Voltage regulation and control method based on dynamic line impedance characteristic remodeling

Abstract

The invention discloses a voltage regulation and control method based on dynamic line impedance characteristic remodeling, solves the voltage out-of-limit problem of a medium / low voltage power distribution network, and belongs to the technical field of new energy power generation and power grids. The method comprises the steps of determining a voltage out-of-limit problem existing in a power distribution network according to a power grid impedance ratio, and selecting a grid-connected voltage maximum value and a collapse critical value according to the corresponding problem; calculating compensation target values T1 and T2 of the equivalent impedance ratio of the power grid corresponding to the maximum grid-connected voltage value and the collapse critical value; in combination with the SOC of the direct-current energy storage system, the working mode of the series converter is determined, and compensation impedance corresponding to the maximum value of the grid-connected voltage and the collapse critical value is calculated; determining a droop self-regulation control curve parameter according to the grid-connected voltage maximum value and the voltage collapse critical value, and calculating the real-time series converter compensation impedance according to the droop self-regulation control curve parameter and the series converter compensation resistance and compensation reactance corresponding to the grid-connected voltage maximum value and the grid-connected voltage critical value; dynamic impedance remodeling of the medium / low-voltage power distribution network is achieved, and the voltage out-of-limit problem is solved.

Description

Technical Field

[0001] The present invention relates to a voltage control method based on dynamic line impedance characteristic reshaping, belonging to the technical field of new energy power generation and power grid. Background Art

[0002] Photovoltaic power generation technology is undergoing a structural transformation from centralized power stations to distributed intelligent grid-connected systems. In the context of new power system construction, medium and low voltage distribution networks have gradually formed an active network architecture with multi-node distributed energy interconnection. However, as the terminal link of power transmission, the traditional distribution network is originally designed based on the unidirectional transmission mode of feeder flow. When dealing with high-penetration distributed power generation, it exposes the following system defects: (1) Network impedance characteristic mismatch: The medium and low voltage distribution network has a resistive dominant characteristic, and its grid impedance ratio (R / X) is significantly higher than that of the transmission network, resulting in the system voltage being much more sensitive to active power fluctuations than reactive power, causing the effectiveness of traditional voltage regulation strategies to decline; (2) Bidirectional power flow conflict: There is an inherent phase deviation between the timing characteristics of photovoltaic power generation and the load demand curve. The reverse transmission of power flow during the peak power generation period at noon causes a voltage rise effect at the common connection point; (3) Tightening of safety boundary constraints: The problem of distributed power generation protective disconnection caused by overvoltage forms a negative coupling relationship between the new energy absorption capacity and the grid carrying capacity, which seriously limits the improvement of new energy penetration in medium and low voltage distribution networks.

[0003] Currently, voltage regulation in medium and low voltage distribution networks primarily relies on the following technical means: expansion and transformation of distribution network feeders, tap adjustment of on-load tap-changing transformers, deployment of reactive power compensation devices, integration of large-scale energy storage systems, and active power limitation of distributed generation. However, these methods have significant technical bottlenecks:

[0004] (1) Feeder upgrades involve line reconstruction and equipment replacement, which have inherent drawbacks such as large project investment and long renovation period.

[0005] (2) The on-load voltage regulator is limited by its mechanical structure and exhibits a discrete step voltage regulation characteristic. Moreover, its regulation range and dynamic response speed cannot meet the requirements of high-fluctuation power supply access.

[0006] (3) Reactive power compensation technology and reactive power-voltage coordinated control strategy have the ability to regulate voltage over a wide range. However, under the high-resistance network characteristics (R / X>1), the system voltage is significantly more sensitive to changes in active power than reactive power, which seriously weakens the voltage support efficiency of the reactive power compensation device. At the same time, it triggers chain problems such as redundant configuration of compensation capacity, surge in additional line losses, and degradation of the power factor at the grid connection point.

[0007] (4) Large-scale energy storage systems can effectively solve the overvoltage problem caused by the high proportion of renewable energy grid connection through dynamic power regulation, and at the same time realize the peak-valley load transfer function of the power system. However, due to the strong coupling characteristics of energy storage capacity and the excess power of distributed power sources, as the penetration rate of distributed power sources increases, the capacity of energy storage systems increases accordingly, and the cost-effectiveness is relatively low;

[0008] (5) Although the active power reduction control of distributed power sources has the characteristics of rapid response, it is essentially dependent on the active reduction of renewable energy power generation. This not only causes a decline in the utilization rate of renewable energy, but also forms a system-level negative regulation mechanism that inhibits the access of high-penetration distributed power sources. It is difficult to adapt to the new energy consumption needs under the dual carbon goals.

[0009] Therefore, this invention breaks through the traditional "source-side power-constrained" voltage control paradigm and creatively proposes a voltage regulation method based on dynamic grid impedance reshaping. By utilizing series converters to construct a virtual impedance dynamic compensation loop, this method achieves real-time optimization of the distribution network's equivalent impedance ratio (R / X). While maintaining the grid-connected system's power transfer characteristics, it also keeps voltage fluctuations within safe thresholds and ensures 100% power absorption of renewable energy generation systems. Summary of the Invention

[0010] To address the voltage over-limit problem in medium / low voltage distribution networks, the present invention provides a voltage control method based on dynamic line impedance feature reshaping.

[0011] A voltage control method based on dynamic grid impedance feature reshaping of the present invention includes:

[0012] S1. Determine the voltage over-limit problem in the distribution network based on the grid impedance ratio, and select the maximum grid voltage and collapse threshold according to the corresponding problem;

[0013] S2, calculating the compensation target values ​​T1 and T2 of the grid equivalent impedance ratio corresponding to the maximum grid voltage and the collapse critical value;

[0014] S3. Determine the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid-connected voltage and the collapse critical value according to the impedance ratio compensation target of the series converter;

[0015] S4. Determine the droop self-regulating control curve parameters according to the maximum grid-connected voltage and the collapse critical value. Calculate the real-time series converter compensation resistance and compensation reactance according to the droop self-regulating control curve parameters and the series converter compensation resistance and compensation reactance corresponding to the maximum grid-connected voltage and the collapse critical value, and realize segmented compensation of the grid impedance ratio in different working ranges of the distribution network.

[0016] As a preferred embodiment, in S1, based on the relationship between the grid voltage safety allowable range and the grid impedance ratio, the voltage limit problem existing in the distribution network is determined, and the maximum grid voltage and the collapse critical value are selected according to the corresponding problem, including:

[0017] When the grid impedance ratio When the grid has an overvoltage problem, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for:

[0018] U pcc_max =(1+D%)U g

[0019] U pcc_critical =(1-D%)U g

[0020] Among them, k is the voltage safety threshold coefficient, D ranges from 0 to k, U g Indicates the distribution network voltage;

[0021] When the grid impedance ratio When the grid has an overvoltage problem, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for:

[0022]

[0023] When the line impedance ratio When the power grid has both overvoltage and undervoltage problems, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for:

[0024] U pcc_max =(1+D%)U g

[0025] U pcc_critical =(1-D%)U g

[0026] When the line impedance ratio When the grid has undervoltage problem, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for:

[0027]

[0028] Preferably, in S2, the method of calculating the corresponding compensation target values ​​T1 and T2 of the grid equivalent impedance ratio according to the maximum grid voltage and the collapse critical value includes:

[0029]

[0030] Among them, U pcc_max Indicates the expected value of the maximum grid voltage, U pcc_critical It represents the expected value of the grid voltage collapse threshold, U g Indicates the distribution network voltage.

[0031] Preferably, in S3, based on obtaining the state of charge SOC of the DC side energy storage system, it is determined that the series converter is in the charging / discharging mode or the minimum compensation impedance mode, and the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid-connected voltage and the collapse critical value are determined in different modes.

[0032] Preferably, when the series converter is in the charge / discharge mode, the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid-connected voltage and the collapse critical value are determined according to the residual capacity of the series compensator output voltage:

[0033] When I max (X g -T1R g )≥U semax When R sep =0,

[0034] When I max (X g -T1R g )<U semax hour, X sep =X g -T1(R g -R sep );

[0035] Among them, R g To compensate for the front grid resistance, X g To compensate for the front grid reactance, I max is the maximum current of the transmission line, U semax is the maximum output voltage of the series converter, P seref is the charging / discharging power given value of the series converter, R sep 、X sep are the compensation resistance and compensation reactance of the series converter corresponding to the maximum value of the grid-connected voltage respectively;

[0036] When I max (X g -T2R g )≥U semax hour,

[0037] When I max (X g -T2Rg )<U semax hour, X sen =X g -T2(R g -R sen );

[0038] R sen 、X sen are the compensation resistance and compensation reactance of the series converter corresponding to the critical value of grid-connected voltage collapse.

[0039] Preferably, in S3, when the series converter is in the minimum compensation impedance mode, the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid voltage and the collapse critical value are:

[0040] X sep =X g -T1(R g -R sep )

[0041] X sen =X g -T2(R g -R sen )

[0042] Among them, R g To compensate for the front grid resistance, X g To compensate for the front grid reactance, R sep 、X sep are the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid voltage; R sen 、X sen are the compensation resistance and compensation reactance of the series converter corresponding to the critical value of grid-connected voltage collapse.

[0043] Preferably, in said S4, the droop self-regulating control curve parameters include:

[0044]

[0045] Among them, K droop , U0 is the slope and intercept of the droop self-regulating control curve.

[0046] Preferably, in S4, the real-time series converter compensation resistance and compensation reactance are:

[0047]

[0048] Where N is the series converter turns ratio, R se is the real-time series converter compensation resistance, X seCompensate reactance for series converters in real time.

[0049] As a preference,

[0050] Among them, U sd 、U sq are the dq axis components of the voltage at the connection point between the series converter and the transmission line, U sed 、U seq They are the dq axis components of the series converter output voltage respectively.

[0051] The present invention has the following beneficial effects: The present invention utilizes the impedance reshaping function of the series converter to adjust the grid impedance ratio without upgrading the grid configuration, reducing the maximum deviation of the grid-connected voltage and fundamentally solving the voltage over-limit problem. The present invention reduces the distribution network's demand for reactive power through series compensation, reduces transmission line losses, and improves the transmission efficiency of the new energy grid-connected system. The present invention reduces the demand for series converter capacity for distribution network voltage regulation through an optimal compensation impedance solution algorithm, simplifies the compensation impedance solution process, reduces the demand for energy storage capacity of the series compensator, and improves the economic benefits of the series voltage compensation method. The present invention implements online charging and discharging of the series converter while ensuring the normal operation of the distribution network voltage regulation function through a series power exchange strategy based on double-degree-of-freedom decoupling, and achieves long-term grid-connected operation of the series converter without an external parallel device. The present invention fully considers the distribution network operating range, grid-connected voltage, and grid impedance ratio through a stable boundary solution method based on grid impedance characteristics and a dynamic impedance calculation method based on droop coefficient self-adjustment. While ensuring normal system power transmission, the present invention dynamically adjusts the grid equivalent impedance ratio and reduces the fluctuation range of the new energy grid-connected voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Equivalent analysis model for series converters connected to distributed energy systems;

[0053] Figure 2 This is a structural diagram of the series converter connected to the distributed energy system;

[0054] Figure 3 A voltage control flow chart reshaped based on dynamic grid impedance characteristics;

[0055] Figure 4 Distribution network U for distributed generation system pcc -P characteristic curve;

[0056] Figure 5 This is a flow chart of the method for solving the stability boundary based on the impedance characteristics of the power grid;

[0057] Figure 6Flowchart for calculating compensation impedance for series converter mode selection and maximum grid voltage and collapse threshold

[0058] Figure 7 Flowchart of the dynamic impedance calculation method based on droop coefficient self-adjustment;

[0059] Figure 8 Control block diagram of voltage regulation method based on dynamic line impedance characteristic reshaping;

[0060] Figure 9 Grid-connected voltage, transmission line power, and grid-connected current of the distributed generation system before compensation, where (a) is the grid-connected voltage, (b) the transmission line power, and (c) is the grid-connected current;

[0061] Figure 10 Grid-connected voltage, transmission line power, and grid-connected current of the distributed generation system after compensation, where (a) is the grid-connected voltage, (b) the transmission line power, and (c) is the grid-connected current;

[0062] Figure 11 are the output voltage and output power of the series converter, where (a) is the output voltage and (b) is the output power. DETAILED DESCRIPTION

[0063] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0064] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0065] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0066] To address the limited effectiveness of existing conventional voltage regulation methods in medium and low voltage distribution networks, this implementation breaks through the traditional "source-side power-constrained" voltage control paradigm and innovatively proposes a voltage regulation method based on dynamic grid impedance reshaping. By utilizing series converters to construct a virtual impedance dynamic compensation loop, this method achieves real-time optimization of the distribution network's equivalent impedance ratio (R / X). This approach maintains the power transfer characteristics of the grid-connected system, keeps voltage fluctuations within safe thresholds, and ensures 100% power absorption of renewable energy generation systems.

[0067] The equivalent analysis model of the series converter added to the distributed renewable energy grid-connected system is as follows: Figure 1As shown in the figure, the distributed generation system is connected to the distribution network through a public grid connection point, and the generated power is sent to the grid through the transmission line. pcc is the effective value of the grid-connected voltage of the distributed generation system, R g +jX g is the grid impedance, U g is the effective value of the large power grid voltage, U s is the effective value of the voltage at the connection point between the series converter and the distribution network.

[0068] The structural diagram of the series converter connected to the distributed new energy grid-connected system is as follows: Figure 2 As shown, the converter is connected to the transmission line through a series transformer, and its output voltage vector U is adjusted by se The amplitude of the transmission line current and its phase difference with the transmission line current I are equivalent to inserting an adjustable compensation impedance R in series. se +jX se , change the grid impedance ratio (R / X), and then adjust the new energy grid voltage U pcc P and Q are the active power and reactive power injected by the grid voltage, U se is the effective value of the output voltage of the series converter, I is the effective value of the transmission line current, P2 and Q2 are the total active power and reactive power input to the distribution network, P se , Q se It is the active power and reactive power output by the series converter.

[0069] The voltage control method based on dynamic grid impedance characteristic reshaping of this embodiment is applicable to high-penetration new energy grid-connected systems, and the method includes:

[0070] Step 1: Collect data of distributed energy system and determine the U of the series converter connected to the distributed energy system. pcc -P characteristic curve, U pcc Indicates the grid voltage, P indicates the active power of the grid point, according to U pcc -P characteristic curve to obtain the grid voltage safety allowable range and grid impedance ratio (R g / X g ), calculate the corresponding safe range of the grid impedance ratio, determine the voltage over-limit problem in the distribution network before compensation, determine the maximum grid voltage and collapse critical value based on the corresponding problem, and calculate the corresponding target values ​​T1 and T2 of the grid equivalent impedance ratio;

[0071] Among them, the data collected from the distributed energy system include the transmission line current I, the connection point voltage U s , series converter output voltage U se , calculate the power injected into the grid connection point, including active power P and reactive power Q, Q = Q2-Q se ,P=P2-P se ;

[0072] According to U pcc -P characteristic curve to obtain the grid voltage and grid voltage safety allowable range [(1-k)U g ,(1+k)U g ], and after deduction, the safe range of the grid impedance ratio is obtained, as shown in the following formula:

[0073]

[0074] Where k is the voltage safety threshold coefficient.

[0075] Assuming k = 7%, the safe allowable range of grid voltage is [(1-7%)U g ,(1+7%)U g ], when the grid impedance is R g / X g ∈(0.6817, +∞), the power grid has an overvoltage problem, that is, U pcc_max >(1+7%)U g 、U pcc_critical >(1+7%)U g , select the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for:

[0076] U pcc_max =(1+2%)U g

[0077] U pcc_critical =(1-2%)U g

[0078] When the grid impedance is R g / X g ∈(0.4653,0.6817), the power grid has an overvoltage problem, that is, U pcc_max >(1+7%)U g , select the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for:

[0079]

[0080] When the line impedance is R g / X g ∈(0.3807,0.4653), the power grid has both overvoltage and undervoltage problems, that is, U pcc_max >(1+7%)U g 、U pcc_critical <(1-7%)U g , select the maximum grid voltage U pcc_maxand the collapse critical value U pcc_critical is:

[0081] U pcc_max =(1 + 2%)U g

[0082] U pcc_critical =(1 - 2%)U g

[0083] When the line impedance ratio R g / X g ∈(0, 0.3807), there is an undervoltage problem in the power grid, that is, U pcc_critical <(1 - 7%)U g , select the maximum grid-connected voltage U pcc_max and the collapse critical value U pcc_critical as:

[0084]

[0085] According to the maximum grid-connected voltage U pcc_max and the grid-connected voltage collapse critical value U pcc_critical , calculate the corresponding power grid equivalent impedance ratio compensation targets T1 and T2 respectively. As shown in the following formula:

[0086]

[0087] Step 2: Determine the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid-connected voltage and the critical value according to the impedance ratio compensation target of the series converter, including: First, obtain the state of charge SOC of the DC-side energy storage system, determine the operation mode of the series converter. In order to avoid repeated switching of the working mode at the SOC boundary condition, a hysteresis buffer is added between different working modes. The specific selection method is as follows:

[0088] Obtain the state of charge SOC of the energy storage system and judge the operation mode of the series converter. When 80 < SOC < 100% or 0% < SOC < 20%, it is in the charge / discharge mode. When 40% < SOC < 60%, it is in the minimum compensation impedance control mode:

[0089]

[0090] Among them, for the solution algorithm of the optimal compensation impedance mode, according to the power grid impedance R g , X g and the compensation target, calculate the compensation impedance under the constraint conditions of the minimum output voltage and apparent power of the series converter. The specific method includes:

[0091] First, deduce the output voltage U se and the apparent power S seRegarding compensation target T and grid impedance R g 、X g , compensation impedance R se 、X se The relationship is shown as follows:

[0092]

[0093] Where U se 、S se , I are the output voltage, apparent power and transmission line current of the series converter respectively.

[0094] Obtain the corresponding compensation impedance R under the conditions of the series converter output voltage and the lowest apparent power. se 、X se The calculation formula is as follows:

[0095]

[0096] Step 3 uses a two-degree-of-freedom decoupled series power exchange strategy. Based on the state of charge (SOC) of the energy storage system on the DC side of the series converter and the remaining capacity of the converter output voltage, the solution algorithm for the compensation impedance of the series converter is adjusted to achieve dynamic adjustment of the energy storage system SOC and maintain it within the normal operating range. The specific calculation method is as follows:

[0097] According to the above derivation relationship, in the three modes, solve the compensation impedance R corresponding to T1 and T2 sep , X sep , R sen , X sen :

[0098]

[0099] Among them, U semax is the maximum output voltage of the series converter, P seref is the charging / discharging power given value of the series converter, R sep 、X sep are the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid voltage; R sen 、X sen The series converter compensation resistor and reactance correspond to the critical grid voltage collapse value, respectively. In charge / discharge mode, when the series converter output voltage capacity is insufficient, the compensation resistor is kept at 0, and the series converter compensation reactance corresponding to the maximum and critical grid voltage values ​​is calculated based on the maximum voltage capacity. When the series converter output voltage capacity is sufficient, the energy storage device is charged / discharged using a fixed resistance value to adjust the SOC.

[0100] Step 4: Determine the droop self-regulating control curve parameters based on the maximum grid voltage and the voltage collapse threshold. Calculate the real-time series converter compensation resistance and compensation reactance based on the droop self-regulating control curve parameters and the corresponding series converter compensation resistance and compensation reactance at the maximum and critical grid voltages, and perform segmented compensation for different distribution network impedance ratios (R / X).

[0101] According to the maximum grid voltage U pcc_max and the grid voltage collapse critical value U pcc_critical , calculate the droop self-regulating control curve parameters as shown below:

[0102]

[0103] Where K droop , U0 is the slope and intercept of the droop control curve.

[0104] Calculation is based on the large grid voltage U g , connection point voltage U s , calculate the grid-connected voltage U of the distributed generation system pcc , as shown below:

[0105]

[0106] Among them, U sd 、U sq are the dq axis components of the voltage at the connection point between the series converter and the transmission line, U sed 、U seq are the dq axis components of the series converter output voltage respectively, and N is the turns ratio of the series converter.

[0107] According to the grid-connected voltage U pcc , Compensation impedance target R sep , X sep , R sen , X sen , according to the droop self-regulating control curve parameters, the series compensation impedance R is calculated in real time se +jX se , to achieve different U pcc -P working area impedance reshaping voltage regulation, as shown in the following equation:

[0108]

[0109] The innovations of this implementation are mainly as follows:

[0110] This embodiment provides a method for solving the stability boundary based on the grid impedance characteristics. In a high-penetration distributed generation grid-connected system, according to the grid-connected system U pcc -P working characteristics, combined with the grid power P, Q, grid impedance Rg 、X g , large grid voltage U g , the safe allowable range of grid voltage, calculate the safe range of grid impedance ratio, judge the voltage problem of distribution network before compensation, select the maximum grid voltage and critical grid voltage, and calculate the corresponding compensation target value T1 and T2 of grid equivalent impedance ratio.

[0111] This embodiment provides an optimal compensation impedance solution algorithm based on the grid impedance R g 、X g As well as the compensation target T, the compensation impedance is calculated under the constraints of minimizing the output voltage and apparent power of the series converter.

[0112] This embodiment provides a double-degree-of-freedom decoupling series power exchange strategy, which is based on the state of charge SOC of the DC side energy storage system of the series converter and the converter output voltage U se The remaining capacity of the energy storage system is adjusted by adjusting the compensation impedance of the series converter to achieve dynamic regulation of the SOC of the energy storage system and maintain it within the normal operating range.

[0113] This embodiment provides a dynamic impedance calculation method based on droop coefficient self-adjustment. pcc_max and critical grid voltage U pcc_critical The expected value after compensation and the corresponding compensation impedance are used to solve the droop control coefficient and collect the connection point voltage U s , series converter output voltage U se , calculate the grid-connected voltage U of the distributed generation system pcc On this basis, the compensation impedance R is adjusted in real time se 、X se , realize dynamic compensation of grid-connected voltage, reduce the fluctuation range of grid-connected voltage, and fundamentally solve the overvoltage problem.

[0114] This embodiment also provides a series converter voltage control system for dynamic grid impedance characteristic reshaping, and its overall control block diagram is as follows: Figure 8 As shown, it includes a signal acquisition and processing unit, a coordinate transformation unit, an impedance reshaping target selection unit, a compensation impedance solution unit, a dynamic impedance calculation unit, and an output voltage calculation unit. The signal acquisition unit samples the transmission line current i and the connection point voltage u at the current moment. s , series converter inductor current i se , output voltage u se As well as the state of charge SOC of the DC energy storage system, first, the connection point voltage u s The reference voltage phase θ is sent to the phase-locked loop and is then sent to the coordinate transformation unit as the reference phase for park transformation.

[0115] Next, the coordinate transformation unit calculates the transmission line current i and the connection point voltage u. s , series converter inductor current i se , output voltage u se Perform park transformation to obtain the dq axis component u sd 、u sq 、u sed 、u seq 、i d 、i q 、i sed 、i seq Among them, u sd 、u sq 、u sed 、u seq The signal is sent to the signal processing unit to calculate the effective value of the grid-connected voltage of the distributed generation system U pcc '.

[0116] Furthermore, through actual measurement, the grid impedance R is obtained g 、X g , sent to the impedance reshaping target selection unit, according to the grid voltage safety range, calculate the corresponding impedance ratio safety range, determine whether the grid has voltage limit problem, select the maximum grid voltage and collapse critical value according to the corresponding problem, and calculate the corresponding compensation targets T1 and T2 respectively. g 、X g Send it to the compensation impedance solution unit to calculate the compensation impedance reference value R corresponding to the maximum and critical values ​​of the grid-connected voltage sep +jX sep 、R sen +jX sen ; The maximum grid-connected voltage and critical voltage U pcc_max 、U pcc_critical And the grid voltage compensation impedance reference value R sep +jX sep 、R sen +jX sen Send it to the dynamic impedance calculation unit to solve the droop self-regulating control curve parameter K droop , U0, combined with the real-time grid voltage effective value U pcc ', solve the compensation impedance value R of the series converter in real time se 、X se ;

[0117] Furthermore, the dq axis component of the transmission line current i d 、i q , compensation impedance R se 、X seand transformer turns N are sent to the output voltage calculation unit to solve the output voltage given value u of the series converter sedref 、u seqref ;

[0118] Finally, the series converter output voltage, inductor current and output voltage given value are sent to the voltage and current double closed loop controller, and the voltage and current double closed loop control in the dq coordinate system is adopted. The voltage outer loop sets the output voltage given value u sedref 、u seqref Respectively with the sampling value u sed 、u seq The difference is sent to the proportional-integral (PI) controller, and the calculated converter inductor current set value i sedref 、i seqref The current inner loop sets the converter inductor current to a given value i sedref 、i seqref Respectively with the sampling value i sed 、i seq The difference is sent to the proportional-integral controller, and the result of the operation is v h As the modulation signal of the converter.

[0119] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. A voltage control method based on dynamic line impedance feature reshaping, characterized in that: The method comprises: S1. Determine the voltage over-limit problem in the distribution network based on the grid impedance ratio, and select the maximum grid voltage and collapse threshold according to the corresponding problem; S2, calculating the compensation target values ​​T1 and T2 of the grid equivalent impedance ratio corresponding to the maximum grid voltage and the collapse critical value; S3. Determine the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid-connected voltage and the collapse critical value according to the impedance ratio compensation target of the series converter; S4. Determine the droop self-regulating control curve parameters according to the maximum grid-connected voltage and the collapse critical value. Calculate the real-time series converter compensation resistance and compensation reactance according to the droop self-regulating control curve parameters and the series converter compensation resistance and compensation reactance corresponding to the maximum grid-connected voltage and the collapse critical value, and realize segmented compensation of the grid impedance ratio in different working ranges of the distribution network.

2. The voltage control method based on dynamic line impedance characteristic reshaping according to claim 1, characterized in that: In S1, based on the relationship between the grid voltage safety allowable range and the grid impedance ratio, the voltage limit problem in the distribution network is determined. The maximum grid voltage and collapse threshold are selected according to the corresponding problem, including: When the grid impedance ratio When the grid has an overvoltage problem, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for: U pcc_max =(1+D%)U g U pcc_critical =(1-D%)U g Among them, k is the voltage safety threshold coefficient, D ranges from 0 to k, U g Indicates the distribution network voltage; When the grid impedance ratio When the grid has an overvoltage problem, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for: When the line impedance ratio When the power grid has both overvoltage and undervoltage problems, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for: U pcc_max =(1+D%)U g U pcc_critical =(1-D%)U g When the line impedance ratio When the grid has undervoltage problem, the maximum grid voltage U pcc_max and the collapse threshold U pcc_critical for:

3. The voltage control method based on dynamic line impedance characteristic reshaping according to claim 1, characterized in that: In S2, the method for calculating the corresponding compensation target values ​​T1 and T2 of the grid equivalent impedance ratio according to the maximum grid voltage and the collapse critical value includes: Among them, U pcc_max Indicates the expected value of the maximum grid voltage, U pcc_critical It represents the expected value of the grid voltage collapse threshold, U g Indicates the distribution network voltage.

4. The voltage control method based on dynamic line impedance feature reshaping according to claim 1, characterized in that: In S3, based on the state of charge (SOC) of the DC side energy storage system, it is determined whether the series converter is in the charging / discharging mode or the minimum compensation impedance mode, and the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid-connected voltage and the collapse critical value are determined in different modes.

5. The voltage control method based on dynamic line impedance characteristic reshaping according to claim 4, characterized in that: When the series converter is in the charging / discharging mode, the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid voltage and the collapse threshold are determined according to the residual capacity of the series compensator output voltage: When I max (X g -T1R g )≥U semax When R sep =0, When I max (X g -T1R g )<U semax hour, X sep =X g -T1(R g -R sep ); Among them, R g To compensate for the front grid resistance, X g To compensate for the front grid reactance, I max is the maximum current of the transmission line, U semax is the maximum output voltage of the series converter, P seref is the charging / discharging power given value of the series converter, R sep 、X sep are the compensation resistance and compensation reactance of the series converter corresponding to the maximum value of the grid-connected voltage respectively; When I max (X g -T2R g )≥U semax When R sen =0, When I max (X g -T2R g )<U semax hour, X sen =X g -T2(R g -R sen ); R sen 、X sen are the compensation resistance and compensation reactance of the series converter corresponding to the critical value of grid-connected voltage collapse.

6. The voltage control method based on dynamic line impedance characteristic reshaping according to claim 4, characterized in that: In S3, when the series converter is in the minimum compensation impedance mode, the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid voltage and the collapse critical value are: Among them, R g To compensate for the front grid resistance, X g To compensate for the front grid reactance, R sep 、X sep are the compensation resistance and compensation reactance of the series converter corresponding to the maximum grid voltage; R sen 、X sen are the compensation resistance and compensation reactance of the series converter corresponding to the critical value of grid-connected voltage collapse.

7. The voltage control method based on dynamic line impedance feature reshaping according to claim 1, characterized in that: In S4, the droop self-regulating control curve parameters include: Among them, K droop , U0 is the slope and intercept of the droop self-regulating control curve.

8. The voltage control method based on dynamic line impedance characteristic reshaping according to claim 7, characterized in that: In S4, the real-time series converter compensation resistance and compensation reactance are: Where N is the series converter turns ratio, R se is the real-time series converter compensation resistance, X se Compensate reactance for series converters in real time.

9. The voltage control method based on dynamic line impedance characteristic reshaping according to claim 8, characterized in that: Among them, U sd 、U sq are the dq axis components of the voltage at the connection point between the series converter and the transmission line, U sed 、U seq They are the dq axis components of the series converter output voltage respectively.

Images