Series Inverter Research Articles

UPFC based transmission line power load flow control under different operating methods

In this paper the methods to control operation of shunt and series inverters using power flow controller (UPFC) is analyzed with real power flow in power system transmission line. These operation mode using UPFC are executed to reduce Swaying in the control framework transport. The execution about every system may be resolved toward the predefined administrative control. Those arrangement What's more shunt converter working under four separate blending from claiming working modes may be used to ponder An example force framework organize. The line flow in MW oscillation damping is predicated with various modes of operations and verified same with MATLAB/ SIMULINK.

Single-Stage Three-Phase Grid-Tied PV System With Universal Filtering Capability Applied to DG Systems and AC Microgrids

This paper proposes a single-stage three-phase four-wire grid-connected photovoltaic (PV) system operating with a dual compensating strategy and feedforward control loop (FFCL). Besides injection of active power into the grid, the PV system operates as a unified power quality conditioner (UPQC), suppressing load harmonic currents and compensating reactive power. Furthermore, regulated, balanced, and harmonic-free output voltages are provided to the load. Since the PV-UPQC is based on a dual compensation strategy, the series converter operates as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, seamless transition can be achieved from the interconnected to the islanding operation modes, and vice versa, without load voltage transients. Moreover, to overcome problems associated with sudden solar irradiation changes, fast power balance involving the PV array and the grid is obtained, since the FFCL acts on the generation of the series inverter current references. As a result, the dynamic responses of both inverter currents and dc-bus voltage are improved. Detailed analysis involving the active power flow through the inverters is performed allowing proper understanding of the PV-UPQC operation. Experimental results are presented to evaluate both dynamic and static performances of the PV-UPQC tied to the electrical distribution system.

Hybrid inverter concept for extreme bandwidth high‐power AC source

A hybrid inverter concept for switch-mode power amplifiers as used, e.g. in power-hardware-in-the-loop testing is proposed. A main converter operating from the supplying DC voltage generates a multilevel output voltage by means of parallel-interleaved operation of several bridge legs and combination of the bridge leg output voltages with coupled inductors into a multilevel waveform. A second, series-connected inverter features a floating DC bus with only a fraction of the main converter's DC voltage, which enables a significantly higher switching frequency. The series inverter compensates the deviation of the main inverter's multilevel output voltage from the reference voltage, whereby pulse-width modulation with sawtooth carriers is employed, and hence defines the effective switching frequency of the hybrid inverter's overall output voltage. This allows for a higher output filter cutoff frequency and ultimately features a significant increase of the full-range system bandwidth, which improves by more than an order of magnitude for the considered 100 kVA example system compared with a conventional approach. Finally, closed-loop circuit simulations verify the high performance of the proposed system.

High‐efficiency voltage source converter with low switching power losses for application in islanded microgrids

In the conventional inverter, the switching power losses cause the inverter efficiency to decrease at high switching frequencies. In this study, a new structure of a single-phase voltage-source inverter with low switching losses is proposed, for application in islanded AC grids. This converter is composed of two single-phase series inverters, with different switching frequencies. The main feature of the proposed converter is that, the total losses of the proposed converter are fewer than the total losses of a conventional single-phase inverter, at high switching frequencies. The proposed converter is designed by the appropriate power transistors in the market. By providing a suitable method for calculating the transistor power losses, the switching and conduction losses of the proposed converter are calculated, and compared with losses of a conventional single-phase inverter. The mathematical model of the proposed converter is derived and used along with root-locus and frequency-response analysis, for designing the controllers. The performance of the proposed converter has been assessed using the simulation studies in MATLAB/SIMULINK software environment.

Electric double layer on renewable liquid (Cd–Ga) electrode in dimethylformamide solutions

The double-layer characteristics on a renewable liquid (Cd–Ga) electrode (0.3 at % Cd) in dimethylformamide (DMF) solutions of various electrolytes are studied by the methods of differential capacitance and open-circuit streaming electrode. The zero-charge potentials unaffected by specific adsorption of ions and the parameters characterizing the (Cd–Ga)–DMF chemisorptive interaction (chemisorption potential drop of solvent and two-dimensional pressure of chemisorbed DMF dipoles) are determined. The results are compared with similar results for the (Cd–Ga)/gamma-butyrolactone (GBL) interface. The energy of (Cd–Ga)–solvent chemisorptive interaction increases with the transition from GBL to DMF due to the increase in the donor number of solvent. The adsorbability of halide ions at the (Cd–Ga)/DMF interface is judged based on the PZC shift in 0.1 М solutions of LiCl, LiBr, and LiI with respect to the PZC in solutions of a surface-inactive electrolyte. On the (Cd–Ga)/DMF interface, the inverted series of surface activity of halide ions is observed. Whereas on Hg and Bi electrodes the surface activity increases in the series Cl– < Br– < I–, on the (Cd–Ga) electrode and also on Ga and (In–Ga) electrodes the activity varies in the inverted sequence I‒ < Br– < Cl–.

Testing for the Equality of Integration Orders of Multiple Series

Testing for the equality of integration orders is an important topic in time series analysis because it constitutes an essential step in testing for (fractional) cointegration in the bivariate case. For the multivariate case, there are several versions of cointegration, and the version given in Robinson and Yajima (2002) has received much attention. In this definition, a time series vector is partitioned into several sub-vectors, and the elements in each sub-vector have the same integration order. Furthermore, this time series vector is said to be cointegrated if there exists a cointegration in any of the sub-vectors. Under such a circumstance, testing for the equality of integration orders constitutes an important problem. However, for multivariate fractionally integrated series, most tests focus on stationary and invertible series and become invalid under the presence of cointegration. Hualde (2013) overcomes these difficulties with a residual-based test for a bivariate time series. For the multivariate case, one possible extension of this test involves testing for an array of bivariate series, which becomes computationally challenging as the dimension of the time series increases. In this paper, a one-step residual-based test is proposed to deal with the multivariate case that overcomes the computational issue. Under certain regularity conditions, the test statistic has an asymptotic standard normal distribution under the null hypothesis of equal integration orders and diverges to infinity under the alternative. As reported in a Monte Carlo experiment, the proposed test possesses satisfactory sizes and powers.

Combined Operation of a New Power Angle Control Unit Vector Template Based Unified Power Quality Conditioner and Fuel Cell Stack Supply with Effective Utilization of Shunt and Series Inverter

This article presents a new power angle control unit vector template based simplified approach for controlling a unified power quality conditioner for a single-phase distribution system along with a boost converter based fuel cell stack source supplying to the load via both shunt and series inverters under voltage interruption condition, thus reducing the burden on the shunt inverter. The power angle control concept is embedded with a unit vector template method for efficient utilization of both inverters of the unified power quality conditioner, namely shunt and series. Each of the major power quality disturbing elements in a single-phase distribution system, such as harmonic distortions in current and voltage, voltage sag and swell, reactive power demand, and voltage interruption, is properly handled along with an ease of implementation. A fuel cell stack combined with a boost converter is used as an independent external source during voltage interruption for maintaining the supply chain to the load through both available inverters, thus reducing the burden and effective rating of the shunt inverter. The entire system is implemented using MATLAB/SIMULINK (The Math Works, Natick, MA) and is also implemented with RT-LAB (OPAL-RT Technologies, Montreal, QC, Canada) for real time simulative analysis.

Power Angle Control-based Method for Interline Unified Power Quality Conditioner and Multi-converter Unified Power Quality Conditioner under Unbalanced and Distorted Load Conditions

This article proposes a new control approach for an interline unified power quality conditioner and a multi-converter unified power quality conditioner to optimize the utilization of the inverters of these structures. In this method, the series active power filter is controlled by the application of a power angle control concept to compensate an unbalanced voltage (asymmetrical voltage sag/swell with or without phase angle jumps) and also partial-load reactive power for power factor correction. Since voltage variation (sag/swell, unbalance, etc.) is a short-duration power quality problem in distribution systems, under normal operating conditions, series inverters are not utilized effectively in conventional methods. By using the proposed method, optimal utilization of series inverters of both structures and also a reduction in the shunt inverter rating of a multi-converter unified power quality conditioner will be achieved. Also, the shunt active power filter is controlled to compensate the unbalanced current, harmonics, and neutral current of a three-phase four-wire system and to take part in power factor correction. The proposed approach is validated through MATLAB/SIMULINK-based (The MathWorks, Natick, Massachusetts, USA) simulation and the results are discussed.

Management of reactive power sharing & power quality improvement with SRF-PAC based UPQC under unbalanced source voltage condition

This paper is proposed to establish a new control algorithm for UPQC (unified power quality conditioner) to improve power quality and manage effectively equal reactive power sharing between shunt and series inverter of UPQC under unbalanced source voltage condition. The extraction of instantaneous power angle for reactive power sharing faces difficulty with unbalanced source voltage condition. This paper presents a new SRF (synchronous reference frame) based PAC (power angle control) method using decoupled load current parameters for efficient utilization and coordination of UPQC inverters. The proposed controller contributes in improvement of source current and load voltage harmonic profile, provides efficient way of load reactive power compensation and load voltage compensation for sag, swell and unbalanced condition. Effect of source voltage variations in the form of sag, swell or unbalancing on variable power angle estimation and reactive power calculations are also validated through a mathematical analysis. SRF based PAC control approach and PAC based UVT (unit vector template) control approach is adapted for estimating the reference signals of shunt and series inverter respectively and thus reducing the need of extra computation. The simulation and experimental analysis is carried out using Matlab/Simulink software package for computer simulation and a dSPACE based experimental setup for real time verifications.

Ramification filtrations of certain abelian Lie extensions of local fields

Let G⊂xFq〚x〛 (q is a power of the prime p) be a subset of formal power series over a finite field such that it forms a compact abelian p-adic Lie group of dimension d≥1. We establish a necessary and sufficient condition for the APF extension of local field corresponding to (Fq⸨x⸩,G) under the field of norms functor to be an extension of p-adic fields. We then apply this result to study invertible power series over a ring of p-adic integers which commute with a fixed noninvertible power series under composition.

High‐performance unified power quality conditioner using command generator tracker‐based direct adaptive control strategy

This study proposes a command generator tracker-based direct adaptive control technique (CGT-DAC) in a three-phase three-wire unified power quality conditioner (UPQC). This proposed CGT-DAC improves the PQ issues such as current and voltage harmonics, sag/swell and voltage unbalance in the power system distribution network. CGT is a model reference control law for a linear time-invariant system with known coefficients and is formulated for the generation of reference signals for both shunt and series inverter. Furthermore, CGT can adaptively regulate the DC-link capacitor voltage without utilising additional controller. Moreover, DAC is designed to track a linear reference model to reduce the tracking error between model reference output and measured signal to be controlled. Therefore, the proposed CGT-DAC approach provides more robustness, flexibility and adaptability in all operating conditions of the power system over a conventional proportional–integral (PI) controller. This proposed control strategy of UPQC is validated through MATLAB/SIMULINK followed by the experimental system of real-time-hardware-in the loop-based OPAL-RT system and adequate results are reported after a comparative assessment with the conventional PI-controller.

Resistive optimization with enhanced PLL based nonlinear variable gain fuzzy hysteresis control strategy for unified power quality conditioner

This paper proposes a Resistive Optimization Technique (ROT) incorporated with enhanced phase-locked loop (EPLL) based Nonlinear Variable Gain Fuzzy (NVGF) hysteresis control strategy for three-phase, three-wire Unified Power Quality Conditioner (UPQC) for compensating current harmonics, reactive power, voltage sag/swell, voltage harmonics and voltage unbalance present in the power system distribution network. This novel resistive optimization control strategy is exploited for reference signal generation for both shunt and series inverter. This proposed algorithm adaptively regulates the DC-link capacitor voltage without utilizing additional controller circuit and makes the control system simple as it does not involve any complex optimization methods. Furthermore, a nonlinear variable gain fuzzy based hysteresis controller is proposed for controlling the hysteresis band, which effectively reduces the band violation and improves the tracking behavior of UPQC during load transient, distortion and unbalanced supply conditions of power system. The proposed control strategy of UPQC is validated through MATLAB/SIMULINK followed by the experimental setup accomplished with real-time-hardware-in the loop (HIL) system OPAL-RT simulator and adequate results are reported after a comparative assessment with the conventional PI and hysteresis controller.

Modeling and Simulation of PLL-Controlled Circuit of Series Resonant Inverter in High Frequency Induction Heating

This paper analyses the necessity of PLL (Phase Locked Loop-controlled) circuit for series resonant inverter in high frequency induction heating power supply. We were interested in modeling and simulation of an inverter with SIT (Static Induction Transistor) functioning at resonance and intended for the induction heating of high frequency ferromagnetic cylindrical piece. During the heating of the ferromagnetic piece, the resistive and inductive equivalent parameters of the inductor-load varied with the temperature. Thus it became necessary to vary the frequency of operation of the inverter to maintain the resonance. An order by PLL was employed for the continuation of the frequency resonance. The model simulation of the resonant inverter series model was established in MATLAB/Simulink. The simulation results indicate that this circuit can keep the power-factor angle just changing within an acceptable range. It can guarantee the inverter to operate in the small-inductive condition, reduce the switching losses of SITs, and enhance the security of the power supply. Also, the obtained results show that the proposed electrical circuit track perfectly the resonance frequency even around the Curie temperature of the material despite the large variation of the frequency near the Curie point.

A Fuzzy Tuned Adaptive PI Controller Based UPFC to Improve Power Oscillations Damping in Multi Machine Power System

In this paper, a fuzzy tuned adaptive PI controller (FTAPIC) was proposed for the series inverter of a unified power flow controller (UPFC), which controls the real power flow in a transmission line, to improve power system oscillations damping. In the proposed control method the parameters of a PI controller namely proportional gain (Kp) and integral gain (Ki) were adjusted on-line by a fuzzy logic controller (FLC). The proposed FTAPIC controller was designed using a very simple control knowledge base and simple membership functions (MFs). To compare performances of the proposed FTAPIC and the standard PI controller, transient response studies were conducted using MATLAB/Simulink® software, over a wide range of operating conditions. The simulation results have shown that the UPFC equipped with a FTAPIC provide better performance compared to UPFC equipped with standard PI controller.

Extended Reference Signal Generation Scheme for Integration of Unified Power Quality Conditioner in Grid-connected Photovoltaic System

—This article proposes an extended reference signal generation scheme for the integration of a three-phase four-wire unified power quality conditioner in a grid-connected photovoltaic system. The photovoltaic–unified power quality conditioner provides compensation against voltage harmonics, current harmonics, and voltage interruption for the whole day. It also transmits the power generated in the photovoltaic system to the load. The proposed topology utilizes the green energy source with an energy storage unit to address the DC-link voltage requirement of the shunt and series active power filters of the unified power quality conditioner. The high-selectivity filter is used in the shunt inverter control scheme for reference current generations. The series inverter in the unified power quality conditioner is used for supplying a part of reactive power required by the load and for compensation of sag/swell, supply voltage unbalance, and distortions. This is achieved by controlling the phase angle and magnitude of series-injected voltage called the power angle control method. The simulation and experimental studies are carried out to validate the effectiveness of the proposed photovoltaic-based three-phase four-wire unified power quality conditioner.

Suitable Single-Phase to Three-Phase AC–DC–AC Power Conversion System

This paper presents a single-phase to three-phase power conversion system with parallel rectifier and series inverter to cope with single-phase to three-phase asymmetry. Such converter guarantees both reduction in the input current processed by rectifier circuit and reduction of the output voltage processed by the inverter circuit. It is worth mentioning that, in spite of proposing a topology with features not yet observed on the technical literature, this paper presents a comprehensive model of the proposed converter, modulation strategy, and a general comparison with the conventional configuration. Simulated and experimental results are also presented.

A Novel Ten-Switch Topology for Unified Power Quality Conditioner

This paper proposes a new topological configuration for a unified power quality conditioner (UPQC). Generally, the power structure of the three-phase three-wire UPQC consists of two back-to-back connected six-switch inverters. For this configuration, out of 12 switches, six of the series inverter switches will be underutilized most of the time. To improve the semiconductor utilization and consequently to reduce the total switch count, this paper proposes a new reduced switch topology for the UPQC. The proposed topology is realized using only ten switches and retains all the performance merits of the 12-switch UPQC while minimizing its underutilization without increasing the switch VA rating. The paper provides a detailed analytical study and evaluation by comparing the proposed topology with the twelve- and nine-switch-based UPQC system configurations. The feasibility of the proposed topology is validated through experimental investigation.

Universal curves in the center problem for Abel differential equations

We study the center problem for the class ${\mathcal{E}}_{{\rm\Gamma}}$ of Abel differential equations $dv/dt=a_{1}v^{2}+a_{2}v^{3}$, $a_{1},a_{2}\in L^{\infty }([0,T])$, such that images of Lipschitz paths $\tilde{A}:=(\int _{0}^{\cdot }a_{1}(s)\,ds,\int _{0}^{\cdot }a_{2}(s)\,ds):[0,T]\rightarrow \mathbb{R}^{2}$ belong to a fixed compact rectifiable curve ${\rm\Gamma}$. Such a curve is said to be universal if whenever an equation in ${\mathcal{E}}_{{\rm\Gamma}}$ has center on $[0,T]$, this center must be universal, i.e. all iterated integrals in coefficients $a_{1},a_{2}$ of this equation must vanish. We investigate some basic properties of universal curves. Our main results include an algebraic description of a universal curve in terms of a certain homomorphism of its fundamental group into the group of locally convergent invertible power series with the product being the composition of series, explicit examples of universal curves, and approximation of Lipschitz triangulable curves by universal ones.

High-Power VSC-Based Simultaneous Positive- and Negative-Sequence Voltage Regulator

A voltage-source converter-based static synchronous compensator (STATCOM) is used in transmission and distribution systems for the purpose of voltage regulation and reactive power compensation. In the transmission level, angle-controlled STATCOMs are of primary interest due to their high efficiency and excellent waveform quality. There is a considerable number of angle-controlled STATCOMs installed in the different utilities in the U.S. Despite the high efficiency and good voltage quality, this type of STATCOM shows poor performance under ac system faults. They are usually tripped under severe unbalanced condition and system faults to protect the switches from huge negative-sequence current flow. This paper provides a solution to improve the transmission-level STATCOM performance under power system faults. The proposed solution is based on adding a single-phase inverter in series with the converter dc bus. One specific controller is designed which provides the capability of simultaneously controlling positive- and negative-sequence voltages. The results are supported by detailed simulation studies on the New York Power Authority STATCOM model using PSCAD/EMTDC.

A Control Strategy with Series-Parallel Inverter for Micro-Grid Operation

For the different operation mode of micro-grid, an improved droop control method and a parallel inverter was proposed depending on the study of micro-grid inverter. Grid-connected interface contains a series inverter and a parallel inverter, and can be switched to select different work mode. The parallel inverter can eliminate harmonic, compensate three-phase imbalanced current to improve the quality of the power delivered to the utility grid. In islanding operation mode, the improved droop control strategy was applied, where an integral controller was introduced. So it can reduce the inverter output voltage amplitude. Thereby it can restrain circulation and realize the power of self-distribution. The effectiveness and feasibility are verified by the simulation result.