POWER CONVERSION APPARATUS, POWER CONDITIONER, AND POWER GENERATION SYSTEM

• US 20100232192A1
• Filed: 02/23/2010
• Published: 09/16/2010
• Est. Priority Date: 03/13/2009
• Status: Active Grant

• Current Assignee: Tokyo Institute of Technology (National University Corporation Tokyo Institute of Technology), Omron Corporation
• Original Assignee: Tokyo Institute of Technology (National University Corporation Tokyo Institute of Technology), Omron Corporation
• Inventors: Mabuchi, Masao, Tsubota, Yasuhiro, Mizokami, Takao, Fujita, Hideaki
• Granted Patent: US 8,184,462 B2
• Time in Patent Office: Days
• US Class Current: 363/124
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• 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: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A first chopper circuit generates a first sequence of square wave voltages having a voltage level that changes to a positive side by chopping a direct current voltage at a system frequency. A second chopper circuit generates a second sequence of square wave voltages having a voltage level that changes to a negative side by chopping a direct current voltage at a frequency twice as high as the system frequency. The second chopper circuit further generates a third sequence of square wave voltages having a voltage level that changes to the positive and negative side in turns in the manner of sinusoidal wave by summing the first sequence of square wave voltages and the second sequence of square wave voltages. A third chopper circuit chops the third sequence of square wave voltages at a frequency determined by a timing that depends on if a voltage difference thereof to a sinusoidal wave voltage results in a positive value or a negative value and outputting the chopped third sequence of square wave voltages as a charge/discharge output. The third chopper circuit PWM-controls the charge/discharge output at a PWM frequency so that the difference is corrected to thereby generate a sinusoidal wave voltage that continuously changes to the positive and negative sides.

Claims

1. A power conversion apparatus comprising:

a first square wave voltage generator for chopping a direct current voltage at a first frequency and thereby generating a first sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to a positive side relative to a first reference potential;

a second square wave voltage generator for using a potential of the first sequence of square wave voltages as a second reference potential, the second square wave voltage generator chopping an output of the first square wave voltage generator at a second frequency higher than the first frequency and thereby generating a second sequence of square wave voltages including a plurality of square wave voltages having a voltage level lower than the voltage level of the first sequence of square wave voltages on the positive side that changes to a negative side relative to the second reference potential, the second square wave voltage generator further summing the first and second sequences of square wave voltages and thereby generating a third sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to the positive and negative sides in turns in the manner of sinusoidal wave relative to the first reference potential;

a third square wave voltage generator for chopping the third sequence of square wave voltages at a third frequency determined by a timing that depends on if a voltage difference thereof to a sinusoidal wave voltage results in a positive value or a negative value and outputting the chopped third sequence of square wave voltages as a charge/discharge output; and

a sinusoidal wave voltage generator for PWM-controlling the charge/discharge output of the third square wave voltage generator at a PWM frequency higher than the third frequency so that the voltage difference between the third sequence of square wave voltages and the sinusoidal wave voltage is corrected and gaining the sinusoidal wave voltage that continuously changes to the positive and negative sides relative to the first reference potential using the third sequence of square wave voltages and the PWM-controlled output.

2. The power conversion apparatus as claimed in claim 1, wherein

the first square wave voltage generator includes a first switching circuit having first and second two switching elements connected in series to each other,

the first switching circuit is connected in parallel to a first capacitor connected to between positive and negative electrodes of a direct current power source,

the first and second switching elements are switched on and off in turns at the first frequency,

the second square wave voltage generator includes a parallel connection circuit having a second capacitor and a second switching circuit,

one parallel connection side of the parallel connection circuit is connected to a connecting portion where the first and second switching elements are serially connected to each other,

the second switching circuit has third and fourth two switching elements connected in series to each other,

the third and fourth switching elements are switched on and off in turns at the second frequency,

the third square wave voltage generator includes a parallel connection circuit having a third capacitor and a third switching circuit,

the third switching circuit has fifth and sixth two switching elements connected in series to each other,

a connecting portion where the fifth and sixth switching elements are serially connected to each other is connected to a connecting portion where the third and fourth switching elements are serially connected to each other,

the fifth and sixth switching elements are switched on and off in turns at the third frequency,

the sinusoidal wave voltage generator includes a fourth switching circuit connected in parallel to the parallel connection circuit of the third square wave voltage generator,

the fourth switching circuit has seventh and eighth two switching elements connected in series to each other, and

the seventh and eighth switching elements are PWM-controlled at the PWM frequency higher than the third frequency.

3. The power conversion apparatus as claimed in claim 1, wherein

the first frequency is 50 Hz or 60 Hz equal to a system frequency of a commercial power source, and

the second frequency is a frequency twice as high as the first frequency.

4. A power conditioner for converting a direct current power outputted from a direct current power source into an alternating current power for utility interconnection with a commercial power source, comprising:

a first square wave voltage generator for chopping the direct current voltage from the direct power source at a first frequency equal to a system frequency and thereby generating a first sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to a positive side relative to a first reference potential;

a second square wave voltage generator for using a potential of the first sequence of square wave voltages as a second reference potential, the second square wave voltage generator chopping an output of the first square wave voltage generator at a second frequency a predetermined number of times as high as the first frequency and thereby generating a second sequence of square wave voltages including a plurality of square wave voltages having a voltage level lower than the voltage level of the first sequence of square wave voltages on the positive side that changes to a negative side relative to the second reference potential, the second square wave voltage generator further generating a third sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to positive and negative sides in turns in the manner of sinusoidal wave relative to the first reference potential by summing the first and second sequences of square wave voltages;

a third square wave voltage generator for chopping the third sequence of square wave voltages at a third frequency determined by a timing that depends on if a voltage difference thereof to an output command results in a positive value or a negative value and outputting the chopped third sequence of square wave voltages as a charge/discharge output; and

a sinusoidal wave voltage generator for PWM-controlling the charge/discharge output of the third square wave voltage generator at a PWM frequency higher than the third frequency so that the voltage difference between the sequence of square wave voltages and the sinusoidal wave voltage is corrected and gaining the sinusoidal wave voltage that continuously changes to the positive and negative sides relative to the first reference potential using the third sequence of square wave voltages and the PWM-controlled output, the sinusoidal wave voltage generator further outputting the sinusoidal wave voltage to a load.

5. The power conditioner as claimed in claim 4, wherein

the first square wave voltage generator includes a first switching circuit having first and second two switching elements connected in series to each other,

the first switching circuit is connected in parallel to a first capacitor connected to between positive and negative electrodes of a direct current power source,

the first and second switching elements are switched on and off in turns at the first frequency,

the second square wave voltage generator includes a parallel connection circuit having a second capacitor and a second switching circuit,

one parallel connection side of the parallel connection circuit is connected to a connecting portion where the first and second switching elements are serially connected to each other,

the second switching circuit has third and fourth two switching elements connected in series to each other,

the third and fourth switching elements are switched on and off in turns at the second frequency,

the third square wave voltage generator includes a parallel connection circuit having a third capacitor and a third switching circuit,

the third switching circuit has fifth and sixth two switching elements connected in series to each other,

a connecting portion where the fifth and sixth switching elements are serially connected to each other is connected to a connecting portion where the third and fourth switching elements are serially connected to each other,

the fifth and sixth switching elements are switched on and off in turns at the third frequency,

the sinusoidal wave voltage generator includes a fourth switching circuit connected in parallel to the parallel connection circuit of the third square wave voltage generator,

the fourth switching circuit has seventh and eighth two switching elements connected in series to each other, and

the seventh and eighth switching elements are PWM-controlled at the PWM frequency higher than the third frequency.

6. The power conditioner as claimed in claim 4, wherein

the first frequency is 50 Hz or 60 Hz equal to a system frequency of a commercial power source, and

the second frequency is a frequency twice as high as the first frequency.

7. The power conditioner as claimed in claim 5, wherein

the first frequency is 50 Hz or 60 Hz equal to a system frequency of a commercial power source, and

the second frequency is a frequency twice as high as the first frequency.

8. A power generation system comprising:

a direct current power source; and

a power conditioner connected to the direct current power source, wherein

the power generation system converts a direct current power generated by the direct current power source into an alternating current power using the power conditioner for utility interconnection with a commercial power source, and

the power conditioner comprises;

a first square wave voltage generator for chopping the direct current voltage from the direct power source at a first frequency relevant to a system frequency and thereby generating a first sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to a positive side relative to the first reference potential;

a second square wave voltage generator for using a potential of the first sequence of square wave voltages as a second reference potential, the second square wave voltage generator chopping an output of the first square wave voltage generator at a second frequency a predetermined number of times as high as the first frequency and thereby generating a second sequence of square wave voltages including a plurality of square wave voltages having a voltage level lower than the voltage level of the first sequence of square wave voltages that changes to a negative side relative to the second reference potential on the positive side, the second square wave voltage generator further generating a third sequence of square wave voltages including a plurality of square wave voltages having a voltage level that changes to the positive and negative sides in turns in the manner of sinusoidal wave relative to the first reference potential by summing the first and second sequences of square wave voltages;

a third square wave voltage generator for chopping the third sequence of square wave voltages at a third frequency determined by a timing that depends on if a voltage difference thereof to a sinusoidal wave voltage results in a positive value or a negative value and outputting the chopped third sequence of square wave voltages as a charge/discharge output; and

a sinusoidal wave voltage generator for PWM-controlling the charge/discharge output of the third square wave voltage generator at a PWM frequency higher than the third frequency so that the voltage difference between the sequence of square wave voltages and the sinusoidal wave voltage is corrected and gaining the sinusoidal wave voltage that continuously changes to the positive and negative sides relative to the first reference potential using the third sequence of square wave voltages and the PWM-controlled output, the sinusoidal wave voltage generator further outputting the sinusoidal wave voltage to a load.