According to market trends, electric vehicles (EVs) will capture an increasing share of the market and eventually replace internal combustion engine vehicles. In the future, DC fast-charging stations will replace or integrate with gas stations, powered by renewable energy sources such as solar and wind. A critical factor in EV adoption will be the ability to charge vehicles in less than 15 minutes. This article explores the role of energy storage systems in EV fast-charging infrastructure and introduces related solutions from ADI.
Energy storage systems stabilize the grid by managing power peaks
The automotive market is undergoing rapid transformation, with forecasts predicting explosive growth in EV sales - reaching 10 million units by 2025 and exceeding 50 million by 2040, when total vehicle sales are expected to hit 100 million. This means that by 2040, 50% of all vehicles sold will be fully electric.
However, meeting the surging demand for EV charging will require local grid power peaks exceeding 1 MW, which could overwhelm existing infrastructure. Significant investments will be needed to upgrade transmission lines and centralized power plants to handle the increased base load. Since this load is impulsive, it must be merged with the intermittent energy generated by renewables like solar and wind.
Energy storage systems offer an elegant solution to this challenge. By storing electrical energy in batteries using electrons and chemistry methods, this energy can then be used to enhance EV charging, stabilize the grid by smoothing power peaks, or provide backup power during blackout.
For EV charging needs, slow overnight charging at home can be accomplished using simple wall-box or, for homes equipped with solar generation systems and storage batteries, multi-kilowatt DC chargers. When EVs are on the road, fast charging can be achieved via public charging piles or superfast charging at future fueling stations.
In a future characterized by intermittent power loads, integrating EVs and intermittent energy sources like solar and wind into the grid presents challenges. For instance, intermittent loads such as EVs will require upgraded transmission lines to handle higher power peaks.
Energy storage systems for EV charging infrastructure present significant market opportunities
Considering all potential applications, the energy storage system market is projected to surpass 1,000 GW in power generation and 2,000 GWh in capacity by 2045, a dramatic increase from today's 10 GW/20 GWh. Within this growth, energy storage systems for EV charging infrastructure represent a vast market opportunity.
Private and public AC charging infrastructure, while simple, is power-limited. Level 1 AC chargers operate at 120 V with a maximum output of 2 kW, while Level 2 chargers reach 240 V and 20 kW. In both cases, the onboard charger handles AC-to-DC conversion. Wall box AC charging stations function more as metering and protection devices than chargers. Due to cost, size, and weight constraints, onboard chargers for cars are typically rated below 20 kW.
In contrast, DC charging enables higher-power EV charging. Level 3 chargers are rated for up to 450 V DC and 150 kW, while the latest superchargers (equivalent to Level 4) exceed 800 V and 350 kW. For safety, the voltage limit is set to 1,000 V DC when the output connector is plugged into the vehicle. With DC chargers, power conversion occurs in the charging pile, and DC output directly connects the pile to the vehicle’s battery, eliminating the need for an onboard charger and saving space and weight. However, during this transitional phase, where EV charging infrastructure remains fragmented and varies by region/country, most EVs include a small 11 kW onboard charger to allow AC outlet charging when needed.
SiC MOSFETs deliver efficiency advantages for modern power electronics designs
In modern power electronics designs, converters based on silicon carbide (SiC) power MOSFETs achieve high efficiency. Compared to silicon insulated gate bipolar transistors (IGBTs), they improve efficiency by 5% (at maximum load) to 20% (at partial load). For example, a 500 kW photovoltaic inverter with 5% higher efficiency reduces losses by 25 kW or increases output by 25 kW - equivalent to the energy consumption of five households or the output of a large heat pump providing hot water or cooling a charging station building in the summer.
For DC charging piles and energy storage system chargers, two design approaches are viable: using large monolithic power converters rated above 100 kW or many small converters rated at 25 kW to 50 kW in parallel. Both solutions have pros and cons. Today, the market favors multiple small converters due to economies of scale and simplified design. However, an intelligent energy management system is essential.
Even for these DC-DC converters, switching from silicon IGBTs to SiC MOSFETs offers significant efficiency gains, space savings, and weight reduction, albeit at a slightly higher cost - currently 25% more, expected to drop to 5% within next five years. The efficiency gains alone can offset this cost increase. In a PFC inverter, a 5% efficiency improvement on 1 MW translates to 50 kW in savings, totaling 250 kW across the system. This is equivalent to adding an extra charging pile or better balancing energy consumption against actual load demands.
The driving method for SiC MOSFETs is key to achieving the required switching frequency, which balances system design costs (influenced by the MOSFETs, the coils, and the inductors) with efficiency. Designers target switching frequencies between 50 kHz and 250 kHz. Gate driver requirements are becoming more stringent, particularly in terms of shorter propagation delays and improved short-circuit protection.
Complete solutions for power drive applications
To meet the demands of power drive applications, ADI offers the ADuM4136, an isolated gate driver featuring advanced iCoupler® technology. This isolation enables a common-mode transient immunity (CMTI) of 150 kV/µs, allowing SiC MOSFETs to be driven at hundreds of kHz. With features like desaturation protection for fault management, designers can reliably drive single or parallel SiC MOSFETs up to 1,200 V. The ADuM4136 is optimized for driving IGBTs and supports unipolar or bipolar secondary supplies, including negative gate drive if needed.
An isolated gate driver requires a power supply. The combination of the ADuM4136 gate driver and the LT3999 push-pull controller forms a low-noise, high-efficiency building block for managing SiC MOSFETs. The LT3999 controls a bipolar isolated power supply for the ADuM4136. Its ultra-low EMI noise design and switching frequency of up to 1 MHz enable a compact and cost-effective solution.
The LT3999 includes two 1 A current-limited power switches that switch out of phase. The duty cycle is programmable to adjust output voltage. The switching frequency can be set up to 1 MHz and synchronized to an external clock for precise harmonic control. The input operating range is configured using precision undervoltage and overvoltage lockouts. In shutdown mode, supply current drops below 1 µA. A user-defined RC time constant provides adjustable soft-start by limiting inrush current at startup. The LT3999 is available in a 10-lead MSOP or a 3 mm × 3 mm DFN package with an exposed pad.
For accurate monitoring, a multi-cell (up to 18 cells) battery monitoring IC with a total measurement error below 2.2 mV can be used, such as the LTC6813-1. All 18 cells can be measured in 290 µs, with lower data acquisition rates available for noise reduction. Its 0 V to 5 V measurement range suits most battery chemistries. Multiple battery stack monitors can be connected in series to monitor long high-voltage battery strings simultaneously. Each monitor features an isolated serial peripheral interface (isoSPI) for high-speed, RF-immune, long-distance communication. Multiple devices are daisy-chained with a single host processor connection, and the daisy chain operates bidirectionally to ensure communication integrity even if a fault occurs. The IC can be powered directly from the battery stack or an isolated supply. It includes passive cell balancing with individual PWM duty cycle control, an onboard 5 V regulator, nine general-purpose I/O lines, and a sleep mode that reduces current consumption to 6 µA.
To mitigate system noise before it affects BMS performance, the stack monitor’s converter uses a sigma-delta (Σ-Δ) topology with six user-selectable filter options for noisy environments. The Σ-Δ approach inherently reduces EMI and transient noise by averaging multiple samples per conversion. In ADI’s portfolio, the LTC681x and LTC680x families represent the state of the art in battery stack monitors, with the 18-channel LTC6813 being a standout example.
Conclusion
Addressing the challenges of future DC fast-charging infrastructure will hinge on power conversion and energy storage systems. ADI’s solutions for energy storage systems ensure reliable sense, measure, connect, interpret, secure, and power all the physical phenomena, generating reliable and robust data for advanced algorithms. In EV charging infrastructure, these algorithms will optimize the conversion of renewable energy into usable power, enhancing system efficiency.