A major automotive challenge for a cleaner future

The demand to reduce CO2 emissions is driving global transportation equipment manufacturers to achieve lower and lower emission standards, which requires them to not only improve the efficiency of internal combustion engines, but also to transition to alternative powertrains such as hybrid vehicles and pure electric vehicles.

These new powertrains have expanded the automotive industry’s demand for electric motors, especially traction motors and starter/generators, which are already in traditional vehicles equipped with electric power steering, electric pumps and electric parking brakes.

Existing sensing technologies and their limitations

Rotor position sensors can be used to improve motor performance under closed-loop control. Using rotor position sensors allows for excellent torque control under all load conditions, including during startup. As well as high-precision angle control during braking and holding conditions, better rotation control at high speeds. This not only improves the overall efficiency of the motor, but also reduces noise and vibration as well as heat generation.

Specifically, these new sensors are used to improve accuracy, reduce size and weight, and reduce total BOM cost. Stray field immunity not only improves the reliability of sensors used in complex electromagnetic environments, but is also another important condition required for developing better motors. Of course, motor position sensors not only need longer life and durability, but also need to work in harsh environments such as high temperature, humidity, and dust.

The automotive industry recently uses magnetic position sensors or resolvers that use Hall elements or xMR elements. Among them, magnetic position sensors face the problem of insufficient detection accuracy when applied to multi-pole motors and can only be used for shaft-end applications. Although resolvers can use a through-shaft structure to achieve the application of multi-pole motors, they are not only expensive and bulky, but also take up more space.

A new era in motor control

In response to the need for high-precision detection in both end-of-shaft and through-shaft configurations, Renesas Electronics has developed the IPS2550. This revolutionary new product is a position sensor for high-speed motors with a sine/cosine output interface that supports a maximum motor speed of 600krpm with an accuracy of 0.2% full scale. The sensor has a standard 2-layer printed circuit board consisting of the IPS2550 and external passive components and a metal target mounted on the motor shaft.

IPS2550 is based on the physical principle of eddy current effect and uses 3 coil groups (1 for transmitting and 2 for receiving).

The IPS2550 position sensor is up to 1/10th the thickness and 1/100th the weight, significantly reducing the BOM cost when using a resolver solution. The IPS2550 position sensor is able to match the number of sectors of the sensing coil with the number of poles, thereby providing the most advanced solution for multi-pole motors, which is not possible with magnetic position sensors. This innovative approach improves accuracy, reduces weight, size, and overall system cost, and is a major technological advancement.

Challenges in sensor element design

For sensors based on the eddy current effect such as the IPS2550, the design of the sensing element is the key to obtaining good accuracy characteristics. Renesas has developed a set of tools for position sensor design. In addition, Renesas has a database called Customer Reference Board catalog (CRB) that has different combinations of sizes and poles, as well as multiple sensor design examples that can be easily and quickly applied to motors. These reference designs can be provided to customers in the form of Garbar files for manufacturing circuit boards.