Adjustable torque limit
By using frequency converters to regulate speed, appropriate torque limits can be set to protect machinery from damage, thereby ensuring the continuity of the process and the reliability of the product. Current frequency converter technology allows not only adjustable torque limits but also torque control accuracy to reach approximately 3% to 5%. Under standard operating frequency (SOC) conditions, motors can only be controlled by detecting current values or thermal protection, and cannot operate by setting precise torque values as in frequency converter control.
Controlled stopping method
Just like controllable acceleration, in variable frequency speed control, the stopping method can be controlled, and there are different stopping methods to choose from (deceleration stop, free stop, deceleration stop + DC braking). Similarly, it can reduce the impact on mechanical parts and motors, thereby making the entire system more reliable and increasing its lifespan accordingly.
Energy saving
Centrifugal fans and water pumps can significantly reduce energy consumption by adopting frequency converters, a fact demonstrated in over a decade of engineering experience. Since the final energy consumption is a ratio of the cube of the motor speed, the return on investment is faster with frequency converters.
Reversible operation control
In inverter control, reversible operation control can be achieved without additional reversible control devices; only the phase sequence of the output voltage needs to be changed, which reduces maintenance costs and saves installation space.
Reduce mechanical transmission components
Since vector control frequency converters combined with synchronous motors can achieve efficient torque output, they can save on mechanical transmission components such as gearboxes, ultimately forming a direct frequency conversion drive system. This reduces costs and space requirements while improving stability.
It requires less power to start up.
Since motor power is directly proportional to the product of current and voltage, the power consumed by a motor directly started at mains frequency will be significantly higher than that required for variable frequency starting. Under certain operating conditions, where the power distribution system has already reached its maximum capacity, the power surge generated by directly starting the motor at mains frequency can severely impact other users on the same grid, potentially leading to warnings or even fines from the grid operator. Using a variable frequency drive (VFD) for motor starting and stopping avoids these problems.
Controllable acceleration function
Variable frequency speed control (VFD) allows for zero-speed start-up and uniform acceleration according to user needs, with selectable acceleration curves (linear acceleration, S-curve acceleration, or automatic acceleration). In contrast, starting at mains frequency generates severe vibrations in the motor or connected mechanical shafts and gears. This vibration further exacerbates mechanical wear and tear, reducing the lifespan of mechanical components and the motor. Additionally, VFD starting can be used in applications such as filling lines to prevent bottles from tipping over or being damaged.
Adjustable running speed
Variable frequency speed control can optimize the process and can be quickly changed according to the process. Speed changes can also be achieved through remote control PLC or other controllers.
Control the starting current of the motor
When a motor is started directly at the mains frequency, it will generate 7 to 8 times its rated current. This current value will significantly increase the electrical stress on the motor windings and generate heat, thus reducing the motor's lifespan. Variable frequency drive (VFD), on the other hand, allows for zero-speed, zero-voltage starting (with appropriate torque boost). Once the frequency and voltage relationship is established, the VFD can drive the load using V/F or vector control methods. Using VFD can significantly reduce starting current and increase winding capacity. The most direct benefit for users is further reduced motor maintenance costs and a corresponding increase in motor lifespan.
Reduce voltage fluctuations in power lines
When a motor starts at mains frequency, the current increases dramatically, and the voltage also fluctuates significantly. The magnitude of the voltage drop depends on the power of the starting motor and the capacity of the power distribution network. This voltage drop can cause voltage-sensitive equipment in the same power supply network to malfunction, trip, or operate abnormally; for example, PCs, sensors, proximity switches, and contactors may all malfunction. However, by using variable frequency speed control, the voltage drop can be minimized because it allows for gradual starting at zero frequency and zero voltage.
