1. Feedback brake [Inverter energy feedback device: IPC closed and energized].
The feedback braking method uses active frequency converter technology to convert regenerated electrical energy into AC power that returns to the grid at the same frequency as the grid in order to achieve braking.
Dedicated energy feedback braking unit for frequency converters
Energy feedback braking requires voltage in-phase control, feedback current control, etc.
Advantages of regenerative braking:
It can operate in four quadrants, and power feedback can improve system efficiency;
Disadvantages of regenerative braking:
(1) This feedback braking method can only be used when the grid voltage is stable and not prone to failure (grid voltage fluctuation is no more than 10%). Because when the generator braking is running, the grid voltage failure time is greater than 2ms, which may cause commutation failure and damage to the device.
(2) During feedback, there is harmonic pollution in the power grid;
(3) The control is complex and the cost is high.
II. Energy Consumption Braking
The energy-saving braking method absorbs the regenerative electrical energy of the motor through chopping and braking resistors, and uses the braking resistor in the DC circuit to achieve rapid braking of the frequency converter.
Advantages of regenerative braking:
It has a simple structure, causes no pollution to the power grid (compared to feedback mechanisms), and has low cost;
Disadvantages of regenerative braking:
The operating efficiency is low, especially during frequent braking, which consumes a lot of energy and increases the capacity of the braking resistor.
III. Shared DC bus feedback brake
The principle of the common DC bus feedback braking method is to feed the regenerative energy of motor A back to the common DC bus, and then motor B consumes the regenerative energy.
Ordinary DC bus feedback braking methods can be divided into two types: common DC balance bus feedback braking method and ordinary DC loop bus feedback braking method.
IV. DC Braking
Definition of DC braking:
DC braking generally refers to a situation where, when the inverter's output frequency approaches zero, the motor speed drops to a certain value. The inverter then converts the DC current in the stator windings of the asynchronous motor, creating a static magnetic field. At this point, the motor is in a regenerative braking state, while the rotor, during rotation, cuts off the static magnetic field, generating braking torque, thus causing the motor to stop quickly.
It can be used to accurately stop or brake the motor before starting, or to address irregular rotation caused by external factors.
Elements of DC braking:
The value of the DC braking voltage is essentially the set value of the braking torque. Obviously, the inertia of a towing system is relatively large, and the DC braking voltage value is correspondingly larger. Typically, a frequency converter with a rated output of approximately 15-20% DC voltage has a voltage of approximately 60-80V, which is a percentage of the braking current used.
The DC braking time, which is the time it takes for the DC current to enter the stator winding, should be slightly longer than the actual shutdown time.
As the inverter's operating frequency decreases, the starting frequency of DC braking begins to shift from regenerative braking to DC braking, which is related to the load braking time requirements. If there are no strict requirements, the starting frequency of DC braking should be set as low as possible.
