CN116205179A - Semi-physical simulation method of single-phase photovoltaic grid-connected inverter based on FPGA - Google Patents

Semi-physical simulation method of single-phase photovoltaic grid-connected inverter based on FPGA Download PDF

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CN116205179A
CN116205179A CN202310221502.6A CN202310221502A CN116205179A CN 116205179 A CN116205179 A CN 116205179A CN 202310221502 A CN202310221502 A CN 202310221502A CN 116205179 A CN116205179 A CN 116205179A
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grid
simulation
connected inverter
fpga
main circuit
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刘青
侯琪
赖渲瑜
侯卓延
路若萱
艾凤明
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Hebei University of Technology
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    • G06F30/34—Circuit design for reconfigurable circuits, e.g. field programmable gate arrays [FPGA] or programmable logic devices [PLD]
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Abstract

The invention discloses a semi-physical simulation method of a single-phase photovoltaic grid-connected inverter based on an FPGA, which comprises the steps of firstly solving a mathematical equation of a simulated object according to a physical circuit model of the simulated object, and then establishing a grid-connected inverter main circuit simulation model by using a programming language of NI LabVIEW software patterning; and then downloading the simulation model into an FPGA development board, and restoring the running process of the actual grid-connected inverter by utilizing a clock module and logic resources of the FPGA to realize real-time adjustment and performance analysis of the grid-connected inverter. The method is flexible, simple and feasible, and compared with a commercial semi-physical simulation platform, the cost is greatly reduced under the same performance condition.

Description

Semi-physical simulation method of single-phase photovoltaic grid-connected inverter based on FPGA
Technical Field
The invention belongs to the technical field of new energy control, and particularly relates to a semi-physical simulation method of a single-phase photovoltaic grid-connected inverter based on an FPGA.
Background
The current power system mainly uses centralized power generation, and along with the wide access of new energy, the power grid structure is obviously changed and gradually evolves to the distributed power generation structure. The output device of the photovoltaic grid-connected system is a grid-connected inverter, the grid-connected inverter is a core component and a technical key of the photovoltaic grid-connected power generation system, and the grid-connected inverter converts direct current generated by the photovoltaic array into alternating current identical to a power grid. The inverter is used as a core carrier for new energy grid connection, bears multiple responsibilities such as electric energy quality management, running state monitoring and switching, power distribution and the like, and the control performance of the inverter determines success or failure of new energy grid connection. However, the control difficulty of the inverter is increasing due to factors such as the use of the high-order LCL filter, the intermittence of the new energy, the weak grid characteristics caused by the large-scale grid connection of the new energy, and the like. Therefore, the semi-physical simulation system for the new energy grid-connected application scene becomes the subject of competitive research at home and abroad.
By means of the new energy grid-connected semi-physical simulation system, the novel inverter control algorithm can be rapidly and conveniently verified, meanwhile, the novel inverter control algorithm has safety and repeatability, and the research and development efficiency and reliability of the new energy grid-connected system can be remarkably improved. However, most of the existing semi-physical simulation methods are based on MATLAB model libraries, and the semi-physical simulation systems of the companies such as OPAL-RT and RTDS need to be bound with hardware products during use. However, the given model library has the problem of low openness of the model itself, and the price of hardware products is very expensive, and varies from hundreds of thousands to hundreds of thousands of yuan.
Disclosure of Invention
Aiming at the defects existing in the current semi-physical simulation technology, the invention provides a semi-physical simulation method of a single-phase photovoltaic grid-connected inverter based on an FPGA, which solves a mathematical equation of a simulated object according to a physical circuit model of the simulated object and establishes a grid-connected inverter main circuit simulation model by using a programming language of NI LabVIEW software imaging; and then downloading the simulation model into an FPGA development board, and restoring the running process of the actual grid-connected inverter by utilizing a clock module and logic resources of the FPGA to realize real-time adjustment and performance analysis of the grid-connected inverter.
The technical scheme for solving the technical problems is as follows: the semi-physical simulation method for the single-phase photovoltaic grid-connected inverter based on the FPGA comprises the following steps:
step (1): establishing a grid-connected inverter main circuit model
According to the main circuit structure of the selected grid-connected inverter, a mathematical model of a main circuit is constructed by taking two principles of Euhm law and kirchhoff law in circuit science as theoretical basis, namely, a series of circuit equation sets are written according to voltage and current which are satisfied by a branch circuit where a capacitor and an inductor in the circuit are located.
Step (2): derivation of a set of state space equations
Selecting the side inductance current of the grid-connected inverter as i L Grid-connected current at grid-connected side is i G Capacitor voltage v C Discretizing the continuous differential form of the circuit equation set in the step (1) for the state variables, converting the continuous circuit equation about the time variable t into a differential equation based on a forward Euler method, and obtaining a state space equation set about three state variables.
Step (3): simulation model establishment
And (3) establishing a simulation model of the grid-connected inverter main circuit by using an NI LabVIEW graphical programming language in a simulation computer according to the state space equation set deduced in the step (2).
Step (4): semi-physical simulation calculation
And (3) downloading the simulation model of the grid-connected inverter main circuit established in the step (3) into a general FPGA development board. Determination of V by structure of grid-connected inverter main circuit DC And v inv And uses "select" logic to achieve this relationship. Setting a timing cycle period by using a clock module of the FPGA, giving initial values of all parameters in a state space equation set, and solving the state variable of the current simulation time step by using the state variable of the known last simulation time step in each simulation time step by using the parallel high-speed calculation function of the FPGA in combination with the clock module according to the mathematical relationship among the state variables given by the equation; at the same time, the state variable values are output at each simulation time step, and the state variables are digitally and analog output in real time and input to a real controllerFor analysis processing, the real controller outputs PWM signals. The PWM signals are input into a grid-connected inverter main circuit simulation model in the FPGA after passing through a digital input/output module, simulation solution of the next switching period is carried out, and the semi-physical simulation of the photovoltaic grid-connected system is realized continuously.
Compared with the prior art, the invention has the beneficial effects that:
1. modeling is carried out on a main circuit of the grid-connected inverter, the semi-physical simulation of the grid-connected inverter based on the FPGA is realized, and the requirement of the current grid-connected inverter experiment verification is met.
2. The modeling method is open and flexible, and can be used for self-defining the solving method of the simulation model according to the purpose of the experiment or the simulation precision requirement.
3. The modeling method is simple and feasible, can realize model solving by using a graphical programming method, does not need complex text programming language, and greatly improves program development efficiency.
4. The modeling method can be used for realizing semi-physical simulation of a general FPGA development board, and compared with a commercial semi-physical simulation platform, the cost is greatly reduced under the same performance condition.
Drawings
Fig. 1 is a circuit structure diagram of a grid-connected inverter according to an embodiment of a semi-physical simulation method of a single-phase photovoltaic grid-connected inverter based on an FPGA of the present invention.
Fig. 2 is a simulation model of a main circuit of a grid-connected inverter according to an embodiment of a semi-physical simulation method of a single-phase photovoltaic grid-connected inverter based on an FPGA of the present invention.
Fig. 3 is a waveform diagram of grid-connected current at the grid-connected side in an implementation process of an embodiment of a semi-physical simulation method of a single-phase photovoltaic grid-connected inverter based on an FPGA of the present invention.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings.
In the embodiment, a simulation model is built by taking a grid-connected inverter main circuit in a single-phase photovoltaic grid-connected system as an object.
The invention provides a semi-physical simulation method of a single-phase photovoltaic grid-connected inverter based on an FPGA, which comprises the following steps:
(1) Establishing a grid-connected inverter main circuit model
The main circuit of the grid-connected inverter adopts a common single-phase full-bridge inverter circuit, and the filter is an LCL type filter. The inverter module of the grid-connected inverter main circuit adopts a single-phase full-bridge inverter circuit, as shown in figure 1, Q in the figure 1 ～Q 4 Is four fully-controlled power switch devices, V DC Direct-current voltage output to inverter for front-stage photovoltaic module, v inv For single-phase full-bridge inverter circuit output voltage, inductance L 1 Capacitance C and inductance L 2 Constitute LCL filter, v G For the grid voltage, R 1 And R is 2 Is equivalent resistance. Let the inductor current at the inverter side now be i L Grid-connected current at grid-connected side is i G The voltage of the capacitor C is v C . Let S 1 ～S 4 For switching device Q 1 ～Q 4 When switching device Q x When conducting, S x When the switching device Q is =1 x When turned off, S x =0. Therefore, when Q 1 And Q 4 Simultaneously conducting, i.e. S 1 ＝S 4 When=1, v inv ＝V DC The method comprises the steps of carrying out a first treatment on the surface of the When the switch tube Q 2 And Q 3 Simultaneously conducting, i.e. S 1 ＝S 4 When=0, v inv ＝-V DC 。
The grid-connected inverter main circuit contains an inductor L 1 Capacitance C and inductance L 2 And the three energy storage elements are used for establishing a grid-connected inverter main circuit model according to the Euhm law and the kirchhoff voltage and current law in the circuit science, so that three circuit equations can be established. Firstly, writing the first two equations according to ohm law and kirchhoff voltage law, then writing the third equation according to ohm law and kirchhoff current law, and establishing a grid-connected inverter main circuit model as follows:
Figure BDA0004116940010000041
(2) Derivation of a set of state space equations
A system of state space equations is a collection that contains the input, output and state variables of the system and expresses them in terms of first order differential equations. Firstly, selecting state variables, and selecting memory quantity i of energy storage element L 、i G And v C As a state variable; the three circuit equations listed in the step (1) are arranged as follows:
Figure BDA0004116940010000051
since FPGA is a way of digital signal processing, the continuous differential form di in the equation is needed L (t)/dt、di G (t)/dt and dv C (t)/dt discretization, i.e. in { i } L [(n+1)T]–i L (nT)}、{i G [(n+1)T]–i G (nT) } and { v C [(n+1)T]–v C (nT) } replaces di respectively L 、di G And dv C Wherein T is the simulation step length of the grid-connected inverter main circuit model. Let x= L, G, the same applies below to obtain i X [(n+1)T]Regarding i X Equation sum v of (nT) C [(n+1)T]With respect to v C The equation for (nT) is as follows:
Figure BDA0004116940010000052
by this step, the continuous circuit equation with respect to the time variable t is converted into a forward differential equation, where a forward euler method is used, and the adopted simulation step size is sufficiently small, so that the method can ensure not only sufficiently high accuracy but also a small calculation amount. Columns are written in the form of a system of state space equations:
Figure BDA0004116940010000053
(3) Simulation model establishment
And (3) establishing a simulation model of the grid-connected inverter main circuit in a simulation computer according to the state space equation set deduced in the step (2) by using an NI LabVIEW graphical programming language, as shown in figure 2.
(4) State variable output
And (3) downloading the simulation model of the grid-connected inverter main circuit established in the step (3) into a general FPGA development board. According to the above system of state space equations, the value of each state variable in the next simulation step needs to be calculated by solving the values of the state variables in the previous simulation step. For a semi-physical simulation system, real-time performance needs to be considered for model solving, so that calculation of values of each simulation time step of each state variable is controlled to be completed in one simulation step length, and a clock module of the FPGA can complete the task in cooperation with logic resources. The calculation result of the last simulation time step can be stored in the shift register, and after a certain amount of basic operation is performed, the result is stored continuously and used for solving the next simulation time step. Therefore, the above-described process realizes a function of a timing cycle in which the operation content is cyclically operated at a predetermined cycle. Meanwhile, the cycle period of the timing cycle can be set by itself, that is, the simulation step size, and in this embodiment, the simulation step size is set to 1/(10 MHz). Given the initial values of the parameters in the state space equation, V DC ＝400V，L 1 ＝1.5mH，R 1 ＝0.5Ω，C＝15μF，L 2 ＝0.5mH，R 2 =0.5Ω, and according to the mathematical relationship between the state variables given by the equation, at each simulation time step, is calculated from the known i X (nT)、v C (nT), solving for i X [(n+1)T]、v C [(n+1)T]. In addition, V is formed by the structure of the grid-connected inverter main circuit DC And v inv The theoretical relationship of (2) is: when S is 1 ＝S 4 ＝1，v inv ＝V DC When S 1 ＝S 4 ＝0，v inv ＝-V DC This relationship is implemented using "select" logic.
Through the solution of the method, i is realized by using a clock module and logic resources of the FPGA L 、i G And v C The real-time solution of the grid-connected inverter main circuit can be simulated to run. The method realizes three stepsThe parallel solution of the state variables avoids the simplification and calculation of the matrix in the traditional state equation method, does not need an additional matrix algorithm, and greatly improves the program development efficiency.
The grid-connected inverter main circuit simulation model is associated with an external real controller, and a control loop of the real controller is i L -v C -i G The three-loop control mode (inner loop on left side, outer loop on right side) of the control system, the specific control mode is DB-DB-PI, as shown in figure 1. In the figure, the PLL represents a phase-locked loop, so as to track the phase and frequency of an output signal to an input signal, i.e. the output and the input have the same frequency and phase; DB-DB-PI is a special three-ring control structure of grid-connected inverter, namely, an inner ring and an intermediate ring adopt a DB control mode, an outer ring adopts a PI control mode, DB is Dead-Beat control, and PI is proportional integral (Proportional integral) control.
The state variable i of the grid-connected inverter main circuit simulation model calculated in the FPGA is calculated L 、i G And v C Digital-to-analog output (DAC) is performed in real time for analysis processing (sampling, summing, proportional, integral, clipping, modulation) by the real controller, which outputs PWM (pulse width modulation) signals. PWM signals are input into a grid-connected inverter main circuit simulation model in the FPGA after passing through a digital input/output (DIO) module, and simulation solution of the next simulation time step is carried out. Therefore, the real controller and the grid-connected inverter main circuit simulation system in the FPGA form a complete semi-physical simulation system, the operation process of the semi-physical simulation system is shown as a figure 3, and the light-color waveform in the figure is grid-connected current i G The dark waveform is the grid-connected current reference value i G REF According to the waveform diagram of the grid-connected inverter, the phase of the two waveforms in the diagram is consistent, and the grid-connected current is synchronous with the reference value of the grid-connected current, so that the expected effect is realized, and the modeling method can realize the semi-physical simulation of the single-phase grid-connected inverter based on the FPGA. For a single-phase photovoltaic grid-connected inverter, the hardware selection of the controller is various, including but not limited to a DSP controller and an FPGA controller; the software selection of the controller, i.e. the control strategy, can be divided into single-loop control, double-loop control and three-loop control according to the number of controlled quantitiesAnd the control can realize the control of the grid-connected inverter.
The invention is applicable to the prior art where it is not described.

Claims (2)

1. The semi-physical simulation method of the single-phase photovoltaic grid-connected inverter based on the FPGA is characterized by comprising the following steps of:
step (1): establishing a grid-connected inverter main circuit model
According to the main circuit structure of the selected grid-connected inverter, a mathematical model of a main circuit is constructed by taking two principles of Euhm law and kirchhoff law in circuit science as theoretical basis, namely, a series of circuit equation sets are written according to voltage and current which are satisfied by a branch circuit where a capacitor and an inductor in the circuit are positioned;
step (2): derivation of a set of state space equations
Selecting the side inductance current of the grid-connected inverter as i L Grid-connected current at grid-connected side is i G Capacitor voltage v C Discretizing the continuous differential form of the circuit equation set in the step (1) for the state variables, converting the continuous circuit equation about the time variable t into a differential equation based on a forward Euler method, and obtaining a state space equation set about three state variables;
step (3): simulation model establishment
Establishing a simulation model of a grid-connected inverter main circuit by using a NILabVIEW graphical programming language in a simulation computer according to the state space equation set deduced in the step (2);
step (4): semi-physical simulation calculation
Downloading the simulation model of the grid-connected inverter main circuit established in the step (3) into a general FPGA development board; determination of V by structure of grid-connected inverter main circuit DC And v inv And uses "select" logic to achieve this relationship; setting a timing cycle period by using a clock module of the FPGA, giving initial values of all parameters in a state space equation set, and using a parallel high-speed calculation function of the FPGA to cooperate with the clock module according to mathematical relations among state variables given by the equation, wherein in each simulation time step, the known last time step is used for calculating the state variablesSolving the state variable of the current simulation time step by the state variable of the simulation time step; meanwhile, outputting state variable values at each simulation time step, carrying out digital analog output on the state variables in real time, inputting the state variables into a real controller for analysis and processing, and outputting PWM signals by the real controller; the PWM signals are input into a grid-connected inverter main circuit simulation model in the FPGA through a digital input/output module, simulation solution of the next simulation time step is carried out, and the simulation is continuously circulated, so that semi-physical simulation of the photovoltaic grid-connected system is realized.
2. The semi-physical simulation method of the single-phase photovoltaic grid-connected inverter based on the FPGA, which is disclosed in claim 1, is characterized in that an inversion module of a grid-connected inverter main circuit adopts a single-phase full-bridge inversion circuit, and a filter is an LCL type filter.
CN202310221502.6A 2023-03-08 2023-03-08 Semi-physical simulation method of single-phase photovoltaic grid-connected inverter based on FPGA Pending CN116205179A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117452822A (en) * 2023-11-13 2024-01-26 中原工学院 Repeated control technology programming implementation method based on C language

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117452822A (en) * 2023-11-13 2024-01-26 中原工学院 Repeated control technology programming implementation method based on C language

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