Using the Powerful SABER Simulator for Simulation, Modeling, and Analysis of Power Systems, Circuits, and Devices

Steve Chwirka Avant! Corporation 9205 SW Gemini Dr Beaverton, Or, 97008

Abstract - Power systems are some of the most diffi- cult types of designs to simulate. They contain high fre- quency switching of currents and voltages into inductors and across capacitors, multiple feedback loops (voltage, current, motor speed, etc), non-linear magnetics, high power device models, DSP, motors, generators, fuses, power distribution, thermal modeling, non-linear sources (battery, Solar array, etc), and loads. In Addition, sche- matic capture, post processing of the waveforms, links to critical tools, and a powerful mixed-signal mixed technol- ogy modeling language are needed. There is no one tool that can provide 100% of capabilities to 100% of the engineers, however there is no single tool more powerful than SABER This paper will show how SABER pro- vides all the above capability and more.

INTRODUCTION There are many simulation tools out on the market these

days, and many are spice derivatives. Spice was originally developed for ICs, however it has been used in the power market with vaned results. SABER was developed from scratch and is a true mixed-signal, mixed technology equa- tion solving simulation tool. This means SABER was clevel- oped to handle all the difficult non-linear, feedback type power systems. These can include not only the electrical analog parts of the system, but also the digital, mechanical, thermal, and magnetic blocks. Unlike other simulators which try to emulate the behavior of non-electrical blocks using electrical components, SABER models these other engineer- ing disciplines in there native domain.

0-7803-6561-5/00/$10.00 0 2000 IEEE 172

SIMULATJON There are three basic stages involved in simulation, cap-

turing your design, running the analyses, and interpreting the results. Figure one shows SaberSketch which is one of the schematic capture tools available with SABER. A good schematic capture provides the capability to document the design as well as providing the input to simulation. This includes providing several graphics formats that can be imported to report generation tools (i.e. Power Point, Framemaker, etc) Sabersketch can write to 12 of the main formats such as tiff, bmp, jpeg, etc. Sabersketch also has the capability to view waveforms on the schematic or back annotate simulation results onto the schematic. This could be used to interface with the test groups or for presentations in design reviews. All of SABER analyses can be invoked from user friendly pull down menus within SaberSketch. All of SABER'S tools run on Unix and PCs (WindowsNT). The tool looks exactly the same on all platefoms and the files are interchangeable. Other schematic capture tools that link with SABER are Mentor Graphics, Innoveda (formally Viewlogic), and Cadence.

Some of the available simulation analyses available with SABER are DC (Note that in SABER the user doesn't have to do a DC analysis prior to doing a Transient or AC analy- sis, as is the case with other simulators. This is an important capability if the user wishes to simulate the natural start-up of a power system, or to avoid DC convergence problems), DCT (DC Transfer - i.e. can be used to create characteristic curves for models. i.e. the common Id vs. Vds vs. Vgs of MOSFETs as an example), TRansient (Time domain simula-

Once the design has been captured, it can be simulated.

tion), small signal ac (lets the user view the frequency response of the system), distortion, noise, pole-zero, vary, sensitivity (Note SABER can perform sensitivity analysis on any measurement available in SABER. i.e. - since there is an automatic measurement for phase margin, the user can deter- mine how sensitive the phase margin is to components in the system.), Stress (determines the thermal and electrical stress of components), Fourier and FFT (for evaluation of the har- monic content of a waveform).

SaberScope is shown in Figure below and is used for post processing and viewing the simulation results. Just simulat- ing the design is only part of what simulation tools do to aid the design engineer. Evaluating the results can be as time consuming (if not more) as the actual simulation. Saber- Scope was developed to aid the engineer in quickly evaluat- ing data so to make the overall simulation effort much more effective. Automatic measurements available in Saberscope allow the user to very quickly obtain valuable data. One example is the automatic measure of the duty cycle of a con- verter during start-up. Some current mode converters are duty cycle sensitive and can develop instabilities, this mea- surement would allow the user to very quickly look at the duty cycle vs. time during the start-up or transients to see if there is a possibility of unstable regions. Some of the other automatic measurements include peak-peak, Avg, RMS, lowlhigh pass 3db filter points, slope. fallhse times, Period Frequency, pulse width, overshoot, settle time, etc. In addi- tion, Saberscope provides a patented waveform calculator which can be used to perform a variety of functions on the waveforms.

173

MODELING In many of the other simulation tools, modeling was an over- looked capability. When the engineer needed specialized models, it was extremely difficult to create them. The engi- neer would be forced to emulate the characteristic of some component using electrical devices or dependent sources. This type of modeling was not intuitive, took a long time, and often would add complexity to the system that the simu- lator is trying to analyze. SABER's MAST modeling lan- guage was created as part of the SABER simulator and not an after thought. MAST allows the users to very quickly cre- ate models based on the set of characteristic equations directly. The models are therefore very straight forward and can be understood by others. Using a modeling language also aids the convergence capability of the simulator. Figure below shows an average model written in MAST for a for- ward converter operating in both CCM and DCM. It should be noted that SABER can also read C and fortran programs and several versions of spice netlists.

MAST is a powerful modeling language and is used for everything from system level descriptions to circuit level block modeling, to very detailed device modeling. There have been many papers written about power device model- ing using SABERS MAST, and how it provides the needed capabilities to accurately model a detailed power device to be used in a circuit simulator. In addition, many power device vendors have discovered the power of SABER and MAST, and have been creating MAST models for their prod-

ucts. One example is Motorola's web site which contains SABER models and gives the following description in the "readme" files : (http://www.mot-sps.codmodels/) "The SPICE model is based on the available elements in SPICE based electrical simulators and may have limited accuracy and convergence capabilities due to fundamental limitations in SPICE based simulators. Specifically, this model DOES NOT produce an accurate prediction of some non-linear capacitance effects, non-linear leakage character- istics, soft-knee breakdown, weak inversion characteristics, body diode forward and reverse recovery mechanisms, and maximum device ratings. The SABER model is a more accurate model that includes all non-linear capacitances, non-linear leakage characteristics, soft-knee breakdown, weak inversion characteristics, body diode forward and reverse recovery mechanisms, and maximum stress ratings. The model is available for use with the SABER(TM) simula- tor from Analogy and is written in MAST(TM), an Analog Hardware Description Language (AHDL). The SABER model is well suited for power circuit simulation."

Another example is Infineon (Siemans) at http:// www.infineon.com/products/power/simulat.htm under the "model descriptiondapplication notes" talks about SABER'S thermal modeling : "SABER, unlike SPICE offers the possi- bility of creating complete system descriptions in MAST, a programming language unique to SABER developed by Analogy. This offers great freedom in the modeling of com- plex functions or systems and enables a more intuitive

174

MODELING Cont’d

MAST also enables the clean separation of thermal and electrical variables and therefore avoids error sources such as the accidental loading of a thermal node with an electrical network.” It should be noted that the above quotes contain the word “Analogy” , however Avant! Corporation bought Analogy in early 2000.

The use of a modeling language is not new to the dig-

main IEEE standard modeling languages used by them. Recently these two languages have evolved to include an analog capability (Verilog-AMs, VHDL-AMs) Avant! is presently working on a new generation of simulation tools which will provide the capability to import models of any language (VHDL-AMs, Verilog-AMs, MAST, spice netlists) SABER’S “MCT”

(Magnetic Component Tool) provides the user with a friendly menu dnven way to create magnetic component models to be used in SABER. Figures dis- play the MCT tool. The resultant magnetic com- ponent model will con- tain non-linear hysteresis, eddy current losses in the core, air gap effects, Flux leakage (leakage Inductance), Skin and proximity effects in the coil, and winding capacitances.

SABER also provides a tool called “AMS” (Analog Model Synthesis) which can automatically create a saber model based on the transfer hnction of a circuit block. This tool also includes a TDSA model which enables the user to perform a large signal ac analysis on the actual cir- cuit, without the need for average models.

In addition to SABER’s MAST modeling language, SABER provides several mod- eling tools to aid the engineer in development of models. One of these tools is the “TLU” (Table Lookup) modeling tool. This tool provides a user interface to creating a 5 dimension table look up model. Other modeling tools include a menu driven fuse charactenzation tool, an IGBT characterization tool, and a magnetic component model- ing tool.

SABER also offers a comprehensive library of existing models that have been developed over the years. These include close to 1000 generic models that can be character- ized by the users, and close to 25,000 characterized compo- nents. Figure on the next page shows a small sample of SABERS electro-mechanical library. The SABER library consist of electrical (analog and digital), electro-mechani- cal (motors, generators, alternators), thermal, optical, mag- netic, control systems, Z domain, and hydraulic.

175

Figure below shows a matrix of some of the tools that interface with SABER.

CONCLUSION The purpose of this paper was

to inform power engineers about the capabilities of the SABER simulator. SABER has been used extensively in all market areas of power design (automotive, tele- com, consumer, industrial, trans- portation, aerospace, etc). SABER’S powerful schematic

cation of agreement between the models and practice.

I I I I

I I I I I

Tesla X Verilon i X Weva X X

176