5.2. Fundamental performance

Key operation waveforms and power conversion efficiency were measured using the experimental setup shown in Figure 11. All substrings were removed, and the DPP converter was

Figure 10. Photograph of the 30-W prototype.


Table 1. Circuit element list.

Figure 11. Experimental setup for waveform and efficiency measurement.

powered by an external power supply Vext. A variable resistor Rvar was connected to Cout1 in order to emulate current flow directions under the PV1-shaded condition shown in Figure 8.

light load region, the DPP converter operated in DCM and its efficiency was around 90%. The heavy load region corresponded to CCM, in which the efficiency gradually declined due to the

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Solar array simulators (E4361A, Keysight Technologies) were used to emulate shaded and unshaded PV substring characteristics, as shown in Figure 14(a). The short circuit current of the shaded substring PV1 was set to be half that of unshaded substrings. String characteristics as a whole were manually swept using an electronic load operating in the resistance mode. The

Figure 14. (a) Individual PV substring characteristics and (b) string characteristics with and without DPP converter.

increased Joule loss.

Figure 13. Measured power conversion efficiency.

5.3. Laboratory testing

The measured key operation waveforms in DCM are shown in Figure 12. Although oscillations due to the resonance between the output capacitance of the MOSFET and Lmg were observed in vQ and vVM, the measured waveforms matched well with the theoretical ones shown in Figure 7. The measured power conversion efficiency is shown in Figure 13. In the

Figure 12. Measured key operation waveforms when PV1 is partially shaded.

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Figure 13. Measured power conversion efficiency.

light load region, the DPP converter operated in DCM and its efficiency was around 90%. The heavy load region corresponded to CCM, in which the efficiency gradually declined due to the increased Joule loss.

#### 5.3. Laboratory testing

powered by an external power supply Vext. A variable resistor Rvar was connected to Cout1 in order to emulate current flow directions under the PV1-shaded condition shown in Figure 8. The measured key operation waveforms in DCM are shown in Figure 12. Although oscillations due to the resonance between the output capacitance of the MOSFET and Lmg were observed in vQ and vVM, the measured waveforms matched well with the theoretical ones shown in Figure 7. The measured power conversion efficiency is shown in Figure 13. In the

Figure 11. Experimental setup for waveform and efficiency measurement.

142 Solar Panels and Photovoltaic Materials

Figure 12. Measured key operation waveforms when PV1 is partially shaded.

Solar array simulators (E4361A, Keysight Technologies) were used to emulate shaded and unshaded PV substring characteristics, as shown in Figure 14(a). The short circuit current of the shaded substring PV1 was set to be half that of unshaded substrings. String characteristics as a whole were manually swept using an electronic load operating in the resistance mode. The

Figure 14. (a) Individual PV substring characteristics and (b) string characteristics with and without DPP converter.

ΔV-controlled equalization with ΔVref = 1.0 V was implemented. As a reference, the string characteristic without the proposed DPP converter was also measured.

Measured string characteristics with and without the DPP converter are shown and compared in Figure 14(b). Without the DPP converter, two MPPs were observed, and the maximum power was merely 110 W at Vstring = 23.6 V. With the proposed DPP converter, on the other hand, the local MPP disappeared, and maximum power increased to as high as 130 W at Vstring = 34.0 V, corresponding to 18.2% improvement. Thus, the experimental results demonstrated the proposed DPP converter drastically increases the power yield from a partially shaded string.

The prototype of the proposed DPP converter was operated in conjunction with a commercial MPPT converter (SS-MPPT-15 L, Morningstar) to demonstrate its compatibility. The measured Vstring and extracted power are shown in Figure 15. The MPPT converter periodically swept the string characteristic in search for the global MPP location and subsequently kept extracting the maximum power of approximately 130 W.

#### 5.4. Field testing

The field test using a real PV panel was also performed emulating a partial shading condition, as shown in Figure 16. A standard 72-cell monocrystalline PV panel was used for the experiment, and one of the substrings was covered with a postcard to emulate a partial shading condition. The irradiance in the field test was measured using a pyranometer. The measured string characteristics with and without the proposed DPP converter prototype are shown in Figure 17. Without the DPP converter, two power maxima were observed, and the extractable maximum power was approximately 39 W at the irradiance level of 372 W/m<sup>2</sup> . With the DPP converter, the maximum power increased to as high as 46.1 W, in spite of the lower irradiance level of 356 W/m<sup>2</sup> .

6. Conclusions

Figure 16. Field test setup.

The single-switch DPP PWM converter to preclude the partial shading issues has been proposed in this chapter. The proposed DPP converter can be derived by integrating the FFRI and VM into a single unit. The switch count of the proposed DPP converter is only one, thus achieving the simplified circuit. The operation analysis was performed, and the voltage con-

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version ratios in DCM and CCM were mathematically yielded.

Figure 17. String characteristics with and without DPP converter in the field test.

Figure 15. Measured power conversion efficiency.

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Figure 16. Field test setup.

ΔV-controlled equalization with ΔVref = 1.0 V was implemented. As a reference, the string

Measured string characteristics with and without the DPP converter are shown and compared in Figure 14(b). Without the DPP converter, two MPPs were observed, and the maximum power was merely 110 W at Vstring = 23.6 V. With the proposed DPP converter, on the other hand, the local MPP disappeared, and maximum power increased to as high as 130 W at Vstring = 34.0 V, corresponding to 18.2% improvement. Thus, the experimental results demonstrated the proposed DPP converter drastically increases the power yield from a partially

The prototype of the proposed DPP converter was operated in conjunction with a commercial MPPT converter (SS-MPPT-15 L, Morningstar) to demonstrate its compatibility. The measured Vstring and extracted power are shown in Figure 15. The MPPT converter periodically swept the string characteristic in search for the global MPP location and subsequently kept extracting the

The field test using a real PV panel was also performed emulating a partial shading condition, as shown in Figure 16. A standard 72-cell monocrystalline PV panel was used for the experiment, and one of the substrings was covered with a postcard to emulate a partial shading condition. The irradiance in the field test was measured using a pyranometer. The measured string characteristics with and without the proposed DPP converter prototype are shown in Figure 17. Without the DPP converter, two power maxima were observed, and the extractable

converter, the maximum power increased to as high as 46.1 W, in spite of the lower irradiance

. With the DPP

maximum power was approximately 39 W at the irradiance level of 372 W/m<sup>2</sup>

characteristic without the proposed DPP converter was also measured.

shaded string.

144 Solar Panels and Photovoltaic Materials

5.4. Field testing

level of 356 W/m<sup>2</sup>

.

Figure 15. Measured power conversion efficiency.

maximum power of approximately 130 W.

Figure 17. String characteristics with and without DPP converter in the field test.

#### 6. Conclusions

The single-switch DPP PWM converter to preclude the partial shading issues has been proposed in this chapter. The proposed DPP converter can be derived by integrating the FFRI and VM into a single unit. The switch count of the proposed DPP converter is only one, thus achieving the simplified circuit. The operation analysis was performed, and the voltage conversion ratios in DCM and CCM were mathematically yielded.

The 30-W prototype of the proposed DPP converter was built, and its fundamental operation performance was measured. Experimental equalization tests emulating partial shading conditions were performed using solar array simulators or a real PV panel. With the prototype of the proposed DPP converter, local MPPs disappeared, and extractable maximum powers significantly increased, demonstrating the efficacy and performance of the proposed DPP converter.

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