The existing electrical infrastructure struggles with numerous challenges and limitations, highlighting the need for a modernization effort. Electricity, widely known for its environmental friendliness and safety, remains a preferred energy source. The century-old electric grid urgently needs upgrades for better efficiency and cost-effectiveness. It mainly depends on sending power over long distances from various sources, which is less than 30% efficient. This outdated infrastructure not only raises environmental concerns but also presents vulnerabilities during natural disasters.

Figure 1 Wind and solar energy used in the U.S

A huge amount of electricity gets lost as heat during long-distance travel, causing energy waste. It's not viable to use wind and solar power consistently because they're not always available, and connecting everything nationwide is tedious. However, more power can be cleanly generated from sources like coal and natural gas. In the U.S., there is a well-connected natural gas pipeline system to help reduce these losses and increase efficiency. Recent developments in wide bandgap (WBG) power switching devices, using materials like silicon carbide (SiC) and gallium nitride (GaN), promise substantial improvements in electrical and thermal performance compared to traditional silicon devices.

Ⅰ. Distributed Microgrids for Sustainable Electricity

Developing the next generation of energy infrastructure demands a dual focus: not only efficient energy generation but also its clean and effective utilization. Currently, 70% of generated energy is wasted, implying the inefficiency of today's AC electricity infrastructure.

Figure 2 Proposed distributed energy infrastructure with local microgrids.

A solution is proposed, as seen in Figure 2, involving sustainable and efficient distributed electricity systems. In this model, local microgrids operate independently or in isolation from the primary AC utility grid, a departure from the current standalone AC grid. Renewable energy sources like solar panels, wind turbines, and fuel cells play a significant role in fulfilling local electricity requirements with minimal power losses during distribution. Direct current (DC) electricity utilization gains appeal in this context, especially for DC-compatible loads and when electricity derives from clean sources.

This approach offers several advantages. Utilizing the extensive natural gas supply in the US, which benefits from a well-established pipeline network, enhances reliability. Furthermore, this natural gas-based infrastructure exhibits resilience in the face of disasters, unlike the current AC grid, which is susceptible to superstorms. Augmenting system efficiency and resilience, advanced power electronics employ wide bandgap (WBG) semiconductors, controlled by sensor-based feedback and information technology. This system optimizes engine speed according to load variations.

Figure 3 Schematic diagram of a redefined natural gas (NG) powered CHP generator.

Figure 3 shows how this system serves diverse purposes: electric vehicle (EV) charging, building heating, hot water supply, and local electricity generation. It provides a flexible and sustainable solution for various energy requirements. A notable aspect is the direct use of DC electricity when both the energy source and the load are DC-compatible. This eliminates the need for AC-DC conversion, decreasing energy losses and enhancing efficiency. For instance, solar-powered DC data centers and battery chargers are gaining popularity due to the benefits of DC utilization.

Ⅱ. WBG Power Converters

Wide-bandgap (WBG) power diodes and three-terminal switches have entered the commercial market with better specifications as to their predecessors. These devices can handle up to 100 amps of current and voltage ratings of up to 1.7 kV. The key to their enhanced quality, as depicted in Figure 4, lies in the superior electrical and thermal properties of WBG semiconductors compared to traditional silicon devices. This advantage is derived from parameters such as thermal conductivity (τ), specific electrical conductivity (ısp), and the critical electrical field strength (Ec) required to trigger avalanche breakdown.

Figure 4 Thermal performance of WBG devices at 300K.

For applications that demand voltage-blocking capabilities under 900 volts, lateral gallium nitride (GaN) power transistors have gained prominence due to their superior on-state performance in comparison to both vertical GaN and 4H-silicon carbide (SiC) power devices. However, as voltage requirements exceed this threshold, lateral GaN transistors face limitations in scalability, necessitating the use of vertical WBG power devices. The adoption of WBG power-switching technologies must be done carefully. While cost is often a driving factor when replacing silicon power switches in applications that seek increased energy efficiency, WBG power devices offer the potential for reductions in the size and cost of power systems due to their superior thermal and electrical performance.

Crystal defects pose a significant challenge in WBG power semiconductors, affecting die yield, device performance, and field reliability. Overcoming this challenge requires a deep understanding of the role of crystal defects and the development of low-temperature material synthesis processes that can yield defect-free single-crystal large wafers at a low manufacturing cost. Additionally, packaging and thermal management are formidable challenges in manufacturing high-power modules capable of operating at high junction temperatures.

For high-power industrial applications like inverters, there must be a larger power density. In such systems, the power section accommodates standard silicon insulated-gate bipolar transistors (IGBT) and SiC power metal-oxide-semiconductor field-effect transistors (MOSFET) modules with varying power ratings.

Common gate drive and control electronics simplify the design. The DC capacitor bank is reconfigurable to meet different capacitance and voltage rating requirements, and a family of filter magnetics caters to multiple applications. The software is modular to support AC and/or DC power generation and motor drive applications. To evaluate the thermal performance of the inverter platform, a test was setup consisting of an airflow machine capable of varying air flow rates. A laminar flow element measured the incoming air rate to cool the power semiconductor module. Various thermocouples were inserted to measure the case temperatures of the semiconductor chips, while the power module thermistor temperature was also monitored. Variable resistive load banks allow the adjustment of loads, and the input energy is supplied by a variable DC power supply.

Ⅲ. Conclusion

To maximize the potential of clean energy and advanced technology, a system combining local microgrids with the primary utility grid is crucial. These microgrids can function independently when necessary. Moreover, transitioning to direct current for electricity transmission, both within and outside these microgrids, depends on cost-effectiveness, safety considerations, and policy support. This shift represents a cleaner step towards a more sustainable and reliable energy system.