Frequency Inverter

A frequency inverter also called frequency converter, is a power control conversion device to convert normal power supply (50Hz or 60Hz) to another frequency power by inner power semiconductor on/off behaviors, to control electric motors in variable speed operations. Variable frequency control is changing the frequency supply to the motor stator windings to achieve variable speed control purposes.

The frequency inverter is mainly consisted of a rectifier (AC to DC), filter, inverter (DC to AC), braking unit, drive unit, detection unit and micro processing unit etc. The control circuit controls the main circuit, the rectifier circuit converts AC power into DC power, DC intermediate circuit smoothes the rectifier circuit output, then the inverter circuit reverses DC current into AC current again.

Inverter.com offers universal frequency inverters, single phase input and output frequency inverter, 1-phase to 3-phase frequency inverter and three phase frequency inverter, widely used in various loads.

The Difference between Power Inverter and Frequency Inverter

• The power inverter is a device that can convert DC into AC and the frequency inverter is a component used to change the AC frequency.
• The power inverter can convert DC power (battery, accumulator jar) into AC power (sinusoidal wave of 220V and 50 Hz), and the frequency can also be adjusted. The frequency inverter can convert the input AC into the AC with required frequency and then output it. The work principles include AC-DC-AC or AC-AC. The common rule is AC-DC-AC, based on which the AC is converted into DC first and then the DC is converted into AC. This is also the process of rectifying and inverting.
• The frequency inverter includes the frequency adjustment part. However, the inverter only has fixed output frequency.

Why Choose a Frequency Inverter?

• Adjustable torque limit: After adjusting the speed by frequency conversion, the corresponding torque limit can be set to protect the machine from damage, so as to ensure the continuity of the process and the reliability of the product. At present, the frequency conversion technology makes not only the torque limit adjustable, but also the control accuracy of the torque reach about 3%-5%. In the power frequency state, the motor can only be controlled by detecting the current value or thermal protection, but can not be operated by setting the precise torque value as in the frequency conversion control.
• Controllable stopping mode: Like controllable acceleration, the stopping mode can be controlled in the frequency control system and different stopping modes can be selected (decelerated parking, free parking, decelerated parking + DC braking). Similarly, it can reduce the impact on mechanical components and motors, thus making the whole system more reliable and prolonging the service life accordingly.
• Energy-saving: The energy saving of frequency inverter is mainly manifested in the application of fans and pumps: In order to ensure the reliability of production, all kinds of manufacturing machine have a certain amount of surplus when they are designed and equipped with power drive. When the motor fails to run under full load, it may not meet the requirements of power drive or excess torque increases the consumption of active power, resulting in waste of electrical energy. For traditional equipment such as fans and pumps, the frequency control method is to adjust the air supply and water supply by adjusting the baffle and valve opening at the inlet or outlet, where has a large input power, and a large amount of energy is consumed in the process of closure by the baffle and valve. In the use of frequently control, when the flow requirement is decreased, the frequency control can be achieved by reducing the speed of the pump or fan.
• Reversible operation control: In the control of frequency inverter, there is no need for additional reversible control devices to realize reversible operation control, just change the phase sequence of output voltage, which can reduce maintenance costs and save installation space.
• Reduce mechanical transmission components: At present, vector control converter plus synchronous motor can achieve high-efficient torque output, thus saving mechanical transmission components, such as gearboxes, and ultimately constituting a direct frequency conversion drive system. Thus, the cost and space can be reduced and the stability can be improved.

How to Select Frequency Inverter?

• The supply input voltage and the number of phases: They should correspond to the values specified in the frequency inverter data sheet. The motor's power output and its rated current. These specifications should be about 10% higher for a frequency inverter. It is not desirable to make a larger power reserve unless you plan to upgrade. Firstly, such reserve will cost much more, and secondly, the accuracy of motor control may be degraded.
• The nature of the load: If the load involves constant operation of the motor at peak power: e.g. hoists, presses, attention should be paid to the duration of the peak load and its permissible value.
• Ability to maintain operation within the required frequency range: The desired operating principle of the motor braking system. For example, in high power systems with frequent start/stop cycles, it makes sense to consider the purchase of a more expensive frequency inverter with regenerative braking. Initial hardware costs will be offset by the energy savings.
• The need to connect additional sensors: For example, in pump systems, the presence of pressure sensor feedback will increase accuracy and economy.
• Support of protocols and availability of remote control and monitoring ports: Compliance with these requirements is important for centralised or automated control.
• The installation and operating conditions must take account of the environmental parameters of the room in which the frequency inverter will be installed.