High Voltage Conversion Research Articles

Dynamic interaction analysis among different control loops and stability enhancement strategy for MMC-HVDC systems

This paper presents the dynamic interaction analysis method among different control loops of MMC-HVDC (Modular Multilevel Converter High Voltage Direct Current) systems, and proposes an improved control strategy with feedback regulation loop and low-pass filter loop for stability enhancement. The small-signal cascade model of MMC with dc voltage control loop, ac current control loop and differential-mode ripple capacitor voltages loop is firstly established, which clearly shows the analytical interactions of inner capacitor voltage response and system input power’s dynamics with simplified closed/open-loop transfer functions. Then the small-signal dynamic analysis of MMC is conducted based on the derived closed/open-loop transfer functions, which reveals the interactions between the system stability and key control loops, as well as the main parameters of the MMC-HVDC system by both the Nyquist criteria and the pole-zero theory. Next, the feedback regulation loop and low-pass filter loop are proposed and introduced in the MMC control system to maximize stability enhancement performance during disturbances, and system dynamic response under the proposed control with different parameters are also explored through theoretical analysis. Finally, several cases on a benchmark two-terminal MMC-HVDC simulation model are carried out in PSCAD/EMTDC to verify the proposed control strategy.

Generation and Comparative Analysis of High-Voltage Gain Nonisolated DC–DC Converters With Ladder Switched Capacitor and Coupled Inductor

A design methodology for creating a set of high-voltage gain DC–DC converters is presented and discussed in this article. The proposed generation is based on ladder switched capacitor (SC) with coupled inductor. So, eight high-voltage converters with a single switch without increasing the number of components are proposed. Detailed evaluations about the derivation of each topology, comparative analysis among main features of each converter are presented. These converters are evaluated in different aspects, such as principle of operation, voltage gain, sensibility of the output voltage, total voltage stress (TVS), total current stress (TCS), ZCS, charging mode compared to the standard SCs cells, design guidelines, power density, power losses, and estimated efficiency. By these comparisons, the main feature and limitations of the analyzed converters are recognized. Thus, four topologies were chosen to be evaluated experimentally, considering 200 W, 30 V, 400 V, and 50 kHz. The combination of the techniques provides the best trend off on the comparative analysis carried out in this work. The results show that attention should be paid to choosing the best position to include a technique. In this case, the best choice was BCISC-V converter, which presented the best voltage gain, TCS, ZCS, and efficiency characteristics.

An Inrush Current Suppression Strategy for UHV Converter Transformer Based on Simulation of Magnetic Bias

The Ultra High Voltage (UHV) converter transformer may generate serious inrush current during closing. It will cause commutation voltage distortion and easily result in commutation failure of converters on the same commutation bus. Due to the change of flux amplitude and phase caused by closing resistance in the Ultra High Voltage Direct Current (UHVDC) system, it is difficult to determine the closing time of the converter transformer when considering the influence of residual flux. Therefore, this paper first analyses the existing closing resistance strategy, and constructs the magnetic bias function according to the influence characteristics of closing resistance on the flux and phase. Then an inrush current suppression strategy based on magnetic bias simulation is proposed for star connection and delta connection of UHV converter transformers, which can accurately calculate the ideal closing time of mutual cancellation between the residual flux and bias flux during closing. Finally, the no-load closing model of the UHV converter transformer is established by PSCAD/EMTDC for simulation analysis of the feasibility, real-time verification is carried out using the RTDS closed-loop experimental platform. The results show that the proposed inrush current suppression strategy can effectively suppress the inrush current under different residual flux conditions.

Grid-integrated single phase solar PV system employed with single switch high gain boost converter

• This paper deals with a grid-integrated single phase solar photovoltaic system (GISPSPS) employed with a single switched based high gain boost converter. The significant contributions in this paper are; • The dynamic model of HGBC including effective series resistance (ESR) of passive elements is developed for improving accuracy with slight increase in complexity of model. Then its stability analysis is carried out under different solar irradiations (i.e. 300, 500, 800 and 1000 W/m 2 ) using an eigenvalue plot. • The HGBC control is obtained using the sliding mode control (SMC) for PPE under change in solar irradiations. In proposed SMC only two sensing signals PV panel voltage and current (i.e. v pv and i pv ) are needed for PPE in comparison to three sensing signals PV panel voltage, current and DC link voltage (i.e. v pv , i pv and v dc ) require in SMC of ref. [10] . • The control of FBVSC is obtained by a F i OGI controller. The F i OGI provides noise-less extraction of synchronization signal, under presence of DC offset and noise in grid voltage. However, FOGI used in ref. [10] exhibits poor performance under presence of noise in grid supply voltage. This paper presents a grid-integrated single phase solar photovoltaic (PV) system (GISPSPS) with its modeling, design and control. The GISPSPS consists of a single switch based high gain boost converter (HGBC) and full bridge voltage source converter (FBVSC). The HGBC, boost the low PV panel voltage and extracts the optimum PV power. The HGBC allows high voltage conversion ratio and possesses less voltage stresses on power devices. The optimum PV power is extracted via a sliding mode control (SMC) strategy that generates the switching signal for the switch of HGBC. The FBVSC delivers PV power to the single phase utility grid, as well as load connected at point of interfacing (POI). A fifth order generalized integrator (F i OGI) is developed for FBVSC control to ensure harmonic suppression and DC offset rejection capability during extraction of fundamental grid voltage. Experimental validation of proposed GISPSPS and its control is also verified.

High Voltage Gain Bidirectional DC-DC Converters for Supercapacitor Assisted Electric Vehicles: A Review

Integration of supercapacitor alongwith battery in electric vehicles (EVs) improves the life cycle of the battery. Additionally, supercapacitor supplies or absorbs a large amount of instantaneous power during sudden demand such as acceleration or regenerative braking operation, hence also improve the dynamics of the internal power system. However, a major challenge with supercapacitor is that its terminal voltage is low and varies in a wide range during charging and discharging operation. Thus, a high voltage conversion ratio based bidirectional DC-DC converters are required to connect the lower supercapacitor voltage to higher DC-link voltage. The steep voltage conversion ratio with continuous gain based bidirectional DC-DC converters are an integral part of such applications. Various high gain converters exist in the literature such as isolated, non-isolated, cascaded, switched, flying capacitor, and coupled inductor based DC-DC converters, however all these converters have some limitations in context to high gain/high power applications. Therefore, to understand the development of next-generation high voltage gain bidirectional DC-DC converter, this paper focus to comprehensively review and classify various bidirectional step-up DC-DC converters based on their characteristics and voltage-boosting techniques. Further, practical suitability of the reviewed converters and future research directions in switched capacitor converters in context to EVs are also discussed in detail.

Approach to Inertial Compensation of HVdc Offshore Wind Farms by MMC With Ultracapacitor Energy Storage Integration

Recent studies have shown that the grid connection of offshore wind farms through modular multilevel converter–high voltage direct current (MMC-HVdc) transmission system has brought low inertia issue. It is an urgent requirement for offshore wind farms to compensate for the inertia. After analysis and evaluation in this article, it is found that integrating an ultracapacitor energy storage system (UESS) into an MMC has an advantage comprehensively considering cost, size, and dynamic. Based on the evaluation, this article proposes an approach to inertial compensation of HVdc offshore wind farms by MMC-UESS integration. An ultracapacitor is selected as an energy storage element (ESE) for its high power density since the inertial response is a short-term response and it is hoped that added ESE does not significantly increase the size of an MMC submodule. Batteries with high energy density but low power density are not suitable for such applications. The optimal operating voltage of a UESS and the control scheme between MMC loops and inertial emulation are proposed in this article. Experimental results from real-time simulation and a downscaled prototype are presented to verify the effectiveness of the proposed method.

Calculation and Characteristics Analysis for Radiated Electromagnetic Field of High Voltage Converter Valve

Calculation and analysis of the radiated electromagnetic field by the high voltage converter valve are very important for the electromagnetic compatibility analysis between the various components of the converter system. First, the electromagnetic radiation calculation process of the converter valve is proposed. Then, according to the actual engineering application, a DC transmission simulation system of the converter system was built, and the current of the converter valve tower arm was obtained. Subsequently, according to the actual size, a 3D calculation model of the converter valve tower was established, and an MoM-based calculation method for the electromagnetic field of the converter valve tower was proposed. Finally, the attenuation characteristics and azimuth characteristics of the converter valve tower are analyzed, and the distribution rules of the radiated electromagnetic field inside the high voltage converter valve hall are clarified, which provide a theoretical foundation for the evaluation of the electromagnetic compatibility of the converter system.

Active switched‐capacitor based ultra‐voltage gain quadratic boost DC‐DC converters

AbstractThis paper presents active switched capacitor integrated ultra‐voltage gain quadratic boost converters (ASC‐QBC). The step‐up conversion ratio provided by quadratic boost converter is not ample to meet the renewable microsource applications. The active switched capacitor integrated quadratic boost converter is a propitious alternate to acquire high voltage conversion ratios. A simple diode‐capacitor voltage lift arrangement is used in one of the introduced converters, thereby further enhancing the voltage gain and also reducing the input current ripple to a greater extent. The voltage stress on semiconductor devices is greatly alleviated with the aid of diode‐capacitor voltage lift arrangement. The input current ripple aspects with green energy sources along with control feasibility of the proposed converters against input voltage and load perturbations are experimentally demonstrated for a power rating of 100 W. The theoretical analysis and performance indices of proposed converters are validated with a fabricated laboratory prototype.

Distributed Optimal Power Flow for VSC-MTDC Meshed AC/DC Grids Using ALADIN

The increasing application of voltage source converter (VSC) high voltage direct current (VSC-HVDC) technology in power grids has raised the importance of incorporating DC grids and converters into the existing transmission network. This poses significant challenges in dealing with the resulting optimal power flow (OPF) problem. In this paper, a recently proposed nonconvex distributed optimization algorithm -- Augmented Lagrangian based Alternating Direction Inexact Newton method (ALADIN), is tailored to solve the nonconvex AC/DC OPF problem for emerging voltage source converter (VSC) based multiterminal high voltage direct current (VSC-MTDC) meshed AC/DC hybrid systems. The proposed scheme decomposes this AC/DC hybrid OPF problem and handles it in a fully distributed way. Compared to the existing state-of-art Alternating Direction Method of Multipliers(ADMM), which is in general, not applicable for nonconvex problems, ALADIN has a theoretical convergence guarantee. Applying these two approaches to (VSC-MTDC) coupled with an IEEE benchmark AC power system illustrates that the tailored ALADIN outperforms ADMM in convergence speed and numerical robustness.

Fully Soft Switched Interleaved High Step-Up/Down Bidirectional Converter With no Pulsating Current at Low Voltage Source

In this article, a fully soft switched interleaved bidirectional buck/boost converter with high voltage conversion ratio (VCR) and no pulsating current at low voltage source is proposed. Winding cross-coupled inductors technique is employed in order to increase VCR and mitigate current ripple at low voltage side. Moreover, soft switching conditions for all semiconductor devices are provided and the leakage inductances energy of coupled inductors are absorbed in both high step-up/down operating modes. Furthermore, the reverse recovery problem of all diodes is removed due to zero current switching turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> . All the mentioned advantages are achieved for a bidirectional converter with two interleaved phases in both high step-up/down operating modes by only one clamp circuit consisting of a clamp capacitor and two active switches. Also, the body diodes of the main switches are utilized as the main diodes to reduce the element count. The converter performance is validated by theoretical analysis and an 800 W prototype circuit in both operating modes.

An Interleaved Soft Switched High Step-Up Boost Converter With High Power Density for Renewable Energy Applications

In this article, a novel soft switched interleaved boost structure with a simple auxiliary circuit is proposed which is suitable for stand-alone loads or ac grid applications. In this topology, coupled inductors and switched capacitor cells of parallel modules are merged to obtain high voltage conversion ratio. The converter also has the capability of adding extra switched capacitor cells to attain very high voltage gain. To provide soft-switching condition in the wide range of output power, a new zero-voltage transition auxiliary circuit is employed which is responsible for soft switching of both phases and benefits from low conduction losses, the minimum number of semiconductor elements, and only one auxiliary gate-driver. These merits provide very high efficiency at both full-load and light loads. More importantly, no auxiliary magnetic components are utilized by taking advantage of the leakage inductance of coupled inductors for the resonant network. All semiconductor components operate under soft switching alleviating the reverse recovery problem and switching losses. Besides, the converter benefits from common ground between input and output which simplify voltage feedback. The experimental results of the interleaved converter prototype with 400-V output voltage at 400 W and 100 kHz switching frequency are provided. The full load efficiency of 98% was achieved and the power density was observed 1.9 W/Cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

An Ultra High Step-Up Dual-Input Single-Output DC–DC Converter Based on Coupled Inductor

This article introduces a new coupled inductor based dual-input ultra-high step-up dc–dc converter with a high voltage conversion ratio, low voltage stress across semiconductor components, and high efficiency features. The coupled inductor and voltage multiplier circuit (VMC) techniques have been utilized to enhance the voltage gain. The blocking voltages of power switches are clamped by VMC at low values and can be controlled via the turn ratio of the coupled inductors that decreases the voltage rate of power switches and converter's cost. The presented dual-input structure can transfer power to the load from two independent voltage sources. Besides, the inputs and output ports are common ground, which can reduce the electromagnetic interference influences. Operation modes delineation, steady-state analysis, and comparison section are provided for describing the proposed structure performance. Finally, to confirm the effectiveness of the presented topology, experimental waveforms with a 200 W output power at 50 kHz switching frequency are presented.

A Single Switch High Step-Up DC-DC Converter Based on Tri-Winding Coupled Inductor for Renewable Energy Applications

This article introduces a novel nonisolated single-switch high step-up DC-DC converter using a tri-winding coupled inductor (TWCL) for renewable energy applications such as PV systems. Also, the voltage multiplier cell (VMC) is used to attain a high voltage gain. The used VMC acts as a passive clamp circuit and reduces the voltage stress across the power switch. So, a low voltage-rated power switch can be used in the presented converter. The suggested topology uses only one power switch with low on-state resistance (RDS-ON), which leads to a simple control circuit and decreases the conduction losses. Highefficiency, operating with low duty cycle, low peak voltage over semiconductor elements, low turns ratio, the number of the coupled inductor, and high voltage conversion ratio are the significant benefits of the recommended DC-DC converter. To show the achievement of the presented structure, operational mode principles, steady-state, efficiency calculations, and comparison results are provided. Finally, a 120 W experimental prototype with 200 V output voltage and 50 kHz switching frequency is built to prove the usefulness of the suggested high step-up converter. The efficiency is measured 92.11% at rated power.

Application of Convolutional and Feedforward Neural Networks for Fault Detection in Particle Accelerator Power Systems

High voltage converter modulators (HVCM) provide power to the accelerating cavities of the Spallation Neutron Source (SNS) facility. HVCMs experience catastrophic failures, which increase the downtime of the SNS and reduce beam time. The faults may occur due to different reasons including failures of the resonant capacitor, core saturation due to the magnetic flux, insulated-gate bipolar transistor (IGBT) failures, and others. We recently have setup a HVCM test stand to develop and test machine learning models for anomaly detection and fault prognostics. In this work, we propose binary classifiers and autoencoder architectures based on convolutional (CNN) and feedforward neural networks (FNN) to facilitate distinguishing normal from faulty waveforms coming from the HVCM during operation. The results indicate that the CNN binary classifier is the best model among the four showing very stable performance in the training and testing sets with impressive precision and recall metrics, reaching up to 99% with a very small uncertainty. The FNN classifier shows the least performance with a large uncertainty in its metrics. The performances of the two autoencoders based on CNN and FNN were in between, showing very good performance nonetheless.

High step‐up MIMO DC–DC power converter control‐based pole placement

AbstractThis paper introduces a new high step‐up multi‐input multi‐output (MIMO) DC–DC converter control‐based pole placement suitable for photovoltaic system applications. The suggested topology has a high stability current control. Low element number, high voltage conversion ratio, and low ripple input current are the main advantages of the proposed converter. The capability to use several energy resources with different voltage/current characteristics, increase the number of inputs and outputs arbitrary without duty‐cycle limitation, and control each input unit power switch independently are other advantages. The operation principle of the suggested topology, steady‐state analysis in continuous condition mode (CCM), and parameter design are analyzed. A comparison between the suggested topology and other converters is applied. Two‐input two‐output version of the suggested topology in 200 W at an operating 50 kHz switching frequency is analyzed. Finally, the Typhoon HiL‐404 emulating setup is applied to verify the performance and efficiency of the suggested high‐step‐up MIMO DC–DC power converter.

Research on dual-mode fault suppression strategy of AC isolation and current limiting based on hybrid MMC

Abstract The DC side fault of the high voltage DC transmission system based on modular multilevel converters high voltage DC (MMC-HVDC) is easily affected by the double influence of AC transient electrical quantity infeed and overvoltage and overcurrent, seriously threatening the safe operation of the power grid. Aiming at the problem above, a fault suppression strategy in dual mode of isolation and current limiting is proposed. Based on the half-bridge-full-bridge hybrid MMC, the fault transient mathematical model considering AC feed and sub-module switching feed is analyzed. AC isolation module with double conduction self-resistance structure and current-limiting control module is constructed, which can be adaptively adjusted to the system’s direct current parameters. The ±500 kV double-ended hybrid MMC system model is established to verify the scheme’s effectiveness. In addition, the influence of high AC modulation parameters on the suppression effect is investigated. PSCAD/EMTDC simulation results show that AC active and reactive power feed-in peaks are reduced by 388.69 MW and 119.82 Mvar, respectively, under dual-mode control. The peak value of DC overvoltage and overcurrent is reduced by 1211.53 kV and 22.5 kA, respectively, the fault self-clearing time is shortened by 43 ms, and the fault suppression effect is remarkable. In the high AC modulation ratio operating state, the modulation parameters are positively correlated with the AC power feed and negatively correlated with the overvoltage and overcurrent of the DC system. The research results provide support for the fault protection scheme of the hybrid MMC flexible and direct power grid.

A study on improving the efficiency of non-isolated buck-boost bidirectional DC–DC converter

ABSTRACT In battery-based systems such as hybrid electric propulsion system for ships that use electric propulsion and DC grid, bidirectional converters are often used as interfaces between high-voltage power sources and low-voltage batteries for the purpose of storing excess energy and the fields of application for bidirectional converters are steadily expanding. This study proposes a new bidirectional converter with a high voltage conversion rate and low switch voltage stress. The proposed converter allows current to flow between modules by adding only one capacitor compared to a conventional bidirectional converter. To check the effectiveness of the proposed method, PSIM software by Powersim co. Ltd. was used to perform simulation tests. It was confirmed that the high voltage conversion rate was 4 times that of a conventional bidirectional converter in step-up mode and 1/4 that of a conventional bidirectional converter in step-down mode. Therefore, low-voltage components, such as MOSFETs, GTOs, etc., can be applied in the DC–DC converters thanks to the 1/4 voltage that is required in each switching time.

An Intra-Body Power Transfer System With 1-mW Power Delivered to the Load and 3.3-V DC Output at 160-cm of on-Body Distance.

This paper presents an intra-body power transfer (IBPT) system that can deliver power greater than 1 mW across an on-body distance of 160 cm. A system simulation model is built for the characterization of the channel and optimization of the power transfer. Our system analysis and experimental validation demonstrate that 1 MHz is an optimal carrier frequency for IBPT in terms of power delivered to the load (PDL) and power efficiency (PE). Prototype TX and RX boards were built, and an IC was fabricated in a 180-nm CMOS process for the RX. The proposed RX IC consists of a voltage doubler (VD) and a charge pump (CP) to obtain a sufficiently high voltage conversion ratio (VCR). Among various rectifier topologies, the VD is the optimal topology for the power receiver front-end because the parasitic ground coupling capacitances, which inevitably exist in the IBPT system, act as an inherent input-coupling capacitance for the VD. The implemented VD utilizes a dynamic VTH compensation (DVC) for its diode components. Compared to the conventional static VTH compensation (SVC), DVC in the VD reduces the reverse leakage current of the diode, thus maximizing the power conversion efficiency (PCE) and VCR. In addition, the PDL is enhanced by inserting an inductor on the TX board. It reduces the backward-path impedance without increasing the RX volume, boosting the PDL by up to 9.9 times compared to the PDL without the inductor insertion. The proposed IBPT system delivers up to 178.8 μW of power at 11.7% of maximum power efficiency with 3.3-V DC output voltage and even 1.385 mW of power with the inductor insertion, supporting various biomedical wearable sensors, such as ECG sensor modules.

Analysis and Design of Efficient Interleaved Bidirectional Converter With Winding Cross Coupled Inductors

This article presents a nonisolated bidirectional converter (BDC) with high voltage conversion ratio. The structure of winding-cross-coupled-inductors (WCCIs) is developed in the two-phase interleaved BDC to achieve the excellent features of current-ripple-cancellation, current sharing, and high voltage-gain. Furthermore, the proposed topology uses two active and passive clamp circuits to recover the coupled inductors’ leakage energy and to maintain the overall efficiency at a high level providing zero voltage switching (ZVS) in boost mode. A rearrangement is applied to high-voltage-side switches to avoid the interference of clamp circuits operation in boost and buck modes. Detailed analysis and design methodology of the proposed converter are provided and a high gain 500 W, 48 V/380 V prototype is implemented to verify the performance of the proposed converter. Peak efficiencies of 96% and 94.3% are measured for boost and buck modes, respectively.

A Control Strategy for Ground Fault on the AC Side of MMC-HVDC System.

This study explores a control strategy for a flexible Modular Multilevel Converter-High Voltage Direct Current (MMC-HVDC) system when there is an asymmetrical fault with the AC side system voltage. Aiming at the characteristic that the fault system has a negative sequence current path, this paper proposes a positive/negative sequence controller to ensure the output of original active power, and the validity of the proposed control strategy is verified by using simulation software PSCAD/EMTDC.