Adaptive fault ride-through operation control method and device for inverter-type distributed power supply

Abstract

The present invention provides an adaptive fault ride-through operation control method and related devices for an inverter-type distributed power supply. According to the inverter-type distributed power supply fault ride-through requirements and the grid-connected inverter current limit value, the voltage of the grid connection point when the output current of the inverter-type distributed power supply reaches the maximum allowable value, that is, the boundary voltage, is calculated, and the corresponding fault ride-through control strategy is selected according to the magnitude relationship between the grid connection point voltage and the boundary voltage. The present invention enables the inverter-type distributed power supply to always output the maximum allowable output current during the fault ride-through period, and adaptively adjusts the distribution of active current and reactive current according to the grid connection point voltage. On the one hand, it can increase the fault current output by the inverter-type distributed power supply when a minor fault occurs in the system, thereby improving the protection sensitivity; on the other hand, it can improve the ability of the inverter-type distributed power supply to output reactive power, raise the grid connection point voltage of the inverter-type distributed power supply, and enhance the fault ride-through capability of the inverter-type distributed power supply.

Description

Technical Field

[0001] The present invention belongs to the field of inverter-type distributed power supply grid-connected control, and in particular relates to inverter-type distributed power supply fault ride-through control. Background Art

[0002] As China vigorously promotes the development of renewable energy, the penetration rate of inverter-type distributed power sources in distribution networks is increasing, and their impact on grid stability is growing. When a grid fault causes a system voltage drop, if the inverter-type distributed power source is directly disconnected from the grid, it will seriously affect the transient stability of the grid and even cause the system to disconnect, triggering a large-scale power outage. Therefore, the inverter-type distributed power source must have the same fault ride-through capability as conventional generators. When the voltage at the inverter-type distributed power source's grid connection point drops, the inverter-type distributed power source can remain connected to the grid and provide a certain amount of reactive power to the grid to support grid voltage recovery until the grid voltage returns to normal, thereby "riding through" the fault.

[0003] A common fault ride-through control strategy for inverter-type distributed power sources (DGs) is as follows: within the maximum allowable output current range of the DG's grid-connected inverter, reactive current output is prioritized. For every 1% drop in the positive-sequence voltage at the DG's grid connection point, the DG provides 2% reactive current to the system. If the remaining capacity can guarantee the DG's rated active power output, the active current is calculated based on the DG's rated power and the positive-sequence voltage at the grid connection point. If the remaining capacity cannot guarantee the DG's rated active power output, the remaining capacity is used to output the active current. The inventors have found that when this inverter-type distributed power supply fault ride-through operation control strategy is adopted, when the voltage drop at the inverter-type distributed power supply grid-connected point is not large, the inverter-type distributed power supply can ensure the output of rated active power while providing the corresponding reactive current to the system, and leave a certain margin. The output current of the inverter-type distributed power supply grid-connected inverter does not reach the maximum allowable output current, the output fault current of the inverter-type distributed power supply is small, and the difference with the current amplitude during normal operation is very small, which is not conducive to reliable protection action; at this time, the output capacity of the inverter-type distributed power supply is not fully utilized, and the inverter-type distributed power supply's ability to support grid voltage still has room for improvement. Summary of the Invention

[0004] In order to solve the deficiencies in the prior art, the first aspect of the present invention proposes an adaptive fault ride-through operation control method for an inverter-type distributed power supply. According to the fault ride-through requirements of the inverter-type distributed power supply and the current limiting value of the grid-connected inverter, that is, the maximum allowable output current of the grid-connected inverter, the voltage at the grid connection point when the output current of the inverter-type distributed power supply reaches the maximum allowable output current is calculated, which is called the boundary voltage. By comparing the positive sequence voltage at the grid connection point of the inverter-type distributed power supply with the boundary voltage of the inverter-type distributed power supply, the corresponding fault ride-through control strategy is adaptively selected to ensure that the inverter-type distributed power supply always outputs the maximum allowable output current during the fault ride-through period, and adaptively adjusts the distribution of active current and reactive current according to the grid connection point voltage.

[0005] This invention addresses the problem of traditional fault ride-through control strategies underutilizing the output capacity of inverter-type distributed power supplies when the grid connection point voltage drops slightly. This allows the inverter-type distributed power supply to consistently output its maximum allowable output current during fault ride-through, and adaptively adjusts the active and reactive current distribution based on the grid connection point voltage. This increases the fault current output by the inverter-type distributed power supply during minor system faults, thereby improving protection sensitivity. Furthermore, it enhances the inverter-type distributed power supply's reactive power output capability, raising the grid connection point voltage and strengthening its fault ride-through capability.

[0006] In order to achieve the above object, the present invention adopts the following technical solution to achieve: a method for controlling adaptive fault ride-through operation of an inverter-type distributed power supply, characterized by comprising:

[0007] Collect the three-phase voltage of the inverter-type distributed power grid connection point;

[0008] Performing positive-sequence and negative-sequence separation on the three-phase voltage at the grid-connected point of the inverter-type distributed power supply to obtain a positive-sequence voltage at the grid-connected point of the inverter-type distributed power supply;

[0009] Based on the positive sequence voltage of the inverter-type distributed power supply grid connection point, judging the voltage drop condition of the inverter-type distributed power supply grid connection point;

[0010] The operation of the inverter-type distributed power supply is controlled according to the judgment result, so that the inverter-type distributed power supply always outputs the maximum allowable output current during the fault ride-through period.

[0011] The control of the inverter-type distributed power supply operation according to the voltage drop condition of the inverter-type distributed power supply grid connection point is as follows:

[0012] If the positive sequence voltage per unit value of the inverter-type distributed power grid connection point is higher than 0.9, the inverter-type distributed power grid continues to operate according to the normal state control strategy;

[0013] If the positive sequence voltage per unit value of the inverter-type distributed generation grid connection point is lower than 0.2, the inverter-type distributed generation will be immediately cut off from the distribution network;

[0014] If the per-unit value of the positive sequence voltage at the grid-connected point of the inverter-type distributed power generation is between 0.2 and 0.9, the inverter-type distributed power generation enters the fault ride-through state, and the control mode of the inverter-type distributed power generation is switched from the dual-loop control of the power outer loop and the current inner loop to the single-loop control of the current inner loop.

[0015] The positive-sequence voltage of the inverter-type distributed power supply grid connection point obtained by performing positive-sequence and negative-sequence separation on the collected three-phase voltage of the inverter-type distributed power supply grid connection point is specifically:

[0016] Taking phase A as the reference phase, the symmetrical component method is used to calculate the positive sequence voltage of the three-phase voltage at the grid connection point of the inverter-type distributed power supply. The calculation process is shown in the following formula:

[0017]

[0018] In the formula ,u a 、u b 、u c are the voltages of phase A, phase B, and phase C at the grid connection point of the inverter-type distributed power supply; u a0 、u a1 、u a2 They are the zero-sequence, positive-sequence and negative-sequence components of the A-phase voltage at the grid-connected point of the inverter-type distributed generation.

[0019] The dual-loop control of the power outer loop and the current inner loop is specifically as follows:

[0020] The current inner loop adopts a vector control strategy based on the grid voltage-oriented current closed loop in a synchronous rotating coordinate system;

[0021] The outer power loop adopts PQ control, and the output value of the difference between the active power reference value and the active power measured value after PI adjustment is used as the reference value of the d-axis current of the inner current loop; the inverter-type distributed power supply outputs at unity power factor, and the reference value of the q-axis current of the inner current loop is set to 0;

[0022] According to the instantaneous reactive power theory, the expressions of the system's active power P and reactive power Q in the synchronous rotating coordinate system are:

[0023]

[0024] Where: e d 、e q is the dq component of the network side voltage of the grid-connected inverter; i d 、i q is the dq component of the AC side output current of the grid-connected inverter;

[0025] When oriented based on grid voltage, it is oriented to the d-axis, i.e., e q =0, then formula (4) is simplified to

[0026]

[0027] The vector control strategy uses Park transformation to transform the AC quantity in the stationary coordinate system into the DC quantity in the synchronous rotating coordinate system, and then adopts a typical PI controller design to achieve zero static error control of the AC current, as follows:

[0028] According to Kirchhoff's law, in the three-phase stationary abc coordinate system, the voltage equation of the grid-connected inverter is:

[0029]

[0030] According to Park transformation, the grid-connected inverter voltage equation (2) in the three-phase stationary abc coordinate system is transformed into the grid-connected inverter voltage equation in the synchronous rotating coordinate system:

[0031]

[0032] Where: u d 、u q is the dq component of the AC side output voltage of the grid-connected inverter; e d 、e q is the dq component of the network side voltage of the grid-connected inverter; i d 、i q is the dq component of the AC side output current of the grid-connected inverter; L is the inductance of the grid-connected inverter filter; R is the resistance of the grid-connected inverter output line; ω is the grid angular frequency;

[0033] Adopting the feedforward decoupling strategy, the feedforward quantity -ωLi is introduced into the AC voltage output of the grid-connected inverter. q and +ωLi d , so that it is combined with the coupling term +ωLi in equation (3) q and -ωLi d The decoupling between the d and q axes is achieved by canceling each other out. The decoupled system is converted into two independent and completely equal parts, which are controlled separately.

[0034] The switching from the dual-loop control of the power outer loop and the current inner loop to the single-loop control of the current inner loop is specifically as follows:

[0035] Disconnect the power outer loop and stop using the output value of the difference between the reference value and the measured value of active power after PI adjustment as the current reference value of the current inner loop. Directly give the current reference value of the current inner loop according to the inverter-type distributed power supply fault ride-through control equation.

[0036] The current inner loop current reference value is directly given according to the inverter-type distributed power supply fault ride-through control equation, specifically:

[0037] According to the fault ride-through requirements of the inverter-type distributed power supply and the current limit value of the grid-connected inverter, that is, the maximum allowable output current i max , calculate the boundary voltage U k The boundary voltage U k It is the per-unit voltage value of the grid connection point when the output current of the inverter distributed power source reaches the maximum allowable output current;

[0038] When the positive sequence voltage per unit value of the inverter type distributed power grid connection point is [U k ,0.9], the inverter-type distributed power supply outputs the corresponding active current according to the active power requirement, and the remaining capacity outputs all reactive current; the inverter-type distributed power supply uses the fault ride-through control equation A to calculate the current reference value of the current inner loop during the fault ride-through process;

[0039] When the positive sequence voltage per unit value of the inverter type distributed power grid connection point is between [0.2, U k ], the inverter-type distributed power supply outputs reactive current first according to the fault ride-through requirement, and outputs active current with the remaining capacity; the inverter-type distributed power supply uses the fault ride-through control equation B to calculate the current reference value of the current inner loop during the fault ride-through process.

[0040] The boundary voltage U k The specific calculation method is:

[0041] After a short circuit occurs in the power grid, the output current of the inverter-type distributed power supply will increase, which is limited by the maximum allowable output current i of the grid-connected inverter. max , the output current of the inverter distributed power supply will not increase infinitely, and its constraint equation is:

[0042]

[0043] Where: i dref is the d-axis current reference value; i qref is the q-axis current reference value; i N is the rated current of the inverter of the inverter-type distributed power grid-connected inverter; m is a constant with a value range of [1,2];

[0044] According to the fault ride-through requirement, the inverter-type distributed power supply grid-connected point should provide at least 2% reactive current for every 1% drop in positive sequence voltage; the output current of the inverter-type distributed power supply should reach the maximum allowable output current i of the grid-connected inverter by calculating the formula (7). max The boundary voltage value:

[0045]

[0046] Where: P is the rated active power; U k is the boundary voltage; k is the reactive current compensation coefficient, and its value range is [2,6].

[0047] The fault ride-through control equation A is specifically: the reference values ​​of the d-axis and q-axis currents in the current inner loop are:

[0048]

[0049] Where: P ref is the active power reference value; is the positive sequence voltage at the grid connection point of the inverter type distributed generation; α is the per unit positive sequence voltage at the grid connection point of the inverter type distributed generation during the fault ride-through period;

[0050] When α∈(U k ,0.9), the inverter-type distributed power supply outputs reactive current i q The ratio λ to the positive sequence voltage drop value β at the grid connection point of the inverter type distributed power supply is:

[0051]

[0052] Where, the positive sequence voltage drop value at the grid connection point of the inverter-type distributed power supply β = 1-α. At this time, λ is always greater than 2, which meets the fault ride-through requirement of the inverter-type distributed power supply, that is, for every 1% drop in the positive sequence voltage at the grid connection point, at least 2% reactive current is provided.

[0053] The fault ride-through control equation B is specifically: the reference values ​​of the d-axis and q-axis currents in the current inner loop are:

[0054]

[0055] When α∈(1-m / 2,U k ), the inverter-type distributed power supply outputs reactive current i q The ratio λ to the positive sequence voltage drop value β at the grid connection point of the inverter type distributed power supply is always 2, which meets the fault ride-through requirement of the inverter type distributed power supply, that is, at least 2% reactive current is provided for every 1% drop in the positive sequence voltage at the grid connection point.

[0056] The present invention also provides an inverter-type distributed power supply adaptive fault ride-through operation control device, comprising:

[0057] Three-phase voltage sampling module, used to sample the three-phase voltage of the inverter-type distributed power grid connection point;

[0058] The positive sequence voltage acquisition module is used to separate the positive and negative sequence of the three-phase voltage of the inverter distributed power grid connection point to obtain the positive sequence voltage of the inverter distributed power grid connection point;

[0059] A voltage drop judgment module is used to judge the voltage drop of the inverter type distributed power supply grid connection point based on the positive sequence voltage of the inverter type distributed power supply grid connection point;

[0060] The operation control module is used to control the operation of the inverter distributed power supply according to the voltage drop of the inverter distributed power supply grid connection point, so that the inverter distributed power supply always outputs the maximum allowable output current during the fault ride-through period.

[0061] The positive sequence voltage acquisition module is specifically used to:

[0062] Taking phase A as the reference phase, the symmetrical component method is used to calculate the positive sequence voltage of the three-phase voltage at the grid connection point of the inverter-type distributed power supply. The calculation process is shown in the following formula:

[0063]

[0064] In the formula ,u a 、u b 、u c are the voltages of phase A, phase B, and phase C at the grid connection point of the inverter-type distributed power supply; u a0 、u a1 、u a2 They are the zero-sequence, positive-sequence and negative-sequence components of the A-phase voltage at the grid-connected point of the inverter-type distributed generation.

[0065] The operation control module is specifically used to: if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is higher than 0.9, the inverter distributed power supply continues to operate in grid connection according to the normal state control strategy; if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is lower than 0.2, the inverter distributed power supply is immediately cut off from the distribution network; if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is between 0.2 and 0.9, the inverter distributed power supply enters the fault ride-through state, and the control mode of the inverter distributed power supply is switched from the dual-loop control of power outer loop and current inner loop to the single-loop control of current inner loop.

[0066] On the other hand, the present invention provides an electronic device, characterized in that it includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the processor executes the computer program, it implements the inverter-type distributed power supply adaptive fault ride-through operation control method as described in the first aspect.

[0067] Another aspect of the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the inverter-type distributed power supply adaptive fault ride-through operation control method as described in the first aspect.

[0068] Compared with the prior art, the present invention has the following advantages: 1. The adaptive fault ride-through operation control method of an inverter-type distributed power supply of the present invention fully utilizes the output capacity of the grid-connected inverter of the inverter-type distributed power supply. During the fault ride-through period, the output current of the grid-connected inverter is always the maximum allowable output current, which can improve the protection sensitivity. 2. Compared with the traditional inverter-type distributed power supply fault ride-through operation control strategy, the adaptive fault ride-through operation control method of an inverter-type distributed power supply of the present invention provides more reactive power to the system while ensuring that the inverter-type distributed power supply outputs the same active power. 3. Compared with the traditional inverter-type distributed power supply fault ride-through operation control strategy, the adaptive fault ride-through operation control method of an inverter-type distributed power supply of the present invention has a better effect on raising the grid-connected point voltage of the inverter-type distributed power supply during the fault ride-through period. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 is a flow chart of the present invention;

[0070] Figure 2 This is the control block diagram of the inverter-type distributed power grid-connected inverter;

[0071] Figure 3 When the inverter type distributed power source adopts the control equation A, the inverter type distributed power source outputs reactive current i q The relationship between the ratio λ and β of the positive sequence voltage drop value β at the grid connection point of the inverter type distributed generation;

[0072] Figure 4 This is a structural diagram of the inverter-type distributed power supply connected to the distribution network;

[0073] Figure 5 It is the output current waveform of the inverter type distributed power supply;

[0074] Figure 6 It is the active power waveform output by the inverter type distributed power supply;

[0075] Figure 7 It is the reactive power waveform diagram output by the inverter type distributed power supply;

[0076] Figure 8 It is the positive sequence voltage waveform of the inverter type distributed power supply grid connection point. DETAILED DESCRIPTION

[0077] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0078] The constant m is set to 1.5, that is, the maximum allowable output current of the inverter-type distributed power grid-connected inverter is 1.5 times the rated current; the reactive current compensation coefficient k is set to 2; the overall process is as follows Figure 1 shown.

[0079] A method for controlling an inverter-type distributed power supply to adaptively control fault ride-through operation includes the following steps:

[0080] Step 1: Sample the three-phase voltage of the inverter distributed power grid connection point, calculate the positive sequence voltage of the inverter distributed power grid connection point based on the three-phase voltage of the inverter distributed power grid connection point, and use the positive sequence voltage of the inverter distributed power grid connection point to perform voltage drop detection;

[0081] The specific method of voltage drop detection is as follows:

[0082] Taking phase A as the reference phase, the symmetrical component method is used to calculate the positive sequence voltage of the three-phase voltage at the grid connection point of the inverter-type distributed power supply. The calculation process is shown in the following formula:

[0083]

[0084] In the formula ,u a 、u b 、u c are the voltages of phase A, phase B, and phase C at the grid connection point of the inverter-type distributed power supply; u a0 、u a1 、u a2 They are the zero-sequence, positive-sequence and negative-sequence components of the A-phase voltage at the grid-connected point of the inverter-type distributed generation.

[0085] Step 2: Based on the positive sequence voltage of the inverter-type distributed power grid connection point obtained in step 1, determine the voltage drop situation of the inverter-type distributed power grid connection point;

[0086] The per-unit value of the positive sequence voltage of the inverter distributed power grid connection point is calculated according to the positive sequence voltage of the inverter distributed power grid connection point. The per-unit value of the positive sequence voltage of the inverter distributed power grid connection point is the ratio of the positive sequence voltage of the inverter distributed power grid connection point to the rated voltage of the system;

[0087] When the per-unit value of the positive sequence voltage at the grid connection point of the inverter distributed power generation is higher than 0.9, the inverter distributed power generation continues to operate in grid connection according to the normal state control strategy; when the per-unit value of the positive sequence voltage at the grid connection point of the inverter distributed power generation is lower than 0.2, the inverter distributed power generation is immediately removed from the distribution network, otherwise it goes to step 3;

[0088] Step 3: Based on the positive sequence voltage of the inverter distributed power grid connection point obtained in step 1, the voltage drop of the inverter distributed power grid connection point is judged. When the per-unit value of the positive sequence voltage of the inverter distributed power grid connection point is between 0.2 and 0.9, the inverter distributed power enters the fault ride-through state, and the control mode of the inverter distributed power is switched from the dual-loop control of power outer loop and current inner loop to the single-loop control of current inner loop. Figure 2 This is the control block diagram of the inverter-type distributed power grid-connected inverter;

[0089] The specific dual-loop control of power outer loop and current inner loop is:

[0090] The inner current loop uses a vector control strategy based on a grid voltage-directed current closed loop in a synchronously rotating coordinate system. The Park transformation is used to convert the AC quantity in the stationary coordinate system into a DC quantity in the synchronously rotating coordinate system. A typical PI controller design is then used to achieve zero-static-error control of the AC current.

[0091] According to Kirchhoff's law, in the three-phase stationary abc coordinate system, the voltage equation of the grid-connected inverter is:

[0092]

[0093] According to Park transformation, the grid-connected inverter voltage equation (2) in the three-phase stationary abc coordinate system is transformed into the grid-connected inverter voltage equation in the synchronous rotating coordinate system:

[0094]

[0095] Where: u d 、u q is the dq component of the AC side output voltage of the grid-connected inverter; e d 、e q dq components of the network-side voltage of the grid-connected inverter; i d 、i q is the dq component of the AC side output current of the grid-connected inverter; L is the inductance of the grid-connected inverter filter; R is the resistance of the grid-connected inverter output line; ω is the grid angular frequency.

[0096] Adopting the feedforward decoupling strategy, the feedforward quantity -ωLi is introduced into the AC voltage output of the grid-connected inverter. q and +ωLi d , so that it is combined with the coupling term +ωLi in equation (3)q and -ωLi d The decoupling between the d and q axes is achieved by canceling each other out. The decoupled system is converted into two independent and completely equal parts, which are controlled separately.

[0097] The outer power loop uses PQ control, using the difference between the active power reference and the measured active power after PI adjustment as the reference value for the d-axis current in the inner current loop. The inverter-type distributed power supply operates at unity power factor, and the reference value for the q-axis current in the inner current loop is set to 0.

[0098] According to the instantaneous reactive power theory, the expressions of the system's active power P and reactive power Q in the synchronous rotating coordinate system are:

[0099]

[0100] When oriented based on grid voltage, it is oriented to the d-axis, i.e., e q =0, then formula (4) is simplified to

[0101]

[0102] The control mode is converted from the dual-loop control of power outer loop and current inner loop to the single-loop control of current inner loop as follows:

[0103] Disconnect the power outer loop and stop using the output value of the difference between the reference value and the measured value of active power after PI adjustment as the current reference value of the current inner loop. Directly give the current reference value of the current inner loop according to the inverter-type distributed power supply fault ride-through control equation.

[0104] Step 4: According to the fault ride-through requirements of the inverter-type distributed power supply and the current limit value of the grid-connected inverter, that is, the maximum allowable output current i of the grid-connected inverter max , calculate the voltage per unit value of the grid connection point when the output current of the inverter distributed power source reaches the maximum allowable output current, which is called the boundary voltage U k .

[0105] The calculation of the boundary voltage is as follows:

[0106] After a short circuit occurs in the power grid, the output current of the inverter-type distributed power supply will increase, which is limited by the maximum allowable output current i of the grid-connected inverter. max , the output current of the inverter distributed power supply will not increase infinitely, and its constraint equation is:

[0107]

[0108] Where: i dref is the d-axis current reference value; i qref is the q-axis current reference value; i NIt is the rated current of the inverter of the inverter-type distributed power grid-connected inverter.

[0109] According to the fault ride-through requirements, the inverter-type distributed power supply grid-connected point should provide at least 2% reactive current for every 1% drop in positive sequence voltage. The output current of the inverter-type distributed power supply reaches the maximum allowable output current i of the grid-connected inverter by calculating formula (7): max The boundary voltage value.

[0110]

[0111] Where: P is the rated active power; U K is the boundary voltage.

[0112] Combining equations (6) and (7), we can get the boundary voltage U at this time: k =0.719. When the per-unit value of the positive-sequence voltage at the grid-connected point of the inverter-type distributed generation is between [0.719, 0.9], the inverter-type distributed generation can output the rated active power while outputting reactive current according to the fault ride-through requirements. When the per-unit value of the positive-sequence voltage at the grid-connected point of the inverter-type distributed generation is between [0.2, 0.719], the inverter-type distributed generation prioritizes outputting reactive current according to the fault ride-through requirements, and outputs active current with the remaining capacity.

[0113] Step 5: When the positive sequence voltage per unit value of the inverter type distributed power grid connection point is at the boundary voltage U k When is between and 0.9, the inverter-type distributed power supply uses the fault ride-through control equation A to calculate the current reference value of the inner current loop during the fault ride-through process.

[0114] The fault ride-through control equation A is specifically:

[0115] When the per-unit value of the positive sequence voltage at the grid-connected point of the inverter-type distributed power generation is between [0.719, 0.9], the inverter-type distributed power generation outputs the corresponding active current according to the active power requirement, and the remaining capacity outputs all reactive current. The reference values ​​of the inner current loop d-axis and q-axis currents are:

[0116]

[0117] Where: P ref is the active power reference value; is the positive sequence voltage of the inverter type distributed generation grid connection point; α is the per unit positive sequence voltage of the inverter type distributed generation grid connection point during the fault ride-through period.

[0118] When α∈(0.719,0.9), the inverter-type distributed power supply outputs reactive current i q The ratio λ to the positive sequence voltage drop value β at the grid connection point of the inverter type distributed power supply is:

[0119]

[0120] In the formula, the positive sequence voltage drop value of the inverter type distributed power grid connection point is β = 1-α. The relationship between λ and β is as follows: Figure 3 At this time, λ is always greater than 2, which meets the fault ride-through requirement of the inverter-type distributed power supply, that is, for every 1% drop in the positive sequence voltage at the grid connection point, at least 2% of reactive current must be provided.

[0121] Step 6: When the positive sequence voltage per unit value of the inverter type distributed power grid connection point is between 0.2 and the boundary voltage U k When , the inverter-type distributed power supply uses the fault ride-through control equation B to calculate the current reference value of the current inner loop during the fault ride-through process;

[0122] The fault ride-through control equation B is specifically:

[0123] When the per-unit value of the positive sequence voltage at the grid-connected point of the inverter-type distributed power generation is between [0.2, 0.719], the inverter-type distributed power generation outputs reactive current first according to the fault ride-through requirement, and outputs active current with the remaining capacity. The reference values ​​of the d-axis and q-axis currents in the current inner loop are:

[0124]

[0125] When α∈(0.25,0.719), the inverter-type distributed power supply outputs reactive current i q The ratio λ to the positive sequence voltage drop value β at the grid connection point of the inverter type distributed power supply is always 2, which meets the fault ride-through requirement of the inverter type distributed power supply, that is, at least 2% reactive current is provided for every 1% drop in the positive sequence voltage at the grid connection point.

[0126] The structure diagram of inverter-type distributed power supply connected to the distribution network is as follows: Figure 4 As shown in the figure, when the distribution network system parameters are determined, Figure 4 When a three-phase short circuit fault occurs at the fault point F, the proposed adaptive fault ride-through operation control method is applied to the inverter-type distributed power supply connected to the distribution network to obtain the implementation status of the proposed control strategy.

[0127] The present invention is built in PSCAD / EMTDC as follows Figure 4 The simulation model is shown. The simulation is set to occur at fault point F at 0.5 seconds, and the fault lasts for 1 second. To compare the output current, output active and reactive power, and positive sequence voltage of the grid-connected inverters of the inverter-type distributed generation, the traditional fault ride-through control strategy is used for the first 0.5 seconds, while the proposed adaptive fault ride-through control method is used for the last 0.5 seconds.

[0128] Figure 5The figure shows the output current of the inverter distributed power supply when a three-phase short circuit fault occurs at the fault point F. When the traditional fault ride-through operation control strategy is adopted, the output current of the inverter distributed power supply is only 1.13pu. When the proposed adaptive fault ride-through operation control method is adopted, the output current of the inverter distributed power supply reaches i max , the output capacity of the inverter-type distributed power grid-connected inverter is fully utilized and the protection sensitivity is improved.

[0129] Figure 6 Figure 2 shows the active power output of the inverter-type distributed generation (IDG) when a three-phase short-circuit fault occurs at fault point F. The active power output of the IGG when the proposed adaptive fault ride-through control method is the same as the active power output of the IGG when the traditional fault ride-through control strategy is used.

[0130] Figure 7 Figure 2 shows the reactive power output of the inverter-type distributed generation (IDG) when a three-phase short-circuit fault occurs at fault point F. The reactive power output of the IGG using the proposed adaptive fault ride-through control method is significantly greater than that of the traditional fault ride-through control strategy, thus better supporting the grid connection point voltage.

[0131] Figure 8 Figure 2 shows the positive-sequence voltage of the inverter distributed generation (DCG) during a three-phase short-circuit fault at fault point F. Compared with the traditional fault ride-through control strategy, the proposed adaptive fault ride-through control method effectively improves the positive-sequence voltage of the DCG during the fault.

[0132] Simulation verification shows that the present invention makes full use of the output capacity of the inverter-type distributed power supply grid-connected inverter. On the one hand, it can increase the fault current output by the inverter-type distributed power supply when a minor fault occurs in the system, thereby improving the protection sensitivity; on the other hand, it can improve the ability of the inverter-type distributed power supply to output reactive power, raise the voltage at the grid-connected point of the inverter-type distributed power supply, and enhance the fault ride-through capability of the inverter-type distributed power supply.

[0133] An embodiment of the present invention further provides an adaptive fault ride-through operation control device for an inverter-type distributed power supply, comprising:

[0134] Three-phase voltage sampling module, used to sample the three-phase voltage of the inverter-type distributed power grid connection point;

[0135] The positive sequence voltage acquisition module is used to separate the positive and negative sequence of the three-phase voltage of the inverter distributed power grid connection point to obtain the positive sequence voltage of the inverter distributed power grid connection point;

[0136] A voltage drop judgment module is used to judge the voltage drop of the inverter type distributed power supply grid connection point based on the positive sequence voltage of the inverter type distributed power supply grid connection point;

[0137] The operation control module is used to control the operation of the inverter distributed power supply according to the voltage drop of the inverter distributed power supply grid connection point, so that the inverter distributed power supply always outputs the maximum allowable output current during the fault ride-through period.

[0138] The positive sequence voltage acquisition module is specifically used to:

[0139] Taking phase A as the reference phase, the symmetrical component method is used to calculate the positive sequence voltage of the three-phase voltage at the grid connection point of the inverter-type distributed power supply. The calculation process is shown in the following formula:

[0140]

[0141] In the formula ,u a 、u b 、u c are the voltages of phase A, phase B, and phase C at the grid connection point of the inverter-type distributed power supply; u a0 、u a1 、u a2 They are the zero-sequence, positive-sequence and negative-sequence components of the A-phase voltage at the grid-connected point of the inverter-type distributed generation.

[0142] The operation control module is specifically used to: if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is higher than 0.9, the inverter distributed power supply continues to operate in grid connection according to the normal state control strategy; if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is lower than 0.2, the inverter distributed power supply is immediately cut off from the distribution network; if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is between 0.2 and 0.9, the inverter distributed power supply enters the fault ride-through state, and the control mode of the inverter distributed power supply is switched from the dual-loop control of power outer loop and current inner loop to the single-loop control of current inner loop.

[0143] Another embodiment of the present invention provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the above-mentioned inverter-type distributed power source adaptive fault ride-through operation control method is implemented.

[0144] Another embodiment of the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the above-mentioned inverter-type distributed power supply adaptive fault ride-through operation control method is implemented.

[0145] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0146] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0147] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0148] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. An adaptive fault ride-through control method for inverter-type distributed power supply, characterized in that: include: Collect the three-phase voltage of the inverter-type distributed power supply grid connection point; Separating the positive and negative sequence of the three-phase voltage at the grid-connected point of the inverter-type distributed power source to obtain the positive sequence voltage at the grid-connected point of the inverter-type distributed power source; Based on the positive sequence voltage of the inverter-type distributed power source grid connection point, judging the voltage drop condition of the inverter-type distributed power source grid connection point; Controlling the operation of the inverter-type distributed power source according to the judgment result, so that the inverter-type distributed power source always outputs the maximum allowable output current during the fault ride-through period; The inverter-type distributed power supply is controlled to operate according to the judgment result as follows: If the positive sequence voltage per unit value of the inverter-type distributed power grid connection point is higher than 0.9, the inverter-type distributed power source continues to be connected to the grid according to the normal state control strategy; If the positive sequence voltage per unit value of the inverter-type distributed generation grid connection point is lower than 0.2, the inverter-type distributed generation will be immediately cut off from the distribution network; If the per-unit value of the positive sequence voltage at the grid connection point of the inverter-type distributed power source is between 0.2 and 0.9, the inverter-type distributed power source enters the fault ride-through state, and the control mode of the inverter-type distributed power source is switched from the dual-loop control of the power outer loop and the current inner loop to the single-loop control of the current inner loop; The switching from the dual-loop control of the power outer loop and the current inner loop to the single-loop control of the current inner loop is specifically as follows: Disconnect the power outer loop, stop using the output value of the difference between the reference value and the measured value of active power after PI adjustment as the current reference value of the current inner loop, and directly give the current reference value of the current inner loop according to the inverter-type distributed power supply fault ride-through control equation; The current inner loop current reference value is directly given according to the inverter-type distributed power supply fault ride-through control equation, specifically: According to the fault ride-through requirements of the inverter-type distributed power supply and the current limit value of the grid-connected inverter, that is, the maximum allowable output current i of the grid-connected inverter max , calculate the boundary voltage U k ; The boundary voltage U k It is the voltage per unit value of the grid connection point when the output current of the inverter-type distributed power source reaches the maximum allowable output current; When the positive sequence voltage per unit value of the inverter type distributed generation grid connection point is [U k ,0.9], the inverter-type distributed power source outputs the corresponding active current according to the active power requirements, and the remaining capacity outputs all reactive current; the inverter-type distributed power source uses the fault ride-through control equation A to calculate the current reference value of the current inner loop during the fault ride-through process; When the positive sequence voltage per unit value of the inverter type distributed generation grid connection point is between [0.2, U k ], the inverter-type distributed power supply outputs reactive current first according to the fault ride-through requirement, and outputs active current with the remaining capacity; the inverter-type distributed power supply uses the fault ride-through control equation B to calculate the current reference value of the current inner loop during the fault ride-through process; The boundary voltage U k The specific calculation method is: After a short circuit occurs in the power grid, the output current of the inverter-type distributed power supply will increase, which is limited by the maximum allowable output current i of the grid-connected inverter. max , the output current of the inverter distributed power supply will not increase infinitely, and its constraint equation is: Where: i dref is the d-axis current reference value; i qref is the q-axis current reference value; i N is the rated current of the inverter of the inverter-type distributed power grid-connected inverter; m is a constant, and its value range is [1,2]; According to the fault ride-through requirements, the inverter-type distributed power supply provides at least 2% reactive current for every 1% drop in the positive sequence voltage at the grid-connected point; the output current of the inverter-type distributed power supply reaches the maximum allowable output current i of the grid-connected inverter by calculating formula (7): max The boundary voltage value: Where: P is the rated active power; U k is the boundary voltage; k is the reactive current compensation coefficient, and its value range is [2,6].

2. The method for controlling the adaptive fault ride-through operation of an inverter-type distributed power supply according to claim 1, characterized in that: The positive-sequence voltage of the inverter-type distributed power grid connection point is obtained by performing positive-sequence separation on the three-phase voltage of the inverter-type distributed power grid connection point: Taking phase A as the reference phase, the positive sequence voltage of the three-phase voltage of the inverter-type distributed power grid connection point is calculated using the symmetrical component method. The calculation process is shown in the following formula: Where α = e j120° ,u a 、u b 、u c are the A-phase, B-phase, and C-phase voltages of the inverter-type distributed power grid connection point; u a0 、u a1 、u a2 They are the zero-sequence, positive-sequence and negative-sequence components of the A-phase voltage at the grid-connected point of the inverter-type distributed generation.

3. The method for controlling the adaptive fault ride-through operation of an inverter-type distributed power supply according to claim 1, characterized in that: The power outer loop and current inner loop dual loop control are specifically as follows: The current inner loop adopts a vector control strategy based on the grid voltage oriented current closed loop in a synchronous rotating coordinate system; The power outer loop adopts PQ control, and the output value of the difference between the active power reference value and the active power measured value after PI adjustment is used as the reference value of the d-axis current of the current inner loop; the inverter-type distributed power supply outputs at unity power factor, and the reference value of the q-axis current of the current inner loop is set to 0; According to the instantaneous reactive power theory, the expressions of the active power P and reactive power Q of the system in the synchronous rotating coordinate system are: Where: e d 、e q is the dq component of the network side voltage of the grid-connected inverter; i d 、i q is the dq component of the AC side output current of the grid-connected inverter; When oriented based on grid voltage, it is oriented to the d-axis, i.e. e q =0, then formula (4) is simplified to 4. The method for controlling the adaptive fault ride-through operation of an inverter-type distributed power supply according to claim 3, characterized in that: The vector control strategy is to use Park transformation to transform the AC quantity in the stationary coordinate system into the DC quantity in the synchronous rotating coordinate system, and then use the typical PI controller design to achieve zero static error control of the AC current, as follows: According to Kirchhoff's law, in the three-phase stationary abc coordinate system, the voltage equation of the grid-connected inverter is: According to Park transformation, the grid-connected inverter voltage equation (2) in the three-phase stationary abc coordinate system is transformed into the grid-connected inverter voltage equation in the synchronous rotating coordinate system: Where: u d 、u q is the dq component of the AC side output voltage of the grid-connected inverter; e d 、e q is the dq component of the network side voltage of the grid-connected inverter; i d 、i q is the dq component of the AC side output current of the grid-connected inverter; L is the inductance of the grid-connected inverter filter; R is the output line resistance of the grid-connected inverter; ω is the grid angular frequency; The feedforward decoupling strategy is adopted to introduce feedforward quantity -ωLi into the output AC voltage of the grid-connected inverter. q +ωLi d , so that it is coupled with the coupling term +ωLi in equation (3) q and -ωLi d The decoupling between the d and q axes is achieved by cancelling each other out. The decoupled system is converted into two independent and completely equal parts, which are controlled separately.

5. The method for controlling the adaptive fault ride-through operation of an inverter-type distributed power supply according to claim 1, characterized in that: The fault ride-through control equation A is specifically: the current inner loop d-axis and q-axis current reference values ​​are: Where: P ref is the active power reference value; is the positive sequence voltage of the inverter type distributed generation grid connection point; α is the per unit value of the positive sequence voltage of the inverter type distributed generation grid connection point during the fault ride-through period; When α∈(U k ,0.9), the inverter-type distributed power supply outputs reactive current i q The ratio λ to the positive sequence voltage drop value β at the grid connection point of the inverter type distributed generation is: In the formula, the positive sequence voltage drop value of the inverter type distributed power supply grid connection point β = 1-α; at this time, λ is always greater than 2, which meets the fault ride-through requirements of the inverter type distributed power supply, that is, for every 1% drop in the positive sequence voltage at the grid connection point, at least 2% of reactive current is provided.

6. The method for controlling the adaptive fault ride-through operation of an inverter-type distributed power supply according to claim 1, characterized in that: The fault ride-through control equation B is specifically: the current inner loop d-axis and q-axis current reference values ​​are: When α∈(1-m / 2,U k ), the inverter-type distributed power supply outputs reactive current i q The ratio λ to the positive sequence voltage drop value β at the grid connection point of the inverter-type distributed power supply is always 2, which meets the fault ride-through requirement of the inverter-type distributed power supply, that is, at least 2% reactive current is provided for every 1% drop in the positive sequence voltage at the grid connection point.

7. An inverter-type distributed power adaptive fault ride-through operation control device using the inverter-type distributed power adaptive fault ride-through operation control method of claim 1, characterized in that: include: Three-phase voltage sampling module, used to sample the three-phase voltage of the inverter-type distributed power grid connection point; A positive-sequence voltage acquisition module is used to separate the positive and negative sequences of the collected three-phase voltage of the inverter-type distributed power source grid-connected point to obtain the positive-sequence voltage of the inverter-type distributed power source grid-connected point; A voltage drop judgment module, used to judge the voltage drop of the inverter-type distributed power supply grid connection point based on the positive sequence voltage of the inverter-type distributed power supply grid connection point; The operation control module is used to control the operation of the inverter-type distributed power supply according to the voltage drop of the inverter-type distributed power supply grid connection point, so that the inverter-type distributed power supply always outputs the maximum allowable output current during the fault ride-through period.

8. The adaptive fault ride-through operation control device for inverter-type distributed power supply according to claim 7, characterized in that: The positive sequence voltage acquisition module is specifically used for: Taking phase A as the reference phase, the positive sequence voltage of the three-phase voltage of the inverter-type distributed power grid connection point is calculated using the symmetrical component method. The calculation process is shown in the following formula: Where α = e j120° ,u a 、u b 、u c are the A-phase, B-phase, and C-phase voltages of the inverter-type distributed power grid connection point; u a0 、u a1 、u a2 They are the zero-sequence, positive-sequence and negative-sequence components of the A-phase voltage at the grid-connected point of the inverter-type distributed generation.

9. The inverter-type distributed power source adaptive fault ride-through operation control device according to claim 7, characterized in that: The operation control module is specifically used for: if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is higher than 0.9, the inverter distributed power supply continues to be grid-connected and operated according to the normal state control strategy; if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is lower than 0.2, the inverter distributed power supply is immediately cut off from the distribution network; if the positive sequence voltage per unit value of the inverter distributed power supply grid connection point is between 0.2 and 0.9, the inverter distributed power supply enters the fault ride-through state, and the control mode of the inverter distributed power supply is switched from the power outer loop and current inner loop dual-loop control to the current inner loop single-loop control.

10. An electronic device, characterized in that: The invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the adaptive fault ride-through operation control method of the inverter-type distributed power supply as described in any one of claims 1 to 6 is implemented.

11. A non-transitory computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the method for controlling the adaptive fault ride-through operation of an inverter-type distributed power supply as described in any one of claims 1 to 6 is implemented.

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