Front-end Dc-dc Converter Research Articles

The use of a front-end ZVZCS DC-DC converter for an IoT VFD inverter system in the paddle wheel machine drive applications

This research paper proposes the integration of power electronics and internet of things (IoT) technologies to apply in shrimp farms. By focusing on the design of a front-end converter, a three-level half-bridge (3L-HB) DC-DC converter with the zero voltage and zero current switching (ZVZCS) technique is chosen to be the front-end power converter to supply the DC bus voltage for the variable frequency drive (VFD) inverter for the paddle wheel machine in the shrimp pond. To confirm the effectiveness and possibility of the proposed concept, the circuit was theoretically designed and tested at 540 V DC of the input voltage, 700 V DC of the DC bus voltage and 3 kW of rated power. It is found that, the front-end converter can step up the DC bus to be 700 V DC which is enough for operating the VFD inverter. All switches can achieve the soft switching condition ZVZCS resulting in decreasing the switching loss and increasing the reliability of the circuit. The maximum experimental efficiency of the front-end converter is 94.9% at 75% of a full load. In addition, the introductory concept of using the IoT system also presents to improve the shrimp farming method.

A Family of Single-Phase Single-Stage Boost Inverters

H-bridge inverter is a common topology used for single-phase applications. Due to its limited voltage gain, a two-stage power conversion with a front-end dc-dc converter is usually adopted to accommodate the low dc source voltage. Recently, single-stage boost inverters are gaining significant interest due to their higher power efficiency and compactness. This paper presents a family of boost inverters with continuous dc source current. By the incorporation of merely a power switch and a boost inductor to the first leg of H-bridge, voltage-boosting and 3-level generation can be simultaneously achieved within a single-stage operation. All potential topologies using the same number of components are derived. An extension to generate five voltage levels with voltage gain enhancement is also proposed. The operation of the proposed boost inverters is thoroughly analyzed. Simulation and experimental results are presented for verification.

Impedance-Edited Multiple Low-Frequency Harmonic Current Adaptive Suppression

In the two-stage inverter, a large amount of low-frequency harmonic current will emerge in the front-end dc-dc converter and input dc voltage source. The low-frequency harmonic current will reduce the service life of the dc source and decrease the efficiency of the system. Additionally, the main components of low-frequency harmonic current fluctuate with uncertainty. To address those issues, an adaptive current suppression method based on impedance editing of the source-stage dc-dc converter is proposed in this paper. Compared with the traditional active power filter (APF), the proposed adaptive low-frequency harmonic current suppression method does not require additional circuits, which will never decrease the system efficiency but reduce the cost. More importantly, when the amplitude of the main components of harmonic current fluctuates, adaptive multiple bandpass filters are proposed to adaptively suppress the main harmonic current, which never influences the dynamic performance. In addition, the virtual impedance is connected in parallel with the bus capacitor to reduce the bus-voltage overshoot. The key parameters design of the proposed control strategy is given and the dynamic response of the proposed control strategy is also discussed. Finally, a prototype of 900W was fabricated and tested.

The Currents Coordinative Control Strategy for Integrated Motor-Drive and Battery-Charging System Based on the Split-Field-Winding DSEM in Driving Mode

This paper proposes a currents coordinative control strategy for the integrated motor-drive and battery-charging (IMB) system based on the split-field-winding doubly salient electromagnetic machine (DSEM) in driving mode, where the field windings are reused as the filter inductance of the front-end DC-DC converter. The combined strategy of maximum field current and the minimum copper loss control methods with respect to the error between the reference and feedback speed of DSEM is given. Compared to the traditional constant field control of DSEM, the copper loss in steady-state operation could be reduced significantly for higher efficiency, especially in light load conditions, and the maximum output power could also be obtained to improve the dynamic performance of the proposed system. The effectiveness and reliability of the proposed control strategy are verified by simulation and experiment results.

A New Topology of Single-Phase Common Ground Buck-Boost Inverter With Component Voltage Rating Reduction

The combination of conventional front-end DC-DC converter and H-bridge inverter has been proposed with common-ground (CG) characteristic and voltage booting capability. However, it has drawback of low modulation index utilization which causes high component voltage rating and small conversion efficiency. In this paper, a new topology of a single-phase common-ground buck-boost inverter (1P-CG-BBI) is presented to overcome existing drawbacks of conventional CG inverters. The proposed 1P-CG-BBI uses one more active-switch and one more diode than traditional CG inverter. Note that the proposed inverter still shares the same ground for DC input source and AC output voltage, which completely eliminates the leakage current. A hybrid pulse width modulation (PWM) technique is introduced to control the buck-boost stage. Accordingly, the buck-boost stage of the 1P-CG-BBI operates similar to a conventional DC-DC boost converter in the positive half cycle. In the negative half cycle, this stage behaves as a traditional inverting DC-DC buck-boost converter. Accordingly, the DC-DC operation and DC-AC operation can be controlled, independently. Consequently, the modulation index can be significantly improved compared to previous CG inverters. High modulation index tends to reduce component voltage rating and increase system efficiency. A comparison study has been discussed to highlight these advantages. Simulation results conducted using PSIM software are considered to verify the operation of the proposed inverter. A laboratory prototype is also developed to further demonstrated the accuracy of theory. Accordingly, the proposed inverter obtains 93.12% and 91.83% efficiency at 550-W for buck and boost operating, respectively.

Low Frequency Current Ripple Suppression for Two-Stage Single-Phase Inverter Based on Impedance Editing

The instantaneous output power of the two-stage single-phase inverter pulsates at double-line frequency, generating a large amount of second harmonic current (SHC) in the front-end dc-dc converter and input dc source. The SHC is harmful to the system performance. To address the issue, a control strategy based on port-impedance editing, where inductor current feedforward (ICFF) and bus voltage feedforward paths are employed, is proposed to reduce the low frequency ripple in the article. Due to only bandpass filter employed in each feedforward path, the proposed control scheme is relatively easy to be implemented. Under the control strategy, the dc-bus port-impedance of dc-dc converter is increased rapidly at double-line frequency, while staying low impedance for other frequencies. What is more, different ICFF paths are taken into insight to obtain optimized path. Meanwhile, the small signal model of front-end dc-dc converter is established and the design principle of key parameters is provided for the derived control strategy. Furthermore, the dynamic response with bandwidth limitation is also discussed in this article. Finally, a two-stage single-phase inverter prototype was fabricated and tested. The experimental results verify the performance of the proposed strategy with SHC reduction.

Second Harmonic Current Reduction Control for Two-Stage Inverter with a New Inductor Current Feedback Path

The instantaneous output power of the two-stage inverter pulsates at twice the output frequency, resulting in the second harmonic current (SHC) in the front-end dc-dc converter. To reduce the SHC in the inductance branch while maintaining good dynamic performance, this paper proposes a control scheme based on a new inductor current feedback path in the front-end buck converter. In the scheme, through the equivalent gain, the virtual resistor, and the bandpass filter, the inductor current is fed to the front of the voltage regulator. The feedback function simplification is studied and the implementation of the proposed scheme is illustrated. With considerations of both reducing the SHC and improving the dynamic performance, the parameter design approach for the feedback function is also presented for the proposed SHC reduction control scheme, and the performance analysis and comparison from the viewpoint of output impedance are provided. The simulation model and the prototype of a 10 kW two-stage inverter are constructed. The simulation and experimental results about the low SHC in the front-end buck converter and the fast dynamic response during the load transient verify the effectiveness of the proposed scheme.

An Insight into the Second-Harmonic Current Reduction Control Strategies in Two-Stage Converters

Due to the components at twice the fundamental frequency of output voltage in the instantaneous output power of a two-stage single-phase inverter (TSI), the second harmonic current (SHC) is generated in the front-end dc-dc converter (FDC). To reduce the SHC, optimizing the control strategy of the FDC is an effective and costless approach. From the view of visual impedance, this paper conducts an intensive study on the SHC reduction strategies. Origin of the SHC is illustrated first. Then, the equivalent circuit models of the FDC under different control strategies are proposed to analyse the SHC propagation characteristic. The derived model can offer a better insight into how the inductor SHC is affected by the control parameters. According to the derived models, a synthesis of different control strategies is presented and the relevant parameters are listed for control design to achieve better suppression effect. The benefits and limitations of these control strategies are also discussed. Based on the proposed equivalent circuit models, several optimization methods are proposed to enhance the effect. A 1500 VA TSI prototype is built and simulated on MATLAB/Simulink, verifying the effectiveness of the proposed optimization methods. This paper is aimed to provide a guideline for the control design and control optimization of the TSIs.

Research on the Intelligent Control Strategy of the Fuel Cell Phase-Shifting Full-Bridge Power Electronics DC-DC Converter

With the aggravation of energy problems, the development and utilization of new energy has become the focus of all countries. As an effective new energy, the fuel cell has attracted the attention of scholars. However, due to the particularity of proton exchange membrane fuel cell (PEMFC), the performance of traditional PI controlled phase-shifted full-bridge power electronics DC-DC converter cannot meet the needs of practical application. In order to further improve the dynamic performance of the converter, this paper first introduces several main topologies of the current mainstream front-end DC-DC converter, and analyzes their performance in the fuel cell system. Then, the operation process of the phase-shifted full-bridge power electronics DC-DC converter is introduced, and the shortcomings of the traditional PI control are analyzed. Finally, a double closed-loop adaptive fuzzy PI controller is proposed, which is characterized by dynamically adjusting PI parameters according to different working states to complete the intelligent control of phase-shifted full-bridge DC-DC converter. The simulation results in MATLAB/Simulink show that the proposed algorithm has good a control effect. Compared with the traditional algorithm, the overshoot and stabilization time of the system are shorter. The algorithm can effectively suppress the fluctuation of the output current of the fuel cell converter, and is a very practical control method.

An Electrolytic Capacitor-Free Half Bridge Class-D Audio Amplifier System Without Bus-Voltage Pumping

Conventional half bridge class-D audio amplifier (HB-CDAA) systems typically suffer from serious bus-voltage pumping. Such a bus-voltage pumping increases the device stress and deteriorates the total harmonic distortion and noise (THD+N) of HB-CDAA. To reduce the bus-voltage pumping of HB-CDAA system, large electrolytic capacitors are usually required at the input of downstream HB-CDAA, which seriously affects the power density of HB-CDAA system. In this article, an electrolytic capacitor-free HB-CDAA system without bus-voltage pumping is proposed, which consists of a front-end bipolar-symmetric-outputs (BSO) bidirectional dc-dc converter and a downstream HB-CDAA. By providing a bidirectional current flowing path in the front-end dc-dc converter, the bus-voltage pumping of the HB-CDAA system is eliminated without using large electrolytic capacitors. Zero voltage switching (ZVS) of all switches in the front-end BSO dc-dc converter can be achieved over the full audio load range. Compared with the HB-CDAA system with a unidirectional front-end dc-dc converter, the proposed audio amplifier system benefits from high power density, low-output voltage THD+N, and voltage stress of switches. The bus-voltage pumping problem is identified, the operation of the proposed HB-CDAA system is analyzed, and the design parameters of the converter are derived to ensure ZVS of all switches. Experimental results with a 40-W prototype of the proposed audio amplifier system are presented to verify the design.

An Overview and Comprehensive Comparative Evaluation of Constant-Frequency Voltage Buck Control Methods for Series Resonant DC–DC Converters

The paper focuses on galvanically isolated series-resonant dc-dc converters with a low quality factor of a magnetically integrated resonant tank. These converters can be controlled at a constant switching frequency to achieve the input voltage buck regulation. The paper compares various buck control methods, such as conventional pulse-width modulation, hybrid pulse-width modulation, shifted pulse-width modulation, hybrid shifted pulse-width modulation, improved shifted pulse-width modulation, asymmetrical pulse-width modulation, pulse-width modulation, and hybrid pulse-width modulation applied to the series-resonant dc-dc converter. The study considers step-up implementation of the series-resonant dc-dc converter topology with the voltage doubler rectifier, which makes it suitable as a front-end dc-dc converter for the integration of renewable energy sources in dc microgrids. The voltage buck control methods considered were compared analytically in terms of the cumulative power losses calculated theoretically. The theoretical results were compared with the experimental measurements to confirm the calculations and benchmark the voltage buck control methods. The experimental validation was performed using a 250 W prototype that demonstrated the hybrid PSM achieves the best performance. The experimental results were found in good agreement with analytically predicted values of the power loss.

Hybrid Connected Unified Power Quality Conditioner Integrating Distributed Generation With Reduced Power Capacity and Enhanced Conversion Efficiency

In this article, a hybrid connected unified power quality conditioner integrating distributed generation (HCUPQC-DG) is proposed. Two dc ports are created at the dc link of the HCUPQC-DG, in which one low-voltage (LV) dc port is directly connected to distributed generation (DG), and the other high-voltage (HV) dc port is indirectly connected to DG through the front-end dc-dc converter. With the hybrid connected configuration, the HV is designed to ensure the dc-ac voltage conversion capability, whereas the LV, i.e., the voltage of DG, can be relatively low and vary in a wide range. Besides, most active power can be directly transferred from DG to the ac load or grid through the direct power flow path. Hence, the conversion efficiency is enhanced, and the power capacity of the front-end dc-dc converter is significantly reduced. The operating principle and the control and modulation strategies of the proposed HCUPQC-DG are discussed. Moreover, the power flow through the HCUPQC-DG is analyzed in detail to understand the system operation. Experimental results with a 3-kVA prototype are provided to verify the feasibility and effectiveness of the proposed HCUPQC-DG.

Second Harmonic Current Reduction for Two-Stage Inverter With DCX-LLC Resonant Converter in Front-End DC–DC Converter: Modeling and Control

In a two-stage inverter, the instantaneous output power pulsates at twice the output frequency (2fo), generating the second harmonic current (SHC), which will propagate into the front-end dc-dc converter. This article aims for suppressing the SHC in the front-end dc-dc converter with dc transformer (DCX)-LLC resonant converter. The small-signal model of the DCX-LLC resonant converter is proposed, and based on which, the unified small-signal model of the preregulator+LLC converter is built. Then, the basic ideas for reducing the SHC are proposed, including the determination of the filter capacitors in the preregulator+LLC converter and the control approach. After that, from a perspective of output impedance, the control schemes for reducing the SHC in the front-end preregulator+LLC converter are proposed. By inserting a notch filter in the voltage loop and/or introducing a virtual impedance in series with the output rectifier of the LLC resonant converter, the output impedance of the preregulator+LLC converter at 2fo is increased and, thus, the SHC can be reduced. Finally, a 6-kVA two-stage three-phase inverter with boost+LLC converter as the front-end dc-dc converter was fabricated and tested. The experimental results are provided to verify the proposed control schemes.

Design and Development of Non-Isolated Modified SEPIC DC-DC Converter Topology for High-Step-Up Applications: Investigation and Hardware Implementation

A new non-isolated modified SEPIC front-end dc-dc converter for the low power system is proposed in this paper, and this converter is the next level of the traditional SEPIC converter with additional devices, such as two diodes and splitting of the output capacitor into two equal parts. The circuit topology proposed in this paper is formulated by combining the boost structure with the traditional SEPIC converter. Therefore, the proposed converter has the benefit of the SEPIC converter, such as continuous input current. The proposed circuit structure also improves the features, such as high voltage gain and high conversion efficiency. The converter comprises one MOSFET switch, one coupled inductor, three diodes, and two capacitors, including the output capacitor. The converter effectively recovers the leakage energy of the coupled inductor through the passive clamp circuit. The operation of the proposed converter is explained in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The required voltage gain of the converter can be acquired by adjusting the coupled inductor turn’s ratio along with the additional devices at less duty cycle of the switch. The simulation of the proposed converter under CCM is carried out, and an experimental prototype of 100 W, 25 V/200 V is made, and the experimental outcomes are presented to validate the theoretical discussions of the proposed converter. The operating performance of the proposed converter is compared with the converters discussed in the literature. The proposed converter can be extended by connecting voltage multiplier (VM) cell circuits to get the ultra-high voltage gain.

The Optimized Triloop Control Strategy of Integrated Motor-Drive and Battery-Charging System Based on the Split-Field-Winding Doubly Salient Electromagnetic Machine in Driving Mode

An integrated motor-drive and battery- (IMB) charging system based on the split-field-winding doubly salient electromagnetic machine (DSEM) is proposed in this article, where field winding of DSEM is integrated as the filter inductance of the front-end dc-dc converter. In the driving mode, the coupling relationship between the front-end dc-dc converter and rear-end inverter for DSEM is deduced, and the corresponding basic control method is given to achieve independent control of the front-end dc-dc converter and rear-end inverter based on the power balance of the cascade converter. Due to the constraints analysis of the IMB system in the dynamic procedure, an optimized triloop control strategy of speed, power, and dual-threshold voltage is proposed to improve output performance. Finally, the simulation model and experimental platform are established to verify the effectiveness and the steady and dynamic performance of the IMB system with the proposed driving control strategy.

Transmitter Side Control of a Wireless EV Charger Employing IoT

This paper presents a transmitter side control scheme for a series-series compensated wireless power transfer (SS-WPT) system for electric vehicle (EV) charging applications. The proposed control scheme matches the reflected load impedance, by controlling accordingly the front-end dc-dc converter (FEC) of the SS-WPT system. The proposed control scheme drives the FEC, through an optimizer which takes into account the misalignment but also the operational conditions of the system to achieve high efficiency throughout the entire charging process – regardless the EV type, the misalignment conditions or the on-board charger. The novelty of the proposed optimizer lies upon its universal characteristic, which makes it compatible to various SS-WPT topologies. As such, the proposed charging concept is a universal solution, which optimizes the system efficiency regardless the receiver side on-board charger topology (single-stage or double-stage), technical characteristics or control scheme that implements the charging profile. Finally, for the necessary communication between the transmitter and the receiver sides, the Internet of Things (IoT) is employed, offering a low-cost and flexible solution that overcomes compatibility problems between wireless antennas. Simulation and experimental results validate the feasibility of the proposed control scheme, highlighting the efficacy of the proposed wireless charging process.

Output Power Stabilization for Wireless Power Transfer System Employing Primary-Side-Only Control

The output power of a wireless power transfer (WPT) system depends highly on the load and the coupling conditions, which are variable in practical applications generally. In order to attain stable output power with high transfer efficiency under various coupling condition and load, this paper proposes a series-series compensated WPT system based on parity-time ( PT ) symmetry with front-end DC-DC converter and a novel primary-side-only control strategy. The strategy comprises the negative resistance control of PT -symmetric circuit, the online load identification approach by PT -symmetry, and the power closed-loop control method. The advantages are that the mutual inductance information is not needed, and dual-side wireless communication as well as the secondary-side control circuit is avoided, which compresses the volume of the secondary side, simplifies the control algorithm, and improves the robustness of the system. With the proposed primary-side-only control strategy, the output power is coupling-independent and can automatically stabilize at specified values over reasonable variations both in coupling coefficient and load. The experimental results obtained from a prototype are included. They confirm the proposed control strategy and indicate that system can stably output 200 W and 400 W with the maximum error 4.10% and 3.40% respectively when the coupling coefficient and loads vary, and achieves high overall efficiency at 91.9%.

A Practical Approach to the Design of a Highly Efficient PSFB DC-DC Converter for Server Applications

The phase shift full bridge (PSFB) is a widely known isolated DC-DC converter topology commonly used in medium to high power applications, and one of the best candidates for the front-end DC-DC converter in server power supplies. Since the server power supplies consume an enormous amount of power, the most critical issue is to achieve high efficiency. Several organizations promoting electrical energy efficiency, like the 80 PLUS, keep introducing higher efficiency certifications with growing requirements extending also to light loads. The design of a high efficiency PSFB converter is a complex problem with many degrees of freedom which requires of a sufficiently accurate modeling of the losses and of efficient design criteria. In this work a losses model of the converter is proposed as well as design guidelines for the efficiency optimization of PSFB converter. The model and the criteria are tested with the redesign of an existing reference PSFB converter of 1400 W for server applications, with wide input voltage range, nominal 400 V input and 12 V output; achieving 95.85% of efficiency at 50% of the load. A new optimized prototype of PSFB was built with the same specifications, achieving a peak efficiency of 96.68% at 50% of the load.

Disturbance-Observer-Based DC-Bus Voltage Control for Ripple Mitigation and Improved Dynamic Response in Two-Stage Single-Phase Inverter System

Two-stage single-phase inverter system has found many applications in distributed generators and grid-connected systems. However, the existence of double-line frequency ripple on the dc-bus voltage due to single-phase inverter's operation has given rise to some design and reliability issues. Some of these are the degradation in the quality of inverter's output voltage and shortening of dc-bus capacitor's lifetime. The problem is rooted in the controller design of the front-end dc-dc converter, which is often designed based on a simplified mathematical model of the dc-dc converter that fails to account for some complex phenomena, such as system's nonlinearities and circuit parameter variations due to temperature and aging effects. In this paper, a disturbance-observer-based control is proposed where these unmodeled effects are treated in the form of lumped disturbance and compensated for in a feed-forward manner. The major advantage of this control solution is that only minimal plant information is needed for controller design and that a decoupled composite controller can be realized, where the feedback compensator is designed to meet certain stability criteria while the disturbance-observer-based feed-forward compensator is designed to handle fast transient events. A prototype of a dual-active-bridge (DAB) dc-dc converter implemented with disturbance-observer-based control is constructed to verify its effectiveness. Experimental results show that the dynamic response of the DAB converter is significantly improved and the double-line frequency ripple on the dc-bus voltage is effectively suppressed by the proposed control solution.

Interview

Dr Xiaolong Li from Southwest Jiaotong University, China, talks to Electronics Letters about the background to his paper ‘Two-switch equalizer for series-connected battery stack using Zeta type converter and symmetrical capacitor-diode circuit’, page 1600. Xiaolong Li Energy storage systems are widely applied in various applications, including electric vehicles, renewable energy systems, etc. In most energy storage systems, lithium-ion batteries and super-capacitors are used. However, lithium-ion batteries and super-capacitors are usually connected in series to provide high-voltage, and voltages of these cells are gradually unbalanced because of non-uniform individual cell properties such as capacitance, internal impedance and self-discharge rate. Therefore, equalisation circuits are required to prevent over-charging and over-discharging of series-connected lithium-ion battery and super-capacitor stacks. Our team focuses on voltage equalisation to extend battery life and I think it is one of the most interesting areas to work in within the battery-circuit field. Various designs of battery equalisers have been proposed. However, most of them require multiple switches and/or a multi-winding transformer, thus they have issues in terms of circuit and/or control complexity/reliability, modularity, or size. In our Letter, a two-switch equaliser for series-connected battery stack using Zeta-type converter and symmetrical capacitor-diode circuit is proposed for voltage equalisation of series-connected batteries. The proposed equaliser consists of a Zeta-type front-end DC-DC converter and symmetrical capacitor-diode circuit, which only uses two active switches and two magnetic components. Thus, the design benefits from small circuit volume and is flexible for extension. Furthermore, the equaliser can work under open-loop, which makes its control simple. High operational efficiency is achieved due to zero voltage switching of all switches. In my opinion, the novelty of the work is significant. To avoid short-circuit events of battery cells during the equalisation process, most active equalisers require multiple switches and/or multi-winding transformers to achieve equalisation, thus they have the disadvantages of high cost or complex control or large size. With rectifier bridges and DC blocking capacitors, our proposed equaliser can efficiently prevent short-circuit events in battery cells. Furthermore, without multiple switches and multi-winding transformers, this equaliser benefits from small size, control simplicity and low cost. First, in order to avoid using multiple switches or a multi-winding transformer, a symmetrical capacitor-diode bridge was designed as the back-end circuit. Through the analysis of the characteristics of DC-DC converters and simulation of the equaliser, a Zeta converter is designed as the front-end circuit. After that, the operation mode of the proposed equaliser is analysed and its equivalent circuit is presented to simplify circuit analysis and parameters design. There are lots of considerations that are required when designing battery equalisation schemes, for example, the question of which front-end circuit should be chosen, how to design the parameters and so on. The final device has been tested and demonstrated in our lab using our energy management platform and three-battery equaliser prototype. We think our equaliser provides a new idea for other scholars. Our equaliser can be directly used in energy storage systems which need low cost and small size equalisation circuits. Some improved circuits and ideas with smaller size and higher efficiency may be derived from the proposed circuit. We also hope that the research will be used in the battery designs of electric vehicles. The use of diodes can reduce the control complexity and number of switches, but it also increases the loss of the circuit. We have therefore been working on how to increase the efficiency of the equaliser. With the development and use of batteries and super-capacitors in energy storage systems, voltage equalisation circuits will be one of the most important circuit components. Therefore, we predict that a low-cost, high-efficiency and small size equalisation circuit will be more significant and popular.