Zero-voltage switching for bidirectional buck/boost converter using hybrid discontinuous current mode

A design methodology is presented for a full-bridge Power Factor Corrector (PFC) converter with two control schemes: the well-known Continuous Current Mode (C.C.M) and Triangular Current Mode (T.C.M). The second one is an extension of the Discontinuous Current Mode (D.C.M). The converter is composed of one high frequency leg and one leg switching at the grid frequency and includes the EMC (common and differential mode) filter. This work highlights the impact of the modulation scheme on the design of passive components and on the overall losses. A pareto front in the efficiency (η) vs power density (ρ) domain is derived for both modulation schemes and for natural convection cooling. We show that, when EMC issues are considered, the T.C.M poses more constraints for partial load operation, superseding the full-load design. Finally, it is shown that for non-interleaved converters C.C.M modulation is better than T.C.M modulation, resulting in higher density converters.

The state-space modeling and related order reduction problems of switching DC-DC converters operating in discontinuous (D) mode are treated in this paper. A unified discrete-time full-order model is proposed assuming the discontinuous current and voltage mode (DCVM) as a general operation mode from which the discontinuous current mode (DCM), the discontinuous voltage mode (DVM), and continuous made (CM) derive as special cases. Such a model permits a straightforward study of the control-to-output response, in each operation mode. The order reduction of the transfer function is carried out by means of the principal component analysis considering the joint controllability and observability properties of the circuit. It is shown that a proper order reduction can be gained not only in DC mode, as expected, but also in DV and DCV modes. A substantial difference between DC and DV modes is also evidenced in terms of controllability. The frequency analysis and state-space model order reduction for a Cuk converter are proposed to show that the method is free of the limitations affecting other methods of analysis and that its predictions fit experimental measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

For the power management of a wireless power transfer system for implantable mechanical heart pumps, an additional boost DC-DC converter stage is needed in order to control the power delivered to the implant. Particularly, battery powered and implantable medical devices pose special demands on the efficiency and/or power density of the employed converters. Accordingly, soft-switching and/or high switching frequencies must be targeted. Modulation schemes that allow for Zero-Voltage-Switching (ZVS) such as Triangular Current Mode (TCM) offer a highly efficient operation, but suffer from a large operating frequency variation, which is mainly limited by the digital control. Therefore the Clamp-Switch TCM (CL-TCM) converter can be employed which allows also for the control of the switching frequency variation. In this paper, the CL-TCM and the TCM converter are compared regarding the power conversion efficiency and the power density of the converter. Since the CL-TCM converter is not well known in the literature, the converter is analysed in detail and a modulation scheme is explained that allows for ZVS for all switches in the entire range of operation. In addition, the requirements for ZVS and a control scheme (i.e. timing calculations) are provided for the converter in order to limit the maximum switching frequency. The modulation and control scheme are verified with a hardware prototype. Finally, the performance of the CL-TCM converter is measured and compared to the performance of the converter operated in TCM mode. The measurements show that the CL-TCM converter offers similar performance compared to the TCM operation at lower inductor power density, but has the advantage of a significantly reduced switching frequency variation. In applications, where a very high power density is needed, the TCM converter outperforms the CL-TCM converter in terms of efficiency.

A single-stage power factor correction ac/dc converter based on zero voltage switching (ZVS) full bridge topology with two series-connected transformers is proposed in this paper. The proposed converter offers a very wide ZVS range due to the configuration of two series-connected transformers. It features a high efficiency over wide load ranges. Furthermore, it shows the low voltage stress on a dc link capacitor. The proposed converter also gives the high power factor and low input current harmonics complied with IEC 61000-3-2 Class D requirements by integrating a boost stage operated in a discontinuous current mode. The ZVS conditions, large signal modeling, and design procedure are discussed in detail. Experimental results are presented to show the validity of the proposed converter.

Recently, energy network systems with energy storage such as batteries have been focused on using for electric vehicles and power grid systems. Therefore, the Dual Active Bridge (DAB) dc-dc converter has been focused on because it has some unique advantages, such as bi-directional power transmission and high efficiency by Zero-Voltage-Switching (ZVS). However, hard switching and surge current are critical issues at light load. For the improvement of this problem, "masked-switching control (MSC)" was reported previously. However, another hard switching and surge current has confirmed at medium load by MSC. In this paper, the adaptive control method is proposed that can reduce surge current and operate ZVS at medium load. By experimental results, 1.4% of maximum power efficiency improvement at the medium load is confirmed. From the results, it can be seen that the proposed control method can achieve ZVS and realization of high power efficiency with wide load range.

This paper proposes a discontinuous current mode (DCM) feedback current control for a single-phase grid-tied inverter in order to minimize a LCL filter without worsening total harmonic distortion (THD) of a grid current. In DCM, there are two nonlinearities occurring in the transfer functions; the first non-linearity occurs in the duty-ratio-to-current transfer function which worsens the current command response, whereas the second nonlinearity occurs in the disturbance-to-current transfer function which reduces the disturbance effect. In the proposed DCM current control, the first nonlinearity is compensated by utilizing the duty ratio at the previous calculation period in order to achieve the same control performance of the current command response as in continuous current mode. Meanwhile, the second nonlinearity is utilized in order to reduce the disturbance effect when the LCL filter with a small impedance is applied. Furthermore, a design procedure of the LCL filter is introduced under the condition that the impedance of the LCL filter can be minimized without worsening the grid current THD by applying the proposed DCM control. A 1-kW 100-kHz inverter with several LCL filters of different impedances (3.0%, 0.6% and 0.04%) is constructed in order to confirm the operation of the proposed DCM current control. As a result, the grid current THD is reduced from 8.5% to 3.7% at rated load. Furthermore, the inductor volume is reduced by 77.0%, whereas the converter loss is reduced by 17.1%.

The demand for highly efficient and dynamic electric vehicles (EVs) has increased dramatically. The traction inverter, a pivotal component in an EV powertrain, plays a crucial role. This study is dedicated to designing a traction inverter with focus on achieving high efficiency and elevated power density and mitigating electromagnetic interference (EMI) issues. To realize these objectives, autonomous gate drivers (AGDs) are proposed and designed using LTspice simulation software. The aim is to achieve zero voltage switching (ZVS) at both turn-on and turn-off through the utilization of triangular current mode (TCM) control on the gate driver. The AGDs implement a current modulation scheme by sensing the current and voltage and generating gate-source voltage signals with minimal delays. The implemented current modulation scheme by the AGDs results in an efficiency exceeding 99% for a 10 kW power rating. The sinusoidal output waveforms not only contribute to extending the motor lifespan by mitigating sharp-edge voltages but also bring advantages such as reduced switch stress, decreased EMI, and simplified thermal management.

In future dc distributed power systems, high performance high voltage dc-dc converters with redundancy ability are welcome. However, most existing high voltage dc-dc converters do not have redundancy ability. To solve this problem, a wide load range zero-voltage switching (ZVS) three-level (TL) dc-dc converter is proposed, which has some definitely good features. The primary switches have reduced voltage stress, which is only Vin/2. Moreover, no extra clamping component is needed, which results simple primary structure. Redundancy ability can be obtained by both primary and secondary sides, which means high system reliability. With proper designing of magnetizing inductance, all primary switches can obtain ZVS down to 0 output current, and in addition, the added conduction loss can be neglected. TL voltage waveform before the output inductor is obtained, which leads small volume of the output filter. Four secondary MOSFETs can be switched in zero-current switching (ZCS) condition over wide load range. Finally, both the primary and secondary power stages are modular architecture, which permits realizing any given system specifications by low voltage, standardized power modules. The operation principle, soft switching characteristics are presented in this paper, and the experimental results from a 1 kW prototype are also provided to validate the proposed converter.

This paper presents a theoretical analysis of a resonant LLC DC-DC converter operating in continuous current mode with zero voltage switching (ZVS). On the base of modeling the processes in the tank circuit with differential equations, expressions for the fundamental quantities for both step-down and step-up modes are derived. The conditions for the transition to the discontinuous current mode are determined. The boundary of the ZVS operating area is defined. Output characteristics of the converter are plotted graphically for different values of circuit and control parameters.

In recent years, a system using renewable energy has attracted attention, and power converters with high power efficiency and low cost are required. Dual Active Bridge (DAB) DC- DC converters are attracting attention because of their high power-efficiency due to Zero Voltage Switching (ZVS) operation over a wide load range. However, when the voltage input/output ratio is different from the turns ratio of the transformer, there is a disadvantage that the ZVS operation cannot be achieved at light loads, and the power efficiency drops. Therefore, this paper proposes a digital control method that can improve power efficiency at light loads regardless of the voltage input/output conversion ratio. In the experiment, it was confirmed that the power efficiency at light loads could be improved by about 10% when the input/output ratio is 200V / 150V, 150V / 100V, and 125V / 75 V.

This article presents a soft-switched buck converter employing autonomous gate drivers (AGDs) for high-performance power electronic systems. Operating at a 400~V dc-link, representative of electric vehicle (EV) and industrial applications, the converter achieves zero-voltage switching (ZVS) during both turn<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-on</small> and turn<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-off</small> through fully analog AGD circuitry and optimized snubber capacitance. The converter operates in triangular current mode (TCM), leveraging the inherent inductor current ripple to enable ZVS without digital control. Experimental results demonstrate reliable soft switching, reduced switching losses, and effective suppression of voltage overshoot under realistic operating conditions. Although validated using a buck converter, the proposed AGD concept is directly applicable to more complex topologies, including three-phase inverters with sinusoidal reference currents, relevant to EV traction drives, renewable energy systems, and industrial converters. This work highlights a scalable, hardware-efficient approach for improving efficiency and performance in next-generation high-voltage power converters.

Three-phase synchronous generator-rectifier systems (TPSGRSs) with LC filters would exist discontinuous current mode (DCM) at their DC sides in cases of light loading or large filter capacitors contained. It is difficult to establish mathematical model of these generator-rectifier systems operating in DCM. To solve this problem, a new modeling method is proposed by substituting controlled rectifier in series with Boost circuit for diode rectifier in a TPSGRS. Considering the influence of inner resistances of inductances, we establish a new large signal mathematical model of TPSGRSs using switching function and principle of harmonic balance. The new model is compared to detailed simulations as well as physical tests, and is validated to be accurate in capturing large disturbance behaviors of TPSGRS operating in both continuous current mode (CCM) and DCM.

This article introduces a three-mode variable-frequency zero-voltage switching (ZVS) modulation method for the four-switch buck+boost converter. This method makes this circuit concept well suited for applications, such as wireless power charging of electric vehicles, where this circuit operates as a power buffer between the resonant converter and the battery with the function to implement the required charging profile. Herein, the buck+boost converter operation is subdivided into three operating regions according to the converter static voltage gain, i.e., buck-, buck-boost- and boost-type modes. A ZVS turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> triangular current mode (TCM) control is adopted for buck-type and boost-type modes. In the buck-boost-type mode when the input-to-output voltage gain is close to unit, all the possible modulation cases are studied thoroughly based on the phase shift of the two half bridges in a full switching period. The selection of the most suitable modulation scheme is performed to minimize the rms value of the inductor current while taking into account the simplification of the practical implementation. Closed-form equations are derived, which makes it easy to implement in practice. The proposed strategy is described, analyzed, and finally verified through a 3 kW surface mounted device (SMD) silicon carbide (SiC) <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> -based laboratory prototype with designed input voltage of 300–600 V and the typical output voltage of 400 V class battery. The efficiency from the measured results is remarkably high, i.e., between 99.2% and 99.6% in a power range from 1 to 3 kW. Finally, tests for the operating mode transitions demonstrated the feasibility of the proposed modulation method. The power density of this converter is 4.86 kW/L.

This paper presents the design of new highfrequency transformer isolated bidirectional dc-dc converter modules connected in module-cascaded solid state transformer (SST). A phase-shift dual active bridge (DAB) converter is employed to achieve high-frequency galvanic isolation, bidirectional power flow, and zero voltage switching (ZVS) of all switching devices, which leads to low switching losses even with high-frequency operation. Bidirectional DC-DC converter is crucial to the power transmission in SST. The proposed DAB converter consists of two three-leg bridges and a high-frequency transformer with winding shunting taps. Furthermore, the commutation inductance connected in series with the transformer in the conventional DAB converter is integrated into the transformer windings, thus, enjoying smaller volume and higher power density. By changing the number of primary winding turns, leakage inductance, which is the key parameter in the energy transfer process of DAB converter, can be adjusted on a large scale, enabling the possibility of reducing loss over wide load range. Additionally, time-sharing circuit topology and operation mode are adopted to adapt to the output power by detecting the output current as the feedback. As a result, the efficiency at both light and heavy load can be significantly improved compared with the conventional DAB converter, and, therefore, high efficiency over wide load range and high power density can be achieved. Besides, the additional bridge arm structure along with a flexible control scheme provides possible high-level fault tolerance. Finally, the simulation results on a 2-kW DAB converter module switching at 10kHz are presented to validate the theoretical analysis.

A three-phase current-fed dc/dc converter with a three-leg high frequency transformer for fuel cells