Ingilala Jagadeesh and V. Indragandhi*
School of Electrical Engineering, Tamilnadu, India
Abstract
In this paper, we reported isolated DC–DC converters. Based on the review, the performances of isolated converters are evaluated. DC–DC CLCC and Dual active bridge (DAB) converters can attain bidirectional power flow, wide gain range, galvanic isolation, high power density and high energy efficiency for bidirectional electric vehicle charging systems. Gallium Nitride (GaN) devices have zero reverse recovery losses, very low gate drive losses and low output charge compared to a silicon MOSFET, which makes GaN devices relevant for high-efficiency power converters.
Keywords: Solar PV, isolated converters, electric vehicles (EV), bi-directional converters
The maximum voltage gain of the cascaded boost converter, switched-capacitor converter and switched inductor converter are limited because of the high duty cycle. To overcome this problem, forward converter, bridge converter, fly-back and push-pull converter type isolated converters used to step-up the voltage [1]. Another common DC–DC isolated converter is the resonant converter, which can be used for the soft switching in the whole load spectrum. The full-bridge DC–DC current fed converter is used to reduce the input current ripple. To attain smooth switching conditions and to transfer energy the transformer parasitic elements are worked as resonant elements [2, 3]. An isolated auxiliary current pump module is operated as a generic supporting module for step-down/step-up DC–DC converters [4]. The three-port bidirectional isolated converter is designed for concurrent power managing of a rechargeable battery, PV panel, and load [5]. The current mode control system is designed and implemented in conjunction with an isolated auxiliary current pump module for interleaved boost converters [6]. The isolated power converter contains three-winding transformer, two full-bridge rectifiers and a half-bridge inverter. The switching circuit is connected in parallel or series can be applied to isolated power converters to regulate the voltages [7]. The Isolated modular DC–DC converters need to be worked by an extreme ac-link frequency in order to decrease the size of the network, but this will result in boosted switching losses and reduced efficiency [8].
DC–DC isolated converters are widely applied in battery chargers for EVs. These isolated converters interface between energy storage unit along with DC voltage connection. DAB and CLLC DC–DC converters can achieve galvanic isolation, wide gain range, high energy efficiency, bidirectional power flow, high power density and therefore have potential applications [9].
During the charging condition, the highest efficiency of the HBCLLC circuit is 96.5% and FBCLLC circuit is 95.0% in the discharging mode 97.4% and 96.1% respectively shown in Figures 13.1a and b. For the HBDAB and FBDAB circuits during the charging mode, the highest efficiencies are 93.9% and 95.1% in the discharging mode 94.3% and 93.5% (Figure 13.2a). At light load conditions the DAB switches lose ZVS and the single-phase shift control technique generates huge reactive power which decreases the efficiency in Bidirectional HBCLLC resonant converter circuit. Based on the high-frequency a DAB-BDC control strategy is derived from the conventional buck and boost DC–DC converter technique. The converter strategy ensures that buffering inductor current is controlled in BCM or DCM which outcomes in high efficiency (Figure 13.2b).
The DAB DC–DC converter is presented in Figure 13.3. The current fed hybrid DC–DC DAB converter is used to decrease the high-frequency input ripple current. All the power MOSFETs switches using the ZVS technique. The DAB converter is designed for low-voltage FC power conditioning systems. The input side consists of two inductors and four power MOSFETs. The output side consists of four MOSFETs.
The auxiliary half-bridge contains two power MOSFETs and two capacitors. The input and output sides are linked by the transformer T. Here, the transformer turns ratio is 1: n.
The maximum conversion efficiency is more than 95%. With increasing output power, the efficiency increases until the efficiency reach its maximum value.
An interleaved bidirectional DC–DC isolated converter as shown in Figure 13.4. Switching losses are fairly decreased due to soft switching of semi-conductor switches that is ZVS of secondary switches and ZCS of primary switches. The converter operates in the reverse mode as a conventional full-bridge DC–DC voltage-fed converter by a load side filter. To attain ZCS of the low voltage side and ZVS of the high voltage side, normal phase modification modulation can be hired [11]. The efficiency comparison presented in Figure 13.5.
The DC/DC bidirectional Three phase converter technique combines the six-leg converter and three-phase DAB converters. The topology can increase the power capability and withstand high currents of the DAB converter, preserving related modulation technique without changing its main features. Compared to conventional current fed bidirectional DC-DC converters this converter has additional switches (Figure 13.6).
A three-phase DC–DC converter used as bidirectional converter in between the source and battery of the vehicle. The proposed DC–DC bidirectional converter with six leg inverter have more current capability compared to DAB converter. This converter is relevant for EV charging.
The DC–DC isolated power converters extensively used in EV and dc microgrids. The CLLC converters are slightly better than the DAB converters for comprehensive bidirectional EV charge systems. The voltage stress and di/dt value of the isolated three-port DC–DC bidirectional converter main switch have been decreased compared to the equivalent hard-switched converter. The converter peak efficiency is 94.5%. The LLC can achieve an efficiency of 98.39% undercharging condition and 97.80% in discharged condition. The GaN converter achieved 98.8% efficiency at 50% of the full load.
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