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Design of an Automatic Control Algorithm for Energy-Efficient ...

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6 The optimiser: <strong>an</strong> evolutionary algorithm approach 52<br />

<strong>for</strong>mulations are nonlinear <strong>an</strong>d c<strong>an</strong> contain discontinuities. Finally, it is <strong>an</strong> aim that the<br />

algorithm c<strong>an</strong> be used in future developments <strong>of</strong> the MUTE car (presented in Chapter 9).<br />

This may imply ch<strong>an</strong>ges in the HVAC-system <strong>an</strong>d integration <strong>of</strong> new components. The<br />

extension <strong>of</strong> the controller <strong>an</strong>d its adaption should not be too complicated.<br />

In summary the optimiser algorithm should fulfil the following criteria:<br />

• Robust<br />

• Safe<br />

• Low computational ef<strong>for</strong>t<br />

• H<strong>an</strong>dles discontinuities<br />

• Easy to extend<br />

6.2.2 Gradient based algorithms<br />

For the majority <strong>of</strong> online optimisation problems a so-called gradient method are used.<br />

A prominent <strong>an</strong>d efficient gradient-based optimisation algorithm is sequential quadratic<br />

programming (SQP) [31]. SQP exploits the first <strong>an</strong>d second order derivative in<strong>for</strong>mation.<br />

Compared to other algorithms, this generally leads to a lower number <strong>of</strong> function<br />

evaluations. On the other h<strong>an</strong>d it imposes more requirements on the system <strong>an</strong>d objective<br />

functions. As such it c<strong>an</strong>not h<strong>an</strong>dle non-continuous differentiable objective functions.<br />

Discrete variables are not applicable in this algorithm as well.<br />

Due to these downsides no gradient based method is applied.<br />

6.2.3 Evolutionary algorithms<br />

Evolutionary algorithms (EA) are stochastic methods that were first developed in the<br />

seventies. They were used to solve stationary optimisation problems, <strong>for</strong> example in<br />

construction design.<br />

This class <strong>of</strong> stochastic methods is inspired by biological evolution. A number<br />

<strong>of</strong> sets <strong>of</strong> design variables (so-called individuals) <strong>for</strong>ms a population. Each <strong>of</strong> them gets<br />

assigned a fitness value with the help <strong>of</strong> the cost function �, which could also be a vector <strong>of</strong>

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