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Three-phase balance and two brakes of the inverter

Dec 28, 2020

Three-phase balance and two brakes of the inverter

Three-phase balance of the inverter

In actual maintenance, the inverter u, v, w three-phase output imbalance can be divided into three situations:   

(1) The inverter display shows: (missmg moto phase) output phase loss. If the detection circuit is faulty, by directly checking the igbt module and drive circuit, the conclusion is that the igbt module is damaged and the drive circuit is also defective. The problem can basically be solved by replacing the igbt module and the components on the drive circuit such as optocoupler, pnp, npn pair of drive transistors, electrolytic capacitors, and voltage regulator tubes.  

(2) The difference between the inverter output u, v, w is about 100v, (output 380v as an example) there is no drive voltage and drive signal waveform in the drive circuit between s1 and s6, by measuring the output terminals u, v , Between w-p.  

(3) DC voltage between u, v, w-n, it can be found that the driving voltage of this road is abnormal or there is no driving signal waveform, which causes a phase difference caused by a phase of u, v, w not working normally. The solution is to check whether the drive circuit voltage is normal, whether the optocoupler is broken, whether the electrolytic capacitor is leaking, etc. The 6-channel waveform measured by the oscilloscope meets the technical requirements, and the problem can be solved. 

There is another phenomenon that the difference between the three-phase output AC voltage of the inverter u, v, and w is greater than 3%. Although it can be used, it cannot be used for a long time and with a large load. This is mainly caused by the asymmetry of the main components of the driving circuit s1~s6, such as the technical parameters of the transistor, the parameters of the voltage regulator, the liquid dryness of the capacitor, the leakage and the leakage, etc., the loss of the components on the 6-way driving circuit makes it There are certain differences in the parameters, resulting in a slight potential difference between the inverter output u, v, w. Although the above situation can be used, it is not technically acceptable. Our company is pursuing excellence and screening and aging of various devices, such as transistor technical parameters and zener tube technical parameters consistent, matching, etc., to ensure that the drive signal in the drive circuit meets the technical requirements, to ensure that the igbt module is saturated and the conduction time is consistent by the device The above quality assurance, when the repaired frequency converter is doing the load test, the motor sound is light when the motor is running, and the motor with the same power and the same power load before and after the repair, the three-phase current of the motor is relatively small .

There are two types of inverter parking.

One form is called "brake parking". Then this "brake to stop", there are more ways. For example, OFF1 parking means stopping by braking at a certain slope deceleration, or OFF3 "emergency braking" parking (stopping according to the motor's limit braking capacity).

Braking and parking methods include: DC braking (that is, a certain amount of DC power is supplied to the electricity); dynamic braking (energy consumption by resistance); hybrid braking (DC braking + dynamic braking); Inject into the grid); mechanical brake with brake.

Braking also includes mechanical braking (such as holding brake), dynamic braking (brake resistance, reverse braking, DC braking, etc.), feedback braking, etc. Whether or not braking is required is related to the running state of the motor. When the required parking time is less than the free stop time during ramp parking, the brake needs to be used; sometimes the motor needs to be braked during normal operation, such as when the hook is lowered.

One form is called "free parking". As the name implies, it is to quickly "power off" the motor, and let the motor coast to stop by its own inertial force (OFF2 stop);

Parking is divided into ramp parking and free parking (fast parking is also ramp parking, but the ramp is steeper).

In the drive system composed of power grid-frequency converter-motor-load, energy can be transferred in both directions. When the motor is in the motor working mode, the electrical energy is transferred from the power grid to the motor via the frequency converter and converted into mechanical energy to drive the load. Therefore, the load has kinetic energy or potential energy; when the load releases this energy to change the motion state, the motor is driven by the load and enters The generator working mode converts mechanical energy into electrical energy and feeds it back to the previous inverter. This feedback energy is called regenerative braking energy, which can be fed back to the grid through the inverter, or consumed in the braking resistor on the inverter's DC bus (energy consumption braking).

Where braking energy is generated

1. The lowering process of the donkey head of the beam pumping unit

2. Rapid deceleration process of large inertia load

3. Decentralization process of lifting equipment