Can the frequency converter save electricity?How much will be saved?

The principle of frequency converter power saving, just like a shrewd housekeeper, skillfully adjust the power consumption in the home. In some scenarios, it can even save up to 40 percent, but in other cases, it can consume more power than a disconnected converter if not used properly. The frequency converter mainly realizes energy saving through light load pressure reduction. When dragging the rotation distance load, because the speed change is not large, even if the voltage is reduced, the energy saving effect is relatively weak. However, in the fan environment, when a small air volume is required, the electric opportunity reduces the speed, and the energy consumption of the fan is proportional to the 1.7 power of the speed, which means that the rotation distance of the motor will drop sharply, and the energy saving effect becomes very obvious.

 When two identical motors are operating at 50 HZ, one uses a frequency converter and the other does not. When the speed and torque reach the rated state of the motor, the frequency converter can not actually save power, but it can improve the power factor. When the torque of the motor does not reach the rated torque, if the automatic energy saving operation is enabled, the frequency converter can save part of the power through the step-down operation, although this saving is not significant. As for the no-load state, the energy-saving effect of the drag load is not obvious.

 As for the concept of closed-loop control, I think it does deserves further discussion. The closed-loop control seems too narrow and limited to the speed sensor feedback. In fact, the closed-loop control covers a broader range, including the frequency control during vector control, which is a closed-loop control inside the device. In contrast, V / F control is open loop control. In addition, the PID regulator feedback control of physical quantities such as temperature, pressure and flow rate also belongs to the category of closed-loop control, and these can be adjusted by frequency converter. Therefore, we should not limit the concept of closed-loop control to a narrow range.

 Under what circumstances can the frequency converter really save power? First of all, we need to clarify the fact that it is not an energy-saving inverter that can be achieved on all occasions. In fact, in some cases, the use of a frequency converter may not bring a significant power saving effect. In addition, as a part of the electronic circuit, the frequency converter itself also consumes a certain amount of electricity, usually accounting for about 3-5% of its rated power.

 However, when the converter is power saving, it does operate at power frequency. However, to achieve this function, the following three conditions must be met: First, the equipment needs to be high power and mainly used for fan / pump load; second, the device itself needs to have power saving function, which usually requires software support; finally, the equipment needs to be long-term continuous operation. Only under these premises, we can truly experience the power saving effect of frequency converter.

 So, in the use of frequency converter, the motor starting current and starting torque is what? When the motor is started through the frequency converter, with the acceleration of the motor, the frequency and voltage will also increase accordingly. This limits the starting current to less than 150% of the rated current (specific values may vary from 125% to 200%). In contrast, when starting directly with the power frequency power supply, the starting current may be as high as 6-7 times the rated current, which can cause a large mechanical and electrical impact. With the frequency converter start, the smooth start process can be realized (although the start time will be longer), and the starting current and starting torque will be more stable. Specifically, the starting current is usually 1.2-1.5 times of the rated current, and the starting torque is 70% -120% of the rated torque. For the frequency converter with automatic torque enhancement function, the starting torque can even exceed 100%, thus allowing the motor to start in the full load state.

 In addition, sometimes in the same plant, when the large motor starts, it may cause the nearby operating frequency converter to stop working. This is because the motor generates a starting current corresponding to its capacity, which leads to a voltage drop in the transformer on the stator side of the motor. When the motor capacity is large, the impact of this voltage drop is also more obvious. Therefore, the inverter connected to the same transformer may be misjudged as undervoltage or instantaneous stop, which triggers the protection function (IPE) and causes the inverter to stop operation.

 Finally, there are some restrictions on the installation direction of the frequency converter. Since the structure inside and back of the inverter is designed to optimize the cooling effect, the ventilation relationship between the top and bottom is also very important. For the unit type frequency converter, whether it is installed in the disk or hanging on the wall, it should be installed vertically, and keep the vertical state as far as possible. This ensures that the heat inside the frequency converter can be discharged smoothly, so as to maintain its stable operation.

 Under what circumstances can the frequency converter save electricity? The answer is that when the motor is running below the rated frequency, the inverter adjusts the running speed of the motor to match it according to the actual load demand, so as to avoid the waste of energy. So, if the motor is directly put into a fixed frequency frequency, not soft start, is it ok? The answer is that it is feasible in low frequency cases, but if the frequency is too high, close to the condition that the power frequency power supply directly starts, then the too large starting current may exceed the bearing capacity of the frequency converter, resulting in the motor unable to start.

 What problems do we need to pay attention to when the motor is running over 60Hz? First, the feasibility of the machinery and device operation at this high speed needs to be evaluated, including factors such as mechanical strength, noise and vibration. Secondly, the motor enters the constant power output range, and its output torque must be able to maintain the work demand, especially if the output power of the fan and pump is proportional to the cubic speed. In addition, the high-speed operation may affect the bearing life, which also needs to be fully considered. Finally, discuss the motors above the medium capacity, especially the 2-pole motor, when running above the 60Hz.

 Can the inverter drive the gear motor? The answer is not absolute, it needs to be evaluated according to the structure and lubrication mode of the reducer. Generally speaking, the maximum limit frequency of the gear can be considered as 70~80Hz. Low-speed continuous operation may cause damage to the gear when lubricating with oil. As for whether the inverter can drive a single-phase electric generator, is it feasible to use a single-phase power supply? The answer is not recommended. For the single-phase governor switch starting machine, under the working point, the auxiliary winding may be burned; while for the capacitor starting or capacitor operation motor, the capacitor explosion may be induced. Of course, there are also small-capacity frequency converters that can use a single-phase power supply for operation.

 As for the power consumed by the inverter itself, it is related to the type of the inverter, running state, use frequency and other factors, and the specific value is difficult to generalize. But generally speaking, the efficiency of the frequency converter below 60Hz is about 94%~96%. For the internal regenerative brake inverter, if the loss of braking is considered, the power consumption will increase, which needs special attention in the design of the operating plate.

 Why can't it work continuously in the whole 6-60 Hz area? This is because the general motor uses the external fan on the shaft or the blade on the rotor end ring to cool. When the speed is reduced, the cooling effect will decrease, resulting in the motor can not bear the same heat as the high-speed operation. To solve this problem, it is necessary to reduce the load torque at low speed, or to use a larger capacity of the frequency converter and the motor combination, or even to use a special motor.

 When using the motor with the brake, the brake excitation circuit power supply shall be taken from the input side of the frequency converter. If the brake moves while the converter is in output power, the overcurrent will be cut off. Therefore, it is necessary to move the brake after the frequency converter stops the output.

 If you want to use the motor with the capacitor to improve the power factor, but the motor cannot start, the reason may be that the current of the converter flows into the capacitor to improve the power factor, resulting in the charging current of the capacitor and the overcurrent of the converter.The solution is to operate the capacitor after removal, or to access the AC reactor on the input side of the inverter to improve the power factor.

As for the life of the frequency converter, although it is a static device, but there are also such as filter capacitor, cooling fan and other consumption devices. Through regular maintenance and maintenance of these devices, the inverter is expected to have a life of more than 10 years.