Hybrid Voltage Source Research Articles

Double‐input triple‐output non‐isolated DC–DC converter based on coupled inductor with high step‐up output voltages

SummaryThis paper introduces a new non‐isolated double‐input triple‐output (DITO) high voltage gain DC–DC converter with a wide range of applications, including hybrid voltage source systems, solar home appliances, DC‐bus power distribution systems, and electrical vehicles (EVs). The proposed DITO converter interfaces two hybrid voltage sources to supply three different output loads with varying voltage and power levels. Compared to conventional converters of the same type, the proposed DITO converter offers several advantages, including operation for all duty cycles, integration of hybrid energy sources to transfer power to multiple loads, high voltage conversion ratio for all three‐output ports, a higher ratio of total voltage gain to total components number, common grounded input and output DC ports, simultaneous DC voltage regulation of three‐output ports by tuning separate controlling parameters of duty cycles, an additional turns ratio of coupled inductors to increase the voltage gain of output ports, and medium voltage stress on switches. The proposed DITO converter utilizes a new single‐switch single‐coupled‐inductor DC–DC structure, which is analyzed and verified through a prototype implementation for 25 and 30 V input voltages and 210, 330, and 400 V output voltages with a total power of 480 W. The experimental results confirm the simulation results and theoretical analysis.

A New Hybrid Voltage Source Converter With Reduced Active Switch Count for HVDC Applications

This paper presents a new hybrid voltage source converter topology with reduced active switch count for HVDC applications. It consists of a block of switches in the upper converter arms and cascaded switch-diode cells in the lower converter arms. The cascaded switch-diode cells in the lower converter arms produce a multilevel output voltage while the switch blocks in the upper converter arms perform rectification. The switches in the upper converter arms conduct for one-third of the fundamental line period as dictated by the relative magnitude of the input line-to-neutral voltages. Only one of the three phase blocks of switches conduct at a time. Compared to other voltage source converter topologies with similar structure and operation to this topology, the proposed topology has lower number of devices. Therefore, it has lower converter footprint and cost. More importantly, it reduces the semiconductor device power losses significantly due to the lower number of active switches (lower switching loss) and the lower number of devices in current conduction path (lower conduction loss). The basic operation principle of the proposed converter and its associated control strategy that regulates the power exchange between the converter, and the ac and dc networks are described in detail and verified using both simulation and experimental results.

Security-Constrained Unit Commitment for Hybrid VSC-MTDC/AC Power Systems With High Penetration of Wind Generation

This paper presents the solution to the security-constrained unit commitment (SCUC) problem for hybrid voltage source converter (VSC) based multi-terminal DC/AC (VSC-MTDC/AC) power systems with high penetration of wind generation. The formulated SCUC model presents a detailed representation of the VSCs with two different VSC control strategies considered, constant DC voltage control (master-slave control) and DC voltage droop control. In addition, Grid Code for wind farm connection is considered. Benders decomposition is used to solve the formulated SCUC problem by decomposing it into a master problem for solving unit commitment (UC) and hourly transmission security check subproblems. The final SCUC solution provides an economic and secure operation and control strategy for the meshed MTDC/AC system. Numerical tests illustrated the efficiency of the proposed SCUC model.

Integrated Grid-connected Hybrid Power Generating System with Optimized PLL-based Power Control

In this paper, grid-connected photovoltaic-wind energy, including a battery energy storage system (BESS) with a novel topology base proposed controller, is presented. The battery can be reflected in a smooth and stable output under variation of weather and load conditions for the grid-connected system. Robust phase-locked loop- (PLL) based hybrid Voltage Source Converter (VSC) controller is designed to enhance power quality (PQ) with mitigating power fluctuation at DC-link by applied BESS on the DC side. The results can be summarized in 2 stages; in the 1st stage, the performance of the designed hybrid system can be analyzed with untuned parameters of the converter, and in the 2nd stage, a simple strategy base proposed controller to improve the operation stability and analyze the PQ of the hybrid power generating (HPG) system is developed. Finally, the proposed hybrid system is modeled in MATLAB/Simulink and the simulation results as obtained are compared with an existing controller.
 HIGHLIGHTS
 
 Performance analysis of design a grid connected hybrid power generating system
 The system achieved stability and reliability with proposed controllers
 The presence of a battery, providing smooth movement of the generated power of the system
 A coordinated controller designed to improve power fluctuation and power quality
 Highly robust grid-connected HPG system designed using hybrid VSC and bidirectional controller
 
 GRAPHICAL ABSTRACT

Interoperability of Modular Multilevel and Alternate Arm Converters in Hybrid HVDC Systems

This paper demonstrates the interoperability of an emerging alternate arm converter (AAC) with the state-of-the-art modular multilevel converter (MMC) in high-voltage direct current (HVDC) systems based on a hybrid VSC-HVDC system. The paper also showcases the parameter derivation of the hybrid HVDC system and its detailed control structure. The study provides preliminary steps towards detailed analysis of AAC interoperability in complex hybrid dc grid configurations. A detailed set of results based on the 800 MVA hybrid voltage source converter (VSC)-HVDC system showcases the interoperability performance of the AAC under different operating scenarios and verifies its associated control functions.

State Estimation for Hybrid VSC Based HVDC/AC: Unified Bad Data Detection Integrated With Gaussian Mixture Model

The High Voltage Direct Current (HVDC) is an emerging technology that transmits power over long distances and at a higher capacity than the traditional AC systems. Integration of HVDC into modern power networks requires vital modification to the Supervisory, Control and Data Acquisition (SCADA) system, particularly in power system applications. For instance, the state estimator toolbox is an essential software to estimate the network AC and DC systems states. However, the state estimator may fail due to severely corrupted data, a.k.a bad data; hence, an additional data treatment is needed. This paper presents a unified bad data detection block for Weighted Least Squares (WLS) state estimation algorithm. The bad data detection block works for hybrid Voltage Source Converter (VSC)-HVDC/AC transmission systems. It improves the traditional Largest Normalized Residual (LNR) method by integrating the Gaussian Mixture Model (GMM) algorithm. This method reduces the time needed for bad data detection, increases the algorithm robustness, and enhances estimation accuracy. The Cigre B4 network is used as a test case to validate this work on a hybrid VSC-HVDC/AC network. Also, grid load and generation data from the UK is used to construct the simulation measurements and the GMM model. Simulation results show that the modified GMM-LNR has considerably reduced the detection time and improved the WLS accuracy.

A Selective Fault Clearing Scheme for a Hybrid VSC-LCC Multi-Terminal HVdc System

A selective fault clearing scheme is proposed for a hybrid voltage source converter (VSC)-line commutated converter (LCC) multi-terminal high voltage direct current (HVdc) transmission structure in which two small capacity VSC stations tap into the main transmission line of a high capacity LCC-HVdc link. The use of dc circuit breakers (dc CBs) on the branches connecting to VSCs at the tapping points is explored to minimize the impact of tapping on the reliability of the main LCC link. This arrangement allows clearing of temporary faults on the main LCC line as usual by force retardation of the LCC rectifier. The faults on the branches connecting to VSC stations can be cleared by blocking insulated gate bipolar transistors (IGBTs) and opening ac circuit breakers (ac CB), without affecting the main line’s performance. A local voltage and current measurement based fault discrimination scheme is developed to identify the faulted sections and pole(s), and trigger appropriate fault recovery functions. This fault discrimination scheme is capable of detecting and discriminating short circuits and high resistances faults in any branch well before 2 ms. For the test grid considered, 6 kA, 2 ms dc CBs can easily facilitate the intended fault clearing functions and maintain the power transfer through healthy pole during single-pole faults.

DC fault ride‐through capability and STATCOM operation of a HVDC hybrid voltage source converter

High voltage direct current (HVDC) transmission systems are becoming increasingly popular when compared to conventional AC transmission methods. HVDC voltage source converters (VSC) can offer advantages over traditional HVDC current source converter topologies; as such, it is expected that HVDC-VSCs will be further exploited with the growth of HVDC transmission. This study presents the DC fault ride through capability and new static synchronous compensator (STATCOM) modes of operation for the recently published alternate arm converter, intended for the HVDC market. Operation and fault ride through of the converter during a local terminal to terminal short circuit of the DC-link is demonstrated; during the fault STATCOM operation is also demonstrated.