Elevator energy feedback device suppliers remind you that the mechanical energy (potential energy, kinetic energy) on the moving load is converted into electrical energy (regenerated electrical energy) through the energy feedback device and sent back to the AC power grid for use by other nearby electrical equipment. This reduces the energy consumption of the power grid by the motor drive system per unit time, thereby achieving the goal of energy conservation. The various hardware components of the energy feedback device form an important foundation for the operation of the energy feedback system.
1. Power inverter circuit
In the power inverter circuit, the direct current stored on the DC bus side of the elevator frequency converter during the operation of the elevator traction machine in the power generation state is converted into alternating current by controlling the on/off of the switch. It is the main circuit of the elevator energy feedback system, which has different structures according to different classifications of inverter circuits. By controlling the on/off of the switch, the DC power stored on the DC bus side of the elevator frequency converter during the operation of the traction machine in the power generation state is converted into AC power. In a circuit, the upper and lower switches on the same bridge arm cannot conduct simultaneously, and the conduction time and duration of each item are controlled according to the inverter control algorithm.
2. Grid synchronization circuit
The phase synchronization control plays a key role in whether the elevator can effectively feedback the energy on the DC bus to the power grid. The grid synchronization circuit adopts grid line voltage synchronization, and in order to avoid dead zone effects during commutation, switches are operated at 120 degrees on the same bridge arm. The logical relationship between the grid synchronization signal and the zero crossing signal of the power grid is obtained through a comparator, and the relationship between the grid synchronization signal of each switching device and the power grid voltage is obtained through Multisim simulation. Each switch has a working angle of 120 degrees and is spaced 60 degrees in sequence. At any time, only two switch tubes in the inverter bridge are conductive, ensuring safe and reliable operation. Additionally, each two switches operate in the highest voltage range of the power grid line, resulting in high inverter efficiency.
3. Voltage detection control circuit
Due to the high voltage on the DC bus side of the elevator frequency converter, it is necessary to first use resistors for voltage division, and then isolate and reduce the bus voltage through Hall voltage sensors, and convert it into a low voltage signal. In the voltage detection control circuit, hysteresis tracking comparison control method is adopted, which adds positive feedback on the basis of the comparator and provides two comparison values for the comparator, namely the upper and lower threshold values. Implemented by hardware circuits, control is both fast and accurate. The voltage detection control circuit can not only avoid the instantaneous superposition of interference signals on the voltage signal, causing the output state of the comparator to shake, but also prevent the energy feedback system from starting and closing too frequently.
4. Current detection control circuit
In the process of energy feedback, the current must meet its power requirements, and the power fed back to the grid must be greater than or equal to the maximum power when the traction machine is in the generating state, otherwise the voltage drop on the DC bus will continue to rise. When the voltage of the power grid is constant, the energy feedback power of the system is determined by the feedback current. In addition, the feedback current must be limited within the rated range of the inverter power switch device. Moreover, the reactance choke between the power grid and the inverter allows large currents to pass through while minimizing the volume of the reactor. Therefore, the inductance of the reactor must be a small value to ensure energy feedback. The speed of current change is very fast. Simultaneously using current hysteresis control can effectively control the feedback current and prevent overcurrent accidents.
5. Main control circuit
The central processing unit of the elevator energy feedback system is the main control circuit, which is used to control the operation of the entire system. The main control circuit consists of a microcontroller and peripheral circuits, which generate high-precision PWM waves based on control algorithms; On the other hand, based on the grid synchronization signal, IPM fault control ensures the safe and effective implementation of the entire energy feedback process.
6. Logic protection control circuit
The synchronization signal for grid connection, control signals for voltage and current, IPM fault signal, and drive signal output from the main control circuit all need to pass through the logic protection control circuit for logical operation, and finally be sent to the power inverter circuit to control the feedback process. In this way, it can ensure that the AC power output from the inverter is synchronized with the grid, and also block the drive signal in case of overcurrent, overvoltage, undervoltage, and IPM faults in the circuit, stopping the energy feedback process.