Wiring and implementation methods of various speed regulation methods of frequency converter

The problem of frequency converter speed regulation generally includes stepped speed regulation and stepless speed regulation.

Stepped speed regulation means that the frequency of the inverter cannot be changed continuously, and you can only use a switch to select a pre-set frequency. Common ones include multi-speed settings and simple PLC program settings.

Stepless speed regulation can achieve continuous or arbitrary frequency operation of the inverter and is also a commonly used frequency conversion method, which is mainly achieved by analog and communication control methods.

Let's take INVT's inverter as an example:

The above picture is the front view of the inverter. Local speed regulation can be achieved by adding and subtracting the keyboard numbers and setting the frequency with the potentiometer on the keyboard. Other methods can be achieved through the terminals below.

Among them, AI2, AI3, and 10V are used for analog input, and AO1 and AO2 are analog output terminals. According to its user manual, AI2 is a voltage (0~10v) or (0~20ma) signal control, and AI3 is a -10v~+10v signal control. The green frame represents the multi-speed terminal, and the blue 485 communication interface can use the MODBUS protocol for communication (half-duplex).

The above are the wiring and implementation methods of various speed control methods. Below we briefly explain the settings of various methods:

1. Speed ​​regulation of this machine

The local speed regulation can be realized through the keyboard numbers and the local potentiometer. The keyboard numbers are used to modify the parameters of P00.10. The frequency command needs to be selected as 0 (keyboard digital setting). The local potentiometer is an analog speed regulation method. The analog potentiometer setting on the rotary keyboard needs to be selected as 1 (analog AI1).

2. Multi-speed speed regulation

This is the simplest frequency setting method, which belongs to step-by-step speed regulation. Set the frequency value according to work needs and set the multi-function terminal S to the corresponding frequency. We only need to complete it by connecting the terminals. For example, set S3 to 30Hz, S4 to 35Hz, and S5 to 40Hz. If the S3 terminal is connected, the inverter will run at a frequency of 30Hz, and if the S5 terminal is connected, it will run at 40Hz.

3. Analog control

This is a commonly used inverter control method, which controls the inverter through analog signals. Generally, the control signal and the inverter output frequency are in a proportional relationship. We set the maximum value of the inverter to 50.00Hz, and 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 to 6v if we want to output 30.

So what produces this analog quantity? Generally, there are external potentiometers (same principle as local potentiometers) and some DA digital-to-analog devices (PLC connection). External potentiometers generally have three terminal interfaces. The two terminals are connected to the 10v and GND of the inverter or an external 10V DC power supply. The middle one is the output voltage signal connected to the AI2 terminal (note that the same source is required). The DA module is generally connected to the PLC and controlled digitally, that is, a 30.00Hz signal is directly given to the PLC, which is converted into analog control through the DA module.

4. Communication control

The wiring of communication control is very simple, especially when multiple frequency converters are used for speed regulation. MODBUS protocol or CAN bus is often used for communication (communication supported by the frequency converter). Now most frequency converters support MODBUS communication. Just connect the RS485 interfaces together. However, programming in PLC may be more troublesome. MODBUS communication data formats include ASCII code and RTU mode. Different frequency converters may support different modes.

As for the frequency of the inverter controlled by the human-machine PLC in the question, multi-speed, analog, and communication are all possible. The analog requires a DA expansion module, and the communication requires a communication module (if it is not equipped). The human-machine interface (touch screen) can actually directly control the inverter (supported by the com port), and it also uses the MODBUS protocol.