CN109193787B - Harmonic path identification method for power distribution network containing new energy - Google Patents
Harmonic path identification method for power distribution network containing new energy Download PDFInfo
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- CN109193787B CN109193787B CN201811263740.9A CN201811263740A CN109193787B CN 109193787 B CN109193787 B CN 109193787B CN 201811263740 A CN201811263740 A CN 201811263740A CN 109193787 B CN109193787 B CN 109193787B
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Abstract
The invention relates to a method for identifying a harmonic path of a power distribution network containing new energy, which is characterized by comprising the steps of constructing the relation between a harmonic current source and branch harmonic current, solving the probability density function of line harmonic current by using the probability density function of a function variable, and solving the relation between line harmonic current information entropy and harmonic source information entropy by using the definition of information entropy. The method analyzes the branch harmonic current from the network angle to determine the distribution way of the harmonic current so as to obtain rich information, has clear physical concept, is scientific and reasonable, has simple calculation, accurate identification path, easy realization, high engineering value, can improve the identification efficiency of the harmonic path and the like.
Description
Technical Field
The invention relates to the field of safe and economic operation of a power distribution network of a power system, in particular to a harmonic path identification method of a power distribution network containing new energy, which is applied to a harmonic path identification technology of the power distribution network containing new energy.
Background
Wind power and photovoltaic are widely applied at home and abroad as clean energy. The proportion of wind power, photovoltaic installed capacity and generated energy to the total installed capacity and the total generated energy in the whole country is gradually improved. The new energy power generation brings a large amount of clean energy, and simultaneously introduces a large amount of harmonic waves to a power grid due to the inverter structure. How to evaluate and analyze the distribution problem of the harmonic current of the power grid after the new energy is accessed has important significance for safe and economic operation of the new energy power distribution network.
At present, the harmonic research on a new energy power distribution network mainly has two aspects, namely, the research on the influence mechanism of the new energy harmonic, for example, the relation of influence factors such as the harmonic output and the irradiation of the new energy is analyzed by modeling a new energy inverter, but the research has certain defects and cannot comprehensively analyze the influence of each factor on the new energy power distribution network; and secondly, new energy harmonic suppression control research, for example, the output impedance of the inverter is adjusted by optimizing the algorithm of the inverter so as to avoid the inverter from resonating with a power grid, but the method has limited control effect and is quite complex to implement.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide the harmonic path identification method for the new energy-containing power distribution network, which is scientific and reasonable, simple in calculation, accurate in identification path, easy to realize and high in engineering value and can improve the harmonic path identification efficiency. The purpose of the invention is realized by the following technical scheme: a method for identifying a harmonic path of a power distribution network containing new energy is characterized by comprising the following steps:
1) constructing a functional relation between a harmonic current source and branch harmonic current;
the equation of the node voltage containing the voltage source is (1):
U＝ZI (1)
wherein: z is a node impedance matrix, I is a node current source vector, and U is a node voltage column vector;
② branch current IijThe relationship with the node voltage is (2):
Iij＝(Ui-Uj)/Zij (2)
wherein: zijIs branch impedance, Ui、UjThe voltage of the I side and the j side of the same branch circuit, IijIs a branch current;
and (3) combining the formula (1) and the formula (2) to obtain a linear relation formula of the harmonic current source and the branch harmonic current, wherein the linear relation formula is as follows:
Ibc＝ZbcZI (3)
wherein: zbcIs a branch impedance matrix, IbcIs a branch harmonic current vector;
2) solving the probability density function of the line harmonic current by using the probability density function of the function variable;
thirdly, the harmonic current of the branch obeys the probability density function which is the same as that of the current source, and the expression is (4):
G(Ibc)＝K F((ZbcZ)-1I) (4)
wherein: f ((Z)bcZ)-1I) Is (Z)bcZ)-1I probability density function, K is (Z)bcZ)-1Determinant of G (I)bc) Is a probability density function of branch harmonic current;
3) the method comprises the steps of solving the relation between the line harmonic current information entropy and the harmonic source information entropy by using the definition of the information entropy;
the expression of the information entropy is (5):
wherein: x is a random variable, xiIs the ith random variable, m is xiThe number of values, H (x), is an information entropy function, P (x)i) X is represented byiProbability of (log)a(P(xi) Is P (x)i) A is the base of the logarithm;
the information entropy expression of the harmonic current source is formula (6):
wherein: p (x)1，x2。。。，xn) Is a random variable xiA density function of (a); i.e. i1Is a first variable x1Cyclic variable of inIs a variable xnThe loop variable of (2). n is the number of x variables, k1Corresponding variable x1Number of distribution values, knIs xnTaking the number of values in the distribution;
the information entropy is a measurement index of information distribution, for the harmonic waves of the power system, when the entropy is the maximum, the information obeys uniform distribution, the corresponding power system is always in a stable state, and when the harmonic waves are transited from the stable state to a transient state, the entropy is changed from large to small; the entropy of the current source is larger than that of the branch current, and the entropy is gradually reduced in the process of flowing from the current source to the load, namely the entropy is continuously lost in the flowing of energy in a power grid.
Compared with the existing method for analyzing the harmonic wave from the inverter, the method for identifying the harmonic wave path of the power distribution network containing new energy has the advantages of clear physical concept, scientific and reasonable design, simple calculation, accurate identification path, high engineering value, capability of improving the identification efficiency of the harmonic wave path and the like.
Detailed Description
The following describes the method for identifying the harmonic path of the power distribution network containing new energy in detail.
The invention discloses a method for identifying a harmonic path of a power distribution network containing new energy, which comprises the following steps of:
1) constructing a functional relation between a harmonic current source and branch harmonic current;
the equation of the node voltage containing the voltage source is (1):
U＝ZI (1)
wherein: z is a node impedance matrix, I is a node current source vector, and U is a node voltage column vector;
② branch current IijThe relationship with the node voltage is (2):
Iij＝(Ui-Uj)/Zij (2)
wherein: zijIs branch impedance, Ui、UjThe voltage of the I side and the j side of the same branch circuit, IijIs a branch current;
and (3) combining the formula (1) and the formula (2) to obtain a linear relation formula of the harmonic current source and the branch harmonic current, wherein the linear relation formula is as follows:
Ibc＝ZbcZI (3)
wherein: zbcIs a branch impedance matrix, IbcIs a branch harmonic current vector;
2) solving the probability density function of the line harmonic current by using the probability density function of the function variable;
thirdly, the harmonic current of the branch obeys the probability density function which is the same as that of the current source, and the expression is (4):
G(Ibc)＝K F((ZbcZ)-1I) (4)
wherein: f ((Z)bcZ)-1I) Is (Z)bcZ)-1I probability density function, K is (Z)bcZ)-1Determinant of G (I)bc) Probability density of harmonic current for branchA degree function;
3) the method comprises the steps of solving the relation between the line harmonic current information entropy and the harmonic source information entropy by using the definition of the information entropy;
the expression of the information entropy is (5):
wherein: x is a random variable, xiIs the ith random variable, m is xiThe number of values, H (x), is an information entropy function, P (x)i) X is represented byiProbability of (log)a(P(xi) Is P (x)i) A is the base of the logarithm;
the information entropy expression of the harmonic current source is formula (6):
wherein: p (x)1，x2。。。，xn) Is a random variable xiA density function of (a); i.e. i1Is a first variable x1Cyclic variable of inIs a variable xnThe loop variable of (2). n is the number of x variables, k1Corresponding variable x1Number of distribution values, knIs xnTaking the number of values in the distribution;
the information entropy is a measurement index of information distribution, for the harmonic waves of the power system, when the entropy is the maximum, the information obeys uniform distribution, the corresponding power system is always in a stable state, and when the harmonic waves are transited from the stable state to a transient state, the entropy is changed from large to small; the entropy of the current source is larger than that of the branch current, and the entropy is gradually reduced in the process of flowing from the current source to the load, namely the entropy is continuously lost in the flowing of energy in a power grid.
Claims (1)
1. A method for identifying a harmonic path of a power distribution network containing new energy is characterized by comprising the following steps:
1) constructing a functional relation between a harmonic current source and branch harmonic current;
the equation of the node voltage containing the voltage source is (1):
U＝ZI (1)
wherein: z is a node impedance matrix, I is a node current source vector, and U is a node voltage column vector;
② branch current IijThe relationship with the node voltage is (2):
Iij＝(Ui-Uj)/Zij (2)
wherein: zijIs branch impedance, Ui、UjThe voltage of the I side and the j side of the same branch circuit, IijIs a branch current;
and (3) combining the formula (1) and the formula (2) to obtain a linear relation formula of the harmonic current source and the branch harmonic current, wherein the linear relation formula is as follows:
Ibc＝ZbcZI (3)
wherein: zbcIs a branch impedance matrix, IbcIs a branch harmonic current vector;
2) solving the probability density function of the line harmonic current by using the probability density function of the function variable;
thirdly, the harmonic current of the branch obeys the probability density function which is the same as that of the current source, and the expression is (4):
G(Ibc)＝K F((ZbcZ)-1I) (4)
wherein: f ((Z)bcZ)-1I) Is (Z)bcZ)-1I probability density function, K is (Z)bcZ)-1Determinant of G (I)bc) Is a probability density function of branch harmonic current;
3) the method comprises the steps of solving the relation between the line harmonic current information entropy and the harmonic source information entropy by using the definition of the information entropy;
the expression of the information entropy is (5):
wherein: x is a random variable，xiIs the ith random variable, m is xiThe number of values, H (x), is an information entropy function, P (x)i) X is represented byiProbability of (log)a(P(xi) Is P (x)i) A is the base of the logarithm;
the information entropy expression of the harmonic current source is formula (6):
wherein: p (x)1，x2, … , xn) Is a random variable xiA density function of (a); i.e. i1Is a first variable x1Cyclic variable of inIs a variable xnN is the number of x variables, k1Corresponding variable x1Number of distribution values, knIs xnTaking the number of values in the distribution;
the information entropy is a measurement index of information distribution, for the harmonic waves of the power system, when the entropy is the maximum, the information obeys uniform distribution, the corresponding power system is always in a stable state, and when the harmonic waves are transited from the stable state to a transient state, the entropy is changed from large to small; the entropy of the current source is larger than that of the branch current, and the entropy is gradually reduced in the process of flowing from the current source to the load, namely the entropy is continuously lost in the flowing of energy in a power grid.
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