SiC MOSFETs Help Improve HVAC Energy Efficiency

In the past ten years, SiC MOSFETs have gradually been widely used in various fields such as switching power supplies, photovoltaic power generation, electric vehicles, high-speed rail, and power grids. Their reliability and cost performance have been significantly improved, and have been fully verified by the market. A large number of facts show that the third-generation semiconductor era represented by SiC has arrived.

This article is compiled from EETimes, the author Shenzhen Pengyuan Electronics Co., Ltd.

Achieving carbon peak by 2030 and carbon neutrality by 2060 is an important strategic decision made by the Chinese government after careful consideration, and it is also an inevitable choice to build a community with a shared future for mankind. Energy saving, emission reduction and low-carbon development have become new trends in the industry.

In the heating, ventilation and air conditioning (HVAC) industry, the new energy efficiency standard has been officially implemented on July 1, 2020. From the comparison between the old and new standards, it can be seen that the new standard has been upgraded to a higher level, which puts forward higher requirements for energy-saving technologies in the HVAC industry. The improvement in energy efficiency levels in the HVAC industry also presents new challenges for engineers. HVAC systems have been in use for many years, and a 1% increase in energy efficiency can cost quite a bit.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Figure 1 Comparison of new and old energy efficiency standards for HVAC

In the past ten years, SiC MOSFETs have gradually been widely used in various fields such as switching power supplies, photovoltaic power generation, electric vehicles, high-speed rail, and power grids. Their reliability and cost performance have been significantly improved, and have been fully verified by the market. A large number of facts show that the third-generation semiconductor era represented by SiC has arrived.

The new semiconductor technology represented by SiC provides a new way to improve the comprehensive performance of HVAC, not only can optimize the performance of HVAC system, but also can significantly improve system efficiency, promote HVAC to meet or even exceed new energy efficiency standards, and make HVAC meet Higher cost performance.

As we all know, the third-generation semiconductor SiC has obvious advantages in elemental properties compared with silicon. But prices are still the bottleneck, as there is no mass production like traditional silicon materials. SiC MOSFET prices have fallen sharply as Wolfspeed will complete the world’s first 8-inch SiC production line. Shenzhen Pengyuan Electronics Co., Ltd. has developed a 16kW R&D prototype. The results show that the use of SiC MOSFETs in HVAC systems not only improves system performance, but also has cost-effectiveness advantages.

Compared with the traditional silicon IGBT, the switching power consumption of SiC MOSFET is only one tenth, and the on-resistance drop is also very significant, which can appropriately increase the switching frequency of the compressor controller. The prototype boosts the switching frequency to 16kHz, which is beyond the listening frequency range of the human ear, significantly reducing the harsh electromagnetic noise that can be heard by the human ear. It can be seen from Figure 2 that the SiC MOSFET has no inflection point voltage, only a certain on-resistance, and the on-voltage and current have a linear relationship, so the on-voltage drop and power consumption are significantly reduced. When the HVAC is running under stable conditions, the compressor controller will work in light load or ultra-light load mode to achieve better energy saving effect.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Figure 2 Comparison of turn-on characteristics of SiC MOSFET and traditional silicon IGBT

Shenzhen Pengyuan Electronics used iPowerSiM power consumption and efficiency simulation software to simulate a prototype of a 16kVA compressor controller, which uses Wolfspeed’s 40mΩ, 1200V SiC MOSFET. Simulation results show that the efficiency can also be as high as 98.6% at a high switching frequency of 16kHz.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Fig. 3 Simulation of power consumption and efficiency of 16kW SiC controller based on iPowerSiM simulation software

In order to reduce the cost, the prototype in the scheme adopts the Bootstrap power supply method common in the air-conditioning industry, which generates a negative voltage in the circuit with intellectual property rights and control strategies to drive the SiC MOSFET and improve the gate reliability of the SiC MOSFET. Usage habits, size and cost control.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Figure 4 SiC compressor controller prototype

For the prototype in the scheme, the switching frequency is increased, and the voltage change rate is appropriately reduced, so as to avoid the common mode current damage caused by the high dv/dt of SiC on the insulation layers such as motor bearings and windings. However, the controller can still achieve peak efficiencies as high as 98%, which is 0.5% higher than traditional silicon IGBTs at full load, and 1%-5% higher at light and ultra-light loads (as shown).

SiC MOSFETs Help Improve HVAC Energy Efficiency
Fig.5 SiC controller efficiency curve and comparison

Finally, the switching frequency of the sample based on SiC MOSFET is 16kHz, which is 1-2 times higher than that of traditional IGBT, and the dead time is reduced by more than half, which reduces the difficulty of system compensation and achieves a better output current waveform. The system significantly reduces audible electromagnetic noise, has better NVH (Noise (Noise), Vibration (Vibration) and Harshness (Comfort)), which can reduce the design difficulty and cost of the sound insulation system.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Figure 6 Advantages of SiC-based compressor controllers

Prototypes using SiC MOSFETs can improve system efficiency by 1%-5%, reduce requirements and costs for thermal dissipation design, and improve motor harmonic current, torque ripple, and dynamic response. The cost of the C3M0040120K SiC MOSFET used in the prototype in the current scheme is almost equal to the cost of the silicon IGBT module, better than the IPM module, and can achieve better performance without increasing the system cost, which means quite high commercialization value. If SiC devices are used to reduce the cost of thermal diffusion systems and sound insulation systems, and to reduce electricity bills due to high efficiency and low energy consumption, the most intuitive is electricity bills, then the prototype in the scheme has higher economic value.

According to research by Bloomberg New Energy Finance (BNEF), the global electricity consumption of residential and commercial air conditioners reached 193.2 billion kWh in 2018, of which China accounted for 34%, ranking first in the world. If converted at an average energy efficiency improvement rate of 2%, 40 billion kWh of electricity can be saved, which is almost half of the annual power generation of the Three Gorges Dam. To this end, in order to achieve the new energy efficiency standards for air conditioners, to achieve the major strategic goals of energy conservation and emission reduction advocated by the state, and to rapidly improve the energy efficiency of today’s HVAC, it has great strategic significance and economic benefits. Among them, the inverter air conditioner has the highest utilization rate and the largest electricity consumption.

Another field is electric vehicles, which have developed rapidly in recent years, but the cruising range in winter has been significantly reduced, which has been criticized by users, mainly because the heating function of electric vehicles in winter is mostly completed by electric drive. PTC (Positive Temperature Coefficient) resistance heater, although the COP (Coefficient Of Performance) heating energy efficiency ratio of PTC is close to 1, but still about 30%-50% of the battery capacity is used for heating, which undoubtedly greatly shortens the cruising range.

However, if a wide temperature range and high efficiency silicon carbide heat pump air conditioning system is used, the energy consumption can be reduced by more than 60%, and the energy efficiency ratio COP under heating conditions in winter can reach 2-4, which is several times that of the current PTC heating mode. The winter cruising range can be improved by up to about 25%, which is much higher than the 5-10% increase – this is the performance improvement in SiC MCUs (motor control units) for electric vehicles.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Figure 7 Comparison of Roewe Ei5 heat pump and PTC in the heating energy consumption test (data from the Internet)

In addition, the silicon carbide heat pump air conditioner is adopted to make full use of the principle of cold and heat exchange inside and outside the car. In winter, the motor, iron core and battery can be used to heat the whole vehicle to realize the recycling and reuse of waste heat, thereby further reducing waste.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Figure 8 Automotive heat pump thermal management system (picture from the Internet)

At present, Tesla Model Y, BMW i3, Volkswagen’s new e-Golf model, Mercedes-Benz EQC model, Audi R8 e-tron electric version, as well as BYD, SAIC, GAC New Energy, Weilai, etc. have announced the use or future use of heat pump air conditioners system.

SiC MOSFETs Help Improve HVAC Energy Efficiency
Figure 9 Audi R8 e-tron electric vehicle heat pump air conditioning system (picture from the Internet)

With the explosive growth of the third-generation semiconductors, the increase in production capacity will be synchronized with the substantial cost reduction. The application of silicon carbide MOSFETs in heat pump air conditioners will improve the cruising range of electric vehicles in winter and ease the anxiety of cruising range users. In the application of air conditioning, the performance and efficiency of HVAC will be significantly improved, and the heat and electricity consumption generated by the system will be reduced, thus providing a new way to achieve the strategic goal of carbon peaking and carbon neutrality.

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