Final Year Project (Week 19)

Week 19

Optimization the performance of ASHP by adding algorithm 

I have modified the optimum stare codes and integrated it into the original top level codes, which will call the optimum start file and output a revised SAP mat. Then the new SAP data will send to the ASHP & Radiator system and start the heating system as required. I have obtained two temperature plots from the heating system, one is original version of system and the other is system with optimum start algorithm.

                                                  (  The yearly energy needs 1.8043e+04 W)

                                              (  The yearly energy needs 1.9717e+04 W)
It can be seen that the temperature tracking is better when adding the optimum starter, which will reach the setting value on time. Even for the short required time period (2 hours), the temperature tracking performance has been improved a lot.
However, there will also exists a problem that comes with the optimum starter. When applying optimum starter, the heat pump will start running before the SAP setting time, which means the operation time will be longer than before. So the power consumption will improves a lot and this will affect the overall performance of system.
At the same time, the primary target of my project is to replace gas boiler heating system. The heat pump is more slow than gas boiler, so the heat pump must beat it on the aspect of power consumption.
There still exists another problem is that the value of COP is between 1.5 to 5, the range is too wide to acceptable, I prefer a range between 3 to 5. Meanwhile, the maximum value of heat pump output is beyond the typical value. Both of the problem will be analysis for later weeks.

Final Year Project (Week 18)

Week 18

Modification of the PDF controller

After another week of modification of the model, I find that the problem is not fix on the ASHP but the controller itself. The system can`t be stable if the controlled parameters' value change. So I finally decides use a constant value of both Kp and Ki.
Faced with the critical damping situation, the relation between "g" and "p" can be obtained, then the value of Kp and Ki could be calculated as well.

  ( Hence the value of g is set as 1/(3*300) )
The simulation results show that a better temperature tracking is obtained. The improvement is mainly focus on the oscillation, on the tracking plots is perfect smooth. However, for the period of the 2 hours, the room temperature can`t reach the target value as SAP required. The reason may due to the slow response and time constant of ASHP heating system.
In order to solve the problem, or at least to reduce the error range. One possible solution is to adding a optimum starter for the heating system. The optimum start algorithm will calculate a pre-start time based on the SAP requirement, so the heat pump will begin to operating before the SAP time point, in order to achieve the required temperature in advance or on time.

The simplest way is to operate the heat pump 3 times of time constant in advance. As for my project, I have modified a previous algorithm codes and its performance will be better than the plots shown above.

Final Year Project (Week 17)

Week 17

Debugging of the PDF controller

After a week of debugging and modification, the output (zone temperature) is finally around the target value (21 degree or 294 F). However, there always exists oscillation. Meanwhile, the temperature can`t achieve the target value when the SAP time period is short like 2 hours.

It is not easy to find the problem, because there many equations and connect with each other to form many loops. The reason may due to the calculation of COP or Max heat pump output, may due to the calculation of PDF control, may also due to the value setting of parameters within radiator system. Meanwhile, it`s hard to separate anyone cause while keeps others the same. 

After a meeting with my supervisor, he advises me to consider the model separately. Replacing the "ASHP & Radiator" block with an ideally transfer function, then try to find out the best suitable value of controlled value for Kp and Ki. After that, put the original "ASHP & Radiator" block back and find whether the problem is from controller or heat pump itself. I will use this method for the next week.  

Final Year Project (Week 16)

Week 16

Debugging of the PDF controller

A disappointed week, I have tried to modified the PDF controller in order to keep its stability. However, the tracking of temperature is so bad. The heating system can`t control the room temperature at 21 degree as SAP requirement. Meanwhile, when adding a filter after the transfer function, the control signal will exists large negative value.

I think my final year project has met a biggest problem, it acts like a bottleneck of the project. The next week I will continue to find method to solve the existing problem.

Final Year Project (Week 15)

Week 15

Implementation of PDF controller 

Last week, I have deduced the expression of h(x(t)), which could be used for the calculation of both Kp and Ki. So the task of this week is to implement it into Simulink and combine with previous heating system model, in order to complete the control system. The completed block can be referred as below:

The schedule is based on the equations that obtained last week. The output h(x(t)) will then connect to the PDF controller block, aimed to produce the value of both Kp and Ki for each time step (60 seconds).

However, the simulation results becomes worse when compared with the model without control system. The results is too strange to be explained. One possible reason is the value of controlled parameters change too fast, then the system can`t be stable. Another possible reason is that the integral will not stop when the heat pump limitation is met. So I tried to add an additional judgment block, which will set the integral controlled parameter to zero. The schedule is shown below even though the results indicated its useless.

Final Year Project (Week 14)

Week 14

Design the PDF controller based on ASHP & Radiator & IDEAS heating system 

The task for this week is to apply the PDF control theory for my heating system. Due to the complication of the 4th order system, there needs a simplification for system equations. There are 9 equations and could be combined with three differential equations for heat pump output, temperature of water and temperature of radiator respective.

However, this is not the simplest form, because the controller parameters' value can`t be obtained from these equations directly. After a series of complicated transform, substitution and calculations, a final equation is obtained as shown below:

 Where:

Then we can find out the expression of h(x(t)), which could be used to calculated the value of two control parameters:

Then the CB can be approximate as the way that shown below, meanwhile, the value of Kp and Ki can be deduced as a dynamic form. The next step is to implement this into Simulink model, analysis the simulation results. 

Final Year Project (Week 13)

Week 13

Design of PDF 

Due to the difference between PI control and PDF control, the design will not similar as what I learned before. In specific, the calculation of Kp and Ki could be explained as the notes shown below:

However, for the house model, the system time constant is very large and the closed loop transfer equation could be approximated to a more specific form. At the same time, the damping ratio could be presented, which is required to equal 1 for critical damping situation.

The theory that present above is based on a linear system. As for the 4th order heating system, the design method of PDF will be different, which is also a more general method. Hence, the value of "g" will be chosen as (1/3*tau), which means the controller time constant and is tightly relate to the SAP Responsivity. The next task is to find out the "CB", followed by designing a dynamic PDF controller for the heating system. It will be a great challenge.