A method for rapidly supporting AC-side grid control in a DC system

Abstract

This invention provides a method for rapidly supporting the AC-side power grid control in a DC system. The method includes: setting power grid operating threshold ranges for three control strategies (approximation control, precise adjustment, and constant output) considering angular frequency deviation, rate of change, and integral quantity; establishing fuzzy PID control rules required for the approximation control strategy; measuring the real-time voltage value at the grid connection point using a voltage transformer (TV) to calculate the angular frequency deviation, rate of change, and integral quantity; determining the current operating range of the power grid by judging the angular frequency deviation, rate of change, and integral quantity; and then controlling the DC system to switch between the three strategies according to the operating state to achieve rapid support for the AC-side power grid. This invention can precisely adjust the control system parameters according to the real-time conditions of the AC power grid, improving the inertia damping level of the power grid.

Description

Technical Field

[0001] This invention relates to the field of DC system control technology, specifically a method for DC systems to quickly support AC-side grid control. Background Technology

[0002] New energy systems, characterized by volatility, intermittency, and randomness, exacerbate grid frequency oscillations, seriously threatening the safe and stable operation of the grid. While traditional synchronous generators, with their large inertia and strong damping characteristics, can support grid stability to some extent, their frequency regulation capabilities are gradually becoming insufficient as the proportion of new energy installed capacity increases. In recent years, DC transmission technology has developed rapidly, with its quantity and capacity gradually increasing, providing a new approach to quickly support the stable operation of the grid.

[0003] DC systems typically employ PI control strategies. However, PI control has inherent limitations, such as susceptibility to integral saturation and system overshoot, which affect grid stability. To address this, some researchers have adopted fuzzy PID control to improve control performance. However, fuzzy PID control struggles to simultaneously consider multiple system parameters, limiting the potential of DC systems in supporting AC grids. Therefore, there is an urgent need to research control methods that can comprehensively consider multiple system parameters and fully leverage the advantages of DC systems in supporting AC grids, thereby enhancing grid stability and reliability. Summary of the Invention

[0004] In view of this, this invention addresses the shortcomings of current DC system control methods by proposing a control method for DC systems to quickly support AC-side power grids. This method considers the effects of angular frequency deviation, rate of change, and integral quantity indices, enabling DC systems to quickly support AC-side power grids.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for rapidly supporting AC-side grid control in a DC system includes the following steps:

[0007] Step 1: Based on the operation of the power grid where the DC system is located, set the power grid operation threshold range for three control strategies. The three control strategies include approximation control, precise regulation, and constant output. The power grid operation threshold range includes angular frequency deviation, rate of change, and integral quantity index.

[0008] Step 2: Based on the threshold range of the approximation control strategy, establish the required fuzzy PID control rules to obtain the proportional coefficient, derivative coefficient, and integral coefficient of the approximation control strategy.

[0009] Step 3: Measure the real-time voltage value at the grid connection point using a voltage transformer (TV), and calculate the angular frequency deviation, rate of change, and integral quantity;

[0010] Step 4: Determine the grid operating range by using angular frequency deviation, rate of change, integral quantity, and grid operating threshold range. Based on the determined grid operating range, control the DC system to switch between three strategies to achieve rapid support for the AC grid.

[0011] Furthermore, in step one, the angular frequency deviation Δω and the rate of change R of the approximation control strategy are set. ω The maximum and minimum control thresholds, wherein the control thresholds are respectively Δω m , Δω n R m R n ; Set the angular frequency deviation Δω and rate of change R of the precise adjustment strategy ω and integral quantity I ω The maximum and minimum control thresholds, wherein the control thresholds are respectively Δω pm , Δω pn R pm R pn I m I n .

[0012] Furthermore, step two specifically includes:

[0013] Based on the power grid operating threshold range, the angular frequency deviation and rate of change in the threshold range of the approximation control strategy are fuzzified, and their fuzzy subsets are positive large, positive medium, positive small, zero, negative small, negative medium, and negative large. A trapezoidal membership function is adopted, and a proportional coefficient k is established according to the actual operating conditions. p Differential coefficient k i and integral coefficient k d Fuzzy rule table;

[0014] The fuzzy PID parameter adjustment expression for the approximation control strategy, obtained from the fuzzy rule table, is as follows:

[0015] k p (k)=k p (k-1)+Δk p (k)

[0016] k i (k)=k i (k-1)+Δk i (k)

[0017] k d (k)=k d (k-1)+Δk d (k)

[0018] Where, Δk p (k), Δk i (k), Δk d(k) represents the adjustment amounts of the proportional coefficient, derivative coefficient, and integral coefficient of the approximation control strategy at the k-th sampling time;

[0019] The proportional coefficient, derivative coefficient, and integral coefficient of the approximation control strategy are obtained by using the fuzzy PID parameter adjustment expression.

[0020] Furthermore, step three, which calculates the angular frequency deviation, rate of change, and integral, specifically includes:

[0021] Calculate the angular frequency deviation using the following formula:

[0022] Δω(k)=ω ref -ω′(k)

[0023] Where Δω(k) is the angular frequency deviation value at the kth sampling; ω ref ω is the reference value for angular frequency; ω'(k) is the average angular frequency value at the kth sampling.

[0024] The rate of change of angular frequency is calculated using the following formula:

[0025]

[0026] Among them, R ω (k) represents the rate of change of angular frequency at the kth sampling; T s Sampling time;

[0027] The integral of the angular frequency is calculated using the following formula:

[0028]

[0029] Among them, I ω (k) represents the integral value of the angular frequency at the kth sampling.

[0030] Furthermore, step four specifically includes:

[0031] 1) When all grid operating indicators do not exceed the control threshold of the precise regulation strategy, the DC system adopts a constant output strategy to achieve system active power output, i.e.

[0032]

[0033] Among them, K p K i These are the proportional and differential gains of the constant output strategy, respectively; P ref P(k) is the active power reference value; P(k) is the active power output of the DC system at the k-th sampling time; i d0 (k) represents the d-axis reference value of the output current at the kth sampling time;

[0034] 2) When any one of the grid operation indicators exceeds the control threshold of the precise regulation strategy but does not exceed the control threshold of the approximation control strategy, the DC system adopts the precise regulation strategy to actively support the grid:

[0035]

[0036] Among them, K' p K' i These represent the proportional and derivative gains of the precise adjustment strategy; D p The proportional gain is used to precisely adjust the angular frequency deviation of the strategy; ω(k) is the angular frequency at the kth sampling.

[0037] 3) When either the angular frequency deviation or the rate of change at the DC system's grid connection point exceeds the control threshold of the approximation control strategy, the DC system employs a fuzzy PID-based approximation control strategy to rapidly support the AC-side grid.

[0038]

[0039] Where, k p (k), k i (k), k d (k) represent the proportional, derivative, and integral coefficients of the approximation control strategy in step two, respectively, at the k-th sampling time; D' p The proportional gain is used to approximate the angular frequency deviation of the control strategy.

[0040] This invention has the following advantages: 1) Based on the real-time status of angular frequency deviation, rate of change, and integral quantity indicators, three control strategies (approximation control, precise adjustment, and constant output) are flexibly adopted, significantly enhancing the stability of the power grid frequency. Moreover, this invention has a simple structure and is easy to implement.

[0041] 2) The fuzzy PID approximation control strategy can adjust the PID parameters online according to the real-time operation of the power grid, ensuring that the DC system can quickly support the power grid under large disturbances. When the power grid disturbance is small, the precise adjustment strategy ensures the friendly interaction capability between the DC system and the AC power grid. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating one embodiment of a method for rapidly supporting AC-side grid control in a DC system provided by the present invention.

[0043] Figure 2 For angular frequency deviation Δω and integral I ω Relationship diagram between control strategy threshold range;

[0044] Figure 3 R is the rate of change of angular frequency ω and integral quantity Iω Relationship diagram with control strategy threshold range;

[0045] Figure 4 A control block diagram for a method to rapidly support AC-side grid control in a DC system;

[0046] Figure 5 This is the main circuit structure diagram. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] The main circuit structure diagram of this invention is as follows: Figure 5 As shown, it includes: a DC system control module, a converter module, and an SVPWM module. The DC system control module transmits the reference waveform of the control method of the present invention to the converter module through the SVPWM module to realize DC system control.

[0049] like Figure 1 The diagram shows a flowchart of a method for rapidly supporting AC-side grid control in a DC system. The method includes the following steps:

[0050] Step 1: Based on the operating conditions of the power grid where the DC system is located, set the power grid operating threshold range for three control strategies (approximation control, precise regulation, and constant output). The indicators include angular frequency deviation, rate of change, and integral quantity.

[0051] Based on the actual grid conditions, three control strategies (approximation control, precise regulation, and constant output) are set for the grid operation threshold range, i.e., the control threshold range of the DC system. The angular frequency deviation Δω and rate of change R of the approximation control strategy are set. ω The maximum and minimum control thresholds, wherein the control thresholds are respectively Δω m , Δω n R m R n ; Set the angular frequency deviation Δω and rate of change R of the precise adjustment strategy ω and integral quantity I ω The maximum and minimum control thresholds, wherein the control thresholds are respectively Δω pm , Δω pn R pm R pn I m I n .

[0052] Angular frequency deviation Δω and integral I ω The relationship with the threshold ranges of the three strategies (approximation control, precise adjustment, and constant output) is as follows: Figure 2 As shown.

[0053] Angular frequency change rate R ω and integral quantity I ω The relationship with the threshold ranges of the three strategies (approximation control, precise adjustment, and constant output) is as follows: Figure 3 As shown.

[0054] Angular frequency deviation Δω, rate of change R ω and integral quantity I ω When any item enters a higher priority threshold range, the DC system adopts the higher priority control strategy. The priority order from high to low is approximation control, precise regulation, and constant output.

[0055] Step 2: Based on the threshold range of the approximation control strategy, establish the required fuzzy PID control rules to obtain the proportional, derivative, and integral coefficients of the approximation control strategy.

[0056] Based on the power grid operating threshold range, the angular frequency deviation and rate of change in the threshold range of the approximation control strategy are fuzzified, with the fuzzy subsets being positive large, positive medium, positive small, zero, negative small, negative medium, and negative large. A trapezoidal membership function is adopted, and a proportional coefficient k is established based on actual operating conditions. p Differential coefficient k i and integral coefficient k d A fuzzy rule table.

[0057] To further enhance the advantages of proportional, derivative, and integral coefficients in control and regulation, the proportional coefficient adjustment Δk... p The fuzzy rule table can be represented as Table 1:

[0058] Table 1

[0059]

[0060] Differential coefficient adjustment Δk i The fuzzy rule table can be represented as Table 2:

[0061] Table 2

[0062]

[0063] Differential coefficient adjustment Δk d The fuzzy rule table can be represented as Table 3:

[0064] Table 3

[0065]

[0066] The fuzzy PID parameter tuning expression for the approximation control strategy is:

[0067] k p (k)=k p (k-1)+Δk p (k)

[0068] k i (k)=k i (k-1)+Δk i (k)

[0069] k d (k)=k d (k-1)+Δk d (k)

[0070] Where, k p (k), k i (k), k d (k) represents the proportional, derivative, and integral coefficients of the approximation control strategy at the k-th sampling time; Δk p (k), Δk i (k), Δk d (k) represents the adjustment amounts of the proportional, derivative, and integral coefficients of the approximation control strategy at the k-th sampling time.

[0071] Step 3: Use a voltage transformer (TV) to measure the real-time voltage value at the grid connection point, and calculate the angular frequency deviation, rate of change, and integral quantity.

[0072] The real-time voltage value at the grid connection point is measured by a voltage transformer (TV), and the angular frequency deviation, rate of change, and integral quantity are calculated using the following formulas.

[0073] Calculate the angular frequency deviation using the following formula:

[0074] Δω(k)=ω ref -ω′(k)

[0075] Where Δω(k) is the angular frequency deviation value at the kth sampling; ω ref ω is the reference value for angular frequency; ω'(k) is the average angular frequency value at the kth sampling.

[0076] The rate of change of angular frequency is calculated using the following formula:

[0077]

[0078] Among them, R ω (k) represents the rate of change of angular frequency at the kth sampling; T s Sampling time.

[0079] The integral of the angular frequency is calculated using the following formula:

[0080]

[0081] Among them, I ω (k) represents the integral value of the angular frequency at the kth sampling.

[0082] Step 4: Determine the operating range of the power grid by judging the angular frequency deviation, rate of change, and integral quantity. Then, control the DC system to switch between three strategies for different operating conditions to achieve rapid support for the AC side power grid.

[0083] The DC system is zonally regulated based on angular frequency deviation, rate of change, and integral quantity, such as... Figure 4 As shown, the specific implementation process is as follows:

[0084] 1) When all grid operating indicators do not exceed the control threshold of the precise regulation strategy, the DC system adopts a constant output strategy to achieve system active power output, i.e.

[0085]

[0086] Among them, K p K i These are the proportional and differential gains of the constant output strategy, respectively; P ref P(k) is the active power reference value; P(k) is the active power output of the DC system at the k-th sampling time; i d0 (k) is the d-axis reference value of the output current at the kth sampling time.

[0087] 2) When any one of the power grid operation indicators exceeds the control threshold of the precise regulation strategy but does not exceed the control threshold of the approximation control strategy, the DC system adopts the precise regulation strategy to actively support the power grid.

[0088]

[0089] Among them, K' p K' i These represent the proportional and derivative gains of the precise adjustment strategy; D p The proportional gain is used to precisely adjust the angular frequency deviation of the strategy; ω(k) is the angular frequency at the kth sampling.

[0090] 3) When either the angular frequency deviation or the rate of change at the DC system's grid connection point exceeds the control threshold of the approximation control strategy, the DC system employs a fuzzy PID-based approximation control strategy to rapidly support the AC-side grid.

[0091]

[0092] Among them, D' pThe proportional gain is used to approximate the angular frequency deviation of the control strategy.

[0093] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for rapidly supporting AC-side grid control in a DC system, characterized in that, Includes the following steps: Step 1: Based on the operation of the power grid where the DC system is located, set the power grid operation threshold range for three control strategies. The three control strategies include approximation control, precise regulation, and constant output. The power grid operation threshold range includes angular frequency deviation, rate of change, and integral quantity index. Step 2: Based on the threshold range of the approximation control strategy, establish the required fuzzy PID control rules to obtain the proportional coefficient, derivative coefficient, and integral coefficient of the approximation control strategy. Step 3: Measure the real-time voltage value at the grid connection point using a voltage transformer (TV), and calculate the angular frequency deviation, rate of change, and integral quantity; Step 4: Determine the grid operating range by using angular frequency deviation, rate of change, integral quantity, and grid operating threshold range. Based on the determined grid operating range, control the DC system to switch between three strategies to achieve rapid support for the AC grid.

2. The method for rapidly supporting AC-side grid control in a DC system as described in claim 1, characterized in that: In step one, the angular frequency deviation Δω and the rate of change R of the approximation control strategy are set. ω The maximum and minimum control thresholds, wherein the control thresholds are respectively Δω m , Δω n R m R n ; Set the angular frequency deviation Δω and rate of change R of the precise adjustment strategy ω and integral quantity I ω The maximum and minimum control thresholds, wherein the control thresholds are respectively Δω pm , Δω pn R pm R pn I m I n .

3. The method for rapidly supporting AC-side grid control in a DC system as described in claim 1, characterized in that: Step two specifically includes: Based on the power grid operating threshold range, the angular frequency deviation and rate of change in the threshold range of the approximation control strategy are fuzzified, and their fuzzy subsets are positive large, positive medium, positive small, zero, negative small, negative medium, and negative large. A trapezoidal membership function is adopted, and a proportional coefficient k is established according to the actual operating conditions. p Differential coefficient k i and integral coefficient k d Fuzzy rule table; The fuzzy PID parameter adjustment expression for the approximation control strategy, obtained from the fuzzy rule table, is as follows: k p (k)=k p (k-1)+Δk p (k) k i (k)=k i (k-1)+Δk i (k) k d (k)=k d (k-1)+Δk d (k) Where, Δk p (k), Δk i (k), Δk d (k) represents the adjustment amounts of the proportional coefficient, derivative coefficient, and integral coefficient of the approximation control strategy at the k-th sampling time; The proportional coefficient, derivative coefficient, and integral coefficient of the approximation control strategy are obtained by using the fuzzy PID parameter adjustment expression.

4. The method for rapidly supporting AC-side grid control in a DC system as described in claim 1, characterized in that: Step three involves calculating the angular frequency deviation, rate of change, and integral quantity, specifically including: The angular frequency deviation is calculated using the following formula: Give(k)=ω ref -ω′(k) Where Δω(k) is the angular frequency deviation value at the kth sampling; ω ref ω is the reference value for angular frequency; ω'(k) is the average angular frequency value at the kth sampling. The rate of change of angular frequency is calculated using the following formula: Among them, R ω (k) represents the rate of change of angular frequency at the kth sampling; T s Sampling time; The integral of the angular frequency is calculated using the following formula: Among them, I ω (k) represents the integral value of the angular frequency at the kth sampling.

5. The method for rapidly supporting AC-side grid control in a DC system as described in claim 3, characterized in that... Step four specifically includes: 1) When all grid operating indicators do not exceed the control threshold of the precise regulation strategy, the DC system adopts a constant output strategy to achieve system active power output, i.e. Among them, K p K i These are the proportional and differential gains of the constant output strategy, respectively; P ref P(k) is the active power reference value; P(k) is the active power output of the DC system at the k-th sampling time; i d0 (k) represents the d-axis reference value of the output current at the kth sampling time; 2) When any one of the grid operation indicators exceeds the control threshold of the precise regulation strategy but does not exceed the control threshold of the approximation control strategy, the DC system adopts the precise regulation strategy to actively support the grid: Among them, K' p K' i These represent the proportional and derivative gains of the precise adjustment strategy; D p The proportional gain is used to precisely adjust the angular frequency deviation of the strategy; ω(k) is the angular frequency at the kth sampling. 3) When either the angular frequency deviation or the rate of change at the DC system's grid connection point exceeds the control threshold of the approximation control strategy, the DC system employs a fuzzy PID-based approximation control strategy to rapidly support the AC-side grid. Where, k p (k), k i (k), k d (k) represent the proportional, derivative, and integral coefficients of the approximation control strategy in step two, respectively, at the k-th sampling time; D' p The proportional gain is used to approximate the angular frequency deviation of the control strategy.

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