Low-Voltage Ride-Through Control Method and Device for Energy Storage Inverters Based on Active Support

Abstract

The present invention discloses a low-voltage ride-through control method based on an active support type energy storage converter, comprising: analyzing the variation law of the virtual impedance and introducing it into the reactive power-voltage loop of the active support type energy storage converter; calculating the modulation voltage according to the virtual impedance and the internal electromotive force and forming signals for controlling the turning on and off of the power tubes of the energy storage converter; extracting the real-time phase angle of the grid voltage by using a phase-locked loop; orienting with the real-time phase angle as the axis, during the low-voltage ride-through period, calculating the corresponding frequency compensation amount, and simultaneously calculating the minimum value of the power angle between the internal electromotive force and the grid voltage and the minimum output value of the q-axis component of the internal electromotive force; orienting with the real-time phase angle as the axis, after the grid voltage recovers, calculating the corresponding frequency compensation amount and voltage compensation amount; introducing the frequency compensation amount and the voltage compensation amount into the active power-frequency loop and the reactive power-voltage loop of the active support type energy storage converter respectively to obtain new frequency and voltage reference values, thereby forming a closed-loop negative feedback.

Description

Technical Field

[0001] This application relates to the technical field of low voltage ride through control of power grids, and particularly to a low voltage ride through control method and device for an energy storage converter based on active support. Background Art

[0002] Renewable energy power generation has strong randomness and volatility, posing great challenges to the power balance of power systems. Adding energy storage is an effective way to solve this problem. Currently, energy storage systems have made application progress in aspects such as smoothing the power output of power stations, peak shaving and valley filling, tracking plan processing, and AGC frequency modulation, which can increase the stability of power systems. Existing renewable energy power generation mainly uses current controlled inverters. However, current controlled inverters rely on the existing power grid, acting as controlled current sources and lacking the ability of active support. In addition, large-scale renewable energy power generation is generally located in remote areas far from load centers, and their access points present a high impedance weak grid state, which easily leads to a series of resonance instability accidents in current controlled renewable energy power generation. Existing energy storage converters generally operate in the PQ control mode. Although to a certain extent, they can support the power grid by improving the power outer loop to simulate a synchronous generator, they are still essentially current controlled inverters. Therefore, the support for the power grid is passive and it is difficult to effectively improve the stability of photovoltaic power generation under a weak grid.

[0003] To improve the problem of unstable grid connection control of renewable energy power generation under a weak grid, the energy storage converter can be configured as an active support type converter, that is, a voltage controlled converter, such as virtual synchronous generator (VSG) control or droop control. Its advantages are: it has stronger stability under a weak grid and has the ability of independent support. However, the active support type energy storage converter is prone to overcurrent and has low precision in reactive power control during fault ride through.

[0004] For example, virtual synchronous generation technology makes the inverter have similar frequency and voltage output external characteristics to a synchronous generator by introducing virtual inertia and damping coefficients, improving the frequency stability of the microgrid and enabling friendly grid connection of distributed power sources. However, traditional VSG control does not have the ability of low voltage ride through, is difficult to provide reactive power support, and is prone to problems such as grid frequency distortion, overlimit of output voltage and current amplitude.

[0005] In response to the above problems, relevant researchers have proposed a variety of low-voltage ride-through technologies. However, many traditional low-voltage ride-through technologies focus on fault current limiting during low-voltage ride-through, ignoring that when the grid voltage drops and is removed, the grid voltage and the amplitude and phase of the grid-connected point voltage will jump, which will cause faults. In addition, the grid frequency and voltage value will be distorted when the grid voltage drop is removed, which will cause the grid output current and output power to be distorted. To ensure the safe and stable operation of the power grid, grid codes generally require the grid frequency to be maintained within a deviation range of the rated frequency ±0.2 Hz, and the grid voltage to be maintained within a deviation range of the nominal voltage ±10%. This requires that during the grid voltage drop, the grid can not only limit the current but also operate stably on the premise that the frequency and voltage meet the requirements.

[0006] Liu Hang et al. proposed a low-voltage ride-through technology of adding quantitative virtual impedance to VSG in the literature titled "VSG Low-Voltage Ride-Through Strategy Based on Quantitative Design of Virtual Impedance" (High Voltage Engineering, 2022(48): pp. 245-256). Its control principle is as Figure 3 shown. The overall control strategy of this literature is to simulate the stator impedance by introducing virtual impedance into the traditional VSG control. Subtract the voltage drop on the virtual impedance from the internal potential to obtain the dq-axis modulation signal of the inverter. Input the obtained modulation signal into the voltage-current double-loop control, and finally perform SVPWM modulation on the voltage signal obtained by the double-loop control to form the switching control signal of the energy storage converter. This strategy limits the magnitude of the fault current during low-voltage ride-through and designs the value of the virtual impedance based on the principle of generating more reactive power. After the grid voltage is restored, immediately remove the virtual inductor added during the voltage drop period and recalculate the value of the virtual resistor required to suppress the inrush current at this time to limit the transient inrush current.

[0007] Based on the above method of adding quantitative virtual impedance to limit the current, different VSG active loop and reactive loop control methods are adopted during voltage drop and recovery to maintain the stable operation of the grid. However, this control strategy ignores the jumps in the grid voltage phase and amplitude during the grid voltage drop and recovery processes. The jumps in the grid voltage phase and amplitude will cause the difference between the VSG output voltage and the grid voltage phase and amplitude to be too large, resulting in distortion of the grid-connected point voltage during the grid voltage drop and recovery processes, and at the same time, the grid frequency will also fluctuate greatly. Summary of the Invention

[0008] The purpose of the embodiments of this application is to provide a low-voltage ride-through control method and device for an energy storage converter based on active support, which can not only provide a certain amount of reactive power support while limiting the current, but also ensure that the fluctuations of the grid voltage and frequency during the low-voltage ride-through process are within the allowable range.

[0009] According to the first aspect of the embodiments of the present application, a low-voltage ride-through control method based on an active support type energy storage converter is provided, including:

[0010] S1: Analyze the variation law of the virtual impedance during the grid voltage dip and during the grid voltage recovery, and introduce the virtual impedance link into the reactive power-voltage loop of the active support type energy storage converter to simulate the stator impedance in a synchronous generator;

[0011] S2: Calculate the voltage drop on the virtual impedance, and then subtract the voltage drop on the virtual impedance from the internal potential to obtain the two components of the modulation voltage of the active support type energy storage converter on the dq axes. These two components then pass through the voltage-current double closed-loop module, the coordinate transformation module, and the SVPWM module in sequence to form signals for controlling the turning on and off of the power tubes of the energy storage converter;

[0012] S3: Use the phase-locked loop module to extract the real-time phase angle of the grid voltage during the low-voltage ride-through;

[0013] S4: During the low-voltage ride-through, with the real-time phase angle as the axis for orientation, perform dq coordinate transformation on the internal potential of the active support type energy storage converter to obtain the component of the internal potential on the q axis and compare it with the reference value of the internal potential q-axis voltage. The difference between the two is calculated by a PI regulator to obtain the frequency compensation amount, calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the internal potential q-axis component. During the low-voltage ride-through, the internal potential q-axis component must be greater than this minimum output value to ensure that the frequency fluctuation range of the grid is within 0 to 0.2 Hz;

[0014] S5: After the grid voltage is restored, with the real-time phase angle as the axis for orientation, perform dq coordinate transformation on the output voltage of the active support type energy storage converter to obtain the component Ud on the d axis d and the component Uq on the q axis q , compare these two components with the corresponding reference values respectively, calculate the differences respectively and then calculate the frequency compensation amount and voltage compensation amount of the active support type energy storage converter through a PI regulator, and determine the compensation time of the frequency compensation amount and voltage compensation amount;

[0015] S6: Introduce the frequency compensation amount and voltage compensation amount into the active power-frequency loop and reactive power-voltage loop of the active support type energy storage converter respectively, and superimpose them with the original frequency reference value and voltage reference value to obtain new frequency reference values and voltage reference values, thereby forming a closed-loop negative feedback.

[0016] Further, in S1, analyzing the variation law of the virtual impedance during the grid voltage dip and during the grid voltage recovery includes:

[0017] Denote the impedance between the internal potential and the grid voltage during the grid voltage dip as RF +jω s L F , where R F is the resistance between the potential and the grid voltage during the grid voltage dip, ω s is the angular frequency of the grid voltage, L F is the inductance between the potential and the grid voltage during the grid voltage dip. The above impedance includes the total impedance R0 + jω s L0 between the internal potential and the grid voltage before the dip and the virtual impedance R v +jω s L V added by the control module to achieve low-voltage ride-through. Among them, R0 is the total resistance between the internal potential and the grid voltage before the dip, L0 is the total inductance between the internal potential and the grid voltage before the dip, R v is the virtual resistance added to achieve low-voltage ride-through, and L V is the virtual inductance added to achieve low-voltage ride-through; Denote the loop impedance after voltage recovery as R vR +jω s L vR , where R vR is the loop resistance after voltage recovery, and L vR is the loop inductance after voltage recovery. The above impedance includes the total impedance R0 + jω s L0 between the internal potential and the grid voltage before the dip and the virtual resistance R v added to achieve low-voltage ride-through; Denote i sF (t) as the output current of the active support type energy storage converter after the grid voltage dip, and i R (t) as the output current of the active support type energy storage converter during the grid voltage recovery stage. According to the three-element rule, we can get:

[0018]

[0019]

[0020] Where: i SF (t) is the steady-state current component after the grid voltage dip; i SF0 is the initial value of the steady-state current after the grid voltage dip; i0 is the current value at the moment of the grid voltage dip; τ F is the impulse current decay time constant after the grid voltage dip, and this constant is determined by the loop impedance after the grid voltage dip, that is, τ F = L F / R F ; i sR (t) is the steady-state current component after voltage recovery; i SF1 is the current value at the moment immediately before the grid voltage recovery; isR0 is the initial value of the steady-state current after the grid voltage is restored; τ R is the decay time constant of the inrush current after the grid voltage is restored, and this constant is determined by the loop impedance after the grid voltage is restored, that is, τ R = L vR / R vR ;

[0021] According to the three-element rule, during the grid voltage sag, there is a risk of steady-state overcurrent and transient overcurrent in the grid current. During the grid voltage restoration, the amplitude of the transient current in the grid current is larger, but there is no risk of steady-state overcurrent; the smaller the time constant, the more beneficial it is to reduce the transient current. Therefore, after the grid voltage is restored, the control module immediately removes the virtual reactance added during the grid voltage sag and retains the virtual resistance added during the grid voltage sag to suppress the inrush current. From the decay characteristics of the exponential function, it can be seen that the transient current component has almost decayed to 0 after 4τ R , so after 4τ R , the control module reduces the value of the virtual resistance to 0.

[0022] Furthermore, calculate the voltage drop across the virtual impedance, and then subtract the voltage drop across the virtual impedance from the internal potential to obtain the two components of the modulation voltage of the active support type energy storage converter on the dq axis, including:

[0023] Calculate the two components u mod_d and u mod_q of the modulation voltage of the active support type energy storage converter on the dq axis through the following formula:

[0024]

[0025]

[0026] where: E is the internal potential, i od and i oq are the d-axis component and q-axis component obtained by dq transformation of the output current i oabc of the active support type energy storage converter respectively, and ω s is the angular frequency of the grid voltage.

[0027] Furthermore, calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the q-axis component of the internal potential, including:

[0028] Freeze the reactive-voltage loop in the active support type energy storage converter, and let q ref = Q, Q ref is the reference voltage, and Q is the actual output voltage, so that the active support type energy storage converter outputs a rated internal potential with an amplitude of 311V;

[0029] Adjust the reference value U of the component of the output voltage on the q-axis q_ref , so as to adjust the power angle δ between the internal potential of the active support type energy storage converter and the grid voltage, thereby controlling the active and reactive power values output by the active support type energy storage converter to the grid;

[0030] During the low voltage ride-through period, set the minimum power angle value between the internal potential of the active support type energy storage converter and the grid voltage to δ min , which is equivalent to setting the value of U q-ref to the minimum value U of the component of the output voltage on the q-axis that meets the requirements of low voltage ride-through q-ref-min .

[0031] Furthermore, in S4, the specific calculation method of the frequency compensation amount Δω is as follows:

[0032]

[0033]

[0034]

[0035] where: K p_ω and K p_δ are given proportionality coefficients, K i_ω and K i_δ are given integral coefficients, s is the Laplace operator, and f is the actual frequency of the grid.

[0036] Furthermore, in S5, the frequency compensation amount Δω′ and voltage compensation amount ΔU′ of the active support type energy storage converter are calculated through the following formulas:

[0037]

[0038]

[0039] where: 311 and 0 are the reference quantities of the given d-axis voltage and q-axis voltage respectively, K p_ω′ and K p_U′ are given proportionality coefficients, K i_ω′ and K i_U′ are given integral coefficients, and S is the Laplace operator.

[0040] Furthermore, in S5, the specific method for determining the compensation time of the frequency compensation amount and voltage compensation amount is as follows:

[0041] Continuously detect the phase difference between the output voltage phase of the active support type energy storage converter and the grid voltage phase. When the phase difference between the two is zero, stop the frequency compensation during the grid voltage recovery;

[0042] Continuously detect the value of the virtual resistance. When the value of the virtual resistance is 0, it means that the virtual resistance has been completely removed, and the voltage compensation during the grid voltage recovery is stopped.

[0043] Further, in S6, the frequency reference value ω′ of the active support type energy storage converter during low voltage ride through and recovery is calculated by the following formula ref and the voltage reference value U′ ref :

[0044]

[0045] U′ ref =U ref +ΔU′ = E ref +k q (Q ref -Q)+ΔU'

[0046] where: ω m is the angular frequency of the virtual prime mover, k ω and k q are the droop coefficients of the active - frequency loop and the reactive - voltage loop respectively, P m is the active power output by the virtual prime mover, P ref is the reference value of the active power output by the virtual prime mover, E ref is the reference value of the given voltage in the virtual excitation controller, Q ref is the reference value of the reactive power in the virtual excitation controller, and Q is the reactive power output by the active support type energy storage converter.

[0047] According to the second aspect of the embodiments of the present application, a low - voltage ride - through control device based on an active support type energy storage converter is provided, including:

[0048] A virtual impedance analysis module, configured to analyze the variation law of the virtual impedance during the grid voltage dip and the grid voltage recovery, and introduce the virtual impedance link into the reactive - voltage loop of the active support type energy storage converter to simulate the stator impedance in the synchronous generator;

[0049] A modulation voltage calculation module, configured to calculate the voltage drop on the virtual impedance, and then subtract the voltage drop on the virtual impedance from the internal potential to obtain the two components of the modulation voltage of the active support type energy storage converter on the dq axes. These two components then pass through the voltage - current double - closed - loop module, the coordinate transformation module, and the SVPWM module in sequence to form signals for controlling the on - off of the power tubes of the energy storage converter;

[0050] A phase angle extraction module, configured to extract the real - time phase angle of the grid voltage during low - voltage ride through by using the phase - locked loop module;

[0051] The low-voltage ride-through compensation module is used to perform dq coordinate transformation on the internal potential of the active support type energy storage converter with the real-time phase angle as the axis during low-voltage ride-through, obtain the component of the internal potential on the q-axis, compare it with the reference value of the internal potential q-axis voltage, calculate the frequency compensation amount through a PI regulator for the difference between the two, calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the internal potential q-axis component. During low-voltage ride-through, the internal potential q-axis component must be greater than this minimum output value to ensure that the frequency fluctuation range of the grid is within 0 to 0.2 Hz;

[0052] The grid voltage recovery compensation module is used to perform dq coordinate transformation on the output voltage of the active support type energy storage converter with the real-time phase angle as the axis after the grid voltage recovers, obtain the component Ud of the output voltage on the d-axis d and the component Uq of the output voltage on the q-axis q , compare these two components with the corresponding reference values respectively, calculate the differences respectively, and then calculate the frequency compensation amount and voltage compensation amount of the active support type energy storage converter through a PI regulator, and determine the compensation time of the frequency compensation amount and voltage compensation amount;

[0053] The frequency and voltage reference value synthesis module is used to introduce the frequency compensation amount and voltage compensation amount into the active power-frequency loop and reactive power-voltage loop of the active support type energy storage converter respectively, and superimpose them with the original frequency reference value and voltage reference value to obtain new frequency reference values and voltage reference values, thereby forming a closed-loop negative feedback.

[0054] According to the third aspect of the embodiments of the present application, an electronic device is provided, including:

[0055] One or more processors;

[0056] A memory for storing one or more programs;

[0057] When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0058] The technical solutions provided by the embodiments of the present application may include the following beneficial effects:

[0059] As can be seen from the above embodiments, the present application can change the current decay time constant by setting different virtual impedance values during grid voltage dips and grid voltage recoveries, and can provide a certain amount of reactive power support while limiting the current. By setting different frequency compensation amounts and voltage compensation amounts during grid voltage dips and grid voltage recoveries, and thus adjusting the reference values of the grid frequency and the output voltage of the energy storage converter, it is possible to ensure that the fluctuations of the grid voltage and frequency during low-voltage ride-through are within the allowable range.

[0060] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and do not limit this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with this application, and are used together with the specification to explain the principles of this application.

[0062] Figure 1 is a flowchart of a low-voltage ride-through control method based on an active support type energy storage converter shown according to an exemplary embodiment.

[0063] Figure 2 is a control diagram of a low-voltage ride-through control method based on an active support type energy storage converter shown according to an exemplary embodiment.

[0064] Figure 3 is a variation diagram of the virtual impedance added during low-voltage ride-through.

[0065] Figure 4 is a schematic diagram of the regulation of the power angle difference between the internal potential of the active support type energy storage converter and the grid voltage.

[0066] Figure 5 is a block diagram of the frequency and amplitude compensation algorithms during grid voltage dip and grid voltage recovery, where (a) is the frequency compensation during low-voltage ride-through, and (b) is the frequency compensation and voltage compensation after grid voltage recovery.

[0067] Figure 6 is a control diagram of a traditional low-voltage ride-through method based on virtual impedance.

[0068] Figure 7 is a waveform diagram of a traditional low-voltage ride-through strategy based on virtual resistance, where (a) is the voltage waveform diagram, (b) is the current waveform diagram, and (c) is the frequency waveform diagram.

[0069] Figure 8 is a waveform diagram of a low-voltage ride-through strategy shown according to an exemplary embodiment, where (a) is the voltage waveform diagram, (b) is the current waveform diagram, and (c) is the frequency waveform diagram.

[0070] Figure 9 is a block diagram of a low-voltage ride-through control device based on an active support type energy storage converter shown according to an exemplary embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0071] Exemplary embodiments will be described in detail herein, and examples thereof are shown in the accompanying drawings. When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0072] The terms used in this application are for the purpose of describing particular embodiments only and are not intended to limit the present application. The singular forms "a", "said", and "the" used in this application and the appended claims are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0073] Figure 1 is a flowchart of a low-voltage ride-through control method based on an active support type energy storage converter shown according to an exemplary embodiment. Figure 2 is a control diagram of a low-voltage ride-through control method based on an active support type energy storage converter shown according to an exemplary embodiment. The method may include the following steps:

[0074] S1: Analyze the variation law of the virtual impedance during the grid voltage dip and during the grid voltage recovery, and introduce the virtual impedance link into the reactive power-voltage loop of the active support type energy storage converter to simulate the stator impedance in a synchronous generator;

[0075] S2: Calculate the voltage drop across the virtual impedance, and then subtract the voltage drop across the virtual impedance from the internal potential to obtain the two components u mod_d and u mod_q of the modulation voltage of the active support type energy storage converter on the dq axes. These two components then pass through the voltage-current double closed-loop module, the coordinate transformation module, and the SVPWM module in sequence to form signals for controlling the on and off of the power tubes of the energy storage converter;

[0076] S3: Use the phase-locked loop module to extract the real-time phase angle θ g of the grid voltage during the low-voltage ride-through;

[0077] S4: During the low-voltage ride-through, orient with the real-time phase angle θ g as the axis, perform dq coordinate transformation on the internal potential E abc of the active support type energy storage converter to obtain the component U q of the internal potential on the q axis and compare it with the reference value U q-refCompare them, and the difference between the two is calculated by a PI regulator to obtain the frequency compensation amount Δω. Calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the q-axis component of the internal potential. During the low-voltage ride-through period, the q-axis component of the internal potential must be greater than this minimum output value to ensure that the frequency fluctuation range of the power grid is within 0 to 0.2 Hz;

[0078] S5: After the grid voltage is restored, with the real-time phase angle θ g as the axis orientation, perform dq coordinate transformation on the output voltage u oubc of the active support type energy storage converter to obtain the component U d of the output voltage on the d-axis and the component U q on the q-axis. Compare these two components with the corresponding reference values (the reference value of the d-axis component is 311 V, and the reference value of the q-axis component is 0 V) respectively, calculate the differences respectively, and then calculate the frequency compensation amount Δω′ and voltage compensation amount ΔU′ of the active support type energy storage converter through a PI regulator, and determine the compensation time of the frequency compensation amount Δω′ and voltage compensation amount ΔU′;

[0079] S6: Introduce the frequency compensation amount Δω′ and voltage compensation amount ΔU′ into the active power - frequency loop and reactive power - voltage loop of the active support type energy storage converter respectively, and superimpose them with the original frequency reference value ω ref and voltage reference value U ref to obtain the new frequency reference value ω′ ref and voltage reference value U′ ref , thereby forming a closed-loop negative feedback.

[0080] As can be seen from the above embodiments, the present application can change the current decay time constant by setting different virtual impedance values during the grid voltage drop period and the grid voltage recovery period, and can provide a certain amount of reactive power support while limiting the current. The present application can adjust the reference values of the grid frequency and the output voltage of the energy storage converter by setting different frequency compensation amounts and voltage compensation amounts during the grid voltage drop period and the grid voltage recovery period, and can ensure that the fluctuations of the grid voltage and frequency during the low-voltage ride-through process are within the allowable range.

[0081] In the specific implementation of S1: Analyze the change law of the virtual impedance during the grid voltage drop period and the grid voltage recovery period, and introduce the virtual impedance link into the reactive power - voltage loop of the active support type energy storage converter to simulate the stator impedance in the synchronous generator;

[0082] Specifically, Figure 3 is the change diagram of the virtual impedance added during the low-voltage ride-through period. L v is the virtual inductor, L v = 18 mH, R vis a virtual resistor, and R v = 4.3 Ω during the grid voltage dip. Within 4 time constants after the grid voltage recovery, R v = 2.4 Ω. After 4 time constants, its value is 0.

[0083] By setting different virtual impedance values during the grid voltage dip and grid voltage recovery, thereby changing the current decay time constant, it is possible to provide a certain amount of reactive power support while limiting the current.

[0084] In the specific implementation of S2: Calculate the voltage drop across the virtual impedance, and then subtract the voltage drop across the virtual impedance from the internal potential to obtain the two components u mod_d and u mod_q of the modulation voltage of the active support type energy storage converter on the dq axes. These two components then pass through the voltage-current double closed-loop module, coordinate transformation module, and SVPWM module in sequence to form signals for controlling the on and off of the power tubes of the energy storage converter;

[0085] Specifically, first use a Hall current sensor to collect the three-phase output current I oa ~I oc of the active support type energy storage converter; then input the collected three-phase output current into the virtual impedance link, and subtract the voltage drop generated on the virtual impedance at this time from the internal potential E of the active support type energy storage converter to obtain the modulation voltage u mod of the active support type energy storage converter; finally, use the dq transformation module to perform dq transformation on the modulation voltage to obtain the d-axis component u mod_d and q-axis component u mod_q of the modulation voltage in the rotating d-q coordinate system; the transformation matrix of the dq transformation is as follows:

[0086]

[0087] Finally, the components of the modulation voltage of the active support type energy storage converter on the dq axes are obtained as shown in the following formula:

[0088]

[0089]

[0090] where: θ is the phase of the internal potential of the active support type energy storage converter, ω s = 100π rad / s, which is the rated angular frequency of the grid voltage.

[0091] In the specific implementation of S3: Use the phase-locked loop module to extract the real-time phase angle θ g of the grid voltage during the low voltage ride-through;

[0092] Specifically, under the condition of stable grid voltage, the active support type energy storage converter can simulate the self-synchronization characteristic of a synchronous generator, synthesize a voltage vector by using the phase angle output by the active power loop and the voltage amplitude output by the reactive power loop, so as to achieve self-synchronization grid connection. However, under the condition of grid voltage fault, the active support type energy storage converter cannot simulate the self-synchronization characteristic of a synchronous generator. Therefore, it is necessary to rely on a phase-locked loop module to complete grid connection, and use the built-in phase-locked loop module in Matlab / simulink to extract the real-time phase angle θ of the grid voltage g , whose input is the three-phase values of the grid voltage and the output is the real-time phase angle of the grid voltage.

[0093] In the specific implementation of S4: during low voltage ride-through, with the real-time phase angle θ g as the axis orientation, perform dq coordinate transformation on the internal potential E abc of the active support type energy storage converter to obtain the component U q of the internal potential on the q-axis, and compare it with the reference value U q_ref of the internal potential q-axis voltage. The difference between the two is calculated by a PI regulator to obtain a frequency compensation amount Δω, calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the internal potential q-axis component. During low voltage ride-through, the internal potential q-axis component must be greater than this minimum output value to ensure that the frequency fluctuation range of the grid is within 0 - 0.2 Hz;

[0094] Specifically, Figure 4 is the schematic diagram for regulating the power angle difference between the internal potential of the active support type energy storage converter and the grid voltage, calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the internal potential q-axis component, including:

[0095] Freeze the reactive power-voltage loop in the active support type energy storage converter, make Q ref = Q, Q ref is the reference voltage, Q is the actual output voltage, so that the active support type energy storage converter outputs a rated internal potential with an amplitude of 311V;

[0096] Adjust the reference value U q_ref of the component of the output voltage on the q-axis to adjust the magnitude of the power angle δ between the internal potential of the active support type energy storage converter and the grid voltage, so as to control the active and reactive power values output by the active support type energy storage converter to the grid;

[0097] During low voltage ride-through, set the minimum power angle value between the internal potential of the active support type energy storage converter and the grid voltage to δ min , which is equivalent to setting the value of U q_ref to the minimum value U q_ref_min of the component of the output voltage on the q-axis that meets the requirements of low voltage ride-through. The two satisfy the following formula:

[0098]

[0099]

[0100] The frequency compensation amount Δω during low-voltage ride-through is calculated by using a PI regulator according to the following formula:

[0101]

[0102] where: K p_ω and K p_δ are given proportionality coefficients, K i_ω and K i_δ are given integral coefficients, s is the Laplace operator, and f is the actual frequency of the power grid.

[0103] In the specific implementation of S5: After the grid voltage is restored, with the real-time phase angle θ g as the axis orientation, the output voltage u oabc of the active support type energy storage converter is subjected to dq coordinate transformation to obtain the component U d on the d-axis and the component U q on the q-axis of the output voltage. These two components are respectively compared with the corresponding reference values (the reference value of the d-axis component is 311V, and the reference value of the q-axis component is 0V), the differences are calculated respectively, and then the frequency compensation amount Δω′ and voltage compensation amount ΔU′ of the active support type energy storage converter are calculated through a PI regulator, and the compensation times of the frequency compensation amount Δω′ and voltage compensation amount ΔU′ are determined;

[0104] Specifically, the frequency compensation amount Δω′ and voltage compensation amount ΔU′ of the active support type energy storage converter are calculated through the following formulas:

[0105]

[0106]

[0107] where: 311 and 0 are respectively the reference quantities of the given d-axis voltage and q-axis voltage, K p_ω′ and K p_U′ are given proportionality coefficients, K i_ω′ and K i_U′ are given integral coefficients, and S is the Laplace operator.

[0108] Figure 5It is a block diagram of a frequency and amplitude compensation algorithm during grid voltage sag and grid voltage recovery. By setting different frequency compensation amounts and voltage compensation amounts during grid voltage sag and grid voltage recovery, the reference values of grid frequency and the output voltage of the energy storage converter are adjusted, which can ensure that the fluctuations of grid voltage and frequency during the low-voltage ride-through process are within the allowable range.

[0109] In the specific implementation of S6: The frequency compensation amount Δω′ and voltage compensation amount ΔU′ are respectively introduced into the active power-frequency loop and reactive power-voltage loop of the active support type energy storage converter, and are superimposed with the original frequency reference value ω ref and voltage reference value U ref to obtain a new frequency reference value ω′ ref and voltage reference value U′ ref , thereby forming a closed-loop negative feedback.

[0110] Specifically, the frequency reference value ω′ ref and voltage reference value U r ′ ef of the active support type energy storage converter during low-voltage ride-through and recovery are calculated through the following formulas:

[0111]

[0112]

[0113] Where: ω m is the angular frequency of the virtual prime mover, k ω and k q are the droop coefficients of the active power-frequency loop and reactive power-voltage loop respectively, P m is the active power output by the virtual prime mover, P ref is the reference value of the active power output by the virtual prime mover, E ref is the reference value of the given voltage in the virtual excitation controller, Q ref is the reference value of the reactive power in the virtual excitation controller, and Q is the reactive power output by the active support type energy storage converter.

[0114] The low-voltage ride-through control method of the energy storage converter based on active support proposed by the present invention is simulated, and compared with the simulation of the traditional low-voltage ride-through control method based on virtual impedance. Figure 6 It is the control diagram of the traditional low-voltage ride-through method based on virtual impedance. Under the control of the two methods, the grid voltage drops by 0.5 p.u. from 0.7 s to 1.3 s. When using the traditional control strategy based on quantitative virtual impedance, refer to Figure 7It can be seen from (a), (b), and (c) in [reference] that during the voltage dip, the current is effectively limited and no overcurrent effect occurs. However, after the grid voltage recovers, the grid-connected point current changes periodically, and the maximum current value is approximately 13 p.u., which significantly exceeds the allowable value of the grid. The grid-connected point voltage is actively compensated during the grid voltage dip. During the grid voltage recovery period, the grid-connected point voltage also shows a similar periodic change, with a maximum value of approximately 2 p.u. The frequency fluctuates severely after the grid voltage dip, reaching approximately 51.7 Hz at its worst. When the low-voltage ride-through control strategy of the present invention is adopted, referring to Figure 8 It can be seen from (a), (b), and (c) in [reference] that during the grid voltage recovery period, the current basically remains in a stable state, and the maximum current value is around 1.4 p.u. During the grid voltage recovery period, the grid-connected point voltage value also basically remains in a stable state. The grid-connected point frequency also remains around 50 Hz, and the maximum fluctuation range is within ±0.2 Hz.

[0115] In summary, compared with the traditional low-voltage ride-through method, the control method of the present invention has a simple structure, fast dynamic response, and excellent steady-state performance. Its characteristic of using a PI regulator to quickly eliminate errors can quickly adjust the power angle between the internal potential of the active support type energy storage converter and the grid voltage when the grid voltage dips, so as to make the energy storage converter output the corresponding active power value and maintain the stability of the grid frequency. In addition, during the grid voltage recovery period, it quickly compensates the phase difference and amplitude difference between the output voltage u oabc of the active support type energy storage converter and the grid voltage u gabc reduces the delay time of system stability, and can also significantly reduce the overshoot amplitude of the grid-connected point current at the moment of grid voltage dip occurrence and removal. By adding a control method with a virtual impedance and amplitude and phase compensation link, the control ability of the energy storage converter during the grid voltage dip is enhanced, the power quality of the grid is improved, a smooth low-voltage ride-through process during the grid voltage dip is achieved, and the simplicity and rapidity of control are improved at the same time.

[0116] Corresponding to the foregoing embodiments of the low-voltage ride-through control method based on the active support type energy storage converter, the present application also provides embodiments of a low-voltage ride-through control device based on the active support type energy storage converter.

[0117] Figure 9 FIG. [figure number] is a block diagram of a low-voltage ride-through control device based on an active support type energy storage converter shown according to an exemplary embodiment. Referring to Figure 9 , the device includes:

[0118] The virtual impedance analysis module 1 is used to analyze the variation law of the virtual impedance during the grid voltage dip and during the grid voltage recovery, and introduce the virtual impedance link into the reactive power-voltage loop of the active support type energy storage converter to simulate the stator impedance in the synchronous generator;

[0119] The modulation voltage calculation module 2 is used to calculate the voltage drop on the virtual impedance, and then subtract the voltage drop on the virtual impedance from the internal potential to obtain the two components of the modulation voltage of the active support type energy storage converter on the dq axes. These two components then pass through the voltage-current double closed-loop module, the coordinate transformation module, and the SVPWM module in sequence to form signals for controlling the turning on and off of the power tubes of the energy storage converter;

[0120] The phase angle extraction module 3 is used to extract the real-time phase angle of the grid voltage during the low voltage ride-through using the phase-locked loop module;

[0121] The low voltage ride-through compensation module 4 is used to, during the low voltage ride-through, perform dq coordinate transformation on the internal potential of the active support type energy storage converter with the real-time phase angle as the axis orientation, obtain the component of the internal potential on the q axis and compare it with the reference value of the internal potential q-axis voltage. The difference between the two is calculated by the PI regulator to obtain the frequency compensation amount, calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the internal potential q-axis component. During the low voltage ride-through, the internal potential q-axis component must be greater than this minimum output value to ensure that the frequency fluctuation range of the grid is within 0 to 0.2 Hz;

[0122] The grid voltage recovery compensation module 5 is used to, after the grid voltage recovers, perform dq coordinate transformation on the output voltage of the active support type energy storage converter with the real-time phase angle as the axis orientation, obtain the component Ud on the d axis d and the component Uq on the q axis q , compare these two components with the corresponding reference values respectively, calculate the differences respectively and then calculate the frequency compensation amount and voltage compensation amount of the active support type energy storage converter through the PI regulator, and determine the compensation time of the frequency compensation amount and voltage compensation amount;

[0123] The frequency-voltage reference value synthesis module 6 is used to introduce the frequency compensation amount and voltage compensation amount into the active power-frequency loop and reactive power-voltage loop of the active support type energy storage converter respectively, and superimpose them with the original frequency reference value and voltage reference value to obtain new frequency reference values and voltage reference values, thereby forming a closed-loop negative feedback.

[0124] Regarding the device in the above embodiments, the specific manners in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated here.

[0125] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the descriptions in the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this application. Those of ordinary skill in the art can understand and implement it without creative work.

[0126] Correspondingly, this application also provides an electronic device, including: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the low-voltage ride-through control method based on the active support type energy storage converter as described above.

[0127] Correspondingly, this application also provides a computer-readable storage medium, on which computer instructions are stored, and when the instructions are executed by a processor, the low-voltage ride-through control method based on the active support type energy storage converter as described above is implemented.

[0128] After considering the specification and practicing the content disclosed herein, those skilled in the art will readily think of other embodiments of this application. This application is intended to cover any variations, uses, or adaptations of this application, which follow the general principles of this application and include common general knowledge or conventional technical means in the technical field not disclosed in this application. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of this application are pointed out by the claims.

[0129] It should be understood that this application is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is only limited by the appended claims.

Claims

1. A low voltage ride-through control method based on an active support type energy storage converter, characterized in that, Including: S1: Analyze the variation law of the virtual impedance during the grid voltage dip and during the grid voltage recovery, and introduce the virtual impedance link into the reactive-voltage loop of the active support type energy storage converter to simulate the stator impedance in the synchronous generator; S2: Calculate the voltage drop on the virtual impedance, and then subtract the voltage drop on the virtual impedance from the internal potential to obtain the two components of the modulation voltage of the active support type energy storage converter on the dq axes. These two components then pass through the voltage-current double closed-loop module, the coordinate transformation module, and the SVPWM module in sequence to form signals for controlling the turn-on and turn-off of the power tubes of the energy storage converter; S3: Use the phase-locked loop module to extract the real-time phase angle of the grid voltage during the low voltage ride-through; S4: During the low voltage ride-through, with the real-time phase angle as the axis orientation, perform dq coordinate transformation on the internal potential of the active support type energy storage converter to obtain the component of the internal potential on the q axis and compare it with the reference value of the internal potential q-axis voltage. The difference between the two is calculated by the PI regulator to obtain the frequency compensation amount. Calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the internal potential q-axis component. During the low voltage ride-through, the internal potential q-axis component must be greater than this minimum output value to ensure that the frequency fluctuation range of the grid is within 0 to 0.2 Hz; S5: After the grid voltage is restored, with the real-time phase angle as the axis for orientation, perform dq coordinate transformation on the output voltage of the active support type energy storage converter to obtain the component Ud of the output voltage on the d-axis d and the component Uq of the output voltage on the q-axis q , compare these two components with the corresponding reference values respectively, calculate the differences respectively, then calculate the frequency compensation amount and voltage compensation amount of the active support type energy storage converter through a PI regulator, and determine the compensation time of the frequency compensation amount and voltage compensation amount; S6: Introduce the frequency compensation amount and the voltage compensation amount into the active power-frequency loop and the reactive-voltage loop of the active support type energy storage converter respectively, and superimpose them on the original frequency reference value and voltage reference value to obtain new frequency reference values and voltage reference values, thereby forming a closed-loop negative feedback.

2. The low-voltage ride-through control method according to claim 1, characterized in that, In S1, analyzing the variation law of the virtual impedance during the grid voltage dip and during the grid voltage recovery includes: Denote the impedance between the electromotive force and the grid voltage during the grid voltage dip as R F +jω s L F , where R F is the resistance between the electromotive force and the grid voltage during the grid voltage dip, ω s is the angular frequency of the grid voltage, L F is the inductance between the electromotive force and the grid voltage during the grid voltage dip. The above impedance includes the total impedance R0 + jω s L0 between the internal electromotive force and the grid voltage before the dip and the virtual impedance R v +jω s L V added additionally by the control module to achieve low voltage ride-through. Wherein, R0 is the total resistance between the internal electromotive force and the grid voltage before the dip, L0 is the total inductance between the internal electromotive force and the grid voltage before the dip, R v is the virtual resistance added additionally to achieve low voltage ride-through, and L V is the virtual inductance added additionally to achieve low voltage ride-through; Denote the loop impedance after the voltage recovery as R vR +jω s L vR , where R vR is the loop resistance after the voltage recovery, and L vR is the loop inductance after the voltage recovery. The above impedance includes the total impedance R0 + jω s L0 between the internal electromotive force and the grid voltage before the dip and the virtual resistance R v added to achieve low voltage ride-through; Denote i sF (t) as the output current of the active support type energy storage converter after the grid voltage dip, and i R (t) as the output current of the active support type energy storage converter during the grid voltage recovery stage. According to the three-element rule, we can obtain: Where: i SF (t) is the steady-state current component after the grid voltage sags; i SF0 is the initial value of the steady-state current after the grid voltage sags; i0 is the current value at the moment of the grid voltage sag; τ F is the decay time constant of the inrush current after the grid voltage sags, and this constant is determined by the loop impedance after the grid voltage sags, that is, τ F = L F / R F ; i sR (t) is the steady-state current component after the voltage recovers; i SF is the current value at the moment immediately before the grid voltage recovers; is the initial value of the steady-state current after the grid voltage recovers; τ R is the decay time constant of the inrush current after the grid voltage recovers, and this constant is determined by the loop impedance after the grid voltage recovers, that is, τ R = L vR / R vR ; According to the three-element rule, during the grid voltage sag, there is a risk of steady-state overcurrent and transient overcurrent in the grid current. During the grid voltage recovery, the amplitude of the transient current in the grid current is larger, but there is no risk of steady-state overcurrent. The smaller the time constant, the more beneficial it is to reduce the transient current. Therefore, after the grid voltage recovers, the control module immediately removes the virtual reactance added during the grid voltage sag and retains the virtual resistance added during the grid voltage sag to suppress the inrush current. From the decay characteristics of the exponential function, it can be seen that the transient current component has almost decayed to 0 after 4τ R After that, it is almost decayed to 0. Therefore, after 4τ R After that, the control module reduces the value of the virtual resistance to 0.

3. The low-voltage ride-through control method according to claim 1, characterized in that In S2, calculating the voltage drop on the virtual impedance, and then subtracting the voltage drop on the virtual impedance from the internal potential to obtain the two components of the modulation voltage of the active support type energy storage converter on the dq axes includes: Calculate the two components \(u_{d}\) and \(u_{q}\) of the modulation voltage of the active support type energy storage converter on the dq axis through the following formula: mod_d and \(u_{q}\) mod_q : Where: E is the internal electric potential, i od and i oq are respectively the d-axis component and the q-axis component obtained after the dq transformation of the output current i oabc of the active support type energy storage converter, and ω s is the angular frequency of the grid voltage.

4. The low-voltage ride-through control method according to claim 1, wherein In S4, calculating the minimum value of the power angle between the internal potential and the grid voltage, and giving the minimum output value of the internal potential q-axis component includes: Freeze the reactive power-voltage loop in the active support type energy storage converter, and make Q ref = Q, where Q ref is the reference voltage and Q is the actual output voltage, so that the active support type energy storage converter outputs a rated internal electromotive force with an amplitude of 311V; Adjust the reference value U of the component of the output voltage on the q-axis q_ref , so as to adjust the magnitude of the power angle δ between the internal electromotive force of the active support type energy storage converter and the grid voltage, thereby controlling the active and reactive power values output by the active support type energy storage converter to the grid; During low voltage ride-through, set the minimum power angle value between the internal potential of the active support type energy storage converter and the grid voltage as δ min , so as to equivalently set the value of U q_ref to the minimum value U q-ref_min of the component of the output voltage that meets the low voltage ride-through requirements on the q-axis. The two satisfy the following formula:

5. The low-voltage ride-through control method according to claim 1, characterized in that In S4, the specific calculation method of the frequency compensation amount Δω is: Where: K p_ω and K p_δ are given proportionality coefficients, K i_ω and K i_δ are given integral coefficients, s is the Laplace operator, and f is the actual frequency of the power grid.

6. The low-voltage ride-through control method according to claim 1, characterized in that In S5, the frequency compensation amount Δω′ and the voltage compensation amount ΔU′ of the active support type energy storage converter are calculated through the following formulas: Where: 311 and 0 are respectively the reference values of the given d-axis voltage and q-axis voltage, K p_ω′ and K p_U′ are the given proportionality coefficients, K i_ω′ and K i_U′ are the given integral coefficients, and S is the Laplace operator.

7. The low-voltage ride-through control method according to claim 1, wherein In S5, the specific method for determining the compensation time of the frequency compensation amount and the voltage compensation amount is: Continuously detect the phase difference between the output voltage phase of the active support type energy storage converter and the grid voltage phase. When the phase difference between the two is zero, stop the frequency compensation during the grid voltage recovery; Continuously detect the value of the virtual resistance. When the value of the virtual resistance is 0, it means that the virtual resistance has been completely removed, and stop the voltage compensation during the grid voltage recovery.

8. The low-voltage ride-through control method according to claim 1, characterized in that, In S6, the frequency reference value ω′ of the active support type energy storage converter during low voltage ride-through and recovery is calculated by the following formula ref and the voltage reference value U′ ref : U′ ref = U ref + ΔU′ = E ref + k q (Q ref - Q) + ΔU′ where: ω m is the angular frequency of the virtual prime mover, k ω and k q are the droop coefficients of the active - frequency loop and the reactive - voltage loop respectively, P m is the active power output by the virtual prime mover, P ref is the reference value of the active power output by the virtual prime mover, E ref is the reference value of the given voltage in the virtual excitation controller, Q ref is the reference value of the reactive power in the virtual excitation controller, and Q is the reactive power output by the active - support type energy storage converter.

9. A low voltage ride-through control device based on an active support type energy storage converter, characterized in that, Including: A virtual impedance analysis module, which is used to analyze the variation law of the virtual impedance during the grid voltage dip and during the grid voltage recovery, and introduce the virtual impedance link into the reactive-voltage loop of the active support type energy storage converter to simulate the stator impedance in the synchronous generator; A modulation voltage calculation module, which is used to calculate the voltage drop across the virtual impedance, and then subtract the voltage drop across the virtual impedance from the internal potential to obtain the two components of the modulation voltage of the active support type energy storage converter on the dq axes. These two components then pass through a voltage-current double closed-loop module, a coordinate transformation module, and an SVPWM module in sequence to form signals for controlling the turning on and off of the power transistors of the energy storage converter; A phase angle extraction module, which is used to extract the real-time phase angle of the grid voltage during low voltage ride-through by using a phase-locked loop module; A low voltage ride-through compensation module, which is used to, during low voltage ride-through, perform dq coordinate transformation on the internal potential of the active support type energy storage converter with the real-time phase angle as the axis orientation, obtain the component of the internal potential on the q axis and compare it with the reference value of the q-axis voltage of the internal potential. The difference between the two is calculated by a PI regulator to obtain a frequency compensation amount, calculate the minimum value of the power angle between the internal potential and the grid voltage, and give the minimum output value of the q-axis component of the internal potential. During low voltage ride-through, the q-axis component of the internal potential must be greater than this minimum output value to ensure that the frequency fluctuation range of the grid is within 0 to 0.2 Hz; The grid voltage restoration compensation module is used to perform dq coordinate transformation on the output voltage of the active support type energy storage converter with the real-time phase angle as the axis orientation after the grid voltage is restored, so as to obtain the component Ud of the output voltage on the d axis d and the component Uq of the output voltage on the q axis q , compare these two components with the corresponding reference values respectively, calculate the differences respectively, then calculate the frequency compensation amount and voltage compensation amount of the active support type energy storage converter through a PI regulator, and determine the compensation time of the frequency compensation amount and voltage compensation amount; A frequency-voltage reference value synthesis module, which is used to introduce the frequency compensation amount and the voltage compensation amount into the active power-frequency loop and the reactive power-voltage loop of the active support type energy storage converter respectively, and superimpose them on the original frequency reference value and voltage reference value to obtain new frequency reference values and voltage reference values, thereby forming a closed-loop negative feedback.

10. An electronic device, characterized in that, Comprising: One or more processors; A memory, which is used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1-8.

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