The energy feedback mode enables energy to be fed back to the grid by reversing the renewable electricity generated when the motor is braked into alternating current at the same frequency as the grid, rather than consuming energy through resistors. Its core processes include:
Energy conversion: In the power generation state of the electric motor, the stator winding generates a reverse induction current, which increases the DC bus voltage after rectification by the inverter.
Inverse control: When the motherboard voltage exceeds the threshold (e.g. 1.2 times the effective value of the grid voltage), the controllable transformer (e.g. IGBT) switches to the active inverted state, reversing the DC to the AC to the power grid.
Synchronous adjustment: the control circuit detects the grid voltage, frequency and phase in real time to ensure that the feedback current is synchronized with the grid and to avoid harmonic pollution.
Key Components and Functions
Power Module
It consists of IGBT, which controls the energy flow direction through PWM modulation to achieve rectification and reversal mode switching.
Need to withstand high-voltage shocks, such as power elevator frequency converter using four quadrant modules to support bidirectional energy flow.
Filter Circuit
The high-level harmonic generated by the reversal process is filtered out, usually composed of LC circuits, to ensure that the quality of the feedback meets the grid standards.
Control Circuit
Dynamically adjust the inverter trigger angle to maintain the motherboard voltage stability (such as automatically reducing the feedback power when the grid voltage fluctuates).
Typical Application Scenarios
Lifting equipment: When discharging heavy goods, the motor generates power, and the energy feedback unit can recover more than 80% of renewable energy.
Elevator system: Four-quadrant frequency converters achieve energy savings through feedback braking, such as the modular rectification design of the power lift.
Rail Traffic: High power feedback when train braking, need grid compatibility support.
Comparison of energy consumption braking and feedback braking
Characteristics Energy Consumption Brake Energy Feedback
Energy to Resistor Heat Consumption Feedback to Grid Reuse
Low efficiency (energy waste) High (energy saving rate up to 30%)
Low cost (only braking resistance required) High cost (complex reverse control required)
Applicable power Small and medium power (<100kW) High power (>100kW)
Technical Challenges and Solutions
Grid Compatibility
It is necessary to detect the voltage fluctuation range of the grid (e.g. ± 20%) to avoid feedback current impacting the grid.
Harmonic suppression
Reduce THD (total harmonic distortion) to <5% by using multi-stage filtering (such as LC+ active filtering).
Dynamic Response
The control circuit must complete the mode switch within 10ms to prevent the bus line overvoltage.