Elevator energy-saving equipment suppliers remind you that with the continuous development of technology, frequency converters have gradually begun to be used in our ordinary lives, such as air conditioning, elevators, and heavy industry. The use of variable frequency technology in air conditioning has become well-known to people, but there is little knowledge about the use of variable frequency technology in elevators.
At present, most elevators use variable frequency speed regulation and variable voltage speed regulation, with frequency converters accounting for almost half of elevators. The most common elevator standard is a logic board+frequency converter. The former is the operator who monitors the feedback of each signal in the elevator, while the latter is entirely composed of motor starting and braking actuators. Let's start with the most intuitive external circuit. Firstly, the frequency converter can achieve stepless speed regulation of the motor by simply connecting the three main wires of the motor: R, S, and t. To gain a deeper understanding of the principle of frequency conversion speed regulation, taking a three-phase asynchronous motor as an example, in the three-phase symmetry of the stator winding of the three-phase asynchronous motor, a rotating magnetic field is generated, which cuts the rotor conductor and induces current in the rotor winding. The current will cause the rotor winding to generate a rotating magnetic field force, thereby driving the rotor to rotate. The output frequency determines the rotational speed of the rotating magnetic field, thereby achieving speed regulation of the rotor. There is a formula for synchronous speed n=60f/p, which is related to this. Of course, this level refers to the number of stator windings. We usually find that the voltage of the inverter in the inverter monitoring menu is proportionally higher or lower, because at the rated operating frequency, if the frequency voltage is lower in certain situations, it will cause strong magnetism and even burn the car. On the other hand, if the flow rate is not enough, it will directly cause the output torque of the electric motor.
The main circuit of a typical frequency converter consists of three parts: a rectifier circuit, an intermediate circuit, and an inverter circuit. The rectifier circuit is relatively simple and directly passes through a three-phase rectifier bridge (power diode uncontrolled rectifier, thyristor controlled uncontrolled rectifier) for direct current, also known as DC bus voltage. When the intermediate circuit between the rectifier circuit and the inverter circuit, including general circuits, filtering circuits, and brake blocks, is used, the inverter can see a large capacitor that serves as a filter regulator. Because the rectifier DC pulsation still needs to be filtered, it can provide a relatively stable DC power supply. The external braking resistor box of the inverter module is also used. In this large capacity, when the host decelerates and brakes, the motor will enter the generator, and the power inverter circuit can store electrical energy in the large capacitor. When forced to move too many power settings, the inverter controls the external braking resistor to consume excess force, thereby avoiding overvoltage converter. Finally, the inverter circuit is the most important and vulnerable part of an inverter. The general frequency modulation control methods are divided into two categories: PAM (Pulse Amplitude Modulation) and PWM (Pulse Width Modulation). However, PAM also needs to be matched with controllable rectifier circuits in some frequency converters, which requires high triggering requirements and has greater defects. PWM control is the most commonly used method. PWM modulation is a switching device based on high-frequency inverter circuits, which controls the output frequency modulation period by changing the voltage pulse width. It is now used in more switching devices such as IGBT, and then affects the motor (inductive load) with high-frequency pulses, helping to generate sine waves and control voltage and frequency, thereby achieving stepless speed regulation.
Elevator frequency converter is not only a specialized instrument for elevator control, but also a high-end product among small and medium power frequency converters. It improves elevator efficiency, runs smoothly, and extends equipment lifespan. Combined with PLC or microcomputer control, it further demonstrates the superiority of contactless control: simplified wiring, flexible control, reliable operation, and convenient maintenance and fault monitoring. Installing an elevator feedback energy-saving device on the elevator frequency converter can effectively convert the regenerated electrical energy stored in the capacitor of the elevator frequency converter into AC electrical energy and send it back to the power grid, turning the elevator into a green "power plant" to supply power to other equipment and saving energy.