# Review of Recent Type-2 Fuzzy Controller Applications
## 3 Review of IT2 FLSs
### Power Management and Electrical Control  
An energy management system was also controlled using an IT2 FLC [74]. In this application, a hybrid electrical vehicle was tested, which managed three sources of power: batteries, super-capacitors and the fuel cell system. The inputs of the FLC were vehicle speed, reference power, battery power, super-capacitor system power, fuel cell system power, battery voltage, battery state-of-charge and super-capacitor state-of-charge. The system was evaluated using a computer simulation, and it was shown that FL energy management was able to fulfill the energy requirements of the vehicle. This controller was tested using an actual heavy duty vehicle [75]. The energy management system design was a result of using the knowledge of several experts. During the experimental validation of the IT2 FLCs, it was found that the controller was able to handle the energy management in hybrid electric vehicles. This paper did not cover the optimization of the IT2 FLC; therefore, it was determined that an IT2 FLC was not necessarily better than a T1 FLC. A T2 FLC was also designed for power systems [76]. For power systems, small magnitude changes and low frequency oscillations could occur. If this persists for long periods of time, this could lead to a loss of synchronization and possibly blackouts. This paper presents a power system stabilizer (PSS) based on a synergetic control approach. A T2 controller was designed that was found to suppress unwanted oscillations rapidly. The results indicated good performance and satisfactory dynamic behavior compared to the T1 controller. IT2 FLCs have also been used to control numerous electronic components for industrial power systems. In a paper by [PERSON] and [PERSON], a power system was improved by utilizing a thyristor controlled series capacitor (TCSC) [77]. Often, industrial generators are controlled by a PSS to improve the damping of multi-machine power systems. Unfortunately, there is a frequency range from (0.2 Hz to 1.0 Hz), which is not sufficiently damped using a PSS alone. Using a TCSC can however improve the damping of the power system if the parameters are optimized. Due to the dynamic operation of the power system, the IT2 FLC was proposed. In these conditions the controller was tested and managed to handle the non-linearity of the power system better than a fixed-gain tuned controller. It was also found that since the TCSC worked in parallel with the PSS, it was also able to damp small perturbations within the whole system. Power systems applications are a popular process to analyze IT2 FLCs. In a paper by [PERSON] _et al._, an IT2 FLC was designed for a TCSC [78]. This controller was developed to improve the damping of power system oscillations. Simulations were done to compare the effectiveness of particle swarm optimization (PSO), T1 FL and T2 FL. It was determined that the T2 FLC was more effective than the PSO and T1 FL methods. The robustness was tested using different operating conditions, various disturbances and with different parameter variations. Voltage regulation is also an issue, which can be improved using IT2 FLCs [79]. In this example, the controller was designed to regulate the voltage of a synchronous generator. The uncertainty stems from changing turbine outputs, loads and transmission line parameters. In order to maintain constant power, an exciter was connected to the generator. During the simulations, the IT2 FLC controller surpassed the performance of traditional PID controllers during the step response. Load frequency control (LFC) applications were also investigated for electrical power systems during their design and operation [80]. The FLC was applied to a two-area interconnected reheat thermal power system. Typically for these applications, a PI controller is used exclusively. When they are tuned, the gain is fixed, which can negatively affect the performance when there is a wide range of operating conditions.