Energy storage converter parallel control method and system

Abstract

The application belongs to the technical field of power electronic control, and particularly relates to a kind of energy storage converter parallel control method and system.The method comprises: after Clark transformation, Park transformation of three-phase voltage signal and three-phase current signal output by inverter, active power and reactive power are calculated;Reference value of voltage loop and current loop is calculated, and prediction value is superimposed on current loop to obtain direct axis front end voltage and cross axis front end voltage, and then direct axis voltage and cross axis voltage are calculated;Direct axis voltage and cross axis voltage are subjected to SPWM modulation, and inverter bridge arm switch tube is driven to turn on and off to control inverter output.The prediction value superimposed in the application can quickly compensate the reference value required by current loop when load mutates, and then maintain the stability of voltage.

Description

Technical Field

[0001] This invention belongs to the field of power electronic control technology, specifically relating to a parallel control method and system for energy storage converters. Background Technology

[0002] Energy storage converters typically operate in droop mode, automatically adjusting voltage and frequency to support the power grid. With increasing demand for down-grid energy storage, such as requiring converters to mimic synchronous generator characteristics to improve grid strength, modularization of energy storage products with lower power outputs is also a trend, with multiple modules connected in parallel becoming commonplace. In microgrids, sudden load changes and three-phase imbalances are frequently encountered.

[0003] When the load changes abruptly, the current required to maintain the voltage changes drastically, and the outer voltage loop cannot keep up with the change quickly. This causes the reference value of the current loop to be inconsistent with the actual current required in a short period of time, resulting in a significant change in the output voltage.

[0004] When the three-phase load is unbalanced, without a dedicated algorithm, an unbalanced voltage will be output, containing a large amount of negative sequence voltage. Traditional unbalanced compensation methods detect the magnitude of the negative sequence voltage and output negative sequence current to eliminate it. However, when multiple energy storage converters are connected in parallel, since the AC voltage sampling point for each converter is the same, without a master coordinator, it is easy for the magnitude of the negative sequence current output by each energy storage converter to compensate for the unbalanced load to differ. Specifically, some energy storage converters output excessive negative sequence current to compensate for the unbalance and adjust the voltage to balance, while other energy storage converters, believing the voltage is already balanced, do not increase the negative sequence current output. This difference in output will lead to problems such as zero-sequence circulating current and excessive load on individual modules. Summary of the Invention

[0005] To overcome the problems in the prior art, this invention proposes a parallel control method and system for energy storage converters.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] A parallel control method for energy storage converters, wherein multiple energy storage converter modules operate in parallel, and each module has a hardware topology of a three-level inverter, the control method includes the following steps:

[0008] Step 1. Perform Clark transformation on the three-phase voltage signal and three-phase current signal output by the inverter to obtain the two-phase voltage and two-phase current in the αβ coordinate system;

[0009] Step 2. Perform Park transformation on the two-phase voltage and two-phase current in the αβ coordinate system to obtain the direct-axis voltage and current components and the quadrature-axis voltage and current components;

[0010] Step 3. Calculate the active power and reactive power based on the direct-axis voltage and current components and the quadrature-axis voltage and current components;

[0011] Step 4. Adjust the reference voltage and frequency using a droop control method based on the active power and reactive power. The reference voltage is obtained by coordinate transformation to obtain the direct-axis component of the three-phase reference voltage, and the quadrature-axis component is set to 0.

[0012] Step 5. The difference between the direct-axis component of the reference voltage and the direct-axis voltage component is passed through the voltage loop controller to obtain the reference value of the direct-axis current loop. Similarly, the reference value of the quadrature-axis current loop is obtained.

[0013] Step 6. The direct-axis predicted value is superimposed on the direct-axis current loop reference value. The difference between the direct-axis compensation value and the inner loop current reference value and the direct-axis current component is calculated by the current loop controller to generate the direct-axis front-end voltage.

[0014] Parallel to the quadrature axis current loop reference value, the quadrature axis prediction value is superimposed on the quadrature axis current loop reference value. The difference between the quadrature axis compensation value and the inner loop current reference value and the quadrature axis current component is calculated by the current loop controller to generate the quadrature axis front-end voltage.

[0015] Taking into account historical forecasts, proportional coefficients, voltage amplitudes, and the inverse change of direct-axis load, the direct-axis forecast and quadrature-axis forecast for the current period are calculated.

[0016] The compensation amount superimposed in step 6 is specifically as follows:

[0017] The DSOGI algorithm is used to separate the inverter's negative sequence voltage. Using 0 as a reference value and the negative sequence voltage as feedback, during PI modulation, the integral of the PI loop in the negative sequence voltage loop is multiplied by the decaying quantity to obtain the reference negative sequence current. Specifically:

[0018]

[0019]

[0020] In the formula, i du It is the direct-axis negative sequence compensation current. i du_1 This is the output of the previous cycle on the direct axis. U - d It is a direct-axis negative sequence voltage. U - d_1This is the input for the previous cycle on the direct axis; i qu This is the cross-axis negative sequence compensation current. i qu_1 This is the output of the previous cycle on the cross axis. U - q It is the quadrature-axis negative sequence voltage. U - q_1 The input for the previous cycle of the quadrature axis; P is the proportional coefficient, I is the integral coefficient; T is the calculation period, and I is the frequency. f The reciprocal of ξ; ξ is a gradually decreasing quantity;

[0021] Step 7. Feedforward compensation of the direct-axis front-end voltage, direct-axis coupling component, and voltage direct-axis component, and sum them to obtain the direct-axis voltage; feedforward compensation of the quadrature-axis front-end voltage, quadrature-axis coupling component, and voltage quadrature-axis component, and sum them to obtain the quadrature-axis voltage;

[0022] Step 8. The direct-axis voltage and quadrature-axis voltage are modulated by SPWM to drive the inverter bridge arm switching transistors to switch on and off to control the inverter output.

[0023] Furthermore, in step 1, the three-phase voltage signal and three-phase current signal output by the inverter are subjected to Clark transformation to obtain the two-phase voltage in the αβ coordinate system. Two-phase current Specifically:

[0024]

[0025]

[0026]

[0027]

[0028] in, U a , U b , U c This refers to the three-phase voltage signal output by a three-level inverter. I a , I b , I c This refers to the three-phase current signal output by the three-level inverter.

[0029] Furthermore, in step 2, the two-phase voltage and two-phase current in the αβ coordinate system are subjected to Park transformation to obtain the direct-axis voltage components.U d Current components I d Voltage components along the cross axis U q Current components I q Specifically:

[0030]

[0031]

[0032]

[0033]

[0034] In the formula, θ For the current voltage angle, Current current angle.

[0035] Furthermore, in step 3, there is active power. P reactive power Q The calculation is as follows:

[0036]

[0037] .

[0038] Furthermore, in step 4, a droop control method is used to adjust the reference voltage. U and frequency f :

[0039]

[0040]

[0041] In the formula, f 0 is the reference frequency. K f The droop slope is the frequency. U 0 is the reference voltage. K u This represents the voltage droop slope.

[0042] Furthermore, the compensation amount in step 6 includes the direct axis prediction amount. i dt and cross axis prediction i qt Specifically:

[0043]

[0044]

[0045] in,

[0046] Z d = i d ÷ U amp

[0047]

[0048] In the formula, i dt_1 、i qt_1 This is the predicted value from the previous calculation period. Z d_1 、Z q_1 This is the reciprocal of the load calculated in the previous cycle. k 1 is the proportionality coefficient.

[0049] Furthermore, the specific calculation method for ξ is as follows:

[0050] ;

[0051] In the formula, k 2 is the proportionality coefficient.

[0052] A parallel control system for an energy storage converter includes: a Clark converter module, a Park converter module, a power calculation module, a droop calculation module, an outer loop voltage module, a current loop control module, a feedforward module, and an SPWM module;

[0053] The Clark transformation module is used to perform Clark transformation on the three-phase voltage signal and three-phase current signal output by the inverter to obtain the two-phase voltage and two-phase current in the αβ coordinate system;

[0054] The Park transformation module is used to perform Park transformation on two-phase voltages and two-phase currents in the αβ coordinate system to obtain direct-axis voltage and current components and quadrature-axis voltage and current components.

[0055] The power calculation module is used to calculate active power and reactive power based on the direct-axis voltage component, current component, and quadrature-axis voltage component and current component.

[0056] The droop calculation module is used to adjust the reference voltage and frequency according to the active power and reactive power using the droop control method. The reference voltage is obtained by coordinate transformation to obtain the direct axis and quadrature axis components of the three-phase reference voltage.

[0057] The outer loop voltage module is used to pass the difference between the direct-axis component of the reference voltage and the direct-axis voltage component through the voltage loop controller to obtain the reference value of the direct-axis current loop, and set the reference value of the quadrature-axis current loop to 0;

[0058] The current loop control module is used to superimpose a direct-axis predicted value onto the direct-axis current loop reference value. The difference between the direct-axis compensation value and the inner loop current reference value and the direct-axis current component is calculated by the current loop controller to generate the direct-axis front-end voltage. In parallel, the quadrature-axis predicted value is superimposed onto the quadrature-axis current loop reference value. The difference between the quadrature-axis compensation value and the inner loop current reference value and the quadrature-axis current component is calculated by the current loop controller to generate the quadrature-axis front-end voltage.

[0059] The feedforward module is used for feedforward compensation of the direct-axis front-end voltage, the direct-axis coupled component, and the voltage direct-axis component, which are then added together to obtain the direct-axis voltage; the feedforward compensation of the quadrature-axis front-end voltage, the quadrature-axis coupled component, and the voltage quadrature-axis component are also added together to obtain the quadrature-axis voltage.

[0060] The direct-axis voltage and quadrature-axis voltage of the SPWM module are modulated by SPWM to drive the inverter bridge arm switching transistors to switch on and off to control the inverter output.

[0061] Furthermore, it also includes a negative sequence voltage control module, which is used to separate the inverter's negative sequence voltage using the DSOGI algorithm. With 0 as the reference value and the negative sequence voltage as the feedback, the integral of the PI of the negative sequence voltage loop is multiplied by the gradually decreasing amount during PI modulation to obtain the reference negative sequence current. It also includes a load current prediction module, which estimates the load size in real time, predicts the reference values ​​required for the quadrature axis and direct axis current loops, and compensates for them.

[0062] Compared with the prior art, the present invention has the following technical effects:

[0063] (1) The present invention calculates the active and reactive loads based on voltage and current sampling, and then calculates the current loop reference value compensation amount based on the load change, and superimposes it onto the reference values ​​of the direct axis and quadrature axis of the current loop respectively. When the load changes suddenly, it quickly compensates the reference value required by the current loop and maintains the voltage stable near the set value.

[0064] (2) In order to eliminate the negative sequence voltage caused by unbalanced load, the present invention uses the DSOGI algorithm to separate the negative sequence voltage, takes 0 as the reference value, and uses the negative sequence voltage as feedback. After PI modulation, a reference negative sequence current is obtained and superimposed on the reference values ​​of the current direct axis and quadrature axis. In order to prevent the output of each module from being unbalanced, the integral of the PI of the negative sequence voltage loop is multiplied by the gradual reduction amount, so that the larger the negative sequence current, the smaller the gradual reduction amount ξ. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the hardware topology of the present invention;

[0066] Figure 2 This is an overall control block diagram of the present invention;

[0067] Figure 3 This is a flowchart of the negative order compensation calculation with gradual elimination in this invention;

[0068] Figure 4 This is a diagram illustrating the effect of the current prediction algorithm during load changes in this invention.

[0069] Figure 5 This is a diagram showing the negative sequence current output by the present invention with / without the fading algorithm. Detailed Implementation

[0070] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0071] Reference Figures 1-5 This invention discloses a parallel control method for energy storage converters, in which multiple energy storage converter modules operate in parallel. The DC side can use different power supplies or share a common DC bus. The hardware topology of each module is a conventional three-level inverter. The method specifically includes the following steps:

[0072] Step 1. Perform Clark transformation on the three-phase voltage and three-phase current signals output by the inverter to obtain the two-phase voltage and two-phase current in the αβ coordinate system;

[0073] Clark transform is performed on the three-phase voltage and three-phase current signals output by the inverter to obtain the two-phase voltages in the αβ coordinate system. Two-phase current Specifically:

[0074]

[0075]

[0076]

[0077]

[0078] in, U a , U b , U c This refers to the three-phase voltage signal output by a three-level inverter. I a , I b , I c This refers to the three-phase current signal output by the three-level inverter.

[0079] Step 2. Perform Park transformation on the two-phase voltage and two-phase current in the αβ coordinate system to obtain the direct-axis voltage and current components and the quadrature-axis voltage and current components;

[0080] Perform a Park transform on the two-phase voltage and two-phase current in the αβ coordinate system to obtain the direct-axis voltage components. U d Current components I d Voltage components along the cross axis U q Current components I q Specifically:

[0081]

[0082]

[0083]

[0084]

[0085] In the formula, θ For the current voltage angle, Current current angle.

[0086] Step 3. Calculate the active power and reactive power based on the direct-axis voltage and current components and the quadrature-axis voltage and current components;

[0087] Active power P reactive power Q The calculation is as follows:

[0088]

[0089] .

[0090] Step 4. Adjust the reference voltage and frequency using a droop control method based on the active and reactive power. The reference voltage is obtained by coordinate transformation to obtain the direct-axis component of the three-phase reference voltage, and the quadrature-axis component is set to 0. The frequency is directly applied to the switching frequency of the controller.

[0091] Adjusting the reference voltage using a droop control method U and frequency f :

[0092]

[0093]

[0094] In the formula, f 0 is the reference frequency.K f The droop slope is the frequency. U 0 is the reference voltage. K u This represents the voltage droop slope.

[0095] Step 5. The difference between the direct-axis component and the direct-axis voltage component of the reference voltage is passed through the voltage loop controller to obtain the reference value of the direct-axis current loop. The difference between the quadrature-axis component and the quadrature-axis voltage component of the reference voltage is passed through the voltage loop controller to obtain the reference value of the quadrature-axis current loop.

[0096] SPWM uses a dual closed-loop control system: an outer voltage loop and an inner current loop. The outer voltage loop controls the DC-side voltage of the SPWM rectifier, while the inner current loop controls the current according to the current command output from the outer loop.

[0097] Step 6. The direct-axis predicted value is superimposed on the direct-axis current loop reference value. The difference between the direct-axis compensation value and the inner loop current reference value and the direct-axis current component is calculated by the current loop controller to generate the direct-axis front-end voltage.

[0098] In parallel, the quadrature axis prediction is superimposed on the quadrature axis current loop reference value. The difference between the quadrature axis compensation value and the inner loop current reference value and the quadrature axis current component is calculated by the current loop controller to generate the quadrature axis front-end voltage.

[0099] In some embodiments, when the load changes abruptly, the essence of the voltage change is that the output current suddenly changes, but due to the limitations of the voltage loop, the reference value of the current loop cannot change abruptly. The output current has a linear relationship with the load; therefore, in this embodiment, the current loop input is predicted based on the degree of load change. Active and reactive loads are calculated based on voltage and current sampling, and then the current loop reference value compensation is calculated based on the load change, and these are respectively superimposed on the direct-axis current loop reference value. i d and cross-axis current loop reference value i q On the reference value.

[0100] When the load changes abruptly, the current loop quickly compensates for the reference value required to maintain the voltage stable near the set value.

[0101] The compensation amount includes the direct axis prediction amount. i dt and cross axis prediction i qt Specifically:

[0102]

[0103]

[0104] in,

[0105] Z d = i d ÷ U amp

[0106]

[0107] In the formula, i dt_1 、i qt_1 This is the predicted value from the previous calculation period. Z d_1 、Z q_1 This is the reciprocal of the load calculated in the previous cycle. k 1 is a proportionality coefficient, which should be selected appropriately based on the degree of voltage change without the prediction algorithm. Usually, a value of several tens is sufficient.

[0108] In other embodiments, to eliminate negative sequence voltage caused by unbalanced loads, the DSOGI algorithm is used to separate the negative sequence voltage. Using 0 as a reference value and the negative sequence voltage as feedback, a reference negative sequence current is obtained through PI modulation and superimposed on the current. i d and i q Based on the reference value. To prevent unbalanced output of each module, the integral of the PI of the negative sequence voltage loop is multiplied by a gradually decreasing amount (a number slightly less than 1), denoted as ξ, so that the larger the negative sequence current, the smaller ξ becomes.

[0109] The formula for the DSOGI algorithm is as follows:

[0110]

[0111]

[0112] In the formula, q U is the phase shift factor, representing a 90° phase shift. αβ U is obtained by Clark transformation. + αβ and U - αβ The positive and negative sequence voltages under the αβ axis can be obtained by the Park transform. d , q Positive and negative sequence voltages U under the axis + d U + q U - d U - q .

[0113] In this embodiment, the DSOGI algorithm is used to separate the inverter negative sequence voltage. With 0 as the reference value and the negative sequence voltage as the feedback, the integral of the PI of the negative sequence voltage loop is multiplied by the gradually decreasing amount during PI modulation to obtain the reference negative sequence current.

[0114] The diminishing returns are multiplied by the integral of the PI in the negative sequence voltage loop. Taking the direct axis as an example, the specific steps are as follows:

[0115]

[0116] In the formula, i du It is the direct-axis negative sequence compensation current. i du_1 This is the output of the previous cycle. U - d It is a direct-axis negative sequence voltage. U - d_1 This is the input for the previous cycle; P is the proportional coefficient, and I is the integral coefficient. Parameter selection can prioritize integration; reference proportional / integral values ​​are: for a 100kW capacity, P=0.005, I=1000. Increase the parameters as the capacity increases. T is the calculation period, directly equal to the reciprocal of the frequency obtained from the droop calculation, i.e., 1 / f .

[0117] Similarly, taking the intersection axis as an example, the specific details are as follows:

[0118]

[0119] In the formula, i qu This is the cross-axis negative sequence compensation current. i qu_1 This is the output of the previous cycle. U - q It is the quadrature-axis negative sequence voltage. U - q_1 This is the input for the previous cycle; P is the proportional coefficient, and I is the integral coefficient. Parameter selection can prioritize integral coefficients. For reference, for a 100kW capacity, P=0.005, I=1000. Increase the parameters as the capacity increases.

[0120] ξ is a gradually decreasing quantity, and the specific calculation method for ξ is as follows:

[0121] ;

[0122] In the formula, i du and i qu For the negative sequence compensation currents of the direct axis and quadrature axis,k 2 is the proportional coefficient, which should be selected appropriately based on the system switching frequency. k The larger the value of 2, the faster the output of each module reaches equilibrium, but... k 2. An excessively large value will result in a large steady-state error, meaning that a small amount of negative sequence voltage will still exist under steady-state conditions. k Reference values: 100kW capacity, 20kHz switching frequency. k 2 = 0.00002.

[0123] Step 7. Direct-axis front-end voltage and direct-axis coupling component ωL and voltage direct axis component U d feedforward compensation U d_m The sums yield the direct-axis voltage; the quadrature-axis front-end voltage and the quadrature-axis coupling component. ωL and voltage cross-axis components U q feedforward compensation U q_m The sum of these values ​​yields the quadrature-axis voltage.

[0124] in, ω Angular velocity at power frequency ( L is the line inductance. U q_m and U d_m The AC and DC axis voltage components are obtained by Clark and Park from the AC sampling voltage.

[0125] Step 8. The direct-axis voltage and quadrature-axis voltage are modulated by SPWM to drive the inverter bridge arm switching transistors to switch on and off to control the inverter output.

[0126] The present invention also discloses a parallel control system for energy storage converters, including: a Clark converter module, a Park converter module, a power calculation module, a droop calculation module, an outer loop voltage module, a current loop control module, a feedforward module, and an SPWM module;

[0127] The Clark transformation module is used to perform Clark transformation on the three-phase voltage signal and three-phase current signal output by the inverter to obtain the two-phase voltage and two-phase current in the αβ coordinate system;

[0128] The Park transformation module is used to perform Park transformation on two-phase voltages and two-phase currents in the αβ coordinate system to obtain direct-axis voltage and current components and quadrature-axis voltage and current components.

[0129] The power calculation module is used to calculate active power and reactive power based on the direct-axis voltage and current components and the quadrature-axis voltage and current components.

[0130] The droop calculation module is used to adjust the reference voltage and frequency according to the active power and reactive power using the droop control method. The reference voltage is obtained by coordinate transformation to obtain the direct axis and quadrature axis components of the three-phase reference voltage.

[0131] The outer loop voltage module is used to pass the difference between the direct-axis component of the reference voltage and the direct-axis voltage component through the voltage loop controller to obtain the reference value of the direct-axis current loop, and set the reference value of the quadrature-axis current loop to 0;

[0132] The current loop control module is used to superimpose the direct-axis predicted value onto the direct-axis current loop reference value. The difference between the direct-axis compensation value and the inner loop current reference value and the direct-axis current component is calculated by the current loop controller to generate the direct-axis front-end voltage. In parallel, the quadrature-axis predicted value is superimposed onto the quadrature-axis current loop reference value. The difference between the quadrature-axis compensation value and the inner loop current reference value and the quadrature-axis current component is calculated by the current loop controller to generate the quadrature-axis front-end voltage.

[0133] The feedforward module is used for feedforward compensation of the direct-axis front-end voltage, direct-axis coupled component, and voltage direct-axis component, which are summed to obtain the direct-axis voltage; the feedforward compensation of the quadrature-axis front-end voltage, quadrature-axis coupled component, and voltage quadrature-axis component are summed to obtain the quadrature-axis voltage;

[0134] The direct-axis and quadrature-axis voltages of the SPWM module are modulated by SPWM to drive the inverter bridge arm switches to turn on and off, thereby controlling the inverter output.

[0135] The system also includes a negative sequence voltage control module, which is used to separate the inverter negative sequence voltage using the DSOGI algorithm. With 0 as the reference value and the negative sequence voltage as the feedback, the integral of the PI of the negative sequence voltage loop is multiplied by the gradually decreasing amount during PI modulation to obtain the reference negative sequence current.

[0136] The system also includes a load current prediction module, which estimates the load size in real time, predicts the reference values ​​required for the quadrature axis and direct axis current loops, and compensates for them.

[0137] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for parallel control of energy storage converters, characterized by, A plurality of energy storage converter modules are operated in parallel, each module having a three-level inverter hardware topology, and a control method comprising the following steps: Step 1. Perform Clark transformation on three-phase voltage signals and three-phase current signals output by the inverter to obtain two-phase voltage and two-phase current in the αβ coordinate system; Step 2. Perform Park transformation on the two-phase voltage and two-phase current in the αβ coordinate system to obtain a direct-axis voltage component, a direct-axis current component, and a quadrature-axis voltage component and a quadrature-axis current component; Step 3. Calculate active power and reactive power according to the direct-axis voltage component, the direct-axis current component, the quadrature-axis voltage component, and the quadrature-axis current component; Step 4. Adjust a reference voltage and a frequency according to the active power and the reactive power by using a droop control method, wherein the reference voltage is obtained by coordinate transformation to obtain a direct-axis component of a three-phase reference voltage, and the quadrature-axis component is set to 0; Step 5. Obtain a reference value of a direct-axis current loop by passing a difference between the reference voltage direct-axis component and the direct-axis voltage component through a voltage loop controller, and obtain a reference value of a quadrature-axis current loop by passing a difference between the reference voltage quadrature-axis component and the quadrature-axis voltage component through the voltage loop controller; Step 6. Superimpose a direct-axis prediction quantity on the direct-axis current loop reference value, and obtain a direct-axis front-end voltage by passing a difference between a direct-axis compensation quantity and an inner loop current reference value and the direct-axis current component through a current loop controller; Superimpose a quadrature-axis prediction quantity on the quadrature-axis current loop reference value in parallel, and obtain a quadrature-axis front-end voltage by passing a difference between a quadrature-axis compensation quantity and the inner loop current reference value and a quadrature-axis current component through the current loop controller; Comprehensively consider historical prediction quantities, proportional coefficients, voltage amplitudes, and reciprocal changes of direct-axis loads to calculate direct-axis prediction quantities and quadrature-axis prediction quantities of a current period; The superimposed compensation quantity in step 6 is specifically: A negative sequence voltage of the inverter is separated by using a DSOGI algorithm, 0 is taken as a reference value, and the negative sequence voltage is taken as feedback, and when PI modulation is performed, a reference negative sequence current is obtained by superimposing a fading quantity on an integral quantity of a negative sequence voltage loop PI, and the superimposed compensation quantity is specifically: wherein i du is the direct axis negative sequence compensation current, i du_1 is the direct axis output of the previous cycle, U - d is the direct axis negative sequence voltage, U - d_1 is the direct axis input of the previous cycle; i qu is the quadrature axis negative sequence compensation current, i qu_1 is the quadrature axis output of the previous cycle, U - q is the quadrature axis negative sequence voltage, U - q_1 is the quadrature axis input of the previous cycle; P is a proportional coefficient, I is an integral coefficient; T is a calculation period, is the inverse of the frequency f ; ξ is a decay amount; Step 7. Feed forward compensate the direct-axis front-end voltage, a direct-axis coupling component, and the voltage direct-axis component, and add them to obtain a direct-axis voltage; feed forward compensate the quadrature-axis front-end voltage, a quadrature-axis coupling component, and the voltage quadrature-axis component, and add them to obtain a quadrature-axis voltage; Step 8. Pass the direct-axis voltage and the quadrature-axis voltage through SPWM modulation to drive switching tubes of inverter bridge arms to turn on and off to control inverter output.

2. The energy storage converter parallel control method of claim 1, wherein, The three-phase voltage signal and the three-phase current signal output by the inverter are subjected to Clark transformation in step 1 to obtain two-phase voltage , two-phase current , specifically: wherein U a , U b , U c is a three-phase voltage signal output by the three-level inverter, I a , I b , I c is a three-phase current signal output by the three-level inverter.

3. The energy storage converter parallel control method of claim 2, wherein, Park transformation is performed on the two-phase voltage and two-phase current in the αβ coordinate system in step 2 to obtain a direct-axis voltage component U d , a current component I d and a quadrature-axis voltage component U q , a current component I q , specifically: In the formula, θ current voltage angle, current current angle.

4. The energy storage converter parallel control method of claim 3, wherein, The active power in step 3 P , the reactive power Q is calculated as follows: 。 5. The energy storage converter parallel control method of claim 4, wherein, The step 4 adjusts the reference voltage using a droop control method U and frequency f : wherein f 0 is a reference frequency, K f is a frequency droop slope, U 0 is a reference voltage, K u is a voltage droop slope.

6. The energy storage converter parallel control method of claim 4, wherein, The compensation amount in step 6 includes a direct-axis predicted quantity i dt and a quadrature-axis predicted quantity i qt Specifically, wherein, Z d = i d ÷ U amp wherein i dt_1 、i qt_1 is the prediction of the previous calculation period, Z d_1 、Z q_1 is the load inverse calculated for the previous period, k 1 is a proportionality factor.

7. The energy storage converter parallel control method of claim 1, wherein, The specific calculation method of ξ is: ； In the formula, k 2 is a proportionality factor.

8. A system for controlling the parallel operation of energy storage converters, using a method for controlling the parallel operation of energy storage converters according to any one of claims 1 to 7, characterized in that, including: a Clark transformation module, a Park transformation module, a power calculation module, a droop calculation module, an outer loop voltage module, a current loop control module, a feed forward module, and an SPWM module; the Clark transformation module is used to perform Clark transformation on three-phase voltage signals and three-phase current signals output by the inverter to obtain two-phase voltage and two-phase current in the αβ coordinate system; the Park transformation module is used to perform Park transformation on the two-phase voltage and the two-phase current in the αβ coordinate system to obtain a direct-axis voltage component, a direct-axis current component, and a quadrature-axis voltage component and a quadrature-axis current component; the power calculation module is used to calculate active power and reactive power according to the direct-axis voltage component, the direct-axis current component, the quadrature-axis voltage component, and the quadrature-axis current component; The droop calculation module is configured to adjust the reference voltage and frequency by using a droop control method according to active power and reactive power, and the reference voltage is obtained by coordinate transformation to obtain the direct-axis and quadrature-axis components of three-phase reference voltage; The outer loop voltage module is configured to obtain the reference value of the direct-axis current loop by passing the difference between the reference voltage direct-axis component and the direct-axis voltage component through a voltage loop controller, and set the reference value of the quadrature-axis current loop to 0; The current loop control module is configured to superimpose the direct-axis prediction on the direct-axis current loop reference value, and calculate the difference between the direct-axis compensation and the inner loop current reference value and the direct-axis current component through a current loop controller to generate a direct-axis front-end voltage; in parallel, superimpose the quadrature-axis prediction on the quadrature-axis current loop reference value, and calculate the difference between the quadrature-axis compensation and the inner loop current reference value and the quadrature-axis current component through a current loop controller to generate a quadrature-axis front-end voltage; The feedforward module is configured to perform feedforward compensation on the direct-axis front-end voltage, the direct-axis coupling component and the voltage direct-axis component, and add them to obtain the direct-axis voltage; perform feedforward compensation on the quadrature-axis front-end voltage, the quadrature-axis coupling component and the voltage quadrature-axis component, and add them to obtain the quadrature-axis voltage; The SPWM module is configured to perform SPWM modulation on the direct-axis voltage and the quadrature-axis voltage, drive the on-off of the inverter bridge arm switch tube to control the output of the inverter.

9. The energy storage inverter parallel control system of claim 8, wherein, The negative sequence voltage control module is configured to separate the inverter negative sequence voltage by using a DSOGI algorithm, take 0 as the reference value, take the negative sequence voltage as the feedback, multiply the integral of the PI of the negative sequence voltage loop by the fading amount when the PI is modulated, and obtain the reference negative sequence current; the load current prediction module is configured to estimate the load size in real time, predict the reference value required by the quadrature-axis and direct-axis current loops, and compensate.

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