Zero-sequence circulating current suppression method and control device for multiple parallel converters

Abstract

The invention relates to the technical field of wind power generation and power electronic control, and discloses a multi-parallel converter zero-sequence circulating current suppression method and control device.The method comprises the steps that three-phase currents of a plurality of parallel modules are collected, and the three-phase currents and the total current of the three-phase currents are converted into corresponding dqo axis currents under a rotating coordinate system; based on the dqo-axis current, calculating a modulation voltage given value for loop control of a plurality of parallel modules, and based on the modulation voltage given value, generating PWM signals corresponding to the parallel modules; and the PWM signal is isolated and amplified and then is used for driving control of power devices in the parallel modules, so that zero-sequence circulating current suppression control between the parallel modules is realized. Through the total current control loop and the d, q and o axis current control loops, zero-sequence current and non-uniform current between the modules can be suppressed, overlarge voltage and current stress of power devices caused by unbalanced current distribution inside the modules and between the modules is avoided, and the reliability and the electric energy quality of the system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation and power electronic control, and in particular to a method and a control device for suppressing zero-sequence circulating current of multiple parallel converters. Background Art

[0002] In recent years, countries around the world are vigorously developing new energy sources, among which the development of wind energy is an important way. In order to improve the efficiency of wind energy acquisition and the economy of wind power, wind turbines are constantly developing in the direction of large-scale. At present, the single-unit capacity of onshore wind turbines has exceeded 10MW, and the maximum single-unit capacity of offshore wind turbines has reached 18MW. It is expected that 20MW-level wind turbines will be released soon.

[0003] In order to meet the power conversion and grid connection requirements of large wind turbines, wind power converters need to provide conversion capacity that matches the capacity of wind turbines, so the capacity of high-power wind power converters continues to increase.

[0004] At present, the mainstream topology of wind power converters is back-to-back three-phase PWM converters. In order to increase the converter capacity, parallel means need to be adopted at all levels, first, IGBT device-level parallel, second, power module parallel, and third, cabinet parallel. In addition to special design at the hardware level, power module parallel also requires special software control strategies to achieve system stability and reliability.

[0005] For high-power wind power converters, a multi-parallel structure is generally used to achieve capacity improvement, that is, the machine-side converter and the grid-side converter use multiple power modules in parallel, and each grid-side power module is connected to the grid in parallel through the grid-side reactor, and each machine-side power module is connected to the motor in parallel through the machine-side reactor. Due to the differences in IGBT switching time, reactor parameters, and PWM control signal dead zone in each parallel power module, uneven current is prone to occur between the parallel modules, among which zero-sequence circulating current is the most difficult engineering and technical problem, which will cause some parallel power modules in the converter to overload, affect the efficiency of the converter, and threaten the system reliability. Summary of the invention

[0006] In order to solve the problem of zero-sequence circulating current and parallel uneven current in multiple parallel converters, the present invention proposes a method and a control device for suppressing zero-sequence circulating current in multiple parallel converters, which can effectively suppress the zero-sequence circulating current of parallel modules and the uneven current problem between modules.

[0007] The technical solution adopted by the present invention is as follows:

[0008] On the one hand, the present invention provides a method for suppressing zero-sequence circulating current of multiple parallel converters, comprising:

[0009] Collect three-phase currents of multiple parallel modules, and convert the three-phase currents and the total current into corresponding dqo-axis currents in a rotating coordinate system;

[0010] Calculating a modulation voltage set value for loop control of a plurality of parallel modules based on the dqo axis current, and generating a PWM signal corresponding to the parallel modules based on the modulation voltage set value;

[0011] The PWM signal is isolated and amplified and then used for driving control of power devices in parallel modules, thereby realizing zero-sequence circulating current suppression control between parallel modules.

[0012] Furthermore, if there are three parallel modules, namely, a first parallel module, a second parallel module and a third parallel module, the three-phase currents of the plurality of parallel modules are collected, and the three-phase currents and the total current thereof are converted to the corresponding dqo-axis currents in the rotating coordinate system, including: collecting the three-phase currents i of the reactors corresponding to the first parallel module, the second parallel module and the third parallel module; abc1 、i abc2 and i abc3 , calculate the total current i based on these three sets of currents abc Then, these four sets of currents are rotated and transformed to obtain the dqo axis current i corresponding to the stationary coordinate system. dqo1 、i dqo2 、i dqo3 and i dqo .

[0013] Furthermore, the loop control includes: dividing the current loop control in the stationary coordinate system into three groups of control loops, including a group of total current control loops and two groups of module current control loops; the total current control loop includes two current loops of d and q axes, and the module current control loop includes three current loops of d, q and o axes.

[0014] Furthermore, the total current control loop adopts the total given current i of the dq axis of the converter dref 、i qref As given values, the d and q axis currents i d 、i q As feedback, after controller calculation and decoupling, the AC side voltage output reference value u of the parallel module is obtained. dref 、u qref ; Set the voltage output reference value u dref 、u qref After pulse width modulation, the IGBT control signal PWM1 of the first parallel module is obtained.

[0015] Furthermore, the d-axis and q-axis given currents of the module current control loop are set to the total given current i dref 、i qref1 / 3 of the given current of the o-axis is set to 0; the d, q, and o-axis currents of the second parallel module and the third parallel module are respectively used as feedback, and the difference between each given value and the feedback value is obtained after control operation and limiting to obtain the d, q, and o-axis voltage reference value u dqo1ref and u dqo2ref , where d and q axis voltage reference value u dq1ref 、u dq2ref With voltage reference value u dqref The sum is used as the AC side voltage output reference value of the second parallel module and the third parallel module respectively; and then combined with the respective o-axis voltage reference value u of the second parallel module and the third parallel module o1ref 、u o2ref , after pulse width modulation, the IGBT control signals PWM2 and PWM3 of the second parallel module and the third parallel module are obtained respectively.

[0016] On the other hand, the present invention provides a zero-sequence circulating current control device for multiple parallel converters, comprising:

[0017] A current collection unit is configured to collect three-phase currents of a plurality of parallel modules;

[0018] A rotation conversion unit, configured to convert the three-phase current and the total current thereof into a corresponding dqo axis current in a rotating coordinate system;

[0019] A current control unit, configured to calculate a modulation voltage set value for loop control of a plurality of parallel modules based on the dqo axis current;

[0020] A PWM modulation generation unit is configured to generate a PWM signal corresponding to the parallel module based on the modulation voltage given value;

[0021] The PWM isolation and amplification unit is configured to isolate and amplify the PWM signal and use it for driving control of power devices in the parallel modules, thereby realizing zero-sequence circulating current suppression control between the parallel modules.

[0022] Furthermore, if there are three parallel modules, namely, a first parallel module, a second parallel module and a third parallel module, the three-phase current i of the reactor corresponding to the first parallel module, the second parallel module and the third parallel module is collected by the current collection unit. abc1 、i abc2 and i abc3 , the total current i is calculated based on these three sets of currents through the rotation transformation unit abc , and the four sets of currents are rotated and transformed to obtain the dqo axis current i corresponding to the stationary coordinate system dqo1 、i dqo2 、i dqo3 and i dqo .

[0023] Furthermore, the loop control of the current control unit includes: dividing the current loop control in the stationary coordinate system into three groups of control loops, including a group of total current control loops and two groups of module current control loops; the total current control loop includes two current loops of d and q axes, and the module current control loop includes three current loops of d, q, and o axes.

[0024] Furthermore, the total current control loop adopts the total given current i of the dq axis of the converter dref 、i qref As given values, the d and q axis currents i d 、i q As feedback, after controller calculation and decoupling, the AC side voltage output reference value u of the parallel module is obtained. dref 、u qref ; Set the voltage output reference value u dref 、u qref After pulse width modulation, the IGBT control signal PWM1 of the first parallel module is obtained.

[0025] Furthermore, the d-axis and q-axis given currents of the module current control loop are set to the total given current i dref 、i qref 1 / 3 of the given current of the o-axis is set to 0; the d, q, and o-axis currents of the second parallel module and the third parallel module are respectively used as feedback, and the difference between each given value and the feedback value is obtained after control operation and limiting to obtain the d, q, and o-axis voltage reference value u dqo1ref and u dqo2ref , where d and q axis voltage reference value u dq1ref 、u dq2ref With voltage reference value u dqref The sum is used as the AC side voltage output reference value of the second parallel module and the third parallel module respectively; and then combined with the respective o-axis voltage reference value u of the second parallel module and the third parallel module o1ref 、u o2ref , after pulse width modulation, the IGBT control signals PWM2 and PWM3 of the second parallel module and the third parallel module are obtained respectively.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention adopts total current dq axis current control and module current dqo axis current control, wherein the first module does not need a separate dqo axis current control loop, and directly adopts the dq axis given voltage calculated by the total current control, and the given voltages of other parallel modules are compensated by the dq axis given voltage calculated by the total current control loop. The present invention can reduce the total number of current control loops and improve the steady-state and dynamic current sharing capabilities.

[0028] 2. The multi-parallel converter zero-sequence circulating current suppression method and control device provided by the present invention are aimed at the problems of zero-sequence circulating current and uneven current in the multi-parallel topology in the wind power converter. Through the control of the total current dq-axis current controller and the parallel module dqo-axis current controller, it can effectively avoid zero-sequence current and uneven current between parallel modules, and avoid excessive voltage and current stress of power devices caused by unbalanced current distribution within the modules and between modules, which is beneficial to improving the reliability and power quality of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention relates to a schematic structural diagram of a wind power generation energy conversion system using multiple parallel grid-side converters.

[0030] Figure 2 It is a composition schematic diagram of a zero-sequence circulating current control device for multiple parallel converters of the present invention.

[0031] Figure 3 This is one of the control schematic diagrams of a method for suppressing zero-sequence circulating current of multiple parallel converters of the present invention.

[0032] Figure 4 This is the second control schematic diagram of a method for suppressing zero-sequence circulating current of multiple parallel converters of the present invention.

[0033] Figure 5 This is the third control schematic diagram of a method for suppressing zero-sequence circulating current of multiple parallel converters of the present invention.

[0034] Figure numerals: 11 is grid-side converter No. 1, 12 is grid-side converter No. 2, 13 is grid-side converter No. 3; 21 is motor-side converter No. 1, 22 is motor-side converter No. 2, 23 is motor-side converter No. 3. DETAILED DESCRIPTION

[0035] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are now described. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0036] The grid-side converter with parallel modules is one of the key components in the wind power generation energy conversion system. One end of the motor-grid converter is connected to the DC bus voltage, and the other end is connected to the grid through a transformer. Figure 1 As shown, the wind power generation energy conversion system consists of a wind turbine, a motor-side converter, a DC bus voltage, a grid-side converter, a transformer and a grid.

[0037] In order to solve the problems of zero-sequence circulating current and parallel uneven current in multiple parallel converters, the present embodiment provides a method for suppressing zero-sequence circulating current in multiple parallel converters, including: collecting three-phase currents of multiple parallel modules, converting the three-phase currents and the total current to the corresponding dqo-axis currents in the rotating coordinate system; calculating the modulation voltage set value for loop control of multiple parallel modules based on the dqo-axis current, and generating a PWM signal of the corresponding parallel module based on the modulation voltage set value; isolating and amplifying the PWM signal and using it for driving control of power devices in the parallel modules, thereby realizing zero-sequence circulating current suppression control between the parallel modules.

[0038] like Figure 2 As shown, this embodiment also provides a zero-sequence circulating current control device for multiple parallel converters, including a current acquisition unit, a rotation conversion unit, a current control unit, a PWM modulation generation unit and a PWM isolation amplifier unit. Among them, the current acquisition unit is configured to collect three-phase currents of multiple parallel modules; the rotation conversion unit is configured to convert the three-phase current and its total current into the corresponding dqo axis current in the rotating coordinate system; the current control unit is configured to calculate the modulation voltage set value for loop control of multiple parallel modules based on the dqo axis current; the PWM modulation generation unit is configured to generate a PWM signal corresponding to the parallel module based on the modulation voltage set value; the PWM isolation amplifier unit is configured to isolate and amplify the PWM signal for the drive control of the power device in the parallel module, thereby realizing the zero-sequence circulating current suppression control between the parallel modules.

[0039] Specifically, taking three parallel modules as an example, the method for suppressing zero-sequence circulating current of multiple parallel converters of this embodiment is described in detail.

[0040] First, the three-phase current i of the reactor corresponding to the first parallel module, the second parallel module and the third parallel module is collected in real time. abc1 、i abc2 and i abc3 , calculate the total current i based on these three sets of currents abc Then, these four sets of currents are rotated and transformed to obtain the dqo axis current i corresponding to the stationary coordinate system. dqo1 、i dqo2 、i dqo3 and i dqo .

[0041] Then, the current loop control in the stationary coordinate system is completed, which is divided into three groups of control loops in total, including one group of total current control loop and two groups of module current control loops. The total current control loop includes two current loops of d and q axes, and the module current control loop includes three current loops of d, q, and o axes.

[0042] Preferably, the total current control loop uses the total given current i of the dq axis of the converter dref 、i qref As given values, the d and q axis currents i d 、i q As feedback, after controller calculation and decoupling, the AC side voltage output reference value u of the parallel module is obtained. dref 、u qref ; Set the voltage output reference value u dref 、u qref After pulse width modulation, the IGBT control signal PWM1 of the first parallel module is obtained. The control logic is as follows: Figure 3 shown.

[0043] Preferably, the d-axis and q-axis given currents of the module current control loop are set to the total given current i dref 、i qref 1 / 3 of the given current of the o-axis is set to 0; the d, q, and o-axis currents of the second parallel module and the third parallel module are respectively used as feedback, and the difference between each given value and the feedback value is obtained after control operation and limiting to obtain the d, q, and o-axis voltage reference value u dqo1ref and u dqo2ref , where d and q axis voltage reference value u dq1ref 、u dq2ref With voltage reference value u dqref The sum is used as the AC side voltage output reference value of the second parallel module and the third parallel module respectively; and then combined with the respective o-axis voltage reference value u of the second parallel module and the third parallel module o1ref 、u o2ref , after pulse width modulation, the IGBT control signals PWM2 and PWM3 of the second parallel module and the third parallel module are obtained respectively. The control logic is as follows Figure 4 and Figure 5 shown.

[0044] Finally, the PWM signals of the first parallel module, the second parallel module and the third parallel module are isolated and amplified and then used to drive the IGBT switches of each power module, so that zero-sequence circulating current suppression and current sharing control between the modules can be achieved.

[0045] The above-mentioned multi-parallel converter zero-sequence circulating current suppression control method is mainly aimed at the zero-sequence current and uneven current problems of parallel modules caused by electrical parameter differences in the grid-side converter parallel modules in the wind power converter. Through the total current control loop, d, q, and o-axis current control loops, the zero-sequence current and uneven current between modules can be suppressed, avoiding excessive voltage and current stress of power devices caused by unbalanced current distribution within and between modules, which is beneficial to improving the reliability and power quality of the system.

[0046] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for suppressing zero-sequence circulating current of multiple parallel converters, characterized in that: include: Collect three-phase currents of multiple parallel modules, and convert the three-phase currents and the total current into corresponding dqo-axis currents in a rotating coordinate system; Calculating a modulation voltage set value for loop control of a plurality of parallel modules based on the dqo axis current, and generating a PWM signal corresponding to the parallel modules based on the modulation voltage set value; The PWM signal is isolated and amplified and then used for driving control of power devices in parallel modules, thereby realizing zero-sequence circulating current suppression control between parallel modules.

2. A method for suppressing zero-sequence circulating current of multiple parallel converters according to claim 1, characterized in that: If there are three parallel modules, namely, a first parallel module, a second parallel module and a third parallel module, the three-phase currents of the plurality of parallel modules are collected, and the three-phase currents and the total current thereof are converted to the corresponding dqo axis currents in the rotating coordinate system, including: Collect the three-phase current i of the reactor corresponding to the first parallel module, the second parallel module and the third parallel module abc1 、i abc2 and i abc3 , calculate the total current i based on these three sets of currents abc Then, these four sets of currents are rotated and transformed to obtain the dqo axis current i corresponding to the stationary coordinate system. dqo1 、i dqo2 、i dqo3 and i dqo .

3. A method for suppressing zero-sequence circulating current of multiple parallel converters according to claim 2, characterized in that: The loop control includes: dividing the current loop control in a stationary coordinate system into three groups of control loops, including a group of total current control loops and two groups of module current control loops; the total current control loop includes two current loops of d and q axes, and the module current control loop includes three current loops of d, q and o axes.

4. A method for suppressing zero-sequence circulating current of multiple parallel converters according to claim 3, characterized in that: The total current control loop adopts the total given current i of the dq axis of the converter dref 、i qref As given values, the d and q axis currents i d 、i q As feedback, after controller calculation and decoupling, the AC side voltage output reference value u of the parallel module is obtained. dref 、u qref ; Set the voltage output reference value u dref 、u qref After pulse width modulation, the IGBT control signal PWM1 of the first parallel module is obtained.

5. A method for suppressing zero-sequence circulating current of multiple parallel converters according to claim 4, characterized in that: The d and q axis given currents of the module current control loop are set to the total given current i dref 、i qref 1 / 3 of the given current of the o-axis is set to 0; the d, q, and o-axis currents of the second parallel module and the third parallel module are respectively used as feedback, and the difference between each given value and the feedback value is obtained after control operation and limiting to obtain the d, q, and o-axis voltage reference value u dqo1ref and u dqo2ref , where d and q axis voltage reference value u dq1ref 、u dq2ref With voltage reference value u dqref The sum is used as the AC side voltage output reference value of the second parallel module and the third parallel module respectively; and then combined with the respective o-axis voltage reference value u of the second parallel module and the third parallel module o1ref 、u o2ref , after pulse width modulation, the IGBT control signals PWM2 and PWM3 of the second parallel module and the third parallel module are obtained respectively.

6. A zero-sequence circulating current control device for multiple parallel converters, characterized in that: include: A current collection unit is configured to collect three-phase currents of a plurality of parallel modules; A rotation conversion unit, configured to convert the three-phase current and the total current thereof into a corresponding dqo axis current in a rotating coordinate system; A current control unit, configured to calculate a modulation voltage set value for loop control of a plurality of parallel modules based on the dqo axis current; A PWM modulation generation unit is configured to generate a PWM signal corresponding to the parallel module based on the modulation voltage given value; The PWM isolation and amplification unit is configured to isolate and amplify the PWM signal and use it for driving control of power devices in the parallel modules, thereby realizing zero-sequence circulating current suppression control between the parallel modules.

7. A zero-sequence circulating current control device for multiple parallel converters according to claim 6, characterized in that: If there are three parallel modules, namely the first parallel module, the second parallel module and the third parallel module, the three-phase current i of the reactor corresponding to the first parallel module, the second parallel module and the third parallel module is collected by the current collection unit. abc1 、i abc2 and i abc3 , the total current i is calculated based on these three sets of currents through the rotation transformation unit abc , and the four sets of currents are rotated and transformed to obtain the dqo axis current i corresponding to the stationary coordinate system dqo1 、i dqo2 、i dqo3 and i dqo .

8. A zero-sequence circulating current control device for multiple parallel converters according to claim 7, characterized in that: The loop control of the current control unit includes: dividing the current loop control in the stationary coordinate system into three groups of control loops, including one group of total current control loops and two groups of module current control loops; the total current control loop includes two current loops of d and q axes, and the module current control loop includes three current loops of d, q and o axes.

9. A zero-sequence circulating current control device for multiple parallel converters according to claim 8, characterized in that: The total current control loop adopts the total given current i of the dq axis of the converter dref 、i qref As given values, the d and q axis currents i d 、i q As feedback, after controller calculation and decoupling, the AC side voltage output reference value u of the parallel module is obtained. dref 、u qref ; Set the voltage output reference value u dref 、u qref After pulse width modulation, the IGBT control signal PWM1 of the first parallel module is obtained.

10. A zero-sequence circulating current control device for multiple parallel converters according to claim 9, characterized in that: The d and q axis given currents of the module current control loop are set to the total given current i dref 、i qref 1 / 3 of the given current of the o-axis is set to 0; the d, q, and o-axis currents of the second parallel module and the third parallel module are respectively used as feedback, and the difference between each given value and the feedback value is obtained after control operation and limiting to obtain the d, q, and o-axis voltage reference value u dqo1ref and u dqo2ref , where d and q axis voltage reference value u dq1ref 、u dq2ref With voltage reference value u dqref The sum is used as the AC side voltage output reference value of the second parallel module and the third parallel module respectively; and then combined with the respective o-axis voltage reference value u of the second parallel module and the third parallel module o1ref 、u o2ref , after pulse width modulation, the IGBT control signals PWM2 and PWM3 of the second parallel module and the third parallel module are obtained respectively.

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