태양광 패널 하드웨어 모사장치의 모델링과 안정도 해석 및 제어 기법 연구

Abstract

Photovoltaic (PV) power generation has received renewed global interest from researchers worldwide as they are eco-friendly and readily available. PV systems are still undergoing significant changes, particularly in extracting maximum power from these modules at any given point. Maximum power point tracking (MPPT) algorithms emerged as a solution to extracting power at any instance. These algorithms need to execute to maintain the operating point on maximum power point. However, this cannot be accomplished under standard insolation and temperature conditions. A solar array simulator (SAS) scheme is demanded to address this, making it easy to incorporate varying temperature profiles and insolation levels while the same tests as many times as desired. PV systems exhibit a highly non-linear characteristic curve which makes simulation a challenge for researchers.

This paper is a stuy on modeling, system stability, and control method for a solar panel hardware simulator (Solar Array Simulator, SAS) used for the purpose of testing a photovoltaic system. The contents and contribution of this paper are as follows. same as

First, the stability of the control loop of the solar panel simulating device is structurally explained. First, in Chapter 2, the SAS system is classified mainly into a reference generator, a power stage and controller, and a load system connected to a photovoltaic panel replicator and modeled it. In particular, the reference generator is modeled and generalized using a super-ellipse approximation for convenience of analysis. The power stage is divided into constant resistance (CR), constant voltage (CV), and constant current (CC) loads, according to the type of load system. In Chapter 3, the SAS system is divided into the current control method (CRC) and voltage control method (VRC) in the primary control method, and voltage sensing (VS), current sensing (CS), and resistance sensing (RS) in the load sensing method. , the stability analysis is conducted for the type of load system as mentioned above. As a result, it is proved through theory and experiment that the resistance sensing voltage reference control (RS-VRC) method is excellent in stability according to the operating point.

Second, a method for extending the operating range of the SAS system is proposed. In the solar I-V curve, when the operating point moves to the open-circuit voltage and short circuit current regions, the voltage control method and the current control method have advantages, respectively, so a hybrid control method selects two or more different controllers are used. In this case, mode switching occurred, and there is an issue in that the response characteristics deteriorated. To supplement this, the MRS-VRC and MRS-CRC methods are proposed as a modified resistance sensing (MRS) method that adds an offset voltage and current by modifying the resistance sensing method, and the improvements are verified through simulation and hardware.

Third, in order to prepare for a case where a rapid operating point change is necessary, a high-speed reference generation algorithm is studied. In the diode equivalent model equation of a solar panel, which is mainly used in past studies, the current-voltage relational expression appears in the implicit form. To generate the reference, an iterative algorithm is used, or a look-up table is generated. However, the Lambert-Ω function, which changes it to an explicit form, has been proposed. However, since the Lambert function also uses iterative calculations, the speed is not fast, so in this paper, a solar panel reference generation method using the approximate Lambert function is proposed. In addition, for a more simplified analysis model, a super-ellipse approximation is proposed in this paper, and its accuracy was verified to be relatively good. This model is used for stability analysis in Chapters 2 and 3 of this paper because the equations are quite simple. On the other hand, as a power stage circuit to solve the problem of rapid load change, especially the voltage reduction time delay caused by the output capacitor, a bidirectional converter structure is proposed instead of the conventional unidirectional converter structure, and its performance is verified by simulation.

Through the above research, it is expected that the SAS system can be made more robust to changes in load or insolation by establishing a method for improving the stability of the SAS system, increasing the operating range, and establishing a high-speed control method.