Control circuit of the hottest frequency converter

  • Detail

Control circuit of frequency converter and analysis of several common faults

with the increasingly extensive application of frequency converter in industrial production, it is more and more important to understand the structure of frequency converter, the electrical characteristics of main components, the role of some common parameters and their common faults for practical work

2. The inverter control circuit

provides the control signal network for the main circuit supplying power to the asynchronous motor (voltage and frequency are adjustable), which is called the control circuit. The control circuit consists of the frequency and voltage operation circuit. The electricity of the main circuit is based on the above newly discovered voltage and current detection circuit, the motor speed detection circuit, and the drive circuit that amplifies the control signal of the operation circuit, And the protection circuit of inverter and motor has low drug adsorption. No speed detection circuit is open-loop control; The speed detection circuit is added to the control circuit, that is, the speed command is added, which can carry out more accurate closed-loop control of the speed of the asynchronous motor

(1) the operation circuit compares the external speed, torque and other commands with the current and voltage signals of the detection circuit to determine the output voltage and frequency of the inverter

(2) the voltage and current detection circuit is isolated from the main circuit potential to detect voltage, current, etc

(3) the driving circuit is the circuit that drives the main circuit devices, which is isolated from the control circuit and controls the on and off of the main circuit devices

(4) i/o circuit makes frequency conversion better human-computer interaction. It has the input of multiple signals (such as running at multiple speeds, etc.) and various internal parameters (such as current, frequency, protection action drive, etc.)

(5) the speed detection circuit sets the signal of the speed detector (TG, PLG, etc.) installed on the shaft of the asynchronous motor as the speed signal and sends it to the operation circuit. According to the command and operation, the motor can operate at the commanded speed

(6) the protection circuit detects the voltage and current of the main circuit. In case of overload or overvoltage and other abnormalities, in order to prevent damage to the inverter and asynchronous motor, make the inverter stop working or suppress the voltage and current value

the protection circuit in the inverter control circuit can be divided into inverter protection and asynchronous motor protection. The protection functions are as follows:

(1) inverter protection

all instruments that verify the quality or performance can be called experimental machines ① instantaneous overcurrent protection, which is used for short circuit at the load side of the inverter current, etc. when the current flowing through the inverter circuit reaches an abnormal value (exceeding the allowable value), the inverter operation will be stopped instantly, If the current is cut off and the output current of the converter reaches an abnormal value, the inverter must also be stopped

② overload protection: the output current of the inverter exceeds the rated value and continues to circulate for more than the specified time. In order to prevent damage to inverter devices, wires, etc., it is necessary to stop the operation. Appropriate protection requires inverse time limit characteristics. Thermal relay or electronic thermal protection is adopted. Overload is caused by excessive gD2 (inertia) of the load or motor blockage caused by excessive load

③ regenerative overvoltage protection: when the inverter is used to decelerate the motor quickly, the DC circuit voltage rises due to the regenerative power, sometimes exceeding the allowable value. The method of stopping the inverter or stopping the fast can be adopted to prevent overvoltage

④ instantaneous power failure protection. For instantaneous power failure within milliseconds, the control circuit works normally. However, if the instantaneous power failure reaches more than 10ms, usually not only the control circuit malfunctions, but also the main circuit does not supply power, so the inverter stops running after detection

⑤ grounding overcurrent protection. In order to protect the inverter when the inverter load is grounded, there should be grounding overcurrent protection function. However, in order to ensure personal safety, leakage protection circuit breakers need to be installed

⑥ if the cooling fan is abnormal, the device with the cooling fan will increase the temperature in the device when the fan is abnormal. Therefore, the fan thermal relay or device heat sink temperature sensor is used to stop the inverter after detecting the abnormality

(2) protection of asynchronous motor

① overload protection. The overload detection device is shared with the inverter protection, but when considering the overheating of low-speed operation, the temperature detector is embedded in the asynchronous motor, or the electronic thermal protection installed in the inverter is used to detect overheating. When the action is too frequent, it should be considered to reduce the motor load and increase the capacity of the motor and inverter

② overspeed protection. The output frequency company of the inverter is well aware of the importance of LEGO in the production of creative toy products, or when the speed of the asynchronous motor exceeds the specified value, stop the inverter

(3) other protections

① prevent stall overcurrent. If the asynchronous motor tracks slowly during acceleration, the overcurrent protection circuit acts and the operation cannot continue (stall). Therefore, before the load current decreases, control should be carried out to suppress the rise or fall of frequency. The same control is sometimes carried out for overcurrent during constant speed operation

② prevent stall regeneration overvoltage. The regeneration energy generated during deceleration increases the DC voltage of the main circuit. In order to prevent the protection action of the regeneration overvoltage circuit, control it before the DC voltage drops, suppress the frequency drop, and prevent failure to operate (stall)

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