Power conversion apparatus for interconnection with a three-phrase ac power supply

1. A power conversion apparatus for interconnection with a three-phase AC power supply, the power conversion apparatus comprising:

a power converter having first to third arms connected by delta connection; and

a control device configured to control the power converter, wherein

each of the first to third arms includes one unit converter or a plurality of converters connected in series,

the unit converter includes

a power storage device connected between a pair of output terminals, and

a plurality of switching devices configured to generate, between the pair of output terminals, an output pulse dependent on a voltage value of the power storage device,

the control device includes

a first control unit configured to generate a voltage command value for controlling a current flowing between the three-phase AC power supply and the power converter such that a full voltage representative value representing voltage values of all the power storage devices agrees with a DC voltage command value,

a second control unit configured to generate a zero-phase voltage command value for controlling a circulating current flowing through the delta connection such that the voltage values of the power storage devices are balanced among the first to third arms,

a computation unit configured to combine the voltage command value generated by the first control unit and the zero-phase voltage command value generated by the second control unit to generate an output voltage command value for controlling an output voltage of each of the unit converters, and

a generation unit configured to generate a gate signal for controlling switching operations of the plurality of switching devices in accordance with the output voltage command value, and

the control device is configured to remove a control amount of the full voltage representative value from a computation of the zero-phase voltage command value in the second control unit to cause the first control unit and the second control unit not to interfere with each other.

2. The power conversion apparatus according to claim 1 , wherein during transient fluctuations in which each of the power storage devices is charged and discharged, the second control unit is configured to perform control of eliminating an imbalance in the voltage value of the power storage device between the first to third arms, independently of control of the full voltage representative value by the first control unit.

3. The power conversion apparatus according to claim 1 , wherein

the second control unit is configured to

generate first to third arm current command values for controlling first to third arm currents flowing through the first to third arms, respectively, such that each of a first deviation between a first representative value representing the voltage values of the power storage devices in the first arm and the full voltage representative value, a second deviation between a second representative value representing the voltage values of the power storage devices in the second arm and the full voltage representative value, and a third deviation between a third representative value representing the voltage values of the power storage devices in the third arm and the full voltage representative value attains to zero, and

perform a control computation for causing the first to third arm currents to follow the first to third arm current command values, respectively, to generate the zero-phase voltage command value, and

the second control unit is configured to remove a common component included in common in the first to third representative values from each of the first to third deviations for generating the first to third arm current command values.

4. The power conversion apparatus according to claim 3 , wherein the common component is a zero-phase component of the first to third deviations.

5. The power conversion apparatus according to claim 3 , wherein the common component depends on a deviation between the voltage command value and the full voltage representative value.

6. The power conversion apparatus according to claim 3 , wherein

the second control unit includes a controller configured to perform a control computation for setting each of the first to third deviations to zero to generate the first to third arm current command values, and

the first to third deviations are input to the controller with the common component removed.

7. The power conversion apparatus according to claim 3 , wherein

the second control unit includes a controller configured to perform a control computation for setting each of the first to third deviations to zero to generate the first to third arm current command values,

the controller includes

a proportioner, and

an integrator connected in series with the proportioner, and

an output of the proportioner is provided to the integrator with the common component removed.

8. The power conversion apparatus according to claim 3 , wherein the second control unit includes

a coordinate transformation unit configured to transform the first to third deviations to two-phase deviations by three-phase to αβ transformation, and

a controller configured to perform a control computation for setting each of the two-phase deviations to zero.

9. The power conversion apparatus according to claim 3 , wherein

the second control unit includes a controller configured to perform a control computation for setting each of the first to third deviations to zero to generate the first to third arm current command values, and

the controller includes

first to third proportioners configured to perform proportional control on the first to third deviations,

first and second integrators connected in series with the first to third proportioners, and

a coordinate transformation unit connected between the first to third proportioners and the first and second integrators and configured to perform three-phase to αβ transformation on outputs of the first to third proportioners.

10. The power conversion apparatus according to claim 3 , wherein the second control unit is configured of a discrete system.