Series Inverter Research Articles

Composition of Involutive Power Series, and Reversible Series

For each natural number n, we characterise the invertible series (under composition) that are the composition of n proper involutions. We work with formal power series in one variable over a field of characteristic zero. We also describe the reversible series (those conjugate to their own inverses), and the series that are the composition of n reversible series.

Extrinsic properties of automorphism groups of formal groups

We prove two conjectures on the automorphism group of a one-dimensional formal group law defined over a field of positive characteristic. The first is that if a series commutes with a nontorsion automorphism of the formal group law, then that series is already an automorphism. The second is that the group of automorphisms is its own normalizer in the group of all invertible series over the ground field. A consequence of these results is that a formal group law in positive characteristic is determined by any one of its nontorsion automorphisms.

교류전기철도 전력품질 향상을 위한 직.병렬 보상장치 적용에 관한 연구

본 논문에서는 병렬 인버터를 통한 고조파 보상은 물론 직렬 인버터로 전압강하 보상 및 부하불평형 문제도 해결할 수 있는 보상설비에 대하여 특성을 분석하였다. 제안하는 설비의 구조와 제어방법을 제시하고, 제어방법의 효과를 검증하기 위하여 전기철도 급전시스템과 보상설비를 모델링하여 모의계산을 수행하여 그 결과를 제시하였으며, 본 논문에서는 기존의 급전선로 전압강하 보상시스템의 단점을 보완하기 위해 DC-Link를 공유하는 직렬과 병렬형 인버터를 Scott 변압기 2차 측의 T상과 M상에 두어 다양한 보상 특성을 확인하였다. 본 논문에서 제안하는 시스템은 급전선로의 전기차로 인해 발생하는 고조파전류를 병렬인버터를 통해 제거하여 154[㎸] 3상 모선으로의 유입을 차단하게 된다. 또한 모선의 선간단락, 일선지락 등의 사고로 발생되는 급전선로의 순간전압강하 혹은 순간전압상승 등을 보상하여 지속적인 전압공급을 가능하게 됨을 확인하였다. 더불어 철도의 기동 등으로 인한 순간적인 전압의 강하에 있어서도 직렬인버터를 통한 보상으로 인해 전압의 지속적인 유지를 확보할 수 있음을 확인하였다. 본 논문에서는 이러한 다양한 보상동작을 수행할 수 있는 제안된 시스템의 동작을 PSCAD/ EMTDC를 통해 검증하였으며, 향후 시스템 제작에 따른 특성분석에 용이하게 적용될 것으로 보인다.

Robust Control Scheme for a Microgrid With PFC Capacitor Connected

Capacitors are widely used for power-factor correction (PFC) in power systems. When a PFC capacitor is installed with a certain load in a microgrid, it may be in parallel with the filter capacitor of the inverter interfacing the utility grid and the local distributed-generation unit and, thus, change the effective filter capacitance. Another complication is the possibility of occurrence of resonance in the microgrid. This paper conducts an in-depth investigation of the effective shunt-filter-capacitance variation and resonance phenomena in a microgrid due to a connection of a PFC capacitor. To compensate the capacitance-parameter variation, an Hinfin controller is designed for the voltage-source- inverter voltage control. By properly choosing the weighting functions, the synthesized Hinfin controller would exhibit high gains at the vicinity of the line frequency, similar to traditional high- performance P+ resonant controller and, thus, would possess nearly zero steady-state error. However, with the robust Hinfin controller, it will be possible to explicitly specify the degree of robustness in face of parameter variations. Furthermore, a thorough investigation is carried out to study the performance of inner current-loop feedback variables under resonance conditions. It reveals that filter-inductor current feedback is more effective in damping the resonance. This resonance can be further attenuated by employing the dual-inverter microgrid conditioner and controlling the series inverter as a virtual resistor affecting only harmonic components without interference with the fundamental power flow. And finally, the study in this paper has been tested experimentally using an experimental microgrid prototype.

Protection of Microgrids During Utility Voltage Sags

Microgrids are systems with clusters of microgenerators, which are installed for distributed power generation. When interfaced to the utility grid, microgrids are exposed to common utility power-quality disturbances. In particular, during utility-voltage sags, large line currents can flow along distribution feeders connecting the micro- and utility grids. To limit this flow of large line currents and, hence, protect the microgrids, this paper proposes two current-limiting algorithms, namely, the RL feedforward and flux-charge-model feedback algorithms, for controlling a series inverter connected between the micro- and utility grids during utility voltage sags. Both methods function by inserting a large virtual RL or L impedance in series with the distribution feeder to limit the line-current flow. Detailed descriptions, controller designs, and comparisons of both algorithms are presented. Phasor analyses of both methods are also presented to show how the inserted RL or L values can be optimally tuned to improve the inverter damping performance and minimize its injected voltages and circulating power under all operation conditions. Lastly, both methods have been tested in simulation and in experiments using an emulated laboratory microgrid system

Coaxial coil towed EMI sensor array for UXO detection and characterization

A new broadband electromagnetic induction (EMI) array sensor, GEM-5, for detecting and characterizing Unexploded Ordnance (UXO) has been developed in order to provide high production rates for EMI surveys. The sensor consists of a single rectangular loop transmitter around a linear array of seven pairs of coaxial receiver coils, with each coil in a pair located at the same vertical distance above and below the loop transmitter. The coil pairs are wired in an inverted series so that the signal consists of the difference between the voltage induced in the upper and lower coils. This particular configuration provides a high degree of primary field cancellation, dense spatial sampling rate due to simultaneous and continuous operation of all sensors, suppression of motion-induced and environmental noise, and strong source fields at typical UXO burial depths providing deep detection range. Our prototype tests indicate that the array yields a lower static and motion-induced noise over the critical low frequencies than that of existing sensors, and in particular, the signal-to-noise ratio at 90 Hz is 32 dB higher. Environmental noise can be largely removed from the difference measurements. The field test results from UXO test sites show that the prototype sensor has smoother background and appears to detect more seeded targets than the GEM-3 concentric sensor, however some of that gain can be attributed to higher power transmitter electronics.

Lifting endomorphisms of formal A-modules over finite fields

Lubin conjectures that for an invertible series to commute with a noninvertible series with only simple roots of iterates, two such commuting power series must be endomorphisms of a single formal group. In this paper, we show that if the reduction of these two commuting power series are endomorphisms of a formal group, then themselves are endomorphisms of a formal group.

A grid-interfacing power quality compensator for three-phase three-wire microgrid applications

This paper proposes a grid-interfacing power quality compensator for three-phase three-wire microgrid applications with consideration of both the power quality of the microgrid and the quality of currents flowing between the microgrid and utility system. It is proposed that two inverters connected in shunt and series are used for each distributed generation (DG) system in the microgrid. In each inverter, both positive- and negative-sequence components are controlled to compensate for the effects caused by the unbalanced utility grid voltages. Specifically, the shunt inverter is controlled to ensure balanced voltages within the microgrid and to regulate power dispatches among parallel-connected DG systems, while the series inverter balances the line currents by injecting appropriate voltage components. A current-limiting algorithm is also proposed and integrated within the inverter control schemes to protect the microgrid from large fault currents during utility voltage sags. The proposed compensator has been tested in simulations and experimentally using a laboratory hardware prototype.

Combined Operation of Unified Power-Quality Conditioner With Distributed Generation

This paper describes analysis results of a combined operation of the unified power quality conditioner with the distributed generation. The proposed system consists of a series inverter, a shunt inverter, and a distributed generator connected in the dc link through a rectifier. The proposed system can compensate voltage sag and swell, voltage interruption, harmonics, and reactive power in both interconnected mode and islanding mode. The performance of proposed system was analyzed using simulations with power system computer aided design/electromagnetic transients dc analysis program, and experimental results with the hardware prototype. The proposed system can improve the power quality at the point of installation on power distribution systems or industrial power systems.

Microgrid Power Quality Enhancement Using a Three-Phase Four-Wire Grid-Interfacing Compensator

This paper presents a three-phase four-wire grid-interfacing power quality compensator for microgrid applications. The compensator is proposed for use with each individual distributed generation (DG) system in the microgrid and consists of two four-phase-leg inverters (a shunt and a series), optimally controlled to achieve an enhancement of both the quality of power within the microgrid and the quality of currents flowing between the microgrid and the utility system. During utility grid voltage unbalance, the four-phase-leg compensator can compensate for all the unwanted positive-, negative-, and zero-sequence voltage-current components found within the unbalanced utility. Specifically, the shunt four-leg inverter is controlled to ensure balanced voltages within the microgrid and to regulate power sharing among the parallel-connected DG systems. The series inverter is controlled complementarily to inject negative- and zero-sequence voltages in series to balance the line currents, while generating zero real and reactive power. During utility voltage sags, the series inverter can also be controlled using a newly proposed flux-charge current-limiting algorithm to limit the flow of large fault currents between the micro- and utility grids. The performance of the proposed compensator has been verified in simulations and experimentally using a laboratory prototype.

Non-Equilibrium State Capacitor-Voltage Stabilization in a Hybrid Asymmetric Nine-Level Inverter: Nonlinear Model-Predictive Control

In symmetric multilevel inverters, there is a tradeoff between the output quality and the reliability and efficiency of the converter. New asymmetric and hybrid solutions, using different voltages and devices in various parts of the inverter, promise significant improvements for medium-voltage applications. This paper investigates such a hybrid asymmetric nine-level inverter. It consists of a three-phase three-level main inverter, with a two-leg two-level sub inverter in series with each phase (Fig 1). To keep the power part simple and the efficiency high, the sub inverters have no feeding from the net and can only supply reactive power. But the nonsupplied intermediate-circuit capacitors form an unstable system. This paper proposes a control method to stabilize their voltages. Power balancing is guaranteed by varying the common-mode voltage, using an on-line nonlinear model-predictive controller. The controller predicts the system evolution as a function of the control inputs. A cost function of system and control quantities is iteratively minimized in real time, to ñnd the optimal control to apply to the system. Simulations and measurements demonstrate stable behaviour in steady state and during transients. The originality of this paper is the application of nonlinear model-predictive control in power electronics.

Two Separate Continually Online-Trained Neurocontrollers for a Unified Power Flow Controller

The crucial factor affecting the modern power systems today is load flow control. The Unified Power Flow Controller (UPFC) provides an effective means for controlling the power flow and improving the transient stability in a power network. The UPFC has fast complex dynamics and its conventional control is based on a linearized model of the power system. This paper presents the design of neurocontrollers to provide better damping during transient and dynamic control. Two separate neurocontrollers are used for controlling the UPFC, one neurocontroller for the shunt inverter and the other for the series inverter. Simulation studies carried out in the PSCAD/EMTDC environment is described and results show the successful control of the UPFC and the power system with two neurocontrollers. Performances of the neurocontrollers are compared with the conventional proportional plus integral controllers for system oscillation damping under different operating conditions for large disturbances.

Special Issue on BIT CMOS Built-In Test Architecture for High-Speed Jitter Measurement

Timing measurements for gigahertz clock frequencies require high accuracy and resolution. This paper proposes a scalable built-in self-test (BIST) method that measures accumulated period jitter over a programmable number of periods, without using another reference clock. This on-chip method uses a charge pump to convert time to a voltage, which is digitized by an all-digital flash analog-to-digital converter (ADC). The ADC employs multiple chains of inverter strings composed of three series inverters instead of the popular analog comparators. The inverter thresholds set the reference voltages for triggering given an input dc value. The output is calibrated and converted to jitter measurement. The design using a 0.25 /spl mu/m BiCMOS process, with an input range of 625 MHz-1 GHz, shows that a resolution of 70 ps root mean square (rms) jitter can be achieved, while occupying 0.0575 mm/sup 2/ area with a very conservative layout style. The design has been fabricated and tested, and the test results are presented.

Non-commutative Hopf algebra of formal diffeomorphisms

This paper deals with two Hopf algebras which are the non-commutative analogues of two different groups of formal power series. The first group is the set of invertible series with the group law being multiplication of series, while the second is the set of formal diffeomorphisms with the group law being a composition of series. The motivation to introduce these Hopf algebras comes from the study of formal series with non-commutative coefficients. Invertible series with non-commutative coefficients still form a group, and we interpret the corresponding new non-commutative Hopf algebra as an alternative to the natural Hopf algebra given by the co-ordinate ring of the group, which has the advantage of being functorial in the algebra of coefficients. For the formal diffeomorphisms with non-commutative coefficients, this interpretation fails, because in this case the composition is not associative anymore. However, we show that for the dual non-commutative algebra there exists a natural co-associative co-product defining a non-commutative Hopf algebra. Moreover, we give an explicit formula for the antipode, which represents a non-commutative version of the Lagrange inversion formula, and we show that its coefficients are related to planar binary trees. Then we extend these results to the semi-direct co-product of the previous Hopf algebras, and to series in several variables. Finally, we show how the non-commutative Hopf algebras of formal series are related to some renormalization Hopf algebras, which are combinatorial Hopf algebras motivated by the renormalization procedure in quantum field theory, and to the renormalization functor given by the double-tensor algebra on a bi-algebra.

Carrier PWM algorithm with optimised switching loss for three-phase four-leg multilevel inverters

A novel approach to analyse a four-leg multilevel inverter as a model of two simple inverters in series is presented and a carrier-based SVPWM method is proposed. To obtain the optimised switching loss, the zero sequence function is controlled by redundant parameters. The PWM analysis is simplified, and the use of complicated three-dimensional SVPWM concepts is avoided.

Computer simulation of induction heating system with series inverter

The paper presents the results of computer simulation of the process of induction heating with series transistor inverter. In the simulation of induction heating system the coupled harmonic electromagnetic and transient thermal fields were combined with the simulated real energy source. As a source, the transistor bridge inverter with series resonant circuit was applied. The source parameters (inductor voltage and frequency) depend on the load parameters obtained by numerical calculations of the coupled fields. As the examples, the induction heating before hardening of stationary cylindrical workpiece and of the moving flat workpiece were considered. The simulation results were compared with these obtained in the simulation at constant inductor voltage and frequency.

On heights of $p$-adic dynamical systems

When we consider the properties of the iterates of a noninvertible endomorphism of a formal group, all the roots of iterates of the endomorphism are simple and the full commuting family contains both invertible and noninvertible series. Experimental evidence seems to suggest that for an invertible series to commute with a noninvertible series with only simple roots of iterates, two such commuting power series must be endomorphisms of a single formal group. Lubin proposed four conjectures to support this conjecture. In this paper, we provide answers to these four conjectures.

A robust control method to improve the performance of a unified power flow controller

Abstract The unified power flow controller (UPFC) modeled in synchronous reference frame is investigated for the control of power flow in a transmission system. An ac voltage vector generated by a GTO-based inverter is injected in series with the phase voltage in the transmission line to control real and reactive power flow. A robust H ∞ controller is proposed to regulate line currents in both the shunt and series inverters of the UPFC. The controller ensures robust performance and internal stability of the UPFC against power system disturbances and unstructured parameter variations. Conventional PI control system performance is compared with that based on the proposed scheme to highlight excellent robustness features in the new scheme.

Strategies for handling UPFC constraints in steady-state power flow and voltage control

The unified power flow controller (UPFC), with its unique combination of fast shunt and series compensation, is a powerful device which can control three power system parameters. In planning and designing such devices in power systems, power engineers must consider the impact of device internal limits on its performance. This paper develops a power injection model (PIM) based UPFC control approach to consider a number of internal limits imposed on the UPFC, including series injection voltage magnitude, line current through the series inverter, real power transfer between the shunt inverter and series inverter, shunt side current and shunt injection voltage magnitude. Constrained control strategies are proposed and tested on a 28-node test system. The numerical results illustrate the effectiveness of the proposed method.

FAST PROCEDURE SOLVING UNIVERSAL KEPLER'S EQUATION

We developed a procedure to solve a modification of the standard form of the universal Kepler’s equation, which is expressed as a nondimensional equation with respect to a nondimensional variable. After reducing the domain of the variable and the argument by using the symmetry and the periodicity of the equation, the method first separates the case where the solution is so small that it is given an inverted series. Second, it separates the cases where the elliptic, parabolic, or hyperbolic standard forms of Kepler’s equation are suitable. Here the separation is done by judging whether detouring these nonuniversal equations will cause a 1-bit loss of information to their nonuniversal solutions or not. Then the nonuniversal equations are solved by the author’s procedures to solve the elliptic Kepler’s equation (Fukushima, 1997a), Barker’s equation (Fukushima, 1998), and the hyperbolic Kepler’s equation (Fukushima, 1997b), respectively. And their nonuniversal solutions are transformed back to the solution of the universal equation. For the rest of the case, we obtain an approximate solution by solving roughly the approximated cubic equation as we did in solving Barker’s equation. Then the correction to the approximate solution is obtained by Halley’s method precisely. There the special function appeared in the universal equation is rewritten into a combination of similar special functions of small arguments, so that they are efficiently evaluated by their Taylor series. Numerical measurements showed that, in the case of Intel Pentium II processor, the new method is 10–25 times as fast as Shepperd’s method (Shepperd, 1985) and 7–13 times as fast as the standard Newton method.