Next generation compressors promise outstanding efficiency – the ultimate combination for new screw compressor range.


Southern Cross Compressors announce the imminent launch of permanent magnet, variable frequency technology combined with next generation, 2-Stage screw airends. Developed by parent company Kaishan Corporation, these revolutionary new compressors offer industry a unique integrated systematic optimisation of the compressor unit, advanced permanent magnet motor and  Kaishan 2-stage technology to achieve outstanding energy efficiency.

Martin Curd, Southern Cross National Sales Manager stated, “This unique integrated combination is a game changer in the compressed air industry offering unsurpassed efficiency in compressors all the way down to 22kW. We can now offer a superior range of advanced energy saving compressors for virtually any industry application”.

2-Stage air compressors are up to 20% more efficient compared to a typical single stage compressor. As the compression ratio is spread over two distinct airends, customers get the benefits of both higher efficiency and longer bearing life.

Kaishan general manager Dr Yan Tang, one of the world’s foremost experts in air compressor development stated. “With global energy costs constantly rising, we are continually developing higher efficiency compressors that meet and surpass international energy standards. The high ◦◦efficiency of our newly developed 2-Stage screw units is the fundamental reason for our PMVF compressor’s class leading performance. Our unique package design and engineering offers obvious technological advantages including screw compressor unit efficiency, drive motor efficiency and overall unit control”.

Rare earth material technology gives the permanent magnet synchronised motors higher possible rotating speeds, wider operating parameters and increased energy efficiency. Within its wide operating speed range the PMVF compressors are able to maintain extremely high motor efficiency compared to those utilising conventional drive motors.

With an operating variable speed turndown range of 7:1 (conventional VS compressors 4:1), Kaishan’s PMVF operates at peak efficiency even with an 80% reduction in air output. It also offers far greater integrated control precision through an advanced PID control algorithm providing highly stable supply pressures.

The fully enclosed, oil cooled PM motor generates very little heat resulting in a longer life. No cooling fan means significantly lower noise and less fan drag compared to conventional motors. The motor is heat resistant to 180⁰ C and cannot be magnetised. With no external electrical excitation, the rotor utilises rare earth technology to eliminate speed slippage, fundamental wave iron and cope per loss maintaining a power factor close to 1.

The precision speed adjustment capability (1/30000) greatly reduces discharge fluctuations of the new range of air compressors.

Motor angular position sensors are not required, simplifying the system and improving both stability and reliability. Torque can be compensated at any angle within 360⁰ to achieve perfect torque control and the utilisation of bus voltage is greater than 93% being much greater than conventional inverters.

Once a mains frequency screw air compressor deviates from its designated working specifications, its efficiency drops. Kaishan’s PMVF technology is able to adjust the motor’s rotating speed according to demand variables in the required air volume at any time. By regulating the volume of air output, the compressor is able to maintain maximum efficiency under all usage demands from 15-100%. Particularly in widely fluctuating demands, Kaishan’s PMVF type air compressors demonstrate a remarkable energy saving capacity as high as 50% over conventional types.

Southern Cross is in the final stages of obtaining all necessary statutory approvals for the new range which is expected to be launched later this year.


Total efficiency values were recorded during development trials comparing the usage of a 37kW conventional air compressor with a MPVF type based on 8000 identical operating hours per annum. The results displayed an energy saving of 281,200kW with the conventional model compared to 183,250kW with the Kaishan PMVS model…  An astounding saving of 97,680kW 

Why permanent magnet motors?

The AC induction motor is often referred to as the workhorse of the industry because it offers users simple, rugged construction, easy maintenance and cost-effective pricing. Despite its popularity, the AC induction motor has limitations: It is not a constant-speed machine, it is not inherently capable of providing variable-speed operation and they are energy intensive to operate.

Permanent magnet motors are the next generation offering both excellent performance with fewer losses and therefore lower operating costs.

A conventional induction motor consists of two key parts: a stator and a rotor. The electric current passes through the stator to produce a rotating magnetic field. This in turn induces a current in the rotor, which creates a second magnetic field. The interaction between these two magnetic fields produces turning torque, causing the rotor to turn.

The induction motor shaft and the magnetic field do not turn at the same pace. Due to losses in bearings and other elements, the rotor cannot keep up with the field and turns below the magnetic field synchronous speed. This is called slip, measured in RPM, which increases with increasing load.

High-speed permanent magnet motors offer increased energy efficiency compared to conventional asynchronous induction motors. A permanent magnet motor utilising an oil cooled housing offers not only reliable operation, but significantly lower losses.

Permanent magnet synchronous torque motors offer higher torque and fewer losses with faster acceleration and deceleration, compared to asynchronous induction type motors, and this is advantageous with compressors as they rapidly vary their output to match customer demand.

  • Energy efficiency over a wide speed range
  • Desired output power in smaller frame sizes
  • Variable speed operation in constant-torque and variable-torque applications
  • Lower routine and long-term maintenance