Bringing BLDC designs to market faster
01 December 2021
PI BridgeSwitch RDK
Electric motors are currently the largest consumers of electricity in the world by a large margin: indeed, the Energy Research Centre of the Netherlands (ECN) estimates that 45% of all electricity generated globally is consumed by electric motors. Therefore, as part of the push towards higher energy efficiency, legislation is being introduced to raise the required efficiency of motors.
This full version of this article was originally featured in the December 2021 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.
Here, Cristian Ionescu-Catrina, Senior Product Marketing Manager at specialist in integrated circuits (ICs) for energy-efficient power conversion, Power Integrations (PI) discusses how brushless DC (BLDC) motors can help address this need – and how PI can help engineers bring BLDC designs to market faster…
In July 2021, the EU implemented its “Regulation on electric motors & variable speed drivers (EU) 2019/1781” to add a minimum efficiency limit on some motors that were previously excluded from the standard, as well as reduce the time allowed for other types of motors to come into line with efficiency requirements. The trend shown by such regulations is obvious: the minimum permitted efficiency will keep increasing over time. New motor designs should therefore be made as efficient as possible to negate the risk of legislated replacement before their operational lifetime is over.
A wide variety of motors are covered by these laws, from the large motors found in infrastructure pumps to the tiny motors that power PC fans. Size is not the only consideration – the type of motor also matters. Previously, brushed DC motors were widely used, but they were relatively inefficient with limited reliability – the brushes would wear down over time and require replacement. The need for higher efficiency and increased reliability over a wide variety of operating speeds and loads has resulted in brushless DC (BLDC) motors becoming widely adopted for new designs.
BLDC motors eliminate the need for the physical contact between the brush and commutator. This one step eliminates the mechanical losses caused by friction and makes BLDC motors more suitable for long-term deployment. Since the rotor does not need to be powered, brushes and slip rings are eliminated, along with the commutator assembly, simplifying construction. This also allows BLDC motors to output more torque per watt than a brushed DC motor, in a much smaller package. BLDC motors use a permanent magnet as a rotor, which interacts with the electromagnetic fields generated by the stator coils. These coils are turned on and off in a precise pattern to ensure the rotor turns efficiently. This pattern is determined by a microcontroller (MCU) algorithm and uses sensors embedded in the motor to provide real-time feedback for accurate control. The microcontroller sends signals to switches controlling the current through the coils. Although MCU control adds some increased complexity to the motor driver, it provides a greater degree of flexibility and precision.
As legislation concerning motor efficiency targets the operation of the whole motor assembly, each stage must be made to operate optimally to minimise overall losses. This includes the inverter used to supply power to the motor. The inverter’s performance is limited by heat. In addition to reducing the operational life of the inverter, poor thermal performance stops it from delivering sufficient current to the motor drive when the driver is overheated. The typical solution to thermal problems is to use a heat sink, or an auxiliary fan in some cases. Neither solution is ideal. Both are bulky, which negates the advantage of having a smaller motor, and both lead to higher BOM (bill of materials) count, increased design complexity and a less mechanically robust design.
BLCD motor [shutterstock_1281511474]
Power Integrations (PI), with extensive experience in developing highly integrated high-voltage ICs for offline power conversion and gate driving, tackles this problem from two different directions. The first is to provide an efficient architecture that minimises the heat dissipated. The second is to separate the phase drivers into individual ICs to provide a scalable solution that is flexible enough to support single-phase and multi-phase motors. The small amount of heat generated from losses in each driver is spread across the PCB (printed circuit board), rather than concentrated in a single hotspot.
The result is its BridgeSwitch™ family of integrated half-bridge (IHB) motor drivers, suitable to drive synchronous motors (BLDC or permanent magnet synchronous motors (PMSM)), as well as asynchronous motors (for example, AC induction). BridgeSwitch devices can be up to 98.5% efficient and are intended for inverter designs ranging from 30 W (typical I RMS = 0.2 A) to 400 W (typical I RMS = 1.1 A). BridgeSwitch ICs incorporate the low- and high-side drivers, a controller, a level shifter and two N-channel 600 V fast-recovery epitaxial-diode FETs (FREDFETs), with integrated lossless current sensing. FREDFETs have extremely fast recovery body diodes, making them ideal for driving inductive loads. They offer a significant reduction in switching losses, as well as a soft-recovery characteristic to reduce EMI (electromagnetic interference).
BridgeSwitch ICs are self-powered, which allows the use of a simpler system power supply (such as PI’s LinkSwitch™-TN2) to drive the microcontroller. A small non-isolated driver can be used, rather than the multi-output isolated flyback seen in conventional designs, further reducing the BOM, design complexity and board space. Built-in inverter diagnostics reduce the number of sensors required and the MCU processing overhead. BridgeSwitch ICs incorporate many hardware-based fault protection and external system-level monitoring functions. This hardware implementation not only provides a faster response than software protection, but also makes it much easier to gain UL/IEC 60730 approval due to the architecture’s hard-wired, cycle-by-cycle, low- and high-side overcurrent protection and onboard monitoring. The hardware implementation of these features means software requirements to meet UL/IEC 60730 are reduced from Class B to Class A, eliminating the need to recertify after software updates.
To allow designs to get to market even more quickly, PI has also developed several BLDC reference design kits (RDKs) for the BridgeSwitch family. The new reference designs provide up to 400 W output power without requiring a heatsink, and support applications with higher RMS currents in thermally challenging environments, such as compressors, range hoods, and residential and commercial fans and pumps.
To further simplify the design process, PI has introduced Motor-Expert™, a motor control configuration and diagnostics application which provides a graphical user interface for all parameters and commands, as well as a terminal emulator for interacting with the motor controller in serial mode. A Motion Scope feature provides linear graphs of important controller variables, viewable in real time.
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