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High-Speed Adaptive Control Microsystem for Active Cell Balancing


An active cell balancer is a circuit that ensures that charges are balanced in a series connected cells (e.g. battery cells). It takes charge out of a higher cell and dumps it into a lower charged one bi-directionally. Also, it has the capacity to insert or draw continuous current into any or all of the cells simultaneously within all the operating modes (charge, discharge or standing modes). Through this mechanism, it makes sure that cells are protected from over-charge, over-discharge and over-voltage. This is because regardless of battery mechanism, all cells have a finite Ah capacity and consequently in a series connection, any slight mismatch in the state of charge (SOC) could cause some cells to overcharge or discharge above the others causing cell deterioration and reduction in the system lifetime.

A fundamental challenge in realizing a cells balancer is overcoming the inherent offset (>10mV) in CMOS technology. There is also a need to sense low current and this requires integrating high precision Opamp and comparators monolithically. Because voltage references could be sources of errors, there is a requirement to develop them to work across different temperatures values while also providing high precision values. Designing these components is very difficult since their minimum performance imposes the performance boundaries of the system. We propose a mixed design with capacity to actively balance energy cells using a feedback loop and H-bridge. It is designed to provide cell equalization, reliability and longevity in battery cells by avoiding over- and under-voltage conditions. It monitors the state of the cells, triggers compensation signal whenever necessary in real time.

We combine a mix of switched capacitor techniques to design an integrated balancer (with analog front-ends) which continuously monitors batteries state of cells, resolves 1mV variation, and equalizes in real time. Using auto-zeroing amplifiers and novel adaptive hysteretic comparators with on-chip reference trimming, it offers high precision and performance. It beats many industry leading products in the number of supported cells and detection voltages. This is a product of an industrial collaboration and its core details are protected. It is engineered to be the industry first product in its market segment. The chip can find applications in solar panels, electric vehicles and other alternative energy solutions. The whole idea is to make the system smaller and move from the domain of discreet components to monolithic integrated circuits as our picture shows.

battery