Bus Converter Research Articles

An Improved Suppression Method of AC Transient Overvoltage for Line Commuted Converter Based High Voltage Direct Current Considering AC-DC System Coupling

Commutation failures in line commuted converter-based high voltage direct current (LCC-HVDC) transmission systems leads to an increase in the converter bus voltage of the rectifier station, thus resulting in AC transient overvoltage in the sending-end grid. The transient overvoltage could lead to the disconnection of renewable energy generation and threaten the stable operation of the sending-end grid. However, the influences of the coupling between AC and DC systems caused by the interaction between the active and reactive power of the sending-end grid, the AC bus voltage of the rectifier station, and the DC current are ignored. The AC transient overvoltage cannot be accurately suppressed. Therefore, in this study, the transient voltage characteristics of the rectifier station under a commutation failure of the inverter station are analyzed. The influence of LCC-HVDC control on the AC bus voltage of a rectifier station through the active and reactive power of the rectifier station is analyzed. A dynamic model of the AC bus voltage of a rectifier station under an AC-DC system coupling is established. The calculation method of the command value of the DC current of the rectifier station is proposed by a predictive control model, and an improved suppression method for AC transient overvoltage is proposed. The case studies show that the accuracy and effectiveness of the suppression of AC transient overvoltage are improved by considering the coupling between AC and DC systems.

Overvoltage Suppression Strategy of LCC-HVDC Delivery System Based on Hydropower Phase Control Participation

In a high-voltage direct current (HVDC) transmission system, commutation failure at the receiving end may lead to transient overvoltage at the sending end converter bus of the weak alterative current (AC) system. Firstly, the principle calculation method of overvoltage generation at the sending end after commutation failure is analyzed. Combined with the output characteristics of the hydroelectric excitation system, a coordinated control strategy for hydroelectric and DC systems is proposed. Since the voltage and current values at the DC outlet of the rectifier side change first after a fault occurs at the receiving end, the relationship equation between DC voltage and AC bus voltage is derived and it is used as an input signal to construct additional excitation control for hydropower stations. The proposed strategy is verified by establishing a simulation hydrogen–wind–solar model bundled via a DC sending system in PSCAD/EMTDC. The simulation results illustrate that the transient overvoltage suppression rates are all more than 35%, and the maximum is 38.53%. The proposed strategy can reduce the overvoltage by 0.126 p.u. compared with the International Council on Large Electric Systems (CIGRE) standard control strategy.

Reactive Power Demand Estimation and Dynamic Reactive Power Optimal Allocation for HVDC Receiving Network

The transient voltage stability of the receiver system is severely challenged by the AC-DC interaction and the short electrical distance between individual DC drop points of the receiver network. Firstly, the dynamic reactive power of DC receiver system is analyzed in this paper. The analysis of the dynamic reactive power in the DC receiver system is presented in this paper. In addition, the evaluation method for the reactive power necessary to sustain the voltage of the converter bus AC system is proposed, taking into consideration the voltage drop mechanism when a DC block occurs. Finally, a mechanism for the reactive power dynamic optimization of the AC-DC receiving power network is proposed based on the sensitivity of the transient voltage track index. The optimal access node is determined by quantitatively evaluating the bus transient voltage increase of the inverter station when each node is connected to the dynamic compensation device of reactive power, and the simulation calculation is carried out by the actual power network to validate the performance of the methodology.

Phase Shift Regulated Resonant Switched-Capacitor-Based Intermediate Bus Converter for 48 V Data Center Power System

Phase Shift Regulated Resonant Switched-Capacitor-Based Intermediate Bus Converter for 48 V Data Center Power System

The Switching Bus Converter: A High-Performance 48-V-to-1-V Architecture with Increased Switched-Capacitor Conversion Ratio

The Switching Bus Converter: A High-Performance 48-V-to-1-V Architecture with Increased Switched-Capacitor Conversion Ratio

Sigma Converter Family With Common Ground for the 48 V Data Center

The 48 V bus architecture has become a standard in modern Data Centers, due to the increasing power demands of digital loads. This requires low-profile, high-density Intermediate Bus Converters, able to efficiently step-down the input bus. Usually, this bus has a wide variation (40 V to 60 V), and the VRM must withstand the whole converted range, with a negative impact on efficiency due to design oversizing. A regulated IBC can address this issue, enabling a fine-tuned VRM design. In this paper, a novel regulated Regulated Hybrid Switched Capacitor sigma converter family (RHSC) is proposed, which enables regulation without sacrificing efficiency or power density. This is enabled by a new architecture featuring the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sigma</i> connection of a high-efficiency, unregulated converter with a low-power, regulated one sharing the same <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GND</i> domain, i.e. without the need of functional isolation. With this approach, efficiency and regulation can coexist in a single converter. This work includes the full analysis and design tools for the new RHSC family, together with two demonstrators: a 1.2 kW, 48 V to 12 V down-solution and a 750 W, 48 V to 5.1 V 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{th}$</tex-math></inline-formula> brick module, both exceeding a power density of 1 kW/in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> .

Cooperative Voltage and Frequency Regulation with Wind Farm: A Model-Based Offline Optimal Control Approach

Converter blocking is a serious malfunction encountered in high voltage direct current (HVDC) transmission systems. During sending-end converter blocking, the resultant active power and reactive power surplus in the sending-end power system lead to a severe increase in bus voltage and grid frequency. Consequently, this poses a substantial threat to the stability of the power system. Traditional control techniques generally control the frequency and voltage separately, which makes it challenging to regulate them jointly. This research paper introduces a collaborative approach for optimal control of voltage and frequency to address this issue. State space models for converter bus voltage and grid frequency prediction are developed using the bus voltage sensitivity matrices and system swing equation. The regulation of the converter bus voltage and grid frequency are intrinsically integrated using the explicit model predictive control (EMPC). When blocking occurs and results in an increase in the converter bus voltage and grid frequency, the EMPC controller regulates the output of active power and reactive power from the wind farm to realize the cooperative regulation of the converter bus voltage and grid frequency. The applicability and effectiveness of this strategy have been confirmed through simulation studies.

Review of the calculation of DC-link capacitor current

In the voltage source power electronic converter, DC-link capacitors usually work as buffering elements between the DC and AC sides. The high failure rate and large space occupied by the DC-link capacitors directly affect the reliability and power density of the converters. The analysis and calculation of the DC-link capacitor current is crucial to achieve the refined design of converters. In this work, the analysis and calculation methods of DC-link capacitor current are divided into three categories, according to the calculation principle, namely, simulation method, RMS analysis method, and spectral analysis method, and their calculation methods are summarized. First, the types of capacitors and their characteristics are briefly introduced. Second, the three-phase two-level converter is taken as an example to introduce the basic principles, calculation steps, application scope, advantages, and disadvantages of the latter two methods in detail, as well as the influence of non-ideal factors, such as the output ripple on the calculation results. This work also discusses the calculation of the multi-level converter’s DC-link capacitor current spectrum and the current characteristics of multi-phase converters, which are rarely reported. Third, the problem of resonance between the DC-link capacitors and the DC bus inductor is introduced. For the distributed arrangement of multiple DC-link capacitors on DC bus converters, this study proposes a method based on a constant current source equivalent circuit, which can accurately calculate the DC-link capacitor current spectrum that is affected by loop current and resonance. Finally, the current problems and future directions of the DC-link capacitor design are pointed out.

A Coupled-Inductor-Based Nonisolated DC-DC Converter With High Step-Down and Wide Input Voltage

In the data center applications, the bus converter not only needs to achieve high step-down gain but also can keep stable output for data back-up when the bus voltage drops dramatically due to fault. Thus, a coupled-inductor-based nonisolated DC-DC converter with high step-down and wide input range is proposed in this paper. The proposed converter utilizes the coupled inductor to obtain the high step-down capability and the series-capacitor to achieve zero voltage switching and zero magnetizing currents, which can help reduce switching loss and core loss. Thanks to the feature of the voltage gain, lower conduction loss at low input voltage and wider input voltage can be ensured. The feasibility of the converter is verified by detailed theoretical analysis and a prototype with the 36∼60V input voltage, 3.3V output voltage, and the 1∼10A output current. The efficiency of the prototype can be maintained above 90% under all conditions, and the peak efficiency is 95.8%.

High-Frequency 12 V Regulated LLC Bus Converter With Integrated Multiphase Inverse Coupled Resonant Inductor

In the application of 48 V bus converter, the traditional multiphase regulated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter has some shortcomings, such as insufficient gain range, low light-load efficiency, and difficult current sharing. In order to improve the performance, this article investigates a comprehensive design scheme of multiphase interleaved magnetic integrated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter, which can extend the gain range and achieve active current sharing simultaneously. First, a new structure of multiphase inverse coupled resonant inductor and magnetic integrated transformer is proposed. Then, a high-precision magnetic circuit model is constructed to optimize the design of integrated inductor and transformer. On this basis, the three-phase interleaved magnetic-integrated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter prototype is manufactured, which has a 36–75 V input voltage range and a 12 V regulated output voltage. In addition, the prototype can output 1080 W power in a quarter brick and has a power density of 716 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The maximum efficiency at rated input voltage is 97.5% and remains above 96% over the main input voltage range. As shown by the quantitative performance comparison results, the proposed converter is superior to other state-of-the-art solutions in terms of the comprehensive performance.

VDCOL Parameter Optimization Method for Improving Voltage Stability of DC Receiving Terminal Power Grid

This research based on different startup and operation modes of Heilongjiang receiving power grid, The influence of anti disturbance capability of converter bus on DC recovery characteristics. A VDCOL parameter optimization configuration scheme based on multi feed short circuit ratio (MSCR) is proposed. Through the DC near fault simulation analysis, it is verified that the proposed VDCOL parameter optimization scheme reduces the overall wattless power demand of converter station, and improve Heilongjiang receiving-end grid voltage stability.

Optimal Design of a Matrix Planar Transformer in an LLC Resonant Converter for Data Center Applications

The 48-V bus converter has been gradually adopted in intermediate bus architecture. The ever-growing development of data centers consumes significant power, thereby pushing power converters to be more efficient. This article focuses on the optimization of the transformer for an LLC resonant converter used in data centers, which is the second stage operating as a dc transformer to realize the isolation and a fixed voltage step-down ratio. The front stage is a multiphase buck converter. The magnetic core geometry reported in this article for the LLC enables a single turn for both primary and secondary windings. Compared with the previous research, the improved interleaving winding scheme benefits from reduced conduction path, lower ac resistance, and smaller core volume. Ansys 3D simulation performs the design and optimization of the magnetic core. The proposed magnetic core, winding layout, and design optimization are verified in the 30-/5-V 660-W LLC resonant converter. It has higher current stress but achieves a higher efficiency of 97.7%, better thermal performance, and lower components count than the state of the art.

Performance Comparison Analysis of a High Voltage DC LLC Resonant Converter for Telecom and Datacenter Applications

Intermediate Bus Architecture (IBA) is used for power distribution in information communication technology (ICT) equipment due to the flexibility of its power distribution and cost-effectiveness compared to centralized or DC-mediated power. The reason for IBA's good performance in this context is its greater reliability and efficient Intermediate Bus Converter (IBC). Existing IBAs comprise low-voltage systems with multiple power, resulting in power loss. This study outlines the need for a high-voltage DC-to-DC converter to solve the problems associated with conventional 48 VDC converters. A 300 W LLC series resonant converter is utilized for the design and analysis of converter efficiency and losses across various input voltages. The results indicate that the maximum converter efficiency is &gt;92% at full load. MATHCAD is used to analyze the performance of the LLC converter and understand the suitable operating zones for zero-voltage-switching. The LLC converter's efficiency is investigated for multiple input voltage ranges. The LLC converter is designed and developed in MATLAB and the results of the simulation are presented. Trade-offs in the LLC converter's design are also discussed, with the goal of operating the converter in an optimal manner and achieving the maximum possible efficiency.

Research on bus converter for SAR satellite composited bus system

The composite bus system is a new type of satellite power system, which is suitable for high-power SAR satellites. The bus converter in the compound bus system is very important. This paper analyzes the design requirements of the bus converter, selects PSM LLC as the topology of the bus converter, and verifies the rationality of the scheme through simulation.

An optimized multi-modular resonant switched capacitor converter

The switched capacitor converters have the advantages of high efficiency and high power density, which are widely used in data centers, distributed photovoltaic power generation, and other fields. In this paper, an optimized multi-modular resonant switched capacitor converter (MMRSCC) is proposed for an intermediate bus converter in the power supply system of data centers. By removing the inductance of part of the coupled resonant circuit, the converter can eliminate the influence of the parameter difference of passive components, and no additional voltage clamp circuit is needed, which improves the power density. At the same time, the half-bridge with the same switching action on the rectifier side is combined into one, which reduces the number of switching devices and is more conducive to improving the voltage conversion efficiency. In addition, the inductor of the basic unit of the resonant switched capacitor with the same state is shared to reduce the volume of the passive device, further improve the power density, and optimize the MMRSCC. Finally, the correctness of the topology is verified by simulation on the PLECS.

Two-Stage Factorized Power Architecture DC–DC Converter for Spacecraft Secondary Power Supply System

In this article, we propose a two-stage factorized power architecture (FPA) dc–dc converter, which caters to applications that require high efficiency, high power density, low ripple, and high dynamic response of space-borne low-voltage and high-current power supply. The first-stage 48 V intermediate bus converter (IBC) adopts the six-phase interleaving magnetic integration buck converter (IMIBC). A new array high symmetry multi-phase coupled inductor (CI) is constructed, and a general zero-voltage switching (ZVS) control strategy is proposed. The designed IBC provides 2.4 kW power with a density of up to 1400 W/in3 and efficiency up to 97.15%. The second-stage point of load converter (POLC) adopts the four-phase interleaving magnetic integration LLC dc/dc transformer (DCX). A new method of current sharing, which is based on the inverse coupling resonant inductor, is proposed. This method yields good current sharing under a 15% mismatch of resonance parameters. A highly symmetrical four-phase resonant CI and a four-phase magnetic integration transformer are developed; the design of magnetic components is optimized by constructing a high-precision magnetic circuit mode. The designed POLC has a power density of up to 700 W/in3 and an efficiency of up to 97.1%. Finally, the experimental prototype is fully tested against a similar type of Vicor’s products. According to the results, the power supply designed in this article has several benefits with regard to efficiency, power density, transient response speed, and ripple.

A 48–80-V Input 2-MHz Adaptive ZVT-Assisted Bus Converter With Light-Load Efficiency Improvement

This article presents a dc–dc bus converter with a new soft-switching scheme. Adaptive zero-voltage transition (AZVT) is proposed to enable ZVS turn-on of the power FET via a ZVT auxiliary branch for removing the switching loss of the converter. In AZVT, the current of the auxiliary branch is discontinuous and its peak value is controlled to decrease with the load current. This feature not only minimizes the conduction loss of the auxiliary branch but also significantly improves the light-load power efficiency of the converter. In addition, a high-voltage flipped current sensor (HVFCS) is developed to enable fast and accurate auxiliary inductor current sensing for supporting proper AZVT control in the MHz range. The proposed converter was validated using three 100-V e-mode GaN FETs together with the proposed AZVT controller and gate drivers implemented in a 0.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , 120-V CMOS process. The proposed AZVT converter supports a wide input range from 48 to 80 V, operates at 2 MHz, and provides the power efficiency improvements up to 14.5% and 8.7% over the hard-switching operation at the input voltages of 48 and 80 V, respectively. Compared with the state-of-the-art designs, the proposed converter not only obtains >90% power efficiency over a load range of 6–60 W but also improves light-load efficiency by over 5% with more than two times higher switching frequency.

Research on improving transient voltagestability of energy storage system

The transient overvoltage and voltage sags caused by DC blocking in HVDC transmission systems cause great harm to the stable operation of transmission equipment and power system. This paper analyzes the AC/DC equivalent circuit model of battery energy storage system, and deduces the calculation method of the transient voltage of the converter bus at the rectifier side when the remaining reactive power compensation capacity of the converter station is known. According to the results of regulating the transient voltage of the bus at the dc latched rear end of the energy storage station, the calculation method of reactive power of charge and discharge of the energy storage station is further derived. On this basis, the reactive power control method of regulating the transient voltage of the bus at rectifier side of the energy storage station is given. The power system comprehensive simulation program based on IEEE-39 node system is used to conduct simulation analysis to verify the correctness and effectiveness of the theoretical analysis, and the conclusion is drawn that the energy storage power station has a good regulating effect on the voltage fluctuation caused by DC blocking after being connected to the grid.

A Comprehensive Study of HVDC Link with Reserve Operation Control in a Multi-Infeed Direct Current Power System

The Korean government is targeting the development of a renewable energy penetration of 30–35% by 2040 of the total generation. These conditions will decrease network stability due to a lack of inertia, especially in isolated systems, such as Jeju Island. HVDC systems with several balancing arrangements of reserve operation are used to maintain variability and uncontrollability of RES penetration. This paper presents the fast frequency reserves of HVDC control systems for frequency stability enhancement in the isolated power system by using a combined frequency containment process with grid stability standards. A new MIDC reserve operation control with angle and voltage deviation at the bus converter was developed to provide a faster and more appropriate balancing arrangement compared to the other concept. In addition, two layers of energy and transfer-capacity flexibility were considered to prevent the need to hunt for that balancing arrangement, as well as low nadir frequency, unavailability of the reserve and other constraints caused by each region having a different network size, HVDC interconnection capacity, and type. The proposed control schemes were verified by simulations on the Korean power system model implemented in PSS/E for different sizes of disturbance.

Primary frequency regulation scheme applicable to LCC – VSC series hybrid HVDC considering AC voltage stability at receiving end

The penetration of high proportion renewable energy generation in the load center reduces the inertia of the power system and causes frequency stability problems. Series hybrid HVDC (e.g., BaiHeTan-JiangSu) with landing point at load center should play an important role in primary frequency regulation. Thus, this paper proposes a control scheme that coordinates line-commutated converter (LCC) and voltage-source converter (VSC) operation of the series hybrid HVDC (SHHVDC) and couples inertia emulation control with droop control (CIEDC). The CIEDC absorbs or releases the energy stored in the augmented capacitor of VSC for inertia emulation through regulating DC voltage. Then the DC voltage of LCC is coupled with the DC voltage of VSC through the voltage distribution coefficient. Meanwhile, the DC voltage of the inverter side is used to transmit the frequency information to the rectifier side to change the DC current order value without communication-based. Next, The equivalent DC input resistance based on communication-free is introduced to obtain the reactive power variation caused by LCC, which is transmitted to the reactive power control link in VSC to suppress the AC side converter bus voltage fluctuation. Finally, The CIEDC control scheme is verified by case studies in the event of slight AC fault and step load variation compared with the Fixed-Inertia Emulation Control Scheme (FIEC) and conventional droop control (CDC) in AC bus voltage stability, frequency deviation, rate of change of frequency (RoCoF).