Multirate Partial Differential Equations Research Articles

Efficient simulation of DC‐AC power converters using multirate partial differential equations

AbstractSwitch‐mode power converters are used in various applications to convert between different voltage (or current) levels. They use transistors to switch on and off the input voltage to generate a pulsed voltage whose arithmetic average is the desired output voltage of the converter. After smoothening by filters, the converter output is used to supply devices. The simulation of these switch‐mode power converters by conventional time discretization is computationally expensive since a high number of time steps is necessary to properly resolve the unknown state variables and detect switch events of the excitation. This paper proposes a multirate method based on the concept of multirate partial differential equations (MPDEs), which splits the solution into fast varying and slowly varying parts. The method is designed to work with pulse‐width modulated (PWM) excitation with a constant switching cycle and varying duty cycle. It is applicable to problems in which the circuit part generating the pulsed voltage, i.e., consisting of transistors, diodes, and voltage sources, can be approximated by an ideal PWM excitation. Switching‐event detection is no longer necessary and a much smaller number of time steps are required for a decent resolution, thus leading to a highly efficient method. The important case of varying duty cycles in the MPDE framework is addressed for the first time.

Multirate PWM balance method for the efficient field-circuit coupled simulation of power converters

The field-circuit coupled simulation of switch-mode power converters with conventional time discretization is computationally expensive since very small time steps are needed to appropriately account for steep transients occurring inside the converter, not only for the degrees of freedom (DOFs) in the circuit, but also for the large number of DOFs in the field model part. An efficient simulation technique for converters with idealized switches is obtained using multirate partial differential equations, which allow for a natural separation into components of different time scales. This paper introduces a set of new PWM eigenfunctions which decouple the systems of equations and thus yield an efficient simulation of the field-circuit coupled problem. The resulting method is called the multirate PWM balance method.

Efficient Simulation of DC–DC Switch-Mode Power Converters by Multirate Partial Differential Equations

In this paper, Multirate Partial Differential Equations (MPDEs) are used for the efficient simulation of problems with 2-level pulsed excitations as they often occur in power electronics, e.g., DC-DC switch-mode converters. The differential equations describing the problem are reformulated as MPDEs which are solved by a Galerkin approach and time discretization. For the solution expansion two types of basis functions are proposed, namely classical Finite Element (FE) nodal functions and the recently introduced excitation-specific pulse width modulation (PWM) basis functions. The new method is applied to the example of a buck converter. Convergence, accuracy of the solution and computational efficiency of the method are numerically analyzed.

Solving Nonlinear Circuits With Pulsed Excitation by Multirate Partial Differential Equations

In this paper the concept of Multirate Partial Differential Equations (MPDEs) is applied to obtain an efficient solution for nonlinear low-frequency electrical circuits with pulsed excitation. The MPDEs are solved by a Galerkin approach and a conventional time discretization. Nonlinearities are efficiently accounted for by neglecting the high-frequency components (ripples) of the state variables and using only their envelope for the evaluation. It is shown that the impact of this approximation on the solution becomes increasingly negligible for rising frequency and leads to significant performance gains.

A method of characteristics for solving multirate partial differential equations in radio frequency application

In communication electronics, radio frequency applications are characterised by widely separated time scales. This behaviour increases both computation costs and problems during numerical simulation. A new signal model that transforms the ODE into a PDE model, can serve as a basis for more efficient numerical methods. From one point of view, it can be regarded as a multirate scheme applied to the underlying ODE. Based on an analysis of this model, we present a method of characteristics to solve the PDE system with periodic boundary conditions. This technique exploits the special form of information transport in the given system.