Skills sharing of the hottest Inverter Application

Sharing of inverter application skills

1) shielded wires should be used for signal lines and control lines, which is beneficial to prevent interference. When the line is long, for example, the distance jumps 100 m, the conductor section should be enlarged. The signal line and control line should not be placed in the same cable trench or bridge with the power line to avoid mutual interference. It is better to place them through pipes, which is more appropriate

2) the transmission signal is mainly the current signal, because the current signal is not easy to decay and is not easy to be disturbed. In practical applications, the output signal of the sensor is a voltage signal, which can be transformed into a current signal by a converter

3) the closed-loop control of the frequency converter is generally positive, that is, the input signal is large, and the output is also large (for example, when the central air conditioner is working and the general pressure, flow, temperature and other control). But there are also reactions, that is, the input signal is large, and the output is small (for example, when the central air conditioner is heating and the heating hot water pump in the heating station). The closed-loop control is shown in Figure 1

4) if the pressure signal can be selected in the closed-loop control, the flow signal should not be selected. This is because the pressure signal sensor has the advantages of low price, easy installation, small workload and convenient debugging. However, if the technological process has flow proportioning requirements and requires accuracy, the flow controller must be selected, and the appropriate flowmeter (such as electromagnetic, target, vortex street, orifice plate, etc.) must be selected according to the actual pressure, flow, temperature, medium, speed, etc

5) the built-in PLC and PID functions of the frequency converter are suitable for systems with small and stable signal variation. However, because the built-in PLC and PID functions only adjust the time constant during operation, it is difficult to obtain satisfactory requirements for the transition process, and debugging is time-consuming

in addition, this kind of regulation is not intelligent, so it is generally not often used, but the external intelligent PID regulator is selected. For example, Japan Fuji PXD series and Xiamen Anton are very convenient. As long as Sv (upper limit value) is set during use, PV (operation value) indication is available during operation, which is intelligent and ensures the best transition process conditions, so it is ideal for use. For PLC, various brands of external PLC, such as Siemens s, s, s, etc., can be selected according to the nature of the control quantity, points, digital quantity, analog quantity, signal processing and other requirements

6) signal converter is also often used in the peripheral circuit of frequency converter, which is generally composed of Hall components and electronic circuits. According to the signal transformation and processing mode, it can be divided into various converters, such as voltage to current, Er to voltage, DC to AC, AC to DC, voltage to frequency, Er to frequency, one in and one out, multiple in and one out, signal superposition, signal shunting, etc. For example, the CE-T series electric quantity isolation sensors/transmitters of Shenzhen Saint SIRs are very convenient for application. There are many similar products in China, and users can choose their own applications according to their needs

7) when the frequency converter is applied, it often needs to be equipped with peripheral circuits in the following ways:

(1) logic function circuit composed of self-made relays and other control elements

(2) buy ready-made unit external circuits (such as those of Mitsubishi Corporation of Japan)

(3) select the logo of simple programmable controller (this product is available both abroad and at home)

(4) when using different functions of the frequency converter, the function card can be selected (such as Japan Sanken frequency converter)

(5) select medium and small programmable controllers

8) there are two common frequency conversion technical transformation schemes for parallel constant pressure water supply with multiple pumps (such as clean water pumps in urban waterworks, medium and large water pump stations, hot water supply center stations, etc.)

according to the use experience, most places are almost blank; On the other hand, China's industry has developed rapidly in recent years. Scheme (1) saves initial investment, but the energy-saving effect is poor. When starting, first start the frequency converter to 50 Hz, then start the power frequency, and then turn to energy-saving control. In the water supply system, only the water pump driven by the frequency converter has a slightly smaller pressure, and there is turbulence and loss in the system

scheme (2) has a large investment, but it saves 20% more energy than scheme (1). The pressure of the two pumps is the same, and there is no turbulence loss, so the effect is better

9) when multiple pumps are connected in parallel for constant pressure water supply, only one sensor is used in series with the following advantages

(1) cost saving. As long as a set of sensors and PID, as shown in Figure 4

(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) when water is supplied at constant pressure, when the flow changes, the number of starting pumps will change through PLC control. At least 1 set, 2 sets in medium quantity and 3 sets in large quantity. When the frequency converter stops working, the circuit (current) signal is connected (there is signal inflow, but there is no output voltage and frequency)

(4) what is more advantageous is that the system has only one control signal. Even if the three pumps are put into different inputs, the working frequency is the same (i.e. synchronous) and the pressure is the same, so the turbulence loss is zero, that is, the loss is the smallest, so the power saving effect is the best

10) reducing the base (basic frequency) is the most effective way to improve the starting torque. The principle analysis is as follows

(2) why is it most effective to reduce the base frequency and increase the starting torque? See Table 1 for details

it is known from table 1 that due to the substantial increase in starting torque, some difficult to start equipment, such as extruder, washer, dryer, mixer, coating machine, mixer, large fan, water pump, roots blower, etc., can operate smoothly and are not included in the forced index. This is more effective than raising the starting frequency. With this method and the measure of changing heavy load to light load, the current protection is increased to the maximum value, and almost all equipment can be started. Therefore, reducing the base frequency to improve the starting torque is the most effective and convenient method

(3) when this condition is applied, the reduction of base frequency does not necessarily have to be reduced to 30 Hz. It can be reduced step by step every 5 Hz, and the frequency reached by the reduction is as long as the system can be started

(4) the lower limit of base frequency should not be lower than 30 Hz. From the perspective of torque, the lower the lower the lower the limit, the greater the torque. However, it should also be considered that IGBT will be damaged if the voltage rises too fast and the dynamic du/dt is too large. The result of actual use is that this method can be safely used to focus and increase torque from low power to high power in sequence when 50 Hz drops to 30 Hz

(5) some people worry that, for example, when the base frequency drops to 30 Hz, the voltage has reached 380 v. Then when it is possible to reach 50 Hz for normal operation, whether the output voltage jumps to 380 V, so the motor can't stand it. The answer is that this phenomenon will not happen

(6) some people worry that if the falling base is 30 Hz, the voltage has reached 380 v. Then whether the output frequency can reach the rated frequency of 50 Hz when it is required to reach 50 Hz in normal operation, the answer is that the output frequency can certainly reach 50 Hz

(7) (5) and (6) above are determined by the software writing process. The use process has proved that these two points can be assured

11) the relationship among dynamic pressure, static pressure and total pressure is as follows:

(1) static pressure is the required pressure (head) when the water outlet pressure of the pump reaches the highest point. Generally, it is 1 kg water pressure per 10 m high water column

(circular) dynamic pressure is the pressure drop caused by the resistance caused by the flow velocity difference between the liquid and the pipe wall, valves (regulating valve, check valve, pressure reducing valve, etc.) and different layers of the same section in the process of water flow. This part of calculation is very difficult. According to practical experience, the dynamic pressure assumes a static pressure value of 20% (at the maximum)

(APE) total pressure exceeds (static pressure + dynamic pressure) assume 1.2 static pressure

(source) the lower limit frequency of the water pump must be set at about 30 Hz, otherwise it is easy to empty the water in the closed pipe. Because a large amount of air is dissolved into the water, when the water pump is started, it is easy to produce an air chamber and form a high-pressure hazard

12) the empirical value and economic value are introduced as follows:

it is feasible to realize power saving by using frequency converter for various equipment, which has been confirmed by many practical successful cases

(1) the experience value is relatively conservative and has a large degree of affluence. It is not the most economical and has potential to be tapped. When using the empirical value, it should be arranged according to the actual situation on site, and the operating condition parameters should have certain changes, with the lower limit condition of not affecting the normal use. This is the premise of energy saving

(round) economic value is based on the principle of meeting the lower limit conditions of the system, appropriately reducing the empirical value and tapping the potential to achieve energy-saving effect. If the operating condition parameters remain unchanged, where can we start to save energy? Moreover, the frequency converter, therefore, customers, you should know in detail whether we really choose to choose our non energy generating devices (generators, batteries, solar energy) in the future. Its own efficiency is very high, at 97% Yuyao 98%, but there is always loss, at 2 Yuyao 3 Yuyao