CN111342494B - Energy storage converter communication-line-free parallel connection strategy based on bus voltage event detection - Google Patents

Energy storage converter communication-line-free parallel connection strategy based on bus voltage event detection Download PDF

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CN111342494B
CN111342494B CN202010265925.4A CN202010265925A CN111342494B CN 111342494 B CN111342494 B CN 111342494B CN 202010265925 A CN202010265925 A CN 202010265925A CN 111342494 B CN111342494 B CN 111342494B
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energy storage
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storage converter
frequency
pcc
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CN111342494A (en
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易皓
吕念
王振雄
卓放
龚培娇
唐启迪
王瑞
李建伟
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Xian Jiaotong University
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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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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Abstract

The invention discloses an energy storage converter communication-line-free parallel strategy based on bus voltage event detection, which is based on the background that the distance between the load ends of the energy storage converters is close, realizes the power equalization of each energy storage converter by acquiring a voltage signal of a public end of a PCC point as a public event signal and based on a PCC voltage feedback method, and utilizes the event signal of the PCC voltage as a synchronous signal for realizing the voltage frequency recovery of each energy storage converter based on the principle of an event detection mechanism, thereby avoiding the requirement of each energy storage converter on communication interconnecting lines. The strategy control method is simple and practical, convenient to improve, good in system expansibility, low in construction cost of the multi-machine parallel system without the interconnection line and relatively practical in engineering application value.

Description

Energy storage converter communication-line-free parallel connection strategy based on bus voltage event detection
Technical Field
The invention belongs to the technical field of energy storage converter control, and particularly relates to a communication-line-free parallel strategy for an energy storage converter based on bus voltage event detection.
Background
The defects of traditional fossil energy enable related research of new energy to be rapidly developed, the power generation capacity of distributed power supplies such as the new energy is small, power needs to be supplied in parallel generally, an energy storage converter is used as a carrier of a distributed power supply, and the parallel control technology of the energy storage converter becomes a hotspot of research. The droop control is frequently adopted when the energy storage converters are connected in parallel, due to the fact that droop characteristics generally face problems of power distribution, voltage frequency recovery and the like, under inductive line impedance, distribution of active power can be automatically and evenly divided according to droop coefficients, distribution of reactive power can be affected by line impedance, and when line impedance is inconsistent, reactive power output of the energy storage converters is uneven.
Under the inductive line impedance, the traditional active-frequency and reactive-voltage droop control is adopted, the voltage and the frequency can deviate along with the change of the load power, the output voltage and the frequency of the energy storage converters are detected in real time and compared with a rated value, then the voltage and frequency deviation values of the energy storage converters are synchronously compensated to the energy storage converters, and finally the output values of the energy storage converters can be stabilized at the rated value through a PI controller. The method needs mutual communication among the energy storage converters to realize synchronous compensation, when the compensation is asynchronous, the output error of the energy storage converters can be accumulated, and finally the energy storage converter parallel system is unstable and collapses, so that the energy storage converters need to use communication lines to realize synchronization. However, the use of communication lines increases the complexity of the system, and in particular, decreases the stability of the system as the number of parallel devices increases.
Disclosure of Invention
Aiming at the problems, the invention provides a communication-line-free parallel strategy for energy storage converters based on bus voltage event detection, and the control strategy realizes the synchronous secondary recovery of the power average and the voltage frequency of each energy storage converter on the premise of avoiding the requirement of communication interconnection lines among the energy storage converters.
In order to achieve the aim, the invention relates to a communication-line-free parallel strategy of an energy storage converter based on bus voltage event detection, which comprises a power average strategy and a voltage frequency recovery strategy,
1) the power sharing strategy comprises the following steps:
1.1, sampling the bus voltage V of the PCC pointPCC；
1.2, measuring the real-time reactive power Q output by the ith energy storage converteritAnd utilizes the reactive power Q output by the ith energy storage converteritCalculating the command voltage V after droop controlrefi，
1.3, generating line voltage V of PCC of energy storage converterPCCAnd the command voltage V after droop controlref1The deviation of (a) is integrated, the result of the integration E1As the actual output voltage of the energy storage converter;
1.4 at Vrefi＝VPCCObtaining the output reactive power Q when the ith energy storage converter is stableiThe expression of (a) is:
Figure BDA0002441241880000021
rated voltage of ith energy storage converter, DqiThe droop coefficient of the ith energy storage converter is obtained;
1.5, setting the rated voltages of all the energy storage converters running in parallel to be equal and the droop coefficients to be equal, so that the output reactive powers of all the energy storage converters can be equal;
2) the voltage frequency recovery strategy comprises the following steps:
2.1, sampling the voltage frequency of a PCC point bus;
2.2, establishing an event detection mechanism by using the PCC voltage frequency information, wherein an event signal is used as a synchronous signal for secondary compensation unification of each energy storage converter;
2.3, measuring the actual output voltage V and the actual output frequency omega of the energy storage converter, and calculating the deviation value (V) of the output voltage and the rated value of the energy storage converter0V) calculating a deviation value (omega) of the frequency from a nominal value0ω) wherein V0For rated voltage, omega, of energy-storing converters0The rated frequency of the energy storage converter;
2.4, waiting for a secondary compensation synchronous event signal, if no secondary compensation event signal exists, repeating the step 2.1 to the step 2.3, otherwise, performing the step 2.5;
and 2.5, when the event signal is triggered, each energy storage converter superposes the voltage compensation value delta V on the actual output voltage V of the energy storage converter, and superposes the frequency compensation value delta omega on the actual output frequency omega of the energy storage converter, so that the synchronous voltage frequency recovery is realized.
Further, in step 2.2, the PCC bus voltage frequency deviation exceeding 0.02Hz is used as an event signal of the secondary compensation synchronous action of each energy storage converter.
Further, in step 1.2, the reactive voltage droop relation is
Figure BDA0002441241880000031
Rated voltage of ith energy storage converter, DqiAnd the droop coefficient of the ith energy storage current transformer is shown.
Further, in step 1.2, the actual output voltage E of the energy storage converteriThe expression of (a) is:
Figure BDA0002441241880000032
kqiis the integrator parameter of the ith energy storage current transformer.
Further, when the secondary compensation event signal occurs, the dynamic adjustment process of the parallel system is completed and then the step 2.5 is performed.
Further, in step 2.5, the calculation formula of δ V of the secondary voltage amplitude is: δ V ═ kpV(V0-V)+kiV∫(V0-V)dt，kpVIs a voltage compensation value proportionality coefficient, kiVIs the voltage compensation value integral coefficient.
Further, in step 2.5, the compensation value δ ω for the secondary voltage frequency recovery is calculated as: δ ω ═ kpf(ω0-ω)+kif∫(ω0-ω)dt，kpfAs a frequency compensation value proportional coefficient, kifIs the frequency compensation value integral coefficient.
Further, in step 2.5, when the step recovery improvement is performed by using the zero-crossing point signal of the PCC bus voltage, the frequency compensation value δ ω is one recovery step, and one recovery step is 0.005HZ-0.1HZAnd voltage frequency recovery is realized.
Compared with the prior art, the invention has at least the following beneficial technical effects:
the control strategy is based on the background that the distance between the load ends of the energy storage converters is short, the PCC bus voltage signals are obtained to serve as common event signals of all the energy storage converters, the event signals of the PCC voltage are used as synchronous action signals of all the energy storage converters for achieving voltage frequency recovery based on an event detection principle, and therefore the requirement for communication interconnection lines among all the energy storage converters is avoided.
Each energy storage converter acquires a PCC bus voltage signal, and the problem of power sharing of the energy storage converters without interconnection lines and with multiple parallel machines is solved based on a PCC voltage feedback method. The PCC bus voltage is utilized to realize the power equalization and voltage frequency recovery of the energy storage converter when the energy storage converter does not have the interconnected line and is in off-grid parallel operation. The whole system has good control performance, the problems of power equalization and voltage frequency recovery are solved by collecting PCC bus information, and the construction cost of interconnection lines among the energy storage converters is saved.
For the problem of secondary recovery of voltage frequency, aiming at the defect that the traditional method needs a communication line to realize synchronous compensation, an event signal of PCC bus voltage is used as a synchronous signal to realize secondary recovery. The control method is simple and easy to implement, easy to improve and upgrade, economical without an interconnection communication line, capable of improving the stability of the system, simple in control structure, easy to implement and relatively practical in engineering application value.
For the problem of power sharing, a PCC voltage feedback method is adopted, and the PCC bus voltage is used as a uniform reference potential to realize power distribution. The PCC voltage feedback method is used as a feasible power sharing strategy, has the advantages of simple and easy control, high response speed and the like, and does not need to acquire power information of other energy storage converters. The PCC bus voltage is sampled in real time and fed back to a reference instruction of droop control, the reaction speed is high, and the quality of electric energy of an original circuit cannot be influenced.
Drawings
FIG. 1 is a schematic diagram illustrating a communication-line-less parallel strategy control for an energy storage converter based on bus voltage event detection according to the present invention;
FIG. 2 is a control block diagram of a PCC voltage feedback method according to the present invention;
FIG. 3 is a schematic analysis diagram of the PCC voltage feedback method introduced in the present invention;
FIG. 4a is a schematic diagram of secondary frequency recovery according to the present invention;
FIG. 4b is a schematic diagram of the secondary voltage recovery introduced by the present invention;
FIG. 5a is a block diagram of a frequency recovery control based on event detection signals according to the present invention;
FIG. 5b is a block diagram of the voltage recovery control based on the event detection signal according to the present invention;
FIG. 6a is a waveform of active power of an energy storage converter in a communication-line-less parallel strategy simulation waveform based on bus voltage event detection for an energy storage converter according to the present invention;
FIG. 6b is a graph of reactive power waveforms of the energy storage converter in a communication-line-less parallel strategy simulation waveform based on bus voltage event detection for the energy storage converter according to the present invention;
FIG. 6c is a waveform of the output frequency of the energy storage converter in the communication-line-less parallel strategy simulation waveform based on bus voltage event detection for the energy storage converter according to the present invention;
FIG. 6d is a waveform of the output voltage amplitude of the energy storage converter in the communication-line-less parallel strategy simulation waveform based on bus voltage event detection for the energy storage converter according to the present invention;
FIG. 7a is a graph of frequency quadratic step recovery;
FIG. 7b is a partial enlarged view of FIG. 7 a;
fig. 7c is a graph of the output active power of the step-by-step recovery converter.
Detailed Description
In order to make the objects and technical solutions of the present invention clearer and easier to understand. The present invention will be described in further detail with reference to the following drawings and examples, wherein the specific examples are provided for illustrative purposes only and are not intended to limit the present invention.
In the following, the invention is explained in terms of power averaging and voltage frequency recovery:
1) power sharing strategy:
the control schematic diagram of the energy storage converter multi-machine parallel system without the interconnection lines is shown in fig. 1, no interconnection communication line is arranged between the energy storage converters, the load ends are close to each other, on one hand, the power supply load is close to the energy storage converters, the line impedance is small, on the other hand, the energy storage converters output LCL filtering, the line impedance can be ignored compared with the filter inductance L, and therefore the filter inductance L is approximately considered as the output impedance of the energy storage converters. And the droop control is adopted to realize the interconnection-free multi-machine parallel connection of the energy storage converter. In the line impedance, the inductive part X is far larger than the resistive part R, so the output impedance is inductive, and the droop control can adopt the traditional active-frequency and reactive-voltage droop control, and the specific control relation is as follows:
Figure BDA0002441241880000051
in the above formula, ωratedRated frequency of the output of the energy-storing converter, EratedRated voltage, P, of the output of the energy-storing converterratedRated active power, Q, output by the energy-storage converterratedRated reactive power, m, output by the energy storage converterPIs the droop coefficient of active power, nQIs the droop coefficient of the reactive power, PiIs the active power, Q, actually output by the ith energy storage converteriIs the reactive power, omega, actually output by the ith energy storage converteriIs the frequency of the actual output of the ith energy storage converter, EiThe actual output voltage of the ith energy storage converter is obtained.
Under the inductive line impedance, the active power and the reactive power output by a single energy storage converter when a plurality of energy storage converters are connected in parallel are respectively as follows:
Figure BDA0002441241880000061
in the above formula, EiIs the actual output voltage, V, of the ith energy storage converterPCCIs a bus of a parallel systemVoltage, deltaiIs the phase angle difference between the output voltage of the ith energy storage converter and the bus voltage, (X)Zi+XLi) Is the output impedance of the line on which the ith energy storage converter is located, where XZiLine impedance value X of line where ith energy storage converter is locatedLiAnd the inductive impedance value of the line where the ith energy storage current transformer is located.
The existing research shows that the energy storage converter can realize the equipartition of active power distribution in a stable state under the inductive line impedance condition, while the reactive power distribution is influenced by the line impedance, and when the line impedance is inconsistent, the reactive power distribution cannot realize the equipartition, so measures need to be taken to realize the reactive power distribution.
Under the background that the energy storage converter is not provided with the interconnection lines and is connected in parallel, a method with communication conditions cannot be adopted, and extremely small line impedance is ignored, so that voltage drop on the line impedance can also be ignored, the output voltage of the energy storage converter LCL can be approximate to PCC bus voltage, measurement of the PCC bus voltage can be achieved in engineering, and finally, a PCC voltage method is adopted to achieve uniform reactive power division.
The principle of the PCC voltage feedback method is to provide a uniform reference potential to achieve the reactive power distribution problem. The specific structural block diagram is shown in figure 2,
Figure BDA0002441241880000062
rated reference voltage, V, of energy-storing converterref1Is a command voltage after droop control, Dq1Is the droop coefficient of the energy storage converter, and the PCC bus voltage V of the energy storage converterPCCThe command voltage V after feedback and droop controlref1Comparing, integrating the deviation of the two, and obtaining an integration result E1As the actual output voltage of the energy storage converter. Detailed principle analysis is shown in fig. 3:
when the line impedance values of the two energy storage converters are different, a reactive unequal phenomenon can be generated, for example, point a in fig. 3 represents the reactive power of the energy storage converter a when the system voltage is stable, point B represents the corresponding reactive power of the energy storage converter B when the system voltage is stable, and the line of the energy storage converter aThe impedance value is larger than the line impedance value of the energy storage converter B, the reactive power output by the energy storage converter A obtained from the graph is small, and the corresponding output voltage value of the energy storage converter A is higher. When a PCC voltage feedback method is added, the actual output voltage of the energy storage converter is changed into the command voltage V after droop controlref1Integral with the difference in PCC voltage, i.e. for Δ EaAnd Delta EbDue to the large line impedance of the energy storage converter a, fig. 3 shows that the output voltage of the energy storage converter a is higher, and the corresponding Δ E is largeraAnd is also larger, so that the pair deltae after PCC voltage feedbackaThe integral value of (a) is also larger, namely the output voltage of the energy storage converter (A) is improved, so that the reactive power output by the energy storage converter (A) is improved. Through continuous feedback and adjustment, the output reactive power of the energy storage converter A is continuously increased, and when the parallel system is stable, the output reactive power of the energy storage converter A is equal to that of the energy storage converter B. And the active power can be automatically and equally divided under the impedance of an inductive line, so that the problem of power distribution is solved.
The feasibility of the PCC voltage feedback method is derived from the theoretical point of view, as follows, from fig. 2:
for the energy storage converter a, there are:
Figure BDA0002441241880000071
in the above formula, E1Is the actual output voltage of the energy storing converter a,
Figure BDA0002441241880000072
rated voltage, V, of energy-storing converter Aref1Is a command voltage after droop control, Dq1Is the droop coefficient, Q, of the energy storage converter A1Is the output reactive power, V, of the energy-storing converter APCCIs the PCC bus voltage, kq1Is the integrator parameter of the energy storage converter a.
Similarly, for the energy storage converter B, there are:
Figure BDA0002441241880000073
in the above formula, E2Is the actual output voltage of the energy storage converter B,
Figure BDA0002441241880000074
rated voltage, V, of energy-storing converter Bref2Is a command voltage after droop control, Dq2Droop coefficient, Q, of energy-storing converter B2Is the output reactive power of the energy storage converter B, VPCCIs the PCC bus voltage, kq2Is the integrator parameter of the energy storage converter B.
When the steady state is reached, the output voltage of the energy storage converter is kept stable, the input of the integrator is 0, and therefore:
Figure BDA0002441241880000081
in the above formula, Vref1Is the command voltage, V, of the energy-storing converter Aref2Is the command voltage, V, of the energy-storing converter BPCCIs the PCC bus voltage.
And substituting the equations into the droop relational expressions corresponding to the energy storage converters respectively to obtain:
Figure BDA0002441241880000082
in the above formula, Q1,Q2Respectively output reactive power of the energy storage converter A and the energy storage converter B,
Figure BDA0002441241880000083
rated voltage, V, of energy storage converter A and energy storage converter B, respectivelyPCCIs the PCC bus voltage, Dq1,Dq2Droop coefficients of energy storage converter A and energy storage converter B respectively
Rated voltage of energy storage converter A and energy storage converter B
Figure BDA0002441241880000084
And sag factor Dq1＝Dq2Then there is Q1＝Q2Therefore, the problem of reactive power sharing is solved by adopting a PCC voltage feedback method.
2) Voltage frequency recovery:
the energy storage converter can realize approximate distribution of power and stabilization of voltage frequency under the condition of no interconnection line by adopting droop control, wherein the distribution error of the power can be corrected by the PCC voltage feedback method, and the voltage or frequency offset caused by the droop control needs to be recovered by secondary control.
For a single energy storage converter, the droop control has the following influence:
Figure BDA0002441241880000085
wherein, omega is the actual output frequency of the energy storage converter, and V is the actual output voltage of the energy storage converter; omega0Rated frequency, V, for a single energy-storing converter0The voltage is the rated voltage of a single energy storage converter, P is the actual output active power of the single energy storage converter, Q is the actual output reactive power of the single energy storage converter, m is the droop coefficient of the active frequency, and n is the droop coefficient of the reactive power. As can be obtained from the formula 1.7, the voltage and frequency offsets of the energy storage converters are different due to different output powers (output active power — output reactive power), so that the offsets of the energy storage converters need to be compensated by secondary adjustment, and the compensation method is to superimpose a compensation value on the basis of the original droop control:
Figure BDA0002441241880000091
wherein:
Figure BDA0002441241880000092
in the above formula, kpVIs a voltage compensation value proportionality coefficient, kiVIs the voltage compensation value integral coefficient; k is a radical ofpfAs a frequency compensation value proportional coefficient, kifIs the frequency compensation value integral coefficient.
When secondary compensation is carried out, the energy storage converter measures the output voltage and frequency of the energy storage converter in real time, compares the measured value with a rated value set by the energy storage converter, obtains a real-time frequency compensation value delta omega and a real-time voltage compensation value delta V by performing PI integration on a difference value, and when a parallel system is stable, omega is present0＝ω,V0After the droop control is subjected to secondary compensation, the voltage amplitude and the frequency can be restored to the rated values, and the specific effects are as shown in fig. 4a and fig. 4 b:
as shown in fig. 4a, the secondary frequency recovery diagram is shown, where the primary control adopts droop control, resulting in the stable state of the energy storage converter being point a, the output frequency being ω, and there is frequency offset, and through the secondary control, a δ ω value is compensated based on the primary control, the stable state of the energy storage converter being point b, and the output frequency being the nominal value ω0Realizing frequency recovery; similarly, as shown in the schematic diagram of fig. 4b, the droop control is adopted in the primary control, so that the stable state of the energy storage converter is point a, the output voltage is V, voltage deviation exists, a δ V value is compensated on the basis of the primary control through the secondary control, the stable state of the energy storage converter is point b, and the output voltage is a rated value V at the moment0And voltage recovery is realized. The compensation method of the secondary control is simple and easy to implement, but the problem of how to solve the problem of compensation synchronization exists, when the compensation is asynchronous, errors are accumulated along with the increase of the compensation times, so that the power distribution deviation is larger and larger, and finally, a multi-machine parallel system is broken down, the existing solution method adopts a central controller to communicate with each energy storage converter, and a unified compensation signal is issued by the central controller when the compensation is needed; and another solution idea is to adopt adjacent communication between the energy storage converters, and adopt consistency theories such as graph theory and the like to realize secondary compensation under the condition of weak communication, so as to reduce communication cost. In order to realize the secondary synchronization recovery problem under the condition of no interconnected communication line, the invention adopts an event detection mechanism to provide uniform synchronization supplementAnd (4) compensating the signal.
Each energy storage converter can acquire the voltage information of the PCC bus, so that the PCC bus information is used as a uniform event signal of the multi-machine parallel system of the energy storage converters, and event triggering is that the frequency shift of the PCC voltage and the frequency exceeds a specified value. The specific process is that the energy storage converter detects the PCC bus voltage frequency information in real time, when the frequency deviation is within a specified range, an event signal is not triggered, and the multi-machine parallel system of the energy storage converter is kept stable by droop control; when the frequency deviation exceeds a specified range, the event signal is triggered, each energy storage converter receives a unified event signal, the dynamic adjustment process is avoided through certain time delay, secondary compensation of voltage and frequency is carried out on the basis of droop control, the rated value is recovered, and the process is repeated. The control schematic diagram is shown in FIG. 5:
calculating the frequency deviation (ω) based on the frequency recovery control block diagram of the event detection signal as shown in FIG. 5a0- ω), when an event signal is triggered, a dynamic adjustment process is avoided through a delay link, a compensation value δ ω can be obtained through the deviation value by a PI controller, and a frequency compensation value is superposed on active-frequency droop control to realize frequency recovery; similarly, the voltage deviation (V) is calculated based on the voltage recovery control block diagram of the event detection signal as shown in FIG. 5b0V), when an event signal is triggered, a compensation value delta V can be obtained through a time delay link and a PI controller, and the voltage compensation value is superposed on the reactive-voltage droop control to realize voltage recovery;
an energy storage converter communication-line-less parallel strategy based on bus voltage event detection comprises two parts: a power-sharing strategy and a voltage-frequency recovery strategy.
1. Power sharing strategy-PCC voltage feedback method:
1.1, sampling the voltage information of a PCC point bus;
1.2, measuring the output voltage and the output current of the energy storage converter, taking an A power equalization control block diagram of the energy storage converter as an example, as shown in figure 2, measuring the real-time reactive power Q output by the energy storage converter1tAnd constructing a reactive voltage droop relational expression
Figure BDA0002441241880000101
Rated voltage of energy-storage converter A, Dq1Is the droop coefficient of the energy storage converter A, and obtains the command voltage V after droop controlref1。
1.3, storing the PCC bus voltage V of the converterPCCThe command voltage V after feedback and droop controlref1Comparing and integrating the deviation of the two, i.e. E1＝kq1∫(Vref1-VPCC)dt，kq1Is the integrator parameter, the integration result E1As the actual output voltage of the energy storage converter;
1.4, under the action of an integrator, V is present when the integrator is stableref1＝VPCCThen combining with the reactive voltage droop relational expression
Figure BDA0002441241880000111
The reactive power of the energy storage converter A when the output reactive power is stable can be calculated
Figure BDA0002441241880000112
1.5, the same control strategy is carried out on the energy storage converter B, and when the reactive power output by the energy storage converter B is stable, the control strategy is that
Figure BDA0002441241880000113
Rated voltage of energy-storage converter B, Dq2Is the droop coefficient of the energy storage converter B.
1.6 rated voltage of energy storage converter A and energy storage converter B
Figure BDA0002441241880000114
And sag factor Dq1＝Dq2Then there is Q1＝Q2And the problem of reactive power sharing is solved by adopting a PCC voltage feedback method.
2. Voltage frequency recovery strategy-secondary compensation strategy based on event detection
2.1, sampling the voltage and frequency information of the PCC point bus;
2.2, establishing an event detection mechanism by using PCC voltage frequency information, taking the PCC bus voltage frequency deviation exceeding 0.02Hz as an event signal, and taking the event signal as a synchronous signal unified by secondary compensation of each energy storage converter;
2.3, measuring the actual output voltage V and the frequency omega of the energy storage converter, and respectively calculating the output voltage and the deviation value (V) of the frequency of the energy storage converter and a rated value0-V) and (ω)0ω) wherein V0And ω0Rated voltage and rated frequency respectively;
2.4, waiting for the event signal of the secondary compensation, and repeating the steps if no event signal exists;
and 2.5, when an event signal occurs, avoiding a dynamic adjustment process through the same delay link, and performing PI integration on the voltage and frequency deviation value to respectively obtain compensation values delta V, delta omega of secondary voltage frequency recovery, which is shown in a formula (1.9).
And 2.6, superposing the voltage and frequency compensation values delta V and delta omega to corresponding droop control according to the synchronous signals to realize voltage frequency recovery.
The invention provides an energy storage converter communication-line-free parallel strategy based on bus voltage event detection, an MTALB + PLECS software platform is adopted to build an energy storage converter interconnection-line-free off-network multi-machine parallel system platform, the proposed control scheme and related algorithms are subjected to simulation verification, and the correctness and reliability of the method are proved.
As shown in fig. 6a to 6d, the simulation results are that the load is applied when t is 4s and t is 10s, and in fig. 6a to 6d, the energy storage converter a is shown in gray and the energy storage converter B is shown in black.
As can be seen from fig. 6a, the active power of the energy storage converters is loaded at t-4 s and t-10 s, respectively, the output active power of the two energy storage converters is increased, and the active power can be equally divided;
as can be seen from fig. 6b, the reactive power of the energy storage converters is loaded at t-4 s and t-10 s, respectively, the output reactive power of the two energy storage converters is increased, and the reactive power can be equally divided;
it can be seen from fig. 6c that when the output frequency of the energy storage converter is t 4s, the frequency deviates from the rated value by 50Hz and exceeds 0.02Hz, the synchronization event triggers, the energy storage converter starts the secondary recovery, the frequency of the energy storage converter is recovered to the rated value, and when t is 10s, the secondary recovery process is started again, so that the output frequency of the energy storage converter is stabilized at 50Hz again.
It can be seen from fig. 6d that when the voltage amplitude of the PCC bus of the energy storage converter is t ═ 4s, the synchronization event is triggered, the energy storage converter starts secondary recovery, when the voltage amplitude of the PCC bus energy storage converter is recovered to the rated value 314V, and t ═ 10s, the secondary recovery process starts again, and finally, the voltage amplitude of the PCC bus is stabilized at 314V.
The simulation result shows that the method well solves the problems of power equalization and voltage frequency recovery of the energy storage converter non-interconnection line off-grid multi-machine parallel system, the strategy of the invention 'the energy storage converter non-communication line parallel strategy based on bus voltage event detection' has excellent performance, high reliability and easy realization, and provides high reference value for the problems of power equalization and voltage frequency recovery of the energy storage converter non-interconnection line off-grid multi-machine parallel system.
In the secondary recovery process, because the continuous PI recovery link has larger problems in terms of errors and realization difficulty, the further improvement can adopt a discrete step recovery process, taking the frequency secondary recovery of the energy storage converters as an example, each energy storage converter measures the zero crossing point of the PCC bus voltage, when the zero crossing point is reached, a frequency recovery step length is superposed on the output frequency of the energy storage converter, each energy storage converter carries out synchronous frequency step recovery, and when the frequency deviation is smaller than an allowable deviation value, the recovery process is stopped. And the event signal is also used as a synchronous signal for uniformly starting compensation of each energy storage converter, so that the output frequency of the energy storage converter can be recovered to be close to a rated value after step accumulation for a certain time, and error accumulation caused by a continuous adjusting process can be reduced by adopting a discrete step recovery improvement strategy. Taking the frequency adjustment of the energy storage converter as an example, a simulation is built on an MATLAB + space software platform to verify the strategy, and the simulation results are shown in FIGS. 7a to 7 c. In fig. 7a to 7c, the grey representation represents the energy storage converter a and the black representation represents the energy storage converter B. Fig. 7a and 7b show that when t is 3s, the frequency offset is caused by loading and exceeds a specified range, an event signal is triggered, through a 1.5s delay link, the energy storage converter starts a secondary frequency stepping recovery process, the output frequency of the energy storage converter is restored in a grading manner according to a PCC zero crossing point signal, and the output frequency of the energy storage converter can be stabilized near a rated value of 50Hz at the end, so that a better secondary frequency recovery effect can be realized, and the error accumulation and the engineering realization difficulty are reduced. As can be seen from fig. 7 c: in the process of frequency recovery, active power equalization is not affected, and similarly, a similar improvement strategy can be adopted for a voltage recovery strategy.
The strategy control method is simple and practical, convenient to improve, good in system expansibility, low in construction cost of the multi-machine parallel system without the interconnection line and relatively practical in engineering application value.
While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

1. A communication-line-free parallel strategy for an energy storage converter based on bus voltage event detection is characterized by comprising a power equalization strategy and a voltage frequency recovery strategy,
1) the power sharing strategy comprises the following steps:
1.1, sampling the bus voltage V of the PCC pointPCC；
1.2, measuring the real-time reactive power Q output by the ith energy storage converteritAnd utilizes the reactive power Q output by the ith energy storage converteritCalculating the command voltage V after droop controlrefi，
1.3, generating line voltage V of PCC of energy storage converterPCCAnd the command voltage V after droop controlref1The deviation of (a) is integrated, the result of the integration E1As energy-storing convertersThe actual output voltage of (d);
1.4 at Vrefi＝VPCCObtaining the output reactive power Q when the ith energy storage converter is stableiThe expression of (a) is:
Figure FDA0003173929020000011
Figure FDA0003173929020000012
rated voltage of ith energy storage converter, DqiThe droop coefficient of the ith energy storage converter is obtained;
1.5, setting the rated voltages of all the energy storage converters running in parallel to be equal and the droop coefficients to be equal, so that the output reactive powers of all the energy storage converters can be equal;
2) the voltage frequency recovery strategy comprises the following steps:
2.1, sampling the voltage frequency of a PCC point bus;
2.2, establishing an event detection mechanism by using the PCC voltage frequency information, wherein an event signal is used as a synchronous signal for secondary compensation unification of each energy storage converter;
2.3, measuring the actual output voltage V and the actual output frequency omega of the energy storage converter, and calculating the deviation value (V) of the output voltage and the rated value of the energy storage converter0V) calculating a deviation value (omega) of the frequency from a nominal value0ω) wherein V0For rated voltage, omega, of energy-storing converters0The rated frequency of the energy storage converter;
2.4, waiting for a secondary compensation synchronous event signal, if no secondary compensation event signal exists, repeating the step 2.1 to the step 2.3, otherwise, performing the step 2.5;
2.5, when the event signal is triggered, each energy storage converter superposes the voltage compensation value delta V on the actual output voltage V of the energy storage converter, and superposes the frequency compensation value delta omega on the actual output frequency omega of the energy storage converter, so that the synchronous voltage frequency recovery is realized;
in step 2.5, when the step recovery improvement is performed by using the zero-crossing point signal of the PCC bus voltage, the frequency compensation value δ ω is a recovery step lengthOne recovery step size is 0.005HZ-0.1HZAnd voltage frequency recovery is realized.
2. The energy storage converter communication-line-free parallel strategy based on bus voltage event detection according to claim 1, wherein in step 2.2, PCC bus voltage frequency deviation exceeding 0.02Hz is used as an event signal for secondary compensation synchronous action of each energy storage converter.
3. The energy storage converter communication-line-less parallel strategy based on bus voltage event detection as claimed in claim 1, wherein in step 1.2, the reactive voltage droop relation is
Figure FDA0003173929020000021
Figure FDA0003173929020000022
Rated voltage of ith energy storage converter, DqiAnd the droop coefficient of the ith energy storage current transformer is shown.
4. The communication-line-less parallel strategy for energy storage converters based on bus voltage event detection as claimed in claim 1, wherein in step 1.2, the actual output voltage E of the energy storage converteriThe expression of (a) is: ei＝kqi∫(Vrefi-VPCC)dt，kqiIs the integrator parameter of the ith energy storage current transformer.
5. The communication-line-less parallel strategy for the energy storage converters based on bus voltage event detection as claimed in claim 1, wherein when the secondary compensation event signal occurs, the dynamic adjustment process of the parallel system is completed and then step 2.5 is performed.
6. The communication-line-less parallel strategy for energy storage converters based on bus voltage event detection as claimed in claim 1Characterized in that, in the step 2.5, the calculation formula of δ V of the secondary voltage amplitude is: δ V ═ kpV(V0-V)+kiV∫(V0-V)dt，kpVIs a voltage compensation value proportionality coefficient, kiVIs the voltage compensation value integral coefficient.
7. The energy storage converter communication-line-less parallel strategy based on bus voltage event detection as claimed in claim 1, wherein in step 2.5, the compensation value δ ω for secondary voltage frequency recovery is calculated by the formula: δ ω ═ kpf(ω0-ω)+kif∫(ω0-ω)dt，kpfAs a frequency compensation value proportional coefficient, kifIs the frequency compensation value integral coefficient.
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