Detailed explanation of the forward and reverse control principle of the inverter

Many production machines use inverters to control the forward and reverse rotation of the motor. The circuit is shown in Figure 1-1. The inverter is explained using Siemens MM440 as an example. DIN1 is actually the control terminal 5, DIN2 is actually the control terminal 6, and +24V is terminal 9. When DIN1 and +24V are short-circuited, the inverter controls the motor to rotate forward; when DIN2 and +24V are short-circuited, the inverter controls the motor to rotate reversely.

(1) The role of each component in the circuit

① Press the SB1 button to power on the inverter.

② Press the SB2 button to power off the inverter.

③SB3 button controls the forward start of the motor.

④SB4 button, reverse start.

⑤SB5 button, the motor stops.

⑥KA1 relay, forward control.

⑦KA2 relay, reverse control.

(2) Key points of circuit design

① The KM contactor is still only used as the power on and off control of the inverter, not as the operation and stop control of the inverter. Therefore, the power off button SB2 is still blocked by the operation relay KA1 or KA2, so that SB2 does not work during operation. The role of the contactor KM: When the protection function of the inverter is activated, the power supply can be quickly cut off through the contactor; self-locking and interlocking control can be easily realized.

② The control circuit is connected in series with the alarm output contacts 18 and 20. When the inverter fails and alarms, the control circuit is cut off, KM is disconnected and the machine stops.

③The main command button is used to control the inverter's power on and off, and the motor's forward and reverse operation.

④ The forward and reverse relays KA1 and KA2 are interlocked, and the forward and reverse switching cannot be performed directly. The machine must be stopped before changing the direction.

(3) Forward and reverse control of the inverter

① Forward rotation. When SB1 is pressed, the KM coil is energized and attracted, its main contact is connected, and the inverter is powered on and in standby state. At the same time, the auxiliary normally open contact of KM makes the KM coil self-locking. At this time, if SB3 is pressed, the KA1 coil is energized and attracted, and its normally open contact KA1 connects to the DIN1 terminal of the inverter, and the motor rotates forward. At the same time, its other normally open contact closes to make the KA1 coil self-locking, and the normally closed contact is disconnected, so that the KA2 coil cannot be energized.

② Reverse. If you want to reverse the motor, first press SB5 to stop the motor. Then press SB4, the KA2 coil is energized and its normally open contact KA2 is closed, connecting the inverter REV terminal, and the motor reverses. At the same time, its other normally open contact KA2 is closed to make the KA2 coil self-locking, and the normally closed contact KA2 is disconnected, so that the KA1 coil cannot be energized.

③Stop. When power is cut off, SB5 must be pressed first to de-energize the KA1 and KA2 coils, disconnect their normally open contacts (motor decelerates and stops), and release the bypass power supply to SB2. Only then can SB2 be pressed to cut off the power of the inverter. When the inverter fault alarm occurs, the control circuit is cut off and the inverter main circuit is powered off.

④Characteristics of the control circuit.

a. Self-locking keeps the circuit status continuous. KM is self-locking and keeps energized. KA1 is self-locking and keeps forward rotation. KA2 is self-locking and keeps reverse rotation.

b. Interlocking maintains a smooth transition of the inverter state to prevent the inverter from being impacted. KA1 and KA2 are interlocked, and the forward and reverse operation cannot be directly switched; KA1 and KA2 lock SB2 to ensure that the power cannot be directly cut off and stopped during operation.

c. The on and off of the main circuit is controlled by the control circuit, making the operation safer and more reliable.

(4) Parameter setting The parameter setting of the inverter is shown in Table 1-2. The parameters of the motor in all the following tables, such as rated voltage and rated current, should be determined according to the actual situation. Machine state. At the same time, the auxiliary normally open contact of KM makes the KM coil self-locking. At this time, if SB3 is pressed, the KA1 coil is energized and attracted, and its normally open contact KA1 connects to the DIN1 terminal of the inverter, and the motor rotates forward. At the same time, its other normally open contact closes to make the KA1 coil self-locking, and the normally closed contact is disconnected, so that the KA2 coil cannot be energized.

② Reverse. If you want to reverse the motor, first press SB5 to stop the motor. Then press SB4, the KA2 coil is energized and its normally open contact KA2 is closed, connecting the inverter REV terminal, and the motor reverses. At the same time, its other normally open contact KA2 is closed to make the KA2 coil self-locking, and the normally closed contact KA2 is disconnected, so that the KA1 coil cannot be energized.

③Stop. When power is cut off, SB5 must be pressed first to de-energize the KA1 and KA2 coils, disconnect their normally open contacts (motor decelerates and stops), and release the bypass power supply to SB2. Only then can SB2 be pressed to cut off the power of the inverter. When the inverter fault alarm occurs, the control circuit is cut off and the inverter main circuit is powered off.

④Characteristics of the control circuit.

a. Self-locking keeps the circuit status continuous. KM is self-locking and keeps energized. KA1 is self-locking and keeps forward rotation. KA2 is self-locking and keeps reverse rotation.

b. Interlocking maintains a smooth transition of the inverter state to prevent the inverter from being impacted. KA1 and KA2 are interlocked, and the forward and reverse operation cannot be directly switched; KA1 and KA2 lock SB2 to ensure that the power cannot be directly cut off and stopped during operation.

c. The on and off of the main circuit is controlled by the control circuit, making the operation safer and more reliable.

4) Parameter setting The parameter setting of the inverter is shown in the table. The parameters of the motor in all the following tables, such as rated voltage and rated current, should be determined according to the actual situation.

[Example 1-3] The inverter is powered on and off when the output is stopped. Why is it generally not allowed to cut off the power when it is running?

Solution: ① The reason is due to the internal circuit of the inverter. Sudden power failure is not good for the safe operation of the main circuit.

② Load reasons: The power supply suddenly fails, the inverter stops outputting immediately, and the running motor is in a free stop state, which may also have an impact on certain operating occasions.