Circuit for converting solar energy into AC power

• US 5,576,533 A
• Filed: 10/17/1994
• Issued: 11/19/1996
• Est. Priority Date: 10/17/1994
• Status: Expired due to Fees

• Current Assignee: Premier TDO Co., Ltd.
• Original Assignee: Premier Global Corporation, Ltd.
• Inventors: Tantraporn, Wirojana
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US08/323,816
• Time in Patent Office: 764 Days
• Field of Search: 250/214 R, 250/214 SG, 250/214.1, 250/214 RC, 250/216, 363/98, 363/132, 363/27, 363/17, 323/906, 204/196, 204/197, 136/291, 136/293, 315/86, 307/64
• US Class Current: 250/214.00R
• CPC Class Codes: H01L 31/02021 for solar cells electrical connection means, e.g. junction boxes, specially adapted for structural association with photovoltaic modules H02S40/34
• CPC Class Codes: H02M 7/516 Self-oscillating arrangements
• CPC Class Codes: H02M 7/521 in a bridge configuration
• CPC Class Codes: Y02B 10/10 Photovoltaic [PV]
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 136/293 Circuits
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

A circuit for converting solar energy into ac power for supplementary household power has a number of solar photovoltaic cells connected in parallel in groups, with the various groups connected in series (30), and a bridge arrangement of four switching devices (31, 32, 33, 34) each operated to pass current in one direction, with the series-connected groups of cells (30) connected between positive and negative bridge terminals (1, 2), and means for connecting the bridge arms (3, 4) across the primary coils of a transformer (312), with the secondary coils thereof connected to the switching devices to control the phase of passed current, the output at the bridge arms (3, 4) being connectable to the household ac.

Claims

1. A circuit for converting solar energy into ac power supplementary to household ac power, comprising the combination of:

a plurality of solar photovoltaic cells chosen to be as nearly identical as possible;

means for connecting said cells in parallel in one or more groups of a certain number of cells, each group having a group short-circuit current, such that when illuminated the group'"'"'s short-circuit current exceeds a value of application interest;

means for connecting said groups of parallel-connected cells in series forming an ensemble such that the open-circuit voltage of the ensemble is 5-20% greater than an absolute value of a peak voltage of the household ac power;

four units of switching devices each of which can be operated to pass a current in one direction and having a positive and a negative electrode, the units being connected in a bridge configuration in which the positive electrodes of two units are electrically connected at a first terminal, the negative electrodes of the two other units are electrically connected at a second terminal, and in which one unit of said two units is connected to one unit of said other two units, through a third terminal, the other unit of said two units being connected to the other unit of said other two units through a fourth terminal;

means for connecting the ensemble comprising the series connected groups of parallel solar cells to said bridge with the positive voltage terminal of the ensemble connected to the first bridge terminal and the negative voltage terminal of the ensemble to the second bridge terminal;

an isolation transformer having a primary coil and a pair of input terminals and at least four low voltage secondary output coils which are isolated from one another and from the primary coil, each having a pair of output terminals;

means for connecting the third and fourth terminals of said bridge to the terminals of the primary coil of the transformer;

plug which can be plugged into the ac power line; and

means for connecting the output terminals of each secondary coil across a pair of control electrodes of the switching devices such that in use the voltages on the control electrodes of the devices on the opposite arms of the bridge have the same ac phase as each other and a phase which is 180°

different from the ac phase on the control electrodes of the other two switching devices on adjacent arms of the bridge.

2. A circuit as defined in claim 1, further comprising more than one isolation transformer, the primary coils of which are connected in parallel and the individual secondary coils serving to control respective switching devices.

3. A circuit as defined in claim 1, wherein the switching devices are silicon-controlled rectifiers (SCRs).

4. A circuit as defined in claim 3, further comprising a rectifier with appropriate voltage and current ratings connected in electrical series with said ensemble of solar cells, the series being connected between the first and second terminals of the bridge such that by rectification the current can only flow from the ensemble to the first terminal of the bridge.

5. A circuit as defined in claim 3, wherein "on" control signal for controlling each switching device is of low voltage high current type and an "off" control signal is of the high voltage low current type.

6. A circuit as defined in claim 1, wherein the switching devices are selected from the group comprising Field-Effect Transistors (FET), bipolar transistors, Insolated-Gate Bipolar Transistors (IGBT), Gate-Turn-Off Thyristors (GTO), and MOS-Controlled Thyristors (MCT).

7. A plurality of circuits, each as defined in claim 1, connected across pairs of lines of three-phase ac power lines, to provide supplementary power.

8. A plurality of circuits as defined in claim 7, arranged to provide different amounts of supplemental current into different one-phase pairs of the three-phase lines.