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In recent years, with the growth of demand for self-driving tours, outdoor camping, and emergency power supplies, portable energy storage is ushering in a new development opportunity. On November 11, at the 2022 International Integrated Circuit Exhibition and Seminar (IIC Shenzhen) High-Efficiency Power Management and Power Device Forum, Dr. Hu Zongbo from Zhuhai GaN Future Technology Co., Ltd. (hereinafter referred to as GaN Future Technology) gave a detailed introduction on the development trends of portable energy storage and the design and application advantages of GaN Future Technology’s GaN bidirectional inverter.
Dr. Hu Zongbo from GaN Future Technology
Development Trends of Portable Energy Storage
Under the influence of the pandemic, many industries have been significantly impacted in recent years, but some sectors, such as energy storage, have shown continuous growth. As a niche application area, the energy storage industry is mainly divided into grid-side storage and user-side storage, with portable energy storage becoming a hot application product for home consumers.
Data shows that among the top 5 outdoor power supply companies globally, 4 are Chinese brands, such as Huabao New Energy, Delan Minghai, Zhenghao Innovation, and Anker Innovation. Among them, Huabao New Energy has the largest market share, with a production volume of 835,000 units in 2021, followed by Zhenghao Technology, Delan Minghai, and Anker Innovation.
Dr. Hu Zongbo stated that portable energy storage can be visually understood as a large charging treasure, which features safety, portability, stability, and environmental friendliness. It provides various interfaces such as AC, DC, Type-C, USB, and PD, meeting the power supply needs of most consumer electronic devices.
From the perspective of portable energy storage application scenarios, they can be divided into two categories: one is for outdoor leisure and entertainment, such as hiking, camping, fishing, cycling, RVs, and travel, with the main markets being in China and the United States; the other is for emergency preparedness, mainly addressing the demand for electricity during natural disasters or emergencies, with Japan being a major market for emergency preparedness applications and Europe also showing strong demand for portable energy storage in the context of the Russia-Ukraine conflict.
Dr. Hu Zongbo introduced that the core device of portable energy storage is the bidirectional inverter, which includes battery PACK, BMS, inverter, output circuit board, charger, and MPPT. He also mentioned that portable energy storage is showing a trend of integrating inverters and chargers into one, namely the bidirectional inverter PCS, which not only saves costs, space, and weight but also provides greater charging power, further enhancing user experience.
So, what kind of topology architecture does the bidirectional inverter adopt? Dr. Hu Zongbo explained that the DC side adopts a fully resonant soft-switching dual full-bridge LLC topology, where Lm_H builds a resonant network for boost discharge mode, which can enhance gain. The AC side uses a totem pole without a bridge PFC, with the main characteristics being: first, the topology is simple, with fewer components, truly no rectifier bridge, high conversion efficiency, and energy can flow bidirectionally; second, Q1/Q2 are high-frequency devices, preferably GaN; Q1/Q2 are always complementary in conduction at the switching frequency; third, Q3/Q4 are line frequency devices, generally ordinary Si MOSFETs; Q3/Q4 are always complementary in conduction at line frequency; fourth, zero-crossing points can easily cause common-mode interference and current spikes, and control timing needs special handling.
Under the above topology architecture, why is GaN a relatively good solution? Dr. Hu Zongbo stated, “From different dimensions, comparing working frequencies, IGBTs typically operate in the mid-low frequency range, such as around 20kHz, SiC at around 50kHz, but GaN can operate at least up to 65kHz, and we can even achieve 100kHz – 120kHz. In terms of conversion efficiency, under a 2000W testing condition, GaN’s conversion efficiency is actually 0.2% higher than that of SiC and significantly higher than that of IGBT.”
By comparing IGBT, SiC MOSFET, and GaNext GaN, we can see that GaNext GaN has significant advantages in working frequency, conversion efficiency, Vgs_th lower limit, typical Vgs, Tj, Qrr, and other dimensions. Even compared to SiC MOSFET, it has advantages such as no need for negative voltage shutdown, lower driving voltage, and smaller driving losses. At the same time, in terms of pricing, IGBT is the lowest, while SiC has a significantly higher price due to its wafer generation, cutting, packaging, and testing, while GaN is a cost-effective material. Moreover, GaN does not require paralleling an SBD like IGBT, thus reducing reverse recovery losses and improving efficiency.
Thus, it is evident that GaN is the best choice for differentiated marketing in the bidirectional inverter market. Dr. Hu Zongbo believes that newcomers in portable energy storage must stand out in a fiercely competitive market environment by focusing on two aspects: first, new battery technology—semi-solid or all-solid batteries, which can increase energy density by 30%-50%, featuring lighter weight and larger capacity, although the price may be slightly higher; second, differentiated bidirectional inverter technology—GaN Inside, which refers to the technology of GaN bidirectional inverters.
The main advantages of GaN bidirectional inverters are: 1. High efficiency in charging, saving 5% in charging energy; 2. High efficiency in inversion, extending inversion time by 5%; 3. High frequency and high power density, reducing the weight of magnetic devices by 40%, making it easy to carry; 4. High efficiency, meeting portable fanless design, IP54 waterproof design, and allowing for heat conduction.
Why Choose GaNext GaN Devices?
Currently, GaN is no longer an unfamiliar technology, especially since 2018, when GaN led a wave of consumer enthusiasm in PD fast charging. However, GaN has actually gone beyond the scope of small power consumer applications, and its future applications will expand to kilowatt levels and above.
Dr. Hu Zongbo stated that GaNext is the preferred supplier of GaN Based PCS bidirectional inverters. Comparing E-mode GaN and GaNext GaN two different GaN technology routes, in terms of Vgs_th lower limit, E-mode GaN is 1.2V, while GaNext GaN is 3V; in hard-switching bridge circuits, E-mode GaN is prone to direct conduction; in terms of Vgs upper limit, E-mode GaN is 7V, while GaNext GaN is 20V; hard-switching high-frequency high-power E-mode GaN is prone to failure; E-mode GaN typically requires -3V voltage shutdown, making the entire driver circuit relatively complex; E-mode GaN requires paralleling an SBD to reduce reverse recovery losses, but this increases switching losses, costs, and PCB space; E-mode GaN mainly covers medium and small power applications. He also pointed out that GaN Future Technology’s GaN devices are positioned against SiC and have alternative materials, ensuring a continuous supply from the perspective of industrial chain safety.
In the design of GaN devices, Dr. Hu Zongbo introduced that GaN Future Technology adopts a compact cascaded GaN device design technology that ensures the safety of device applications and significantly reduces the risk of failure under high-frequency hard-switching conditions. At the same time, this design uses a die-on-die stacking method, integrating low-voltage Si + high-voltage GaN to achieve high stability, high performance, and high capacity manufacturability among other characteristics.
“Inspired by GaN’s application in PD fast charging in 2018, GaN Future Technology began vigorously expanding GaN applications in bidirectional inverters from 2021, focusing on the application scenario of portable energy storage.” Dr. Hu Zongbo also stated that in order to achieve differentiated competition, GaN Future Technology began exploring industrial applications from the third quarter of last year and started delivering GaN bidirectional inverter solutions for portable energy storage in outdoor power supplies from the first quarter of this year.
EET Electronic Engineering Magazine Original
