Overview

Power conversion is a common element in almost all electronic devices and is implemented in various topologies. However, new applications have unique demands that force engineers to develop AC-DC and DC-DC converters with the optimum balance of performance and efficiency. However, this is not always easy.

Choosing the right topology is just the beginning of the challenge and requires careful selection of power components. Also, as new semiconductor technologies enter the market, engineers have the opportunity to discover and evaluate new solutions to traditional problems.

This article provides background on the development of new semiconductor technologies and provides examples of innovative components arranged to provide appropriate functionality for current and future power conversion applications. In three installments, I will explain why high efficiency is necessary, topologies, and figures of merit.

Modern society is supported by electronics and electromechanics. Whether at home or in business, we cannot imagine life without the myriad of gadgets that keep us productive, comfortable, informed and entertained. Whether it's the variable frequency and amplitude three-phase AC used in a 500kW industrial motor, or the 0.6V DC used in a digital processor, these devices require electrical power to run. From the potential energy contained in fossil fuels and renewables to the generation of CPU core voltages, we need a stage of power conversion with minimal loss to the environment. However, as global energy consumption continues to increase, reaching approximately 180,000 TWh in 2019, imperfect conversion efficiency will result in heat generation and global warming, which will affect both energy suppliers and consumers. It will cost both parties.

Internationally, efforts are being made to reduce energy consumption as much as possible, but as the world's economies modernize, it is inevitable that energy consumption will increase. At the same time, governments are setting targets for energy reduction. For example, in the European Union (EU), by 2030, all member countries are required to reduce energy consumption from primary energy sources by 32.5% compared to 2007 levels.

Behind this is the explosive growth in demand for electronic devices in markets such as IoT, electric vehicles, 5G, and data centers. The final stage of power conversion in these applications is unsurprisingly the most numerous and has huge market value. For example, DC-DC converters will grow at an annual rate of 17.5% to $8.5 billion in 2019 and $22.4 billion in 2025, with communication equipment applications driving the increase. It is clear that the power conversion process must be made ever more efficient in order to achieve the targeted energy savings in the growing market.

Near the end load, efficiency is impacted by local temperature rise, as well as the economic and environmental costs of wasted energy. But this just moves the extra heat elsewhere, which itself consumes even more energy. Therefore, reduction of loss is essential in power conversion design.

new application

DC-DC conversion, either directly or as an intermediate stage, has always been an integral part of switch-mode power supplies, but over the years power and voltage levels have changed significantly. Early equipment power supplies converted rectified mains AC, perhaps to 12V DC for analog and general use, and a relatively loosely regulated 5V for TTL logic. Today, most of the power is consumed in the power rails of digital circuits, which need to be more accurate, often below 1V. For the same power, using a lower voltage results in higher current levels and higher interconnect losses. Also, a fixed voltage drop like a conventional rectifier diode becomes a large percentage of the final voltage, further increasing losses.

Server farms are said to account for about 1% of the world's energy demand, and the conversion efficiency from the primary energy source to the final load voltage is clearly important in this application. To address this problem, an "intermediate bus" is used to provide power at a proportionally lower current with a higher DC voltage when a "point of load" DC-DC converter delivers the final voltage. A distributed method is used. Intermediate buses are cascaded to minimize losses throughout the installation, but the current trend is to generate 48V from the primary AC source, combine the battery backup at this point, and 48V to sub at the load. A direct conversion to 1V (Figure 1). This eliminates the need for a second intermediate bus, but the high final down-conversion ratio poses efficiency concerns and requires high-performance solid-state switches.

Practical electric vehicles have gone from science fiction to mainstream in just a few years, creating a completely new application field for power conversion and gaining great market value. The high-power traction inverter, which converts the direct current from the high-voltage battery into the three-phase motor drive, obviously plays that role, but there are many other stages. Conventional EVs use a 12V battery that needs to be charged from the traction battery via a DC-DC converter.

The converter is designed for bi-directional energy flow so that excess charge can be used for traction in an emergency. It also has an on-board charger (OBC). AC-DC converters are also bi-directional to return energy to the grid for load leveling of utility companies. In-vehicle control, safety and infotainment electronics are, of course, mostly digital, with numerous dedicated DC-DC converters providing local power rails and, on the other hand, roadside and domestic A fast charger supplies traction battery voltage at power levels of several hundred kW. In vehicles, the wattage lost in power conversion reduces the range, while in chargers it leads to higher running costs and a longer payback period. Therefore, efficiency is important, and high-voltage semiconductor switches with low loss are required.

In the industrial world, the impact of the Industrial Internet of Things (IIoT) and "Industry 4.0" has led to the introduction of a large number of low power consumption sensors and actuators into the market. These sensors and actuators work with batteries, energy harvesting, or PoE (Power over Ethernet), rather than the traditional centralized arrangement of equipment and a large power supply. A DC converter is required.

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