Method of operating a power supply system having parallel-connected inverters, and power converting system

• US 6,285,572 B1
• Filed: 02/28/2000
• Issued: 09/04/2001
• Est. Priority Date: 04/20/1999
• Status: Expired due to Term

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Morita, Isao, Madenokouji, Masaki, Onizuka, Keigo, Makino, Yasuhiro
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/514,767
• Time in Patent Office: 554 Days
• Field of Search: 363/72, 363/70, 363/76, 363/79, 363/50, 363/56, 363/54, 363/37, 363/41, 315/307
• US Class Current: 363/72
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/10 The dispersed energy generation being of fossil origin, e.g. diesel generators
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 2300/28 The renewable source being wind energy wind motors F03D
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects

Abstract

A method whereby a plurality of inverters for converting DC power outputted from a DC power supply, such as solar cells or fuel cells, to AC power are operated efficiently without being biased to particular inverters. The number of inverters to be run is determined in correspondence with at least one output value of the DC output or AC output, and the determined number of inverters are selected and made to run from among the plurality of inverters on the basis of a predetermined rule. In addition, a parallel-connected system is disclosed for enabling efficient and appropriate parallel-in operation by the use of inverters, with one of the inverters controlling the remaining inverters and effecting system interconnection protection.

Claims

1. A method of operation for a power supply system having a plurality of inverters connected in parallel with a DC power supply whose generated electric energy increases or decreases, in which said inverters convert an electric output from said DC power supply to frequency- and voltage-controlled AC power and output the AC power to a system, the method comprising:

(a) setting any one of the inverters to serve as a master unit and the other inverters to serve as slave units, wherein the master unit controls the slave units;

(b) allowing said master unit to control said slave units on the basis of at least one of an increase or decrease in the electric energy from the DC power supply and an increase or decrease in the AC power outputted from said inverters; and

(c) controlling operation of said inverters on the basis of DC power available, the controlling causing more inverters to run if sufficient DC power is available and fewer inverters to run if there is insufficient DC power, wherein said controlling operates any one of said inverters such that the amount of AC power outputted from said any one of said inverters increases or decreases in correspondence with an increase or decrease in the amount of electric power outputted from the DC power supply, and said controlling operates remaining ones of said invertes at a predetermined standard value.

2. The method of claim 1, wherein, in the first step, when running is suspended, said master unit sets, as a master unit to be used at a start of the next running, an inverter having the lowest amount of output AC power or shortest running time from among all of the inverters, and sets the remaining inverters as slave units.

3. The method of claim 1, wherein, in the first step, when running is suspended, said master unit orders the slave units in an ascending order starting from the slave unit having the lowest amount of output AC power or the shortest running time.

4. The method of claim 3, wherein, in the first step, the ordering of the slave units is randomly set by using random numbers.

5. The method of claim 1, further comprising the steps of connecting each inverter to a remote controller for remotely controlling the inverter and connecting the remote controllers to one another so that the remote controllers can transmit and receive signals to and from one another, and wherein the operating of said inverters is effected through said remote controllers in the second step.

6. The method of claim 1, wherein, in the second step, the master unit operates the slave units in accordance with an amount of electric power output from said DC power supply.

7. The method of claim 1, wherein, in the second step, a number of slave units which are to run is determined on the basis of whether the DC power is increasing or decreasing, which is estimated by a first differential of the electric power output from said DC power supply.

8. The method of claim 1, wherein, in at least one of the first and second steps, an inverter which is ineffective is excluded from being an object of running.

9. A system for converting DC power to AC power, comprising:

(a) a plurality of inverters, each inverter being adapted to receive DC power and convert the DC power to AC power; and

(b) a controller connected to the inverters and controlling operation of said inverters on the basis of DC power available, the controller causing more inverters to run if sufficient DC power is available and fewer inverters to run if there is insufficient DC power, wherein said controller operates any one of said inverters such that the amount of AC power outputted from said any one of said inverters increases or decreases in correspondence with an increase or decrease in the amount of electric power outputted from the DC power supply, and said controller operates remaining ones of said inverters at a predetermined standard value.

10. The system of claim 9, wherein said controller is inside of each of said inverters.

11. The system of claim 9, wherein said controller is outside of each of said inverters.

12. The system of claim 9, wherein said any one of said inverters effects maximum power point tracking control by following the increase or decrease in DC power inputted to said any one of said inverters, and said remaining ones of said inverters are subjected to constant-level energy control for constantly obtaining maximum outputs.

15. The system of claim 9, wherein said controller includes remote controllers which are respectively connected to said plurality of inverters and communication means for connecting said remote controllers with one another.

17. A system of claim 9, wherein, when running of said generator is suspended, said master unit sets a master unit to be used during the start of the next running of said generator.

19. The system of claim 9, wherein, when running of said generator is suspended, said master unit sets as a master unit to be used during the start of the next running of said generator an inverter having the lowest amount of output power or shortest running time from among said inverters including said master inverter.

13. A system for converting generated electric power to AC power, wherein a plurality of inverters provided respectively with a protector for effecting system interconnection protection for a commercial power supply are connected in parallel, and electric power generated by a generator is converted to electric power corresponding to a commercial power supply and is outputted from a number of inverters which number is determined on the basis of the amount of generated electric power, comprising:

a controller for effecting protected operation of said plurality of inverters by a protector provided in at least one of said inverters when at least two of said inverters are running.

14. The system of claim 13, wherein said controller sets one master unit, and the system interconnection protection of said plurality of inverters is effected by said protector of said master unit.

16. The system of claim 13, wherein said controller includes remote controllers which are respectively connected to said plurality of inverters and communication means for connecting said remote controllers with one another.

18. A system of claim 13, wherein, when running of said generator is suspended, said master unit sets a master unit to be used during the start of the next running of said generator.

20. The system of claim 13, wherein, when running of said generator is suspended, said master unit sets as a master unit to be used during the start of the next running of said generator an inverter having the lowest amount of output power or shortest running time from among said inverters including said master inverter.