GB2501512A

GB2501512A - Battery Balancing and Heating Apparatus

Info

Publication number: GB2501512A
Application number: GB1207267.4A
Authority: GB
Inventors: Paul Thomas Faithfull; John Roberts
Original assignee: Potenza Technology Ltd
Current assignee: Potenza Technology Ltd
Priority date: 2012-04-25
Filing date: 2012-04-25
Publication date: 2013-10-30
Also published as: GB201207267D0

Abstract

A battery cell state of charge balancing apparatus which utilises resistive loads switched across cells within a battery pack in order to balance the state of charge in individual cells (or groups of cells connected in parallel) and/or to generate heat for the purpose of heating the battery to a defined operating temperature to allow battery charging.

Description

Battery Balancing and Heating Apparatus This invention relates to a device that both balances cell voltages in a battery and provides a heating function.

A battery pack made up of a number of cells or groups of cells connected in series often has a cell balancing apparatus attached. The purpose of this apparatus is to balance the level of charge, voltage or energy in each of the cells by some means such that each cell can deliver the same total output of energy. By this means the overall usable energy of the pack is maximised by minimising the differential between the lowest state of charge and highest state of charge cell or cell group.

The overall useable energy of the battery pack is defined by the charge or energy storage capacity of the cells, the number of cells connected in parallel, and the differential in state of charge between the most charged and least charged cell or cell group in the series string.

Where an imbalance in state of charge exists in a string of series connected cells or cell groups, the limit of energy which can be provided to the cells (charging) is defined by the cell or cell group with the highest state of charge, and the limits of energy which can be extracted (discharge) by the cell or cell group with the lowest state of charge. The overall energy delivery capability of the battery pack is limited to the overall specification of energy capacity for the pack minus the differential between the equivalent cross pack energy capacity of the highest and lowest state of charge cells i.e. mirroring the capacity of these cells across the whole pack.

One common method of cell balancing involves the usc of resistive devices to burn off energy from cells identified to have a higher state of charge than other cells in the battery pack.

This method of cell balancing converts the excess stored electrical energy with a cell into heat. Current flowing through a resistive device generates heat as a function of the current and the resistance of the resistive element.

Commonly battery management systems minimise this heat generation for cost reasons, and also so as to not put heat into the battery pack as a whole.

Battery systems, notably but not exclusively for automotive use, are required to operate across a range of ambient temperatures, typically from -40 degrees centigrade to +60 degrees Centigrade. At lower temperatures, some battery chemistries, for example, Lithium Iron Phosphate will not accept charge into the battery without the potential to cause either damage, or a reduction in useable battery life. Some battery chemistries will output charge from the battery at a lower temperature than the limit on charge acceptance.

The present invcntion proposes a rcsistive balancing apparatus with a heat generative capability for battery cell heating. The generated heat is applied to the cells within the battery either by direct or indirect means. The heat generated is utilised to heat the battery cells to a temperature at which they can accept charge.

The benefits of the present invention are the integration of dual functionality of balancing and heating into a single component, thus removing the requirement for separate balancing and heating systems. Heating and balancing maybe undertaken simultaneously, or heating alone can be implemented by switching in all resistive elements (applying the same load to all cells and thus not impacting on the overall balancing of the cells).

Thc invention will now bc dcscribcd by way of example and with reference to the accompanying drawing in which: Figure 1 shows the circuit layout of three cells connected to a resistive balancing apparatus with a switch controlling current flow across each resistive element.

In figure 1, a switch, either solid state or mechanical can be closed creating a circuit connecting a cell to a resistive load, for example, resistor, lamp etc. The resistive load temperature rises as current flows through the load. The heat energy being created by the resistive load can be applied into the battery pack, to the cells either by locating the resistive load within the pack, or if mounted remotely, through either passing air or liquid past the resistive elements to transfer heat to the air/liquid. This air/liquid is then passed into the battery pack in the vicinity of the cells and heat transfer occurs to the cells.

The quantity of heat produced can be moderated through control of the switches, either by the number of switches closed or the duty cycle of the switching.

If the balancing itsistive loads are located remotely from the cells a gas or liquid maybe passed across the resistive loads or attached heat sinks in order to transfer heat via some means such as ducting from the resistive loads to the cells. A valve or diverting means maybe introduced to allow cell state of charge balancing to occur without introducing heat to thc battery cells by diverting thc heat transfer medium outside of the cell enclosure.

Claims

Claims 1. A resistive battery cell state of charge balancing apparatus with a heat generative capability for battery cell heating.
2. A battery cell balancing system according to claim 1, which utilises high currents in resistive loads to generate sufficient heat to act as a heat source for battery heating.
3. A battery cell balancing system according to preceding claims, which has a means to transfer generated heat from the resistive loads to the cells, either through direct contact, or means of passing a gas or liquid over the resistive load in order to transfer heat to cells located remotely to the resistive load.
4. A battery cell balancing system according to claim I and claim 2 which can independently switch one or more resistive loads across a single cell or group of cells connected in parallel, and which has a resistive load for each group of cells connected in series such that the generation of heat can be moderated by the number of cells connected to loads or the duration of time the cells are connected to the loads.
5. A battery cell balancing system according to preceding claims which can switch all loads on simultaneously in order to generate heat without affecting the state of charge balance between cells connected in series.
6. A battery cell balancing system according to claim 3, which can direct heated air or liquid into the area of the battery system cells or outside of the battery system enclosure through a fluid diverting mechanism, e.g. a valve.
7. A battery cell balancing system according to claim 5, which can switch on resistive loads when the cell temperature is too low for charging, but not too low for discharge capability and sufficient charge is available within the cells to provide heating.