Novel transformer-flux-balancing control of dual-active-bridge bidirectional converters

Abstract

In this paper, a novel flux-balancing method for the isolated dual-active-bridge (DAB) bidirectional converter based on direct control of the magnetizing current is proposed. In the proposed method, the dc component of the primary and secondary current is controlled by providing two control loops; one to keep the average magnetizing current approximately zero and the other to keep the average primary and secondary current approximately zero. The performance of the proposed fluxbalancing control is experimentally evaluated on a 3.3-kW DAB prototype designed for automotive applications.978-1-4799-6735-3/15/$31.00 ©2015 IEEE

Flux-Balance Control for LLC Resonant Converters with Center-Tapped Transformers

“…The switching frequency is f s = 126.21 kHz. The magnetizing DC current can be estimated to be I Lm,DC,est = 20 mA, using (15). The magnetizing DC current estimated from the experimental result is close to the value obtained from the simulations, which confirms the effectiveness of the approach proposed in this paper.…”

“…The switching frequency is fs = 127.01 kHz. The magnetizing DC current can be estimated as ILm,DC,est = 400 mA using (15), which is approximately the same as the simulated result, although the experimental result does not measure the magnetizing DC current directly. Figure 20 shows the simulated and experimental results of the LLC resonant converter at full load in steady-state with the flux-balance loop control, for the same mismatched condition as that in Figure 19.…”

“…where i Lm,DC,est [n] represents the estimated magnetizing DC current. Equation (15) reveals that the estimated magnetizing DC current can be approximated as the sum of i Lm,p [n] and i Lm,n [n], divided by 2, which is a very simple method to obtain the magnetizing DC current. The block diagram of the DC magnetizing current estimator is shown in Figure 10.…”

“…Besides, the DC magnetizing current of the LLC resonant converter is difficult to sense directly. An indirect method to sense the magnetizing current was used [15], which involved sensing the currents at the primary and secondary side, simultaneously and subtracting them to obtain the magnetizing current. Then, the DC component was obtained using a low-pass filter.…”

Comparative evaluation of capacitor-coupled and transformer-coupled dual active bridge converters

“…But in both cases, the transformer design is not a trivial problem, especially when the voltage conversion ratio is greater than 1:2 or 1:3 [17]. Transformers in bidirectional converters are also susceptible to saturation, which requires passive or active methods for flux balancing [18]. Even for low power application, higher switching frequencies can cause problems in magnetic components.…”