POWER ELECTRONIC SIMULATIONS and PRODUCT DEVELOPMENT CYCLE

At PEG, we practice an integrative approach involving simulation in the complete product development cycle. It is important to understand the role of simulation in every phase of the product development cycle. Below is a summary of how simulation can be used in each stage:

1. Concept Phase:

During this phase, use simulation tools to verify circuit operation. One must start small using idle component models and build the system in stages. Each stage work should be saved. It is important to understand the theory and state of the art behind the circuit you are about to simulate. Without proper theoretical foundation, you will not be able to obtain useful information from simulation.

Also, for majority of the engineers, a process methodology or steps to design must include simulation. Simulation is most effective when the circuit behavior is not well understood and one can construct several what-if scenarios or use simulation to build a repertoire of questions to be answered about the design problem at hand. Simulation effectiveness improves with experience and time. An engineering department must be dedicated to it. As with any other skill, to yield simulation as a potent competitive weapon, one must spend significant time and resources to hone it. A frivolous relationship or experimental tinkering with simulation tools will not yield any fruitful results.

2. Design Phase:

During design phase, as you begin to transform your work into schematics, one must pay careful attention to component selection and component models can be incorporated (especially in Spice based tools) one at a time.

Do not be too ambitious to incorporate a host of models at one time. Also realize that incorporating each component model is never required. One must be quite prudent in incorporating essential component models. Just remember Pareto’s principle – 20% or less determine 80% or more of the outcome. This must always be kept in mind

3. Prototype Phase:

During this phase as prototypes are built, one must pay careful attention to collecting data during incoming inspection (mechanical variables) and testing (electrical variables). Here, we always recommend to use the suppliers who would also build production units. It is important to do so to understand supplier capabilities and process variations.

4. First Article Phase:

During this phase as First Articles are built, one must pay careful attention to collecting data during incoming inspection (mechanical variables) and testing (electrical variables). During this phase, use statistics to understand variable distributions and correlation between various parameters. These correlations may change from the prototype stage.

It is important to start forming new hypothesis can tremendously expedite the whole product development cycle. During this phase, PEG strongly recommends using statistics to understand variable distributions and correlation between various variables. It is important to start forming hypothesis on what could be troublesome variables which are going to effect the performance. Those variations must be incorporated into Simulations to re-characterize the system and understand overall performance variations.

5. Pre-Production/Production Phase:

During this phase as Pre- Production or Production units are built, one again must pay careful attention to collecting data during incoming inspection (mechanical variables), in-process inspection (mechanical and electrical variables) and final testing (electrical variables). During this phase, we use statistics to understand variable distributions and correlation between various parameters.

These correlations may change from the earlier phases. It is important to start forming fresh hypothesis on what could be troublesome variables which are going to effect the system performance. Those variations must be incorporated into Simulations to re- characterize the system and understand overall performance variations. This is the process of continuous improvement and PEG’s integrated approach, if followed rigorously, yields not only superior products but also strong infrastructure capabilities.

There is always an “Edison approach” to design. With this approach, you will need to spend countless hours and follow rigorous and scientific method of design of experiments as well as truthful collection of data. “Edison approach” is simply too expensive and unaffordable in today’s world. Nevertheless, with enough money and time, such approach is always possible.

LTSpice and PSpice are great tools for Power Electronic circuits barring their annoying and most irritating convergence problems. These convergence problems are a great waste of time and a source of frustration. However, there has been a steady rise in the tools and techniques in the Spice arena, especially for the Power Electronics and Motor Control areas. Spice and other available tools expertise can be wielded effectively in launching new products through short product development cycles. By no means, is PEG claiming that Spice expertise in Power Electronics alone is sufficient to cut the time from concept to production. However, it is an important tool to have in the bag.

For Power Electronics Circuits, PEG recommends the following approach to using Spice during the Concept Phase only:

Before you build your own circuit model, search to see if similar circuits are available in the public domain. A great engineer always builds her/his work on what is already available. Do not reinvent the wheel.
Always start with the most idle circuit model of components. Simplicity is the key. Sub-circuits are great in ensuring that small parts of circuits can be made to work first. It is always prudent to use simple, well-tested models.
Now, transient analysis using idle components will get you only so far. Small Signal modeling is an important step in being able to overcome convergence problems as well as understand the circuit behavior fully. This technique requires state space averaging and is most vital in simulating Power Electronic circuits. PEG specializes in small signal modeling of the Power Electronic circuits and if you run into hot waters using this technique, we are happy to help.
Control loop compensation is not a simple matter for most of the Power Electronic circuits. However, the compensator can be easily designed using the small signal modeling techniques.
Once the above steps are followed and we have a working simulation, we can begin to run various what-if scenarios to understand the circuit behavior in time domain as well as frequency domain.