DC motor types and it's features

 

Electric motors are fundamental machines that transform electrical energy into mechanical energy, finding applications across numerous sectors like home appliances, robotics, pumps, and increasingly in electric vehicles (EVs). Among the types, DC motors, short for "direct current," stand out. These motors are ubiquitous, powering everything from power tools to toys. Within the realm of DC motors, there's a division between brushed and brushless variants, each with its unique characteristics and applications. Brushed motors rely on physical brushes to transmit electrical current to the rotor, while brushless motors use electronic commutation for more efficient operation and reduced maintenance requirements. This diversity in electric motor technology underscores its importance and adaptability in modern industries.

Brushed DC motors

The physical contact between the brushes and commutator in brushed motors causes wear and tear on both components over time. Additionally, the process of making and breaking electrical contact between the brush and commutator generates sparks, leading to electrical noise and potential safety hazards. Furthermore, the friction between these parts generates mechanical noise, contributing to the overall operational noise of the motor. These factors underscore the drawbacks of brushed DC motors and highlight the advantages of brushless alternatives in terms of efficiency, durability, and reduced noise.

Brushed DC motors can be further classified into two main types: permanent magnet motors and electromagnet motors, each with distinct characteristics. 

Permanent magnet motors utilize a fixed magnet within the rotor, which interacts with the electromagnetic field generated by the stator to produce motion. These motors are known for their simplicity, compactness, and high efficiency.

On the other hand, electromagnet motors rely on an electromagnet in the rotor, which is energized by the electrical current flowing through the brushes and commutator. These motors offer greater control over the magnetic field and torque, making them suitable for applications requiring variable speed and precise control.

Understanding the differences between these two types of brushed DC motors allows for informed selection based on specific application requirements and performance criteria.

Permanent magnet brushed DC motors

Permanent magnets have the remarkable property of retaining their magnetism over an extended period without relying on external magnetic fields or electrical currents. When permanent magnets are integrated into the stator of a brushed DC motor, it creates what's known as a permanent magnet brushed DC motor. These motors benefit from the inherent magnetic field provided by the permanent magnets in the stator, simplifying the motor's construction and improving its efficiency and reliability. By leveraging this magnetic field, permanent magnet brushed DC motors offer robust performance in various applications.

Permanent magnet synchronous motors (PMSMs) are a type of AC motor distinguished by the use of permanent magnets integrated into or mounted on the motor rotor surface to generate a magnetic field. These magnets, often made of neodymium iron boron, possess exceptional magnetic properties, such as high magnetic field intensity per square centimeter, earning them the moniker "super magnets" or "powerful magnets."

In the realm of electric vehicles (EVs), PMSMs are highly favored for their remarkable torque density and efficiency. Their compact size belies their robust performance, owing to the concentrated magnetic field generated by the neodymium iron boron magnets. This high magnetic field density not only enhances motor strength but also contributes to improved efficiency, crucial for maximizing the range and performance of EVs.

Beyond the automotive sector, permanent magnet motors find widespread use in various applications, including auxiliary automotive motors, model cars, boats, and more. These motors can further be categorized based on rotor design, with options such as slotted, slotless, and coreless configurations, each offering unique benefits in terms of efficiency, power density, and performance characteristics. This diversity underscores the adaptability and versatility of permanent magnet motors across different industries and applications.

The exceptional efficiency and magnetic field density of permanent magnet motors enable them to achieve comparable performance with traditional motors while being significantly smaller. This compactness is particularly advantageous in applications where space is limited or weight reduction is crucial, such as in electric vehicles (EVs), where smaller motors contribute to improved overall vehicle efficiency and range.

Furthermore, the high efficiency of permanent magnet motors translates to reduced energy consumption in EVs, a critical factor in extending battery life and maximizing driving range. By minimizing energy loss during operation, these motors help optimize the performance and efficiency of electric propulsion systems.

Additionally, the long magnetic life of super magnets, which can last up to around 400 years, ensures sustained efficiency and reliability over extended periods. This longevity contributes to the durability and longevity of permanent magnet motors, making them a reliable choice for various applications, including EVs and renewable energy systems.

Overall, the combination of compact size, high efficiency, and long-term reliability makes permanent magnet motors a compelling choice for modern electric propulsion systems, offering significant advantages in performance, energy efficiency, and sustainability.

Permanent magnet motors can be divided into two types: Interior Permanent Magnet Motors (IPM) and Surface Permanent Magnet Motors (SPM). Both types generate magnetic flux by fixing permanent magnets on or inside the rotor. Surface permanent magnet motors attach magnets to the external surface of the rotor, while interior permanent magnet motors embed magnets inside the rotor. These will explained later on.

Electromagnet brushed DC motors

An electromagnet is made up of a core of magnetic material around which is wound a coil of wire. An electromagnet only becomes magnetized when a current is passed through the coil. Electromagnet brushed DC motors use an electromagnet to generate their magnetic flux.

Electromagnet motors are divided into shunt motors, series motors, or separately excited motors depending upon how the rotor winding and field winding are connected together. In terms of motor output, these configurations are used in mid-range to heavy-duty motors.

　

Brushless DC (BLDC) motors

Brushless DC motors feature longer life and more efficient operation than their brushed counterparts. Brushless DC motors require a drive circuit (driver) that works by detecting the magnetic orientation of the rotor and supplying current to the winding accordingly. Because this drive circuit causes the motor to turn, brushless DC motors do not require a commutator and brushes.

This lack of a commutator and brushes avoids the need for maintenance and gives brushless motors a longer life. Recent years have seen the development of a wide variety of mechanisms that use brushless DC motors, especially in the automotive industry as well as in home appliances and precision machinery. Brushless DC motors that use permanent magnets in the rotor are called permanent magnet brushless DC motors (PM motors) or permanent-magnet synchronous motors.

Brushless DC motors are used in a wide range of applications and can be divided into the following types based on how the permanent magnet is fitted into the rotor.

        ·      SPM motors: The permanent magnets are attached to the side surface of the rotor.

        ·      IPM motors: The permanent magnets are embedded in the interior of the rotor.

The embedded magnets of IPM motors make them mechanically safer than SPM motors and capable of faster speeds.

The two types of motors have the following characteristics.

SPM: Surface permanent magnet

SPM motors have permanent magnets attached to the surface of the rotor. Surface permanent magnet motors fix magnets to the rotor’s surface, and their mechanical strength is lower, limiting the motor’s maximum safe mechanical speed. Additionally, regardless of the rotor’s position, the measured inductance values at the rotor terminals remain consistent. So, surface permanent magnet motor design largely relies on the magnetic torque component to generate torque.

IPM: Interior permanent magnet

IPM motors are a type of permanent-magnet synchronous motor (PMSM). They are rotating field motors that have permanent magnets embedded inside the rotor. Interior permanent magnet motors embed magnets inside the rotor, offering better mechanical performance and suitability for high-speed operation. These motors also have a relatively higher Lq/Ld ratio. Because of this, interior permanent magnet motors can generate torque by utilizing both magnetic torque and reluctance torque, adapting to various electric vehicle requirements.

For example, IPM motors are used in hybrid and full electric vehicles. These high-performance motors are able to operate over a wide range of speeds, allowing them to match the high speed of a vehicle engine.

SPM and IPM for inner-rotor BLDC motor

The Objective of IPM and SPM

For high-speed applications like traction motors, interior permanent magnet motors are the optimal choice, using fewer magnet materials and achieving a certain degree of torque. In addition to magnetic torque, these motors use reluctance torque to achieve high torque, responding to the rotation of high-speed motors through vector control.

Simultaneously, by better controlling the magnetization of the magnetic path, interior permanent magnet motors can operate efficiently over a wide speed range. Mechanical reliability is also improved, as magnets do not detach due to centrifugal force, and the rotor is more robust. Under the same power, interior permanent magnet motors can save 30% of energy consumption.

DC motors are found in a wide range of applications

DC motors are found in many different applications, not just in daily life, but also in offices and factories. Examples from the home include refrigerators and water heaters, also fans and other air conditioning systems. Commercial uses include copiers and printers as well as the ATMs operated by banks.

These are just some of the many areas of our daily lives in which DC motors are found, with other examples including vehicles, medical and measurement equipment, and residential building systems for things like ventilation.

The Influence of Hybrid and Electric Vehicles in the Industry

The major advantage of interior permanent magnet motors lies in their high-speed performance, making them particularly advantageous in the applications of vehicles. On the other hand, the power-speed curve of surface permanent magnet motors roughly forms a hyperbolic shape, gradually rising to a quasi-constant power region within a narrow speed range and then decreasing.

For decades, surface permanent magnet motors have dominated the permanent magnet motor market. However, the rise of hybrid and electric vehicles in recent years has driven an increased demand for interior permanent magnet motors. Interior permanent magnet motors exhibit constant power over a wider speed range and offer good solutions for applications like traction and auxiliary motors.

In vehicle applications, interior permanent magnet motors have distinct advantages over surface permanent magnet motors. The design of interior permanent magnet motors allows better control of magnetic path magnetization. They can provide a larger range or more consistent torque, and through a technique, designers can change their performance by applying current. The technique mainly involves adjusting the stator magnetic field to partially counteract the influence of the permanent magnet.