研究目的
The main objective of a photovoltaic (PV) system’s control is power maximization. The voltage corresponding to the maximum power point (maximum power point voltage, MPPV) of each photovoltaic module (or set of modules) depends on the weather conditions. Thus, maximum power point tracking (MPPT) is needed.
研究成果
The sliding mode control was applied to make a set of photovoltaic modules track the maximum power point voltage. The use of this control improved the dynamics of the system and its response to perturbations in the load or in the irradiance. The control algorithm was implemented in a buck-boost converter, which is able to supply a voltage lower and higher than the input voltage, as required by telecommunications applications, amongst others. The system proved to be efficient with both wire and wireless communication, and in both cases the dynamic performance was improved.
研究不足
The wireless communication makes the signals have more noise than that obtained in the case with wire connection due to the wireless communication effect. This type of communication implies a variable delay in the signal processing and data transmission. The delay is also affected by the distance between the buck-boost converter and the base station and by the interferences created by other systems that use the same frequency. As the delay increased, the system efficiency decreased.
1：Experimental Design and Method Selection:
The sliding mode control (SMC) is applied to a buck-boost converter integrated in a PV system supplying a resistive load. The SMC makes the modules track the MPPV calculated by an algorithm which previously obtains it. This algorithm applies a regression plane to obtain the reference voltage using a modified P&O.
2：Sample Selection and Data Sources:
A commercial PV module was chosen to be part of the experimental platform. Its features under standard conditions, 1000 W/m2 and 25°C, are detailed.
3：List of Experimental Equipment and Materials:
The experimental platform contains three photovoltaic modules. The modules feed a built buck-boost converter working with an input voltage of 10 V as minimum and 70 V as maximum. The maximum output voltage is 100 V. The maximum power that can be transferred is 70 W. The load is a 220 ? resistor.
4：Experimental Procedures and Operational Workflow:
The sliding control was implemented in a dsPIC30F4011 low-cost microcontroller, being supervised via a local internet connection. The sliding control has to regulate the DC/DC converter’s input voltage to reach the MPP through the MOSFET switching controlling the duty cycle. The PWM frequency is 20 kHz whereas the sampling time of the control is 5 ms.
5：Data Analysis Methods:
The system was tested with different irradiances, 670 W/m2 until 33 s, 490 W/m2 until 68 s, and 690 W/m2 until 95 s, to finish with an irradiance of 330 W/m2.
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