Power conversion device

• US 8,754,549 B2
• Filed: 07/23/2009
• Issued: 06/17/2014
• Est. Priority Date: 07/24/2008
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Kawakami, Tomoyuki, Iwata, Akihiko, Okuda, Tatsuya
• Primary Examiner(s): Fureman, Jared
• Assistant Examiner(s): Pham, Duc M
• Application Number:
  US13/055,153
• Publication Number:
  US 20110121661A1
• Time in Patent Office: 1,790 Days
• Field of Search: 307/110
• US Class Current: 307/110
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

In a power conversion device which performs DC/DC conversion, an inverter circuit (20), which is formed of one or more single-phase inverters (20a) and (20b) connected in series to each other, is connected in series to a DC power supply (1) in its subsequent stage. In further subsequent stage, a smoothing capacitor (6) connected to the inverter circuit (20) via a rectifier diode (5), and a shorting switch (4) which bypasses the smoothing capacitor (6) are provided. The shorting switch (4) is switched ON to charge capacitors (25) and (35) included in the single-phase inverter (20a) and (20b), respectively, whereas the shorting switch (4) is switched OFF to discharge the capacitors (25) and (35), whereby the voltage of the smoothing capacitor (6) is controlled.

Claims

1. A power conversion device comprising:

an inverter circuit

including a plurality of single-phase inverters which each include at least one semiconductor switch device and a DC voltage source, and which are connected in series at their AC sides, and

having an AC side connected in series to an output of a DC power supply thereby to superimpose a total sum of outputs of the single-phase inverters onto an output of the DC power supply;

a smoothing capacitor configured to smooth an output from the inverter circuit which is connected to the inverter circuit in its subsequent stage via a first switch configured to switch between conduction and non-conduction; and

a shorting switch which has one end connected to the inverter circuit, and the other end connected to a negative terminal of the smoothing capacitor, wherein

DC/DC conversion is performed by utilizing charge/discharge of DC power in the inverter circuit, and

the inverter circuit is configured to control each single-phase inverter and the shorting switch such that reception and delivery of electric power of each DC voltage source of each single-phase inverter, is balanced.

2. The power conversion device according to claim 1, wherein the first switch is a rectifier diode.

3. The power conversion device according to claim 1, wherein the one end of the shorting switch is connected to a negative terminal of the DC voltage source of the single-phase inverter that is in the last stage of the plurality of single-phase inverters included in the inverter circuit.

4. The power conversion device according to claim 3, wherein, of the plurality of single-phase inverters, the single-phase inverter that is connected in the last stage includes a half-bridge inverter.

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

in controlling each single-phase inverter and the shorting switch such that the reception and the delivery of the electric power of each DC voltage source of each single-phase inverter, is balanced, the inverter circuit is controlled by a plurality of control modes, each formed based on a combination of output control of each single-phase inverter and ON/OFF control of the shorting switch, and the control modes are set such that reception and delivery of electric power of each DC voltage source, the reception and delivery being caused by the output from each single-phase inverter, are balanced.

6. The power conversion device according to claim 5, wherein

each of the plurality of control modes has a boost ratio for DC/DC conversion, and

the boost ratio is selected by determining and switching to one of the control modes in accordance with the voltage of the DC power supply.

7. The power conversion device according to claim 6, wherein switching among the control modes is performed by selecting one of the control modes in a manner as to minimize variation of an output voltage of the power conversion device, the variation being caused by voltage variation of the DC power supply.

8. The power conversion device according to claim 6, wherein

the ratio of the voltages of the DC voltage sources of the single-phase inverters is variably set, and

the plurality of control modes are set such that the ratio of the voltages determined based on the control modes comprises several types.

9. The power conversion device according to claim 5, wherein in control using the control modes, the ratio of the voltages of the DC voltage sources of the single-phase inverters are adjusted by adjusting a duty ratio of positive and negative voltage outputs of each single-phase inverter without changing the control of the shorting switch.

10. The power conversion device according to claim 5, wherein

switching among the control modes is performed by comparing a voltage determination value set in advance with the voltage of the DC power supply, and

a hysteresis width is set for the voltage determination value.

11. The power conversion device according claim 5, wherein a predetermined control operation of the power conversion device is repeated in constant cycles, the predetermined control operation being based on the control modes which are each formed based on the combination of the output control of each single-phase inverter and the ON/OFF control of the shorting switch, and in one cycle of the predetermined control operation, reception and delivery of electric power of each DC voltage source, the reception and delivery being caused by the output from each single-phase inverter, are balanced.

12. The power conversion device according to claim 11, wherein the one cycle of the predetermined control operation includes at least two different control operation periods.

13. The power conversion device according to claim 12, wherein except for a case where each single-phase inverter does not generate voltage during the one cycle, the one cycle includes at least one control operation period during which each single-phase inverter outputs a positive voltage and at least one control operation period during which the single-phase inverter outputs a negative voltage.

14. The power conversion device according to claim 13, wherein in the one cycle, a total sum of the control operation periods during which each single-phase inverter outputs the positive voltage is equal in length to a total sum of the control operation periods during which the single-phase inverter outputs the negative voltage.

15. The power conversion device according to claim 1, wherein voltage values Vc (k) of a plurality (N pieces) of the DC voltage sources are set such that the ratio of the voltages is represented by powers of two (1:

2;

4;

2^N-1).

16. The power conversion device according to claim 1, wherein, of voltage values Vc (k) of a plurality (N pieces) of the DC voltage sources, a maximum voltage Vc (N) and a minimum voltage Vc (1) satisfy an relational expression below,

Vc(N)≦

(Σ

Vc(k);

k=1˜

N−

1)+Vc(1).

17. A power conversion device comprising:

an inverter circuit

including one or more single-phase inverters which each include a bridge circuit wherein a diode is connected in series to a semiconductor switch device and a DC voltage source, and which are connected in series at their AC sides, and

having an AC side connected in series to an output of a DC power supply thereby to superimpose a total sum of outputs of the single-phase inverters onto an output of the DC power supply;

a smoothing capacitor configured to smooth an output from the inverter circuit which is connected to the inverter circuit in its subsequent stage via a first switch configured to switch between conduction and non-conduction; and

a shorting switch which has one end connected to the inverter circuit, and the other end connected to a negative terminal of the smoothing capacitor, wherein

DC/DC conversion is performed by utilizing charge/discharge of DC power in the inverter circuit, and

the inverter circuit is configured to control each single-phase inverter and the shorting switch such that reception and delivery of electric power of each DC voltage source of each single-phase inverter, is balanced.

18. The power conversion device according to claim 17,

wherein the DC voltage source of each single-phase inverter includes a capacitor, and

the power conversion device further comprising

a voltage detector configured to detect a voltage of the DC power supply, wherein

the inverter circuit is subjected to output control in accordance with the voltage of the DC power supply and thereby a voltage of each capacitor is controlled.

19. The power conversion device according to claim 17, further comprising

a voltage detector configured to detect a voltage of the DC power supply, and to detect a voltage of the DC voltage source of each single-phase inverter, wherein

the inverter circuit is subject to output control in accordance with the voltage of the DC power supply, and

the shorting switch is switched ON unless voltages of the DC voltage sources all exceed respective setting voltage values, and the shorting switch is switched OFF when the voltages of the DC voltage sources exceed the respective setting voltage values.

20. The power conversion device according to claim 17, further comprising

a voltage detector configured to detect the voltage of the DC power supply, wherein

the inverter circuit is subject to output control in accordance with the voltage of the DC power supply and is controlled such that the charge/discharge of the DC power is switched upon switching ON/OFF the shorting switch.

21. The power conversion device according to claim 17,

wherein the diode in the bridge circuit is a body-diode built in a MOSFET, and the MOSFET with the body-diode is connected in series to the semiconductor switch device.