Near-end information estimation-based grid-connected converter voltage support control method

Abstract

The invention discloses a grid-connected converter voltage support control method based on near-end information estimation, and belongs to the technical field of grid-connected conversion. The control strategy technology comprises the following steps: (1) grid-connected point voltage estimation; (2) generating a reactive instruction; and (3) current loop control. Compared with the prior art, the grid-connected point information can be estimated only by sampling the machine side current and the capacitor voltage, the hardware cost of a sampling circuit is saved, communication delay is avoided, and the rapidity and precision of voltage support are guaranteed.

Description

Technical Field

[0001] The present invention belongs to the field of electrical engineering and relates to a grid-connected converter technology, and in particular to a grid-connected converter voltage support control method based on proximal information estimation. Background Art

[0002] As the proportion of new energy sources connected to the power grid continues to increase, the power grid gradually shows the characteristics of a weak power grid, and there is an urgent need for grid-connected converters to provide voltage support for the power grid to a certain extent. At present, most new energy grid-connected converters use current loop control and have a certain overload capacity, which creates favorable conditions for transforming the existing grid-connected converter control system and outputting reactive power to support the grid voltage.

[0003] The document "Sun Biaoguang, Yang Zekun. Active damping strategy of capacitor current feedback for LCL type grid-connected inverter based on second-order phase compensator [J]. Acta Energiae Solaris Sinica, 2024, 45(08): 229-239. DOI: 10.19912 / j.0254-0096.tynxb.2023-0640." proposes an active damping strategy based on capacitor current detection. However, this method increases the capacitor current sampling and increases the initial construction cost of the grid-connected converter.

[0004] "N.-B. Lai, A. Tarrasó, G.N. Baltas, L.V. Marin Arevalo and P. Rodriguez. External Inertia Emulation Controller for Grid-Following Power Converter. IEEE Transactions on Industry Applications, vol. 57, no. 6, pp. 6568-6576, Nov.-Dec. 2021, doi: 10.1109 / TIA.2021.3108350." Aβplications, Vol. 57, No. 6, pp. 6568-6576, Nov-Dec 2021, doi: 10.1109 / TIA.2021.3108350.) A station controller is proposed to detect the grid voltage signal in real time, calculate the power reference value of each grid-connected converter in the station, and send it to the grid-connected converter through industrial communication means, so as to achieve voltage support. However, there is a certain delay in industrial communication, which affects the control performance of voltage support.

[0005] In summary, the existing solutions still have the following disadvantages:

[0006] 1) It is difficult for existing grid-connected converters to detect the grid-connected point voltage and grid-connected current. They can only sample the machine-side current and capacitor voltage, which makes the voltage support control less accurate.

[0007] 2) The power instructions of existing grid-connected converters are usually issued by the station controller communication, which has a certain delay, affecting the speed and accuracy of voltage support, and is prone to reverse adjustment; Summary of the invention

[0008] The problem to be solved by the present invention is to overcome the limitations of the above-mentioned scheme and propose a grid-connected converter voltage support control method based on proximal information estimation. The control method does not change the adoption point of the original grid-connected converter. It can estimate the grid-connected point voltage and other information only based on the machine-side current and capacitor voltage, and utilizes the overload design of the grid-connected converter to support and control the grid-connected voltage through the estimated value.

[0009] To solve the technical problem of the present invention, the present invention provides a grid-connected converter voltage support control method based on proximal information estimation. The topological structure of the grid-connected converter to which the control method is applied includes a DC side power supply, a converter, a three-phase LC filter, a transformer and a three-phase grid impedance. The three-phase LC filter includes a three-phase filter inductor, a three-phase filter capacitor and a three-phase damping resistor; the DC side power supply, the converter, the three-phase filter inductor, the transformer and the three-phase grid impedance are connected in series in sequence, and the other end of the three-phase grid impedance is connected to the three-phase grid; one end of the three-phase filter capacitor is connected between the three-phase filter inductor and the transformer, and the other end is connected to the three-phase damping resistor, and the other end of the three-phase damping resistor is grounded; the voltage support control method includes grid point voltage estimation, reactive power command generation and current loop control, and includes the following steps:

[0010] Step 1: Grid connection point voltage estimation

[0011] Step 1.1, sample the actual value of the three-phase filter capacitor voltage v c_A , v c_B , v c_C , phase-lock it to get the capacitor voltage frequency ω c and the capacitor voltage dq axis component V c_d , V c_q , for capacitor voltage frequency ω c Integrate to get the capacitor voltage phase angle θ c ;

[0012] Sampling the actual value of the current on the converter side i inv_A ,i inv_B ,i inv_C And the current αβ axis component i of the converter side current is obtained by the current transformation formula 1 from the three-phase stationary coordinate system to the two-phase stationary coordinate system inv_α ,i inv_β Then, the current dq axis component I of the converter side is obtained by the current transformation formula 2 from the two-phase stationary coordinate system to the rotating coordinate system. inv_d , I inv_q ;

[0013] Step 1.2, calculate the estimated value of the three-phase filter capacitor current dq axis I c_d , I c_q and the estimated value of the grid-connected point voltage dq axis V pcc_d , V pcc_q , and its calculation formula is:

[0014]

[0015] Among them, C f is the capacitance of the three-phase filter capacitor, R d is the resistance of the three-phase damping resistor, L t is the leakage inductance value of the grid-connected transformer;

[0016] Step 2: Reactive power command generation

[0017] Step 2.1, estimate the value V according to the dq axis of the grid connection point voltage pcc_d , V pcc_q , calculate the estimated value of the grid voltage amplitude V pccM , Given the grid-connected point voltage amplitude rated value V nAmp , and calculate the grid-connected point voltage amplitude rated value V nAmp The estimated value of the voltage amplitude at the grid connection point V pccM Deviation ΔV pccM , ΔV pccM =V nAmp -V pccM ;

[0018] Calculate reactive power command Q set , the calculation formula is as follows:

[0019]

[0020] Among them, k p_qset is the proportional coefficient of the voltage-reactive loop, k i_qset is the integral coefficient of the voltage-reactive loop, s is the Laplace operator, and ε is the deviation integral action range ratio;

[0021] Step 2.2, for reactive power command Q set Limit and obtain the reactive power instruction Q after limitation set_lim , the calculation formula is as follows:

[0022]

[0023] Among them, S n is the rated capacity of the grid-connected converter, λ is the reactive power instruction limit multiple;

[0024] Step 3, current loop control

[0025] According to the given active power command P set and the reactive power command Q after limitation set_lim Calculate the current dq axis command I on the converter side inv_dset , I inv_qset , the calculation formula is as follows:

[0026]

[0027] Calculate the d-axis component U of the modulation wave voltage md and the modulation wave voltage q-axis component U mq , the calculation formula is as follows:

[0028]

[0029] Among them, k iP is the proportionality coefficient of the current loop, k iI is the integral coefficient of the current loop, k f is the voltage feed-forward coefficient, k d is the dq decoupling coefficient.

[0030] Preferably, the current transformation formula 1 and the current transformation formula 2 in step 1 are as follows:

[0031]

[0032]

[0033] The beneficial effects of the present invention relative to the prior art are:

[0034] 1. Only sampling the machine-side current and capacitor voltage is required to estimate the grid connection point information, saving the hardware cost of the sampling circuit;

[0035] 2. Communication delay is avoided, and the speed and accuracy of voltage support are guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The topological structure diagram of the grid-connected converter to which the control method of the present invention is applied.

[0037] Figure 2 The figure is a simplified diagram of a grid-connected voltage support control method based on proximal information estimation involving the control method of the present invention.

[0038] Figure 3 It is the voltage waveform of the grid connection point when the control method of the present invention is not adopted.

[0039] Figure 4 The voltage waveform of the grid connection point using the control method of the present invention. DETAILED DESCRIPTION

[0040] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0041] Figure 1 The topological structure diagram of the grid-connected converter to which the control method of the present invention is applied is as follows: Figure 1It can be seen that the topological structure of the grid-connected converter to which the control method is applied includes a DC side power supply, a converter, a three-phase LC filter, a transformer and a three-phase grid impedance, wherein the three-phase LC filter includes a three-phase filter inductor, a three-phase filter capacitor and a three-phase damping resistor. The DC side power supply, the converter, the three-phase filter inductor, the transformer and the three-phase grid impedance are connected in series in sequence, and the other end of the three-phase grid impedance is connected to the three-phase grid; one end of the three-phase filter capacitor is connected between the three-phase filter inductor and the transformer, and the other end is connected to the three-phase damping resistor, and the other end of the three-phase damping resistor is grounded.

[0042] exist Figure 1 Up, V dc is the DC side voltage, R g is the resistance value of the resistor in the three-phase power grid impedance, L g is the inductance value of the three-phase grid impedance, Grid is the three-phase grid, PCC is the common coupling point. 10 represents the DC side power supply, 20 represents the converter, 30 represents the three-phase LC filter, 40 represents the transformer leakage inductance, 50 represents the three-phase line impedance, and 60 represents the three-phase grid.

[0043] The grid-connected converter circuit parameters in this embodiment are: V dc =770V, the rated output line voltage of the converter is 380V / 50Hz, the rated power of the converter is 20kW, C f =11.6uF, R d =2.1811Ω, L f =0.9mH, L t =1.4mH, L g =7.7mH, R g =0.27Ω. In this embodiment, the converter is a three-phase full-bridge inverter circuit.

[0044] Figure 2 FIG. 1 is a schematic diagram of a grid-connected voltage support control method based on proximal information estimation related to the control method of the present invention. Figure 2 It can be seen that the voltage support control method of the present invention includes grid connection point voltage estimation, reactive power command generation and current loop control, and includes the following steps:

[0045] Step 1: Grid connection point voltage estimation

[0046] Step 1.1, sample the actual value of the three-phase filter capacitor voltage v c_A , v c_B , v c_C , phase-lock it to get the capacitor voltage frequency ω c and the capacitor voltage dq axis component V c_d , V c_q , for capacitor voltage frequency ω c Integrate to get the capacitor voltage phase angle θc ;

[0047] Sampling the actual value of the current on the converter side i inv_A ,i inv_B ,i inv_C And the current αβ axis component l of the converter side current is obtained by the current transformation formula 1 from the three-phase stationary coordinate system to the two-phase stationary coordinate system inv_α ,i inv_β Then, the current dq axis component I of the converter side is obtained by the current transformation formula 2 from the two-phase stationary coordinate system to the rotating coordinate system. inv_d ,i inv_q .

[0048] In this embodiment, the current transformation formula 1 and the current transformation formula 2 are as follows:

[0049]

[0050]

[0051] Step 1.2, calculate the estimated value of the three-phase filter capacitor current dq axis I c_d , I c_q and the estimated value of the grid-connected point voltage dq axis V pcc_d , V pcc_q , and its calculation formula is:

[0052]

[0053] Among them, C f is the capacitance of the three-phase filter capacitor, R d is the resistance of the three-phase damping resistor, L t is the leakage inductance of the grid-connected transformer.

[0054] Step 2: Reactive power command generation

[0055] Step 2.1, estimate the value V according to the dq axis of the grid connection point voltage pcc_d , V pcc_q , calculate the estimated value of the grid voltage amplitude V pccM , Given the grid-connected point voltage amplitude rated value V nAmp , and calculate the grid-connected point voltage amplitude rated value V nAmp The estimated value of the voltage amplitude at the grid connection point V pccM Deviation ΔV pccM , ΔV pccM =V nAmp -V pccM .

[0056] Calculate reactive power command Q set , the calculation formula is as follows:

[0057]

[0058] Among them, k p_qset is the proportional coefficient of the voltage-reactive loop, k i_qset is the integral coefficient of the voltage-reactive loop, s is the Laplace operator, and ε is the deviation integral action range ratio.

[0059] Step 2.2, for reactive power command Q set Limit the reactive power command Q after the limit set_lim , the calculation formula is as follows:

[0060]

[0061] Among them, S n is the rated capacity of the grid-connected converter, and λ is the reactive power instruction limit multiple.

[0062] Step 3, current loop control

[0063] According to the given active power command P set and the reactive power command Q after limitation set_lim Calculate the current dq axis command I on the converter side inv_dset , I inv_qset , the calculation formula is as follows:

[0064]

[0065] Calculate the d-axis component U of the modulation wave voltage md and the modulation wave voltage q-axis component U mq , the calculation formula is as follows:

[0066]

[0067] Among them, k iP is the proportionality coefficient of the current loop, k iI is the integral coefficient of the current loop, k f is the voltage feed-forward coefficient, k d is the dq decoupling coefficient.

[0068] In this embodiment, k p_qset =60, k i_qset =10000,ε=10%,S n =20000,λ=0.83,k iP =5, k iI =200, k f =0, k d =0.

[0069] In order to verify the beneficial effects of the present invention, the present invention was simulated. Figure 3The voltage waveform of the grid connection point when the control method of the present invention is not adopted is: Figure 4 The voltage waveform of the grid connection point using the control method of the present invention. When the simulation runs for 1s, the grid voltage amplitude drops to 0.9pu, and when the simulation runs for 1.5s, the grid voltage amplitude reaches 1pu. Figure 3 and Figure 4 It can be seen from the comparison that by adopting the control method of the present invention, the grid-connected voltage of the converter is effectively supported.

Claims

1. A voltage support control method for a grid-connected converter based on proximal information estimation, wherein the topological structure of the grid-connected converter to which the control method is applied comprises a DC side power supply, a converter, a three-phase LC filter, a transformer and a three-phase grid impedance, wherein the three-phase LC filter comprises a three-phase filter inductor, a three-phase filter capacitor and a three-phase damping resistor; the DC side power supply, the converter, the three-phase filter inductor, the transformer and the three-phase grid impedance are sequentially connected in series, and the other end of the three-phase grid impedance is connected to the three-phase grid; one end of the three-phase filter capacitor is connected between the three-phase filter inductor and the transformer, and the other end is connected to the three-phase damping resistor, and the other end of the three-phase damping resistor is grounded; characterized in that The voltage support control method includes grid connection point voltage estimation, reactive power instruction generation and current loop control, and includes the following steps: Step 1: Grid connection point voltage estimation Step 1.1, sample the actual value of the three-phase filter capacitor voltage v c_A , v c_B , v c_c , phase-lock it to get the capacitor voltage frequency ω c and the capacitor voltage dq axis component V c_d , V c_q , for capacitor voltage frequency ω c Integrate to get the capacitor voltage phase angle θ c ; Sampling the actual value of the current on the converter side i inv_A ,i inv_B ,i inv_C And the current αβ axis component i of the converter side current is obtained by the current transformation formula 1 from the three-phase stationary coordinate system to the two-phase stationary coordinate system inv_α ,i inv_β Then, the current dq axis component I of the converter side is obtained by the current transformation formula 2 from the two-phase stationary coordinate system to the rotating coordinate system. inv_d ,i inv_q ; Step 1.2, calculate the estimated value of the three-phase filter capacitor current dq axis I c_d , I c_q and the estimated value of the grid-connected point voltage dq axis V pcc_d , V pcc_q , and its calculation formula is: Among them, C f is the capacitance of the three-phase filter capacitor, R d is the resistance of the three-phase damping resistor, L t is the leakage inductance value of the grid-connected transformer; Step 2: Reactive power command generation Step 2.1, estimate the value V according to the dq axis of the grid connection point voltage pcc_d , V pcc_q , calculate the estimated value of the grid voltage amplitude V pccM , Given the grid-connected point voltage amplitude rated value V nAmp , and calculate the grid-connected point voltage amplitude rated value V nAmp The estimated value of the voltage amplitude at the grid connection point V pccM Deviation ΔV pccM , ΔV pccM =V nAmp -V pccM ; Calculate reactive power command Q set , the calculation formula is as follows: Among them, k p_qset is the proportional coefficient of the voltage-reactive loop, k i_qset is the integral coefficient of the voltage reactive loop, s is the Laplace operator, and v is the deviation integral action range ratio; Step 2.2, for reactive power command Q set Limit and obtain the reactive power instruction Q after limitation set_lim , the calculation formula is as follows: Among them, S n is the rated capacity of the grid-connected converter, λ is the reactive power instruction limit multiple; Step 3, current loop control According to the given active power command P set and the reactive power command Q after limitation set_lim Calculate the current dq axis command I on the converter side inv_dset , I inv_qset , the calculation formula is as follows: Calculate the d-axis component U of the modulation wave voltage md and the modulation wave voltage q-axis component U mq , the calculation formula is as follows: Among them, k iP is the proportionality coefficient of the current loop, k iI is the integral coefficient of the current loop, k f is the voltage feed-forward coefficient, k d is the dq decoupling coefficient.

2. The method for controlling grid-connected converter voltage support based on proximal information estimation according to claim 1, characterized in that: The current transformation formula 1 and the current transformation formula 2 in step 1 are as follows:

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