As an example, Delta Electronics shows an application with an air compressor. The trend in the compressor world is to remove the gearbox between the compressor and the electric motor. This eliminates energy losses in the transmission and also reduces mechanical maintenance. Because the transmission is usually used to obtain higher rotation speeds, other properties are now expected from the electric motor. The normal output frequency of 50 Hz is thus increased to, for example, 1000 to 1500 Hz. Applications for this kind of compressors can be found in chillers, turbo fans, gas turbines and flywheel energy storage applications. Delta has developed a High-Speed (HS) inverter series especially for these applications which can drive these high speed motors. These motors are usually equipped with special bearings to reduce friction losses, so-called electro-mechanical bearings. For these magnetic bearings, Delta has developed an additional unit to activate the magnetic field in time in order to minimize the losses as much as possible. This special drive can easily be connected to the DC bus of the applied HS frequency inverter.
Challenges in efficiency
Raising the efficiency standards on standard induction (IM) electric motors is a continuous process. For these induction motors, there are a total of four efficiency levels, IE1 to IE4. The efficiency level for standard induction motors up to 1,000 kW was raised from IE2 to level IE3 on 1 July 2021. In 2023, induction motors up to a power of 200 kW will even have to move to the IE4 standard. These higher levels are becoming increasingly difficult to achieve in practice, due to the choice of material and the quantity of material already used to achieve the desired IE3 level. This means that the challenge now is to develop other constructions, such as permanent magnet (PMA SynRM) and synchronous (SynRM) reluctance motors. With these variants, a fourth (IE4) and even a fifth efficiency level (IE5) can now be achieved. All these variations in motors require a different control from the frequency inverter. To provide easy choices, Delta has equipped its advanced frequency inverters with a standard firmware to control both induction (IM) and permanent magnet (PM) motors and synchronous reluctance motors (PMA SynRM & standard SynRM). The company does this to simplify the control in many applications and to guarantee choices with these new IE3 and in 2023 IE4 motors.
Efficiency level of inverters
Following the efficiency standard for electric motors, this year (1 July 2021) the new guidelines for frequency converters came into force. The efficiency level for frequency converters can be divided into three efficiency grades: IE0 to IE2. According to this new standard, every three-phase frequency controller with a connection voltage between 100 and 1000 Vac and within a power range of 0.12 to 1000 kW must meet the IE2 level. The losses must be indicated on the type plate of the AC drive in question. These losses are determined at full load, which means at an output frequency >90%, and at 100% full load current. The Delta inverters meet this new standard, mentioned in the IEC 61800-9-2.
The third part of this efficiency standard is the power drive (PDS) part, the combination of an AC drive and an electric motor. This power drive standard can also be divided into the same three gradations as for the frequency inverters, now called IES0 to IES2. Because the length of the motor cable between the frequency converter and the motor has an influence on the efficiency of the entire drive system, a standard length has been laid down in this standard. Of course, it is possible to deviate from this standard length if it is clearly specified, including the switching frequency of the frequency converter.
Advanced energy function
These are just some of the possibilities at Delta Electronics. For example, for pumps there is the possibility to set the operation at the best efficiency point (BEP). The firmware is provided with various standard solutions to control multiple pumps. Special parameters for energy saving have also been added. For example, there is a standard energy function which reduces the output voltage at the same output frequency if the motor is not fully loaded. But also an advanced energy function has been developed, which follows the real-time load characteristic of the motor. By the necessary auto-tuning of the frequency converter to the motor, the most optimal energy saving is obtained. A more simple
A derivative of this (without auto-tuning) is used by a well-known escalator manufacturer. To give you some figures: an unloaded escalator consumes about 1.2 kW. With this special energy-saving function, the energy consumption is reduced to less than 500 W. This results in a saving of at least 700 W, which in turn will result in considerable cost savings on an annual basis.