The Institution of Engineering and Technology. The pulse-width amplitude modulation (PWAM) method was proposed for the single-phase quasi-Z-source inverter (qZSI)-based photovoltaic (PV) power system to reduce quasi-Z-source (qZS) impedance values while improving efficiency. The method modified sinusoidal pulse-width modulation (SPWM) of the qZSI by combining pulse-amplitude modulation (PAM) and a varied dc-link voltage envelope was produced. The SPWM worked at low dc-link voltage, lowering voltage stress and avoiding shoot-through switching. The PAM worked at the varied dc-link voltage, reducing the number of switching events. As a result, the power dissipation decreased compared to working at the constant dc-link voltage. This study further investigates the PWAM-based single-phase qZS PV inverter system. An improved topology with control strategy is proposed for its grid-connected and standalone operation. Design method of impedance parameters is detailed. The performance in boost and buck operation is discussed when the single-phase qZSI using SPWM and PWAM. Simulation and experimental results verify outstanding features of the PWAM for single-phase qZSI, and the proposed approach for dual-mode operation of the PWAM-based single-phase qZS PV power system.