## 1 Introduction  
Recently, the problems of shortage of fossil fuel sources and global warming effects have become more and more severe. People have begun to seek various possible solutions to those problems. One of the potential options is the use of sun energy, which not only provides an alternative energy source but also improves environmental pollution. Therefore, high concentration photovoltaics (HCPV) have attracted much attention in recent years, because of their high efficiency. HCPV systems require a solar tracker to generate power compared to conventional non-concentration photovoltaic systems. The solar tracker is the key component in the HCPV system to enable accurate and stable tracking. The Institute of Nuclear Energy Research (INER) has developed a HCPV high power generation system with III-V solar cells, as an alternative source to the application of solar photovoltaics (PV) and as a dependable energy source for mankind [1,2]. And also one MW HCPV demonstration power plant [3] (Figure 1), which covers an installation area of 2 hectares, installed at Lujhu in December 2009, generating over 1 million kWh per year, and reducing carbon dioxide emissions by approximately 660 tons annually. It is a milestone for Taiwan's government to have put the policy of energy saving and carbon reduction into practice. In the literature, common sun tracking systems consist of open-loop and closed-loop types [4]. The sun ephemeris provides the apparent position of the sun in the sky at a given moment in time, at a given point on the earth. Facilitating formula, position counters and control methods according to the sun ephemeris, enable the solar tracker to aim at the sun. This is called open-loop control [5]. The other method of sun tracking is by using the sun position sensor to detect and maneuver the solar tracker. However, both open loop and close loop methods have their individual problems of high tracking error, such as the installation error, and influence of clouds on the sun position sensor. In [6], a lookup table was pre-established to obtain the position of the sun at any time and then the direction of tracking mechanism is adjusted to point to the direction of the sun. In [7] a type of on-off control was utilized for two-axis sun tracking. On the other hand, common closed-loop control methodologies include robust proportional (P) control, proportional-integral (PI) control, derivative (D)-like control, proportional-integral-derivative (PID) control [8, 9, 10, 11], fuzzy control [12, 13, 14, 15], Linear-Quadratic Regulator(LQG) control [16] or H-infinity(H\(\infty\)) control [17,18]. Various controllers have individual advantages and disadvantages [17]. For instance, PID control and fuzzy control could be good options when an accurate model of the tracking system is absent, while LQG or H\(\infty\) control are preferred if higher accuracy tracking performance or tracking robustness against exogenous disturbance, such as wind gusts or cloud effects, is the main concern [19, 20, 21]. Therefore, a hybrid method combining both algorithms is now proposed [22, 23, 24, 25]. Up to date, the research of hybrid strategy for keeping the solar tracker in a precise position has needed a large amount of random access memory (RAM) to store parameters such as tracker position data or to use frequent search functions to search for the sun position precisely, even though those functions violate low cost principles and reduce the motor life-span respectively. An alternative idea of employing logic-based supervisor (LBS) control has had a great impact on sun tracking systems. Control using logic-based switching [26,27] has been proposed and employed, Switching between controllers is a subject of special interest: the process to be controlled might change the mode of operation so as to render no single controller capable of guaranteeing closed-loop stability. Switching between controllers might be crucial in protecting the process against wind-up effects.