CN107508311A - The method and system of the lifting operational efficiency of parallel connection type wind electric converter - Google Patents

Abstract

The invention provides a method-level system for improving the operating efficiency of a parallel wind power converter, including: according to the efficiency values of each working point of the converter in the parallel wind power converter, using a numerical fitting method to obtain a parallel wind power converter The efficiency curve and efficiency function of the converter; the optimal efficiency and the optimal power distribution ratio of each operating point of the parallel wind power converter are calculated offline by optimizing the objective function; the optimal power distribution ratio obtained by the offline calculation is made into a search The table sets the power distribution ratio of each operating point of the parallel wind power converter. By optimizing the power distribution between each parallel converter, the overall efficiency of the parallel converter is improved. This method only needs to modify the control strategy of the parallel converter without adding other equipment, and has fast dynamic response and high control flexibility.

Description

Method and system for improving operating efficiency of parallel wind power converters

technical field

The present invention relates to the field of electrical technology, in particular to a method and system for improving operating efficiency of a parallel wind power converter.

Background technique

Currently, renewable energy is developing rapidly, especially wind power and photovoltaics. With the increasing maturity of wind power technology, wind power has developed on a large scale around the world. With the continuous development of onshore wind power resources, wind power has begun to develop from land to sea, and large-capacity offshore wind turbines is a development trend. High reliability is the most basic requirement for offshore wind power converters. The parallel operation of multiple converters can greatly improve the reliability of wind power converters. Therefore, offshore wind power converters are generally implemented in parallel with multiple converters.

Under the traditional control mode, the parallel converter system mostly adopts the power sharing mode to operate, and this mode is suitable for applications where the load power is stable. For wind power converters, the random and fluctuating characteristics of wind energy make the load power on the converter fluctuate greatly, and the average load power is lower than 50% of the rated power. The operating efficiency of the converter depends on its load power, and its efficiency varies greatly at different operating points, especially at low-load operating points, where its efficiency is much lower than the rated efficiency. Power sharing control is not suitable for parallel wind power converter systems, and a new operation control strategy needs to be proposed to improve its overall operation efficiency.

At present, domestic and foreign research on improving the efficiency of converters is focused on improving the efficiency of a single converter, mainly including the use of new power devices, optimization of converter topology, optimization of modulation methods and control algorithms, etc. The method for improving the operating efficiency of the parallel converter system under fluctuating power has not been reported yet. For example, the invention patent with the publication number CN105870957A discloses a dynamic DC bus voltage control method for improving the efficiency of back-to-back converters. The invention dynamically adjusts the reference value of the DC bus voltage to make the converter self-adaptive to work at the minimum DC bus voltage On, thereby reducing the electrical stress of the power electronic device and improving the efficiency of the converter. This method is only applicable to the improvement of the efficiency of a single converter, not applicable to the improvement of the efficiency of the parallel system, and the dynamic adjustment of the given value of the bus will cause large voltage fluctuations on the DC capacitor, increase the capacitor stress, and reduce the capacitance and system. reliability.

Contents of the invention

In view of the defects in the prior art, the purpose of the present invention is to provide a method for improving the operating efficiency of parallel wind power converters.

According to the method for improving the operating efficiency of the self-adaptive optimization combination of parallel wind power converters provided by the present invention, it includes:

Numerical fitting step: according to the efficiency value of each working point of the converter in the parallel wind power converter, use the numerical fitting method to obtain the efficiency curve and efficiency function of the parallel wind power converter;

Optimizing the objective function step: by optimizing the objective function, calculate the optimal efficiency and optimal power distribution ratio at each operating point of the parallel wind power converter offline;

The step of making the look-up table: make the optimal power distribution ratio obtained by off-line calculation into a look-up table, and set the power distribution ratio at each operating point of the parallel wind power converter.

Preferably, in the step of optimizing the objective function, the optimal efficiency and the optimal power distribution ratio at each operating point of the parallel wind power converter are calculated offline through the optimized objective function with a power resolution of 1‰.

Preferably, it also includes:

Adaptive optimization combination control step: obtain the power command of each converter under any working condition through a lookup table, and realize adaptive optimization combination control.

Preferably, the optimization objective function is:

g=max{η _T (P _IN,1 ,P _IN,2 ,...P _IN,i ...P _IN,n )};

η _T (P _IN,1 ,P _IN,2 ,…P _IN,i …P _IN,n ) is the total efficiency of the parallel system when the input power is P _IN , P _IN,i is the input power of converter i, i =1, 2...n.

Preferably, the constraint conditions for optimizing the objective function are:

P _R is the rated power of a single converter.

A system for improving operating efficiency of a parallel wind power converter according to the present invention includes:

Numerical fitting module: according to the efficiency value of each operating point of the converter in the parallel wind power converter, use the numerical fitting method to obtain the efficiency curve and efficiency function of the parallel wind power converter;

Optimal objective function module: calculate the optimal efficiency and optimal power distribution ratio of parallel wind power converters at each operating point by optimizing the objective function offline;

Lookup table making module: make the optimal power distribution ratio obtained by off-line calculation into a lookup table, and set the power distribution ratio at each operating point of the parallel wind power converter.

Preferably, in the step of optimizing the objective function, the optimal efficiency and the optimal power distribution ratio at each operating point of the parallel wind power converter are calculated offline through the optimized objective function with a power resolution of 1‰.

Preferably, it also includes:

Adaptive optimization combination control step: obtain the power command of each converter under any working condition through a lookup table, and realize adaptive optimization combination control.

Preferably, the optimization objective function is:

g=max{η _T (P _IN,1 ,P _IN,2 ,...P _IN,i ...P _IN,n )};

η _T (P _IN,1 ,P _IN,2 ,…P _IN,i …P _IN,n ) is the total efficiency of the parallel system when the input power is P _IN , P _IN,i is the input power of converter i, i =1, 2...n.

Preferably, the constraint conditions for optimizing the objective function are:

P _R is the rated power of a single converter.

Compared with the prior art, the present invention has the following beneficial effects:

1. The optimal combined control of each converter is realized through the control technology of the converter itself, without adding any auxiliary equipment;

2. It can realize the load adaptive optimization of each parallel converter;

3. Fast response.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Figure 1 is a schematic structural diagram of a parallel converter system;

Figure 2 is a schematic diagram of power conversion of parallel converters;

Fig. 3 is a flowchart of a method for improving operating efficiency of a parallel wind power converter;

Figure 4 is an efficiency curve diagram of a single converter;

Fig. 5 is the algorithm flowchart of optimizing objective function;

Fig. 6 is an optimized efficiency curve diagram of two converter parallel systems;

Fig. 7 is a power distribution diagram of an optimal combination of two converter parallel systems;

Fig. 8 is the static efficiency curve diagram of the parallel system under the combined control of power sharing and self-adaptive optimization;

Fig. 9 is a static power distribution diagram of two converters under the control of power equalization and adaptive optimal combination;

Fig. 10 is a wind power curve diagram;

Fig. 11 is the dynamic efficiency curve diagram of the parallel system under the control of power equalization and adaptive optimization combination;

Fig. 12 is a dynamic power allocation diagram of each parallel converter under power sharing and adaptive optimal combination control.

detailed description

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

The present invention proposes an adaptive optimization combined control method for parallel-connected wind power converters, and realizes the improvement of the overall efficiency of the parallel-connected converters by optimizing the power distribution among the parallel-connected converters. This method only needs to modify the control strategy of the parallel converter without adding other equipment, and has fast dynamic response and high control flexibility.

Parallel converter refers to a system composed of several independent three-phase voltage source converters (VSC) sharing the AC bus. As shown in Figure 1, each converter can independently perform active and reactive current decoupling control. According to the fluctuation of wind power, the number of converters is automatically combined and the load power borne by each converter is optimized in real time, thereby improving the overall efficiency of the parallel converter system.

Taking n converters connected in parallel as an example, the power conversion diagram is shown in Figure 2, η _T (P _IN ) is the total efficiency of the parallel system when the input power is P _IN , P _IN and P _OUT are the total input of the parallel system , output power, P _IN,i , P _OUT,i are the input and output power of converter i respectively, η _i (P _IN,i ) is the efficiency of converter i when the input power P _IN,i , the parallel type converter The overall efficiency of the device is:

Since each converter is the same, η _i (P) = η (P) (i = 1, 2...n), η (P) indicates the efficiency of the converter when the input power is P, and the subscript indicates the conversion The converter efficiency of converter i when the input power is P, because the efficiency curves of all converters are the same, so it is represented by η(P), where P and η are the simplifications of the previous P _in and η _i , parallel type The overall efficiency of the converter can be simplified as:

Create an optimization objective function:

g=max{η _T (P _IN,1 ,P _IN,2 ,...P _IN,i ...P _IN,n )}

The constraints are:

The rated power of a single converter is P _R , in order to simplify the analysis, the per unit system is adopted, then 0≤P _n ≤1. In order to realize the adaptive optimal combination of the full power section of the parallel converter, the optimal efficiency and the optimal power distribution ratio at each operating point of the system are calculated offline with a power resolution of 1‰.

Taking the parallel connection of two converters as an example, the optimized efficiency and power distribution ratio curves under the adaptive optimization combined control are shown in Fig. The power distribution ratio is convenient for online self-adaptive optimization combination, and the speed of control algorithm is improved.

As shown in Figure 3, the specific implementation steps of this method are as follows:

Numerical fitting: According to the efficiency value of each working point of the converter, use the numerical fitting method to obtain its efficiency curve and efficiency function.

Optimize the objective function: use the objective function to calculate the optimal efficiency and the optimal power distribution ratio at each operating point of the parallel system offline, with a power resolution of 1‰.

Make a lookup table: Make the power distribution ratio obtained by offline optimization into a lookup table, set the power distribution ratio at each operating point of the parallel system, and improve the speed of the control algorithm.

Adaptive optimal combination control: The power command of each converter under any working condition is obtained through a look-up table to realize adaptive optimal combination control and improve the overall efficiency of the system.

As shown in Figure 1, taking a 3MW/4MVA parallel wind power converter as an example, its interface grid voltage is 690V/50Hz, and it is composed of two 2MVA converters connected in parallel, and the DC bus capacitor of each converter is 38.8mF , the given value of the DC bus voltage is 1100V, the switching frequency is 3kHz, the LCL filter parameters are: converter side inductance is 100μH, intermediate filter capacitor is 668.4μF, grid equivalent inductance is 170μH, and the power module adopts SKiiP1814GB17E4 of Semikron Company -3DUW.

According to the parameters of the above-mentioned parallel wind power converter, a simulation analysis system is established based on Matlab/Simulink to verify the static and dynamic performance of the adaptive optimization combined control method:

(1) Static: efficiency optimization at each operating point of the converter;

(2) Dynamic: adaptively optimize system efficiency under fluctuating power.

According to the efficiency curve of a single converter in Figure 4, use the MATLAB curve fitting tool cftool to obtain the fitting efficiency function of the converter, and use the objective function to calculate the optimal power distribution ratio at each operating point of the system offline. The optimization algorithm flow is shown in Figure 5 Shown, wherein, the intermediate variables generated by the program calculation include:

P _{1_opt} represents the optimal power allocation value of converter 1;

P _{2_opt} represents the optimal power allocation value of converter 2;

g _{_opt} represents the optimal value of the optimization function;

P represents the operating power value of the system;

P _1i represents the ith working point of converter 1;

P _2i represents the i-th operating point of the converter 2;

η _i represents the efficiency of the parallel system at the i-th operating point;

P ₁ represents the power allocation value of converter 1 when the system input power is P;

P ₂ represents the power allocation value of converter 2 when the system input power is P;

η _op represents the optimal efficiency of the parallel system when the system input power is P.

The optimal efficiency curve of the parallel system is shown in Figure 6. According to the optimal power allocation in Figure 5, the operating efficiency of the parallel system is optimal. The power distribution example of the optimal combination of the parallel system is shown in Figure 7. The system load power is lower than 0.329pu, and the system is in the stand-alone operation mode; the load power is higher than 0.329pu, and the power of each converter is optimally distributed.

Figure 8 and Figure 9 respectively show the static efficiency curve and static power distribution of the parallel system under the power sharing control and adaptive optimization combined control strategy, and the comparative analysis shows that:

(1) When the load power of the converter is lower than 38% of the rated power, the adaptive optimal combination control can effectively improve the operating efficiency of the parallel system.

(2) When the load power of the converter is lower than 32.9% of the rated power, under the adaptive optimal combination control strategy, only one converter in the parallel system actually operates, and the optimal control strategy can combine the operation of the converter according to the load power quantity.

Figure 10 is the wind power curve of the wind turbine for 70 minutes, and Figure 11 and Figure 12 are the dynamic efficiency curve of the parallel system and the dynamic power distribution of each converter under the power sharing control and adaptive optimization combined control strategy respectively when the wind power fluctuates , comparative analysis shows that:

(1) The adaptive optimization combined control strategy can improve the overall efficiency of the parallel converter system under fluctuating power.

(2) The adaptive optimization combination strategy can automatically combine the running number of converters and optimize the load power borne by each converter in real time according to the fluctuation of wind power.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims (10)

1. A kind of 1. method of the lifting operational efficiency of parallel connection type wind electric converter, it is characterised in that including：

   Numerical fitting step：According to the efficiency value of each operating point of converter in parallel connection type wind electric converter, numerical fitting side is utilized Method, obtain the efficiency curve and efficiency function of parallel connection type wind electric converter；

   Optimization object function step：By under each operating point of optimization object function off-line calculation parallel connection type wind electric converter most Excellent efficiency and optimal power allocation ratio；

   Look-up table making step：Look-up table is made in the optimal power allocation ratio that off-line calculation is obtained, and setting parallel connection type wind-powered electricity generation becomes Flow the power-division ratios under each operating point of device.
2. 2. the method for the lifting operational efficiency of parallel connection type wind electric converter according to claim 1, it is characterised in that described Optimization object function step is each by optimization object function off-line calculation parallel connection type wind electric converter with 1 ‰ power resolution Optimum efficiency and optimal power allocation ratio under operating point.
3. 3. the method for the lifting operational efficiency of parallel connection type wind electric converter according to claim 1, it is characterised in that also wrap Include：

   Adaptive optimization combines rate-determining steps：The power instruction of each converter under any operating mode is obtained by look-up table, realized Adaptive optimization combination control.
4. 4. the method for the lifting operational efficiency of parallel connection type wind electric converter according to claim 1, it is characterised in that optimization Object function is：

   G=max { η_T(P_IN,1,P_IN,2,…P_IN,i…P_IN,n)}；

   η_T(P_IN,1,P_IN,2,…P_IN,i…P_IN,n) it is that input power is P_INWhen parallel system gross efficiency, P_IN,iFor converter i's Input power, i=1,2 ..., n.
5. 5. the method for the lifting operational efficiency of parallel connection type wind electric converter according to claim 4, it is characterised in that optimization Bound for objective function is：

   <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <msub> <mi>P</mi> <mrow> <mi>I</mi> <mi>N</mi> </mrow> </msub> <mo>=</mo> <mstyle> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <msub> <mi>P</mi> <mrow> <mi>I</mi> <mi>N</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> </mstyle> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> <mo>&amp;le;</mo> <msub> <mi>P</mi> <mrow> <mi>I</mi> <mi>N</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>&amp;le;</mo> <msub> <mi>P</mi> <mi>R</mi> </msub> </mtd> </mtr> </mtable> </mfenced>

   P_RFor the rated power of single inverter.
6. A kind of 6. system of the lifting operational efficiency of parallel connection type wind electric converter, it is characterised in that including：

   Numerical fitting module：According to the efficiency value of each operating point of converter in parallel connection type wind electric converter, numerical fitting side is utilized Method, obtain the efficiency curve and efficiency function of parallel connection type wind electric converter；

   Optimization object function module：By under each operating point of optimization object function off-line calculation parallel connection type wind electric converter most Excellent efficiency and optimal power allocation ratio；

   Look-up table makes module：Look-up table is made in the optimal power allocation ratio that off-line calculation is obtained, and setting parallel connection type wind-powered electricity generation becomes Flow the power-division ratios under each operating point of device.
7. 7. the system of the lifting operational efficiency of parallel connection type wind electric converter according to claim 6, it is characterised in that described Optimization object function step is each by optimization object function off-line calculation parallel connection type wind electric converter with 1 ‰ power resolution Optimum efficiency and optimal power allocation ratio under operating point.
8. 8. the system of the lifting operational efficiency of parallel connection type wind electric converter according to claim 6, it is characterised in that also wrap Include：

   Adaptive optimization combines rate-determining steps：The power instruction of each converter under any operating mode is obtained by look-up table, realized Adaptive optimization combination control.
9. 9. the system of the lifting operational efficiency of parallel connection type wind electric converter according to claim 6, it is characterised in that optimization Object function is：

   G=max { η_T(P_IN,1,P_IN,2,…P_IN,i…P_IN,n)}；

   η_T(P_IN,1,P_IN,2,…P_IN,i…P_IN,n) it is that input power is P_INWhen parallel system gross efficiency, P_IN,iFor converter i's Input power, i=1,2...n.
10. 10. the system of the lifting operational efficiency of parallel connection type wind electric converter according to claim 9, it is characterised in that excellent Changing bound for objective function is：

    <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <msub> <mi>P</mi> <mrow> <mi>I</mi> <mi>N</mi> </mrow> </msub> <mo>=</mo> <mstyle> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <msub> <mi>P</mi> <mrow> <mi>I</mi> <mi>N</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> </mstyle> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> <mo>&amp;le;</mo> <msub> <mi>P</mi> <mrow> <mi>I</mi> <mi>N</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>&amp;le;</mo> <msub> <mi>P</mi> <mi>R</mi> </msub> </mtd> </mtr> </mtable> </mfenced>

    P_RFor the rated power of single inverter.