Parallel operation of solar inverters refers to a technical configuration in which the AC output terminals of multiple inverters are connected to a common grid busbar, while their DC inputs are connected to separate photovoltaic (PV) strings, enabling them to supply power in a coordinated manner.
Core Objectives
1. Capacity Expansion: Since individual inverters have limited power ratings (typically 8–15 kW for residential units and 50–255 kW for commercial units), parallel connection allows for the development of megawatt-scale power plants-for example, ten 100 kW inverters connected in parallel can achieve a 1 MW output.
2. Enhanced Reliability: In the event of a single unit failure, the remaining inverters can continue to generate 70%–90% of the system's total power, preventing a complete system shutdown.
Key Technical Requirements
1. Synchronization Control: The output voltage, frequency, and phase must be perfectly synchronized (voltage deviation <1%, phase difference <1°). Failure to do so results in circulating current losses (which, in severe cases, can exceed the rated current by 20%).
2. Current Sharing (Load Balancing): Each inverter must distribute the load proportionally based on its capacity, with deviations kept below 5% to prevent individual units from becoming overloaded and experiencing a reduced service life.
Implementation Methods
1. Centralized Parallel Connection: Typically used for large-scale ground-mounted power plants, where the AC outputs of multiple inverters are integrated via an AC combiner box.
2. String-based Parallel Connection: A common solution for commercial and industrial rooftops; each inverter is connected to its own PV strings, with coordination achieved through dedicated communication lines between the units.
3. Micro-inverter Parallel Connection: These units feature built-in parallel functionality for "plug-and-play" operation, though they come at a higher cost.
Essential Equipment Support
It is necessary to select inverter models explicitly designed for parallel operation (such as the Huawei SUN2000 series or the GoodWe MT series) and to incorporate a synchronization controller or an energy management system (EMS) to facilitate real-time regulation. V. Practical Application Data
Taking a 100kW commercial system as an example:
- Single 100kW inverter: Power generation drops to zero in the event of a failure.
- Five 20kW units in parallel: Power generation remains above 80% if one unit fails.
- While the initial cost of a parallel system is approximately 15% higher, the average availability increases from 97% to 99.5%.