Multi-objective controller for power quality of low voltage energy storage DSTATCOM

Abstract

The embodiment of the present invention provides a multi-objective controller for power quality of a low-voltage energy storage DSTATCOM. The positive sequence controller realizes smooth control of photovoltaic fluctuation active power based on a low-pass filter, and avoids voltage over-limit when a large amount of active reverse current appears; the negative sequence control loop realizes compensation for the three-phase imbalance of the common point voltage based on virtual complex admittance, and optimizes the negative sequence compensation current output by the energy storage DSTATCOM by deriving the optimal admittance angle; the self-anti-disturbance technology is introduced, and the disturbance in the current control system is estimated by establishing a second-order extended state observer, and compensation is performed in the current control loop to effectively improve the anti-disturbance capability and dynamic performance of the current control inner loop; by giving full play to the flexible compensation capability of the energy storage DSTATCOM, the influence of the uncertainty of the output of distributed photovoltaic power sources on the voltage stability of the low-voltage area can be reduced, and the three-phase imbalance at the common point can be effectively controlled.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of power quality management of distribution networks, and in particular to a multi-objective power quality controller for low-voltage energy storage DSTATCOM. Background Art

[0002] The large-scale access of new energy, single-phase loads, etc. to the distribution network will cause multiple power quality problems such as voltage fluctuations, voltage over-limit, and three-phase imbalance. Low-voltage substations are usually at the end of the distribution line, and the above-mentioned power quality problems are more prominent. Low-voltage static synchronous compensator (ie DSTATCOM) is a widely used distribution network power quality compensation device, but conventional DSTATCOM usually only has reactive power compensation function and cannot provide active power compensation. Since low-voltage distribution lines mainly present resistance characteristics, the node voltage is mainly affected by active power, so the voltage adjustment ability of traditional DSTATCOM based on reactive power compensation is reduced. In addition, the active output of new energy such as wind power and photovoltaics has obvious fluctuation characteristics, and it is also necessary to be equipped with power quality management equipment with certain active compensation capabilities to smooth the active fluctuation components. Summary of the invention

[0003] The embodiment of the present invention provides a low-voltage area energy storage DSTATCOM power quality multi-objective controller, which enables the energy storage DSTATCOM to comprehensively improve the power quality of distributed photovoltaic low-voltage areas.

[0004] The embodiment of the present invention provides a low-voltage area energy storage DSTATCOM power quality multi-objective controller, including an inverter, an energy storage system, a modulation module, a positive sequence control module and a negative sequence control module:

[0005] The energy storage system is connected to the DC side of the inverter, and the energy storage system is used to provide a stable DC voltage and active energy for the inverter;

[0006] The inverter is used to convert the direct current of the energy storage system into alternating current;

[0007] The positive sequence control module is used to output a positive sequence voltage modulation signal to control the energy storage type DSTATCOM to perform photovoltaic output smoothing control and voltage limiting control at the common point;

[0008] The negative sequence control module is used to output a negative sequence voltage modulation signal to control the energy storage DSTATCOM to perform three-phase unbalanced compensation of the common point voltage;

[0009] The modulation module is used to compare the positive and negative sequence voltage superposition signals with the carrier, output PWM pulses, and control the inverter to output the correct AC voltage.

[0010] Preferably, the negative-sequence control module is used to collect and separate the negative-sequence voltage component at the common point, and multiply the negative-sequence voltage component by the virtual complex admittance to obtain a negative-sequence compensation current reference instruction.

[0011] Preferably, the virtual complex admittance model is obtained by outputting the worst common point voltage imbalance and voltage imbalance compensation target and tracking and compensating through a PI controller.

[0012] Preferably, the negative sequence compensation current reference instruction is:

[0013]

[0014] In the above formula, is the negative sequence voltage phasor of the common connection point PCC, is the negative sequence compensation current phasor reference instruction of energy storage type DSTATCOM, Y is the virtual admittance module, is the virtual admittance angle, and j is the imaginary unit.

[0015] Preferably, the virtual admittance angle for:

[0016]

[0017] In the above formula, X g and R g are the reactance and resistance of the line impedance respectively.

[0018] Preferably, the total active reference instruction of the positive sequence control loop includes an active compensation amount for smoothing high frequency fluctuation components in photovoltaic output and an active compensation amount for voltage limiting control.

[0019] Preferably, the active reference total instruction is:

[0020]

[0021] In the above formula, The total active reference command of the positive sequence control module, It is the reference for active compensation of high-frequency fluctuation component of photovoltaic output. is the active compensation reference for voltage limit control, T f is the filtering time constant, is the positive sequence active power output by the photovoltaic power source, and s is the Laplace operator.

[0022] Preferably, the positive sequence control module and the negative sequence control module establish a d-axis current inner loop and a q-axis current inner loop based on an auto-disturbance rejection method.

[0023] An embodiment of the present invention provides a multi-objective controller for power quality of a low-voltage energy storage DSTATCOM. The positive-sequence controller realizes smooth control of fluctuating active power based on a low-pass filter, and avoids voltage over-limit when a large amount of active reverse current appears; the negative-sequence control loop realizes compensation for the three-phase imbalance of the common point voltage based on a virtual complex admittance, and optimizes the negative-sequence compensation current output by the energy storage DSTATCOM by deriving the optimal admittance angle; the self-anti-disturbance technology is introduced, and the disturbance in the current control system is estimated by establishing a second-order extended state observer, and compensation is performed in the current control loop to effectively improve the anti-disturbance capability and dynamic performance of the current control inner loop; by giving full play to the flexible compensation capability of the energy storage DSTATCOM, the influence of the uncertain output of distributed photovoltaic power sources on the voltage stability of the low-voltage area can be reduced, and the three-phase imbalance at the common point can be effectively controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A control block diagram of a multi-objective controller for power quality of a low-voltage energy storage DSTATCOM according to an embodiment of the present invention;

[0026] Figure 2 A topological structure diagram of a low-voltage area including photovoltaic and energy storage STATCOM according to an embodiment of the present invention;

[0027] Figure 3 A schematic diagram of the grid-connected active power of a photovoltaic power source before and after compensation by the energy storage DSTATCOM according to an embodiment of the present invention;

[0028] Figure 4 It is a response diagram of the output active power of the energy storage DSTATCOM under the multi-objective controller of the power quality of the energy storage DSTATCOM in the low-voltage area according to an embodiment of the present invention;

[0029] Figure 5 The output active power waveform diagram of the energy storage DSTATCOM according to the embodiment of the present invention;

[0030] Figure 6 is a curve showing a change in the common point voltage unbalance degree according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the embodiments of the present application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0033] The terms "first" and "second" in the embodiments of the present application are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a system, product or device comprising a series of parts or units is not limited to the listed parts or units, but optionally also includes parts or units that are not listed, or optionally also includes other parts or units inherent to these products or devices. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0035] Since energy storage has a certain active storage capacity and as costs are further controlled, energy storage is increasingly used in today's power systems. Therefore, an energy storage system can be installed on the DC side of DSTATCOM to enable DSTATCOM to have four-quadrant regulation capabilities for active and reactive power.

[0036] Therefore, the embodiment of the present invention provides a low-voltage area energy storage DSTATCOM power quality multi-objective controller, which fully utilizes the active power compensation capability of the energy storage DSTATCOM and realizes the energy storage DSTATCOM to comprehensively improve the power quality of the distributed photovoltaic low-voltage area. The following will be explained and introduced through multiple embodiments.

[0037] Figure 1 The present invention provides a low-voltage area energy storage DSTATCOM power quality multi-objective controller, including an inverter, an energy storage system, a modulation module, a positive sequence control module and a negative sequence control module:

[0038] The energy storage system is connected to the DC side of the inverter, and the energy storage system is used to provide a stable DC voltage and active energy for the inverter;

[0039] The positive sequence control module and the negative sequence control module are independent of each other and output respective modulation voltage signals;

[0040] The inverter is used to convert the direct current of the energy storage system into alternating current;

[0041] The positive sequence control module is used to output a positive sequence voltage modulation signal;

[0042] The negative sequence control module is used to output a negative sequence voltage modulation signal;

[0043] The modulation module is used to compare the positive and negative sequence voltage superposition signals with the carrier, output PWM pulses, and control the inverter to output the correct AC voltage.

[0044] Figure 1 middle, It is the total active reference command of the positive sequence control loop. is the total reactive power reference command of the positive sequence control loop, The energy storage DSTATCOM outputs positive sequence active power. is the positive sequence d and q axis reference current, are positive and negative sequence voltage modulation signals respectively, is the common point negative sequence d and q axis voltage, are the negative sequence d and q axis reference currents, u s,abc The voltage modulation signal is superimposed. In the positive sequence control module and the negative sequence control module, the d and q axis current inner loops introduce the anti-disturbance technology to improve the dynamic performance and anti-disturbance performance of the current inner loop. The positive sequence control module is used for smooth control of photovoltaic output and prevents the problem of voltage over-limit when the photovoltaic output is large. The active reference total instruction of the positive sequence control loop consists of two parts, one is the active compensation amount used to smooth the high-frequency fluctuation component in the photovoltaic output, and the other is the active compensation amount used for voltage limit control.

[0045] The active reference total instruction is:

[0046]

[0047] In the above formula, The total active reference command of the positive sequence control module, It is the reference for active compensation of high-frequency fluctuation component of photovoltaic output. is the active compensation reference for voltage limit control, T f is the filtering time constant, is the positive sequence active power output by the photovoltaic power source, and s is the Laplace operator.

[0048] The negative sequence control module is used to control the energy storage DSTATCOM to output negative sequence compensation current, thereby improving the three-phase imbalance of the common point voltage. The negative sequence compensation current reference instruction is obtained by collecting and separating the negative sequence voltage component at the common point and multiplying it by the virtual complex admittance.

[0049] Based on the above embodiment, as a preferred implementation, the negative sequence compensation current reference instruction is:

[0050]

[0051] In the above formula, is the negative sequence voltage phasor of the common connection point PCC, is the negative sequence compensation current phasor reference instruction of energy storage type DSTATCOM, Y is the virtual admittance module, is the virtual admittance angle, and j is the imaginary unit.

[0052] Based on the above embodiment, as a preferred implementation, the virtual complex admittance angle is obtained by outputting the worst common point voltage imbalance and voltage imbalance compensation target through tracking and compensation by a PI controller. It can be optimized based on the line impedance, and the selection basis is as follows:

[0053]

[0054] In the above formula, X g and R g are the reactance and resistance of the line impedance respectively.

[0055] In the above embodiment, the positive-sequence and negative-sequence current control loops introduce the anti-disturbance technology, and estimate the disturbance in the current control system by establishing a second-order extended state observer, and compensate it in the current control loop, thereby effectively improving the anti-disturbance capability and dynamic performance of the current control inner loop.

[0056] By building Figure 2 The typical distribution network low-voltage area simulation system shown in the figure tests the comprehensive power quality management performance of the energy storage DSTATCOM in the embodiment to verify the effectiveness of the controller described in the present invention.

[0057] Figure 2The photovoltaic power source generates electricity according to the actual light intensity in a certain area. The power supply side of the distribution network simulates the three-phase unbalanced condition of the common point voltage by setting a single-phase grounding fault. When the energy storage DSTATCOM is started, only the positive sequence control module is put into use. At t=200s, the negative sequence control module is enabled.

[0058] Figure 3 The figure shows the grid-connected active power of the photovoltaic power source before and after compensation by the energy storage DSTATCOM. As can be seen from the figure, the output of the photovoltaic power source before compensation shows more violent fluctuations due to changes in light intensity, and the climbing rate is high. After compensation, the grid-connected active power becomes smooth. In addition, when the photovoltaic output is large and the common point voltage is at risk of exceeding the limit (fluctuation exceeds 5%), the energy storage DSTATCOM will absorb part of the photovoltaic output, thereby limiting the common point voltage amplitude to a safe range, such as Figure 4 shown. Figure 5 It is the output active power waveform of the energy storage DSTATCOM. Figure 6 It is the variation curve of the common point voltage imbalance. It can be seen that when the negative sequence control module is put into use, the energy storage DSTATCOM can effectively improve the imbalance of the common point to less than 2%.

[0059] In summary, an embodiment of the present invention provides a multi-objective controller for power quality of a low-voltage energy storage DSTATCOM, in which a positive-sequence controller realizes smooth control of fluctuating active power based on a low-pass filter, and avoids voltage exceeding the limit when a large amount of active reverse current appears; a negative-sequence control loop realizes compensation for the three-phase imbalance of the common point voltage based on a virtual complex admittance, and optimizes the negative-sequence compensation current output by the energy storage DSTATCOM by deriving the optimal admittance angle; an anti-disturbance technology is introduced, and a second-order extended state observer is established to estimate the disturbance in the current control system, and compensate for it in the current control loop, thereby effectively improving the anti-disturbance capability and dynamic performance of the inner loop of the current control; by giving full play to the flexible compensation capability of the energy storage DSTATCOM, the influence of the uncertain output of distributed photovoltaic power sources on the voltage stability of the low-voltage area can be reduced, and the three-phase imbalance at the common point can be effectively controlled.

[0060] The various embodiments of the present invention can be combined arbitrarily to achieve different technical effects.

[0061] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented by software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in this application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website site, computer, server or data center to another website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line) or wireless (e.g., infrared, wireless, microwave, etc.) mode. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state hard disk SolidStateDisk), etc.

[0062] Those skilled in the art can understand that to implement all or part of the processes in the above-mentioned embodiments, the processes can be completed by computer programs to instruct related hardware, and the programs can be stored in computer-readable storage media. When the programs are executed, they can include the processes of the above-mentioned method embodiments. The aforementioned storage media include: ROM or random access memory RAM, magnetic disk or optical disk and other media that can store program codes.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-objective controller for power quality of low-voltage energy storage DSTATCOM, characterized in that: Including inverter, energy storage system, modulation module, positive sequence control module and negative sequence control module: The energy storage system is connected to the DC side of the inverter, and the energy storage system is used to provide a stable DC voltage and active energy for the inverter; The inverter is used to convert the direct current of the energy storage system into alternating current; The positive sequence control module is used to output a positive sequence voltage modulation signal to control the energy storage type DSTATCOM to perform photovoltaic output smoothing control and voltage limiting control at the common point; The negative sequence control module is used to output a negative sequence voltage modulation signal to control the energy storage DSTATCOM to perform three-phase unbalanced compensation of the common point voltage; The negative sequence control module is used to collect and separate the negative sequence voltage component at the common point, and multiply the negative sequence voltage component by the virtual complex admittance to obtain a negative sequence compensation current reference instruction; The negative sequence compensation current reference instruction is: In the above formula, is the negative sequence voltage phasor of the common connection point PCC, is the negative sequence compensation current phasor reference instruction of energy storage type DSTATCOM, Y is the virtual admittance module, is the virtual admittance angle, j is an imaginary unit; the virtual admittance modulus is obtained by outputting the worst common point voltage unbalance and voltage unbalance compensation target and tracking and compensating through a PI controller; The modulation module is used to compare the positive and negative sequence voltage superposition signals with the carrier, output PWM pulses, and control the inverter to output the correct AC voltage.

2. The low voltage area energy storage DSTATCOM power quality multi-objective controller according to claim 1 is characterized in that: The virtual admittance angle for: In the above formula, X g and R g are the reactance and resistance of the line impedance respectively.

3. The low voltage area energy storage DSTATCOM power quality multi-objective controller according to claim 1 is characterized in that: The active reference total instruction of the positive sequence control module includes active compensation for compensating high-frequency fluctuation components in photovoltaic output and active compensation for voltage limit control.

4. The low-voltage area energy storage DSTATCOM power quality multi-objective controller according to claim 3 is characterized in that: The active reference total instruction is: In the above formula, The total active reference command of the positive sequence control module, It is the reference for active compensation of high-frequency fluctuation component of photovoltaic output. is the active compensation reference for voltage limit control, T f is the filtering time constant, is the positive sequence active power output by the photovoltaic power source, and s is the Laplace operator.

5. The low voltage area energy storage DSTATCOM power quality multi-objective controller according to claim 1 is characterized in that: The positive sequence control module and the negative sequence control module establish a d-axis current inner loop and a q-axis current inner loop based on an auto-disturbance rejection method.

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