Control method of damping controller for suppressing middle-frequency resonance of power grid port

Abstract

The invention discloses a control method of a damping controller for suppressing the medium-frequency resonance of a power grid port, the damping controller comprises a power outer loop control unit and a voltage and current inner loop control unit, and the power outer loop control unit comprises a direct current bus voltage loop, an active power outer loop and a reactive power outer loop. The voltage and current inner loop control unit comprises an AC voltage loop and an AC current loop. According to the control method of the damping controller, intermediate-frequency resonance between near-end or background harmonic voltage and power grid equipment can be effectively suppressed, the adaptability of grid-connected equipment to a weak power grid is improved, and meanwhile a certain compensation effect on harmonic current is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a control method of a damping controller for suppressing mid-frequency resonance at a grid port. BACKGROUND

[0002] As one of the main energy sources of new energy power generation, the large-scale access of wind power to the power system has led to serious power quality problems in some areas. In the wind power grid-connected system, the electrical energy output by the wind power needs to be connected to the AC power grid through a converter, and the output current of the converter often fails to meet the harmonic requirements. In addition, there are a large number of power electronic conversion devices in the grid-connected system, and there is interaction between the devices and between the devices and the line impedance, which can easily cause a series of resonance problems.

[0003] For resonance, there are many causes, among which the existence of voltage and current harmonics is a key factor causing network resonance of the system, and in a parallel network, impedance remodeling in a specific frequency band can also provide necessary damping effect to the resonance system, so a resonance suppression and filtering device with fast dynamic response is the core to solve the problem.

[0004] The existing quality management solutions are: 1) using a current source type active power filter to eliminate harmonics; 2) using a voltage source type active power filter to filter harmonic voltage; 3) using a passive filter to eliminate harmonics; and 4) a hybrid filter. Among them, the current source type active power filter has the following disadvantages: the stability of the multi-parallel system is significantly reduced, and the response speed of the phase-locked loop is slow (when the response speed of the phase-locked loop is fast, the system stability is poor); the voltage source type active power filter has the following disadvantages: the response speed of the phase-locked loop is slow (when the response speed of the phase-locked loop is fast, the system stability is poor), and the system loop architecture results in slow dynamic response speed of the harmonic voltage ring; the passive filter has the following disadvantages: large-capacity inductors and capacitors are additionally added, which are easy to resonate with the grid impedance, can only filter specific harmonics, and may cause over-compensation or under-compensation; and the hybrid filter has the following disadvantages: high system complexity, and the need for a coordinated control strategy.

[0005] Therefore, how to solve the above technical problems and achieve the suppression of near-end or background harmonic voltage and mid-frequency resonance between grid devices while having a certain compensation effect on harmonic current is the direction that the person skilled in the art is committed to researching. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a control method of a damping controller for suppressing mid-frequency resonance at a grid port.

[0007] To achieve the above object, the technical scheme adopted by the present application is: a control method of a damping controller for inhibiting intermediate frequency resonance in a power grid port, the damping controller comprising a power outer loop control unit and a voltage and current inner loop control unit, the power outer loop control unit comprising a DC bus voltage loop, an active power outer loop and a reactive power outer loop, the voltage and current inner loop control unit comprising an AC voltage loop and an AC current loop, the control method of the damping controller comprising the following steps:

[0008] 1) the DC bus voltage loop adopts PI control, and the output thereof is taken as the given value of the active power outer loop; the active power outer loop adopts P control, and the output thereof is superposed with the frequency ω gLPF of the power grid to obtain the control output frequency, and the control output frequency is taken through integration to obtain the reference voltage phase θ;

[0009] 2) the fundamental wave voltage U a , U b , U c on the high-pass capacitor side of the damping controller is sampled, the reference voltage phase θ output by the active power outer loop is adopted, and the components U d , U q , V0 of the fundamental wave voltage are calculated by using abc / dq constant-amplitude transformation, and the specific expression is as follows:

[0010]

[0011] 3) the components U d , U q of the fundamental wave voltage obtained in step 2) are taken to calculate the fundamental wave voltage amplitude V g by using the following formula, and the fundamental wave voltage amplitude is taken as the reference voltage V g in the reactive power outer loop; the output of the reactive power outer loop is superposed with the value of the reference voltage V ref to obtain the reference voltage amplitude V la of the AC voltage loop;

[0012]

[0013] 4) the fundamental wave current I lb , I lc on the bridge side of the damping controller is sampled, the reference voltage phase θ output by the active power outer loop is adopted, and the components I d , I q , I0 of the fundamental wave current are calculated by using abc / dq constant-amplitude transformation;

[0014]

[0015] 5) the frequency ω g of the power grid voltage is obtained by phase locking the power grid voltage, and the filtered frequency ω gLPF is obtained through first-order low-pass filtering;

[0016] 6) The component U of the fundamental voltage d U q and the component I of the fundamental current d I q Calculations are performed to obtain the actual output active power P. fd and reactive power Q fd The specific expression is as follows:

[0017]

[0018] 7) By using the reference voltage amplitude V ref The reference voltage V in the two-phase coordinate system is calculated from the phase θ of the reference voltage. α and V β The specific expression is as follows:

[0019]

[0020] Then, using the reference voltage V α and V β The reference voltage V in the three-phase abc coordinate system was calculated. a V b V c The specific expression is as follows:

[0021]

[0022] 8) Using the reference voltage in the three-phase abc coordinate system obtained in step 7) as the given command for the AC voltage loop, the fundamental voltage U on the high-pass capacitor side... a U b U c As the feedback value of the AC voltage loop, the AC current loop outputs a command after being controlled by the AC voltage loop.

[0023] As a specific implementation, the control method further includes step 9): the AC current loop is given and the inductor current feedback is fed through the control output modulation signal of the AC current loop to generate three-phase drive signals Sa, Sb, and Sc.

[0024] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0025] 1) The basic control architecture of the damping controller mentioned in the technical solution of the present invention utilizes the charging and discharging characteristics of the DC bus capacitor to redesign the structure of the power outer loop control unit, thereby improving the stability of the system and providing a certain degree of active support capability, thus enhancing the reliability of the power grid.

[0026] 2) The control method of the application makes the device port present voltage source characteristics, significantly improving the adaptability of the grid-connected device itself to weak grids;

[0027] 3) The reference voltage V g generated by the fundamental voltage positive sequence detection in the control method of the application and the frequency ω g of the grid voltage generated by the phase-locked loop meet the requirements of damping controller in realizing the suppression of mid-frequency resonance in the grid port and wide grid voltage and wide working frequency range. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The control block diagram of the damping controller for suppressing mid-frequency resonance in the grid port according to the application;

[0029] Figure 2 The flow chart of power calculation in the control method of the damping controller for suppressing mid-frequency resonance in the grid port according to the application;

[0030] Figure 3 The control block diagram of the phase-locked loop in the control method of the damping controller for suppressing mid-frequency resonance in the grid port according to the application;

[0031] Figure 4 The high-pass capacitor side fundamental voltage positive sequence voltage detection block diagram of the damping controller for suppressing mid-frequency resonance in the grid port according to the application. DETAILED DESCRIPTION

[0032] The technical solutions of the application will be further described below in combination with the accompanying drawings Figures 1-4 and specific embodiments.

[0033] A control method of a damping controller for suppressing mid-frequency resonance in the grid port, the damping controller comprising a power outer loop control unit and a voltage and current inner loop control unit, the power outer loop control unit comprising a DC bus voltage loop, an active power outer loop and a reactive power outer loop, and the voltage and current inner loop control unit comprising an AC voltage loop and an AC current loop.

[0034] Here, the power outer loop control unit is redesigned by using the characteristics of charging and discharging of the DC bus capacitor, improving the stability of the system, making it have certain active support ability and enhancing the reliability of the grid.

[0035] The control method of the damping controller comprises the following steps:

[0036] 1) The DC bus voltage loop adopts PI control, and the output thereof is given as the active power outer loop; the active power outer loop adopts P control, and the output thereof is superimposed with the grid frequency ω gLPF to obtain the control output frequency, and the control output frequency is integrated to obtain the reference voltage phase θ;

[0037] 2) Sampling damping controller high-pass capacitor side fundamental voltage U a U b U c Using the phase θ of the reference voltage output from the active power outer loop, the component U of the fundamental voltage is calculated using the abc / dq constant amplitude transformation. d U q V0, the specific expression is as follows:

[0038]

[0039] 3) Based on the fundamental voltage component U obtained in step 2), d U q The fundamental voltage amplitude is calculated using the following formula and used as the reference voltage V in the reactive power outer loop. g The output of the reactive power outer loop and the reference voltage V g The superimposed value is used as the reference voltage amplitude V of the AC voltage loop. ref ;

[0040]

[0041] 4) Sampling damping controller bridge-side fundamental current I la I lb I lc Using the reference voltage phase θ of the active power outer loop output, the component I of the fundamental current is calculated by abc / dq constant amplitude transformation. d I q 、I0;

[0042]

[0043] 5) Obtain the frequency ω of the grid voltage through grid voltage phase-locking. g The filtered frequency ω is obtained after a first-order low-pass filter. gLPF ;

[0044] 6) The component U of the fundamental voltage d U q and the component I of the fundamental current d I q Calculations are performed to obtain the actual output active power P. fd and reactive power Q fd The specific expression is as follows:

[0045]

[0046] 7) By using the reference voltage amplitude V ref The reference voltage V in the two-phase coordinate system is calculated from the phase θ of the reference voltage.α and V β , the specific expression is as follows:

[0047]

[0048] Then the reference voltage V α and V β The reference voltage V a , V b , V c in the three-phase abc coordinate system is calculated, the specific expression is as follows:

[0049]

[0050] 8) The reference voltage in the three-phase abc coordinate system obtained in step 7) is taken as the given instruction of the alternating current voltage loop, the fundamental voltage U a , U b , U c on the high-pass capacitor side is taken as the feedback value of the alternating current voltage loop, and the alternating current voltage loop is controlled to output the alternating current loop given instruction;

[0051] 9) The alternating current loop given and the inductance current feedback are controlled to output the modulation signal through the alternating current loop, and the three-phase drive signal Sa, Sb, Sc is generated.

[0052] Here, V g is generated by the fundamental voltage positive sequence detection, and ω g is generated by the phase-locked loop to meet the requirements of damping controller in realizing the suppression of medium frequency resonance in the grid port and wide grid voltage and wide working frequency range; in addition, through the characteristics of the instantaneous fundamental voltage loop in the wide frequency range and high gain, the voltage source characteristics are enhanced, the harmonic voltage is effectively controlled, and the grid-side voltage is purified.

[0053] The above embodiments are only for illustrating the technical concept and characteristics of the present application, the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A control method for a damping controller to suppress intermediate frequency resonance at a power grid port, characterized in that, The damping controller includes a power outer loop control unit and a voltage and current inner loop control unit. The power outer loop control unit includes a DC bus voltage loop, an active power outer loop, and a reactive power outer loop. The voltage and current inner loop control unit includes an AC voltage loop and an AC current loop. The control method of the damping controller includes the following steps: 1) The DC bus voltage loop uses PI control, and its output serves as the reference for the active power outer loop. The active power outer loop uses P control, and its output is related to the grid frequency ω. gLPF The control output frequency is obtained by superposition, and the reference voltage phase θ is obtained by integration of the control output frequency. 2) Sampling damping controller high-pass capacitor side fundamental voltage U a U b U c Using the phase θ of the reference voltage output from the active power outer loop, the component U of the fundamental voltage is calculated using the abc / dq constant amplitude transformation. d U q V0, the specific expression is as follows: 3) Based on the fundamental voltage component U obtained in step 2), d U q The fundamental voltage amplitude is calculated using the following formula and used as the reference voltage V in the reactive power outer loop. g The output of the reactive power outer loop and the reference voltage V g The superimposed value is used as the reference voltage amplitude V of the AC voltage loop. ref ; 4) Sampling damping controller bridge-side fundamental current I la I lb I lc Using the reference voltage phase θ of the active power outer loop output, the component I of the fundamental current is calculated by abc / dq constant amplitude transformation. d I q 、I0; 5) Obtain the frequency ω of the grid voltage through grid voltage phase-locking. g The filtered frequency ω is obtained after a first-order low-pass filter. gLPF ; 6) The component U of the fundamental voltage d U q and the component I of the fundamental current d I q Calculations are performed to obtain the actual output active power P. fd and reactive power Q fd The specific expression is as follows: 7) By using the reference voltage amplitude V ref The reference voltage V in the two-phase coordinate system is calculated from the phase θ of the reference voltage. α and V β The specific expression is as follows: Then, using the reference voltage V α and V β The reference voltage V in the three-phase abc coordinate system was calculated. a V b V c The specific expression is as follows: 8) Using the reference voltage in the three-phase abc coordinate system obtained in step 7) as the given command for the AC voltage loop, the fundamental voltage U on the high-pass capacitor side... a U b U c As the feedback value of the AC voltage loop, the AC current loop outputs a command after being controlled by the AC voltage loop.

2. The control method for a damping controller to suppress intermediate frequency resonance at a power grid port according to claim 1, characterized in that, The control method further includes step 9): the AC current loop is given and the inductor current feedback is fed through the control output modulation signal of the AC current loop to generate three-phase drive signals Sa, Sb, and Sc.

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