CN104638634A - Direct current micro-grid oscillation suppression method based on band-pass filter in master-slave mode - Google Patents

Abstract

The invention relates to a direct current micro-grid oscillation suppression method based on a band-pass filter in a master-slave mode. The direct current bus voltage is controlled by a main power supply, a voltage and current dual-loop control mode is adopted, the method aims at two kinds of oscillation modes possibly occurring in a direct current micro-grid, a control system of the main power supply is improved, a feedback channel using output voltage and output current as the feedback quantity is newly added, two groups of corresponding oscillation suppression links are formed, and in a high-frequency component oscillation suppression link, the output voltage of a feedback quantity direct current bus is used as the compensation quantity to be added to the reference voltage of the main power supply control system after passing through a high-frequency band-pass filter; in a low-frequency component oscillation suppression link, the output current of the feedback quantity main power supply is used as the compensation quantity to be added onto the reference voltage of the main power supply control system after passing through a low-frequency band-pass filter. The direct current micro-grid oscillation suppression method has the advantages that the stable operation of the system can be ensured, the realization is simple, and the reliability is higher.

Description

Based on the direct-current grid oscillation suppression method of band pass filter under master slave mode

Technical field

The present invention is the control method that can suppress system oscillation unstability in a kind of direct-current grid, belongs to distributed power generation microgrid field.

Background technology

Improve constantly along with the attention rate of user to power supply reliability and the quality of power supply and the various forms of regenerative resource such as solar energy, wind energy utilizes in a large number, micro-capacitance sensor obtains the extensive concern of Chinese scholars as the effective way of distributed power source access electrical network.Micro-capacitance sensor generally refers to the small grids form multiple distributed power source, energy storage device and load coupled together by power electronic equipment, can be incorporated into the power networks, with traditional bulk power grid positive energy exchange, again can independent operating, become the isolated system of an energy stable operation.

Relative to interchange micro-capacitance sensor, direct-current grid has a lot of notable feature.First, most distributed power source, as photovoltaic cell, wind-driven generator etc., is all export direct current (or there is the intermediate link of direct current) substantially; And numerous household electrical appliance and office equipment inherently need DC power supply normally to work.If they received in direct-current grid, conversion link can be reduced, improve energy utilization rate.Meanwhile, there is no stationary problem and the reactive power flowing of equipment room in direct-current grid, make the cooperation control between current transformer more easy.

At present, distributed AC servo system mostly is for the oscillation suppression method in direct-current grid, namely needs the control loop of all parallel power electronic devices in improved system.But when the structure of system changes, as dropped into new power supply or excision DC load, these distributed damping controller parameters all need to carry out corresponding adjustment, otherwise the normal operation of possibility influential system.This also brings difficulty to real world applications.

Summary of the invention

The object of the invention is to the above-mentioned deficiency overcoming prior art, the direct-current grid oscillation suppression method based on band pass filter under a kind of master slave mode is provided.Technical scheme of the present invention is as follows:

Based on the direct-current grid oscillation suppression method of band pass filter under a kind of master slave mode, DC bus-bar voltage is controlled by main power source, adopt electric current and voltage double-loop control mode, it is characterized in that, the method is for two kinds of oscillation modes that may occur in direct-current grid, by improving the control system of main power source, newly-increased with output voltage v _dcwith output current i _ofor the feedback path of feedback quantity, form two groups of corresponding vibrations and suppress link, and be added to the reference voltage v of main power source control system as compensation rate _dcrefon, the higher-order of oscillation that two groups of vibrations suppress link may be able to occur in suppression system respectively and low-frequency oscillation, wherein,

High fdrequency component vibration suppresses link to be by feedback quantity DC bus-bar voltage v _dcby being added to as compensation rate on the reference voltage of main power source control system after high freguency bandpass filter, thus the higher-order of oscillation that suppression may occur, the transfer function adopted is:

$G_{\mathrm{com}1}\left(s\right)=K_1\frac{2{\mathrm{\ξ}}_1{\mathrm{\ω}}_{1}s}{s^2+2{\mathrm{\ξ}}_1{\mathrm{\ω}}_{1}s+{{\mathrm{\ω}}_1}^2}$

Wherein ω ₁get main power source closed-loop control transfer function △ v _dc/ △ v _dcrefresonance frequency; ξ ₁for the bandwidth of high freguency bandpass filter, value is 1; K ₁be used for the relation of coherent system damping and the stability of a system as proportional gain, the characteristic root distribution map according to system chooses more excellent parameter, span 0.3-0.7;

Low frequency component vibration suppresses link to be by the output current i of feedback quantity main power source _oby being added to as compensation rate on the reference voltage of main power source control system after low frequency bandpass filter, thus the low-frequency oscillation that suppression may occur, the transfer function adopted is:

$G_{\mathrm{com}2}\left(s\right)=K_2\frac{2{\mathrm{\ξ}}_2{\mathrm{\ω}}_{2}s}{s^2+2{\mathrm{\ξ}}_2{\mathrm{\ω}}_{2}s+{{\mathrm{\ω}}_2}^2}$

Wherein ω ₂get the resonance frequency of constant power load entrance side LC filter; ξ ₂for the bandwidth of low frequency bandpass filter, value is 0.2; K ₂characteristic root distribution map according to system chooses more excellent parameter, span 0.3-0.7.

Preferably, described direct-current grid oscillation suppression method, main power source closed-loop control transfer function is:

$\frac{{\mathrm{\Δv}}_{\mathrm{dc}}}{{\mathrm{\Δv}}_{\mathrm{ref}}}=\frac{(1-D)V_{\mathrm{dc}}{G}_i{G}_v-(\mathrm{sL}+R_L)I_L{G}_i{G}_v}{(\mathrm{sL}+R_L+V_{\mathrm{dc}}{G}_i)(\mathrm{sC}-I_L{G}_i{G}_v)+(1-D+I_L{G}_i)(1-D+V_{\mathrm{dc}}{G}_i{G}_v)}$

Wherein C, L/R _l, D is respectively the duty ratio of the electric capacity of voltage regulation of main power source current transformer, filter inductance and equivalent resistance and switching tube, G _i, G _vbe respectively the transfer function of inner and outer ring PI controller, draw Bode diagram by this transfer function, the ω of high freguency bandpass filter ₁get the frequency corresponding to resonance spikes.

The present invention adopts centralized damping control strategy, using the damping controller of main power source as direct current system, only needs the local information utilizing main power source, without the need to increasing extra sensor hardware circuit, without using communication.By improving the control loop of main power source, with the electric current and voltage of primary power outlet side for feedback signal, introducing additional oscillation suppressor, just can suppress the oscillatory occurences of the different frequency that may occur in direct current system, ensure the stable operation of system.The method realizes simple, and reliability is higher.

Accompanying drawing explanation

Fig. 1 is DC micro power grid system structure chart under master slave mode of the present invention;

Fig. 2 is DC micro power grid system characteristic root distribution map of the present invention;

Fig. 3 is main power source closed-loop control transfer function △ v of the present invention _dc/ △ v _dcrefbode diagram;

Fig. 4 is main power source small-signal control block diagram of the present invention;

Fig. 5 is main power source equivalent output impedance Z of the present invention _{out_cl}(s) frequency characteristic figure;

Fig. 6 is main power source oscillation suppression method control loop block diagram of the present invention;

Fig. 7 is that DC micro power grid system of the present invention adds oscillation suppressor post-simulation oscillogram.

Embodiment

Below according to Figure of description, introduce technical scheme of the present invention in detail.

Under typical case's master slave mode, the structure of DC micro power grid system as shown in Figure 1.This direct-current grid primarily of a main power source, several form from power supply and DC load, wherein each distributed power source, energy storage etc. are all equivalent to desirable direct voltage source, and DC load all represents with resistance.Consider that in side circuit, distributed power source has with a certain distance from load, in this direct-current grid from power supply all by one section of connection to DC bus.DC-DC current transformer in micro-capacitance sensor adopts Boost type topological structure, and main power source is electric current and voltage double-loop control, constant to maintain DC bus-bar voltage, from power acquisition Current Control, for load provides required power.

The present invention is based on the stability analysis conclusion of DC micro power grid system.As shown in Figure 2, can be obtained by small-signal analysis, there is the characteristic root of two groups of instability in system, wherein eigenvalue 1 is higher-order of oscillation component, and characteristic root 2 is low-frequency oscillation component.When eigenvalue 1 or 2 enters unit circle outside, z territory, DC micro power grid system Unstable oscillation.

The present invention proposes a kind of direct-current grid oscillation suppression method based on band pass filter, using main power source as centralized damping controller, utilize local data acquisition information, improve the control loop of main power source, realize the function suppressing system oscillation.Concrete grammar is as follows:

1) when each sampling period starts, A/D sample circuit is utilized to gather the capacitance voltage value v of main power source outlet side _dc, output current value i _owith the inductor current value i of DC-DC current transformer _l, and the digital quantity after conversion is sent to the control module of current transformer.

2) utilize digital algorithm by capacitance voltage value v _dcby obtaining the compensate component v of Voltage Reference after the process of higher-order of oscillation component filters _com1.This high fdrequency component oscillation suppressor is be made up of a band pass filter and proportional compensation device in essence, and its transfer function can be expressed as

$G_{\mathrm{com}1}\left(s\right)=K_1\frac{2{\mathrm{\ξ}}_1{\mathrm{\ω}}_{1}s}{s^2+2{\mathrm{\ξ}}_1{\mathrm{\ω}}_{1}s+{{\mathrm{\ω}}_1}^2}$

Wherein ω ₁get main power source closed-loop control transfer function △ v _dc/ △ v _dcrefresonance frequency; ξ ₁for the bandwidth of band pass filter, can value be 1 usually; K ₁be used for the relation of coherent system damping and the stability of a system as proportional gain, more excellent parameter can be chosen according to the characteristic root distribution map of system, be generally 0.3-0.7.

Solid line in Fig. 3 is main power source closed-loop control transfer function △ v _dc/ △ v _dcrefbode diagram, its expression formula is as follows

$\frac{{\mathrm{\Δv}}_{\mathrm{dc}}}{{\mathrm{\Δv}}_{\mathrm{ref}}}=\frac{(1-D)V_{\mathrm{dc}}{G}_i{G}_v-(\mathrm{sL}+R_L)I_L{G}_i{G}_v}{(\mathrm{sL}+R_L+V_{\mathrm{dc}}{G}_i)(\mathrm{sC}-I_L{G}_i{G}_v)+(1-D+I_L{G}_i)(1-D+V_{\mathrm{dc}}{G}_i{G}_v)}$

Wherein C, L/R _l, D is respectively the duty ratio of the electric capacity of voltage regulation of main power source current transformer, filter inductance and equivalent resistance and switching tube, G _i, G _vbe respectively the transfer function of inner and outer ring PI controller.In Fig. 3, the resonance spikes of solid line is the basic reason producing unstability eigenvalue 1, the therefore ω of band pass filter ₁need the frequency of getting corresponding to resonance spikes.Frequency characteristic after the dotted line representative increase electric capacity of voltage regulation C of Fig. 3, finds that resonance peak obviously reduces.When the value of holding capacitor C is constant, high fdrequency component oscillation suppressor puts into operation, and shown in Fig. 3 dotted line, this controller can play the effect identical with increasing capacitance.

3) utilize digital algorithm by main power source output current i _oby obtaining the compensate component v of Voltage Reference after the process of low-frequency oscillation component filters _com2.This low frequency component oscillation suppressor is be made up of a band pass filter and proportional compensation device in essence, and its transfer function can be expressed as

$G_{\mathrm{com}2}\left(s\right)=K_2\frac{2{\mathrm{\ξ}}_2{\mathrm{\ω}}_{2}s}{s^2+2{\mathrm{\ξ}}_2{\mathrm{\ω}}_{2}s+{{\mathrm{\ω}}_2}^2}$

Wherein ω ₂get the resonance frequency of constant power load entrance side LC filter; ξ ₂for the bandwidth of band pass filter, in order to reduce influencing each other between high freguency bandpass filter, can value be 0.2 usually; K ₂determine the size of main power source equivalent output impedance under this resonance frequency, more excellent parameter can be chosen according to the characteristic root distribution map of system, be generally 0.3-0.7.

In order to verify that this oscillation suppressor regulates the ability of main power source equiva lent impedance, the equivalent output impedance method for solving of main power source under small-signal of having derived below.

Fig. 4 is main power source small-signal control block diagram, and dotted portion is additional low frequency component vibration inhibitory control loop, can obtain the equivalent output impedance Z of main power source _{out_cl}(s) be

$Z_{\mathrm{out}\_\mathrm{cl}}\left(s\right)=-\frac{{\mathrm{\Δv}}_{\mathrm{dc}}\left(s\right)}{{\mathrm{\Δi}}_o\left(s\right)}{|}_{{\mathrm{\Δv}}_i\left(s\right)=0}=\frac{Z_{\mathrm{out}}+Z_{\mathrm{out}}{G}_{\mathrm{id}}{G}_i-A_{\mathrm{io}}{G}_{\mathrm{vd}}{G}_i}{1+G_{\mathrm{id}}{G}_i+G_{\mathrm{vd}}{G}_v{G}_i}$

Wherein open-loop voltage gain A _vo(s) be

$A_{\mathrm{vo}}\left(s\right)=\frac{{\mathrm{\Δv}}_{\mathrm{dc}}\left(s\right)}{{\mathrm{\Δv}}_i\left(s\right)}{|}_{{\mathrm{\Δi}}_o\left(s\right),\mathrm{\Δd}\left(s\right)=0}=\frac{1-D}{{\mathrm{LCs}}^2+R_L\mathrm{Cs}+{(1-D)}^2}$

Open-loop output impedance Z _out(s) be

$Z_{\mathrm{out}}\left(s\right)=-\frac{{\mathrm{\Δv}}_{\mathrm{dc}}\left(s\right)}{{\mathrm{\Δi}}_o\left(s\right)}{|}_{{\mathrm{\Δv}}_i\left(s\right),\mathrm{\Δd}\left(s\right)=0}=\frac{\mathrm{Ls}+R_L}{{\mathrm{LCs}}^2+R_L\mathrm{Cs}+{(1-D)}^2}$

Control duty ratio-output voltage transfer function G _vd(s) be

$G_{\mathrm{vd}}\left(s\right)=\frac{{\mathrm{\Δv}}_{\mathrm{dc}}\left(s\right)}{\mathrm{\Δd}\left(s\right)}{|}_{{\mathrm{\Δv}}_i\left(s\right),{\mathrm{\Δi}}_o\left(s\right)=0}=\frac{-{\mathrm{LI}}_{L}s-R_L{I}_L+V_i}{{\mathrm{LCs}}^2+R_L\mathrm{Cs}+{(1-D)}^2}$

Open loop input admittance Y _io(s) be

$Y_{\mathrm{io}}\left(s\right)=\frac{{\mathrm{\Δi}}_L\left(s\right)}{{\mathrm{\Δv}}_i\left(s\right)}{|}_{{\mathrm{\Δi}}_o\left(s\right),\mathrm{\Δd}\left(s\right)=0}=\frac{\mathrm{Cs}}{{\mathrm{LCs}}^2+R_L\mathrm{Cs}+{(1-D)}^2}$

Input current-inductive current transfer function A _io(s) be

$A_{\mathrm{io}}\left(s\right)=-\frac{{\mathrm{\Δi}}_L\left(s\right)}{{\mathrm{\Δi}}_o\left(s\right)}{|}_{{\mathrm{\Δv}}_i\left(s\right),\mathrm{\Δd}\left(s\right)=0}=\frac{-(1-D)}{{\mathrm{LCs}}^2+R_L\mathrm{Cs}+{(1-D)}^2}$

Control duty ratio-inductive current transfer function G _id(s) be

$G_{\mathrm{id}}\left(s\right)=\frac{{\mathrm{\Δi}}_L\left(s\right)}{\mathrm{\Δd}\left(s\right)}{|}_{{\mathrm{\Δv}}_i\left(s\right),{\mathrm{\Δi}}_o\left(s\right)=0}=\frac{{\mathrm{CV}}_{\mathrm{dc}}s+I_L(1-D)}{{\mathrm{LCs}}^2+R_L\mathrm{Cs}+{(1-D)}^2}$

Fig. 5 is the equivalent output impedance Z of main power source _{out_cl}s the frequency characteristic of (), the solid line in figure and dotted line represent the equivalent output impedance adding main power source before and after low frequency component oscillation suppressor respectively.Be easy to get by figure, after this oscillation suppressor puts into operation, main power source increases at the equivalent output impedance at design resonance frequency place, therefore can suppress system resonance on the basis not increasing system excess loss.

4) the reference v of main power voltage outer shroud _refby direct voltage with reference to v _dcref, bucking voltage component v _com1and v _com2three incorporating aspects form.Outer voltage is by current transformer outlet side electric capacity of voltage regulation voltage v _dcwith PI controller composition, for current inner loop provides current reference i _ref.Current inner loop is by inductive current i _lwith PI controller composition, finally generate the modulation wave signal d of Boost type DC-DC current transformer.

5) modulation wave signal and triangular wave compare, and obtain the duty cycle signals of switching tube, thus control opening and shutoff of converter switches pipe.

Fig. 6 is main power source oscillation suppression method control loop block diagram.

Fig. 7 is the simulation waveform figure after DC micro power grid system adds oscillation suppressor, and Fig. 7 (a), (b) represent DC bus-bar voltage v respectively _dcwith main power source output current i _oinstantaneous value waveform.Build simulation model as shown in Figure 1 with Matlab/Simulink, t=2.5s moment load puts into operation, has now occurred the oscillating component of two kinds of frequencies in direct current system, system oscillation unstability.T=2.7s, 2.8s moment high and low frequency component oscillation suppressor successively comes into operation.As seen from the figure: during 2.7s, in direct current system, the oscillating component of relative high frequency disappears, and it is inner that unstability eigenvalue 1 comes back to z territory unit circle; The oscillating component amplitude of 2.8s moment rather low-frequency reduces gradually, and after 3.1s, busbar voltage and output current recover stable again, and system gets back to normal operating condition.Therefore the direct-current grid oscillation suppression method based on band pass filter under a kind of master slave mode proposed by the invention is practical, effectively can increase system damping, the periodic swinging occurred in suppression system, ensures system stable operation.

Claims (2)

1. under a master slave mode based on the direct-current grid oscillation suppression method of band pass filter, DC bus-bar voltage is controlled by main power source, adopt electric current and voltage double-loop control mode, it is characterized in that, the method is for two kinds of oscillation modes that may occur in direct-current grid, by improving the control system of main power source, newly-increased with output voltage v _dcwith output current i _ofor the feedback path of feedback quantity, form two groups of corresponding vibrations and suppress link, and be added to the reference voltage v of main power source control system as compensation rate _dcrefon, the higher-order of oscillation that two groups of vibrations suppress link may be able to occur in suppression system respectively and low-frequency oscillation, wherein,

High fdrequency component vibration suppresses link to be by feedback quantity DC bus-bar voltage v _dcby being added to as compensation rate on the reference voltage of main power source control system after high freguency bandpass filter, thus the higher-order of oscillation that suppression may occur, the transfer function adopted is:

$G_{\mathrm{com}1}\left(s\right)=K_1\frac{2{\mathrm{\ξ}}_1{\mathrm{\ω}}_{1}s}{s^2+2{\mathrm{\ξ}}_1{\mathrm{\ω}}_{1}s+{{\mathrm{\ω}}_1}^2}$

Wherein ω ₁get main power source closed-loop control transfer function △ v _dc/ △ v _dcrefresonance frequency; ξ ₁for the bandwidth of high freguency bandpass filter, value is 1; K ₁be used for the relation of coherent system damping and the stability of a system as proportional gain, the characteristic root distribution map according to system chooses more excellent parameter, span 0.3-0.7;

Low frequency component vibration suppresses link to be by the output current i of feedback quantity main power source _oby being added to as compensation rate on the reference voltage of main power source control system after low frequency bandpass filter, thus the low-frequency oscillation that suppression may occur, the transfer function adopted is:

$G_{\mathrm{com}2}\left(s\right)=K_2\frac{2{\mathrm{\ξ}}_2{\mathrm{\ω}}_{2}s}{s^2+2{\mathrm{\ξ}}_2{\mathrm{\ω}}_{2}s+{{\mathrm{\ω}}_2}^2}$

Wherein ω ₂get the resonance frequency of constant power load entrance side LC filter; ξ ₂for the bandwidth of low frequency bandpass filter, value is 0.2; K ₂characteristic root distribution map according to system chooses more excellent parameter, span 0.3-0.7.

2. direct-current grid oscillation suppression method according to claim 1, is characterized in that, main power source closed-loop control transfer function is:

$\frac{\mathrm{\Δ}{v}_{\mathrm{dc}}}{\mathrm{\Δ}{v}_{\mathrm{ref}}}=\frac{(1-D)V_{\mathrm{dc}}{G}_i{G}_v-(\mathrm{sL}+R_L)I_L{G}_i{G}_v}{(\mathrm{sL}+R_L+V_{\mathrm{dc}}{G}_i)(\mathrm{sC}-I_L{G}_i{G}_v)+(1-D+I_L{G}_i)(1-D+V_{\mathrm{dc}}{G}_i{G}_v)}$

Wherein C, L/R _l, D is respectively the duty ratio of the electric capacity of voltage regulation of main power source current transformer, filter inductance and equivalent resistance and switching tube, G _i, G _vbe respectively the transfer function of inner and outer ring PI controller, draw Bode diagram by this transfer function, the ω of high freguency bandpass filter ₁get the frequency corresponding to resonance spikes.