Method for controlling direct-current side voltage of network-forming type converter based on current amplitude limiting control

Abstract

The invention discloses a current amplitude limiting control-based DC side voltage control method for a network-constructed converter, and the method comprises the steps: firstly constructing a power function, a DC side dynamic function and a droop control function of the converter based on a simplified circuit model and a control strategy of the network-constructed converter, and building a large signal model; then, according to the influence of a control strategy of current amplitude limiting control on the output power, a power function is updated, and the large signal model is updated; and finally, according to a large signal model, analyzing the influence of a transient fault on the DC side voltage, in a droop control strategy, using DC voltage feedback control, amplifying a derivative of the square of the DC side voltage, and feeding back the derivative to an active power loop to control the converter. According to the invention, no extra circuit element is needed, the direct-current side voltage stability of the network construction converter during the fault period can be improved only by adding the feedback control containing the direct-current side voltage signal to the active ring, the working condition when the system is stable is not influenced, and the system stability is improved under the condition that the cost is not increased.

Description

Technical Field

[0001] This invention relates to a DC-side voltage control method for a grid-type converter based on current limiting control, belonging to the field of power electronics technology. Background Technology

[0002] With the advancement of the "dual-carbon" goal, an increasing number of new energy sources are being connected to the grid via voltage source converters. As power electronic devices, converters have no rotating parts and offer a very fast response. Traditional converters employ grid-connected control, a strategy based on phase-locked loops (PLLs). However, with the increasing scale of grid connection, this strategy cannot provide inertia support, posing many challenges to the stable operation of the system. To ensure the stable operation of the power system, grid-connected converters play a crucial role due to their frequency support and voltage regulation capabilities.

[0003] To ensure that power electronic devices are not damaged by overcurrent, current limiting control needs to be added to the converter's control loop. However, after adding limiting control, if the DC side operates in constant power input mode, the DC bus voltage cannot remain stable after a transient occurs. At this time, the DC side voltage change can be divided into two situations: overvoltage and undervoltage. Overvoltage may trigger overvoltage protection or damage the DC side capacitor, while undervoltage may cause overmodulation of the converter, affecting the inverter process. Therefore, maintaining a stable DC side voltage after a transient is crucial for maintaining system stability. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the prior art, the present invention provides a DC side voltage control method for grid-type converters based on current limiting control, which can improve system stability, alleviate DC side voltage instability during transients, and extend fault clearing time.

[0005] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0006] A method for controlling the DC-side voltage of a grid-connected converter based on current limiting control includes the following steps:

[0007] Step 1: Based on the simplified circuit model and control strategy of the grid-type converter, construct the power function, DC-side dynamic function and droop control function of the converter, and establish a large-signal model;

[0008] Step 2: Based on the impact of the current limiting control strategy on the output power, update the power function and the large-signal model;

[0009] Step 3: Analyze the impact of transient faults on DC-side voltage based on the large-signal model. In the droop control strategy, DC voltage feedback control is used. The derivative of the square of the DC-side voltage is amplified and fed back to the active power loop of the droop control to control the converter.

[0010] Traditional grid-type converters focus on AC side (frequency, reactive power) control, lacking coordinated control of DC side voltage under transient faults and current limiting conditions. This invention focuses on DC side control, deeply connecting "current limiting control → power function update → large-signal model → DC voltage feedback (square derivative feedback)", breaking through the traditional framework of separating protection and control. For the first time, the derivative of the square of the DC side voltage (reflecting the rate of change of capacitor energy) is fed back to the active power circuit, directly linking energy dynamics with power regulation. This can approach the problem of DC voltage drop and runaway under transient faults, overcoming the control blind spot of existing technologies under strong transient disturbance conditions.

[0011] Specifically, in step 1, based on the simplified circuit model and control strategy of the grid-type converter, the power function, DC-side dynamic function, and droop control function of the grid-type converter are constructed, and a large-signal model is established; including the following steps:

[0012] (11) Ignoring line resistance and considering only line inductance, establish a simplified circuit model of the converter output port-line-grid bus of the grid-type converter. Based on the simplified model, design the power function of the converter output port, including the output active power function and the output reactive power function:

[0013]

[0014] X g =ωL g

[0015] Where: P e and Q e These represent the output active power and output reactive power of the converter, respectively; ω and V are the angular frequency and voltage at the converter output port, respectively; E g Where L is the grid voltage, δ is the phase angle, and L is the phase angle. g X is the equivalent inductance of the transmission line. g For line inductance;

[0016] (12) Ignoring power losses of converter components, design the DC-side dynamic function based on the input and output power of the converter:

[0017]

[0018] Where: C dc For DC side capacitor, V dc P is the DC side voltage. dIt is the input active power on the DC side of the converter;

[0019] (13) Based on the droop control strategy, design the droop control function:

[0020]

[0021]

[0022] Where: P ref and Q ref These are the active power reference value and the reactive power reference value, respectively, ω p and ω q K represents the cutoff angular frequencies of the low-pass filters on the active and reactive branches, respectively. p and K q ω0 and V0 are the droop coefficients for the active and reactive branches, respectively, and the rated angular frequency and rated voltage are the rated angular frequency and rated voltage, respectively.

[0023] (14) Based on the power function, DC-side dynamic function, and droop control function, establish a large-signal model:

[0024]

[0025] When the system is in a steady state, the input active power P d Equal to the output active power P e Output active power P e Equal to the active power reference value P ref That is, P e =P d =P ref .

[0026] Due to the limitations of small-signal models, existing technologies mostly rely on qualitative descriptions of transient fault mechanisms. This invention innovatively designs a modeling method that uses a large-signal model to achieve quantitative analysis of transient processes (such as the mathematical laws governing phase angle changes and DC-side energy oscillations). This provides a precise mathematical basis for subsequent current-limiting control and voltage feedback strategies, upgrading control parameter design from experience-based debugging to model derivation, and significantly improving control accuracy.

[0027] Specifically, in step 2, based on the impact of the current limiting control strategy on the output power, the power function is optimized, and the large-signal model is optimized; this includes the following steps:

[0028] (21) Update the power function based on the impact of the current limiting control strategy on the output power:

[0029] P e =I max E g cosδ* =P sm cosδ *

[0030] Q e =I max E g sinδ * =P sm sinδ *

[0031] P sm =I max E g

[0032] (22) Update the large-signal model based on the updated power function:

[0033]

[0034] Among them: I max δ represents the maximum output current value of the converter under the current limiting control strategy. * The phase angle P under the current limiting control strategy. sm This represents the maximum output active power.

[0035] In existing technologies, current limiting and control are parallel and independent. This invention designs current limiting and control as a series coupled relationship, and adapts to fault conditions through model self-updating, which is a control-protection collaborative mechanism. This mechanism can solve the control oscillation problem caused by power calculation deviation during current limiting, improve the power regulation accuracy during faults, and avoid the problem of control instability after current limiting.

[0036] Specifically, in step 3, based on the large-signal model analysis of the impact of transient faults on the DC-side voltage, the droop control strategy uses DC voltage feedback control. The derivative of the square of the DC-side voltage is amplified and fed back to the active power loop of the droop control to control the converter. This includes the following steps:

[0037] (31) Analyze the fault type according to the following conditions:

[0038] Scenario ①: When a voltage drop occurs, but the fault current is less than or equal to I. max At that time, the output active power P e Less than the input active power P d Input active power P d A portion of the flow goes to the DC-side capacitor, and the charging of the DC-side capacitor causes the DC-side capacitor voltage to rise.

[0039] Scenario 2: When a voltage drop occurs and the fault current increases to the level that triggers current limiting control, but the system still has a balance point, the power angle curve changes, and the output active power P...e Increased demand leads to higher input active power P. d The DC-side capacitor remains unchanged, and the DC-side capacitor compensates for insufficient power. The discharge of the DC-side capacitor causes the DC-side capacitor voltage to drop.

[0040] Scenario 3: When a voltage drop occurs, the fault current increases to the level that triggers current limiting control, and the system has no equilibrium point, the output active power P e Less than the input active power P d Input active power P d The excess portion flows to the DC-side capacitor, causing the DC-side capacitor voltage to rise.

[0041] (32) Based on the analysis of the fault types, the above problems can be solved by adding DC voltage feedback control to the active power loop of the droop control. The derivative of the square of the DC side voltage is amplified and fed back to the active power loop to control the converter. The virtual power angle function at this time is designed as follows:

[0042]

[0043] Where: P s K is a virtual work angle function. pl V is the magnification factor. d This represents the d-axis component of the converter output port voltage.

[0044] The relationship between the converter output port voltage and the grid voltage can be expressed as:

[0045]

[0046] Where: V d and V q I represents the component of the converter output port voltage on the dq axis. oq and I od E represents the component of the converter output port current on the dq axis. d and E q Represents the components of the grid voltage on the dq axis:

[0047]

[0048] Because the converter's output current is controlled along the d-axis under current limiting control, I oq =0, then:

[0049] V d =E g cosδ *

[0050] Substituting the converter output port voltage and grid voltage into the virtual output active power function, the virtual power angle function under DC voltage feedback control is expressed as:

[0051]

[0052] In a traditional active power loop, the feedback parameter is only the converter's output active power P. e In this invention, by adding feedback control containing a DC-side voltage signal, the output active power P of the converter is controlled. e By performing control, indirect control of the DC-side voltage can be achieved;

[0053] (33) Due to the system equilibrium Therefore, the magnification factor K pl It doesn't work; it only applies during the period from the onset of the system failure to the restoration of balance. Amplification factor K pl This will change the feedback input of the active power loop; by changing the amplification factor K pl To change the maximum value of the virtual power angle:

[0054] After the transient, if the fault current is less than or equal to I max If the fault type is determined to be case ①, then the amplification factor K is not considered. pl Make adjustments;

[0055] After the transient, if the fault current is greater than I max If the derivative of the square of the DC-side voltage is negative, then the fault type is determined to be case ②, where the DC-side capacitor voltage drops. This can be corrected by increasing the amplification factor K. pl This speeds up the time it takes for the system to reach the equilibrium point and mitigates the drop in DC-side capacitor voltage.

[0056] After the transient, if the fault current is greater than I max If the derivative of the square of the DC-side voltage is positive, then the fault type is determined to be case ③, where the DC-side capacitor voltage rises. This can be mitigated by reducing the amplification factor K. pl Slow down the output active power P e The drop rate reduces the rise in DC-side capacitor voltage.

[0057] In existing technologies, DC-side voltage control often employs steady-state PI regulation (which only feeds back the voltage amplitude), resulting in a delayed response to transient energy surges (such as rapid charging and discharging of capacitors during a fault), leading to large voltage fluctuation overshoot and slow recovery. This invention targets the rate of energy change, upgrading from steady-state voltage balance to transient energy regulation, breaking through the physical limitations of traditional voltage feedback, and solving the problem of transient voltage runaway.

[0058] Beneficial Effects: The DC-side voltage control method for grid-type converters based on current limiting control provided by this invention has the following significant advantages compared to existing technologies: 1. By incorporating a control strategy of current limiting control, compared to grid-type converters that do not consider current limiting control, it can protect power electronic devices from damage due to overcurrent; 2. By adding DC voltage feedback control to the active power loop of droop control, it can alleviate the drop in DC-side capacitor voltage of the converter during transients; 3. By changing the amplification factor of voltage feedback control, it can alleviate the problem of DC-side capacitor voltage rise of the converter when the system has no balance point after a transient, and extend the fault clearing time; 4. It requires no additional circuit components, is easy to modify, has low cost, and is easy to promote. Attached Figure Description

[0059] Figure 1 A simplified circuit model of converter output port-line-grid bus for grid-type converters;

[0060] Figure 2 Vector relationship between converter output port voltage and grid voltage for triggering current limiting control;

[0061] Figure 3 The power angle curve is shown when current limiting control is not triggered under a grid voltage dip fault.

[0062] Figure 4 The power angle curve for triggering current limiting control under grid voltage dip faults, where the system has a balance point;

[0063] Figure 5 The power angle curve for triggering current limiting control under grid voltage dip faults, but where the system has no equilibrium point;

[0064] Figure 6 This is a schematic diagram of DC voltage feedback control;

[0065] Figure 7 The virtual power angle curves under different amplification factors under DC-side voltage feedback;

[0066] Figure 8 Simulated waveforms of converter output active power and DC side capacitor voltage changes under current limiting control triggered by grid voltage dip fault and with the system having a balance point.

[0067] Figure 9 Simulated waveform of converter output current under current limiting control triggered by grid voltage drop fault and with system equilibrium point.

[0068] Figure 10 Simulated waveforms of converter output power and DC side voltage changes under current limiting control triggered by grid voltage dip fault but without system equilibrium point;

[0069] Figure 11 Simulated waveform of converter output current under current limiting control triggered by grid voltage drop fault but without system balance point. Detailed Implementation

[0070] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0071] like Figure 1 The diagram shows a simplified circuit model of a grid-type converter, including the converter output port, line, and grid bus. It comprises a constant power supply, a three-phase half-bridge converter (composed of power electronic switching devices), and a low-pass output LC filter (including a filter inductor L). f and filter capacitor C f ), current limiting control, and droop control with filtering (including active and reactive loops, i.e.) Figure 1 The system incorporates Pf control and QV control, along with dual closed-loop voltage and current control. The DC side receives the input active power P from a constant power supply. d The power is inverted into AC power by a three-phase half-bridge converter, and then filtered out for high-frequency harmonics by a low-pass output LC filter before being transmitted through the transmission line (including the equivalent inductance L). g and equivalent resistance R g ) Provides output active power P to the power grid e and output reactive power Q e Ultimately, this achieves DC-AC energy conversion and grid connection.

[0072] based on Figure 1 The DC-side voltage control of the grid-type converter based on current limiting control is explained in detail below with specific implementation steps.

[0073] Step 1, establish as follows Figure 1 The simplified circuit model and control strategy of the grid converter are shown, and the power function, DC-side dynamic function and droop control function of the grid converter are obtained. A large-signal model is also established.

[0074] Step 1.1: Ignore the line resistance and only consider the line inductance. According to... Figure 1 A simplified circuit model of a grid-type converter is presented, along with the design of its output active power function and output reactive power function.

[0075]

[0076] X g =ωL g

[0077] In the simplified circuit model, P e and Q eThese represent the output active power and output reactive power of the converter, respectively; ω and V are the angular frequency and voltage at the converter output port, respectively; L f and C f These are the filter inductor and filter capacitor, respectively, L g and R g These represent the equivalent inductance and equivalent resistance of the transmission line, respectively; ω and V are the angular frequency and voltage (equal to the point of common coupling voltage) at the converter output port; E g X is the grid voltage, δ is the phase angle; g For line inductance.

[0078] Step 1.2: Ignoring power losses of converter components, design the DC-side dynamic function based on the input and output power of the converter:

[0079]

[0080] Where: C dc For DC side capacitor, V dc P is the DC side voltage. d It is the input active power on the DC side of the converter.

[0081] Step 1.3: Based on the droop control strategy, design the droop control function:

[0082]

[0083] Where: P ref and Q ref These are the active power reference value and the reactive power reference value, respectively, ω p and ω q K represents the cutoff angular frequencies of the low-pass filters on the active and reactive branches, respectively. p and K q ω0 and V0 are the droop coefficients for the active and reactive branches, respectively, and the rated angular frequency and rated voltage, respectively.

[0084] Considering that the rated angular frequency ω0 is usually used as a reference value for the power grid frequency, we have:

[0085]

[0086] Step 1.4: Establish the large-signal model based on the power function, DC-side dynamic function, and droop control function:

[0087]

[0088] When the system is in a steady state, the input active power P d Equal to the output active power P e Output active power P e Equal to the active power reference value Pref That is, P e =P d =P ref .

[0089] Step 2: Based on the impact of the current limiting control strategy on the output power, update the power function and the large-signal model.

[0090] Step 2.1, as follows Figure 2 The figure shows the grid voltage E under the current limiting control strategy. g The vector relationship between the power supply and the converter output port voltage V is used to update the power function:

[0091] P e =I max E g cosδ * =P sm cosδ *

[0092] Q e =I max E g sinδ * =P sm sinδ *

[0093] P sm =I max E g

[0094] Among them: I max δ represents the maximum output current value of the converter under the current limiting control strategy. * The phase angle is under the current limiting control strategy.

[0095] Step 2.2: Update the large-signal model based on the updated power function:

[0096]

[0097] Where: P sm This represents the maximum output active power.

[0098] Step 3: Analyze the impact of transient faults on DC-side voltage based on the large-signal model. In the droop control strategy, DC voltage feedback control is used to amplify the derivative of the square of the DC-side voltage and feed it back to the active power circuit to control the converter.

[0099] Step 3.1: When the system is in a steady state, the output active power P e Equal to the input active power P d That is, P e =P dThe input active power P d If the current remains constant, according to the DC-side dynamic function, the DC-side capacitor voltage remains unchanged, and there is no energy exchange between the capacitors. When a system fault occurs, the maximum value of the power angle curve decreases, and the output active power P... e Not equal to the input active power P d That is, P e ≠P d The input active power P d To maintain the DC-side dynamic function, the energy stored in the DC-side capacitor participates in the exchange, causing some power to flow out or into the DC-side capacitor, resulting in voltage instability. Whether current limiting control is triggered after a fault and whether there is a balance point determine the direction of power flow in the DC-side capacitor. Fault type analysis is performed according to the following conditions:

[0100] Case ①: such as Figure 3 As shown, when the voltage drop is not significant and current limiting control is not triggered, the fault current is less than or equal to I. max Output active power P e Less than the input active power P d That is, P e <P d At this time, the input active power P d A portion of the flow goes to the DC-side capacitor, and the charging of the DC-side capacitor causes the DC-side capacitor voltage to rise.

[0101] Case ②: such as Figure 4 As shown, when the voltage drop deepens and the fault current becomes excessive, triggering current limiting control but the system still has a balance point, the power angle curve changes, and the output active power P... e Increased demand leads to higher input active power P. d Unchanged, i.e., P e >P d Input active power P d Insufficient to provide output active power P e Therefore, the DC-side capacitor makes up for the insufficient power, and the discharge of the capacitor causes the DC-side capacitor voltage to drop.

[0102] Situation ③: such as Figure 5 As shown, when the voltage drop continues to increase, triggering current limiting control and the system has no equilibrium point, the output active power P... e Less than the input active power P d That is, P e <P d Input active power P d The excess portion flows to the DC-side capacitor, increasing the voltage of the DC-side capacitor.

[0103] Step 3.2: Based on the analysis of the fault types, in the droop control strategy, [the following will be implemented / implemented]: Figure 1 The active power ring has been improved to Figure 6 The DC voltage feedback control shown amplifies the derivative of the square of the DC side voltage and feeds it back to the active power circuit to control the converter. The virtual power angle function is designed as follows:

[0104]

[0105] Where: P s K is a virtual work angle function. pl V is the magnification factor. d This represents the d-axis component of the converter output port voltage.

[0106] The relationship between the converter output port voltage and the grid voltage can be expressed as:

[0107]

[0108] Where: V d and V q I represents the component of the converter output port voltage on the dq axis. oq and I od E represents the component of the converter output port current on the dq axis. d and E q Represents the components of the grid voltage on the dq axis:

[0109]

[0110] Because the converter's output current is controlled along the d-axis under current limiting control, I oq =0, then:

[0111] V d =E g cosδ *

[0112] Substituting the converter output port voltage and grid voltage into the virtual output active power function, the virtual power angle function under DC voltage feedback control is expressed as:

[0113]

[0114] Step 3.3: By changing the magnification factor K pl The maximum value of the virtual power angle was changed, and experimental verification was conducted.

[0115] Since situation ① usually occurs before situation ②, the voltage drop in the grid is not significant, and the output active power P eThe voltage quickly returns to a stable value, so the DC-side capacitor voltage does not change significantly. Therefore, this invention mainly studies DC voltage feedback control under conditions ② and ③. For condition ②, the control system can accelerate the arrival at the equilibrium point, thereby reducing the discharge time of the DC-side capacitor and mitigating the voltage drop. Since there is no equilibrium point in condition ③, the output active power P... e The output active power P has been decreasing, so the control system can be used to slow down the output active power P. e The decrease in power output reduces the active power P in the same amount of time. e With input active power P d The difference reduces the charging power of the DC-side capacitor, ultimately alleviating the rise in DC-side capacitor voltage, and also slows down the output active power P. e The rate of decline is reduced, thus correspondingly extending the fault clearing time.

[0116] To verify the superiority of this solution, simulation analysis was performed in MATLAB / Simulink. The system parameters are shown in Table 1. The fault occurred at 0.7s and was cleared at 2s. Figure 7 As shown, when the magnification factor K is changed pl At that time, the virtual power angle P can be changed. s The maximum value.

[0117] The derivative of the square of the DC side voltage, after being amplified by the factor K pl After magnification, add Figure 1 The active power loop (Pf control) in the middle has the following control effect: Figure 7 As shown, K pl =0 represents a virtual power angle curve without added control.

[0118] When the system has an equilibrium point after the transient state, such as Figure 7 As shown in (a), by increasing the magnification factor K pl The value can increase the virtual work angle P s The maximum value, the output active power P of the converter. e The DC-side capacitor voltage and output current variation curves are shown below. Figure 8 and Figure 9 As shown, the voltage drop phenomenon of the DC-side capacitor is significantly alleviated, and the output current of the converter is more stable.

[0119] When the system has no equilibrium point after the transient state, such as Figure 7 As shown in (b), by reducing the amplification factor K pl Virtual power angle P can be increased s The maximum value, according to the droop control function, is the virtual power angle P. s With active power reference value P ref As the difference decreases, the rate of change of the angular frequency ω slows down, which in turn slows down the output active power P.e The drop rate, the output active power P of the converter e The DC-side capacitor voltage and output current variation curves are shown below. Figure 10 and Figure 11 As shown, the rise in DC-side capacitor voltage in the system is significantly alleviated. Under the same fault clearing time, the power curve without improved control becomes unstable, thus the fault clearing time is significantly extended, and the output current of the converter becomes more stable.

[0120] Table 1 System Parameters

[0121] parameter numerical values <![CDATA[Rated voltage V0]]> 100V <![CDATA[DC side voltage V dc > 460V <![CDATA[Active power reference value P ref > 1kW <![CDATA[Input active power P d > 1kW <![CDATA[Rated frequency f0]]> 50Hz <![CDATA[DC side capacitor C dc > 3mF

[0122] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for controlling the DC-side voltage of a grid-type converter based on current limiting control, characterized in that: Includes the following steps: Step 1: Based on the simplified circuit model and control strategy of the grid-type converter, construct the power function, DC-side dynamic function and droop control function of the converter, and establish a large-signal model; Step 2: Based on the impact of the current limiting control strategy on the output power, update the power function and the large-signal model; Step 3: Analyze the impact of transient faults on DC-side voltage based on the large-signal model. In the droop control strategy, DC voltage feedback control is used. The derivative of the square of the DC-side voltage is amplified and fed back to the active power loop of the droop control to control the converter.

2. The DC-side voltage control method for a grid-type converter based on current limiting control according to claim 1, characterized in that: In step 1, based on the simplified circuit model and control strategy of the grid-type converter, the power function, DC-side dynamic function, and droop control function of the grid-type converter are constructed, and a large-signal model is established; including the following steps: (11) Establish a simplified circuit model of the converter output port-line-grid bus of the grid-type converter, and design the power function of the converter output port based on the simplified model, including the output active power function and the output reactive power function: X g =ωL g Where: P e and Q e These represent the output active power and output reactive power of the converter, respectively; ω and V are the angular frequency and voltage at the converter output port, respectively; E g Where L is the grid voltage, δ is the phase angle, and L is the phase angle. g X is the equivalent inductance of the transmission line. g For line inductance; (12) Design the DC-side dynamic function based on the input and output power of the converter: Where: C dc For DC side capacitor, V dc P is the DC side voltage. d It is the input active power on the DC side of the converter; (13) Based on the droop control strategy, design the droop control function: Where: P ref and Q ref These are the active power reference value and the reactive power reference value, respectively, ω p and ω q K represents the cutoff angular frequencies of the low-pass filters on the active and reactive branches, respectively. p and K q ω0 and V0 are the droop coefficients for the active and reactive branches, respectively, and the rated angular frequency and rated voltage are the rated angular frequency and rated voltage, respectively. (14) Based on the power function, DC-side dynamic function, and droop control function, establish a large-signal model: When the system is in a steady state, the input active power P d Equal to the output active power P e Output active power P e Equal to the active power reference value P ref That is, P e =P d =P ref .

3. The DC-side voltage control method for a grid-type converter based on current limiting control according to claim 1, characterized in that: In step 2, based on the impact of the current limiting control strategy on the output power, the power function is optimized, and the large-signal model is optimized; this includes the following steps: (21) Update the power function based on the impact of the current limiting control strategy on the output power: P e =I max And g cosδ * =P sm cosδ * Q e =I max E g sinδ * =P sm sinδ * P sm =I max E g (22) Update the large-signal model based on the updated power function: Among them: I max δ represents the maximum output current value of the converter under the current limiting control strategy. * The phase angle P under the current limiting control strategy. sm This represents the maximum output active power.

4. The DC-side voltage control method for a grid-type converter based on current limiting control according to claim 1, characterized in that: In step 3, the impact of transient faults on the DC-side voltage is analyzed based on the large-signal model. In the droop control strategy, DC voltage feedback control is used. The derivative of the square of the DC-side voltage is amplified and fed back to the active power loop of the droop control to control the converter. This includes the following steps: (31) Analyze the fault type according to the following conditions: Scenario ①: When a voltage drop occurs, but the fault current is less than or equal to I. max At that time, the output active power P e Less than the input active power P d Input active power P d A portion of the flow goes to the DC-side capacitor, and the charging of the DC-side capacitor causes the DC-side capacitor voltage to rise. Scenario 2: When a voltage drop occurs and the fault current increases to the level that triggers current limiting control, but the system still has a balance point, the power angle curve changes, and the output active power P... e Increased demand leads to higher input active power P. d The DC-side capacitor remains unchanged, and the DC-side capacitor compensates for insufficient power. The discharge of the DC-side capacitor causes the DC-side capacitor voltage to drop. Scenario 3: When a voltage drop occurs, the fault current increases to the level that triggers current limiting control, and the system has no equilibrium point, the output active power P e Less than the input active power P d Input active power P d The excess portion flows to the DC-side capacitor, causing the DC-side capacitor voltage to rise. (32) Add DC voltage feedback control to the active power loop of the droop control, and amplify the derivative of the square of the DC side voltage and feed it back to the active power loop to control the converter. The virtual power angle function at this time is designed as follows: Where: P s K is a virtual work angle function. pl V is the magnification factor. d This represents the d-axis component of the converter output port voltage; The relationship between the converter output port voltage and the grid voltage can be expressed as: Where: V d and V q I represents the component of the converter output port voltage on the dq axis. oq and I od E represents the component of the converter output port current on the dq axis. d and E q Represents the components of the grid voltage on the dq axis: Because the converter's output current is controlled along the d-axis under current limiting control, I oq =0, then: V d =And g cosδ * Substituting the converter output port voltage and grid voltage into the virtual output active power function, the virtual power angle function under DC voltage feedback control is expressed as: (33) By changing the magnification factor K pl To change the maximum value of the virtual power angle: After the transient, if the fault current is less than or equal to I max If the fault type is determined to be case ①, then the amplification factor K is not considered. pl Make adjustments; After the transient, if the fault current is greater than I max If the derivative of the square of the DC-side voltage is negative, then the fault type is determined to be case ②, where the DC-side capacitor voltage drops. This can be corrected by increasing the amplification factor K. pl This speeds up the time it takes for the system to reach the equilibrium point and mitigates the drop in DC-side capacitor voltage. After the transient, if the fault current is greater than I max If the derivative of the square of the DC-side voltage is positive, then the fault type is determined to be case ③, where the DC-side capacitor voltage rises. This can be mitigated by reducing the amplification factor K. pl Slow down the output active power P e The drop rate reduces the rise in DC-side capacitor voltage.

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