High-performance magnetic sensors accelerate electric vehicle charging

Environmental policies are leading us to achieve zero-emission targets in most of the world’s major cities by 2050. Achieving zero-emission transportation is critical to reducing polluting air particles present in many urban environments and controlling associated health issues. To this end, entrepreneurial and technological strategies have emerged to support electric vehicle (EV) fast-charging infrastructure.

China is the leading market for the booming electric vehicle industry, followed by the United States and Europe. Government ambitions are driving China’s EV momentum. The country aims to have more than 6 million electric vehicles on the road within the next two years. Because the batteries in electric vehicles are still bulky and expensive, the focus is now on building an efficient charging infrastructure. Advanced magnetic components can help designers achieve safety, reliability, and high performance for the growing charging network.

Figure 1: Sensors and devices used in electric vehicles

Microcontrollers, power management ICs for power control, and various sensors complete the electronic ecosystem of an EV (Figure 1).

Electric Vehicles

A plug-in electric vehicle is a motor vehicle that can be charged from an external power source. There are two basic types:

Battery electric vehicles (BEVs) are fully electric and have no internal combustion engine. They get all the energy they need from an external power source.

A plug-in hybrid electric vehicle (PHEV) has a propulsion system based on an internal combustion engine that works in conjunction with an electrical management system. Charging control is supported by a communication protocol between the electric vehicle and the charging station. The protocol uses a pulse width modulation (PWM) signal to control the charging cycle.

Electric vehicle charging mode

An EV charging station is a network infrastructure that provides electrical energy to the vehicle battery. Charging stations standardized according to IEC 61851 are equipped with a range of connectors that meet automotive standards. Generally speaking, EV charging is divided into three main types, classified according to the output power and the charging time required to charge the battery of an EV or PHEV.

Fast charging models can be either AC or DC. The fastest AC chargers have a nominal output of about 40 kW, while most fast DC chargers have a minimum output of 50 kW. Both can charge most electric vehicles to 80% in about 40 to 60 minutes, depending on the battery capacity.

Level 2 fast charging configurations range from 7 kW to 22 kW and can typically fully charge an EV in three to four hours. Slow chargers are also commonly used for overnight, home use. They have a nominal output of about 3 kW and typically take six to 12 hours to provide a full charger for a pure EV, or two to four hours for a PHEV.

The IEC 62196 international standard classifies four charging modes, describing the general characteristics of electric vehicles and charging equipment. Mode 1 is a low-current AC charging method used primarily for light vehicles, such as mopeds. For safety reasons, the use of Mode 1 is prohibited in some regions, including the United States and Europe. This mode does not provide specific protection (except for magnetic thermal differential protection for domestic quads) or any communication between the vehicle and the charging hardware structure.

Mode 2 is an AC method used as a temporary solution. It is an intermediate mode between Mode 1 and Mode 3 (described later). Mode 2 is used when a vehicle equipped for Mode 3 charging must be charged using a suitable low-power adapter. It relies on the universal Schuko connector. A cable equipped with an In-Cable Control Box (ICCB) or In-Cable Control and Protection Device (IC-CPD) is used to perform the differential protection function. This mode is mainly used for home refueling or occasional or emergency refueling, and is commonly used in apartments and commercial parking lots.

Figure 2: General block diagram of IC-CPD

IC-CPD is well suited to charging vehicles flexibly and safely. The IC-CPD control system (Figure 2) is divided into two parts: control electronics and power electronics. The control part includes a microcontroller, drive circuits, and a control pilot. The control pilot is primarily responsible for the communication between the EV and the energy source, handling the maximum allowed current that may flow to charge the battery. On the power electronics side of Figure 2, two relays are required so that the charging process can be shut down in the event of a fault.

EV charging requires residual current sensors to meet new standards, including IEC 62752 and IEC 60364-7-722, and avoid hazardous situations when the vehicle battery (DC) is connected to the household power supply (AC). Sensors are essential to detect leakage currents that can flow through the IC-CPD into the battery and then into the Type A residual current device (RCD), shutting down the RCD’s safety function. Vacuumschmelze (VAC) offers a sensor based on the magnetic gate principle that provides excellent resolution and accuracy even in harsh electrical and environmental conditions (Figures 3 and 4). This compact sensor design is ideal for IC-CPDs, but can also be used with a wall-mounted charging box for Mode 3 charging.

Figure 3: Typical application of the Vacuumschmelze VAC 4641-X900 sensor

Integrating the VAC differential current (DI) sensor into an IC-CPD or wall box provides full current sensitivity and electrical safety for EV charging electronics at a low cost. If the sensor detects a fault current, the corresponding output will change its state. Design variants with integrated primary conductors for single-phase or three-phase systems as well as through-variants are available. From a thermal design perspective, the VAC 4641-X900 is capable of withstanding full load currents of up to 80 A. The measurement range for differential current is between 0 and 300 mA. From DC to kilohertz, the measurement resolution is 0.2mA, fully compatible with relevant European and American standards.

Figure 4: Inside the VAC 4641-X900 sensor

Mode 3 is the recommended AC method for everyday charging and includes important intelligent control features. Mode 3 Type 2 connectors are the standard connectors in Europe, defined by EU directives and several standards (e.g., IEC 61851), for private or public use. Using 11 kW to 43 kW of power in standard three-phase system times (Figure 5), Mode 3 offers improvements over Mode 2 in terms of charging time.

Figure 5: Block diagram of a public charging station

The control electronics for Mode 3 are more complex, with added features such as HMI, billing interface and communication for remote service applications. In terms of power electronics, Mode 3 requires current measurement for all three phases, as well as reliable energy metering during billing. For current measurement, VAC offers closed-loop current sensors based on a magnetic field probe design for high measurement accuracy. The compact design offers an integrated primary conductor for direct PCB mounting. The standard product portfolio is extensive, but VAC can also provide custom solutions with cost-effective designs. VAC current transformers allow power to be measured, providing very linear measurements with high dynamic range and high output signals.

Figure 6: Overview of electric vehicle charging modes

Mode 4 is currently the fastest DC charging method. The goal is to charge about 80% of the battery in 15 minutes. Typical charging powers are between 150 kW and 400 kW (Figure 6).

In modes 1, 2 and 3, the battery charger circuit is installed on the vehicle and powered directly from the mains voltage (220/400 V). In mode 4, the charger is installed in the charging station. The car is therefore charged with direct current to the actual charging voltage of the battery. The voltage is however regulated by the car's control system, which can remotely control the battery charger placed at the delivery point using a suitable communication protocol. Depending on the system used, the charging voltage can reach 1,000 V and the current can reach 400 A; cooling is usually required to keep the battery temperature low. The current system used for mode 4 charging is CHAdeMO ("CHArge de MOve", or mobile charging), suitable for charging up to 62.5 kW (500 V, 125 A). With this system,

In addition to these four modes, there are others that are being tested or awaiting standardization. "Wireless" (inductive, capacitive) charging methods using special plates placed on the pavement in parking lots are becoming increasingly relevant. Inductive charging with "paddles" is based on plug-in connectors without electrical contacts. Unregulated DC charging with a fixed charging voltage is a potentially interesting option for the future as DC low-voltage distribution networks develop.

Figure 7: General block diagram of a DC charging station

Figure 7 shows a block diagram of a DC charging station. An AC/DC converter is required in the power electronics. The power transformer guarantees safe galvanic isolation as defined by IEC 61851. The material selection is defined by shallow losses and high excitation levels, enabling a very compact and low heat dissipation solution. The nanocrystalline VAC solution exhibits low energy losses to suit EV applications.