Hybrid AC/DC microgrids

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Problem 1
Figure 1 shows a hybrid AC/DC microgrids where the AC subgrid consists of three inverter-coupled DERs and three constant-impedance loads, and the DC subgrid consists of three DC/DC converter coupled DERs and three constant-resistance load. The AC/DC subgrids are coupled by interlinking-converters (IC).

Figure 1 Topology of a hybrid AC/DC microgrid.
The AC/DC inverter is governed with the following droop characteristics:
(1)
(2)
where fmaxi, Emaxi, fi, Ei, Dpi, Dqi, Pac_i, and Qac_i are the maximum allowable frequency and voltage; actual output frequency, voltage, active/reactive droop coefficients, actual active power output, and reactive power output of the i-th AC DER, respectively. Vmaxj, Vj, rj, and Pdc_j are the maximum allowable voltage, actual output voltage, DC droop coefficient and actual output power of the j-th DC DER, respectively.
The IC is governed with the following bidirectional droop characteristics:
(3)
(4)
where fpu is the normalized AC bus frequencies. Vpu is the normalized DC bus voltages. kf and kv are sensitivity coefficients to AC frequency and DC voltage, respectively. GPI(t) is the primary PI unit to equalize fpu and Vpu. Qref is set to zero since there is no reactive power in DC sub-grid.

The parameters for the operation of hybrid microgrids are set as below:
• Frequency set-points of AC MG are: f1,n = 50 Hz, f1,max = 50.5 Hz, f1,min = 49.5 Hz.
• Frequency set-points of DC MG are: Vdc,n = 800 V, Vdc, max = 840 V, Vdc,min = 760 V.
Besides the primary control, the division control is applied to the hybrid AC/DC microgrid (note that the division control mode can be activated by the step signal applied to the secondary control switch). Individual AC/DC subgrids in division mode have the capability of operating as self-controlled entities with different operating objectives by utilizing their local sparse communication networks.
In each simulation case, we assume an AC load (i.e., Load 2 in the simulation model) is suddenly connected/disconnected to the AC subgrid at t = 3.0s and t = 6.0s. Subsequently, a DC load is suddenly connected to the DC subgrid at t =9.0s, and the IC enables real power exchanges.
Provide a plot with the time axis from 1-12 s in each simulation case, including the following four subplots (each subplot should include a title, axes labels and units): power generation of each AC/DC DER (kW); operating frequency of the AC subgrid (Hz); operating voltage of the DC subgrid (V); real power exchange enabled by IC (kW). Based on the simulation results,
Discuss the impact of division control scheme on the power sharing performance of the AC/DC subgrids by (in)activating the step signal for the secondary control switch.
Discuss the effect of the following droop coefficients kf and kv of IC on the division operation of hybrid AC/DC microgrids,
1) Case 1:
2) Case 2:
3) Case 3:
4) Case 4:

Problem 2:
Conduct a MATLAB/Simulink simulation for a hybrid AC/DC microgrid in the unification control mode based on the attached. mdl files. At t = 3.0s and t = 6.0s, a AC load is suddenly connected/disconnected to the AC subgrid. At t = 9.0s, a DC load is suddenly connected to the DC subgrid. The unification scheme is applied to the active power sharing and the operating frequency in the hybrid system;
In MATLAB/Simulink, the following two cases are to be simulated:
1) Case 1: hybrid AC/DC microgrid operates in unification mode.
2) Case 2: hybrid AC/DC microgrid operates in unification mode at t=4s, when the AC DER1 outage occurs.
Provide a plot with the time axis from 1-12s in each simulation case, including the following four subplots (each subplot should include a title, axes labels and units): power generation of each AC/DC DER (kW); operating frequency measured at the AC terminal of the IC (Hz); voltage magnitude measured at the DC terminal of the IC (V); real power exchange enabled by the IC (kW).
Based on the simulation results, discuss the effects of DER outage on the operation of hybrid AC/DC microgrids in unification mode.

 

 

Sample Solution

ow” information, Mary is able to recognize and remember the color red. If the Ability Hypothesis is true, Mary gains the ability to remember the experience of seeing red. After experiencing red for the first time, you can remember the experience, and therefore imagine the recreation of seeing red. Lewis also argues that another important ability gained is t`he ability to recognize. If Mary sees the color red again, she will recognize it immediately. Lewis uses the example of Vegemite. If you taste Vegemite at a later time, you will remember (or recognize) you have tasted it in the past. From this, you will be able to put a name to the taste experience. Lewis also argues that these abilities could originate from essentially anywhere – even magic. His main point is that experience, not lessons, is the best method of learning what a new experience is like. Overall, Lewis agrees that knowledge is gained from experiencing red, but believes the knowledge gained is “know-how” information, which is phenomenal, and therefore physicalism is valid. Lewis argues that information and ability are different physical knowledges – this is why physicalism can be true and consistent with the conclusion that Mary gains new knowledge. It is important to consider Lewis’ anti-qualia argument. Although the Ability Hypothesis may seem persuasive to David Lewis, there are several weaknesses. First, when we are shown an unfamiliar color, we actually do learn information about its relative properties compared to other colors (i.e. similarities and compatibilities). For example, we are able to evaluate how red is similar to orange and how it is different. We also learn its impact on our mental states. Physicalism overestimates human cognitive abilities. We have over a million neurons in our brain, and we are nowhere near to gaining a comprehensive view of human cognitive abilities. As any cognitive science major (such as me) knows, understanding what each and every neuron in our brain does is, at a minimum, a long way off. Yet, physicalism assumes we have the power to fully articulate all elements of the world around us and the complexity of our environment. This is not supportable and is a major flaw in his argument. Both Lewis and Jackson agree that some things cannot be learned in a black and white room. The weakness of Lewis’ argument is that he fails to acknowledge the cognitive differences between us and those who do not share similar obdurate mental states. Despite this weakness, there are some strengths for Lewis’ materialistic argument. Lewis removes the inability to assure the non-physical exists. Because he emphasizes the learning of abilities rather than new experiences, his theory relies on the physical and validates that physicalism could be correct. His opponents, dualists, believe that mind and body are separate entities, which is anti-physical. The largest problem with dualis

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