Characterization of the imidization of the aromatic polyimide LARC-160

The polyimide resin LARC-160 was prepared from diethyl-3,3′,4,4′-benzophenone tetracarboxylate (BTDE), ethyl-5-norbornene-2,3-dicarboxylate (NE), and Jeffamine AP-22. The imidization reactions of NE and BTDE were studied by HPLC, ¹³C-NMR, and IR. NE imidizes slowly at 12°C; BTDE imidizes when the resin is heated above 100°C. Both imidization reactions proceed directly to the imide. Neither amic acid is present in significant quantities at any stage of the imidization reactions. The monomer mixture has been stored at 12°C for periods up to 14 months. The effects of resin aging at this temperature on the chemical composition of the resin monomer mixture and the imidized polymer formed on curing were investigated. Aging the resin monomer mixture has the effect of partially advancing the imidization reaction. Aging also results in the formation of slightly higher-molecular-weight polyimide chains after curing of the resin at 140 and 180°C. Bisnadimide (BNI) is observed as a major reaction product, regardless of resin age.     

Formation of subwavelength grating on molybdenum mirrors using a femtosecond Ti:sapphire laser system operating at 10 Hz

We report formation of subwavelength surface grating over large surface area of molybdenum mirror by multiple irradiation of amplified femtosecond laser pulses from a homemade Ti:sapphire oscillator-amplifier laser system in a raster scan configuration. The laser system delivered 2 mJ, 80 fs duration laser pulses at a pulse repetition rate of 10 Hz. Various parameters such as pulse fluence, number of pulses, laser polarization, scan speed, and scan steps were optimized to obtain uniform subwavelength gratings. Energy dispersive x-ray spectroscopy measurements were conducted to analyze the elemental composition of mirror surfaces before and after laser treatment.     

Applications of one-cycle control to improve the interconnection of a solid oxide fuel cell and electric power system with a dynamic load

Adding distributed generation (DG) is a desirable strategy for providing highly efficient and environmentally benign services for electric power, heating, and cooling. The interface between a solid oxide fuel cell (SOFC), typical loads, and the electrical grid is simulated in Matlab/Simulink and analyzed to assess the interactions between DG and the electrical grid. A commercial building load profile is measured during both steady-state and transient conditions. The load data are combined with the following models that are designed to account for physical features: a One-Cycle Control grid-connected inverter, a One-Cycle Control active power filter, an SOFC, and capacitor storage. High penetration of DG without any power filter increases the percentage of undesirable harmonics provided by the grid, but combined use of an inverter and active power filter allows the DG system interconnection to improve the grid tie-line flow by lowering total harmonic distortion and increasing the power factor to unity.     

One-Cycle Control and Its Applications in Power Quality Control and Renewable Power Generation （1）

One-Cycle Control（OCC） is a universal method to control single or three-phase power components/modules such as MOS-FET, IGBT,MCT, Silicon Carbide, etc. to realize four quadrant power conversion so as to perform as grid-connected inverters, active power filters,power factor corrected rectifiers, flexible ac transmission system components, and etc. Due to its fast speed, simplicity, stability,and universal adaptability, One-cycle control promises unmatched performance, cost effectiveness, and robustness. This paper shows some basic building blocks for grid-connected applications, countless combinations of which can be configured to meet the power processing needs of the industry, transportation, defense, and power systems.     

Synthesis of Multilevel Converters Based on Single- and/or Three-Phase Converter Building Blocks

This paper synthesized a family of multilevel converters that is constructed by using multiple well-developed single- and/or three-phase converter building blocks. The resulting advantages include a modular structure that leads to convenient construction and maintenance as well as easy extension to higher voltage levels. One successful example from this family is the cascaded H-bridge converter, which is now widely used for volt-amperes reactive (VAR) compensation and motor drive applications due to its many advantages. Another emerging member is the Hexagram converter, composed of six interconnected three-phase converter modules, which has many eminent features such as lowered component count and lowered dc energy storage requirement compared to the cascaded H-bridge converter, and thus, is a promising candidate for high-power applications.     

Combinatorial chemistry in insects: a library of defensive macrocyclic polyamines

The pupal defensive secretion of the coccinellid beetle Epilachna borealis is composed principally of a combinatorial library of macrocyclic polyamines. These compounds constitute a previously unrecognized family of natural products, characterized by extremely large-ring lactonic structures derived from a small set of (2-hydroxyethylamino)alkanoic acids. The combinatorial assembly of these simple building blocks generates a high degree of structural diversity, which is further increased by slow, spontaneous intramolecular rearrangement of the macrocycles.     

Switching flow-graph nonlinear modeling method formultistate-switching converters

Switching power converters operating in a multistate switching mode (more than two states) feature multidimensional control over their state variables. In this paper, a large-signal multistate modeling method is developed based on the switching flow-graph method to study the steady-state and dynamic properties of pulse-width-modulated (PWM) multistate-switching power converters for the continuous conduction mode. This modeling method translates a switching power converter directly to its graphic dynamic model and uses graphical representation to reveal the cause and effect relationship of the dynamics within a multidimensional power converter. A three-state buck-boost circuit is conceived with two duty ratios controlling two outputs as an example to test this modeling method. Experimental results confirm the theoretical prediction. This multistate-switching flow-graph modeling method is very general, easy to use and accurate, and it provides deep physical insight for engineering design     

A general three-phase PFC controller for rectifiers with a parallel-connected dual boost topology

A general constant-frequency power-factor-correction (PFC) controller is proposed for three-phase rectifiers with parallel-connected dual-boost topologies. This paper shows that unity power factor and low current distortion in all three phases can be realized by one-cycle control using one integrator with reset along with a few near and logic components. This new extension of one-cycle control provides the core PFC function to the dual-boost topologies. It does not require multipliers, as used in most other control approaches to scale the current reference according to the output power level. In each 60/spl deg/ of AC line cycle, only two switches are switched at high frequency; therefore the switching losses are significantly reduced. All switches are switched at low current, which results in reduced current ratings. This control method is simple and general. It is applicable to three-phase rectifiers that can be decoupled into parallel-connected dual-boost topologies by slight modification of the logic circuit. This control method is verified by experimental results. The proposed controller is suitable to be integrated into a three-phase PFC control chip.     

A new PWM controller with one-cycle response

This paper proposes a new nonlinear control technique that has one-cycle response, does not need a resetable integrator in the control path, and has nearly constant switching frequency. It obtains one-cycle response by forcing the error between the switched variable and the control reference to zero each cycle, while the on and off pulses of the controller are adjusted each cycle to ensure near constant switching frequency. The small switching frequency variation due to changes in the reference signal and supply voltage and delays in the circuit are quantified. Using double-edge modulation, the switching frequency variation is further reduced, thus, the associated signal distortion is minimized. An experimental 0-20 kHz bandwidth 95 W RMS power audio amplifier using the control method demonstrates the applicability of this control technique for high-fidelity audio applications. The amplifier has a power supply ripple rejection (PSRR) of 63 dB at 120 Hz. Additionally, the total harmonic distortion plus noise (THD+N) is less than 0.07% measured with a power supply ripple of 15%     

Unified constant-frequency integration control of active powerfilters-steady-state and dynamics

An active power filter (APF) is a device that is connected in parallel to and cancels the reactive and harmonic currents from a group of nonlinear loads so that the resulting total current drawn from the AC mains is sinusoidal. This paper presents a unified constant-frequency integration (UCI) APF control method based on one-cycle control. This method employs an integrator with reset as its core component to control the pulse width of an AC-DC converter so that its current draw is precisely opposite to the reactive and harmonic current draw of the nonlinear loads. In contrast to previously proposed methods, there is no need to generate a current reference for the control of the converter current, thus no need for a multiplier and no need to sense the AC line voltage, the APF current, or the nonlinear load current. Only one AC current sensor is used to sense the AC main current and one DC voltage sensor is used to sense the DC capacitor voltage. The control method features constant switching frequency operation, minimum reactive and harmonic current generation, and simple analog circuitry. It provides a low cost and high performance solution for power quality control. Steady-state and dynamic study is presented in this paper. Design example is given using a two-level AC-DC boost topology. A prototype was developed to demonstrate the performance of the proposed APF. This control method is generalized to control a family of converters that are suitable for APF applications. All findings are supported by experiments and simulation