Elevator energy-saving feedback device supplier reminds you that elevator frequency converter is a specialized instrument used for elevator control. Elevator specific frequency converter is a high-end product among small and medium power frequency converters, which improves elevator efficiency, runs smoothly, and extends equipment life. Combined with PLC or microcomputer control, it further demonstrates the superiority of contactless control: simplified circuit, flexible control, reliable operation, convenient maintenance and fault monitoring. How to choose the appropriate frequency converter plays an indispensable role in elevators.
1. Power selection
In elevator applications, 7 can be selected based on the power level 616G5 frequency converters of various specifications such as 5kW, 11kW, 15 kW, 18.5kW, 22kW, 30kW, etc., with built-in braking units below 15kW and DC reactors above 18.5kW. Usually, in elevator applications, frequency converters also require the selection of braking units and braking resistors; It is also necessary to configure the PG speed card to obtain the speed feedback signal of the encoder; AC reactors are also required for long-term generator operation and other special locations. The frequency converter is generally selected based on the power amplification level of the motor. In order to achieve the ideal control performance of the frequency converter, the power of the frequency converter should meet the following requirements:
1) The capacity of the frequency converter must be greater than the output required by the load, that is:
2) The capacity of the frequency converter cannot be lower than that of the motor, that is:
3) The current I0 of the frequency converter should be greater than the current of the motor, that is:
4) The capacity of the frequency converter during startup should meet the following formula:
Among them, P0N - rated output power of the frequency converter (kW);
I0N - Rated current of frequency converter (A);
GD ² - Conversion of motor shaft end (N · m ²);
TA - Acceleration time (s); (The above quantities can be determined according to the load requirements);
K-current waveform compensation coefficient (taken as 1.05~1.10 for PWM control mode);
TL load torque (N · m);
η - motor efficiency (usually taken as 0.85);
Cos φ - power factor of the motor (usually taken as 0 75);
The required output power of the motor shaft for PM load (kW);
IM motor rated current (A);
UN - Rated voltage of electric motor (V);
NN - Rated speed of electric motor (r/min).
2. Selection of braking resistor
The selection of braking resistor is very important. If the resistance value of the braking resistor is too large, the braking torque will be insufficient. If the resistance value of the braking resistor is too small, the braking current will be too large and the resistor will heat up, which is difficult to solve. For situations where the lifting height is large and the motor speed is high, the resistance value of the resistor can be appropriately reduced to obtain a higher braking torque (the recommended resistance value is generally selected as 120% of the braking torque), but the resistance value cannot be lower than the minimum value specified by the manufacturer. If the minimum value cannot meet the braking torque, it is necessary to replace the frequency converter with a higher power level.
3. Selection of installing energy-saving feedback devices for elevators
The conventional method for handling this part of electrical energy in a variable frequency elevator is to install a braking unit and a braking resistor at the DC capacitor end. When the voltage across the capacitor reaches a certain value, the braking unit will activate, and the excess electrical energy will be converted into thermal energy through the braking resistor and dissipated into the air. Install an energy-saving feedback device for elevators to replace the braking unit and braking resistor. By automatically detecting the DC bus voltage of the frequency converter, the DC voltage of the DC link of the frequency converter is reversed into an AC voltage with the same frequency and phase as the grid voltage. After multiple noise filtering links, it is connected to the AC grid to achieve the goals of green, environmental protection, and energy conservation.
The energy-saving feedback device for elevators is to invert the electrical energy generated by the traction machine of the elevator under unbalanced load conditions into high-quality AC power of the same frequency and phase as the power grid, which is returned to the local power grid. For use in elevator motherboards, elevator shaft lighting, car lighting, car fans, and nearby areas with loads (or other parallel elevators and ancillary equipment).