Single Phase Shift Modulation Research Articles

Variable Switching Frequency for ZVS over Wide Voltage Range in Dual Active Bridge

The Dual Active Bridge (DAB) converter is known for its advantageous characteristics, including bidirectionality, galvanic isolation, and soft-switching operation. However, achieving Zero Voltage Switching (ZVS) across the complete operation range is not guaranteed, particularly through a wide input–output voltage ratio. This paper explores the integration of the switching frequency as a control variable in the DAB converter to ensure ZVS operation across a wide voltage range, employing Single Phase Shift (SPS) modulation. The study evaluated the RMS and reactive currents under variable switching frequency, presenting the advantages of this approach. Moreover, it includes a design-oriented analysis of the ZVS limits and their relationship with the switching frequency, aiming to ensure ZVS at any operating point. Experimental results validated the theoretical analysis, while presenting the main advantages of variable switching frequency implementation.

Single-Phase Shift Modulation of DAB Converter in Typhoon HIL Simulation

Solid-state transformer (SST) could be a solution for a future distribution system, in which many renewable energy sources (RES) are integrated. The SST consists of a single-phase dual-active bridge (DAB) converter, which is scale-down the dc voltage level. The control objective of the DAB converter used in the SST is to control its output voltage. This control strategy consists of a proportional-integral (PI) controller and a single-phase shift (SPS) modulation. Numerous literatures have mentioned about the SPS modulation for the DAB converter. However, they do not provide procedures in implementing the SPS modulation in the real controller. This paper aims to develop the SPS modulation in the real controller of the STM32F446RE microcontroller. The proposed SPS modulation is based on a master-slave timer feature, which is available in the STM32 microcontroller. The development process and testing of the complete control strategy of the DAB converter were carried out in the hardware-in-the-loop (HIL) simulation using Typhoon HIL. This scheme speeds up the development of process and reduces the costs. The experiment in the HIL environment shows that proposed control strategy of the DAB converter consisting of the PI controller and the SPS modulation is successfully implemented in the real microcontroller of the STM32F446RE. The proposed control strategy of the DAB converter is capable of bidirectional power flow, which is useful for integrating distributed generators in the load side. Moreover, this control strategy can reject the disturbance caused by loads.

An Improved Adaptive Sinusoidal Single Phase Shift Modulation for Bidirectional Single-Stage Onboard EV Chargers

An Improved Adaptive Sinusoidal Single Phase Shift Modulation for Bidirectional Single-Stage Onboard EV Chargers

Dynamic Performance Enhancement of a Triple Active Bridge With Power Decoupling-Based Configurable Model Predictive Control

The multiport active bridge (MAB) converter has been recently proposed aiming to increase the power density and the availability of electrical power distribution systems. However, the dynamic performance of proportional-integral (PI) controller for MAB voltage control is characterized by a relatively slow response and large overshoot. To address this issue, a power decoupling based configurable control (PDC-MPC) strategy inspired by the model predictive control (MPC) was developed. The proposed control strategy can achieve good transient performance and high control flexibility with good precision to comply to DC voltage regulations. In this paper, the PDC-MPC was investigated and implemented in a triple active bridge (TAB) converter with multi-winding high frequency transformers. The operating principle of the PDC-MPC is divided into two phases: prediction of the DC current through a binary search and decoupling of the desired power of each isolated virtual branch to its phase shift angles under the single phase shift (SPS) modulation strategy. Steady-state and dynamic performances of the proposed PDC-MPC for TAB converters were analysed using modified cost function and predictive models. Simulation and experiments were conducted to validate the theoretical analyses.

A Robust Voltage Control of DAB Converter With Super-Twisting Sliding Mode Approach

This article presents a supertwisting sliding mode control (ST-SMC) for the isolated dc-dc bi-directional dual active bridge (DAB) power converter for enhanced output voltage regulation. The sliding mode control (SMC) is well-known for its robustness and improved dynamic performance for a nonlinear system. However, it includes the drawback of chattering and degradation of tracking performance. Here, the suggested ST-SMC scheme incorporates the advantages of a sliding mode controller and subsequently eliminates the problem of chattering. The average model of DAB under single phase-shift modulation is considered for controller design, which simplifies the design process. Thus, improved dc-link voltage stability and high robustness for accurate reference voltage tracking are obtained. Further, the proposed scheme provides a robust control for parameter uncertainties as well as the steady-state output voltage contains less ripple when compared to the classical SMC and proportional-integral controller. The experimental results for a 2 kW DAB converter are provided to validate the effectiveness and the robustness of the proposed strategy.

Model predictive current control for dual-active-bridge dc-dc converter with single-phase shift modulation

This paper proposes a model predictive current control for the dual-active bridge (DAB) dc-dc converter with single-phase shift modulation. The DAB dc-dc converter model is established using the averaging method. To eliminate the steady-state error caused by model uncertainties, the integral of feedback error is combined with the state error to form the augmented system for the control design. Moreover, the controller gain can be systematically tuned by only one tuning scalar variable, making the proposed controller easy to implement. Furthermore, an offline optimization problem is used for computing the controller gain, so real-time computation burden is significantly reduced, enabling the use of low-cost DSP controller. Overshoot-free and fast convergence performance of output current can be achieved using the proposed method in simulations and Typhoon HIL emulator.

Dynamic Enhancement for Dual Active Bridge Converter with a Deadbeat Current Controller.

This paper investigates the deadbeat current controllers for isolated bidirectional dual-active-bridge dc-dc converter (IBDC), including the peak current mode (PCM) and middle current mode (MCM). The controller uses an enhanced single phase shift (ESPS) modulation method by exploiting pulse width as an extra control variable in addition to phase shift ratio. The control variables for PCM controllers are derived in detail and the two different current controllers are compared. A double-closed-loop control method is then employed, which could directly control the high-frequency inductor current and eliminate the transient DC current bias of the transformer. Furthermore, load feedforward was introduced to further enhance the dynamic of the converter. With the proposed control method, the settling time could be reduced within several PWM cycles during load disturbance without transient DC current bias. A 5 kW IBDC converter prototype was built and the settling time of 6 PWM cycles during load change with voltage regulation mode was achieved, which verifies the superior dynamic performance of the control method.

Comparative analysis of dual active bridge dc–dc converter employing Si, SiC and GaN MOSFETs for G2V and V2G operation

Electric vehicles (EVs) are ideally suited for carbon footprint reduction and energy-efficient transportation. EV battery chargers comprise of cascade connection of ac–dc and dc–dc converters. With the bidirectional dc–dc converters, EV chargers can implement grid-to-vehicle (G2V) and vehicle-to-grid (V2G) functionality. Dual active bridge (DAB) converter is a bidirectional dc–dc converter that can support G2V and V2G operation. DAB converters are operated at high switching frequencies (fsw) leading to higher switching loss. This issue can be addressed by employing SiC and GaN-MOSFETs, which work with lesser switching losses and can operate at much higher fsw. This paper presents a detailed comparative analysis of DAB converter employing Si, SiC and GaN MOSFETs for G2V and V2G operation. The EV charging system with a DAB converter employing V2G and G2V operation is modeled in PSIM software. Single phase shift (SPS) modulation technique is employed for DAB converter. The system operation is analyzed for V2G and G2V operation with the fsw of 20 kHz, 50 kHz, 100 kHz and 200 kHz. The performance comparison reveals that DAB converter with GaN-MOSFETs has the highest operating efficiency. To validate the DAB operation with SPS modulation, experimental studies have been carried out with SPS modulation being implemented on TMS320F28335 DSP using SimCoder Module of PSIM. A step-by-step procedure to implement the modulation technique with SimCoder is also provided.

Reduction in Circulating Current With Improved Secondary Side Modulation in Isolated Current-Fed Half Bridge AC–DC Converter

Current-fed half bridge converter with bidirectional switches on ac side and a full bridge converter on dc side of a high frequency transformer is an optimal topology for single stage galvanically isolated ac-dc converter for onboard vehicle charging application. AC side switches are actively commutated to achieve zero current switching (ZCS) using single phase shift modulation (SPSM) and discontinuous current phase shift modulation (DCPSM). Furthermore, zero voltage turn-on (ZVS) is achieved for dc side switches. Compared to SPSM, DCPSM maintains a constant peak current in the converter throughout the grid cycle of ac mains voltage. However, constant peak current contributes to a high circulating current near the zero crossings of ac mains voltage and also at light load conditions.This paper proposes an improved discontinuous current phase shift modulation (IDCPSM) to increase the efficiency of the converter across different loading conditions. A dual control variable is adopted to actively reduce the circulating current while maintaining soft switching of both ac and dc side switches across the grid cycle of ac mains voltage. A 1.5 kW laboratory prototype has been developed to experimentally validate the analysis, design and improvement in performance for different loading conditions.

Natural Boundary Transition and Inherent Dynamic Control of a Hybrid-Mode-Modulated Dual-Active-Bridge Converter

This article proposes a hybrid-mode modulation strategy for the single-phase dual-active-bridge (DAB) dc–dc converter that realizes soft switching in the whole operating range. Different from existing modulation methods that are usually dependent on complex mathematical optimization processes, the presented article reveals that the simple trapezoidal continuous conduction mode and triangular discontinuous conduction mode inspired by a quasi-single-active-bridge operation can naturally and sequentially extend the soft-switching boundary of the conventional single-phase-shift (SPS) modulation to the full range in both the buck and boost modes. Meanwhile, the transformer rms current is also reduced. Moreover, a fast-dynamic control with inherent seamless mode transitions is realized by introducing the predictive-current SPS modulation. The proposed hybrid-mode modulation strategy with closed-form solutions can be easily implemented in a generalized closed-loop controller, which enables an ultrawide-voltage-range operation of the DAB converter with significantly elevated efficiency and fast transient responses. The effectiveness of the proposed method is validated by comprehensive experimental results from a small-scale DAB prototype.

Dual-Active-Bridge Model and Control for Supporting Fast Synthetic Inertial Action

This article proposes a dual-active-bridge control to support the fast synthetic inertial action in DC microgrids. First of all, the selection of the isolated DC/DC converter to link an energy storage system with the DC bus in a microgrid is analyzed and the advantages of the dual-active-bridge converter controlled by a single-phase shift modulation justify its selection. An active front-end can be then adapted to connect the DC bus with an AC grid. Secondly, this paper presents the design of a discrete PI controller for supporting fast synthetic inertial action. In particular, a discrete dual-active-bridge model based on the transferred power between both converter bridges, which overcomes the approximations of the output current linearization model, is proposed. Moreover, the article introduces a novel equation set to directly and dynamically tune discrete PI parameters to fulfill the design frequency specifications based on the inversion formulae method. In this way, during the voltage/power transients on the DC bus, the controller actively responds and recovers those transients within a grid fundamental cycle. Since the developed set of control equations is very simple, it can be easily implemented by a discrete control algorithm, avoiding the use of offline trial and error procedures which may lead to system instability under large load variations. Finally, the proposed control system is evaluated and validated in PLECS simulations and hardware-in-the-loop tests.

High-Frequency-Linked Three-Port Converter With Optimized Control Strategies Based on Power System Load Flow Concepts for PV-Battery Systems

This article proposes an optimized modulation and control strategy for high-frequency-linked three-port converters (HFL-TPCs), which is conceptually derived from the generalized load flow equations of a typical power system. The power system analogy explains why single phase shift (SPS) modulation results in higher reactive currents that reduce the overall converter efficiency. The SPS converter also loses zero-voltage switching (ZVS) at lower power operations. The proposed optimized quintuple phase shift (QPS) modulation method allows dynamic control of duty cycles of the HF square wave voltages that potentially control the real and reactive power flows of the HFL-TPC. The QPS modulation phase variables are applied to derive the generalized models of the HFL-TPC using a harmonic analysis approach. Harmonic analysis and the optimized modulation strategy greatly simplify the theoretical analysis of the HFL-TPC compared to a piecewise time-domain approach. A detailed power loss model of the HFL-TPC is also discussed. To verify the practical feasibility of the proposed optimized modulation strategies, a 60-V, 400-W HFL-TPC is built and tested. Simulation and experimental results show that the proposed modulation method reduces reactive power, improves efficiency, and maintains the ZVS operation over a wide voltage and power range.

A Hybrid Switching Modulation of Isolated Bidirectional DC-DC Converter for Energy Storage System in DC Microgrid

Isolated bi-direction DC-DC converters are widely used for energy storage systems (ESS) of DC microgrids. Particularly, a current-fed isolated bi-directional DC-DC converter (CF-IBDC) receives much attention due to its merits such as the naturally attenuated current ripple on the battery side. However, high efficiency cannot be obtained at the light and heavy load conditions under the conventional control methods. In this paper, a hybrid switching modulation is proposed to improve the power conversion efficiency of the CF-IBDC under light and heavy load conditions. The duty cycle of the secondary sides and the phase shift angle are independently controlled according to the amount of the transferred power. The control strategy is based on the optimization of zero-voltage switching (ZVS) conditions and the minimization of the circulating current in the power converter. Using the proposed control algorithm, the ZVS capability can be obtained under the entire load condition, and the circulating current can be minimized under the single phase-shift modulation (SPSM). Experimental results with a 1-kW laboratory prototype CF-IBDC validate the effectiveness of the proposed modulation algorithm.

Deadbeat Control With Bivariate Online Parameter Identification for SPS-Modulated DAB Converters

Deadbeat control is considered an efficient method of controlling dual active bridge (DAB) converters among the different control methods presented in recent years. The conventional deadbeat control is heavily reliant on the precise values of the system model parameters. However, in DAB converters, system model parameters such as series inductance and output capacitance suffer from mismatches due to operating conditions, manufacturing tolerance, and aging. Thus, the inevitable result is degradation in the steady-state and dynamic performance of the output voltage. In order to compensate for this drawback of deadbeat control, this study proposes an adaptive online parameter identification approach for DAB converters operating under single phase-shift (SPS) modulation. From the matrix form of linear equations in deadbeat control, the least-squares analysis (LSA) approach is utilized to solve the solution by a simple 2-by-2 matrix inverse calculation. Thus, series inductance and output capacitance are identified straightforwardly. Meanwhile, the predicted value of the phase-shift ratio is updated using sampled measurement values in deadbeat control after every sampling step, which can control the output voltage. The benefits of the proposed algorithm are demonstrated by theoretical analysis, simulation, and experimental results under a variety of parameter mismatches and operational circumstances.

Cascaded Voltage and Current Control for a Dual Active Bridge Converter with Current Filters

The paper describes the cascaded voltage and current control for a bidirectional DC/DC converter in Dual Active Bridge (DAB) topology. The typical DAB converter circuit was extended by additional current filters, which allow it to operate in application fields with high requirements on current ripples. The core concept of the presented solution is usage of the modified Single Phase Shift (SPS) modulation, which allows to compensate for the DC-bias current occurring in dynamic states and provides a settling time of half switching cycle during transients. Its features were utilized to build a simplified dynamic model of the converter. The linear Proportional-Integral (PI) controllers are used in both voltage and current control loops. Based on the developed dynamic models, the tuning rules for both controllers were derived. In both cases, a number of the tuned parameters were reduced from two to one (which can present a great practical value for application engineers). The proposed solutions are validated based on a laboratory prototype. An important part of the experiments was devoted to non-linear effects occurring near the current limitation boundary of the system. The paper ends with a brief discussion regarding the future research directions.

A Dual Rising Edge Shift Algorithm for Eliminating the Transient DC-Bias Current in Transformer for a Dual Active Bridge Converter

This paper deals with a well-known problem of the transient DC-bias current occurring during a phase shift transition in dual active bridge (DAB) DC/DC converters. This phenomenon, if not compensated, can cause damage to the converter or deteriorate its performance. One aim of this paper is to present a solution which allows for the elimination of the undesired transient DC-bias component in current waveforms. This solution is the dual rising edge shift (DRES) compensation algorithm. It provides a very simple implementation and fast settling time within the first half of a switching period. Moreover, the solution is independent on any measurements or system parameter values. It is based on the double-sided single phase shift (DSSPS) modulation, which is described in detail along with a converter model in steady-state. Then, the mechanisms leading to the transient DC-bias are explained, and the compensation algorithm is derived. The performance of the algorithm has been tested using a laboratory prototype. A comprehensive set of tests, involving rapid step changes in power flow and frequency sweep, are provided. Finally, the features of the proposed algorithm are briefly discussed.

Deadbeat Current Controller for Bidirectional Dual-Active-Bridge Converter Using an Enhanced SPS Modulation Method

This letter proposes a deadbeat current controller for isolated bidirectional dual-active-bridge DC-DC converter. The controller uses an enhanced single phase shift modulation method by exploiting pulse width as an extra control variable besides phase shift ratio, the only control variable of the conventional single phase shift modulation. The current reference can be tracked within one switching cycle during the bidirectional power transmission and transition of the two directions. Deadtime effect is studied and the compensation method for the controller is proposed. Parameter robustness is analyzed by mathematical derivation and the online autotuning method for the inductance is presented. The proposed deadbeat current controller is simple and easy for implementation. Moreover, it shows superior dynamic performance, which is verified by experimental results during the transient processes of the converter. The effectiveness of the autotuning method is also validated by the prototype experiment.

An Improved Modulation Scheme of Active Commutated Current-Fed Bidirectional dc/dc Converter

Active commutated or naturally clamped techniques have emerged as a new solution to achieve wide range soft-switching and eliminate the necessity of active clamping circuit of current-fed bidirectional dc/dc converter. Multiple typical modulation schemes have been proposed, which include single phase-shift (SPS) modulation, dual phase-shift (DPS) modulation, and discontinuous current SPS (DCSPS) modulation. DCSPS provides the lowest circulating current compared with prior two modulations, but it suffers from the problem of resonance and high peak current at partial loads. This article proposes a DCDPS modulation based on the existing modulations. The duty cycles of the two legs on the high-voltage side are controlled to be unsymmetrical to solve the current resonance problem in DCSPS. Extra phase shift is introduced to achieve much lower circulating current at wide range load conditions. Zero current switching (ZCS) of primary switches and zero voltage switching (ZVS) of secondary switches can be achieved over wide input range and wide load range. A 250-W laboratory converter prototype has been built. Experimental results are presented to validate the analysis and design.

Enhanced DAB for Efficiency Preservation Using Adjustable-Tap High-Frequency Transformer

Efficient dc-dc power-conversion with wide-span voltage-regulation is crucial to a sustainable and robust power electronics system. Dual-active-bridge (DAB) offers straight-forward regulation and its transformer enables voltage step-up/down required for many applications, such as battery chargers and bus converters for dc distribution systems. However, losing soft-switching at light loads or when operating at voltage gains far from the turns ratio severely degrades the efficiency of DAB, especially at high switching frequencies. In this article, we demonstrate an enhanced DAB (E-DAB) topology which employs an adjustable-tap transformer to extend the soft-switching over wider voltage gains and increase the power-transfer capability. By a proper tap adjustment and with single phase-shift modulation, the proposed gallium nitride (GaN)-based converter achieved a peak efficiency of 97.4% with an overall efficiency greater than a conventional DAB for voltage gains of up to 2.8 times higher. Employing a quasi-planar matrix transformer with integrated leakage inductance at 300 kHz allowed for an extremely high power density of 10 kW/l (7.5 kW/l with cooling). The tapped transformer did not incur extra losses to the topology. The gain versus power-transfer characteristic for soft-switching operation was derived for the E-DAB and its improvement in efficiency was experimentally verified over a wide power range.

Enhanced Dual-Active-Bridge DC–DC Converter for Balancing Bipolar Voltage Level of DC Distribution System

Conventional dual-active-bridge (DAB) dc–dc converters have a limited structure to balance the bipolar voltage level of the bipolar dc distribution system. Therefore, to regulate the bipolar voltage level, additional voltage balancers are needed for the DAB converters, which eventually requires more devices resulting in low power conversion efficiency and low power density. This article proposes an enhanced DAB dc–dc converter that can balance the bipolar voltage level without the additional voltage balancers. The bipolar voltage level can be tightly regulated under entire unbalanced load condition and even when there is no-load at one side of the dc poles. Besides, its zero-voltage-switching capability can be extended to cover the entire load range, including the no-load condition. Furthermore, the proposed converter can be operated by using a simple single phase-shift modulation. Therefore, its control algorithm can be easily implemented in digital controllers. Finally, the theoretical analysis and the effectiveness of the proposed DAB converter are validated by a 3-kW prototype converter.