The benefits brought by Gallium Nitride (GaN) also introduce challenges in control and optimisation.
Programmable digital control offers a solution to these challenges by enabling dynamic adjustments. Combining GaN with digital control is enabling highly efficient, reliable, and scalable power.
Rising global demand is driving the need for better power electronics in applications ranging from consumer to e-mobility, data centres, and industrial. Some of the expectations now influencing this power demand include:
- Faster charging: Standards like USB PD make it possible to supply power to more diverse applications. This is also raising the expectation of faster charging. Demand for higher power output is one reason why wide bandgap (WBG) power technologies like gallium nitride (GaN) have become so relevant. This also comes with the need for more intelligence, like letting the drive adjust its parameters based on load needs.
- Smaller form factors: The improved efficiency and simpler power conversion topologies offered by GaN are pivotal in achieving higher power densities, which is required for size and weight reductions. GaN devices can be switched at significantly higher frequencies, enabling reductions in the physical size of passive components and the implementation of advanced topologies, such as the bridgeless totem-pole power factor correction (PFC) base converter.
- Increased energy efficiency: This is a critical requirement, particularly for power generation and distribution systems, in the global effort to reduce greenhouse gas emissions and establish more sustainable energy generation and usage.
The Need for Power Factor Correction (PFC)
PFC ensures that the current drawn by a load is synchronised with the voltage provided by the source. It reduces the reactive power extracted from the grid, which is required to preserve the efficiency of electrical power systems.
The design of power supplies has been substantially impacted by PFC regulations. The objective of these regulations is to enhance the overall efficacy of electrical systems and decrease harmonic distortion. In the EU, household switched-mode power supplies with output power above 75W must comply with the standard EN61000-3-2. The easiest way to comply is to integrate an active PFC in the design.
Active PFC topologies can use high-frequency transformers to achieve higher switching frequencies and reduce the size of the PFC inductor, and power MOSFETs with low on-resistance and fast switching rates to minimise power losses in the PFC circuit. This approach may incur additional design considerations around EMC. They also need advanced control circuits to precisely regulate the input current and maintain high power factor.
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Challenges of GaN Control
GaN has changed the power electronics industry, offering significant advantages in terms of faster switching speeds, higher efficiency, and smaller form factors with respect to silicon FETs. However, its unique characteristics also present new challenges for control engineers.
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With the ongoing shift to renewable energy and the electrification of transport and industry, the demand for higher power and greater energy efficiency in electronics is increasing. Wide bandgap technologies including SiC and GaN bring many advantages.
WBG OVERVIEWTo fully leverage the benefits of GaN, power supply designers are turning to more complex topologies such as active flyback and totem-pole bridgeless converters. These topologies can achieve higher power densities and efficiencies, but they also require more sophisticated control strategies.
Totem-pole PFC circuits, in particular, can be challenging to control, due to the lack of a reverse diode. This can result in the inductor current flowing in reverse at close to zero-crossing if the FETs are still conducting. Efficiency in these applications requires greater effort in control algorithm development and implementation.
Hard switching continuous conduction mode (CCM) operation, while offering higher efficiency, can increase switching losses at the higher frequencies needed for compact GaN-based power supplies. Critical conduction mode (CrCM) totem pole converters with zero voltage switching (ZVS) can mitigate these losses, but they require complex, variable-frequency switching controllers.
The LLC and synchronous rectifier stages of GaN-based power supplies require a revised approach to managing dead time. Using existing silicon-based analogue controllers can be particularly challenging in these more complex topologies.
What is GaN and why is it becoming such an important power technology? A snippet of Thomas Hauer's interview with electropages
Advantages of Digital Control in Power Topologies
Digital control has become increasingly important in power topologies due to its many benefits over analogue control. One of its key strengths lies in its flexibility and adaptability. Unlike analogue control, digital systems are programmable, allowing them to easily adjust to changing operating conditions, load variations, and regulatory requirements. Additionally, digital control can efficiently implement complex algorithms, resulting in enhanced performance and robustness.
Another significant advantage is the precision and accuracy offered by digital control. With higher resolution compared to analogue systems, digital systems provide more accurate control over power factor and output voltage. Moreover, digital signals are less prone to noise and drift, ensuring consistent and reliable performance.
Digital control also improves efficiency. It allows for optimised control that minimises power losses and boosts overall efficiency through advanced techniques like adaptive and predictive control. Furthermore, digital systems often require fewer components, which leads to smaller and more compact power supply designs.
Beyond performance and efficiency, digital control introduces advanced features such as fault detection and protection mechanisms that enhance reliability and safety. It also supports seamless integration with communication networks and other digital systems, enabling remote monitoring and control.
Lastly, digital control reduces development time. Through simulation and modelling, these systems can be extensively tested before implementation, which lowers development time and costs. Digital control also supports rapid prototyping and testing of different strategies, accelerating the development process.
Multiple analogue controllers can be replaced with a single, smart digital controller—typically a microcontroller. This simplifies both the design and tuning of the entire power supply. This approach works well with standard PFC topologies, offering improvements in power density and efficiency. Additionally, the microcontroller can incorporate supervision and protection features for the GaN devices.
Conclusion
The integration of GaN devices with sophisticated digital control represents a significant advancement in power electronics. By addressing the challenges associated with GaN implementation, this approach enables more efficient, reliable, and scalable power systems. To discuss your PFC needs, whether using GaN, SiC, or silicon, talk to the Avnet Silica Power Specialists.
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