A frequency converter circuit consists of several major components, including a control section, a rectification section, an inverter section, and an intermediate DC link section. It is a power control device that integrates microelectronics and frequency conversion technologies. Frequency converters have protection functions, capable of detecting overload, overvoltage, and overcurrent in equipment and taking protective measures to prevent hardware damage. In addition, frequency converters also have energy-saving functions, adjusting motor power according to actual usage requirements to avoid unnecessary energy consumption and save energy. However, not all fields are suitable for using frequency converters for energy saving. For some equipment, using frequency converters not only fails to achieve energy savings but may also consume significant amounts of energy again; therefore, their use must be rational. On the other hand, frequency converters can provide power factor compensation for energy saving, comprehensively improving the stability and reliability of power grid operation. Frequency converters are a new type of power technology that emerged when DC speed control technology could not meet the demands.
Correct usage of frequency converter
1. How to correctly select a frequency converter
When selecting a frequency converter, the appropriate control method should be chosen based on the actual production type, control area, speed accuracy when the converter is static, and torque requirements during startup. A suitable standard code should consider both the converter's applicability and its economic efficiency to ensure the basic indicators and requirements of the process and production are met. When selecting a frequency converter, the number of poles of the controlled motor should not exceed four under normal conditions; otherwise, the converter capacity will need to be increased. Under the same motor power conditions, compared to overload torque control mode, the frequency converter's specifications can be downgraded. To reduce interference from mains power sources , inductors can be added to intermediate circuit sections or the frequency converter input circuit, or isolation transformers can be installed. Generally, if the distance between the motor and the frequency converter exceeds fifty meters, an inductor and a power EMI filter should be connected in series between them; shielded cables can also be used.
There are different types of frequency converters. The correct choice of frequency converter must be made based on its rated power, rated current, rated voltage, overload capacity, and other required parameters. Generally, the basic functions of ordinary frequency converters can meet routine usage requirements, but it depends on the specific situation. For example, the maximum operating power of the frequency converter may need to be increased according to the load and operating environment. Furthermore, some specialized industries require more specialized frequency converters.
2. How to correctly install a frequency converter [Frequency Converter Accessories]
Carefully read the instruction manual and follow the wiring instructions. To prevent electric shock caused by leakage inside the inverter, ensure the inverter is stably grounded to avoid leakage caused by radio frequency interference.
3. Correct use during operation
(1) When the motor speed is controlled by the frequency converter, the motor noise and temperature rise are higher than when the power frequency is used. When the motor is running at low speed, the temperature rise of the motor is higher due to the low speed of the motor fan blades. In this case, it is important to reduce the load appropriately and pay attention to ventilation and cooling to prevent the motor temperature rise from exceeding the maximum limit.
(2) The impedance of the power supply line should be appropriately increased. When the frequency converter is connected to the low-voltage power grid, if the frequency converter is very close to the distribution transformer, or if the capacity of the distribution transformer is about 10 times greater than the capacity of the frequency converter, if the circuit impedance is too small, a large inrush current will be generated on the frequency converter at the moment of connection, directly damaging the rectifier components of the frequency converter. Therefore, if the impedance is small, an AC reactor should be installed between the transformer and the frequency converter.
4. Proper maintenance during operation
(1) When using a frequency converter to start and stop to control speed, circuit breakers and contactors cannot be used for direct operation, otherwise the frequency converter will lose control, resulting in serious consequences. Therefore, in this case, circuit breakers and contactors cannot be used; instead, the control terminals of the frequency converter should be used for operation.
(2) When a frequency converter drives a regular motor to operate at constant torque, the time spent running at low speed should be controlled, because prolonged low-speed operation will worsen the motor's heat dissipation and increase its temperature rise. Therefore, a frequency converter motor should be selected for prolonged low-speed constant torque operation.
(3) During routine maintenance, check whether the resistance value of the external braking resistor connected to the frequency converter is greater than the allowable value of the braking resistor connected to the frequency converter. If the terminal that should be connected to the braking resistor is inserted incorrectly, it will cause a short circuit in the switch during braking. Therefore, while meeting the braking requirements, the braking resistor should be appropriately larger.
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