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In digital control system, there are two basic techniques for finding the best digital controller.

First, called the discrete equivalent, we find the continuous compensation and then discretize (best approximate) that compensater. We can verify our design by simulation. However, this technique may need some tuning to the digital controller but it simulates the real implementation.

Second, called the exact discrete design, we approximate the plant model to a discrete model so the whole system will be in the Z-domain. Then, we design the controller using the discrete tools and techniques.

This technique has a drawback. It approximates the plant via one of the approximation methods such as ZOH, Tustin, etc.

From simulation perspective, it may not reflect the exact real implementation. The only way to have a simulation that match the real implementation is to have a combined continuous (plant) and discrete (controller) blocks as we have.

Thus, after the design process, I may have to run a simulation with the digital controller as well as the continuous plant that really reflect the real implementation. Some tuning may be required.

Is the exact discrete design (all blocks in Z-domain) simulation identical to the real implementation as I understood from few books which did not mention that drawback ?

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