Inverter and simple fault analysis

- Oct 28, 2019-

Below a preliminary understanding of the inverter and simple fault analysis

General inverter is voltage type inverter, using ac-direct-ac working mode, that is, the input is ac power supply, ac voltage three-phase rectifier bridge rectified into dc voltage, and then dc voltage by three-phase bridge inverter circuit transformation into voltage regulation frequency modulation three-phase ac output to the load.When the inverter is powered on, due to the capacity of the flat wave capacitors in dc side is very large, the charging current is very big, often use a starting resistance to limit the charging current, common starting two circuits, inverter power charge, after the completion of control circuit through the relay contact resistance or thyristor will short out, burn out starting circuit fault general performance for the starting resistance, frequency converter fault alarm display for the dc bus voltage, general designer in the design of inverter starting circuit, in order to select the starting resistance, reduce the volume of the inverter are choose smaller, resistance in 10 ~ 50 Ω, power is 10 ~ 50 w.

400 Watt inverter

When the ac input power of the inverter is frequently on, or the contacts of the bypass contactor are not in good contact, and the conduction resistance of the bypass thyristor is increased, the starting resistance will be burnt out.If this is the case, you can buy resistance of the same specification for replacement, and must find out the cause of the lead resistance burned out.If the fault is caused by the switching on and off of the power supply frequency on the input side, this phenomenon must be eliminated before the inverter can be put into use.These devices must be replaced if the fault is caused by bypass relay contacts or bypass thyristors.

A three-phase inverter is normal, for example, but less than speed, through inspection, frequency converter and trouble-free, parameters set up correctly, control input signal is normal, electricity runtime test occurs about inverter dc bus voltage is 450 v, normal for 580 ~ 600 v, and test the input side, found that missed a phase, the cause of the problem is one of the input side of a air switch is usually caused by poor contact, why don't the inverter input lacks alarm can still work in low frequency band?In fact, when the inverter lacks a phase input, it can work. The lower limit of bus voltage of most inverter is 400V, that is, when the dc bus voltage drops below 400V, the inverter reports the dc bus low voltage fault.When two-phase input, the dc bus voltage is 380*1.2 = 452V>400V.When the inverter is not running, by to the wave of the capacitance effect, also can achieve normal dc voltage, a new type of frequency converter is adopted PWM control technology, regulating the work of FM in the inverter bridge is completed, so in the low frequency input phase can still work, but because of low low input voltage and output voltage, lead to the low induction motor torque, frequency couldn't get on.

When such fault display occurs, first check whether acceleration time parameters are too short, torque lifting parameters are too large, and then check whether the load is too heavy.If no these phenomenon, can disconnect the output side of current transformer and dc side of the hall current testing point, reset after the operation, look to whether flow occurred, if appear, is likely to be 1 PM module failure, because 1 PM module contains over-voltage and over current, under voltage, overload, overheating, lack of phase, short circuit protection function, and the fault signal is the output of the module control pin Fn pin sent to the micro control unit, micro control unit receives the fault information, on the one hand, the blockade pulse output, on the other hand, fault information displayed in the panel, usually replace 1 PM module.

Inverter overvoltage fault, generally is a thunderstorm weather, because the lightning series into the inverter power supply, the inverter dc side of the voltage detector action trip, in this case, usually only need to disconnect the inverter power for about 1min, and then close the power, can be reset;Another case is inverter drive big inertia load, overpressure phenomenon occurs, because in this case, the reduction of frequency converter to stop belongs to the regenerative braking, in the process of stop, output frequency of frequency converter according to the linear decline, the frequency of the motor and load is higher than the output frequency of frequency converter, motor load in power state, the mechanical energy into electrical energy, and is absorbed by the flat wave inverter dc side capacitor, when this energy is enough big, can produce the so-called "pump up phenomenon", inverter dc side voltage will be more than dc bus voltage of the biggest and tripping, for this kind of failure,One is to set the deceleration time parameter longer or increase the brake resistance or increase the brake unit;The second is to set the stop mode of the frequency converter as free stop.

Motor heating, inverter overload displayFor the inverter has been put into operation if there is such a failure, we must check the load condition;For newly installed inverter if appear this kind of failure, is likely to be V/F curve parameter Settings or motor has a problem, a new frequency converter, for example, its is a frequency conversion motor drive, motor rated parameters of 220 V / 50 hz, and the inverter factory set to 380 V / 50 hz, because do not have the right to set the inverter installation personnel V/F parameter, lead to motor running for a period of time after the rotor magnetic saturation, the motor speed is reduced, fever and overload.Therefore, this parameter must be set before the new inverter is used. In addition, the load cannot be set correctly when using the speed sensorless vector control mode of the inverter.

Single Phase VFD

Parameters such as voltage, current, capacity rating of the motor, can also lead to the motor thermal overload, there is a situation is to set the inverter carrier rate is too high, heating can also lead to motor overload, and finally a case is inverter electrical designers design often work in low frequency band, without considering the work in the low frequency motor cooling variation problem, hot work after a period of time the motor overload, for this, must be equipped with cooling device.