Technology

I. Background

The physical principle of production of mechanical force by the interactions of an electric current and a magnetic field was known as early as 1821. Electric motors of increasing efficiency were constructed throughout the 19th century. Maxwell’s equations which describe the electromagnetism were discovered by Maxwell in 1861. The AC induction motor was invented by Nikola Tesla in 1924 and became the most commonly used motor type and remains so today due to its simple construction. It has the characteristic that motor shaft speed is proportional to the applied frequency and inversely proportional to the number of poles. In summary, there are 3 types of motors in the current motor industries:

  • AC Induction motor
  • Brushless DC motor
  • Brush DC motor

They all have different pros and cons for different application. In general, the energy efficiency of the existing motor is much less than 90% special for low power motor. Electrical motors constructed according NEMA Design B must meet the efficiencies below:

Power (hp) Minimum Nominal Efficiency
1 – 4 78.8
5 – 9 84.0
10 – 19 85.5
20 – 49 88.5
50 – 99 90.2
100 – 124 91.7
> 125 92.4
This gives you the idea that the efficiency for better design motor which can meet the NEMA required. The most motor in the market may not even meet this requirement. However, the efficiency for the digital motor can achieve much higher ranges as we desired.The major reason that all existing motors cannot achieve higher efficiency is that the mechanical design still based on the same principle over 60 years. All wires are winded in a circular pattern and around a laminated metal to minimize the Eddy current. The electronic control was also introduced in the last 30 years to improvement the performance such as brushless DC motor; however, the improvement is limited comparing with the digital motor or ACT motor.

This is the time to revolutionary improvement for motor industry using modern digital control technology

II. ACT Motor Technology

Digital motor or ACT motor is a variable speed and variable torque with high efficiency motor system. The motor system can be operated at a wide range of speeds and torques with high efficiency. The system consists of the mechanical motor and the control units. The description for each unit is as the followings:

  •  Mechanical Motor Unit:

The motor mechanical design consists of rotor with permanent magnets and the wire winding in the stator. The rotor can be single or double rotors for each motor depending on the power requirement. The double rotors can provide the best efficiency motor. Strongest permanent magnets made by neodymium are used in the rotor. Three phase copper wires are wound in the longitudinal direction in the stator. S shape winding pattern instead of circular pattern is used to ensure all 3 vectors, current, magnetic flux and the moving direction, are all orthogonal at all time. This winding pattern can also maintain the power factor to be close to 1. No laminating steel is used in the stator to eliminate all Eddly currents and magnetic loss. This motor device is US patented. There is no brush and no hall sensor or encoder required. The only moving parts are the bearing and rotor. Therefore, the motor is reliable and easy to maintain for long lasting life.

Digital Motor wire winding

The major innovative design for digital motor is in the wires winding. In the conventional motor, all wires are wound around laminated silicon steel in a circular pattern. This is because the silicon steel is the best magnetic conductor such that the magnetic force can be concentrate at center position. In contrast the digital motor wires winding in fact achieve the following functions:

 

  1. Three vectors; magnetic flux, wire direction or current direction and the motor moving directions are orthogonal for all positions. From Maxwell equation the force equals cross product of the current and the magnetic flux. The cross product of two vectors is maximum when the vectors are orthogonal. This means that this winding confutation can provide the maximum force for a given magnetic flux and current.
  2. The wires are wound in S pattern instead of circular pattern; this will result in the minimum amount of copper wire. As we know all wires have resistance and can generate heat. The less wire will generate less heat. Also, the inductance for S pattern winding is about one tenth of the inductance of the circular pattern for the same amount of wire. The less inductance means higher power factor. The higher power factor means better efficiency.
  3. No conducting material except wires in the stator. This means that we totally eliminate all eddy current and magnetic loss. Therefore, the digital motor achieves high efficiency.

 

These design functionality are US patented with patent number US7,687,959. In fact, these are the major reasons that digital motor can achieve much higher efficiency comparing with all motors in the markets.

  • Digital Control Unit:

The digital control unit consists of DSP and driver boards. DSP board is the low voltage system with CPU, control inputs in both switches and turning nub or paddle and RS232 output. The output can display RPM, power level and number of revolutions (or going range). CAN bus and category 5 communication port are also in placed for central control of the multiple systems. The driver board is a high voltage and high current system and capable to deliver high power to drive the motor. The control software is developed to optimize the current injection for 3 phases in close loop to achieve the high efficiency.  Zero crossing detection for the motor wires is used for the close loop feedback. No additional sensor is required. The control unit is able to drive the motor from very low speed such as 100 RPM to the maximum speed of 3,000 rpm or more depending on the DC voltage provided. All necessary protections are build-in such as power isolation between 2 boards and over current protection. If the motor overloaded and cause the motor stop, the controller will automatically stop to prevent burning the motor. Due to its “smart” functionality of the controller, it is perfect ok to select the large power rating motor to operate at lower load. For instant, you can use a 5HP rated motor to perform any task under 5HP. In fact, it will provide even higher efficiency while it works at lower load. It is contrast to all other motors in the markets.

 

2.1 Comparing with all motors in the markets

Induction motor is widely used in our daily life. The principle of the induction motor is to create a rotating magnetic field in the stator by coils such that an induced voltage will be generated in the rotor. Since the rotor is a close loop circuit, the induced current is form by the induced voltage. The induced current in the rotor in fact will cause the rotor rotated. Therefor there are always two currents running against each other to create force. The more current will generate more heat. Brushless DC motor using permanent magnets in the rotor and wire winding in the stator to produce proper magnetic field to produce the rotational force. In summary the following is the table comparing the digital motor with brushless DC motor and induction motor.

The following is the comparison table:

  Digital Motor Brushless DC motor AC induction motor
Speed Control 0 to the maximum speed with very accurate controlled Only for higher speed and not very accurate Need VFD (Variable Frequency Driver) to change the speed. Need encoder to do speed control
Delivered torque Response to the load instantly with no speed reduction Speed will slow down Torque is limited at low speed
Efficiency 90 to 95% range in wide range of speeds and torques. Close to 100% at no load or little load. 80% for the design speed and torque. Drop to 50% for lower speed and torque.

 

Up to 90% for large horse power 70 to 80% for small horse power at a design speed and torque. It goes down to 40% at lower speed and torque.
Turning direction Both directions. No need switch wires. Only one direction. Switch wire to run reverse direction. Need to switch wires to run reverse direction.
Power factor Very high close to 1 Relative low in 0.8 range Very low in 0.7 range
Size and weight Smaller and less weight, 25lbs for 5HP Larger and heavier, 40lbs for 5HP Heavier about 85lbs for 5HP

 

II Prototype D150 Motor

 

D150 is a prototype motor. The rotor is a 6” (about 150mm) in diameter built by steel tube and 5” in length. Double rotor is used with 24 neodymium magnets on each rotor. Eight 26 gauge copper wires are used for the stator winding. There are 3 phases with 6 wire leads which are connected to the control unit. The total weight of the motor is 20 lbs.

 

Fig 1  Performance Chart for D150 motor

 

From Fig 1, if we operate the D150 motor at 3000 rpm with 1.242 NM torques or 390 watt mechanical powers the efficiency is 95%. If we operate the same motor at the same speed but higher torque of 2.62 NM or 823 watt, the efficiency will be reduced to 90%. At the same speed for a loading of 4.16 NM or power 1308 watt (almost 2 Hp), the efficiency is 85%. It is still much better than NEMA design B requirement of 78.8%.

For any given speed and torque we always can design a digital motor which gives 95% or better efficiency. It is the trade off the size of the motor and efficiency. For a given digital motor design it can operate at much wider speed and torques plane. Since it is the close loop control, the energy consumption is always optimized to response the mechanical load automatically until it exceeds the physical limits.

 

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