Improved deadbeat current prediction control method based on Jure criterion

Abstract

The invention discloses an improved dead-beat current prediction control method based on Jure criterion, and the method specifically comprises the following steps: 1, collecting the grid-side inductive current and grid-connected point voltage of a T-type three-level inverter, and constructing a mathematical model under an alpha-beta coordinate system; 2, performing forward Euler discretization on the model constructed in the step 1 to obtain a deadbeat current prediction control model after order reduction; 3, predicting the control model obtained in the step 2 by using Newton interpolation to obtain predicted current and voltage; 4, converting the prediction result obtained in the step 3 to obtain the output voltage of the inverter; 5, solving the value range of lambda through a Jure criterion; and step 6, according to a solving result in the step 5, utilizing a pulse signal to drive on-off of a switching tube in the converter. According to the invention, the problem that the existing deadbeat current prediction control precision and the dynamic performance are not high is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic control and stability analysis, and relates to an improved deadbeat current prediction control method based on Jury criterion. Background Art

[0002] With the rapid development of "double high" (high proportion of new energy and high proportion of power electronics) power grids, grid-connected inverters, as new energy grid-connected interface devices, usually need to be connected to weak power grids. Due to the characteristics of weak power grids, the voltage support capacity is low, the grid impedance is large, and it is easily affected by fluctuations and disturbances, so higher requirements are put forward for the control strategy of grid-connected equipment. Predictive control, due to its strong robustness and fast dynamic response, can effectively cope with grid fluctuations in weak power grid environments, improve the stability and control accuracy of the system, and become an ideal choice for weak power grid control strategies of grid-connected inverters. To this end, an improved deadbeat current predictive control based on Jury criterion is proposed. Compared with the traditional deadbeat control, which is highly dependent on hardware parameters, the quality and accuracy of the output current waveform are low, and the control of high-frequency harmonics is relatively limited. The proposed scheme reduces the order of the deadbeat current predictive control model by introducing the coupling coefficient λ, which simplifies the design of the controller, reduces the dependence on hardware parameters, improves the quality and accuracy of the output current waveform, and improves the suppression of high-frequency harmonics. The appropriate parameter λ is selected in combination with the Jury criterion, which effectively improves the stability and robustness of the system, overcomes the shortcomings of traditional deadbeat control, and retains the advantages of fast response and high-precision tracking of deadbeat control. Summary of the invention

[0003] The purpose of the present invention is to provide an improved deadbeat current prediction control method based on Jury criterion, which solves the problem of low accuracy and dynamic performance of existing deadbeat current prediction control.

[0004] The technical solution adopted by the present invention is an improved deadbeat current prediction control method based on Jury criterion, which specifically includes the following steps:

[0005] Step 1, collecting the grid-side inductor current and grid-connected point voltage of the T-type three-level inverter, and constructing a mathematical model in the αβ coordinate system;

[0006] Step 2: Perform forward Euler discretization on the model constructed in step 1, and calculate the inductor current i L and the grid-side inductor current i g The coupling relationship between them is used to obtain the reduced-order deadbeat current predictive control model;

[0007] Step 3, predicting the control model obtained in step 2 using Newton interpolation to obtain predicted current and voltage;

[0008] Step 4, converting the prediction result obtained in step 3 to obtain the output voltage of the inverter;

[0009] Step 5, solving the value range of λ by Jury criterion;

[0010] Step 6: Based on the solution of step 5, a pulse signal is used to drive the switch tube in the converter to turn on and off.

[0011] The present invention is also characterized in that:

[0012] The specific process of step 1 is:

[0013] Step 1.1, collect the grid-side inductor current and grid-connected point voltage of the T-type three-level inverter. The mathematical model of the grid-connected inverter in the three-phase static abc coordinate system is shown as follows:

[0014]

[0015]

[0016] In the formula, L is the filter inductor on the inverter side; C f is the filter capacitor of the LCL filter; L g The grid side is the filter inductor; i La 、i Lb 、i Lc are the currents flowing through the filter inductor L in the abc coordinate system; i ga 、i gb 、i gc is the current flowing through the filter inductor L in the abc coordinate system g Current; u inva 、u invb 、u invc is the phase voltage on the inverter side in the abc coordinate system; u Ca 、u Cb 、u Cc is the filter capacitor voltage in the abc coordinate system; u ga 、u gb 、u gc is the grid-side phase voltage in the abc coordinate system;

[0017] Step 1.2: Arrange formulas (1) to (3) to obtain L and i g The equation is shown in formula (4):

[0018]

[0019] Step 1.3, perform abc-αβ coordinate transformation on equation (4) to obtain equation (5):

[0020]

[0021] In the formula, i Lα 、i Lβ is the current flowing through the filter inductor L in the αβ coordinate system, i gα 、i gβ is the current flowing through the filter inductor L in the αβ coordinate system g Current, u invα 、u invβ is the phase voltage on the inverter side in the αβ coordinate system; u gα 、u gβ is the grid-side voltage in the αβ coordinate system.

[0022] The specific process of step 2 is:

[0023] Step 2.1, perform forward Euler discretization on equation (5), as shown in equation (6):

[0024]

[0025] In the formula, u invα (k) and u invβ (k) is the grid voltage at time k in the αβ coordinate system; i gα (k+1), i gβ (k+1) is the current flowing through the filter inductor L at time k+1 in the αβ coordinate system g Current; i gα (k), i gβ (k) is the current flowing through the filter inductor L at time k in the αβ coordinate system g Current; u gα (k) and u gβ (k) is the grid voltage at time k in the αβ coordinate system; T s is the switching cycle; i Lα (k+1), i Lβ (k+1) is the current flowing through the filter inductor L at time k+1 in the αβ coordinate system; i Lα (k), i Lβ (k) is the current flowing through the filter inductor L at time k in the αβ coordinate system;

[0026] Step 2.2: Use the following formula (7) to convert the k+1 moment into the k moment i L The difference between the k+1 moment and the k moment is g The λ-fold difference is used to express the reduced-order deadbeat current prediction control model, and equation (8) is obtained:

[0027]

[0028]

[0029] Step 2.3: According to equation (8), the inverter output voltages uinvα(k+1) and uinvβ at time k+1 are obtained: β (k+1), as shown in formula (9):

[0030]

[0031] The specific process of step 3 is:

[0032] Step 3.1, let (f(x i )-f(x j )) / (x i -x j ) is called the function f(x) at point x i 、x j The first-order difference quotient of i , x j ],(f[x 1 , x 2 , ..., x k ]-f[x 0 , x 1 , ..., x k -1]) / (x k -x 0 ) is called f(x) at x 0 、x 1 、x 2 , ..., x k The k-order difference quotient of

[0033] f(x) = f(x) 0 )+f[x,x 0 ](xx 0 )

[0034] f(x) = f(x) 0 )+f[x 0 , x 1 ](xx 0 )+f[x,x 0 , x 1 ](xx 0 )(xx 1 )

[0035] f(x) = f(x) 0 )+f[x 0 , x 1 ](xx 0 )+…+f[x 0 , x 1 , …, x n ](xx 0 )(xx 1 )…(xxn-1 )+f[x,x 0 …, x n ](xx 0 )(xx 1 )…(xx n-1 ) (10)

[0037] Step 3.2: Use Newton interpolation to predict the grid-connected current i at time k+1 gα (k+1), i gβ (k+1), as shown in the following formula (11):

[0038]

[0039] In the formula, i gα * 、i gβ * is the expected value of the grid-connected current, that is, the current value at time k+2, i gα (k), i gβ (k) is the current value at time k, i gα (k-1), i gβ (k-1) is the current value at time k-1, i gα (k-2), i gβ (k-2) is the current value at time k-2;

[0040] Step 3.3: Use Newton interpolation to predict the grid voltage u at time k+1 gα (k+1),u gβ (k+1), as shown in the following formula (12):

[0041]

[0042] In the formula, u gα (k) and u gβ (k) is the voltage value at time k, u gα (k-1),u gβ (k-1) is the voltage value at time k-1, u gα (k-2),u gβ (k-2) is the voltage value at time k-2.

[0043] The specific process of step 4 is:

[0044] The grid-connected current i at time k+1 obtained in step 3 gα (k+1), i gβ (k+1) and grid-side voltage u gα (k+1),u gβSubstitute (k+1) into equation (9) to obtain the inverter output voltage u at time k+1 invα (k+1),u invβ (k+1), as shown in formula (13):

[0045]

[0046] The specific process of step 5 is:

[0047] Step 5.1, the transfer function G from inverter voltage to grid current ig (s) is:

[0048]

[0049] in,

[0050] Step 5.3, use the residue theorem to calculate G ig (s) is z-transformed to obtain G ig (z):

[0051]

[0052] Where, Ts is the switching period;

[0053] Step 5.4, according to equation (13), the discrete transfer function of the improved deadbeat predictive controller is:

[0054]

[0055] Step 5.5, combining equation (15) and equation (16), the closed-loop transfer function Φ(z) of the deadbeat control system is obtained as equation (17):

[0056]

[0057] Step 5.6, according to equation (17), the closed-loop characteristic equation of the discrete system is obtained as:

[0058] D(z)=1+G pc (z)K PWM (z)G ig (z) (18)

[0059] Step 5.7, apply Jury's criterion to equation (18) and express the closed-loop characteristic equation using polynomial expansion:

[0060] D(z)=a n z n +…+a 2 z 2 +a 1 z 1 +a0 z 0 (19)

[0061] The characteristic equation of the deadbeat control system is expressed by polynomial expansion:

[0062] D(z)=a 3 z 3 +a 2 z 2 +a 1 z 1 +a 0 z 0 (20)

[0064] in:

[0065]

[0066] Step 5.8, solve the value range of λ according to the Jury criterion.

[0067] The specific process of step 5.8 is:

[0068] Step 5.8.1, construct the Jury array;

[0069] Step 5.8.2, the highest power of the characteristic equation of the deadbeat control system is cubic, so only the third row element b needs to be solved. k Then, as shown in the following formula (25):

[0070]

[0071] Step 5.8.3, use the Jury array to determine the necessary and sufficient conditions for all roots of the characteristic equation D(z) = 0 to be located within the unit circle on the z plane, and solve for the range of the λ parameter. The necessary and sufficient conditions are as follows:

[0072] aD(1)>0;

[0073] b.(-1) n D(-1)>0;

[0074] c.|a 0 |>a n ;

[0075] d.|b 0 |>|b n-1 |,|c 0 |>|c n-2 |,...,|m 0 |>|m 2 |;

[0076] Step 5.8.4, according to the grid-connected inverter system parameters, the value range of λ is obtained as shown in formula (26):

[0077] λ∈(0, 0.8)

[0078] (26).

[0079] The specific process of step 6 is:

[0080] Substitute the value of λ solved in step 5 into equation (13), and finally obtain the inverter output voltage u at time k+1 invα (k+1) and u invβ (k+1), after αβ-abc transformation, it is sent to SPWM modulation and converted into a corresponding pulse signal, which is used to drive the on and off of the switch tube in the converter.

[0081] The beneficial effect of the present invention is that the present invention first proposes a method for simplifying the control model based on the coupling relationship between the inductance and capacitance of the LCL type three-phase grid-connected inverter, by establishing a control model including the k+1 moment and the k moment i L and i g The original third-order control equation is reduced to a functional relationship. The complexity of the control strategy is effectively simplified, the main dynamic characteristics of the system are retained, and the accuracy and stability of the system in rapid response are ensured; secondly, by introducing the Jury criterion to determine the appropriate value range of the selection coefficient λ, the robustness and stability of the system are further enhanced, so that the system can maintain reliable control performance under various operating conditions and disturbances; in addition, the voltage and current are predicted and controlled using the Newton interpolation algorithm, which greatly improves the control accuracy and the dynamic response of the system, making the system more accurate in tracking the reference signal, reducing the prediction error, and improving the power quality and control effect. These improvements enable the present invention to exhibit excellent performance in a complex grid-connected environment, and have good practicality and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 It is a deadbeat current prediction control block diagram in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0083] Figure 2 It is a closed-loop feedback predictive current control block diagram in discrete domain in the improved deadbeat current predictive control method based on Jury criterion of the present invention;

[0084] Figure 3 It is a zero-pole diagram in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0085] Figure 4It is a grid-connected current simulation waveform diagram obtained by using improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0086] Figure 5 It is a grid-connected current FFT analysis diagram obtained by using improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0087] Figure 6 This is the grid-connected current simulation waveform obtained by using traditional deadbeat control;

[0088] Figure 7 This is the FFT analysis diagram of the grid-connected current obtained using traditional deadbeat control;

[0089] Figure 8 It is a simulation waveform diagram of the phase relationship of the output current and voltage of the grid side A phase obtained by the improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0090] Fig. 9 It is a simulated waveform diagram of the phase relationship of the output current and voltage of the grid side A phase obtained by the traditional deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0091] Fig.10 The simulated waveform of the load current jump from 10A to 15A obtained by using the improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0092] Fig.11 The simulated waveform of the load current jump from 10A to 15A obtained by using the traditional deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0093] Fig.12 An experimental waveform diagram of the grid-connected current obtained by using the improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0094] Fig.13 The experimental waveform diagram of the phase relationship of the output current and voltage of the grid side A phase obtained by the improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention;

[0095] Fig.14 The improved deadbeat current prediction control method based on Jury criterion of the present invention uses improved deadbeat control to obtain a load current experimental waveform diagram of a current jump from 10A to 15A. DETAILED DESCRIPTION

[0096] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0097] Example 1

[0098] The improved deadbeat current prediction control method based on Jury criterion of the present invention refers to Figure 1 , including the following steps:

[0099] Step 1: Collect the grid-side inductor current and grid-connected point voltage of the T-type three-level inverter, write the KVL and KCL equations, and obtain the mathematical model in the αβ coordinate system after abc-αβ transformation. When modeling, all switching devices are considered to be ideal devices, and the on-off time delay of the devices is not considered;

[0100] Step 2: Perform forward Euler discretization on the model obtained in step 1, and calculate the inductor current i L and the grid-side inductor current i g The coupling relationship between them is obtained, and the reduced-order deadbeat current predictive control model is obtained.

[0101] Step 3: Use Newton interpolation to predict the grid-connected current i at time k+1 in equation (2): gα (k+1), i gβ (k+1), and the grid-side voltage u at time k+1 gα (k+1),u gβ (k+1). Among them, the grid-connected current i at time k+2 gα (k+2), i gβ (k+2) is the given current i obtained by the voltage outer loop control gα * ,i gβ * .

[0102] To find the inverter output voltage u at time k+1 invα (k+1),u invβ (k+1), we need to know the grid-connected current i at time k+2 gα (k+2), i gβ The grid-connected current i at time (k+2) and time k+1 gα (k+1), i gβ (k+1), and the grid-side voltage u at time k+1 gα (k+1),u gβ (k+1). Among them, the grid-connected current i at time k+2 gα (k+2), i gβ (k+2) is the given current i obtained by the voltage outer loop control gα * ,i gβ* ; Grid-connected current i at time k+1 gα (k+1), i gβ (k+1) and the grid-side voltage u at time k+1 gα (k+1),u gβ (k+1) needs to be predicted through Newton interpolation.

[0103] Step 4: The i obtained by Newton interpolation prediction in step 3 gα (k+1), i gβ (k+1), and get the inverter output voltage u at time k+1 invα (k+1),u invβ (k+1);

[0104] Step 5: To ensure the stability of the control system, optimize the dynamic response, and improve the harmonic suppression capability and control accuracy, the value range of λ is solved by the Jury criterion;

[0105] Step 6: Based on the solution of step 5, a pulse signal is used to drive the switch tube in the converter to turn on and off.

[0106] Example 2

[0107] The specific process of step 1 is:

[0108] Step 1.1, collect the grid-side inductor current and grid-connected point voltage of the T-type three-level inverter, and write the KVL and KCL equations. When modeling, all switching devices are considered to be ideal devices, and the on-off time delay of the devices is not considered. The mathematical model of the grid-connected inverter in the three-phase static abc coordinate system is as follows:

[0109]

[0110]

[0111] In the formula, L is the filter inductor on the inverter side; C f is the filter capacitor of the LCL filter; L g The grid side is the filter inductor; i La ,i Lb ,i Lc is the current flowing through the filter inductor L in the abc coordinate system; i ga ,i gb ,i gc is the current flowing through the filter inductor L in the abc coordinate system g Current, also the grid-connected current; u inva ,u invb ,u invc is the phase voltage on the inverter side in the abc coordinate system; u Ca ,u Cb ,uCc is the filter capacitor voltage in the abc coordinate system; u ga ,u gb ,u gc is the grid-side phase voltage in the abc coordinate system.

[0112] Step 1.2, sort out equations (1) to (3) to obtain L and i g The equation is shown in formula (4):

[0113]

[0114] Step 1.3, perform abc-αβ coordinate transformation on equation (4) to obtain equation (5):

[0115]

[0116] In the formula, i Lα ,i Lβ is the current flowing through the filter inductor L in the αβ coordinate system, which is also the inverter side current; i gα ,i gβ is the current flowing through the filter inductor L in the αβ coordinate system g Current, also the grid-connected current; u invα ,u invβ is the phase voltage on the inverter side in the αβ coordinate system; u gα ,u gβ is the grid-side voltage in the αβ coordinate system.

[0117] Example 3

[0118] The specific process of step 2 is as follows:

[0119] Step 2.1, perform forward Euler discretization on equation (5), as shown in equation (6):

[0120]

[0121] In the formula, u invα (k)u invβ (k) is the grid voltage at time k in the αβ coordinate system; i gα (k+1), i gβ (k+1) is the current flowing through the filter inductor L at time k+1 in the αβ coordinate system g Current; i gα (k), i gβ (k) is the current flowing through the filter inductor L at time k in the αβ coordinate system g Current; u gα (k) and u gβ (k) is the grid voltage at time k in the αβ coordinate system; T s is the switching cycle; iLα (k+1), i Lβ (k+1) is the current flowing through the filter inductor L at time k+1 in the αβ coordinate system; i Lα (k), i Lβ (k) is the current flowing through the filter inductor L at time k in the αβ coordinate system.

[0122] Step 2.2, since these are all moment values, and the inductor current i on the inverter side L and the grid-side inductor current i g There is a certain coupling relationship. Therefore, in equation (6), we can use (7) to convert the k+1 moment to the k moment i L The difference between the k+1 moment and the k moment is g The λ times difference is used to express the reduced-order deadbeat current prediction control model, where λ is a variable constant coefficient representing the coupling coefficient of the filter, and equation (8) is obtained:

[0123]

[0124] Step 2.3: According to equation (8), the inverter output voltage u at time k+1 can be obtained: invα (k+1),u invβ (k+1), as shown in formula (9):

[0125]

[0126] Example 4

[0127] The specific process of step 3 is as follows:

[0128] Step 3.1, write out the Newton interpolation polynomial, (f(x i )-f(x j )) / (x i -x j )(i≠j) is called the function f(x) at point x i 、x j The first-order difference quotient of i , x j ],(f[x 1 , x 2 , ..., x k ]-f[x 0 , x 1 , ..., x k -1]) / (x k -x 0 ) is called f(x) at x 0 , x 1 , x 2 , ..., x k The k-order difference quotient of

[0129] f(x) = f(x) 0 )+f[x,x 0 ](xx 0 )

[0130] f(x) = f(x) 0 )+f[x 0 , x 1 ](xx 0 )+f[x,x 0 , x 1 ](xx 0 )(xx 1 )

[0131] f(x) = f(x) 0 )+f[x 0 , x 1 ](xx 0 )+…+f[x 0 , x 1 , …, x n ](xx 0 )(xx 1 )…(xx n-1 )+f[x,x 0 …, x n ](xx 0 )(xx 1 )…(xx n-1 ) (10)

[0133] Step 3.2: Use Newton interpolation to predict the grid-connected current i at time k+1 gα (k+1), i gβ (k+1):

[0134]

[0135] In the formula, i gα * 、i gβ * is the expected value of the grid-connected current, that is, the current value at time k+2, i gα (k), i gβ (k) is the current value at time k, i gα (k-1), i gβ (k-1) is the current value at time k-1, i gα (k-2), i gβ (k-2) is the current value at time k-2.

[0136] Step 3.3: Use Newton interpolation to predict the grid voltage u at time k+1gα (k+1),u gβ (k+1):

[0137]

[0138] In the formula, u gα (k) and u gβ (k) is the voltage value at time k, u gα (k-1),u gβ (k-1) is the voltage value at time k-1, u gα (k-2),u gβ (k-2) is the voltage value at time k-2.

[0139] Example 5

[0140] The specific process of step 4 is as follows:

[0141] The grid-connected current i at time k+1 obtained in step 3 gα (k+1), i gβ (k+1) and grid-side voltage u gα (k+1),u gβ Substituting (k+1) into equation (9) further obtains the inverter output voltage u at time k+1 invα (k+1),u invβ (k+1), as shown in formula (13):

[0142]

[0143] Example 6

[0144] The specific process of step 5 is as follows:

[0145] Step 5.1: To ensure system stability, optimize dynamic response, and improve harmonic suppression capability and control accuracy, it is necessary to determine the value range of λ. Figure 2 As shown in the closed-loop feedback prediction current control block diagram, it is necessary to solve the discrete transfer function Gpc(z) of the improved deadbeat prediction controller and the discrete transfer function G of the LCL filter. ig (z), and finally the closed-loop transfer function Φ(z) of the deadbeat control system is obtained. PWM (z) is the equivalent proportional link of PWM modulation. The grid-connected current feedback is unit negative feedback, so H is set to 1.

[0146] Step 5.2, write the transfer function G from inverter voltage to grid current ig (s) is:

[0147]

[0148] in,

[0149] Step 5.3, use the residue theorem to calculate G ig (s) is z-transformed to obtain G ig (z), where Ts is the switching period:

[0150]

[0151] Step 5.4, according to equation (13), the discrete transfer function of the improved deadbeat predictive controller is:

[0152]

[0153] Step 5.5, combining equation (15) and equation (16), the closed-loop transfer function Φ(z) of the deadbeat control system is obtained as equation (17):

[0154]

[0155] Step 5.6, according to equation (17), the closed-loop characteristic equation of the discrete system is obtained as:

[0156] D(z)=1+G pc (z)K PWM (z)G ig (z) (18)

[0157] Step 5.7, apply Jury's criterion to equation (18) and express the closed-loop characteristic equation using polynomial expansion:

[0158] D(z)=a n z n +…+a 2 z 2 +a 1 z 1 +a 0 z 0 (19)

[0159] The characteristic equation of the deadbeat control system is expressed by polynomial expansion:

[0160] D(z)=a 3 z 3 +a 2 z 2 +a 1 z 1 +a 0 z 0 (20)

[0162] in:

[0163]

[0164] Step 5.8, solve the value range of λ according to the Jury criterion:

[0165] 1) First, the Jury array needs to be constructed according to certain rules, and its form is shown in Table 1:

[0166] Table 1 Jury array

[0167]

[0168]

[0169] 2) According to the polynomial expansion of the characteristic equation of the deadbeat control system, the highest power is 3, so we only need to solve the element b in the third row. k (k=0,1,2) then:

[0170]

[0171] 3) Use the Jury array to determine the necessary and sufficient conditions that all roots of the characteristic equation D(z)=0 are located within the unit circle on the z plane, and solve for the range of the λ parameter. The necessary and sufficient conditions are as follows:

[0172] eD(1)>0;

[0173] f.(-1) n D(-1)>0;

[0174] g.|a 0 |>a n ;

[0175] h.|b 0 |>|b n-1 |,|c 0 |>|c n-2 |,…,|m 0 |>|m 2 |.

[0176] Step 5.9, combined with the following system parameter table, the value range of λ is obtained as shown in formula (26), and is substituted into formula (13):

[0177] Table 2 Grid-connected inverter system parameters

[0178] parameter Numeric Inverter side inductance L / mH 5 <![CDATA[Filter capacitor C f / F]]> <![CDATA[5*10 -5 ]]> <![CDATA[Grid-side inductor L g / mH]]> 0.6 <![CDATA[Switching frequency f s / Hz]]> 20k

[0179] λ∈(0, 0.8)

[0180] (26).

[0181] Step 6: Substitute the value of λ obtained in step 5 into equation (13), and finally obtain the inverter output voltage u at time k+1:invα (k+1) and u invβ (k+1), after αβ-abc transformation, it is sent to SPWM modulation and converted into a corresponding pulse signal, which is used to drive the on and off of the switch tube in the converter.

[0182] Example 7

[0183] Figure 3 The zero-pole diagram is drawn by the improved deadbeat current predictive control method based on Jury criterion of the present invention. The value range of λ is solved by Jury criterion, and λ equal to 0.7 is brought into the control system to draw the closed-loop zero-pole diagram of the system. It can be seen that the pole distribution of the response is 0.9286+0.3688i, 0.9286-0.3688i, 0.625+0.1329i, 0.625-0.1329i, and -0.1158+0i, which are all within the unit circle. Therefore, the system is stable, which proves the effectiveness of solving λ based on Jury criterion.

[0184] Figure 4 and Figure 5 They are respectively a waveform diagram of the grid-connected current obtained by using the improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention, and an FFT analysis diagram. Figure 4 Given the expected current value of 10A, the actual output value is 10.02A, which shows that the prediction accuracy is relatively high.

[0185] Figure 5 The horizontal axis is the harmonic order n, and the vertical axis is the content of each harmonic. From the figure, it can be seen that the THD content of the current calculated by using the improved zero-beat control is 0.48%, and the waveform quality is high.

[0186] Figure 6 and Figure 7 They are the waveform diagram of the grid-connected current obtained by using traditional deadbeat control and the FFT analysis diagram. Figure 6 Given the expected current value is 10A, the actual output value is 9.903A. Figure 4 It can be seen that its prediction accuracy is low. Figure 7 The horizontal axis is the harmonic number n, and the vertical axis is the content of each harmonic. Figure 5 , using traditional deadbeat control to calculate the THD content of its current is 1.03%, and the waveform quality is poor.

[0187] Figure 8 and Fig. 9They are respectively a simulation waveform diagram of the phase relationship of the grid-side A-phase output current and voltage obtained by the improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention, and a simulation waveform diagram of the phase relationship of the grid-side A-phase output current and voltage obtained by the traditional deadbeat control. It can be found that the grid-connected current and voltage of the improved deadbeat current prediction control and the traditional deadbeat control are in phase, which ensures the effective transmission and utilization of electric energy and can maintain the stability and efficiency of the power grid.

[0188] Fig.10 In the improved deadbeat current prediction control method based on Jury criterion of the present invention, the current waveform at the grid-side inductance of the inverter is obtained by using the improved deadbeat control at 1.04s when the current increases from 10A to 15A. The response time is short, only 721μs, and the dynamic response is fast.

[0189] Fig.11 The current waveform at the grid-side inductor of the inverter is obtained by using traditional deadbeat control. When the current changes from 10A to 15A at 1.04s, the response time is short, only 500μs, and the dynamic response is fast. Fig.10 , which is 221μs faster, but it sacrifices some filtering characteristics and may be insufficient in harmonic suppression and current quality.

[0190] Fig.12 This is an experimental waveform diagram of the grid-connected current obtained by using the improved deadbeat control in the improved deadbeat current prediction control method based on Jury criterion of the present invention. The expected current value is 10A, and the actual output value is 9.86A. The waveform quality is high, which verifies the feasibility of the proposed scheme.

[0191] Fig.13 The experimental waveform diagram of the phase relationship of the output current and voltage of the grid-side phase A obtained by the improved deadbeat control in the improved deadbeat current prediction control method based on the Jury criterion of the present invention shows that the grid-connected current and voltage of the improved deadbeat current prediction control are in phase, which ensures the effective transmission and utilization of electric energy, maintains the stability and efficiency of the power grid, and verifies the feasibility of the proposed scheme;

[0192] Fig.14 The improved deadbeat current prediction control method based on Jury criterion of the present invention uses the improved deadbeat control to obtain the load current experimental waveform of the current jumping from 10A to 15A. The pink-purple vertical line in the figure is the time interval measurement line, which is used to observe the time interval of the dynamic response of the load current jumping from 10A to 15A. It can be seen that the response time is short, only 1.03ms, which is close to the simulation result, verifying the feasibility of the proposed scheme;

[0193] The improved deadbeat current prediction control based on Jury criterion is aimed at the deadbeat control of traditional LCL grid-connected inverters. It aims to improve the accuracy and response speed of the system while maintaining the original third-order system structure and not ignoring the filter capacitor. It performs time delay compensation through Newton interpolation prediction. In order to reduce the complexity of digital control when predicting the grid current at time k+3, the i in discrete state is established. L and i g The corresponding functional relationship is reduced to a lower order. At the same time, in order to ensure the stability of the system, the value range of λ is obtained based on the Jury criterion to ensure the stable operation of the system.

Claims

1. An improved deadbeat current prediction control method based on Jury criterion, characterized in that: The specific steps include: Step 1, collecting the grid-side inductor current and grid-connected point voltage of the T-type three-level inverter, and constructing a mathematical model in the αβ coordinate system; Step 2: Perform forward Euler discretization on the model constructed in step 1, and calculate the inductor current i L and the grid-side inductor current i g The coupling relationship between them is used to obtain the reduced-order deadbeat current predictive control model; Step 3, predicting the control model obtained in step 2 using Newton interpolation to obtain predicted current and voltage; Step 4, converting the prediction result obtained in step 3 to obtain the output voltage of the inverter; Step 5, solving the value range of λ by Jury criterion; Step 6: Based on the solution of step 5, a pulse signal is used to drive the switch tube in the converter to turn on and off.

2. The improved deadbeat current prediction control method based on Jury criterion according to claim 1, characterized in that: The specific process of step 1 is as follows: Step 1.1, collect the grid-side inductor current and grid-connected point voltage of the T-type three-level inverter. The mathematical model of the grid-connected inverter in the three-phase static abc coordinate system is shown in the following equations (1) to (3): In the formula, L is the filter inductor on the inverter side; C f is the filter capacitor of the LCL filter; L g The grid side is the filter inductor; i La 、i Lb 、i Lc are the currents flowing through the filter inductor L in the abc coordinate system; i ga 、i gb 、i gc is the current flowing through the filter inductor L in the abc coordinate system g Current; u inva 、u invb 、u invc is the phase voltage on the inverter side in the abc coordinate system; u Ca 、u Cb 、u Cc is the filter capacitor voltage in the abc coordinate system; u ga 、u gb 、u gc is the grid-side phase voltage in the abc coordinate system; Step 1.2: Arrange formulas (1) to (3) to obtain L and i g The equation is shown in formula (4): Step 1.3, perform abc-αβ coordinate transformation on equation (4) to obtain equation (5): In the formula, i Lα 、i Lβ is the current flowing through the filter inductor L in the αβ coordinate system, i gα 、i gβ is the current flowing through the filter inductor L in the αβ coordinate system g Current, u invα 、u invβ is the phase voltage on the inverter side in the αβ coordinate system; u gα 、u gβ is the grid-side voltage in the αβ coordinate system.

3. The improved deadbeat current prediction control method based on Jury criterion according to claim 2 is characterized in that: The specific process of step 2 is: Step 2.1, perform forward Euler discretization on equation (5), as shown in equation (6): In the formula, u invα (k) and u invβ (k) is the grid voltage at time k in the αβ coordinate system; i gα (k+1), i gβ (k+1) is the current flowing through the filter inductor L at time k+1 in the αβ coordinate system g Current; i gα (k), i gβ (k) is the current flowing through the filter inductor L at time k in the αβ coordinate system g Current; u gα (k) and u gβ (k) is the grid voltage at time k in the αβ coordinate system; T s is the switching cycle; i Lα (k+1), i Lβ (k+1) is the current flowing through the filter inductor L at time k+1 in the αβ coordinate system; i Lα (k), i Lβ (k) is the current flowing through the filter inductor L at time k in the αβ coordinate system; Step 2.2: Use the following formula (7) to convert the k+1 moment into the k moment i L The difference between the k+1 moment and the k moment is g The λ-fold difference is used to express the reduced-order deadbeat current prediction control model, and equation (8) is obtained: Step 2.3: According to equation (8), the inverter output voltage u at time k+1 is obtained: invα (k+1),u invβ (k+1), as shown in formula (9):

4. The improved deadbeat current prediction control method based on Jury criterion according to claim 3 is characterized in that: The specific process of step 3 is as follows: Step 3.1, let (f(x i )-f(x j )) / (x i -x j ) is called the function f(x) at point x i 、x j The first-order difference quotient of i , x j ], (f[x1, x2, ..., x k ]-f[x0, x1, ..., x k -1]) / (x k -X0) is called the sum of f(x) at x0, x1, x2, ..., x k The k-order difference quotient of f(x)=f(x0)+f[x,x0](x-x0) f(x)=f(x0)+f[x0,x1](x-x0)+ f[x,x0,x1](x-x0)(x-x1) f(x)=f(x0)+f[x0,x1](x-x0)+ ...+f[x0,x1,...,x n ](x-x0) (x-x1)…(xx n-1 )+f[x,x0 …,x n ](x-x0)(x-x1)…(xx n-1 ) (10) Step 3.2: Use Newton interpolation to predict the grid-connected current i at time k+1 gα (k+1), i gβ (k+1), as shown in the following formula (11): In the formula, i gα * 、i gβ * is the expected value of the grid-connected current, that is, the current value at time k+2, i gα (k), i gβ (k) is the current value at time k, i gα (k-1), i gβ (k-1) is the current value at time k-1, i gα (k-2), i gβ (k-2) is the current value at time k-2; Step 3.3: Use Newton interpolation to predict the grid voltage u at time k+1 gα (k+1),u gβ (k+1), as shown in the following formula (12): In the formula, u gα (k) and u gβ (k) is the voltage value at time k, u gα (k-1),u gβ (k-1) is the voltage value at time k-1, u gα (k-2),u gβ (k-2) is the voltage value at time k-2.

5. The improved deadbeat current prediction control method based on Jury criterion according to claim 4 is characterized in that: The specific process of step 4 is as follows: The grid-connected current i at time k+1 obtained in step 3 gα (k+1), i gβ (k+1) and grid-side voltage u gα (k+1),u gβ Substitute (k+1) into equation (9) to obtain the inverter output voltage u at time k+1 invα (k+1),u invβ (k+1), as shown in formula (13):

6. The improved deadbeat current prediction control method based on Jury criterion according to claim 5 is characterized in that: The specific process of step 5 is as follows: Step 5.1, the transfer function G from inverter voltage to grid current ig (s) is: in, Step 5.3, use the residue theorem to calculate G ig (s) is z-transformed to obtain G ig (z): Where, Ts is the switching period; Step 5.4, according to equation (13), the discrete transfer function of the improved deadbeat predictive controller is: Step 5.5, combining equation (15) and equation (16), the closed-loop transfer function Φ(z) of the deadbeat control system is obtained as equation (17): Step 5.6, according to equation (17), the closed-loop characteristic equation of the discrete system is obtained as: D(z)=1+G pc (z)K PWM (z)G ig (z) (18) Step 5.7, apply Jury's criterion to equation (18) and express the closed-loop characteristic equation using polynomial expansion: The characteristic equation of the deadbeat control system is expressed by polynomial expansion: <h2 style=";text-align:left;direction:ltr">D(z) = a3z<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> +a2z<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +a1z<h2 style=";text-align:left;direction:ltr"> 1 <h2 style=";text-align:left;direction:ltr"> +a0z<h2 style=";text-align:left;direction:ltr"> 0 (20) in: Step 5.8, solve the value range of λ according to the Jury criterion.

7. The improved deadbeat current prediction control method based on Jury criterion according to claim 6 is characterized in that: The specific process of step 5.8 is as follows: Step 5.8.1, construct the Jury array; Step 5.8.2, the highest power of the polynomial expansion of the characteristic equation of the deadbeat control system is cubic, so only the third row element b needs to be solved k Then, as shown in the following formula (25): Step 5.8.3, use the Jury array to determine the necessary and sufficient conditions for all roots of the characteristic equation D(z) = 0 to be located within the unit circle on the z plane, and solve for the range of the λ parameter. The necessary and sufficient conditions are as follows: aD(1)>0; b.(-1) n D(-1)>0; c.|a0|>a n ; d.|b0|>|b n-1 |,|c0|>|c n-2 |,…,|m0|>|m2|; Step 5.8.4, according to the grid-connected inverter system parameters, the value range of λ is obtained as shown in formula (26): λ∈(0,0.8) (26).

8. The improved deadbeat current prediction control method based on Jury criterion according to claim 7, characterized in that: The specific process of step 6 is as follows: Substitute the value of λ solved in step 5 into equation (13), and finally obtain the inverter output voltage u at time k+1 invα (k+1) and u invβ (k+1), after αβ-abc transformation, it is sent to SPWM modulation and converted into a corresponding pulse signal, which is used to drive the on and off of the switch tube in the converter.

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