DC Voltage Control Research Articles

Multi-level model predictive control for all-electric ships with hybrid power generation

Power availability to preserve propulsion is a vital issue in the shipping industry which relies on persistent power generation and maintaining the stability of the power and propulsion system. Since the introduction of on-board all-electric Direct Current Power and Propulsion Systems (DC-PPS) with hybrid power generation, which are more efficient compared to direct-diesel and Alternating Current (AC) all-electric configurations, there have been extensive investigations on stabilization and power generation control to enable robust and reliable performance of DC-PPS during different ship operations. In this paper, a multi-level approach is proposed for hybrid power generation control. For this goal, first, a mathematical model is proposed for each power system component and then, the overall on-board power system is modeled in a state space format. Then, a multi-level Model Predictive Control (MPC) approach is proposed for the DC voltage control which unlike conventional droop control approaches, takes the DC current generated by power sources into account explicitly. The performance of the proposed approach is evaluated via several simulation experiments with a high fidelity model of a high voltage DC-PPS. The results of this paper lead to enabling more effective approaches for power generation and stability control of constant power loaded microgrids.

Design of power quality enhanced sustainable bidirectional electric vehicle charging station in distribution grid

Integration of electric vehicle charging stations with the distribution grid rises the grid current harmonics. In this article, a sustainable bidirectional electric vehicle charging station in the distribution grid is designed. The quality of the charging station is improved by employing an adaptive neuro-fuzzy controlled distribution static compensator. The proposed sustainable bidirectional electric vehicle charging station comprises a 3-phase bidirectional ac-dc converter, bidirectional chopper, distribution static compensator and a lithium-ion battery. The bidirectional converters facilitate power flow from grid to vehicle and vice-versa. The decoupled current and dc voltage control method has been implemented for a 3-phase bidirectional converter. A multi-step current control strategy is exploited to control the bidirectional chopper. Distribution static compensator alleviates the grid current harmonics. The proposed system performance is evaluated with two kinds of controllers such as proportional – integral and adaptive neuro-fuzzy controller based on the distribution static compensator dc-side voltage and grid current harmonics. The proposed system has been modelled in MATLAB/Simulink and validated through software in the loop setup comprising of dSPACE (DS1202) hardware. The validated results show that the adaptive neuro-fuzzy controller provides better performance.

Sub-/Super-SCI Influencing Factors Analysis of VSC-HVDC and PMSG-Wind Farm System by Impedance Bode Criterion

A sub-/super-synchronous interaction (sub-/super-SCI) can occur between a voltage source converter-based high-voltage direct current (VSC-HVDC) and the permanent magnet synchronous generator (PMSG)-based wind farms with long AC transmission lines. However, the influencing factors have not been properly analyzed. In this paper, these are deconstructed and mathematically analyzed from detailed small-signal impedance equations in the dq-frame and the corresponding Bode stability criterion. Distinguishing conclusions from existing papers are obtained by studying the controllers’ bandwidths instead of their coefficients. The impacts of AC line impedance on system stability are also investigated. From the analysis of their compositions in impedance structure, the VSC-HVDC bandwidths and the wind farm phase-locked loop (PLL) bandwidth and power ratio, and the AC line impedance have various influences on the system stability. Meanwhile, the wind farm outer DC voltage and inner current control bandwidths have little impact on system stability. The results of these studies show that the magnitude in the axes q-axes impedance interaction is the essential factor for system instability. Our studies also show system stability is more sensitive to the HVDC bandwidths than the wind converter PLL bandwidth. The simulation results verify our theory conclusions.

Mm-Wave Through-Load Element for On-Wafer Measurement Applications

This paper presents an innovative Through-Load element aimed at characterization applications at mm-wave frequencies. The proposed structure can behave as a Through connection or as a 50-Ω load depending on a DC control voltage. Among other potential applications, this system can be used to implement a transfer switch or an attenuator. A demonstrator was fabricated and measured in the STM 55-nm BiCMOS technology. Over a wide bandwidth, from 55 GHz up to 170 GHz, experimental measurements demonstrate a maximum 1.6-dB of insertion loss when behaving as a Through connection and a minimum 14-dB of insertion loss when behaving as a 50-Ω load. In both cases, the return loss is better than 10 dB. The insertion loss at 90 GHz is 0.6 dB for the Through connection and 20 dB for the 50-Ω load connection.

A 28-GHz Switched-Beam Antenna with Integrated Butler Matrix and Switch for 5G Applications.

This work presents a 28-GHz Butler matrix based switched-beam antenna for fifth-generation (5G) wireless applications. It integrates a 1 × 4 microstrip antenna, a 4 × 4 Butler matrix, and a single-pole four-throw (SP4T) absorptive switch in a single planar printed circuit board and is housed in a metal enclosure. Co-integration of a packaged switch chip with the Butler matrix based switched-beam antenna greatly enhances the form factor and integration level of the entire system. A wideband two-section branch line coupler is employed to minimize the phase and magnitude errors and variations of the Butler matrix. The aluminum metal enclosure stabilizes the electrical performances, reduces the sidelobes, and improves the structural stability. The fabricated antenna with the metal enclosure assembled has a dimension of 37 × 50 × 6.2 mm3. With an RF input signal fed to the antenna’s input port through a single Ka-band connector, and the switching states chosen by 2-bit dc control voltages, the antenna successfully demonstrates four directional switched beams. The beam switching operations are verified through the over-the-air far-field measurements. The measured results show that the four beam steering directions are −43°, −17°, +10°, +34° with side lobe levels < −5.3 dB at 28 GHz. The antenna also shows reasonably wideband radiation patterns over 27–29 GHz band. The 10-dB impedance bandwidth is 25.4–27.6 GHz, while a slightly relaxed 8-dB bandwidth is 25.2–29.6 GHz. Compared to previous works, this four-directional switched-beam antenna successfully exhibits the advantages of high integration level and satisfactory performances for the 28-GHz 5G wireless applications.

A Diode-MMC AC/DC Hub for Connecting Offshore Wind Farm and Offshore Production Platform

A diode rectifier-modular multilevel converter AC/DC hub (DR-MMC Hub) is proposed to integrate offshore wind power to the onshore DC network and offshore production platforms (e.g., oil/gas and hydrogen production plants) with different DC voltage levels. The DR and MMCs are connected in parallel at the offshore AC collection network to integrate offshore wind power, and in series at the DC terminals of the offshore production platform and the onshore DC network. Compared with conventional parallel-connected DR-MMC HVDC systems, the proposed DR-MMC hub reduces the required MMC converter rating, leading to lower investment cost and power loss. System control of the DR-MMC AC/DC hub is designed based on the operation requirements of the offshore production platform, considering different control modes (power control or DC voltage control). System behaviors and requirements during AC and DC faults are investigated, and hybrid MMCs with half-bridge and full-bridge sub-modules (HBSMs and FBSMs) are used for safe operation during DC faults. Simulation results based on PSCAD/EMTDC validate the operation of the DR-MMC hub.

An improved control strategy for current source converter-based HVDC using fundamental frequency modulation

When pulse width modulation (PWM) is applied in a high-voltage current source converter (CSC) based on fully controlled devices, there are some concerns arising, such as large DC voltage fluctuations, high switching losses, and a narrow power operation range. To solve these problems, the CSC-based HVDC using fundamental frequency modulation (FFM-CSC) is proposed. First, the topology of the CSC is introduced. Then, an independent control strategy for FFM-CSC is presented, which can be used to realize univariate control of DC voltage or DC current. The mathematical model of CSC is also analyzed, and on this basis, a coordinated control strategy is proposed for FFM-CSC to decouple the active and reactive power. An outer loop power controller and an inner loop current controller are designed, and the power operation range is investigated. Finally, an FFM-CSC simulation model is built in PSCAD/EMTDC. The simulation results show that there are smaller DC voltage fluctuations, lower switching losses, and a wider power operation range under the proposed FFM-CSC control strategy.

Implementation of DC voltage controllers on enhancing the stability of multi-terminal DC grids

Because of the increasing penetration of intermittent green energy resources like offshore wind farms, solar photovoltaic, the multi-terminal DC grid using VSC technology is considered a promising solution for interconnecting these future energies. To improve the stability of the multi-terminal direct current (MTDC) network, DC voltage control strategies based on voltage margin and voltage droop technique have been developed and investigated in this article. These two control strategies are implemented in the proposed model, a ±400 kV meshed multi-terminal MTDC network based on VSC technology with four terminals during the outage converter. The simulation results include the comparison and analysis of both techniques under the outage converter equipped with constant DC voltage control, then the outage converter equipped with constant active power control. The simulation results confirm that the DC voltage droop technique has a better dynamic performance of power sharing and DC voltage regulation.

Parametric Stability Assessment of Single-Phase Grid-Tied VSCs Using Peak and Average DC Voltage Control

A type of peak-value dc voltage control (denoted as PK control) was proposed in the literature for supporting the use of a smaller dc-side capacitance when the single-phase voltage source converter is operated as a static synchronous compensator. Although it was demonstrated to operate stably under several conditions, it will be revealed in this article how the PK control will suffer from a more severe small-signal stability issue under nonideal grid conditions than the conventional method of controlling the average value of the dc voltage (denoted as Avr control). Especially, it will be shown how the PK control is sensitive to some of the control parameters. To obtain these results, a parameter-oriented stability analysis method is developed in the linear time-periodic framework. Then, it is utilized for parametric stability assessments of the Avr and PK control. Finally, both frequency- and time-domain experimental results verified the effectiveness and accuracy of the applied method in the presented analysis.

A VSG-Based Coordinated DC Voltage Control for VSC-HVDC to Participate in Frequency Regulation

In this paper, a coordinated DC voltage control strategy is proposed based on the VSG (virtual synchronous generator) method for the VSC-HVDC transmission system to participate in the frequency regulation of the connected weak grid. The voltage and power control capability of the VSC-HVDC is explored to attenuate the rate of change of frequency and to diminish the deviation of frequency. This is realized by the coordinated control of DC voltages at both the sending and the receiving ends with the VSG method. A small-signal model is established to investigate the dynamics of the control system. A tuning method for the selection of control parameters is also discussed in detail. The validity and superiority of the proposed control strategy are tested in the scenarios of sudden load changes and short circuit faults.

ADALINE Harmonics Extraction Algorithm applied to a Shunt Active Power Filter based on an Adaptive Fuzzy Hysteresis current control and a fuzzy DC voltage controller

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Small-Disturbance Stability Limit of a Grid-Connected Wind Farm With PMSGs in the Timescale of DC Voltage Dynamics

This paper analytically derives the small-disturbance stability limit of a grid-connected wind farm with multiple PMSGs in the timescale of DC voltage dynamics. The derived stability limit reveals the mechanism about how the dynamics of DC voltage control and the PLLs may jointly affect the small-disturbance stability of the wind farm. Flagging the impact of PMSGs by a computational function, the stability limit indicates that decreasing value of flagging function or/and increasing maximum eigenvalue of network reactance matrix implies increased instability risk. Particularly, increasing the loading conditions and number of PMSGs in the wind farm or/and the length of transmission line connecting the wind farm with main grid may make the wind farm more prone to the loss of small-disturbance stability. Although the stability limit is derived under the assumption of identical dynamics of PMSGs, the derived small-disturbance stability limit can be applied to approximately assess the small-disturbance stability of the wind farm in the timescale of DC voltage dynamics, where dynamics of PMSGs may be either similar or considerably different. The approximate small-disturbance stability assessment is simple because the assessment does not need to establish the parametric model of the wind farm.

Reduced-Order Modeling and Comparative Dynamic Analysis of DC Voltage Control in DC Microgrids Under Different Droop Methods

Droop control has been well adopted for multi-source multi-load DC microgrids (MGs) due to its inherent modularity and reliability by only using local measurements, especially with the most commonly-used voltage-current droop ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V-I</i> ) mode. While another implementation named current-voltage droop ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</i> ) mode also can be adopted. With the same value of droop gain in these two modes, a DC MG will have the same steady-state feature, but its dynamic performance of DC voltage control may be different. Our primary motivation is to investigate this phenomenon from the perspective of equivalent <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> circuits. This paper proposes a generic reduced-order modeling method suitable for exploring the dynamic stability of DC voltage control with these two modes. By ignoring fast inner current control dynamic, each droop based DC voltage control unit can be modeled as a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> parallel circuit in these two modes, which is convenient for modular modeling and extension. With these models, the essential cause of system dynamic stability difference and the physical meaning of key control parameters in these two modes can be revealed in an intuitive way. In addition, if the inner current control with slow dynamic cannot be ignored in some specific scenarios, a modified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> model can be still obtained to analyze its influence. Moreover, based on reduced-order models, analytical solutions of dynamic performance indexes have been obtained, through which the impact of control parameters on dynamic performance of DC bus voltage can be characterized. Finally, the effectiveness of the proposed reduced-order modeling method has been verified by detailed simulation and experiment results.

Improving the Corrosion Resistance of Wrought ZM21 Magnesium Alloys by Plasma Electrolytic Oxidation and Powder Coating

Plasma Electrolytic Oxidation (PEO) was applied to extruded ZM21 Mg alloys to improve their corrosion resistance in a chloride-containing environment. PEO was carried out in DC mode and voltage control in a fluoride-free electrolyte. Potentiodynamic polarization tests in 3.5 wt.% NaCl aqueous solution and neutral salt spray (NSS) tests were carried out. Microstructural and profilometric characterization, as well as NSS tests were performed in different conditions: (i) bare ZM21, (ii) PEO-treated ZM21, (iii) powder-coated ZM21 (without PEO interlayer), and (iv) PEO-treated ZM21 with powder coating top layer (carboxyl-functionalized polyester resin). The PEO + powder coating double layer was identified as the best-performing corrosion protection.

Study of a common control strategy for grid-connected shunt active photovoltaic filter without DC/DC converter

This paper partially validates a published patent. A common control strategy for grid-connected three-phase three-wire shunt active filter with photovoltaic generator, without DC/DC converter, that compensates the electrical grids perturbations (harmonics, reactive power, unbalanced currents, etc.) is studied. The maximum power of the photovoltaic generator is generated and fed to the grid/loads. In the proposed common control strategy, with an advanced phase locked loop, an extended instantaneous real and imaginary powers method is proposed to identify, jointly or individually, all current perturbations, as well as the current at maximum photovoltaic power in phase with the grid fundamental voltage. Furthermore, the DC voltage control loop is the maximum power-based, unlike the conventional control loop that is based on the maximum current, which allows easier integration of the maximum photovoltaic power into the extended instantaneous powers algorithm. Besides, the current control law is implemented in a single control loop only that simplifies the design. In this work, with the absence of the DC/DC converter, which makes the overall structure more reliable and economical, the output of the adapted perturb & observe algorithm is the voltage at maximum power. Finally, the studied structure is validated via real textile factory case study while using the experimental real measurements provided by power quality analysers. Indeed, under the new modelling strategy of 97% accuracy, the maximum photovoltaic current is injected while ensuring a unity power factor, balanced current with 0.16% of unbalance factor, as well as almost 1% total harmonic distortion of current at the grid side.

Coordinated DC voltage control strategy of hybrid HVDC with multi‐infeed MMC inverters considering commutation failures

Coordinated DC voltage control strategy of hybrid HVDC with multi‐infeed MMC inverters considering commutation failures

Coordinated Control of Multi-terminal MVDC Distribution Network with Photovoltaic Power Station

In order to solve the problem of grid connection and absorption of large-scale photovoltaic power stations, the grid connection scheme of photovoltaic power stations connected to the two-end flexible DC transmission system based on DC voltage, active power and AC voltage control is adopted. Using RTDS simulation software, a DC power distribution system model including a photovoltaic power station and two MMCs was constructed, and the operating characteristics of the system were analyzed in detail. The simulation results show that when the output power of the photovoltaic power station fluctuates or the DC load changes, the system can maintain stable operation.

A Modified SVM Strategy for Single-Phase Cascaded Photovoltaic Inverter

The DC voltage imbalance of a single-phase cascaded photovoltaic inverter will decrease the quality of output voltage. The general modulation method needs to add power balance control to restrain the imbalance and make the control system complicated. To address the issue, a modified Space Vector Modulation (SVM) method is presented in this paper. The modulation method combines the DC voltage control of each unit with the modulation method to achieve DC voltage control of each unit in vector selection, eliminating the need for additional power balance control, thereby simplifying the control system. The modified space vector modulation can not only make the DC voltage rapidly track the DC voltage instruction of each cell through vector selection but also ensure the quality of output voltage waveform when the DC voltage of each cell is imbalanced. The effectiveness of the modified SVM method is verified, and the simulation model has built by using MATLAB/Simulink.

Controllable-Dual Bridge Fault Current Limiter for Interconnection Micro-Grids

Different types of fault current limiters (FCLs) have been developed and designed based on non-superconducting DC reactors (NSDRs). This paper proposes a controllable dual-bridge FCL (CDBFCL) based on the NSDR for use in an AC-type micro-grid. It includes a NSDR and two series and shunt bridge circuits. The series bridge is based on diode semiconductor switches and is coupled in series with the line via a transformer. The shunt bridge is based on thyristor semiconductor switches and is coupled in parallel with the line. The shunt bridge provides a variable voltage source. It compensates for the DC side voltage drop due to NSDR resistance and semiconductor switches during normal operating condition. In addition, by controlling the shunt bridge firing angle, it produces a controllable DC voltage, which can control the fault current amplitude during a fault. The structure, principle operating work, and control system of the proposed CDBFCL are presented. The CDBFCL performance is studied analytically and through simulation by the PSCAD/EMTDC software. In addition, the simulation results are compared with those obtained experimentally from a prototype CDBFCL and show a close correlation.

Experimental evaluation of negative-sequence voltage compensation in distribution networks by a modular multilevel static synchronous compensator

This paper presents a negative-sequence voltage compensation strategy of a distribution network by using a static synchronous compensator based on modular multilevel converter. Mathematical relations of the static compensator are used to derive small-signal linearised models, in the synchronous reference frame, and to design voltage and current controllers to compensate for unbalanced voltages at the point of common coupling. Moreover, a comprehensive model of the DC bus voltage with a control loop implementation are presented. Furthermore, a notch filter is connected in the feedback path of the DC voltage control loop to eliminate the oscillation in the DC voltage. Digital simulations results, obtained with a 10 MVA / 24 kV MMC-DSTATCOM with 14 submodules per arm, will be used to validate the small-signal linearised mathematical models, and the performance of the designed controllers, during steady-state and faulty grid conditions. In addition experimental results obtained with a small-scale MMC prototype, with 03 submodules per arm, will be presented to demonstrate the feasibility of the compensation strategy proposed here.