The development and innovation of new power systems in the industrial sector, electric motors, and relative control require discrete high-performance components. In recent years, the power electronics semiconductor market has seen
EVERYTHING IS “POWER”
Today, it is well known among the electronic power community that silicon carbide (SiC) and gallium-nitride (GaN) semiconductor materials show superior properties, allowing operations at higher voltages, higher temperatures and higher switching frequencies with respect to common silicon-based devices.
“We can see the market is clearly split into three segments” said Dave Dwelley, Chief Technology Officer at Maxim Integrated. “Each of these segments suits a different semiconductor material. The low voltage segment, roughly 50 volts and below, is well-suited to silicon devices. The advantages that III-V semiconductor types have, the GaNs and the SiCs and the gallium arsenides of the world, are overcome by either their cost structures, they’re just not made in the same volumes that silicon is made in, so they don’t have the same cost advantages, or by other technical concerns.
Gallium nitride is a good example, where the actual internal transistor is extremely high performance, but the conductors that get the current out of the transistor and onto the circuit board are not as good as with silicon.
At a very low voltage, these conductors become the dominant resistance and, as a result, GaN does not show advantages in performance. For voltages below 50 volts, silicon is the answer. For voltages between 50 and maybe 400 volts, we think that GaN proves to be a better option as that’s the region of operation where the parasitic effects don’t hurt as much, and GaN is rapidly getting a better cost structure. Then above about 500, 600, up to thousands of volts, silicon carbide has a very good story to tell.”
A factor that gives SiC an advantage in industrial systems is probably represented by the ability of the SiC to withstand the conditions of “avalanche,” as can happen with inductive loads, even with the values of GaN being improved.
The use of SiC devices in the context of motor control and electrical power control applications is currently representing a real moment of innovation, in particular for the automotive and industrial automation control.
The motor control IC also helps with the performance of various operations, such as selecting the forward or backward rotation of the motor, selecting and adjusting the speed, protecting against overloads, limiting or adjusting the torque and protecting against faults.
The automotive and transport industry should hold the largest market share in terms of number and value in servo motors and drives until 2022 due to the rapid changes in production technology, innovation, and technical progress. There is also a strong demand for servo drives, controllers and motors around the world, as they help companies improve production efficiency. Current technology for motor control involves the use of microelectronic devices to offer better control of speed, position, and torque, as well as greater efficiency.
For each type of motor there are piloting and speed and/or torque control techniques: ranging from simple control of voltage and current in DC and universal motors, to the use of inverters for AC motors, to the feedback switching of different phases in brushless motors, up to digital circuits for the complex stepper motor driving sequences (figure 1).
“Detecting stalls or overload conditions, or wringing every ounce of performance out of a motor without overheating or causing electrical damage are areas where we use a combination of a motor control powertrain, and a bit of intelligence to watch the motor. This ensures that the motor is behaving the way the application expects it to behave, and making sure nothing has gone wrong, requiring action to protect the circuitry or the motor.”
Power supply designers, battery management systems, and motorized drives often face the need to measure the current accurately. Current measurement is an integral part of power electronics. Current transducers (not to be confused with a current transformer) can measure both DC and AC currents. The most used technology for current transducers is the Closed Loop Hall Effect or Closed Loop Flux Gate. Typically, the power requirements are in the below 30 mA range regardless of the supply voltage.
“A hall sensor, or a current sensor using a resistive shunt, provide ways of detecting the current going into a motor – both DC and AC components of that current” as said by Dave. “Different motors and different strategies need different sensors. Current sensing that allows the controller to make a better choice as to what to do with the motor, that is where we see differentiation. Maxim’s strategy is based largely around resistive current sensing. We have several current sensing products aimed at that market, and as we build more and more sophisticated motor control devices, that functionality will be built into the motor driver. You’ll see more and more products like that coming.”
The design of any Hall effect detection device requires a magnetic system capable of responding to the physical parameter detected through an electronic input interface. The Hall effect sensor detects the magnetic field and produces an analog or digital signal suitably converted into a standard according to the requirements of the electronic system (figure 2).
The motor control activity is part of many industrial fields, in particular, that of the emerging electric vehicle market. “The thing that makes an electric vehicle unique is the traction motor, the electric traction motor. That traction motor needs two things. It needs the motor controller, and it needs a battery management system.” In many markets, energy efficiency and motor control are two elements or challenges for the proper functioning of the overall system.
When it comes to electric vehicles, perhaps we can consider energy harvesting. Recovering the energy dissipated by the vehicle during motion and braking is the concept behind energy harvesting on the road. Strong motivations support the affirmation of the electric car: first of all, the one concerning environmental compatibility, and secondly, but not of secondary importance, the one concerning functional simplicity and energy efficiency.
Functional simplicity is a consequence of the fact that the combustion engine is made up of hundreds of functional parts all interacting with each other and in motion, while the electric car engine consists only of the electric motor which is functionally the only propulsion component being in movement.
“Energy harvesting is an interesting area. It has tremendous applications in electronic space in general, but in vehicles, it’s somewhat more of a corner use case because when a vehicle is driving, it’s using a huge amount of energy. This is why the battery packs are so big. What that generally means, since the traction motor is using 90% of the energy, and the HVAC system is using almost all of the rest, the remaining functions in the car, it doesn’t matter how much energy they use, because there’s this gigantic battery down under the floorboards, between the seats.” As said by Dave.
The energy problem for the next generation systems will play a key role in making the application of microelectronic technologies particularly pervasive, such as sensor systems in the Internet of Things and even more so in the emerging “Internet of Everything effective”.
“The challenge is not just gathering the energy when the energy is available to be harvested, but also storing the energy in between those times, and then signaling the system when the energy storage finally runs out, so that when the energy does come back, it can wake up gracefully.”
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Maurizio Di Paolo Emilio is power electronics editor and European correspondent at AspenCore and editor of Power Electronics News.