Solar Optiverter – A Novel Hybrid Approach to the Photovoltaic Module Level Power Electronics

ABSTRACT

 In this paper the concept of an Optiverter is proposed as a novel class of photovoltaic (PV) module level power electronics systems. Functionally, the Optiverter is a hybrid technology that combines the ultrawide maximum power point tracking (MPPT) voltage window of the PV power optimizers with the direct AC connectivity and inherent safety of the PV microinverters. Thanks to the advanced multimode control with variable DC-link and the shade-tolerant MPPT algorithm, the proposed Optiverter ensures efficient energy harvest from the PV module in different shading scenarios. To justify the superiority of the concept, the performance of a 300 W prototype of the PV Optiverter was experimentally compared to that of the industrial microinverters in different operation conditions, including an extreme case with opaque shading of two out of three substrings of the PV module.

INDEX TERMS

1.      Photovoltaic systems

2.      Module-level power electronics

3.      Microinverter

4.      Power optimizer

5.      Maximum power point tracking

6.      Partial shading

7.      Efficiency

BLOCK DIAGRAM:

Fig. 1. Generalized schematics of MLPE based grid-connected PV systems: with PVPOs (a) and with PVMICs (b)

EXPECTED SIMULATION RESULTS:

Fig. 2. Voltage and current waveforms of the Optiverter operating with JinkoSolar JKM300M-60 PV module under uniform irradiance of 800 W/m2 and nominal cell temperature of 45 °C: input voltage and current (a), DC-link voltage and current (b), and grid voltage and current (c).

Fig. 3. Electromagnetic compatibility test results: conducted emission in the range of 0.15 MHz to 30 MHz (a) and radiated emission in the range of 30 MHz to 1000 MHz (b).

CONCLUSIONS

 The novel concept of the PV Optiverter with an ultra-wide input voltage range was proposed and justified as a shadetolerant solution for residential and small commercial PV installations, which is compatible with a wide variety of modern residential PV modules. It outperforms conventional microinverters under partial shading due to the implementation of the shade tolerant MPPT and can deliver power under severe opaque shading conditions, when the microinverters fail to capture any power due to their limited input voltage regulation range. Moreover, it is compatible with emerging high power PV modules due to increased power rating for avoiding the power clipping. These features result from the application of the galvanically isolated ultra-wide range buck-boost dc-dc converter and the novel control principle with the variable DC-link voltage that optimizes efficiency in the most probable input voltage operating range. This enables the shade tolerant MPPT through P-V curve scanning. Hence, the PV Optiverter can be used as a versatile solution for residential and small commercial PV installations. Using single stock keeping unit for different PV modules decreases installation and shipping costs as well as staff training expenses. The qZSSRC topology is not the only possible option to be used in the Optiverter and other DC-DC converter topologies with comparable performance could be applied. Also, Optiverter design for a wide input voltage range could impose limitations on the efficiency. However, improvements are possible at light load with cycle skipping modulation, and by use of reconfigurable rectifiers at high DC voltage gain.

REFERENCES

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