Working groups in the International Organization for Standardization (ISO) have developed standards for everything from the operating range and charging timing of high-power charging stations (H PCs) to communication and interfaces. In Europe and the United States, cooperation has been initiated with Charin (Electric Vehicle Charging Interface Initiative) and his proposed "Combined Charging System" (CCS). Other countries have developed similar standards, including Japan's CHAdemo and China's GB T. Certain car manufacturers are also focusing on the development of proprietary charging solutions. For manufacturers looking to participate in this market, a modular approach is the obvious way to go. This article will talk about how to achieve this with a modular approach.
For decades, car owners have been unwittingly spoiled by the ubiquitous network of petrol stations. The idea that the optimal course must be planned around the refueling station does not come to their minds at all. However, it is important to consider buying or leasing a pure electric vehicle.
BEV), this is probably one of the first questions that comes to mind. While many people use electric vehicles primarily for short trips within range, there are exceptions such as weekend trips or annual holidays that need to be recharged.
When parked at home, our BEV can be charged slowly overnight. Many large cities and towns have also begun to deploy public charging stations, so that we can also charge our cars while shopping. The reality is that, at least for long-distance travel, electric vehicles need to be charged in a time close to the time it takes to refuel a combustion engine locomotive. A 22kW home AC charging pile can provide a range of about 200 kilometers after charging for 120 minutes. If you want to reduce this time to 7 minutes, you need a 350kW fast DC charging station.
For manufacturers looking to participate in this market, opting for a modular solution is the obvious way to go. The modular approach facilitates the reuse of certain components of the end product, such as a common enclosure and cooling solution, while at the same time selecting interfaces, cables, and electronic components according to the needs of the target market.
Power electronics design methods for fast DC charging piles
Charging stations with fast-charging high-power charging stations (HPCs) require a dedicated low- or medium-voltage (LV MV) electrical infrastructure to power them. It is expected that this will be mainly installed in places such as highway service stations along intercity traffic arteries. The input AC power supply transmits electrical energy to the isolation transformer, which is then converted from the secondary side to direct current. The use of double secondary winding y transformers is a common solution.
Figure 1: The rectifier unit can be easily implemented by using a 1200V CoolSictm MOSFET module.
Figure 2: Half-bridge modules in an Easy 2B package (e.g., F3L15MR12W2M1 B69) are ideal for Vienna rectification.
These phase-shifting transformers are combined with multi-pulse rectifiers and operate in series or parallel to reduce the harmonic content at the input. In this design, although isolation can be achieved by selecting a suitable DC DC topology, a transformer with improved harmonic content is also required. The first design decision to make here is whether to use a general-purpose AC bus or a general-purpose DC bus.
In the case of the universal AC busbar method, the secondary side of the transformer supplies power to multiple AC DC rectifier units, which in turn supply power to their own DC units. The advantage of this approach is that it simplifies the overall design concept of the charging pile. However, each AC DC rectifier unit requires filters, controllers, and sensors, which makes the total cost higher. At this time, it is not mandatory to support grid-facing energy recuperation, such as vehicle-to-grid (V2G) and vehicle-to-building (V2B)). However, if this requirement changes, it will further increase the cost and complexity.
The universal DC bus method means that one AC DC rectifier unit outputs DC voltage to supply power to all DC units. This approach has proven to be superior because it reduces the number and cost of components while also improving overall efficiency. When V2G and V2B become mandatory, it will be easier to upgrade. The DC bus is also easier to integrate with other energy systems that may be deployed (e.g., local battery energy storage systems, photovoltaic power generation systems, etc.). Finally, the current DC charging pile standard also supports the use of a single rectifier unit as the front end of multiple battery chargers in a centralized charging station. The main disadvantage is that the volume of such a high-power rectifier unit will be relatively large.
Charging stations that support 2-3MW power prefer a universal DC bus solution, which can be used to power 6-8 high-power DC charging units.
Introduction to the AC DC rectifier unit
High-efficiency AC DC rectifier circuits are made possible thanks to the latest power transistor technology, high-performance microcontrollers (MCUs) and digital signal processors (DSPs). On the one hand, they ensure the extraction of sinusoidal currents, low harmonic distortion (THDI 5%) and independent control of active and reactive power from the grid, and on the other hand, timely dynamic response control. Operating in a power factor correction mode ensures that reactive power losses from the grid are eliminated. Finally, bidirectional energy flow between the DC side and the AC side becomes fairly straightforward if the chosen topology supports it.
Two-level voltage source converters (2L-VSCs) are one of the most widely used topologies. It consists of an array of 6 switching devices (typically IGBTs or SiC MOSFETs) and a capacitor that acts as a DC bus with an output voltage higher than the input voltage. The rectifier unit also supports bidirectional energy flow and provides a fully adjustable power factor. The switching control can be either pulse-width modulation (PWM) or space vector modulation (SVM).
This rectifier unit is easily implemented with the help of the 1200V CoolSictm MOSFET module FS45MR12W1M1 B11 (Fig. 1). The module consists of six switching devices, all of which are integrated in the same EasyPackTM 1B package, which features a low spurious design and an integrated NTC temperature sensor. Half-bridge solutions such as the FF11MR12W1M1 B11 in the EasyDualTM 1B package can also be considered. Based on the design of these devices, power can be reached from 60 to 100kW at an on/off frequency of 25-45kHz.
If bidirectional energy flow is not required, the Vienna three-phase three-level rectifier will become a popular solution. It requires only three active switches and is capable of positive and negative boost power factor correction (PFC). When the control circuit fails, it can prevent the loss.
In the event of a short circuit at the outgoing or input terminals, it can even operate normally without losing a phase input. Assembly with discrete components can be a lot of work, but in high-power applications, integrated power modules are more commonly used.
By using the F3L15MR12W2M1 B69, an SIC module based on the Easy 2B package, a positive and negative boost PFC Vienna rectifier can be implemented (Figure 2). Each module contains two 1200V fast rectification diodes, two 1600V slow rectification diodes, and two 1200V, 15M SiC MOSFETs. Three modules in this Easy 2B package make it easy to design a compact, high-current, low-loss rectifier unit (Figure 3).
Variable DC output charging voltage is available
Charin defines a DC charger that supports an output voltage between 200V and 920V, can provide a maximum current of 500A, and can operate in a power range of up to 350kW. There are a range of isolated and non-isolated DC DC topologies that can be used to address this challenge.
Regardless of which topology you choose, there are several key requirements that must be met. Physical size and overall cost are key requirements, but electromagnetic interference (EMI) regulations must also be complied with. At the same time, zero-voltage or zero-current switching (ZVS ZCS) for maximum efficiency and support the maximum power required. Finally, make sure that the voltage and current ripple at the output is minimized, thus preventing the battery from overheating.
Fig: Useeasy 2b viennaRectifiers and full bridgesdc/dcmodule60kwHigh-efficiency design.
High switching frequency (hfThe topology of the isolation transformer (e.g., a full bridgel_l_cResonant converter) is known at the resonant frequency.
It is known for its highest efficiency. Since the primary side switch works inzvs, the secondary side diode works onzcsSo they're also inherently efficient. Unfortunately, the wide output voltage range required to support makes it very challenging to develop charging stations in this way.
Considering that the output power is greater than100kw, and isolation can be ensured by grid-side transformers, so non-isolated liters can be usedStep-down converters. In a multiphase configuration, it can be reached at its highestefficiency. This method can also significantly reduce the number of by.
Current fluctuations caused by voltage fluctuations. The modular design makes it easy to adapt its size and operating parameters to a wide range of requirements, including changes in output, performance or form factor.
Thermal solutions
While power converters can now achieve incredible levels of efficiency, when fast DC chargers are running at full load, only, equivalent to there3.5kwThe power is dissipated in the form of heat. Cables alone can add every meter100wadditional wear and tear. Forced air cooling can no longer meet the requirements of high-power charging piles (hpcNot only power electronics but also terminals and cables need to be cooled with liquid cooling.
The challenge here is that many liquid coolants are flammable, degradable, corrosive and toxic. waterGlycol mixtures have proven to be a common coolant for wires and terminals today. Dielectric coolants have also been successfully developed, including successful applicationsitt cannonHigh-power charging piles (hpc), ).3mtm novectm。The cooling system is paired with a stand-alone or centralized radiator (depending on the configuration of the charging station).
Conclusion
The acceptance of BEVs depends to some extent on the available charging infrastructure. While some of these concerns can be alleviated by better promoting the existing network of charging stations, it is also necessary to invest in high-power chargers with fast DC charging technology to alleviate people's anxiety about range on long journeys. Liquid cooling will be an essential component of a heat dissipation solution, requiring the selection of electrical topologies and components that are both efficient and easy to integrate with the mechanical system corresponding to the heat dissipation method. Silicon carbide devices, including diodes and switches, will form an integral part of the design, from the rectifier unit to the DC DC topology chosen to achieve the battery charge output.
New energy charging piles
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