The invention and application of semiconductor devices have profoundly changed the development process of human history for nearly 50 years. Entering the 21st century, semiconductor devices are ubiquitous and have become the cornerstone of building an information-based society. Meanwhile, the role of power semiconductors in improving power conversion efficiency makes them the cornerstone of building a low-carbon society. The energy-saving effect of semiconductor technology is obvious. The world's first electronic computer ENIAC using electronic tubes weighed 30 tons and consumed up to 200kW of electricity, while today's semiconductor computing devices with the same function weigh only a few grams and consume less than 1W of electricity. Meanwhile, power semiconductors play a crucial role in the conversion, storage, and transmission of electrical energy in solar photovoltaic and wind power generation systems. It can be seen that the utilization of renewable energy and the improvement of energy conversion device efficiency are inseparable from the innovative application of semiconductor technology.

Silicon Si devices have undergone years of development and have changed the face of household appliances. DC speed regulation technology has become the main technical measure for improving the efficiency of household air conditioners and other motors. It is worth noting that the technological development of new devices such as silicon carbide SiC, gallium nitride GaN, and gallium oxide Ga2O3 can not only improve power conversion efficiency by reducing device energy consumption, but also promote the development of household appliance technology in terms of reducing external dimensions and improving heat resistance.

Improving energy efficiency is a broad topic. In terms of household appliances, the narrow definition of improving efficiency mainly refers to enhancing the energy utilization efficiency of household appliances during operation. At present, countries have basically regulated the energy utilization efficiency of household appliances, and energy efficiency labels and energy efficiency rating systems are common regulatory methods. And in a broad sense, improving efficiency also requires considering the energy consumption of the manufacturing process, the energy consumption of raw materials, and the indirect energy efficiency impact during operation. The efficiency issue discussed in this article is limited to a narrow scope and only focuses on measures to improve energy utilization efficiency through technological advancements. The article will emphasize the role of power semiconductors in enhancing the energy utilization efficiency of household appliances.

Material substitution for power semiconductors

Household electricity accounts for about one-third of the total electricity consumption in the United States. It is predicted that in the next 10 years, the number of households in the United States will increase by 11%, while thanks to power semiconductor technology, household electricity consumption in the United States will only increase by 6%. A survey report indicates that 6% to 10% of all electricity applications in the United States involve converting AC power to DC power. Due to the poor efficiency of existing power sources, 3% to 4% of the total electricity consumption in the United States is consumed internally within the power sources; By improving product design, using microelectronic control devices, and power semiconductors such as field-effect transistors (FETs) and diodes to enhance power efficiency, it can save 1% to 2% of the total electricity consumption in the United States. This means that power semiconductor technology has the potential to save $3 billion to $6 billion annually.

Nowadays, the development of power semiconductor technology is not only reflected in the increasingly widespread application of high-efficiency LED lighting fixtures, but also in high-power household appliances such as air conditioners, refrigerators, washing machines, and induction cookers. The application of power semiconductors has exceeded the scope of controller driven power supplies. High power power semiconductor drive technology has changed the original operation mode and energy conversion process of products, with significant energy-saving effects. Improving the power conversion efficiency of household appliances and reducing standby energy consumption are currently widely adopted energy-saving measures. Semiconductor manufacturing companies, power conversion component manufacturing companies, and household appliance manufacturers are striving to make these losses smaller.

Electric motors are the main power consuming components of most white goods. Although speed control and variable torque control technologies have long been known for their role in improving motor efficiency and have been widely used in the industrial field, before the emergence of power semiconductors, these technologies were difficult to apply to compact and relatively difficult to maintain household appliances. For example, before being equipped with a semiconductor commutator, a DC motor with speed regulation function uses a mechanical commutator, which usually has a lifespan of less than 1000 hours and makes the driving power supply bulky and expensive. In the late 1970s, Japanese companies applied power semiconductor technology to the speed control of air conditioning refrigeration compressors, achieving a maintenance free operation of 100000 hours for the entire machine. At the same time, the external dimensions of the driving power supply were greatly reduced, allowing it to be placed inside the air conditioner at a significantly lower price. The Japanese market has basically completed the transition from fixed speed to variable frequency speed regulation in less than 10 years. Although the variable frequency power supply consumes about 10% of the electricity, utilizing the variable speed and torque functions of variable frequency speed regulation during operation can reduce the average electricity consumption of residential air conditioning by about 30%. At the same time, in winter heat pump operation mode, it has the ability to significantly increase heating capacity, which also promotes the widespread application of heat pump heating technology.

The technological development trend of power semiconductors that play a switching role in devices such as frequency converters and transformers, such as metal oxide semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), and diodes, is to shift from mainstream Si semiconductor materials to compound semiconductor materials such as SiC and GaN, making significant progress in improving efficiency and reducing volume.

The Fraunhofer Institute for the Promotion of Applied Research (ISE) in Germany has currently increased the efficiency of the inverter used in solar photovoltaic power generation devices to 98.5%. The power loss of the new inverter has been reduced by about 50% compared to the original similar inverters of the institution. The adoption of SiC devices instead of Si devices on a single-phase inverter with a rated power of 5kW has become a key factor in significantly improving efficiency. These SiC devices are produced by Cree, a US based company that solved the manufacturing process problem of 6-inch diameter SiC substrates in 2010 and achieved mass production, creating conditions for a significant reduction in SiC device manufacturing costs.

The higher efficiency improvement of new semiconductor devices is mainly due to the lower internal power consumption of the devices. Under the same circuit structure, replacing the diode from Si material to SiC material can reduce power consumption by about 30%; If transistors are replaced simultaneously, power consumption can be reduced by about 50%. The power consumption is reduced, and the heat generation is also reduced, thereby achieving energy-saving of power conversion devices.

In addition to low power consumption, GaN and SiC also have characteristics suitable for miniaturization. Firstly, devices made from the above two materials can achieve high-speed switching several times faster than Si components, significantly reducing the size of peripheral circuit components such as inductors, thereby achieving miniaturization of power conversion device circuits. Secondly, SiC and GaN components can also operate in high-temperature environments above 200 ℃ that Si components cannot adapt to. With the same heat generation, they can reduce the external dimensions of the cooling device for power conversion devices.

With the acceleration of the industrialization of GaN and SiC power semiconductors, the development of new peripheral circuits that fully utilize their characteristics has become an urgent task, such as the design of driver circuits that can achieve high-speed operation and electromagnetic noise countermeasures based on high-frequency switches. To enable these power semiconductors to operate in high temperature environments exceeding 200 ℃, in addition to using heat-resistant and low-cost solder materials, high-temperature resistant packaging materials are also required for chip installation. The advancement of these peripheral circuit technologies is the key to unleashing the effectiveness of GaN and SiC devices.

Industrialization of Silicon Carbide Devices

In October 2010, Mitsubishi Electric Corporation of Japan announced that it would begin selling household air conditioners using Schottky barrier diodes (SBDs) made of SiC as the driving power source for DC speed regulating compressors in the 2011 freeze year. This is the world's first household appliance to use SiC power semiconductors, marking the beginning of the industrialization of a new generation of power semiconductors represented by SiC in the household appliance industry.

The first batch of household air conditioners using SiC devices are Mitsubishi Electric's Foggy Peak MoveEye series products, including the MSZ-ZW281S with a rated cooling capacity of 2.8kW and the MSZ-ZW361S with a rated cooling capacity of 3.6kW. According to the plan, the Wufeng MoveEye series will cover a customized cooling capacity range of 2.2kW~7.1kW, and other models will gradually replace Si devices with SiC devices. Although the price of SiC devices is still relatively high at present, Mitsubishi Electric has not reflected the cost changes in the overall price, but has absorbed the increased costs by offering discounts.

This batch of air conditioners still uses insulated gate bipolar transistor IGBT, with Si diode replaced by SiC SBD, only used for DC speed regulation compressor drive power supply. From an energy-saving perspective, using SiC SBD can reduce the energy conversion loss of the compressor drive power supply by about 60%, and reduce the overall power consumption of the air conditioner by about 2%. If it is necessary to further improve the efficiency of power conversion and reduce the size of the driving power supply, all other power semiconductors need to be replaced with SiC devices to achieve the replacement of IGBT with SiCMOSFET. Mitsubishi Electric's move aims to accelerate the development of the SiC market, bring the price of SiC devices into a reasonable range as soon as possible, and strive to achieve the industrialization goal of SiCMOSFET in 2013-2014, thereby gaining a competitive advantage in the power semiconductor market. Mitsubishi Electric plans to replace all IGBTs with SiCMOSFETs, and SiC devices will not only be used in compressor drive power supplies, but also in the power supply part of the main control board. If all SiC devices are used, the external dimensions of the power electronic module of the main control board will be reduced to about 50% of the current size.

Mitsubishi Electric has released a series of energy-saving prospect verification results for the use of all SiC power conversion devices. The motor frequency converter with an output power of 11kW, developed using SiC SBD and SiCMOSFET, has reduced power consumption by approximately 70% compared to similar machines manufactured by Mitsubishi Electric using Si devices. At the same time, the volume of the prototype SiC frequency converter is smaller than that of the Si frequency converter, and the overall volume of the machine using SiC devices is only about 1/4 of that using Si devices. In addition, the power consumption of the SiC motor inverter with an output power of 3.7 kW, which Mitsubishi Electric has tested, is about 54% lower than that of the Si motor inverter.

The verification results show that the energy-saving effect of SiC motor frequency converter with an output power of 20kW is more significant. The SiC motor frequency converter with a rated output power of 20kW and a switching frequency of 20kHz reduces power consumption by about 90% compared to similar IGBT products made of ordinary Si. It is reported that this is achieved by shortening the switching time to improve the switching speed of SiC devices, thereby reducing power consumption. In order to accelerate the switching speed, the gate drive circuit needs to achieve high speed, improve the driving method, reduce parasitic inductance in the drive circuit, and thus shorten the switching time to about 50%. Meanwhile, increasing the switching speed may lead to an increase in surge voltage, thereby damaging SiC devices. To avoid this problem, the new product reduces parasitic inductance in the circuit by improving the configuration and circuit wiring of SiC devices to suppress surge voltage. Compared with the Si motor frequency converter with an output power of 20kW, the parasitic inductance of the SiC motor frequency converter is only 1/5~1/10 of the former.

In February 2011, Mitsubishi Electric announced the successful development of the "All SiC" intelligent power module IPM, a power semiconductor device that uses SiC for both transistors and diodes. In addition to using SiC devices, IPM also integrates overcurrent protection circuits and drive circuits into the module. In general, it is difficult to achieve both increasing current density and reducing losses in power components, but due to the use of SiC power components, IPM can achieve this win-win situation. Compared with IGBTs composed of Si devices, the current density of the new module has increased by about 3 times, while the inverter power consumption has been reduced by about 70%. In addition, the volume of the new module is about half of the original module of the same type.

The Japan Electric Power Central Research Institute has successfully developed an inverter using SiC diodes for connecting distributed power systems. The rated output power of this inverter is 3.3 kW, the output voltage is single-phase 200V, and the conversion efficiency is as high as 96.4%. It is currently the product with the highest energy conversion efficiency among similar power electronic conversion devices, mainly used for power regulation in household solar power generation systems and fuel cell systems. This inverter consists of a chopper that regulates DC voltage and a single-phase inverter that converts DC to AC, and achieves high conversion efficiency by reducing the recovery current of diodes on the chopper circuit. Compared with the highest performance product that originally used Si diodes, the power loss of this inverter has been reduced by 15%; By increasing the switching frequency of the chopper circuit, the size of the device has been reduced by 15%.