Method for calculating probabilistic power flow of ship AC-DC hybrid power system based on taguchi method

Abstract

The present application relates to a kind of ship ac-dc hybrid power system probabilistic power flow calculation method based on Taguchi method, by introducing the Taguchi in quality engineering, with ac-dc hybrid power flow calculation combination forms ship ac-dc hybrid probabilistic power flow calculation method, can further reduce the number of calculations, improve calculation efficiency;Through ship ac-dc hybrid probabilistic power flow calculation can master each node state in system, and then carry out power distribution and improve the economy of system;The method of the present application is not limited to fixed network structure, with wide applicability and good extensibility, can be applied to different types of ships even land transport tools.

Description

Technical Field

[0001] This invention relates to power system operation and ship technology, and particularly to a probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method. Background Technology

[0002] Compared to AC, DC power systems in shipboard electrical systems offer advantages such as simplified power generation equipment, reduced system hierarchy and equipment redundancy, effective material savings, and reduced fuel consumption. DC-powered shipboard electrical systems eliminate the need for reactive power compensation, facilitating the limitation and management of fault currents and thus improving power flow controllability. With the advent of new power electronic converters, existing AC equipment is interconnected with numerous DC devices, resulting in a hybrid AC / DC power system on board ships.

[0003] Due to the influence of ship navigation and complex sea conditions, the operation of ship AC / DC hybrid power systems exhibits strong randomness and uncertainty, seriously affecting the safe and stable operation of ships. To more accurately describe the uncertainties during ship operation, probabilistic power flow calculation of AC / DC hybrid systems is an effective tool for assessing the operational uncertainty and safety stability of ship power systems. However, currently, there is no probabilistic power flow calculation method for ship AC / DC hybrid power systems.

[0004] Probabilistic power flow methods utilize statistical knowledge to incorporate uncertainties into power flow calculations, establishing multivariate nonlinear equations and solving them using various methods. Currently, statistically based probabilistic power flow calculation methods can be broadly categorized into simulation methods, approximation methods, and analytical methods. Among these, simulation methods offer accurate results but involve significant computational burdens and are inefficient. Considering their accuracy advantage, Monte Carlo simulation is typically chosen as the benchmark method to evaluate the accuracy of other methods. Approximation methods leverage the distribution characteristics of input variables and consider the interrelationships between them, and can be further subdivided into point estimation methods, moment estimation methods, and state transformation methods; their computational efficiency can be further improved. Analytical methods commonly employ semi-invariant methods and sequence operation methods, offering fast computation speeds but complex calculation processes. Summary of the Invention

[0005] To improve the efficiency of probabilistic power flow calculation for hybrid AC / DC power systems on ships and save computational costs, a probabilistic power flow calculation method based on the Taguchi method is proposed. This method fully explores the characteristics of each component in the system and ensures the accuracy and reliability of the calculation results through reasonable mathematical modeling and optimization calculation.

[0006] The technical solution of this invention is: a probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method.

[0007] 1) Determine the topology of the ship's AC / DC hybrid power system;

[0008] 2) Establish mathematical models of cables, converters, and DC-DC converters in the system, and together with the traditional AC system model, form mathematical modules for each node of the AC / DC hybrid power system;

[0009] 3) Based on the uncertain variables and their corresponding level values ​​in the ship's AC / DC hybrid power system, establish the Taguchi orthogonal matrix. The Taguchi orthogonal matrix is ​​used to determine the experimental method and number of experiments.

[0010] 4) Based on the topology of the ship's AC / DC hybrid power system in step 1), determine the bus type and power flow calculation convergence conditions, and determine the initial values ​​for AC / DC hybrid power flow calculation;

[0011] 5) Calculate the node admittance matrix based on the mathematical modules of each node in the AC / DC hybrid power system;

[0012] 6) Calculate the parameters of each node in the DC network: Use the power flow calculation method to solve for the voltage offset, power offset and current offset of each node in the DC system, and calculate the final values ​​of voltage, power and current of each node after iteration.

[0013] 7) Calculate the parameters of each node in the AC network: Use power flow calculation methods to solve for the final values ​​of voltage, power and current at each node of the AC system;

[0014] 8) Construct a Jacobian matrix from the voltage magnitude and corresponding phase angle of the system nodes. Determine whether the Jacobian matrix needs to be corrected. If no correction is needed, proceed to the next step. If correction is needed, use the Jacobian matrix to obtain the correction amount for the voltage magnitude and phase angle, correct the AC / DC variables and converter variables, and repeat steps 5) to 7).

[0015] 9) Determine whether the power flow calculation convergence condition is met; determine whether all experiments in the Taguchi orthogonal experimental table have been completed. If met, output the statistical values ​​of voltage, power and current.

[0016] Furthermore, in step 3), the orthogonality principle of the Taguchi method orthogonal matrix is ​​as follows: the number of level values ​​of each variable appearing in each column is the same; all experimental groups appearing in each pair of columns have the same frequency of level values ​​of each variable appearing in any two experimental groups.

[0017] Furthermore, in the ship's AC / DC hybrid electric system, the uncertain variable is the load of the electric propulsion system. The power values ​​of the electric propulsion system load corresponding to two points are selected from the cumulative distribution probability of the electric propulsion system load as two level values ​​of the Taguchi method.

[0018] Furthermore, in step 6), the DC system power flow expression for the i-th node in the power flow calculation method is:

[0019]

[0020]

[0021] Where j is the system node associated with node i, P and Q are the active and reactive power absorbed by the load at node i, respectively, U is the voltage at node i, θ is the phase difference of the voltage at node i, G and B are the conductance and susceptance between nodes i and j; k is the DC node on the branch where node i is located, U dk I dk , The DC voltage and current output by the converter corresponding to DC node k, as well as the power factor of the converter, are the phase angle.

[0022] The corrected equation is obtained by applying the Taylor expansion formula to the above equation; the values ​​of the Jacobian matrix elements are obtained; the power and current offsets are obtained, and the new power and current values ​​are calculated; the voltage offset and the new voltage value are obtained.

[0023] Furthermore, in step 7), the power flow calculation method for the i-th node in the AC system is expressed as:

[0024]

[0025]

[0026] In the formula, j is the system node associated with node i, P and Q are the active power and reactive power absorbed by the load of node i, respectively, U is the voltage of node i, θ is the phase difference of the voltage of node i, and G and B are the conductance and susceptance between nodes i and j.

[0027] The above equation is modified using the Taylor expansion formula; the values ​​of the Jacobian matrix elements are obtained; the power and current offsets are obtained, and the new power and current values ​​are calculated.

[0028] Furthermore, in step 8), the end value of the iteration is used to determine whether the AC / DC mixed power flow calculation termination condition is met during the iterative calculation process. The calculation process is the reverse process of step 5).

[0029] The beneficial effects of this invention are as follows: This invention provides a probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method. By introducing the Taguchi method from quality engineering and combining it with AC / DC hybrid power flow calculation, a probabilistic power flow calculation method for ship AC / DC hybrid systems can be formed, further reducing the number of calculations and improving computational efficiency. Through ship AC / DC hybrid probabilistic power flow calculation, the state of each node in the system can be understood, thereby enabling power allocation and improving the system's economy. This invention's method is not limited to a fixed network structure, has wide applicability and good scalability, and can be applied to different types of ships and even land transportation vehicles. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the probabilistic power flow calculation method described in this invention;

[0031] Figure 2 This is a power consumption curve of an AC / DC hybrid electric propulsion system.

[0032] Figure 3 This is a load probability density distribution curve of an AC / DC hybrid power system with electric propulsion system.

[0033] Figure 4 This is a cumulative load probability distribution curve of an AC / DC hybrid power system with electric propulsion system.

[0034] Figure 5 This is a single-line diagram of the ship AC / DC hybrid power system of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0036] like Figure 1 As shown, the specific steps of the ship AC / DC mixed probabilistic power flow calculation method based on the Taguchi method provided by this invention are as follows:

[0037] 1. Determine the topology of the ship's AC / DC hybrid power system;

[0038] 2. Establish mathematical models of cables, converters, and DC-DC converters in the system, and together with the traditional AC system model, form mathematical modules for each node of the AC / DC hybrid power system to ensure the integrity of the probabilistic power flow calculation of the AC / DC hybrid power system;

[0039] 3. Based on the uncertain variables and their corresponding level values ​​in the ship's AC / DC hybrid power system, establish the Taguchi orthogonal matrix. The Taguchi orthogonal matrix is ​​used to determine the experimental method and number of experiments.

[0040] 4. Based on the topology of the ship's AC / DC hybrid power system in step 1, determine the bus type and power flow calculation convergence conditions, and determine the initial values ​​for AC / DC hybrid power flow calculation;

[0041] 5. Calculate the node admittance matrix based on the mathematical modules of each node in the AC / DC hybrid power system, namely the mathematical model of the cable branch, the mathematical model of the converter, and the mathematical model of the DC converter;

[0042] 6. Calculate the parameters of each node in the DC network: Use power flow calculation methods to solve for the voltage offset, power offset and current offset of each node in the DC system, and calculate the final values ​​of voltage, power and current of each node after iteration.

[0043] 7. Calculate the parameters of each node in the AC network: Use power flow calculation methods to solve for the final values ​​of voltage, power and current at each node of the AC system;

[0044] 8. Construct a Jacobian matrix from the voltage magnitude and corresponding phase angle of the system nodes. Determine whether the Jacobian matrix needs to be corrected. If no correction is needed, proceed to the next step. If correction is needed, use the Jacobian matrix to obtain the correction amount for the voltage magnitude and phase angle, correct the AC / DC variables and converter variables, and repeat steps 5 to 7.

[0045] 9. Determine whether the power flow calculation convergence condition is met; determine whether all experiments in the Taguchi orthogonal experimental table have been completed. If so, output the statistical values ​​of voltage, power, and current.

[0046] The Jacobian matrix is ​​a matrix formed by arranging first-order partial derivatives in a specific manner; its determinant is called the Jacobian matrix. In power flow calculations for AC / DC hybrid power systems, the Jacobian matrix serves to correct for AC / DC variables and converter variables.

[0047] Example:

[0048] A: Establishment of Taguchi Orthogonal Matrix: Establish Taguchi orthogonal experimental tables based on the uncertain variables and their level values ​​in AC / DC hybrid power systems.

[0049] The Taguchi method, originating from quality engineering, is an experimental method that achieves high efficiency with low cost. The Taguchi orthogonal matrix is ​​used to determine the experimental method and number of experiments. In the Taguchi orthogonal matrix, the rows represent the parameter settings in the experimental combinations, and the columns represent the values ​​of uncertain variables in each experimental group.

[0050] Based on the uncertain variables and their values ​​in the AC / DC hybrid power system, an orthogonal matrix using the Taguchi method is constructed. The orthogonality principle is: 1) the number of level values ​​of each variable appearing in each column is the same; 2) all experimental groups of level values ​​of each variable appear in every two columns, and the frequency of all experimental groups of level values ​​of each variable appearing in any two columns is the same.

[0051] For conventional orthogonal methods, a sampling method with a regular distribution can be used to obtain values. However, to adapt to the irregular load fluctuations of the Taguchi method orthogonal array and the characteristics of ship electric propulsion systems, two points corresponding to the load power values ​​of the electric propulsion system are selected from the cumulative load distribution probability of the electric propulsion system as two level values ​​for the Taguchi method. The Taguchi method orthogonal matrix is ​​then applied to discretize the relevant uncertainties in the power flow calculation of the AC / DC hybrid power system.

[0052] Taking a set of 7 variables, with 2 level values ​​for each variable, as an example, Table 1 shows the orthogonal array L8(2). 7 ):

[0053] Table 1

[0054] A B C D E F G 1 1 1 1 1 1 1 1 2 1 1 1 2 2 2 2 3 1 2 2 1 1 2 2 4 1 2 2 2 2 1 1 5 2 1 2 1 2 1 2 6 2 1 2 2 1 2 1 7 2 2 1 1 2 2 1 8 2 2 1 2 1 1 2

[0055] B: AC / DC hybrid power flow calculation

[0056] Based on the characteristics of the ship's medium-voltage DC power system, B-1 defines the bus type and establishes models of generator sets, propulsion motors, etc.

[0057] During ship operation, the load on electric propulsion is affected by marine environmental factors such as wind, waves, and currents, as well as ship size. Under different operating conditions and environmental conditions, the load demand of the electric propulsion system varies significantly, and its demand curve exhibits strong randomness and volatility. Figure 2 As shown.

[0058] The load probability density distribution function of an electric propulsion system based on kernel density function fitting, such as Figure 3 As shown. From Figure 3 It can be seen that the load variation of the electric propulsion system is irregular and cannot be described by a normal regular distribution. However, the probability variation range is 0-1. After dividing the probability variation range equally, two symmetrical points can be taken as the load levels of the electric propulsion system corresponding to probabilities of 0.25 and 0.75, which can be used as the level values ​​of the Taguchi orthogonal matrix. By uniformly taking the two points with probabilities of 0.25 and 0.75 in the cumulative power demand distribution curve of the electric propulsion system, these two points are taken as the two level values ​​of the uncertain variables in the AC / DC hybrid power system, as shown below. Figure 4 As shown.

[0059] The AC power flow calculation for the i-th node in B-2 can be expressed as:

[0060]

[0061]

[0062] In the formula, j is the system node associated with node i, P and Q are the active power and reactive power absorbed by the load of node i, respectively, U is the voltage of node i, θ is the phase difference of the voltage of node i, and G and B are the conductance and susceptance between nodes i and j.

[0063] The DC power flow calculation for the i-th node, connected to the AC system via converters and transformers, can be expressed as follows:

[0064]

[0065]

[0066] Where k is the DC node on the branch where node i is located, U dk I dk , The DC voltage and current output by the converter corresponding to DC node k, as well as the power factor of the converter, are the phase angle.

[0067] B-4 calculates the node admittance matrix based on the mathematical models of cable branches, converters, and DC-DC converters.

[0068] B-5 uses power flow calculation methods to solve for the voltage offset, power offset, and current offset of each node in a DC system, and calculates the final values ​​of voltage, power, and current of each node after iteration.

[0069] B-6 uses power flow calculation methods to solve for the final values ​​of voltage, power and current at each node of the AC system;

[0070] B-7 determines whether the power flow calculation of each node parameter is satisfied. If satisfied, proceed to the next step. If not satisfied, calculate the Jacobian matrix correction, correct the AC / DC variables and converter variables, and repeat B-4) to B-6).

[0071] B-8 determines whether all experiments in the Taguchi method orthogonal matrix have been completed. If so, output the statistical values ​​of voltage, power, and current.

[0072] Existing methods for calculating probabilistic AC / DC mixed power flow on ships often employ the Monte Carlo method or the two-point method. Based on the Taguchi method from quality engineering, and combined with AC / DC mixed power flow calculation, a novel probabilistic AC / DC mixed power flow calculation method has been developed, but there is currently no related research or application.

[0073] The AC / DC hybrid probabilistic power flow calculation method proposed in this project can reduce the number of probabilistic power flow calculations. Taking a ship with a power supply capacity of 100MW and a propulsion power of 2×40MW as an example, its power system structure is as follows: Figure 5 As shown in Table 2, the probabilistic power flow calculation results for the AC system are presented in Table 3, and the probabilistic power flow calculation results for the DC system are presented in Table 3. The ship AC / DC hybrid probabilistic power flow calculation method based on the Taguchi method proposed in this scheme can provide a foundation for subsequent research such as ship power system planning, static safety analysis, real-time online analysis, and risk assessment, and further improves the efficiency of probabilistic power flow calculation.

[0074] Table 2

[0075]

[0076]

[0077] Table 3

[0078]

[0079] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0080] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A probabilistic power flow calculation method for a ship's AC / DC hybrid power system based on the Taguchi method, characterized in that, 1) Determine the topology of the ship's AC / DC hybrid power system; 2) Establish mathematical models of cables, converters, and DC-DC converters in the system, and together with the traditional AC system model, form mathematical modules for each node of the AC / DC hybrid power system; 3) Based on the uncertain variables and their corresponding level values ​​in the ship's AC / DC hybrid power system, establish the Taguchi orthogonal matrix. The Taguchi orthogonal matrix is ​​used to determine the experimental method and number of experiments. 4) Based on the topology of the ship's AC / DC hybrid power system in step 1), determine the bus type and power flow calculation convergence conditions, and determine the initial values ​​for AC / DC hybrid power flow calculation; 5) Calculate the node admittance matrix based on the mathematical modules of each node in the AC / DC hybrid power system; 6) Calculate the parameters of each node in the DC network: Use power flow calculation methods to solve for the voltage offset, power offset and current offset of each node in the DC system, and calculate the final values ​​of voltage, power and current of each node after iteration. 7) Calculate the parameters of each node in the AC network: Use power flow calculation methods to solve for the final values ​​of voltage, power and current at each node of the AC system; 8) Construct a Jacobian matrix from the voltage magnitudes and corresponding phase angles of the system nodes. Determine if the Jacobian matrix needs correction. If no correction is needed, proceed to the next step. If correction is needed, use the Jacobian matrix to calculate the correction amounts for the voltage magnitudes and phase angles, correct the AC / DC variables and converter variables, and repeat steps 5) to 7). 9) Determine whether the power flow calculation convergence condition is met; determine whether all experiments in the Taguchi orthogonal experimental table have been completed. If met, output the statistical values ​​of voltage, power and current.

2. The probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method according to claim 1, characterized in that, In step 3), the orthogonality principle of the Taguchi method orthogonal matrix is ​​as follows: the number of level values ​​of each variable appearing in each column is the same; all experimental groups appearing in each pair of columns have the same level value of each variable, and the frequency of all experimental groups appearing in each pair of columns has the same frequency.

3. The probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method according to claim 2, characterized in that, The uncertain variable in the ship's AC / DC hybrid electric system is the load of the electric propulsion system. The power values ​​of the electric propulsion system load corresponding to two points are selected from the cumulative distribution probability of the electric propulsion system load as two level values ​​of the Taguchi method.

4. The probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method according to claim 1, characterized in that, In step 6) of the power flow calculation method, the first i The DC power flow expression for each node is: in, j For nodes i Associated system nodes P Gi For nodes i The active power generated by the generator; P Li For nodes i The active power absorbed by the load; Q Gi For nodes i The reactive power generated by the generator; Q Li The reactive power absorbed by the load at node i; U i For nodes i Voltage, θ ij For nodes i, j The phase difference of the voltage between them. G ij , B ij For nodes i, j The electrical conductivity and susceptance between them; k For nodes i DC node on the branch, U dk , I dk , φ k DC node k The corresponding DC output voltage and current of the converter, as well as the power factor and phase angle of the converter; The corrected equation is obtained by applying the Taylor expansion formula to the above equation; the values ​​of the Jacobian matrix elements are obtained; the power and current offsets are obtained, and the new power and current values ​​are calculated; the voltage offset and the new voltage value are obtained.

5. The probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method according to claim 1, characterized in that, In step 7) of the power flow calculation method, the first i The power flow representation of the AC system with nodes is as follows: In the formula, j For nodes i Associated system nodes P Gi For nodes i The active power generated by the generator; P Li For nodes i The active power absorbed by the load; Q Gi For nodes i The reactive power generated by the generator; Q Li The reactive power absorbed by the load at node i; U i For nodes i Voltage, θ ij For nodes i, j The phase difference of the voltage between them. G ij , B ij For nodes i, j The electrical conductivity and susceptance between them; The corrected equation is obtained by applying Taylor expansion to the above equation; Find the values ​​of the Jacobian matrix elements; find the power and current offsets, and calculate the new power and current values.

6. The probabilistic power flow calculation method for ship AC / DC hybrid power systems based on the Taguchi method according to claim 1, characterized in that, In step 8), the end value of the iteration is used to determine whether the AC / DC mixed power flow calculation termination condition is met during the iterative calculation process. The calculation process is the reverse process of step 5).

Images