switch in reactive power compensation, but now it is used for motor starting. The motor I want to use is the kind of motor that is directly connected to three-phase electricity, so I need to use 3 IGBTs and 3 relays.

maychang

New Electrician Seeking Guidance Posted on 2020-4-2 13:01 Awesome! You are worthy of being a master. This is the same project as the other problem you guided me to before. It is indeed not a soft start circuit, but just similar. It...

"The motor I want to use is the kind that is directly connected to three-phase electricity"

That is a three-phase AC motor, most likely an induction motor.

This may not be suitable for IGBTs. If you use IGBTs, you need six. And many IGBTs do not have diodes inside. If there are no diodes inside the IGBT, then you need six diodes.

You can consider using three bidirectional thyristors. The bidirectional thyristor has a larger current capacity than IGBT and is easier to trigger.

电工新手求指导

maychang posted on 2020-4-2 15:01 "The motor I want to use is the kind that is directly connected to three-phase electricity." That is a three-phase AC motor, most of which is an induction motor. This...

Has Chang made a similar circuit? Or is there a schematic diagram?

电工新手求指导

New electrician seeking guidance Posted on 2020-4-3 09:38 Has Brother Chang made a similar circuit? Or is there a similar schematic diagram?

I feel like drawing a schematic is also a headache.

maychang

New electrician seeking guidance Posted on 2020-4-3 09:38 Has Brother Chang made a similar circuit? Or is there a similar schematic diagram?

If we talk about the schematic diagram, it is very simple, that is, three bidirectional thyristors and relay contacts are connected in parallel and in series on the three phase lines.

But it is too early to say "similar circuits". At least you need to know the model and power of the three-phase AC motor (so you know the rated current and starting current) before you can choose what type of bidirectional thyristor to use. After selecting the bidirectional thyristor, you can consider how to trigger the three thyristors. In your first post, you said that the AC voltage should be triggered by zero crossing. Major semiconductor companies have zero-triggered optocouplers, such as MOC3061, etc. However, whether such a zero-triggered optocoupler can output enough trigger current to trigger the bidirectional thyristor you selected still needs to be verified by referring to the manual. Whether the selected zero-triggered optocoupler can withstand the voltage level you use also needs to be considered. After these two are selected, you need to consider how your microcontroller controls the optocoupler. The output current of the general microcontroller I/O port is not enough to control the optocoupler.

maychang

New electrician seeking guidance Posted on 2020-4-3 09:38 Has Brother Chang made a similar circuit? Or is there a similar schematic diagram?

These three bidirectional thyristors have no common terminal, so they must be triggered by optocoupler isolation. If the optocoupler is not enough to trigger the bidirectional thyristor, you should also consider whether there are other ways to trigger the bidirectional thyristor.

maychang

A novice electrician is looking for guidance. Posted on 2020-4-3 09:39 I feel that drawing schematics is also a headache

Drawing a schematic is easy, but designing a circuit according to the requirements is a headache. Just like a single-chip microcomputer, writing a program is easy, but constructing a program framework (process) is a headache.

电工新手求指导

maychang posted on 2020-4-3 11:26 If we talk about the schematic diagram, it is very simple, that is, three bidirectional thyristors and relay contacts are connected in parallel and in series with three phase lines. But to say "similar circuit...

I'll ask Brother Chang again after I further clarify these points.

电工新手求指导

maychang posted on 2020-4-3 11:32 Drawing a schematic is very simple, but designing a circuit according to the requirements is a headache. Just like a single-chip microcomputer, writing a program is a simple matter, constructing a program framework (process) ...

Brother Chang, do you have a component library for three-phase motors? I searched in the Proteus library and didn't find this component.

maychang

A novice electrician is looking for guidance. Posted on 2020-4-3 14:18 Brother Chang, do you have a component library for three-phase motors? I searched in the proteus library and there is no such component.

Proteus may not be able to simulate three-phase motors, and other electronic simulation software has never heard of simulating three-phase AC motors.