A novel control approach for two-stage power converters in stand-alone solar photovoltaic system

ABSTRACT

This paper presents a multi-advantageous control technique for two-stage converters, namely DC-DC boost converter and three-phase voltage source inverter (VSI) in stand-alone energy-stored solar photovoltaic (SPV) system. Two-stage converter traditionally used two simultaneous control actions – DC-side control logic for boost converter and AC-side voltage control loop for VSI to maintain standard load voltage, thereby variable load powers are supported. Here, both duty ratio and modulation index (MI) are mutually adjusted to maintain load powers. In contrast, proposed single loop control philosophy only regulates duty ratio for supporting active and reactive load powers under varying solar or load conditions, but MI is always kept at fixed value of one per unit. With fixed and highest value of MI, significant benefits are obtained as reduction of voltage stress on power semiconductor switches and improved harmonic spectrums at VSI’s output. Simulation and down-scaled experimental works are performed to validate proposed control concept.

KEYWORDS:

• Solar photovoltaic (SPV)
• DC-DC boost converter
• voltage source inverter (VSI)
• DC bus voltage
• total harmonic distortion (THD)

Nomenclature

Symbols	=
$V_{pv},I_{pv}$	=	Output voltage, current of SPV
$V_0,V_l$	=	Output voltage of VSI, load voltage
$D,M,\omega$	=	Duty ratio, modulation index, angular frequency
$L_f,C_f$	=	Filter inductance and capacitance
$I_l,V_{dc},I_{dc}$	=	Load current, DC link voltage, current
$P_l,Q_l$	=	Active and reactive load power respectively
$PI$	=	Proportional integral controller
Superscripts	=
$\wedge$	=	Peak value
$\ast$	=	Reference value

Disclosure statement

No potential conflict of interest was reported by the author.