Functional Design of the mCCHP-RES System - Design for Micro-Combined Cooling, Heating and Power Systems - page 325

3.5

3

2.5

2

1.5

1

0.5

0

0 1 2 3 4 5 6 7 8

x 10 4

time [s]

Fig. 92 Evolution of PI control (dot) and of heterogeneous control (solid line)

AC

u p = P

ff

u

c

V sp V

u

fb

u cS

B

SM

c

VC

Fig. 93 Feed-forward control of the battery voltage

produced electric power with the consumed one, the feed-forward control has a
reduced ef

ciency, so that the use of this solution is not an important problem.
In the thermal subsystem, the balance between the produced power and the
consumed one is achieved through the temperature control loop for the thermal tank
(see Fig. 20 ). The u ph control given by the controller from this loop modi es the

power of the pellet tank. The design of the control law in the loop mentioned above
is done depending on the control possibilities offered by the pellet tank: discrete 0/1
control, by imposing a minimum period between two successive starts of the tank;
continuous control using a PI controller and, eventually, the heterogeneous control.
The last control is necessary when the loads are under a speci ed threshold and the

control should be of 0/1 type. All these solutions could be similarly applied in the
cases presented for the control of the Stirling engine.

5.1.2 The Higher Level of the Hierarchical Control System

The fundamental objective of this level is to control the temperature inside the
building. In modern control systems of buildings an optimal control structure is
implemented, in relation to a criterion that provides a trade off between quality
requirement regarding the thermal comfort and energy saving requirement.