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Publication# Analog microelectronic emulation for dynamic power system computation

Abstract

Power system dynamic simulators can be classified according to multiple criteria, including speed, precision, cost and modularity (topology, characteristics and model). Existing simulators are based on time-consuming numeric algorithms, which provide very precise results. But the evolution of the power grid constantly changes the requirements for simulators. In fact, power consumption is steadily increasing; therefore, the power system is always operating closer to its limits. Moreover, focus is put on decentralized and stochastic green energy sources, leading to a much more complex and less predictable power system. In order to guarantee security of supply under these conditions, real-time control and online security assessment are of the utmost importance. The main requirement for power system simulators in this context thus becomes the simulation time. The simulator has to be able to reproduce power system phenomena much faster than their real-time duration. An effective way to accelerate computation time of power system stability simulators is based on analog emulation of the power system grid. The idea is to avoid the heavy, time-consuming numerical matrix calculations of the grid by using an instantaneous analog Kirchhoff grid, with which computation becomes intrinsically parallel and the simulation time independent of the power system topology size. An overview of the power system computation history and the evolution of microelectronics highlights that the renaissance of dedicated analog computation is justified. Modern VLSI technologies can overcome the drawbacks which caused the disappearance of analog computation units in the 1960s. This work addresses therefore the development of a power system emulation approach from its theoretical principles to the behavioral design and the microelectronic implementation of a first demonstrator. The approach used in this research is called AC emulation approach and is based on a one-to-one mapping of components of the real power system (generator, load and transmission line) by emulating their behavior on a CMOS microelectronic integrated circuit (ASIC). The signals propagating on the emulated grid are the shrunk and downscaled current and voltage waves of the real power system. The uniqueness of this emulation approach is that frequency dependence of the signals is preserved. Therefore, the range of phenomena that can be emulated with an AC emulator depends only on the implemented models. Within the framework of this thesis, we restrict our developments to transient stability analysis, as our main focus is put on emulation speed. v We provide behavioral AC emulation models for the three main power system components. Thereby, special attention is paid to the generator model, which is shown to introduce a systematic error. This error is analyzed and reduced by model adaptation. Behavioral simulation results validate the developed models. Moreover, we suggest custom programmable analog building blocks for the implementation of the proposed behavioral models. During their design, application specific requirements, as well as imperfections, calibration, mismatch and process-variation aspects, are taken into account. In particular, the design of the tunable floating inductance used in all three AC emulation models is discussed in detail. In fact, major design challenges have to be addressed in order to achieve an inductance suitable for our application. Finally, a first AC emulation demonstrator is presented. A benchmark using a fixed two- machine topology has been implemented using a 0.35μm 3.3V CMOS technology. The characteristics of the emulated components (i.e. generators and transmission lines) are reprogrammable, allowing short circuits to be emulated at different distances from the generator. The emulated phenomena are shown to be 10′000 times faster than real time, therefore proving the high-speed capabilities of AC emulation.

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Analog computer

An analog computer or analogue computer is a type of computer that uses the continuous variation aspect of physical phenomena such as electrical, mechanical, or hydraulic quantities (analog signals

Emulator

In computing, an emulator is hardware or software that enables one computer system (called the host) to behave like another computer system (called the guest). An emulator typically enables the hos

Computation

A computation is any type of arithmetic or non-arithmetic calculation that is well-defined. Common examples of computations are mathematical equations and computer algorithms.
Mechanical or electron

Laurent Fabre, Maher Kayal, Ira Nagel

This paper presents a microelectronic emulation approach for high-speed power system computation. First, the problems of existing power system simulators are detailed. This shows that microelectronic emulation is a possible solution for solving the speed problems of existing simulators. Second, this paper presents one specific emulation approach, the so-called AC emulation approach. The ultimate objective of the AC emulation approach is the realization of a power system emulator which reproduces simultaneously a large number of phenomena of different time constants or frequencies with a much higher speed than real time. Frequency dependence of the elements is preserved and the signals propagating in the emulated network are the shrunk or downscaled current and voltage waves of the real power network. The models of the power network components are detailed. Special attention is paid to the generator model which was shown to introduce a systematic error. This systematic error is quantified, analyzed and optimized. Moreover behavioral simulation results confirm the feasibility of this approach which in turn lays the foundation for such an emulator.

2010Modern society is dependent on reliable electricity for security, health, communication, transportation, finance, computers and nearly all aspects of the contemporary life. Providing reliable electricity is a very complex challenge. It involves real-time metering, real-time assessment, control and coordination of hundreds of production centers. Power consumption is steadily increasing and the power system is always operating closer to its limits. Introduction to smart-grid provides more and more data to be collected for the operation center by means of smart-metering for a better knowledge of the system. Moreover, focus is put on decentralized and stochastic green energy sources, leading to a much more complex and less predictable power system. Guarantying security of supply with these new requirements involves further enhancement for faster power system simulators. Indeed, they can provide online security assessment for better real-time control. Time-domain simulations are probably the most demanding in term of computation power. Existing time-domain simulators are based on time-consuming algorithm and targets very precise results. An effective way to accelerate the computational speed of power system assessment simulators is to use analog or mixed-signal emulation. Instead computing numerical matrix calculations of the grid this technique is based on a quasi-instantaneous analog Kirchhoff solver. It provides an intrinsic parallel computer and simulation time is independent of the analyzed power system topology size. This work addresses the development of a new power system emulation approach based on mixed-signal dedicated electronics hardware. Mixed-signal or hybrid electronics uses the coexistence of both digital and analog implementation. The digital functions are intended to facilitate the model portability when analog functions are used for achieving parallelism and speed enhancement. This thesis covers theoretical principles to the realization of a first power system emulation-on-chip (PSEoC) by means of application specific integrated circuit (ASIC). Moreover, different hardware platform (HDP) have been designed, realized and tested for demonstrating the performances by measurement. Within the framework of this work, we restrict our developments to transient stability and cover applications such N-1 contingency analysis and Critical Clearing Time (CCT) analysis. The approach used is called the phasor emulation (PE) approach. It is based on a mathematical abstraction of the grid where the transmission lines are represented by multiple programmable resistive networks, connected in array with CMOS analog switches. Generators and loads model are then computed through current-techniques blocks, embedded processors or FPGAs. Four HDP are presented: - The first electronics implementation provides a quasi-full analog computer and illustrates the limitations in terms of accuracy of such implementation without calibration. - The second uses multiple embedded 32-bit processors with analog emulation of the grid. It illustrates a comparison in term of accuracy between standard electronic and ASIC implementations (0.35um 3.3V CMOS technology) for a 16 node reconfigurable power system topology. - The third uses multiple FPGA processing units with analog emulation of the grid. It covers applications such N-1 contingency analysis and Critical Clearing Time (CCT) analysis for a 96 nodes reconfigurable power system topology. - Finally, the forth is based on PSEoC and the design of a dedicated ASICs developed for time-domain power system emulation. Main enhancement of this development is the design and realization of hybrid R-A/D C-A/D converter in 0.35um 3.3V CMOS technology. The emulated phenomena are shown to be between 100 to 1000 time faster than the real-time phenomena proving the high-speed capabilities of mixed-signal emulation approach.

Laurent Fabre, Maher Kayal, Ira Nagel

This paper introduces a microelectronic emulation approach for high-speed power system computation. First, the problems of existing power system simulators are detailed. This shows that microelectronic emulation is a possible solution for the speed problems of existing simulators, using emulation of the power grid to build an instantaneous connection between multiple differential equation solving blocks each one using the results of the others. Second, this paper presents one specific emulation approach, the so-called AC emulation approach. The ultimate objective of the AC emulation approach is the realization of a power system emulator which can simultaneously reproduce a large number of phenomena of different time constants or frequencies (excluding electromagnetic phenomena) with a much higher speed than real time. Frequency dependence of the elements is preserved and the signals propagating in the emulated network are the shrunk or downscaled current and voltage waves of the real power network. The models of the power network components are detailed and the microelectronic implementations are proposed. Moreover, behavioral simulation results confirm the feasibility of this approach which in turn lays the foundation for such an emulator.