The harm of 2.1 overvoltage
The overvoltage of the inverter mainly refers to the overvoltage of the DC circuit of the base, and the primary harm of the overvoltage of the base DC circuit is that:
(1) the magnetic circuit of the motor is saturated. For the motor, the main voltage is too high, which will increase the flux of the core of the motor, which may cause the magnetic circuit to be saturated, and the exciter current is too large, resulting in the excessive temperature rise of the motor.
(2) harm the insulation of the motor. Base of DC voltage pulse amplitude increases, the inverter output voltage is too large, has a great influence on the motor insulation life;
(3) have a direct impact on the base of DC loop filter capacitor life, which will cause the capacitor burst. Therefore, the converter manufacturers usually restrain the DC overvoltage value of the base in the DC800V control. Once the voltage exceeds the fetter value, the inverter will maintain the trip according to the constraint request.
2.2 overvoltage factors
In general, the factors that can lead to the overvoltage of the DC circuit are the following two aspects:
(1) overvoltage from the input side of the power supply
Under normal conditions, the power supply voltage is 380V, allowing the fault to be -5% ~ +10%. After three phase bridge full wave rectification, the peak value of base DC is 591V, and the general supply voltage does not cause the inverter to trip due to over voltage. The Overvoltage on the input side of the power supply mainly refers to the impact Overvoltage on the power side, such as the overvoltage caused by lightning and the overvoltage formed by the compensation capacitor when closing or disconnecting. The primary characteristic is that the voltage change rate is dv/dt and the amplitude is very large.
Countermeasures for 2.3 overvoltage
(1) increasing the absorption equipment on the power input side to reduce the overvoltage factor
For the Overvoltage on the input side of the power supply side, the overvoltage caused by lightning and the overvoltage formed during the closing or breaking of the compensation capacitor may occur, it is possible to solve the problem of parallel surge absorption device or series reactor in the input side. To this point, the equipment in our factory is designed to take into account the input line reactor in the input side, and enhance the ability of the inverter to resist voltage changes.
(2) the method of increasing the inverter circuit on the input side
The best way to deal with the power of DC circuit in the inverter base is to add the inverter circuit on the input side, which can feed the excess energy back to the power grid. To this point, we consider the equipment with feedback when the equipment is selected.
(3) finding solutions from the parameters that the frequency converter has set
When the control requirements are met, the braking time or deceleration time is properly added or extended (especially for the shutdown of the large inertia load).
In the process of skills if not bound load deceleration time is too short, don't set the inverter deceleration time parameters, and the kinetic energy release load too fast, this parameter is set to the base circuit voltage is limited, especially should pay attention to the large load setting parameters of inertia. It is assumed that the process of technology is limited to the time of load deceleration. In the limited time, the overvoltage tripping phenomenon occurs in frequency converter, so we must set the function of inverter's self stalling.