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BLDC sensors avoid the need for chopper stabilisation

04 November, 2013

Honeywell Sensing and Control has developed a new sensor technology for brushless DC (BLDC) motors that removes the need to use chopper stabilisation. It claims that this results in faster response times, higher accuracies and minimal electrical noise levels, without needing extra filtering.

At the heart of the new technology is a quad Hall-effect magnetic sensing element and proprietary programming that result in a sensitive, stable sensor capable of operating across a wide range of temperatures in a variety of applications – especially where efficient, quiet operation in needed – such as robotics, HVAC and domestic appliances.

The new technology is said to overcome the drawbacks of chopper stabilisation, and to bring performance advantages, such as improved jitter performance.

Electronically-commutated BLDC motors are growing in popularity due to their higher efficiencies compared to those that use mechanical commutation. But BLDC motor designers have traditionally had to turn to chopper stabilisation to mitigate for sensitivity and stabilisation issues over a wide operating temperature range.

Hall-effect sensors measure changes in magnetic fields and communicate the position of the motor shaft to a controller which determines when to apply the current to the motor coils to make the magnets rotate at the right orientation. For optimum efficiency, the rotor position needs to be measured as accurately as possible. However, the longer it takes for the sensor to respond to the changes in magnetic field, the less accurate this position is, potentially affecting motor efficiency.

Chopper stabilisation requires continual averaging of the induced voltage across the Hall elements to determine the output signal. This slows down the sensor switching and can result in errors as a motor spins faster.

Hall-effect sensors can be placed (from left): at the end of a motor shaft; around a ring magnet attached to the shaft; or inside the motor

According to Honeywell, motors using its stabilisation-free sensors are commutated at, or closer to, the correct time, resulting in higher accuracies and efficiencies. The quad Hall effect devices measure voltages in four directions, making them less susceptible to stress-induced errors than single or dual Hall effect devices.

Honeywell has tested the new sensors against several traditional chopper-stabilised products, including some claimed to offer higher sensitivities. The tests involved mounting and centring samples as close to each other as possible so that they all experienced the same environment on a circular target with 48 magnetic pole pairs used to trigger the product samples.

Honeywell says that its new technology delivered significantly better performance in areas ranging from sensitivity and repeatability to response times. Comparison testing showed that the non-chopper-stabilised parts had a repeatable output with a response time that was 10–20µs faster than the chopper-stabilised products.

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