A grid-forming converter control method and system for suppressing switching oscillations

Abstract

The application discloses a grid-connected converter control method and system for inhibiting switching oscillation, comprising: acquiring the internal potential phase angle and the port voltage phase angle of a grid-connected system of a grid-connected converter considering virtual impedance, and determining the system power angle based on the internal potential phase angle and the port voltage phase angle; wherein the grid-connected converter considering virtual inductance sets virtual inductance between the output voltage and the port voltage; calculating the first output current in the normal mode and the second current instruction value output by the voltage loop in the current limiting mode based on the system power angle; acquiring the power angle corresponding to the current limiting of the first output current in the normal mode; determining the system power angle threshold value based on the power angle corresponding to the current limiting of the first output current in the normal mode; and determining the control strategy of the current limiter based on the system power angle, the system power angle threshold value and the second current instruction value, so as to inhibit the switching oscillation of the grid-connected system of the grid-connected converter based on the control strategy.

Description

Technical Field

[0001] This invention relates to the field of grid-type converter technology, and more specifically, to a grid-type converter control method and system for suppressing switching oscillations. Background Technology

[0002] With the rapid development of new energy sources, power electronic converters (GFM-VSCs), as key devices connecting new energy sources and the power grid, have been deployed on a large scale in power systems. Among various types of power electronic converters, grid-connected converters (GFM-VSCs) have emerged as a prominent player due to their autonomous voltage generation capabilities. GFM-VSCs can simulate the operating characteristics of synchronous generators, thus providing reliable voltage and frequency support in power systems and demonstrating broad engineering application prospects. However, when the system experiences large disturbances, the relatively constant internal potential of the GFM-VSC, which maintains voltage source characteristics, makes it prone to fault overcurrent. Fault overcurrent will cause overheating of the internal components, potentially leading to device damage. Therefore, additional current limiting strategies are indispensable for GFM-VSCs.

[0003] Current limiters are a common current limiting method. By adding a current reference value saturation module, they can ensure accurate current limiting of the converter under fault scenarios. Currently, the mainstream types of current limiters include: ring current limiters, angle-priority current limiters, d-axis priority current limiters, and axis-priority current limiters. Among them, angle-priority current limiters, with their ability to flexibly adjust the current angle according to control requirements, provide the system with a wider range of control adjustment space. However, when a system uses an angle-priority current limiter, it may experience switching oscillations during the fault recovery phase. These oscillations will cause the output current of the GFM-VSC to contain a large number of harmonics, which will adversely affect the power quality of the system.

[0004] Therefore, a control method for grid-type converters that suppresses switching oscillations is needed. Summary of the Invention

[0005] This invention proposes a control method and system for grid-type converters to suppress switching oscillations, in order to solve the problem of how to suppress switching oscillations in grid-type converters.

[0006] To address the aforementioned problems, according to one aspect of the present invention, a method for controlling a grid-type converter to suppress switching oscillations is provided, the method comprising:

[0007] The internal potential phase angle and port voltage phase angle of the grid-connected system of the grid-connected converter taking into account virtual impedance are obtained, and the system power angle is determined based on the internal potential phase angle and port voltage phase angle; wherein, the grid-connected converter taking into account virtual inductive reactance sets virtual inductive reactance between the output voltage and the port voltage.

[0008] Based on the system power angle, calculate the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode;

[0009] Obtain the power angle corresponding to the first output current reaching the current limit in normal mode;

[0010] The system power angle threshold value is determined based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit.

[0011] The control strategy of the current limiter is determined based on the system power angle, the system power angle threshold value, and the second current command value, so as to suppress the switching oscillation of the grid-connected system of the grid-connected converter.

[0012] Preferably, determining the system power angle based on the internal potential phase angle and the port voltage phase angle includes:

[0013] δ p =θ-θ p ,

[0014] Where, δ p θ is the system power angle; θ is the output voltage phase angle; θ p This represents the phase angle of the port voltage.

[0015] Preferably, the calculation of the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode based on the system power angle includes:

[0016] ,

[0017] ,

[0018] Among them, I r (δ p () represents the first output current; E represents the converter output voltage; The port voltage is represented by j; j represents a complex number; δ p The system's power angle; X V For virtual sensory impedance; I ref (δ p ) represents the second current command value; I max φ is the current limiting value; φ is the current angle. This is the proportional gain of the voltage controller.

[0019] Preferably, the determination of the system power angle threshold value based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit includes:

[0020] δ th =0.9δ I ,

[0021] Where, δth δ is the system power angle threshold value; I This is the power angle corresponding to the first output current reaching the current limit in normal mode.

[0022] Preferably, the control strategy for determining the current limiter based on the system power angle, the system power angle threshold value, and the second current command value includes:

[0023] ,

[0024] ,

[0025] Among them, I dref1 This is the d-axis current reference value output by the current limiter; I qref1 This is the q-axis current reference value output by the current limiter; I dref This refers to the d-axis component of the second current command value output by the voltage loop in current-limiting mode; I qref This refers to the q-axis component of the second current command value output by the voltage loop in current-limiting mode; I ref This is the reference value for the output current; I max For current limiting; θ i For current angle; I t δ is the variable current limiting value; p The system power angle; δ th I is the system power angle threshold value; s I is the converter output current. n This is the rated current.

[0026] According to another aspect of the present invention, a grid-type converter control system for suppressing switching oscillations is provided, the system comprising:

[0027] The system power angle determination unit is used to obtain the internal potential phase angle and port voltage phase angle of the grid-connected system of the grid-connected converter taking into account virtual impedance, and to determine the system power angle based on the internal potential phase angle and port voltage phase angle; wherein, the grid-connected converter taking into account virtual inductive reactance sets virtual inductive reactance between the output voltage and the port voltage.

[0028] The output current determination unit is used to calculate the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode based on the system power angle.

[0029] The power angle calculation unit is used to obtain the power angle corresponding to the first output current reaching the current limit in normal mode.

[0030] The system power angle threshold value determination unit is used to determine the system power angle threshold value based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit.

[0031] The control unit is used to determine the control strategy of the current limiter based on the system power angle, the system power angle threshold value, and the second current command value, so as to suppress the switching oscillation of the grid-connected system of the grid-connected converter based on the control strategy.

[0032] Preferably, the system power angle determination unit determines the system power angle based on the internal potential phase angle and the port voltage phase angle, including:

[0033] δ p =θ-θ p ,

[0034] Where, δ p θ is the system power angle; θ is the output voltage phase angle; θ p This represents the phase angle of the port voltage.

[0035] Preferably, the output current determining unit calculates the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode based on the system power angle, including:

[0036] ,

[0037] ,

[0038] Among them, I r (δ p () represents the first output current; E represents the converter output voltage; The port voltage is represented by j; j represents a complex number; δ p The system's power angle; X V For virtual sensory impedance; I ref (δ p ) represents the second current command value; I max φ is the current limiting value; φ is the current angle. This is the proportional gain of the voltage controller.

[0039] Preferably, the power angle calculation unit, wherein the system power angle threshold determination unit determines the system power angle threshold value based on the power angle corresponding to when the first output current in normal mode reaches the current limit, including:

[0040] δ th =0.9δ I ,

[0041] Where, δ th δ is the system power angle threshold value; I This is the power angle corresponding to the first output current reaching the current limit in normal mode.

[0042] Preferably, the control unit determines the control strategy of the current limiter based on the system power angle, the system power angle threshold value, and the second current command value, including:

[0043] ,

[0044] ,

[0045] Among them, I dref1 This is the d-axis current reference value output by the current limiter; I qref1 This is the q-axis current reference value output by the current limiter; I dref This refers to the d-axis component of the second current command value output by the voltage loop in current-limiting mode; I qref This refers to the q-axis component of the second current command value output by the voltage loop in current-limiting mode; I ref This is the reference value for the output current; I max For current limiting; θ i For current angle; I t δ is the variable current limiting value; p The system power angle; δ th I is the system power angle threshold value; s I is the converter output current. n This is the rated current.

[0046] According to another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the methods for controlling a grid-type converter to suppress switching oscillations.

[0047] According to another aspect of the present invention, the present invention provides an electronic device, comprising:

[0048] The aforementioned computer-readable storage medium; and

[0049] One or more processors for executing a program in the computer-readable storage medium.

[0050] This invention provides a control method and system for a grid-connected converter to suppress switching oscillations, comprising: acquiring the internal potential phase angle and port voltage phase angle of the grid-connected converter system considering virtual impedance, and determining the system power angle based on the internal potential phase angle and port voltage phase angle; wherein, the grid-connected converter considering virtual inductive reactance sets a virtual inductive reactance between the output voltage and the port voltage; calculating a first output current in normal mode and a second current command value of the voltage loop output in current-limiting mode based on the system power angle; acquiring the power angle corresponding to when the first output current in normal mode reaches the current limit; determining a system power angle threshold value based on the power angle corresponding to when the first output current in normal mode reaches the current limit; and determining a control strategy for a current limiter based on the system power angle, the system power angle threshold value, and the second current command value, so as to suppress switching oscillations of the grid-connected converter system based on the control strategy. This invention optimizes the traditional current limiter and adaptively adjusts the current limiting trigger condition according to the power angle change, effectively suppressing switching oscillations while ensuring output current safety. It can further guarantee the output current safety of grid-type devices and the power quality of the system, and also further ensure the safe and reliable operation of power systems with a high proportion of power electronic equipment and a high proportion of new energy. Attached Figure Description

[0051] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0052] Figure 1 A flowchart of a grid-type converter control method 100 for suppressing switching oscillations according to an embodiment of the present invention;

[0053] Figure 2 This is a schematic diagram of the GFM-VSC grid-connected system structure according to an embodiment of the present invention;

[0054] Figure 3 This is a diagram of the GFM-VSC control structure according to an embodiment of the present invention;

[0055] Figure 4 The equivalent circuit diagram of the GFM-VSC grid-connected system according to an embodiment of the present invention is shown below.

[0056] Figure 5 This is the GFM-VSC switching oscillation principle according to an embodiment of the present invention;

[0057] Figure 6 The equivalent circuit diagram of the GFM-VSC grid-connected system considering virtual impedance according to an embodiment of the present invention is shown below.

[0058] Figure 7 This is a schematic diagram illustrating the operating principle of the rate limiting strategy proposed according to an embodiment of the present invention.

[0059] Figure 8The waveform diagram is a simulation diagram of the conventional strategy according to an embodiment of the present invention;

[0060] Figure 9 The simulation waveform diagram is shown for the proposed strategy according to an embodiment of the present invention.

[0061] Figure 10 This is a schematic diagram of the structure of a grid-type converter control system 1000 for suppressing switching oscillations according to an embodiment of the present invention. Detailed Implementation

[0062] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0063] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0064] Figure 1 This is a flowchart of a grid-type converter control method 100 for suppressing switching oscillations according to an embodiment of the present invention. Figure 1 As shown, the grid-connected converter control method for suppressing switching oscillations provided by the embodiments of the present invention effectively suppresses switching oscillations by optimizing the traditional current limiter and adaptively adjusting the current limiting trigger condition according to the power angle change, while ensuring the safety of the output current. This further guarantees the output current safety of the grid-connected device and the power quality of the system, and also further ensures the safe and reliable operation of power systems containing a high proportion of power electronic equipment and a high proportion of new energy sources. The grid-connected converter control method 100 for suppressing switching oscillations provided by the embodiments of the present invention starts from step 101. In step 101, the internal potential phase angle and port voltage phase angle of the grid-connected converter system considering virtual impedance are obtained, and the system power angle is determined based on the internal potential phase angle and port voltage phase angle; wherein, the grid-connected converter considering virtual inductive reactance sets a virtual inductive reactance between the output voltage and the port voltage.

[0065] Preferably, determining the system power angle based on the internal potential phase angle and the port voltage phase angle includes:

[0066] δ p =θ-θ p ,

[0067] Where, δ p θ is the system power angle; θ is the output voltage phase angle; θ p This represents the phase angle of the port voltage.

[0068] In step 102, the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode are calculated based on the system power angle.

[0069] Preferably, the calculation of the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode based on the system power angle includes:

[0070] ,

[0071] ,

[0072] Among them, I r (δ p () represents the first output current; E represents the converter output voltage; The port voltage is represented by j; j represents a complex number; δ p The system's power angle; X V For virtual sensory impedance; I ref (δ p ) represents the second current command value; I max φ is the current limiting value; φ is the current angle. This is the proportional gain of the voltage controller.

[0073] In step 103, the power angle corresponding to the first output current reaching the current limit in normal mode is obtained.

[0074] In step 104, the system power angle threshold value is determined based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit.

[0075] Preferably, the determination of the system power angle threshold value based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit includes:

[0076] δ th =0.9δ I ,

[0077] Where, δ th δ is the system power angle threshold value; I This is the power angle corresponding to the first output current reaching the current limit in normal mode.

[0078] In step 105, a control strategy for the current limiter is determined based on the system power angle, the system power angle threshold value, and the second current command value, so as to suppress the switching oscillation of the grid-connected system of the grid-connected converter based on the control strategy.

[0079] Preferably, the control strategy for determining the current limiter based on the system power angle, the system power angle threshold value, and the second current command value includes:

[0080] ,

[0081] ,

[0082] Among them, I dref1 This is the d-axis current reference value output by the current limiter; I qref1 This is the q-axis current reference value output by the current limiter; I dref This refers to the d-axis component of the second current command value output by the voltage loop in current-limiting mode; I qref This refers to the q-axis component of the second current command value output by the voltage loop in current-limiting mode; I ref This is the reference value for the output current; I max For current limiting; θ i For current angle; I t δ is the variable current limiting value; p The system power angle; δ th I is the system power angle threshold value; s I is the converter output current. n This is the rated current.

[0083] The grid-connected topology of GFM-VSC based on current limiter is as follows: Figure 2 As shown, U dc For DC voltage, L f and C f These are the filter inductor and filter capacitor for the GFM-VSC, respectively; Z g Indicates line impedance; I f I s and U pcc These represent the output current, line current, and output voltage of the GFM-VSC, respectively. The control mechanism mainly includes virtual synchronous machine (VSG) control and voltage-current dual closed-loop control, with the specific control structure as follows: Figure 3 As shown.

[0084] Figure 3 (a) illustrates the VSG control structure, which includes active-frequency control and reactive-voltage control to generate the output voltage reference vector E=E∠θ. The active-frequency control simulates the rotor motion characteristics of a synchronous machine, and its expression is as follows:

[0085] ,

[0086] In the formula, J is the virtual inertia; D p P is the damping coefficient;ref ω0 and ω are the active power reference values; ω0 and ω are the rated angular frequency and virtual angular frequency of the GFM-VSC, respectively.

[0087] Reactive power-voltage control encompasses various control modes such as constant voltage control, constant reactive power control, and QV droop control. The control structures can be interchanged. To simplify the analysis, this invention adopts a constant voltage control structure.

[0088] Figure 3 (b) shows the voltage and current inner loop control structure, which is designed to quickly track given values ​​of voltage and current. Figure 3 In (b), E dref and E qref It is the dq-axis component of the converter voltage reference value; U d and U q It is the dq-axis component of the output voltage; U md and U mq It is the dq-axis component of the modulation voltage; I dref and I qref It is the dq-axis component of the voltage loop output current command; I dref1 and I qref1 It is the dq-axis component of the limiter output current reference value; I fd and I fq It is the dq-axis component of the output current; I sd and I sq This is the dq-axis component of the line current. To address fault overcurrent issues, a current limiter is embedded between the voltage loop and the current loop. This is achieved by adjusting the d-axis reference value I of the voltage loop output current. dref and q-axis reference value I qref To limit the output current of the GFM-VSC, the current limiter output can be expressed as:

[0089] ,

[0090] In the formula, I max It is the maximum current limit value, and φ is the current angle, the value of which can be set by the user.

[0091] When the GFM-VSC is operating normally, it behaves as an equivalent voltage source, and its equivalent circuit diagram is as follows: Figure 4 As shown in (a). Where X and R are the line reactance and line resistance, respectively. Assuming X >> R, the active power expression for the GFM-VSC output is:

[0092] ,

[0093] In the formula, δ is the power angle of the GFM-VSC, and its expression is δ=θ-θ g .

[0094] In traditional strategies, when the GFM-VSC is in current-limiting operation mode, it behaves as an equivalent current source, such as... Figure 4 As shown in (b). The expression for the active power output of the GFM-VSC in current-limiting mode is:

[0095] .

[0096] The conditions for GFM-VSC to enter and exit rate limiting mode are as follows:

[0097] ,

[0098] In the formula, I f (δ) represents the first output current in normal mode; I ref (δ) is the second current command value output by the voltage loop in current-limiting mode, and its expression is:

[0099] ,

[0100] ,

[0101] Based on the above formula, plot I on the I-δ plane. f (δ) and I ref The (δ) curve is used to explain the generation process of switching oscillations in GFM-VSC during the fault recovery phase, such as... Figure 5 As shown. The running trajectory of GFM-VSC during the entire fault process is abcdefa. Define δ I Output current I in normal mode f (δ) reaches the current limit I max The corresponding work angle, δ II For voltage loop output current command I ref (δ) reaches the current limit I max The corresponding work angle. According to δ I and δ II The size relationship can be divided into the following two working conditions:

[0102] (1) δ I ≥δ II

[0103] Under this specific operating condition, the GFM-VSC will not experience switching oscillations, such as Figure 5 As shown in (a). Initially, the GFM-VSC operates at the stable equilibrium point a. When a fault occurs, the system operating point shifts from point a to point b, entering current-limiting mode. During the fault, the system power angle increases, and the operating point shifts from point b to point c. The fault is cleared at point c, at which point I... ref >I maxUnder these conditions, the system remains in current-limiting mode. Due to system inertia, the power angle continues to increase, and the operating point shifts from point c to point d. At point d, the system frequency synchronizes with the grid frequency, and the power angle reaches its maximum value δ. max Subsequently, the GFM-VSC decelerates, its power angle decreases, and its operating point shifts from point d to point e. At point e, I satisfies... ref =I max And I f max Under the condition of equation (6), the system immediately exits the current limiting mode, the operating point moves from point e to point f, and finally stabilizes at the equilibrium point a.

[0104] (2) δ I <δ II

[0105] Under this specific operating condition, GFM-VSC may experience switching oscillations, such as... Figure 5 As shown in (b). When the system clears the fault at point c, I occurs. ref max And I f >I max In the case of GFM-VSC simultaneously satisfying the conditions for entering and exiting the current limiting mode, the system will switch between normal mode and current limiting mode, thus generating oscillation. o The system switching oscillation interval is defined as S. o =[δ I ,δ II As the system's operating point travels along the path cde, it remains in a switching oscillation state until it reaches point e, at which point I satisfies... ref max And I f =I max Under certain conditions, the system will leave the oscillation range and exit the current limiting mode, eventually stabilizing at the equilibrium point a.

[0106] In summary, whether a GFM-VSC generates switching oscillations depends on δ. I and δ II The size relationship, if δ I ≥δ II If δ is true, then GFM-VSC will not produce switching oscillations; conversely, if δ is false, then GFM-VSC will not produce switching oscillations. I <δ II If δ falls within the oscillation range, then the GFM-VSC will exhibit switching oscillations.

[0107] Therefore, this invention proposes an improved current limiting method based on switching oscillation suppression.

[0108] ​​​In practical applications, the phase and amplitude of grid voltage are difficult to measure, making it difficult to directly calculate the system power angle using grid voltage as a reference. Given the proposed strategy's need for power angle information, this invention introduces virtual inductive reactance to calculate the system power angle using the GFM-VSC port voltage as a reference. The phase of the port voltage is accurately obtained using a phase-locked loop (PLL). Furthermore, the virtual inductive reactance not only obtains power angle information but also serves a power decoupling function.

[0109] Specifically, in this invention, after introducing virtual inductive reactance, the reference value vector of the output voltage becomes:

[0110] ,

[0111] In the formula, θ f =θ s +π / 2, θ s This represents the phase of the output current.

[0112] Furthermore, the equivalent circuit of the GFM-VSC grid-connected system under the action of virtual impedance is obtained, such as... Figure 6 As shown. Where X v The virtual inductive reactance is represented by the port voltage vector U. pcc ∠θ p Then, taking into account the virtual impedance, the GFM-VSC power angle δ p =θ-θ p Where θ is the output voltage phase angle; θ p This represents the phase angle of the port voltage.

[0113] The first output current I in normal mode f (δ p This can be represented as:

[0114] ,

[0115] Because of C f If the capacitance value is small and the effect of capacitor current is ignored, then the second current command I output by the voltage loop in current-limiting mode... ref (δ p This can be represented as:

[0116] .

[0117] Based on the above current, plot I on the I-δ plane. f (δ) and I ref (δ) curve, and based on δ I <δ II The operating conditions determine the system switching oscillation range [δ] I δ II Then, based on the minimum value δ of the system switching oscillation interval...I Determine the system power angle threshold value δ th =0.9δ I Then, based on the system power angle, the system power angle threshold value, and the second current command value, a control strategy for the current limiter is determined to suppress the switching oscillation of the grid-connected converter system.

[0118] The specific expression of the improved current limiter of this invention is as follows:

[0119] ,

[0120] In the formula, I t This is the variable current limit value, and its specific expression is as follows:

[0121] ,

[0122] In the formula, I dref1 This is the d-axis current reference value output by the current limiter; I qref1 This is the q-axis current reference value output by the current limiter; I dref This refers to the d-axis component of the second current command value output by the voltage loop in current-limiting mode; I qref This refers to the q-axis component of the second current command value output by the voltage loop in current-limiting mode; I ref This is the reference value for the output current; I max For current limiting; θ i For current angle; I t δ is the variable current limiting value; p The system power angle; δ th I is the system power angle threshold value; s I is the converter output current. n This is the rated current. Ideally, δ can be set to... th =δ I However, considering the sampling error and the dynamic influence of the current, we take δ. th =0.9δ I .

[0123] The following can be determined from the first current and second current command values:

[0124] When I s ≤I n At this time, GFM-VSC is in the normal operation phase, and at this time I t =I max ;

[0125] When I s >I n And δ p ≤δ th At that time, the GFM-VSC was in a fault phase, and the system had no risk of switching oscillation.t Keep as I max .

[0126] When I s >I n And δ p >δ th At this time, the GFM-VSC is in a fault phase and the system is at risk of switching oscillation. t =0.

[0127] The operating principle of the improved limiter is as follows: Figure 7 As shown. After the fault is cleared, during the movement of the system operating point along trajectory cde, due to I ref >I t The system remains in rate-limited mode. At operating point e, there is δ p =δ th I t Switch to I max At this time, I ref t And I f max The system switches from current-limiting mode to normal operation mode. After a series of dynamic processes, it eventually stabilizes at equilibrium point a. In summary, by adaptively adjusting I during the fault phase... t This avoids the occurrence of switching oscillation and also limits the output current of the GFM within a safe range.

[0128] The grid-type converter control method for suppressing switching oscillations proposed in this invention optimizes the traditional current limiter and adaptively adjusts the current limiting trigger condition according to the power angle change, thereby suppressing switching oscillations while ensuring the safety of the output current.

[0129] To verify the effectiveness of the proposed control method, based on Figure 2 The system structure was simulated, and the fault conditions were set as follows: a metallic ground fault occurred on the grid side at t=2s and was cleared at t=2.15s, with a current angle φ=1rad. Figure 8 and Figure 9 Simulation results are presented for both traditional and improved limiters. Figure 8 It can be seen that after the fault is cleared, due to the power angle δ p Crossing δ I The GFM-VSC exhibited switching oscillations. When δ p Less than δ I At this time, the system switches to normal operation. Figure 9 It can be seen that after the fault is cleared, due to I t In δ p >δ th When it is 0, it causes I ref >I​​t Therefore, GFM-VSC remains in rate-limiting mode, when δ p Less than δ th Subsequently, the system switched to normal operation. In summary, the simulation verified that the improved current limiter can effectively avoid the switching oscillation phenomenon of GFM-VSC.

[0130] Figure 10 This is a schematic diagram of the structure of a grid-type converter control system 1000 for suppressing switching oscillations according to an embodiment of the present invention. Figure 10 As shown, the grid-type converter control system 1000 for suppressing switching oscillations provided in this embodiment of the invention includes: a system power angle determination unit 1001, an output current determination unit 1002, a power angle calculation unit 1003, a system power angle threshold value determination unit 1004, and a control unit 1005.

[0131] Preferably, the system power angle determination unit 1001 is used to obtain the internal potential phase angle and port voltage phase angle of the grid-connected system of the grid-connected converter taking into account virtual impedance, and to determine the system power angle based on the internal potential phase angle and port voltage phase angle; wherein, the grid-connected converter taking into account virtual inductive reactance sets virtual inductive reactance between the output voltage and the port voltage.

[0132] Preferably, the system power angle determination unit 1001 determines the system power angle based on the internal potential phase angle and the port voltage phase angle, including:

[0133] δ p =θ-θ p ,

[0134] Where, δ p θ is the system power angle; θ is the output voltage phase angle; θ p This represents the phase angle of the port voltage.

[0135] Preferably, the output current determination unit 1002 is used to calculate the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode based on the system power angle.

[0136] Preferably, the output current determining unit 1002 calculates the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode based on the system power angle, including:

[0137] ,

[0138] ,

[0139] Among them, I r (δ p () represents the first output current; E represents the converter output voltage; The port voltage is represented by j; j represents a complex number; δ p The system's power angle; X V For virtual sensory impedance; I ref (δ p ) represents the second current command value; I max φ is the current limiting value; φ is the current angle. This is the proportional gain of the voltage controller.

[0140] Preferably, the power angle calculation unit 1003 is used to obtain the power angle corresponding to the first output current reaching the current limit in normal mode.

[0141] Preferably, the system power angle calculation unit 1004 is used to determine the system power angle threshold value based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit.

[0142] Preferably, the system power angle threshold determination unit 1004 determines the system power angle threshold value based on the power angle corresponding to when the first output current in normal mode reaches the current limit, including:

[0143] δ th =0.9δ I ,

[0144] Where, δ th δ is the system power angle threshold value; I This is the power angle corresponding to the first output current reaching the current limit in normal mode.

[0145] Preferably, the control unit 1005 is used to determine the control strategy of the current limiter based on the system power angle, the system power angle threshold value, and the second current command value, so as to suppress the switching oscillation of the grid-connected system of the grid-connected converter based on the control strategy.

[0146] Preferably, the control unit 1005 determines the control strategy of the current limiter based on the system power angle, the system power angle threshold value, and the second current command value, including:

[0147] ,

[0148] ,

[0149] Among them, I dref1 This is the d-axis current reference value output by the current limiter; I qref1 This is the q-axis current reference value output by the current limiter; I dref This refers to the d-axis component of the second current command value output by the voltage loop in current-limiting mode; I qref This refers to the q-axis component of the second current command value output by the voltage loop in current-limiting mode; Iref This is the reference value for the output current; I max For current limiting; θ i For current angle; I t δ is the variable current limiting value; p The system power angle; δ th I is the system power angle threshold value; s I is the converter output current. n This is the rated current.

[0150] The grid-type converter control system 1000 for suppressing switching oscillations in an embodiment of the present invention corresponds to the grid-type converter control method 100 for suppressing switching oscillations in another embodiment of the present invention, and will not be described again here.

[0151] According to another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the methods for controlling a grid-type converter to suppress switching oscillations.

[0152] According to another aspect of the present invention, the present invention provides an electronic device, comprising:

[0153] The aforementioned computer-readable storage medium; and

[0154] One or more processors for executing a program in the computer-readable storage medium.

[0155] The present invention has been described with reference to a few embodiments. However, it will be apparent to those skilled in the art that other embodiments besides those disclosed above fall equivalently within the scope of the present invention.

[0156] Generally, all terms used in this invention are interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed unless explicitly stated otherwise.

[0157] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0158] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations 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, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0159] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0160] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0161] 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, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A control method for a grid-type converter to suppress switching oscillations, characterized in that, The method includes: The internal potential phase angle and port voltage phase angle of the grid-connected system of the grid-connected converter taking into account virtual impedance are obtained, and the system power angle is determined based on the internal potential phase angle and port voltage phase angle; wherein, the grid-connected converter taking into account virtual inductive reactance sets virtual inductive reactance between the output voltage and the port voltage. The system power angle is used to calculate the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode; wherein, the grid-type converter outputs the first output current; Obtain the power angle corresponding to the first output current reaching the current limit in normal mode; The system power angle threshold value is determined based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit. Among them, the control link of the grid-connected system of the grid-type converter includes: virtual synchronous machine control and voltage-current dual closed-loop control, with the current limiter embedded between the voltage loop and the current loop. The control strategy of the current limiter is determined based on the system power angle, the system power angle threshold value, and the second current command value, so as to suppress the switching oscillation of the grid-connected system of the grid-connected converter.

2. The method according to claim 1, characterized in that, Determining the system power angle based on the internal potential phase angle and the port voltage phase angle includes: δ p = θ - θ p ， in, δ p The system power angle; θ The phase angle of the output voltage; θ p This represents the phase angle of the port voltage.

3. The method according to claim 1, characterized in that, Based on the system power angle calculation, the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode are calculated, including: ， ， in, I f ( δ p ) represents the first output current; E represents the converter output voltage; U pcc The port voltage is represented by j; j represents a complex number. δ p The system's power angle; X V For virtual sensory resistance; I ref ( δ p () represents the second current command value; I max This is the current limiting value; For current angle; This is the proportional gain of the voltage controller.

4. The method according to claim 1, characterized in that, The system power angle threshold value is determined based on the power angle corresponding to when the first output current in normal mode reaches the current limit, including: δ th =0.9 δ I ， in, δ th This is the system power angle threshold value; δ I This is the power angle corresponding to the first output current reaching the current limit in normal mode.

5. The method according to claim 1, characterized in that, The control strategy for the current limiter is determined based on the system power angle, the system power angle threshold value, and the second current command value output by the voltage loop, including: ， ， in, I dref1 For the output of the current limiter d Shaft current reference value; I qref1 For the output of the current limiter q Shaft current reference value; I dref This refers to the d-axis component of the second current command value output by the voltage loop in current-limiting mode. I qref This refers to the q-axis component of the second current command value output by the voltage loop in current-limiting mode. I ref This is the reference value for the output current. I max Current limiting; θ i For current angle; I t This is the variable current limit value; δ p The system power angle; δ th This is the system power angle threshold value; I s For the converter output current; I n This is the rated current.

6. A grid-type converter control system for suppressing switching oscillations, characterized in that, The system includes: The system power angle determination unit is used to obtain the internal potential phase angle and port voltage phase angle of the grid-connected system of the grid-connected converter taking into account virtual impedance, and to determine the system power angle based on the internal potential phase angle and port voltage phase angle; wherein, the grid-connected converter taking into account virtual inductive reactance sets virtual inductive reactance between the output voltage and the port voltage. An output current determination unit is used to calculate the first output current in normal mode and the second current command value of the voltage loop output in current-limiting mode based on the system power angle; wherein, the grid-type converter outputs the first output current; The power angle calculation unit is used to obtain the power angle corresponding to the first output current reaching the current limit in normal mode. The system power angle threshold determination unit is used to determine the system power angle threshold value based on the power angle corresponding to the current limit when the first output current in normal mode reaches the current limit. Among them, the control link of the grid-connected system of the grid-type converter includes: virtual synchronous machine control and voltage-current dual closed-loop control, and the current limiter is embedded between the voltage loop and the current loop. The control unit is used to determine the control strategy of the current limiter based on the system power angle, the system power angle threshold value, and the second current command value, so as to suppress the switching oscillation of the grid-connected system of the grid-connected converter based on the control strategy.

7. The system according to claim 6, characterized in that, The system power angle determination unit determines the system power angle based on the internal potential phase angle and the port voltage phase angle, including: δ p = θ - θ p ， in, δ p The system power angle; θ The phase angle of the output voltage; θ p This represents the phase angle of the port voltage.

8. The system according to claim 6, characterized in that, The output current determination unit calculates the first output current in normal mode and the second current command value output by the voltage loop in current-limiting mode based on the system power angle, including: ， ， in, I f ( δ p ) represents the first output current; E represents the converter output voltage; U pcc The port voltage is represented by j; j represents a complex number. δ p The system's power angle; X V For virtual sensory resistance; I ref ( δ p () represents the second current command value; I max This is the current limiting value; For current angle; This is the proportional gain of the voltage controller.

9. The system according to claim 6, characterized in that, The system power angle threshold determination unit determines the system power angle threshold value based on the power angle corresponding to when the first output current in normal mode reaches the current limit, including: δ th =0.9 δ I ， in, δ th This is the system power angle threshold value; δ I This is the power angle corresponding to the first output current reaching the current limit in normal mode.

10. The system according to claim 6, characterized in that, The control unit determines the control strategy for the current limiter based on the system power angle, the system power angle threshold value, and the second current command value, including: ， ， in, I dref1 For the output of the current limiter d Shaft current reference value; I qref1 For the output of the current limiter q Shaft current reference value; I dref This refers to the d-axis component of the second current command value output by the voltage loop in current-limiting mode. I qref This refers to the q-axis component of the second current command value output by the voltage loop in current-limiting mode. I ref This is the reference value for the output current. I max Current limiting; θ i For current angle; I t This is the variable current limit value; δ p The system power angle; δ th This is the system power angle threshold value; I s For the converter output current; I n This is the rated current.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the method as described in any one of claims 1-5.

12. An electronic device, characterized in that, include: The computer-readable storage medium as described in claim 11; as well as One or more processors for executing a program in the computer-readable storage medium.

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