ELEC5206 Chap.4 Classifying PV Power System Architectures
Classifying PV Power System Architectures
This lecture organises grid-tied PV systems by where maximum power point tracking and power electronics are applied. After the conventional labels of site, grid connection and capacity, and the requirements a grid-tied inverter must meet, it introduces centralised MPPT, with one inverter for a subarray or array, and distributed MPPT at string, module, submodule or cell level.
Partial shading and module mismatch motivate the distinction: a series string forces one current through every module, so a shaded module creates a multi-peak power curve and losses that a single tracker cannot recover. The chapter compares microinverters, module DC/DC converters in parallel or series, and submodule converters inside the junction box, and closes with the cost and robustness trade-offs between them.
The chapter also explains why many countries no longer require grounded PV, which favours transformerless single-stage inverters, and why series module converters are efficient but vulnerable to a single failure while parallel ones are robust but need a high step-up ratio.
What this chapter covers
- 01
Classification by site, grid connection and capacity
- 02
Basic and grid-support requirements for grid-tied inverters
- 03
Single-stage and double-stage centralised inverters, with or without isolation
- 04
MPPT granularity: centralised versus distributed tracking
- 05
Module mismatch, tolerance and partial shading
- 06
The two-peak curve and the split between direct and series losses
- 07
Module-level options: microinverter, parallel DC/DC and series DC/DC
- 08
Submodule and cell-level converters
Worked example · free
Classifying three rooftop layouts
- 1(a) Centralised MPPT: simple and cheap, but it assumes identical modules, so mismatch and shading cost power.
- 1(b) Distributed MPPT at module level with parallel microinverters: robust and modular, but high step-up conversion is hard to make efficient.
- 1(c) Distributed MPPT at submodule level with series outputs: cheap low-voltage parts in the junction box, but a single failure breaks the string.
Key terms
- Centralised MPPT
- A system in which tracking and power electronics act only at subarray or array level, in one central inverter.
- Distributed MPPT
- A system in which tracking and power electronics act at string, module, submodule or cell level.
- Microinverter
- A module-integrated parallel inverter that converts one module's DC output directly to grid AC.
- Power tolerance
- The manufacturer's stated spread of module power around the rating, for example plus or minus 1%.
- Galvanic isolation
- Transformer separation between the PV array and the grid, allowing a DC terminal and the AC neutral to share earth.
- Anti-islanding protection
- A basic grid requirement that stops the inverter energising a disconnected section of network.
Classifying PV Power System Architectures FAQ
Why does a single shaded module affect the whole string?
Series connection forces one current through every module. When the shaded module's photocurrent falls below the string current, its bypass diode conducts or it limits the current, so the string curve develops two peaks and the healthy modules are held away from their own maximum power points.
Is a microinverter always better than a string inverter?
No. Module-level tracking recovers mismatch and shading losses and keeps working if one unit fails, but each unit must step a low module voltage up to grid level efficiently, and the system costs more. On an unshaded roof of matched modules the advantage is small.
What are the capacity classes used in the lecture?
Small systems are up to 50 kW, intermediate systems run from 50 kW to 1 MW, and large systems are 1 MW and above. These labels sit alongside the site and grid-connection labels in the conventional classification, before the lecture introduces the granularity-based scheme.
Why might a grid authority require transformer isolation?
Isolation separates the PV array galvanically from the network, so one DC terminal and the AC neutral can share the same earth ground. Where grounded PV is no longer required, the transformer only adds cost and loss, which is why many modern systems use a single-stage transformerless inverter instead.
Exam move
Draw the granularity ladder from array down to cell and write one product example and one trade-off on each rung. Practise splitting a shading loss into its direct and series parts with numbers of your own, since that is the only calculation in the topic.
Then rehearse two comparison answers: centralised versus distributed tracking, and series versus parallel module converters, each ending with a recommendation for a named roof. Learn one industry example per module-level option, because comparison answers improve with a concrete product.
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