I. Energy Consumption Braking
The energy-saving braking method uses a chopper and a braking resistor, which is set in the DC circuit, to absorb the regenerative electrical energy of the motor and achieve rapid braking of the frequency converter.
Advantages of regenerative braking: simple structure, no pollution to the power grid (compared to regenerative braking), and low cost;
Disadvantages of energy-efficient braking: low operating efficiency, especially during frequent braking, which will consume a lot of energy and increase the capacity of the braking resistor.
II. Regenerative Braking
Regenerative braking employs active inverter technology to convert regenerated electrical energy into alternating current with the same frequency and phase as the power grid, which is then fed back to the grid, thus achieving braking. Achieving energy regenerative braking requires conditions such as voltage synchronization and phase control, and regenerative current control.
Advantages of regenerative braking: It can operate in four quadrants, and the regenerative braking improves the system efficiency;
Disadvantages of regenerative braking: (1) This regenerative braking method can only be used under stable grid voltage conditions where faults are unlikely to occur (grid voltage fluctuations are no more than 15%). Because when generating braking is running, if the grid voltage fault time is greater than 2ms, commutation failure may occur, damaging the device. (2) During regenerative braking, there is harmonic pollution to the grid. (3) Control is complex and the cost is high.
III. DC Braking
DC braking generally refers to the process where, when the frequency converter output frequency is close to zero and the motor speed drops to a certain value, the frequency converter redirects DC current to the stator winding of the asynchronous motor, forming a static magnetic field. At this time, the motor is in a state of energy consumption braking, and the rotating rotor cuts the static magnetic field to generate braking torque, causing the motor to stop quickly.
It can be used in situations requiring precise stopping or when the brake motor rotates irregularly due to external factors before starting.
1. Elements of DC braking
(1) The DC braking voltage value is essentially setting the magnitude of the braking torque. Obviously, the greater the inertia of the drive system, the larger the DC braking voltage value should be. Generally, the rated output voltage of a frequency converter with a DC voltage of about 15-20% is about 60-80V. Some use the percentage value of the braking current.
(2) DC braking time, which is the time for DC current to be applied to the stator winding, should be slightly longer than the actual required stopping time;
(3) DC braking start frequency: At what frequency does the inverter start to switch from regenerative braking to DC braking? This is related to the load's requirements for braking time. If there are no strict requirements, the DC braking start frequency should be set as low as possible.
IV. DC regenerative braking
The principle of the shared DC bus regenerative braking method is as follows: the regenerative energy of motor A is fed back to the common DC bus, and then its regenerative energy is consumed by motor B;
The shared DC bus regenerative braking method can be divided into two types: shared DC equalization bus regenerative braking and shared DC circuit bus regenerative braking.
1. Shared DC Balancing Bus Regenerative Braking: The shared DC balancing bus regenerative braking method utilizes a connection module connected to the DC circuit bus. The connection module includes a reactor, fuse, and contactor, and must be designed individually based on specific requirements. Each inverter has relative independence and can be connected to or disconnected from the DC bus as needed.
2. Shared DC circuit bus regenerative braking: The shared DC circuit bus regenerative braking method connects only the inverter section to a common DC bus.
