A frequency converter (VFD) is a power control device that uses the on-off function of a power semiconductor device to convert a commercial frequency power supply to another frequency. It can realize functions such as soft start of AC asynchronous motor, variable frequency speed regulation, improvement of running accuracy, change of power factor, overcurrent/overvoltage/overload protection, etc. What issues should be paid attention to when using VFD?

Eight issues using vfd

1. Signal lines and control lines should use shielded lines, which is beneficial to prevent interference. When the line is long, for example, when the distance is 100 meters, the cross section of the wire should be increased. Signal lines and control lines should not be placed in the same cable trench or bridge as power lines to avoid mutual interference. It is better to put it in through the pipe, which is more suitable.

2. The transmission signal is mainly based on the current signal, because the current signal is not easy to attenuate and interfere. In fact, the signal output by the sensor is a voltage signal, which can be converted into a current signal by a converter.

3. The VFD closed-loop control is generally positive, that is, the input signal is large and the output is also large (such as when the central air conditioner is working, and the general pressure, flow, and temperature are controlled). But it also has the opposite effect, that is, the input signal is large and the output is small (such as when the central air conditioner is heating or the heating station is heating the hot water pump). The closed-loop control is shown in Figure 1.

4. If the pressure signal can be used for closed-loop control, do not use the flow signal. This is because the pressure signal sensor has the advantages of low price, easy installation, small workload, and convenient debugging. However, if the flow ratio and precision are required in the process, the flow controller must be selected. The appropriate flowmeter (such as electromagnetic, target, vortex, orifice, etc.) should be based on the actual pressure, flow, temperature, medium, speed to choose.

5. VFD has built-in PLC and PID functions, which is suitable for systems with small signal changes and relatively stable performance. However, because the built-in PLC and PID functions only adjust the time constant during work, it is difficult to meet the requirements for too many processes, and debugging takes time.

In addition, this adjustment is not intelligent, so it is not commonly used. Instead, use an external smart PID regulator.

6. Signal converters are often used in VFD peripheral circuits, generally composed of Hall elements and electronic circuits. According to the signal conversion and processing method, it can be divided into voltage-current converter, current-voltage converter, DC-AC converter, AC-DC converter, voltage-frequency converter, current-frequency converter, one-in-one-out converter, multi-input-one Output converters, signal superposition converters and signal splitting converters. For example, Shenzhen’s CE-T series electrical isolation sensor/transmitter is very convenient to use. There are many similar products in China, and users can choose their own applications according to their needs.

7.In the application of VFD, peripheral circuits are often required. The method is often:

(1) A logic function circuit composed of self-made relays and other control components;
(2) Purchase ready-made unit external circuits;
(3) Choose a simple programmable controller.
(4) When using different functions of VFD, you can choose a function card;
(5) Select small and medium-sized programmable controllers.

8.When multiple pumps are connected in parallel for constant pressure water supply, only one sensor is needed for signal series connection, and its advantages are as follows:

(1) Cost saving. Only one set of sensors and PID is required.
(2) Since there is only one control signal, the output frequency is the same, that is, the same frequency, so the pressure is also the same, and there is no turbulence loss.
(3) During constant pressure water supply, when the flow rate changes, the number of pumps to be started will change through PLC control. 1 set at least, 2 sets in moderate amount, 3 sets in large amount. When the VFD stops working, the circuit (current) signal is a channel (signal flows in, no output voltage and frequency).
(4) More advantageously, since the system has only one control signal, even if the inputs of the three pumps are different, but the working frequency is the same (that is, synchronous), and the pressure is the same, so the turbulence loss is zero, that is, the loss is the smallest, and the power saving effect is the best.

A frequency converter (VFD) is a power control device that uses the on-off function of a power semiconductor device to convert a commercial frequency power supply to another frequency. It can realize functions such as soft start of AC asynchronous motor, variable frequency speed regulation, improvement of running accuracy, change of power factor, overcurrent/overvoltage/overload protection, etc. What issues should be paid attention to when using VFD?

Eight issues using vfd

1. Signal lines and control lines should use shielded lines, which is beneficial to prevent interference. When the line is long, for example, when the distance is 100 meters, the cross section of the wire should be increased. Signal lines and control lines should not be placed in the same cable trench or bridge as power lines to avoid mutual interference. It is better to put it in through the pipe, which is more suitable.

2. The transmission signal is mainly based on the current signal, because the current signal is not easy to attenuate and interfere. In fact, the signal output by the sensor is a voltage signal, which can be converted into a current signal by a converter.

3. The VFD closed-loop control is generally positive, that is, the input signal is large and the output is also large (such as when the central air conditioner is working, and the general pressure, flow, and temperature are controlled). But it also has the opposite effect, that is, the input signal is large and the output is small (such as when the central air conditioner is heating or the heating station is heating the hot water pump). The closed-loop control is shown in Figure 1.

4. If the pressure signal can be used for closed-loop control, do not use the flow signal. This is because the pressure signal sensor has the advantages of low price, easy installation, small workload, and convenient debugging. However, if the flow ratio and precision are required in the process, the flow controller must be selected. The appropriate flowmeter (such as electromagnetic, target, vortex, orifice, etc.) should be based on the actual pressure, flow, temperature, medium, speed to choose.

5. VFD has built-in PLC and PID functions, which is suitable for systems with small signal changes and relatively stable performance. However, because the built-in PLC and PID functions only adjust the time constant during work, it is difficult to meet the requirements for too many processes, and debugging takes time.

In addition, this adjustment is not intelligent, so it is not commonly used. Instead, use an external smart PID regulator.

6. Signal converters are often used in VFD peripheral circuits, generally composed of Hall elements and electronic circuits. According to the signal conversion and processing method, it can be divided into voltage-current converter, current-voltage converter, DC-AC converter, AC-DC converter, voltage-frequency converter, current-frequency converter, one-in-one-out converter, multi-input-one Output converters, signal superposition converters and signal splitting converters. For example, Shenzhen’s CE-T series electrical isolation sensor/transmitter is very convenient to use. There are many similar products in China, and users can choose their own applications according to their needs.

7.In the application of VFD, peripheral circuits are often required. The method is often:

(1) A logic function circuit composed of self-made relays and other control components;
(2) Purchase ready-made unit external circuits;
(3) Choose a simple programmable controller.
(4) When using different functions of VFD, you can choose a function card;
(5) Select small and medium-sized programmable controllers.

8.When multiple pumps are connected in parallel for constant pressure water supply, only one sensor is needed for signal series connection, and its advantages are as follows:

(1) Cost saving. Only one set of sensors and PID is required.
(2) Since there is only one control signal, the output frequency is the same, that is, the same frequency, so the pressure is also the same, and there is no turbulence loss.
(3) During constant pressure water supply, when the flow rate changes, the number of pumps to be started will change through PLC control. 1 set at least, 2 sets in moderate amount, 3 sets in large amount. When the VFD stops working, the circuit (current) signal is a channel (signal flows in, no output voltage and frequency).
(4) More advantageously, since the system has only one control signal, even if the inputs of the three pumps are different, but the working frequency is the same (that is, synchronous), and the pressure is the same, so the turbulence loss is zero, that is, the loss is the smallest, and the power saving effect is the best.

continue reading

Related Posts