Inverter device with a control unit

1. An inverter device connected to an AC system via a reactor, the inverter device comprising:

a conversion unit configured to convert DC power outputted from a power supply, to AC power, and output the converted AC power to the AC system via the reactor; and

a control unit configured to control the conversion unit, wherein

the conversion unit includes:

a step-up circuit configured to step up a DC input voltage value of the DC power; and

an inverter circuit configured to convert power given from the step-up circuit, to AC power, and

the control unit

calculates an output current target value based on an input power value of the DC power and a voltage value of the AC system, and calculates a current target value and a voltage target value for the inverter circuit based on the output current target value, to control the inverter circuit, and

calculates a current target value for the step-up circuit based on a current target value and a voltage target value that are common with the inverter circuit, and on the DC input voltage value, to control the step-up circuit, and

thereby controls output of the AC power.

2. The inverter device according to claim 1 , wherein

a smoothing capacitor is provided between the step-up circuit and the inverter circuit, and

the current target value for the step-up circuit is calculated based on the DC input voltage value and on a value obtained by adding reactive power passing through the smoothing capacitor to a power target value that is based on the current target value and the voltage target value for the inverter circuit.

3. The inverter device according to claim 1 , wherein

a smoothing capacitor is provided between the step-up circuit and the inverter circuit, and

the current target value for the step-up circuit is calculated based on the DC input voltage value and on a value obtained by adding reactive power passing through the smoothing capacitor and power loss in the inverter device to a power target value that is based on the current target value and the voltage target value for the inverter circuit.

4. The inverter device according to claim 1 , wherein

an output smoothing capacitor is provided at a stage subsequent to the reactor, and

in the case where the current target value for the step-up circuit is Iin*, the current target value and the voltage target value for the inverter circuit are Iinv* and Vinv*, respectively, the output current target value is IA*, an electrostatic capacitance of the output smoothing capacitor is Ca, the voltage value of the AC system is Va, and the DC input voltage value is Vg, the following expressions are satisfied:

I in*=( I inv*× V inv*)/ Vg

I inv*= Ia*+Ca ×( dVa/dt ).

5. The inverter device according to claim 1 , wherein

an output smoothing capacitor is provided at a stage subsequent to the reactor, and

in the case where the current target value for the step-up circuit is Iin*, the current target value and the voltage target value for the inverter circuit are Iinv* and Vinv*, respectively, the voltage value of the AC system is Va, the output current target value is Ia*, the DC input voltage value is Vg, and current flowing through the output smoothing capacitor is Ica, the following expressions are satisfied:

I in*=( I inv*× V inv*)/ Vg

I inv*= Ia*+Ica.

6. The inverter device according to claim 2 , wherein

in the case where the current target value for the step-up circuit is Iin*, the current target value and the voltage target value for the inverter circuit are Iinv* and Vinv*, respectively, an electrostatic capacitance of the smoothing capacitor is C, a voltage target value for the step-up circuit is Vo*, and the DC input voltage value is Vg, the following expression is satisfied:

I in*={( I inv*× V inv*)+ C ×( dVo*/dt )× Vo*}/Vg.

7. The inverter device according to claim 2 , wherein

in the case where the current target value for the step-up circuit is Iin*, the current target value and the voltage target value for the inverter circuit are Iinv* and Vinv*, respectively, a voltage target value for the step-up circuit is Vo*, the DC input voltage value is Vg, and current flowing through the smoothing capacitor is Ic, the following expression is satisfied:

I in*={( I inv*× V inv*)+ Ic×Vo*}/Vg.

8. The inverter device according to claim 3 , wherein

in the case where the current target value for the step-up circuit is Iin*, the current target value and the voltage target value for the inverter circuit are Iinv* and Vinv*, respectively, an electrostatic capacitance of the smoothing capacitor is C, a voltage target value for the step-up circuit is Vo*, the DC input voltage value is Vg, and power loss of the inverter device is P LOSS , the following expression is satisfied:

I in*={( I inv*× V inv*)+ C ×( dVo*/dt )× Vo*+P LOSS }/Vg.

9. The inverter device according to claim 3 , wherein

in the case where the current target value for the step-up circuit is Iin*, the current target value and the voltage target value for the inverter circuit are Iinv* and Vinv*, respectively, a voltage target value for the step-up circuit is Vo*, the DC input voltage value is Vg, current flowing through the smoothing capacitor is Ic, and power loss of the inverter device is P LOSS , the following expression is satisfied:

I in*={( I inv*× V inv*)+ Ic×Vo*+P LOSS }/Vg.

10. The inverter device according to claim 4 , wherein

the control unit selects, as the voltage target value for the step-up circuit, the larger one of the DC input voltage value and an absolute value of the voltage target value for the inverter circuit, and

in the case where an inductance of the reactor is La, the voltage target value Vinv* for the inverter circuit is calculated by the following expression:

V inv*= Va+La ( dI inv*/ dt ).

11. The inverter device according to claim 1 , wherein

the control unit performs maximum power point tracking control for the power supply, based on average values of the DC input voltage value and a DC input current value of the DC power given from the power supply, the average values being respectively calculated from results of plural measurements of the DC input voltage value and the DC input current value.

12. The inverter device according to claim 11 , wherein

the average values of the DC input voltage value and the DC input current value are respectively obtained from results of plural measurements of the DC input voltage value and the DC input current value performed at time intervals shorter than a half cycle of the AC system during a period that is an integer multiple of the half cycle of the AC system.

13. The inverter device according to claim 1 , wherein DC power is outputted from the AC system to the power supply.