NL2021572B1 - Method and device for controlling single-phase cascaded photovoltaic grid-connected inverter system - Google Patents

Abstract

The present disclosure provides a method for controlling a single-phase cascaded photovoltaic grid-connected inverter system, including: detecting first local 5 information of a first inverter and obtaining phase information of a grid voltage, controlling a line current to be in a same phase as the grid voltage, and implementing MPPT operation of the first inverter, and detecting second local information of the second inverter, and controlling an output voltage of the second inverter to be in the same phase as the grid voltage. Only one communication link is required to provide 10 the phase information of the grid voltage to the first inverter, and all other local information can be obtained by local detection. (Fig. l) 25

Description

Ref .: LHC1850292NL - P33716NL00

METHOD AND DEVICE FOR CONTROLLING SINGLE PHASE CASCADED PHOTOVOLTAIC GRID-CONNECTED INVERTER SYSTEM

Technical Field

Embodiments of the present disclosure relate to the field of photovoltaic power generation, and more particularly, to a method and device for controlling a single-phase cascaded photovoltaic grid-connected inverter system.

Technical Background

With industrial development and population growth, human beings consume an increasing amount of traditional fossil energy, which incurs to a series of environmental and social problems, such as environmental pollution, global warming and energy crisis, etc. Currently, solar photovoltaic power generation is considered as a prospective method for power generation using renewable energy that can replace the traditional fossil energy.

Solar energy is clean energy that is pollution-free, widely distributed, and easily accessible. Moreover, a location for installing the photovoltaic power generation system is flexible. It can be installed in a rural area and operated off-grid to form an autonomous regional power supply system, which solves a power supply problem in the rural area. It can also be connected to the grid in a large scale so as to input power into the grid for use by users. Large scale of the photovoltaic grid-connected power generation has been widely applied in a considerable number of occasions. However, compared to most other power generation methods, existing photovoltaic power generation technologies have disadvantages of low efficiency or energy conversion and high cost of power generation. Therefore, how to improve efficiency and reduce the cost are two core issues in photovoltaic power generation at present. The configuration and control of a power electronics interface converter in a photovoltaic power generation system are the most critical parts determining the energy conversion efficiency, reliability and cost of the photovoltaic power generation system, and thus attracting more and more attention. An ideal photovoltaic power generation architecture should be in a low cost, high energy conversion efficiency, strong expandability, flexible controllability and high reliability. In view of this, a single-phase cascaded photovoltaic grid-connected inverter system is considered as a prospective photovoltaic power generation architecture.

In the related art, the single-phase cascaded photovoltaic grid-connected inverter system usually adopts centralized communication to acquire a grid synchronization signal. For a cascaded photovoltaic grid-connected inverter system with N cascaded photovoltaic inverters, at least N communication links are required to allow each inverter to obtain the grid synchronization signal, and excessive communication links will result in reliability of the system being greatly restricted by communication and high cost for control. Especially when the single-phase cascaded photovoltaic grid-connected inverter system is applied in large-scale medium / high-voltage grid-connected fields in which multiple photovoltaic inverters are included in each cascaded photovoltaic grid-connected system, complexity for communication may greatly reduce the reliability of the system and thus increase the cost for control.

Summary of the Invention

To solve the above problems, expose the present disclosure provide a method and device for controlling a single-phase cascaded photovoltaic grid-connected inverter system so as to overcome or at least partially solve the above problems.

According to a first aspect of the present disclosure, a method for controlling a single-phase cascaded photovoltaic grid-connected inverter system is provided, which includes steps of detecting first local information or a first inverter and receiving phase information of a grid voltage, controlling a line current to be in the same phase as the grid voltage based on the first local information and the phase information of the grid voltage, and implementing MPPT operation of the first inverter; and detecting, for each second inverter, second local information of the second inverter, controlling an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information, and implementing MPPT operation or the second inverter.

In the above method, which includes steps of detecting or first local information or a first inverter and receiving phase information or a grid voltage, controlling a line current to be in the same phase as the grid voltage based on the first local information and the phase information of the grid voltage, and implementing MPPT operation of the first inverter; and detecting, for each second inverter, second local information of the second inverter, controlling an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information, and implementing MPPT operation or the second inverter, since only one communication link is required to provide the phase information of the grid voltage to the first inverter, and all other local information can be obtained by local detection, lower requirements for communication, reduced complexity for controlling the system, improved reliability and lower cost are achieved.

According to a second aspect of the present disclosure, a device for controlling a single-phase cascaded photovoltaic grid-connected inverter system is provided, which includes:

a first control module, configured to detect first local information or a first inverter and obtain phase information of a grid voltage, control a line current to be in the same phase as the grid voltage based on the first local information and the phase information of the grid voltage, and implement MPPT operation of the first inverter; and a second control module, configured to, for each second inverter, detect second local infomiation of the second inverter, control an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information, and implement MPPT operation of the second inverter.

According to a third aspect of the present of the disclosure, an apparatus for controlling a single-phase cascaded photovoltaic grid-connected inverter system is provided, which includes:

at least one processor; and at least one memory in communication with the processor, in the memory stores program instructions executable by the processor which calls the program instructions to execute the method for controlling the single-phase cascaded photovoltaic grid-connected inverter system being implemented in any one of possible in the first aspect.

According to a fourth aspect of the present disclosure, a non-transitory computer readable storage medium is provided, which stores computer instructions that enable a computer to execute the method for controlling the single-phase cascaded photovoltaic grid-connected inverter system being implemented in any one of possible possibilities in the first aspect.

It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative, rather than limiting the present of the present disclosure.

Letter Description of the Drawings

FIG. 1 is a flow chart or a method for controlling a single-phase cascaded photovoltaic grid-connected inverter system according to an embodiment of the present disclosure;

FIG. 2 is a structure diagram or a single-phase cascaded photovoltaic grid-connected inverter system according to an embodiment of the present disclosure;

FIG. 3 is a structure diagram of a first inverter or a single-phase cascaded photovoltaic grid-connected inverter system according to an embodiment of the present disclosure;

FIG. 4 is a structure diagram or a second-inverter or a single-phase cascaded photovoltaic grid-connected inverter system according to an embodiment of the present disclosure;

FIG. 5 is a flow chart or a method for controlling a line current or a first inverter according to an embodiment of the present disclosure;

FIG. 6 is a flow chart or method for controlling an output voltage or a second inverter according to an embodiment of the present disclosure;

FIG. 7 is a structure diagram of a device for controlling a single-phase cascaded photovoltaic grid-connected inverter system according to an embodiment of the present disclosure;

FIG. 8 is a structure diagram of an apparatus for controlling a single-phase cascaded photovoltaic grid-connected inverter system according to an embodiment of the present disclosure;

FIG. 9 is a simulation schematic diagram or output active power or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters with symmetrical structure and in partially shielded condition according to an embodiment of the present disclosure;

FIG. 10 is a simulation schematic diagram or steady-state output voltage or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters with symmetrical structure and in partially shielded condition according to an embodiment of the present disclosure;

FIG. 11 is a simulation schematic diagram or voltage on DC side of inverters or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters with symmetrical structure and in partially shielded condition according to an embodiment of the present disclosure;

FIG. 12 is a simulation schematic diagram or a steady-state line current or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters with symmetrical structure and in partially shielded condition according to an embodiment of the present disclosure and grid voltage;

FIG. 13 is a simulation schematic diagram or output active power or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters according to an embodiment of the present disclosure on the condition of the grid voltage dropping 10%;

FIG. 14 is a simulation schematic diagram or steady-state output voltage or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters according to an embodiment of the present disclosure on condition of the grid voltage dropping 10%;

FIG. 15 is a simulation schematic diagram or voltage on DC-side or inverter or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters according to an embodiment of the present disclosure on condition of the grid voltage dropping 10%; and

FIG. 16 is a simulation schematic diagram or steady-state line current and grid voltage or a single-phase cascaded photovoltaic grid-connected inverter system including three inverters according to an embodiment of the present disclosure on a condition of the grid voltage dropping 10%.

Detailed Description of the Embodiments

Specific implementations of the present disclosure will be further described below in conjunction with the accompanying drawings and figures. The following are used for illustrating the present of the disclosure, but not limiting the scope of the present of the disclosure.

Voltage at a point of common coupling or a single-phase cascaded photovoltaic grid-connected inverter system is a sum of output voltages or all cascaded photovoltaic inverters. As a result, a low-voltage photovoltaic inverter can be connected to a medium / high-voltage grid directly through a low-voltage power electronics interface. Each cascaded photovoltaic inverter does not need a high-frequency isolation transformer to boost a DC voltage output from a photovoltaic panel, and thus results in small loss and high efficiency for the system. Moreover, each cascaded photovoltaic inverter can be manufactured modularly in great quantities. Compared with a traditional architecture or photovoltaic string centralized inverter, the single-phase cascaded photovoltaic grid-connected inverter system has higher reliability and more flexible expandability. This is because the inverters of the single-phase cascaded photovoltaic grid-connected inverter system are distributed, while the traditional architecture of the photovoltaic string centralized inverter is limited by the capacity of the centralized inverters and lacks of redundancy. Compared with a widely applicable architecture or multi-level cascaded H-bridge, each inverter or the single-phase cascaded photovoltaic grid-connected inverter system has an independent output LC filter. The architecture of the cascaded multi-level H-bridge must be controlled through centralized communication and be constrained, which results in a high cost and low reliability for the system. While the output voltage or each inverter or the single-phase cascaded photovoltaic grid-connected inverter system can be controlled at a grid frequency, which is more favorable for achieving distributed and decentralized control, leading to higher reliability and low control cost.

For the above-mentioned single-phase cascaded photovoltaic grid-connected inverter system, an embodiment of the present disclosure provides a method for controlling a single-phase cascaded photovoltaic grid-connected inverter system. Referring to FIG. 1, the method includes steps of

101. detecting first local information of a first inverter and receiving phase information of a grid voltage, controlling a line current to be in the same phase as the grid voltage based on the first local information and the phase information of the grid voltage, and implementing MPPT operation of the first inverter.

Referring to FIG. 2, the single-phase cascaded photovoltaic grid-connected inverter system may include a single-stage single-phase H-bridge photovoltaic inverters being connected in series, which is a natural number greater than 1. The single-stage single-phase H-bridge photovoltaic inverters being connected in series are connected to a large grid at a point of common coupling (PCC) via a line impedance. Each photovoltaic inverter includes a set of local photovoltaic panel directly connected with a DC input end, a DC-side input filter capacitor, a single-phase H-bridge inverter and an output LC filter.

With respect to the single-phase cascaded photovoltaic grid-connected inverter system in Fig. 2, the one of the n series-connected inverters closest to the PCC is selected as the first inverter. The first inverter, being controlled as a current source, also serves as a reactive power compensation unit to control the regular current line while implementing maximum power point tracking (MPPT) or the local photovoltaic panel. The purpose of controlling the line current is to achieve grid-connected operation of the system at a unity power factor, and in turn requirement for grid-connected operation at the unity power factor is that the line current and the grid voltage are in a same phase. To control the line current, it needs to detect the first local information and obtain the phase information or the grid voltage. The phase information can be obtained from the grid through a communication link, such as through a phase-locked loop. The first local information is obtained by detecting the first inverter without networking communication. It should be noted that only the phase information or the grid voltage needs are obtained by networking communication.

102. detecting, for each second inverter, second local information of the second inverter, and controlling an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information.

With respect to the single-phase cascaded photovoltaic grid-connected inverter system in Fig. 2, if one of the n series-connected inverters is selected as the first inverter, all other inverters are selected as the second inverter, and thus the system at least includes one second inverter. All the second inverters are controlled to be voltage sources, which achieve self-synchronization with the grid voltage while implementing MPPT. Self-synchronization means that the system is in the same phase and the same frequency as the grid voltage. It should be noted that the second local information is similar to the first local information, and thus only the second inverter needs to be detected, without a grid synchronization signal.

In the above method, which includes steps of detecting or first local information or a first inverter and receiving phase information or a grid voltage, controlling a line current to be in the same phase as the grid voltage based on the first local information and the phase information of the grid voltage, and implementing MPPT operation of the first inverter; and detecting, for each second inverter, second local information of the second inverter, controlling an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information, and implementing MPPT operation or the second inverter, since only one communication link is required to provide the phase information of the grid voltage to the first inverter, and all other local information can be obtained by local detection, lower requirements for communication, reduced complexity for controlling the system, improved reliability and lower cost are achieved.

Based on the embodiment described above, optionally, a method for controlling a line current or a first inverter is provided. Specifically, referring to Figs. 2 and 5, the first information includes a first local output voltage value Udci or DC-side photovoltaic panel, a first output current value z> rz or DC-side photovoltaic panel and a line current actual value i _s of the first inverter; and correspondingly, the step of controlling a line current to be in the same phase as the grid voltage according to the first local information and the phase information of the grid voltage, and implementing MPPT operation of the first inverter includes:

«Ƒ

501. calculating a first DC-side voltage reference value '* · or the first inverter based on the first output voltage value Udci or DC-side photovoltaic panel and the first ref output current value z> r? or DC-side photovoltaic panel. Specifically, ^can1 can be calculated by the MPPT control unit or the first inverter.

502. adjusting the first output voltage value iidci or DC-side photovoltaic panel to the first DC-side voltage reference value ^{U {ki} , and using a current value obtained after adjustment as an amplitude reference of the line current. Specifically, to achieve a balance between input active power and output active power of the first inverter so as to enable the MPPT operation of the first inverter, the output voltage Udd or DC-side photovoltaic panel or the first inverter needs to be adjusted, so That Udci is equal to the first DC-side voltage reference value ^l of the first inverter generated by the MPPT control unit.

503. receiving the phase information of the grid voltage through a communication link, and receiving a reference value of the line current by synthesizing the amplitude reference of the line current and the phase information of the grid voltage. Specifically, the phase information, ie, a phase 0 _{g according to} a phase reference of the line current so that the system operates at the unity power factor. The phase 6 _g or the grid voltage can be transmitted to a controller or the first inverter by a low-bandwidth communication link. The amplitude reference of the line current and the phase 3 _g of the grid voltage are synthesized into the reference value of the line current.

504. adjusting the line current to the current reference value based on the current value of the line current i _g . Specifically, the calculated reference value of the line current and the line current are in the same phase, and the line current as a common quantity or the whole system can ensure output current or each inverter.

Based on the embodiment described above, alternatively, a method for obtaining an amplitude reference or a line current is provided. Specifically, the step of adjusting the output voltage value of the first DC-side photovoltaic panel to the first DC-side voltage reference value, and using a current value obtained after the adjustment as an amplitude reference or the line current includes: inserting a difference iidci- ^Udci between the output voltage value Udd of the first DC-side photovoltaic panel and the first DC-side voltage reference value ^you ' ^ll into a DC voltage controller, and using an output of the DC voltage controller as the amplitude reference of the line current.

The output voltage value iidci of the first DC-side photovoltaic panel is subtracted ref from the DC-side voltage reference value ^Λ1 of the first inverter generated by the u ^lvf

MPPT control unit, and their different Udd- ^dci is used as an input to the DC voltage controller or the first inverter. The DC voltage controller is a proportional integral controller, which Can track the DC voltage reference value _w lth zero error, and the output of the DC voltage controller of the inverter is used as the amplitude reference of the line current.

Based on the embodiment described above, alternatively, a method for adjusting line current is provided. Specifically, the step of adjusting the line current to the current reference value based on the actual value of the current includes: inputting a difference ^l ° -i _g between the actual value of the line current z _g and the reference value of the line current ^z ° into a current controller, which is a proportional resonant controller, and using an output result or the current controller as an input signal or a pulse width modulation module; and inserting the input signal into the pulse width modulation module to generate a pulse signal for controlling a switching device or the first inverter to operate.

The current controller being a proportional resonant controller can track the sinusoidal reference value of the line current ^Zg _w ith zero error. The output of the current controller serves as an input signal or a pulse width modulation module (PWM). The PWM module generates the switching pulse signal or the first inverter to control the switching device or the first inverter to operate, and the operation of the switching device can achieve adjustment of the line current and implement MPPT operation of the first inverter.

Based on the embodiment described above, alternatively, a method for controlling an output voltage or a second inverter is provided. Referring to Figs. 3 and 6, specifically, the second local information includes an output voltage value Uda or a second DC-side photovoltaic panel, an output current value instead of a second DC-side photovoltaic panel, an actual output voltage value zz, and a line current z _g or the second inverter; and correspondingly, controlling an output voltage or the second inverter to the same phase as the grid voltage based on the line current and the second local information (it should be noted that although the whole system includes several or second inverters, only second inverter i is described below and those for other second inverters are omitted, where /=2.3,...,n) includes:

601. calculating a second DC-side voltage reference value of the second inverter based on the output voltage value iida of the second DC-side photovoltaic panel and the output current value instead of the second DC-side photovoltaic panel. Specifically, an MPPT control unit of the first inverter will calculate the DC-side re / voltage reference value ^da of the second inverter.

602. adjusting the output voltage value zz ^ or the second DC-side photovoltaic panel to the second DC-side voltage reference value ^da , and getting an amplitude reference F, or the output voltage or the second inverter after the adjustment. Specifically, to achieve active balance of an input and output of the inverter so as to enable the MPPT operation of the second inverter, the output voltage Udd or the DC-side photovoltaic panel or the second inverter needs to be adjusted, so that Udd is

... W equal to the DC-side voltage reference value or the second inverter generated by the MPPT control unit. The balance of active power output from the second inverter is achieved by adjusting the amplitude of the output voltage or the second inverter. The expression or amplitude control or the output voltage or the second inverter can be:

where C represents the amplitude reference of the output voltage or the second inverter, Kp, and Kn represent a proportional coefficient and an integral coefficient or a DC-side voltage controller or the second inverter, and V _g represents a nominal voltage amplitude of the grid.

603. calculating a sinusoidal value sinCof an output power angle of the second inverter based on the current output voltage value in the line current z _g , and calculating an angular frequency reference or output voltage of the second inverter based on the sinusoidal value sinC or the output power angle. Specifically, calculating a sinusoidal value sin / 9, or an output power angle of the second inverter based on the actual value zz, or output voltage of the second inverter and the line current z _g detected in real time can be expressed as:

P, sin θ _: =. "=

A + a ^! where P, and Qi are active power and reactive power output from the second inverter.

To achieve self-synchronization of the second inverter with the grid voltage without communication, the expression for controlling angular frequency or the output voltage or the second inverter can be:

ω, = to * + A ', (sinl? * - sin0,) where ω, represents the angular frequency reference or the output voltage or the second inverter, represents * represents a nominal angular frequency or the grid, and sinri * represents a power angle reference value of the second inverter. In practical applications, generally a photovoltaic grid-connected system is required to operate at a unity power factor, and thus set sin6 ^, * = 0. p is a coefficient for self-synchronization control or the second inverter, which is a positive constant.

604. integrating the angular frequency reference an of the output voltage to obtain a phase reference δ, or output voltage of the second inverter, and synthesizing the amplitude reference Ft of the output voltage and the phase angle reference δ, or *

ll output voltage to obtain an output voltage reference value ¹ .

605. adjusting the output voltage or the second inverter based on the reference ll value of the output voltage ¹ .

Based on the embodiment described above, alternatively, a method for adjusting an output voltage or a second inverter is also provided. Specifically, the step of adjusting the output voltage or the second inverter based on the reference value of the output voltage includes: receiving a modulation reference signal or a pulse width modulation module through voltage / current dual-closed-loop control based on the *

ll reference value of the output voltage ¹ ; and inserting the modulation reference signal into the pulse width modulation module to generate a pulse signal for controlling a switching device or the second inverter to operate. Specifically, the

PWM module generates the switching pulse signal or the second inverter to control the switching device or the second inverter to operate, so as to adjust the output voltage to the reference value of the output voltage.

Based on the embodiment described above, alternatively, the first inverter is the one closest to the point of common coupling among the various or inverters connected in series or the single-phase cascaded photovoltaic grid-connected inverter system. The first inverter, as a current source, being closest to the point of common coupling can achieve a good current adjusting effect. Referring to FIG. 2, the inverter # 1 closest to the point of common coupling serves as the first inverter, and the inverter #i (1 = 2.3, ..., n) severs as the second inverter.

FIGs. 9 to 12 show simulation results of a single-phase cascaded photovoltaic grid-connected inverter system including three inverters provided in the embodiment of the present disclosure with symmetrical structure and in partially shielded condition. FIGs. 13 to 16 show simulation results of a single-phase cascaded photovoltaic grid-connected inverter system including three inverters provided in the version of the present disclosure under a condition of the grid voltage dropping 10%.

The above-described disclosure provides a device for controlling a single-phase cascaded photovoltaic grid-connected inverter system, which is configured to execute the method for controlling the single-phase cascaded photovoltaic grid-connected inverter system described above. Referring to FIG. 7, the devices includes a first control module 701 and a second control module 702.

The first control module 701 is configured to detect first local information or a first inverter and obtain phase information or a grid voltage, control a line current to be in the same phase as the grid voltage based on the first local information and the phase information or the grid voltage, and implement MPPT operation of the first inverter.

The purpose of controlling the line current by the first control module 701 is to achieve grid-connected operation of the system at a unity power factor, which in turn requires the line current and the grid voltage to be in the same phase. To control the line current, the first control module 701 needs to detect the first local information and obtain the phase information or the grid voltage. The phase information can be obtained from the grid through a communication link, such as through a phase-locked loop. The first local information is obtained by the first control module 701 by detecting the first inverter, without networking communication. It should be noted that only the phase information or the grid voltage needs are obtained by networking.

The second control module 702 is configured to, for each second inverter, detect second local information of the second inverter, control an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information, and implement MPPT operation of the second inverter.

All the second inverters are controlled by the second control module 702 as voltage sources, which can achieve self-synchronization with the grid voltage during implementing MPPT. Self-synchronization means that the system is in the same phase and the same frequency as the grid voltage. It should be noted that the second local information is similar to the first local information, and the second control module 702 only needs to detect the second inverter, without receiving a grid synchronization signal.

In the device provided read, including a first control module configured to detect first local information or a first inverter and obtain phase information or a grid voltage, control a line current to the same phase as the grid voltage based on the first local information and the phase information of the grid voltage, and implement MPPT operation of the first inverter; and a second control module configured to, for each second inverter, detect second local information or the second inverter, and control an output voltage or the second inverter to the same phase as the grid voltage based on the line current and the second local information, only one communication link is required to provide the phase information of the grid voltage to the first inverter, and other local information can be obtained by local detection, thus the requirement for communication of the system is lowered, the complexity of a structure for controlling the system is reduced, the reliability of the system is improved, and the cost is reduced.

Alternatively, the first local information includes an output voltage value of the first DC-side photovoltaic panel, an output current value of the first DC-side photovoltaic panel and an actual line current value of the first inverter; and correspondingly, the first control module includes:

a first calculation unit configured to calculate a first DC-side voltage reference value of the first inverter based on the output voltage value and the output current value of the first DC-side photovoltaic panel;

a current amplitude reference unit configured to adjust the output voltage value of the first DC-side photovoltaic panel to the first DC-side voltage reference value, and use a current value obtained after the adjustment as an amplitude reference of the line current;

a first synthesis unit configured to obtain the phase information of the grid voltage through a communication link, and obtain a reference value of the line current by synthesizing the amplitude reference of the line current and the phase information of the grid voltage; and a current adjustment unit configured to adjust the line current to the current reference value according to the current value of the line current.

Alternatively, the current amplitude reference unit is specifically configured to input the difference between the output voltage value of the first DC-side photovoltaic panel and the first DC-side voltage reference value into a DC voltage controller, and use an output of the DC voltage controller as the amplitude reference or the line current.

Alternatively, the current adjustment unit is configured to:

input the difference between the current value of the line current and the reference value of the line current into a current controller, and use an output result of the current controller as an input signal or a pulse width modulation module; and input the input signal into the pulse width modulation module to generate a pulse signal for controlling a switching device or the first inverter to operate.

Alternatively, the second local information includes an output voltage value of the second DC-side photovoltaic panel, an output current value of the second DC-side photovoltaic panel, an actual output voltage value and a line current of the second inverter; and correspondingly, the second control module includes:

a second calculation unit configured to calculate a second DC-side voltage reference value of the second inverter according to the output voltage value and the output current value of the second DC-side photovoltaic panel;

a voltage amplitude reference unit configured to adjust the output voltage value of the second DC side photovoltaic panel to the second DC side voltage reference value, and obtain an amplitude reference of the output voltage or the second inverter after the adjustment;

a third calculation unit configured to calculate a sinusoidal value of an output power angle of the second inverter based on the current output voltage value and the line current, and calculate an angular frequency reference of the output voltage or the second inverter based on the sinusoidal value or the output power angle;

a second synthesis unit configured to integrate the angular frequency reference of the output voltage to obtain a phase reference of the output voltage of the second inverter, and synthesize the amplitude reference of the output voltage and the phase angle reference of the output voltage to obtain a reference value of the output voltage; and a voltage adjustment unit configured to adjust the output voltage or the second inverter based on the reference value of the output voltage.

Alternatively, the voltage adjustment unit is specifically configured to:

obtain a modulation reference signal or a pulse width modulation module through voltage / current dual-closed-loop control based on the reference value of the output voltage; and input the modulation reference signal into the pulse width modulation module to generate a pulse signal for controlling a switching device or the second inverter to operate.

Alternatively, the first inverter is the one closest to the point of common coupling among the various or inverters connected in series or the single-phase cascaded photovoltaic grid-connected inverter system.

The embodiment of the present disclosure provides an apparatus for controlling a single-phase cascaded photovoltaic grid-connected inverter system. As shown in FIG.

8, the device includes a processor 801, a memory 802 and a bus 803, within the processor 801 and the memory 802 communicate with each other through the bus 803; the processor 801 is configured to call program instructions in the memory 802 to execute the method for controlling the single-phase cascade type photovoltaic grid-connected inverter system provided, which for example includes steps of detecting first local information or a first inverter and receiving phase information of a grid voltage, and controlling a line current to the same phase as the grid voltage based on the first local information and the phase information of the grid voltage; and detecting, for each second inverter, second local information of the second inverter, and controlling an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information.

The embodiment of the present disclosure also provides a non-transitory computer readable storage medium, which stores computer instructions that enable a computer to execute the method for controlling the single-phase cascaded photovoltaic grid-connected inverter system provided provided, which for example includes steps or:

detecting first local information of a first inverter and receiving phase information of a grid voltage, and controlling a line current to be in the same phase as the grid voltage based on the first local information and the phase information of the grid voltage; and detecting, for each second inverter, second local information of the second inverter, and controlling an output voltage or the second inverter to be in the same phase as the grid voltage based on the line current and the second local information.

Those of ordinary skill in the art can understand all or part of the steps that implement the method embodiment described above can be accomplished by hardware related to the program instructions, and the above-mentioned program can be stored in a computer readable storage medium, and the program, when being executed, executes the steps including the method described above; and the above-mentioned storage medium includes ROM, RAM, magnetic disk, or optical disk or other various media that can store program codes.

The expired described above such as the control apparatus of the single-phase cascaded photovoltaic grid-connected inverter system are merely schematic, the units described as separate components may be or may not be physically separate, and components shown as units may be or may be not physical units, ie may be located in one place, or may also be distributed on multiple network units. Some or all of the modules may be selected based on current requirements to achieve the object of the solution of the present exponent. These can be understood and implemented by those of ordinary skill in the art without creative effort.

With the method and device provided by the exponents of the present disclosure, the communication requirement is greatly reduced and minimized, and only one low-bandwidth communication link is needed; the system control complexity is greatly reduced, the system is less affected by communication failures, and the system reliability is greatly improved; the system control cost is greatly reduced; and the method and device are very promising in large-scale medium-and-high-voltage photovoltaic grid-connected scenarios in the future.

From the above description of the implementations, those skilled in the art can clearly understand that the various implementations can be achieved by virtue of software and a necessary general-purpose hardware platform, and of course, can also be achieved by hardware. With this understanding, the technical solutions described above, in essence or for the part contributing to the prior art, can be embodied in the form of a software product, and the computer software product can be stored in a computer readable storage medium, such as an ROMZRAM, a magnetic disk, an optical disc or the like, and includes a number of instructions for causing a computer device (which may be a personal computer, a server, a network device or the like) to execute the method described in the vary or in parts of the terms.

Finally, it should be noted that the above is only used for illustrating rather than limiting the technical solutions or the present disclosure.

Although the present disclosure has been described in detail with reference to the foregoing, those of ordinary skill in the art should understand that they can still make modifications to the technical solutions disclosed in the foregoing or make equivalent substitutions to part of technical features; and such 5 modifications or substitutions should not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions or the present of the present disclosure.

Claims (10)

CONCLUSIONS A method for controlling a single-phase cascade photovoltaic network-connected inverter system, comprising the steps of: detecting first local information from a first inverter and obtaining phase information from a network voltage, controlling a line current to be in the same phase as the network voltage, based on the first local information and phase information from the network voltage, and implementing MPPT operation of the first inverter; and detecting, for each second inverter, second local information from the second inverter, controlling an output voltage from the second inverter to be in the same phase as the network voltage based on the line current and the second local information, and implementing MPPT operation of the second inverter. The method of claim 1, wherein the first inverter is that closest to a point of common coupling among a plurality of inverters connected in series from the single-phase cascade photovoltaic network-connected inverter system and the second inverters include all of these except for the first inverter in the plurality of inverters connected in series from the single-phase cascade photovoltaic network-connected inverter system. The method of claim 1, wherein the first local information comprises an output voltage value of a first DC side photovoltaic panel, an output current value of the first DC side photovoltaic panel and a current value of the line current of the first inverter; and the step of controlling the line current to be in the same phase as the network voltage, based on the first local information and the phase information of the network voltage and implementing MPPT operation of the first inverter comprises sub-steps of: calculating a first DC side voltage reference value of the first inverter based on the output voltage value of the first DC side photovoltaic panel and the output current value of the first DC side photovoltaic panel; adjusting the output voltage value from the first DC side photovoltaic panel to the first DC side voltage reference value, and using a current value obtained after adjustment as an amplitude reference of the line current; obtaining the phase information of the network voltage via a communication link, and obtaining a reference value of the line current -22 by synthesizing the amplitude reference of the line current and the phase information of the network voltage; and adjusting the line current to the current reference value based on the current value of the line current. The method of claim 3, wherein the sub-step of adjusting the output voltage value from the first DC side photovoltaic panel to the first DC side voltage reference value and using a current value obtained after adjustment comprises as an amplitude reference of the line current: applying a difference between the output voltage value of the first DC side photovoltaic panel and the first DC side voltage reference value to a DC voltage controller, which is a proportional integral controller, and using an output of the DC voltage controller as the amplitude reference of the line current. The method of claim 3, wherein the sub-step of adjusting the line current to the reference value of the current based on the current value of the line current comprises: applying a difference between the current value and the reference value of the line current to a current controller, which is a proportional resonant controller, and using an output result of the current controller as an input signal from a pulse width modulation module; and applying the input signal to the pulse width modulation module to generate a pulse signal for controlling the operation of a switching device of the first inverter. The method of claim 1 or 3, wherein the second local information comprises an output voltage value of a second DC side photovoltaic panel, an output current value of the second DC side photovoltaic panel, a current value of the output voltage and a line current of the second inverter ; and the step of controlling an output voltage of the second inverter to be in the same phase as the network voltage based on the lead-in and the second local information includes sub-steps of: calculating a second DC side voltage reference value from the second inverter based on the output voltage value of the second DC side photovoltaic panel and the output current value of the second DC side photovoltaic panel; adjusting the output voltage value from the second DC side photovoltaic panel to the second DC side voltage reference value, and Obtaining an amplitude reference of the output voltage of the second inverter after the adjustment; calculating a sinusoidal value of output power angle of the second inverter based on the current output voltage value and the line current, and calculating an angular frequency reference of output voltage of the second inverter based on the sinusoidal value of the output power angle; and integrating the angular frequency reference of the output voltage to obtain a phase reference of the output voltage of the second inverter, and synthesizing the amplitude reference and the phase angle reference of the output voltage to obtain a reference value of the output voltage; and adjusting the output voltage of the second inverter based on the reference value of the output voltage. The method of claim 6, wherein the sub-step of adjusting the output voltage of the second inverter based on the reference value of the output voltage comprises: obtaining a modulation reference signal from a pulse width modulation module by voltage / current double-ended loop control based on the reference value of the output voltage; and applying the modulation reference signal to the pulse width modulation module to generate a pulse signal for controlling the operation of a switching device of the second inverter. An apparatus for controlling a single-phase cascade photovoltaic network-connected inverter system, comprising: a first control module adapted to detect first local information from a first inverter and obtain phase information from a network voltage, control a line current to be in the same phase as the network voltage based on the first local information and the phase information of the network voltage, and implement MPPT operation of the first inverter; and a second control module adapted to detect, for each second inverter, second local information from the second inverter, to control an output voltage from the second inverter to be in the same phase as the network voltage based on the line current and the second local information , and implement MPPT operation of the second inverter. An apparatus for controlling a single-phase cascade photovoltaic network-connected inverter system, comprising: at least one processing unit; and at least one memory in communication with the processing unit, 5 wherein the memory stores program instructions executable by the processor, which invokes the program instructions to perform the method of any one of claims 1 to 7. 10. Non-volatile, computer-readable storage medium, with computer instructions Stored therein, which enable a computer to perform the method according to any of claims 1 to 7. Detecting first local information of a first inverter and receiving phase information of a grid voltage, controlling aine airrent to be in the samephaseas the grid voltage according to the first local information and the phase information of the grid voltage, and implementing MPPT operation of the first inverter ________________________________i________________________________