Synchronous Voltage Research Articles

Dual Resonant Voltage Droop Compensation for Bipolar Solid-State Marx Generator Topologies

This paper discusses a novel methodology to increase the voltage droop compensation range in generalized solid-state bipolar high-voltage Marx modulators with one resonant stage. To maintain the modularity characteristic of bipolar Marx modulators, the imbedding of additional resonant stages is not straightforward. Nevertheless, this paper proposes to add a second resonant stage to the already existing resonant-type voltage droop compensation stage. This second stage increases the voltage droop compensation percentage of a generalized solid-state bipolar Marx generator. The compensation of the bipolar pulse voltage droop is now achieved by adding two auxiliary synchronous compensation resonant voltages, to the output capacitive decaying voltage. Simulation and experimental results are presented for six Marx plus two resonant stages, 16% voltage droop, with 3-kV pulse amplitude, 100- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> pulsewidth, 40-ms relaxation time, and 10-Hz pulse repetition rate.

Control of AC/DC Modular Multilevel Converter

In recent years, a special attention is paid to grid connected multilevel converters. These converters have specific use in industry in a high power, medium-voltage and high-voltage applications. This paper presents new control algorithm for single-phase AC/DC modular multilevel converter with target application as a traction converter connected directly to trolley wire. The proposed control strategy presents resonant controllers for converter current control with fundamental frequency adaptation. The fundamental frequency estimation and voltage synchronization is based on Second Order General Integrator Phase Locked Loop (SOGI-PLL). Furthermore, this paper presents robust voltage balancing technique for multilevel converter based on energy calculation of DC-link capacitances. It provides voltage balancing of multilevel converter cells with unbalanced load. The resulting control algorithm has low total harmonic distortion of converter trolley current even under unbalanced load condition. The algorithm was experimentally verified on the low voltage laboratory prototype with 3 H-bridge cells.DOI: http://dx.doi.org/10.5755/j01.eie.24.6.22282

Comparative Performance Analysis of AVR Controllers Using Modern Optimization Techniques

Automatic voltage regulator (AVR) system is an important device to regulate synchronous generator output voltage. Controllers are used to provide better stability and faster response for AVR system and this article shows two types of controllers: proportional-integral-derivative (PID) and proportional-integral-derivative-acceleration (PIDA) controllers. Harmony search algorithm (HSA), local unimodal sampling (LUS), and teaching learned based optimization (TLBO) are the optimization techniques used to tune each controller parameters. Integrated square error (ISE) is used as an objective function to minimize error in voltage for better stability and response. Transient response, root locus, and bode diagram are calculated for each controller using the three optimization techniques. The results are compared with other optimization techniques to find out the best performance and stability for an AVR system. The results show also which controller is better. Robustness analysis is made on the best system to check terminal voltage response with respect to load variation to ensure that this system can be applied for the AVR of synchronous generator in power system.

Initial Excitation Issues of Synchronous Generator with VSI Inverter in Varying Rotational Speed Operation

Abstract Synchronous self-excited generators still are and probably will be the most popular 3-phase alternators installed in inland power stations so onboard of seagoing ships. Because of fuel savings and environmental restrictions Diesel, dual-fuel and gas propulsion engines for alternators of wide-range varying revolutions drives are increasingly used. There must be efficient way of creating 3-phase voltages of desired constant parameters ensured when generator produces variable amplitudes and frequencies of voltages because of changing rotational speed. As the control method modified field oriented control widely used with squirrel cage induction machines was chosen. This control method involves decoupling of currents and control voltages to flux and torque components and keeping them in optimal (orthogonal) condition. In order to obtain proper excitation and operation of such generator several factors have to be taken into account. Nonlinear dependence of voltage generated from rotational speed of self-excited synchronous generator is one of the factors that affects initial excitation process thus specific control method while generator startup. Theoretical background of synchronous generator excitation and voltage source inverter adopted FOC control method along with experimental results obtained in laboratory test bench of 5,5 kW generator and conclusions were presented.

Research of the alternator on the stand – efficiency aspect

The article discusses the methodology of testing an alternator at a stand to determine its energy efficiency. The efficiency was calculated on the basis of the measurement of the electric power supplied to the drive motor and the power generated by the alternator, taking into account the mechanical and electrical losses of the motor and the belt drive. The efficiency of the machine as a three-phase synchronous generator, without rectifier and voltage regulator, was also determined in order to assess the influence of electronic components on the overall efficiency of the machine. The tests were performed for various rotational speeds and loads. Various physical factors and phenomena that have a negative impact on the efficiency of energy conversion in the vehicle electrical supply system are discussed.

Discrete-Time Complex Bandpass Filters for Three-Phase Converter Systems

In this paper, a first-order complex bandpass filter (CBF) derived in the discrete frequency domain is proposed as a building block for the complex signal processing unit in three-phase converter systems. The first-order discrete CBF can be directly implemented in a digital system, is stable at all center frequencies, and has a low computational burden. The first-order CBF is extended to a $p$ th-order discrete CBF. A normalized frequency-locked loop (FLL) is then developed that allows the frequency adaption to satisfy a desired settling time regardless of the input signal magnitude or discrete CBF form. The $p$ th-order discrete CBF-FLL was tested on an FPGA in the form of two industrial applications: voltage synchronization under grid fault and extraction of an unknown frequency component. The second-order discrete CBF-FLL offered significantly improved stopband attenuation and frequency estimation relative to the first-order discrete CBF-FLL, for a small increase in computational burden.

Comparative Study of Reactive Power Compensator Methods for Integration of Renewable Energy Sources

The integration of renewable energy sources with power system network brought a number of challenges. One of them is imperfect power quality. The power quality is the primary goal of an electrical power distribution system network. The assessment of demand for reactive power, required for inductive loads, limits the quality of power. In the past, many inductive power compensating techniques were used to control the inductive loads. A flexible alternating current transmission system (FACTS) devices like static synchronous compensator (STATCOM) and voltage source converter (SVC) are the state-of-the-art and the most modern reactive power compensators in order to deal with renewable energy sources. The current paper presents the study of the olden times of reactive power control methods used in the past and state-of-the-art reactive power control method through STATCOM & SVC. This paper also discusses effects of STATCOM and SVC on power system to progress the power quality .i.e. improvement in the power transfer capability of the transmission system and voltage stability for the distribution system.

A robust phase-locked loop against fundamental frequency deviations and harmonic distortions

This paper proposes a frequency-adaptable method for computing the phase associated with the positive sequence components from the measured grid voltages. It relies on a simple procedure in which the positive sequence is separated from the negative one through a suitable decomposition of the synchronous voltage vector onto the stationary αβ frame. The procedure performance is enhanced by means of an one-cycle Fourier filter. The positive sequence voltages are then handled by a synchronous-reference frame phase-locked loop (SRF-PLL) algorithm. The structure composed of the positive-sequence estimator and the SRF-PLL is called a one cycle Fourier PLL (OCF-PLL). The OCF-PLL is robust against voltage harmonic distortions due to the OCF frequency-response characteristic. The frequency adaptability is obtained through the series connection of two OCF-PLL blocks. In the first block the fundamental frequency is computed by the SRF-PLL. This frequency is supplied to the second OCF-PLL block which computes the positive phase of the original measured voltages. Also, in this paper, the frequency adaptability is mathematically demonstrated. The method is initially evaluated by means of simulated voltages. Then, an experimental setup has been designed, in which the proposed method has been implemented in a digital signal processor (DSP) and tested on voltages produced by a programmable power supply able to emulate distorted and unbalanced voltages. The results prove the technique efficacy.

Energy harvesting potential of bendable concrete using polymer based piezoelectric generator

Piezoelectric materials have gained a lot of attention in the last few decades as they introduce a renewable and sustainable approach for energy harvesting from vibrations or mechanical deformation in our environment. Among piezoelectric materials, polyvinylidene fluoride (PVDF) is one of the most commonly used piezoelectric polymers due to its high flexibility and piezoelectric performances. In this work, engineered cementitious composites (ECC) incorporating flexible PVDF based piezo polymer has been investigated as an innovative energy harvesting system to scavenge energy from mechanical deflection of ECC. Synchronous flexural test and voltage data recordings were employed to evaluate the voltage capture efficiency of two different lengths of PVDF (41 mm and 73 mm). The various loading rates of four-point bending tests were conducted to assess the energy harvesting performance. The results show that the voltage/power generated by the system is more efficient for longer PVDF samples as compared to the shorter ones when subjected to the four-point flexural test. High loading rates were found to be favorable for energy harvesting. The experimental results lay a solid foundation for potential energy harvesting application of the new cementitious composite system for development of multi-function building materials.

Hybrid synchronous generator output voltage control with energy storage

Hybrid synchronous generator output voltage control with energy storage

Mitigation of Current Distortion in a Three-Phase Microinverter With Phase Skipping Using a Synchronous Sampling DC-Link Voltage Control

To improve light load efficiency, a three-phase photovoltaic (PV)-based microinverter may operate in single-phase, two-phase or three-phase mode depending on the available input power. Therefore, its dc-link capacitor may be subjected to large peak-to-peak voltage ripple when operating in phase skipping mode. This paper determines the minimum value of the dc-link capacitor by allowing the maximum acceptable voltage ripple on the dc link. This allows for the use of film capacitors instead of electrolytic capacitors in order to improve the microinverter reliability. Unfortunately, higher dc-link voltage ripple introduces harmonic distortion on the inverter output current waveform if it is not compensated for by the dc-link voltage controller. This paper proposes a simple synchronous control method to regulate the dc-link voltage with the presence of large voltage ripple. The dc-link voltage controller is synchronized with the phase-locked loop and samples the average value of dc-link voltage without introducing unwanted harmonics into the voltage sense path. Experimental results were obtained from a 300-W three-phase half-bridge microinverter prototype to verify the proposed dc-link voltage control performance. Inverter output current total harmonic distortion of 1.6% was achieved even though the dc-link peak-to-peak voltage ripple reached as high as 87 V with 219-V split dc-link voltage. Dynamic response is fast enough to easily track the most extreme ramp change in input PV power.

Complex-Coefficient Complex-Variable Filter for Grid Synchronization Based on Linear Quadratic Regulation

Advanced digital filter is important for grid voltage synchronization, harmonic information extraction, and converter control. The complex variable filter (CVF) such as the reduced order generalized integrator is one of the most prevalent filters. However, it is proven in this paper that the real coefficient CVF achieves performance identical to the real variable filter such as the second-order generalized integrator. It implies that the advantages of CVF are not fully utilized. Therefore, in this paper, the real coefficient is extended to a complex one leading to a complex coefficient CVF (CC-CVF), and the filter performance of CVF for extracting the harmonics is significantly improved. Furthermore, linear quadratic regulation is employed to design the complex coefficients to achieve a better dynamic performance. Finally, the CC-CVF is enhanced with frequency estimation capability. The proposed CC-CVF is verified by extensive simulations and experiments.

Measurements of electric characteristics in high-current high-pressure discharge with current amplitude of 590–1200 kA by magnetic probe

Soft x-ray radiation (SXR) oscillation were registered for discharge with current amplitude of 1200 kA at initial hydrogen pressure of 5 MPa. Near current maximum the fluctuations of SXR from the channel have been registered. Speed of current channel contraction, channel radius and its oscillation amplitude for current amplitude of 1200 kA were measured by magnetic probe with extrapolation for currents of 590 and 900 kA. The electric field strength in discharge channel and near electrode voltage drops was determined by comparison of channel radius oscillations with synchronous voltage changing. Also this method was used for oscillation amplitude estimation at current of 1200 kA. Satisfactory agreement for the estimations was received. Oscillation amplitudes are needed for calculation of x-ray intensity modulation. Channel plasma parameters were determined for contraction near current maximum.

An Analytical Approach to Detect Generator Loss of Excitation Based on Internal Voltage Calculation

The excitation system of a synchronous generator has a major role in proper operation and control of the generator. Loss of excitation (LOE) may cause harmful effects on the both generator and power system. This paper presents a new approach to detect LOE based on calculating the synchronous generator internal voltage. This parameter is considerably sensitive to LOE and can be used as a straightforward index to discriminate LOE events from system disturbances more quickly and robustly than the conventional indices. A novel and practical technique with minimum computational burden is presented to calculate the generator internal voltage. To evaluate the proposed algorithm, LOE events in a multimachine test system are investigated. In addition, the proposed approach is experimentally evaluated on a 10 kVA synchronous generator. Performed studies demonstrate that the proposed strategy not only noticeably decreases the LOE relay operation time, but also desensitizes its maloperation to system disturbances.

Modifikasi Topologi Pengendali PID untuk Automatic Voltage Regulator Generator Sinkron

Automatic voltage regulator (AVR) is one of key elements in an excitation system which controls the synchronous generator terminal voltage in an electrical power generation plant. PID control algorithm in an AVR has been designed to obtain good response towards voltage reference without considering the effect of torque disturbance. This paper proposes a PID with modified topology for a digital AVR in order to regulate the generator terminal voltage in more speedy and more accurate, while maintaining robustness against torque disturbance. Performance of the digital AVR has been compared with conventional PID controller through experiments using a hardware in the loop (HIL) system. The experiment results show that the proposed PID with modified topology provides better performance than the conventional PID controller. Under torque disturbance, the proposed algorithm provides 83% smaller steady state error and 4.8 second shorter settling time compared to the conventional PID controller. When the reference voltage changes, compared to the conventional PID controller, the proposed algorithm provides 15% smaller steady state error, 79% smaller overshoot, and 0.2 second shorter settling time.

Grid voltage synchronization algorithms for grid-connected power converters

Grid voltage synchronization algorithms for grid-connected power converters

Optimal Placement of STATCOM using Two Stage Algorithm for Enhancing Power System Static Security

In recent years, there has been a consistent increase in power demand which has resulted in heavy line flows, greater losses, and may threaten system security and stability. The power system consists of diversified loads with rapid variations in its reactive power requirement. STATCOM is a shunt compensator used for fast response when the reactive power of the load is changing rapidly. This paper presents STATCOM modeled as synchronous voltage source. In this work, optimum location and optimal parameters of STATCOM have been determined. The objective is to minimize system power loss by controlling device parameters. In this work, a two-stage approach is proposed for optimal placement of STATCOM. In the first stage, optimal location of STATCOM is obtained by generalized approach which is based on sensitivity analysis and in the second stage STATCOM parameter setting is done using Newton- Raphson (N-R) power flow technique. This approach is implemented on 14-bus test system. Voltages in the network, power flows and power loss before and after placing the STATCOM have been compared. It is observed that, after placement of STATCOM voltage profile is improved and power loss is minimized in the system. Proposed algorithm is implemented in MATLAB.

Signal synchronization for massive data storage in modular battery management system with controller area network

One of the key battery performances which can be described as the resistance characteristic is the cell voltage response with dynamic currents, and it requires synchronous cell voltages and current. But due to inevitable network latency in modular battery management system (BMS) with controller area network (CAN), cell voltages and current are usually asynchronous. We firstly analyze the sampling and the storage process of battery signals to study the asynchronous mechanism in BMS. We develop an on-line synchronization method using a “global clock” from the master controller to decrease the time delay as much as possible. And we further propose a model based sync method based on the frequency division equivalent circuit model (FDECM) for the battery pack. The low frequency cell difference model is used to identify cell “resistances difference”, and then the optimal time compensation for cell voltages is obtained when the minimum mean absolute derivative (MAD) value of identified resistance differences is reached according to the low frequency characteristic of cell “resistances difference”. The proposed methods are verified by simulation and experiment. The current and cell voltages in the data logger of BMS can be synchronized when the optimal compensation time is applied respectively for each cell. The data after synchronization can meet the requirements of further data analysis and processing, which is of great significance to enhance and improve the control strategy of BMS.

Synchronous circadian voltage rhythms with asynchronous calcium rhythms in the suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN), the master circadian clock, contains a network composed of multiple types of neurons which are thought to form a hierarchical and multioscillator system. The molecular clock machinery in SCN neurons drives membrane excitability and sends time cue signals to various brain regions and peripheral organs. However, how and at what time of the day these neurons transmit output signals remain largely unknown. Here, we successfully visualized circadian voltage rhythms optically for many days using a genetically encoded voltage sensor, ArcLightD. Unexpectedly, the voltage rhythms are synchronized across the entire SCN network of cultured slices, whereas simultaneously recorded Ca2+ rhythms are topologically specific to the dorsal and ventral regions. We further found that the temporal order of these two rhythms is cell-type specific: The Ca2+ rhythms phase-lead the voltage rhythms in AVP neurons but Ca2+ and voltage rhythms are nearly in phase in VIP neurons. We confirmed that circadian firing rhythms are also synchronous and are coupled with the voltage rhythms. These results indicate that SCN networks with asynchronous Ca2+ rhythms produce coherent voltage rhythms.

Voltage Control in Distributed Generation Systems Based on Complex Network Approach

In this paper, a new approach for modeling of voltage control problem in distributed generation systems based on the complex network theory is proposed. Distributed generationsystems (DGS) including renewable energy sources are highly complex nonlinear dynamical systems by nature. There are many theoretical and practical challenges to apply the existing control technologies to them. The novel approach, introduced in this paper, embeds the complex network theory into the voltage control problem of DGS; i.e. the voltage control of DGS is introduced as a synchronization problem in complex networks. Complex network methodology shows a promising simplification inthe analysis as well as timely response in large-scale systems. Thanks to the well-developed graph theory as well as advancements in control of multi-agent systems,the model presented in this paper, candealwith real-time hierarchical multi-objective requirements of control problems in DGS. Finally, the pinning control approach is applied to the model in order to solve the voltage synchronization problem of the microgrid.