Cell Balancing Method in Flyback Converter without Cell Selection Switch of Multi-Winding Transformer

Abstract

-This paper presents a cell balancing method for a single switch flyback converter with a multi-winding transformer. The conventional method using a flyback converter with a multi-winding transformer is simple and easy to control, but the voltage of each secondary winding coil might be non-uniform because of the unequal effective turn-ratio. In particular, it is difficult to control the nonuniform effect using turn-ratios because secondary coil has a limited number of turns. The nonuniform secondary voltages disturb the cell balancing procedure and induce an unbalance in cell voltages. Individual cell control by adding a switch for each cell can reduce the undesirable effect. However, the circuit becomes bulky, resulting in additional loss. The proposed method here uses the conventional flyback converter with an adjustment made to the output filters of the cells, instead of the additional switch. The magnitude of voltage applied to a particular cell can be reduced or increased according to the adjusted filter and the selected switching frequency. An analysis of the conventional converter configuration and the filter design method reveals the possibility of adequate cell balancing control without any additional switch on the secondary side.

A Modular Cell Balancer Based on Multi-Winding Transformer and Switched-Capacitor Circuits for a Series-Connected Battery String in Electric Vehicles

“…Moreover, the buck-boost converter-based balancers need intelligent control and a large number of the switches resulting in relative complex control scheme and high cost. In the MWT-based balancing topologies [10,17,18], the multi-winding transformer needs to be considered as the main drawback due to not only the stringent requirement for parameter matching for the turns ratio but also the requirement to change the number of secondary windings. These lead to a mismatch between the leakage inductance that caused a charge imbalance drawback by itself.…”

“…The MWTFC-based balancer equalizes the voltage of cells in the SCBS by selectively turning the switches S k on or off according to the constant duty cycle (D) simultaneously. Figure 2 shows an active cell balancing circuit using the MWT with the forward converter structure and operating modes [17,18,21,25,28]. This circuit consists of N series-connected cells.…”

“…Flyback converter [18] 1 n --1 (n primary windings) Forward converter [17] n 1 --1 (n primary windings)…”

“…Recently, the cell balancing methods have been introduced [10][11][12][13][14][15][16][17][18][19][20] and reviewed [7,8,[21][22][23], as represented in Figure 1. There are two main ways to equalize a battery cell, which are passive and active methods [8,22].…”

“…There are two main ways to equalize a battery cell, which are passive and active methods [8,22]. Resistors are used in the passive cell balancing methods, which are connected The balancing method based on a multi-winding transformer (MWT) [18][19][20]24,25] has advantages such as fast balancing speed, simple control technique, and repudiation of voltage sensors. Nevertheless, this circuit has the complexity of fabricating MWT, a limited number of windings due to the parameter matching for the turns ratio, and leakage inductance, especially for a large number of cells.…”