Cree, in order to reduce its dependence on the competitive lighting market, has expanded into power and RF products under its Wolfspeed brand. Wolfspeed currently produces advanced 150 mm epitaxial silicon carbide (SiC) wafers.
Engineers can leverage this capability to design high-power switching circuits and systems with energy-saving, size reduction, and reliability advantages not possible with commercially available silicon devices of comparable ratings.
Power MOSFETs
Cree has developed a silicon carbide power MOSFET that offers the blocking voltage necessary for fast switching required by today’s high-efficiency power converters. When coupled with their wide bandgap Schottky diodes, this allows designers to implement critical switching circuits using all-SiC components for solar inverters, industrial motor drives and PFC (power factor correction), boost and high frequency dc-dc power architectures with reduced switching losses of three times those achievable using commercially available silicon power MOSFETs of comparable ratings.
MOSFETs are field-effect transistors equipped with an insulating layer between their source and drain regions and gate. A MOSFET can operate either in enhancement or depletion mode depending on its doping level between its n-layers and p-layers; its on-state resistance is determined by current flowing between drain and source; its value will depend on both gate voltage and drain-source voltage values.
MOSFET datasheets specify a maximum drain to source voltage that, should it exceed, could lead to overpowering power dissipation and possible breakdown. As such, any device exceeding its maximum drain to source voltage must be connected via diodes for protection; otherwise it risks becoming damaged from excessive power dissipation and break down entirely. Increasing gate to source voltage reduces lifetime while leading to poor RDSon.
Solar Inverters
Solar inverters are key balance of system (BOS) components that convert variable direct current output from solar panels into utility frequency alternating current, providing AC output that can either feed into the grid or power on-grid residential and commercial solar systems. Solar inverters usually offer special functionality tailored to photovoltaic solar energy systems like maximum power point tracking and anti-islanding protection.
Traditionally, large central inverters or string inverters transform DC input from multiple solar panels to AC in one pass – this system is typically found in larger residential and commercial systems with rooftop solar arrays producing significant quantities of electricity.
Microinverters isolate each solar panel from its neighboring modules electronically and allow for optimal power harvesting through module-level maximum power point tracking, ensuring that shading issues, snow or debris lines on any one panel or partial shaded roof don’t dramatically reduce overall output of the system.
Solar inverters can connect with batteries to manage charging and discharging of energy from them, helping organise battery charging/discharging processes. Although relatively rare in Australia, this hybrid inverter is perfect for homes that feature roofs facing in different directions or complex roof structures; additionally it helps reduce wire clutter while simplifying stock management.
Motor Drive Control
Motor drives (also referred to as VFD or variable speed drives) are an integral component of machines, used to regulate DC and AC motor speeds to their desired levels. There are various methods available to do this such as linear control or pulse width modulation (PWM); PWM is currently the most commonly employed due to its greater efficiency.
Motor drives rely on a controller, comprised of user interface unit, error detector and amplifier circuit to operate effectively. The user interface unit enables operators to interact with the motor drive via input devices such as keyboards, potentiometers and switches; whereas, error detector compares input signals against reference signals to generate an output signal that displays speed errors; finally amplifier circuit increases or decreases drive voltage depending on this output signal.
The gate driver circuit serves as an intermediary between controller and power semiconductor switches such as MOSFETs and insulated-gate bipolar transistors (IGBTs). It converts low current control signals from microcontroller to high current power pulses that activate switches, with these pulses then being transformed into alternating current running through motor coils for desired speed. Opposite-polarity switch pairs can then be activated to reverse direction; eliminating manual wiring swapping to change its rotation.
Electric Vehicles
Electric vehicles (EVs) operate by using electricity instead of fuel, and can be charged from renewable resources or the grid. As a result, EVs produce much lower emissions and noise pollution compared to their fossil fuel counterparts, with much faster acceleration times as well as the capability of using regenerative braking to convert kinetic energy back into electricity.
Global electric vehicle sales are expanding quickly, driven by national policies and incentives as well as price competition. Sales of EVs are projected to top 17 million units by 2024 – which would save an estimated 6 million barrels of oil a day from being consumed – equivalent to approximately one in five cars on the road!
EV manufacturers are looking for ways to cut costs and improve performance by increasing battery cell technology. Their goals include increasing power density and lifespan while developing hybrid electric powertrains, charging infrastructures and plug-in solutions.
Electric Vehicles require batteries of high quality and reliability that offer long-term performance and safety. Most EV batteries use lithium-ion cells packed into cylindrical, prismatic or pouch-style housings; their capacity is typically measured in kilowatt-hours and serve as their primary source of power.
Cree’s silicon carbide technologies are unlocking innovative power solutions for electric vehicles (EVs). They allow more efficient conversion of energy to propulsion, smaller, lighter batteries and reduced costs; all helping make EVs more affordable while speeding the transition away from fossil fuels towards renewable energy.
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