# Power Management Strategy for an Autonomous DC Microgrid
## 4 Experimental Tests  
Three tests of the proposed power management system are carried out over three different weather profiles, making it possible to show all nine possible cases. To compare fuel cost and fuel consumption with the power management strategy presented in Reference [27], in which the DG cost is not considered, case 9 presented in Figure 3 is changed to a simple load-following mode, i.e., producing the same amount of power as load demand, while not recharging the electrochemical battery bank and the SC. To simplify this comparison, a PV source emulator following three real MPPT generation profiles is used instead of a real PV system; these profiles were recorded at Compiegne in France during our previous work. Moreover, it is notable that a simple and arbitrary load power demand profile is considered in this study. To illustrate and prove the effectiveness of the proposed power management strategy, an experimental platform is set up, as illustrated in Figure 4.  
All the algorithms were programmed in MATLAB/Simulink and implemented in the dSPACE 1006 real-time control system. The rated DC bus voltage was chosen as 400 V according to Reference [29]. Regarding the SC self-discharging, the average self-discharging current was fitted to be 0.03 A, according to the curve given in Figure 2. The parameters of the DC microgrid components, of which more details can be found in the published paper [27], are listed in Table 1, and the considered values of imposed constraints are given in Table 2. Each DC source is connected to a DC/DC reversible Boost converter so as to interface with the 400 V DC bus, and the DG is connected to an active full bridge rectifier. All the converters are commanded by a classical PWM controller at a frequency of 12 kHz.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Components** & **Parameters** \\ \hline PV source emulator & 2 kW under STC \\ Lead-Acid Battery bank & 96 V/130 Ah \\ DG fixed speed SDMO Technic 6500 E AVR & 5.2 kW rated \\ Minimal DG power generation & 2 kW \\ SC Maxwell modules BMOD0094 P075 B02 & 94 F/75 V \\ DC load emulator & 2.6 kW \\ \hline \hline \end{tabular}
\end{table}
Table 1: Components for the microgrid system.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline \(SOC_{B\_MAX}\) & 60\% & \(SOC_{SC\_MAX\_MAX}\) & 90\% \\ \(SOC_{B\_MIN}\) & 40\% & \(SOC_{SC\_MAX\_MIN}\) & 85\% \\ \(P_{B\_MAX}\) & 1 kW & \(SOC_{SC\_MIN\_MAX}\) & 50\% \\ \(P_{B\_MIN}\) & \(-1\) kW & \(SOC_{SC\_MIN\_MIN}\) & 45\% \\ \(v_{DCref}\) & 400 V & \(D\) & 1 h \\ \hline \hline \end{tabular}
\end{table}
Table 2: Arbitrary values and constraints.  
Figure 4: Autonomous DC microgrid experimental platform.  
In addition, it was assumed that 20% of load power is non-critical and can be shed and the other 80% is uninterruptable and its supply should be guaranteed by the DG. Regarding the DG, a one-hour duty-cycle was proposed as a good trade-off between fuel consumption and start-up frequency. Given that the electrochemical battery bank's capacity was too great for the power level of the installed system, in order to observe all the cases, \(SOC_{B}\) was limited to within a narrow range. Similarly, the electrochemical battery bank's power was limited at the same power level as the PV source. In addition, SC power was not limited, but the same amount of power could cause great current in the case of low SC voltage, which can be harmful to the experimental equipment. Thus, the lower bound of \(SOC_{SC}\) was limited to a minimum of 45%, since it was quadratically proportional to the SC voltage.  
Depending on the weather day profile, the three chosen days represented three types of solar irradiance: Mixed high irradiance with strong fluctuations and low solar irradiance without fluctuations (Test 1, 8 July 2016); high solar irradiance with strong fluctuations (Test 2, 9 July 2016); and high solar irradiance almost without fluctuations (Test 3, 10 July 2016).