# Performance Validation of Control Algorithm Considering Independent Generator Torque Control in PCS
## 2 Wind Turbine and Control Algorithm
### Control Algorithm
#### 2.2.2 Mode Switching Logic  
The control transition logic uses the current operating state of the wind turbine to determine and decide on the appropriate control mode. The mode switch applied in previous studies utilizes feedback from the rated power, measured generator power, rated generator speed, measured generator speed, fine pitch angle, and measured pitch angle to assess the control mode [13]. Figure 4 shows the structure of the mode switch. The S-R flip-flop logic circuit receives an input signal of 0 or 1, determined by the operating state of the wind turbine, and generates an output signal of 0 or 1 based on the truth table presented in Table 2. The output signal passes through a NOT logic gate and is output as the final value of the mode switch, where 0 corresponds to Region II and 1 corresponds to Region III, thus contributing to the execution of control based on these operating regions. However, the mode switch has limitations, as it causes a sudden decrease in generator torque and  
Figure 3: Structure of the pitch PI control algorithm [13]. Figure 2: Overall schematic of the power control algorithm considering the PCS torque control. generator power at the moment of transition from pitch control to torque control. Although the application of the PCS torque control alleviates the tendency for a sudden decrease in generator torque and power, it still shows a persistent tendency for reduction across the entire operational range. To overcome these limitations, the previously proposed Set Point Smoother (SPS) was modified and applied [29], and the design process excluded torque control, focusing solely on pitch control. Equation (1) shows the formula for calculating the change in the generator speed used in the design of the SPS, utilizing the rated generator torque, measured generator torque, gain value, and rated generator speed as inputs. The change in the generator speed is used to calculate the error value for the pitch PI control. Typically, the error applied in the pitch PI control is calculated as the difference between the rated generator speed and the measured generator speed. However, by adding the change in the generator speed to the error calculation term, the error value can be altered, thereby changing the pitch control commands. Figure 5 illustrates the overall schematic of the power control algorithm with the modified control transition logic applied. Equation (2) presents the formula for error calculation, and the structure of the pitch PI control is modified and applied as shown in Figures 3 and 6. \[\Delta\Omega_{g}=\frac{T_{g}-T_{g,\ rated}}{T_{g,\ rated}}k_{T}\Omega_{g,\ rated} \tag{1}\]  
\[\Omega_{g,\ error}=\Omega_{g}-\Omega_{g,\ rated}+\Delta\Omega_{g} \tag{2}\]  
When considering the operating area of Region II, the measured generator torque is always lower than the rated generator torque, resulting in the generator speed change being negative. In this case, according to Equation (1), the generator speed error value increases in the negative direction, and the pitch PI control generates a negative pitch command to overcome this error. However, the blade pitch angle has a minimum pitch angle limit (low limit) of \(-0.8\) degrees, meaning that a command of \(-0.8\) degrees is always sent to the blade pitch actuator controller. When considering the operating area of Region II-1/2, the generator speed change remains negative, but as conditions approach the rated state, its absolute value becomes very small. At this point, when combined with the rated generator speed in Equation (2), the pitch control operating point is adjusted, allowing the command to be generated and sent in a direction biased toward the dominant direction at each moment. This enables the pitch control and torque control to operate smoothly  
Figure 4: Structure of the mode switch [13].