FTM / Security & Encryption / Panasonic — EV Charging
While efficiency and reliability are key considerations for designing electric vehicle (EV) charging stations, OEMs must also make safety a top priority. Charging EVs quickly requires the use of high current, and an operator holding a charging gun could be at risk of injury or death unless measures are in place to safely manage charging.
To protect operators from electrical injury, charging guns need a protective locking mechanism which confirms the gun is properly seated in the charging port before allowing live current to flow through the relay. Because all charging current passes through the relay, the relay must protect against power events such as an internal weld that could result in a short circuit. OEMs also need to select the right capacitor technology to not only filter interference from power to increase efficiency and reliability, but also to minimize the risk of a capacitor exploding if a short circuit occurs.
Protective locking mechanisms
Figure 1 shows the construction of a charging gun which uses a snap-action switch. Note that the full charge does not pass through the snap-action switch but rather is controlled by it. For basic safety, snap-action switches should be sealed to provide an extra level of protection against short circuits in case the charging gun is accidentally dropped in a puddle of water during operation.
A variety of snap-action switches are available, depending on charging requirements. For applications which need to support up to a 2 A switching current, the ABS Series is a reliable, small form-factor switch. For lower-current requirements, the ASQM and ASQMR Series provide reliable switching. ASQM Series snap-action switches are the smallest option available and can provide silent operation. ASQMR Series switches include internal resistors which can detect and differentiate between an open circuit and a short circuit so the system can safely shut itself down (see Figure 2).
Safe and reliable relays
It is important to select the right type of relay for an application. EV designs can supply ac or dc, and may be based on a single-phase or three-phase model. Single-phase designs use a higher current than three-phase designs and so must be rated for higher power. Relays such as the Panasonic HE-PV Series provide high current protection at a competitive price.
Relays can also implement a variety of features which improve EV performance. For example, a relay with low coil-holding power releases some of the power on the coil once the relay is activated, thus consuming less energy.
One of the challenges for EV manufacturers is to keep pace with fast-changing regulations from organizations such as UL and the IEC. Recently, new regulations made the relays used in today’s EVs obsolete for many new designs.
To keep its customers on the leading edge of technology, Panasonic continues to innovate and advance its relay technology so it can deliver new products which meet today’s and tomorrow’s requirements. Panasonic builds on proven technology such as the HE-S Series family to develop the next generation of reliable and safe EV components, giving OEMs a preview of what’s coming in future.
Our forthcoming relay designs – details of which are available under a non-disclosure agreement – address the latest changes to UL and IEC standards, including IEC62955, IEC61851, and UL2231. For example, if a three-phase relay welds, creating a short circuit, the relay needs to shut down power. To improve safety, new regulations require that four open contacts (instead of two) be used to detect a short circuit. Figure 3 shows how an auxiliary contact using a low current is used to monitor the high-current contacts. An auxiliary contact simplifies the design of charging stations by integrating weld/short-circuit detection into a single package, eliminating the need for several external components. This also leads to a smaller overall footprint and lower system cost.
Panasonic continues to develop innovative safety capabilities in its relays. The AQV258H5 Series PhotoMOS® relays, for example, are used in a dc fast charger which must be able to handle high voltages and meet stringent creepage and clearance requirements. With the ability to detect whether its internal insulation has deteriorated, an AQV258H5 Series PhotoMOS relay can handle a high voltage in a small package without compromising safety.
Efficient capacitors designed for safety
Capacitors are useful for interference filtering to reduce noise in incoming current. Capacitors are used in a wide range of applications, and it is important to select the right capacitor for the type of charger being designed (see Figure 4, left side).
Home chargers, for example, typically supply an ac output. For these chargers, Panasonic’s ECQ-UA Series film capacitor supports ac outputs at voltages between 275 V and 310 V. In contrast, public chargers typically provide DC current, at up to 480 V in superchargers. Panasonic’s ECW-FG Series and EZP-V Series families of film capacitors are rated for operation between 600 V and 1,100 V dc, with the ECW-FG Series for lower-voltage chargers and the EZP-V Series for higher-voltage chargers.
Film capacitors can also be used in the car, with the EZP-V Series filtering the dc-link from the compressor and the ECW-FG Series filtering the dc-dc step-down conversion from the 300 V to 450V lithium battery output to 12 V/24 V accessories (see Figure 4, right side).
One of the advantages of using Panasonic film capacitors is their metallized design. Built using a pure aluminum film, these film capacitors provide higher resistance to humidity and corrosion for extreme weather applications compared to capacitors that use aluminum zinc metallization, which corrodes faster.
Panasonic film capacitors also use patterned metallization (see Figure 5). Rather than having a single, long film, the film is segmented internally using fuse-function technology. This creates independent cells which can be isolated from each other. If a single, long film is used, film failure results in the failure of the complete capacitor. With fuse-function technology, a failure in one cell is isolated from the rest of the film. While this leads to a drop in overall capacitance, it avoids immediate failure of the capacitor. In addition, if the film capacitor does end up failing completely, it results in an open circuit rather than a closed circuit which still passes power through it.
Segmented cells increase the overall reliability of a charging system and increase user safety by mitigating against the effects of power malfunctions. The impact of a power event on a traditional capacitor can be extensive and create a short circuit. Because of its segmented cells, Panasonic film capacitors experience less impact during a power event.
For lower-voltage EV applications such as accessories, Panasonic’s hybrid capacitors use a combination of aluminum and polymer electrolytes for higher electrical conductivity, leading to better filtering, less electrical noise, and greater efficiency (see Figure 6).
Hybrid capacitors also support high ripple current – up to 5.8 A – and a low equivalent series resistance (ESR). High ripple current is important for applications such as power steering which require high current. Low ESR equates to lower heat dissipation, reducing degradation of the electrolyte which occurs at high temperatures. Together, high ripple current and low ESR result in higher endurance and prolonged operating life.
To cope with the extreme environmental conditions which chargers might be exposed to – either outside in the direct sun or mounted in a hot garage – hybrid capacitors are available which support operation at up to 150˚C. Vibration-proof models are also available which can handle up to 30 G of vibration force (compared with 10 G for standard models).
And as the EV market evolves, Panasonic continues to develop innovative technology to improve the performance, efficiency, and safety of EV charging stations.
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