Abstract : This paper addresses two types of production sites for electric motors—those requiring short-time stoppage and those requiring instantaneous stoppage. It details two methods for interchangeably using frequency converter control circuits and the Y-Δ start circuit, analyzing their working principles and applicable conditions to achieve both short-time and instantaneous motor stoppage. Keywords : Frequency converter; Control circuit; Y-Δ start circuit; Circuit switching KEY WORDS: converter; control circuit; Y-Δ start circuit; circuit switching The frequency converter industry has developed rapidly, and the industrial scale of frequency converter products is growing. Since the advent of AC frequency converters in the 1960s, they have been widely used in industrialized countries in the 1980s. In the 1990s, with the strengthening of people's awareness of energy conservation and environmental protection, the application of frequency converters has become more and more popular. Since the frequency converter can provide precise speed control and conveniently control the rising, falling and speed change of mechanical transmission, it can be applied in most motor drive applications. Frequency conversion can not only improve the efficiency of the process (speed change does not depend on the mechanical parts), but also save more energy than the original fixed speed motor. The advantages of using frequency conversion speed control are: (1) Controlling the starting current of the motor. When the motor is started directly by the power frequency, it will generate 7-8 times the rated current of the motor. This current value will increase the electrical stress of the motor windings and generate heat, thereby reducing the life of the motor. Variable frequency speed control can start at zero speed and zero voltage. Once the relationship between frequency and voltage is established, the frequency converter can drive the load to work according to v/F or vector control. Using variable frequency speed control can significantly reduce the starting current, improve the winding bearing capacity and the life of the motor. (2) Reduce voltage fluctuations in power lines. When the motor starts at the power frequency, the current increases dramatically and the voltage also fluctuates significantly. The magnitude of the voltage drop will depend on the power of the starting motor and the capacity of the power distribution network. The voltage drop will cause voltage-sensitive equipment in the same power supply network to trip or malfunction, such as PCs, sensors, proximity switches and contactors, which will all malfunction. However, after using variable frequency speed control, since it can start gradually at zero frequency and zero voltage, the voltage drop can be eliminated to the greatest extent. (3) Lower power required for starting. The power of the motor is proportional to the product of the current and voltage. Therefore, the power consumed by the motor starting directly at the power frequency will be much higher than the power required for variable frequency starting. In some operating conditions, the power distribution system has reached its maximum limit. The current generated by directly starting the motor at the power frequency will seriously affect other users on the same network, and will be subject to warnings from the power grid operator. Even fines. If a frequency converter is used for motor start-stop, such problems will not occur. (4) Controllable acceleration function. Variable frequency speed regulation can start at zero speed and accelerate smoothly according to the user's needs, and its acceleration curve can also be selected. When starting at the power frequency, the motor or the shaft or gears of the connected mechanical parts will be subjected to severe vibration. This vibration will aggravate mechanical wear and loss and reduce the life of mechanical parts and motors. In addition, variable frequency start can also be applied to the filling production line to prevent bottles from tipping over or being damaged. (5) Adjustable running speed. Variable frequency speed regulation can optimize the process and can be changed quickly according to the process. Speed ​​changes can also be achieved through remote control PLC or other controllers. (6) Adjustable torque limit. After variable frequency speed regulation, the corresponding torque limit can be set to protect the machinery from damage. This ensures the continuity of the process and the reliability of the product. Current frequency conversion technology not only has adjustable torque limits, but also torque control accuracy can reach about 3%-5%. Under power frequency conditions, the motor can only be controlled by detecting the current value or thermal protection, and cannot be operated by setting a precise torque value as in frequency conversion control. (7) Stopping mode can be controlled. Just like controllable acceleration, in frequency conversion speed regulation, the stopping mode can be controlled, and there are different stopping modes to choose from (deceleration stop, free stop, deceleration stop + DC braking). Similarly, it can reduce the impact on mechanical parts and motors, thereby making the whole system more reliable and increasing its lifespan accordingly. (8) Energy saving. Centrifugal fans or water pumps can significantly reduce energy consumption after using frequency converters, which has been demonstrated in more than ten years of engineering experience. (9) Reversible operation control. In frequency converter control, reversible operation control can be achieved without additional devices, only by changing the phase sequence of the output voltage, which can reduce maintenance costs and save installation space. (10) Reduce mechanical transmission parts. Currently, vector control frequency converters combined with synchronous motors can achieve efficient torque output, thus saving mechanical transmission components such as gearboxes, reducing costs and space, and improving stability. Frequency converters, with their high output torque, soft start, and automatic energy-saving operation, are widely used in three-phase motor speed regulation and control; the control circuit is shown in Figure 1. Traditional motor starting circuits are divided into two types: direct starting and reduced-voltage starting. The former involves the interchangeability of direct starting and the frequency converter control circuit, making the switching between power frequency and frequency conversion relatively easy. However, the interchangeability of the "Y-Δ" reduced-voltage starting circuit used when the motor is under no-load or light-load conditions with the frequency converter control circuit requires further discussion on how to achieve optimal balance. Frequency converters may malfunction during operation due to external factors (such as overvoltage or undervoltage) and internal factors (such as component damage). If these malfunctions cannot be repaired in time, the motor cannot operate. Only "Y-Δ" starting can ensure normal starting and continuous operation of the motor. After the frequency converter is repaired, the circuit is switched back. This necessitates solving the problem of interchangeability between the frequency converter control circuit and the "Y-Δ" starting circuit. The following describes two interchangeable circuits between the "Y-Δ" starting circuit and the inverter circuit. A typical "Y-Δ" starting circuit is shown in Figure 2. To minimize circuit modifications, an inverter is added without adding contactors to save power. The control circuit in Figure 2 is maintained, only the main circuit wiring is adjusted; the modified circuit is shown in Figure 3. The working principle of Figures 2 and 3 is as follows: When the power switch Qs is closed and the start button sB is pressed, the contactors KM1 and KM2, and the time relay KT coil are energized. The main contacts and self-locking contacts of KM1 close, and the main contacts of KM2 close and the interlocking contacts open. That is, the inverter is powered by KM1 and KM2. Since the KM...Y' connection point has been removed in Figure 3, the inverter is temporarily powered by KM1. To reduce KM1...Y' ... For independent power supply, the delay time of the KT coil can be adjusted to zero before closing Qs (when using the circuit in Figure 2, the delay time of the KT coil needs to be adjusted to the required delay value), or the delay setting value of the KT coil can be kept unchanged (because the original setting time of the KT coil is relatively short). After the time relay delay, the normally open contact of KT closes and the normally closed contact opens, de-energizing the KM coil and opening the main contacts, temporarily maintaining power supply to the inverter via KM. Simultaneously, the interlock contact of KM closes, energizing the KM coil and closing the main contacts and self-locking point, allowing the inverter to be powered by both KM. and KM. At this time, the interlock contact of KM opens, de-energizing the KT coil. Therefore, the power supply requirements of the inverter are met, enabling the inverter to control the motor. The motor is now reconnected as shown in the "△" connection in Figure 3, satisfying the safe current-carrying factor of the contactor and wires, resulting in good reliability and safety. Its advantage is that when the inverter malfunctions and cannot operate, only KM needs to be adjusted. The wiring method for the KM main contacts involves adding a "Y" connection point to the KM main contacts to form the reduced-voltage starting circuit in Figure 2, ensuring normal motor operation. After the inverter is repaired, the control circuit in Figure 2 and the circuit in Figure 3 can be used to control the motor operation. This method can only be used in production sites where the motor can be stopped briefly. [align=center] [/align] For production sites where continuous operation is only allowed to stop momentarily, the switching method in Figure 4 should be adopted. The working principle of the inverter control circuit and the "Y-△" starting circuit interchange in Figure 4 is as follows: When Qs is closed and the start button SB is pressed, the K ground coil is energized and the main contacts close to form the inverter power supply; at the same time, the K battery self-locking contact and auxiliary contact close, energizing the KM coil and closing the main contacts to supply power to the motor. In this way, part of the inverter output directly supplies the three taps of the motor, and the other part supplies the KM contacts to control the other three taps of the motor, realizing the inverter control of the motor operation. When using the "Y-△" reduced-voltage starting circuit, simply press the stop button SB, then immediately press SB:. At this time, the KM1, KM2, and KT coils are energized, and the main contacts and self-locking contacts of KM1 close; the main contacts of KM2 close, and the interlocking contacts open, starting the motor in a "Y" connection. After the set delay time, the normally open contact of KT closes, and the normally closed contact opens, de-energizing the KM2 coil and opening its main contacts, temporarily de-energizing the motor. Simultaneously, the interlocking contacts of KM2 close, energizing the KM1 coil, and its main contacts and self-locking contacts close, changing the motor to a "△" connection and allowing it to enter stable operation. At the same time, the interlocking contact of KM2 opens, de-energizing the KT coil, thus achieving reduced-voltage starting control of the motor. The reverse is also true. The characteristic of this control circuit is that the interchangeability can be achieved simply by pressing the stop and start buttons, ensuring continuous production without requiring a short-term motor stop. [b][align=center]For details, please click: A Brief Discussion on the Application of Frequency Converters[/align][/b]