In previous editions, we discussed two critical indicators on the PV side of an inverter: the maximum over-sizing ratio and the maximum PV input voltage. Now, we will take a deep dive into the remaining parameters on the PV side, analyzing them one by one. Understanding these parameters is crucial as they directly impact the selection of PV modules, system reliability and safety, and overall efficiency. During power plant design phase, each parameter must be carefully evaluated to ensure stable system operation and optimal power generation.

1. Maximum Input Current

Definition: The maximum operating current allowed to pass through the PV side of an inverter.

The input current is especially critical in scenarios with high peak power currents, such as those involving thin-film PV modules. When selecting an inverter, it is essential to ensure that its maximum DC current specification meets the requirements of thin-film modules. The current of each MPPT-connected PV string should remain below the inverter’s DC current limit to prevent overcurrent damage. Additionally, the current variation of PV modules during real-world operation must be taken into account. The inverter’s DC input current should always stay within its maximum limit. If the PV module’s output current exceeds this limit, it may lead to current-limited operation and potential inverter damage, reducing power generation efficiency and return on investment.

Note: Inverter specifications typically indicate the MPPT working current rather than the input current of a single PV string. When connecting multiple PV strings to a single MPPT, ensure that: Number of strings * Maximum output current per string < Maximum input current allowed by a single MPPT.

 2.Maximum Short-Circuit Current

Definition: The maximum short-circuit current that the inverter’s DC input can withstand.

When a short circuit occurs at the output of a PV panel, it generates a large short-circuit current. If this current exceeds the maximum short-circuit current that the inverter can handle, the inverter may suffer damage. The maximum short-circuit current that an inverter can handle is primarily determined by factors such as design parameters, internal circuit structure, and component durability.

Reminder: When selecting PV modules, ensure that their short-circuit current does not exceed the inverter’s maximum short-circuit current rating. Before designing the system, adjust the number or configuration of PV modules according to the rated short-circuit current of the PV panels and the inverter’s maximum short-circuit current. If the selected module’s short-circuit current is too high, the inverter may malfunction or even be damaged. Conversely, if the short-circuit current is too low, the inverter may not operate at full conversion capacity, reducing the system’s overall power generation efficiency.

 3.Rated Input Voltage

Definition: The recommended operating voltage of PV modules in series (MPP voltage).

When the input current requirement is met, the PV system achieves its highest efficiency when operating at the rated voltage. If the PV input voltage is too low, power loss in the inverter’s boost circuit increases. If the PV input voltage is too high, it can cause power losses in the inverter control circuit and may also trigger frequent system alarms, especially in low temperatures when PV voltage rises beyond safe limits. Therefore, when designing the power station, PV modules should be configured to operate at the rated input voltage while considering actual solar irradiance conditions and the electrical characteristics of the PV modules to maximize system efficiency.