The 16 Most Commonly Used Parameters of Inverters ( II )

9. Electronic thermal overload protection

This function is set to protect the motor from overheating. It is used by the CPU in the Inverter to calculate the temperature rise of the motor based on the operating current value and frequency, thereby providing overheating protection. This function is only applicable to "one to one" situations, and in "one to many" situations, thermal relays should be installed on each motor. Electronic thermal protection setting value (%)=[Motor rated current (A)/Inverter rated output current (A)] × 100%.

10. Frequency limitations

The upper and lower limits of the frequency output amplitude of the Inverter. Frequency limit is a protective function designed to prevent incorrect operation or failure of external frequency setting signal sources, which may cause excessive or low output frequency, in order to prevent damage to equipment. Set according to the actual situation in the application. This function can also be used for speed limiting. For some belt conveyors, due to the limited amount of material conveyed, in order to reduce mechanical and belt wear, an Inverter can be used for driving, and the upper frequency limit of the Inverter can be set to a certain frequency value, which can make the belt conveyor run at a fixed and lower working speed.

11. 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 an external analog signal (voltage or current), and this function can be used to adjust the output frequency when the frequency setting signal is at its lowest. When the frequency setting signal of some Inverters is 0%, the deviation value can be applied within the range of 0 to fmax, and some Inverters (such as Mingdian House and Sanken) can also set the bias polarity. If during debugging, when the frequency setting signal is 0%, the output frequency of the Inverter is not 0Hz, but xHz, then setting the bias frequency to a negative xHz can make the output frequency of the Inverter 0Hz.

12. Frequency setting signal gain

This function is only effective when setting the frequency using an external analog signal. It is used to compensate for the inconsistency between the external set signal voltage and the internal voltage of the Inverter (+10v); At the same time, it is convenient to select signal voltage for analog settings. When the analog input signal is at its maximum (such as 10V, 5V, or 20mA), calculate the frequency percentage that can output the f/V graph and set it as a parameter; If the external signal is set to 0-5V, and the output frequency of the Inverter is 0-50Hz, set the gain signal to 200%.

13. Torque limitation

It can be divided into two types: driving torque limit and braking torque limit. It is based on the output voltage and current values of the Inverter, and torque calculation is carried out by the CPU. It can significantly improve the impact load recovery characteristics during acceleration, deceleration, and constant speed operation. The torque limiting function can achieve 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 automatically accelerates and decelerates according to the torque setting value.

The drive torque function provides powerful starting torque. During steady-state operation, the torque function controls the motor slip and limits the motor torque to the maximum set value. When the load torque suddenly increases, even if the acceleration time is set too short, it will not cause the Inverter to trip. If the acceleration time is set too short, the motor torque will not exceed the maximum set value. A high driving torque is beneficial for starting, and setting it at 80-100% is more appropriate.

The smaller the braking torque setting value, the greater the braking force, which is suitable for situations of rapid acceleration and deceleration. If the braking torque setting value is set too much, overvoltage alarm phenomenon may occur. If the braking torque is set to 0%, the total amount of regeneration applied to the main capacitor can approach 0, so that the motor can decelerate to a stop without tripping when decelerating without using the braking resistor. However, on some loads, such as when the braking torque is set to 0%, there may be a brief idle phenomenon during deceleration, causing the Inverter to repeatedly start and the current to fluctuate significantly. In severe cases, it may cause the Inverter to trip, and attention should be paid.

14. Acceleration and deceleration mode selection

Also known as acceleration/deceleration curve selection. Generally, Inverters have three types of curves: linear, nonlinear, and S, and most of them choose linear curves; Nonlinear curves are suitable for variable torque loads, such as fans; The S-curve is suitable for constant torque loads, and its acceleration and deceleration changes are relatively slow. When setting, the corresponding curve can be selected based on the load torque characteristics, but there are exceptions. When debugging the Inverter of a boiler induced draft fan, the author first selects a non-linear curve for the acceleration and deceleration curve, and when the Inverter is operated together, it trips. Adjusting and changing many parameters has no effect, and then changing it to an S curve will be normal. The reason for this is that before starting, the induced draft fan rotates on its own due to the flow of flue gas and reverses to become a negative load. This selects the S-curve, which slows down the frequency rise speed at the beginning of the start, thus avoiding the occurrence of Inverter tripping. Of course, this is the method used for Inverters without DC braking function for starting.

15. Torque Vector Control

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

Nowadays, almost all Inverters adopt non feedback vector control. Due to the ability of Inverters to compensate for slip based on the magnitude and phase of the load current, the motor has very hard mechanical characteristics, which can meet the requirements for most occasions without the need to set a speed feedback circuit outside the Inverter. The setting of this function can be selected between valid and invalid according to the actual situation. The related function is slip compensation control, which is used to compensate for speed deviation caused by load fluctuations, and can add the slip frequency corresponding to the load current. This function is mainly used for positioning control.

16. Energy saving control

Fans and water pumps both belong to reduced torque loads, meaning that as the speed decreases, the load torque decreases proportionally to the square of the speed. Inverters with energy-saving control functions are designed with a dedicated V/f mode, which can improve the efficiency of motors and Inverters. This mode can automatically reduce the output voltage of the Inverter based on the load current, thereby achieving energy-saving goals. It can be set to be effective or ineffective according to specific circumstances.

It should be noted that the nine and ten parameters are very advanced, but some users are unable to enable these two parameters during equipment renovation, that is, the Inverter trips frequently after activation, and everything is normal after shutdown.

The reason for this is that:

(1) there is a significant difference in the parameters between the original motor and the motor required for the Inverter.

(2) Insufficient understanding of parameter setting function, such as energy-saving control function can only be used in V/f control mode and cannot be used in vector control mode.

(3) The vector control method has been enabled, but manual setting and automatic reading of motor parameters have not been carried out, or the reading method is incorrect.

   Unleash the power of industrial automation with Rockss Automation, the leading provider of a diverse range of variable frequency drives, drivers, motors, and more. With our extensive inventory and dedicated repair team, we are your one-stop solution for all your industrial automation needs.