## 2 Analysis of the Operating Mechanism of a Hybrid Plant Station Primary Frequency Regulation
### Multi-Energy Cooperative Frequency Regulation Control Strategy Based on the EEMD Algorithm  
Based on the EEMD algorithm, this chapter researches the control strategy of the P2H device and SCESS, the multi-energy cooperative frequency regulation control strategy of a hybrid plant station based on the EEMD algorithm proposed.  
Considering that the electric hydrogen production device is affected by its own operating status and dynamic characteristics, its control strategy is established as follows: when the system frequency drops, the compensated power of a hybrid plant station is \(P_{\text{WSP}}\), and the electric hydrogen production device cannot independently undertake the power command. Therefore, after the total frequency regulation power command \(P_{\text{WSP}}\) is processed by the EEMD algorithm, the electric hydrogen production device can assume the low-frequency power component \(P_{\text{P2H}}\). It is divided by the terminal voltage of the electric hydrogen production device \(U_{\text{el}}\) to obtain the current reference value \(I_{\text{elref}}\). \(I_{\text{elref}}\) subtracts the current \(I_{\text{el}}\) of the electric hydrogen production device and generates \(D_{\text{el}}\) through the PI link, which then generates a PWM wave and acts on the switching element to realize power control of the electric hydrogen production device. The supercapacitor absorbs/compensates the high-frequency components of the \(P_{\text{WSP}}\) processed by the EEMD algorithm. The high-frequency power component \(P_{\text{sc}}\) and the voltage \(U_{\text{sc}}\) of the supercapacitor are divided to obtain the current reference value \(I_{\text{scref}}\). After the subtraction of the \(I_{\text{scref}}\) and the feedback current \(I_{\text{sc}}\), the \(D_{\text{sc}}\) is generated through the PI link. Then, the PWM wave is generated to act on the switching element to realize the power control of the supercapacitor.  
Combined with the above control strategies for each unit of a hybrid plant station, a primary frequency regulation control strategy based on the EEMD algorithm of a hybrid plant station is established. The control flow chart is shown in Figure 6.  
Figure 5: Impact of different parameter values on the EEMD processing results.  
As shown in Figure 6, the change in load power causes the system frequency to change suddenly. The phase-locked loop first locks the angular velocity of the grid and then obtains the real-time value of the system frequency. The grid frequency has a reasonable fluctuation range, and 0.03 Hz is the system frequency regulation dead zone. Hybrid plant stations within this range do not participate in system frequency regulation. When the system frequency decreases, the control strategy of the hybrid power station is as follows: When a sudden increase in load causes a system power imbalance, the compensation power \(P_{\text{WSP}}\) required by the hybrid power station is calculated by Equation (7). This power command is used as the output signal of the EEMD algorithm. Frequency division processing Finally, an IMF component with a lower frequency is used as the power response signal (\(P_{\text{PZH}}\)) for electric hydrogen production. The power control link controls the electric hydrogen production unit load reduction in response to the system frequency regulation. The other high-frequency power components constitute the power response signal \(P_{\text{sc}}\) of the supercapacitor. Through the power control link of the supercapacitor, the supercapacitor is controlled to release power to realize power compensation quickly. The electric hydrogen production device and energy storage device cooperate to assist the frequency recovery of the system so that a hybrid plant station has the same frequency regulation capacity as the traditional power station.  
Figure 6: Control flow chart of the hybrid plant station.