Automation

Electronic SoC’s
An integrated modeling and design approach

The Industrial Electronics Society (IES) of the IEEE has recently encouraged and approved the formation of a new Technical Committee on Electronic Systemson- a-Chip (ESoC) for industry. This Committee aims to promote professional activities in the area of electronics used in the modern industry. Dr. Marcian Cirstea, Senior Member IEEE, IES Technical Committee Head of Design and Technology Department, Faculty of Science and Technology, Anglia Ruskin University, Cambridge discussess

The recent fast progress of Electronic Design Automation (EDA) techniques and VLSI technology has created the opportunity for the development of complex and compact high performance controllers for power electronic systems [1]. Nowadays, the design engineer is using modern EDA tools to create, simulate and verify a design, and, without committing to hardware, can quickly evaluate complex systems and ideas with very high confidence in the “right first time” correct operation of the final product. The proposed approach extends the traditional use of High Level Programming Languages to encompass the holistic modeling of power electronic systems. The outcome is a design environment that allows all functional aspects of the system to be considered simultaneously, therefore maximizing operational performance in order to achieve high efficiency and power quality, while simultaneously allowing the rapid prototyping of a digital controller on an FPGA hardware development platform.

Successful innovation often means a design that achieves a desirable cluster of performance characteristics, subject to certain constrains, and holistic modeling of complex technical systems can constitute the first step towards novel designs of high performance. This method is correlated with a powerful international movement and leading edge research, directed towards the development of holistic models for complex electronic systems. The EDA international community joined forces in year 2000 under Accellera [2], assuming the mission to drive forward the worldwide development and use of standards required by systems, semiconductor and design tools companies, which enhance a language-based design automation process.

Recently, the Industrial Electronics Society of the IEEE initiated the setup of a new technical committee concerned with electronic systems-on-a-chip for industry [3].

This article is concerned with the holistic modelling of power electronic systems and rapid design and prototyping of associated digital controllers. The method deals with the functional modeling of integrated electronic systems using the behavioural features of Hardware Description Languages and then targeting Field Programmable Gate Arrays (FPGAs) for the implementation of the optimized digital controllers. Two case studies using VHDL [4] for power electronic system modeling, simulation, controller design and implementation are presented. The control systems, based on neural networks and fuzzy logic, are implemented using FPGAs. There are major advantages of the new approach, such as: a unique modelling and evaluation environment for complete power electronic systems, the same environment is used for the digital controller design and compact FPGA rapid prototyping, fast design development, short time to market, a CAD platform independent model, reusability of the model / design, generation of valuable IP, Concurrent Engineering basic rules (unique EDA environment and common design database) are fulfilled. A specific advantage demonstrated by the case studies is that the implementation of artificial intelligent algorithms is facilitated / streamlined. This modelling / design approach is validated experimentally.

2. The Holistic Modelling and Design Approach
Traditionally, mathematical models have been developed to evaluate the functionality of global engineering systems.

However, the practical development of each part of the system needs then to be separately addressed. This often involves the use of other CAD tools and/or different software platforms, with the design itself being developed in a different environment. Recent advance in CAD methodologies / languages has brought the functional description of design and practical hardware implementation closer. System level modelling languages (such as Handel- C, System-C) and Hardware Description Languages (such as VHDL, Verilog) enable the underpinning mathematical description and the electronic design implementation to be simultaneously addressed in a unique environment, supported by a range of major Computer Aided Engineering platforms. Synthesis tools can compile such designs into a variety of target technologies.

A holistic system level approach to the design and development of an electronic system enables a top-down design methodology, which begins with modelling an idea at an abstract level, and proceeds through the iterative steps necessary to further refine this into a detailed system. A test environment is developed early in the design cycle. As the design evolves to completion, the language is able to support a complex detailed digital system description and the test environment will check compliance with the original specification. Concepts are tested before investment is made in hardware / physical implementation.

In terms of holistic modelling of complex power electronic systems, with elements such as electric motors, generators, power converters and a variety of controllers, system level modelling languages offer advantages such as:
● Simultaneous consideration of the mathematical aspects of engineering systems (functional / behavioural description) and the detailed electronic hardware design, in the same unique environment, normally supported by a range of Computer Aided Design platforms.
● Ability to handle all levels of abstraction. The system can be simulated as an overall model during all stages of the electronic controller design, which can be subsequently targeted for “system on a chip” silicon implementation.
● Fast implementation & relatively short time to market.
● Easy hardware implementation of Artificial Intelligence.
● Versatile reusable models / design modules are generated, in accordance with modern principles of design reuse.

Simulation results are valuable to check the behaviour of a model, but on many occasions it is the hardware validation of a controller that provides significant information before the decision is taken to invest in an Application Specific Integrated Circuit (ASIC). The cheapest and fastest way to validate the design of a novel digital controller is via a prototype board containing re-programmable devices such as FPGAs. This shortens the time to correct any design problem and it ensures an error free design before permanent ASIC implementation. The prototype board can also be used for the hardware testing of other system components.

The DK4 design suite from Celoxica [5] allows Handel-C (high level language similar with C) functional modelling of an electronic system. Handel-C produces an Electronic Design Interchange Format (EDIF) output when compiling the design for hardware target. The Xilinx placement and routing tools are used to translate the EDIF format into hardware layout, enabling rapid hardware implementation onto development boards containing FPGAs. The compiler can also generate Hardware Description Language format code such as VHDL, allowing combination with other hardware elements in systemson-a-chip designs.

The general benefits of holistic modelling, combined with the advantages of System Level Design / Hardware Description Languages and FPGA implementation, enable the efficient investigation of electronic system topologies employing complex controllers, with efficient use of resource.

3. Case studies
A. Neural PWM Induction Motor Drive
This example formulates an improved induction motor predictive current control algorithm compared to that proposed in [6], by not ignoring the stator resistance and incorporating an on-line inductance estimator that allows a more accurate internal voltage calculation. A new neural networks induction motor control method that combines a predictive PWM current control strategy with the neural approach is analysed [7], [1]. The method avoids part of the calculations used by classical vector control. The design is performed using VHDL, so that a versatile reusable design module is obtained and FPGA is targeted for hardware implementation. The controller operation is based upon a symmetrical three-phase equivalent circuit of the induction motor. The drive system ( Figure 1) was tested by VHDL simulation and laboratory experiments.

The VHDL controller design includes neural networks and classical digital circuits. The equations describing the PWM inverter and the motor were digitised and, in conjunction with the digital controller, were transformed into a holistic behavioural VHDL system model, which was simulated.

As shown by the VHDL simulation results illustrated in Figure 2, which were confirmed by experimental tests, the control system generates the appropriate PWM switching signals for the 6 IGBTs in the power inverter. This current control strategy can be applied to a range of power systems, providing a relatively simple digital controller.

B. Fuzzy Logic Controller for stand Alone Synchronous Generators
A second example describes the study and design of an electronic control system allowing variable speed operation of diesel driven stand alone synchronous generators [8], [1].

The system is shown in Figure 4. A fuzzy logic based control scheme, which can isolate the final output frequency of the system from the effects of speed variations, is simulated and designed. The fuel valve of the diesel engine is dependant on the d.c. link voltage input to the controller.

The complete system was modelled and simulated using VHDL and then the circuit design of the controller was synthesised and implemented into a Xilinx XC4010 FPGA for rapid prototyping.

Figure 3 shows the d.c. voltage response (experimental result) to a load current step increase (from 10 A to 20 A, at 20s), with the fuzzy logic FPGA controller connected to the system. The desired d.c. voltage is set at 250 V. The graph shows that the controller is successful in stabilising the generator system. The main achievements of this system are:
● the control system maintains the output voltage at the desired magnitude and frequency against changes in Vdc which arise from changes in speed and/or load, thus allowing the system to operate at the most efficient speed.
● the system provides a suitable platform for the study of efficient diesel engine variable speed generators.

4. Conclusions
A modelling technique is proposed for the holistic investigation of power electronic systems. This is based on System Level Modelling / Hardware Description Languages and allows rapid FPGA prototyping of the controllers. The sample controllers were developed from ideas, through the design and simulation stages, to complete systems in a short time, giving further advantages such as a high degree of flexibility, a reliable framework for design verification and high confidence in the correct first time operation.

The VHDL approach also provides multiple choices for the implementation target technology and universal compatibility of the design (as IP block) with respect to multiple existing modern CAD tools. This allows the easy integration of electronic controller models in complex electronic system models. It can be estimated that similar holistic modelling methodologies will be increasingly used in the future. There is a wide range of applications for FPGA controlled power electronic systems in automation, robots, electric drives and generator systems.

References
[1] M.N. Cirstea, A. Dinu, J. Khor, M. McCormick. Neural and Fuzzy Logic Control of Drives and Power Systems. Elsevier Ltd., Oxford, 2002.
[2] http://www.accellera.org/
[3] http://vega.unitbv.ro/~ieee
[4] D.L. Perry: “VHDL”, McGraw-Hill, 3rd Ed., 2002.
[5] http://www.celoxica.com
[6] S. Nabae, M. Ogasawara, and H. Akagi, “A new control scheme for current controlled PWM inverters”, in IEEE Trans. Ind. Appl., vol IA-22, no. 4, July/August 1986, pp. 697-701.
[7] A. Dinu, “FPGA Neural Controller for Three Phase Sensorless Induction Motor Drive Systems”, PhD Thesis, De Montfort University, 2000.
[8] J. Khor, “Intelligent Fuzzy Logic Control of Generators”, PhD, De Montfort University, UK, 1999.

Acknowledgements
Acknowledgements are due to Dr. Andrei Dinu and Dr. Jeen Ghee Khor for their research on the case studies presented. Thanks are also due to Newage AVK SEG, Stamford, UK, for their support in carrying out some of the xperimental tests, to Prof. Malcolm McCormick for his general support and to De Montfort University, Leicester, UK.