WO2022226709A1 - 考虑功率控制的永磁同步风机接入弱电网稳定性分析方法 - Google Patents
考虑功率控制的永磁同步风机接入弱电网稳定性分析方法 Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
- G01R19/2513—Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
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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
- H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
- H02J3/0012—Contingency detection
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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
- H02J3/381—Dispersed generators
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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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
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- 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
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
Definitions
- the invention relates to a stability analysis method for a permanent magnet synchronous fan connected to a weak grid considering the influence of power control, and belongs to the field of stability analysis of a new energy power generation system in a power system.
- Permanent magnet synchronous wind turbine (PMSG) has the advantages of high energy conversion efficiency, good operation reliability and strong controllability, and the proportion of installed capacity continues to increase.
- PMSG Permanent magnet synchronous wind turbine
- a suitable maximum power tracking algorithm must be adopted, among which the disturbance observation method does not need to measure the wind speed and has good practical value.
- the perturbation observation method contains nonlinear discontinuous links, which makes the traditional small-signal stability analysis methods difficult to apply.
- Conventional stability analysis methods generally ignore the power control loop based on the perturbation observation method.
- the description function method can well complete the modeling of nonlinear elements and the stability analysis of the system.
- the present invention proposes a stability analysis method for a permanent magnet synchronous fan connected to a weak grid considering the influence of power control, which fully considers the nonlinear links in the power loop and improves the accuracy of stability analysis.
- the invention aims to propose a stability analysis method for a permanent magnet synchronous wind turbine connected to a weak power grid considering the influence of power control.
- the permanent magnet synchronous fan includes a wind turbine, a generator, a machine-side converter, a DC capacitor, a grid-side converter, a filter, a machine-side converter controller and a grid-side converter controller.
- the generator-side converter controller includes a power loop, a speed loop, and a generator-side current loop;
- the grid-side converter controller includes a voltage loop and a grid-side current loop.
- the present invention adopts following technical scheme:
- Step 1 Obtain the main parameters of the permanent magnet synchronous fan, and establish the wind turbine, generator and machine-side converter, machine-side converter controller, DC capacitor, grid-side converter and filter, and grid-side converter respectively.
- the mathematical model of the wind turbine controller is linearized in the dq coordinate system, and the steady-state operating parameters are calculated to obtain the wind turbine, generator and machine-side converter, machine-side converter controller, DC capacitor, grid-side converter. Small-signal models of converters and filters, grid-side converter controllers.
- Step 2 Based on the description function method, the power loop in the machine-side converter controller is modeled, and its mathematical expression is
- ⁇ is the power loop disturbance step size
- T p is the power loop control period
- P ref is the reference value of the output power of the permanent magnet synchronous fan
- P is the output power of the permanent magnet synchronous fan
- P n is the permanent magnet synchronous fan at the current sampling time n.
- P n-1 is the output power of the permanent magnet synchronous fan at the last sampling time
- ⁇ g is the generator speed
- ⁇ g,n is the generator speed at the current sampling time
- ⁇ g,n-1 is the generator speed at the previous sampling time.
- the symbolic function in the formula can be modeled by the description function, and the description function is
- A represents the amplitude of the input signal
- Step 3 Considering the influence of the AC weak grid, the linear part of the weak grid and the small-signal model of the power ring mode are combined with the small-signal model of the permanent magnet synchronous fan established in step 1, and the transfer function G(s) of the linear part of the system is deduced.
- Step 4 Draw G(s) and -1/N(A) curves in the complex plane, and analyze the stability of the system based on the description function method.
- the specific method is that if G(s) contains the right half-plane pole, the system must not Stable; if G(s) does not contain the right half-plane pole, the system stability is judged by the relationship between the G(s) trajectory and the -1/N(A) trajectory:
- G(j ⁇ ) G Re ( ⁇ )+jG Im ( ⁇ )
- G Re represents the complex real part
- G Im represents the complex imaginary part
- ⁇ 0 is the oscillation angular frequency
- a 0 is the oscillation amplitude ;
- step 1 the small-signal models of the wind turbine, the generator, the machine-side converter, and the machine-side converter controller are established as follows:
- J is the moment of inertia of the equivalent lumped mass block of the wind turbine and the generator
- T m is the mechanical torque of the generator
- T e is the electromagnetic torque of the generator
- s is the parameter introduced by the Laplace change.
- the electromagnetic torque of the generator is the electromagnetic torque of the generator.
- n p is the number of pole pairs of the generator
- i qr is the stator current of the q-axis generator
- ⁇ f is the permanent magnet flux linkage of the generator.
- the mechanical torque of the generator is the mechanical torque of the generator.
- K cpr and K cir are the proportional and integral parameters of the PI control of the machine-side current loop, respectively.
- K ⁇ p and K ⁇ i are the proportional and integral parameters of the speed loop PI control, respectively.
- the superscript c represents the dq coordinate system of the machine-side converter controller. It is the reference value of generator speed. Linearizing it, the small-signal model of the machine-side converter controller can be obtained as
- step 1 the process of establishing the small signal model is as follows:
- C dc is the DC capacitor
- i dc1 is the grid-side DC current
- i dc2 is the machine-side DC current
- i dg is the grid-side converter AC port d
- q-axis currents d dg
- d qg is the output duty ratio of the grid-side converter controller in the dq coordinate system.
- u dc is the DC voltage
- i dr , i qr are the generator stator currents in the d and q coordinate systems, respectively
- d dr , d qr are the output duty ratios of the controller of the machine-side converter in the dq coordinate system, which are linearized , the small-signal model of the DC capacitance can be obtained as
- step 1 the process of establishing the small-signal model of the grid-side converter and the grid-side converter controller is as follows:
- L f is the filter inductance
- ⁇ is the power frequency angular frequency
- ⁇ 100 ⁇ rad/s
- i dg and i qg are the d and q-axis currents of the AC ports of the grid-side converter, respectively
- d dg and d qg are the dq coordinates
- u dc is the DC voltage
- u dg and u qg are the d and q-axis voltages of the grid-connected points, respectively.
- K cpg and K cig are the proportional and integral parameters of the grid-side current loop PI control, respectively.
- K vp and K v9 are the proportional parameter and integral parameter of the grid-side voltage loop PI control, respectively, and U dcref is the DC voltage reference value.
- a phase-locked loop is used to keep the wind turbine synchronized with the grid.
- the superscript c represents the grid-side converter controller dq coordinate system. Linearizing the model, the small-signal model of the grid-side converter controller can be obtained as
- phase-locked loop dynamics should also be considered in the grid-side converter, and its mathematical model is
- K ppll and K ipll are the proportional and integral parameters of the phase-locked loop PI controller, respectively, is the q-axis voltage of the grid-connected point in the dq coordinate system of the grid-side converter controller. Linearizing it, we get
- variables ⁇ x d and ⁇ x q can represent grid-side converter output currents ⁇ i dg , ⁇ i qg , grid-connected point voltages ⁇ u dg , ⁇ u qg or grid-side controller output duty ratios ⁇ d dg , ⁇ d qg , represents the steady-state component of the corresponding variable
- the small-signal model of the phase-locked loop can be derived, that is,
- step 3 is specifically:
- the AC weak grid is represented by the series equivalent inductance of an ideal voltage source, and its mathematical model is established as
- L g is the equivalent inductance of the weak grid
- u ds and u qs are the ideal voltage source voltages of the d and q axes, respectively
- idg and i qg are the d and q axis currents of the AC ports of the grid-side converter, respectively.
- the output power of the permanent magnet synchronous fan is
- T f represents the power sampling filter period
- 1/(1+T f s) is the power sampling filter delay
- 1/(1+1.5T ps ) is the controller and PWM delay.
- the present invention applies the description function method to the stability analysis of the grid-connected system of the permanent magnet synchronous fan, fully considers the nonlinear links in the power loop based on the disturbance observation method, and overcomes the inability of the traditional small signal analysis method to apply to discontinuous , the problem of nonlinear links.
- the description function method can quantitatively calculate the oscillation frequency and amplitude, which provides an important basis for oscillation prevention and suppression.
- Figure 1 shows the topological structure of permanent magnet synchronous fan (A) and its controller structure (B and D are coordinate transformation, C is phase-locked loop, E is machine-side converter controller, and F is grid-side converter controller )
- FIG. 2 shows the distribution of G(s) poles
- Fig. 3 is the curve of G(s) and -1/N(A) when the value of L g is changed
- FIG. 1 The topological structure of the permanent magnet synchronous fan according to the present invention and its controller are shown in FIG. 1 , including a wind turbine, a generator, a machine-side converter, a DC capacitor, a grid-side converter, and a filter.
- the wind turbine captures wind energy and converts it into mechanical energy.
- Both the machine-side converter and the grid-side converter are two-level voltage source converters.
- the machine-side converter converts the alternating current output from the permanent magnet synchronous generator into direct current.
- the grid-side converter inverts the DC power into a power-frequency AC power and connects it to the grid.
- the generator-side converter controller includes power loop (P&O), speed loop (H ⁇ ), and generator-side current loop (H cr );
- the grid-side converter controller includes voltage loop (H v ) and grid side current loop (H cg ).
- PLL phase-locked loop
- abc/dq and dq/abc coordinate transformation link
- the main parameters of the permanent magnet synchronous fan are obtained as shown in Table 1, and the wind turbine, the generator and the machine-side converter, the machine-side converter controller, and the DC capacitor are respectively established.
- s is the parameter introduced by the Laplace change
- J is the moment of inertia of the equivalent lumped mass block of the wind turbine and generator
- ⁇ g is the rotational speed of the generator
- T m is the mechanical torque of the generator
- T e is the electromagnetic field of the generator.
- n p is the number of pole pairs of the generator
- ⁇ f is the permanent magnet flux linkage of the generator
- B t is the linearization constant of the mechanical torque of the wind turbine.
- R s and L s are the generator rotor resistance and armature inductance respectively
- ⁇ e is the rotor electrical angular velocity
- ⁇ e n p ⁇ g .
- i dr , i qr are the generator stator currents in the dq coordinate system
- d dr , d qr are the output duty ratios of the machine-side converter controller in the dq coordinate system
- u dc is the DC voltage.
- K cpr and K cir are the proportional and integral parameters of the PI control of the machine-side current loop, respectively.
- K ⁇ p and K ⁇ i are the proportional and integral parameters of the speed loop PI control, respectively. is the reference value of the generator speed, is the steady-state value of the rotor electrical angular velocity, and the superscript c represents the dq coordinate system of the converter controller.
- C dc is the DC capacitance
- i dg and i qg are the d and q-axis currents of the AC ports of the grid-side converter, respectively
- d dg and d qg are the output duty ratios of the grid-side converter controller in the dq coordinate system.
- L f is the filter inductance
- ⁇ is the power frequency angular frequency
- ⁇ 100 ⁇ rad/s
- i dg , i qg are the d and q-axis currents of the AC port of the grid-side converter, respectively
- d dg , d qg are the dq coordinate system off-grid
- the output duty ratio of the side converter controller, u dg and u qg are the d and q-axis voltages of the grid-connected points, respectively.
- K cpg and K cig are the proportional and integral parameters of the grid-side current loop PI control, respectively.
- K vp and K vi are the proportional parameters and integral parameters of the grid-side voltage loop PI control, respectively.
- K ppll and K ipll are the proportional parameter and integral parameter of the phase-locked loop PI controller, respectively.
- the second step is to model the power loop in the controller of the machine-side converter based on the description function method.
- the mathematical model is
- the symbolic function in the formula can be modeled by the description function, and the description function is
- the third step is to consider the influence of AC weak grid, the weak grid model is
- the fourth step is to analyze the system stability.
- G(s) and -1/N(A) intersect, indicating that the system is in a critically stable state at this time.
- the DC component is 0.6889MW, the corresponding oscillation frequency is 19.5Hz, and the amplitude is 58kW, which is basically consistent with the theoretical analysis results;
- the DC component is 0.6889MW, the corresponding oscillation frequency is 19.5Hz, and the amplitude is 53kW , which is basically consistent with the theoretical analysis results.
- the simulation results verify the validity and accuracy of the analysis method.
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Abstract
本发明涉及一种考虑功率控制影响的永磁同步风机接入弱电网稳定性分析方法。新能源发电多采用扰动观察法进行最大功率跟踪,其中的非线性不连续环节导致稳定性分析困难。本发明基于描述函数法分析了永磁同步风机接入弱电网系统的稳定性,充分考虑了功率环中的非线性不连续环节,使分析结果更加精确。同时,描述函数法是一种可以量化地计算振荡功率和幅值的方法,本发明的分析方法能够为振荡抑制及控制器设计提供良好参照。
Description
本发明涉及一种考虑功率控制影响的永磁同步风机接入弱电网稳定性分析方法,属于电力系统中新能源发电系统稳定性分析领域。
可再生能源发电占比不断提升,风力发电装机容量持续增长,风机并网系统的稳定运行成为重要问题。永磁同步风电机组(PMSG)具有能量转换效率高、运行可靠性好、可控性强的优势,装机占比持续提高。为了更好地利用风能,必须采用合适的最大功率跟踪算法,其中扰动观察法无需测量风速,具有较好的实用价值。然而,扰动观察法隐含非线性不连续环节,导致传统的小信号稳定性分析方法难以适用,常规的稳定性分析方法一般忽视基于扰动观察法的功率控制环。描述函数法可以很好地完成非线性环节建模和系统的稳定性分析,其基本思想是,当系统满足一定假设条件时,在正弦输入作用下,系统非线性环节的输出可用一次谐波分量来近似表示,从而获得非线性环节的近似等效频率特性。因此,本发明基于描述函数法提出一种考虑功率控制影响的永磁同步风机接入弱电网稳定性分析方法,充分考虑功率环中的非线性环节,提高稳定性分析的精确性。
发明内容
本发明旨在提出一种考虑功率控制影响的永磁同步风机接入弱电网稳定性分析方法。所述永磁同步风机包括风力机、发电机、机侧变流器、直流电容、网侧变流器、滤波器、机侧变流器控制器和网侧变流器控制器。机侧变流器控制器中,包含功率环,转速环,机侧电流环;网侧变流器控制器中,包含电压环和网侧电流环。
本发明采用如下技术方案:
步骤一:获取永磁同步风机的主要参数,分别建立风力机、发电机及机侧变流器、机侧变流器控制器、直流电容、网侧变流器及滤波器、网侧变流器控制器的数学模型,并在dq坐标系下进行线性化,计算稳态运行参数,得到风力机、发电机及机侧变流器、机侧变流器控制器、直流电容、网侧变流器及滤波器、网侧变流器控制器的小信号模型。
步骤二:基于描述函数法,对机侧变流器控制器中的功率环进行建模,其数学表达式为
其中,ε为功率环扰动步长,T
p为功率环控制周期,P
ref为永磁同步风机输出功率参考值, P表示永磁同步风机输出功率,P
n为当前采样时刻n的永磁同步风机输出功率,P
n-1为上一采样时刻永磁同步风机输出功率,ω
g表示发电机转速,
表示发电机转速的参考值,ω
g,n为当前采样时刻发电机转速,ω
g,n-1为上一采样时刻发电机转速。sgn(x)为符号函数,当x≥0时,sgn(x)=1,当x<0时,sgn(x)=-1。考虑实际永磁同步风机的功率-转速曲线,可以认为
其中,ω
mpp表示最大功率点处的发电机转速。进而功率环模型可简化为
式中的符号函数可以采用描述函数进行建模,其描述函数为
式中A表示输入信号的幅值。
步骤三:考虑交流弱电网影响,将弱电网、功率环模小信号模型的线性部分与步骤一中建立的永磁同步风机小信号模型联立,推导系统线性部分的传递函数G(s)。
步骤四:在复平面中绘制G(s)与-1/N(A)曲线,基于描述函数法分析系统稳定性,具体方法为,若G(s)包含右半平面极点,则系统必不稳定;若G(s)不包含右半平面极点,则通过G(s)轨迹与-1/N(A)轨迹的关系判断系统稳定性:
a、若G(s)曲线不包围-1/N(A)曲线,则系统是稳定的,不发生振荡;
b、若G(s)曲线与-1/N(A)曲线相交,则系统是临界稳定的,此时系统发生恒幅恒频振荡,可以通过下式计算振荡的频率和幅值
其中,G(jω)=G
Re(ω)+jG
Im(ω),G
Re表示求取复数实部,G
Im表示求取复数虚部,ω
0为振荡角频率,A
0为振荡幅值;
c、若G(s)曲线包围-1/N(A)曲线,则系统是不稳定的。
进一步地,步骤一中,风力机、发电机及机侧变流器、机侧变流器控制器的小信号模型建立如下:
建立风力机的数学模型为
sJω
g=T
m-T
e-Bω
g
式中,J为风力机和发电机的等效集中质量块转动惯量,T
m为发电机机械转矩,T
e为发电机电磁转矩,B为自阻尼系数,此处认为B=0,s为拉普拉斯变化引入的参变量。对该模型进行线性化可得
sJΔω
g=ΔT
m-ΔT
e
发电机的电磁转矩为
n
p为发电机极对数,i
qr为q轴发电机定子电流,ψ
f为发电机永磁体磁链。对该式进行线性化可得
发电机的机械转矩为
T
m=B
tω
g
ΔT
m=B
tΔω
g
由此可得风力机小信号模型,
发电机及机侧变流器的数学模型为
式中,R
s、L
s分别为发电机转子电阻和电枢电感,ω
e为转子电角速度,ω
e=n
pω
g。i
dr、i
qr为dq坐标系下发电机定子电流,d
dr、d
qr为dq坐标系下机侧变流器控制器输出占空比,u
dc为直流电压。对该模型进行线性化,可得发电机及机侧变流器的小信号模型为
建立机侧变流器控制器的数学模型为
其中,
K
cpr、K
cir分别为机侧电流环PI控制的比例参数和积分参数,
K
ωp、K
ωi分别为转速环PI控制的比例参数和积分参数。上标c表示机侧变流器控制器dq坐标系。
为发电机转速的参考值。对其进行线性化,可得机侧变流器控制器的小信号模型为
θ
e=n
pω
g/s
对其进行线性化,可得
由此,机侧变流器控制器dq坐标系与发电机dq坐标系之间变量的转换关系为
则机侧变流器控制器的小信号模型为
进一步地,步骤一中,小信号模型建立过程如下:
建立直流电容的数学模型为
sC
dcu
dc=i
dc2-i
dc1=1.5(d
dri
dr+d
qri
qr)-1.5(d
dgi
dg+d
qgi
qg)
式中,C
dc为直流电容,i
dc1为网侧直流电流,i
dc2为机侧直流电流,i
dg、i
qg分别为网侧 变流器交流端口d、q轴电流,d
dg、d
qg为dq坐标系下网侧变流器控制器输出占空比。u
dc为直流电压,i
dr、i
qr分别为d、q坐标系发电机定子电流,d
dr、d
qr为dq坐标系下机侧变流器控制器输出占空比,对其进行线性化,可得直流电容小信号模型为
进一步地,步骤一中,所述网侧变流器、网侧变流器控制器的小信号模型建立过程如下:
建立网侧变流器及滤波器的数学模型为
式中,L
f为滤波电感,ω为工频角频率,ω=100πrad/s,i
dg、i
qg分别为网侧变流器交流端口d、q轴电流,d
dg、d
qg为dq坐标系下网侧变流器控制器输出占空比,u
dc为直流电压,u
dg、u
qg分别为并网点d、q轴电压。对该模型进行线性化,可得网侧变流器及滤波器的小信号模型为
建立网侧变流器控制器的数学模型为
其中,
K
cpg、K
cig分别为网侧电流环PI控制的比例参数和积分参数,
K
vp、K
v9分别为网侧电压环PI控制的比例参数和积分参数,U
dcref为直流电压参考值。在网侧变流器控制器中,采用锁相环使风机与电网保持同步。上标c表示网侧变流器控制器dq坐标系。对该模型进行线性化,可得网侧变流器控制器的小信号模型为
此外,网侧变流器中还应考虑锁相环动态,其数学模型为
其中,系统dq坐标系与控制器dq坐标系存在一定偏差,二者之间可以通过如下方程相互转换
由此可推导出锁相环小信号模型,即
Δθ=G
pll·Δu
qg
则网侧变流器控制器的小信号模型转变为
进一步地,步骤三具体为:
交流弱电网采用理想电压源串联等效电感表示,建立其数学模型为
式中,L
g为弱电网等效电感,u
ds、u
qs分别为d、q轴理想电压源电压,i
dg、i
qg分别为 网侧变流器交流端口d、q轴电流。将该式线性化,可得
Z
g·Δi
dqg=Δu
dqg
永磁同步风机的输出功率为
P=1.5(i
dgu
dg+i
qgu
qg)
将该式线性化可得
式中,T
f表示功率采样滤波器周期,1/(1+T
fs)为功率采样滤波器延时,1/(1+1.5T
ps)为控制器及PWM延时。
与现有技术相比,本发明的优点在于:
(1)本发明将描述函数法应用于永磁同步风机并网系统稳定性分析中,充分考虑基于扰动观察法的功率环中的非线性环节,克服了传统小信号分析法无法适用于不连续、非线性环节的问题。
(2)当系统处于临界稳定状态时,发生恒幅恒频振荡。描述函数法可以量化地计算振荡 频率和幅值,为振荡预防和抑制提供了重要依据。
图1为永磁同步风机拓扑结构(A)及其控制器结构(B、D为坐标变换,C为锁相环,E为机侧变流器控制器,F为网侧变流器控制器)
图2为G(s)极点分布图
图3为改变L
g值时G(s)与-1/N(A)曲线
图4为L
g=0.1mH时的仿真验证波形(a)与FFT频谱分析(b)
图5为L
g=0.4mH时的仿真验证波形(a)与FFT频谱分析(b)
本发明所述永磁同步风机拓扑结构及其控制器如图1所示,包含风力机、发电机、机侧变流器、直流电容、网侧变流器、滤波器。风力机捕捉风能并转化为机械能,机侧变流器和网侧变流器均为两电平电压源型变换器,其中,机侧变流器将永磁同步发电机输出的交流电转换成直流电,网侧变流器将直流电逆变成工频交流电并入电网。机侧变流器和网侧变流器均采用dq坐标系下的矢量控制方法,通过dq变换将abc三相电压电流转换为d轴和q轴下的电压电流。机侧变流器控制器中,包含功率环(P&O),转速环(H
ω),机侧电流环(H
cr);网侧变流器控制器中,包含电压环(H
v)和网侧电流环(H
cg)。此外,还包含锁相环(PLL)和坐标变换环节(abc/dq和dq/abc)。下面,结合具体实施例对本发明作进一步说明:
本发明的一个实施例中,系统的主要参数如表1所示。
表1 系统主要参数
在本发明的实施例中,第一步,获取永磁同步风机的主要参数如表1所示,分别建立风力机、发电机及机侧变流器、机侧变流器控制器、直流电容、网侧变流器及滤波器、网侧变流器控制器的数学模型,并在dq坐标系下进行线性化,计算稳态运行参数,得到风力机、发电机及机侧变流器、机侧变流器控制器、直流电容、网侧变流器及滤波器、网侧变流器控制器的小信号模型:
sJΔω
g=ΔT
m-ΔT
e
ΔT
m=B
tΔω
g
s为拉普拉斯变化引入的参变量,J为风力机和发电机的等效集中质量块转动惯量,ω
g表示发电机转速,T
m为发电机机械转矩,T
e为发电机电磁转矩。n
p为发电机极对数,ψ
f为发电 机永磁体磁链,B
t为风力机机械转矩线性化常数。
R
s、L
s分别为发电机转子电阻和电枢电感,ω
e为转子电角速度,ω
e=n
pω
g。i
dr、i
qr为dq坐标系下发电机定子电流,d
dr、d
qr为dq坐标系下机侧变流器控制器输出占空比,u
dc为直流电压。
K
cpr、K
cir分别为机侧电流环PI控制的比例参数和积分参数,
K
ωp、K
ωi分别为转速环PI控制的比例参数和积分参数,
为发电机转速的参考值,
为转子电角速度稳态值,上标c表示变流器控制器dq坐标系。
C
dc为直流电容,i
dg、i
qg分别为网侧变流器交流端口d、q轴电流,d
dg、d
qg为dq坐标系下网侧变流器控制器输出占空比。
L
f为滤波电感,ω为工频角频率,ω=100πrad/s,i
dg、i
qg分别为网侧变流器交流端口d、q轴电流,d
dg、d
qg为dq坐标系下网侧变流器控制器输出占空比,u
dg、u
qg分别为并网点d、q轴电压。
K
cpg、K
cig分别为网侧电流环PI控制的比例参数和积分参数,
K
vp、K
vi分别为网侧电压环PI控制的比例参数和积分参数。
K
ppll、K
ipll分别为锁相环PI控制器的比例参数和积分参数。
大写字母及上标*表示对应变量的稳态分量,具体的计算方式如下。
第二步,基于描述函数法,对机侧变流器控制器中的功率环进行建模,其数学模型为
式中的符号函数可以采用描述函数进行建模,其描述函数为
第三步,考虑交流弱电网影响,弱电网模型为
Z
g·Δi
dqg=Δu
dqg
将弱电网模型、功率环模型的线性部分与步骤一中的永磁同步风机小信号模型联立,推导系统线性部分的传递函数G(s)为
其中,
第四步,分析系统稳定性。首先绘G(s)极点图,如图2所示,可以看出G(s)不包含右半平面(实部大于0)极点,因此满足系统稳定的第一个条件。在复平面中绘制G(s)与-1/N(A)图像,如图3所示,G(s)与-1/N(A)相交,说明此时系统处于临界稳定状态。通过计算可知,当L
g=0.1mH时,系统的振荡频率约为129rad/s(20.5Hz),振荡幅值约为61kW;当L
g=0.4mH时,系统的振荡频率约为131rad/s(20.9Hz),振荡幅值约为56kW。当电网强度降低(L
g增大)时,系统振荡幅值减小,说明在特定条件下,电网等效阻抗的增加有利于系统保持稳定。
图4、图5分别为L
g=0.1mH、0.4mH时系统仿真及FFT频谱分析结果。图4中,直流分量为0.6889MW,对应振荡频率为19.5Hz,幅值为58kW,与理论分析结果基本一致;图5中,直流分量为0.6889MW,对应振荡频率为19.5Hz,幅值为53kW,与理论分析结果基本一致。仿真结果验证了所述分析方法的有效性和精确性。
Claims (5)
- 一种考虑功率控制影响的永磁同步风机接入弱电网稳定性分析方法,其特征在于,所述永磁同步风机包括风力机、发电机、机侧变流器、直流电容、网侧变流器、滤波器、机侧变流器控制器和网侧变流器控制器;机侧变流器控制器中,包含功率环,转速环,机侧电流环;网侧变流器控制器中,包含电压环和网侧电流环;该方法包括以下步骤:步骤一:获取永磁同步风机的主要参数,分别建立风力机、发电机及机侧变流器、机侧变流器控制器、直流电容、网侧变流器及滤波器、网侧变流器控制器的数学模型,并在dq坐标系下进行线性化,计算稳态运行参数,得到风力机、发电机及机侧变流器、机侧变流器控制器、直流电容、网侧变流器及滤波器、网侧变流器控制器的小信号模型;步骤二:基于描述函数法,对机侧变流器控制器中的功率环进行建模,其数学表达式为其中,ε为功率环扰动步长,T p为功率环控制周期,P ref为永磁同步风机输出功率参考值,P表示永磁同步风机输出功率,P n为当前采样时刻n的永磁同步风机输出功率,P n-1为上一采样时刻永磁同步风机输出功率,ω g表示发电机转速, 表示发电机转速的参考值,ω g,n为当前采样时刻发电机转速,ω g,n-1为上一采样时刻发电机转速;sgn(x)为符号函数,当x≥0时,sgn(x)=1,当x<0时,sgn(x)=-1;考虑实际永磁同步风机的功率-转速曲线,则其中,ω mpp表示最大功率点处的发电机转速;进而功率环模型可简化为式中的符号函数可以采用描述函数进行建模,其描述函数为式中A表示输入信号的幅值;步骤三:考虑交流弱电网影响,将弱电网、功率环小信号模型的线性部分与步骤一中建立的小信号模型联立,推导系统线性部分的传递函数G(s);步骤四:在复平面中绘制G(s)与-1/N(A)曲线,基于描述函数法分析系统稳定性,具体 方法为,若G(s)包含右半平面极点,则系统必不稳定;若G(s)不包含右半平面极点,则通过G(s)轨迹与-1/N(A)轨迹的关系判断系统稳定性:a、若G(s)曲线不包围-1/N(A)曲线,则系统是稳定的,不发生振荡;b、若G(s)曲线与-1/N(A)曲线相交,则系统是临界稳定的,此时系统发生恒幅恒频振荡,可以通过下式计算振荡的频率和幅值其中,G(jω)=G Re(ω)+jG Im(ω),G Re表示求取复数实部,G Im表示求取复数虚部,ω 0为振荡角频率,A 0为振荡幅值;c、若G(s)曲线包围-1/N(A)曲线,则系统是不稳定的。
- 如权利要求1所述方法,其特征在于,步骤一中,风力机、发电机及机侧变流器、机侧变流器控制器的小信号模型建立如下:建立风力机的数学模型为sJω g=T m-T m-Bω g式中,J为风力机和发电机的等效集中质量块转动惯量,T m为发电机机械转矩,T e为发电机电磁转矩,B为自阻尼系数,此处认为B=0,s为拉普拉斯变化引入的参变量;对该模型进行线性化可得sJΔω g=ΔT m-ΔT e发电机的电磁转矩为n p为发电机极对数,i qr为q轴发电机定子电流,ψ f为发电机永磁体磁链。对该式进行线性化可得发电机的机械转矩为T m=B tω gΔT m=B tΔω g由此可得风力机小信号模型,建立发电机及机侧变流器的数学模型为式中,R s、L s分别为发电机转子电阻和电枢电感,ω e为转子电角速度,ω e=n pω g;对该模型进行线性化,可得发电机及机侧变流器的小信号模型为建立机侧变流器控制器的数学模型为其中, K cpr、K cir分别为机侧电流环PI控制的比例参数和积分参数, K ωp、K ωi分别为转速环PI控制的比例参数和积分参数。上标c表示机侧变流器控制器dq坐标系; 为发电机转速的参考值;对其进行线性化,可得机侧变流器控制器的小信号模型为θ e=n pω g/s对其进行线性化,可得由此,机侧变流器控制器dq坐标系与发电机dq坐标系之间变量的转换关系为则机侧变流器控制器的小信号模型为
- 如权利要求3所述方法,其特征在于,步骤一所述网侧变流器及滤波器、网侧变流器控制器的小信号模型建立过程如下:建立网侧变流器及滤波器的数学模型为式中,L f为滤波电感,ω为工频角频率,ω=100π rad/s,u dg、u qg分别为并网点d、q轴电压;对该模型进行线性化,可得网侧变流器及滤波器的小信号模型为建立网侧变流器控制器的数学模型为其中, K cpg、K cig分别为网侧电流环PI控制的比例参数和积分参数, K vp、K vi分别为网侧电压环PI控制的比例参数和积分参数,U dcref为直流电压参考值;在网侧变流器控制器中,采用锁相环使风机与电网保持同步;上标c表示网侧变流器控制器dq坐标系;对该模型进行线性化,可得网侧变流器控制器的小信号模型为此外,网侧变流器中还应考虑锁相环动态,其数学模型为其中,系统dq坐标系与控制器dq坐标系存在一定偏差,二者之间可以通过如下方程相互转换由此可推导出锁相环小信号模型,即Δθ=G pll·Δu qg则网侧变流器控制器的小信号模型转变为
- 如权利要求4所述方法,其特征在于,所述步骤三具体为:交流弱电网采用理想电压源串联等效电感表示,建立其数学模型为式中,L g为弱电网等效电感,u ds、u qs分别为d、q轴理想电压源电压,i dg、i qg分别为网侧变流器交流端口d、q轴电流;将该式线性化,可得Z g·Δi dqg=Δu dqg永磁同步风机的输出功率为P=1.5(i dgu dg+i qgu qg)将该式线性化可得式中,T f表示功率采样滤波器周期,1/(1+T fs)为功率采样滤波器延时,1/(1+1.5T ps)为控制器及PWM延时。
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