1. Introduction

 

With the advancement of technology and the increase of electrical equipment as well as population growth in the last few decades, energy consumption has increased significantly, especially in the domestic sector. According to the energy balance sheet published by the Ministry of Energy, the consumption share of the household sector in 1400 is 32.2% of the country’s total consumption, which has increased by 7.5% in just one year compared to 2019.

 

About 65% of the electricity consumed in the domestic and industrial sectors belongs to electric motors, and increasing the efficiency and saving the electricity consumption of these types of equipment can have a significant impact on reducing the country’s electricity consumption. So the potential of reducing consumption and economic savings of electric motors used in European Union industries is estimated at 29% and in the United States at about 23%.

 

Electric motors used in the household sector are mainly single-phase induction types with very low efficiency, less than 50%. A large number of these motors cause significant energy losses in the home sector. Therefore, replacing low-efficiency engines with new high-efficiency engines is one of the ways to reduce energy consumption in this sector. On the other hand, in Iran, due to climate changes the increase in air temperature, and the widespread use of cooling and air conditioning equipment in the summer, the peak electricity consumption has been shifted to this season of the year, which has led to problems in the field of providing the required power. During the hot days of the year and as a result of the forced reduction of consumption and blackouts of several hours by the regional electricity companies, the country has become a region that has led to customer dissatisfaction and damages to the production and industrial sectors.

 

According to the analytical report of the water and energy field technology development headquarters, a major part of the power distribution network capacity in peak bar is dedicated to cooling equipment and devices, which has a share of about 35% of the summer peak bar consumption. According to the stated contents, to solve the network peak problem in summer, the most important solution is cooling peaking, with priority in the domestic sector. If it is possible to reduce only ten percent of the electricity consumption in this sector, there will be no need to increase the network capacity to compensate for the lack of electricity supply.

 

Considering the hot and dry climate of Iran, one of the most numerous and most consumed motors is the electric motor used in the water cooler. According to official statistics, about 17 million water cooler engines are active in the country, increasing efficiency and reducing energy consumption in these engines can lead to a 30-50% reduction in electricity consumption and thus freeing up a large part of the country’s power grid capacity in the summer season.

 

According to the stated statistics and materials, and as a result of the need to increase the efficiency in the country’s electricity consumption system, Electrogen Company, as the largest producer of cooling electric motors in the country, has also taken steps towards realizing this goal and since about 7 years ago, a study And it has started its research on the design and production of high-efficiency BLDC motors as well as high-efficiency induction motors with energy grade A to replace the usual cooler electric motors.

 

2- Introduction of BLDC motors

 

The theory of reduction machines is mentioned below. The new principles of modern single-phase electric induction motors were formed after Faraday discovered the phenomenon of electromagnetic induction in 1831, and the first DC motor was built in the 1840s. However, due to the limitation and lack of development of power electronic devices and permanent magnet materials, the successful design of the BLDC motor took place more than a century later. Harrison[1] and Ray[2] filed the first patent for a thyristor commutator circuit to replace mechanical commutator equipment in 1955, which was precisely the most primitive BLDC motor.

 

To create an alternating electromagnetic force and feed the stator conductors, it was necessary to generate the necessary signal to drive the corresponding thyristor. When the engine stopped, no current passed through the conductors and there was no starting torque. As a result, researchers introduced different commutators, and finally, after many tests, a brushless motor with electronic commutation using Hall effect sensors[3] was developed in 1962.

 

In general, brushless permanent magnet motors, or in the term BLDC, are a type of magnet and synchronous motors that use permanent magnets in their rotor structure, and their difference from other types of synchronous magnet motors, i.e. PMSM, is in the way these motors are controlled. Today, permanent magnet motors have been widely used in various industries such as the automotive, aerospace, and home equipment industries due to their advantages such as high efficiency, long life, low noise, and favorable torque-speed characteristics.

 

BLDC motor is one of the electric motors that can replace single-phase induction motors in the common water cooler system. These motors are developed based on DC motors, and in the ideal case, the waveform of the stator current is in the form of 6 bridges and a square, similar to the DC machine. with the difference that electronic commutation has replaced the usual mechanical commutation.

 

In a commutator DC motor, polarity reversal is done by the brushes. While in a BLDC motor, the mechanical brushes are removed and the commutation is done by a power electronics switching circuit using the angular position of the rotor.

 

3- BLDC motor structure

 

In its simplest form, a permanent magnet motor consists of a magnet that acts as a rotor. The stator of these motors is mostly wound in three phases. These coils are balanced and distributed in the stator with a location of 120 inserts relative to each other; so that each phase is energized sequentially. When the stator windings are fed from the power source, they become electromagnets and begin to coil They make a uniform field in the air distance. Although the power source is DC, the switching operation creates an AC voltage with a trapezoidal waveform. In a commutator DC motor, the current polarity is reversed by the brushes. While in a BLDC motor, the mechanical brushes are removed and the commutation is done by an electronic power switching circuit using the angular position of the rotor.

 

In BLDC motors, current passes through two-phase coils at any moment. The current flowing in each coil produces a magnetic field vector. By changing the coils according to Hall effect sensor signals and rotor position, the corresponding coil is activated as N and S poles. The structure of the rotor itself has permanent magnets and the N and S poles of the stator follow and cause the rotor to rotate.

 

In general, the torque in the BLDC motor is produced by the reaction of the magnetic field generated by the stator and the magnetic field of the rotor magnet. By controlling the current that flows in the three coils, a magnetic field can be produced in a specific direction and size by the stator, and as a result, the produced torque can be controlled. In general, the characteristics of the motor depend on the winding of the stator and the arrangement of the magnets in the rotor, and according to the combination of the number of poles and grooves, the induced voltage in each phase of the stator may have different harmonics and, as a result, different waveforms. Permanent magnet motors are divided into two types of motors with sinusoidal induction voltage and trapezoidal induction voltage based on the induced voltage waveform that goes back to the design.

 

4- Advantages and disadvantages of BLDC motors

 

BLDC motors, like any other product, have various advantages and disadvantages, among which the following can be mentioned:

 

High efficiency: among existing motors, BLDC motors have relatively high efficiency. The higher efficiency of this motor is mainly due to the existence of a permanent magnetic field in the rotor, which is a continuous and constant field and, unlike induction motors, does not cause copper loss in the rotor. Also, the removal of sweepers and gearboxes reduces friction and mechanical losses and thus increases efficiency.

 

No need for a gearbox: in BLDC motors, the torque of the machine is constant and maximum efficiency can be obtained in the design speed range, so there is no need for a gearbox.

 

Low noise: due to not needing any mechanical brush or slip ring in BLDC motors, all mechanical noises are eliminated except the noises related to bearings, couplings and load.

 

Less maintenance, longer reliability, and life: Mechanical brushes and slip rings are common sources of failure and uncertainty in DC motors. By removing these components in BLDC motors, the life of the motor depends on the life of insulation, bearings, and the life of magnetic materials, which will have a long life under suitable working conditions. Also, the gearbox is subject to wear and tear is a source of uncertainty, and requires maintenance. Removing it increases reliability.

 

Higher torque density: there is no field winding in BLDC motors, and therefore the necessary space for it is saved and reduces the overall size of the motor.

 

The following can be mentioned among their disadvantages:

 

The price of magnetic materials: the price of permanent magnet materials with higher energy density prevents their use in applications where the price and cost of using these materials is greater than the aforementioned benefits. For example, ceramic magnets, which have the lowest price among magnet materials, also have the lowest energy density. Neodymium magnets have the highest energy density and the price is about 3 times the price of ceramic magnets. Samarium-cobalt magnet materials have an acceptable energy density, but due to the higher working temperature, they are about 9 times more expensive than ceramic magnets.

 

Possibility of demagnetization: the maximum power of the BLDC motor is limited by heat. Too much heat reduces the flux density of magnets and may even cause them to be demagnetized.

 

[1] Harrison

[2] Rye

[3] Hall Effect Sensor