Non-active Power Research Articles

Distributed Control Scheme for Clusters of Power Quality Compensators in Grid-Tied AC Microgrids

Modern electrical systems are required to provide increasing standards of power quality, so converters in microgrids need to cooperate to accomplish the requirements efficiently in terms of costs and energy. Currently, power quality compensators (PQCs) are deployed individually, with no capacity to support distant nodes. Motivated by this, this paper proposes a consensus-based scheme, augmented by the conservative power theory (CPT), for controlling clusters of PQCs aiming to improve the imbalance, harmonics and the power factor at multiple nodes of a grid-tied AC microgrid. The CPT calculates the current components that need to be compensated at the point of common coupling (PCC) and local nodes; then, compensations are implemented by using each grid-following converter’s remaining volt-ampere capacity, converting them in PQCs and improving the system’s efficiency. The proposal yields the non-active power balancing among PQCs compounding a cluster. Constraints of cumulative non-active contribution and maximum disposable power are included in each controller. Also, grid-support components are calculated locally based on shared information from the PCC. Extensive simulations show a seamless compensation (even with time delays) of unbalanced and harmonics current (below 20% each) at selected buses, with control convergences of 0.5–1.5 [s] within clusters and 1.0–3.0 [s] for multi-cluster cooperation.

Comparison and extension of advanced frequency domain non-active power decompositions

This research paper introduces new prospects in the field of power quality and energy transmission efficiency analysis and system design methodology through advanced frequency-domain power definitions. This proposal presents an improved extension of the power theory Currents’ Physical Components (CPC) by L.S. Czarnecki and compares its improvements with the CPC and an extension of the CPC by H. Lev-Ari. This proposal increases the resolution of physical phenomena reducing the power quality and hence contributes to its analysis and improvement. For this purpose, four additional non-active power components compared to the CPC are introduced. In contrast to the extension by H. Lev-Ari, these additional components are obtained from different definitions. In particular, the decomposition of the unbalance component into a spectral uniform and a spectral non-uniform component is novel to frequency-domain power definitions. As the CPC and its extension through H. Lev-Ari already decompose the collinear and shift components into spectral uniform and non-uniform components, the proposal for the unbalance components finally completes this structure. This yields a consistent and intuitive designation of physical phenomena related to spectral non-uniformity constituting as a concretization to the well-known distortion non-active power. Conclusive examples illustrate this improvement using the appertaining non-active power components.

Hybrid VAR compensator operating study under conditions of a three-wire network

The approaches to the control of the hybrid VAR compensator are considered. A hybrid VAR compensator is a passive and active compensator connected in series. The passive part is represented by a thyristor-switched capacitor bank. The power part of the active part is implemented on the basis of an autonomous voltage inverter, connected through a voltage transformer in series with a passive part. Most of the reactive power is compensated by means of the compensator’s passive part. The hybrid compensator combines the advantages of passive (low price, reliability) and active compensators (possibility of smooth control of reactive power, operation in networks with non-sinusoidal currents). This configuration allows to significantly reduce the rated power of the active part, while maintaining the possibility of smooth control of the reactive power. Mathematical modeling of the hybrid system operation in a three-wire network is carried out. Two operating modes are checked: the reactive power compensation mode and the mode of providing the sinusoidal waveform of the network current. The first mode provides fundamental reactive power compensation only (the compensator current is sinusoidal, therefore, provides «insulation» of capacitor bank from higher harmonics) and the second mode provides limitedly non-active power compensation, including distortion power (overvoltages and exceeding the permissible currents of the capacitor bank are not allowed). When choosing a control strategy, the network configuration and the real requirements of power consumers for power quality indicators are taken into account. The efficiency of the proposed model under conditions of non-sinusoidal load current and unbalance of the main’s voltage is provided

Parameter Determination of Coupled and Decoupled Admittance Matrix Methods of the Norton Equivalent Model for an Air Extractor

Context: Studies carried out in low voltage networks have explored the modeling of linear single-phase loads (such as motors) and non-linear ones (such as those based on power electronics). However, induction motors exhibit non-linear characteristics between voltage and current due to the saturation of their magnetic parts. Therefore, it is necessary to study induction motors in the frequency domain with a model that allows reviewing the characteristic nonlinearity of their voltage-current interaction. Methodology: This article presents the frequency domain modeling of a single-phase induction motor used as a silent air extractor (127 V, 60 Hz, 66 W), which presents a capacitive behavior (fp = 0,93 in leading) and harmonic distortion due to a third-order component (7,0%) when fed with a pure sinusoidal voltage of 127 V. Results: This work establishes the parameters of two approaches to the Norton equivalent model (coupled and decoupled admittance matrix) which are used to estimate the distorted current signal and the values ​​of consumed active and non-active power. The results show comparisons errors of P, Q, THDi, and NRMSE indices of less than 7, 4, 14, and 3%, respectively. Conclusions: The parameters of the Norton equivalent model estimated for the single-phase induction motor allow calculating the current signal with a high degree of precision. This signal exhibits nonlinear characteristics and a capacitive behavior due to the permanent presence of a capacitor aiding the start and operation of the engine.

A Coupled-Inductor-Based Soft-Switching Noninverting Buck–Boost Converter With Reduced Auxiliary Component Count

This letter proposes a coupled-inductor-based soft-switching noninverting buck–boost converter (NIBBC) with reduced auxiliary component count. Instead of using multiple auxiliary passive components to achieve soft switching, the proposed coupled-inductor-based NIBBC uses the coupled inductor as the main inductor, and the auxiliary current generated by the magnetic coupling effect is used to obtain the soft switching for all switches. With simple pulsewidth modulation under fixed frequency, full-load range zero-voltage switching can be obtained under a wide voltage range. Unlike the conventional method utilizing the coupled inductor only to generate nonactive power, the coupled inductor of the proposed converter also takes participant in the power transmission. Besides, the added diode can achieve zero current turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> that avoids the diode recovery issue. The operating principle, the soft switching, and the parameter designs are analyzed in this letter. Finally, experimental results have verified the effectiveness of the proposed solution.

Grid-Tied Hybrid AC-DC Microgrid: Finding Optimal Number of Parallel-Connected AC-DC Bidirectional Interfacing Converters

Linking AC and DC microgrids via a bidirectional AC-DC interfacing converter has emerged the hybrid AC-DC microgrid. The DC bus is connected to the grid by a series converter to mitigate the grid voltage’s power quality problems. To enhance the reliability and to increase transferring active and nonactive powers between DC and AC main buses, the AC-DC bidirectional interfacing converters are connected in parallel. In this paper, the optimal number (n) of parallel-connected bidirectional interfacing converters is obtained to minimize the annual cost of investment and the reliability cost. A two-step deciding algorithm is proposed to find n. First, active and nonactive powers between DC and AC buses are obtained with power quality and power flow considerations. Based on two types of powers, two reliability indices are calculated, including the expected energy shortage (EES) based on active power and the expected Volt-Amps shortage (EVAS) based on nonactive power. The sum of two reliability index costs is considered as the reliability cost. Next, a decision-making strategy is executed to determine the optimal n by making a trade-off between minimization of two objectives: the annual cost of investment and the reliability cost. The simulations of a grid-tied hybrid AC-DC microgrid are done with the experimental measurement data of DC and AC loads and distributed generations. Simulation results verify the performance of the represented approach.

A Two-Switch Forward Partial Power Converter for Step-Up/Down String PV Systems

This letter proposes a novel step-up/down series-connected partial power converter (S-PPC) for string photovoltaic (PV) applications. The proposed bidirectional two-switch forward (BFwd) dc–dc S-PPC performs partial power processing, reducing component stresses and losses. The PV active power is unidirectional, but the BFwd alone operates with bidirectional active power flow; with bidirectional current at the input and bipolar voltage at the output, characterizing two distinct modes of operation. To validate the analysis, a 950-W system prototype of the novel BFwd S-PPC was implemented experimentally for a realistic PV application example, where the transformer turns ratio was designed to decrease the nonactive power processed, resulting in a high power factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ &gt;\text{0.75}$</tex-math></inline-formula> ). The prototype reached a rated/peak system efficiency of 98.68%/99.48%. Compared with previously published step-up/down S-PPCs, the BFwd S-PPC employs fewer active switches (and gate drivers), which reduces its complexity and cost; but moreover, increases its performance. In fact, the proposed BFwd S-PPC presents higher efficiencies than most step-up/down S-PPCs in the literature.

MAF-DCGI Based Single-Phase Uninterrupted PV-Battery System Under Unintentional Islanding

The unintentional islanding is a critical issue in grid-connected solar battery systems in case of grid loss. This interrupts the power supply to the loads. Therefore, in this paper, an uninterrupted photovoltaic (PV)-battery energy storage (BES) system is presented to improve the reliability of the power supply. Besides, this system also furnishes the mitigation of load harmonics current and nonactive power compensation along with peak energy optimization for the PV array. The PV-battery system comprises a battery control by converter and an inverter regulated by an adaptive algorithm. The bidirectional controller regulates the voltage of the DC link capacitor. The moving average filter (MAF) - dual cascaded generalized integrator (DCGI) based adaptive control algorithm is used for utility-interactive operation and a voltage-based control algorithm is used for a standalone mode of operation. MAF-DCGI based phase-locked loop (PLL) is used for synchronization and islanding detection mechanism. An energy management system is used to manage the power flow between the devices in different modes of operation and smooth connection to the grid satisfying the IEEE 1547-2018 standard.

Calibration of On-Board Energy Measurement Systems Installed in Locomotives for AC Distorted Current and High Voltage Waveforms and Determination of Its Uncertainty Budget.

Periodic calibrations of Energy Measurement Systems (EMS) installed in locomotives must be carried out to demonstrate the required accuracy established in the EN 50463-2 standard according to European Parliament and Council Directive 2008/57/EC on the interoperability of rail systems within the Community. As a result of the work performed in the “MyRailS” EURAMET project an AC calibration facility was developed consisting of a fictive power source was developed. This fictive power source can generate distorted sinusoidal voltages up to 25 kV-50 Hz and 15 kV-16.7 Hz as well as distorted sinusoidal currents up to 500 A with harmonic content up to 5 kHz or phase-fired current waveform stated in EN50463-2 standard. These waveforms are representative of those that appear during periods of acceleration and breaking of the train. Reference measuring systems have been designed and built consisting of high voltage and high current transducers adapted to multimeters, which function as digital recorders to acquire synchronized voltage and current signals. An approved procedure has been developed and an in-depth uncertainty analysis has been performed to achieve a set of uncertainty formulas considering the influence parameters. Different influence parameters have been analyzed to evaluate uncertainty contributions for each quantity to be measured: rms voltage, rms current, active power, apparent power and non-active power of distorted voltage and current waveforms. The resulting calculated global expanded uncertainty for the developed Energy Measuring Function calibration set up has been better than 0.5% for distorted waveforms. This paper is focused on presenting the complete set of expressions and formulas developed for the different influence parameters, necessary for uncertainty budget calculation of an Energy Measuring Function calibration.

Assessment of power quality parameters and indicators at the point of common coupling in a low voltage power grid with photovoltaic generation emulated

Increased photovoltaic (PV) integration can affect the quality of both voltage and current in low-voltage (LV) power-grid operations. This work evaluates the influence of emulated PV power injection on several power-quality parameters and indicators (P&I) at the point of common coupling in an LV network. The assessed steady-state P&I values are the RMS voltage (VRMS), non-active power (Q), total and harmonic components of voltage (THDv, Vh) and current (THDi, Ih), voltage imbalance (Desbv), and total rated-current distortion (TRD). Fifteen scenarios are emulated, considering the active power derating, shading percentage over the PV panel surface, and number of shaded PV panels. A PQube3 smart meter is used to measure 256 samples/cycle and store 16 cycles of both voltage and current, for each emulated scenario. The results indicate that the Q, Desbv, and TRD meet the reference values in each emulated scenario. However, the following P&I do not comply with the reference values of 66.67% VRMS, 26.67% THDv, and 100% THDi. Moreover, in all scenarios, Vh and Ih do not satisfy at least one harmonic component requirement, mostly the fifth and/or seventh harmonic components.

Resilience Assessment in a Low Voltage Power Grid with Photovoltaic Generation in a University Building

High integration of photovoltaic (PV) systems into the power systems causes negative or positive impacts. Typically, research considers the PV impacts on the RMS voltage, power losses, transformers and feeder stress, and power quality indicators. However, a generalising assessment of the electrical parameters and indicators (P&amp;I) describes the power grid performance. It considers a complete holistic view of the real impacts that many events cause over the power grid operation. Therefore, this research proposes the resilience index in order to quantify and assess the impacts that the PV systems cause in low voltage. This scheme has four stages: i) P&amp;I measurement, ii) P&amp;I normalisation, iii) P&amp;I weights assignment, and iv) resilience index quantification and assessment. The resilience scheme assessment has been applied in a low voltage university building with a PV system interconnected of 11.53 kWp. Monitoring has lasted for a month, with data acquisition every ten minutes. P&amp;I monitored have been RMS voltage, RMS current, active, and non-active power, voltage imbalance, total harmonic distortion of voltage and current, and harmonic components of voltage and current. Results indicate that the PV system has positively affected the resilience index in the point of common coupling and floor four-node because the THDv, Vh, THDi, and Ih improved.

Selecting Shunt Power Capacitors and Non-active Power Compensation Devices for Voltage 1000V

Рассмотрены факторы, влияющие на выбор конденсаторов и устройств компенсации неактивной мощности напряжением до 1000 В. Приведены критерии выбора конденсаторов для устройств компенсации неактивной мощности: коэффициент изменения срока службы, коэффициент использования по реактивной мощности и коэффициент гармонической нагрузки.Проанализированы результаты выбора номинального напряжения конденсаторов для устройств компенсации неактивной мощности. Установлено, что для обеспечения нормативного срока службы устройств компенсации неактивной мощности в рассматриваемых случаях номинальное напряжение конденсаторов должно быть увеличено на 10…20 % по сравнению с типовыми решениями производителей. Срок окупаемости таких решений составляет от 3 до 6 лет при нормативном сроке службы оборудования 15 лет. Для объектов с долей полной мощности нелинейной нагрузки более 50 % в электрической сети напряжением до 1000 В для компенсации неактивной мощности необходимо использовать активные фильтры гармоник.Предложен алгоритм выбора конденсаторов и устройств компенсации неактивной мощности с учетом электромагнитной обстановки в электрической сети, предполагающий использование следующих параметров: коэффициент гармонической нагрузки конденсатора, приведенные годовые затраты.Предложенный алгоритм выбора устройств компенсации неактивной мощности может быть использован в составе методики расчета электрических нагрузок и выбора силового электрооборудования при проектировании трансформаторных подстанций для промышленных объектов, инфраструктурных объектов, жилых и общественных зданий.

Modified Dual Active Bridge DC/DC Converter With Improved Efficiency and Interoperability in Hybrid LCC/VSC HVDC Transmission Grids

DC transmission grids are the promising electrical networks in the near future especially with the high penetration of large-scale renewables. This article proposes a modified version of the dual active bridge (DAB) dc/dc converter with ac link capacitors generating reactive power to compensate for nonactive power consumption, hence mitigating current stresses and losses to improve efficiency. The proposed topology also enables the connectivity of current source line-commutated HVDC and voltage source HVDC technologies particularly during power reversal; a feature which conventional DAB is incapable of doing. Analysis and detailed design of the proposed converter are addressed and a comparative performance analysis is carried out with conventional DAB. Converter principle of operation is explained and MATLAB/Simulink simulations are carried out to verify converter operation particularly under adverse conditions such as rated power reversal and dc fault conditions. A low-scale prototype substantiates the theoretical analysis and simulation results.

Piecewise Fryze power theory analysis applied to PWM DC–DC converters

This study proposes an extension to the well-known Fryze power theory, which allows the development of a mathematical procedure that defines a global factor for the active and non-active power processing in pulse-width modulated (PWM) dc–dc converters. This global factor is the dc power factor. The proposed extension is a vector representation of periodic currents and voltages mapped into a k-dimensional Euclidean space, which permits that all non-active power of all converter elements to be collected into a single figure of merit. To validate the approaches, a 220 W prototype of an isolated dc–dc Ćuk converter architecture was implemented and evaluated. Experimental results have confirmed that both total non-active power, the proposed dc power factor, and system efficiency are correlated. In the worst case of step-down mode, the converter prototype presented the lowest total non-active power of ∼25 var for the turns ratio of 0.567, resulting in the highest dc power factor of 0.135 and prototype efficiency of 80.6%. In step-up mode, it was obtained the lowest total non-active power of ∼1.14 kvar for the turns ratio of 1.764, resulting in the highest efficiency of 88.3% and dc power factor of 0.145.

Uncertainty of the Energy Measurement Function deriving from Distortion Power Terms for a 16.7 Hz Railway

&lt;p class="Abstract"&gt;In electrified railways, harmonic active power terms can be significant in the order of the uncertainty required by the EN 50463-2 standard for power and energy measurements in railways. Nonactive power terms (encompassing reactive and distortion harmonic terms) are much more significant than the sole fundamental reactive power. This work considers the implementation of the EN 50463-2 energy measurement function, including the criteria for the significance of the measured and calculated terms, and it carries out a Monte Carlo analysis to assess the impact of harmonic power terms on the measured energy and its uncertainty.&lt;/p&gt;

Adaptive Control of DC Voltage in Three-Phase Three-Wire Shunt Active Power Filters Systems

This paper is focused on an adaptive controller for the direct current (DC) voltage in three-phase three-wire shunt active power filters systems. Although the controller structure of the proportional-integral (PI) type is determined off-line and does not change, the prescribed DC voltage and the controller parameters are calculated in an adaptation block, depending on the non-active power to be compensated. The adaptive control is based on the design expressions for the DC circuit of the shunt active power filter found by the authors, based on the detailed analysis of its operation, during the active filtering. The performances of the proposed adaptive control and its advantages compared to the classical control (where the prescribed DC voltage and the controller parameters are constant) were first determined on the virtual model of a laboratory setup. Then, the adaptive control was implemented on the dSPACE 1103 control board, which allowed the experimental determinations that prove and support the results obtained on the virtual model.

Self-Adjustable Step-Based Control Algorithm for Grid-Interactive Multifunctional Single-Phase PV-Battery System Under Abnormal Grid Conditions

This article deals with the single-phase grid interactive multifunctional solar PV (photovoltaic) system with seamless power transfer capability. This multifunctional PV-battery system is also helpful to enhance the quality of power in the utility grid. The system provides an uninterrupted power to nonlinear loads during the nonavailability of utility and renewable energy resource. This PV-battery system comprises two stages. First stage is a PV array-boost converter along with a battery energy storage-bidirectional converter that is integrated at dc-link and another is voltage source converter (VSC), which performs the task of harmonics elimination and injection of harvested energy to the utility along with nonactive power compensation. In standalone mode, the shape of load voltage is sustained sinusoidal by islanded technique. A proportional integral controller is used to sustain the dc-link voltage to a specific value. In order to improve the dynamic response of the PV-battery system, a feedforward control for solar PV participation is used. A self-adjustable step-based control is introduced for the VSC in this work. This estimates the real power reflecting portion of the load current in order to show the features of the PV-battery system. Simulation studies are carried out in MATLAB Simulink. The experimental performance of the developed PV-battery system is found satisfactory even under abnormal grid condition.

Active Currents, Power Factor, and Apparent Power for Practical Power Delivery Systems

Concepts of apparent power and power factor as measures of a system's power delivery capability are over a century old but have not been defined in one general, rigorous and acceptable way. Instantaneous power is defined precisely, and average power measured over a selected period is widely accepted. The many ways of defining and measuring reactive and apparent power in single and three phase systems are based on different assumptions and give different results in real cases. Building on definitions in the IEEE Standard 1459-2010, this paper formulates in vector space linear algebra and the frequency domain, the active wire currents as those that cause the minimum losses in a network for the power delivered. Power factor measures the relative efficiency of power delivery as defined by the losses. Apparent power consistent with early terminology is the maximum power that can be sourced for the same original line losses and has the unit of power: Watt. It is identified without requiring the contentious concept of reactive and non-active power components. Measurements based on this approach are independent of assumptions about sinusoidal waveform, voltage and current balance, and frequency-dependent wire resistances, and apply to power delivery systems with any number of wires. The rigor of this novel general formulation is important for technical design of compensators and inverters; analyzing power system losses, delivery efficiency and voltage stability; and electricity cost allocation and pricing.

Geometric Algebra in Nonsinusoidal Power Systems: A Case of Study for Passive Compensation

New-generation power networks, such as microgrids, are being affected by the proliferationof nonlinear electronic systems, resulting in harmonic disturbances both in voltage and current thataffect the symmetry of the system. This paper presents a method based on the application of geometricalgebra (GA) to the resolution of power flow in nonsinusoidal single-phase electrical systems for thecorrect determination of its components to achieve passive compensation of true quadrature current.It is demonstrated that traditional techniques based on the concepts of Budeanu, Fryze or IEEE1459fail to determine the interaction between voltage and current and therefore, are not suitable for beingused as a basis for the compensation of nonactive power components. An example is included thatdemonstrates the superiority of GA method and is compared to previous work where GA approachesand traditional methods have also been used.

Analysis of non-active power in non-sinusoidal circuits using geometric algebra

A new approach for the definition of non-active power in electrical systems is presented in this paper. Through the use of geometric algebra, it is possible to define a new term called geometric non-active power, which is applicable to both sinusoidal and non-sinusoidal systems, and to both linear and nonlinear loads. The classic definitions of distortion and reactive power are compared and discussed in our proposal. We verify how geometric non-active power can appear in both purely resistive and purely reactive systems. The superiority of geometric algebra is revealed through several examples of electrical circuits previously analysed in specialised literature. Furthermore, a new geometrical current decomposition is proposed, for the first time, to provide a greater physical sense to existing geometric power. The results obtained confirm that classic concepts based on apparent power S are based on a lack of physical meaning, which is why geometric algebra theory should be adopted instead.