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The most complete debugging of basic parameters of inverter

2021-01-16

There are many function parameters of frequency converter, generally there are tens or even hundreds of parameters for users to choose. In practical application, it is not necessary to set and debug every parameter, most of them just need to use the factory settings. However, some parameters have a lot to do with the actual use, and some are also interrelated, so they should be set and debugged according to the actual situation. The functions of different types of frequency converters are different, and the names of the same function parameters are not consistent, so this paper takes the basic parameter names of Fuji frequency converter as an example. As the basic parameters are almost all types of inverter, it can be done by analogy.


1、 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 fall from the maximum frequency to 0. The acceleration and deceleration time is usually determined by the rise and fall of frequency setting signal. When the motor accelerates, it is necessary to limit the rising rate of frequency setting to prevent over-current, and when the motor decelerates, it is necessary to limit the falling rate to prevent over-voltage.


Acceleration time setting requirements: the acceleration current shall be limited below the over-current capacity of the frequency converter, so as not to make the over-current stall and cause the frequency converter trip; deceleration time setting points are: to prevent the smooth circuit voltage from being too large, so as not to make the regeneration over-voltage stall and cause the frequency converter trip. The acceleration and deceleration time can be calculated according to the load, but in the debugging, it is often used to set a longer acceleration and deceleration time according to the load and experience, and observe whether there is an over-current and over-voltage alarm by starting and stopping the motor; then the acceleration and deceleration setting time is gradually shortened, and the optimal acceleration and deceleration time can be determined by repeated operation for several times based on the principle of no alarm in operation.


2、 Torque increase


Also known as torque compensation, is to compensate for the motor stator winding resistance caused by low-speed torque reduction, and increase the low frequency range f / V method. When it is set to automatic, the voltage during acceleration can be raised automatically to compensate the starting torque, so that the motor can accelerate smoothly. If manual compensation is adopted, the better curve can be selected through test according to the load characteristics, especially the starting characteristics of the load. For variable torque load, if it is not selected properly, the output voltage at low speed will be too high, and the phenomenon of waste of electric energy will appear. Even when the motor starts with load, the current will be large, and the speed will not go up.


3、 Electronic thermal overload protection


This function is set to protect the motor from overheating. The CPU in the inverter calculates the temperature rise of the motor according to the running current value and frequency, so as to protect the motor from overheating. This function is only applicable to the situation of "one driving one", while in the case of "one driving more", the thermal relay should be installed on each motor.


Electronic thermal protection setting value (%) = [motor rated current (a) / inverter rated output current (a)] × 100%.


4、 Frequency limit


That is, the upper and lower limits of the inverter output frequency amplitude. Frequency limit is a kind of protection function to prevent the output frequency from being too high or too low due to misoperation or external frequency setting signal source failure, so as 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 example, some belt conveyors can be driven by frequency converter in order to reduce the wear of machinery and belt, and the upper limit frequency of frequency converter can be set to a certain frequency value, so that the belt conveyor can run at a fixed and low working speed.

5、 Bias frequency


Some are also called deviation frequency or frequency deviation setting. Its purpose is to adjust the output frequency when the frequency is set by external analog signal (voltage or current), as shown in Figure 1. When the frequency setting signal of some inverters is 0%, the deviation value can act in the range of 0 ~ Fmax, and some inverters (such as mingdianshe and Sanken) can also set the bias polarity. If in debugging, when the frequency setting signal is 0%, the output frequency of frequency converter is not 0Hz, but XHZ, then the output frequency of frequency converter can be 0Hz by setting the bias frequency to negative XHZ.


6、 Frequency setting signal gain


This function is only effective when setting the frequency with 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 frequency converter; at the same time, it is convenient to select the analog set signal voltage. When the analog input signal is the maximum (such as 10V, 5V or 20mA), the frequency percentage of the output f / V graph can be calculated and set as a parameter; when the external set signal is 0 ~ 5V, if the output frequency of the frequency converter is 0 ~ 5V If it is 0 ~ 50 Hz, set the gain signal to 200%.


7、 Torque limit


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


The driving torque function provides powerful starting torque. In steady-state operation, the torque function will control the motor slip and limit the motor torque within the maximum set value. When the load torque suddenly increases, even if the acceleration time is set too short, the inverter will not trip. When the acceleration time is set too short, the motor torque will not exceed the maximum set value. Large driving torque is good for starting, and 80-100% is better.


The smaller the setting value of braking torque is, the greater the braking force is. It is suitable for the occasions of rapid acceleration and deceleration. For example, if the setting value of braking torque is too high, the over-voltage alarm will appear. 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 decelerates, it can also decelerate to stop without using the braking resistor and will not trip. However, on some loads, if the braking torque is set to 0%, there will be a short idling phenomenon during deceleration, which will cause the frequency converter to start repeatedly and the current fluctuates greatly. In serious cases, the frequency converter will trip, which should be paid attention to.


8、 Acceleration and deceleration mode selection


Also called acceleration and deceleration curve selection. Generally, frequency converters have three kinds of curves: linear curve, nonlinear curve and S curve, and most of them choose linear curve; nonlinear curve is suitable for variable torque load, such as fan; s curve is suitable for constant torque load, and its acceleration and deceleration change slowly. When setting, the corresponding curve can be selected according to the load torque characteristics, but there are also exceptions. When debugging the inverter of a boiler induced draft fan, the author first selects the non-linear curve for the acceleration and deceleration curve, and the inverter trips when it runs together. It is ineffective to adjust and change many parameters, and then it is normal after changing to S curve. The reason is: before starting, the induced draft fan rotates automatically due to the flue gas flow, and reverses to become a negative load, so the S curve is selected, so that the rising speed of frequency is slow when starting, so as to avoid the occurrence of frequency converter tripping. Of course, this is the method adopted for the frequency converter without starting DC braking function.


9、 Torque vector control


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


Nowadays, almost all frequency converters adopt no feedback vector control. Because the frequency converter can compensate the slip according to the load current and phase, the motor has very hard mechanical characteristics. For most occasions, it can meet the requirements, and there is no need to set the speed feedback circuit outside the frequency converter. This function can be set according to the actual situation in the effective and invalid to choose one.


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


10、 Energy saving control


Fan and water pump belong to torque reducing load, that is, with the decrease of speed, the load torque and the square of speed decrease in proportion. The inverter with energy-saving control function is designed with special V / F mode, which can improve the efficiency of motor and inverter. It can automatically reduce the output voltage of inverter according to the load current, so as to achieve the purpose of energy saving. It can be designed according to the specific situation Set to valid or invalid.


It should be noted that the nine and ten parameters are very advanced, but some users are unable to enable the two parameters in the equipment transformation, that is, the frequency converter trips frequently after it is enabled, and everything is normal after it is disabled. The reasons are as follows: (1) the difference between the original motor parameters and the motor parameters required by the inverter is too large. (2) For example, the energy-saving control function can only be used in V / F control mode, not in vector control mode. (3) The vector control mode is enabled, but the manual setting and automatic reading of motor parameters are not carried out, or the reading method is improper.


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