POWER CONVERSION DEVICE AND CONTROL METHOD FOR SAME

• US 20190044428A1
• Filed: 08/19/2016
• Published: 02/07/2019
• Est. Priority Date: 10/07/2015
• Status: Active Grant

• Current Assignee: Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Original Assignee: Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Inventors: Okumura, Toshiaki, Ayai, Naoki
• Granted Patent: US 10,461,625 B2
• Time in Patent Office: Days
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources
• CPC Class Codes: H02J 3/32 using batteries with converting means
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/40 Synchronising a generator for connection to a network or to another generator
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02M 1/0048 Circuits or arrangements for reducing losses using snubbers H02M1/34
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02M 3/1584 with a plurality of power processing stages connected in parallel
• CPC Class Codes: H02M 7/4826 operating from a resonant DC source, i.e. the DC input voltage varies periodically, e.g. resonant DC-link inverters
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: H02S 40/32 comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A control unit of a power conversion device calculates a current target value and a voltage target value for a DC/AC converter on the basis of an output current target value, to control the DC/AC converter, and calculates a current target value for the DC/DC converter on the basis of the current target value and the voltage target value, and a voltage target value for the DC/DC converter, to control the DC/DC converter, thereby controlling output of an AC power. The control unit selects, as the voltage target value for the DC/DC converter, a greatest value at a present time, from among a DC voltage value of the DC power supply, an absolute value of a voltage target value for an AC side of the DC/AC converter, and a DC voltage lower limit value which is a predetermined value smaller than a peak value of the absolute value.

Claims

1. A power conversion device provided between an AC grid and a DC power supply which outputs a voltage lower than a peak value of an absolute value of an AC voltage of the AC grid, the power conversion device being configured to perform DC/AC power conversion, the power conversion device comprising:

a filter circuit connected to the AC grid;

a DC/DC converter provided between the DC power supply and a DC bus;

a capacitor connected to the DC bus;

a DC/AC converter provided between the DC bus and the filter circuit; and

a control unit configured to control the DC/DC converter and the DC/AC converter, wherein

the control unit

calculates an output current target value on the basis of an input power value of a DC power and a voltage value of the AC grid, and calculates a current target value and a voltage target value for the DC/AC converter on the basis of the output current target value, to control the DC/AC converter, and

calculates a current target value for the DC/DC converter on the basis of the current target value and the voltage target value for the DC/AC converter and a voltage target value for the DC/DC converter, to control the DC/DC converter, thereby controlling output of an AC power, and

the control unit selects, as the voltage target value for the DC/DC converter, a greatest value at a present time, from among a DC voltage value of the DC power supply, an absolute value of a voltage target value for an AC side of the DC/AC converter, and a DC voltage lower limit value which is a predetermined value smaller than a peak value of the absolute value.

2. The power conversion device according to claim 1, wherein

the DC power supply and the DC/DC converter comprise plural pairs of DC power supplies and DC/DC converters, so that there are a plurality of DC voltage values of the DC power supplies, and

a greatest value of the plurality of DC voltage values is to be compared with the DC voltage lower limit value.

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

the DC voltage lower limit value is selected so as to shorten a period during which a reactive power occurs, and prolong a period during which the reactive power is zero.

4. The power conversion device according to claim 3, wherein

the DC voltage lower limit value is selected so that the period during which the reactive power occurs becomes equal to or shorter than half an AC (½

) cycle.

7. The power conversion device according to claim 2, wherein

the DC voltage lower limit value is selected so as to shorten a period during which a reactive power occurs, and prolong a period during which the reactive power is zero.

8. The power conversion device according to claim 7, wherein

the DC voltage lower limit value is selected so that the period during which the reactive power occurs becomes equal to or shorter than half an AC (½

) cycle.

5. A control method executed by a power conversion device provided between an AC grid and a DC power supply which outputs a voltage lower than a peak value of an absolute value of an AC voltage of the AC grid, the power conversion device including:

a filter circuit connected to the AC grid;

a DC/DC converter provided between the DC power supply and a DC bus;

a capacitor connected to the DC bus; and

a DC/AC converter provided between the DC bus and the filter circuit, the power conversion device being configured to perform DC/AC power conversion, the method comprising;

as a basic control method,

calculating an output current target value on the basis of an input power value of a DC power and a voltage value of the AC grid, and calculating a current target value and a voltage target value for the DC/AC converter on the basis of the output current target value, to control the DC/AC converter, and

calculating a current target value for the DC/DC converter on the basis of the current target value and the voltage target value for the DC/AC converter and a voltage target value for the DC/DC converter, to control the DC/DC converter, thereby controlling output of an AC power; and

as an extensional control method,

selecting, as the voltage target value for the DC/DC converter, a greatest value at a present time, from among a DC voltage value of the DC power supply, an absolute value of a voltage target value for an AC side of the DC/AC converter, and a DC voltage lower limit value which is a predetermined value smaller than a peak value of the absolute value.

6. A power conversion device provided between an AC grid and a DC power supply which outputs a voltage lower than a peak value of an absolute value of an AC voltage of the AC grid, the power conversion device being configured to perform DC/AC power conversion, the power conversion device comprising:

a filter circuit connected to the AC grid;

a DC/DC converter provided between the DC power supply and a DC bus;

a capacitor connected to the DC bus;

a DC/AC converter provided between the DC bus and the filter circuit; and

a control unit configured to control the DC/DC converter and the DC/AC converter, wherein

the control unit

calculates an output current target value on the basis of an input power value of a DC power and a voltage value of the AC grid, and calculates a current target value and a voltage target value for the DC/AC converter on the basis of the output current target value, to control the DC/AC converter, and

calculates a current target value for the DC/DC converter on the basis of the current target value and the voltage target value for the DC/AC converter and a voltage target value for the DC/DC converter, to control the DC/DC converter, thereby controlling output of an AC power, and

the control unit selects, as the voltage target value for the DC/DC converter, a greatest value at a present time, from among a DC voltage value of the DC power supply, an absolute value of a voltage target value for an AC side of the DC/AC converter, and a DC voltage lower limit value which is a predetermined value smaller than a peak value of the absolute value, and the control unit causes a period during which a part of a pulsating current waveform of the absolute value appears, to be equal to or shorter than half of one pulsating current cycle.