On the road to success with BLDC motors
25 September 2009
Brushless direct current motors are often referred to as ‘green motors’ because of their efficiency and therefore low power consumption. However, implementation of the activation electronics requires expert knowledge.
Brush-Less Direct Current motors (BLDC) or Electronically Commutated (EC) motors display exceptional efficiency, usually around 70% or more. In some BLDC motors with several hundred Watts of power, the fan specialist ebm-papst Mulfingen achieves up to 85% efficiency. Compared with traditional single-phase motors, also known as asynchronous motors, which generally demonstrate efficiency between approximately 40% and a maximum of 60%, BLDC motors offer enormous energy-saving potential. According to Helmut Lipp, Head of Electronics Development at ebm-papst, it is worth switching to direct current motors: “The additional expense for electronics motors is recovered relatively quickly by the end-user thanks to reduced power consumption. In most cases, the higher investment costs have been recovered within one year.”
Integration of electronics into the motor
Power electronics in which the circuit breakers are designed as MOFSETs or IGBTs are required in order to process the motor currents in such a way that the BLDC motor achieves the required torque. “ebm-papst’s objective is to integrate the motor electronics within the motor itself so that the buyer or end-user has no contact at all with the electronics”, explained Lipp. “Although in marketing terms the customer will be using a BLDC motor, it should be possible to connect the motor itself as easily as an alternating current motor used in the past.”
The reason behind this strategy is very simple: ebm-papst is aiming to directly replace the energy-wasting asynchronous motors in existing applications. With this approach, the company, which is based in Mulfingen, Germany, aims to dispel its customers’ reservations and unease related to electronics by making the electronically controlled direct current motor just as easy to connect as, for example, an asynchronous motor. For this reason, it is essential to accommodate the electronics in as little space as possible, thus requiring a high degree of integration. In the past, ebm-papst used individual activation components. However, these take up a relatively large amount of space on the circuit board and inside the fan element. In future, the fan specialist is to replace many of these with modules where the power components are integrated into the casing.
This advanced integration also leads to improved quality because fewer individual components are used. On the other hand, BLDC motors cost more than conventional uncontrolled motors. Nevertheless, using a BLDC motor within a system is often no more expensive than using a conventional alternating current motor, and can even be less expensive in a number of cases.
Control without extra expense
Changing the speed of a normal alternating current motor (single-phase motor, asynchronous machine) requires external electronics, e.g. in the form of a phase-controlled modulator or a frequency converter. A package of this kind, consisting of a conventional alternating current motor and the relevant electronics, is more expensive than an EC motor with integrated electronics as it does not involve cabling of any kind.
One advantage of the brushless motor is that extra expense for control and regulation is extremely low due to the fact that most of the necessary electronics are already available in the form of the motor’s commutation electronics, which are required in any case. As a result, the power components already form part of the BLDC activation while the digital control components, e.g. in the form of a microcontroller, cost no more than a few pence/cents. Therefore, the motor’s additional ‘intelligence’ is available at little extra cost. This dispenses with the need for the old AC motor regulation (phase-controlled modulation, etc.), which in turn causes the business model to change: with the previous technology, the user bought a motor and a control system. With the BLDC motor, the user only buys a motor. However, the motor can be controlled using the electronics which it needs anyway due to system-related properties.
Controlling air according to requirements
Normally, ebm-papst constructs complete ventilators as opposed to pure motors. The purpose of these ventilators is to vary the air-flow according to requirements: a greater flow is needed when it is warm in order to remove the heat from a system; less is required when it is cold. The air-flow is therefore regulated by means of a temperature sensor, for example. This sensor is either already integrated into the motor or directly connected to the motor for mobile use by means of a small external cable. As a result, the user only connects the power supply and an additional sensor, if necessary. Moreover, the electronics can provide the user with feedback regarding the speed at which the motor actually operates. This feedback may be given in the form of a defined number of pulses per minute or via a bus system such as CAN, LON, Modbus or ebm-Bus.
ebm-papst supplies fans for wafer fabs and gas blowers, blowers for residential ventilation etc., as well as fans for white goods (modern refrigerators contain EC motors), heating systems, air-conditioning systems (e.g. heat exchangers on supermarket roofs, chilled cabinets) and numerous other systems. These chilling cabinets usually contain only very small motors. In the past, most of these always used a shaded pole motor. In this case, there are even greater benefits to be gained from switching to a BLDC motor, as a shaded pole motor operates at only around 20% efficiency. The fact that ebm-papst is now replacing these motors with BLDC motors, with between 60% and 70% efficiency, creates enormous power-saving potential. However, since these shaded pole motors are extremely cheap or inexpensive, BLDC motors for such applications used to be much too expensive. As a result of high energy costs and the desire to save energy, EC motors are also gaining ground here while the electronics required to control the motor are also becoming less-and-less expensive.
Good both ecologically and economically
It was only following the introduction of electronically commutated motors into heating technology that system providers became aware of the enormous energy-saving potential provided by this technology: “Increasing efficiency from 40% to 80% can result in considerable energy savings in building technology, air-conditioning technology, ventilation technology, etc.”, explained Lipp. “As energy prices rose, BLDC technology also became increasingly interesting from an economic perspective. Some of our customers focus on the energy-saving in their advertising. Such customers generally approach us directly.”
Just as major PC microprocessor manufacturers carry out end-customer marketing to ensure that the consumer purchases a PC containing the ‘right’ processor, ebm-papst has also approached its end-customers: “We have informed purchasers within major supermarket chains that the additional costs for a chilling cabinet with electronically commutated motors can be recovered within as little as one year”,said Lipp. “This philosophy or marketing approach has proven to be successful in other areas too.”
EC motors not only for fans
In the course of time, end-consumers have also changed their thinking habits and many house owners are now aware of the fact that outdated heating pumps needlessly waste electricity. The use of electronically commutated heating pumps with the appropriate efficiency regulation more or less doubles efficiency, thus halving energy consumption. End-customers can therefore easily calculate how quickly the costs of replacing old heating pumps, the majority of which are in the 60 W to 100 W output class, can be recovered.
As little as five years ago, no one was interested in heating pump energy consumption; now that has all changed. While the extra expense of the electronics for controlling a BLDC motor amounts to little more than €10 and an EC motor costs between 20% and 30% more than a simple alternating current motor, the sale of such a pump still provides an interesting margin because the green movement is currently good for marketing. Although ebm-papst does not produce heating pumps, this example illustrates the great potential connected with the use of electronically commutated direct current motors, even in applications other than ventilation technology.
ebm-papst provides BLDC motors for the range between 10 W and approximately 6 kW. Where motors in the lower output range are concerned, the pro-rata extra expense for the EC motor tends to be rather higher because certain absolutely essential passive components do not become significantly smaller upwards of a certain power class. For example, an EMC filter for a 1 A motor costs roughly the same as the corresponding component for a motor which only consumes 300 mA. Therefore, the extra expense for an electronically commutated motor at the lower power limit may approach 50%. While the extra expense for the electronics tends to be lower in the upper power class, an EC motor is always less expensive than an alternating current motor with a control system.
Operation of a direct current motor is usually louder than an alternating current motor because the rotor of a BLDC motor contains a permanent magnet with north-south transitions, which are noticeable at the transition to the stator and which are audible in the form of noise. This is also referred to as pole sensitivity.
For around five years, ebm-papst has been in possession of a technology allowing BLDC motors to be operated at the same noise level as normal asynchronous motors. As a result, electronically commutated BLDC motors do not need to suffer drawbacks in terms of noise. Here, the technology and expertise are located primarily in the software that specifies the signal form with which the current enters the coil.
With regard to noise, a regulated BDLC motor brings clear benefits compared to a regulated asynchronous motor. ebm-papst generally provides motors with a control input which, in most cases, determines the temperature. If the maximum cooling power is not required, the speed can be reduced. This automatically makes the motor quieter and reduces energy consumption. Two years ago, manufacturers would still have wanted politicians to become involved and provide relevant legislation. Now, the market regulates itself independently in this respect because companies wish to save energy.
ebm-papst achieved a real quantum leap by bringing noise under control. Another quantum leap was making the electronics small enough to be integrated into the motor. “In the past, the electronics were on the outside, which meant that the customer faced considerable expense in terms of cabling”, said Lipp. “As a result of miniaturising the electronics, achieved with EBV’s help, our customers now only have to connect a normal network cable.” Power semiconductors have become less expensive with time while considerable advances have been made in the field of microelectronics. Every BLDC motor now contains a microcontroller. Finally, the need to conserve energy has provided an additional boost.
A great benefit for ebm-papst is the fact that power modules are now also available for the lower power ranges. “As little as two years ago, ebm-papst was not aware of a suitable power module in the 100 W to 150 W range on the market because all these modules were only available for larger motors”, said Lipp. “As a result, the activation electronics for this lower power class had to be discreetly structured – a necessity which took up a lot of space and involved considerable expense. The fact that the FAE from EBV drew our attention to the new power modules, while also providing the necessary technical support, enabled us to implement the system in a much smaller installation space and at lower costs.” Lipp pointed out that ebm-papst always “received the necessary support at short notice” when technical problems occurred – both from EBV and, as in the case of the lower power range modules, Fairchild.
ebm-Papst now manufactures its products in such high numbers that new variants are also increasingly possible: the design for a customer-specific or application-specific ASIC, 100,000 elements of which are then produced each year. Lipp commented: “EBV now also supports product definition. For this purpose, EBV, ebm-papst and the semiconductor manufacturer jointly define a customer-specific or application-specific product. There are already numerous instances in which this type of co-operation has functioned perfectly.”
EMC and PFC
Compensatory EMC measures are absolutely essential due to the rapid activation and deactivation of the inductivities within the motor. These EMC filters are already integrated into the motors produced by ebm-Papst. The requirements regarding interference resistance and transient emissions are therefore fulfilled. As a result, ebm-papst delivers a genuine plug-and-play motor solution.
There is currently no active PFC for the smaller motors up to around 200 W. Only a passive switch for correcting the power factor is available. Nevertheless, Lipp is confident: “Active correction will also become available for smaller motors. In England, the idle currents already have to be paid for and the active PFC is already a matter of course for motors upwards of 250 W at ebm-papst.”
Stephan Hubert is a Regional Sales Manager for EBV Elektronik.
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