Energy Storage Systems (ESS) play a crucial role in building a low-carbon world and are among the most rapidly growing industrial applications. Several factors drive this growth, including aggressive policies aligned with decarbonization goals in various countries, the rising demand for storage and control of renewable energy sources such as solar power, and the ongoing cost reduction of lithium-ion batteries. This article introduces the architecture of ESS, alongside the products and solutions provided by onsemi.
Battery energy storage systems relieve grid pressure from EV charging
ESS are a widely researched application, and they store energy through methods such as electrochemical storage (batteries), mechanical storage (compressed air), and thermal storage (molten salt). This article will focus on battery storage systems connected to solar inverter systems.
Battery Energy Storage Systems (BESS) are widely used in both residential and commercial sectors. In residential applications, BESS can serve as a backup power source to prevent unexpected power outages and save costs by shifting energy from low-value periods to high-value periods. In larger commercial systems, BESS can efficiently store and manage the free, clean energy produced by solar inverters, achieving low carbon emissions. Another key feature of BESS today is its ability to alleviate the grid pressure caused by the growing demand for electric vehicle charging.
A BESS consists of four parts: battery pack, Battery Management System (BMS), Power Conversion System (PCS), and Energy Management System (EMS), and is suitable for both commercial and residential applications. The battery pack consists of battery cells, with high-voltage modules integrated into racks or banks to achieve higher capacity. Typically, the charging and discharging voltage range is from 50V to 1100V, depending on the battery voltage and circuit topology. The BMS is an electronic system that manages rechargeable batteries by ensuring they operate within the Safe Operating Area (SOA), monitoring the operating states, and calculating and reporting real-time data to achieve longer operational life. The PCS is another important subsystem that connects the battery pack to the grid and/or loads for bidirectional energy conversion. It largely determines the system’s cost, size, and performance. The EMS is a software-based computer-aided system used by grid operators to monitor, control, and optimize the performance of generation or transmission systems.
Compared to IGBTs, SiC devices have more advantages in high-voltage, high-current applications, such as enabling high-frequency switching. While IGBTs are still the preferred choice for BESS design, combining SiC devices in certain sections can deliver outstanding performance, considering the different switching strategies. For instance, in a bidirectional inverter using A-NPC, where a dedicated switching strategy requires high switching frequency for inner switches, SiC devices can be selected for the inner legs to reduce switching losses, while the other switches can still use low VCE(SAT) IGBTs to keep costs manageable.
Three-level configuration reduces power loss and current ripple
The three-level I-NPC and three-level ANPC are common bidirectional topologies in PCS, designed to match the increasing output power. Compared to two-level topologies, three-level topologies require more components, driving signals, and more complicated control structures. However, the advantages are evident: the goal of the three-level configuration is to reduce power loss and current ripple through halved applied voltage, as well as improve EMI performance.
The NXH800H120L7QDSG is onsemi's new QDual3 1200 V 800 A half-bridge IGBT power module. The integrated Field Stop Trench 7 IGBT and Gen.7 diode provide lower conduction and switching losses, enabling designers to achieve high efficiency and excellent reliability. By paralleling multiple QDual3 modules, a three-level ANPC module can be formed, with a system output power reaching 1.6 MW to 1.8 MW.
DESAT (Desaturation) is one of the important protection features in high-power conversion. It helps prevent IGBTs/MOSFETs from being damaged due to short circuits by shutting down the switches as fast as possible. The NCD57000 integrates desaturation detecting function, and when the VCESAT reaches the target value, the internal STO (soft turn-off) MOSFET is activated to discharge the gate capacitor, reducing over-voltage stress and losses caused by high dV/dt. Additionally, this single-channel gate driver features high source/sink current (4 A/6 A), 5 kVrms galvanic isolation, as well as other protection features such as UVLO and active Miller clamp.
Below are some key products from onsemi for battery energy storage system applications. First, auxiliary power supplies are typically designed using QR (Quasi-Resonant) flyback topology with primary-side regulation. The NCP1362 is a primary-side PWM controller for low-power offline SMPS. The main advantage of using the NCP1362 is that it does not require optocoupled feedback, improving power supply reliability. It also turns off the switch at low VDS to improve efficiency and reduce heat. The NCP1362 is a primary-side QR flyback controller that does not require secondary feedback circuits and can perform valley-lockout QR peak current mode control, with optimized light-load efficiency and standby performance.
A distributed energy storage system might consist of hundreds of PCS and control units. Modern command centers need more complex connectivity solutions to meet the growing node and computing demands. onsemi’s NCN26010 is one of the first controllers in the market to comply with the 802.3cg standard. It offers excellent noise immunity, exceeding the noise immunity level in IEEE 802.3cg, with a range of over 50 meters and reducing up to 70% of the required cabling, cutting installation costs by up to 80%, and lowering software maintenance costs.
The EliteSiC 1200 V MOSFET is a new series of 1200 V M3S planar SiC MOSFETs optimized for high-temperature operation, with improved parasitic capacitance for high-frequency operation. At VGS = 18 V, RDS(ON) = 22 mΩ, with ultra-low gate charge (QG(TOT)) = 137 nC. It features high-speed switching, low capacitance (COSS = 146 pF), and uses a four-pin package with Kelvin Source.
The Field Stop VII 1200 V IGBT is a new series of 1200 V Trench Field Stop VII IGBTs with trench narrow mesas and proton implant multiple buffers to provide fast-switching and low VCE(SAT) types. It improves parasitic capacitance for high-frequency operation and features common packages. Its target applications are energy infrastructure and factory automation.
The Field Stop VII IGBT PIM NXH800H120L7QDSG features high efficiency and controllability with Field Stop Trench 7 IGBT and Gen.7 diodes. It supports 1200 V, 800 A 2-in-1 half-bridge configuration, offering a 10% higher power density and 10% lower energy losses compared to leading competitive products. It also features low thermal resistance, isolated base plate, NTC thermistors, solderable pins, and press-fit pins (as required), with a low inductive layout.
Important factors to follow when selecting a gate driver
When selecting a gate driver, it is crucial to consider factors such as the current driving capability, fault detection, immunity to noise, propagation delay, compatibility, and more. However, not all of these factors may be equally important for every application. For example, unlike IGBTs, the output characteristics of SiC MOSFETs are more like a variable resistance and lack a saturation region, meaning that the normal desaturation detecting principle does not work. One solution is to use current sensors to detect overcurrent or temperature sensors to detect abnormal temperatures.
The NCP51561 is a dual-channel isolated gate driver with a 4.5A/9A source/sink peak current. It features a typical propagation delay of 36 ns, with a maximum delay matching of 5 ns, and supports single or dual input modes via ANB. It supports 5 kV galvanic isolation and has a CMTI of ≥ 200 kV/μs. It comes in a SOIC-16WB package with a creepage distance of 8mm.
The NCD57080 / NCD57090 are single-channel isolated gate drivers with a 6.5A source/sink peak current. They offer split output active Miller clamp or negative bias versions, support 3.3V, 5V, and 15V logic inputs, and provide 3.5 kV galvanic isolation. Their CMTI is ≥ 100 kV/μs. The NCD57080 comes in a SOIC-8 package with a creepage distance of 4mm, while the NCD57090 is in an SOIC-8WB package with a creepage distance of 8mm.
The NCD57100 is a single-channel isolated gate driver with a 7A source/sink peak current, UVLO, and DESAT protection. It supports a wide bias voltage range, including negative VEE, and is compatible with 3.3V, 5V, and 15V logic inputs. It also provides 3.5 kV galvanic isolation and has a CMTI of ≥ 100 kV/μs. The driver comes in an SOIC-16WB package with a creepage distance of 8mm.
Common bidirectional AC-DC topology requirements
In common topologies of bidirectional AC-DC converters, the three-phase full-bridge converter features a simple circuit, easy control, and fewer components. However, the switches must withstand the full bus voltage and spikes and require high-capacity transformers, which increase cost and end-system size. Wide-bandgap components are preferred to reduce THD and inductor size.
The single /three-phase totem-pole converter can improve efficiency, EMI, and THD, and reduce the quantity of switching events per cycle. It has fewer switches and higher power density but requires wide-bandgap components to minimize recovery losses. It also exhibits zero-crossing point noise and common-mode noise.
The three-phase three-level converter adopts a three-level configuration, which can reduce THD and voltage stress on certain switches. It requires more gate drivers and more complicated control but offers better efficiency and higher cost, and is a proven configuration in solar inverter designs.
In common bidirectional DC-DC topologies, the buck-boost converter can expand the charging/discharging voltage range to improve battery utilization. It can achieve bidirectional power conversion during charging and discharging and has fewer components and is easy to control. The selection of components can depend on the battery voltage.
The dual active bridge converter can operate with phase-shift modulation to achieve Zero Voltage Switching (ZVS) under high loads. Mismatched currents at the both stages can cause unexpected losses. To achieve the expected efficiency, complex designs are required for phase shift, transformer, and frequency. In high-frequency/high-voltage operations, wide-bandgap components are the preferred choice, as they reduce output current ripple, thus minimizing output capacitor size. This is the preferred choice for high-power applications, supporting isolated conversion for safety.
The CLLC resonant converter can achieve bidirectional conversion based on LLC by adding one capacitor. Through complicated frequency modulation and passive selection, it achieves high efficiency in both directions. Additional DC-DC conversion is required to achieve a wide output range, ensuring good efficiency. It has better efficiency than DAB across the entire load range and supports isolated conversion for safety.
onsemi offers a complete product line for battery energy storage systems, including bidirectional AC-DC and bidirectional DC-DC converters, isolated gate drivers, power management, signal conditioning and control, logic and memory, interfaces, and more, meeting the one-stop shopping needs of customers.
Conclusion
Battery energy storage systems play a crucial role in modern energy structures. They not only effectively enhance the utilization efficiency of renewable energy but also provide reliable support for grid stability and electricity flexibility. With continuous technological innovation, the safety, lifespan, and cost-effectiveness of energy storage systems are continually improving, driving their widespread application in residential, commercial, industrial, and large-scale power infrastructure. onsemi offers a complete product line required for designing battery energy storage systems, which will accelerate the design speed of related application products and help seize market opportunities.
