A method and system for controlling the stable output of an inverter

Abstract

The application discloses a kind of method and system for controlling the stable output of inverter, obtain grid voltage, input to the inverter main circuit control model of pre-constructed including improved feedforward decoupling and PI link, output stable voltage;The construction of inverter main circuit control model including improved feedforward decoupling and PI link includes: obtaining the main circuit topology of LC type inverter to be processed, analyzing main circuit topology determines the mathematical model under the two-phase rotating dq coordinate system of main circuit topology;Improved feedforward decoupling is used to the current inner loop decoupling of mathematical model, and the voltage loop considering the dynamic link of current loop is obtained;According to the PI parameter of current inner loop and voltage outer loop set by voltage loop considering the dynamic link of current loop, the inverter main circuit control model of the improved feedforward decoupling and PI link is obtained according to the PI parameter of current inner loop and voltage outer loop.It is advantageous: it can effectively suppress the output voltage fluctuation of inverter under large disturbance, improve the dynamic response speed of system.

Description

Technical Field

[0001] This invention relates to a method and system for controlling the stable output of an inverter, belonging to the field of inverter parameter control technology. Background Technology

[0002] Vigorously developing clean energy and replacing coal-fired power with renewable energy sources such as wind and solar power is an important way for my country to achieve its "carbon peak and carbon neutrality" goals in the energy sector. Three-phase LC inverters typically employ a dual closed-loop PI control method with an inner current loop and an outer voltage loop to improve the control accuracy and dynamic response capability of the VSI system. This control can be further divided into inductor current inner loop control and capacitor current inner loop control, depending on the controlled variable in the inner current loop.

[0003] Both inductor current inner loop and capacitor current inner loop control achieve the same voltage tracking effect. However, when using the capacitor current as the inner loop control variable, the current inner loop does not contain load current disturbance information, thus the capacitor current inner loop has better load disturbance immunity than the inductor current inner loop. Conversely, when using the inductor current inner loop, the inductor current is the current flowing through the switching transistor, and limiting it can achieve current limiting protection for the switching transistor. Therefore, the inductor current inner loop has stronger current protection capability than the capacitor current inner loop. Furthermore, adding load current feedforward to the control system can improve the load disturbance immunity of the inductor current inner loop. Therefore, this paper uses zero-pole cancellation to treat the current inner loop as a first-order inertial element. Using the symmetrical optimal method, the PI parameter tuning of the voltage outer loop is simplified to the tuning of the symmetry coefficient k. Based on phase margin and controller bandwidth constraints, the range of values ​​for k is given, suppressing the fluctuation of the VSI output voltage under large disturbances. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a method and system for controlling the stable output of an inverter.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for controlling the stable output of an inverter, comprising:

[0006] The grid voltage is obtained and input into a pre-built inverter main circuit control model that includes improved feedforward decoupling and PI links, and a stable voltage is output.

[0007] The construction of the inverter main circuit control model, which includes improved feedforward decoupling and PI link, includes:

[0008] Obtain the main circuit topology of the LC inverter to be processed, analyze the main circuit topology, and determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system.

[0009] An improved feedforward decoupling method is used to decouple the inner current loop of the mathematical model, resulting in a voltage loop that considers the dynamic elements of the current loop.

[0010] Based on the voltage loop considering the dynamic link of the current loop, the PI parameters of the inner current loop and the outer voltage loop are set, and the improved feedforward decoupling and PI link inverter main circuit control model is obtained based on the PI parameters of the inner current loop and the outer voltage loop.

[0011] Furthermore, the step of obtaining the main circuit topology of the LC inverter to be processed and analyzing the main circuit topology to determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system includes:

[0012] The main circuit of the LC inverter adopts a three-phase full-bridge topology. The midpoint of the three bridge arms of the inverter is connected to an LC filter, and the output voltage is the terminal voltage of the filter capacitor.

[0013] Choosing the filter capacitor voltage (i.e., the output voltage) and the filter inductor current as the controlled objects, ensuring parameter consistency in the three-phase system, and neglecting the parasitic resistance of the filter capacitor, the circuit equations are obtained according to Kirchhoff's voltage and current laws:

[0014]

[0015] In equation (1), L is the filter inductance, R is the parasitic resistance of the filter inductance L, C is the filter capacitor, and i a i b i c Let i be the three-phase current of the filter inductor. oa i ob i oc The inverter output current, u a u b u c u is the voltage at the midpoint of the inverter bridge arm. oa u ob u oc t represents the inverter output voltage, and t represents time.

[0016] By using the equal-amplitude Park transform to transform equation (1) from the three-phase stationary abc coordinate system to the mathematical model in the two-phase rotating dq coordinate system, we can obtain the following:

[0017]

[0018]

[0019] In equations (2) and (3), i d i q i od i oq u d u qu od u oq These are the d-axis and q-axis components of the filter inductor current, inverter output current, inverter bridge arm midpoint voltage, and inverter output voltage, respectively, with ω being the angular frequency.

[0020] Furthermore, the improved feedforward decoupling method is used to decouple the mathematical model from the inner current loop, resulting in a voltage loop that considers the dynamic elements of the current loop, including:

[0021] The closed-loop transfer function of the current loop is equivalent to a first-order inertial element, that is:

[0022]

[0023] In equation (6), G ci (s) is a first-order inertial element, s is the independent variable, and τ i The time constant of the current loop. k ip k is the proportionality coefficient of the inner current loop. ii Let be the integral coefficient of the inner current loop. A feedforward decoupling control approach is used to achieve voltage control decoupling, letting

[0024]

[0025] In equation (7), i dref i is the reference current along the d-axis. qref i is the reference current along the q-axis. ud i uq The output of the voltage loop PI controller, i.e.

[0026]

[0027] In equation (8), k up and k ui These are the proportional and integral coefficients of the voltage loop PI controller, u odref u oqref The reference voltages for the d and q axes;

[0028] After performing a Laplace transform on equation (7), substituting equation (6) into it yields the voltage loop considering the dynamic elements of the current loop, as shown in equation (10).

[0029]

[0030] Furthermore, the step of setting PI parameters for the inner current loop and outer voltage loop based on the voltage loop considering the dynamic link of the current loop, and obtaining the improved feedforward decoupling and PI link inverter main circuit control model based on the PI parameters of the inner current loop and outer voltage loop, includes:

[0031] The open-loop transfer function of the inner current loop is:

[0032]

[0033] In the formula, G oi (s) is the open-loop transfer function of the inner current loop, k ip k is the proportionality coefficient of the inner current loop. ii The integral coefficient of the inner current loop;

[0034] τ i The expression:

[0035]

[0036] In the formula, f s This refers to the switching frequency of the inverter.

[0037] From equation (6), the open-loop transfer function of the voltage loop is:

[0038]

[0039] In equation (14), G ou (s) is the open-loop transfer function of the voltage loop, k up τ is the voltage loop proportionality coefficient. u The integral time constant;

[0040] From equation (14), the closed-loop transfer function of the voltage loop is obtained as follows:

[0041]

[0042] In the formula, G cu (s) is the closed-loop transfer function of the voltage loop, b0 is a constant, and b1 is the integration time constant;

[0043]

[0044]

[0045] In equation (16), k is the symmetry coefficient, which can be obtained from equations (15) and (16).

[0046] k up =C / (k 1 / 2 τ i ), τ u =kτ i (17)

[0047] Substituting equation (17) into equation (14), we obtain the simplified open-loop transfer function of the voltage loop as follows:

[0048]

[0049] Open-loop crossover frequency ω of the voltage loop x satisfy:

[0050]

[0051] In the formula, G ou (jω x ) is the open-loop transfer function of the voltage loop, and j is the impedance angle of 90° in the complex frequency domain;

[0052] Equation (19) is obtained after simplification.

[0053] ω x =1 / (τ) i k 1 / 2 (20)

[0054] The phase margin γ of the voltage loop is

[0055] γ=∠G ou (jω x ) (twenty one)

[0056] From equations (18)(20)(21), we get

[0057] γ(k)=arctan([(k-1) / (2k 1 / 2 )]) (twenty two)

[0058] In the formula, γ(k) is the phase margin;

[0059] The phase margin γ(k) should be taken as 30°~60°, so:

[0060] 3≤k≤13.9282 (23)

[0061] The cutoff frequency ω of the voltage loop b for:

[0062]

[0063]

[0064] Let h = τ i ω b Substituting h into equation (25) and simplifying, we obtain the following relationship between h and k:

[0065] k 3 h 6 +(k 3 -2k 5 / 2 )h 4 -(k 2 +2k 3 / 2 )h 2 -1 = 0 (26)

[0066] If the inner ring bandwidth is at least twice the outer ring bandwidth, then...

[0067] h = τ i ω b ≤0.5 (27)

[0068] From equation (27), it can be seen that in order to satisfy the bandwidth constraint, we have

[0069] k≥10.4721 (28)

[0070] Combining this with equation (23), the range of values ​​for k that satisfy the bandwidth and phase margin constraints is obtained as follows:

[0071] 10.4721≤k≤13.9282 (29)

[0072] By connecting the second-order filtering stage in series with the differentiating stage, we obtain the transfer function G of the differentiating stage. l(s) The expression:

[0073]

[0074] In equation (30), the transfer function G of the differential element is... l(s) This is equivalent to a bandpass filter, where ω0 is the cutoff frequency of the bandpass filter and ω0 is the outer loop bandwidth. b 3 to 5 times;

[0075] The inverter main circuit control model, which includes improved feedforward decoupling and PI elements, is determined based on the open-loop transfer function of the current inner loop, the open-loop transfer function of the voltage loop, and the transfer function of the differential element.

[0076] Furthermore, the control process of the inverter main circuit control model, which includes improved feedforward decoupling and PI links, includes:

[0077] u is calculated based on the mathematical model of the input grid voltage and the main circuit topology in the two-phase rotating dq coordinate system. od u oq i od i oq ;

[0078] According to u od u oq i od i oq The reference currents of the d-axis and q-axis of the mathematical model of the two-phase rotating dq coordinate system of the main circuit topology are calculated from the reference voltages of the d and q axes of the mathematical model of the two-phase rotating dq coordinate system of the main circuit topology.

[0079] Then through the current inner loop transfer function G oi(s) and voltage outer loop transfer function G ou (s) Calculate the d-axis and q-axis components of the filter inductor current;

[0080] Through the differential element transfer function G l (s) Suppress the noise of the d-axis and q-axis components of the filter inductor current, obtain the components in the stable dq coordinates, and then convert them to obtain the stable output voltage.

[0081] A system for controlling the stable output of an inverter includes:

[0082] The acquisition module is used to acquire the grid voltage;

[0083] The processing module is used to input the grid voltage into a pre-built inverter main circuit control model that includes improved feedforward decoupling and PI links, and output a stable voltage.

[0084] The construction of the inverter main circuit control model, which includes improved feedforward decoupling and PI link, includes:

[0085] Obtain the main circuit topology of the LC inverter to be processed, analyze the main circuit topology, and determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system.

[0086] An improved feedforward decoupling method is used to decouple the inner current loop of the mathematical model, resulting in a voltage loop that considers the dynamic elements of the current loop.

[0087] Based on the voltage loop considering the dynamic link of the current loop, the PI parameters of the inner current loop and the outer voltage loop are set, and the improved feedforward decoupling and PI link inverter main circuit control model is obtained based on the PI parameters of the inner current loop and the outer voltage loop.

[0088] The beneficial effects achieved by this invention are as follows:

[0089] The inner current loop is equivalent to a first-order inertial element by employing zero-pole cancellation. Using the symmetrical optimal method, the PI parameter tuning of the outer voltage loop is simplified to the tuning of the symmetry coefficient k, and the range of values ​​for k is given based on phase margin and controller bandwidth constraints. To suppress VSI output voltage fluctuations under large disturbances, an improved feedforward control strategy is proposed. The proposed controller parameter tuning method is computationally simple, exhibits good inverter steady-state performance, and has strong practicality. Furthermore, the improved feedforward compensation strategy proposed in this paper can effectively suppress inverter output voltage fluctuations under large disturbances and improve the system's dynamic response speed. Attached Figure Description

[0090] Figure 1 This is a diagram of an inverter topology provided by the present invention;

[0091] Figure 2This is a block diagram of an improved decoupling control for a voltage loop provided by the present invention. Detailed Implementation

[0092] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0093] A method for controlling the stable output of an inverter includes:

[0094] The grid voltage is obtained and input into a pre-built inverter main circuit control model that includes improved feedforward decoupling and PI links, and a stable voltage is output.

[0095] The construction of the inverter main circuit control model, which includes improved feedforward decoupling and PI link, includes:

[0096] Obtain the main circuit topology of the LC inverter to be processed, analyze the main circuit topology, and determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system.

[0097] An improved feedforward decoupling method is used to decouple the inner current loop of the mathematical model, resulting in a voltage loop that considers the dynamic elements of the current loop.

[0098] Based on the voltage loop considering the dynamic link of the current loop, the PI parameters of the inner current loop and the outer voltage loop are set, and the improved feedforward decoupling and PI link inverter main circuit control model is obtained based on the PI parameters of the inner current loop and the outer voltage loop.

[0099] Further, the process of obtaining the main circuit topology of the LC inverter to be processed and analyzing the main circuit topology to determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system includes:

[0100] The main circuit of the LC inverter adopts a three-phase full-bridge topology. The midpoint of the three bridge arms of the inverter is connected to an LC filter, and the output voltage is the terminal voltage of the filter capacitor.

[0101] The output voltage (i.e., the voltage across the filter capacitor) and the current of the filter inductor are selected as the controlled objects. Assuming the parameters of the three-phase system are consistent, and ignoring the parasitic resistance of the filter capacitor, based on... Figure 1 Using Kirchhoff's voltage and current laws, we obtain the circuit equations:

[0102]

[0103] In equation (1), L is the filter inductance, R is the parasitic resistance of the filter inductance L, C is the filter capacitor, and i a i b i c Let i be the three-phase current of the filter inductor. oa i obi oc The inverter output current, u a u b u c u is the voltage at the midpoint of the inverter bridge arm. oa u ob u oc t represents the inverter output voltage, and t represents time.

[0104] To reduce the number of control variables and achieve zero steady-state error tracking of command values ​​through a PI controller, equation (1) is transformed from the three-phase stationary abc coordinate system to the two-phase rotating dq coordinate system using the equal-amplitude Park transformation, resulting in:

[0105]

[0106]

[0107] In equations (2) and (3), i d i q i od i oq u d u q u od u oq These are the d-axis and q-axis components of the filter inductor current, inverter output current, inverter bridge arm midpoint voltage, and inverter output voltage, respectively, with ω being the angular frequency.

[0108] Furthermore, the LC inverter employs an inner loop control strategy for inductor current and an outer loop control strategy for voltage in order to achieve independent control of the d-axis and q-axis components and better limit the output current. As shown in equations (2) and (3), the Park transformation introduces strong coupling between the d-axis and q-axis components of the system, requiring decoupling. In equation (2), the d-axis and q-axis currents, besides being controlled by the variable u... d u q In addition to the influence of the coupling voltage ωLi, it is also affected by the coupling voltage ωLi q -ωLi d and output voltage u od u oq To achieve decoupling control, reduce the impact of output voltage disturbances on the inner current loop output, and improve the system's tracking and disturbance rejection performance, a feedforward decoupling method is adopted.

[0109]

[0110] In equation (4), u md u mq For three-phase modulated wave u m The d and q axis components, k pwm For the bridge arm gain, for an SPWM inverter, there is u id u iq The output of the current loop PI controller, i.e.

[0111]

[0112] In equation (5), k ip and k ii These are the proportional and integral coefficients of the current loop PI controller, i dref i qref Let be the reference currents for the d and q axes. From equations (2) and (4), the decoupling control of the inner current loop can be obtained.

[0113] Furthermore, the improved feedforward decoupling method is used to decouple the mathematical model for the inner current loop, resulting in a voltage loop that considers the dynamic elements of the current loop, including:

[0114] According to equation (3), the d-axis and q-axis voltages are subject to the control quantity i. d i q In addition to the influence of the coupling current ωCu, it is also affected by the coupling current ωCu oq -ωCu od and output current i od i oq The impact needs to be decoupled. Through PI parameter design, the closed-loop transfer function of the current loop can be equivalent to a first-order inertial element, i.e.:

[0115]

[0116] In equation (6), τ i The time constant of the current loop. τ i The value of is very small; in this embodiment, it is 1 / 10 of the bandwidth angular frequency of the current loop. At this time, G ci Since (s)≈1, the same feedforward decoupling control approach is used to achieve voltage control decoupling, let

[0117]

[0118] In equation (7), i dref i is the reference current along the d-axis. qref i is the reference current along the q-axis. ud i uq The output of the voltage loop PI controller, i.e.

[0119]

[0120] In equation (8), k up and k ui These are the proportional and integral coefficients of the voltage loop PI controller, u odref u oqrefThese are the reference voltages for the d and q axes.

[0121] During steady-state operation of the inverter, G ci (s) can be equivalent to a proportional element, thus simplifying the decoupling design of the voltage loop. However, when large load disturbances occur, the output current changes at a large rate, exhibiting a high-frequency state. In this case, to reduce transient impacts and voltage fluctuations, G ci (s) cannot be simply regarded as a proportional element. Based on the above analysis, the voltage loop feedforward decoupling strategy is improved.

[0122] After performing a Laplace transform on equation (3), substituting equation (6) into it, we get...

[0123]

[0124] Among them, u od (s) and u oq (s) represent the d-axis and q-axis component functions of the inverter output voltage, respectively, i dref (s) and i qref (s) represent the reference current functions for the d-axis and q-axis, respectively, i od (s) and i oq (s) are the d-axis and q-axis component functions of the inverter output current, respectively;

[0125] After performing a Laplace transform on equation (7), substituting equation (6) into it yields the voltage loop considering the dynamic element of the current loop, as shown in equation (10).

[0126]

[0127] Substituting equation (10) into equation (9), it can be found that the voltage loop improved feedforward decoupling strategy shown in equation (10) can achieve the decoupling effect and takes into account the dynamic link of the current loop.

[0128] Furthermore, the PI parameter design of the inner current loop implements the differential element. Following the design principle of "inner loop first, then outer loop," the controller parameters of the inner current loop are designed first. Ignoring the current signal sampling delay and the small inertia characteristic of PWM control, the open-loop transfer function of the inner current loop can be obtained as follows:

[0129]

[0130] In the formula, G oi (s) is the open-loop transfer function of the inner current loop, k ip k is the proportionality coefficient of the inner current loop. ii The integral coefficient of the inner current loop;

[0131] Transfer function in There is a stable pole at a certain point, which is usually very close to the origin, causing a slow system response. Therefore, this pole is eliminated by using the zero point of the PI controller. Let... At this point, the closed-loop transfer function of the system is shown in equation (6), and the design formula for the current loop PI controller is:

[0132]

[0133] Bandwidth of the current loop It must be much smaller than the inverter's switching angular frequency, and in order to ensure the fast following performance of the current loop, τ i The value of should be small enough, and the bandwidth of the current loop should be equal to the inverter switching angular frequency. τ i The expression:

[0134]

[0135] In equation (13), f s This is the switching frequency of the inverter.

[0136] Furthermore, the PI parameter design of the outer voltage loop realizes the differentiating element. Ignoring the sampling delay of the voltage signal, the open-loop transfer function of the voltage loop can be obtained from equation (6) as follows:

[0137]

[0138] In equation (14), It is a Type II system, and the parameters are designed according to the "symmetric optimal" method.

[0139] From equation (14), the closed-loop transfer function of the voltage loop is obtained as follows:

[0140]

[0141] In the formula, G cu (s) is the closed-loop transfer function of the voltage loop, b0 is a constant, b1 is the integration time constant, and b2 and b3 are simplified symbols for the following formulas.

[0142]

[0143] In equation (16), k is the symmetry coefficient, which can be obtained from equations (15) and (16).

[0144] k up =C / (k 1 / 2 τ i ),τ u =kτ i (17)

[0145] Substituting equation (17) into equation (14), we obtain the simplified open-loop transfer function of the voltage loop as follows:

[0146]

[0147] The open-loop crossover frequency ωx of the voltage loop satisfies:

[0148]

[0149] After simplification, we can obtain

[0150] ω x =1 / (τ) i k 1 / 2 (20)

[0151] The phase margin γ of the voltage loop is

[0152] γ=∠G ou (jω x ) (twenty one)

[0153] From equations (18)(20)(21), we can obtain

[0154] γ(k)=arctan([(k-1) / (2k 1 / 2 )]) (twenty two)

[0155] After the above design, γ is uniquely determined by k. For system stability, the phase margin should be between 30° and 60°, which yields:

[0156] 3≤k≤13.9282 (23)

[0157] The cutoff frequency ωb of the voltage loop is:

[0158]

[0159]

[0160] Let p = τ i ω b Substituting p into equation (25) and simplifying, we can obtain the following relationship between p and k:

[0161] k 3 p 6 +(k 3 -2k 5 / 2 )p 4 -(k 2 +2k 3 / 2 )p 2 -1 = 0 (26)

[0162] Treating the inner current loop as a "sampling element," it samples the reference current signal given by the outer voltage loop. According to Shannon's sampling theorem, in order to track the signal given by the outer loop, the bandwidth of the inner loop must be at least twice the bandwidth of the outer loop. Therefore, we have...

[0163] p = τ i ω b ≤0.5 (27)

[0164] From equation (27), it can be seen that in order to satisfy the bandwidth constraint, we have

[0165] k≥10.4721 (28)

[0166] Combining this with equation (23), we can see that the range of values ​​for k that satisfy the bandwidth and phase margin constraints is:

[0167] 10.4721≤k≤13.9282 (29)

[0168] As can be seen from equations (6) and (10), the improved feedforward compensation control strategy proposed in this paper contains a differentiating element, which amplifies noise. Therefore, the second-order filter element is connected in series with the differentiating element to suppress noise. At this time, the transfer function G of the differentiating element can be obtained. l(s) The expression:

[0169]

[0170] In equation (30), G l(s) This is equivalent to a bandpass filter, where ω0 is the cutoff frequency of the bandpass filter. To ensure the dynamic characteristics of the control system, ω0 is taken as the bandwidth of the control system. b 3 to 5 times.

[0171] The inverter main circuit control model, which includes improved feedforward decoupling and PI elements, is determined based on the open-loop transfer function of the current inner loop, the open-loop transfer function of the voltage loop, and the transfer function of the differential element.

[0172] like Figure 2 As shown, the control process of the inverter main circuit control model, which includes improved feedforward decoupling and PI link, includes:

[0173] u is calculated based on the mathematical model of the input grid voltage and the main circuit topology in the two-phase rotating dq coordinate system. od u oq i od i oq ;

[0174] According to u od u oq i od i oqThe reference currents of the d-axis and q-axis of the mathematical model of the two-phase rotating dq coordinate system of the main circuit topology are calculated from the reference voltages of the d and q axes of the mathematical model of the two-phase rotating dq coordinate system of the main circuit topology.

[0175] Then through the current inner loop transfer function G oi (s) and voltage outer loop transfer function G ou (s) Calculate the d-axis and q-axis components of the filter inductor current;

[0176] Through the differential element transfer function G l (s) Suppress the noise of the d-axis and q-axis components of the filter inductor current, obtain the components in the stable dq coordinates, and then convert them to obtain the stable output voltage.

[0177] Accordingly, the present invention also provides a system for controlling the stable output of an inverter, comprising:

[0178] The acquisition module is used to acquire the grid voltage;

[0179] The processing module is used to input the grid voltage into a pre-built inverter main circuit control model that includes improved feedforward decoupling and PI links, and output a stable voltage.

[0180] The construction of the inverter main circuit control model, which includes improved feedforward decoupling and PI link, includes:

[0181] Obtain the main circuit topology of the LC inverter to be processed, analyze the main circuit topology, and determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system.

[0182] An improved feedforward decoupling method is used to decouple the inner current loop of the mathematical model, resulting in a voltage loop that considers the dynamic elements of the current loop.

[0183] Based on the voltage loop considering the dynamic link of the current loop, the PI parameters of the inner current loop and the outer voltage loop are set, and the improved feedforward decoupling and PI link inverter main circuit control model is obtained based on the PI parameters of the inner current loop and the outer voltage loop.

[0184] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0185] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0186] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0187] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0188] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of controlling a stable output of an inverter, characterized by, include: The grid voltage is obtained and input into a pre-built inverter main circuit control model that includes improved feedforward decoupling and PI links, and a stable voltage is output. The construction of the inverter main circuit control model, which includes improved feedforward decoupling and PI link, includes: Obtain the main circuit topology of the LC inverter to be processed, analyze the main circuit topology, and determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system. An improved feedforward decoupling method is used to decouple the inner current loop of the mathematical model, resulting in a voltage loop that considers the dynamic elements of the current loop. The PI parameters of the inner current loop and the outer voltage loop are set according to the voltage loop considering the dynamic link of the current loop. Based on the PI parameters of the inner current loop and the outer voltage loop, the improved feedforward decoupling and PI link inverter main circuit control model is obtained. The improved feedforward decoupling method is used to decouple the mathematical model from the inner current loop, resulting in a voltage loop that considers the dynamic elements of the current loop, including: The closed-loop transfer function of the current loop is equivalent to a first-order inertial element, that is: (6)； In formula (6), is a first-order inertia link, τ i is a time constant of the current loop, τ i = , is a proportional coefficient of the current inner loop, is an integral coefficient of the current inner loop, and voltage control decoupling is realized by using a feedforward decoupling control idea, i.e. (7)； In formula (7), is the reference current for the d-axis, is the reference current for the q-axis, od , oq , od , oq are the d-axis and q-axis components of the inverter output current and inverter output voltage, respectively, ω is the angular frequency, C is the filter capacitance, and ud , uq is the output of the voltage loop PI controller, i.e.: (8)； In formula (8), k up and k ui are proportional coefficient and integral coefficient of the voltage loop PI controller respectively, u odref and u oqref are d, q axis reference voltages; After performing a Laplace transform on equation (7), substituting equation (6) into it yields the voltage loop considering the dynamic element of the current loop, as shown in equation (10). (10)。 2. The method of claim 1, wherein, The process of acquiring the main circuit topology of the LC inverter to be processed and analyzing the main circuit topology to determine the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system includes: The main circuit of the LC inverter adopts a three-phase full-bridge topology. The midpoint of the three bridge arms of the inverter is connected to an LC filter, and the output voltage is the terminal voltage of the filter capacitor. Choosing the filter capacitor voltage (i.e., the output voltage) and the filter inductor current as the controlled objects, ensuring parameter consistency in the three-phase system, and neglecting the parasitic resistance of the filter capacitor, the circuit equations are obtained according to Kirchhoff's voltage and current laws: (1)； In formula (1), L is a filter inductance, R is a parasitic resistance of the filter inductance L, i a , i b , i c is a three-phase current of the filter inductance, i oa , i ob , i oc is an inverter output current, u a , u b , u c is an inverter bridge arm midpoint voltage, u oa , u ob , u oc is an inverter output voltage, and t is time. By using the equal-amplitude Park transform to transform equation (1) from the three-phase stationary abc coordinate system to the mathematical model in the two-phase rotating dq coordinate system, we can obtain the following: (2)； (3)； In formula (2), formula (3), i d , i q , i od , i oq , u d , u q , u od , u oq are the filtered inductor current, the inverter output current, the inverter bridge arm midpoint voltage, the d-axis and q-axis components of the inverter output voltage, respectively, and ω is the angular frequency.

3. The method of claim 2, wherein, The step of setting PI parameters for the inner current loop and outer voltage loop based on the voltage loop considering the dynamic link of the current loop, and obtaining the improved feedforward decoupling and PI link inverter main circuit control model based on the PI parameters of the inner current loop and outer voltage loop, includes: The open-loop transfer function of the inner current loop is: (11)； wherein Gp is the open loop transfer function of the current inner loop, Kp is the proportional coefficient of the current inner loop, Ki is the integral coefficient of the current inner loop; ; τ i Expression: (13)； In the formula, f s is the switching frequency of the inverter; From equation (6), the open-loop transfer function of the voltage loop is: (14)； In formula (14), is the open-loop transfer function of the voltage loop, is the proportional coefficient of the voltage loop, is the integral time constant; From equation (14), the closed-loop transfer function of the voltage loop is obtained as follows: ； wherein is the closed loop transfer function of the voltage loop, is a constant, is the integration time constant; (15)； (16)； In equation (16), k is the symmetry coefficient, which can be obtained from equations (15) and (16): (17)； Substituting equation (17) into equation (14), we obtain the simplified open-loop transfer function of the voltage loop as follows: (18)； The open loop shear frequency ω of the voltage loop x satisfies: (19)； In the formula, is the voltage loop open-loop transfer function, is the impedance angle 90° in the complex frequency domain; After simplifying equation (19), we get: (20)； The phase margin γ of the voltage loop is: (21)； From equations (18), (20), and (21), we get: (22)； In the formula, is the phase angle margin; Phase angle margin Should be taken 30° ~ 60°, get: (23)； The cut-off frequency ω of the voltage loop is given by: b is given by: (24)； (25)； Let h = τ i ω b Substitute h into equation (25) and simplify, we get the following relationship between h and k: (26)； If the inner ring bandwidth is at least twice the outer ring bandwidth, then: (27)； From equation (27), we know that in order to satisfy the bandwidth constraint, we have: (28)； Combining this with equation (23), the range of values ​​for k that satisfy the bandwidth and phase margin constraints is obtained as follows: (29)； The second-order filter link and the differential link are connected in series to obtain the transfer function G of the differential link l(s) Expression: (30)； In formula (30), the transfer function G of the differential element l(s) corresponds to a band-pass filter, ω0is the cut-off frequency of the band-pass filter, and ω0is 3-5 times the outer loop bandwidth ω b . The inverter main circuit control model, which includes improved feedforward decoupling and PI elements, is determined based on the open-loop transfer function of the current inner loop, the open-loop transfer function of the voltage loop, and the transfer function of the differential element.

4. The method of claim 3, wherein, The control process of the inverter main circuit control model, which includes improved feedforward decoupling and PI link, includes: According to the input grid voltage and the mathematical model in the two-phase rotating dq coordinate system of the main circuit topology, u od , u oq , i od , i oq are calculated. According to u od , u oq , i od , i oq and the d-axis reference voltage and the q-axis reference voltage of the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system are obtained by the mathematical model of the main circuit topology in the two-phase rotating dq coordinate system. The d-axis and q-axis components of the filtered inductance current are calculated by the current inner loop transfer function G oi (s) and the voltage outer loop transfer function G ou (s) through the differential element transfer function G l (s) suppressing the noise of the d-axis and q-axis components of the filtered inductor current, obtaining the components in the dq coordinates after stabilization, and then converting to obtain the output stabilized voltage.

5. A system for controlling the stability of an inverter output, characterized by include: An acquisition module is configured to acquire a grid voltage; A processing module is configured to input the grid voltage into a pre-constructed inverter main circuit control model comprising improved feedforward decoupling and PI links, and output a stable voltage; The construction of the inverter main circuit control model comprising improved feedforward decoupling and PI links comprises: acquiring a main circuit topology of an LC type inverter to be processed, and analyzing the main circuit topology to determine a mathematical model of the main circuit topology in a two-phase rotating dq coordinate system; applying improved feedforward decoupling to the mathematical model to decouple a current inner loop, and obtaining a voltage loop considering a dynamic link of the current loop; setting PI parameters of the current inner loop and the voltage outer loop according to the voltage loop considering the dynamic link of the current loop, and obtaining the inverter main circuit control model comprising improved feedforward decoupling and PI links according to the PI parameters of the current inner loop and the voltage outer loop; the improved feedforward decoupling to the mathematical model to decouple the current inner loop, and obtaining the voltage loop considering the dynamic link of the current loop, comprises: equivalent the closed-loop transfer function of the current loop to a first-order inertia link, that is: (6)； In formula (6), is a first-order inertia link, τ i is a time constant of the current loop, τ i = , is a proportional coefficient of the current inner loop, is an integral coefficient of the current inner loop, voltage control decoupling is realized by using the idea of feedforward decoupling control, and (7)； In equation (7), The reference current for the d-axis is... i is the reference current along the q-axis. od i oq u od u oq ω represents the d-axis and q-axis components of the inverter output current and output voltage, respectively, C represents the filter capacitor, and i represents the angular frequency. ud i uq The output of the voltage loop PI controller is: (8)； In formula (8), k up and k ui are proportional coefficient and integral coefficient of the voltage loop PI controller respectively, u odref and u oqref are d, q axis reference voltages; after Laplace transformation is performed on formula (7), formula (6) is substituted into formula (7), and the voltage loop considering the dynamic link of the current loop is obtained, as shown in formula (10), (10)。

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