Current Source Converter Research Articles

Generalized SVPWM Eliminating Overlap Time for Current Source Converter

Generalized SVPWM Eliminating Overlap Time for Current Source Converter

Grid Integration of Offshore Wind Energy: A Review on Fault Ride Through Techniques for MMC-HVDC Systems

Over the past few decades, wind energy has expanded to become a widespread, clean, and sustainable energy source. However, integrating offshore wind energy with the onshore AC grids presents many stability and control challenges that hinder the reliability and resilience of AC grids, particularly during faults. To address this issue, current grid codes require offshore wind farms (OWFs) to remain connected during and after faults. This requirement is challenging because, depending on the fault location and power flow direction, DC link over- or under-voltage can occur, potentially leading to the shutdown of converter stations. Therefore, this necessitates the proper understanding of key technical concepts associated with the integration of OWFs. To help fill the gap, this article performs an in-depth investigation of existing alternating current fault ride through (ACFRT) techniques of modular multilevel converter-based high-voltage direct current (MMC-HVDC) for OWFs. These techniques include the use of AC/DC choppers, flywheel energy storage devices (FESDs), power reduction strategies for OWFs, and energy optimization of the MMC. This article covers both scenarios of onshore and offshore AC faults. Given the importance of wind turbines (WTs) in transforming wind energy into mechanical energy, this article also presents an overview of four WT topologies. In addition, this article explores the advanced converter topologies employed in HVDC systems to transform three-phase AC voltages to DC voltages and vice versa at each terminal of the DC link. Finally, this article explores the key stability and control concepts, such as small signal stability and large disturbance stability, followed by future research trends in the development of converter topologies for HVDC transmission such as hybrid HVDC systems, which combine current source converters (CSCs) and voltage source converters (VSCs) and diode rectifier-based HVDC (DR-HVDC) systems.

A new modulation for three‐phase current source converter

AbstractThis brief proposes an improved pulse width modulation (PWM) scheme, which uses diode voltage clamping characteristics to achieve the direct control of three‐phase current source converter without any logical transformation. Compared with the traditional indirect carrier modulation scheme—mapping‐PWM, the proposed scheme can solve the disadvantages of low DC current utilization, high switching loss, and complex control process. The generation mechanism of IPWM is analyzed in this brief. Then, based on the generation mechanism, the output characteristics of the system under IPWM are analyzed and compared with the traditional modulation scheme. Finally, the experimental results verify the effectiveness the proposed modulation scheme.

Improved Phase Control With Two Degrees of Freedom for Current Source Converter Using in HVDC Systems

Improved Phase Control With Two Degrees of Freedom for Current Source Converter Using in HVDC Systems

Novel Multilevel Current Source Converter With Asymmetric Configuration: Analysis, Comparison, Modulation, and FPGA Implementation

Novel Multilevel Current Source Converter With Asymmetric Configuration: Analysis, Comparison, Modulation, and FPGA Implementation

Novel Current Source Converter for Integrating Multiple Energy Storage Systems

The increasing penetration of renewable energy sources (RESs) in transmission and distribution systems presents several challenges for grid operators. In particular, the unpredictable behavior of RESs can disrupt the balance between energy production and load demand, potentially affecting the stability of the entire system. Grid-connected energy storage systems (ESSs) offer a possible solution to manage the uncertainty associated with RESs. In fact, ESSs exchange power with the grid through the adoption of suitable energy management strategies, which are typically implemented by power electronics-based grid interfaces. Unlike other current source converter (CSC) solutions described in the literature, which only interface with a single energy storage device, this paper introduces a novel topology for a three-phase delta-type current source converter (D-CSC), which is capable of integrating three independent ESSs using the same number of semiconductors as traditional CSC solutions. Thus, it considerably enhances the flexibility of a power conversion system (PCS) without increasing the number of converter components. In addition, an innovative energy management control strategy is also introduced. This strategy enables the D-CSC to compensate for energy imbalances arising between the three ESSs, which might be caused by several factors, such as different aging characteristics, converter component tolerances, operating conditions, and temperature drifts. Hence, the D-CSC-based interface is capable of proper grid operation even if the three ESSs have different characteristics, thus opening the possibility of employing this converter to integrate both first and second-life devices. First, the topology of the proposed D-CSC is introduced, followed by a detailed mathematical description of its control strategy. The proper grid operation of the D-CSC was tested under different scenarios, considering the grid integration of three independent superconducting magnetic energy storage systems in a marine vessel. The proposed D-CSC is compared to traditional CSC solutions, highlighting the superior performances of the novel converter topology in terms of efficiency, total harmonic distortion of the output currents, and overall cost reduction for the PCS.

An Improved Current-Source-Converter-Based Series-Connected Wind Energy Conversion System

The passive rectifier-based current source converter (CSC) used in the series-connected wind energy conversion system features low cost, high reliability, and simple control, but suffers highly distorted generator stator currents. A new CSC-based wind energy conversion system composed of a multi-phase generator, a passive rectifier, a modular medium-frequency transformer-based converter, and a CSC, is proposed. In addition, two versions of the proposed converter are developed for low- and medium-voltage turbine systems respectively. The operation principle is presented, controls are developed, and simulations and experiments are conducted. Both converters offer excellent generator stator current harmonics performance, while also retaining the advantages of existing CSC-based converters.

Pseudo-Hermitian Coreless Transformer for Current Source Converter

Pseudo-Hermitian Coreless Transformer for Current Source Converter

Novel Coordinated Control Strategy for Step-Up/Down Current-Source Converter

Current-source converter (CSC) is more attractive and increasingly used to occasions with higher requirements for reliability due to inherent anti-short circuit ability. This paper combines the CSC with DC/DC converter to adapt to lower input voltage applications. However, rational allocation of the duty cycle for each switch to achieve the target voltage output and the increase of overall switching times brought by DC/DC converter are major problems. Proposed coordinated control strategy can reasonably take full advantage of degrees of freedom based on the adjustment variable to achieve accurately control of grid-side current and load voltage. In addition, dc-link current pulses according to 6 times grid angular frequency which avoids using the zero-vector to reduce the switching times. Experimental results show the proposed scheme can not only guarantees the power quality at grid side and precise voltage output, but also avoids using zero-vector.

Advancements and comparative analysis of high-voltage direct current transmission technologies

This paper outlines the fundamental principles of high-voltage direct current (HVDC) transmission, elucidating its two primary variants: current-source converter (CSC) HVDC and voltage-source converter (VSC) HVDC. It also undertakes a comparative analysis with high-voltage alternating current (HVAC) technologies, focusing on aspects such as power transmission efficiency and cost-effectiveness, drawing upon prior research findings. Additionally, the paper underscores the critical role of circuit-breakers (CB) as essential components for controlling HVDC systems. HVDC technology plays a pivotal role in augmenting AC transmission systems, facilitating the integration of large-scale renewable energy sources, and enhancing the efficiency of expansive power grids over considerable distances. Its continued evolution and refinement are highly probable, given its indispensable role in the energy landscape.

A Novel Common-Mode Voltage Suppression Strategy for Current Source Converter

The problem of common-mode voltage (CMV) in current source converter (CSC) has been concerned with the development and application of CSC, such as in the transformerless motor drive system. Using a common-mode choke is a popular solution to suppressing CMV. The high-frequency harmonics of the CMV can be eliminated by the common-mode filter. However, the low-order harmonics cannot be eliminated effectively, especially at low modulation index, which may cause common-mode resonance and increase the size of the choke. In this paper, a novel virtual space vector modulation (VSVM) method is proposed, which constructs virtual space vectors by the original vectors. The average value of the CMV produced by each virtual vector is zero. The proposed method can reduce the amplitude and third-order harmonic component of the CMV. In addition, the number of switching transitions in a switching sequence of the proposed method is the same as the conventional 5-segment SVM. The suppression effects of different methods on the low-order harmonics of CMV are compared through simulation and experiments, and the effectiveness of the proposed methods is verified.

Optimized designed [formula omitted]-shape impedance in voltage type [formula omitted]-Source inverter based on average modeling

The Z-source inverter is a desirable power converter topology for voltage source and current source converter applications, which is an exciting alternative for replacing the popular conventional type.This paper presents a novel method for designing voltage-type Z-Source inverters that are innovated based on good voltage source and DC-Link prerequisites such as its current and voltage value. This method is caused to reduce the size of the capacitor and inductor as well as the total cost of the converter, which is applicable in hybrid electric vehicle development. Z-Source inverter‘s output based on its input variables and effects has been investigated to propose to optimize the design/control method. State space equations are obtained, and its model is analyzed to illustrate how the undesired effects of these changes can be omitted or compensated. It has been used to optimize the designed parameters. A prototype experimental Z-Source inverter with a rated power of 500W and switching frequency of 20kHz is developed to demonstrate the validity of the design process. The Simulation and experimental results verify that the proposed method successfully optimizes the x-shape Impedance design.

A Direct Torque Control Method for CSC Based PMSG Wind Energy Conversion Systems

The Current Source Converter (CSC) technology is well suited for high power wind energy applications. Because it drives generally features like simple converter structure, smooth power injection at the grid side and excellent short circuit protection. The main drawback lays its dynamic torque response. An improved Direct Torque Control (DTC) method is proposed in this paper to overcome this drawback. Using DTC method for Permanent Magnet Synchronous Generators (PMSG) in a wind energy system has some advantages such as, simple control system and topology, ease of tracing Maximum available power from the wind and flux weakening control in high wind speeds. The simulation results demonstrate the effectiveness of the proposed control system, good dynamic response and acceptable MPPT capability.

Feedback Control of Doubly-Fed Generator Connected to Current Source Converter

Feedback Control of Doubly-Fed Generator Connected to Current Source Converter

Comparison of a 10 kV SiC Current Switch with two 6.5 kV Series Connected Si SGCTs for Medium Voltage Current Source Converter Applications

Comparison of a 10 kV SiC Current Switch with two 6.5 kV Series Connected Si SGCTs for Medium Voltage Current Source Converter Applications

An Overlap-Time Effect Elimination SVM Based on Vector Bridge Extension for Current-Source Converter

An Overlap-Time Effect Elimination SVM Based on Vector Bridge Extension for Current-Source Converter

MHz Current-Source Converter with Step-Up Feature Based on Resonant Switched-Inductor Unit

MHz Current-Source Converter with Step-Up Feature Based on Resonant Switched-Inductor Unit

Current source converter-based optimal power extraction and power control of a doubly fed induction generator (DFIG) using backstepping control

An improved backstepping control technique for the operation of a doubly fed induction generator (DFIG) powered by a wind turbine (WT) was developed and discussed. It is derived from a current source converter (CSC). The optimal backstepping control (BSC) settings are determined using the CSC approach, which can improve the drive by providing a more rapid dynamic response, greater precision, and stable performance. The CSC approach control function was constructed using the index criterion integral time square error (ITSE) and integral time absolute error (ITAE). With the simulation technique in the MATLAB/Simulink environment, the proposed BSC-CSC effectiveness is confirmed, and analyse the performance by using the PI and SMC control. The results indicate the goals of this work have been achieved in the form of resilience, improved dynamic system efficiency, lowering the harmonic distortion, optimization of stator power, and successfully addressing the problem of model parameter uncertainty.

Modified Transformerless Series-Connected Current Source Converter Without Series-Connected Switches

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Transformerless series-connected current source converters (SC-CSCs) were recently proposed. Compared with existing ones, they eliminate the transformer, giving significant reductions in cost and size. However,</i> they need the use of series-connected switches in medium/high-voltage applications, and as a result, very complicated voltage balancing schemes are required. To address this challenge, a modified transformerless SC-CSC is proposed. In the modified one, the series-connected switches are replaced with a cascaded half-bridge converter, while the left remains the same as existing ones. By doing so, the need for series-connected switches is eliminated, while the advantages of original converters are well retained. In addition, the cascaded half-bridge converter has inherent voltage balancing, reduced switching frequencies, and a unique zero-load feature. The operation principle of the modified converter is presented. The performance is verified by both simulations and lab-scaled experiments.

A coordinated power flow control strategy to enhance the reliability of hybrid ac/dc power grids during cascading faults

Cascading fault is a newly emerging challenge in hybrid ac/dc grids including current source converters (CSCs) which commences from a dc or a long-lasting severe inverter ac fault and ultimately provokes a total blackout at the inverter ac side. Nevertheless, since the cascading faults emanating from dc faults are not accompanied by commutation failure, the prevailing commutation failure elimination strategies are unable to inhibit these contingencies. To obviate such a challenge, this paper proposes a coordinated power flow control strategy which can preclude the blackouts caused by cascading faults initiated from either dc or inverter ac faults, thereby improving the reliability of hybrid ac/dc power grids. To achieve this, a back-to-back voltage source converter (B2B-VSC) is employed which is responsible for controlling both the inverter ac bus voltage and the active power flow of its connected ac line. This would not only mitigate the probability of commutation failure due to the reinforced inverter ac bus voltage, but also enhance the power flow flexibility of the power grid during both normal and fault conditions. In addition, the cost associated with implementation of the proposed strategy is much less than installing several backup parallel lines which are useless under no-fault circumstances. Finally, the practical viability of the proposed strategy is scrutinized through laboratory testing using co-simulation of RTDS and Opal-RT simulators. The obtained results show that the developed strategy can effectively manage the power flow of B2B-VSC and CSC-HVDC systems during different possible fault cases so that the power outage at the inverter ac side is minimized.