Three-phase lcl grid-connected npc inverter system based on fast model predictive control

Abstract

The application provides a three-phase LCL grid-connected NPC inverter system based on fast model predictive control, which comprises a fast model predictive controller, which carries out fast control on the NPC inverter by selecting a calculation sector composed of a current output voltage vector of the NPC inverter and several voltage vectors near the current output voltage vector; and the synchronization of the LCL filter grid-connected current and the power grid is realized by changing the prediction control reference current angle; the calculation sector is a sub-sector composed of output voltage vectors participating in the prediction control calculation on the complex plane of the voltage vectors. The scheme provided by the application realizes the balance of the DC side midpoint voltage by selecting a suitable short vector in the redundant short vector, reduces the calculation amount and avoids the design of the weight coefficient; the calculation amount is further reduced by reducing the calculation sector, so that the fast calculation of the optimal output voltage vector and the fast control purpose are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of three-phase LCL grid-connected NPC inverter control, and particularly relates to a three-phase LCL grid-connected NPC inverter system based on fast model predictive control. BACKGROUND

[0002] With the promotion of policies, new energy power generation has been vigorously developed, and NPC inverters are widely used in high-power medium and low-voltage converter fields due to their small output voltage and current harmonics, halved voltage borne by switching devices, and halved switching loss. The inverter is connected to the grid through a filter, and under the same requirement for THD value, the LCL type filter has the advantages of smaller size and cost compared with other types of inverters, and therefore is widely used. In recent years, with the continuous improvement of the computing power of microprocessors, some relatively complex control methods have been implemented, including fuzzy control, model predictive control, adaptive control, sliding mode control, and neural network control.

[0003] The finite set model predictive control in model predictive control has been widely concerned by domestic and foreign scholars due to its simple principle, easy understanding, no need for overly complex parameter design, and good control performance. However, the traditional FCS-MPC control needs to traverse all switching states, which will produce a high computational burden and a large delay for system control. In view of this problem, many optimization algorithms have been proposed in existing researches, including:

[0004] A fast optimization method of FCS-MPC for T-type three-level grid-connected inverters is proposed, which reduces the prediction number of each control cycle to 3 times by judging the reference current in its 24 subdivided sectors. However, this method not only needs to determine the amplitude of the reference current but also needs to judge the electric angle, which adds new burden to the calculation.

[0005] An adaptive model predictive control strategy for three-phase LCL grid-connected inverters is proposed, which solves the phase correction of the grid-connected current of the LCL filter grid-connected inverter. However, this method is too complex and needs to traverse all inverter output voltage vectors, and does not optimize the large calculation amount of FCS-MPC.

[0006] A fast model predictive control algorithm for two-level inverters based on a single vector is proposed, which directly selects the optimal vector according to the spatial position of the reference current. Although the prediction number of this method is 1, this method is only applicable to two-level inverters, and cannot achieve the same effect when the order of the DC side increases.

[0007] The event-triggered FCS-MPC is proposed. The event-triggered FCS-MPC continues to use the last optimal output vector at the next time point by calculating the cost function of the last optimal output vector at the next time point, and the cost function is still less than a certain value, so as to reduce the calculation amount. When the above condition is not met, the cost function of all output vectors is calculated to obtain the optimal output vector, so that the method does not play a role in reducing the calculation amount in this case, and the burden of the processor is increased.

[0008] In summary of the above literatures, the prior art still has the following shortcomings:

[0009] 1. The existing model predictive control, the addition of additional sensors will introduce more data to be processed, which will make the already complex model predictive control algorithm more complex, and is not conducive to reducing the delay;

[0010] 2. The existing model predictive control, the design of the related weight coefficient is complex, and the unreasonable design of the weight coefficient will affect the control effect, and even lead to system disorder;

[0011] 3. The existing model predictive control is insufficient for the improvement of the three-phase LCL grid-connected NPC inverter, and cannot fully play the performance of the three-phase LCL grid-connected NPC inverter. SUMMARY

[0012] To solve the above technical problems, the present application provides a technical scheme of a three-phase LCL grid-connected NPC inverter based on fast model predictive control, electronic equipment and storage medium to solve the above technical problems.

[0013] The first aspect of the present application discloses a three-phase LCL grid-connected NPC inverter system based on fast model predictive control; the system comprises:

[0014] a three-phase LCL grid-connected NPC inverter and a fast model predictive controller;

[0015] The fast model predictive controller performs fast control on the three-phase LCL grid-connected NPC inverter by selecting a calculation sector composed of the current output voltage vector of the three-phase LCL grid-connected NPC inverter and a plurality of voltage vectors near the current output voltage vector; and realizes the synchronization of the LCL filter grid-connected current and the power grid by changing the prediction control reference current angle; the calculation sector is a sub-sector composed of the output voltage vector participating in the prediction control calculation in the complex plane of the voltage vector.

[0016] According to the system of the first aspect of the present application, the fast model predictive controller comprises:

[0017] The data acquisition module acquires two capacitor voltages on the DC side of the three-phase LCL grid-connected NPC inverter, output current values and an electrical angle of the output current of the three-phase LCL grid-connected NPC inverter, a grid-connected current, an electrical angle of the grid-connected current, a grid voltage value, an electrical angle of the grid voltage, and a number of a current output voltage vector on a complex plane of voltage vectors;

[0018] The reference current value calculation module calculates a reference current value according to the electrical angle of the output current, the electrical angle of the grid-connected current, and the electrical angle of the grid voltage;

[0019] The three-phase LCL grid-connected NPC inverter mathematical model is established according to the collected data, and a calculation formula of the output voltage vector is established;

[0020] The output current prediction model calculation module obtains a prediction value mathematical model of the inverter output current according to the three-phase LCL grid-connected NPC inverter mathematical model and the calculation formula of the output voltage vector;

[0021] The calculation sector and short vector selection module selects a calculation sector and a short vector in the calculation sector according to the two capacitor voltages on the DC side and the number of the current output voltage vector on the complex plane of voltage vectors;

[0022] The control quantity calculation and output module constructs a cost function according to the reference current value and the prediction value mathematical model of the inverter output current, applies the cost function, the calculation sector, and the short vector in the calculation sector, compares the values of the cost function at different output voltage vectors in the next sampling period, selects an optimal switching state, and realizes control of the three-phase LCL grid-connected NPC inverter.

[0023] According to the system of the first aspect of the application, the specific formula for calculating the reference current value according to the electrical angle of the output current, the electrical angle of the grid-connected current, and the electrical angle of the grid voltage includes:

[0024]

[0025] wherein,

[0026] and are the real part and the imaginary part of the reference current vector i * ;

[0027] θ i , θ c , and θ g are the electrical angle of the output current, the electrical angle of the grid-connected current, and the electrical angle of the grid voltage, respectively;

[0028] Id and I qfor a given value by a person;

[0029] The specific method for achieving synchronization of the LCL filtered grid-connected current with the grid by changing the predictive control reference current angle includes:

[0030] The phase difference between the output current of the three-phase LCL grid-connected NPC inverter and the LCL filtered current is calculated, the phase difference is added to the electrical angle of the grid voltage, and is brought into the calculation formula of the reference current value.

[0031] According to the system of the first aspect of the application, the calculation formula of the output voltage vector is,

[0032]

[0033] wherein,

[0034] v is the output voltage vector;

[0035] v aN is the voltage at the a-phase output end of the three-phase LCL grid-connected NPC inverter and the negative end point of the DC side;

[0036] v bN is the voltage at the b-phase output end of the three-phase LCL grid-connected NPC inverter and the negative end point of the DC side;

[0037] v cN is the voltage at the c-phase output end of the three-phase LCL grid-connected NPC inverter and the negative end point of the DC side;

[0038] a in the formula is

[0039] The calculation formula of the mathematical model of the three-phase LCL grid-connected NPC inverter is,

[0040]

[0041] wherein,

[0042] v xc is the voltage of the filter capacitor in each of the a, b and c phases;

[0043] v nN is the voltage at the neutral point of the grid and the negative end point of the DC side;

[0044] i xo and i xg are the output currents and the grid-connected current of the three-phase LCL grid-connected NPC inverter in each of the a, b and c phases, respectively;

[0045] L1 and L2 are filter inductances;

[0046] R1 and R2 are equivalent resistances of the filter inductances;

[0047] C is a filter capacitor;

[0048] L and R are the equivalent inductance and resistance of the transmission line, respectively;

[0049] e x is a three-phase grid voltage.

[0050] According to the system of the first aspect of the application, the specific method for obtaining the predicted value mathematical model of the inverter output current according to the calculation formula of the three-phase LCL grid-connected NPC inverter mathematical model and the calculation formula of the output voltage vector comprises:

[0051] The calculation formula of the three-phase LCL grid-connected NPC inverter mathematical model is brought into the calculation formula of the output voltage vector, and the current derivative is discretized by applying forward Euler approximation to obtain the output current predicted value mathematical model of the three-phase LCL grid-connected NPC inverter:

[0052]

[0053] wherein,

[0054] is the predicted value of the output current at k+1 time;

[0055] i o (k) is the output current value at k time;

[0056] i g (k) is the grid-connected current value at k time;

[0057] i g (k-1) is the grid-connected current value at k-1 time;

[0058] T s is the sampling interval;

[0059]

[0060] According to the system of the first aspect of the application, the method for selecting the calculation sector and the short vector therein according to the two capacitor voltages on the DC side, the current output voltage vector number on the complex plane of the voltage vector comprises:

[0061] The two capacitor voltages on the DC side u c1 and u c2 and the current output voltage vector number x o and y on the complex plane of the voltage vector are used to give the predicted value calculation sector selection variable, and the calculation sector and the short vector therein are selected.

[0062] According to the system of the first aspect of the application, the two capacitor voltages on the DC side u c1 and uc2 and the number x of the current output voltage vector on the complex plane of voltage vectors o and the artificially given predicted value to calculate the sector selection variable, the specific method of selecting the calculation sector and the short vector therein includes:

[0063] according to the number x of the current output voltage vector on the complex plane of voltage vectors o As the initial position, the increment variable and the decrement variable in the artificially given predicted value to calculate the sector selection variable are applied to determine the size of the calculation sector;

[0064] When u c1 >u c2 , the short vector pair i o (k+1) is predicted and calculated, when u c1 <u c2 , the short vector pair i o (k+1) is predicted and calculated.

[0065] According to the system of the first aspect of the application, the cost function is:

[0066]

[0067] wherein,

[0068] g is the cost function;

[0069] and are the real part and the imaginary part of the reference current vector i * at k+1 time;

[0070] and are the real part and the imaginary part of the predicted value of the output current at k+1 time;

[0071] The specific method of selecting the optimal switching state by comparing the values of the cost function of different output voltage vectors in the next predicted sampling period includes:

[0072] The selected short vector is applied to the cost function to calculate a plurality of cost function values, and the minimum cost function value is calculated, and the switching state of the short vector therein is taken as the optimal switching state.

[0073] The second aspect of the application provides an electronic device, the device includes a memory and a processor, the memory stores a computer program, and the computer program is executed by the processor to execute the method in the three-phase LCL grid-connected NPC inverter system based on the fast model predictive control according to the first aspect of the application.

[0074] The third aspect of the present application provides a storage medium storing a computer program capable of being executed by one or more processors and capable of being used to implement the method in the three-phase LCL grid-connected NPC inverter system based on fast model predictive control according to the first aspect of the present application.

[0075] The scheme provided by the present application achieves synchronization of the grid-connected current with the power grid by changing the phase of the reference current electric angle to control the inverter output current in the fast model predictive control; achieves balance of the DC side midpoint voltage, reduces the amount of calculation and avoids design of the weight coefficient by selecting a suitable short vector in the redundant short vector; and further reduces the amount of calculation by narrowing the calculation sector, so that the fast model predictive control only performs optimization calculation near the current optimal output voltage vector, thereby achieving the purpose of fast calculation of the optimal output voltage vector and fast control. BRIEF DESCRIPTION OF DRAWINGS

[0076] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0077] Figure 1 The structural diagram of the three-phase LCL grid-connected NPC inverter system based on fast model predictive control according to an embodiment of the present application;

[0078] Figure 2 The topology diagram of the three-phase LCL grid-connected NPC inverter according to an embodiment of the present application;

[0079] Figure 3 The voltage vector on the complex plane according to an embodiment of the present application;

[0080] Figure 4 The reference current vector diagram according to an embodiment of the present application;

[0081] Figure 5 The flowchart of the fast model predictive control according to an embodiment of the present application;

[0082] Figure 6 The grid-connected current waveform according to an embodiment of the present application;

[0083] Figure 7 The structural diagram of an electronic device according to an embodiment of the present application. DETAILED DESCRIPTION

[0084] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0085] The first aspect of the present application discloses a three-phase LCL grid-connected NPC inverter system based on fast model predictive control, Figure 1 The structure diagram of the three-phase LCL grid-connected NPC inverter system based on fast model predictive control according to the embodiments of the present application is specifically shown in Figure 1 The system comprises:

[0086] a three-phase LCL grid-connected NPC inverter and a fast model predictive controller.

[0087] The fast model predictive controller performs fast control on the three-phase LCL grid-connected NPC inverter by selecting a calculation sector composed of a current output voltage vector of the three-phase LCL grid-connected NPC inverter and several voltage vectors near the current output voltage vector, and realizes synchronization of LCL filter grid-connected current and power grid by changing a prediction control reference current angle. The calculation sector is a sub-sector composed of output voltage vectors participating in prediction control calculation in a complex plane of voltage vectors.

[0088] In some embodiments, the fast model predictive controller comprises:

[0089] a data acquisition module: obtaining two capacitor voltages on the DC side of the three-phase LCL grid-connected NPC inverter, an output current value and an electrical angle of the output current of the three-phase LCL grid-connected NPC inverter, a grid-connected current, an electrical angle of the grid-connected current, a power grid voltage value, an electrical angle of the power grid voltage, and a number of the current output voltage vector in a complex plane of voltage vectors;

[0090] a reference current value calculation module: calculating a reference current value according to the electrical angle of the output current, the electrical angle of the grid-connected current, and the electrical angle of the power grid voltage;

[0091] a three-phase LCL grid-connected NPC inverter mathematical model: establishing a three-phase LCL grid-connected NPC inverter mathematical model and a calculation formula of the output voltage vector according to the collected data;

[0092] an output current prediction model calculation module: obtaining a prediction value mathematical model of the inverter output current according to the three-phase LCL grid-connected NPC inverter mathematical model and the calculation formula of the output voltage vector;

[0093] A sector and short vector selection module: according to the two capacitor voltages on the DC side, the number of the current output voltage vector on the complex plane of voltage vectors, the sector and the short vector in the sector are selected;

[0094] A control quantity calculation and output module: according to the reference current value and the predictive value of the inverter output current, a cost function is constructed; the cost function and the sector and the short vector in the sector are applied to select the optimal switching state by comparing the values of the cost function at different output voltage vectors in the next sampling period, so as to realize the control of the three-phase LCL grid-connected NPC inverter.

[0095] In some embodiments, the specific formula for calculating the reference current value according to the electrical angles of the output current, the grid-connected current and the grid voltage includes:

[0096]

[0097] wherein,

[0098] and are the real part and the imaginary part of the reference current vector i * .

[0099] θ i , θ c and θ g are the electrical angles of the output current, the grid-connected current and the grid voltage, respectively.

[0100] I d and I q are artificially given values.

[0101] The grid-connected current of the LCL filter grid-connected inverter needs to be phase-corrected to achieve synchronization with the grid. If the grid-connected current is not synchronized with the grid voltage, the transmission efficiency of the grid will be reduced, and the greater the phase difference between the current and the voltage, the lower the transmission efficiency. The fast model predictive control algorithm changes the electrical angle of the inverter output current to achieve synchronization between the current after the LCL filter and the grid. By changing the predictive control reference current angle, the LCL filter grid-connected current is synchronized with the grid. The specific method includes:

[0102] The phase difference between the output current of the three-phase LCL grid-connected NPC inverter and the current after the LCL filter is calculated, the phase difference is added to the electrical angle of the grid voltage, and the calculation formula of the reference current value is brought in.

[0103] The topology circuit of the three-phase LCL grid-connected NPC inverter is as follows Figure 2L1 and L2 are filter inductances, R1 and R2 are equivalent resistances of the filter inductances, C is a filter capacitance, L and R are equivalent inductance and resistance of the transmission line, e a 、e b 、e c is a three-phase grid voltage. The output is connected to the grid through an LCL filter. Each of the three phases of the three-phase LCL grid-connected NPC inverter consists of four switches, four freewheeling diodes and two clamping diodes, among which the middle two center switches and diodes allow the output end to be connected to the midpoint voltage of the DC voltage source.

[0104] Each of the three phases of the three-phase LCL grid-connected NPC inverter has three switching states and v xN The size is shown in Table 1, where 1 represents the switch closed, 0 represents the switch open, and x={a,b,c}.

[0105] Table 1

[0106] [SA x ]] [SA x1 ]] [SA x2 ]]> [SA x3 ]]> [SA x4 ]] v xN ]]> + 1 1 0 0 VDC / 2 0 0 1 1 0 0 - 0 0 1 1 -VDC / 2

[0107] For the three phases of the NPC inverter, 27 switching states are generated, and 19 different voltage vectors are generated, as Figure 3 shown.

[0108] In some embodiments, the calculation formula of the output voltage vector is,

[0109]

[0110] where,

[0111] v is the output voltage vector;

[0112] v aN is the voltage at the a-phase output end of the three-phase LCL grid-connected NPC inverter and the negative end point of the DC side;

[0113] v bN is the voltage at the b-phase output end of the three-phase LCL grid-connected NPC inverter and the negative end point of the DC side;

[0114] v cN is the voltage at the c-phase output end of the three-phase LCL grid-connected NPC inverter and the negative end point of the DC side;

[0115] a in the formula represents that there is a 120° phase shift between the phases;

[0116] According to the definition of the variables in the three-phase LCL grid-connected inverter circuit shown in Figure 2 , the calculation formula of the mathematical model of the three-phase LCL grid-connected NPC inverter is,

[0117]

[0118] wherein,

[0119] v xc are the filter capacitor voltages of phase a, b and c respectively;

[0120] v nN is the voltage between the grid neutral point and the negative terminal of the DC side;

[0121] i xo and i xg are the output currents and grid currents of phase a, b and c of the three-phase LCL grid-connected NPC inverter respectively;

[0122] L1 and L2 are filter inductances;

[0123] R1 and R2 are equivalent resistances of the filter inductances;

[0124] C is a filter capacitor;

[0125] L and R are equivalent inductance and resistance of the transmission line respectively;

[0126] e x is a three-phase grid voltage.

[0127] In some embodiments, the specific method of obtaining the predicted value mathematical model of the inverter output current according to the calculation formula of the three-phase LCL grid-connected NPC inverter mathematical model and the calculation formula of the output voltage vector comprises:

[0128] substituting the calculation formula of the three-phase LCL grid-connected NPC inverter mathematical model into the calculation formula of the output voltage vector to obtain,

[0129]

[0130] wherein the last term Let:

[0131]

[0132] then

[0133] Further applying the forward Euler approximation to the current derivative and discretization, as follows,

[0134]

[0135] obtaining,

[0136]

[0137] Since i gThe frequency of the alternating current is much smaller than the sampling frequency, and it can be assumed that the electrical angle does not change significantly within a sampling interval T s Therefore, let

[0138] i g (k+1)-i g (k)=i g (k)-i g (k-1)

[0139] The mathematical model of the output current prediction value of the three-phase LCL grid-connected NPC inverter is as follows:

[0140]

[0141] wherein,

[0142] is the prediction value of the output current at k+1;

[0143] i o (k) is the output current value at k;

[0144] i g (k) is the grid-connected current value at k;

[0145] i g (k-1) is the grid-connected current value at k-1;

[0146] T s is the sampling interval.

[0147] For stable alternating current, the change of the electrical angle is stable and predictable. Since the frequency of the alternating current is much smaller than the sampling frequency, it can be assumed that the electrical angle does not change significantly within a sampling interval T s . Therefore, when calculating the optimal voltage vector output by the NPC inverter at k+1, only the voltage vectors in the vicinity of the voltage vector output by the inverter at k can be calculated, that is, Figure 4 The area with the section line in the above formula, and the size of the sector selection variable, the increment variable up and the decrement variable down can be adjusted according to the prediction value given by a person.

[0148] In some embodiments, the method of selecting the calculation sector and the short vector therein according to the two capacitor voltages on the direct current side, the number of the current output voltage vector on the complex plane of the voltage vector comprises:

[0149] The two capacitor voltages u c1 and u c2 on the direct current side and the number x oand the human given prediction value, select the calculation sector and the short vector within it.

[0150] The 19 voltage vectors outputted by 27 switching states of NPC inverter can be divided into zero vector, short vector, middle vector and long vector according to the magnitude of the vector. Among them, each short vector has two different switching states, the line voltage outputted by the two switching states is the same, but the change of DC side capacitor voltage difference caused by the two switching states is opposite. Making full use of the property of short voltage vector outputted by NPC inverter can effectively reduce the DC side capacitor voltage difference and the processor calculation amount. The DC side capacitor voltage change under each short vector switching state is shown in Table 2.

[0151] Table 2

[0152]

[0153] The DC side two capacitor voltages u c1 and u c2 and the number x o of the current output voltage vector on the complex plane of voltage vector are used to calculate the sector selection variable, and the specific method of selecting the calculation sector and the short vector within it includes:

[0154] According to the number x o of the current output voltage vector on the complex plane of voltage vector, the increment variable up and the decrement variable down in the sector selection variable calculated by the human given prediction value are used as the initial position to determine the size of the calculation sector

[0155] When u c1 > u c2 , the short vector of P group switching state is selected to predict i o (k+1), when u c1 < u c2 , the short vector of N group switching state is selected to predict i o (k+1);

[0156] In some embodiments, the cost function is:

[0157]

[0158] wherein,

[0159] g is the cost function;

[0160] and are the real part and the imaginary part of the reference current vector i * at k+1 time;

[0161] and are the real and imaginary parts of the predicted value of the output current at time k+1;

[0162] The specific method for selecting the optimal switching state by comparing the cost function values of different output voltage vectors in the next sampling period includes:

[0163] The selected short vectors are applied to the cost function to calculate a plurality of cost function values, and the minimum cost function value is calculated, and the switching state of the short vector therein is taken as the optimal switching state.

[0164] In some embodiments, the fast predictive control flow chart is as shown in Figure 5 The two capacitor voltages u c1 and u c2 , the inverter output current value i o , the electrical angle θ i , the grid current i g , the grid voltage value u g and the electrical angle θ g , and the current output voltage vector v in the voltage vector complex plane x o are measured first, and the reference current is generated according to the measured data and given I d and I q , so that the inverter output current after LCL filtering is synchronized with the grid voltage. The x and g values are initialized and set, x=x o -down, which is to limit the sector for the subsequent prediction calculation, and g=∞ is to ensure that the output voltage vectors not calculated are not applied. The short vectors in the calculation sector are reasonably selected for calculation according to the two capacitor voltages u c1 and u c2 . The predicted current values under each output voltage vector selected in the front are calculated through the predicted current calculation formula, and then the errors of these predicted values and the reference values are calculated through the cost function, (G, x o ) = min(g), wherein G and x o are the minimum value in the array g and the corresponding inverter output voltage vector number respectively, so that the output voltage vector with the minimum error is selected as the output, thereby realizing the control of the three-phase LCL grid-connected NPC inverter.

[0165] Embodiment

[0166] When the up value and the down value are set to 4 and 3 respectively, Figure 6 is when the time is 0.3s, the reference value of the three-phase grid current suddenly changes from 200A to 220A, from Figure 6It can be seen from the figure that the actual value of the grid-connected current can quickly and accurately track the reference value of the grid-connected current when the parameter current value changes, which proves that the proposed scheme has good dynamic performance. Table 3 is the THD value of the three-phase grid-connected current in five cycles before and after 0.3s.

[0167] Table 3

[0168] 200A 220A A 1.42％ 1.95％ B 1.68％ 2.31％ C 1.98％ 2.51％

[0169] Compared with the prior art, the technical solutions of the aspects of the present application have the following advantages: by changing the phase of the reference current electric angle to control the output current of the inverter in the fast model predictive control, the grid-connected current is synchronized with the power grid; by selecting a suitable short vector in the redundant short vector, the DC side midpoint voltage is balanced, the calculation amount is reduced, and the design of the weight coefficient is avoided; by reducing the calculation sector, the fast model predictive control only performs optimization calculation near the current optimal output voltage vector, thereby further reducing the calculation amount and achieving the purpose of fast calculation of the optimal output voltage vector and fast control.

[0170] The second aspect of the present application discloses an electronic device comprising a memory and a processor, the memory storing a computer program, and the processor implementing the steps of any one of the three-phase LCL grid-connected NPC inverter methods based on fast model predictive control disclosed in the first aspect of the present application when executing the computer program.

[0171] Figure 7 The structure diagram of the electronic device according to the embodiment of the present application is shown in FIG. 1, Figure 7 As shown in FIG. 1, the electronic device comprises a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. The processor of the electronic device is used to provide calculation and control capabilities. The memory of the electronic device comprises a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operating system and the computer program in the non-volatile storage medium. The communication interface of the electronic device is used to communicate with external terminals in a wired or wireless manner. The wireless manner can be realized through WIFI, operator network, near field communication (NFC) or other technologies. The display screen of the electronic device can be a liquid crystal display screen or an electronic ink display screen. The input device of the electronic device can be a touch layer overlaid on the display screen, or a key, trackball or touchpad arranged on the shell of the electronic device, or an external keyboard, touchpad or mouse, etc.

[0172] Those skilled in the art can understand, Figure 7The structure shown in the figures is only a structural diagram of part of the technical solution of the present disclosure, and does not constitute a limitation on the electronic device to which the technical solution of the present application is applied. The specific electronic device can include more or fewer components than those shown in the figures, or combine certain components, or have a different arrangement of components.

[0173] The third aspect of the present application discloses a storage medium, specifically a computer readable storage medium, and the computer readable storage medium stores a computer program.

[0174] Please note that the technical features of the above embodiments can be combined in any way, and in order to make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present application. The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be construed as a limitation on the scope of the patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. A three-phase LCL grid-connected NPC inverter system based on fast model predictive control, characterized in that, The system comprises a three-phase LCL grid-connected NPC inverter and a fast model predictive controller; The fast model predictive controller controls the three-phase LCL grid-connected NPC inverter by selecting a calculation sector composed of a current output voltage vector and several voltage vectors, and realizes synchronization of the LCL filter grid-connected current with the power grid by changing a predictive control reference current angle; the calculation sector is a sub-sector composed of the output voltage vector participating in the predictive control calculation on a complex plane of the voltage vector; The fast model predictive controller comprises: a data acquisition module that acquires two capacitor voltages on a DC side of the three-phase LCL grid-connected NPC inverter, an output current value and an electrical angle of the output current of the three-phase LCL grid-connected NPC inverter, a grid-connected current, an electrical angle of the grid-connected current, a power grid voltage value, an electrical angle of the power grid voltage, and a number of the current output voltage vector on the complex plane of the voltage vector; a reference current value calculation module that calculates the reference current value according to the electrical angle of the output current, the electrical angle of the grid-connected current, and the electrical angle of the power grid voltage; a three-phase LCL grid-connected NPC inverter mathematical model that establishes a mathematical model of the three-phase LCL grid-connected NPC inverter and a calculation formula of the output voltage vector according to the acquired data; an output current predictive model calculation module that obtains a predictive value mathematical model of the inverter output current according to the mathematical model of the three-phase LCL grid-connected NPC inverter and the calculation formula of the output voltage vector; a calculation sector and a short vector selection module in the calculation sector that selects the calculation sector and the short vector in the calculation sector according to the two capacitor voltages on the DC side and the number of the current output voltage vector on the complex plane of the voltage vector; a control quantity calculation and output module that constructs a cost function according to the reference current value and the predictive value mathematical model of the inverter output current, applies the cost function, the calculation sector, and the short vector in the calculation sector, selects an optimal switching state that minimizes the cost function value by comparing cost function values corresponding to different output voltage vectors in a next predictive sampling period, and selects the optimal switching state to realize control of the three-phase LCL grid-connected NPC inverter; the method of selecting the calculation sector and the short vector in the calculation sector according to the two capacitor voltages on the DC side and the number of the current output voltage vector on the complex plane of the voltage vector comprises: The sector selection variable is calculated using the DC side two capacitor voltages u c1 and u c2 and the current output voltage vector number x o in the voltage vector complex plane and the artificially given prediction value, the calculation sector is selected and the short vector within it. The use of two capacitor voltages u c1 and u c2 and the number x of the current output voltage vector in the complex plane of voltage vectors o and the artificially given prediction value to calculate the sector selection variable, the specific method of selecting the calculation sector and the short vector therein includes: Based on the numbering of the current output voltage vector on the complex plane of the voltage vector x o As the initial position, a manually given computational sector selection variable is applied, which includes an incrementing variable. up and subtracting variables down ,by[ x o - down, x o + up Determine the size of the calculation sector, i.e., the range of voltage vector numbers involved in the prediction calculation; When u c1 >u c2 When selecting the short vector pair of switch states in group P, Perform prediction calculations when u c1 c2 At that time, select N short vector pairs of switch states. Perform predictive calculations;​ Wherein, the P group switching state refers to the short vector switching state that makes the DC side capacitor voltage u c1 decreases and u c2 increases; the N group switching state refers to the short vector switching state that makes the DC side capacitor voltage u c1 increases and u c2 decreases.

2. The three-phase LCL grid-connected NPC inverter system based on fast model predictive control according to claim 1, characterized in that, the specific formula of calculating the reference current value according to the electrical angle of the output current, the electrical angle of the grid-connected current, and the electrical angle of the power grid voltage comprises: wherein, and is the reference current vector the real and imaginary parts of the complex number , and are the electrical angles of the output current, the grid-connected current and the grid voltage, respectively; and is a value given by a human being; the specific method of realizing synchronization of the LCL filter grid-connected current with the power grid by changing the predictive control reference current angle comprises: calculating a phase difference between the output current of the three-phase LCL grid-connected NPC inverter and the LCL filtered current, adding the phase difference to the electrical angle of the power grid voltage, and bringing the result into a calculation formula of the reference current value.

3. The three-phase LCL grid-connected NPC inverter system based on fast model predictive control according to claim 1, characterized in that, the calculation formula of the output voltage vector is wherein, is the output voltage vector; Vdc is the voltage of the DC side negative terminal of the three-phase LCL grid-connected NPC inverter; Vb is the voltage at the b-phase output terminal of the three-phase LCL grid-connected NPC inverter and the negative terminal of the DC side; Vc is the voltage at the c-phase output terminal of the three-phase LCL grid-connected NPC inverter and the negative terminal of the DC side; In the formula For ; the calculation formula of the three-phase LCL grid-connected NPC inverter mathematical model is wherein, Vf for a, b and c phase filter capacitor voltages; Vdc is the voltage of the DC side negative terminal with respect to the grid neutral point; and Ia, Ib, and Ic are the a, b, and c phase output currents of the three-phase LCL grid-connected NPC inverter, respectively; L1 and L2 are filter inductances. R1 and R2 are the equivalent resistance of filter inductance; C is the equivalent capacitance of filter; L and R are the equivalent inductance and resistance of transmission line respectively; e x is the three-phase grid voltage; j is the imaginary part.

4. The three-phase LCL grid-connected NPC inverter system based on fast model predictive control according to claim 3, characterized in that, The specific method for obtaining the predicted value mathematical model of the inverter output current according to the three-phase LCL grid-connected NPC inverter mathematical model and the calculation formula of the output voltage vector comprises: The calculation formula of the three-phase LCL grid-connected NPC inverter mathematical model is brought into the calculation formula of the output voltage vector, and the current derivative is discretized by applying the forward Euler approximation to obtain the output current predicted value mathematical model of the three-phase LCL grid-connected NPC inverter: Wherein, is the predicted value of the output current at time k+1; Ik is the output current value at time k; Ik is the grid-connected current value at time k; is the grid-connected current value at time k-1; is the sampling interval; 。 5. The three-phase LCL grid-connected NPC inverter system based on fast model predictive control according to claim 1, characterized in that, The cost function is: Wherein, g is the cost function; and is the reference current vector at time k+1 the real and imaginary parts of the reference current vector and are the real and imaginary parts of the prediction of the output current at time k+1. The specific method for selecting the optimal switching state by comparing the cost function values of different output voltage vectors in the next sampling period comprises: The selected short vector is brought into the cost function to calculate a plurality of cost function values, and the minimum cost function value is calculated, and the switching state of the short vector is taken as the optimal switching state.

6. An electronic device, comprising: The memory stores a computer program, and the computer program is executed by the processor to execute the method in the three-phase LCL grid-connected NPC inverter system based on the fast model predictive control according to any one of claims 1 to 5.

7. A storage medium, characterized by The computer program stored in the storage medium can be executed by one or more processors, and can be used to implement the method in the three-phase LCL grid-connected NPC inverter system based on the fast model predictive control according to any one of claims 1 to 5.

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