In recent years, there has been lots of emphasis put on the development of renewable energy. While considerable improvement on renewable energy has been made, there are some inherent limitations for these renewable energies. For example, for solar and wind power, there is an intermittent nature. For the fuel cell, the dynamics of electro-chemical reaction is quite slow compared to the electric load. This will not be acceptable for modern electric application, which requires constant voltage of constant frequency. This work proposed and evaluated a new power circuit that can deal with the problem of the intermittent nature and slow response of the renewable energy. The proposed circuit integrates different renewable energy sources as well as energy storage. By integrating renewable energy sources with statistical tendency to compensate each other, the effect of the intermittent nature can be greatly reduced. This integration will increase the reliability and utilization of the overall system. Moreover, the integration of energy storage solves the problem of the slow response of renewable energy. It can provide the extra energy required by load or absorb the excessive energy provided by the energy sources, greatly improving the dynamics of overall system. To better understand the proposed circuit, "Dual Active Bridge" and "Triple Active Bridge" were reviewed first. The operation principles and the modeling were presented. Analysis and design of the overall system were discussed. Controller design and stability issues were investigated. Furthermore, the function of the central controller was explained. In the end, different simulations were made and discussed. Results from the simulations showed that the proposed multi-port DC-DC power converter had satisfactory performance under different scenarios encountered in practical renewable energy application. The proposed circuit is an effective solution to the problem due to the intermittent nature and slow response of the renewable energy.

Developing full-wave simulators for high-frequency circuit simulation is a topic many researchers have investigated. Generally speaking, methods invoking analytic pre-processing of the device¡¦s V-I relations (admittance or impedance) are computationally more efficient than methods employing numerical procedure to iteratively process the device at each time step. For circuits providing complex functionality, two-port or possibly multi-port devices whether passive or active, are sure to appear in the circuits. Therefore, extensions to currently available full-wave methods for handling one-port devices to process multi-port devices would be useful for hybrid microwave circuit designs. In this dissertation, an efficient scheme for processing arbitrary multi-port devices in the finite-difference time-domain (FDTD) method is proposed. The device¡¦s admittance is analytically pre-processed and fitted into one grid cell. With an improved time-stepping expression, the computation efficiency is further increased. Multi-port devices in the circuit can be systematically incorporated and analyzed in a full-wave manner. The accuracy of the proposed method is verified by comparison with results from the equivalent current-source method and is numerically stable.

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The flow-reversal elliptical cylindrical end chamber mufflers of short length are used often in the modern day automotive exhaust systems. The conventional 1-D axial plane wave theory is not able to predict their acoustical attenuation performance in view of the fact that the chamber length is not enough for the evanescent 3-D modes generated at the junctions to decay sufficiently for frequencies below the cut-off frequency. Also, due to the large area expansion ratio at the inlet, the first few higher order modes get cut on even in the low frequency regime. This necessitates a 3-D FEM or 3-D BEM analysis, which is cumbersome and time consuming. Therefore, an ingenious 1-D transverse plane wave theory is developed by considering plane wave propagation along the major-axis of the elliptical section, whereby a 2-port axially short elliptical and circular chamber muffler is characterized by means of the transfer matrix [T] or impedance matrix [Z]. Two different approaches are followed: (1) a numerical scheme such as the Matrizant approach, and (2) an analytical approach based upon the Frobenius series solution of the Webster’s equation governing the transverse plane wave propagation. The convective effects of mean flow are neglected; however the dissipative effects at the ports are taken into account. The TL predicted by this 1-D transverse plane wave analysis is compared with that obtained by means of the 3-D analytical approach and numerical (FEM/BEM) methods. An excellent agreement is observed between this simplified 1-D approach and the 3-D approaches at least up to the cut-on frequency of the (1, 1) even mode in the case of elliptical cylindrical chambers, or the (1, 0) mode in the case of circular cylindrical chambers, thereby validating this 1-D transverse plane wave theory. The acoustical attenuation characteristics of such short chamber mufflers for various configurations are discussed, qualitatively as well as quantitatively. Moreover, the Frobenius series solution enables one to obtain non-dimensional frequencies for determining the resonance peak and trough in the TL graph. The use of this theory is, however, limited to configurations in which both the ports are located along the major axis in the case of elliptical chambers and along the same diameter for circular chambers. The method of cascading the [T] matrices of the 2-port elements cannot be used to analyze a network arrangement of 2-port elements owing to the non-unique direction of wave propagation in such a network of acoustic elements. Although, a few papers are found in the literature reporting the analysis of a network of 2-port acoustic elements, no work is seen on the analysis of a network of multi-port elements having more than two external ports. Therefore, a generalized algorithm is proposed for analyzing a general network arrangement of linear multi-port acoustic elements having N inlet ports and M outlet ports. Each of these multi-port elements constituting the network may be interconnected to each other in an arbitrary manner. By appropriate book-keeping of the equations obtained by the [Z] matrix characterizing each of the multi-port and 2-port elements along with the junction laws (which imply the equality of acoustic pressure and conservativeness of mass velocity at a multi-port junction), an overall connectivity matrix is obtained, whereupon a global [Z] matrix is obtained which characterizes the entire network. Generalized expressions are derived for the evaluation of acoustic performance evaluation parameters such as transmission loss (TL) and insertion loss (IL) for a multiple inlet and multiple outlet (MIMO) system. Some of the characteristic properties of a general multi-port element are also studied in this chapter. The 1-D axial and transverse plane wave analysis is used to characterize axially long and short chambers, respectively, in terms of the [Z] matrix. Different network arrangements of multi-port elements are constructed, wherein the TL performance of such MIMO networks obtained on the basis of either the 1-D axial or 1-D transverse plane wave theory are compared with 3-D FEA carried on a commercial software. The versatility of this algorithm is that it can deal with more than two external or terminal ports, i.e., one can have multiple inlets and outlets in a complicated acoustic network. A generalized approach/algorithm is presented to characterize rigid wall reactive multi-port chamber mufflers of different geometries by means of a 3-D analytical formulation based upon the modal expansion and the uniform piston-driven model. The geometries analyzed here are rectangular plenum chambers, circular cylindrical chamber mufflers with and without a pass tube, elliptical cylindrical chamber mufflers, spherical and hemispherical chambers, conical chamber mufflers with and without a co-axial pass tube and sectoral cylindrical chamber mufflers of circular and elliptical cross-section as well as sectoral conical chamber mufflers. Computer codes or subroutines have been developed wherein by choosing appropriate mode functions in the generalized pressure response function, one can characterize a multi-port chamber muffler of any of the aforementioned separable geometrical shapes in terms of the [Z] matrix, subsequent to which the TL performance of these chambers is evaluated in terms of the scattering matrix [S] parameters by making use of the relations between [Z] and [S] matrices derived earlier. Interestingly, the [Z] matrix approach combined with the uniform piston-driven model is indeed ideally suited for the 3-D analytical formulation inasmuch as regardless of the number of ports, one deals with only one area discontinuity at a time, thereby making the analysis convenient for a multi-port muffler configuration with arbitrary location of ports. The TL characteristics of SISO chambers corresponding to each of the aforementioned geometries (especially the elliptical cylindrical chamber) are analyzed in detail with respect to the effect of chamber dimensions (chamber length and transverse dimensions), and relative angular and axial location of ports. Furthermore, the analysis of SIDO (i.e., single inlet and double outlet) chamber mufflers is given special consideration. In particular, we examine (1) the effect of additional outlet port (second outlet port), (2) variation in the relative angular or axial location of the additional or second outlet port (keeping the location of the inlet port and the outlet ports of the original SISO chamber to be constant) and (3) the effect of interchanging the location of the inlet and outlet ports on the TL performance of these mufflers. Thus, design guidelines are developed for the optimal location of the inlet and outlet ports keeping in mind the broadband attenuation characteristics for a single inlet and multiple outlet (SIMO) system. The non-dimensional limits up to which a flow-reversal elliptical (or circular) cylindrical end chamber having an end-inlet and end-outlet configuration is acoustically short (so that the 1-D transverse plane wave theory is applicable) and the limits beyond which it is acoustically long (so that the 1-D axial plane wave theory is applicable) is determined in terms of the ratio or equivalently, in terms of the ratio. Towards this end, two different configurations of the elliptical cylindrical chamber are considered, namely, (1) End-Offset Inlet (located along the major-axis of the ellipse) and End-Centered Outlet (2) End-Offset Inlet and End-Offset Outlet (both the ports located on the major-axis of the ellipse and at equal offset distance from the center). The former configuration is analyzed using 3-D FEA simulations (on SYSNOISE) while the 3-D analytical uniform piston-driven model is used to analyze the latter configuration. The existence of the higher order evanescent modes in the axially long reversal chamber at low frequency (before the cut-on frequency of the (1, 1) even mode or (1, 0) mode) causes a shift in the resonance peak predicted by the 1-D axial plane wave theory and 3-D analytical approach. Thus, the 1-D axial plane wave analysis is corrected by introducing appropriate end correction due to the modified or effective length of the elliptical cylindrical chamber. An empirical formulae has been developed to obtain the average non-dimensional end correction for the aforementioned configurations as functions of the expansion ratio, (i.e., ), minor-axis to major-axis ratio, (i.e., ) and the center-offset distance ratio, (i.e., ). The intermediate limits between which the chamber is neither short nor long (acoustically) has also been obtained. Furthermore, an ingenious method (Quasi 1-D approach) of combining the 1-D transverse plane wave model with the 1-D axial plane wave model using the [Z] matrix is also proposed for the end-offset inlet and end-centered outlet configuration. A 3-D analytical procedure has also been developed which also enables one to determine the end-correction in axially long 2-port flow-reversal end chamber mufflers for different geometries such as rectangular, circular and elliptical cylindrical as well as conical chambers, a priori to the computation of TL. Using this novel analytical technique, we determine the end correction for arbitrary locations on the two end ports on the end face of an axially long flow-reversal end chamber. The applicability of this method is also demonstrated for determination of the end corrections for the 2-port circular cylindrical chamber configuration without and with a pass tube, elliptical cylindrical chambers as well as rectangular and conical chambers.

The flow-reversal elliptical cylindrical end chamber mufflers of short length are used often in the modern day automotive exhaust systems. The conventional 1-D axial plane wave theory is not able to predict their acoustical attenuation performance in view of the fact that the chamber length is not enough for the evanescent 3-D modes generated at the junctions to decay sufficiently for frequencies below the cut-off frequency. Also, due to the large area expansion ratio at the inlet, the first few higher order modes get cut on even in the low frequency regime. This necessitates a 3-D FEM or 3-D BEM analysis, which is cumbersome and time consuming. Therefore, an ingenious 1-D transverse plane wave theory is developed by considering plane wave propagation along the major-axis of the elliptical section, whereby a 2-port axially short elliptical and circular chamber muffler is characterized by means of the transfer matrix [T] or impedance matrix [Z]. Two different approaches are followed: (1) a numerical scheme such as the Matrizant approach, and (2) an analytical approach based upon the Frobenius series solution of the Webster’s equation governing the transverse plane wave propagation. The convective effects of mean flow are neglected; however the dissipative effects at the ports are taken into account. The TL predicted by this 1-D transverse plane wave analysis is compared with that obtained by means of the 3-D analytical approach and numerical (FEM/BEM) methods. An excellent agreement is observed between this simplified 1-D approach and the 3-D approaches at least up to the cut-on frequency of the (1, 1) even mode in the case of elliptical cylindrical chambers, or the (1, 0) mode in the case of circular cylindrical chambers, thereby validating this 1-D transverse plane wave theory. The acoustical attenuation characteristics of such short chamber mufflers for various configurations are discussed, qualitatively as well as quantitatively. Moreover, the Frobenius series solution enables one to obtain non-dimensional frequencies for determining the resonance peak and trough in the TL graph. The use of this theory is, however, limited to configurations in which both the ports are located along the major axis in the case of elliptical chambers and along the same diameter for circular chambers. The method of cascading the [T] matrices of the 2-port elements cannot be used to analyze a network arrangement of 2-port elements owing to the non-unique direction of wave propagation in such a network of acoustic elements. Although, a few papers are found in the literature reporting the analysis of a network of 2-port acoustic elements, no work is seen on the analysis of a network of multi-port elements having more than two external ports. Therefore, a generalized algorithm is proposed for analyzing a general network arrangement of linear multi-port acoustic elements having N inlet ports and M outlet ports. Each of these multi-port elements constituting the network may be interconnected to each other in an arbitrary manner. By appropriate book-keeping of the equations obtained by the [Z] matrix characterizing each of the multi-port and 2-port elements along with the junction laws (which imply the equality of acoustic pressure and conservativeness of mass velocity at a multi-port junction), an overall connectivity matrix is obtained, whereupon a global [Z] matrix is obtained which characterizes the entire network. Generalized expressions are derived for the evaluation of acoustic performance evaluation parameters such as transmission loss (TL) and insertion loss (IL) for a multiple inlet and multiple outlet (MIMO) system. Some of the characteristic properties of a general multi-port element are also studied in this chapter. The 1-D axial and transverse plane wave analysis is used to characterize axially long and short chambers, respectively, in terms of the [Z] matrix. Different network arrangements of multi-port elements are constructed, wherein the TL performance of such MIMO networks obtained on the basis of either the 1-D axial or 1-D transverse plane wave theory are compared with 3-D FEA carried on a commercial software. The versatility of this algorithm is that it can deal with more than two external or terminal ports, i.e., one can have multiple inlets and outlets in a complicated acoustic network. A generalized approach/algorithm is presented to characterize rigid wall reactive multi-port chamber mufflers of different geometries by means of a 3-D analytical formulation based upon the modal expansion and the uniform piston-driven model. The geometries analyzed here are rectangular plenum chambers, circular cylindrical chamber mufflers with and without a pass tube, elliptical cylindrical chamber mufflers, spherical and hemispherical chambers, conical chamber mufflers with and without a co-axial pass tube and sectoral cylindrical chamber mufflers of circular and elliptical cross-section as well as sectoral conical chamber mufflers. Computer codes or subroutines have been developed wherein by choosing appropriate mode functions in the generalized pressure response function, one can characterize a multi-port chamber muffler of any of the aforementioned separable geometrical shapes in terms of the [Z] matrix, subsequent to which the TL performance of these chambers is evaluated in terms of the scattering matrix [S] parameters by making use of the relations between [Z] and [S] matrices derived earlier. Interestingly, the [Z] matrix approach combined with the uniform piston-driven model is indeed ideally suited for the 3-D analytical formulation inasmuch as regardless of the number of ports, one deals with only one area discontinuity at a time, thereby making the analysis convenient for a multi-port muffler configuration with arbitrary location of ports. The TL characteristics of SISO chambers corresponding to each of the aforementioned geometries (especially the elliptical cylindrical chamber) are analyzed in detail with respect to the effect of chamber dimensions (chamber length and transverse dimensions), and relative angular and axial location of ports. Furthermore, the analysis of SIDO (i.e., single inlet and double outlet) chamber mufflers is given special consideration. In particular, we examine (1) the effect of additional outlet port (second outlet port), (2) variation in the relative angular or axial location of the additional or second outlet port (keeping the location of the inlet port and the outlet ports of the original SISO chamber to be constant) and (3) the effect of interchanging the location of the inlet and outlet ports on the TL performance of these mufflers. Thus, design guidelines are developed for the optimal location of the inlet and outlet ports keeping in mind the broadband attenuation characteristics for a single inlet and multiple outlet (SIMO) system. The non-dimensional limits up to which a flow-reversal elliptical (or circular) cylindrical end chamber having an end-inlet and end-outlet configuration is acoustically short (so that the 1-D transverse plane wave theory is applicable) and the limits beyond which it is acoustically long (so that the 1-D axial plane wave theory is applicable) is determined in terms of the ratio or equivalently, in terms of the ratio. Towards this end, two different configurations of the elliptical cylindrical chamber are considered, namely, (1) End-Offset Inlet (located along the major-axis of the ellipse) and End-Centered Outlet (2) End-Offset Inlet and End-Offset Outlet (both the ports located on the major-axis of the ellipse and at equal offset distance from the center). The former configuration is analyzed using 3-D FEA simulations (on SYSNOISE) while the 3-D analytical uniform piston-driven model is used to analyze the latter configuration. The existence of the higher order evanescent modes in the axially long reversal chamber at low frequency (before the cut-on frequency of the (1, 1) even mode or (1, 0) mode) causes a shift in the resonance peak predicted by the 1-D axial plane wave theory and 3-D analytical approach. Thus, the 1-D axial plane wave analysis is corrected by introducing appropriate end correction due to the modified or effective length of the elliptical cylindrical chamber. An empirical formulae has been developed to obtain the average non-dimensional end correction for the aforementioned configurations as functions of the expansion ratio, (i.e., ), minor-axis to major-axis ratio, (i.e., ) and the center-offset distance ratio, (i.e., ). The intermediate limits between which the chamber is neither short nor long (acoustically) has also been obtained. Furthermore, an ingenious method (Quasi 1-D approach) of combining the 1-D transverse plane wave model with the 1-D axial plane wave model using the [Z] matrix is also proposed for the end-offset inlet and end-centered outlet configuration. A 3-D analytical procedure has also been developed which also enables one to determine the end-correction in axially long 2-port flow-reversal end chamber mufflers for different geometries such as rectangular, circular and elliptical cylindrical as well as conical chambers, a priori to the computation of TL. Using this novel analytical technique, we determine the end correction for arbitrary locations on the two end ports on the end face of an axially long flow-reversal end chamber. The applicability of this method is also demonstrated for determination of the end corrections for the 2-port circular cylindrical chamber configuration without and with a pass tube, elliptical cylindrical chambers as well as rectangular and conical chambers.

Present-day economic and environmental constraints push power systems to be operated closer to their limits. A common limiting factor for power transmission is the risk of voltage instability in recent years. As the ultimate countermeasure to voltage collapse, load shedding is normally considered the last resort, when there are no other alternatives to stop an approaching voltage collapse. The requirements of a practical load shedding scheme are to prevent a power system from voltage collapse and to maximize its reliability. In order to design such a scheme, the following tasks are equally important: 1. Recognizing the approaching voltage collapse. 2. Determining the best load shedding locations. 3. Minimizing the amount of load shedding. This thesis firstly investigates the widely used undervoltage load shedding schemes (UVLS) and the single-port impedance match (SPIM) based schemes. The findings explain the difficulties faced by them. An original load shedding oriented voltage stability monitoring scheme, which involves developing a new multi-port network equivalent, is then developed. With the help of the multi-port network equivalent, the monitoring scheme can not only recognize the approaching voltage collapse in time, but also can easily rank the load buses based on their weakness. The results of ranking are consistent with those obtained from modal analysis method. This thesis then proposes a practical event-driven load shedding scheme based on the experiences learned from the schemes implemented by various utilities. The scheme involves developing a multistage method, which is to optimize the amount of load shedding. A general design procedure for the scheme is presented in the thesis. Using a real 2038 bus system as an example, the design methodology is described in detail. The methodology is expected to help power system engineers develop their own load shedding schemes. A practical emergency demand response scheme is also developed and presented in the appendix. It is aimed at choosing the proper demand response participants and minimizing the total cost while achieving a certain level of operation reserves. / Power Engineering and Power Electronics

Memory unit is one of the fundamental hardware components in system-on-chip (SoC) design, and takes a significant portion of total area cost. Although commercial memory compilers exist, they usually contains memory unit with single-port or dual ports. However, many SoC designs require memory units that support simultaneous multiple reads and writes. They cannot be efficiently generated using the existing memory compilers in the standard cell library. In this thesis, we develop a memory generator that can automatically produce the circuits of multi-port SRAM and all the necessary models required in the standard cell-based design flow. Compared to the design based on dual-port SRAM from memory compilers which usually consists of duplicated copies of SRAM units for supporting multiple write at the same, the proposed design has smaller area cost. Furthermore, we employ various low-power design concepts, including power-gating and adaptive body-bias, to reduce the dynamic and static power of the generated SRAM circuits. Experimental results show that the proposed multi-port SRAM generator can be used to synthesize low-power and low-area register file circuits that support multiple reads and writes at the same time.

With the ever-growing developments of sustainable energy sources such as fuel cells, photovoltaics, and other distributed generation, the need for a reliable power conversion system that interfaces these sources is in great demand. In order to provide the highest degree of flexibility in a truly distributed network, it is desired to not only interface multiple sources, but to also interface multiple loads. Modern multi-port converters use high frequency transformers to deliver the different power levels, which add to the size and complexity of the system. The different topological variations of the proposed multi-port dc-dc converter have the potential to solve these problems. This thesis proposes a unique dc-dc current source converter for multi-port power conversion. The presented work will explain the proposed multi-port dc-dc converter's operating characteristics, control algorithms, design and a proof of application. The converter will be evaluated to determine its functionality and applicability. Also, it will be shown that our converter has advantages over modern multi-port converters in its ease of scalability from kW to MW, low cost, high power density and adaption to countless combinations of multiple sources. Finally we will present modeling and simulation of the proposed converter using the PSIM software. This research will show that this new converter topology is unstable without feedback control. If the operating point is moved, one of the source ports of the multiport converter becomes unstable and dies off supplying very little or no power to the load while the remaining source port supplies all of the power the load demands. In order to prevent this and add stability to the converter a simple yet unique control method was implemented. This control method allowed for the load power demanded to be shared between the two sources as well as regulate the load voltage about its desired value.

This dissertation studies hybrid dc-dc power conversion systems based on multiple-input converters (MICs), or more generally, multiport converters. MICs allow for the integration of multiple distributed generation sources and loads. Thanks to the modular design, an MIC yields a scalable system with independent control in all sources. Additional characteristics of MICs include the improved reliability and reduced cost. This dissertation mainly studies three issues of MICs: efficiency improvement, modeling, and control. First, this work develops a cost-effective design of a highly-efficient non-isolated MIC without additional components. Time-multiplexing (TM) MICs, which are driven by a time-multiplexing switching control scheme, contain forward-conducting-bidirectional-blocking (FCBB) switches. TM-MICs are considered to be subject to low efficiency because of high power loss introduced by FCBB switches. In order to reduce the power loss in FCBB switches, this work adopts a modified realization of the FCBB switch and proposes a novel switching control strategy. The design and experimental verifications are motivated through a multiple-input (MI) SEPIC converter. Through the design modifications, the switching transients are improved (comparing to the switching transients in a conventional MI-SEPIC) and the power loss is significantly reduced. Moreover, this design maintains a low parts-count because of the absence of additional components. Experimental results show that for output power ranging from 1 W to 220 W, the modified MIC presents high efficiency (96 % optimally). The design can be readily extended to a general n-input SEPIC. The same modifications can be applied to an MI-Ćuk converter. Second, this dissertation examines the modeling of TM-MICs. In the dynamic equations of a TM-MIC, a state variable from one input leg is possible to be affected by state variables and switching functions associated with other input legs. In this way, inputs are coupled both topologically and in terms of control actions through switching functions. Coupling among the state variable and the time-multiplexing switching functions complicate TM-MICs’ behavior. Consequently, substantial modeling errors may occur when a classical averaging approach is used to model an MIC even with moderately high switching frequencies or small ripples. The errors may increase with incremental number of input legs. In addition to demonstrating the special features on MIC modeling, this dissertation uses the generalized averaging approach to generate a more accurate model, which is also used to derive a small-signal model. The proposed model is an important tool that yields better results when analyzing power budgeting, performing large-signal simulations, and designing controllers for TM-MICs via a more precise representation than classical averaging methods. Analyses are supported by simulations and experimental results. Third, this dissertation studies application of a decentralized controller on an MI-SEPIC. For an MIC, a multiple-input-multiple-output (MIMO) state-space representation can be derived by an averaging method. Based on the averaged MIMO model, an MIMO small-signal model can be generated. Both conventional method and modern multivariable frequency analysis are applied to the small-signal model of an MI-SEPIC to evaluate open-loop and closed-loop characteristics. In addition to verifying the nominal stability and nominal performance, this work evaluates robust stability and robust performance with the structured singular value. The robust performance test shows that a compromised performance may be expected under the decentralized control. Simulations and experimental results verify the theoretical analysis on stability and demonstrate that the decentralized PI controller could be effective to regulate the output of an MIC under uncertainties. Finally, this work studies the control of the MIMO dc-dc converter serving as an active distribution node in an intelligent dc distribution grid. The unified model of a MIMO converter is derived, enabling a systematical analysis and control design that allows this converter to control power flow in all its ports and to act as a power buffer that compensates for mismatches between power generation and consumption. Based on the derived high-order multivariable model, a robust controller is designed with disturbance-attenuation and pole-placement constraints via the linear matrix inequality (LMI) synthesis. The closed-loop robust stability and robust performance are tested through the structured singular value synthesis. Again, the desirable stability and performance are verified by simulations and experimental results. / text

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