Cun Wang

The frozen leg method is an effective fault-tolerant approach for addressing open-circuit faults in three-phase dual-active-bridge converters, requiring no additional hardware. This method isolates the faulty leg by disabling its two switches so that the converter can continue operating at reduced power levels. Prior literature on the frozen leg method primarily focuses on cases with unity voltage gain or buck mode. However, in boost mode where a higher voltage difference must be overcome, the faulty phase may enter discontinuous current mode (DCM), introducing additional complexity and necessitating a new mathematical framework. Thus, this article presents the first comprehensive investigation of boost mode frozen leg operation, proposing a novel analytical framework for the DCM. The analysis of boost mode is divided into five distinct cases, with corresponding derivations for power, current, and voltage equations. The findings show significant differences in operation compared to buck and unity gain modes. Additionally, this research derives the maximum power transfer achievable in boost mode and conducts a detailed soft-switching analysis. Based on this analysis, a ZVS-guaranteed control strategy is proposed to ensure that the operating points remain within the high-efficiency ZVS region. Experimental results are provided to validate the theoretical analysis.

The three-phase dual-active-bridge converter exhibits an inherent fault-tolerant capability for addressing open-circuit failures (OCFs). The frozen leg method is a notable fault-tolerant technique that mitigates OCFs without additional hardware. Upon OCF detection, this method deactivates the two switches in the faulty leg, enabling the converter to maintain operation at a reduced power level. However, all previous research on the frozen leg method assumes unity voltage gain. Yet, in practical applications, nonunity voltage gain, such as buck operation, is often unavoidable, wherein the voltage, current, and power characteristics significantly deviate from those at unity voltage gain. Thus, this article performs the first investigation of the more complex buck mode of frozen leg operation, and finds the operation must be categorized into three cases. The theoretical analysis derives the voltage, current, and power expressions for these cases, revealing significant deviations from those associated with unity voltage gain. Based on the derived current expressions, a detailed soft-switching analysis for the buck mode is also conducted. Furthermore, the theoretical maximum transferred power in buck mode under the frozen leg operation is proposed, and unique findings for power transfer at zero phase shift are examined. The theoretical analyses are validated through extensive experimental testing.

The three-phase dual-active-bridge (3p-DAB) converter possesses inherent fault-tolerant capability to address open-circuit failures (OCFs). The frozen leg method tackles OCFs without additional hardware by disabling the two switches in the faulty leg, allowing the 3p-DAB to transfer reduced power, generally by maintaining the original phase shift angle. However, prior literature on the frozen leg method focused only on operation with phase shift angles from 0 to π/3. The power transfer characteristics beyond this range, specifically from π/3 to π/2, have not been explored in the literature. To address this gap, this paper derives novel equations to describe the transferred power of a 3p-DAB operating with frozen leg control over the phase shift range of π/3 to π/2. These equations show for the first time that the theoretical maximum power transfer during frozen leg operation is 75.6% of the normal operation maximum power transfer. Further, based on the derived curves, this paper proposes a method to increase power transfer of the frozen leg method by dynamically adjusting the phase shift angle, which would not be possible without the full power transfer curve from 0 to π/2. The soft-switching analysis for the proposed method is also presented. The theoretical analysis and proposed method are validated through extensive experimental testing.

Though electric vehicles have the benefits of zero tailpipe emissions and convenient overnight charging, other challenges remain such as limited driving ranges, slow refueling while on-the-go, lithium supply issues, and emissions from some sources of electricity generation (e.g., coal). Fuel cell powered vehicles address the refueling time issue, which will also ease range concerns if hydrogen fueling stations are available. Furthermore, on-board solar generation can replace a portion of the vehicle’s grid charging needs and extend driving range. For both options, a smaller battery could be used, meaning less lithium is required. However, the power electronic architecture for such a solar fuel cell range extended vehicle (S-FCREV) would be complex and costly with conventional separate converters. Thus, this paper proposes the first practical multi-port converter that can perform all S-FCREV requirements with a low component count, including partial electrical isolation. This paper also proposes a simple Triple PWM and Triple Phase Shift (TPTPS) control scheme to enable flexible power flow between different power sources. A 3.3-kW prototype is designed, built, and tested to validate the topology and control. The experimental results show that the proposed topology achieves 97.8% peak efficiency with the proposed control.

Isolated dc/dc converters play a key role in electric vehicle applications, and novel multiwinding resonant converters have recently been proposed for on-board and off-board charging applications. Some of these topologies have two series capacitors at the dc bus with a mid-point connection to the windings. Parameter mismatch due to manufacturing differences will cause voltage unbalance on these capacitors, which can lead to safety and reliability concerns. However, the well-known capacitor balancing strategies proposed for other topologies are not applicable to these new resonant multiwinding topologies. Thus, this article proposes a novel capacitor voltage-balancing method for a resonant multiwinding converter. The method uses a simple table to decide on balancing switching states. Time-domain analysis is performed to quantify the control cycles required, and an adaptive control strategy is proposed. Experimental results with multiple bus capacitor sizes validate the effectiveness of the proposed method. Furthermore, use of the proposed method is found to slightly increase efficiency.

The auxiliary power module (APM) is a vital component in electric vehicles (EVs) that enables efficient power transfer from the traction battery to low-voltage electrical loads and the 12 V battery. As the EV industry continues to evolve, APM design is facing increasingly stringent challenges, including the need for higher power ratings, higher voltage ranges, higher reliability, and higher power density, with a continued need for efficient operation. However, there is a lack of literature that comprehensively reviews recent APM topologies based on these evolving requirements. This article fills this research gap by comprehensively reviewing current APM topologies from both academia and industry, including unidirectional and bidirectional topologies, single-stage and two-stage topologies, and multifunctional topologies. Furthermore, this article explores several potential future trends for APM design and development.

In three-phase voltage source converters (VSCs), the high-frequency leakage current can be easily suppressed by the common-mode choke, while low-frequency component would be an unfavorable factor to the inductor design. Thus, as the excitation source, the low-frequency common-mode voltage (CMV) should be properly managed. This article analyzes the low-frequency CMV impulse by constructing a 3-D voltage vector space, and a novel modulation method is proposed to eliminate the low-frequency CMV. Meanwhile, a comparative study is conducted between the proposed method and the other four typical space vector pulsewidth modulation (PWM) (SVPWM) method from the view of CMV and differential-mode current (DMC). In the analysis, a double-current-ripple-envelopes method is proposed to describe the current ripples. Besides, the influence of modulation indexes and power factors on DMC are considered and evaluated. And a guiding rule for choosing the appropriate modulation method for three-phase VSCs is provided. Finally, the theoretical analysis and proposed method are experimentally validated under a 5-kW three-phase PWM converter.

Multiple second-order generalized integrators (MSOGI) has been widely used to extract the signal that contains multiple harmonics. The MSOGI needs to be implemented in the discrete-time domain for its practical applications. More critically, the discretization method can greatly affect its performance. The existing discretization methods for MSOGI can be divided into three categories: entire transfer-function discretization, SOGI-transfer-function discretization, and integrator discretization. The theoretical analysis indicates that the first method can avoid the errors caused by unit delay, but it is hard to be digitally realized for high-order transfer functions. The other two methods have nonnegligible errors in both the phase and the quadrature characteristic due to the unit delay. In this letter, we propose a novel discretization method by modifying the structure of integrator discretization. This method can enhance the performance in both the phase and the quadrature characteristic with an acceptable computation burden, which has been theoretically analyzed and experimentally verified.