Method for controlling an interconnected converter and interconnected converter

Abstract

The embodiment of the present application discloses a control method of interconnected converter, interconnected converter is connected with AC subnetwork and DC subnetwork respectively, comprising: obtaining real-time AC frequency of AC subnetwork, real-time DC voltage of DC subnetwork and active power transmission of interconnected converter; calculating AC frequency variation of AC subnetwork, calculating DC voltage variation of DC subnetwork; calculating initial AC frequency when active power transmission of interconnected converter, calculating initial DC voltage when active power transmission of interconnected converter; calculating initial AC frequency when active power transmission of interconnected converter according to real-time AC frequency and AC frequency variation, calculating initial DC voltage when active power transmission of interconnected converter according to real-time DC voltage and DC voltage variation; obtaining initial balance condition of AC subnetwork according to initial AC frequency, obtaining initial balance condition of DC subnetwork according to initial DC voltage. The embodiment of the present application also discloses a kind of interconnected converter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of AC / DC hybrid micro-grid, and particularly relates to a control method of an interconnection converter and the interconnection converter. BACKGROUND

[0002] The AC / DC hybrid micro-grid is composed of an AC sub-grid, a DC sub-grid and an interconnection converter, wherein the interconnection converter connects the AC sub-grid and the DC sub-grid and undertakes the role of power transmission between the AC sub-grid and the DC sub-grid. When the AC / DC hybrid micro-grid is in operation away from the power grid, the power must be transmitted through the interconnection converter to maintain the stable operation of the AC / DC hybrid micro-grid. The current interconnection converter control generally adopts normalized droop control, and the central idea of this control strategy is to maintain the equal power of the AC sub-grid and the DC sub-grid through the power transmission of the interconnection converter. However, this method cannot distinguish the initial power balance status of the AC sub-grid and the DC sub-grid, and the power transmitted by the interconnection converter is always half of the power difference between the AC sub-grid and the DC sub-grid, which leads to unnecessary power transmission and increases the operation loss of the AC / DC hybrid micro-grid. SUMMARY

[0003] Therefore, it is necessary to propose a control method of an interconnection converter and the interconnection converter in view of the above problems.

[0004] The control method of the interconnection converter, the interconnection converter being connected with an AC sub-grid and a DC sub-grid respectively, comprises the following steps.

[0005] Obtaining the real-time AC frequency of the AC sub-grid, the real-time DC voltage of the DC sub-grid and the active power when the interconnection converter transmits power;

[0006] Calculating the AC frequency variation of the AC sub-grid according to the active power and the droop coefficient of the AC sub-grid, and calculating the DC voltage variation of the DC sub-grid according to the active power and the droop coefficient of the DC sub-grid;

[0007] Calculating the initial AC frequency when the interconnection converter does not transmit power according to the real-time AC frequency and the AC frequency variation, and calculating the initial DC voltage when the interconnection converter does not transmit power according to the real-time DC voltage and the DC voltage variation;

[0008] Obtaining the initial balance status of the AC sub-grid according to the initial AC frequency, and obtaining the initial balance status of the DC sub-grid according to the initial DC voltage; and

[0009] Determining the control mode according to the initial balance status of the AC sub-grid and the initial balance status of the DC sub-grid, the control mode being used to control the interconnection converter.

[0010] Optionally, the initial balance condition of the AC sub-network is obtained according to the initial AC frequency, and the initial balance condition of the DC sub-network is obtained according to the initial DC voltage, and specifically comprising:

[0011] The initial AC frequency is normalized to obtain a normalized value of the initial AC frequency, and the initial DC voltage is normalized to obtain a normalized value of the initial DC voltage; and,

[0012] The initial balance condition of the AC sub-network is obtained according to the normalized value of the initial AC frequency, and the initial balance condition of the DC sub-network is obtained according to the normalized value of the initial DC voltage.

[0013] Optionally, the control mode includes mode one, mode two and mode three, wherein the mode one is to adjust the normalized value of the real-time AC frequency and the normalized value of the real-time DC voltage to be consistent, the mode two is to adjust the normalized value of the real-time DC voltage to be 0, and the mode three is to adjust the normalized value of the real-time AC frequency to be 0.

[0014] Optionally, according to the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network, the control mode is determined, and specifically comprising:

[0015] It is judged whether the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network satisfy a preset condition;

[0016] When the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network satisfy the preset condition, the control mode is determined as mode one;

[0017] When the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network do not satisfy the preset condition, it is judged whether the absolute value of the normalized value of the initial AC frequency is greater than the absolute value of the normalized value of the initial DC voltage;

[0018] When the absolute value of the normalized value of the initial AC frequency is greater than the absolute value of the normalized value of the initial DC voltage, the control mode is determined as mode two; or,

[0019] When the absolute value of the normalized value of the initial power of the AC sub-network is less than the absolute value of the normalized value of the initial power of the DC sub-network, the control mode is determined as mode three.

[0020] Optionally, it is judged whether the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network satisfy a preset condition, and specifically comprising:

[0021] It is judged whether the normalized value of the initial AC frequency and the normalized value of the initial DC voltage are of the same sign.

[0022] Optionally, the AC frequency variation of the AC sub-network is calculated according to the active power and the droop coefficient of the AC sub-network, and the DC voltage variation of the DC sub-network is calculated according to the active power and the droop coefficient of the DC sub-network, and specifically calculated by using the following formula:

[0023]

[0024] wherein, Δf is the AC frequency variation of the AC subnetwork, m ac is the droop coefficient of the AC subnetwork, P ic is the active power transmitted by the interconnection converter, ΔV dc is the DC voltage variation of the DC subnetwork, m dc is the droop coefficient of the DC subnetwork.

[0025] Optionally, the initial AC frequency when the interconnection converter has no power transmission is calculated according to the real-time AC frequency and the AC frequency variation, and the initial DC voltage when the interconnection converter has no power transmission is calculated according to the real-time DC voltage and the DC voltage variation, specifically by using the following formulas:

[0026]

[0027] wherein, f' is the initial AC frequency, f is the real-time AC frequency, V d ' c is the initial DC voltage, V dc is the real-time DC voltage.

[0028] Optionally, the initial AC frequency is normalized to obtain the normalized value of the initial AC frequency, and the initial DC voltage is normalized to obtain the normalized value of the initial DC voltage, specifically by using the following formulas:

[0029]

[0030] wherein, f pu is the normalized value of the initial AC frequency, f max is the maximum value of the preset AC frequency, f min is the minimum value of the preset AC frequency, V dc，pu is the normalized value of the initial DC voltage, V dc，max is the maximum value of the preset DC voltage, V dc，min is the minimum value of the preset DC voltage.

[0031] Optionally, the initial balance condition of the AC subnetwork is obtained according to the initial AC frequency, and the initial balance condition of the DC subnetwork is obtained according to the initial DC voltage, specifically including:

[0032] the initial power of the AC subnetwork is obtained according to the initial AC frequency, and the initial power of the DC subnetwork is obtained according to the initial DC voltage; and

[0033] the initial balance condition of the AC subnetwork is obtained according to the initial power of the AC subnetwork, and the initial balance condition of the DC subnetwork is obtained according to the initial power of the DC subnetwork.

[0034] An interconnection converter is connected with an AC sub-network and a DC sub-network respectively, and is used to implement the method.

[0035] The method further analyzes the balance condition of the initial power of the AC sub-network and the DC sub-network by calculating the variation of the AC frequency and the variation of the DC voltage in the AC / DC hybrid micro-grid, and selects the optimal mode as the criterion, so as to optimize the power transmission mode of the interconnection converter, improve the operation efficiency of the AC / DC hybrid micro-grid system, and enhance the frequency stability of the AC sub-network. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0037] Among them:

[0038] Figure 1 The flow chart of the control method of the interconnection converter provided by the embodiment of the present application;

[0039] Figure 2 The first sub-flow chart of the control method of the interconnection converter provided by the embodiment of the present application;

[0040] Figure 3 The second sub-flow chart of the control method of the interconnection converter provided by the embodiment of the present application;

[0041] Figure 4 The internal structure schematic diagram of the AC / DC hybrid micro-grid provided by the embodiment of the present application;

[0042] Figure 5 The active power waveform diagram of the interconnection converter in different states provided by the embodiment of the present application;

[0043] Figure 6 The active power waveform diagram of the interconnection converter in different states in the prior art;

[0044] Figure 7 The power change schematic diagram of the interconnection converter in light load state and heavy load state provided by the embodiment of the present application;

[0045] Figure 8 The third sub-flow chart of the control method of the interconnection converter provided by the embodiment of the present application. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0047] Please refer to Figure 1 which is a flowchart of the control method of the interconnected converter provided by the embodiments of the present application. Please refer to Figure 4 The interconnected converter 920 is connected with the AC subnetwork 930 and the DC subnetwork 910 respectively. The control method of the interconnected converter provided by the embodiments of the present application specifically comprises the following steps.

[0048] In step S101, the real-time AC frequency of the AC subnetwork, the real-time DC voltage of the DC subnetwork and the active power when the interconnected converter transmits the active power are acquired. When the active power of the AC subnetwork and the DC subnetwork deviates from the rated power, the AC frequency and the DC voltage deviate from the rated values, and therefore the AC frequency and the DC voltage represent the power balance status of the AC subnetwork and the power balance status of the DC subnetwork respectively. Specifically, the real-time AC frequency of the AC subnetwork can be measured by using a phase-locked loop, the real-time DC voltage of the DC subnetwork can be measured by using a voltmeter, and the active power when the interconnected converter transmits the active power can be measured by using a power meter. The way of acquiring the real-time AC frequency, the real-time DC voltage and the active power when the interconnected converter transmits the active power is only an example and is not limited.

[0049] In step S102, the AC frequency variation of the AC subnetwork is calculated according to the active power and the droop coefficient of the AC subnetwork, and the DC voltage variation of the DC subnetwork is calculated according to the active power and the droop coefficient of the DC subnetwork. The AC frequency variation of the AC subnetwork is calculated according to the active power and the droop coefficient of the AC subnetwork, and the DC voltage variation of the DC subnetwork is calculated according to the active power and the droop coefficient of the DC subnetwork. Specifically, the following formula (1) is used for calculation.

[0050]

[0051] Wherein, Δf is the AC frequency variation of the AC subnetwork, P ic is the active power transmitted by the interconnected converter, m dc is the droop coefficient of the DC subnetwork.

[0052] In step S103, the initial AC frequency when the interconnected converter does not transmit the active power is calculated according to the real-time AC frequency and the AC frequency variation, and the initial DC voltage when the interconnected converter does not transmit the active power is calculated according to the real-time DC voltage and the DC voltage variation. Specifically, the following formula (2) is used for calculation.

[0053]

[0054] wherein f' is the initial AC frequency, f is the real-time AC frequency, V d c is the initial DC voltage, V dc is the real-time DC voltage.

[0055] In step S104, the initial balance condition of the AC sub-network is obtained according to the initial AC frequency, and the initial balance condition of the DC sub-network is obtained according to the initial DC voltage. For details, refer to steps S1041-S1043, or steps S1042-S1044.

[0056] In step S105, the control mode is determined according to the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network, and the control mode is used to control the interconnection converter. Specifically, the control mode includes mode one, mode two and mode three, wherein mode one is to adjust the per-unit value of the real-time AC frequency and the per-unit value of the real-time DC voltage to be consistent, mode two is to adjust the per-unit value of the real-time DC voltage to be 0, and mode three is to adjust the per-unit value of the real-time AC frequency to be 0.

[0057] In the above embodiment, the local information is collected by the interconnection converter, the change amount of the DC voltage and the change amount of the AC frequency are accurately calculated, the initial power balance condition of the AC / DC hybrid micro-grid is judged, the optimal operation mode is selected, the power transmission mode of the interconnection converter is optimized, unnecessary power transmission loss is reduced, and thus the operation efficiency of the AC / DC hybrid micro-grid system is improved.

[0058] Please refer to Figure 2 which is a sub-step flowchart of step S104 provided by the embodiment of the present application. In step S104, the initial balance condition of the AC sub-network is obtained according to the initial AC frequency, and the initial balance condition of the DC sub-network is obtained according to the initial DC voltage. The specific steps are as follows:

[0059] In step S1041, the initial AC frequency is normalized to obtain the per-unit value of the initial AC frequency, and the initial DC voltage is normalized to obtain the per-unit value of the initial DC voltage. Specifically, the following formula (3) is used for calculation:

[0060]

[0061] wherein f pu is the per-unit value of the initial AC frequency, f' is the initial AC frequency, f max is the preset maximum value of the AC frequency, f min is the preset minimum value of the AC frequency, V dc，pu is the per-unit value of the initial DC voltage, V d c is the initial DC voltage, V dc，max ​​V is the maximum value of the preset DC voltage dc，min V is the minimum value of the preset DC voltage. f pu and V dc，pu are controlled between -1 and 1, thereby reducing the calculation power and improving the operation efficiency of the embodiment.

[0062] In step S1043, the initial balance condition of the AC subnetwork is obtained according to the dimensionless value of the initial AC frequency, and the initial balance condition of the DC subnetwork is obtained according to the dimensionless value of the initial DC voltage.

[0063] In the actual application, the dimensionless droop control is realized, and the AC frequency dimensionless value and the DC voltage dimensionless value are equal through the control link of the interconnected converter, so that the active power of the AC subnetwork and the DC subnetwork is equal. However, when the interconnected converter starts to transmit the active power, the changes of the AC frequency and the DC voltage will be affected not only by the internal power balance conditions of the AC and DC subnetworks, but also by the active power transmitted by the interconnected converter. At this time, the dimensionless values of the AC frequency and the DC voltage can no longer accurately reflect the actual power balance conditions of the AC and DC subnetworks, that is, the initial power balance conditions when the interconnected converter does not transmit the active power. The control strategy of the embodiment considers the initial power balance conditions of the AC subnetwork and the DC subnetwork, thereby reducing unnecessary power transmission.

[0064] Please refer to Figure 3 which is a sub-step flowchart of step S105 provided by the embodiment of the application. In step S105, the control mode is determined according to the initial balance condition of the AC subnetwork and the initial balance condition of the DC subnetwork, specifically including:

[0065] In step S1051, it is judged whether the initial balance condition of the AC subnetwork and the initial balance condition of the DC subnetwork satisfy the preset condition. Further, it is judged whether the dimensionless value of the initial AC frequency and the dimensionless value of the initial DC voltage are of the same sign. Specifically, when the product of f pu and V pu,dc is negative, it indicates that one of the AC subnetwork and the DC subnetwork is running in a light load state, and the other is running in a heavy load state, as shown in Figure 7 .

[0066] In step S1052, when the initial balance condition of the AC subnetwork and the initial balance condition of the DC subnetwork satisfy the preset condition, the control mode is determined as mode one.

[0067] Step S1053: When the initial balance of the AC subnet and the initial balance of the DC subnet do not meet the preset conditions, determine whether the absolute value of the per-unit value of the initial AC frequency is greater than the absolute value of the per-unit value of the initial DC voltage.

[0068] Step S1054: When the absolute value of the per-unit value of the initial AC frequency is greater than the absolute value of the per-unit value of the initial DC voltage, the control mode is determined to be mode two.

[0069] Step S1055: When the absolute value of the per-unit initial power of the AC subnetwork is less than the absolute value of the per-unit initial power of the DC subnetwork, the control mode is determined to be Mode 3. Specifically, compare f... pu and V pu,dc The magnitude of the absolute value, and the smaller of the absolute values, such as Figure 7 V in pu,dc The goal is to control the output and thus prevent unnecessary power transfer.

[0070] In this embodiment, the controller of the interconnected converter selects different control modes based on the initial power balance condition. At this time, the initial AC frequency per unit value and the initial DC voltage per unit value can be used as criteria for selecting the control model of the interconnected converter. When one subgrid is operating under light load and the other under heavy load, such as... Figure 7 As shown, the interconnected converter deviates from the subnetwork with the smaller rated power at the actual power output, that is, as... Figure 7 The DC subgrid in the system is the control target. By transmitting active power, the subgrid is maintained at the rated active power, thereby avoiding unnecessary power flow.

[0071] This embodiment uses MATLAB to simulate the present invention, and the simulation results are used to illustrate that the proposed solution saves power compared to existing technologies. Existing technologies employ a per-unit droop control method. In practical applications, Simulink or other mathematical modeling tools can also be used for simulation. Please refer to Table 1, which shows the main model data of the AC / DC hybrid microgrid. The present invention was simulated under different conditions using an AC / DC hybrid microgrid simulation model. Figure 5 Furthermore, the per-unit droop control method was used to simulate the AC / DC hybrid microgrid. The simulation results are shown in [Figure number missing]. Figure 6 See Table 2 for specific details.

[0072] Table 1. Main Model Data for AC / DC Hybrid Microgrid

[0073]

[0074] Table 2 Power Balance Status of AC Subnetwork and DC Subnetwork

[0075] Time State 1 State 2 State 3 State 4 AC subnetwork +3 kW +1 kW -3 kW -1 kW DC subnetwork -1 kW -3 kW +1 kW +3 kW

[0076] In Table 2, "+" represents that the actual active power is less than the rated active power; "-" represents that the actual active power is greater than the rated active power.

[0077] Comparison of simulation results Figure 5 and Figure 6 It can be seen that the active power transmitted by the interconnected converter is 1 kW after the interconnected converter control method of the application is adopted, while the active power transmitted by the interconnected converter is 2 kW when the per-unit droop control is adopted. It can be seen that the method used in the application can reduce unnecessary active power transmission of the interconnected converter and optimize the active power distribution between the subnets. Since the active power of the AC subnet is directly related to the AC frequency through the droop equation, the frequency stability of the AC subnet is improved while the active power of the AC subnet is optimized.

[0078] In the prior art, when the interconnected converter starts to transmit active power, the changes of the AC frequency and the DC voltage will be affected not only by the power balance status of the AC and DC subnets, but also by the active power transmitted by the interconnected converter. At this time, the per-unit values of the AC frequency and the DC voltage can no longer accurately reflect the actual power balance status of the AC and DC subnets, i.e., cannot reflect the initial power balance status of the AC and DC subnets when the interconnected converter does not transmit active power. This control strategy that does not consider the initial power balance status of the AC and DC subnets will lead to unnecessary power transmission in certain occasions.

[0079] Please refer to Figure 7 , the AC subnet and the DC subnet originally run at points a and b. At this time, the per-unit value of the AC frequency of the AC subnet is greater than 0, and the per-unit value of the voltage of the DC subnet is less than 0, indicating that the AC subnet and the DC subnet run at light load and heavy load respectively, i.e., the actual power of the AC subnet is less than the rated power, and the actual power of the DC subnet is greater than the rated power, and the degree of deviation of the AC subnet from the rated power is greater than that of the DC subnet. If the per-unit droop control is adopted, it can be seen that the AC subnet and the DC subnet finally run at points c and c' respectively. As can be seen from the figure, at this time, V ac,pu = V dc,pu , the AC subnet and the DC subnet both run at light load. As can be seen from Figure 7 , the excessive active power transmitted by the interconnected converter causes the DC subnet to cross the rated state, i.e., at V dc,N = 0, enters the light load state, i.e., at point c', i.e., the interconnected converter transmits unnecessary active power.

[0080] In the embodiment, the initial AC frequency standard value and the initial DC voltage standard value are introduced by combining the droop control equation, so as to accurately depict the initial power balance status of the AC sub-network and the DC sub-network when the interconnection converter does not transmit active power. Then, the initial power balance status of the AC sub-network and the DC sub-network is obtained according to the initial AC frequency standard value and the initial DC voltage standard value, so that different control modes of the interconnection converter are selected according to different initial power balance status, unnecessary power transmission is reduced, and the operation efficiency of the AC-DC hybrid micro-grid system is improved and the system frequency stability is increased.

[0081] Please refer to Figure 8 which is a sub-step flowchart of step S104 provided by the embodiment of the application. In step S104, the initial balance status of the AC sub-network is obtained according to the initial AC frequency, and the initial balance status of the DC sub-network is obtained according to the initial DC voltage. The following steps are as follows:

[0082] In step S1042, the initial power of the AC sub-network is obtained according to the initial AC frequency, and the initial power of the DC sub-network is obtained according to the initial DC voltage. Specifically, the AC frequency of the AC sub-network and the active power of the AC sub-network have the relationship shown in formula (4):

[0083] f = f N -m ac (P ac -P ac,N )(4)

[0084] Wherein, f is the real-time AC frequency of the AC sub-network, f N is the rated AC frequency of the AC sub-network, m ac is the droop coefficient of the AC sub-network, P ac is the active power of the AC sub-network, and P ac，N is the rated active power of the AC sub-network.

[0085] In the embodiment, formula (5) is obtained by using formula (4), and the initial power of the AC sub-network is obtained according to the initial AC frequency.

[0086]

[0087] Wherein, f' is the initial AC frequency of the AC sub-network, f N is the rated AC frequency of the AC sub-network, m ac is the droop coefficient of the AC sub-network, P' ac is the initial power of the AC sub-network obtained according to the initial AC frequency, and P ac,N is the rated active power of the AC sub-network.

[0088] Further, the DC voltage of the DC sub-network and the active power of the DC sub-network have a relationship as shown in formula (6):

[0089] V dc = V dc,N -m dc (P dc -P dc,N )(6)

[0090] Wherein, V dc is the real-time DC voltage of the DC sub-network, V dc，N is the rated DC voltage of the DC sub-network, m dc is the droop coefficient of the DC sub-network, P dc is the active power of the DC sub-network, and P dc，N is the rated active power of the DC sub-network. In this embodiment, formula (7) is obtained by using formula (6), and the initial power of the DC sub-network is obtained according to the initial DC voltage.

[0091]

[0092] Wherein, P d ' c is the initial power of the DC sub-network obtained according to the initial DC voltage, V d ' c is the initial DC voltage, V dc，N is the rated DC voltage of the DC sub-network, m dc is the droop coefficient of the DC sub-network, and P dc，N is the rated active power of the DC sub-network.

[0093] In step S1044, the initial balance state of the AC sub-network is obtained according to the initial power of the AC sub-network, and the initial balance state of the DC sub-network is obtained according to the initial power of the DC sub-network. Specifically, the relationship between the initial power of the AC sub-network and the rated power of the AC sub-network is judged, and the relationship between the initial power of the DC sub-network and the rated power of the DC sub-network is judged; when the initial power of the AC sub-network and the DC sub-network both exceeds the rated power, or when the initial power of the AC sub-network and the DC sub-network both is lower than the rated power, the interconnection converter adopts mode one, and controls the per-unit value of the AC frequency to be equal to the per-unit value of the DC voltage through the control link; when the initial power of the DC sub-network deviates from the rated power of the DC sub-network by a small amount, the interconnection converter adopts mode two, and controls the per-unit value of the DC voltage to be 0 through the control link, that is, controls the DC sub-network to operate in the rated state; when the initial power of the AC sub-network deviates from the rated power of the AC sub-network by a small amount, the interconnection converter adopts mode three, and controls the per-unit value of the AC frequency to be 0 through the control link, that is, controls the AC sub-network to operate in the rated state.

[0094] The application also provides an interconnection converter 920, which will be described in combination withFigure 4 The interconnection converter 920 is connected with the AC sub-network 930 and the DC sub-network 910 respectively, and is used to implement the method according to any one of the above embodiments. The interconnection converter 920 provided in the embodiment is only an example and is not limited.

[0095] In the above embodiment, the power transmission mode of the interconnection converter is optimized, the shortcoming of unnecessary power transmission of the interconnection converter is made up, and the operation loss of the AC-DC hybrid micro-grid system is reduced, which is of great significance to improve the operation efficiency of the AC-DC hybrid micro-grid and optimize the power transmission between the sub-networks.

[0096] Obviously, various modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

[0097] The above disclosure is merely preferred embodiments of the present application and is not intended to limit the scope of the present application. Therefore, equivalent changes made within the scope of the claims of the present application and their equivalents are intended to be included in the scope of the present application.

Claims

1. A control method of an interconnecting converter, characterized by, The interconnection converter is connected with an AC sub-network and a DC sub-network respectively, and the method comprises: obtaining real-time AC frequency of the AC sub-network, real-time DC voltage of the DC sub-network and active power transmission of the interconnection converter; calculating AC frequency variation of the AC sub-network according to the active power and droop coefficient of the AC sub-network, and calculating DC voltage variation of the DC sub-network according to the active power and droop coefficient of the DC sub-network; calculating initial AC frequency of the interconnection converter without active power transmission according to the real-time AC frequency and the AC frequency variation, and calculating initial DC voltage of the interconnection converter without active power transmission according to the real-time DC voltage and the DC voltage variation; obtaining initial balance condition of the AC sub-network according to the initial AC frequency, and obtaining initial balance condition of the DC sub-network according to the initial DC voltage; and determining a control mode according to the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network, wherein the control mode is used to control the interconnection converter; the method of obtaining the initial balance condition of the AC sub-network according to the initial AC frequency and obtaining the initial balance condition of the DC sub-network according to the initial DC voltage specifically comprises: normalizing the initial AC frequency to obtain a normalized value of the initial AC frequency, and normalizing the initial DC voltage to obtain a normalized value of the initial DC voltage; and obtaining the initial balance condition of the AC sub-network according to the normalized value of the initial AC frequency and obtaining the initial balance condition of the DC sub-network according to the normalized value of the initial DC voltage; the control mode comprises mode one, mode two and mode three, wherein the mode one is to adjust the normalized value of the real-time AC frequency and the normalized value of the real-time DC voltage to be consistent, the mode two is to adjust the normalized value of the real-time DC voltage to be 0, and the mode three is to adjust the normalized value of the real-time AC frequency to be 0; the method of determining the control mode according to the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network specifically comprises: judging whether the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network satisfy a preset condition; when the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network satisfy the preset condition, determining that the control mode is the mode one; when the initial balance condition of the AC sub-network and the initial balance condition of the DC sub-network do not satisfy the preset condition, judging whether an absolute value of the normalized value of the initial AC frequency is greater than an absolute value of the normalized value of the initial DC voltage; when the absolute value of the normalized value of the initial AC frequency is greater than the absolute value of the normalized value of the initial DC voltage, determining that the control mode is the mode two; or when the absolute value of the normalized value of the initial power of the AC sub-network is less than the absolute value of the normalized value of the initial power of the DC sub-network, determining that the control mode is the mode three. The judging whether the initial balance conditions of the AC sub-network and the DC sub-network satisfy preset conditions specifically comprises: Judging whether the initial value of the AC frequency and the initial value of the DC voltage are of the same sign.

2. The method of claim 1, wherein, The AC frequency variation of the AC sub-network is calculated according to the active power and the droop coefficient of the AC sub-network, and the DC voltage variation of the DC sub-network is calculated according to the active power and the droop coefficient of the DC sub-network, specifically by using the following formula: wherein Δ f is the AC frequency variation of the AC subnetwork, m ac is the droop coefficient of the AC subnetwork, P ic is the active power transmitted by the interconnecting converter, Δ V dc is the DC voltage variation of the DC subnetwork, m dc is the droop coefficient of the DC subnetwork.

3. The method of claim 1, wherein, The initial AC frequency when the interconnected converter has no power transmission is calculated according to the real-time AC frequency and the AC frequency variation, and the initial DC voltage when the interconnected converter has no power transmission is calculated according to the real-time DC voltage and the DC voltage variation, specifically by using the following formula: wherein, is the initial AC frequency, f is the real-time AC frequency, is the initial DC voltage, V dc is the real-time DC voltage.

4. The method of claim 1, wherein, The initial value of the AC frequency is obtained by normalizing the initial AC frequency, and the initial value of the DC voltage is obtained by normalizing the initial DC voltage, specifically by using the following formula: wherein, f pu is a unit value of an initial AC frequency, f max is a maximum value of a preset AC frequency, f min is a minimum value of a preset AC frequency, V dc，pu is a unit value of an initial DC voltage, V dc，max is a maximum value of a preset DC voltage, V dc，min is a minimum value of a preset DC voltage.

5. The method of claim 1, wherein, The initial balance condition of the AC sub-network is obtained according to the initial AC frequency, and the initial balance condition of the DC sub-network is obtained according to the initial DC voltage, specifically comprising: The initial power of the AC sub-network is obtained according to the initial AC frequency, and the initial power of the DC sub-network is obtained according to the initial DC voltage; and The initial balance condition of the AC sub-network is obtained according to the initial power of the AC sub-network, and the initial balance condition of the DC sub-network is obtained according to the initial power of the DC sub-network.

6. An interconnection converter, characterized by The interconnected converter is connected with an AC sub-network and a DC sub-network respectively, and is used to realize the method according to any one of claims 1-5.

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