What are the four braking methods commonly used in frequency converters?
When the motor is in the working mode of the motor, the electric energy is transferred from the power grid to the motor through the frequency converter, and then converted into mechanical energy to drive the load, so that the load has kinetic energy or potential energy.
When the load releases the energy to change the motion state, the motor is driven by the load and enters the working mode of the generator to convert mechanical energy into electric energy. Feedback to the front level converter.
These feedback energies are called regenerative braking energy, which can be fed back to the power grid through the inverter or consumed in the braking resistance of the inverter DC bus (Energy consumption braking). There are four common braking modes for frequency converters. 1.
Energy consumption braking, energy consumption braking mode absorbs the regenerated electric energy of the motor through chopping wave and braking resistance, and realizes rapid braking of frequency converter by using braking resistance in DC circuit.
Advantages of energy consumption braking: simple structure, no pollution to the power grid (Compared with feedback mechanism)Low cost;
Disadvantages of energy consumption braking: low operating efficiency, especially when braking frequently, it will consume a lot of energy and the capacity of braking resistance will increase. 2. Feedback brake [
Inverter energy feedback device: IPC closing power].
The feedback braking method uses the active inverter technology to convert the regenerated power into AC power returned to the grid at the same frequency as the grid to realize braking.
Special energy feedback braking unit for frequency converter, the realization of energy feedback braking requires voltage phase control, feedback current control, etc. .
Advantages of feedback braking: it can run in four quadrants, and power feedback can improve the efficiency of the system;
Disadvantages of feedback braking: only when the grid voltage is stable and not prone to failure (Grid voltage fluctuation is not more than 10%)Only then can this feedback braking method be adopted.
Due to the power generation braking operation, the power grid voltage failure time is greater than 2 MS, and the phase change fault may occur and the device may be damaged. (2)When feedback, grid harmonic pollution; (3)The control is complex and the cost is high. 3.
DC braking, definition of DC braking: DC braking generally means that when the output frequency of the inverter is close to zero, the motor speed drops to a certain value, and the inverter becomes DC in the stator winding of the asynchronous motor, A static magnetic field is formed.
At this time, the motor is in the state of energy consumption braking, while the rotor cuts off the static magnetic field to generate braking torque when rotating, thus causing the motor to generate braking torque. Stop quickly.
It can be used for irregular rotation caused by accurate stop before starting or external factors of braking motor. .
Elements of DC braking: the value of DC braking voltage is basically the set value of braking torque.
Obviously, the inertia of the towing system is large, and the DC braking voltage value is correspondingly large. Usually, with about 15-
The rated output of the inverter with 20% DC voltage is about 15-20%. The voltage is about 60-80 V, percentage of braking current used;
The DC braking time, that is, the time when the DC current enters the stator winding, should be slightly longer than the actual downtime.
As the frequency of the inverter decreases, the starting frequency of the DC brake begins to change from the energy consumption brake to the DC brake, which is related to the requirement of the load braking time.
If there are no strict requirements, set the starting frequency of DC braking as small as possible. 4.
The principle of the common DC bus feedback brake common DC bus feedback braking mode is to feed back the regeneration energy of motor A to the common DC bus, and then the regeneration energy is consumed by motor B.
The common DC bus feedback braking mode can be divided into two modes: the common DC balanced bus feedback braking mode and the common DC Circuit bus feedback braking mode.