The brushless DC motor suddenly reverses when it is rotating forward, burning out the MOS tube relay

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The brushless DC motor suddenly reverses when it is rotating forward, burning out the MOS tube relay [Copy link]

 

I use MOS tube relays to power the brushless DC motor, and add MOS relays to the positive and negative poles of the DC bus. During operation, I found that when the brushless DC motor suddenly reverses from forward rotation, the MOS relay switch of the DC bus will break down, making the DC power supply unable to control the switch, and the DC power supply is always on to power the motor. May I ask the experts, what is the cause of this? After checking the information, some people said that it is because the sudden reversal of forward rotation will increase the voltage of the DC bus, exceeding the withstand voltage of the MOS relay switch, and the MOS tube is broken down. It is also said that it is because the sudden reversal of forward rotation will cause the motor to output a large current, burning the MOS tube relay.

maychang

"Some also say that sudden reversal of forward rotation will cause the motor to output a large current, burning out the MOS tube relay."

This possibility is very high.

To control the forward and reverse rotation of a DC motor, an H-bridge is usually used.

Please post your "MOS tube relay" control motor schematic diagram for us to see.

chunyang

Since the finished MOS relay is used, there should be parameters. When the motor suddenly reverses, the transient current will be very large, easily exceeding the normal operating current by an order of magnitude. Based on the motor parameters and relay parameters, it can be determined whether it is caused by overcurrent. Similarly, there are parameters for withstand voltage, but overcurrent in sudden turn is more of a concern. When the motor power is large and the load is heavy, this type of condition is not allowed to occur.

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maychang posted on 2020-6-11 12:08 "It is also said that the sudden reversal of forward rotation will cause the motor to output a large current and burn the MOS tube relay." This is very likely. ...

The schematic diagram of the MOS switch relay is shown above. It is designed by myself, not a finished product. The MOS tubes are all damaged, and the TVS tube SMAJ58A is also burned. The motor is a 48V@2000W DC motor.

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chunyang posted on 2020-6-11 19:12 Since the finished MOS relay is used, there should be parameters. If the motor suddenly reverses, the transient current will be very large, easily exceeding the normal operating current by an order of magnitude...

How do you generally protect the circuit when designing it? I am not an expert in motors, so I can only analyze it from experience. It should be that after the forward rotation suddenly reverses, the motor instantly releases a large current, which burns out the positive and negative MOS switches of the DC bus. At the same time, the DC bus voltage may also be very high, which also destroys the TVS tube SMAJ58A. Sir, how do you generally suppress it from the circuit hardware? The figure below is the schematic diagram of the MOS relay I made. Through 4 MOS tubes, the DC bus is controlled to supply power to the motor. The motor has a power of 48V@2000W.

maychang

xiaoxi8592 posted on 2020-6-12 14:31 The schematic diagram of the MOS switch relay is shown above. It is designed by myself, not a finished product. The MOS tubes are damaged, and the TVS tube SMAJ58A is also burned. The electric...

Although I don't know the models and functions of U10 and U12, it seems that this circuit cannot control the forward and reverse rotation of the DC motor. To put it simply: the connection method of the four power tubes in the circuit is wrong.

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xiaoxi8592 posted on 2020-6-12 14:31 The schematic diagram of the MOS switch relay is shown above. It is designed by myself, not a finished product. The MOS tubes are damaged, and the TVS tube SMAJ58A is also burned. The electric...

U10 and U12 are a self-made gate drive module. This circuit controls the switch of the motor DC power supply, but does not control the rotation direction of the DC motor. The motor has its own driver. The fault is that the motor suddenly reverses, which will burn the MOS relay and the TVS tube.

maychang

xiaoxi8592 posted on 2020-6-12 14:31 The schematic diagram of the MOS switch relay is shown above. It is designed by myself, not a finished product. The MOS tubes are damaged, and the TVS tube SMAJ58A is also burned. The electric...

In the figure on the 4th floor, the gates of the two power MOS tubes are directly connected together, and the sources are also directly connected together. This connection method is the connection method used by MOS as a switch in an AC circuit. At this time, the drains of the two MOS tubes are the two ends of the switch.

However, the fourth floor diagram is a DC circuit, so there is no need to use this reverse series connection of two MOS tubes. Because the power supply is DC, only one MOS tube bears the DC voltage when it is turned off, and the other one will not bear the reverse voltage due to the parasitic diode inside the tube. Therefore, one of the two MOS tubes in reverse series (the one that does not bear the reverse voltage when turned off) is useless.

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maychang posted on 2020-6-12 15:19 In the picture on the 4th floor, the gates of the two power MOS tubes above are directly connected together, and the sources are also directly connected together. This connection method is used by MOS...

Yes, this is due to the limited circuit size, using this self-made MOS switch, so as you said, only one MOS tube withstands the reverse voltage. But the DC current is also very large, how do you usually deal with it?

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maychang posted on 2020-6-12 15:19 In the picture on the 4th floor, the gates of the two power MOS tubes above are directly connected together, and the sources are also directly connected together. This connection method is used by MOS...

Can connecting a discharge diode in series between the positive pole of the DC bus and the 48V power supply prevent the bus current from being too large and burning the MOS tube?

maychang

xiaoxi8592 posted on 2020-6-12 15:35 Yes, this is due to the limited circuit volume, using this homemade MOS switch, so as you said, only one MOS tube withstands the reverse voltage. ...

“How do you usually deal with it?”

Judging from the title of the post "The brushless DC motor is rotating forward but suddenly reverses, burning out the MOS tube relay", you want to control the DC motor to rotate forward and reverse, and the MOS tube will burn out when it suddenly reverses from forward rotation.

I said on the 6th floor that "this circuit seems to be unable to control the forward and reverse rotation of the DC motor". From the diagram, I can't tell how you operate the DC motor to change from forward rotation to reverse rotation.

Is the high and low levels of the LHPro_PWR signal in the diagram on the 4th floor used to control forward and reverse rotation?

chunyang

After reading the reply from the original poster, I found that your circuit is just a switch, so your circuit design is incredible. If it is just a switch, you should know the common PMOS power switch and NMOS load drive circuit. All you need to do is to increase the current carrying capacity by connecting multiple tubes in parallel on the basis of this type of circuit. In addition, a 2-kilowatt motor is not small, especially when it is loaded with rated load, it already falls into the category of not allowing sudden reversal as mentioned in the previous post.

maychang

xiaoxi8592 posted on 2020-6-12 15:35 Yes, this is due to the limited circuit volume, using this homemade MOS switch, so as you said, only one MOS tube withstands the reverse voltage. ...

The post title says "brushless DC motor", please confirm that this is correct. I suspect this motor is a brushed permanent magnet DC motor.

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maychang posted on 2020-6-12 16:44 The post title says "brushless DC motor", please confirm it. I suspect this motor is a brushless permanent magnet DC motor.

Brushless DC

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chunyang posted on 2020-6-12 16:22 After reading the reply from the original poster, your circuit is just a switch, so your circuit design is incredible. Just as a switch, the common PMOS power switch, NMOS load...

Due to the limited circuit size, high-power PMOS power switches and NMOS load drive circuits cannot be used, so I designed this small power switch myself.

maychang

xiaoxi8592 posted on 2020-6-13 08:29 Brushless DC

Since it is a brushless DC motor, how do you control the motor to rotate forward or reverse?

It is just like what I asked on the 11th floor: "Is the high level and low level of the LHPro_PWR signal in the 4th floor figure used to control the forward and reverse rotation?"

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maychang posted on 2020-6-13 09:33 Since it is a brushless DC motor, how do you control the motor to rotate forward or reverse? It is just like what I asked on the 11th floor, "Use the L in the 4th floor picture ...

The motor has its own controller. I only provide the motor with 48V DC power supply and CAN communication interface, and send speed and steering instructions through CAN. The LHPro_PWR in the figure is a high-level control power supply to power the motor. The motor is powered on and off through 4 MOS tubes.

maychang

xiaoxi8592 posted on 2020-6-13 13:37 The motor has its own controller. I only provide the motor with 48V DC power supply and CAN communication interface, and send speed and steering instructions through CAN. The LHPro_PWR in the picture ...

That's right.

Your motor is not a brushless DC motor, it is a motor connected to a controller. The 4th floor diagram is just using the LHPro_PWR signal to control whether the 48V DC voltage is applied to the motor.

maychang

xiaoxi8592 posted on 2020-6-13 13:37 The motor has its own controller. I only provide the motor with 48V DC power supply and CAN communication interface, and send speed and steering instructions through CAN. The LHPro_PWR in the picture ...

In the fourth floor diagram, the LHPro_PWR signal is based on GND. Therefore, it must be said that using four MOS tubes to form two bidirectional switches and using U10 and U12 may be too wasteful and excessive.

Please post the instructions of your MOS tube SE85210GA and diode SMAJ58A for everyone to see.

There is a diode in the upper right corner of the 4th floor picture, from LHPro+ to the 48V positive terminal. What is that for? What model are you using?

maychang

xiaoxi8592 posted on 2020-6-13 13:37 The motor has its own controller. I only provide the motor with 48V DC power supply and CAN communication interface, and send speed and steering instructions through CAN. The LHPro_PWR in the picture ...

In your circuit, besides 3.3V, 5V and 48V DC power supplies, do you have any other DC power supplies? 5V is a bit too low to drive the MOS tube.