Power Compensation Research Articles

Power quality improvement in microgrid using custom power devices

Power quality may be caused when maximum AC loads consume reactive power. Distribution STATCOM is a custom power device (CPD) which is used to control the flow of reactive power in the microgrid. Compensation of reactive power and the other power quality issues are being analysed with the help of model predictive control (MPC) algorithm. The detailed modelling and simulations of MPC with DSTATCOM are presented and implemented along with necessary equations in the MATLAB simulink using the Simpower systems tool boxes.

An Evolutionary Algorithm for Application in Compensation of the Reactive Power in Electric Power Distribution

An Evolutionary Algorithm for Application in Compensation of the Reactive Power in Electric Power Distribution

An active filter with inductive storage for compensation of inactive power of a rectifier with a capacitive filter

Compensation of the inactive components of network current of a rectifier with a capacitive filter or a combination thereof under connection of a parallel active filter with inductive storage based on a current inverter is considered. The active filter allows increasing the power coefficient to the maximum values, and this result may be achieved at high values of storage inductance. Modeling of the “rectifier–active filter” system is carried out by spectral methods. It is shown that correction of the switching algorithm by storage-current feedback provides a decrease by three to four times of inductance at the same values of the power factor of the “rectifier–active filter” system. A multistage active filter consisting of a current inverter and voltage inverter with current stabilization on the direct current is proposed. The total cost for the inductive elements in the multistage active filter may reduced by one order with the same values of power factors. Comparison of voltage inverters based on bridge and half-bridge schemes is carried out. Advantages of half-bridge inverters are shown.

Design and fabrication of a differential scanning nanocalorimeter

This paper describes the design, fabrication, and characterization of a differential scanning nanocalorimeter that significantly reduces the sample volume to microliters and can potentially improve the temperature sensitivity to 10 µK. The nanocalorimeter consists of a polymeric freestanding membrane, four high-sensitive low-noise thermistors based on silicon carbide (SiC), and a platinum heater and temperature sensor. With the integrated heater and sensors, temperature scanning and power compensation can be achieved for calorimetric measurement. Temperature sensing SiC film was prepared by using sintered SiC target and DC magnetron sputtering under different gas pressures and sputtering power. The SiC sensing material is characterized through the measurement of current–voltage curves and noise levels. The thermal performance of a fabricated nanocalorimeter is studied in simulation and experiment. The experiment results show the device has excellent thermal isolation to hold thermal energy. The noise test together with the simulation show the device is promising for micro 10 µK temperature sensitivity and nanowatt resolution which will lead to low-volume ultra-sensitive nanocalorimetry for biological processes, such as protein folding and ligand binding.

Analogs and characteristics of compensated asynchronous machines with different numbers of phases

The disadvantages of three-phase asynchronous motors with short-circuited rotors, which are widely used in practice, are discussed. It is determined that the most significant disadvantage is consumption of two types of electric energy from a network: active energy for conversion into mechanical energy accompanied by inevitable heat losses and reactive energy that is not converted into other types of energy, but is expended on generation of the magnetic field required for electromechanical conversion of energy in an electrical machine. It is suggested to use internal capacitive compensation of reactive power to improve the technical and economic indices of asynchronous machines of both motors and generators. In addition, each phase winding of the asynchronous machine stator is divided into two parts equal in number of turns spatially shifted between each other in the core slots by an angle of 30°. These parts are connected according to the scheme of the rotary autotransformer to the electrical capacity at its output. The change of the spatial position of the stator windings leads to a change in time of the action of the phase angles of their electromotive force and, therefore, of currents and voltages without changing the introduced reactive impedances. Thus, the spatial coordinate of the electrical value is converted into the time coordinate in the electromagnetic circuit with a rotating magnetic field. The combination of this property of the stator windings in accordance with the rotary autotransformer with the action of the electrical capacity at its output creates the effect of internal capacitive compensation of reactive power in an asynchronous machine. The ability to use internal capacitive compensation of reactive power in single-phase asynchronous machines is considered. A method of calculation of the characteristics of compensated asynchronous machines taking into account the change of the magnetizing contour resistance is presented. The advantages of compensated asynchronous motors and compensated asynchronous generators are determined. Recommendations as to their effective practical use are given.

Multi‐functional hybrid active power converter and its industrial application for electrolytic copper‐foil

To meet the requirements of high-power compensating occasion such as electrochemical industries, a multifunctional hybrid active power converter (HAPC) with LC series filter is studied to effectively integrate functions of rectification and power compensation. HAPC can be used as a high-power pulse width modulation rectifier to supply its dc load, meanwhile, it can also compensate large amount of reactive and harmonic current without increasing the voltage rating of itself. A compound current control method for HAPC is introduced so as to improve the dynamic tracking performance. The current and voltage dual closed-loop system of HAPC is built in s domain, and the detailed control parameters are designed to tune control performance further. Finally, a set of 800 kVA HAPC system for electrolytic copper-foil is developed. The results show that the HAPC system can achieve expected operation performance and largely improves power quality of power grid.

Capability evaluation of four-leg DSTATCOM for compensating multifarious loads

A four-leg distribution static compensator (FL-DSTATCOM) has been investigated to achieve harmonic elimination, supply current balancing, compensation of reactive power and current in the neutral conductor of a three-phase, four-wire distribution system with various types of static, dynamic and combined loads. The capability of FL-DSTATCOM for compensating reactive power under dynamic condition is evaluated with induction machine having variable load torque. Also, the performance of FL-DSTATCOM is evaluated with combined load, which is a combination of dynamic and unbalanced static loads. The FL-DSTATCOM injects reactive and harmonics components of load current extracted using synchronous reference frame theory. With FL-DSTATCOM, the unbalanced, harmonic and reactive loads will appear to the main power supply as balanced, linear and unity power factor load. Hence, the main power supply would deliver only fundamental frequency positive sequence components of load current. The switching pulses are generated by employing hysteresis current controller. MATLAB/SIMULINK has been used for capability evaluation under multifarious loading conditions considering IEEE standard 519. The simulation results prove that the FL-DSTATCOM is capable of making the supply current as balanced and sinusoidal, maintaining the PF at point of common coupling near to unity and reducing the supply neutral current very close to zero.

Sentence‐HMM state‐based i‐vector/PLDA modelling for improved performance in text dependent single utterance speaker verification

In this paper, we make use of hidden Markov model (HMM) state alignment information in i-vector/probabilistic linear discriminant analysis (PLDA) framework to improve the verification performance in a text-dependent single utterance (TDSU) task. In the TDSU task, speakers repeat a fixed utterance in both enrollment and authentication sessions. Despite Gaussian mixture models (GMMs) have been the dominant modeling technique for text-independent applications, an HMM based method might be better suited for the TDSU task since it captures the co-articulation information better. Recently, powerful channel compensation techniques such as joint factor analysis (JFA), i-vectors and PLDA have been proposed for GMM based text-independent speaker verification. In this study, we train a separate i-vector/PLDA model for each sentence HMM state in order to utilize the alignment information of the HMM states in a TDSU task. The proposed method is tested using a multi-channel speaker verification database. In the experiments, it is observed that HMM state based i-vector/PLDA (i-vector/PLDA-HMM) provides approximately 67% relative reduction in equal error rate (EER) when compared to the i-vector/PLDA. The proposed method also outperforms the baseline GMM and sentence HMM methods. It yields approximately 51% relative reduction in EER over the best performing sentence HMM method.

Dynamic compensation of real and reactive power in wind farms using STATCOM

Summary The dynamic stability of Squirrel Cage Induction Generators (SCIG) based wind turbines may be improved by Static Synchronous Compensator (STATCOM). At the time of starting of wind farm and during short circuit fault the voltage of bus connecting the wind farm reduces drastically ( Chen, 2005 ). A controller for the STATCOM has been developed with its capability to coordinate between the positive and the negative sequences of the grid voltage. This paper investigates effects of Squirrel Cage Induction Generator (SCIG) in combination with a Static Synchronous Compensator (STATCOM) under normal and during fault condition ( Inwai et al., 2005 ). The results show that the STATCOM can regulate the fast changing voltage at the point of common coupling between the wind farm and the grid in normal and during fault condition. Also it can supply the active power during the short circuit fault condition.

Optimal VF-PDPC of grid connected inverter under unbalanced and distorted grid voltages

In this article, an optimal virtual flux predictive direct power control (VF-PDPC) is proposed for three-phase grid connected voltage source inverter (VSI) operating under unbalanced and distorted grid supply voltage. The concept of virtual flux and extension pq theory is introduced in the conventional PDPC, where the former enhances its resilience toward distorted supply voltage while the latter enhances its resilience toward unbalanced supply voltage. The inherent advantages of the conventional PDPC scheme, such as simple implementation, fast dynamic responses, and no demand of modulators are retained. Getting rid of the complicated positive and negative sequence extraction of grid components, power compensation, or any tuning work, the proposed optimal VF-PDPC achieves excellent power tracking capability, and sinusoidal grid currents with low harmonics under various grid voltage conditions. Simulation results are presented to verify the effectiveness of the proposed control scheme when compared to the conventional PDPC, conventional VF-PDPC, and optimal PDPC.

Dynamic Simulation of EAF on RTDS for Compensation Sizing

Large sized electric arc furnaces (EAF) causes power quality problems such as flicker, harmonics etc. due to their unbalanced and non-linear behavior characteristics. The rapid swings in real and reactive power of such non-linear loads causes fast repetitive voltage variations with appreciable voltage distortion caused by harmonics and unbalance. Some form of reactive compensation is usually adopted to limit the disturbances caused by EAF in electric power system, in particular the flicker. This paper highlights the results of a case study, where the arc furnace is modelled using statistical dynamic model of the furnace using real time digital simulator which allows more real time simulations tests to be conducted in a shorter time and also provides a more detailed power system representation for the tests. The investigation of the simulation study results showed that static VAR compensators can be successfully used for reduction of flicker levels, compensation of reactive power and for the regulation of voltage levels in the EAF plant under study.

Modeling and Analysis of a Multilevel Parallel Hybrid Active Power Filter

This paper introduces a new control approach for the Multilevel Parallel Hybrid Active Power Filter (M-PHAPF) which can compensate harmonics and variable reactive power demand of loads by controlling the DC link voltage adaptively in medium voltage applications. By the means of this novel control method, M-PHAPF obtains a better and more efficient performance in the compensation of harmonics and reactive power compared to when using conventional control methods. The performance and stability of the proposed method are verified with a simulation model realized in PSCAD/EMTDC with different case studies. The simulation results demonstrate that harmonic compensation performance meets the requirements of the IEEE-519 standard.

Efficient Photonic Microwave Mixer With Compensation of the Chromatic Dispersion-Induced Power Fading

The conversion gain of a photonic microwave mixer is often limited by the large carrier of the modulated optical signal, and may be further deteriorated by the chromatic dispersion-induced power fading after transmission over fiber. To solve this problem, an efficient photonic microwave mixer based on a dual-electrode Mach–Zehnder modulator is proposed in this paper. The carrier of the modulated optical signal is suppressed by bidirectional use of the modulator in a Sagnac loop, and a 21.9-dB improvement of the conversion gain is achieved in the experiment. In addition, the frequency response of the mixer after transmission over fiber can be tuned by simply adjusting the direct current bias of the modulator. This feature is applied to compensate the dispersion-induced power fading of the mixing product. In the proof of concept experiment, a vector signal centered at 2.4 GHz is up-converted to 16 GHz and transmitted over 25-km single mode fiber. After power compensation, the constellation diagram, error vector magnitude and receiver sensitivity are significantly improved, and are almost as good as that without fiber transmission.

Managerial power, agency cost and executive compensation – an empirical study from China

Purpose Based on the theory of “optimal contracting approach” and “the managerial power approach”, this paper aims to investigate whether senior executives of listed companies in China make use of their power to gain their own private benefits. The paper also compares compensation contracts between state- and private-owned enterprises to test whether there is a significant difference between senior executives from different ownership types of enterprises in terms of compensation contracts. Design/methodology/approach The paper raises four hypotheses based on the theories of “company agency”, “optimal contracting approach” and “managerial power approach”. After that, 5,680 A-share-listed companies of stock market in Shanghai and in Shenzhen Stock Market from 2008 to 2012 were taken as research samples to conduct a series of research analysis, including t-test, reliability analysis and regression analysis, with the help of SPSS 18.0. Findings The senior executives of listed companies in China could make use of their power to increase their own salary to gain power pay and, at the same time, company performance, company size and other factors that are important to influence the executive compensation. This paper further argues that senior executives of private-owned listed companies are more likely to use their power to obtain power pay and increase their own compensation. Additionally, the agency costs of Chinese listed companies are negatively related to the performance pay of senior executives, whereas there is no obvious negative correlation with the power pay of senior executives. Practical implications This paper takes multiple, in-depth approaches to study the relationship among managerial power, agency cost and executive compensation and to find out the differences in compensation contracts of senior executives between private-owned listed companies and state-owned companies. It also provides necessary suggestions to ensure the interests of stockholders, such as: optimizing the management structure of listed companies; improving the transparence of information disclosure of listed companies; establishing effective mechanism of incentive and constraint; and improving and standardizing the market of professional managers. Social implications The compensation contract of senior executives in China is critical to enhance enterprises’ performance, and it will become an important factor that will facilitate the interests of stockholders and management. However, this paper argues that some phenomena of over-payment of senior executives in listed companies cannot be explained by the theory of “optimal contracting approach”, but it is necessary and important to compare the differences of compensation contract of senior executives between private-owned listed companies and state-owned companies. A series of findings are proposed in this paper. Originality/value This paper made use of a principal analysis to extract the main factors that could represent the managerial power from different angles. In addition, this paper also compared the differences between compensation contracts of senior executives between private-owned listed companies and state-owned companies. Additionally, in this paper, the compensation of senior executives was divided into “power compensation” and “performance compensation”, which were used to test the relationship with the management cost of companies.

Compensation of the reactive power in the presence of higher voltage harmonics at coke plants

The capacitive compensation of reactive power in the presence of harmonic distortion in the supply voltage is considered. Such distortion may be introduced both by factors in the external grid and by factors within the enterprise. That must be taken into account in selecting systems for reducing the effect of higher harmonics on compensating capacitor banks and improving the power quality at coke plants.

Switching‐loss reduction technique in active power filters without auxiliary circuits

To reduce the active power filter (APF) system switching loss, the usual method is to apply different soft-switching techniques. However, this would increase the system initial cost. In this study, a switching loss and switching noise reduction control strategy for APF under reactive power and current harmonics compensation is proposed, which can be applied to the existing APF systems in worldwide, thus causing economic benefits. The minimum dc-link operating voltage of APF is computed through both fundamental and harmonic frequencies analysis. Then an adaptive dc-link voltage controller for the APF is proposed, such that the compensating range of the APF is adaptively varied according to the variation of the loading. Thus, the switching loss and switching noise of the APF can be lowered. Moreover, the design criteria of the proportional and integral gains of the adaptive dc voltage controller are presented and discussed. Finally, simulation and experimental results of a 110 V, 5 kVA APF experimental prototype are given to prove the validity of the proposed control strategy for the APF in current quality compensation, and at the same time reducing switching loss and switching noise during operation.

Power efficiency of time-stretch imaging system by using parallel interleaving detection

A 38.88 MHz time-stretch line-scan imaging system with parallel interleaving detection is experimentally demonstrated. Since only half-chromatic dispersion is used to stretch optical pulses for wavelength-to-time mapping, the power efficiency is significantly improved by 6.5 dB. Furthermore, the theoretical analysis indicates that the power loss can be efficiently reduced for scan rates less than 100 MHz. In addition, a mathematical model for signal-to-noise evaluation is derived, including amplified spontaneous emission noise in the power compensation. Thanks to the improvement of the power efficiency by using parallel interleaving detection, the signal quality is enhanced.

Accurate Load Modeling Based on Analytic Hierarchy Process

Establishing an accurate load model is a critical problem in power system modeling. That has significant meaning in power system digital simulation and dynamic security analysis. The synthesis load model (SLM) considers the impact of power distribution network and compensation capacitor, while randomness of power load is more precisely described by traction power system load model (TPSLM). On the basis of these two load models, a load modeling method that combines synthesis load with traction power load is proposed in this paper. This method uses analytic hierarchy process (AHP) to interact with two load models. Weight coefficients of two models can be calculated after formulating criteria and judgment matrixes and then establishing a synthesis model by weight coefficients. The effectiveness of the proposed method was examined through simulation. The results show that accurate load modeling based on AHP can effectively improve the accuracy of load model and prove the validity of this method.

Control Scheme of Energy Storage Power Converter for Active and Reactive Power Balancing in Grid Connected PV Micro-Grids

Micro-Grid (MG) is a small-scale power network associated with Renewable Energy Sources (RES), Energy Storage System (ESS) and local critical loads. MGs can either be connected to the main grid or operate stand-alone. Due to variable nature of RES such as Photovoltaic (PV) solar cells, ESS become necessary to maintain reliability of power supply to critical loads during islanded mode. During grid connected mode, ESS is used to support the grid or MG depending on the grid operator and energy management functions. On the other hand, the power converters interfaced ESS can be used to provide additional services to the main grid, such as reactive power and unbalanced compensation. This paper presents a control strategy for an Energy Storage Power Converter (ESPC) in MGs, in order to mitigate the negative effects of grid connected MGs working with highly unbalanced operation and poor power factor conditions. Simulation results have been carried out by using Matlab – Simulink software to verify the effectiveness of the proposed control scheme.

Table-Based Direct Power Control for Three-Phase AC/DC Converters Under Unbalanced Grid Voltages

This paper proposes a simple but effective direct power control (DPC) strategy for three-phase ac/dc converters operating under unbalanced grid voltage conditions. An extended instantaneous power theory is adapted and applied in the proposed DPC, where the reactive power is expressed in the form of dot product of grid currents and delayed grid voltages. Neither complicated positive/negative sequence extraction of grid voltage/current nor power compensation is required. The switching table suitable to control both active power and reactive power is constructed by analyzing the influence of each converter voltage vector on power slopes. Compared to conventional table-based DPC using original pq theory, the proposed DPC achieves constant active power and reactive power as well as sinusoidal grid currents, while maintaining the simplicity and robustness as much as possible. The presented simulation and experimental results confirm the theoretical study and the effectiveness of the proposed method.