The essence of energy feedback is active inverter, and the realization method of energy feedback of general inverter is to feed renewable energy to the grid with an anti-parallel three-phase inverter at the uncontrolled rectification of the pre-stage of the general inverter. The main circuit of the energy feedback equipment is mainly composed of an inverter bridge composed of thyristors, IGBT and IPM modules and some peripheral circuits.
The output end of the inverter bridge is connected to the input terminals R, S and T of the inverter through three choke reactors, and the input end is connected to the DC side of the general inverter through the blocking diode to ensure the one-way flow of energy in the direction of "inverter-active inverter bridge-power grid". The function of choke reactors is to balance the differential voltage, current limiting and filtering, and play a key role in the regenerative energy feedback to the grid.
The operation process of the system is as follows: when the motor is running, the active inverter equipment is not operating, and the inverter switch pipe is all closed and is in a shutdown state; When the motor is in the state of regenerative power generation, the energy is fed back to the grid by the motor, and the active inverter equipment needs to be activated.
When the motor is in the state of power generation and braking, the regenerative energy of the AC motor charges the energy storage capacitor in the middle of the inverter, resulting in an increase in the voltage of the DC bus, as long as the size of Ud is detected, the condition of the motor can be judged, so as to control the active inverter equipment and realize energy feedback.
When the DC bus voltage exceeds the peak voltage of the grid line due to the energy being fed back to the DC side by the motor, the rectifier bridge of the general inverter is shut down due to the backpressure; When the DC bus voltage continues to rise and exceeds the active inverter operating voltage, the inverter starts to operate and feeds back the energy from the DC side to the power grid. When the DC bus voltage drops to the operating voltage of the enclosed inverter, the active inverter is enclosed.
After the active inverter mode is selected to feed back the regenerative energy generated by the motor when decelerating and braking to the power grid, the general inverter can overcome the inefficiency caused by the traditional general inverter using the braking resistance mode and the lack of satisfying fast braking and frequent forward/reverse rotation, so that the general inverter can operate in four quadrants.
1) Energy feedback control system
A perfect energy feedback control system should be satisfied with the phase, voltage, current and other three aspects of the control conditions, that is, the feedback process must adhere to the synchronization relationship with the phase of the power grid, as long as the DC bus voltage exceeds a certain value before the active inverter equipment is started; The system should be able to control the size of the feedback current, so as to be able to control the braking torque of the motor and achieve precision braking.
2) Two kinds of general-purpose inverter energy feedback equipment
In recent years, some new energy feedback devices have also used intelligent modules such as IPM to simplify the architecture of energy feedback equipment.
(1) Thyristor energy feedback equipment: The main circuit of energy feedback is composed of thyristor equipment, which is also a relatively early energy feedback equipment, which is not only used in the inverter, but also used in the braking of some DC reversible speed regulation systems.
(1) The forward operation status of the general inverter: when the motor is in the electric state, the rectifier of the inverter is operating, while the thyristor equipment in the energy feedback equipment is not triggered, and is in the cut-off state, and the rectifier is in the forward operation. The controllable inverter part of the inverter is triggered, the uncontrollable reverse rectification part is in the cut-off state, and the inverter is in the forward operation.
(2) Reverse operation of general inverter: when the motor is in the power generation condition, the rectifier of the inverter is in the cut-off state, and the thyristor equipment in the energy feedback equipment is triggered to operate. The controllable inverter part of the inverter is still triggered, the uncontrollable reverse rectification part is in the operating condition, and the inverter is in reverse operation.
(2) IGBT energy feedback equipment: the main circuit of energy feedback is composed of IGBT equipment, which is most used in the general inverter, and the freewheeling diode integrated with IGBT equipment can not be used as rectifier equipment under the restriction of the barrier diode connected to the DC side. Its cost should be higher than that of thyristor energy feedback equipment.
(1) Forward operation of the general inverter: when the motor is in the electric condition, the rectifier of the inverter is operating, while the IGBT equipment in the energy feedback equipment is not triggered, and the rectifier is in the forward operation. The IGBT equipment in the inverter is triggered, the uncontrollable reverse rectification part is in the cut-off state, and the inverter is in the forward operation.
(2) Reverse operation of general inverter: when the motor is in the power generation condition, the rectifier of the inverter is cut off, and the IGBT equipment in the energy feedback equipment is triggered. The IGBT equipment in the inverter is still triggered, the uncontrollable reverse rectification part is in the operating condition, and the inverter is in the reverse operation.
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