ANALYSIS OF BATTERIES ACTIVE BALANCE SCHEMES EFFICIENCY

Abstract

The paper reviews the existing circuit solutions of devices for balancing electric batteries. The balancing principle on the basis of capacitive and inductive buffer elements has been described. It was shown the features of their work and the basic calculations for each device type. For circuits with transformer topology, the calculated values for determining the balancing current are indicated. Based on the circuit solutions analysis, the efficiency of using solutions based on inductive buffer elements is numerically determined and proved. Powerful batteries for power supply systems are used in the form of stacks, consisting of a series-parallel connection of single cells. During their operation, there is a problem of uneven discharge or charge, to compensate which it is necessary to make voltage levels balancing in the stack batteries. For safely using electrochemical batteries the using of specialized balancing devices is required. The most efficient, from an energy point of view, are active balancing systems. The analysis of the mathematical model of two types (capacitive and inductive) buffer elements operation allowed to give a qualitative assessment of their efficiency. The first, in comparison with inductive - not only have worse energy characteristics, but also do not allow to perform "scaling" of the device without significant complication of the control system. The current amplitude value in circuits with a capacitive buffer element is limited only by the internal parasitic resistances of the circuit elements, therefore, with a relatively large value of imbalance, in circuit elements (including batteries) takes place a significant energy loss in the form of heat which negatively effects on rechargeable battery parameters. The current amplitude value in the circuit based on inductive buffer elements is limited by the inductance value. It can be calculated at the device design stage. In addition, providing the control system with intermittent converter operation allows to reduce switching losses in the circuit power switches and increases the overall operation efficiency. With a large number of batteries (more than three) should be preferred transformer balancing systems, as a special case of inductive topology.