Ten most commonly used parameters of frequency converters

Ten most commonly used parameters of frequency converters

There are many function parameters of the frequency converter, generally there are dozens or even hundreds of parameters for users to choose. In actual applications, it is not necessary to set and debug each parameter, most of which just need to use the factory settings. However, some parameters have a lot to do with actual usage, and some are interrelated, so they should be set and debugged according to actual conditions.

　　 One, acceleration and deceleration time

　　 The acceleration time is the time required for the output frequency to rise from 0 to the maximum frequency, and the deceleration time is the time required for the output frequency to decrease from the maximum frequency to 0. Usually the frequency setting signal rises and falls to determine the acceleration and deceleration time. When the motor is accelerating, the rate of increase of the frequency setting must be limited to prevent overcurrent, and when the motor is decelerating, the rate of decrease is limited to prevent overvoltage.

Acceleration time setting requirements: limit the accelerating current below the inverter overcurrent capacity, so as not to cause the inverter to trip due to excessive stall speed; the key point of the deceleration time setting is to prevent the smoothing circuit voltage from being too large, and the regeneration overvoltage is prevented from stalling. Trip the frequency converter. The acceleration and deceleration time can be calculated according to the load, but in debugging, it is often adopted to set a longer acceleration and deceleration time according to the load and experience, and observe whether there is an overcurrent and overvoltage alarm by starting and stopping the motor; then gradually set the acceleration and deceleration time Shorten, based on the principle that no alarm occurs during operation, repeat the operation several times to determine the best acceleration and deceleration time.

　　 2. Torque boost

　　 is also called torque compensation, which is a method of increasing the low frequency range f/V to compensate for the decrease in torque at low speed caused by the resistance of the motor stator winding. When set to automatic, the voltage during acceleration can be automatically increased to compensate for the starting torque, so that the motor can accelerate smoothly. If manual compensation is used, a better curve can be selected through tests according to the load characteristics, especially the starting characteristics of the load. For variable torque loads, if the selection is improper, the output voltage at low speed will be too high, and electric energy will be wasted. There will even be a phenomenon that the motor starts with a load and the current is large but the speed does not rise.

　　 Three, electronic thermal overload protection

　　 This function is set to protect the motor from overheating. It is the CPU in the frequency converter that calculates the temperature rise of the motor according to the running current value and frequency to perform overheat protection. This function is only applicable to the occasion of "one tow one", and in the case of "one tow many", thermal relay should be installed on each motor.

　　Electronic thermal protection setting value (%)=[rated current of motor (A)/rated output current of inverter (A)>×100%.

　　Four, frequency limit

　　 is the upper and lower limit value of the inverter output frequency. Frequency limit is a protection function to prevent misoperation or failure of the external frequency setting signal source, which causes the output frequency to be too high or too low to prevent damage to the equipment. It can be set according to the actual situation in the application. This function can also be used for speed limiting. For some belt conveyors, because the material is not too much, in order to reduce the wear of the machine and the belt, it can be driven by an inverter, and the upper limit frequency of the inverter can be set to a certain frequency value , So that the belt conveyor can run at a fixed, low working speed.

　　 5. Bias frequency

　　Some are also called deviation frequency or frequency deviation setting. Its purpose is when the frequency is set by an external analog signal (voltage or current), this function can be used to adjust the output frequency when the frequency setting signal is lowest, as shown in Figure 1. When the frequency setting signal of some inverters is 0%, the deviation value can be applied in the range of 0～fmax, and some inverters (such as Mingdianshe and Sanken) can also set the bias polarity. For example, when the frequency setting signal is 0% during debugging, the output frequency of the inverter is not 0Hz, but xHz, then set the bias frequency to negative xHz to make the inverter output frequency 0Hz.

　　 Six, frequency setting signal gain

　　 This function is only valid when the frequency is set by an external analog signal. It is used to make up for the inconsistency between the external set signal voltage and the internal voltage (+10v) of the inverter; at the same time, it facilitates the selection of the analog set signal voltage. When setting, when the analog input signal is at the maximum (such as 10v, 5v or 20mA), find the frequency percentage that can output the f/V graph and set it as a parameter; if the external setting signal is 0～5v, if the inverter output frequency is 0～50Hz, the gain signal Just set it to 200%.

　　 Seven, torque limit

　　 can be divided into driving torque limit and braking torque limit. It is based on the output voltage and current value of the inverter, through the CPU to calculate the torque, which can significantly improve the impact load recovery characteristics during acceleration, deceleration and constant speed operation. The torque limit function can realize automatic acceleration and deceleration control. Assuming that the acceleration and deceleration time is less than the load inertia time, it can also ensure that the motor will automatically accelerate and decelerate according to the torque setting.

The driving torque function provides a strong starting torque. In steady state operation, the torque function will control the motor slip and limit the motor torque to the maximum set value. When the load torque increases suddenly, even When the acceleration time is set too short, it will not cause the inverter to trip. When the acceleration time is set too short, the motor torque will not exceed the maximum set value. Large driving torque is beneficial to starting, so it is better to set it to 80-100%.

　　 The smaller the braking torque setting value, the greater the braking force, which is suitable for the occasion of rapid acceleration and deceleration. If the braking torque setting value is set too high, an overvoltage alarm will occur. If the braking torque is set to 0%, the total amount of regeneration added to the main capacitor can be close to 0, so that when the motor is decelerating, it can decelerate to a stop without using a braking resistor without tripping. But on some loads, such as when the braking torque is set to 0%, there will be a short idling phenomenon during deceleration, causing the inverter to start repeatedly and the current will fluctuate greatly. In severe cases, the inverter will trip. Pay attention.

　　 Eight, acceleration and deceleration mode selection

　　 is also called acceleration and deceleration curve selection. Generally, inverters have three types of curves: linear, non-linear and S, and most of them choose linear curve; non-linear curve is suitable for variable torque load, such as fan, etc.; S curve is suitable for constant torque load, and its acceleration and deceleration change slowly. When setting, you can select the corresponding curve according to the load torque characteristics, but there are exceptions. When debugging a boiler's induced draft fan inverter, the author first selects the non-linear curve of the acceleration and deceleration curve, and the inverter will trip and adjust when it is operated together. Changing many parameters has no effect, and then it is normal after changing to S curve. The reason is: the induced draft fan rotates by itself due to the flow of flue gas before starting, and reverses to become a negative load. In this way, the S curve is selected to make the frequency rise slower at the beginning of the start, thereby avoiding the frequency converter The occurrence of tripping, of course, is the method used for inverters that do not start the DC braking function.

　　 Nine, torque vector control

　　 Vector control is based on the theoretical belief that asynchronous motors and DC motors have the same torque generation mechanism. The vector control method is to decompose the stator current into the prescribed field current and torque current, and control them separately, and at the same time output the combined stator current to the motor. Therefore, in principle, the same control performance as a DC motor can be obtained. With the torque vector control function, the motor can output the maximum torque under various operating conditions, especially in the low-speed operating area.

Almost all current frequency converters adopt non-feedback vector control. Because the frequency converter can perform slip compensation according to the magnitude and phase of the load current, the motor has very hard mechanical characteristics. It can meet the requirements for most occasions and does not need to be connected to the frequency converter. Set the speed feedback circuit externally. To set this function, you can select one of valid and invalid according to the actual situation.

　　 The related function is slip compensation control, its function is to compensate the speed deviation caused by load fluctuation, and the slip frequency corresponding to the load current can be added. This function is mainly used for positioning control.

　　 Ten, energy saving control

Fans and pumps are all reduced torque loads, that is, as the speed decreases, the load torque decreases in proportion to the square of the speed. The inverter with energy-saving control function is designed with a dedicated V/f mode, which can be improved The efficiency of the motor and the frequency converter, which can automatically reduce the output voltage of the frequency converter according to the load current, so as to achieve the purpose of energy saving, can be set to be valid or invalid according to the specific situation.

　　 It should be noted that the two parameters of ninth and tenth are very advanced, but some users cannot enable these two parameters at all in the equipment modification, that is, the inverter trips frequently after activation, and everything is normal after deactivation. The reasons are: (1) The parameters of the original motor and the motor parameters required by the frequency converter are too different. (2) Insufficient understanding of the function of setting parameters, such as energy saving control function can only be used in V/f control mode, not in vector control mode. (3) Vector control mode is enabled, but manual setting and automatic reading of motor parameters are not performed, or the reading method is improper.