Power System Blockset

Which Integration Method Should Be Used - Continuous or Discrete?

One important feature of the Power System Blockset that has been introduced with version 2, is its ability to simulate electrical systems either with continuous variable time-step integration algorithms or with a fixed time step using a discretized system. For small size systems, the continuous method is usually more accurate. Variable time step algorithms are also faster because the number of steps will be less than with a fixed time step method giving comparable accuracy. When using line-commutated power electronics, the variable-step, event-sensitive algorithms will detect the zero crossings of currents in diodes and thyristors with a high accuracy so that you won`t observe any current chopping. However, for large systems (containing either a large number of states or nonlinear blocks), the drawback of the continuous method is that its extreme accuracy slows down the simulation. In such cases, it is advantageous to discretize your system. In the following two sections, we explain these two methods, their advantages, and their limitations.

What do we mean by "small size" and "large size" systems? Although the distinction is not clear, you can consider small size a system that contains less than 30 electrical states and less than 6 electronic switches. Circuit breakers do not affect the speed too much, because unlike power electronic switches, which are commutated at every cycle, these devices are operated only a couple of times during a test.

Advanced Topics

Simulating with Continuous Integration Algorithms