A grid-connected current balance control method for an inverter system with linear symmetric load

Abstract

The application relates to an inverter system grid-connected current balance control method with linear symmetrical load, namely, a grid-connected current balance control strategy of an adaptive PCC port admittance negative sequence component suppression algorithm based on voltage feedforward under an unbalanced power grid. The PCC port admittance negative sequence component suppression algorithm is that after a PCC voltage negative sequence component extracted by a first-order reduced filter is fed back through a feedforward function, an optimal voltage feedforward amount is obtained through an adaptive optimization algorithm according to a local load condition, and the voltage feedforward amount is fed into a system loop to offset the influence of the PCC voltage negative sequence component on the grid-connected current, then the negative sequence disturbance term in the grid-connected current is eliminated, and finally the balance control of the grid-connected current is realized. The inverter system grid-connected current balance control strategy mentioned in the application is suitable for the inverter system grid-connected operation condition with linear symmetrical load under an unbalanced power grid, the grid-connected current is balanced, and the reliability of the inverter system grid-connected operation is improved.

Description

Technical Field

[0001] This invention belongs to the field of grid-connected power generation control of three-phase power electronic inverters, and specifically relates to a grid-connected current balance control method for inverter systems with linear symmetrical loads. Background Technology

[0002] When a power grid is in operation, the grid may experience phase-to-phase short circuits, single-phase or two-phase short-circuit grounding, etc., which may lead to three-phase unbalanced voltage drops. When the grid voltage is unbalanced, there are a large number of negative sequence components, which have a serious impact on the stable operation of the inverter system connected to the grid: (1) it causes a large error in the voltage detection of the phase-locked loop, affecting the accuracy of the frequency and voltage support provided by the grid; (2) it leads to unbalanced grid current, resulting in a decline in grid quality, which may cause problems such as reduced performance of sensitive loads, malfunction of protection devices, and increased line losses; (3) it causes double-frequency fluctuations in grid power; (4) it causes load voltage or grid current to surge, thereby damaging the devices.

[0003] To achieve grid-connected current balance control under unbalanced power grids, existing technologies mainly employ two control strategies: one is a dual dq negative sequence compensation control strategy that separates positive and negative sequence voltage and current, extracts the DC components of positive and negative sequence voltage and current, and achieves grid-connected current balance control through negative sequence voltage compensation algorithms or negative sequence current compensation algorithms in dual closed-loop control; the other is to eliminate the influence of grid voltage by superimposing the grid voltage feedforward signal onto the modulation wave instead of separating positive and negative sequence voltage, thereby balancing the grid-connected current without affecting the gain, phase margin, and system stability of the current loop, and without causing harmonic amplification problems.

[0004] The first approach, employing a dual dq negative-sequence compensation control strategy with voltage and current positive and negative sequence separation, faces challenges in parameter coordination and finding the optimal solution among multiple voltage and current PI regulators. The second approach, using a voltage feedforward control strategy, does not address solutions for operating conditions with local loads. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a grid-connected current balance control method for inverter systems with linear symmetrical loads. Specifically, it employs a grid-connected current balance control strategy based on an adaptive point of common coupling (PCC) port admittance negative-sequence component suppression algorithm under unbalanced grid conditions. When the inverter system with linear symmetrical loads is running grid-connected, the optimal amplitude and phase frequency values ​​are obtained in an adaptive optimization algorithm based on automatically identified local load conditions. Furthermore, the optimal voltage feedforward is obtained to counteract the influence of the PCC voltage negative-sequence component on the grid-connected current, thereby eliminating the negative-sequence disturbance term in the grid-connected current and ultimately achieving balanced control of the grid-connected current.

[0006] To achieve the above objectives, the technical solution of the present invention is: in an unbalanced power grid inverter system, the q-axis component u of the PCC voltage in the two-phase rotating dq coordinate system is... PCCq The positive-sequence DC component of the voltage along the q-axis is obtained through a third-order generalized integrator (TOGI) filter, and used as the input of the phase-locked loop (PLL) unit to obtain the grid angular frequency ω. g With phase angle θ g ;Based on the inverter bridge arm current sampling value i Lfa i Lfb i Lfc PCC voltage sampling value u PCCa u PCCb u PCCc , grid-connected current sampling value i ga i gb i gc The inverter arm current dq component i is obtained through abc / dq transformation. d i q PCC voltage dq component u PCCd u PCCq , grid-connected current dq component i gd i gq The grid-side current loop uses a PI regulator G. PI2 (s), the proportionality coefficient is k ip_i The integral coefficient is k ii_i Reference value i of the grid-side current loop gd_ref i gq_ref With grid-connected current sampling value i gd i gq The difference is controlled by the PI regulator G. PI2 (s) Obtain the current inner loop reference value i d_ref i q_ref The inverter bridge arm current loop uses a P regulator and a G regulator. PI1 (s), the proportionality coefficient is k ip The reference value i for the inner current loop d_ref i q_ref With inverter bridge arm current sampling value i d i q The difference is controlled by the P regulator G. PI1 (s) Obtain the inner current loop output voltage u iod u ioq u iod u ioq Subtract the output of the active damping unit from the output of the PCC voltage u. PCCd u PCCq Adding them together gives the voltage u d_PWM u q_PWM And the voltage feedforward quantity FB obtained by the adaptive PCC port admittance negative sequence component suppression algorithm. dFB q The input modulation voltage u of the pulse width modulation unit is obtained by adding them together. FBd_PWM u FBq_PWM Finally, the inverter output current is adjusted by regulating the duty cycle of the switching transistor through the pulse width modulation unit, thereby achieving the purpose of balancing the grid-connected current; the output of the active damping unit is the filter capacitor current and the active damping coefficient H. d The product of, where the filter capacitor current i Cd i Cq Inverter bridge arm current i d i q Subtract the load current i obtained from local load identification d1 i q1 Subtract the grid-connected current i gd i gq The current value obtained afterwards.

[0007] The inverter system topology consists of an input source, a three-phase inverter, a local load, and a low-voltage AC grid. The control section includes a dual-loop structure of the inverter bridge arm current inner loop and the grid-side current outer loop, a phase-locked loop (PLL) unit with a third-order generalized integrator (TOGI) filter, an active damping unit, a voltage feedforward unit with an adaptive PCC port admittance negative sequence component suppression algorithm, and a pulse width modulation unit.

[0008] The adaptive PCC port admittance negative-order component suppression algorithm is implemented using the following method:

[0009] Step S1: When the power grid is unbalanced, the PCC voltage u PCC Decomposed into positive-order components u PCCPS With negative order component u PCCNS Among them, the negative order component u PCCNS As a disturbance term, it causes the grid-connected current i g Unbalanced; without affecting the positive-sequence component Y of the PCC port admittance PCCPS Under the premise of adding PCC voltage u PCC Feedforward control, ignoring inductor voltage, the grid-connected current i g for

[0010] i g =G i (s)·i g_ref -[T(s)-F(s)·W(s)]·Y(s·u PCC (1)

[0011] in

[0012]

[0013] i g_ref For the grid-side current loop reference value, Gi Y(s) is the current gain, Y(s) is the PCC port admittance, [T(s)-F(s)·W(s)] is the admittance gain, and H... d R is the active damping coefficient. load X is the load resistance. load For load reactance;

[0014] Step S2: The admittance gain [T(s)-F(s)·W(s)] of the PCC port admittance with added voltage feedforward obtained from step S1 needs to satisfy the condition of equation (2) to realize the negative sequence component Y of the PCC port admittance. PCCNS inhibition;

[0015]

[0016] Right now

[0017]

[0018] Where ω PS The positive sequence angular frequency is equal to the grid angular frequency, ω. PS =ω g ;ω NS The negative sequence angular frequency is equal to the second harmonic of the grid angular frequency, ω. NS =2ω g ω g The fundamental angular frequency of the power grid;

[0019] From equation (3), we can see that the admittance gain [T(s)-F(s)·W(s)] can be equivalent to the transfer function G(s) of the notch filter;

[0020]

[0021] Where, ω re ω is the resonant angular frequency. re =2ω g ;

[0022] From equation (4), the expression for the feedforward function W(s) in the complex domain is derived as follows:

[0023]

[0024] PCC voltage u PCC The positive-sequence component Y of the PCC port admittance after being fed into the system through the feedforward function W(s) PCCPS The negative-sequence component Y of the PCC port admittance remains unchanged. PCCNS Significant attenuation, i.e.

[0025]

[0026] Equation (5) shows that the feedforward function W(s) will exhibit numerical divergence during the process of discretizing from the complex domain to the frequency domain using bilinear transformation. In digital control, this leads to the inability to control the PCC voltage u. PCC The system is directly fed forward by W(s); as can be seen from the analysis of equation (6), the negative sequence component u of the PCC voltage can be fed forward separately. PCCNS Feedforward control to reduce the negative-sequence component Y of the PCC port admittance PCCNS For grid-connected current i g To mitigate the impact of grid-connected current and achieve the goal of balancing grid-connected current;

[0027] Step S3: Extract PCC voltage u PCC negative order component u PCCNS The PCC voltage u in the abc coordinate system PCCa u PCCb u PCCc The PCC voltage u in the αβ coordinate system is obtained through the abc / αβ coordinate transformation. PCCα u PCCβ ; will u PCCα u PCCβ The negative sequence component u of the PCC voltage in the αβ coordinate system is obtained by a first-order reduced-order filter. PCCαNS u PCCβNS , where ω o To extract the angular frequency, ω o =-ω g ; extract the u PCCαNS u PCCβNS The negative sequence component u of the PCC voltage in the dq coordinate system is obtained through the αβ / dq transformation. PCCdNS u PCCqNS The first-order reduced-order filter is

[0028]

[0029] Step S4: Extract the negative sequence component u of the PCC voltage obtained in step S3. PCCNS u PCCNS =u PCCdNS -ju PCCqNS By using the feedforward function W(s=jω) at the negative sequence angular frequency NS When the notch filter is fed into the system, its transfer function G(s=jω) is... NS If ) = 0, then the negative sequence angular frequency point ω = ω NS The frequency domain expression for W(s) is:

[0030]

[0031] in

[0032] M=-ω NS2 C f [L f1 R load +L f2 ·(k ip +H d )]-ω NS C f (k ip +H d )X load +k ip

[0033] N=-ω NS 3 C f L f1 L f2 -ω 2 C f L f1 X load +ω NS [C f (k ip +H d )R load +L f1 ]

[0034] Using vector methods and Euler's formula, W(jω) NS Convert ) to an amplitude-frequency value |W(jω) NS | with phase frequency value The combined form yields the expression FB(jω) after negative sequence voltage feedforward. NS )for

[0035]

[0036] Through the feedforward quantity FB(jω) NS The initial value FB of the feedforward quantity projected onto the vector graph of ) in the dq coordinate system is obtained. d0 FB q0 They are respectively,

[0037]

[0038] in,

[0039]

[0040] Initial value of feedforward FB d0 FB q0 FB is obtained through an adaptive optimization algorithm. d FB q and with voltage u d_PWM u q_PWMThe sums are then fed into the pulse width modulation unit, where the inverter output current is adjusted by regulating the duty cycle of the switching transistors to achieve the purpose of balancing the grid-connected current.

[0041] Optimal feedforward quantity FB d FB q The expression is

[0042]

[0043] Where, θ n Phase frequency value The optimal value, L ω The amplitude frequency value |W(jω) NS )|The value after selection.

[0044] The feedforward amount FB d FB q The adaptive optimization algorithm has the following specific steps:

[0045] Step A1: The system automatically identifies the local load; determined by the inverter bridge arm current i d i q Inverter output voltage u PCCd u PCCq , grid-connected current i gd i gq According to P outg =1.5·(u PCCd ·i gd +u PCCq ·i gq ), Q outg =1.5·(u PCCq ·i gd -u PCCd ·i gq ) Obtain the grid-connected power P outg Q outg According to P out =1.5·(u PCCd ·i d +u PCCq ·i q ), Q out =1.5·(u PCCq ·i d -u PCCd ·i q The total output power P of the inverter is obtained. out Q out Total output power P of the inverter out Q out Subtract grid-connected power P outg Q outg Obtain the power P of the local load out1 Qout1 Thus, the load current i on the local load is obtained. d1 i q1 for

[0046]

[0047] Local load power P out1 Q out1 With local load current i d1 i q1 The second harmonic component is filtered out by a third-order generalized integrator (TOGI) to obtain the DC component P of the local load power. out2 Q out2 DC component of local load current i d_load i q_load The output expression for the TOGI notch filter function is:

[0048]

[0049] Where, ω T =2ω g ;

[0050] The filtered load current i d_load i q_load Obtain the total impedance Z of the local load. load The filtered load power P out2 Q out2 Obtain the power factor angle θ of the local load. _load The total impedance Z load With power factor angle θ _load The resistance value R in the total impedance is obtained. load With reactance value X load The specific expression is

[0051]

[0052] Among them, U N To balance the effective value of the phase voltage of the power grid;

[0053] Step A2: Assign initial amplitude and frequency value L ω_first With the initial value of phase frequency θ n_first And assign adaptive optimal phase frequency value array arr and amplitude frequency value array brr; the initial amplitude frequency value and the initial phase frequency value are given by substituting equation (15) into equation (11), that is, L ω_first =|W(jω) NS )|, Based on the initial phase frequency θ n_first Generate with [θ n_first -n1,θ n_firstLet [+n1] be an array arr within the range, where arr[i] is the i-th number in the array arr, and the array capacity is 2n. a +1, arr[0]~arr[n] a Distribute θ according to an arithmetic progression. n_first ~(θ) n_first +n1), arr[n a +1]~arr[2n a Distribute according to the arithmetic progression rule. Based on the initial amplitude frequency value L ω_first Generate with [L ω_first -n2,L ω_first Let 2n[+n2] be an array brr within the range, where brr[j] is the j-th number in the array brr, and the array capacity is 2n. b +1, where brr[0]~brr[n] b Distribute L according to an arithmetic progression. ω_first ~(L ω_first +n2),brr[n b +1]~brr[2n b Distribute according to the arithmetic progression rule. When a load switch occurs, the initial amplitude-frequency value L is reassigned according to the new load conditions. ω_first With the initial value of phase frequency θ n_first And reassign adaptively optimal phase frequency array arr and amplitude frequency array brr;

[0054] Step A3: Obtain the unbalance value of the grid-connected current; in the dq coordinate system, the grid-connected current i gd i gq The DC positive sequence component i is extracted using a first-order reduced-order filter. gd_p i gq_p and the second harmonic negative sequence component i gd_2n i gq_2n The grid-connected current imbalance GG is obtained; then, the grid-connected current imbalance G is obtained by filtering GG through a third-order generalized integrator TOGI.

[0055] The expression for the grid current imbalance GG is:

[0056]

[0057] The first-order reduction filter in this step is...

[0058]

[0059] Where, ω pp To extract the angular frequency ω from the positive sequence DC component of the grid-connected current. pp =0, ωpc is the cut-off frequency for extracting the DC positive sequence component of the grid-connected current, ω nn is the angular frequency for extracting the double-frequency negative sequence component of the grid-connected current, ω nn =2ω g , ω nc is the cut-off frequency for extracting the double-frequency negative sequence component of the grid-connected current;

[0060] Step A4, performing primary optimization on the phase frequency value θ n ; Substitute the initial amplitude-frequency value brr[0]=L obtained in step A2 ω_first and the initial phase-frequency value arr[0]=θ n_first into formula (12) to obtain new FB d , FB q , feed them into the system, then compare the grid-connected current unbalance G obtained in step A3 with the grid-connected current unbalance standard G1, and judge whether the initial phase-frequency value arr[0] meets the requirement of G<G1; if the requirement is met, proceed to the secondary phase-frequency value optimization of step A5; if the requirement of G<G1 is not met, set i=i+1, select the next value in the array arr and substitute it into formula (12) to generate new FB d and FBq to feed into the system, perform comparative judgment on the new unbalance G calculated in step A3, and cycle repeatedly until the phase frequency value θ that meets the requirement of G<G1 is obtained n =arr[i]; In this optimization process, the amplitude-frequency value remains the initial amplitude-frequency value brr[0];

[0061] Step A5, performing secondary optimization on the phase frequency value θ n ; The amplitude-frequency value L ω still remains the initial amplitude-frequency value brr[0]; Generate an array frr in the range of [arr[i]-n3, arr[i]+n3] according to the optimal phase-frequency value arr[i] obtained in step A4, where n3<n1, frr[m] is the m-th number in the array frr, and the array capacity is 2n c +1, where frr[0]~frr[n c are assigned from arr[i] to (arr[i]+n3) according to the rule of equal difference increment, frr[n c +1]~frr[2n c are assigned according to the rule of equal difference decrement Taking the grid-connected current unbalance standard G2 as the judgment basis, where G2<G1; if frr[m] meets the requirement of G<G2, then θ n =frr[m], and the secondary optimization of the phase frequency value θ n is ended; if the requirement of G<G2 is not met, set m=m+1, select the next value in the array frr and substitute it into formula (12) to generate new FB d, FB q is fed into the system, the new unbalance degree G calculated in step A3 is used for comparison and judgment, and the cycle is repeated until the phase-frequency value θ that meets the requirements is obtained n ;

[0062] Step A6: Optimize the amplitude-frequency value L ω , judge whether the amplitude-frequency value L ω satisfies the grid-connected current unbalance degree G3, where G3<G2<G1; substitute the initial amplitude-frequency value brr[0] and the phase-frequency value θ obtained in step A5 n into formula (12) to obtain new FB d , FB q , after being fed into the system, the grid-connected current unbalance degree G is obtained from step A3. If G<G3 is satisfied, the optimal amplitude-frequency value L is obtained ω =brr[0], and the optimization of the amplitude-frequency value is ended; if G<G3 is not satisfied, j=j+1, select the next value in the brr array and substitute it into formula (12) to generate new FB d , FB q is fed into the system, the new unbalance degree G calculated in step A3 is used for comparison and judgment until the amplitude-frequency value L that meets the requirement of G<G3 is obtained ω ;

[0063] Step A7: Substitute the optimal phase-frequency value θ obtained in step A5 and step A6 n and the amplitude-frequency value L ω into formula (12) to obtain the optimal output value FB of the adaptive PCC port admittance negative sequence component suppression algorithm d , FB q .

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] (1) Under the condition of unbalanced grid voltage, compared with the grid-connected current balance control strategy using voltage and current positive and negative sequence separation dual dq negative sequence compensation, the method proposed by the present invention can reduce the number of PI regulators used and reduce the complexity of PI regulator parameter selection;

[0066] (2) Compared with the existing control strategy that realizes grid-connected current balance through grid voltage feedforward, the method proposed by the present invention focuses on the grid-connected current balance control problem when operating with local loads. According to the local load condition, this method adaptively searches for the optimal value of the feedforward quantity in the PCC port admittance negative sequence component suppression algorithm, so as to offset the influence of the PCC voltage negative sequence component on the grid-connected current, and then eliminate the negative sequence disturbance term in the grid-connected current, so as to achieve the optimal grid-connected current balance control effect under different load conditions. Brief Description of the Drawings

[0067] Figure 1 This is a block diagram of an inverter system in which a PCC port admittance negative sequence component suppression algorithm is added in an embodiment of the present invention;

[0068] Figure 2 This is a block diagram of the grid-connected current balance control strategy for an inverter system with a linear symmetrical load under an unbalanced power grid in an embodiment of the present invention.

[0069] Figure 3 This is a diagram of a dual-closed-loop structure of an inverter control system with PCC voltage feedforward added in an example of the present invention.

[0070] Figure 4 This is an equivalent circuit diagram of a dual-closed-loop inverter control system with PCC voltage feedforward added in an embodiment of the present invention.

[0071] Figure 5 In one example of the present invention, the feedforward quantity FB(jω) NS Vector graph of )

[0072] Figure 6 In an example of the present invention, the feedforward quantity FB d FB q Flowchart of the adaptive selection algorithm. Detailed Implementation

[0073] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0074] This invention provides a grid-connected current balance control method for an inverter system with a linear symmetrical load, namely, a grid-connected current balance control strategy employing an adaptive PCC port admittance negative sequence component suppression algorithm under unbalanced grid conditions. In a specific embodiment, the inverter system topology consists of a three-phase three-port quasi-Z-source inverter and its two port input sources (distributed power source and energy storage unit), local load, and a low-voltage AC grid. The control section includes a dual-loop structure of the grid-side current outer loop inverter bridge arm current inner loop, a phase-locked loop (PLL) unit with TOGI filtering, an active damping unit, a voltage feedforward unit with an adaptive PCC port admittance negative sequence component suppression algorithm, and a pulse width modulation unit, as well as a photovoltaic voltage control loop for the quasi-Z-source inverter to establish DC bus voltage and achieve photovoltaic maximum power point voltage tracking (MPPT). Figure 1 A block diagram of the inverter system with the addition of the PCC port admittance negative sequence component suppression algorithm is given.

[0075] Depend on Figure 2 The block diagram of the grid-connected current balance control strategy for an inverter system with a linear symmetrical load under an unbalanced grid can be obtained as follows: The q-axis component u of the PCC voltage in the two-phase rotating dq coordinate system is then used. PCCqThe positive-sequence DC component of the voltage along the q-axis is obtained by filtering with a third-order generalized integrator (TOGI), and then used as the input to a phase-locked loop (PLL). After passing through the PLL, the grid angular frequency ω is obtained. g With phase angle θ g The inverter bridge arm current sampling value i Lfa i Lfb i Lfc PCC voltage sampling value u PCCa u PCCb u PCCc , grid-connected current sampling value i ga i gb i gc The dq component u of the grid voltage can be obtained through the abc / dq transformation. gd u gq Inverter bridge arm current dq component i d i q PCC voltage dq component u PCCd u PCCq , grid-connected current dq component i gd i gq The grid-side current loop uses a proportional-integral regulator G. PI2 (s), the proportionality coefficient is k ip_i The integral coefficient is k ii_i Reference value i of the grid-side current loop gd_ref i gq_ref , and the grid-connected current sampling value i gd i gq The difference is controlled by the PI regulator G. PI2 (s) can obtain the current inner loop reference value i d_ref i q_ref The inverter bridge arm current loop uses a proportional regulator G. PI1 (s), the proportionality coefficient is k ip The reference value i for the inner current loop d_ref i q_ref With inverter bridge arm current sampling value i d i q The difference is controlled by the P regulator G. PI1 (s) can be used to obtain the inner current loop output voltage u. iod u ioq u iod u ioq Subtract the output of the active damping unit from the output of the PCC voltage u. PCCd u PCCq Adding them together gives the voltage u d_PWM u q_PWM And the voltage feedforward quantity FB obtained by the adaptive PCC port admittance negative sequence component suppression algorithm. d FBq The input modulation voltage u of the pulse width modulation unit is obtained by adding them together. FBd_PWM u FBq_PWM Finally, the inverter output current is adjusted by regulating the duty cycle of the switching transistors through the pulse width modulation unit, thereby achieving the goal of balancing the grid-connected current. The output of the active damping unit is the filter capacitor current and the active damping coefficient H. d The product of, where the filter capacitor current i Cd i Cq Inverter bridge arm current i d i q Subtract the load current i obtained from local load identification d1 i q1 Subtract the grid-connected current i gd i gq The current value obtained afterwards.

[0076] The adaptive PCC port admittance negative-sequence component suppression algorithm is implemented using the following method:

[0077] Step S1: When the power grid is unbalanced, the PCC voltage u PCC It can be decomposed into positive-order components u PCCPS With negative order component u PCCNS Among them, the negative order component u PCCNS As a disturbance term, it causes the grid-connected current i g Unbalanced. Without affecting the positive-sequence component Y of the PCC port admittance. PCCPS Under the premise of adding PCC voltage u PCC Feedforward control; for the sake of simplifying the analysis, the inductance L is ignored. f2 voltage u L2 At this time, by Figure 3 The diagram showing the dual closed-loop structure of the inverter control system with PCC voltage feedforward can be used to obtain the grid-connected current i. g for

[0078] i g =G i (s)·i g_ref -[T(s)-F(s)·W(s)]·Y(s·u PCC (1)

[0079] From equation (1), we can obtain Figure 4 The equivalent circuit diagram of a dual-closed-loop inverter control system with PCC voltage feedforward is shown.

[0080]

[0081] i g_ref For the grid-side current loop reference value, G iY(s) is the current gain, Y(s) is the PCC port admittance, [T(s)-F(s)·W(s)] is the admittance gain, and G... PI1 (s) is the inverter bridge arm current loop proportional regulator, G PI2 (s) is the proportional-integral regulator of the grid-side current loop, H d R is the active damping coefficient. load X is the load resistance. load For load reactance;

[0082] Step S2: The admittance gain [T(s)-F(s)·W(s)] of the PCC port admittance with added voltage feedforward obtained from step S1 needs to satisfy the condition of equation (2) to realize the negative sequence component Y of the PCC port admittance. PCCNS The inhibition.

[0083]

[0084] Right now

[0085]

[0086] Where ω PS The positive sequence angular frequency is equal to the grid angular frequency, ω. PS =ω g ;ω NS The negative sequence angular frequency is equal to the second harmonic of the grid angular frequency, ω. NS =2ω g ω g This is the fundamental angular frequency of the power grid.

[0087] From equation (3), we can see that the admittance gain [T(s)-F(s)·W(s)] can be equivalent to the transfer function G(s) of the notch filter.

[0088]

[0089] Where, ω re ω is the resonant angular frequency. re =2ω g .

[0090] From equation (4), the expression for the feedforward function W(s) in the complex domain is derived as follows:

[0091]

[0092] PCC voltage u PCC The positive-sequence component Y of the PCC port admittance after being fed into the system through the feedforward function W(s) PCCPS The negative-sequence component Y of the PCC port admittance remains unchanged. PCCNS Significant attenuation, i.e.

[0093]

[0094] Equation (5) shows that the feedforward function W(s) will exhibit numerical divergence during the process of discretizing from the complex domain to the frequency domain using bilinear transformation. In digital control, this leads to the inability to control the PCC voltage u. PCC The system is directly fed forward by W(s). Analysis of equation (6) shows that the negative sequence component u of the PCC voltage can be fed forward independently. PCCNS Feedforward control to reduce the negative-sequence component Y of the PCC port admittance PCCNS For grid-connected current i g This will mitigate the impact of grid connection current and achieve the goal of balancing grid-connected current.

[0095] Step S3: Extract PCC voltage u PCC negative order component u PCCNS The PCC voltage u in the abc coordinate system PCCa u PCCb u PCCc The PCC voltage u in the αβ coordinate system is obtained through the abc / αβ coordinate transformation. PCCα u PCCβ ; will u PCCα u PCCβ The negative sequence component u of the PCC voltage in the αβ coordinate system is obtained by a first-order reduced-order filter. PCCαNS u PCCβNS , where ω o To extract the angular frequency, ω o =-ω g ; extract the u PCCαNS u PCCβNS The negative sequence component u of the PCC voltage in the dq coordinate system is obtained through the αβ / dq transformation. PCCdNS u PCCqNS A first-order reduced-order filter is...

[0096]

[0097] Step S4: Extract the negative sequence component u of the PCC voltage obtained in step S3. PCCNS (u PCCNS =u PCCdNS -ju PCCqNS ) through the feedforward function W(s=jω) at the negative sequence angular frequency NS When the notch filter is fed into the system, its transfer function G(s=jω) is... NS If ) = 0, then the negative sequence angular frequency point ω = ω NS The frequency domain expression for W(s) is:

[0098]

[0099] in

[0100] M=-ω NS 2 C f [L f1 R load +L f2 ·(k ip +H d )]-ω NS C f (k ip +H d )X load +k ip

[0101] N=-ω NS 3 C f L f1 L f2 -ω 2 C f L f1 X load +ω NS [C f (k ip +H d )R load +L f1 ]

[0102] Using vector methods and Euler's formula, W(jω) NS Convert ) to an amplitude-frequency value |W(jω) NS | with phase frequency value The combined form yields the expression FB(jω) after negative sequence voltage feedforward. NS )for

[0103]

[0104] pass Figure 5 The feedforward quantity FB(jω) shown NS The vector graph of ) can be used to obtain the initial value of the feedforward quantity FB projected onto the dq coordinate system. d0 FB q0 They are respectively

[0105]

[0106] in,

[0107]

[0108] Initial value of feedforward FB d0 FB q0 FB is obtained through an adaptive optimization algorithm. d FB q and with voltage ud_PWM u q_PWM The signals are added together and then fed into the pulse width modulation unit. By adjusting the duty cycle of the switching transistors, the inverter output current is adjusted to achieve the purpose of balancing the grid-connected current.

[0109] Optimal feedforward quantity FB d FB q The expression is

[0110]

[0111] Where, θ n Phase frequency value The optimal value, L ω The amplitude frequency value |W(jω) NS )|The value after selection.

[0112] Figure 6 The feedforward quantity FB shown d FB q The specific steps of the adaptive optimization algorithm are as follows:

[0113] Step A1: The system automatically identifies the local load. This is determined by the inverter bridge arm current i. d i q Inverter output voltage u PCCd u PCCq , grid-connected current i gd i gq According to P outg =1.5·(u PCCd ·i gd +u PCCq ·i gq ), Q outg =1.5·(u PCCq ·i gd -u PCCd ·i gq ) Obtain the grid-connected power P outg Q outg According to P out =1.5·(u PCCd ·i d +u PCCq ·i q ), Q out =1.5·(u PCCq ·i d -u PCCd ·i q The total output power P of the inverter is obtained. out Q out The total output power P of the inverter out Q out Subtract grid-connected power P outg Qoutg Obtain the power P of the local load out1 Q out1 Thus, the load current i on the local load is obtained. d1 i q1 for

[0114]

[0115] Local load power P out1 Q out1 With local load current i d1 i q1 The second harmonic component is filtered out by a third-order generalized integrator (TOGI) to obtain the DC component P of the local load power. out2 Q out2 DC component of local load current i d_load i q_load The output expression for the TOGI notch filter function is:

[0116]

[0117] Where, ω T =2ω g ;

[0118] The filtered load current i d_load i q_load Obtain the total impedance Z of the local load. load The filtered load power P out2 Q out2 Obtain the power factor angle θ of the local load. _load The total impedance Z load With power factor angle θ _load The resistance value R in the total impedance is obtained. load With reactance value X load The specific expression is

[0119]

[0120] Among them, U N To balance the effective value of the phase voltage of the power grid;

[0121] Step A2: Assign initial amplitude and frequency value L ω_first With the initial value of phase frequency θ n_first And assign adaptive optimal phase frequency value array arr and amplitude frequency value array brr. The initial values ​​of amplitude frequency and phase frequency are given by substituting equation (15) into equation (11), that is, L ω_first =|W(jω) NS )|, Based on the initial phase frequency θ n_first Generate with [θn_first -n1,θ n_first Let [+n1] be an array arr within the range, where arr[i] is the i-th number in the array arr, and the array capacity is 2n. a +1, arr[0]~arr[n] a Distribute θ according to an arithmetic progression. n_first ~(θ) n_first +n1), arr[n a +1]~arr[2n a Distribute according to the arithmetic progression rule. Based on the initial amplitude frequency value L ω_first Generate with [L ω_first -n2,L ω_first [+n2] is an array `brr` with a capacity of 2n, where `brr[j]` is the j-th number in the array `brr`. b +1, where brr[0]~brr[n] b Distribute L according to an arithmetic progression. ω_first ~(L ω_first +n2),brr[n b +1]~brr[2n b Distribute according to the arithmetic progression rule. When a load switch occurs, the initial amplitude-frequency value L is reassigned according to the new load conditions. ω_first With the initial value of phase frequency θ n_first And reassign adaptively optimal phase frequency array arr and amplitude frequency array brr;

[0122] Step A3: Obtain the unbalance value of the grid-connected current. In the dq coordinate system, the grid-connected current i gd i gq The DC positive sequence component i is extracted using a first-order reduced-order filter. gd_p i gq_p and the second harmonic negative sequence component i gd_2n i gq_2n The grid-connected current imbalance GG is obtained. Then, the grid-connected current imbalance G is obtained by filtering GG through a third-order generalized integrator (TOGI).

[0123] The expression for the grid current imbalance GG is:

[0124]

[0125] The first-order reduction filter in this step is...

[0126]

[0127] Where, ω ppis the angular frequency for extracting the DC positive sequence component of the grid-connected current, ω pp =0, ω pc is the cutoff frequency for extracting the DC positive sequence component of the grid-connected current, ω nn is the angular frequency for extracting the double-frequency negative sequence component of the grid-connected current, ω nn =2ω g , ω nc is the cutoff frequency for extracting the double-frequency negative sequence component of the grid-connected current;

[0128] Step A4: Perform primary optimization on the phase-frequency value θ n . Substitute the initial amplitude-frequency value brr[0]=L obtained in step A2 ω_first and the initial phase-frequency value arr[0]=θ n_first into equation (12) to obtain new FB d , FB q . After being fed into the system, the grid-connected current unbalance G obtained in step A3 is compared with the grid-connected current unbalance standard G1 to judge whether the initial phase-frequency value arr[0] meets the requirement of G<G1. If the requirement is met, proceed to the secondary phase-frequency value optimization in step A5; if the requirement of G<G1 is not met, set i=i+1, select the next value in the array arr, substitute it into equation (12) to generate new FB d , FB q to feed into the system, calculate and obtain a new unbalance G through step A3 for comparison and judgment, and cycle repeatedly until a phase-frequency value θ that meets the requirement of G<G1 is obtained n =arr[i]. During this optimization process, the amplitude-frequency value remains the initial amplitude-frequency value brr[0];

[0129] Step A5: Perform secondary optimization on the phase-frequency value θ n . The amplitude-frequency value L ω still remains the initial amplitude-frequency value brr[0]. Generate an array frr with the range of [arr[i]-n3, arr[i]+n3] according to the optimal phase-frequency value arr[i] obtained in step A4, where n3<n1, frr[m] is the m-th value in the array frr, and the array capacity is 2n c +1, in which frr[0]~frr[n c are assigned values from arr[i] to (arr[i]+n3) according to the law of equal difference increment, and frr[n c +1]~frr[2n c are assigned according to the law of equal difference decrement Taking the grid-connected current unbalance standard G2 as the judgment basis, where G2<G1. If frr[m] meets the requirement of G<G2, then θ n =frr[m], and the phase-frequency value θ nfor secondary optimization; if the requirement of G<G2 is not satisfied, then m=m+1, select the next value in the array frr and substitute it into Equation (12) to generate a new FB d , FB q fed into the system, the new unbalance degree G calculated in step A3 is used for comparison and judgment, and the cycle continues until the phase-frequency value θ that meets the requirements is obtained n .

[0130] Step A6: Optimize the amplitude-frequency value L ω , and judge whether the amplitude-frequency value L ω satisfies the grid-connected current unbalance degree G3, where G3<G2<G1. Substitute the initial amplitude-frequency value brr[0] and the phase-frequency value θ obtained in step A5 n into Equation (12) to obtain a new FB d , FB q , after being fed into the system, the grid-connected current unbalance degree G is obtained in step A3. If G<G3 is satisfied, the optimal amplitude-frequency value L ω =brr[0] is obtained, and the optimization of the amplitude-frequency value is ended; if G<G3 is not satisfied, then j=j+1, select the next value in the array brr and substitute it into Equation (12) to generate a new FB d , FB q fed into the system, the new unbalance degree G calculated in step A3 is used for comparison and judgment until the amplitude-frequency value L that meets the requirement of G<G3 is obtained ω .

[0131] Step A7: Substitute the optimal phase-frequency value θ obtained in step A5 and step A6 n and the amplitude-frequency value L ω into Equation (12) to obtain the optimal output value FB of the adaptive PCC port admittance negative sequence component suppression algorithm d , FB q .

[0132] The above description is merely a preferred embodiment of the present invention, and is not intended to impose other forms of limitation on the present invention. Any person skilled in the art may use the technical content disclosed above to make alterations or modifications to equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A grid-connected current balance control method for an inverter system with a linear symmetrical load, characterized in that, When an inverter system with a linear symmetrical load operates in a grid-connected environment under an unbalanced grid, the negative-sequence component of the common coupling point (PCC) voltage extracted by the first-order reduced-order filter is processed by a feedforward function. Based on the automatically identified local load conditions, an adaptive optimization algorithm is used to obtain the optimal amplitude and phase frequency values, thereby obtaining the optimal voltage feedforward quantity. This quantity is then fed into the system loop to counteract the influence of the PCC voltage negative-sequence component on the grid-connected current, thereby eliminating the negative-sequence disturbance term in the grid-connected current and achieving balanced control of the grid-connected current. The inverter system topology includes an input source, a three-phase inverter, a local load, and a low-voltage AC grid. The inverter system control part includes a dual-loop structure of the grid-side current outer loop and the inverter bridge arm current inner loop, a phase-locked loop (PLL) unit with a third-order generalized integrator (TOGI) filter, an active damping unit, a voltage feedforward unit with an adaptive PCC port admittance negative-sequence component suppression algorithm, and a pulse width modulation unit. The specific implementation of this method is as follows: The q-axis component u of the PCC voltage in the two-phase rotating dq coordinate system PCCq The positive-sequence DC component of the voltage along the q-axis is obtained by filtering with a third-order generalized integrator (TOGI), and then used as the input of the phase-locked loop (PLL) unit to obtain the grid angular frequency. With phase angle ;Based on the inverter bridge arm current sampling value i Lfa i Lfb i Lfc PCC voltage sampling value u PCCa u PCCb u PCCc , grid-connected current sampling value i ga i gb i gc The inverter arm current dq component i is obtained through abc / dq transformation. d i q PCC voltage dq component u PCCd u PCCq , grid-connected current dq component i gd i gq The grid-side current loop uses a PI regulator G. PI2 (s), the proportionality coefficient is k ip_i The integral coefficient is k ii_i Reference value i of the grid-side current loop gd_ref i gq_ref With grid-connected current sampling value i gd i gq The difference is controlled by the PI regulator G. PI2 (s) Obtain the current inner loop reference value i d_ref i q_ref The inverter bridge arm current loop uses a P regulator and a G regulator. PI1 (s), the proportionality coefficient is k ip The reference value i for the inner current loop d_ref i q_ref With inverter bridge arm current sampling value i d i q The difference is controlled by the P regulator G. PI1 (s) Obtain the inner current loop output voltage u iod u ioq u iod u ioq Subtract the output of the active damping unit from the output of the PCC voltage u. PCCd u PCCq Adding them together gives the voltage u d_PWM u q_PWM And the voltage feedforward quantity FB obtained by the adaptive PCC port admittance negative sequence component suppression algorithm. d FB q The input modulation voltage u of the pulse width modulation unit is obtained by adding them together. FBd_PWM u FBq_PWM Finally, the inverter output current is adjusted by regulating the duty cycle of the switching transistor through the pulse width modulation unit, thereby achieving the purpose of balancing the grid-connected current; the output of the active damping unit is the filter capacitor current and the active damping coefficient H. d The product of, where the filter capacitor current i Cd i Cq Inverter bridge arm current i d i q Subtract the load current i obtained from local load identification d1 i q1 Subtract the grid-connected current i gd i gq The current value obtained afterwards.

2. The grid-connected current balance control method for an inverter system with a linear symmetrical load according to claim 1, characterized in that, The adaptive PCC port admittance negative-order component suppression algorithm is implemented using the following method: Step S1: When the power grid is unbalanced, the PCC voltage u PCC Decomposed into positive-order components u PCCPS With negative order component u PCCNS Among them, the negative order component u PCCNS As a disturbance term, it causes the grid-connected current i g Unbalanced; without affecting the positive-sequence component Y of the PCC port admittance PCCPS Under the premise of adding PCC voltage u PCC Feedforward control, ignoring inductor voltage, the grid-connected current i g for （1） in i g_ref For the grid-side current loop reference value, G i Y(s) is the current gain, Y(s) is the PCC port admittance, [T(s)-F(s)·W(s)] is the admittance gain, and H... d R is the active damping coefficient. load X is the load resistance. load For load reactance; Step S2: The admittance gain [T(s)-F(s)·W(s)] of the PCC port admittance with added voltage feedforward obtained from step S1 needs to satisfy the condition of equation (2) to realize the negative sequence component Y of the PCC port admittance. PCCNS inhibition; （2） Right now （3） Where ω PS The positive sequence angular frequency is equal to the grid angular frequency, ω. PS =ω g ;ω NS The negative sequence angular frequency is equal to the second harmonic of the grid angular frequency, ω. NS =2ω g ω g The fundamental angular frequency of the power grid; From equation (3), we can obtain that the admittance gain [T(s)-F(s)·W(s)] can be equivalent to the transfer function G(s) of the notch filter; （4） Where, ω re ω is the resonant angular frequency. re =2ω g ; From equation (4), the expression for the feedforward function W(s) in the complex domain is derived as follows: （5） PCC voltage u PCC The positive-sequence component Y of the PCC port admittance after being fed into the system through the feedforward function W(s) PCCPS The negative-sequence component Y of the PCC port admittance remains unchanged. PCCNS Significant attenuation, i.e. （6） Equation (5) shows that the feedforward function W(s) will exhibit numerical divergence during the process of discretizing from the complex domain to the frequency domain using bilinear transformation. In digital control, this leads to the inability to control the PCC voltage u. PCC The system is directly fed forward by W(s); as can be seen from the analysis of equation (6), the negative sequence component u of the PCC voltage can be fed forward separately. PCCNS Feedforward control to reduce the negative-sequence component Y of the PCC port admittance PCCNS For grid-connected current i g To mitigate the impact of grid-connected current and achieve the goal of balancing grid-connected current; Step S3: Extract PCC voltage u PCC negative order component u PCCNS The PCC voltage u in the abc coordinate system PCCa u PCCb u PCCc pass Coordinate transformation yields the PCC voltage u in the αβ coordinate system PCCα u PCCβ ; will u PCCα u PCCβ The negative sequence component u of the PCC voltage in the αβ coordinate system is obtained by a first-order reduced-order filter. PCCαNS u PCCβNS ,in To extract angular frequency, ; extract the u PCCαNS u PCCβNS pass The transformation yields the negative sequence component u of the PCC voltage in the dq coordinate system. PCCdNS u PCCqNS The first-order reduced-order filter is （7） Step S4: Extract the negative sequence component u of the PCC voltage obtained in step S3. PCCNS u PCCNS =u PCCdNS -ju PCCqNS By using the feedforward function at the negative sequence angular frequency Feeding into the system, the transfer function of the notch filter at this time =0, then the negative sequence angular frequency point The frequency domain expression for W(s) is: （8） in Using vector method and Euler's formula Convert to an amplitude-frequency value With phase frequency value By combining the forms, we obtain the expression for the negative sequence voltage feedforward. for （9） Through feedforward The vector graph is used to obtain the initial value of the feedforward quantity FB projected onto the dq coordinate system. d0 FB q0 They are respectively, （10） in, （11） Initial value of feedforward FB d0 FB q0 FB is obtained through an adaptive optimization algorithm. d FB q and with voltage u d_PWM u q_PWM The sums are then fed into the pulse width modulation unit, where the inverter output current is adjusted by regulating the duty cycle of the switching transistors to achieve the purpose of balancing the grid-connected current. Optimal feedforward quantity FB d FB q The expression is （12） Where, θ n Phase frequency value φ NS The optimal value, L ω Amplitude-frequency value The optimal value.

3. The grid-connected current balance control method for an inverter system with a linear symmetrical load according to claim 2, characterized in that, Voltage feedforward FB d FB q The acquisition uses feedforward quantity (FB) d FB q The adaptive optimization algorithm has the following specific steps: Step A1: The system automatically identifies the local load; determined by the inverter bridge arm current i d i q Inverter output voltage u PCCd u PCCq , grid-connected current i gd i gq ,according to Obtain the grid-connected power P outg Q outg ,according to Obtain the total output power P of the inverter out Q out Total output power P of the inverter out Q out Subtract grid-connected power P outg Q outg Obtain the power P of the local load out1 Q out1 Thus, the load current i on the local load is obtained. d1 i q1 for （13） Local load power P out1 Q out1 With local load current i d1 i q1 The second harmonic component is filtered out by a third-order generalized integrator (TOGI) to obtain the DC component P of the local load power. out2 Q out2 DC component of local load current i d_load i q_load The output expression for the TOGI notch filter function is: （14） in, ; The filtered load current i d_load i q_load Obtain the total impedance Z of the local load. load The filtered load power P out2 Q out2 Obtain the power factor angle of the local load. The total impedance Z load With power factor angle The resistance value R in the total impedance is obtained. load With reactance value X load The specific expression is （15） Among them, U N To balance the effective value of the phase voltage of the power grid; Step A2: Assign initial amplitude and frequency value L ω_first With the initial value of phase frequency θ n_first And assign adaptive optimal phase frequency value array arr and amplitude frequency value array brr; the initial amplitude frequency value and the initial phase frequency value are given by substituting equation (15) into equation (11), that is, L ω_first = θ n_first = Based on the initial phase frequency θ n_first Generate with [θ n_first -n1,θ n_first Let [+n1] be an array arr within the range, where arr[i] is the i-th number in the array arr, and the array capacity is 2n. a +1, arr[0]~arr[n] a Distribute θ according to an arithmetic progression. n_first ~(θ n_first +n1), arr[n a +1]~arr[2n a Distribute according to the arithmetic progression (θ) n_first - )~(θ n_first -n1); based on the initial amplitude frequency value L ω_first Generate with [L ω_first -n2, L ω_first Let 2n[+n2] be an array brr within the range, where brr[j] is the j-th number in the array brr, and the array capacity is 2n. b +1, where brr[0]~brr[n] b Distribute L according to an arithmetic progression. ω_first ~(L ω_first +n2),brr[n b +1]~brr[2n b Distribute according to the arithmetic progression (L) ω_first - )~(L ω_first -n2); When the load is switched, the initial amplitude-frequency value L is reassigned according to the new load conditions. ω_first With the initial value of phase frequency θ n_first And reassign adaptively optimal phase frequency array arr and amplitude frequency array brr; Step A3: Obtain the unbalance value of the grid-connected current; in the dq coordinate system, the grid-connected current i gd i gq The DC positive sequence component i is extracted using a first-order reduced-order filter. gd_p i gq_p and the second harmonic negative sequence component i gd_2n i gq_2n The grid-connected current imbalance GG is obtained; then, the grid-connected current imbalance G is obtained by filtering GG through a third-order generalized integrator TOGI. The expression for the grid current imbalance GG is: （16） The first-order reduction filter in this step is... （17） Where, ω pp To extract the angular frequency ω from the positive sequence DC component of the grid-connected current. pp = 0, ω pc The cutoff frequency for extracting the positive sequence DC component of the grid-connected current is ω. nn To extract the angular frequency ω from the second harmonic negative sequence component of the grid-connected current. nn = 2ω g ω nc Extract the cutoff frequency for the second harmonic negative sequence component of the grid-connected current; Step A4: Perform primary optimization on the phase-frequency value θ n ; Set the initial amplitude-frequency value brr[0]=L obtained in step A2 ω_first and the initial phase-frequency value arr[0]=θ n_first into Equation (12) to obtain new FB d , FB q , feed them into the system, then compare the grid-connected current unbalance degree G obtained in step A3 with the grid-connected current unbalance degree standard G1, and judge whether the initial phase-frequency value arr[0] meets the requirement of G<G1; if the requirement is met, proceed to the secondary phase-frequency value optimization of step A5; if the requirement of G<G1 is not met, set i=i+1, select the next value in the array arr and substitute it into Equation (12) to generate new FB d , FBq to feed into the system, calculate the new unbalance degree G through step A3 for comparison and judgment, and cycle repeatedly until the phase-frequency value θ that meets the requirement of G<G1 is obtained n =arr[i]; In this optimization process, the amplitude-frequency value remains the initial amplitude-frequency value brr[0]; Step A5: Perform secondary optimization on the phase-frequency value θ n ; the amplitude-frequency value L ω remains the initial amplitude-frequency value brr[0]; generate an array frr with the range of [arr[i]-n3, arr[i]+n3] according to the optimal phase-frequency value arr[i] obtained in step A4, where n3<n1, frr[m] is the m-th number in the array frr, and the array capacity is 2n c +1, where frr[0]~frr[n c are assigned from arr[i] to (arr[i]+n3) according to the rule of equal difference increment, frr[n c +1]~frr[2n c are assigned from (arr[i]- ) to (arr[i]-n3) according to the rule of equal difference decrement; take the grid-connected current unbalance standard G2 as the judgment basis, where G2<G1; if frr[m] meets the requirement of G<G2, then θ n =frr[m], and the secondary optimization of the phase-frequency value θ n is ended; if the requirement of G<G2 is not met, then m=m+1, select the next value in the array frr to substitute into formula (12) to generate new FB d , FB q fed into the system, and the new unbalance G calculated in step A3 is used for comparison and judgment, and the cycle proceeds until a phase-frequency value θ that meets the requirements is obtained n ; Step A6: Perform optimization on the amplitude-frequency value L ω , and determine whether the amplitude-frequency value L ω satisfies the grid-connected current unbalance G3, where G3<G2<G1; the initial amplitude-frequency value brr[0] and the phase-frequency value θ obtained in Step A5 n are substituted into Equation (12) to obtain new FB d and FB q , which are fed into the system, and the grid-connected current unbalance G is obtained from Step A3. If G<G3 is satisfied, the optimal amplitude-frequency value L ω =brr[0] is obtained, and the amplitude-frequency value optimization is ended; if G<G3 is not satisfied, j=j+1, the next value in the brr array is selected and substituted into Equation (12) to generate new FB d and FB q which are fed into the system, a new unbalance G is calculated through Step A3 for comparison and judgment, until the amplitude-frequency value L that meets the requirement of G<G3 is obtained ω ; Step A7: Calculate the optimal phase frequency value θ obtained in steps A5 and A6. n With amplitude frequency value L ω Substituting into equation (12), we obtain the optimal output value FB of the adaptive PCC port admittance negative-order component suppression algorithm. d FB q .

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