Direct Current Control Research Articles

Cryogenic Analog Microwave Variable Attenuator Using rf-SQUIDs for Quantum Systems

We present the design, fabrication and testing of a low-temperature superconducting (LTS) analog microwave variable attenuator. The two-port circuit includes two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$90^{\circ }$</tex-math></inline-formula> hybrid couplers and a phase shifter to realize a variable attenuation at the output port. The wideband analog phase shifter is implemented using LTS microstrip transmission line (TL) coupled to an array of radio frequency superconducting quantum interference devices (rf-SQUIDs). The phase shift is achieved by passing a dc current through a TL adjacent to the SQUID-loaded microstrip line which controls the flux through the rf-SQUIDs. The proposed variable attenuator shows more than 30 dB of precise analog flat attenuation tuning range over 8 GHz to 12 GHz with a dc control current ranging from 0 mA to 4.5 mA. The device exhibits a wideband operation with variable attenuation seen not only in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X-</i> band but also in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku-</i> band. The device is fabricated using a multilayer niobium-based superconducting process SFQ5ee by MIT Lincoln Laboratory, and has a compact footprint of 1.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{mm}^{2}$</tex-math></inline-formula> . To the best of our knowledge, this is the first implementation of a variable attenuator using distributed rf-SQUIDs. This device has implications in a variety of applications such as cryogenic receivers and qubit circuit measurements.

Centralized power management and control of a Low Voltage DC Nanogrid

This paper discusses FPGA-based power sharing control of a solar PV-powered low-voltage DC (LVDC) nanogrid. The proposed LVDC nanogrid control algorithm monitors power generation, storage, and load power and shifts between sources and load to maintain power balance. The controller effectiveness is studied for varying input and varying load conditions via simulation studies and hardware implementation. A proposed system simulation model with a control algorithm is built into MATLAB and performance analysis is carried out. The power sharing control algorithm and MPPT algorithm are built using Xilinx blocks in MATLAB and programmed into FPGA controller Furthermore, experimentation is carried out on the proposed model to validate the simulation results. Hardware results obtained under different atmospheric and load conditions are presented and discussed.

State and disturbance observer-based predictive control for DC–DC converters integrated with a photovoltaic system

State and disturbance observer-based predictive control for DC–DC converters integrated with a photovoltaic system

Nonlinear state estimator design and implementation for speed control of a BLDC motor drive using square‐root extended H∞$\text{H}_{\infty}$ filter

AbstractSensorless speed control of a brushless DC (BLDC) motor, basically a combined control‐observer design, plays a crucial role in several industries, including electrical and aerospace applications. The key idea is to use only electrical (current) sensors and the remaining mechanical states (speed and rotor position) to be estimated using square‐root extended filter (SREF) for a BLDC motor. These estimated states are then fed‐back to the controller. In most of the designs, it is assumed that the BLDC motor plant parameters are constant; however, in reality, their parameters vary due to various intrinsic and extrinsic conditions. Compared to the conventional extended Kalman filter or its square‐root version, the proposed SREF for the BLDC motor has an inherent tendency to deal with parameter uncertainties and hence improves the robustness of the overall system. The robustness of the proposed scheme is tested at various reference speeds for a closed‐loop BLDC drive; further parametric uncertainties in stator resistance, detuning of inductance, and change in load are considered. The proposed control‐observer strategy using SREF is compared with its counterpart square‐root extended Kalman filter (SREKF), and the experimental results validate the efficacy of SREF for speed control of BLDC motor drive during the nominal conditions and in the presence of parametric uncertainties.

A Multi-Port DC Power Flow Controller Integrated With MMC Stations for Offshore Meshed Multi-Terminal HVDC Grids

Multi-terminal dc (MTDC) systems have the potential to facilitate the integration of offshore wind farms. A dc power flow controller (DPFC) is necessary for meshed multi-terminal high voltage dc (HVDC) grids to regulate the power flow in dc lines. However, DPFCs based on modular multilevel converters (MMCs) require two dc-ac conversion stages and an extra ac transformer, which increases the cost and loss for offshore platforms. This paper proposes a multi-port DPFC that is integrated internally into the offshore MMC station, eliminating the need for an extra transformer and reducing dc voltage ripple. Additionally, the full bridge submodules (FBSMs) in the DPFC can further reduce the number of FBSMs required in the MMC station for dc fault blocking. The proposed DPFC is composed only of cascaded FBSMs connected to the arms of the offshore MMC station, which can exchange power directly with the MMC valve to achieve power balance. By using the MMC station, the proposed DPFC requires a small kVA rating, approximately 1%-5% of the total system power rating. The performance of the proposed DPFC is validated through simulation of a hybrid system of the IEEE 39 bus and the Cigre HVDC benchmark, and also through down-scale experimental testing.

Performance Evaluation of Brushless Direct Current Motor Control Methods through Low-Cost Microcontroller-Based Real-Time Experiments

Brushless direct current (BLDC) motors are high efficiency synchronous motors that are employed in a variety of applications due to prominent features such as long operational life, low maintenance requirements, and great dynamic response. BLDC motors are driven by energizing the motor stator windings with an inverter circuit. To commute the inverter switches, the trapezoidal (120°) method is generally used by considering the back electromagnetic force induced on unenergized phase of BLDC. Furthermore, depending on the application requirements, alternative commutation modes (CM) such as 180°, 150°, and sinusoidal-based approaches are utilized. In the literature, the performance comparison of some CMs was studied for two-phase on operation and three-phase on operation mode as a switching pattern. However, only a few research assessed the performance of two or three commutation modes simultaneously. In this study, the performance comparison of pulse width modulation (PWM) based commutation modes are examined by considering 120°, 180°, 150° modes, and sinusoidal PWM. In this scope, it is the first time that direct digital synthesis (DDS) is addressed as a BLDC control algorithm in a performance comparison study. In experimental studies, a simple and a low-cost drive circuit is designed to acquire the case results. According to the results, the proposed DDS-based sine commutation method is more efficient than other commutation methods and it has lower power consumption at both low and high speeds also a wider operable speed range.

Adaptive Controller for Bridgeless New SEPIC Integrated Landsman Converter for PFC in Induction Motor

The Induction Motor (IM)when powered by an AC supply, results in low power factor because of excessive harmonic contents, which is effectively minimized by adopting proper Power Factor Correction (PFC) technique. This paper proposes an AC-DC bridgeless SEPIC-Landsman converter for a 3ϕVoltage Source Inverter (VSI) fed IM to perform effective PFC and power quality enhancement at AC supply mains. Here, the bridgeless SEPIC-Landsman converter’s switching operation is controlled by the adaptive Proportional Integral (PI) controller for getting a controlled DC output voltage with minimum ripples. A Cascaded Type 2 Fuzzy Logic Controller (CT2FLC) effectively controls speed of the IM and also reduces the peak overshoot problem. Here, the speed control is achieved by adjusting voltage and frequency of 3 IMwith a reduced settling time of 0.2s. The proposed system is modeled with MATLAB Simulink and empirically validated, generating a THD value of 1.69% and an efficiency of 93%. The simulation and hardware results thus obtained confirm an effectiveness and reliable performance of the proposed system.

Two-layer nonlinear control of DC–DC buck converters with meshed network topology

In this paper, we analyse a buck converter network containing arbitrary, up to mild regularity assumptions, loads. Our analysis begins with the primary controller where we propose a novel decentralised Lyapunov function for the interconnection between currents and a bounded integrator. We leverage on this result to study the network as a cascaded interconnection between voltages and bounded currents. We, in addition, propose a distributed optimal secondary control framework to steer voltages close to their nominal operating values. We employ the properties of the Laplacian kernel to show recursive feasibility and input-to-state stability of the closed loop. We demonstrate our results in a meshed topology network containing 6 power converters, each converter feeding an individual constant power load with values changing arbitrarily within a pre-specified range.

Development of a Control Strategy for the Hybrid Energy Storage Systems in Standalone Microgrid

The intermediate energy storage system is very necessary for the standalone multi-source renewable energy system to increase stability, reliability of supply, and power quality. Among the most practical energy storage solutions is combining supercapacitors and chemical batteries. However, the major problem in this kind of application is the design of the power management, as well as the control scheme of hybrid energy storage systems. The focal purpose of this paper is to develop a novel approach to control DC bus voltage based on the reference power's frequency decomposition. This paper uses a storage system combined of batteries and supercapacitors. These later are integrated in the multi-source renewable energy system to supply an AC load. This technique uses the low-pass filters' properties to control the DC bus voltage by balancing the generated green power and the fluctuating load. The hybrid storage system regulates power fluctuations by absorbing surplus power and providing required power. The results show good performances of the proposed control scheme, such as low battery current charge/discharge rates, lower current stress level on batteries, voltage control improvements, which lead to increase the battery life.

Power quality optimization using a novel backstepping control of a three-phase grid-connected photovoltaic systems

&lt;span lang="EN-US"&gt;A novel nonlinear backstepping controller based on direct current (DC) link voltage control is proposed in three-phase grid-connected solar photovoltaic (PV) systems to control the active and reactive power flow between the PV system and the grid with improved power quality in terms of pure sinusoidal current injection with lower total harmonic distortion (THD), as well as to ensure unity power factor, or to compensate for reactive power required by the load, i.e., the electrical grid. The output power of the PV array is supplied to the grid through a boost converter with maximum power point tracking (MPPT) control and an inverter. Simulation results of the proposed controller show good robustness under nominal conditions, parameter variations, and load disturbances, which presents the main advantage of this controller as compared to an existing controller. The performance of this work was evaluated using a MATLAB/Simulink environment.&lt;/span&gt;

Modeling, Control, and Operation of an M-DAB DC–DC Converter for Interconnection of HVDC Grids

Future high-voltage direct-current (HVDC) networks based on voltage source converters (VSCs) will have different structures (asymmetric monopolar, bipolar, or symmetric monopolar), voltage levels, control, and protection schemes. Therefore, dc–dc converters are needed to interconnect those VSC-HVDC grids and several technical issues on their control and operational systems must be adequately addressed. A dc–dc converter based on a modular-dual active bridge (M-DAB) converter is suggested to reach a desirable interconnection of the HVDC grids and regulate power flow (PF) between them. A dynamic averaged model is proposed for the M-DAB converter and its stability is analyzed using the Lyapunov function. Moreover, a new local controller based on nonlinear control theory is proposed for the M-DAB. The new M-DAB local controller is integrated with the energy management system (EMS), by updating the PF equations, to create a complete control structure. Considering the CIGRE DCS3 HVDC test system and the studied M-DAB, static, dynamic simulation, and experimental studies are conducted and the dc–dc converter and the performance of the designed controllers and the EMS are examined and validated.

Time Sequence Machine Learning-Based Data Intrusion Detection for Smart Voltage Source Converter-Enabled Power Grid

Smart inverters of distributed energy resources can enable cloud computing, condition monitoring, result visualization, remote control, and peer-to-peer energy trading in advanced power systems. However, the advent of data injection attacks in the communication architecture can alter measurement characteristics of power grids and have devastating consequences. In this article, we propose a time sequence machine learning-based anomaly detection methodology for detecting cyber intrusion into control signal setpoints and dc voltage signal measurement bias of the voltage source converter (VSC) in wind generators. We first investigated the effects of four types of denial of service, tampering signal, and stealthy-type data intrusion attacks on smart VSCs and overall wind farms. We then proposed a novel time sequence machine learning-based intrusion detection framework that can be implemented to detect different cyberattacks in the VSCs. The performance of the proposed framework has been compared with that of autoencoder and clustering-based intrusion detection framework. The proposed framework was validated by using the IEEE 39 bus power system in the presence of four wind farms in different locations. Using several metrics for intrusion detection performance, we validated the effectiveness of the proposed framework.

Harmonic Characteristics and Negative Sequence Analysis of Regenerative Braking for High-speed Railway

Background: The traction power supply system (TPSS) of railways mainly focuses on power quality analysis. In the study of harmonic and negative order currents, about 80% of the literature analysis are not specific enough， there is a lack of completeness in the simulation system. Objective: Analyze the influence of harmonic and negative current sequences of TPSS on the system circuit, and realize intelligent recognition for different working conditions. Methods: The converter is designed based on the transient direct current control technology and the harmonic model of grid-side regenerative braking is established. According to the parameters of CRH2 (CRH380AL) locomotive, the EMU model is built and run in the TPSS for joint simulation. The availability of the model is verified by combining the harmonic content and voltage level. Then, the distribution of negative sequence current under the no-load, traction and regenerative braking conditions of the system is analyzed in detail, and the negative sequence characteristic waveform under various conditions is obtained, so as to obtain the variation law of negative sequence current under different conditions. Results: Under the regenerative braking condition, the current harmonic distortion is much higher than that under the traction condition. From the analysis of voltage and current phase, the power factor of regenerative braking is also small. In the negative sequence analysis, the tip negative sequence current impact phenomenon occurs mostly during the traction operation of the train, while the current impact effect is weakened during regenerative braking, but the amplitude of the negative sequence fluctuation shows an increasing trend. Conclusion: The energy generated by regenerative braking will be utilized by the locomotive under traction, and these bad electric energy forms will have extremely adverse effects on the process of high-speed train receiving and changing current. These negative sequence analysis results can be used to identify and classify different working conditions and divide and conquer energy compensation actions to achieve energy saving and consumption reduction.

Torque control of a 5 KW, 220 V separately excited DC motor using microcomputer

Fast torque control is crucial for various applications, including diesel-electric locomotives, electric automobiles, and steel plants. The purpose of this paper is to utilize a microcomputer to control the torque of a separately-excited DC motor fed from a single-phase semi-controlled converter. There are numerous strategies to determine torque using direct or indirect methods. The greatest issue of direct strategy using torque meters is that the measuring device must be installed between the motor and the load. In this paper, we avoid this challenge by employing the indirect approach, specifically by monitoring several DC machine-specific quantities such as voltage, current, and speed, which are easier to determine experimentally. This technology is unquestionably helpful in real-world applications since it eliminates any mechanical impact on the installation. This paper describes the system configuration and provides an explanation of the architecture and system features. The simulation of the proposed system using TUSTSIM dynamic simulation program which is capable of simulating the control system with a digital controller in the loop is presented. An implementation of microcomputer-assisted torque control of DC separately excited motor with proportional integral (PI) controllers is presented. A typical oscillography of the driving characteristics is provided along with the experimental results.

A Novel Standalone Implementation of MDNN Controller for DC–DC Converter Resilient to Sensor Attacks—A Design Approach

Power electronic converters have become an integral part of the direct current microgrid (DCMG) systems. The efficient control of these converters will decide the performance of the DC microgrids. With the evolution of cyber physical systems, all these power converters are integrated into the communication networks to achieve intelligent and smart control. Data in the communication networks are highly vulnerable towards cyber-attacks, leaving it unaddressed will lead to substantial economic losses and disasters. This article proposes a standalone implementation of multi-deep neural network (MDNN) based DC-DC converter and its application to detect false data injection (FDI) attacks at the sensor level. A MDNN is developed with a combination of deep neural network (DNN) and error detection network (EDN). DNN is used as the controller to achieve closed loop operation of DC-DC converter and EDN is used to detect and mitigate the FDI attack. Initially, proposed scheme is executed in MATLAB simulink platform with various disturbances at controller level and several attack scenarios are verified with its experimental results.

Optimal power distributed control of the DC microgrid in meshed configuration

This paper proposes a Lyapunov-based power sharing control scheme and a fixed-time-based distributed optimization algorithm to achieve optimal power sharing of sources in a DC microgrid. The Lyapunov-based controller is designed based on so-called ratio consensus protocol, where it drives the sources to a desired proportional power sharing by regulating the voltage profile of the DC microgrid. The distributed optimization optimizer is established by integrating a finite-time weighted consensus algorithm with an iterative algebraic operation, where it calculates the optimal power dispatch on the target of minimizing the generation cost. The optimizer receives the current output power of the controlled DC microgrid and sends the obtained power dispatch to the power sharing controller as the proportionality coefficients. Both the controller and optimizer are carried out in a fully distributed way. Under the framework of the Lyapunov method, stability analysis of the DC microgrid with the proposed control scheme, as well as convergence and optimality analysis of the distributed optimization algorithm, is provided. However, the influence of the time delay of the controller on the system remains to be further investigated in future work.

Grid-Connected PV Inverter Control Strategy Based on the Sliding Mode

The Photovoltaic grid-connected inverter is an essential equipment of photovoltaic grid-connected system. Due to the disadvantages of the traditional PI control method for grid-connected photovoltaic inverters, this paper adopts the integral sliding mode variable structure to control grid-connected inverters. Grid inverter DC control mode was introduced in detail in the sliding mode variable structure control strategy. Using Matlab simulation platform to compare and analyze the traditional PI voltage compensation control strategy and sliding mode variable structure control strategy. From the waveform of the simulation output, the current harmonic at the output of the grid-connected inverter is reduced, and the power factor is increased, with the power factor is close to 1. The control precision, robustness and anti-interference ability of grid-connected system are improved. Which proved the feasibility and the superiority of the proposed control strategy.

Capacitor-Voltage-Balancing Control for Isolated Medium-Voltage AC-DC Modular Matrix Converter

This paper presents a capacitor-voltage-balancing control scheme for an isolated medium-voltage AC-DC converter using level-shifted PWM control of a modular matrix converter (MMxC). The proposed isolated AC-DC converter is composed of the primary MMxC with level-shifted PWM control, high-frequency transformer, and secondary H-bridge circuits. The high-frequency transformer of the proposed circuit can be downsized because the level-shifted PWM control scheme makes the rated frequency of the high-frequency transformer equal to the switching-frequency. The proposed capacitor-voltage-balancing control can compensate for the capacitor voltage imbalance of the MMxC using the positive-sequence and negative-sequence circulating-currents with a power supply frequency and high-frequency voltage. In the proposed control system, the three feedback control systems with DC control variables can be developed to compensate for the capacitor voltage imbalance. The effectiveness of the proposed capacitor-voltage-balancing control scheme and the control systems is verified by experiments using a 200V, 5-kW laboratory prototype.

Current sharing and voltage regulation of parallel DC–DC buck converters: Switching control approach

In this paper, a new framework for distributed switching control of parallel DC–DC buck converters is investigated, which represents voltage regulation and current sharing as two decoupled control design problems. The problem is described as a cascaded switched affine system with the new variables output voltage, total current, and current difference of the load, and by employing distributed min-projection switching technique, switching control signals are provided to achieve both voltage regulation and current sharing control objectives. Stability analysis based on relay control is carried out to guarantee the asymptotic stability of the error signals. Finally, the performance and effectiveness of the proposed control strategy are demonstrated by simulation studies as well as experiments conducted on a laboratory prototype.

Direct current (DC) microgrid control in the presence of electrical vehicle/photovoltaic (EV/PV) systems and hybrid energy storage systems: A Case study of grounding and protection issue

AbstractIn recent years, the interest in using DC microgrids has greatly increased due to their higher efficiency, less complexity, and greater transmission power compared to AC microgrids. To address challenges in DC microgrids in the presence of electrical vehicles (EVs) and the uncertainty of charging EVs, researchers have used PV/EV combination systems with energy storage systems (ESS). Controlling DC microgrids, including PV/EV/ESS, is crucial to cope with the existing challenges. On the other hand, the research on DC microgrids' protection systems is in the early stages, and there are still many challenges in this field. In addition, differences in control systems can pose different challenges for the protection system. The simulation results in this paper demonstrate that considering the best case (use of unipolar resistance grounding system) the DC bus voltage is improved by 22.3% (based on MAPE% data comparison). In the protection part, the empirical‐mode decomposition (EMD) method and selecting a suitable intrinsic mode functions (IMF) have been used to protect the DC microgrid. The proposed protection method has been tested under pole‐to‐pole and pole‐to‐ground fault conditions. The results show that the proposed method is capable of detecting various fault types in the studied microgrid.