Power conversion apparatus
In a power conversion apparatus that boosts a solar light voltage, converts it to AC and supplies AC power to a load or system, power loss is reduced and efficiency is improved. An inverter unit, in which AC sides of three single-phase inverters receive DC power from respective sources with a voltage ratio of 1:3:9 as respective inputs are connected in series. Gradational output voltage control of an output voltage is carried out using the sum of the respective generated AC voltages. Also, a solar light voltage is boosted by a chopper circuit to generate the highest voltage DC power source. When the solar light voltage exceeds a predetermined voltage, the boosting of the chopper circuit is stopped, thereby reducing power loss due to the boosting.
1. A power conversion apparatus comprising:
a plurality of single-phase inverters having respective inputs and outputs and converting input DC power from respective DC power sources to AC power, the outputs of the single-phase inverters being connected in series, wherein
the outputs of the single phase inverters connected in series produce an AC output voltage of the power conversion apparatus, with gradational output voltage control, from a sum of output voltages produced by a combination of the single-phase inverters selected from the plurality of the single-phase inverters, and
the respective DC power sources that provide respective DC voltages input to respective single-phase inverters include a first DC power source producing the highest DC voltage of the DC voltages produced by the respective DC power sources, and second DC power sources; and
a booster circuit including a switch, wherein
the highest DC voltage, produced by the first DC power source, is generated by a third DC power source and is supplied through the booster circuit, and
the single-phase inverter that receives the DC voltage produced by the first DC power source produces an output voltage having an output pulse width that is adjusted so that total power fluctuation, due to charging and discharging of respective second DC power sources, via respective single-phase inverters, is reduced.
2. The power conversion apparatus according to claim 1 , wherein the total power fluctuation in respective second DC power sources via respective single-phase inverters is the sum of respective power fluctuations in respective second DC power sources or the sum of absolute value of respective quantities of power fluctuations.
3. The power conversion apparatus according to claim 1 , wherein, when the voltage of the third DC power source exceeds a predetermined voltage, on-off operation of the switch in the booster circuit is stopped to stop boosting.
4. The power conversion apparatus according to claim 1 , wherein
the AC output voltage of the power conversion apparatus is variable, ranging up to a maximum AC output voltage, and
the DC voltage produced by the first DC power source is lower than the maximum AC output voltage of the power conversion apparatus.
5. The power conversion apparatus according to claim 1 , including two second DC power sources producing substantially equal DC voltages.
6. The power conversion apparatus according to claim 1 , wherein the sum of DC voltages produced by respective second DC power sources is at least equal to 4/9 of the DC voltage produced by the first DC power source.
7. The power conversion apparatus according to claim 1 , wherein the output of a predetermined single-phase inverter of the plurality of single-phase inverters is PWM-controlled, and the PWM-controlled output is combined at each output level to produce the gradational output voltage control.
8. The power conversion apparatus according to claim 1 , wherein a predetermined AC voltage and AC current are output by the power conversion apparatus and supplied to a load, or the predetermined AC voltage output by the power conversion apparatus is connected in parallel with a system, and the third DC power source is linked to the system.