CN112909961A - Direct-current side voltage balance control method of chain type STATCOM - Google Patents

Direct-current side voltage balance control method of chain type STATCOM Download PDF

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CN112909961A
CN112909961A CN202110292303.5A CN202110292303A CN112909961A CN 112909961 A CN112909961 A CN 112909961A CN 202110292303 A CN202110292303 A CN 202110292303A CN 112909961 A CN112909961 A CN 112909961A
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chain
phase
voltage
type statcom
current side
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CN112909961B (en
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章小卫
周京华
景柳铭
胡长斌
朴政国
张贵辰
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North China University of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract

The disclosure relates to a direct-current side voltage balance control method of a chain type STATCOM. Wherein, the method comprises the following steps: generating a direct-current side capacitor voltage mathematical relation in a chain type STATCOM chain link based on a chain type STATCOM loss model circuit; based on the mathematical relation of the direct current side capacitor voltage, the average value of the sum of the direct current side voltages of all the series modules of all the phases of the chain-type STATCOM is used as a command value, and the actual direct current side voltage value of each module is used as a feedback value, so that the direct current side voltage balance control in the phases of the chain-type STATCOM is realized; and performing active compensation on the output voltage of each phase of the chain type STATCOM, and realizing voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM. The method provides an in-phase and inter-phase direct-current side voltage balance control strategy by establishing an inter-phase control mathematical model and an in-phase control mathematical model.

Description

Direct-current side voltage balance control method of chain type STATCOM
Technical Field
The disclosure relates to the field of power electronics, in particular to a voltage balance control method for a direct current side of a chain type STATCOM.
Background
The direct-current side capacitors of each chain unit of the chain type STATCOM are mutually independent, the CPS-PWM is adopted under an ideal condition to ensure that the input power of each chain unit is consistent, but due to the difference and loss of device parameters, PWM pulse delay and other reasons, the direct-current side voltage of each chain unit fluctuates and is unbalanced, and the stable operation and compensation performance of the system are affected. Therefore, in order to ensure the stability and balance of the dc side voltage of each link, the balance control of each link voltage is required.
According to the chain type STATCOM circuit topology, each phase is formed by cascading independent H-bridge power units, and direct-current side capacitors of each chain link are independent, so that a new problem is brought to stable operation of a system. In the actual operation of the device, component parameters of each link unit are different, and the PWM waves output from the controller to the driver also have inconsistent time delay, which may cause imbalance of the capacitor voltage of each link module, thereby affecting the stable operation and compensation performance of the system.
Accordingly, there is a need for one or more methods to address the above-mentioned problems.
It is to be noted that the information disclosed in the above background section is only for enhancement of understanding of the background of the present disclosure, and thus may include information that does not constitute prior art known to those of ordinary skill in the art.
Disclosure of Invention
An object of the present disclosure is to provide a method for controlling dc-side voltage balancing of a chain-type STATCOM, thereby overcoming, at least to some extent, one or more of the problems due to the limitations and disadvantages of the related art.
According to an aspect of the disclosure, a chain-type STATCOM direct-current side voltage equalization control method is provided, which includes:
generating a direct-current side capacitor voltage mathematical relation in a chain type STATCOM chain link based on a chain type STATCOM loss model circuit;
based on the mathematical relation of the direct current side capacitor voltage, the average value of the sum of the direct current side voltages of all the series modules of all the phases of the chain-type STATCOM is used as a command value, and the actual direct current side voltage value of each module is used as a feedback value, so that the direct current side voltage balance control in the phases of the chain-type STATCOM is realized;
and performing active compensation on the output voltage of each phase of the chain type STATCOM, and realizing voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM.
In an exemplary embodiment of the disclosure, the implementing, based on the mathematical relation of the dc-side capacitor voltage, the dc-side voltage equalization control in the chain-type STATCOM phase by using an average value of a sum of dc-side voltages of each phase of each series module of the chain-type STATCOM as a command value and using an actual dc-side voltage value of each module as a feedback value further includes:
based on the mathematical relation of the direct current side capacitor voltage, taking the average value of the sum of the direct current side voltages of all the series modules of each phase of the chain-type STATCOM as a command value, taking the actual direct current side voltage value of each module as a feedback value, and multiplying the feedback value by the single-phase output current after being regulated by a proportional regulator to obtain a first fine adjustment value of the modulation wave of each single-phase module;
and adding the first fine adjustment quantity and the original modulation wave to obtain an in-phase adjustment modulation wave, and adjusting each module of the chain-type STATCOM through the in-phase adjustment modulation wave to absorb active power so as to realize in-phase direct-current side voltage balance control of the chain-type STATCOM.
In an exemplary embodiment of the present disclosure, the method further comprises:
calculating a transfer function of the voltage fine adjustment quantity and the active loss according to the direct current capacitor energy storage and the active loss of the chain type STATCOM power unit;
and calculating the time constant of the transfer function of the voltage fine adjustment quantity and the active loss, and designing a proportional regulator according to the time constant.
In an exemplary embodiment of the disclosure, the performing active compensation on the output voltage of each phase of the chain-type STATCOM, and implementing voltage balancing on the inter-phase dc side of the chain-type STATCOM by adjusting the active power of each phase of the chain-type STATCOM further includes:
calculating the difference value between the average value of each phase of capacitance voltage of the chain-type STATCOM and the average value of all direct-current side capacitance voltages, and generating second fine adjustment quantity of modulation waves of each single-phase module;
and adding the second fine adjustment quantity and the original modulation wave to obtain an interphase modulation wave, compensating the original modulation wave in the reactive current direction, and realizing the voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM.
In an exemplary embodiment of the present disclosure, the steps further include:
and generating an interphase control open-loop transfer function according to the interphase control of the zero sequence injection method, and completing parameter design of the interphase control PI regulator according to the interphase control open-loop transfer function.
The method for controlling the voltage balance of the direct current side of the chain type STATCOM in the exemplary embodiment of the disclosure comprises the following steps: generating a direct-current side capacitor voltage mathematical relation in a chain type STATCOM chain link based on a chain type STATCOM loss model circuit; based on the mathematical relation of the direct current side capacitor voltage, the average value of the sum of the direct current side voltages of all the series modules of all the phases of the chain-type STATCOM is used as a command value, and the actual direct current side voltage value of each module is used as a feedback value, so that the direct current side voltage balance control in the phases of the chain-type STATCOM is realized; and performing active compensation on the output voltage of each phase of the chain type STATCOM, and realizing voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM. The method provides an in-phase and inter-phase direct-current side voltage balance control strategy by establishing an inter-phase control mathematical model and an in-phase control mathematical model.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.
Drawings
The above and other features and advantages of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.
Fig. 1 shows a flow chart of a chain-type STATCOM dc-side voltage balancing control method according to an exemplary embodiment of the present disclosure;
fig. 2 illustrates a single-phase chain STATCOM loss model circuit diagram according to an exemplary embodiment of the present disclosure;
FIG. 3 illustrates a chain STATCOM chain link inter-cell voltage superposition phasor diagram according to an exemplary embodiment of the present disclosure;
FIG. 4 illustrates a chain STATCOM in-phase voltage equalization control block diagram in accordance with an exemplary embodiment of the present disclosure;
FIG. 5 illustrates a chain STATCOM phase-to-phase DC side voltage balancing control block diagram according to an exemplary embodiment of the present disclosure;
fig. 6 illustrates a chain STATCOM zero sequence voltage calculation control block diagram according to an exemplary embodiment of the present disclosure;
FIG. 7 illustrates a chain-type STATCOM in-phase DC-side voltage balancing control architecture in accordance with an exemplary embodiment of the present disclosure;
fig. 8A-8B illustrate a chain STATCOM interphase dc side voltage balancing control architecture diagram according to an exemplary embodiment of the present disclosure.
Detailed Description
Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The same reference numerals denote the same or similar parts in the drawings, and thus, a repetitive description thereof will be omitted.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the embodiments of the disclosure can be practiced without one or more of the specific details, or with other methods, components, materials, devices, steps, and so forth. In other instances, well-known structures, methods, devices, implementations, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure.
The block diagrams shown in the figures are functional entities only and do not necessarily correspond to physically separate entities. That is, these functional entities may be implemented in the form of software, or in one or more software-hardened modules, or in different networks and/or processor devices and/or microcontroller devices.
In the present exemplary embodiment, first, a method for controlling dc-side voltage equalization in a chain-type STATCOM is provided; referring to fig. 1, the method for controlling the dc-side voltage equalization of the chain-type STATCOM may include the following steps:
step S110, generating a mathematical relation of direct-current side capacitor voltage in chain elements of the chain STATCOM based on a chain STATCOM loss model circuit;
step S120, based on the mathematical relation of the direct current side capacitor voltage, taking the average value of the sum of the direct current side voltages of all the series modules of each phase of the chain-type STATCOM as a command value, and taking the actual direct current side voltage value of each module as a feedback value, so as to realize the direct current side voltage balance control in each phase of the chain-type STATCOM;
and S130, performing active compensation on each phase output voltage of the chain type STATCOM, and realizing voltage balance of the interphase direct current side of the chain type STATCOM by adjusting each phase active power of the chain type STATCOM.
The method for controlling the voltage balance of the direct current side of the chain type STATCOM in the exemplary embodiment of the disclosure comprises the following steps: generating a direct-current side capacitor voltage mathematical relation in a chain type STATCOM chain link based on a chain type STATCOM loss model circuit; based on the mathematical relation of the direct current side capacitor voltage, the average value of the sum of the direct current side voltages of all the series modules of all the phases of the chain-type STATCOM is used as a command value, and the actual direct current side voltage value of each module is used as a feedback value, so that the direct current side voltage balance control in the phases of the chain-type STATCOM is realized; and performing active compensation on the output voltage of each phase of the chain type STATCOM, and realizing voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM. The method provides an in-phase and inter-phase direct-current side voltage balance control strategy by establishing an inter-phase control mathematical model and an in-phase control mathematical model.
Next, the direct-current side voltage equalization control method of the chain type STATCOM in the present exemplary embodiment will be further described.
In step S110, a mathematical relation of the dc-side capacitor voltage in the chain of the chain STATCOM may be generated based on the chain STATCOM loss model circuit.
In the embodiment of the present example, as can be known from a chain-type STATCOM circuit topology, each phase of the chain-type STATCOM circuit topology is formed by cascading independent H-bridge power units, and the dc-side capacitances of each chain link are independent of each other, which brings a new problem to the stable operation of the system. In the actual operation of the device, component parameters of each link unit are different, and the PWM waves output from the controller to the driver also have inconsistent time delay, which may cause imbalance of the capacitor voltage of each link module, thereby affecting the stable operation and compensation performance of the system.
FIG. 2 shows a single-phase chain STATCOM loss model circuit, wherein Rdc_iIs a discharge resistor; the other loss models are arranged in a dotted line frame and mainly comprise three parts, namely series loss, parallel loss and mixed loss. The series loss comprises the conduction loss, the line loss and the like of the device, namely the loss which is only related to the current I at the alternating current side and is not related to the voltage at the direct current side is equivalent to the available series resistance R; parallel loss such as device off-state loss, capacitor self-loss and absorption loop loss is only related to DC side voltage and is not related to AC side current I, and parallel resistor R is usedliEquivalence is carried out; mixed losses, e.g. switching losses of the device, related to both the voltage on the DC side and the current on the AC side, by parallel controlled current sources knAnd I is equivalent.
To study the mathematical relationship between the dc side voltage and the loss of the system, a current equation was established for the ith chain link in fig. 2. Obtained according to kirchhoff's law
Figure BDA0002982979460000061
In the formula, CiThe capacitance value of the capacitor at the direct current side of the ith chain link is set; ri＝Rdc_i//Rli；udc_iThe voltage of the capacitor at the direct current side of the ith chain link; k is a radical ofiThe ith chain link mixed loss coefficient; siA switching function for the ith link; i.e. icIs an alternating side current.
udc_iContaining a DC component and an AC component, and can be expressed as
Figure BDA0002982979460000071
In the formula (I), the compound is shown in the specification,
Figure BDA0002982979460000072
and
Figure BDA0002982979460000073
the direct current component and the alternating current component of the direct current side capacitor voltage of the ith chain link are respectively.
icMainly consists of fundamental wave component and harmonic wave component, and the expression is
Figure BDA0002982979460000074
In the formula I1And
Figure BDA0002982979460000075
effective value and phase angle of the fundamental component respectively; i isnAnd
Figure BDA0002982979460000076
respectively, the effective value and the phase angle of the nth harmonic component.
Similarly, the switching function of the chain link also includes the fundamental component and harmonic component, which are expressed as
Figure BDA0002982979460000077
In the formula, MiIs the modulation degree of the fundamental component; thetaiError angle due to drive pulse delay; minAnd thetainRespectively, the modulation and error angle of the nth harmonic component.
Substituting formulae (3-2) to (3-4) into formula (3-1), omittingHarmonic components, and if only u is considereddc_iA direct current component of (2) can be obtained
Figure BDA0002982979460000078
When the system reaches a steady state, the voltage at the DC side is DC, and (3-5) is simplified to obtain
Figure BDA0002982979460000079
As can be seen from the formula (3-6),
Figure BDA00029829794600000710
and modulation degree MiPWM pulse delay error angle thetaiParallel loss RnAnd mixed loss kiI is all related, regardless of the magnitude of the capacitance and the series loss. With the lapse of time, the imbalance of the dc side capacitor voltage is increased due to the loss of each link unit and the difference of pulse delay, and if an effective control strategy is not adopted, the dc side voltage may be over-voltage or under-voltage, which may damage the stable operation of the device.
In step S120, based on the mathematical relation of the dc-side capacitor voltage, an average value of a sum of dc-side voltages of each series module of each phase of the chain-type STATCOM may be used as a command value, and an actual dc-side voltage value of each module may be used as a feedback value, so as to implement dc-side voltage balance control in the phase of the chain-type STATCOM.
In an embodiment of this example, the implementing, based on the mathematical relation of the dc-side capacitor voltages, the dc-side voltage equalization control in each phase of the chain-type STATCOM by using an average value of a sum of dc-side voltages of each series module in each phase of the chain-type STATCOM as a command value and using an actual dc-side voltage value of each module as a feedback value further includes:
based on the mathematical relation of the direct current side capacitor voltage, taking the average value of the sum of the direct current side voltages of all the series modules of each phase of the chain-type STATCOM as a command value, taking the actual direct current side voltage value of each module as a feedback value, and multiplying the feedback value by the single-phase output current after being regulated by a proportional regulator to obtain a first fine adjustment value of the modulation wave of each single-phase module;
and adding the first fine adjustment quantity and the original modulation wave to obtain an in-phase adjustment modulation wave, and adjusting each module of the chain-type STATCOM through the in-phase adjustment modulation wave to absorb active power so as to realize in-phase direct-current side voltage balance control of the chain-type STATCOM.
In the embodiment of the present example, the loss of each chain link unit is inconsistent, which causes the capacitor voltage of each chain link unit in a phase to be biased, that is, the capacitor voltage of the chain link unit with the loss lower than the average active power is higher, and the capacitor voltage of the chain link unit with the loss higher than the average active power is lower, so that the capacitor voltage of each chain link in the phase is unbalanced, the harmonic of the output voltage is increased, and the shutdown of the device may be caused in a severe case.
Therefore, on the basis of the inter-phase dc-side voltage equalization, dc-side capacitor voltage equalization control needs to be performed on each power cell in a phase to ensure the capacitor voltage equalization of the link cells in the phase. Adding a capacitance voltage balance control strategy into a phase needs to meet the requirements that 1) the total output voltage of each phase is not changed; 2) reactive power is not generated, and the influence on current control is avoided. Section 3.1 shows that the method of changing the modulation vector can be used to adjust the dc-side capacitor voltage of each chain link. The simplest control method is to superpose fundamental wave voltages in the same or opposite directions with the output current of each phase, and achieve the purpose of quickly adjusting the capacitance balance of each chain link unit by changing the modulation wave amplitude of each unit.
Taking phase a as an example, the control principle of changing the modulation vector is analyzed, and a voltage superposition phasor diagram between the link units is shown in fig. 3.
To ensure that the output voltage of each phase is constant, the sum of the regulated amounts of the outputs in the phases is zero, i.e.
Figure BDA0002982979460000091
In this case, the total active power of each phase is also unchanged, and the intra-phase voltage balance control block diagram shown in fig. 4 can be obtained without affecting the upper layer control.
In FIG. 4, the average value of the sum of DC voltages of the respective series-connected modules of each phase is calculated
Figure BDA0002982979460000092
As a command value, the actual DC voltage u of each module is setdc_xiAs feedback, the feedback is regulated by a proportional regulator K and multiplied by the output current of the A phase to obtain the fine adjustment quantity delta u of the modulation wave of each module of the A phasecxiAnd adding the value and the original modulation wave to obtain a new modulation wave so as to adjust the magnitude of the active power absorbed by each module and realize the voltage balance of the direct current side of each module.
In step S130, active compensation may be performed on each phase output voltage of the chain-type STATCOM, and voltage balancing between phases of the chain-type STATCOM is achieved by adjusting each phase active power of the chain-type STATCOM.
In this exemplary embodiment, the performing active compensation on the output voltage of each phase of the chain-type STATCOM, and implementing voltage balancing between phases of the chain-type STATCOM by adjusting the active power of each phase of the chain-type STATCOM further includes:
calculating the difference value between the average value of each phase of capacitance voltage of the chain-type STATCOM and the average value of all direct-current side capacitance voltages, and generating second fine adjustment quantity of modulation waves of each single-phase module;
and adding the second fine adjustment quantity and the original modulation wave to obtain an interphase modulation wave, compensating the original modulation wave in the reactive current direction, and realizing the voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM.
In the embodiment of the present example, the loss between the three phases is different, which may cause imbalance of active power between the three phases, and as time is accumulated, the imbalance degree becomes larger, the difference of the dc side voltage of each phase increases, and if the loss is not controlled, the dc side voltage of one phase with larger loss becomes smaller and smaller, and is in an under-voltage operating state; the voltage of the direct current side of one phase with smaller loss is increased more and more until the maximum voltage value is exceeded, the protection is stopped, and the power device is damaged when the protection is serious. Therefore, in order to solve the problem of dc side voltage imbalance, it is necessary to balance and control the dc side voltages between the three phases.
The method for controlling the voltage balance of the interphase direct current side is more, and comprises a zero sequence voltage injection method, a negative sequence voltage injection method, a method for combining zero sequence voltage and negative sequence voltage, split-phase control and the like. A simple control method is proposed, namely, a modulation wave is compensated in the reactive current direction according to the difference value of the average value of each phase capacitance voltage and the average value of the overall direct-current side capacitance voltage. The control method is essentially to perform active compensation on each phase output voltage of the chain type STATCOM, and realize voltage balance of the interphase direct current side by adjusting each phase active power of the chain type STATCOM.
Fig. 5 is a block diagram illustrating the inter-phase dc-side voltage equalization control. Taking phase A as an example, wherein
Figure BDA0002982979460000101
The output control quantity is
Δuca＝K1(∑udc_xi/3N-udc_a)ica (3-10)
In the formula, K1Is a scaling factor.
The above proposed interphase control easily causes the three-phase superimposition amount Δ uca、Δucb、ΔuccAnd the asymmetry causes the output current to contain a negative sequence component, thereby polluting the power grid. The zero sequence voltage injection method can avoid the problem, and the zero sequence voltage is pushed and guided under the balance working condition and a control strategy is given.
The voltage of the power grid is
Figure BDA0002982979460000102
In the formula, E is an effective value of the power grid voltage;
compensating current of
Figure BDA0002982979460000111
In the formula, I and thetaiRespectively, the effective value and the initial phase angle of the compensation current.
The zero sequence voltage is expressed as
Figure BDA0002982979460000112
In the formula, V0And theta0Respectively an effective value and an initial phase angle of the zero sequence voltage.
The zero sequence voltage corresponds to the three-phase average active power of
Figure BDA0002982979460000113
When three-phase direct-current voltages are unbalanced, the three phases consume unequal power, and unequal active power delta P needs to be injecteda、ΔPb、ΔPcTherefore, in order to maintain the balance of the direct current voltage among the three phases, the active power is generated by the zero sequence voltage for balancing, and
Figure BDA0002982979460000114
for convenient calculation, coordinate transformation can be carried out on the three-phase power of the system to obtain a three-phase power expression under an alpha and beta coordinate system as
Figure BDA0002982979460000115
Figure BDA0002982979460000116
Substituting the formulas (3-16) and (3-17) into (3-15) to obtain
Figure BDA0002982979460000121
The zero sequence voltage expression obtained by the formula (3-13) is as follows
Figure BDA0002982979460000122
In the equations (3-19), cos (ω t) and sin (ω t) can be obtained by a phase-locked loop, and fig. 6 shows a zero-sequence voltage calculation control block diagram.
In an embodiment of the present example, the method further comprises:
calculating a transfer function of the voltage fine adjustment quantity and the active loss according to the direct current capacitor energy storage and the active loss of the chain type STATCOM power unit;
and calculating the time constant of the transfer function of the voltage fine adjustment quantity and the active loss, and designing a proportional regulator according to the time constant.
In the embodiment of the present example, taking the phase a as an example, as can be known from the above control, the current of each power unit flowing through the phase a is the same, the ith power unit is used for performing active power analysis, and the energy stored by the dc capacitor of the ith power unit is set as paiActive power loss is Pai_lossFrom FIG. 4, an expression of the relationship between active power is obtained
pai＝K·ΔUdc_ai·Ica·Ica-Pai_loss＝K·ΔUdc_ai·Ica 2-Pai_loss (3-20)
Neglecting the alternating current component, the relationship between the voltage of the ith power unit of the A phase and the charge-discharge balance is
Figure BDA0002982979460000123
Substituting the formula (3-20) into the formula (3-21) to perform Laplace transform to obtain
Figure BDA0002982979460000124
Drawing an in-phase voltage balance control block diagram according to the equation (3-22) as shown in fig. 7, a transfer function of the voltage trimming amount and the active loss can be obtained according to the equation (3-22)
Figure BDA0002982979460000125
The first order function of the formula (3-22) is a time constant of
Figure BDA0002982979460000131
And designing a regulator K for balancing the direct-current side voltage of each phase of each series module according to the determined time constant.
In an embodiment of the present example, the steps further comprise:
and generating an interphase control open-loop transfer function according to the interphase control of the zero sequence injection method, and completing parameter design of the interphase control PI regulator according to the interphase control open-loop transfer function.
In the exemplary embodiment, the analysis is performed here with the phase-to-phase control of the zero-sequence injection method. Taking the A phase equivalent as an H bridge unit as an example, the relation between the A phase voltage and the charge-discharge balance is
Figure BDA0002982979460000132
In the formula, Cdc_aIs equal to A, and Cdc_a＝C/N；Udc_aIs equivalent capacitance DC voltage, and Udc_a＝NUdc；ΔP＝P0a-ΔPsa. By performing the laplacian transform on the above equation, the structure diagram of the inter-phase dc side voltage balance control shown in fig. 8A can be obtained from fig. 6 and equations (3-18).
In fig. 8A, the right side of the dotted line is the control object, the left side of the dotted line is the controller, and the controlled variable is the zero-sequence voltage u0For convenience of control design, the inter-phase dc side voltage equalization control block diagram shown in fig. 8A is simplified, and the simplified control block diagram is shown in fig. 8B.
In FIG. 8B, the interphase control open-loop transfer function is expressed as
Figure BDA0002982979460000133
The PI regulator parameters can be designed according to equations (3-25).
It should be noted that although the various steps of the methods of the present disclosure are depicted in the drawings in a particular order, this does not require or imply that these steps must be performed in this particular order, or that all of the depicted steps must be performed, to achieve desirable results. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step broken down into multiple step executions, etc.
Furthermore, the above-described figures are merely schematic illustrations of processes involved in methods according to exemplary embodiments of the invention, and are not intended to be limiting. It will be readily understood that the processes shown in the above figures are not intended to indicate or limit the chronological order of the processes. In addition, it is also readily understood that these processes may be performed synchronously or asynchronously, e.g., in multiple modules.
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.
It will be understood that the present disclosure is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is to be limited only by the terms of the appended claims.

Claims (5)

1. A method for controlling DC side voltage balance of a chain type STATCOM is characterized by comprising the following steps:
generating a direct-current side capacitor voltage mathematical relation in a chain type STATCOM chain link based on a chain type STATCOM loss model circuit;
based on the mathematical relation of the direct current side capacitor voltage, the average value of the sum of the direct current side voltages of all the series modules of all the phases of the chain-type STATCOM is used as a command value, and the actual direct current side voltage value of each module is used as a feedback value, so that the direct current side voltage balance control in the phases of the chain-type STATCOM is realized;
and performing active compensation on the output voltage of each phase of the chain type STATCOM, and realizing voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM.
2. The method of claim 1, wherein the implementing the dc-side voltage balance control in the chain-type STATCOM phase by using the dc-side capacitor voltage mathematical relation with the average value of the sum of the dc-side voltages of the respective series modules of the chain-type STATCOM phase as a command value and the actual dc-side voltage value of the respective modules as a feedback value further comprises:
based on the mathematical relation of the direct current side capacitor voltage, taking the average value of the sum of the direct current side voltages of all the series modules of each phase of the chain-type STATCOM as a command value, taking the actual direct current side voltage value of each module as a feedback value, and multiplying the feedback value by the single-phase output current after being regulated by a proportional regulator to obtain a first fine adjustment value of the modulation wave of each single-phase module;
and adding the first fine adjustment quantity and the original modulation wave to obtain an in-phase adjustment modulation wave, and adjusting each module of the chain-type STATCOM through the in-phase adjustment modulation wave to absorb active power so as to realize in-phase direct-current side voltage balance control of the chain-type STATCOM.
3. The method of claim 2, wherein the method further comprises:
calculating a transfer function of the voltage fine adjustment quantity and the active loss according to the direct current capacitor energy storage and the active loss of the chain type STATCOM power unit;
and calculating the time constant of the transfer function of the voltage fine adjustment quantity and the active loss, and designing a proportional regulator according to the time constant.
4. The method of claim 1, wherein the active compensation is performed on the output voltage of each phase of the chain-type STATCOM, and the balancing of the dc-side voltage between the phases of the chain-type STATCOM by adjusting the active power of each phase of the chain-type STATCOM further comprises:
calculating the difference value between the average value of each phase of capacitance voltage of the chain-type STATCOM and the average value of all direct-current side capacitance voltages, and generating second fine adjustment quantity of modulation waves of each single-phase module;
and adding the second fine adjustment quantity and the original modulation wave to obtain an interphase modulation wave, compensating the original modulation wave in the reactive current direction, and realizing the voltage balance of the interphase direct current side of the chain type STATCOM by adjusting the active power of each phase of the chain type STATCOM.
5. The method of claim 4, wherein the steps further comprise:
and generating an interphase control open-loop transfer function according to the interphase control of the zero sequence injection method, and completing parameter design of the interphase control PI regulator according to the interphase control open-loop transfer function.
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