CN106026100A - Voltage stability bifurcation analysis method for AC/DC hybrid power distribution network - Google Patents

Abstract

The invention discloses a voltage stability bifurcation analysis method for an AC/DC hybrid power distribution network. According to the method disclosed by the invention, the AC/DC hybrid power distribution network is equivalent to three portions; corresponding controllers are designed based on a differential algebra equation, wherein the controller comprises a voltage loop, a current loop and a stabilizer; voltage stability bifurcation analysis based on active power reference value variations is realized through setting system parameters and control parameters; a bifurcation inflection point and the limit power of voltage stability are determined based on an acquired bifurcation diagram, an optimal parameter of the stabilizer of the system is selected, a bandwidth value corresponding to the maximum stability margin of the system is found out, asymptotic stability analysis, static stability analysis, dynamic stability analysis and transient stability analysis of the system can be realized, a corresponding relation between the stabilizer parameter and the limit power of the system is acquired, feedback control signals of the stabilizer are set finally, and the system is controlled to operate in a range of the maximum stability margin.

Description

A kind of voltage stabilization Bifurcation method of alternating current-direct current mixing power distribution network

Technical field

The invention belongs to alternating current-direct current mixing distribution network technology field, be specifically related to the voltage of a kind of alternating current-direct current mixing power distribution network Stablize Bifurcation method.

Background technology

In the case of the emerging elements such as distributed power source, flexible DC power transmission, electric automobile continue to bring out, conventional electrical distribution Net is occurring the change of essence, alternating current-direct current mixing power distribution network progressively to become the main flow method of operation of following power distribution network.

DC distribution net is the core component of alternating current-direct current mixing power distribution network, is also that current alternating current-direct current mixing distribution is theoretical Emphasis in research and engineer applied.Relative to conventional AC distribution, DC distribution net has a following advantage: (1) circuit cost Low；(2) much less is wanted in the investment of direct current cables dielectric；(3) electric energy loss is little；(4) it is solely dependent upon directly due to the control of DG Stream voltage, the DG of DC distribution net is easier to synthetic operation；(5) change of generating electric energy and consumption load is permissible in DC network Compensate as an entirety；(6) only need to use inverter, system cost and loss significantly to drop with major network junction Low；(7) power supply reliability is high；(8) there is environment-friendly advantage.

Thus, the alternating current-direct current mixing power distribution network comprising DC distribution can implement function such as:

(1) in DC distribution net, various distributed power sources are simple and convenient with the type of attachment of dc bus, it is not necessary to consider to hand over The problems such as the stream frequency of electric power output voltage, phase place；And only needing an AC/DC or DC/DC change of current to change, dc bus is also only Can need to be connected with exchanging bulk power grid by a DC/AC inverter, therefore system cost and loss are substantially reduced.

(2) when bulk power grid breaks down, DC distribution net can disconnect from bulk power grid rapidly；When isolated operation, directly Load in stream power distribution network can obtain continued power, and is not affected by bulk power grid fault.

(3) the highest power supply reliability and the quality of power supply can be provided by being distributed in the current converter of load side.Such as, When somewhere load is short-circuited fault, other loads are unaffected.

(4) change of generated output and load power can compensate as an entirety in DC network, and, The coordination that the control of DC distribution net is more easily implemented between each distributed power source controls.

In addition it should be pointed out that, in current and following significant period of time, AC distribution net will be in leading ground Position, DC distribution net be existing AC distribution net supplement and non-proxy, DC distribution net is still in the early stage of development, and scale is relatively Little, it need further extensive development.At present, research to alternating current-direct current mixing power distribution network both at home and abroad is relatively fewer.

In sum, it is contemplated that the problem that alternating current-direct current mixing power distribution network exists at present, a kind of new alternating current-direct current is needed to mix The voltage stabilization Bifurcation method of power distribution network is to solve the problems referred to above.

Summary of the invention

For overcoming drawbacks described above, the invention provides the voltage stabilization Bifurcation side of a kind of alternating current-direct current mixing power distribution network Method, said method comprising the steps of:

Step 1: alternating current-direct current mixing power distribution network is equivalent to three parts, is respectively as follows: buck type dc-dc power converter cells, LC Filter cell, boost type dc-dc power converter cells；Wherein, buck type dc-dc power converter cells is led to LC filter cell Cross cable to connect, for the voltage stable to dc bus offer；LC filter cell and boost type dc-dc changer list Unit is connected by cable, as the input filter of boost type dc-dc power converter cells, simultaneously as the leakage inductance of cable；

Step 2: determine the differential algebraic equations of alternating current-direct current mixing power distribution network, its computing formula is:

$\left\{\begin{array}{c}\frac{{\mathrm{di}}_{L_1}}{dt}=\frac{1}{L_1}(u_s\·V_e-V_s-R_1\·i_{L_1})\\ \frac{{\mathrm{dV}}_s}{dt}=\frac{1}{C}(i_{L_1}-i_{dc})\\ \frac{{\mathrm{di}}_{dc}}{dt}=\frac{1}{L_f}(V_s-V_{cf}-R_f\·i_{dc})\\ \frac{{\mathrm{dV}}_{cf}}{dt}=\frac{1}{C_f}(i_{dc}-i_{L_2})\\ \frac{{\mathrm{di}}_{L_2}}{dt}=\frac{1}{L_2}(V_{cf}-R_2\·i_{L_2}-(1-u_l\left)V_0\right)\\ \frac{{\mathrm{dV}}_0}{dt}=\frac{1}{C_0}\left(\right(1-u_l)i_{L_2}-\frac{V_0}{R_0})\end{array}\right.$

Wherein, t express time variable, d represents derivation；u_sRepresent that in buck type dc-dc power converter cells, power electronics is opened Close the pulse command of device；u_lRepresent the pulse command of electronic power switch device in boost type dc-dc power converter cells；R_f、 L_fAnd C_fRepresent the resistance of LC filter cell, inductance and electric capacity respectively；C represents the electric capacity of dc bus；L₁、R₁Represent respectively The series inductance of buck type dc-dc power converter cells and resistance；L₂、R₂Represent the electricity of boost type dc-dc power converter cells respectively Sense and resistance；V_eRepresent the equivalent source voltage of buck type dc-dc power converter cells；And i_dcRepresent buck type respectively Dc-dc power converter cells electric current, boost type dc-dc power converter cells electric current and LC filter cell electric current；V_s、V_cfAnd V₀Point Do not represent DC bus-bar voltage, LC filter cell voltage and the output voltage of load；C₀、R₀Represent respectively load electric capacity and Resistance；

Step 3: the controller of design buck type dc-dc power converter cells, including Voltage loop, electric current loop and regulator；Its In, Voltage loop uses linear fractional order PI controller to be corrected；Electric current loop uses indirectly synovial membrane control method, and it controls Statement is generated by equivalent control rule；

Step 4: the controller of design boost type dc-dc power converter cells, it is by the digital control card realization of RT-Lab, For adjusting the active-power P of system output；Wherein, active power reference value P_refComputing formula be:

P_ref=I_ref·V_ref

Wherein, I_ref、V_refRespectively represent systematic survey arrive electric current, the reference value of voltage；I_refDetermined by Voltage loop；

Step 5: determine the sampling rate cycle T of control variable, its computing formula is:

$T=\frac{1}{f_s}$

Wherein, f_sRepresent the switching frequency of changer；

Step 6: Voltage loop expression formula C_vS the computing formula of () is:

$C_v\left(s\right)=K_{pv}+\frac{K_{iv}}{s^{\mathrm{\λ}}}$

Wherein, s represents independent variable, K_pvRepresent proportional gain, K_ivRepresenting integral coefficient, λ represents integration order；

Step 7: design stability device, it is made up of high pass filter based on ratio adjustment link, and this high pass filter exists When system voltage occurs fluctuation, by producing duty cycle signals, the vibration of damping system；

Step 8: initialization system parameter and control parameter, including DC input voitage, buck type dc-dc power converter cells Resistance and inductance, the electric capacity of dc bus, the resistance of wave filter, the electric capacity of wave filter and inductance, boost type dc-dc changer The resistance of unit and inductance, output capacitance, reference voltage, switching frequency, the cut-off frequency of regulator, the mark of voltage and current Rank proportional gain and integral coefficient；

Step 9: based on active power reference value P_refThe voltage stabilization Bifurcation of change；First buck type dc-dc is set The control parameter of power converter cells controller, then initializes regulator, draws V_s、V_cfBifurcation graphs；According to bifurcation graphs, and really Make the fork flex point of voltage stabilization, draw power limit P now₀；At P₀Point, system loses the stability of voltage；When meritorious Power continues to increase so that more than P₀Time, observe the situation of limit cycles oscillations, it is determined whether occur that Hopf diverges；

Step 10: adjust the parameter of regulator, observes power limit point with active power reference value P_refThe track of change, Find out power limit P of maximum_0max；And there is P in selecting system_0maxTime corresponding stabilizer parameter be optimized parameter；

Step 11: the voltage stabilization Bifurcation controlled based on bandwidth；First active power reference value P is set_ref, then Initialize regulator, by adjusting the control parameter of buck type dc-dc power converter cells controller, set current loop control signal Bandwidth so that it is higher than the bandwidth of Voltage loop control signal, system dynamic characteristic analysis based on current loop control, draw system Bifurcation graphs, last viewing system stability margin changes and the variation track that occurs along with bandwidth, finds out system stability nargin Bandwidth numerical value corresponding time big；

Step 12: Asymptotic Stability Analysis, by calculating the characteristic root of system Jacobian matrix, it is judged that the instability of system State, identifies stable operating point and the irregular operation point of system, and observes buck type dc-dc power converter cells and boost When in type dc-dc power converter cells, the bandwidth of control signal changes, power supply through DC network to the wattful power of Load transportation Rate situation of change；

Step 13: different parameters based on regulator arrange, the steady stability situation of viewing system, dynamic stability situation and Transient stability situation, draws the corresponding relation between stabilizer parameter and system limits power, the final feedback setting regulator Control signal, in the range of control system operates in the stability margin of maximum.

Compared with prior art, the voltage stabilization Bifurcation method of a kind of alternating current-direct current of present invention mixing power distribution network have with Lower advantage:

1) the controller design of power converter cells includes Voltage loop, electric current loop and regulator, and wherein regulator has feedback Control signal, increase effectively the stability margin of system；

2) regulator have employed the high pass filter of DC bus-bar voltage, and control accuracy is high；

3) control of regulator uses fractional order PI controller to be corrected, closer to the control characteristic of real system.

Accompanying drawing explanation

Fig. 1 is the structural representation of alternating current-direct current mixing power distribution network of the present invention.

Fig. 2 is the equivalent circuit diagram of alternating current-direct current mixing power distribution network of the present invention.

Fig. 3 is the structural representation of current loop controller of the present invention.

Detailed description of the invention

It is further elucidated with the present invention below in conjunction with the accompanying drawings.

Fig. 1 is the structural representation of alternating current-direct current mixing power distribution network of the present invention, and in Fig. 1, AC system is by every straight device Alternating current is converted to unidirectional current, supplies corresponding load.

The voltage stabilization Bifurcation method of alternating current-direct current mixing power distribution network of the present invention comprises the following steps:

Step 1: alternating current-direct current mixing power distribution network is equivalent to: buck type dc-dc power converter cells, LC filter cell, Boost type dc-dc power converter cells, as shown in Figure 2；Wherein, buck type dc-dc power converter cells is passed through with LC filter cell Cable connects, for the voltage stable to dc bus offer；LC filter cell and boost type dc-dc power converter cells Connected by cable, as the input filter of boost type dc-dc power converter cells, simultaneously as the leakage inductance of cable；

Step 2: determine the differential algebraic equations of alternating current-direct current mixing power distribution network, its computing formula is:

$\left\{\begin{array}{c}\frac{{\mathrm{di}}_{L_1}}{dt}=\frac{1}{L_1}(u_s\·V_e-V_s-R_1\·i_{L_1})\\ \frac{{\mathrm{dV}}_s}{dt}=\frac{1}{C}(i_{L_1}-i_{dc})\\ \frac{{\mathrm{di}}_{dc}}{dt}=\frac{1}{L_f}(V_s-V_{cf}-R_f\·i_{dc})\\ \frac{{\mathrm{dV}}_{cf}}{dt}=\frac{1}{C_f}(i_{dc}-i_{L_2})\\ \frac{{\mathrm{di}}_{L_2}}{dt}=\frac{1}{L_2}(V_{cf}-R_2\·i_{L_2}-(1-u_l\left)V_0\right)\\ \frac{{\mathrm{dV}}_0}{dt}=\frac{1}{C_0}\left(\right(1-u_l)i_{L_2}-\frac{V_0}{R_0})\end{array}\right.$

Wherein, t express time variable, d represents derivation；u_sRepresent that in buck type dc-dc power converter cells, power electronics is opened Close the pulse command of device；u_lRepresent the pulse command of electronic power switch device in boost type dc-dc power converter cells；R_f、 L_fAnd C_fRepresent the resistance of LC filter cell, inductance and electric capacity respectively；C represents the electric capacity of dc bus；L₁、R₁Represent respectively The series inductance of buck type dc-dc power converter cells and resistance；L₂、R₂Represent the electricity of boost type dc-dc power converter cells respectively Sense and resistance；V_eRepresent the equivalent source voltage of buck type dc-dc power converter cells；And i_dcRepresent buck type respectively Dc-dc power converter cells electric current, boost type dc-dc power converter cells electric current and LC filter cell electric current；V_s、V_cfAnd V₀Point Do not represent DC bus-bar voltage, LC filter cell voltage and the output voltage of load；C₀、R₀Represent respectively load electric capacity and Resistance；

Step 3: the controller of design buck type dc-dc power converter cells, including Voltage loop, electric current loop and regulator；Its In, Voltage loop uses linear fractional order PI controller to be corrected；Electric current loop uses indirectly synovial membrane control method, and it controls Statement is generated by equivalent control rule；

Step 4: the controller of design boost type dc-dc power converter cells, it is by the digital control card realization of RT-Lab, For adjusting the active-power P of system output；Wherein, active power reference value P_refComputing formula be:

P_ref=I_ref·V_ref

Wherein, I_ref、V_refRespectively represent systematic survey arrive electric current, the reference value of voltage；I_refDetermined by Voltage loop；

Step 5: determine the sampling rate cycle T of control variable, its computing formula is:

$T=\frac{1}{f_s}$

Wherein, f_sRepresent the switching frequency of changer；

Step 6: Voltage loop expression formula C_vS the computing formula of () is:

$C_v\left(s\right)=K_{pv}+\frac{K_{iv}}{s^{\mathrm{\λ}}}$

Wherein, s represents independent variable, K_pvRepresent proportional gain, K_ivRepresenting integral coefficient, λ represents integration order；

Step 7: design stability device, it is made up of high pass filter based on ratio adjustment link, and this high pass filter exists When system voltage occurs fluctuation, by producing duty cycle signals, the vibration of damping system；

Step 8: initialization system parameter and control parameter, including DC input voitage, buck type dc-dc power converter cells Resistance and inductance, the electric capacity of dc bus, the resistance of wave filter, the electric capacity of wave filter and inductance, boost type dc-dc changer The resistance of unit and inductance, output capacitance, reference voltage, switching frequency, the cut-off frequency of regulator, the mark of voltage and current Rank proportional gain and integral coefficient；

Step 9: based on active power reference value P_refThe voltage stabilization Bifurcation of change；First buck type dc-dc is set The control parameter of power converter cells controller, then initializes regulator, draws V_s、V_cfBifurcation graphs；According to bifurcation graphs, and really Make the fork flex point of voltage stabilization, draw power limit P now₀；At P₀Point, system loses the stability of voltage；When meritorious Power continues to increase so that more than P₀Time, observe the situation of limit cycles oscillations, it is determined whether occur that Hopf diverges；

Step 10: adjust the parameter of regulator, observes power limit point with active power reference value P_refThe track of change, Find out power limit P of maximum_0max；And there is P in selecting system_0maxTime corresponding stabilizer parameter be optimized parameter；

Step 11: the voltage stabilization Bifurcation controlled based on bandwidth；First active power reference value P is set_ref, then Initialize regulator, by adjusting the control parameter of buck type dc-dc power converter cells controller, set current loop control signal Bandwidth so that it is higher than the bandwidth of Voltage loop control signal, system dynamic characteristic analysis based on current loop control, draw system Bifurcation graphs, last viewing system stability margin changes and the variation track that occurs along with bandwidth, finds out system stability nargin Bandwidth numerical value corresponding time big；

Step 12: Asymptotic Stability Analysis, by calculating the characteristic root of system Jacobian matrix, it is judged that the instability of system State, identifies stable operating point and the irregular operation point of system, and observes buck type dc-dc power converter cells and boost When in type dc-dc power converter cells, the bandwidth of control signal changes, power supply through DC network to the wattful power of Load transportation Rate situation of change；

Step 13: different parameters based on regulator arrange, the steady stability situation of viewing system, dynamic stability situation and Transient stability situation, draws the corresponding relation between stabilizer parameter and system limits power, the final feedback setting regulator Control signal, in the range of control system operates in the stability margin of maximum.

Fig. 3 is the structural representation of current loop controller of the present invention.In Fig. 3, i_{L1, ref}Represent electric current i_L1Reference number Value；i_{L1, mes}Represent electric current i_L1Measurement numerical value；V_{S, mes}Represent voltage V_sMeasurement numerical value；K₁、λ₁It is buck type dc-dc to become The control coefrficient of exchange unit；Z represents Laplace transform；D₀Represent the control output of electric current loop；D_stabRepresent the steady of regulator Determine the working cycle；D_sRepresent D₀And D_stabAlgebraical sum；ω_sfRepresent the cut-off frequency of regulator；V_sfRepresent ω_sfThe output of module Voltage.

Claims (1)

1. the voltage stabilization Bifurcation method of an alternating current-direct current mixing power distribution network, it is characterised in that comprise the following steps:

Step 1: alternating current-direct current mixing power distribution network is equivalent to three parts, is respectively as follows: buck type dc-dc power converter cells, LC filtering Device unit, boost type dc-dc power converter cells；Wherein, buck type dc-dc power converter cells and LC filter cell are by electricity Cable connects, for the voltage stable to dc bus offer；LC filter cell leads to boost type dc-dc power converter cells Cross cable to connect, as the input filter of boost type dc-dc power converter cells, simultaneously as the leakage inductance of cable；

Step 2: determine the differential algebraic equations of alternating current-direct current mixing power distribution network, its computing formula is:

$\left\{\begin{array}{c}\frac{{\mathrm{di}}_{L_1}}{dt}=\frac{1}{L_1}(u_s\·V_e-V_s-R_1\·i_{L_1})\\ \frac{{\mathrm{dV}}_s}{dt}=\frac{1}{C}(i_{L_1}-i_{dc})\\ \frac{{\mathrm{di}}_{dc}}{dt}=\frac{1}{L_f}(V_s-V_{cf}-R_f\·i_{dc})\\ \frac{{\mathrm{dV}}_{cf}}{dt}=\frac{1}{C_f}(i_{dc}-i_{L_2})\\ \frac{{\mathrm{di}}_{L_2}}{dt}=\frac{1}{L_2}(V_{cf}-R_2\·i_{L_2}-(1-u_l\left)V_0\right)\\ \frac{{\mathrm{dV}}_0}{dt}=\frac{1}{C_0}\left(\right(1-u_l)i_{L_2}-\frac{V_0}{R_0})\end{array}\right.$

Wherein, t express time variable, d represents derivation；u_sRepresent electronic power switch device in buck type dc-dc power converter cells Pulse command；u_lRepresent the pulse command of electronic power switch device in boost type dc-dc power converter cells；R_f、L_fAnd C_f Represent the resistance of LC filter cell, inductance and electric capacity respectively；C represents the electric capacity of dc bus；L₁、R₁Represent buck type respectively The series inductance of dc-dc power converter cells and resistance；L₂、R₂Represent inductance and the electricity of boost type dc-dc power converter cells respectively Resistance；V_eRepresent the equivalent source voltage of buck type dc-dc power converter cells；And i_dcRepresent that buck type dc-dc becomes respectively Exchange unit electric current, boost type dc-dc power converter cells electric current and LC filter cell electric current；V_s、V_cfAnd V₀Represent straight respectively Stream busbar voltage, LC filter cell voltage and the output voltage of load；C₀、R₀Represent electric capacity and the resistance of load respectively；

Step 3: the controller of design buck type dc-dc power converter cells, including Voltage loop, electric current loop and regulator；Wherein, electricity Pressure ring uses linear fractional order PI controller to be corrected；Electric current loop uses indirectly synovial membrane control method, its control statement Generated by equivalent control rule；

Step 4: the controller of design boost type dc-dc power converter cells, it is realized by the digital control card of RT-Lab, is used for The active-power P of adjustment system output；Wherein, active power reference value P_refComputing formula be:

P_ref=I_ref·V_ref

Wherein, I_ref、V_refRespectively represent systematic survey arrive electric current, the reference value of voltage；I_refDetermined by Voltage loop；

Step 5: determine the sampling rate cycle T of control variable, its computing formula is:

$T=\frac{1}{f_s}$

Wherein, f_sRepresent the switching frequency of changer；

Step 6: Voltage loop expression formula C_vS the computing formula of () is:

$C_v\left(s\right)=K_{pv}+\frac{K_{iv}}{s^{\mathrm{\λ}}}$

Wherein, s represents independent variable, K_pvRepresent proportional gain, K_ivRepresenting integral coefficient, λ represents integration order；

Step 7: design stability device, it is made up of high pass filter based on ratio adjustment link, and this high pass filter is in system When voltage occurs fluctuation, by producing duty cycle signals, the vibration of damping system；

Step 8: initialization system parameter and control parameter, including DC input voitage, the resistance of buck type dc-dc power converter cells With inductance, the electric capacity of dc bus, the resistance of wave filter, the electric capacity of wave filter and inductance, boost type dc-dc power converter cells Resistance and inductance, output capacitance, reference voltage, switching frequency, the cut-off frequency of regulator, the fractional order ratio of voltage and current Example gain and integral coefficient；

Step 9: based on active power reference value P_refThe voltage stabilization Bifurcation of change；First the conversion of buck type dc-dc is set The control parameter of device cell controller, then initializes regulator, draws V_s、V_cfBifurcation graphs；According to bifurcation graphs, and determine The fork flex point of voltage stabilization, draws power limit P now₀；At P₀Point, system loses the stability of voltage；Work as active power Continue to increase so that more than P₀Time, observe the situation of limit cycles oscillations, it is determined whether occur that Hopf diverges；

Step 10: adjust the parameter of regulator, observes power limit point with active power reference value P_refThe track of change, finds out Maximum power limit P_0max；And there is P in selecting system_0maxTime corresponding stabilizer parameter be optimized parameter；

Step 11: the voltage stabilization Bifurcation controlled based on bandwidth；First active power reference value P is set_ref, the most initially Change regulator, by adjusting the control parameter of buck type dc-dc power converter cells controller, set the band of current loop control signal Wide so that it is higher than the bandwidth of Voltage loop control signal, system dynamic characteristic analysis based on current loop control, to draw dividing of system Trouble figure, the variation track that last viewing system stability margin changes along with bandwidth and occurs, when finding out system stability nargin maximum Corresponding bandwidth numerical value；

Step 12: Asymptotic Stability Analysis, by calculating the characteristic root of system Jacobian matrix, it is judged that the unstable shape of system State, identifies stable operating point and the irregular operation point of system, and observes buck type dc-dc power converter cells and boost type When in dc-dc power converter cells, the bandwidth of control signal changes, power supply through DC network to the active power of Load transportation Situation of change；

Step 13: different parameters based on regulator is arranged, the steady stability situation of viewing system, dynamic stability situation and transient state Stable case, draws the corresponding relation between stabilizer parameter and system limits power, the final feedback control setting regulator Signal, in the range of control system operates in the stability margin of maximum.