CN105279368B - A kind of method of three-phase grid system undamped stability analysis - Google Patents
A kind of method of three-phase grid system undamped stability analysis Download PDFInfo
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- CN105279368B CN105279368B CN201510506993.4A CN201510506993A CN105279368B CN 105279368 B CN105279368 B CN 105279368B CN 201510506993 A CN201510506993 A CN 201510506993A CN 105279368 B CN105279368 B CN 105279368B
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Abstract
The present invention relates to system stability analysis fields, improve a kind of method of three-phase grid system undamped stability analysis.In embodiments of the present invention, the mathematical model under discrete digital domain by establishing system, then the zero pole point position that discrete system is obtained according to the mathematical model controls the ratio relation of frequency with resonance, and undamped stability analysis is carried out to system according to the ratio relation, enable grid-connected system to improve stability, submits working efficiency.
Description
Technical field
The invention belongs to system stability analysis field more particularly to a kind of three-phase grid system undamped stability analyses
Method.
Background technology
In recent years, with the aggravation of environmental pollution, fossil energy problem it is in short supply, the development and utilization of regenerative resource by
To the concern of more and more countries, distributed generation system with initial stage due to assuming the spies such as investment is low, generation mode is flexible
It puts and comprehensively utilizes mode as a kind of new energy in great development market.Grid-connected converter is as distributed generation system and electricity
Energy interface unit between net public access point is extremely important component part in distributed generation system.
Due to grid-connected converter generally use high frequency PWM technique, it can contain higher hamonic wave in grid-connected current, therefore need to use
Filter filters out the harmonic noise.Preferable filter effect can not only be obtained using LCL filter, while can be reduced into
This, improves system dynamic responding speed, but since LCL filter is a third-order system, and amplitude versus frequency characte is bent at resonant frequency
There can be resonance spikes on line, -180 ° of phase angle mutation is had on phase-frequency characteristic curve, this can cause system oscillation even unstable
It is fixed.In order to inhibit the harm of resonance, need to carry out damping control to resonance spikes, traditional method has：1), passive Damping Schemes
It is to change sytem matrix by increasing passive damping resistance, increases system damping, inhibit resonance spikes, but this method can increase
Adding system is lost, and reduces system effectiveness.2), active damping schemes are to detect other state variables to introduce multi partitioning control system
System, to increase system damping, this method needs additional sensor, increases cost, while multi partitioning parameter designing is complicated.
It is contacted closely, to the filter effect of system, resonant frequency value, current attenuation between LCL filter parameters
Than etc. important parameters can all generate certain influence, meanwhile, during design, need the restrictive condition considered also very
It is more, such as cost, volume, efficiency, loss, reactive power exchange, therefore the parameter designing of LCL filter is complicated.Traditional design method
Be the LCL filter parameter designed in the case where not considering system stable condition, design complete after using it is passive damping or
Active damping stability control scheme improves the stability of system.
Invention content
The object of the present invention is to provide a kind of methods of three-phase grid system undamped stability analysis, solve the prior art
Present in the above problem.
The technical solution that the present invention solves above-mentioned technical problem is as follows：A kind of three-phase grid system undamped stability analysis
Method, which is characterized in that the described method comprises the following steps：
Establish the mathematical model under the discrete digital domain of system；
The ratio relation of the zero pole point position and resonance control frequency of discrete system is obtained according to the mathematical model；
Undamped stability analysis is carried out to system according to the ratio relation.
Further, the step of mathematical model under the discrete digital domain for establishing system, including：
According to the open-loop transfer function of following formula computing system：
Wherein：
Indicate the resonance angular frequency of LCL filter；
It is k to take system resonance frequencies and the scale factor of sample frequency, i.e.,：
Then the discrete open-loop transfer function of upper plane system can be reduced to following formula：
Wherein：
L indicates current transformer side filter inductance；LgIndicate grid side filter inductance；CfIndicate filter capacitor；R indicates inverter
Equivalent damping resistance on the actual inductance model of side；rgIndicate the equivalent series resistance and simultaneously on grid side actual inductance model
The resistance of cable road；C+Indicate positive direct-current bus capacitor；C-It indicates to bear dc-link capacitance, Kp、TiIt is pi regulator respectively
Proportional gain and integration time constant, TsIndicate the sampling period of discrete system.
Further, described the step of undamped stability analysis is carried out to system according to the ratio relation, including：
As k=0.1, with system open loop gain KpIncrease, the element branches of root locus are intended to from unit circle
Infinity, root locus are located at except unit circle, and there is no stable sections for system；
As k=0.25, with open-loop gain KpIncrease, the root locus element branches of system have positioned at unit circle it
Interior, system there is a possibility that stabilization；
As k=0.4, root locus plot is located within unit circle, with KpIncrease root locus far from unit circle；
I.e. with the increase of k, system can be from unstable and be transitioned into conditional stability.
The beneficial effects of the invention are as follows：Mathematical model under discrete digital domain of the present invention by establishing system, then root
The ratio relation of the zero pole point position and resonance control frequency of discrete system is obtained according to the mathematical model, and according to the ratio
Value relationship carries out undamped stability analysis to system so that grid-connected system can improve stability, submit working efficiency.
Description of the drawings
Fig. 1 is the flow chart of the method for three-phase grid system undamped stability analysis provided in an embodiment of the present invention；
Fig. 2 is the three-phase grid-connected converter physical topological structure filtered based on LCL；
Fig. 3 is three-phase grid-connected converter system structure control block diagram；
Fig. 4 is system discrete domain open-loop transfer function root locus plot figure under different value of K.
Specific implementation mode
The principle and features of the present invention will be described below with reference to the accompanying drawings, and the given examples are served only to explain the present invention, and
It is non-to be used to limit the scope of the present invention.
The specific implementation of the present invention is described in detail below in conjunction with specific embodiment：
Fig. 1 shows the flow of the method for three-phase grid system undamped stability analysis provided in an embodiment of the present invention,
For convenience of description, only list with the relevant part of the embodiment of the present invention, details are as follows：
The method of three-phase grid system undamped stability analysis provided in an embodiment of the present invention, includes the following steps：
Step S10 establishes the mathematical model under the discrete digital domain of system；
Step S20 obtains the ratio of the zero pole point position and resonance control frequency of discrete system according to the mathematical model
Relationship；
Step S30 carries out undamped stability analysis according to the ratio relation to system.
Such as Fig. 2,3,4, as a preferred embodiment of the present invention, according to the root locus of system open loop discrete domain transmission function point
The possibility that analysis system undamped is stablized.The mathematical model under the discrete digital domain of system is established, the control of discrete system is drawn
Structure diagram is as shown in Fig. 3, and current inner loop system is controlled using pi regulator, and specifically, the realization method of step S10 is：
According to the open-loop transfer function of following formula computing system：
Wherein：
Indicate the resonance angular frequency of LCL filter；
It is k to take system resonance frequencies and the scale factor of sample frequency, i.e.,：
Then the discrete open-loop transfer function of upper plane system can be reduced to following formula：
Wherein：
T1-T6It is the power switch tube of 3-phase power converter；L indicates current transformer side filter inductance；LgIndicate grid side filtered electrical
Sense；CfIndicate filter capacitor；R indicates the equivalent damping resistance on inverter side actual inductance model；rgIndicate the practical electricity of grid side
Feel the equivalent series resistance on model and the resistance on grid-connected circuit；C+Indicate positive direct-current bus capacitor；C-It indicates to bear direct current mother
Line capacitance, Kp、TiIt is proportional gain and the integration time constant of pi regulator, T respectivelysIndicate the sampling period of discrete system.
As the preferred embodiment of the present invention, the realization method for carrying out undamped stability analysis to system in step S30 has
Body is：
As k=0.1, with the increase of system open loop gain, the element branches of root locus are intended to nothing from unit circle
Poor big, root locus is located at except unit circle, and there is no stable sections for system；
As k=0.25, with the increase of open-loop gain Kp, the root locus element branches of system have positioned at unit circle it
Interior, system there is a possibility that stabilization；
As k=0.4, root locus plot is located within unit circle, as the increase root locus of Kp is far from unit circle；
I.e. with the increase of k, system can be from unstable and be transitioned into conditional stability.
For actual converter control system, if sample frequency is fixed, resonant frequency can be regarded as becomes ginseng as one
Number.By open-loop transfer function it is recognised that the zero pole point position of discrete system is only related with resonance control frequency ratio k values,
His coefficient only influences the gain of open-loop transfer function.
In embodiments of the present invention, in embodiments of the present invention, the mathematical modulo under the discrete digital domain by establishing system
Type, the zero pole point position that discrete system is then obtained according to the mathematical model control the ratio relation of frequency with resonance, and
Undamped stability analysis is carried out to system according to the ratio relation so that grid-connected system can improve stability, submit work
Make efficiency.
The foregoing is merely presently preferred embodiments of the present invention, is not intended to limit the invention, it is all the present invention spirit and
Within principle, any modification, equivalent replacement, improvement and so on should all be included in the protection scope of the present invention.
Claims (1)
1. a kind of method of three-phase grid system undamped stability analysis, which is characterized in that the described method comprises the following steps：
Establish the mathematical model under the discrete digital domain of system；
The ratio relation of the zero pole point position and resonance control frequency of discrete system is obtained according to the mathematical model；
Undamped stability analysis is carried out to system according to the ratio relation；
The step of mathematical model under the discrete digital domain for establishing system, including：
According to the open-loop transfer function of following formula computing system：
Wherein：
Indicate the resonance angular frequency of LCL filter；
It is k to take system resonance frequencies and the scale factor of sample frequency, i.e.,：
Then the discrete open-loop transfer function of upper plane system can be reduced to following formula：
Wherein：
L indicates current transformer side filter inductance；LgIndicate grid side filter inductance；CfIndicate filter capacitor；Kp、TiIt is that PI is adjusted respectively
The proportional gain of device and integration time constant, TsIndicate the sampling period of discrete system；
Described the step of undamped stability analysis is carried out to system according to the ratio relation, including：
As k=0.1, with the increase of system open loop gain, the element branches of root locus are intended to infinity from unit circle,
Root locus is located at except unit circle, and there is no stable sections for system；
As k=0.25, with open-loop gain KpIncrease, the root locus element branches of system have within unit circle, system
There is a possibility that stable；
As k=0.4, root locus plot is located within unit circle, with KpIncrease root locus far from unit circle；
I.e. with the increase of k, system can be from unstable and be transitioned into conditional stability；
For actual converter control system, if sample frequency is fixed, resonant frequency can be regarded as a variable element；By
Open-loop transfer function it is recognised that discrete system zero pole point position only with resonance control frequency ratio k values it is related, other coefficients
Only influence the gain of open-loop transfer function.
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| CN102290820A (en) * | 2011-08-22 | 2011-12-21 | 中国矿业大学 | LCL (Lower Control Unit) filtering controlled rectifying active damping control method of electric currents on feedback variable current side |
| CN103457265A (en) * | 2013-09-03 | 2013-12-18 | 上海大学 | Passive damping circuit of LCL filter |
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| JP2004364351A (en) * | 2003-06-02 | 2004-12-24 | Fuji Electric Holdings Co Ltd | Control method of interconnected inverter parallel system |
| TW200709544A (en) * | 2005-08-29 | 2007-03-01 | Ind Tech Res Inst | Transformer-free power conversion circuit for parallel connection with commercial electricity system |
| JP5938190B2 (en) * | 2011-10-26 | 2016-06-22 | 株式会社ダイヘン | Phase adjusting device, system counter component generating device, system interconnection inverter system, and phase adjusting method |
| US8957666B2 (en) * | 2013-04-23 | 2015-02-17 | Virgina Tech Intellectual Properties, Inc. | Anti-islanding protection in three-phase converters using grid synchronization small-signal stability |
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|---|---|---|---|---|
| CN102290820A (en) * | 2011-08-22 | 2011-12-21 | 中国矿业大学 | LCL (Lower Control Unit) filtering controlled rectifying active damping control method of electric currents on feedback variable current side |
| CN103457265A (en) * | 2013-09-03 | 2013-12-18 | 上海大学 | Passive damping circuit of LCL filter |
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| LCL滤波并网逆变器的数字单环控制技术研究;殷进军;《中国博士学位论文全文数据库工程科技Ⅱ辑》;20130715(第7期);摘要,正文第24-30页第2.2小节,第32-35页第3.1小节,图3.3 * |
| Limitations of Voltage-Oriented PI Current Control of Grid-Connected PWM Rectifiers With LCL Filters;Joerg Dannehl等;《IEEE Transactions on Industrial Electronics》;20090228;第56 卷(第2期);第380-388页摘要,第I-II,IV小节,图1,5-8 * |
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