Forward Converter Current Fed Equalizer for Lithium Based Batteries in Ultralight Electrical Vehicles

Abstract

In this paper, the concept of a forward balancing technique fed by a buck converter for lithium-based batteries in Electrical Vehicle (EV) applications is investigated. The proposed active topology equalizes eight cells in a series in a battery pack, by using a forward converter for each battery pack and the whole battery packs, using a buck converter. The battery bank consists of four battery packs, which are in series. Therefore, the proposed system will equalize 32 cells in series. In this paper, the proposed circuit employs a single transistor used in a Zero Voltage Switch (ZVS) for the forward converter. In practice, this means a capacitor in parallel with the switch at the same time a demagnetizing of the transformer is obtained. The circuit realizes a low Electromagnetic Interference (EMI) and reduces ringing. To overcome the problem of many pins on a coil former, the transformer secondary windings are made by using hairpin winding, on a ring core. It permits, e.g., having eight secondaries and uniform output voltages. Each secondary winding is made by two hairpin turns using two zero-Ohm resistors in series. The proposed topology has less components and circuitry, and it can equalize multiple battery packs by using a single buck converter and several forward converters for each battery pack. Experimental and simulation results are performed to verify the viability of the proposed topology.

A Ćuk Converter Cell Balancing Technique by Using Coupled Inductors for Lithium-Based Batteries

“…The multi winding transformer has a magnetic core with one primary and multiple secondaries for every cell, as shown in Figure 3. The advantages of transformer balancing circuits are fast balancing time, direct energy transfer is possible between non-neighboring cells and easy to control [24]. However, the secondary winding voltages are not equal due to the nonuniform turn ratio of secondary winding leakage inductance, and also magnetic losses and high cost are its disadvantages [25][26][27].…”

A Single Transformer for Active Cell Equalization Method of Lithium-Ion Batteries with Two Times Fewer Secondaries than Cells

“…Thus, battery equalizers are needed to ensure that all cells in a series-connected battery string are fully charged or discharged. Many battery equalizers have been proposed in the last few years [13][14][15][16][17][18][19][20][21][22]. These applications are divided into a passive balancing technique and an active balancing technique.…”

“…Therefore, the balancing speed is slower as compared to the transformer balancing method. In the second type, the multi-winding transformer has an advantage that direct energy transfer is possible between non-adjacent battery cells [8,9,17,21,[24][25][26][27][28][29][30][31][32][33][34][35][36]. The multi-winding transformer topology has a magnetic core with primary and multi-secondary windings for each cell.…”

A Smart High-Voltage Cell Detecting and Equalizing Circuit for LiFePO4 Batteries in Electric Vehicles

“…For the battery to have a long life, it requires an appropriate battery management system (BMS) to equalize the cells in a battery string. Several cell-balancing strategies have been presented in the literature [8][9][10][11][12][13][14][15]. Slight differences between the series-connected cells in a lithium-ion (Li-ion) battery pack can produce imbalances in cell voltages, and this effect causes great reductions in the charge capacity [16,17].…”

“…The transformer/flyback balancing method is an active balancing method and removes energy from one cell to another cell [11][12][13]15,[26][27][28]. It may have a smaller balancing/executing time.…”