Requirements of EV Charging
While EVs can charge at the home, from a regular domestic supply, this is slow – and best-suited to overnight charging. Instead, many drivers want to charge much faster, and this requires the use of high-power DC charging stations, capable of charging an EV in less than 30minutes.
As well as safely meeting the electrical requirements of handling such large currents and voltages, there’s also a need for effective thermal management to handle the heat produced.
Reliability is essential, as drivers expect to always find a working charger. The EV charging infrastructure must function well in harsh environments, particularly in high temperatures in hotter climates, as well as sub-zero conditions elsewhere. With chargers often in relatively remote locations, the cost of sending a maintenance team to handle a repair is significant – hence operators want to minimise any problems.
Standardisation is key to meeting these goals. For vehicle charging today, one widely-adopted standard is ISO 15118, which enables efficient bidirectional communication between EVs and charging infrastructure, optimising charging efficiency and enabling vehicle-to-grid integration. ISO 15118 supports both AC and DC charging, including high power DC charging.
Depending on the type of component or system, there are various international standards that must be followed. For example, IEC 60502-2 covers requirements for power cables and their accessories that are rated up to 30kV.
Offshore wind turbines experience a hostile environment at sea, with weather extremes and the constant presence of corrosive sea water. Underwater electrical connectors, for both power and data, must be able to withstand large forces, as well as obviously being watertight, and resistant to bacteria. To simplify deployment, ‘wet mate’ connectors may be used, which can be mated and unmated in wet environments without letting in water.
As well as the connectors themselves, the cable jacket and harness need to be robust enough for underwater use. These are typically made from a thermoplastic material, which can be softened and manipulated when heated. Polyethylene (PE) provides excellent long-term sealing, but can be difficult to use, while thermoplastic polyurethane (TPPU) is another option which is flexible and tough.
High voltages are another factor to consider for offshore wind turbines. The turbines generate alternating current (AC) electricity, which they then convert to high voltage direct current (HVDC) before transmitting to shore. Using HVDC minimises power losses, which is important as the distances involved can be relatively large – for example, the world’s largest offshore wind farm, Dogger Bank, is more than 130km off the coast of England.
Solar PV installations have other specific considerations. For example, for safe operation, an in-line fuse is usually needed between solar panels and the electrical systems they connect to. This solar in-line fuse protects against short circuits, overloads and overheating, thus avoiding the risk of fire or damage.
High voltage connectors
As EVs demand more power for longer ranges, high voltage connectors play a vital role. These connectors ensure safe and efficient power transfer in compact spaces, thus enabling fast-charging capabilities, and reducing wait times at charging stations.
DC charging stations can supply high voltages of from 300V to 750V DC directly to a vehicle’s battery (bypassing the vehicle’s own on-board charger), at up to 400A. This requires a three-phase AC input from the grid, and cannot normally be powered from a domestic building.
Connector vendors such as Molex and TE offer power connectors that can handle high currents at the voltages involved in EV charging. For example, TE’s ERNI PowerElements connectors are rated at up to 500A, which means they can handle the 400A required for the highest-power charging mode defined by the IEC 61851 standard2.
Looking ahead, more vehicles will use 800V batteries, increasing the possible charging speed compared to today’s more common 400V. Moving to 800V also enables the use of lower currents, and therefore thinner and lighter-weight cables.
Battery grid-scale storage for renewables
We don’t know when the wind will blow, or when the sun will shine, and of course solar panels don’t work after dark. This means that renewable energy generation can be intermittent, and there is an increasing need for grid-scale storage: systems connected to the power grid which store energy when it’s available, and then release it back to the grid later when it’s needed.
In the past, the most popular technology choice has been pumped-storage hydropower. In these systems, electricity is used to pump water up to a reservoir. When power is needed, the water is released and electricity is generated.
Pumped storage has one major disadvantage: it is only possibly in locations where suitable reservoirs can be built, with a vertical distance between them. Instead, battery storage solutions are becoming more common, as battery technology improves. Battery systems are available in different capacities, and can be located anywhere.
IPE OFF-board connectors and high-current DC filters play a crucial role in ensuring these storage units function properly. Filters are available which are optimised for energy storage applications, to ensure that systems meet the limits of the relevant electromagnetic compatibility (EMC) standards. Similarly, filters for solar PV installations reduce EMC emissions, while also increasing the life of solar panels by protecting them against leakage and high frequency currents from inverters.
To send power to where it is needed, and to cope with intermittent generation from renewables, another option is electricity interconnectors. These are high-voltage cables to connect the electricity systems of countries near each other, for example sending power between Norway and the UK.
Innovative connectors
Heavy-duty connectors and bus bars are essential in managing high-power transfers, to handle the electricity generated by renewables. They ensure that energy is distributed efficiently, minimising losses.
To choose the right power connector or bus bar, you need to know the demands of the application. Specifically, what current and voltage will it be required to handle? For example, most wind turbines generate electricity at a low voltage of 660V, but some larger offshore turbines generate at 3.3kV, which is considered medium voltage. Another issue to consider is switching – while relays are commonly used, if large currents are involved, contactors may be used instead.
For connecting high currents, bus bars may be the best choice. They are usually made from copper, brass or aluminium, depending on where they are being used and the application’s requirements. For high currents, copper is often used, because of its good electrical connectivity. Aluminium is a lightweight alternative, which is also lower cost than copper.
Looking at connectors rather than bus bars, a good option for power transfer can be circular connectors. These are multi-pin connectors that provide a high density of contacts, thus saving space and weight. They are often used where rugged components are needed, with a robust metal or plastic housing enabling them to reliably function in harsh environments with extreme temperatures. They can withstand impact, shock and vibration, and are designed to avoid accidental disconnection.
Another point to consider is whether the connector will need to be mated or removed while power is live. This requires the use of a ‘hot-pluggable connector’ – manufacturers’ data sheets will specify whether a particular connector can be used in this way.
Conclusions
Renewable energy is the bedrock of how we will move to net zero. Low carbon electricity, from sources such as solar and wind, will enable us to cut emissions to reduce the impact of climate change.
To ensure that these energy sources are integrated seamlessly into the power grid, IPE OFF-board products are at the heart of the new infrastructures that are being created. Avnet works with the leading manufacturers of IPE-OFF board products, including Amphenol, Bel, Molex, TE Connectivity, Schurter, and HRS – ensuring our customers have the widest choice of suitable components, whatever their application.
1https://www.iea.org/news/renewable-power-on-course-to-shatter-more-records-as-countries-around-the-world-speed-up-deployment
