A DC-to-AC power converter having a main DC input and a main single-phase AC output , capable to convert and adapt a DC voltage at said main DC input into a sinusoidal AC voltage of fundamental frequency f 0 at said main AC output and capable to deliver a rated power at said main AC output to a load, comprising: - a single DC-to-DC converter having as input said main DC input and having a DC output and a tank capacitor being connected to said DC output , two low frequency diodes biased so as to be able to pass the current from, respectively to, the DC output to, respectively from, the tank capacitor ; - according to a direct path, a bidirectional voltage-type DC-to-AC converter in cascade with the DC-to-DC converter , said bidirectional voltage-type DC-to-AC converter having a DC input-output connected to the DC output and an AC output-input connected to said main AC output ; - according to a bypass path, and in parallel to said bidirectional voltage-type DC-to-AC converter and to said low frequency diodes , a current-type low frequency full switching H-bridge , called hereafter AC forward bridge, having a DC input and a AC output, said DC input being connected to said DC output of the single DC-to-DC converter and said AC output being connected in parallel to said main AC output , said AC forward bridge having a working frequency less than 1 kHz, and preferably 400 Hz or 50/60 Hz ; - control means for controlling said bidirectional voltage-type DC-to-AC converter to deliver at said first AC output-input the sinusoidal AC voltage and for controlling said AC forward bridge to deliver a quasi square-type AC forward current in phase with said sinusoidal AC voltage, said control means being capable to control said bidirectional voltage-type DC-to-AC converter and said AC forward bridge, so that the latter are capable to be operated simultaneously; so that, when the instantaneous voltage between the terminals of said main AC output attains a predetermined level, the low frequency forward AC bridge is switched on, the low frequency diodes being reverse biased and non-conducting and a constant power is supplied by the DC-to-DC converter directly to the load. - a single DC-to-DC converter having as input said main DC input and having a DC output and a tank capacitor being connected to said DC output , two low frequency diodes biased so as to be able to pass the current from, respectively to, the DC output to, respectively from, the tank capacitor ; - according to a direct path, a bidirectional voltage-type DC-to-AC converter in cascade with the DC-to-DC converter , said bidirectional voltage-type DC-to-AC converter having a DC input-output connected to the DC output and an AC output-input connected to said main AC output ; - according to a bypass path, and in parallel to said bidirectional voltage-type DC-to-AC converter and to said low frequency diodes , a current-type low frequency full switching H-bridge , called hereafter AC forward bridge, having a DC input and a AC output, said DC input being connected to said DC output of the single DC-to-DC converter and said AC output being connected in parallel to said main AC output , said AC forward bridge having a working frequency less than 1 kHz, and preferably 400 Hz or 50/60 Hz ; - control means for controlling said bidirectional voltage-type DC-to-AC converter to deliver at said first AC output-input the sinusoidal AC voltage and for controlling said AC forward bridge to deliver a quasi square-type AC forward current in phase with said sinusoidal AC voltage, said control means being capable to control said bidirectional voltage-type DC-to-AC converter and said AC forward bridge, so that the latter are capable to be operated simultaneously; <EOS>