What is an EC motor?
Electronically commutated (EC) motors are designed to run on alternating current (AC) power, but they are actually more similar to direct current (DC) motors. They are essentially permanent magnet brushless DC motors with integrated onboard electronics.
The added electronics allow EC motors to combine the best characteristics of AC and DC motors and then improve them. Therefore, EC motors are in a class of their own.
By utilizing this technology, EC fans are highly efficient and pay for themselves through lower operating costs and longer life. They also offer some operational advantages that are often overlooked.
Motor Design
inner rotor and outer rotor
Electric motors come in many shapes and sizes, with the traditional style being an inner rotor configuration. The stator (stationary part) of an inner rotor motor is fixed to the motor housing. The rotor (rotating part) is located inside the stator and transmits torque through the output shaft. A fan impeller is usually attached to a rotating shaft.
Outer rotor motors are basically the opposite direction, with the rotor spinning outside the stator. This eliminates the need for an output shaft and greatly reduces the overall footprint of the motor and impeller assembly. The fan impeller can be attached directly to the outer rotor, effectively forming a motorized impeller.
AC vs. DC vs. EC
All electric motors have the same function of converting electrical energy into mechanical energy, but do it differently. The method used depends largely on the power supplied to the motor, as this affects how its magnetic field is generated and controlled. Therefore, motors are usually classified as AC, DC or EC. In the fan industry, AC induction motors, DC brush motors, and EC permanent magnet motors are commonly used.
AC induction motors have electrical windings in the stator that provide alternating current to create a rotating magnetic field. The stator magnetic field induces a current in the conductive squirrel-cage rotor, and the interaction between the two fields generates torque on the rotor.
Since the line frequency is fixed, AC motors have a limited speed range, so they are designed to operate at the peak efficiency point on the performance curve.
Beyond this range, efficiency tends to drop significantly. Variable frequency drives (VFDs) can be used to increase or decrease the frequency of AC power, but they tend to be bulky and expensive. This is why AC motors are best suited for applications that do not require variable speed.
DC brushed motors use permanent magnets in the stator to provide a fixed magnetic field. Electrical windings in the rotor induce voltages and are affected by the stator's magnetic field. Changing the supply voltage can make speed control easier for DC motors than for AC motors.
Since they run on DC, they rely on carbon brushes and commutator rings to switch the direction of the current. Wear of these mechanical parts results in louder running noise and shorter life expectancy. Also, DC power supplies are not as common as they used to be, so buying a separate AC-to-DC rectifier means added cost and complexity.
EC motors use permanent magnets and electrical windings to generate a magnetic field in a manner similar to a brushed DC motor. However, as the name suggests, they are electronically commutated rather than mechanically commutated. This is only possible by integrating the on-board electronics into the housing of the EC motor.
On-board electronics include a rectifier that converts AC to DC. An integrated controller then directs the correct amount of current through each winding in the correct direction at the correct time. This creates magnetic poles in the stator, which interact with permanent magnets in the rotor. The position of each magnet is determined by using Hall effect sensors. Suitable magnets are in turn attracted to the poles of the stator. At the same time, the remaining stator windings are charged with reverse polarity. These attractive and repulsive forces combine to achieve rotation and generate optimal torque. Since this is all done electronically, precise motor monitoring and control is possible.
Advantages of EC motors
energy efficiency
EC motors are typically more than 90% efficient compared to traditional fans, reducing EC fan energy consumption by up to 70%.
By adjusting the speed of EC motors to meet demand, the potential for energy savings continues to grow. Shown below are typical efficiencies for a 5 HP, 1800 RPM AC induction motor and equivalent EC motors.
Even compared to on/off operation, the speed modulation provided by EC fans is much more efficient. For example, running an EC fan 80% of the time saves 20% energy, while running it at 80% speed saves nearly 50% energy.
This is only possible with EC technology, which offers very high efficiency across a wide range of speeds. The most obvious benefit of high efficiency is reduced energy consumption. With energy prices rising, this is a key factor to consider. To give an overview of its importance, an example of energy saving at 50% speed is given below. This example assumes an average cost of $0.115/kWh, a variable frequency drive (VFD) efficiency of 86%, and continuous operation of the motor.
While the annual savings may seem negligible, it's important to note that this is for a single fan replacement and doesn't take into account other losses such as wires or belts. In addition to lower operating costs, another factor to consider is possible utility rebates. High efficiency also brings a series of secondary and tertiary benefits, as shown in the figure below.
One of the benefits of high efficiency is reduced energy loss to the environment. These losses usually come in the form of heat and sound. Since EC motors generate less heat, their windings and bearings are under less stress, extending the life of the motor. The lower operating temperature also contributes to higher system efficiency when used in cooling applications. At the same time, quieter operation improves occupant comfort.
Easy to Control
The high efficiency of EC motors is mainly due to the integrated electronics. Efficiency is maintained throughout the entire operable speed range by continuously monitoring motor function and automatically adjusting control inputs. EC motors are typically capable of turning down to 20% of full speed while still maintaining 85% efficiency.
Sensors that generate 0-10 V, PWM or 4-20 mA signals can be connected directly to most EC motors. This provides speed control without the need for complex variable frequency drives (VFDs).
Depending on the application, open-loop and closed-loop control methods can be implemented. Fans with EC motors can control temperature, pressure or choose any parameter to be measured. Constant pressure control is especially useful for pipeline applications, while constant air flow control is ideal for filtration applications. Alternatively, a potentiometer can be connected to provide a manual form of variable speed control.
Versatility
The maximum speed of conventional AC induction motors is limited to a standard rating called synchronous speed. This is a theoretical speed based on the number of electromagnetic poles and the frequency of the power supply.
EC motors, on the other hand, are capable of exceeding rated speed. This enables fans with EC motors to achieve higher capacities in smaller fan packages, as shown below. The extended operating range of EC fans makes it easy to match the performance of a given application. The high capacity of an EC motor combined with the ability to maintain efficiency at part loads enables one EC fan to replace conventional fans of many types and sizes.
Application of EC Motor for Air Conditioning
In everyone's impression, air conditioners always need a lot of electricity, this is because the air conditioner motor needs a lot of electricity to run. Therefore, for a long time, the upgrading direction of air conditioners lies in the research of air conditioner motors. "EC motor" has become an important direction for upgrading the product structure of air-conditioning motors. We not only have EC motors for air conditioners, but also EC motors for air coolers, EC motors for external rotor fans.
The main driving structure of a EC motor is composed of a drive and a motor; our brushless DC motors generally have a power of 50W-4000W and a voltage of 220V/380V.
Advantages of brushless motors in applications:
1. a wider range of flat speeds can be achieved. Brushless DC motors are easier to control and have a wider speed range. It is a real stepless speed regulation system, which can freely adjust the cooling capacity output of the refrigeration system.
2. In the process of speed regulation, the nature of the load in the motor circuit does not change, less harmonics are generated, less impact on the power grid, and more energy-saving.
3. During operation, the temperature rise is relatively low, which is about 20% lower than that of AC asynchronous motor frequency control.
4. The speed control system has high reliability and good dynamic performance. The EC motor has high reliability and does not change the circuit performance of the load during the adjustment process, making the system more stable.
From the characteristics of brushless motors, it can be seen that energy saving, noise reduction, precise temperature regulation, and stepless speed regulation are important performance improvements for refrigeration systems.
