An Energy Storage System Composed of Photovoltaic Arrays and Batteries with Uniform Charge/Discharge

Abstract

The main purpose of this study was to develop a photovoltaic module array (PVMA) and an energy storage system (ESS) with charging and discharging control for batteries to apply in grid power supply regulation of high proportions of renewable energy. To control the flow of energy at the DC load and charge/discharge the battery uniformly, this work adapted a bidirectional buck–boost soft-switching converter and the maximum power point tracking (MPPT) technique of the photovoltaic module array. First, a boost converter is used with the perturb and observe (P&O) method, so that the photovoltaic module array can work at the maximum power point (MPP) at any time. When the output power of the photovoltaic module array is greater than the load power, the excess power is used to charge the battery; on the contrary, if the output power of the photovoltaic module array is lower than the load power, the battery discharges for auxiliary power supply. This makes the voltage of the DC link maintain a constant value. The monitoring circuit sends the voltage and current signals to the TMS320F2809 digital signal processor (DSP) produced by Texas Instruments to control the battery charging/discharging voltage and current. The photovoltaic module array works at the MPP to improve the performance of the overall energy storage system. Finally, the actual test result shows that the soft-switching converter used in this work, when compared to the hard-switching converter, can improve efficiency by nearly 4% when the load power is above 125 W. When the photovoltaic power generation system operation is between 150 W and 400 W, the proposed uniform charging and discharging architecture can rapidly reach uniformity.

Quantitative Design for the Battery Equalizing Charge/Discharge Controller of the Photovoltaic Energy Storage System

“…The current controller for the bidirectional buck-boost soft-switching converter is designed so that the converter can operate under the current continuous conducting mode. Compared to the whole switching period, the auxiliary branch switching time for the bidirectional buck-boost soft-switching converter is comparatively shorter; therefore during the dynamic mode analysis process, the auxiliary branch switching time can be omitted [6,21,22]. In addition, since the main switches of the converter S L and S H are complementarily controlled, the results derived from both the boost mode or the buck mode are the same; therefore, the analysis process below is derived from the dynamic mode of the converter only under the boost mode.…”

“…In order to ensure that Equation (1) meets the requirements regardless of a light load or heavy load, the maximum value of the inductor current I L -that is, the peak value of i L at full load ( ÎL ) max is used to determine the on-time t D of the auxiliary switch, and t D is usually 5~10% of the switching period T [6]. In addition, a margin time t ε is required to obtain a reliable t D , so here, we set t D = 0.1 T = 4 µs, and t ε = 0.01 T = 0.4 µs, and then used Equation ( 1) to derive a maximum resonance inductance value L a1 = L a2 = 18 µH, so we can select a resonance inductance value smaller than 18µH, which would be acceptable.…”

“…The energy storage system for photovoltaic power generation can regulate the power via the bidirectional buck-boost converter to provide stable DC-link voltage output [6]. Since the output power from photovoltaic energy changes due to changing amount of sunlight, in order to maintain the DC-link voltage at a set value, the controller parameters for the bidirectional buck-boost converter must be designed properly so that the converter will have good output performance.…”

“…Since the output power from photovoltaic energy changes due to changing amount of sunlight, in order to maintain the DC-link voltage at a set value, the controller parameters for the bidirectional buck-boost converter must be designed properly so that the converter will have good output performance. The architecture of the commonly adopted traditional P-I controller is simple and does not require complex calculations, but the controller parameters can only be adjusted through the trial-and-error method, thus requiring more time to obtain the controller parameters [6][7][8]. Furthermore, whereas the controller designed using the Bode plot can obtain the controller parameters quickly but does not take the converter's dynamic characteristic of wide operating spectrum into consideration, and thus is only able to obtain the dynamic response under certain conditions; once the operating point changes, the system will be unable to operate under the better performance response [9,10].…”

“…Batteries 2022, 8, x FOR PEER REVIEW 2 of 28 the battery can be used as an auxiliary power supply, so that the microgrid can obtain greater economic benefits while solving the problem of unstable power supply quality from the grid under high renewable energy proportions. The energy storage system for photovoltaic power generation can regulate the power via the bidirectional buck-boost converter to provide stable DC-link voltage output [6]. Since the output power from photovoltaic energy changes due to changing amount of sunlight, in order to maintain the DC-link voltage at a set value, the controller parameters for the bidirectional buck-boost converter must be designed properly so that the converter will have good output performance.…”