The frequency converter can realize one to two or even one more, but it needs to follow some principles. This paper makes a brief analysis: 1. Equipment selection A. When selecting the inverter, when selecting the type, first consider the operating conditions. Whether one or more motors should start and stop at any time during the running of the inverter.
If the motor does not need to be started at any time during the operation of the inverter, it is not necessary to stop or stop. In the selection of the inverter capacity, only the rated power of the inverter is greater than the total power of all the motors, and then one is amplified. The level selection can be. In this case, when performing electrical design, it is necessary to ensure a principle: the inverter is in a stopped state to switch the contactor, input or the operating state of the variable frequency motor; during the operation of the inverter, it is forbidden to start and stop a certain device separately. Or multiple devices.
If the motor needs to be started and stopped at any time during the operation of the inverter, special attention should be paid to the selection of the inverter capacity! First of all, it is necessary to start and stop the total power of the motor at any time, and then multiply this power by 5~7. (In the running process of the inverter, the motor started at any time is equivalent to direct start, and the motor starting current is almost 5~7 times of the rated current. ), and finally add this result to the total power of the motor that does not need to start and stop at any time, and the sum obtained is the theoretical power of the required inverter. If you need a lot of equipment to start and stop, then this power can be used as the selection power of the inverter, no need to re-amplify one level - because it is often difficult to start multiple motors at the same time. If there are few devices that need to start and stop, then this power needs to be amplified by one more level to be the selected power of the inverter.
B. AC contactor selection For motors that need to be started and stopped at any time, an AC contactor is required. For the selection of AC contactor, follow the general selection principle - the rated current of the motor can be amplified by one level.
C. Selection of thermal relay or motor protector For the case of overloading the inverter, in order to protect the safety of each motor and the equipment of the inverter, in principle, a thermal overload relay or a motor protector must be installed in the main circuit of the motor. For the selection of thermal relays, the general selection principle can be followed - the rated current of the motor is within the range of the thermal relay. 2. Other precautions In the case of one inverter driving N motors, if the line is too long, there may be a large distributed capacitance, resulting in a large high-frequency current, resulting in over-current, leakage current, and current. Display accuracy is low, etc. If the line is too long, an output filter is required. The following is an example of a Fuji inverter.
The motor connection below 3.7kW shall not exceed 50 meters, and the motor connection above 3.7kW shall not exceed 100 meters. When driving multiple motors, calculate the total length of the motor wiring.
When there is a thermal relay between the inverter and the motor, especially in the 400V series, the thermal relay may not operate even if the wiring is less than 50. In this case, use the output filter or reduce the carrier frequency of the inverter.
When driving multiple motors, if the output filter is configured, the total length of the motor connection should not exceed 400 meters. 3. Application examples In practical applications, the frequency converter is often used in applications where the motor power is not large (within 7.5 kW), but there are many motors—such as the variable frequency drive of the production line (in the case of many small power motors), The drive motor of the roller kiln and so on. . . . . .
This has the advantages of cost savings, reduced failure rates, and ease of operation and maintenance.
At the time when I first came to work in 1996, the furnace drive in the factory was like this. There are many such furnaces - one 11KW Fuji inverter with 15 0.55KW cycloidal pin gear motors. Moreover, these motors may start and stop at any time---the motor protection switch is set on the local motor, and the motor can be started and stopped at any time to repair the mechanical transmission such as the chain where the motor is located. The average distance of the motor from the inverter is about 30 meters. The system has been in normal operation for many years and no abnormal conditions have been found.
If this kind of working condition does not use more than one drag, then there are 15 motors in one kiln, and how many inverters in those kiln? Isn't the control room inside the inverter warehouse? cost? Maintenance amount? noise? Temperature rise? . . . . . . 4. Electrical drawings Below are just examples of an electrical schematic. The secondary electrical schematic diagram needs to be designed according to the control requirements, and will not be described here. 
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