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;