Dear friends, today we propose to review BLDC and PMS motors (PMSM) and understand the difference between them, so let's go!
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To begin with, let's take a look at each of them separately, and the first in line is the Brushless DC motor (BLDC motor):
Pic. 1 ' BLDC motor structure
A BLDC motor is an upgraded version of a brushed DC Motor. The absence of brushes gives BLDC motors the ability to rotate at high-speed and increased efficiency.
Construction of the BLDC motor says that the permanent magnet acts as a rotating part of the motor called the rotor & the stationary part of the motor is made of coil windings called the stator. The BLDC motor is working on the Lorentz principle which states that whenever we place a current-carrying conductor in a magnetic field it experiences a force. The current-carrying conductor is the stator's coil so the PM rotor experiences force and starts rotating. Stator windings in a trapezoidal manner so DC current is required to run the motor. Hence, the motor will generate trapezoidal back electromotive force (EMF) & produce torque repulsion.
Pic. 2 ' PMSM vs. BLDC diagrams
Permanent Magnet Synchronous Motor (PMSM):
Moving on to the PMSM, it can be seen as an AC counterpart of the Brushless DC motor.
PMSM also comprises a permanent magnet as a Rotor and a Stator with a Coil wound over it. Blauberg Motoren EC motors are classified as PMSM.
Pic. 3 ' PMSM structure
The working principle of PMSM is the same as a synchronous motor, when stator windings are energized, a rotating magnetic field is produced & EMF created rotor is affected by this force and starts rotating at synchronous speed.
The difference is the coil wound over the stator and it is in a sinusoidal manner. So, AC current is required to run the motor. Hence, the motor will generate sinusoidal back EMF & produce low torque repulsion.
Due to low torque repulsion, PMSM got higher and smooth torque with higher efficiency and low noise compared to BLDC motor. PMSM has a higher power density, which will help in reducing the size of the motor. That's why PMSM is better than BLDC motors in terms of performance.
So, let's summarize:
Differences in design and operating principles:
BLDC motors: Characterized by a three-phase stator and a permanent magnet attached to the rotor, BLDC motors generate torque by means of a six-step sequence of current delivery to the stator.
PMSM: With the same configuration of a three-phase stator and rotor magnet, PMSM, unlike BLDC, uses a sinusoidal power supply to generate torque.
Various output current profiles:
BLDC motors: Output a rectangular (or trapezoidal) current profile.
PMSM: Displays a sinusoidal current profile, which contributes to smoother performance.
Long life, reliability, and application options:
BLDC and PMSM have a long service life due to the absence of mechanical brushes.
BLDC motors: Find a niche in industries requiring high speeds and moderate control accuracy, such as fans and pumps.
PMSM: Ideal for applications requiring high control accuracy and high power density. They have proven themselves in the automotive, aerospace, and other industries that require high precision.
Efficiency analysis:
BLDC motors: Demonstrate commendable efficiency at higher speeds.
PMSM: Typically demonstrate high efficiency at low speeds and maintain it flawlessly even at high speeds.
Control dynamics:
BLDC motors: Often considered easier to control because they do not depend on a sinusoidal power supply.
PMSM: Can incorporate more complicated control techniques, especially when integrated with a sine wave driver.
Essentially, both BLDC and PMSM have distinct advantages and disadvantages. The optimal choice between these two motor types depends on the specific application and the unique features of your system, and we can assure you that PMS motors from Blauberg Motoren are the right and best choice!
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Electric motor efficiency has a significant impact on the industrial, consumer, and automotive sectors. Increased efficiency leads to lower greenhouse gas emissions through a reduction in power consumption and increased range between charges - for everything from EV's to your power tools. With electrification continuing to accelerate across our day-to-day living, many wonder what type of motor is best suited to meet these modern day demands.
Historically, the induction motor was the go-to motor design because it was readily available and is a longstanding, proven technology. However, the intrinsic design of the induction motor requiring a slip between rotor and stator will always limit efficiency. With recent advances in permanent magnet materials (energy density), and manufacturing, today's permanent magnet motor designs take performance and energy efficiency usage to new levels not possible with the induction design.
Let's take a deeper dive into both motor designs which then supports the choice of a permanent magnet design over that of the induction motor design. Equally important, understanding how Soft Magnetic Composites (SMC) can transform not only the traditional radial flux design, but new topologies that are driving tomorrows designs and performance levels with reduced heat generation and a more efficient use of copper and magnet material.
Here are a few things to consider when exploring induction vs. permanent magnet motors:
Permanent Magnet Motor vs. Induction Motor Efficiency
The figure below shows the general layout of both the Permanent Magnet motor (on the left) and the induction motor (on the right). In the permanent magnet design, the rotor contains a series of magnets either internal or external to the OD of the rotor. The stator is wound with copper wire creating a magnetic field that interacts with the rotors permanent magnets resulting in rotation and torque. Compare this to the induction motor where rotor and stator are traditionally stamped lamination steel with the motor windings only on the stator which induces an opposing magnetic field in the rotor. This interaction results in rotational torque.
(Comparison of AC induction motor design vs. permanent magnet motor)
Modern high torque motors whether permanent magnet or induction design use three-phase applied current. The three-phase design offers inherently better efficiency and is also self-starting. If the motor is designed to operate at a fixed rotational speed, then the number of stator poles can be adjusted to give the desired speed at the typical fixed frequency of 50 or 60 Hz. For these types of applications, the laminated induction motor is probably the most frequently chosen alternative. However, what if you want to have a variable speed motor? In this configuration, you would need to incorporate a variable frequency power supply to facilitate the variable speed. Although an induction motor would work, in this design, the permanent magnet design offers enhanced performance with greater flexibility.
The fine details of electric motor design are more complex than described below, but this is a great head start for those weighing their options between an induction and permanent magnet motor design.
Permanent Magnet Motor Efficiency
The inherent efficiency of a permanent magnet motor is higher than an induction motor ' eliminating the intrinsic lag of the applied and induced field. Permanent magnet motor run synchronously with the applied frequency - allowing the motor to operate at a speed set by the frequency drive. As you increase the frequency,'total losses in induction motors will be far greater than in permanent magnet motors ' having efficiencies up to 97.5%.
A 50 kW (about 70 HP) permanent motor typically'weighs less than 30 lbs. At any given frequency, the rotational speed of the permanent magnet motor is always greater than that of its induction counterpart due to the inherent slippage necessary in the induction design. The synchronous speed can be represented by the following equation:
Ns = 120 * frequency / pole count
(Ns is synchronous speed. Pole count is the total pole count per phase, including both the north and south poles)
Today, permanent magnet motors are used in applications and platforms such as - the Ford Mustang Mach-E, BMW, Ultium Platforms, Tesla, high efficiency variable frequency HVAC motors, battery powered hand tools and drones...Did you spot the trend here ' everything that is battery powered or dependent upon high efficiency, is a 3 phase permanent magnet motor.
Induction Motors:
As noted earlier, an induction motor operates by the stator winding inducing an opposing current in the rotor (thus creating a magnetic field). That opposing field results in rotor rotation. The lag between the applied stator current and resultant rotor opposing field results in slippage between the applied field and rotation. The maximum speed of an induction motor is represented by the same equation as for the permanent magnet motor. However, inherent with induction is the requirement for slippage (asynchronous operation). As shown in the figure below, when the amount of slip in an induction motor approaches zero, the torque generated also goes to zero. Thus, it is impossible to operate an induction motor synchronously. For example, a two pole AC induction motor operating at 60 Hz will have a synchronous speed of RPM but there is typically a 5% loss in speed due to the slippage; thus, the maximum motor speed will be about / RPM. This intrinsic design characteristic limits the maximum efficiency of the induction motor to about 90- 93%.
The maximum efficiency of an induction motor is 90 / 93% whereas that of a permanent magnet motor is at 97% plus. Although a 4 to 7% improvement doesn't seem like a lot - imagine the cost of operation over a 10 year or more life span and that relatively small improvement in efficiency results in a considerable energy savings with reduced greenhouse gas emissions.
Remember when we mentioned a 50 kW (about 70 HP) permanent motor typically'weighs less than 30 lbs? Well, the weight of a typical 75 horsepower induction motor can exceed 500 pounds! Think of the implications this has for an automobile ' the weight reduction is significant and has a multiplying effect on the total weight of the vehicle.
Cost Vs. Performance
One major consideration in permanent magnet motors is'the cost of the magnets. If you've used high-energy magnets (such as iron neodymium boron), you've felt the pain in your budget (or your boss has). The potential waste of stamping the lamination material only compounds the problem.'
Opportunities for powder metallurgy are abundant in these types of motors. The rotors of a permanent magnet motor can be made via'sintered powder metal, regardless of whether you're taking the internal or external design route. The stator can also be produced via soft magnetic composites. At the'high switching frequencies'expected, the losses in SMCs are lower than that of laminated 3% silicon iron,'further improving the efficiency of this design. Simply put, soft magnetic composites are custom-built for high frequencies.
There's an opportunity for powdered metal to provide additional efficiency to a permanent magnet motor vs. an induction motor. The 3D shape-making capabilities of powder metallurgy'allow you to form the stator to totally encase all the wire in soft magnetic composite to eliminate end turn losses.
These are some of the many advantages that powder metal -- both sintered soft magnetic materials and SMCs -- offers.
Induction Vs. Permanent Magnet Motor Efficiency: The Winner Is...
The clear winner here is the permanent magnet motor. Now, couple the permanent magnet motor, with a unique topology enabled by Soft Magnetic Composite (SMC) technology and your motor will be lighter and more efficient, with a higher torque density and lower bill of material cost ' all while reducing supply chain complications and using a sustainable manufacturing process.
If you need help designing the components to fully leverage the full potential of powder metallurgy for an AC or DC magnetic applications, contact us and check out our resource hub:
(Editor's note: This article was originally published in April and was updated on November 29, and July 27, )
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