1 Introduction
The development of electric vehicles is inseparable from the construction of charging infrastructure. Currently, the mainstream way to replenish energy is still charging. According to different charging currents, it is divided into AC charging and DC charging. In national and international charging standards, charging is divided into four modes. Mode 1 is to directly connect the electric vehicle and the power grid with a suitable connector. Due to the lack of necessary safety protection, most countries and regions prohibit its use. Mode 2 is an AC charging device that can be used with the vehicle. The difference between it and Mode 1 is that a control protection box (IC-CPD) is added to the charging cable. Mode 3 is the AC charging pile, and Mode 4 is the DC charging pile.
Modes 2 and 3 are the main solutions for home charging. A portable charger is usually included with the purchase of a car, and for those with installation facilities, an AC charging station and on-site installation service are also provided. Of course, in addition to choosing the "original charger," users can also purchase various "non-original chargers" on shopping websites.
2. The Popularization of Electric Vehicles
With the increasing popularity of electric vehicles and the expansion of home charging facilities, a problem arises: the power grid will become increasingly unable to handle the load.
As we all know, the electrical load capacity of a typical residential community is actually limited. Many older communities have transformer capacities of around 500kW, which is fine for most households to use for basic tasks like air conditioning and cooking. However, the charging power for electric vehicles is much higher. A standard charging station typically has a capacity of 7kW, and if everyone charges their devices together after get off work in the evening, it can charge up to 70 vehicles, assuming no other appliances are used. Therefore, new residential communities are generally designed with reserved capacity for electric vehicle charging.
A better solution to the grid load problem is to adopt the "orderly charging" approach. Orderly charging means that, while meeting the charging needs of electric vehicles, practical and effective economic or technical measures are used to guide and control the charging of electric vehicles, thereby smoothing the peak and filling the valley of the grid load curve, reducing the variance of the load curve, reducing the construction of power generation capacity, and ensuring the coordinated and interactive development of electric vehicles and the grid.
Orderly charging systems use charging stations as management units. Through automatic negotiation with the equipment within the station, they achieve autonomous balancing of the station, improving its economy and safety. Some charging systems also have data acquisition and control, load forecasting, and real-time adjustment of charging and discharging loads. They provide unified interactive services to users and have comprehensive statistical and analytical functions to meet operational management requirements.
The State Grid Corporation of China has begun constructing smart charging piles with orderly charging capabilities. A recent tender notice from State Grid Nantong Electric Vehicle Service Co., Ltd. included a 30 million RMB smart charging system procurement project. On March 16th, the Shanghai Municipal Administration for Market Regulation released the "Technical Requirements for Intelligent Charging and Interactive Response of Smart Charging Pile for Electric Vehicles" (DB31/T 1296—2021). This standard is the first domestic technical standard to clearly define the specific functional requirements of smart charging piles. It mainly includes applicable scenarios for intelligent charging and interactive response, equipment electrical safety and information security, intelligent charging functions, pile network interactive response requirements, and platform interaction technology requirements. It applies to smart AC charging piles and smart off-board chargers (DC charging piles) that require adjustment of the charging power of electric vehicle power supply equipment.
Of course, as an important energy interface for the future, charging piles can do more than just that. Currently, charging piles are still single-phase power control, but in the future, a vehicle with a nearly 100-kilowatt battery pack can also serve as an energy storage device for the power grid, homes, and buildings. During peak load periods or emergency times, it can perform reverse discharge to help the power grid achieve peak shaving and valley filling, and car owners can also profit from the electricity price difference.
Many manufacturers have also launched integrated photovoltaic, energy storage, and charging equipment, combining photovoltaic power generation, energy storage, and charging. The electricity generated by photovoltaics can be used for electric vehicles and daily household use, while excess electricity can be stored for use at night or in emergencies, or sold back to the grid for profit. Based on differences in electricity prices at different times and users' electricity consumption habits, data analysis can be used to automatically adjust charging and discharging power and energy storage levels, achieving efficient use of electricity. It can be said that the future technological form and business model of charging piles are still full of imagination.
Safety is another crucial issue that cannot be ignored. According to incomplete statistics from professional organizations, from January to December 2020, there were 124 reported car fires in the media, with fires occurring during charging accounting for 23% of the total. This caused enormous losses and cast a shadow over the promotion of electric vehicles. While considering making charging stations smarter, we cannot overlook their safety features and the protection of people. To address serious accidents like car fires, some charging station companies have implemented safety monitoring of the battery during charging, such as collecting data on maximum temperature difference, maximum pressure difference, maximum temperature, and SOC change rate. This data is then shared with the charging platform each time a vehicle is charged. The platform accumulates this charging data to create a historical record for the vehicle, allowing for early warnings in case of any abnormalities during charging.
The most alarming issue is electrical leakage. This is because leakage directly affects the safety of charging vehicles, the power grid, and even people. Charging stations are typically placed outdoors, exposed to sun and rain for extended periods, which can easily cause insulation degradation. If leakage occurs, the consequences could be disastrous.
Besides proper grounding, the selection of a residual current device (RCD) is crucial for charging piles. According to the national standard GB/T 18487.1, charging piles should use either Type B or Type A RCDs. As you can see, unlike the AC type RCDs used in household homes, the basic requirement for charging piles is Type A, which provides protection against both AC and pulsating DC leakage. The biggest difference between Type B and Type A is that Type B adds protection against DC leakage. However, due to the difficulty and cost of testing Type B, most manufacturers currently still choose Type A. The greatest danger of DC leakage is not to human safety, but to the potential failure of existing RCD protection devices, creating a hidden danger. It can be said that the current RCD protection in charging piles has inherent flaws even at the standard level.
The latest Shanghai Municipal Standard for Intelligent Charging and Interactive Response Technology of Electric Vehicle Intelligent Charging Piles has raised the leakage protection to Type B or Type A plus DC 6mA and above protection. It is believed that the national standard will follow suit in the future.
For example, MAGTRON offers products that meet the latest Mode 2 (ICE62752) and Mode 3 (ICE62955) leakage current detection requirements, such as the MAGTRON RCMU101-K series leakage current sensor.
This product series employs Trip signal output, providing European standard AC charging customers with a simple design and high-performance leakage current detection solution. This solution utilizes high-precision adaptive fluxgate sensing technology, enabling accurate and real-time detection of AC and DC residual current. It uses a built-in signal to determine the dedicated State of Charge (SOC) and outputs a Trip signal, fully meeting the DC leakage protection requirements of IEC62752 and IEC62955. Furthermore, the product series comprehensively covers application scenarios in 7kW single-phase, 11kW, and 22kW three-phase AC charging.
