1. Variable Frequency Drive
In the past, variable frequency drives (VFDs) were generally included in electrical equipment such as electric generators and rotary converters. With the advent of semiconductor electronic devices, it has become possible to produce completely independent VFDs.
For frequency converters that require a large amount of computation, such as vector control frequency converters, a CPU for torque calculation and some corresponding circuits are sometimes needed. Variable frequency speed control achieves speed regulation by changing the frequency of the power supply to the motor stator windings.
According to the main circuit operating mode, frequency converters can be classified into voltage-source frequency converters and current-source frequency converters; according to the switching method, they can be classified into PAM control frequency converters, PWM control frequency converters, and high-carrier-frequency PWM control frequency converters; according to the working principle, they can be classified into V/f control frequency converters, slip frequency control frequency converters, and vector control frequency converters; according to the application, they can be classified into general-purpose frequency converters, high-performance special-purpose frequency converters, high-frequency frequency converters, single-phase frequency converters, and three-phase frequency converters.
II. Wiring Method for Variable Frequency Drive
The wiring method for variable frequency drives varies depending on the manufacturer and model, but generally includes the following steps:
1. Disconnect the power supply to ensure safety.
2. Connect the power cord. Connect the power cord to the input terminal block of the frequency converter. Generally, there are L1, L2, L3 and ground wires.
3. Connect the motor wires. Connect the motor wires to the output terminal block of the frequency converter. There are usually U, V, W and ground wires.
4. Connect the control cables as needed.
5. Connect other signal lines, such as temperature sensors, protectors, etc.
6. Install the housing, place the frequency converter in the housing, and then install the housing.
It is important to carefully read the inverter's operating manual and installation instructions before wiring, ensuring compliance with relevant safety regulations and standards. Furthermore, inverter wiring should be performed by qualified technicians to ensure safety and reliability.
Wiring and implementation methods for various speed control methods:
1. Speed adjustment of this machine
Speed adjustment can be achieved via keyboard numeric keypad and local potentiometer. Keyboard numeric keypad adjustment involves modifying the parameter P00.10, requiring the frequency command to be set to 0 (keyboard numeric setting). Local potentiometer is an analog speed adjustment method, set by rotating the analog potentiometer on the keyboard, requiring the frequency command to be set to 1 (analog AI1).
2. Multi-speed adjustment
This is the simplest frequency setting method, which belongs to stepped speed regulation. Set the frequency value according to the work requirements, and set the multi-function terminal S to the corresponding frequency. We only need to connect the terminal to complete the process. For example, set S3 to 30Hz, S4 to 35Hz, and S5 to 40Hz. When terminal S3 is connected, the inverter will run at a frequency of 30Hz, and when terminal S5 is connected, it will run at 40Hz.
3. Analog control
This is a common inverter control method, which uses analog signals to control the inverter. Generally, the control signal and the inverter output frequency are proportional. If we set the inverter's maximum value to 50.00Hz, the frequency corresponding to the control signal 0~10V is 0~50.00Hz. If we want to output 20.00Hz, we should adjust the analog signal to 4V, and if we want to output 30, we should adjust it to 6V.
So what generates this analog signal? Generally, it's generated by an external potentiometer (working on the same principle as the local potentiometer) and a DA (digital-to-analog) converter (connected to the PLC). The external potentiometer typically has three terminals: two end terminals connect to the inverter's 10V and GND, or an external 10V DC power supply; the middle terminal is the output voltage signal, connected to the AI2 terminal (note that they must be from the same source). The DA module is generally connected to the PLC for digital control; that is, a 30.00Hz signal is directly given to the PLC and converted into an analog signal for control.
4. Communication Control
The wiring for communication control is very simple, especially in situations where multiple frequency converters are used for speed control. The MODBUS protocol or CAN bus is often used for communication (communication supported by the frequency converter). Nowadays, most frequency converters support MODBUS communication. You can simply connect the RS485 interfaces together. However, the programming of the PLC may be more complicated. MODBUS communication data format has ASCII code and RTU mode. Different frequency converters may support different modes.
