CN102611131B - For operating the method and system of electricity generation system - Google Patents

Abstract

The present invention relates to methods and systems for operating power generation systems. A photovoltaic (PV) power generation system (100) is described. The system includes a plurality of PV collector units (102) including at least one PV cell (124) and a collector-side single-phase inverter (122). The plurality of PV collector units are configured for coupling with symmetrical polyphase alternating current (AC) loads (18). The system also includes a system controller (108) configured to control operation of the plurality of PV collector units.

Description

Method and system for operating a power generation system

technical field

Embodiments described herein relate generally to photovoltaic (PV) power generation systems, and more specifically, to systems for coupling multiple variable input single-phase direct current (DC) power sources to a symmetrical three-phase alternating current (AC) grid.

Background technique

Solar energy has gradually become an attractive energy source and has been regarded as a clean, renewable form of energy alternative. Solar energy in the form of sunlight can be converted into electricity by solar cells. A more general term for a device for converting light into electrical energy is a "photovoltaic (PV) cell." Sunlight is a subset of light. Thus, solar cells are a subset of photovoltaic (PV) cells. A PV cell includes a pair of electrodes and a light absorbing PV material disposed therebetween. When the PV material is irradiated with light, electrons confined to atoms in the PV material are released by light energy to move freely. In this way, free electrons and holes are generated. These free electrons and holes are effectively separated allowing for continuous extraction of electrical energy. Current commercial PV cells use semiconducting PV materials, typically silicon.

In order to obtain higher current and voltage, the solar cells are electrically connected to form a solar module. In addition to a plurality of solar cells, a solar module may also include sensors, such as irradiance sensors, temperature sensors, and/or power meters. Solar modules can also be connected to form a string of modules. Typically, the DC voltage output by the string of modules is supplied to a grid inverter, such as a DC to AC voltage inverter. The DC to AC voltage inverter converts DC voltage to single-phase or three-phase alternating current (AC) voltage or current. The three-phase AC output can be provided to a power transformer, which steps up the voltage to produce three-phase high voltage AC that is applied to the distribution grid.

Electricity applied to the distribution grid needs to meet grid connectivity expectations. These requirements address safety issues and power quality concerns. For example, grid connectivity expectations include facilitating disconnection of a power generation system from the grid in the event of a transient event such as a power peak or power failure. Another grid connectivity expectation is that generated power is regulated to ensure that the power matches the voltage and frequency of the electricity flowing through the grid. For example, the Institute of Electrical and Electronics Engineers (IEEE) has written a standard (IEEE 1547-2003) addressing grid-connected distributed generation including renewable energy systems. Underwriters Laboratories (UL) has also developed the UL 1741 standard to certify inverters, converters, charge controllers and output controllers for stand-alone power production and grid-connected renewable energy systems. UL 1741 certifies that inverters comply with IEEE1547 for grid connection applications.

Specifically, grid-connected PV power generation systems must meet utility interconnection requirements, which include low voltage ride through (LVRT), voltage regulation, and power factor correction.

Contents of the invention

In one aspect, a photovoltaic (PV) power generation system is provided. The system includes a plurality of PV collector units including at least one PV cell and a collector-side single-phase inverter. These multiple PV collector units are configured to couple with symmetrical polyphase alternating current (AC) loads. The system also includes a system controller configured to control operation of the plurality of PV collector units.

In another aspect, a method for converting direct current (DC) power to alternating current (AC) power for delivery to an electrical load is provided. The DC power is generated from multiple variable input power sources. The method includes providing a plurality of photovoltaic (PV) collector units, each including at least one PV cell and a collector-side single-phase inverter. The plurality of PV collector units are configured to generate a DC voltage and convert the DC voltage to a single phase AC output. The method further includes communicatively coupling at least one system controller to the plurality of PV collector units, and programming the system controller to control operation of the plurality of PV collector units.

In yet another aspect, a power conversion system is provided. The system includes a plurality of collector-side single-phase inverters configured to receive a variable input direct current (DC) voltage. The system also includes a system controller coupled to the plurality of collector-side single-phase inverters and configured to control operation of the plurality of collector-side single-phase inverters. A plurality of collector-side single-phase inverters are configured to provide symmetrical multi-phase alternating current (AC) to electrical loads.

Description of drawings

Figure 1 is a block diagram of a known photovoltaic (PV) power generation system.

2 is a block diagram of a first exemplary embodiment of a PV power generation system including multiple collector-side inverters.

FIG. 3 is a block diagram of a second exemplary embodiment of the PV power generation system shown in FIG. 2 .

FIG. 4 is a block diagram of an exemplary embodiment of a system controller that may be included in the PV power generation system shown in FIG. 2 .

5 is a block diagram of a first alternative embodiment of a PV power generation system including multiple collector-side inverters.

6 is a block diagram of a second alternative embodiment of a PV power generation system including multiple collector-side inverters.

7 is a flowchart of an exemplary method for controlling operation of the PV power generation system shown in FIGS. 2-6 .

detailed description

The methods and systems described herein facilitate controlling multiple variable input single-phase power sources to generate power suitable for distribution and/or transmission on a symmetrical three-phase grid. The methods and systems described herein achieve grid connectivity expectations including, but not limited to, providing steady state and transient symmetry, controlling reactive power, responding to symmetrical or asymmetrical fault currents, shaping ramp rate ) and provide low voltage ride through (LVRT) capability while minimizing capital expenditure, power conversion losses, and line losses. The methods and systems described herein also facilitate supporting grid symmetry during temporary failure or permanent degradation of a portion of a generating resource.

Technical effects of the methods and systems described herein include at least one of: (a) providing a plurality of photovoltaic (PV) collector units each comprising at least one PV cell and a collector-side single-phase inverter, wherein the plurality PV collector units configured to generate a DC voltage and convert the DC voltage to a single-phase AC output; (b) communicatively coupling at least one system controller to the plurality of PV collector units; and, (c) to at least one A system controller is programmed to control the operation of multiple PV collector units.

FIG. 1 is a block diagram of a known photovoltaic (PV) power generation system 10 . System 10 includes PV harvesting device 12 , inverter 14 , transformer 16 , and grid 18 . As referred to herein, grid 18 is a network of conductors and devices configured for distribution and/or transmission of electricity. Typically, the PV collection arrangement 12 includes a plurality of PV module strings coupled, for example, by a DC switching device (not shown in FIG. 1 ) that collects DC voltage from the PV module strings and outputs a DC voltage 30 . The DC voltage 30 is supplied to the inverter 14 . Inverter 14 regulates DC voltage 30 . For example, inverter 14 may be a DC/AC voltage inverter configured to convert DC voltage 30 to three-phase low voltage AC 32 .

Three-phase low voltage AC 32 is supplied to power transformer 16 . Transformer 16 produces three-phase high voltage AC 34 , which is applied to a load, such as grid 18 . System 10 also includes a system controller 36 . System controller 36 is coupled to inverter 14 and is configured to control the operation of inverter 14 .

FIG. 2 is a block diagram of a first exemplary embodiment of a PV power generation system 100 including a plurality of PV collector units 102 . In this first exemplary embodiment, multiple PV collector units 102 are coupled in a delta configuration. FIG. 3 is a block diagram of a second exemplary embodiment of a PV power generation system 100 including a plurality of PV collector units 102 . In this second exemplary embodiment, multiple PV collector units 102 are coupled in a star configuration (also referred to as a wye configuration).

In both the first and second exemplary embodiments, the PV power generation system 100 also includes a grid-side inverter 104 , a power transformer 106 , and a system controller 108 . The PV power generation system 100 provides symmetrical three-phase AC to the grid 18 (shown in FIG. 1 ). Although described herein as providing AC to grid 18, system 100 may provide AC to any suitable load. In the exemplary embodiment, each of plurality of PV collector units 102 includes a PV collection device and a collector-side inverter. For example, the first PV collector unit 120 includes a first collector-side inverter 122 coupled to a first PV collection device 124 . The second PV collector unit 126 includes a second collector-side inverter 128 coupled to a second PV collection device 130 . The third PV collector unit 132 includes a third collector-side inverter 134 coupled to a third PV collector device 136 . The fourth PV collector unit 138 includes a fourth collector-side inverter 140 coupled to a fourth PV collection device 142 . The fifth PV collector unit 144 includes a fifth collector-side inverter 146 coupled to a fifth PV collector 148 . Sixth PV collector unit 150 includes a sixth collector-side inverter 152 coupled to a sixth PV collector device 154 . Although illustrated as including six PV collector units, system 100 may include any suitable number of collector units that allows system 100 to function as described herein. PV collection devices 124, 130, 136, 142, 148, and 154 may include a single PV cell, multiple PV cells assembled into a PV module, multiple PV modules assembled to form a string of PV modules, or allow system 100 to Any other PV cell configuration that works that way.

Since each of the plurality of PV collector units 102 includes a PV collection device and a collector-side inverter, each of the plurality of PV collector units 102 can operate at approximately unity power factor. Near unity power factor operation facilitates delivery of maximum real power to grid 18 with minimum line losses. Furthermore, each of the plurality of PV collector units 102 is also capable of operating at the maximum power point for the inverter/collector combination. More specifically, each collector-side inverter can be individually controlled to match the impedance of the corresponding PV collection device and, therefore, operate at the maximum power point. For example, the first collector-side inverter 122 is controlled by the system controller 108 to operate at the maximum power point for the first PV collection device 124 . Because each of the multiple inverters can operate at a different maximum power point, a unique maximum power is drawn from the PV collection devices 124 , 130 , 136 , 142 , 148 , and 154 .

In a first exemplary embodiment, as shown in FIG. 2 , low voltage single-phase AC 158 output by multiple PV collector units 102 is applied across three conductors (first conductor 160, second conductor 160) of a three-phase system, as shown in FIG. conductor 162 or the third conductor 164). Single-phase inverters 122 , 128 , 134 , 140 , 146 , and 152 may be coupled to three-phase grid 18 such that each inverter is connected between any two of three conductors 160 , 162 , and 164 . Conductors 160 , 162 , and 164 are coupled to power transformer 106 and grid-side inverter 104 .

In a second exemplary embodiment, as shown in FIG. 3 , low voltage single-phase AC 158 output by multiple PV collector units 102 is applied to three conductors of a three-phase system (first conductor 160, second conductor 162 or the third conductor 164). Single-phase inverters 122, 128, 134, 140, 146, and 152 may be coupled to a three-phase grid such that one output of each of the inverters is connected to one of the three conductors while the remaining The output is connected to neutral conductor 166 . Conductors 160 , 162 , 164 , and 166 are coupled to power transformer 106 through grid-side inverter 104 .

Power transformer 106 may be a standard three-phase transformer that produces high voltage three-phase AC 174 for application to grid 18 (shown in FIG. 1 ). In the exemplary embodiment, grid-side inverter 104 stabilizes and regulates the voltage delivered to grid 18 . During steady-state operation of the system 100 , symmetrical three-phase AC is provided by the grid-side inverter 104 . During transient events, such as power peaks along the grid or grid events such as LVRT events, the grid-side inverter 104 for example by detecting and compensating for voltage disturbances (by injecting leading or lagging reactive power onto the grid 18) It is convenient for LVRT and zero voltage ride through (ZVRT). Additionally, the grid-side inverter 104 may also provide power factor correction during steady-state operation.

In the exemplary embodiment, system controller 108 provides control signals 176 to grid-side inverter 104 to perform the functions described herein. Additionally, when a grid event is detected, the system controller 108 provides a power factor reference signal and/or a power curtailment signal to one or more of the plurality of collector units 102, and more specifically, to the collector-side inverter At least one of 122, 128, 134, 140, 146 and 152. The system controller 108 may provide additional information, including real and reactive power commands, to those inverters connected to the common conductor 160 , 162 or 164 . System 100 minimizes the necessary coordination between inverters 122, 128, 134, 140, 146, and 152 to facilitate processing of Generate higher power. System 100 facilitates operating each of multiple collector units 102 at various maximum power points, eliminates DC wiring between collector units 102 and grid-side inverter 104, and provides collector units 102 during grid events rapid reduction.

Furthermore, collector-side inverters 122, 128, 134, 140, 146, and 152 allow system 100 to provide symmetrical three-phase AC even during temporary failure and/or permanent degradation of a subset of multiple PV collector units 102 electricity. For example, system 100 provides symmetrical three-phase AC power even if one or more of collector-side inverters 122, 128, 134, 140, 146, and 152 have failed. If the resulting losses in one or more of the collector-side inverters 122, 128, 134, 140, 146, and 152 lead to an undesired asymmetry in the power generation system 100, then the DC/AC converter 104 is controlled such that the actual and Reactive power is extracted from conductors with excess power generation and provided to conductors with a lack of power generation. In some embodiments, the system 100 may also be controlled such that a controlled asymmetric power generation system is presented to the grid 18 to compensate for grid asymmetries such as single phase faults or asymmetric loads. That is, system 100 facilitates controlling the real and reactive power applied to each of conductors 160, 162, and 164, respectively.

In some embodiments, collector-side inverters 122 , 128 , 134 , 140 , 146 , and 152 each include memory unit 178 . For example, memory unit 178 is disposed within collector-side inverter 122 or is coupled to collector-side inverter 122 . The memory unit 178 stores operating parameters used to control the operation of the collector-side inverter 122 . More specifically, operating parameters that enable inverter 122 to ride through grid events may be stored in memory unit 178 . Grid events may be identified by system controller 108 and/or by inverter 122 . For example, the memory unit 178 may store a threshold grid voltage power command, a voltage ride back command, and/or a reactive power command. In some embodiments, the inverter 122 operates based on the threshold grid voltage power command when the grid voltage is lower than the stored threshold grid voltage. The stored threshold grid voltage may indicate the occurrence of a low voltage ride through event or a zero voltage ride through event. The voltage ride-through return command may include a predetermined period of time after which the inverter 122 is instructed to begin providing power to the grid 18 . The voltage ride-through return command may also include a predetermined ramp rate, thereby instructing the inverter 122 to provide power to the grid 18 . The reactive power command may control the reactive power output of the inverter 122 (including when the inverter 122 is about to provide reactive power). Operation in response to operating parameters stored in memory unit 178 facilitates autonomous control of inverter 122 (eg, controlling inverter 122 based on operating parameters not received from system controller 108 ). Additionally, memory unit 178 may include computer-readable media such as, but not limited to, random access memory (RAM), flash memory, hard disk drive, solid state drive, floppy disk, flash drive, optical disk, digital video disk, and/or or any suitable memory capable of storing, retrieving and/or executing instructions and/or data. Additionally, the system controller 108 may adjust stored operating parameters prior to a grid event.

Furthermore, in some embodiments, multiple PV collector units 102 are geographically dispersed. System controller 108 may control collector unit 120 to provide a different level of reactive power than provided by collector unit 150 . Each of the plurality of geographically dispersed PV collector units 102 is individually controllable to facilitate balanced operation of the PV power generation system 100 and to minimize system losses within the system 100 .

FIG. 4 is a block diagram of an exemplary embodiment of system controller 108 (shown in FIG. 1 ). In some embodiments, the system controller 108 includes a bus 180 or other communication means for communicating information. One or more processors 182 are coupled to bus 180 for processing information, including information from sensors included in PV collector unit 102 . Processor 182 may include at least one computer. As used herein, the term computer is not limited to integrated circuits known in the art as computers, but broadly refers to processors, microcontrollers, microcomputers, programmable logic controllers (PLCs), application-specific integrated circuits and other programmable circuits, and these terms are used interchangeably herein.

System controller 108 may also include one or more random access memory (RAM) 184 and/or other storage devices 186 . RAM 184 and storage device 186 are coupled to bus 180 for storing and communicating information and instructions to be executed by processor 182 . RAM 184 (and/or storage device 186 , if included) may also be used to store temporary variables or other intermediate information during execution of instructions by processor 182 . System controller 108 may also include one or more read-only memories (ROMs) 188 and/or other static memories coupled to bus 180 to store and provide static (eg, unchanging) information and instructions to processor 182 . Processor 182 processes information communicated from a number of electrical and electronic devices, which may include, but are not limited to, irradiance sensors and power meters. Instructions that are executed include, but are not limited to, resident conversion and/or comparator algorithms. The sequence of execution of instructions is not limited to any specific combination of hardware circuitry and software instructions.

The system controller 108 may also include or be coupled to an input/output device 190 . Input/output device 190 may include any device known in the art that provides input data to system controller 108 and/or provides output (such as, but not limited to, solar panel positioning output and/or inverter control output) . Instructions may be retrieved from a storage device 186 comprising, for example, a magnetic disk, a read-only memory (ROM) integrated circuit, a CD-ROM, and/or a DVD, via a remote connection (which is a wired or wireless connection that provides access to one or more electronically accessible media). Provided to RAM 184 . In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the sequence of execution of instructions is not limited to any specific combination of hardware circuitry and software instructions, whether described and/or shown herein. Also, in the exemplary embodiment, input/output devices 190 may include, but are not limited to, computer peripherals associated with an operator interface such as a human-machine interface (HMI), such as a mouse and a keyboard (neither of which are shown in the figure). shown in 4). Additionally, in the exemplary embodiment, additional output channels may include, for example, operator interface monitors and/or alarm devices (neither shown in FIG. 4 ). The system controller 108 may also include a sensor interface 192 that allows the system controller 108 to communicate with sensors. Sensor interface 192 may include one or more analog-to-digital converters that convert analog signals into digital signals that may be used by processor 182 . The system controller 108 may also be coupled to an external monitoring system, such as a supervisory control and data acquisition (SCADA) system, such as a SCADA associated with a utility company and/or substation or network controller.

FIG. 5 is a block diagram of an alternative embodiment 200 of a PV power generation system including multiple PV collector units 102 . Components common to system 100 (shown in FIGS. 2 and 3 ) and system 200 are identified by the same reference numerals. In this embodiment, a PV power generation system 200 includes a grid-side inverter 104 and a system controller 108 . The PV power generation system 200 also includes a power transformer 202 . In this embodiment, the plurality of PV collector units 102 includes a first PV collector unit 120 , a second PV collector unit 126 , a third PV collector unit 132 , and a fourth PV collector unit 138 . Each of the plurality of PV collector units 102 includes a PV collection device and a single-phase collector-side inverter. As described above, the first PV collector unit 120 includes a first collector-side inverter 122 coupled to a first PV collection device 124 . The second PV collector unit 126 includes a second collector-side inverter 128 coupled to a second PV collection device 130 . The third PV collector unit 132 includes a third collector-side inverter 134 coupled to a third PV collector device 136 . The fourth PV collector unit 138 includes a fourth collector-side inverter 140 coupled to a fourth PV collection device 142 .

In this embodiment, PV collector units 102 may each be configured to operate at any power factor including unity power factor. Furthermore, each of the plurality of PV collector units 102 is also capable of operating at the maximum power point for the inverter/harvesting device combination. For example, the first collector-side inverter 122 is configured to operate at a maximum power point for the first PV collection device 124 . Because each of the multiple inverters can operate at a different maximum power point, maximum power is drawn from the PV collection devices 124 , 130 , 136 , and 142 .

In this embodiment, as shown in FIG. 5 , the power transformer 202 outputs three-phase AC from two-phase AC. The first collector unit 120 and the second collector unit 126 are coupled and provide a low voltage AC 260 having a first phase. The third collector unit 132 and the fourth collector unit 138 are coupled and provide a low voltage AC 262 having a second phase. The power transformer 202 will have a low voltage AC 260 of a first phase (i.e. the current provided by the first PV collector unit 120 and the second PV collector unit 126) and a low voltage AC 262 of a second phase (i.e. unit 132 and fourth collector unit 138 ) is split into balanced high voltage three-phase AC 174 for transmission on grid 18 (shown in FIG. 1 ). Power transformer 202 may include, but is not limited to, a Scott-T transformer.

In this embodiment, and as described above with respect to system 100 , grid-side inverter 104 stabilizes and regulates the voltage delivered to grid 18 . During steady-state operation of the system 200 , symmetrical three-phase AC is provided by the grid-side inverter 104 . During transient events, such as power peaks along the grid or grid events such as LVRT events, the grid-side inverter 104 operates, for example, by detecting and compensating for voltage disturbances (by injecting leading or lagging reactive power into the grid 18). Easy access to LVRT. Accordingly, the grid-side inverter 104 may provide power factor correction. In the exemplary embodiment, system controller 108 provides control signals 176 to grid-side inverter 104 to perform the functions described herein. Additionally, when a grid event is detected, system controller 108 provides curtailment signals to one or more of plurality of collector units 102, and more specifically, to at least one of inverters 122, 128, 134, and 140 . The system 200 minimizes the necessary coordination between the inverters 122, 128, 134, and 140 to facilitate processing of commands to the system controller 108 and to facilitate higher power generation from the PV harvesting devices 124, 130, 136, and 142 . System 200 facilitates operating multiple collector units 102 at various maximum power points, facilitates elimination of DC wiring between collector units 102 and grid-side inverter 104, and provides for rapid curtailment of PV collector units 102 during grid events . Furthermore, system 200 reduces wiring complexity when compared to system 100 . Additionally, system 200 reduces the amount of power electronics required in grid-side inverter 104 .

FIG. 6 is a block diagram of another alternative embodiment 300 of a PV power generation system including multiple collector units 102 . Components shared between system 100 (shown in FIGS. 2 and 3 ), system 200 (shown in FIG. 4 ) and system 300 are identified with the same reference numerals.

In this embodiment, as shown in FIG. 6 , a PV power generation system 300 includes a system controller 108 and a power transformer 302 . The plurality of PV collector units 102 includes a first PV collector unit 301, a second PV collector unit 312, a third PV collector unit 314, a fourth PV collector unit 316, a fifth PV collector unit 318, and a sixth PV collector unit. PV collector unit 320 . Each of the plurality of PV collector units 102 includes a PV collection device and a single-phase collector-side inverter. The first PV collector unit 310 includes a first collector-side inverter 330 coupled to the first PV collection device 124 . The second PV collector unit 312 includes a second collector-side inverter 332 coupled to the second PV collector device 130 . The third PV collector unit 314 includes a third collector-side inverter 334 coupled to a third PV collector device 136 . The fourth PV collector unit 316 includes a fourth collector-side inverter 336 coupled to the fourth PV collection device 142 . Fifth PV collector unit 318 includes a fifth collector-side inverter 338 coupled to fifth PV collector device 148 . Sixth PV collector unit 320 includes a sixth collector-side inverter 340 coupled to sixth PV collection device 154 .

In this embodiment, each of the PV collector units 102 is configured to operate over a wide power factor range including unity power factor. The plurality of PV collector units 102 may be configured to operate over a range of power factors, such as, but not limited to, from about -0.9 to full power factor to 0.9. Furthermore, each of the plurality of PV collector units 102 is also capable of operating at the maximum power point for the inverter/harvesting device combination. For example, the first collector-side inverter 330 is configured to operate at a maximum power point for the first PV collection device 124 . Because each of the plurality of inverters 330 , 332 , 334 , 336 , 338 , and 340 can operate at a different maximum power point, maximum power is extracted from the PV collection devices 124 , 130 , 136 , 142 , 148 , and 154 .

In particular, PV power generation system 300 does not include grid-side inverter 104 . In this embodiment, collector-side inverters 330 , 332 , 334 , 336 , 338 , and 340 are rated to stabilize and regulate the voltage delivered to grid 18 (shown in FIG. 1 ). During steady-state operation of system 300 , system controller 108 provides control signals to each of collector-side inverters 330 , 332 , 334 , 336 , 338 , and 340 to provide symmetrical three-phase AC 174 to grid 18 . Additionally, the collector-side inverters 330, 332, 334, 336, 338, and 340 facilitate LVRT during transient events, for example, by detecting and compensating for voltage disturbances (by injecting leading or lagging reactive power into the grid 18). , and thus provide power factor correction. Additionally, collector-side inverters 330 , 332 , 334 , 336 , 338 , and 340 may scale down in response to a scale-down signal from system controller 108 . The system 300 can also be controlled to create an asymmetric unbalanced power generation system with respect to real and reactive power injection in response to grid conditions. For example, system controller 108 may provide a power factor reference signal to collector-side inverters 330 , 332 , 334 , 336 , 338 , and 340 when a grid condition, such as a load fault, is detected. In addition, collector-side inverters 330, 332, 334, 336, 338, and 340 can autonomously respond to grid conditions including high voltage and low voltage ride through conditions, thereby providing Var support, frequency droop response, and automatic voltage regulation. The system controller 108 provides control signals at low data rates to optimize the response of the system 300 and minimize system losses during steady state operation. The system controller 108 may also act as a data acquisition system.

In the embodiment shown in FIG. 6, multiple PV collector units 102 output low voltage single phase AC 342, which is applied to one of three conductors (first conductor 160, second conductor 162, or third conductor 164). . As an example, first inverter 330 and fourth inverter 336 are coupled between first conductor 160 and second conductor 162 . The second inverter 332 and the fifth inverter 338 are coupled between the second conductor 162 and the third conductor 164 . The third inverter 334 and the sixth inverter 340 are coupled between the third conductor 164 and the first conductor 160 . Although illustrated in a delta configuration, the first inverter 330, the second inverter 332, the third inverter 334, the fourth inverter 336, the fifth inverter 338, and the sixth inverter 340 are also Coupling in a star configuration is possible.

Conductors 160 , 162 and 164 are coupled to power transformer 106 . Power transformer 106 outputs high voltage three-phase AC 174 for application to grid 18 .

FIG. 7 is a flowchart 400 of an exemplary method 410 for controlling operation of PV power generation systems 100 , 200 , and 300 (shown in FIGS. 2-5 ). More specifically, method 410 converts direct current (DC) power to alternating current (AC) power for delivery to an electrical load, such as grid 18 (shown in FIG. 1 ), where the DC power is supplied by a plurality of variable input units Phase power sources such as PV harvesting devices 124, 130, 136, 142, 148, and 154 are generated. In the exemplary embodiment, method 410 includes providing 420 a plurality of PV collector units, each comprising at least one PV cell and a collector-side single-phase inverter, the plurality of PV collector units configured to generate a DC voltage and This DC voltage is converted to a single phase AC output. For example, a PV collector unit 102 (shown in FIG. 2 ) is provided 420 and includes PV harvesting devices 124, 130, 136, 142, 148, and 154 that generate a DC voltage, and convert the DC voltage to Collector-side single-phase inverters 122 , 128 , 134 , 140 , 146 and 152 are single-phase AC 158 (shown in FIG. 2 ).

In the exemplary embodiment, method 410 also includes communicatively coupling 422 at least one system controller, such as system controller 108 (shown in FIG. 2 ), to plurality of PV collector units 102 . Method 410 also includes programming 424 system controller 108 to control operation of plurality of PV collector units 102 . Method 410 may also include programming 426 system controller 108 to transmit a curtailment signal to at least one of plurality of PV collector units 102 when a load fault is detected.

The embodiments described above facilitate efficient and cost-effective operation of solar power generation systems. The methods and systems described herein facilitate regulation of electrical power generated by a plurality of solar collector units for delivery to a distribution grid. Power delivered to the grid achieves grid connectivity expectations including, but not limited to, steady-state and transient symmetry, control of reactive power, fault current provisioning, ramp rate shaping, and grid event ride-through. Capital expenditures, power conversion losses and line losses are minimized. The methods and systems described herein facilitate supporting grid symmetry during temporary failure or permanent degradation of a subset of generating resources. Furthermore, embodiments described herein support and control both symmetrical and asymmetrical fault currents.

Embodiments of the solar power generation system are described above in detail. These methods and systems are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be used independently and separately from other components and/or steps described herein.

Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a figure may be referenced and/or claimed in combination with any feature of any other figure.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

parts list

Claims (8)

1. A photovoltaic power generation system comprising: a plurality of PV collector units, each of the plurality of PV collector units comprising at least one PV cell and a collector-side single-phase inverter, each of the plurality of PV collector units configured via at least one transmission line coupled with the grid; a grid-side inverter coupled between the at least one collector-side single-phase inverter of each PV collector unit and the grid, the grid-side inverter being configured to receive a single-phase alternating current (AC) output by a single-phase inverter and providing polyphase AC to the grid, and a system controller, communicatively coupled to each PV collector unit and the grid-side inverter, The system controller is configured to: individually coordinate operation of each of the plurality of PV collector units and the grid-side inverter; and controlling operation of the plurality of PV collector units through at least one of a low voltage ride through (LVRT) event and a zero voltage ride through (ZVRT) event. 2. The system (100) of claim 1, wherein the load fault comprises at least one of a low voltage ride through (LVRT) and a zero voltage ride through (ZVRT) event. 3. The system (100) of claim 1, wherein the collector-side single-phase inverter (122) includes a memory unit (178) storing operating parameters, the collector-side single-phase inverter configured to operate according to the operating parameter in response to at least one of a measured grid condition and a signal from the system controller (108). 4. The system (100) of claim 3, wherein the operating parameters include at least one of a threshold grid voltage power command, a voltage ride back command, and a reactive power command. 5. The system (100) of claim 1, wherein the plurality of PV collector units (102) are configured to separately control real and reactive power applied to each phase of the multi-phase AC load (18) power. 6. The system (100) of claim 1, wherein the system controller (108) is configured to at least one of the following when a load fault is detected: transmitting a power factor reference signal to at least one of the plurality of PV collector units (102), and A curtailment signal is communicated to at least one of the plurality of PV collector units. 7. The system (100) of claim 1, wherein each of the plurality of PV collector units (102) is configured to operate at a maximum power point determined for the respective PV collector unit, and direct current ( DC) voltage is converted to a single-phase alternating current (AC) output. 8. The system (100) of claim 7, further comprising a transformer (106) configured to receive a single-phase AC output and to output said single-phase AC from a plurality of collector-side single-phase inverters Converted to a balanced polyphase AC output.