CN117713193A - Model predictive control method for single-phase cascade H-bridge photovoltaic inverter system - Google Patents
Model predictive control method for single-phase cascade H-bridge photovoltaic inverter system Download PDFInfo
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Abstract
The present disclosure provides a model predictive control method of a single-phase cascade H-bridge photovoltaic inverter system, which is applied to the single-phase cascade H-bridge photovoltaic inverter system, the single-phase cascade H-bridge photovoltaic inverter system is composed of n H-bridge sub-modules connected in series, 2 ac reactors and a power grid, and the method comprises: the method comprises the steps of constructing a loss function corresponding to a k+1 control period, determining a plurality of candidate switch states of a single-phase cascade H-bridge photovoltaic inverter system, determining the value of the loss function corresponding to each candidate switch state, determining the minimum value in the plurality of values, and using the candidate switch state corresponding to the minimum value as the switch state corresponding to the k+1 control period, so that the method for selecting the switch state based on model predictive control can replace carrier modulation, the control effect is good, the control structure is simple, and four control targets of grid-connected current tracking, independent maximum power tracking of each sub-module photovoltaic module, common-mode voltage high-frequency component suppression and switching frequency reduction can be simultaneously realized.
Description
Technical Field
The disclosure relates to the technical field of photovoltaic power generation grid connection, in particular to a model predictive control method of a single-phase cascade H-bridge photovoltaic inverter system.
Background
The cascade H-bridge multi-level inverter has the characteristics of easy modularization expansion, low cost and high output voltage quality, and the direct current side of the cascade H-bridge multi-level inverter can be independently powered by a photovoltaic cell panel, so that the independent maximum power point tracking control of the cascade H-bridge multi-level inverter is possible, and the cascade H-bridge structure is a photovoltaic inverter structure with the most prospect. Meanwhile, leakage current of the cascaded H-bridge grid-connected photovoltaic inverter also becomes an important problem in application of the cascaded H-bridge grid-connected photovoltaic inverter. Due to the lack of transformer isolation, direct electrical connection exists between the photovoltaic panel and the power grid, leakage current can be generated on parasitic capacitance between the photovoltaic panel and the ground, the leakage current can influence the efficiency of the system, the reliability of the system is reduced, the personal safety is threatened, electromagnetic interference is generated, and the like, so that the leakage current is very necessary to be suppressed.
At present, the conventional leakage current suppression method can be mainly divided into the following three types: 1) Using improved topologies such as H5, H6, etc.; 2) Passive filters such as common mode inductors, EMI filters, etc. are used; 3) A suitable modulation strategy is sought.
However, unlike single-module inverter topologies, the contribution of the leakage current of the cascaded H-bridge topology is not only related to the output of this module, but also to the outputs of the other modules of the cascade. Therefore, the method for suppressing the leakage current of the single H-bridge cannot be directly applied to suppression of the topology leakage current of the cascaded H-bridge, and the matching between the existing method for suppressing the leakage current of the single-module inverter and the method for suppressing the leakage current of the cascaded H-bridge inverter is low.
Disclosure of Invention
The present disclosure aims to solve, at least to some extent, one of the technical problems in the related art.
Therefore, the purpose of the disclosure is to provide a model prediction control method, a device, a computer device and a storage medium of a single-phase cascade H-bridge photovoltaic inverter system, wherein the method for selecting a switching state based on model prediction control can replace carrier modulation, has a good control effect and a simple control structure, and can simultaneously realize four control targets of grid-connected current tracking, independent maximum power tracking of each sub-module photovoltaic module, common-mode voltage high-frequency component suppression and switching frequency reduction.
In order to achieve the above objective, a model predictive control method for a single-phase cascaded H-bridge photovoltaic inverter system provided by an embodiment of a first aspect of the present disclosure is applied to a single-phase cascaded H-bridge photovoltaic inverter system, where the single-phase cascaded H-bridge photovoltaic inverter system is composed of n H-bridge sub-modules connected in series, 2 ac reactors, and a power grid, and the method includes:
constructing a loss function corresponding to the k+1th control period;
determining a plurality of candidate switch states of the single-phase cascade H-bridge photovoltaic inverter system;
determining the value of the loss function corresponding to each candidate switch state;
and determining the minimum value in the plurality of values, and using the candidate switch state corresponding to the minimum value as the switch state corresponding to the k+1 control period.
To achieve the above objective, a model predictive control device for a single-phase cascaded H-bridge photovoltaic inverter system according to an embodiment of a second aspect of the present disclosure is applied to a single-phase cascaded H-bridge photovoltaic inverter system, and the single-phase cascaded H-bridge photovoltaic inverter system is composed of n H-bridge sub-modules, 2 ac reactors and a power grid that are connected in series, where the device includes:
the function construction module is used for constructing a loss function corresponding to the k+1th control period;
the first determining module is used for determining a plurality of candidate switch states of the single-phase cascade H-bridge photovoltaic inverter system;
the second determining module is used for determining the value of the loss function corresponding to each candidate switch state;
and the third determining module is used for determining the minimum value in the plurality of values and using the candidate switch state corresponding to the minimum value as the switch state corresponding to the k+1th control period.
Embodiments of the third aspect of the present disclosure provide a computer device, including: the system comprises a memory, a processor and a computer program stored on the memory and capable of running on the processor, wherein the processor realizes the model predictive control method of the single-phase cascade H-bridge photovoltaic inversion system as provided by the embodiment of the first aspect of the disclosure when the processor executes the program.
An embodiment of a fourth aspect of the present disclosure proposes a non-transitory computer readable storage medium, on which a computer program is stored, which when executed by a processor implements a model predictive control method of a single-phase cascaded H-bridge photovoltaic inverter system as proposed by an embodiment of the first aspect of the present disclosure.
A fifth aspect embodiment of the present disclosure proposes a computer program product which, when executed by a processor, performs a model predictive control method of a single-phase cascaded H-bridge photovoltaic inverter system as proposed by the first aspect embodiment of the present disclosure.
According to the model prediction control method, device, computer equipment and storage medium of the single-phase cascade H-bridge photovoltaic inverter system, through constructing the loss function corresponding to the k+1 control period, a plurality of candidate switch states of the single-phase cascade H-bridge photovoltaic inverter system are determined, the value of the loss function corresponding to each candidate switch state is determined, the minimum value in the plurality of values is determined, and the candidate switch state corresponding to the minimum value is used as the switch state corresponding to the k+1 control period.
Additional aspects and advantages of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure.
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The foregoing and/or additional aspects and advantages of the present disclosure will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:
fig. 1 is a flow chart of a model predictive control method of a single-phase cascaded H-bridge photovoltaic inverter system according to an embodiment of the disclosure;
fig. 2 is a circuit topology diagram of a single-phase cascaded H-bridge photovoltaic inverter proposed in accordance with the present disclosure;
FIG. 3 is a predictive control flow chart of a CHB photovoltaic system with a model predictive control algorithm in place of the current control loop according to the present disclosure;
FIG. 4 is a predictive control flow diagram of a CHB photovoltaic system with another model predictive control algorithm in place of a current control loop according to the present disclosure;
fig. 5 is a schematic structural diagram of a model predictive control device of a single-phase cascaded H-bridge photovoltaic inverter system according to an embodiment of the present disclosure;
FIG. 6 illustrates a block diagram of an exemplary computer device suitable for use in implementing embodiments of the present disclosure.
Detailed Description
Embodiments of the present disclosure are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are exemplary only for explaining the present disclosure and are not to be construed as limiting the present disclosure. On the contrary, the embodiments of the disclosure include all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims.
Fig. 1 is a flow chart of a model predictive control method of a single-phase cascaded H-bridge photovoltaic inverter system according to an embodiment of the disclosure.
It should be noted that, the execution main body of the model prediction control method of the single-phase cascade H-bridge photovoltaic inverter system in this embodiment is a model prediction control device of the single-phase cascade H-bridge photovoltaic inverter system, and the device may be implemented in a software and/or hardware manner.
As shown in fig. 1, the model predictive control method of the single-phase cascade H-bridge photovoltaic inverter system is applied to the single-phase cascade H-bridge photovoltaic inverter system, and the single-phase cascade H-bridge photovoltaic inverter system is composed of n H-bridge sub-modules, 2 ac reactors and a power grid which are connected in series, and the method comprises the following steps:
s101: a loss function corresponding to the k+1 control period is constructed.
The loss function, among other things, can be used to evaluate the energy and efficiency lost by the system during operation. The photovoltaic inverter converts direct current generated by the photovoltaic panel into alternating current so as to meet the requirements of a power grid or a load. In this process, some energy loss occurs due to the characteristics of the circuit elements and the control strategy.
In the embodiment of the disclosure, when the loss function corresponding to the k+1 control period is constructed, a reliable judgment basis can be provided for determining the switch state corresponding to the k+1 control period from a plurality of candidate switch states.
S102: a plurality of candidate switch states of the single-phase cascaded H-bridge photovoltaic inverter system are determined.
In the disclosed embodiment, each H-bridge sub-module is composed of 4 MOSFETs with antiparallel diodes, 1 dc capacitor, and 1 photovoltaic string.
The candidate switch states refer to the on and off states of upper and lower switch devices in each H-bridge circuit, and are used for controlling and adjusting the output voltage and frequency of the photovoltaic inverter.
The H-bridge circuit is composed of four switching devices (typically MOSFETs, IGBTs, etc.), two switches on the upper side and the lower side, respectively, which can control the current path between the power supply and the output terminal. In particular, the H-bridge circuit may implement two basic switching states: on and off.
Conduction state: when one of the upper switch and the lower switch is in a conducting state, a current path is established between the power supply and the output terminal. At this time, current may flow from the power source to the output terminal through the corresponding switching device, thereby achieving power delivery to the load or the power grid.
Cut-off state: when the upper switch and the lower switch are in the cut-off state, a current path is disconnected between the power supply and the output end. At this point, current cannot flow from the power source to the output, thereby stopping power to the load or the grid.
The voltage amplitude and the frequency of the output of the photovoltaic inverter can be adjusted by controlling the on and off states of each switching device so as to meet different power supply requirements or load demands. The adjustment of the switch state can be realized by PWM (pulse width modulation) technology, and the on-time and the off-time of the switch can be changed as required, so as to control the conversion process of the electric energy.
For example, as shown in fig. 2, fig. 2 is a circuit topology diagram of a single-phase cascaded H-bridge photovoltaic inverter proposed according to the present disclosure.
S103: and determining the value of the loss function corresponding to each candidate switch state.
It will be appreciated that during operation of the system, as the switching state of each H-bridge circuit changes, the corresponding loss function value may also change. These loss function values reflect the power consumption and efficiency of the various components in the system (e.g., switching devices such as MOSFETs, IGBTs, etc.) under certain switching conditions.
For example, the switching states of the individual H-bridge circuits in a cascaded H-bridge photovoltaic inverter system can affect losses in several ways:
switching loss: there is some loss in the switching operation, including on and off loss and loss in switching. These loss values may be different in different switching states, thereby affecting the energy conversion efficiency of the system.
Conduction loss: since a certain resistance exists inside the conductive device, a certain power loss is generated in the conductive state. The magnitude of the conduction loss may also vary from one switching state to another.
Pin drive loss: the pin drive loss is the energy consumption caused by the drive circuit and the control signal transmission, and the sizes of the pin drive loss can be different in different switch states.
Inductance and capacitance losses: in the system output and the filter circuit, the inductance and capacitance elements also have certain current and voltage losses, and the values of these losses may be different in different switching states.
In the embodiment of the disclosure, when determining the value of the loss function corresponding to each candidate switch state, a reliable judgment basis can be provided for the switch state correspondingly used in the subsequent determination of the k+1 control period.
S104: and determining the minimum value in the plurality of values, and using the candidate switch state corresponding to the minimum value as the switch state corresponding to the k+1 control period.
That is, in the embodiment of the present disclosure, after determining the value of the loss function corresponding to each candidate switch state, the minimum value of the multiple values may be determined, and the candidate switch state corresponding to the minimum value may be used as the switch state corresponding to the k+1 control period.
In this embodiment, a loss function corresponding to the k+1 control period is constructed, a plurality of candidate switch states of the single-phase cascade H-bridge photovoltaic inverter system are determined, the value of the loss function corresponding to each candidate switch state is determined, the minimum value of the plurality of candidate switch states is determined, and the candidate switch state corresponding to the minimum value is used as the switch state corresponding to the k+1 control period, so that the method for selecting the switch state based on model predictive control can replace carrier modulation, the control effect is good, the control structure is simple, and four control targets of grid-connected current tracking, independent maximum power tracking of each sub-module photovoltaic assembly, common-mode voltage high-frequency component suppression and switching frequency reduction can be simultaneously realized.
Optionally, in some embodiments, the first equation corresponding to the loss function is:
wherein lambda is i Weight coefficient lambda representing current tracking control v Weight coefficient lambda representing capacitor voltage balance control g Weight coefficient lambda representing suppression of common-mode voltage high-frequency components c Representing a weight coefficient that reduces the switching frequency of the inverter switching tube,grid-connected current given value i representing the k+1 control period s (k+1) represents a grid-connected current prediction value of the (k+1) th control period,/and->The capacitance voltage given value of the ith H bridge submodule in the (k+1) th control period is represented, and the i available value ranges are 1, 2, … …, n and v pvi (k+1) represents the capacitance voltage prediction value,/of the ith H-bridge sub-module in the k+1 control period>The direct-current side negative electrode and the grounding point g of the ith submodule representing the k+1 control period s Reference value of common-mode voltage between v gigs (k+1) represents the direct-current side negative electrode and the ground point g of the ith submodule in the (k+1) th control period s Predictive value of common-mode voltage between n c (k+1) represents the number of switching operations in the (k+1) th control cycle.
Optionally, in some embodiments, the grid-connected current set point for the k+1 control period and the capacitance voltage set point for the i H-bridge sub-module for the k+1 control period are determined based on:
according to the maximum power tracking algorithm of the ith H bridge sub-module, determining the working voltage of the photovoltaic component in the ith H bridge sub-module under the highest power as the capacitance voltage given value of the ith H bridge sub-module in the (k+1) th control period
Calculating a grid-connected current setpoint based on the second calculationWherein, the second formula is:
wherein the method comprises the steps of，v s,rms (k) Representing the effective value of the grid voltage for the kth control period,representing the maximum power, v, of the photovoltaic assembly in the ith H-bridge sub-module in the k+1 control period s (k) Representing the instantaneous value of the grid voltage for the kth control period.
For example, as shown in fig. 3, fig. 3 is a predictive control flow chart of a CHB photovoltaic system with a model predictive control algorithm instead of a current control loop according to the present disclosure, and a given value of grid-connected currentDC capacitor voltage set value +.>Obtained from the control flow chart shown in fig. 3.
Optionally, in some embodiments, the grid-connected current prediction value of the k+1 control period is calculated by a third formula, where the third formula is:
wherein v is c (k) Cascading H-bridge inverter AC output voltage for kth control period, v s (k) For the grid voltage, i s (k) For grid-connected current, L S Is the inductance of the alternating current reactor, R S Is the resistance of an alternating current reactor, T S The control period of the control is predicted for the model.
Optionally, in some embodiments, the ac output voltage of the H-bridge inverter in the kth control period cascade is calculated by a fourth equation, where the fourth equation is:
wherein S is i1 (k) Representing the kth controlSwitching function of upper tube of left bridge arm of ith H bridge submodule in system period, S i2 (k) The switch function of the upper tube of the right bridge arm of the ith H bridge submodule in the kth control period is represented by binary numbers.
Optionally, in some embodiments, the number of switching operations in the k+1 control period is calculated by a fifth formula, where the fifth formula is:
wherein S is i1 (k+1) represents the switching function of the upper tube of the left arm of the ith H-bridge submodule in the (k+1) th control period, S i2 (k+1) represents the switching function of the upper tube of the right arm of the ith H-bridge submodule in the k+1 control period.
Optionally, in some embodiments, the predicted value of the capacitor voltage of the ith H-bridge submodule in the k+1 control period is calculated according to a sixth expression:
wherein i is pvi (k) Representing the output current of the DC side optical string of the ith H bridge submodule in the kth control period, i ci (k) Representing the current flowing into the H-bridge by the ith H-bridge submodule in the kth control period, and C representing the capacitance value of the capacitor in the H-bridge submodule.
Optionally, in some embodiments, the current flowing into the H bridge by the ith H bridge submodule in the kth control period is calculated by a seventh equation, where the seventh equation is:
i ci (k)＝(S i1 (k)-S i2 (k))i s (k)；
wherein, the range of i can be 1, 2, … … and n.
Optionally, in some embodiments, the predicted value of the k+1-th control period common-mode voltage is calculated by an eighth equation, where the eighth equation is:
optionally, in some embodiments, the reference value of the k+1-th control period common-mode voltage is calculated based on a ninth equation, where the ninth equation is:
wherein α=2pi fT D /(1+2πfT D ) F represents the cut-off frequency of the first-order low-pass filter used, T D Representing the sampling period of the digital controller.
4 control objectives can be achieved among the cascaded H-bridge photovoltaic inverters studied in the present invention:
(1) Grid-connected current tracking control;
(2) Each sub-module photovoltaic module independently tracks the maximum power;
(3) Suppressing high-frequency components of common-mode voltage;
(4) The switching frequency decreases.
First, the output voltage v of the AC side of the inverter is calculated c On-line detection of voltage v of power grid at time k s (k) And grid current i s (k) And calculate the value i of the grid current at the time k+1 s (k+1); for the power grid voltage v obtained by on-line detection s (k) Phase locking to obtain phase theta and calculating current set value at time k+1And is matched with the current calculation value i at the moment k+1 s (k+1) substituting the loss function g together; thus realizing grid-connected current tracking; given value>Working voltage of photovoltaic module under highest power detected by MPPT, capacitance voltage v pvn (k+1) can be directly deduced from the capacitance formula, v of each inversion unit pvn And->Substituting the voltage balance of the direct-current capacitor in the submodule into the loss function g to realize the control of the voltage balance of the direct-current capacitor in the submodule; in addition to this, a common mode voltage v is derived gigs A first-order low-pass filter is designed to filter out high-frequency harmonic waves contained in the common-mode voltage, and the output of the filter is regarded as the reference value of the common-mode voltage +.>And the high-frequency component of the output common-mode voltage of the alternating-current side of the photovoltaic inverter is effectively restrained by substituting the high-frequency component into the loss function g, so that leakage current between the photovoltaic system and a grounding point is reduced. The minimum switching state combination corresponding to the loss function g is selected from all possible switching states, and the switching tube is driven by the driving circuit as output quantity to realize inversion.
The effects of the invention include:
1) The method for suppressing the leakage current of the cascaded H-bridge photovoltaic inverter based on the model predictive control does not need carrier wave to participate in modulation, but replaces carrier wave modulation by the method for selecting the switching state through the model predictive control. The control effect is good, the robustness is strong, the uncertainty, nonlinearity and parallelism of the process can be effectively overcome, and various constraints in the controlled variable and the manipulated variable of the process can be conveniently processed.
2) The invention designs a first-order low-pass filter for filtering out harmonic waves in common-mode voltage, so that the output of the filter is designated as the input of a controller, and a common-mode voltage reference value is provided for an MPC strategy, thereby realizing the suppression of common-mode voltage high-frequency components.
3) The invention realizes grid-connected current tracking control, ensures high-efficiency grid connection, realizes DC capacitor voltage balance control in the submodule, reduces power loss of an inverter, increases reliability of an inverter circuit, reduces switching frequency, reduces loss of switching devices and electromagnetic interference, improves system reliability, and inhibits common-mode voltage on the basis, so that grid-connected efficiency is further improved, and scheme feasibility is stronger.
Alternatively, in some embodiments, the previous control scheme may be further simplified by eliminating the linear capacitance voltage control loop. I.e. using a model predictive control algorithm instead of all linear controllers. As shown in fig. 4, fig. 4 is a predictive control flow diagram of a CHB photovoltaic system in which another model predictive control algorithm is proposed in accordance with the present disclosure in place of a current control loop. This approach is more challenging because a single loss function is used to control both classical cascaded control loops. The advantage is that the design of the PI controller does not require a linear model of the system, and all the control is handled with one predictive model and one loss function. It is very similar to the previous solution, except that the grid reference current is given by MPPT. Assuming no inverter losses, thenCan be obtained by
Fig. 5 is a schematic structural diagram of a model predictive control device of a single-phase cascaded H-bridge photovoltaic inverter system according to an embodiment of the disclosure.
As shown in fig. 5, the model predictive control device 50 of the single-phase cascade H-bridge photovoltaic inverter system is applied to the single-phase cascade H-bridge photovoltaic inverter system, and the single-phase cascade H-bridge photovoltaic inverter system is composed of n H-bridge sub-modules connected in series, 2 ac reactors, and a power grid, and the device includes:
a function construction module 501, configured to construct a loss function corresponding to the (k+1) th control period;
a first determining module 502, configured to determine a plurality of candidate switch states of the single-phase cascaded H-bridge photovoltaic inverter system;
a second determining module 503, configured to determine a value of a loss function corresponding to each candidate switch state;
the third determining module 504 is configured to determine a minimum value of the plurality of values, and use a candidate switch state corresponding to the minimum value as a switch state corresponding to the k+1th control period.
It should be noted that the foregoing explanation of the model prediction control method of the single-phase cascaded H-bridge photovoltaic inverter system is also applicable to the model prediction control device of the single-phase cascaded H-bridge photovoltaic inverter system of this embodiment, and is not repeated here.
In this embodiment, a loss function corresponding to the k+1 control period is constructed, a plurality of candidate switch states of the single-phase cascade H-bridge photovoltaic inverter system are determined, the value of the loss function corresponding to each candidate switch state is determined, the minimum value of the plurality of candidate switch states is determined, and the candidate switch state corresponding to the minimum value is used as the switch state corresponding to the k+1 control period, so that the method for selecting the switch state based on model predictive control can replace carrier modulation, the control effect is good, the control structure is simple, and four control targets of grid-connected current tracking, independent maximum power tracking of each sub-module photovoltaic assembly, common-mode voltage high-frequency component suppression and switching frequency reduction can be simultaneously realized.
FIG. 6 illustrates a block diagram of an exemplary computer device suitable for use in implementing embodiments of the present disclosure. The computer device 12 shown in fig. 6 is merely an example and should not be construed as limiting the functionality and scope of use of the disclosed embodiments.
As shown in FIG. 6, the computer device 12 is in the form of a general purpose computing device. Components of computer device 12 may include, but are not limited to: one or more processors or processing units 16, a system memory 28, a bus 18 that connects the various system components, including the system memory 28 and the processing units 16.
Bus 18 represents one or more of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, a processor, and a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include industry Standard architecture (Industry Standard Architecture; hereinafter ISA) bus, micro channel architecture (Micro Channel Architecture; hereinafter MAC) bus, enhanced ISA bus, video electronics standards Association (Video Electronics Standards Association; hereinafter VESA) local bus, and peripheral component interconnect (Peripheral Component Interconnection; hereinafter PCI) bus.
Computer device 12 typically includes a variety of computer system readable media. Such media can be any available media that is accessible by computer device 12 and includes both volatile and nonvolatile media, removable and non-removable media.
Memory 28 may include computer system readable media in the form of volatile memory, such as random access memory (Random Access Memory; hereinafter: RAM) 30 and/or cache memory 32. The computer device 12 may further include other removable/non-removable, volatile/nonvolatile computer system storage media. By way of example only, storage system 34 may be used to read from or write to non-removable, nonvolatile magnetic media (not shown in FIG. 6, commonly referred to as a "hard disk drive").
Although not shown in fig. 6, a magnetic disk drive for reading from and writing to a removable non-volatile magnetic disk (e.g., a "floppy disk"), and an optical disk drive for reading from or writing to a removable non-volatile optical disk (e.g., a compact disk read only memory (Compact Disc Read Only Memory; hereinafter CD-ROM), digital versatile read only optical disk (Digital Video Disc Read Only Memory; hereinafter DVD-ROM), or other optical media) may be provided. In such cases, each drive may be coupled to bus 18 through one or more data medium interfaces. Memory 28 may include at least one program product having a set (e.g., at least one) of program modules configured to carry out the functions of the various embodiments of the disclosure.
A program/utility 40 having a set (at least one) of program modules 42 may be stored in, for example, memory 28, such program modules 42 including, but not limited to, an operating system, one or more application programs, other program modules, and program data, each or some combination of which may include an implementation of a network environment. Program modules 42 generally perform the functions and/or methods in the embodiments described in this disclosure.
The computer device 12 may also communicate with one or more external devices 14 (e.g., keyboard, pointing device, display 24, etc.), one or more devices that enable a person to interact with the computer device 12, and/or any devices (e.g., network card, modem, etc.) that enable the computer device 12 to communicate with one or more other computing devices. Such communication may occur through an input/output (I/O) interface 22. Moreover, the computer device 12 may also communicate with one or more networks such as a local area network (Local Area Network; hereinafter LAN), a wide area network (Wide Area Network; hereinafter WAN) and/or a public network such as the Internet via the network adapter 20. As shown, network adapter 20 communicates with other modules of computer device 12 via bus 18. It should be appreciated that although not shown, other hardware and/or software modules may be used in connection with computer device 12, including, but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, data backup storage systems, and the like.
The processing unit 16 executes various functional applications and data processing by running programs stored in the system memory 28, for example, implementing the model predictive control method of the single-phase cascade H-bridge photovoltaic inverter system mentioned in the foregoing embodiment.
In order to implement the above-described embodiments, the present disclosure also proposes a non-transitory computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements a model predictive control method of a single-phase cascaded H-bridge photovoltaic inverter system as proposed in the foregoing embodiments of the present disclosure.
In order to implement the above-mentioned embodiments, the present disclosure also proposes a computer program product which, when executed by an instruction processor in the computer program product, performs a model predictive control method of a single-phase cascaded H-bridge photovoltaic inverter system as proposed in the foregoing embodiments of the present disclosure.
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This disclosure is intended to cover any adaptations, uses, or adaptations of the disclosure following the general principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.
It is to be understood that the present disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings, and that various modifications and changes may be effected without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.
It should be noted that in the description of the present disclosure, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Furthermore, in the description of the present disclosure, unless otherwise indicated, the meaning of "a plurality" is two or more.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and further implementations are included within the scope of the preferred embodiment of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the embodiments of the present disclosure.
It should be understood that portions of the present disclosure may be implemented in hardware, software, firmware, or a combination thereof. In the above-described embodiments, the various steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, may be implemented using any one or combination of the following techniques, as is well known in the art: discrete logic circuits having logic gates for implementing logic functions on data signals, application specific integrated circuits having suitable combinational logic gates, programmable Gate Arrays (PGAs), field Programmable Gate Arrays (FPGAs), and the like.
Those of ordinary skill in the art will appreciate that all or a portion of the steps carried out in the method of the above-described embodiments may be implemented by a program to instruct related hardware, where the program may be stored in a computer readable storage medium, and where the program, when executed, includes one or a combination of the steps of the method embodiments.
Furthermore, each functional unit in the embodiments of the present disclosure may be integrated in one processing module, or each unit may exist alone physically, or two or more units may be integrated in one module. The integrated modules may be implemented in hardware or in software functional modules. The integrated modules may also be stored in a computer readable storage medium if implemented in the form of software functional modules and sold or used as a stand-alone product.
The above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, or the like.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although embodiments of the present disclosure have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the present disclosure, and that variations, modifications, alternatives, and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the present disclosure.
Claims (10)
1. The model predictive control method for the single-phase cascade H-bridge photovoltaic inverter system is characterized by being applied to the single-phase cascade H-bridge photovoltaic inverter system, wherein the single-phase cascade H-bridge photovoltaic inverter system consists of n H-bridge sub-modules, 2 alternating current reactors and a power grid which are connected in series, and the method comprises the following steps:
constructing a loss function corresponding to the k+1th control period;
determining a plurality of candidate switch states of the single-phase cascade H-bridge photovoltaic inverter system;
determining the value of the loss function corresponding to each candidate switch state;
and determining the minimum value in the plurality of values, and using the candidate switch state corresponding to the minimum value as the switch state corresponding to the k+1 control period.
2. The method of claim 1, wherein the first equation corresponding to the loss function is:
wherein lambda is i Weight coefficient lambda representing current tracking control v Weight coefficient lambda representing capacitor voltage balance control g Weight coefficient lambda representing suppression of common-mode voltage high-frequency components c Representing a weight coefficient that reduces the switching frequency of the inverter switching tube,a grid-connected current given value, i, representing the k+1 control period s (k+1) represents a grid-connected current prediction value of the k+1 th control period,/->The capacitance voltage given value of the ith H bridge submodule in the (k+1) th control period is represented, and the i available value ranges are 1, 2, … …, n and v pvi (k+1) represents the ith H bridge of the (k+1) th control periodThe capacitance-voltage prediction value of the sub-module,the direct-current side negative electrode and the grounding point g of the ith submodule representing the k+1 control period s Reference value of common-mode voltage between v gigs (k+1) represents the direct-current side negative electrode and the ground point g of the ith submodule of the (k+1) th control period s Predictive value of common-mode voltage between n c (k+1) represents the number of switching operations in the k+1-th control cycle.
3. The method of claim 2, wherein the grid-tied current setpoint for the k+1 control period and the capacitance voltage setpoint for the ith H-bridge sub-module for the k+1 control period are determined based on:
according to the maximum power tracking algorithm of the ith H bridge sub-module, determining the working voltage of the photovoltaic module in the ith H bridge sub-module under the highest power as the capacitance voltage given value of the ith H bridge sub-module in the (k+1) th control period
Calculating the given value of the grid-connected current based on a second formulaWherein the second formula is:
wherein v is s,rms (k) Representing the effective value of the grid voltage for the kth control period,representing the maximum power, v, of the photovoltaic assembly in the ith H-bridge sub-module in the k+1 control period s (k) Represents the kth control weekInstantaneous value of the grid voltage.
4. The method of claim 2, wherein the grid-tie current prediction value for the k+1 control period is calculated from a third equation, wherein the third equation is:
wherein v is c (k) Cascading H-bridge inverter AC output voltage for kth control period, v s (k) For the grid voltage, i s (k) For grid-connected current, L S R is inductance of the alternating current reactor S T is the resistance of the alternating current reactor S The control period of the control is predicted for the model.
5. The method of claim 4, wherein the kth control period cascaded H-bridge inverter ac output voltage is calculated from a fourth equation, wherein the fourth equation is:
wherein S is i1 (k) Representing the switching function of the upper tube of the left bridge arm of the ith H bridge submodule in the kth control period, S i2 (k) Representing the switching function of the upper tube of the right bridge arm of the ith H bridge submodule in the kth control period, wherein the switching function is represented by binary numbers.
6. The method of claim 2, wherein the number of switching actions of the k+1 control period is calculated from a fifth equation, wherein the fifth equation is:
wherein S is i1 (k+1) represents the switching function of the upper tube of the left bridge arm of the ith H bridge submodule in the kth+1 control period, S i2 And (k+1) represents the switching function of the upper tube of the right bridge arm of the ith H bridge submodule in the k+1 control period.
7. The method of claim 2, wherein the predicted value of the capacitor voltage of the ith H-bridge sub-module of the kth+1 control period is calculated by a sixth equation, wherein the sixth equation is:
wherein i is pvi (k) Representing the output current of the DC side optical string of the ith H bridge submodule in the kth control period, i ci (k) Representing the current flowing into the H bridge by the ith H bridge submodule in the kth control period, and C representing the capacitance value of a capacitor in the H bridge submodule.
8. The method of claim 7, wherein the current flowing into the H-bridge by the ith H-bridge submodule of the kth control period is calculated from a seventh equation, wherein the seventh equation is:
i ci (k)＝(S i1 (k)-S i2 (k))i s (k)；
wherein, the range of i can be 1, 2, … … and n.
9. The method of claim 2, wherein the predicted value of the k+1 th control period common mode voltage is calculated from an eighth equation, wherein the eighth equation is:
10. the method of claim 2, wherein the reference value for the k+1 th control period common mode voltage is calculated based on a ninth equation, wherein the ninth equation is:
wherein α=2pi fT D /(1+2πfT D ) F represents the cut-off frequency of the first-order low-pass filter used, T D Representing the sampling period of the digital controller.
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