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Whether it's for a BMS or a motor controller, here are the important details to understand when
to find these important parts of EV.
Electric vehicles continue to grow in popularity and market share, and electric power is the fuel of the future. Current sensors are an important part of today's EVs, which serve two main applications according to Ajibola Fowowe, global product manager at Honeywell.
“The Battery Management System (BMS) uses current sensors, in conjunction with other sensors such as voltage and temperature sensors, to monitor the state of charge and overall life of the battery pack. One of the uses of current sensors is to control engines, where it is hoped that it can quickly detect and isolate the fault in the electric drive,” said Fowowe.
Regardless of the application, there are several considerations EV engineers must understand when choosing among the many current sensors available. Here's what you need to know.
Types of EV current sensors
There are different types of current sensors each with advantages and disadvantages for EV applications.
Closed current sensors
Closed loop current sensors have a feedback system for improved measurement accuracy. The magnetic core concentrates the magnetic field produced by the current flow and provides an electric current equal to the amount of current obtained in the course. This allows the sensor to produce an accurate current measurement. Due to their high accuracy and stability, closed loop sensors are well suited for use in BMS.
The Honeywell CSNV 500 (pictured above) is a closed-loop current sensor rated with a primary current measurement range of ±500 amps direct current. CSNV 500 features Honeywell's proprietary temperature compensation algorithm with CAN digital output, to provide high accuracy readings within ±0.5% error over a temperature range of -40⁰ to 85⁰ C with robust system performance and reliability.
Open loop current sensors
Current loop sensors work on the principle of magnetic induction. They consist of a primary winding, through which current flows, and a secondary winding that measures voltage. Open-loop sensors require more electricity and processing compared to closed-loop sensors, resulting in faster response times. However, they require more calibration because they are sensitive to variations in temperature and magnetic field. This means that they are also slightly more accurate — up to about a 2% error of the primary reading.
The fast response time of open loop current sensors makes them ideal for vehicle control tasks. Automotive control applications do not require the same level of accuracy as a BMS, so the loss of accuracy compared to a closed-loop or flow-gate sensor is not significant.
The Honeywell CSHV line of open loop sensors range from 100 amps to 1,500 amps, and their response times are as fast as six microseconds. They are used for fault classification and fault detection, as well as for controlling the speed of the vehicle. They can also be used in battery management systems that do not require very high precision, such as in hybrid electric vehicles. These sensors use AEC-Q100 integrated circuits suitable for meeting high quality and reliability requirements.
The Honeywell CSHV series is an open loop sensor
Honeywell's CSNV 1500 has both closed loop and open loop operation. This allows the sensor to meet the 1% accuracy requirement, and is designed for applications that require high accuracy. The CSNV 1500 is used for the same EV applications as the CSNV 500, as well as for stationary energy storage and industrial applications.
Flux gate current sensors
Flux gate current sensors measure changes in the flux of the magnetic current as it passes through the magnetic loop, where it can obtain current measurements. The Honeywell CSNV 700 is designed for applications that fall between 500 A and 1,000 A requirements. It has a better zero-offset range and higher sensing range than 500 amps sensors—but also has higher power consumption than a closed-loop sensor. The CSNV 700 has the same accuracy ratings as the CSNV 500, at 0.5%, and uses AEC-Q100 qualified integrated circuits.
Like closed loop sensors, the flux gate sensor is best used in BMS settings that require high accuracy. When using flux gate sensors, however, engineers need to be mindful of their high power requirements, which can consume a lot of battery power.
Honeywell's CSSV 1500 is a combination open loop and flux gate sensor. It is designed to meet the requirements of Automotive Safety Integrity Level C (ASIL-C) for safety critical applications where customers desire a high level of reliability and performance. While most 1500 A sensors use more power, the combination of open loop and flux gate technology uses less power while still meeting accuracy and operational safety requirements. Meets Automotive Safety Integrity Level C (ASIL C) requirements for safety critical applications. This requirement is common to battery electric vehicles (BEV).
Shunt current sensors
A shunt current sensor measures the voltage drop across a resistor and sense placed in a conducting path between the power source and the load. It is an in-line current sensor connected directly to the bus bar; closed loop, open loop and flux gate sensors are contact sensors that do not have that direct connection.
One of the advantages of a shunt sensor is that it can provide a quick current measurement. However, it generates more heat and contributes to power loss in the circuit. This creates a waste of energy for insects. Fowowe says that advances in shunt technology are increasing its appeal in high voltage applications and Honeywell is actively researching the added value that can be derived from the use of shunt technology as a possible combination of current and voltage measurements into a single sensor to reduce overall cost. of BMS.
Another important consideration for current EV sensors
In addition to considering which sensor to use in which application, engineers will also need to consider other variables. Since the sensor needs to work well in a magnetic field, its ability to handle magnetic disturbances is important. For BMS applications that rely on a high level of accuracy, engineers will need to consider the sensor's zero-offset, which is the amount of deviation of the output or reading from the lowest end of the measurement range.
Ease of integration is also important to consider. EVs can use the controller's local network output (CAN bus) or analog output. CAN communication is very common in BMS. The CAN bus communication speed is limited by the CAN protocol to 10 milliseconds, which is acceptable for the BMS. For fast measurements, vehicle control functions use analog output, which can respond in microseconds.
Another feature worth noting is the EV's driving position. EVs need to be able to perform well in any conditions, from a heat wave in Arizona to a blizzard in New York. Therefore, the operating temperature of the sensor must be included. According to Fowowe, Honeywell sensors are designed to maintain performance at temperatures ranging from -40 to 85 degrees Celsius; the sensors feature Honeywell's patented multi-point temperature compensation algorithm to ensure that the sensors can deliver the highest accuracy and performance under any driving condition.
To learn more about current sensors for EVs, visit Honeywell at TTI.