Single-stage H-bridge grid-connected inverters are considered as a simple, compact, and economic topology compared with double-stage converters. A maximum power point tracking (MPPT) control is necessary in photovoltaic (PV) generation system to extract maximum power from the PV arrays. Many MPPT techniques have been proposed and discussed in the literature. Among them, the ripple correlation control (RCC) algorithm is fast and effective, particularly suitable for single-phase configurations since it uses as perturbation the embedded oscillation of dc current and dc voltage at twice of grid frequency (e.g., 100 Hz). The main drawback of this method is the unstable behavior during sudden variation of sun irradiance, where the conventional RCC gives wrong estimation of the power derivative (dP/dV), causing wide dc voltage and dc current overshoots. To overcome this problem, a hybrid RCC-constant voltage regulator algorithm combined to a high-peformance dq grid current controller is proposed to improve the transient performance. The whole grid-connected photovoltaic generation scheme has been implemented numerically by MATLAB/Simulink, verifying steady-state and dynamic performances under different sun irradiance transients. The comparison with the corresponding behavior of a standard RCC algorithm emphasized the effectiveness of the proposed hybrid RCC controller.

A new method to efficiently describe parasitic bipolar structures in junction-isolated smart-power ICs is reported. Both two- and three-dimensional situations are tackled. An automatic simulation code for calculating the parasitic currents injected into the substrate by power devices, which may endanger the functioning of the signal-processing circuits, has been developed. Also, a Java graphical interface has been implemented with the aim of automatically managing the mixed circuit-device simulation. Examples of applications are given with reference to BCD5 technology.

This paper investigates a number of numerical schemes applicable to the solution of the Boltzmann transport equation by means of a spherical-harmonics expansion (SHE). A new scheme is proposed that improves the solution at low energies, keeping the desired accuracy in the calculation of the mean quantities while saving a significant amount of CPU time. This is important in view of the applications of the method since the typical number of nodes to be used in the combined space-energy domain is in the range of 10/sup 4/-10/sup 5/.

The transport model in semiconductors is examined in the case where the effect of distributed gap states is significant like, e.g., in thin-film transistors. A solution scheme is derived for the two additional continuity equations accounting for the trapped charge such that, without loss of generality, the efficiency of the traditional method implemented in the existing device-analysis codes is kept. The dynamic effect of the trapped charge is then examined in the ac operation of a realistic thin-film device, including the analysis of the interelectrode capacitances.

The description of the optical-generation phenomena has been incorporated in the semiconductor-device analysis program HFIELDS, keeping the structural and geometrical flexibility of the original code. To this end a substantial effort has been devoted to the software implementation. The latter required the introduction of a number of optical windows and interleaved material layers through which a radiation with arbitrary spectrum, incidence angle, and polarization state enters the crystal. The corresponding generation rate at each node of the discretization grid is then evaluated by adding up the contribution of each monochromatic component of the impinging radiation. The code equipped with this new capability makes the description of realistic semiconductor optical sensors feasible. Black-body radiation has been incorporated into the code to allow for the simulation of solar cells. After a brief review of the underlying physics, the software implementation is described and a number of examples are illustrated.>

A finite difference boundary fitted grid-generation method for composite and complicated geometries is described. In each region belonging to the domain of interest, a set of points is defined by differential transformation from a regular computational space, maintaining the continuity of coordinate lines crossing the internal boundaries. The definition of the relationship between the nodes yields a finite element mesh. Both the mathematical basis and the algorithmic implementation are shown, followed by an example of application to a realistic semiconductor device.>

Using the hydrodynamic model of semiconductor devices, the authors simulate an abrupt p-n junction under strong reverse bias, accounting for impact ionization by means of electron and hole generation rates dependent on the carrier temperature. They demonstrate the influence of impact ionization as a cooling mechanism on the mean energy and velocity of the carriers, and show that the ionization coefficients alpha /sub n/ and alpha /sub p/ are spatially retarded with respect to the normally used electric-field dependent ones; this results in larger multiplication factors M/sub n/ and M/sub p/. The reason for this effect is traced back to the increased impact-ionization probability of secondary generated carriers having the chance to travel through a larger portion of the high-field region. This is shown qualitatively by discussing the impact ionization integrals, and is estimated quantitatively through the simulation.>

An algorithm allowing the automatic generation of a mesh and accounting for the main physical features of the problem is presented. The adaptivity is provided by a refinement strategy which preserves the characteristics of the initial grid, inserting nodes only in the regions where the solution deviates from a linear behavior. A geometrical interpretation in terms of a monitor surface is given, and various different approaches to the problem are discussed. The efficiency of the algorithm is enhanced by a local solution scheme, which uses previously computed values of all the unknown quantities as boundary conditions for the newly generated nodes. A few examples illustrate the performance of the algorithm.>

A discretization scheme is applied to the hydrodynamic model for semiconductor devices that generalizes the Scharfetter-Gummel method to both the momentum-conservation and the energy-conservation equations. The major advantages of the scheme are: (1) the discretization is carried out without neglecting any terms, thus providing a satisfactory description of such effects as velocity overshoot and carrier heating; and (2) the resulting equations lend themselves to a self-consistent solution procedure similar to those currently used to solve the simpler drift-diffusion equations. Two-dimensional steady-state simulations of an n-channel MOSFET and of an n-p-n BJT (bipolar junction transistor) have been carried out by means of an improved version of the program HFIELDS. Carrier-temperature plots have been obtained with a reasonable computational effort, demonstrating the efficiency of this technique. The results have been compared with those obtained with the standard drift-diffusion model and significant differences in the electron concentration have been found, especially at the drain end of the MOSFET channel.>

In this paper we propose a sensitivity-analysis technique for device design. By this method, we determine the linearized variations of the device terminal characteristics following some change either in the impurity distribution, or in device geometry, such as channel length and oxide thickness. This technique has been implemented in our general-purpose two-dimensional device-analysis program (HFIELDS) and proved to be very efficient, as only the assembly of the RHS and one back-substituton is required in order to achieve the final result. It is believed that the present method can be profitably used for both deterministic and statistical device design.