Programmable photovoltaic submodules for hotspot mitigation

Figures & data

Figure 1. Four series-connected 120W PV modules (a) without and (b) with BPDs.

The current and voltage of four series-connected photovoltaic modules are measured. The Figure has two parts; the upper four photovoltaic modules do not have bypass diodes. The lower four photovoltaic modules have bypass diodes. The rating of each photovoltaic module is 120 Watts.

Table 1. Shading percentages with and without BPDs.

Shaded Modules	Shading Percentage for Each Module	Without BPDs – Pic 5–5	With BPDs
None	0%	Case A	Case AA
Module 1	25%	Case B	Case BB
Modules 1 & 2	50%	Case C	Case CC
Modules 1& 2 & 3	75%	Case D	Case DD

Figure 2. Current-voltage (I-V) curves of the PV system of Figure 1 (a) without and (b) with BPDs.

The figure has two subplots; the left subplot depicts four curves for the current-voltage characteristics of photovoltaic systems without bypass diodes, while the right subplot shows the same curves with bypass diodes. In both plots, the upper curve represents the photovoltaic modules without shading. The second curve represents the photovoltaic modules with 25 percent shading. The third curve represents the photovoltaic modules with 50 percent shading. The last curve (solid line) represents the photovoltaic modules with 75 percent shading.

Figure 3. Proposed model of the PV module. The switches are assigned to different names and disconnect or connect the PV submodules based on pulses received by the microcontroller unit (or by a MATLAB code in the simulation). Each submodule comprises nine series-connected cells.

The four Photovoltaic submodules are represented by submodule 1 to submodule 4. The switches are presented and controlled by MATLAB built-in pulse functions. The radiation level is 1000 W/m2. The current and the voltage of the whole photovoltaic system are tracked for different scenarios.

Figure 4. Structure of the proposed system. The actuators in the controlling unit control the mode of the PV submodules’ connection.

The controlling unit in the upper left box is the central processing unit that controls the actuators (shown in the adjacent box) to switch on/off the internal connections of the PV submodules. This controller unit processes the desired and measured voltage and current readings (shown in the lower box) to choose the most suitable connections for the PV submodules.

Figure 5. (A) Designed and (b) assembled versions of the manufactured printed circuit board for the proposed system.

The upper circuit illustrates the printed circuit board (PCB) developed to minimize the area needed for circuits’ components and their connections. The lower circuit illustrates the actual assembled printed circuit board. The designed PCB performs the same functionality as the experimental design with improved efficiency.

Table 2. Modes of Operation.

Mode	Ns (Series-Connected)	Np (Parallel-Connected)	Current	Voltage
Series	36	1	Lowest	Highest
Parallel	9	4	Highest	Lowest
Mixed	18	2	Moderate	Moderate

Figure 6. Assembled smart PV module as a) illustration and b) real system. The internal connections of the PV submodules are connected to the terminals of the PCB. The switches (transistors) receive pulses from the microcontroller to connect/disconnect the submodules as depicted in Table 3. The switches of the same notation are shown multiple of times just for illustration.

Thirty-six polycrystalline photovoltaic cells with blue color and a PCB with green color are integrated into the same module to control the internal connections of the PV submodules. These connections are represented by transistors.

Table 3. Modes of operation and the corresponding switches’ states.

Mode	Closed switches
(Series) Four submodules are connected in series	S1 and S4
(Parallel) Four submodules are connected in parallel	S1 and S2
(Mixed) Two parallel-connected submodules are connected in series with the other two parallel-connected submodules.	S2, S3, and S4

Table 4. PV submodule’s electrical parameters.

Parameter	Description	Value	Unit
Voc	Open-circuit voltage	5.8	V
Isc	Short-circuit current	9.8	A
Pmax	Maximum power	43.5	W
G	Solar irradiance	1000	W/m^2
Tc	Temperature	25	Degree Celsius

Figure 7. Current- and power-voltage characteristics of the conventional PV module without shading.

The figure has two subplots; the left subplot represents the current-voltage characteristics of the conventional photovoltaic module without shading, while the right subplot represents the power-voltage characteristics of the same conventional photovoltaic module without shading. The graphs indicate some points to show the open-circuit voltage, short-circuit current, and maximum power point values.

Figure 8. Current- and power-voltage characteristics of the smart PV module (series-connected mode) with fully shading one submodule (the upper two plots) and without shading the submodules (the lower two plots).

The figure has four subplots for the series-connected submodules; the upper-left subplot represents the current-voltage characteristics of the smart photovoltaic module with shading, while the upper-right subplot represents the power-voltage characteristics of the same photovoltaic module with shading. The lower-left subplot represents the current-voltage characteristics of the smart photovoltaic module without shading, while the lower-right subplot represents the power-voltage characteristics of the same photovoltaic module without shading. The graphs indicate some points to show the open-circuit voltage, short-circuit current, and maximum power point values.

Figure 9. Current- and power-voltage characteristics of the smart PV module (parallel-connected mode) with fully shading one submodule (the upper two plots) and without shading the submodules (the lower two plots).

The figure has four subplots for the parallel-connected submodules; the upper-left subplot represents the current-voltage characteristics of the smart photovoltaic module with shading, while the upper-right subplot represents the power-voltage characteristics of the same photovoltaic module with shading. The lower-left subplot represents the current-voltage characteristics of the smart photovoltaic module without shading, while the lower-right subplot represents the power-voltage characteristics of the same photovoltaic module without shading. The graphs indicate some points to show the open-circuit voltage, short-circuit current, and maximum power point values.

Figure 10. Current- and power-voltage characteristics of the smart PV module (mixed-connected mode) with fully shading one submodule (the upper two plots) and without shading the submodules (the lower two plots).

The figure has four subplots for the mixed-connected submodules; the upper-left subplot represents the current-voltage characteristics of the smart photovoltaic module with shading, while the upper-right subplot represents the power-voltage characteristics of the same photovoltaic module with shading. The lower-left subplot represents the current-voltage characteristics of the smart photovoltaic module without shading. In contrast, the lower-right subplot represents the power-voltage characteristics of the same photovoltaic module without shading. The graphs indicate some points to show the open-circuit voltage, short-circuit current, and maximum power point values.

Table 5. Conventional PV module’s parameters with and without shading conditions.

Parameter	Description	Measured Values			Unit
		Without shading	Shading one cell	Shading two cells
Voc	Open-circuit voltage	19.72	18.72	4.22	V
Isc	Short-circuit current	1.65	1.68	0.43	A
Pmax	Maximum power	12.75	7.03	18.90	W
Vmax	Voltage at maximum power	11.62	5.88	14.25	V
Imax	Current at maximum power	1.10	1.20	0.29	A

Table 6. Comparison between the parameters of each of the three modes according to different shading conditions.

	Measured Values
	Without shading			Shading one cell			Shading two cells
Parameter	Ser.	Par.	Mix.	Ser.	Par.	Mix.	Ser.	Par.	Mix.	Unit
Voc	17.59	4.64	9.41	14.46	4.67	NA	9.67	4.67	NA	V
Isc	1.18	4.78	2.49	1.20	3.64	NA	1.17	2.32	NA	A
Pmax	9.84	8.31	9.60	7.67	6.25	NA	4.60	3.89	NA	W
Vmax	12.1	2.78	5.97	9.29	2.80	NA	5.98	2.82	NA	V
Imax	0.81	2.99	1.61	0.82	2.24	NA	0.76	1.43	NA	A