EDNE August 2012 - (Page 13)

Accurate energy flow measurement in EVs I n an electric vehicle (EV) or hybrid (HEV) you need to monitor charge flows out of, and into, the traction battery very accurately. This can be the only way of tracking battery charge status – in the transient conditions of acceleration and regenerative braking, terminal voltage is not a good charge-level indicator. At any instant, therefore, you need accurate voltage and current measurements to compute charge flow. For the current detection, LEM proposes its CAB transducer. This is a fluxgate sensor that measures currents to less than 0.1% error. It is non-intrusive (electrically isolated) for safety and lossless detection (no sensing resistor in the primary power path); and it yields a digital output over CAN bus. The CAB transducer ranges up to ±400A, with unlimited overload capacity, and with excellent accuracy: Coulomb-counting error over the driving cycle is reduced to under 0.1%. It is a small panel-mounted module measuring 71 x 52 x 21 mm, excluding mountings, that has an aperture through which the primary (battery feed to the vehicle motors) conductor passes. It operates from the vehicle’s 12V power supply, and is rated for operation from -40 to +105 ºC. The transducer employs LEM’s implementation of the fluxgate principle. Fluxgate transducers use an advanced magnetic current-measurement principle that inherently cancels or nulls many of the offset and drift errors that appear in simpler current-sensing techniques. LEM says that in addition to maintaining battery health, you may be able to reduce battery size and weight. To ensure long battery life, EV and HEV batteries are typically never fully discharged, nor charged to the maximum, and are therefore over-sized compared to their nominal rating. Car makers must further increase this safety margin if they need to make allowance for inaccuracies in energy measurements. Confidence in state-of-charge computation may allow you to reduce those margins. —by Graham Prophet LEM, www.lem.com The primary conductor feeding an EV’s drive motors passes through the aperture in LEM’s CAB sensor. www.edn-europe.com AUGUST 2012 | EDN EUROPE 13 http://digikey.com/europe http://www.lem.com http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE August 2012

Messe München
Messe München
Cover
Contents
Farnell
Microchip
Digi-key
Masthead
Comment
Pulse
Digi-key
Test & Measurement
Agilent Technologies
Understand the digital-output options for high-speed ADCs
Digi-key
Baker's best
Omicron
Cover Story
Digi-key
Generating spatial audio from portable products
Supply Chain
Design Idea
Product Roundup
Tales From The Cube

EDNE August 2012

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