# Review of Power Electronics Technologies in the Integration of Renewable Energy Systems
## 1 Introduction
### Demands for PV Power Generation  
The photovoltaic effect permits solar energy to be directly captured by PV cells or panels, avoiding the need for a mechanical energy conversion stage, which is necessary in wind power systems. As a result, PV power systems often have lower operating requirements than wind power systems. However, far superior results and regulatory requirements have resulted from the rapid expansion of solar PV installations [25; 27; 56; 57]. As shown in Figure 4, these demands for PV power systems can be divided roughly into different groups. Side of the PV Panel: Achieving high energy usage and prolonging the system's lifespan requires optimizing energy harvesting and ensuring regular maintenance, such as PV panel monitoring, is performed. A DC-DC converter usually acts as the initial step to enhance the flexibility of PV inverters. **PV Power Conversion System Side:** PV panels continue to get cheaper, and the system-wide power capacity per generating unit is still reasonably priced. Therefore, it is crucial to consider ways to lower the total expenses while increasing the power converter efficiency. With their high efficiency and power density, transformer-less PV inverters at lower power levels present an acceptable alternative [28; 56]. However, in these systems, the parasitic capacitance between the PV panels [5; 80] and the ground creates a leakage current, which is a serious problem. This is addressed by grid codes such as those in [6; 29], which require that the leakage current be suppressed below predefined limitations (for example, the RMS value must be less than 300 mA) to protect both pieces of equipment. **Utility Grid Side:** As demonstrated in Figure 4, the requirements for PV systems have strengthened, with a particular emphasis on power quality, voltage, and frequency regulation and protection and recovery during exceptional grid voltage scenarios. In this case, the grid current's total harmonic distortion (THD) must be less than 5% [7; 12; 57]. Furthermore, because of their growing power capacity, PV systems require several grid support tasks that were previously solely necessary for wind power systems. IEEE Std. 1547-2018, updated as IEEE Std. 1547-2003 [5; 26; 30; 31; 58], specifies these as reactive power injection, frequency regulation, and low-voltage ride-through (LVRT) support tasks. **Requirements of Grid Integration:** The inherent uncertainty and unpredictability of wind and solar energy derives from the reliance on weather conditions. Renewable energy sources (RESs), such as wind and photovoltaic power systems, are required to contribute to the grid to lessen the intermittency effects [11]. Forecasting power production, changing promptly to changing operating and weather conditions, and establishing flexible power control skills are essential strategies. As is the case under high levels of renewable penetration, a sudden drop in grid voltage could cause an unplanned disconnection, compromising the equipment and system stability and possibly resulting in widespread outages. To overcome these difficulties, RESs must facilitate voltage and frequency regulation during fault ride-through operations. Voltage-reactive and frequency-active power regulation are examples of this [5; 57]. In particular, RESs may employ one of the reactive power regulation modes listed below while operating in low-voltage ride-through (LVRT) mode:* Mode of constant power factor;
* Active power-reactive power mode;
* Voltage-reactive power mode;
* Mode of constant reactive power [5]. Operators of transmission systems can also submit orders for reactive power injection to stabilize and support the grid voltage. The output of wind turbines spinning at lower power levels can be changed up or down to control the frequency flexibly [80]. This illustrates how wind turbines can use power modulation for improved grid frequency regulation.