In the previous lecture, we discussed key parameters such as the maximum input current, maximum short-circuit current, and rated input voltage of inverters. In this session, we will focus on three critical control dimensions in photovoltaic system design: start-up voltage, MPPT (Maximum Power Point Tracking) operating voltage range, the number of MPPTs, and maximum input channels. These parameters not only dictate the dynamic response characteristics of inverters under complex operating conditions, but also directly impact the energy conversion efficiency of PV arrays and the overall system investment returns. Let’s unravel them one by one.

1. Start-up Voltage

Definition: It refers to the threshold at which an inverter establishes its operational power supply. The inverter initiates operation when the PV voltage exceeds this start-up threshold and shuts down when the voltage falls below it.

During the start-up process of the plant, it is critical to ensure that the output voltage of the PV string meets the inverter’s start-up voltage requirement; otherwise, the inverter will fail to activate. Consequently, system design must account for local environmental factors such as solar irradiance intensity and ambient temperature when the sun rises in the local area. And the PV modules should be reasonably selected and configured to guarantee prompt inverter activation post-sunrise, thereby optimizing system efficiency.

2. MPPT operating voltage range

Definition: It refers to the operational voltage range of PV strings within which the inverter is capable of effectively performing maximum power point tracking.

A wider MPPT voltage range enhances the inverter’s adaptability to varying irradiance conditions and module configurations, enabling more precise tracking of the PV module’s maximum power point (MPP) across diverse environmental scenarios, thereby optimizing energy yield. During power plant design, selecting inverters with appropriate MPPT voltage ranges based on local irradiance profiles and PV module characteristics or optimizing string configuration (series quantity and module type) to align the PV string’s operating voltage within the inverter’s MPPT range can significantly improve annual energy harvesting potential.

3. The number of MPPTs & Maximum input channels

Definition: Maximum Input Channels refers to the number of DC input circuits supported by an inverter, typically indicating the maximum allowable PV string connections. The number of MPPTs refers to the number of channels in the inverter that perform Maximum Power Point Tracking.

The varying combinations of maximum input channels and the number of MPPTs significantly influence inverter cost, performance, and reliability. Generally, increasing the number of MPPT channels enhances the inverter’s control precision and adaptability to heterogeneous PV array configurations, enabling compatibility with diverse plant layouts. However, this also escalates system complexity and component costs. During plant design, it is necessary to comprehensively consider and select an inverter with an appropriate number of input channels and MPPT channels based on factors such as array scale, spatial constraints, and budget, so as to achieve optimal cost-effectiveness and sustained system performance.