Abstract
This paper deals with a photovoltaic (PV) system containing a quasi-Z-source inverter (qZSI) and batteries connected in parallel with the qZSI’s lower-voltage capacitor. The control system design is based on knowledge of three transfer functions which are obtained from the novel small-signal model of the considered system. The transfer function from the d-axis grid current to the battery current has been identified for the first time in this study for the considered system configuration and has been utilized for the design of the battery current control loop for the grid-tied operation. The transfer function from the duty cycle to the PV source voltage has been utilized for the design of the PV source voltage control loop. The PV source voltage is controlled so as to ensure the desired power production of the PV source. For the maximum power point tracking, a perturb-and-observe algorithm is utilized that does not require the measurement of the PV source current, but it instead utilizes the battery current during the stand-alone operation and the d-axis reference current during the grid-tied operation. The corresponding tracking period was determined by using the transfer function from the duty cycle to the battery current and in accordance with the longest settling time noted in the corresponding step response. The proposed control algorithm also has integrated protection against battery overcharging during the stand-alone operation. The considered system has been experimentally tested over wide ranges of irradiance and PV panel temperature.
Highlights
Solar energy as a clean and fully renewable source of energy can be harnessed all over the world and directly converted to electricity by means of photovoltaic (PV) systems
This paper presents a control algorithm for the quasi-Z-source inverter (qZSI)-based PV system with the batteries connected in parallel with the lower-voltage capacitor in the impedance network
In the case of temperature of PV panels (Tpv) = 10 ◦ C and Tpv = 50 ◦ C, waveforms shown in Figure 11b,c, respectively, 17 ofthe maximum steady state error amounts to 2.5% and 4.3%, respectively
Summary
Solar energy as a clean and fully renewable source of energy can be harnessed all over the world and directly converted to electricity by means of photovoltaic (PV) systems. In [13,14,15,18], during the grid-tied operation, the maximum power production of the PV source is ensured by the variation of the output qZSI current, whereas the battery current/power is controlled by the variation of the duty cycle (d0 ). In the case of the PV systems with the battery-assisted qZSI, the most commonly utilized maximum power point tracking (MPPT) algorithm is the perturb-and-observe (P&O) algorithm [19,20], due to its simplicity This type of algorithm has been utilized in [13,14,15,16,17,18], and its implementation requires the measurement of the PV source voltage and current. The proposed control strategy was tested experimentally—for both the grid-tied and stand-alone operation—by using the laboratory setup of the considered system
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