A study was made of power reduction control which is used to avoid DC over-voltage for multi-terminal HVDC transmission of offshore wind power. Voltages and frequencies of offshore AC wind farm networks are used for transmitting control signals for the power reduction control. These methods do not require fast communication. Power reduction sharing among the offshore wind farms using the different control signals was analysed. The control systems were also compared against the DC chopper method to prevent a DC overvoltage. Simulation and experiments were carried out to evaluate the control systems. Data comprise experimental and simulation results (all as a functino of time): for increase of offshore, AC network frequency - AC grid voltage, power of converters, DC voltage and ratio of reduction of AC wind-farm voltage ; for reduction of offshore-network voltage – AC grid voltage, power of converters, DC voltage and ratio of frequency of increase of AC wind-farm voltage; using chopper resistor – AC grid voltage, Power of converters, DC voltage and Duty ratio of reduction of DC chopper; for reduction of offshore AC network voltage – Power of converters, DC voltages and Ratio of voltage reduction; for increasing offshore AC network frequency – Power of converters, DC voltages and Ratio of frequency increase; using chopper resistor – Power of converters, DC voltages and Duty ratio of reduction of DC chopper.

Multiterminal HVDC (MTDC) schemes are intended to transfer power from offshore wind farms to land and interconnect the grids of adjacent countries, through Voltage Source Converters (VSC). The modular multilevel converter (MMC) topology of VSCs is a more recent development which has low harmonics, reduced losses and occupies less space. Analyses were caried out of the frequency support characteristics of MMC-based multiterminal HVDC schemes, using the energy transferred from the capacitance of the MMCs, wind turbine rotating mass and other AC systems. A 3-terminal MMCHVDC system was utilised to study the influence of cell capacitance of the submodules and the proposed synthetic inertia constant of the MTDC system on the frequency support capability of the MMC capacitors. The time response and energy capability of the different energy sources of the MTDC system were compared. The data comprises: (influence of equivalent synthetic inertia constant and cell capacitance) active power in per-unit (pu) over time for cases where the synthetic inertia constant is 6.95s, 20.85s and 27.9s; active power in per-unit (pu) over time using a cell-capacitance of 2.5mF, 7.5mF and 10mF; DC voltage in pu over time for cell-capacitance values of 2.5mF, 7.5mF and 10mF; DC Voltage in pu over time for cases where the synthetic inertia constant is 6.95s, 20.85s and 27.9s; (frequency support characteristics of different energy sources due to a sudden 1800 MW generation loss on the main AC grid) active power (pu) over time for the five different cases - no control, DC capacitor only, DC capacitor and wind farms, DC capacitor and other AC system, and coordinated control; DC voltage (pu) over time for the five different cases; frequency (Hz) over for the five different cases; and additional power (pu) over time from equivalent capacitance of MMCs, wind turbine rotating mass and other AC system during the case of coordinated control.

The dataset includes the basic parameters and results for the reliability modelling and evaluation of modular multilevel converters (MMCs) under different redundancy schemes. Data shown in the file ”Basic parameter.xlsx” are the parameters of converters. And the study was based on those parameters. Data shown in the file ”Results_Case A.xlsx” are the results of case A, including the reliability of arms in the load-sharing mode obtained by using different models (as shown in sheet 1), and the reliability of arms under passive schemes calculated by using different models (as shown in sheet 2). Data shown in the file ”Results_Case B.xlsx” are the results of case B, including the MTTF of arms in sheet 1, and the reliability of MMCs in sheet 2. Data shown in the file ”Results_Case C.xlsx” are the results of case C, i.e. the MTTF of converter arms under different redundancy schemes with failure rate ratio varying from 0.1 to 10. Data shown in the file ”Results_Case D.xlsx” are the results of case D, including the reliability of MMCs with different types of passive redundancy schemes in sheet 1, and the design comparison of MMCs with different passive redundancy types in sheet 2.

The research considers the modelling and control of VSC-HVDC transmission system for connecting renewable power and AC grids. It includes: - design of coordinate control strategies for the VSC-HVDC and wind farm together to improve the overall stability performances of the offshore wind energy system - development of anti-fault strategies and post-fault restoration of DC grids - increase of total efficiency and economy of the combined AC/DC grids Analysis and simulation using PSCAD/EMTDC were performed to test and verify the control and operation ideas. The data comprises: Table 1- the parameters of DC devices including VSCs and DC-PFCs used for this study; Table 2 showing the changing of control orders of both VSCs and DC-PFCs to opimise the wind power delivery in a low wind load condition;Table 3 showing the effectiveness of changing control orders; Table 4 and Table 5- giving the results of optimisation of he wind power delivery in a high wind load condition; Table 6 showing the results of long term simulation of coordinating VSCs and DC-PFCs to optimise wind power delivery; Table 7 showing the parameters for modelling the generation of wind power.

The dataset includes the parameters of converters and results obtained by the proposed method shown in Paper "Reliability Analysis of MMCs Considering Sub-module Designs with Individual or Series Operated IGBTs". Data shown in the file ”Basic parameter.xlsx” are the parameters of converters. And the study was based on those parameters. Data shown in the file ”Results_Case A.xlsx” are the results of case A-"Reliability comparison of MMCs", including the converter parameters in sheet 1, failure rate of MMCs in sheet 2, expected voltage capability of an arm and the corresponding standard deviation in sheet 3. Data shown in the file ”Results_Case B.xlsx” are the results of case B-"Influence of IGBT module's failure rate", including the converter parameters in sheet 1, failure rate of MMCs in sheet 2, expected voltage capability of an arm and the corresponding standard deviation in sheet 3. Data shown in the file ”Results_Case C.xlsx” are the results of case C-"Design comparison of MMCs", including the converter parameters in sheet 1, failure rate of MMCs in sheet 2, expected voltage capability of an arm and the corresponding standard deviation in sheet 3.

These data represent analyses of the frequency support characteristics of multi-terminal VSC-HVDC (MTDC) schemes using the energy transferred from wind turbine rotating mass and other AC systems. An alternative coordinated control (ACC) scheme, which gives priority to a frequency versus active power droop fitted to onshore VSCs has been proposed to: (i) transfer wind turbine recovery power to undisturbed AC grids and (ii) allow correct control operation of MTDC systems during multiple power imbalances on different AC grids. The fast frequency response capability of MTDC systems equipped with the proposed ACC scheme is compared against a coordinated control (CC) scheme, which uses a frequency versus DC voltage droop. The frequency control schemes were demonstrated on an experimental test rig which represents a 3-terminal HVDC system. Also, the MTDC frequency support capability when wind farms do not provide extra power was tested using a 4-terminal HVDC system. The data are provided in the folder (Metadata_PWRD) and described in a text file (Quantity_description.txt). The main folder consists of two sub folders namely ‘Results_SectionIV’ and ‘Results_SectionV’. A special software (MATLAB) is required to access the dataset stored in the two folders (‘Results_SectionIV’ and ‘Results_SectionV’). The .txt file describes the location of different quantities (Active Power, DC voltage, frequency and time). The folder named ‘Results_SectionIV’ consists of two .mat files and three .m files. This folder contains PSCAD simulation results and experimental test rig results of a 3-Terminal VSC-HVDC system (shown in Figures 10 - 13, Section IV of the paper). The dataset underpinning the experimental results are stored in the file ‘experimental_results.mat’ with file size 3.4 MB and the dataset obtained from the PSCAD simulation results are stored in ‘simulation_results.mat’ with file size 34 MB. The three .m files houses a set instructions used to process and plot the dataset in the .mat files. Additional data on the experimental test rig parameters and the test system modelled in the PSCAD simulation tool have been included as Appendices A, B and C in the manuscript. The folder named ‘Results_SectionV’ consists of five .mat files and two .m files. This folder contains results obtained from a SIMULINK tool system for a 4-terminal VSC-HVDC system for the case a single imbalance and multiple imbalance (shown in Section V of the paper). The dataset underpinning the results for the case of single power imbalance are stored in three mat files. These are: No_freq_support.mat (file size: 670 KB); CCS_freq_support_1imb.mat (file size: 1.51 MB); ACCS_freq_support_1imb.mat (file size: 1.5 MB). The data underlying results for the case of multiple imbalances are stored the following .mat files - No_freq_support.mat (file size: 670 KB); CCS_freq_support.mat (file size: 1.57 MB); ACCS_freq_support.mat (file size: 1.5 MB). The two .m files contains instructions written to process and plot the dataset in the format that displayed in SectionV of the paper.