A system and method for testing the unbalanced compensation capability of a grid-connected converter

Abstract

The present invention discloses a system and method for testing the unbalanced compensation capability of a grid-type converter, comprising: a variable single-phase load Load and a control switch S load The variable single-phase load Load is used to simulate loads with different characteristics, and its control switch S load Used to control the variable single-phase load Load to be connected to or off the grid; simulate the grid Grid and its control switch S Grid The simulated grid is used to provide a stable voltage for the variable single-phase load Load and simulate a fault. Its control switch S Grid The system is used to control the state of the simulated power grid; the data acquisition device is used to collect the instantaneous three-phase voltage values ​​on the load side of a variable single-phase load. This invention can identify the imbalance suppression performance indicators of a grid-type converter and evaluate the dynamic stability of its imbalance suppression characteristics. The system has a simple and reliable structure, is easy to operate, and can significantly save testing time and costs.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-type converter testing, and in particular to a grid-type converter unbalance compensation capability testing system and a testing method and an evaluation method thereof. Background Art

[0002] With the development of renewable energy generation, the proportion of power electronic equipment in the power grid has gradually increased, and the overall power grid is showing trends such as reduced inertia and weakening strength. To ensure the stable and safe operation of the power grid, power electronic converters need to fulfill or even replace the functions and roles of traditional synchronous motors. Grid-connected converters have emerged as a mainstream development trend. However, there is no consensus on the precise definition and standardization of the dynamic characteristics of grid-connected converters, especially the imbalance suppression characteristics. Therefore, a standardized test method is needed to define their control performance indicators and evaluate the dynamic stability of their imbalance suppression characteristics. Summary of the Invention

[0003] The first purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and provide a grid-type converter unbalance compensation capability testing system, which has a simple and reliable structure, is easy to operate, and can greatly save testing time and cost.

[0004] A second object of the present invention is to provide a method for testing a system for testing the unbalanced compensation capability of a grid-type converter.

[0005] A third object of the present invention is to provide an evaluation method for a grid-type converter unbalance compensation capability testing system.

[0006] The first object of the present invention is achieved by the following technical solution: a grid-type converter unbalance compensation capability testing system, comprising:

[0007] Variable single-phase load Load and its control switch S load The variable single-phase load Load is used to simulate loads with different characteristics, and its control switch S load Used to control the variable single-phase load to be connected to or off the grid;

[0008] Simulated power grid Grid and its control switch S Grid The simulated grid is used to provide a stable voltage for the variable single-phase load Load and simulate a fault. Its control switch S Grid Used to control the state of the simulated power grid;

[0009] Data acquisition device, used to collect the instantaneous value of the three-phase voltage on the load side of the variable single-phase load (V Load,a 、V Load,b 、V Load,c );

[0010] The grid-connected converter GFC is equipped with a grid-connected switch S for controlling its own grid-connected / off-grid state. GFC The grid-type converter GFC and the simulated grid Grid are connected in series through a cable, and the variable single-phase load Load is hung between the grid-type converter GFC and the simulated grid Grid through a cable in parallel. Due to its unbalanced suppression characteristics, the grid-type converter GFC can provide voltage support for the variable single-phase load Load in the event of a grid fault. The data acquisition device is connected to the voltage signal acquisition point on the variable single-phase load Load side through a signal line.

[0011] Preferably, the characteristic load simulated by the variable single-phase load Load is one of a pure resistive load, an inductive load, a capacitive load, or a combination of any two or three of them.

[0012] Preferably, the sampling frequency of the data acquisition device is not less than 10 kHz.

[0013] The second object of the present invention is achieved by the following technical solution: a testing method for a grid-type converter unbalance compensation capability testing system, comprising the following steps:

[0014] 1) Control switch S of the simulated power grid Grid Normally closed state;

[0015] 2) Set the characteristics and capacity of the variable single-phase load;

[0016] 3) Close the grid-connected switch S of the grid-connected converter GFC GFC , connect the grid-forming converter GFC to the simulated grid to ensure synchronization and stable operation with the simulated grid;

[0017] 4) Close the control switch S of the variable single-phase load Load load , connect the variable single-phase load Load to the simulated grid Grid;

[0018] 5) Turn on the data acquisition device and start the wave recording function;

[0019] 6) Gradually increase the power set point P of the grid-connected converter GFC with a specific step size GFC,set , until the power set point P GFC,set The rated power of the grid-type converter GFC is reached, and the grid-type converter GFC is at the rated power set point S n After a certain period of stable operation, disconnect the grid-connected switch S of the grid-connected converter GFC. GFC , cut out the grid-connected converter GFC, and record the disconnection of the grid-connected switch S GFC The time is t step ;

[0020] 7) Stop the data acquisition device after maintaining a specific time;

[0021] 8) Determine whether all the characteristics and capacity combinations of the variable single-phase load simulation have been tested; if completed, end the test; if not, repeat steps 1)-7).

[0022] Preferably, in step 2), the capacity of the variable single-phase load Load is set to 0.25S n , 0.5S n , 0.75S n or S n .

[0023] Preferably, in step 6), the specific step length is 10%S N , where S N is the rated apparent power of the grid-type converter GFC.

[0024] The third object of the present invention is achieved by the following technical solution: a method for evaluating a grid-type converter unbalance compensation capability test system, the method being used to determine the unbalance suppression characteristics of the grid-type converter, the specific process being as follows:

[0025] First, according to the instantaneous value of the three-phase voltage on the Load side of the variable single-phase load (V load,a 、V load,b 、V load,c ), calculate its positive sequence voltage V + and negative sequence voltage V - , calculated as follows:

[0026] Compute the Fourier coefficients of the fundamental component within one fundamental period:

[0027]

[0028]

[0029] Where: f1 is the fundamental frequency; V load,i,cos is the cosine component of the fundamental voltage of one phase in the three-phase; V load,i,sin is the sinusoidal component of the fundamental voltage of one phase in the three phases; V load,i is the instantaneous value of the voltage of one of the three phases; i = a, b, c; t is the actual time series; T is the fundamental wave period;

[0030] The voltage vector components of the fundamental positive sequence components are calculated using the following formula:

[0031]

[0032]

[0033] Where: u 1+,cos is the cosine component of the fundamental voltage positive sequence; u 1+,sin is the sinusoidal component of the fundamental voltage positive sequence;

[0034] The voltage vector components of the fundamental negative sequence component are calculated using the following formula:

[0035]

[0036]

[0037] Where: u 1-,cos is the cosine component of the fundamental voltage negative sequence; u 1-,sin is the sinusoidal component of the fundamental voltage negative sequence;

[0038] The effective value of the line voltage of the fundamental positive sequence component V + :

[0039]

[0040] The effective value of the line voltage of the fundamental negative sequence component V _ :

[0041]

[0042] Calculate the voltage unbalance a using the following formula: u :

[0043]

[0044] In order to determine whether the GFC provides unbalanced current, it is necessary to calculate the voltage imbalance with and without the GFC under different characteristics and capacity combinations simulated by the variable single-phase load. The calculation method is as follows:

[0045] Δa u =a u,withGFC -a u,withoutGFC

[0046] Where: Δa u is the unbalance suppression capability of the grid-type converter GFC, Δa u The larger the absolute value, the more obvious the GFC unbalance suppression capability of the grid-type converter is; a u,withGFC t step a calculated from data collected at a specific time before the moment u value; a u,withoutGFC t step a calculated from data collected at a specific time after the moment u value; t step The grid-type converter GFC is set at the rated power point Sn After stable operation for a certain period of time, disconnect the grid-connected switch S GFC moment.

[0047] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0048] 1. The present invention can clarify the imbalance suppression performance index of the grid-type converter according to the imbalance suppression characteristics of the grid-type converter, and evaluate the dynamic stability of its imbalance suppression characteristics.

[0049] 2. The system structure is simple and reliable, easy to operate, and can save a lot of testing time and cost.

[0050] 3. The present invention provides a systematic approach for testing and evaluating grid-type converters, which is conducive to the rapid development of grid-type converters and even grid-type new energy power generation technologies. At the same time, it can enhance the grid-friendliness of new energy power generation based on power electronic equipment and strengthen the stability of the grid system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the system of the present invention.

[0052] Figure 2 Schematic diagram of the variable single-phase load of the system of the present invention. DETAILED DESCRIPTION

[0053] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0054] like Figure 1 and Figure 2 As shown, this embodiment provides a system for testing the unbalanced compensation capability of a grid-type converter, including:

[0055] Variable single-phase load Load and its control switch S load The variable single-phase load Load is used to simulate loads with different characteristics, and its control switch S load Used to control the variable single-phase load to be connected to or off the grid;

[0056] Simulated power grid Grid and its control switch S Grid The simulated grid is used to provide a stable voltage for the variable single-phase load Load and simulate a fault. Its control switch S Grid Used to control the state of the simulated power grid;

[0057] Data acquisition device, used to collect the instantaneous value of the three-phase voltage on the load side of the variable single-phase load (V Load,a 、V Load,b 、V Load,c );

[0058] The grid-connected converter GFC is equipped with a grid-connected switch S for controlling its own grid-connected / off-grid state. GFC The grid-type converter GFC and the simulated grid Grid are connected in series through a cable, and the variable single-phase load Load is hung between the grid-type converter GFC and the simulated grid Grid through a cable in parallel. Due to its unbalanced suppression characteristics, the grid-type converter GFC can provide voltage support for the variable single-phase load Load in the event of a grid fault. The data acquisition device is connected to the voltage signal acquisition point on the variable single-phase load Load side through a signal line.

[0059] Preferably, the characteristic load simulated by the variable single-phase load Load is one of a pure resistive load, an inductive load, a capacitive load, or a combination of any two or three of them.

[0060] Preferably, the sampling frequency of the data acquisition device is not less than 10 kHz.

[0061] This embodiment also provides a method for testing the above-mentioned grid-type converter unbalance compensation capability testing system, comprising the following steps:

[0062] 1) Control switch S of the simulated power grid Grid Normally closed state;

[0063] 2) Set the characteristics and capacity of the variable single-phase load;

[0064] 3) Close the grid-connected switch S of the grid-connected converter GFC GFC , connect the grid-forming converter GFC to the simulated grid to ensure synchronization and stable operation with the simulated grid;

[0065] 4) Close the control switch S of the variable single-phase load Load load , connect the variable single-phase load Load to the simulated grid Grid;

[0066] 5) Turn on the data acquisition device and start the wave recording function;

[0067] 6) Gradually increase the power set point P of the grid-connected converter GFC with a specific step size GFC,set , until the power set point P GFC,set The rated power of the grid-type converter GFC is reached, and the grid-type converter GFC is at the rated power set point S n Stable operation, maintain for 5 minutes, disconnect the grid-connected switch S of the grid-connected converter GFC GFC , cut out the grid-connected converter GFC, and record the disconnection of the grid-connected switch S GFC The time is t step ;

[0068] 7) After 5 minutes, stop the data acquisition device;

[0069] 8) Determine whether all the characteristics and capacity combinations of the variable single-phase load simulation have been tested; if completed, end the test; if not, repeat steps 1)-7).

[0070] Preferably, in step 2), the capacity of the variable single-phase load Load is set to 0.25S n , 0.5S n , 0.75S n or S n .

[0071] Preferably, in step 6), the specific step length is 10%S N , where S N is the rated apparent power of the grid-type converter GFC.

[0072] This embodiment also provides an evaluation method for the above-mentioned grid-type converter unbalance compensation capability test system. The method is used to determine the unbalance suppression characteristics of the grid-type converter. The specific process is as follows:

[0073] First, according to the instantaneous value of the three-phase voltage on the Load side of the variable single-phase load (V load,a 、V load,b 、V load,c ), calculate its positive sequence voltage V + and negative sequence voltage V - , calculated as follows:

[0074] Compute the Fourier coefficients of the fundamental component within one fundamental period:

[0075]

[0076]

[0077] Where: f1 is the fundamental frequency; V load,i,cos is the cosine component of the fundamental voltage of one phase in the three-phase; V load,i,sin is the sinusoidal component of the fundamental voltage of one phase in the three phases; V load,i is the instantaneous value of the voltage of one of the three phases; i = a, b, c; t is the actual time series; T is the fundamental wave period;

[0078] The voltage vector components of the fundamental positive sequence components are calculated using the following formula:

[0079]

[0080]

[0081] Where: u 1+,cos is the cosine component of the fundamental voltage positive sequence; u 1+,sin is the sinusoidal component of the fundamental voltage positive sequence;

[0082] The voltage vector components of the fundamental negative sequence component are calculated using the following formula:

[0083]

[0084]

[0085] Where: u 1-,cos is the cosine component of the fundamental voltage negative sequence; u 1-,sin is the sinusoidal component of the fundamental voltage negative sequence;

[0086] The effective value of the line voltage of the fundamental positive sequence component V + :

[0087]

[0088] The effective value of the line voltage of the fundamental negative sequence component V _ :

[0089]

[0090] Calculate the voltage unbalance a using the following formula: u :

[0091]

[0092] In order to determine whether the grid-type converter GFC provides unbalanced current, it is necessary to simulate the three characteristics (resistance, inductance, and capacitance) and four capacity levels (25% S n 50% S n , 75% S n The voltage unbalance is calculated for 12 cases with and without grid-connected converter GFC:

[0093] Δa u =a u,withGFC -a u,withoutGFC

[0094] Where: Δa u is the unbalance suppression capability of the grid-type converter GFC, Δa u The larger the absolute value, the more obvious the GFC unbalance suppression capability of the grid-type converter is; a u,withGFC t step a calculated from the data collected 5 minutes before the moment u value; a u,withoutGFC t stepa calculated from data collected 5 minutes after the time u value; t step The grid-type converter GFC is set at the rated power point S n After stable operation for 5 minutes, disconnect the grid-connected switch S GFC moment.

[0095] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A grid-type converter unbalance compensation capability test system, comprising: Variable single-phase load Load and its control switch S load The variable single-phase load Load is used to simulate loads with different characteristics, and its control switch S load Used to control the variable single-phase load to be connected to or off the grid; Simulated power grid Grid and its control switch S Grid The simulated grid is used to provide a stable voltage for the variable single-phase load Load and simulate a fault. Its control switch S Grid Used to control the state of the simulated power grid; Data acquisition device, used to collect the instantaneous value of the three-phase voltage on the load side of the variable single-phase load (V load,a 、V load,b 、V load,c ); The grid-connected converter GFC is equipped with a grid-connected switch S for controlling its own grid-connected / off-grid state. GFC The grid-type converter GFC and the simulated grid Grid are connected in series via a cable, and the variable single-phase load Load is hung between the grid-type converter GFC and the simulated grid Grid via a cable in parallel. Due to its unbalance suppression characteristics, the grid-type converter GFC can provide voltage support for the variable single-phase load Load in the event of a grid fault. The data acquisition device is connected to a voltage signal acquisition point on the variable single-phase load Load side via a signal line; The method for testing the unbalanced compensation capability test system of the grid-type converter comprises the following steps: 1) Control switch S of the simulated power grid Grid Normally closed state; 2) Set the characteristics and capacity of the variable single-phase load; 3) Close the grid-connected switch S of the grid-connected converter GFC GFC , connect the grid-forming converter GFC to the simulated grid to ensure synchronization and stable operation with the simulated grid; 4) Close the control switch S of the variable single-phase load Load load , connect the variable single-phase load Load to the simulated grid Grid; 5) Turn on the data acquisition device and start the wave recording function; 6) Gradually increase the power set point P of the grid-connected converter GFC with a specific step size GFC,set , until the power set point P GFC,set The rated power of the grid-type converter GFC is reached, and the grid-type converter GFC is at the rated power set point S n After a certain period of stable operation, disconnect the grid-connected switch S of the grid-connected converter GFC. GFC , cut out the grid-connected converter GFC, and record the disconnection of the grid-connected switch S GFC The time is t step ; 7) Stop the data acquisition device after maintaining a specific time; 8) Determine whether all the characteristics and capacity combinations of the variable single-phase load simulation have been tested; if completed, end the test; if not, repeat steps 1)-7).

2. A grid-type converter unbalance compensation capability testing system according to claim 1, characterized in that: The characteristic load simulated by the variable single-phase load Load is one of pure resistive load, inductive load, capacitive load, or a combination of any two or three of them.

3. The unbalance compensation capability testing system for a grid-connected converter according to claim 1, characterized in that: The sampling frequency of the data acquisition device is not less than 10 kHz.

4. A grid-type converter unbalance compensation capability testing system according to claim 1, characterized in that: In step 2), the capacity of the variable single-phase load Load is set to 0.25S n , 0.5S n , 0.75S n or S n .

5. A grid-type converter unbalance compensation capability testing system according to claim 1, characterized in that: In step 6), the specific step size is 10%S N , where S N is the rated apparent power of the grid-type converter GFC.

6. The evaluation method of the grid-type converter unbalance compensation capability test system according to any one of claims 1 to 3, characterized in that: This method is used to determine the unbalance suppression characteristics of grid-type converters. The specific process is as follows: First, according to the instantaneous value of the three-phase voltage on the Load side of the variable single-phase load (V load,a 、V load,b 、V load,c ), calculate its positive sequence voltage V + and negative sequence voltage V - , calculated as follows: Compute the Fourier coefficients of the fundamental component within one fundamental period: Where: f1 is the fundamental frequency; V load,i,cos is the cosine component of the fundamental voltage of one phase in the three phases; V load,i,sin is the sinusoidal component of the fundamental voltage of one phase in the three-phase; V load,i is the instantaneous value of the voltage of one of the three phases; i = a, b, c; t is the actual time series; T is the fundamental wave period; The voltage vector components of the fundamental positive sequence components are calculated using the following formula: Where: u 1+,cos is the cosine component of the fundamental voltage positive sequence; u 1+,sin is the sinusoidal component of the fundamental voltage positive sequence; The voltage vector components of the fundamental negative sequence component are calculated using the following formula: Where: u 1-,cos is the cosine component of the fundamental voltage negative sequence; u 1-,sin is the sinusoidal component of the fundamental voltage negative sequence; The effective value of the line voltage of the fundamental positive sequence component V + : The effective value of the line voltage of the fundamental negative sequence component V: Calculate the voltage unbalance a using the following formula: u : In order to determine whether the GFC provides unbalanced current, it is necessary to calculate the voltage imbalance with and without the GFC under different characteristics and capacity combinations simulated by the variable single-phase load. The calculation method is as follows: Yes u = yes u,withGFC -in u,withoutGFC Where: Δa u is the unbalance suppression capability of the grid-type converter GFC, Δa u The larger the absolute value, the more obvious the GFC unbalance suppression capability of the grid-type converter is; a u,withGFC t step a calculated from data collected at a specific time before the moment u value; a u,withoutGFC t step a calculated from data collected at a specific time after the moment u value; t step The grid-type converter GFC is set at the rated power point S n After stable operation for a certain period of time, disconnect the grid-connected switch S GFC moment.

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