Submarine direct current power supply system transient stability improving method based on frequency compensation

Abstract

The invention provides a method for improving transient stability of a submarine direct-current power supply system based on frequency compensation. The method comprises the following steps: acquiring a real-time electrical parameter detection item of a first system; based on the first system real-time electrical parameter detection item, judging whether the system load power is within a power range required by a transient stable operation condition; if not, the switching frequency compensation amount of the input-series output-parallel resonant converter sub-module is calculated; based on the switching frequency compensation amount, determining a switching signal of a sub-module switching tube of the input-series output-parallel resonant converter; acquiring a real-time electrical parameter detection item of a second system; based on a second system real-time electrical parameter detection item, judging whether the system load power is within a power range required by a transient stable operation condition; if yes, conventional frequency conversion control is adopted. The technical blank in the field is effectively filled, and the stability of the submarine direct-current power supply system in the transient process is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system operation control, and particularly relates to a method for improving transient stability of a submarine DC power supply system based on frequency compensation. BACKGROUND

[0002] Stable operation of a submarine DC power supply system is an important basis for ensuring normal operation of a submarine scientific observation network. However, in an extreme environment under the sea, the system is prone to failure, and due to its small inertia and weak damping characteristics, the bus voltage will drop rapidly when a fault occurs, resulting in system instability and failure to normally supply power to submarine scientific instruments. Therefore, it is of great significance to take effective control measures in the transient process after a fault occurs to suppress the bus voltage drop and promote the system to resume stable operation.

[0003] As a core device of a submarine DC power supply system, a submarine converter usually adopts a multi-submodule cascaded structure to achieve conversion of bus voltage from 10kV to 375V. Among them, an input serial output parallel LLC converter (ISOP-LLC) is often selected as a submarine converter due to its high efficiency, strong environmental adaptability, and low electromagnetic interference. Modern submarine DC power supply systems often use multiple complex converter structures including ISOP-LLC. Existing research shows that the voltage conversion link of ISOP-LLC plays a key role in the transient stability of the submarine system, and suppressing the transient drop of the input-output voltage ratio of ISOP-LLC is crucial to reducing the difference between power supply and demand in the transient process. However, the current transient stability improvement methods based on this principle are still relatively limited, and the research is insufficient, especially when facing diversified operating conditions in the actual system. The traditional limiting method lacks adaptability and is difficult to fully meet the dynamic response requirements of the system in the transient process. SUMMARY

[0004] The present application provides a method for improving the transient stability of a submarine DC power supply system based on frequency compensation. To solve the above technical problems, the present application adopts the following technical method: The present application provides a method for improving the transient stability of a submarine DC power supply system based on frequency compensation. The submarine DC power supply system includes an input serial output parallel LLC converter, comprising: Step S101: Collecting a first system real-time electrical parameter detection item; Step S102: Based on the first system real-time electrical parameter detection item, determining whether the system load power is within the power range required by the transient stable operation condition; If not, execute step S103; Step S103: calculating a switching frequency compensation amount of the input series output parallel resonant converter sub-module; Step S104: determining a switching signal of a switching tube of the input series output parallel resonant converter sub-module based on the switching frequency compensation amount; Step S105: collecting a second system real-time electrical parameter detection item; Step S106: judging whether the system load power is within a power range required by the transient state stable operation condition based on the second system real-time electrical parameter detection item; If not, performing step S101.

[0005] Optionally, the determination process of the system transient state stable operation condition is: acquiring a theoretical model of the submarine direct-current power supply system; analyzing the theoretical model of the submarine direct-current power supply system by using a hybrid potential function method to determine the system transient state stable operation condition.

[0006] Optionally, the first system real-time electrical parameter detection item includes a first system load power, a first current flowing through the submarine cable, a first input voltage and a first output voltage of the input series output parallel resonant converter.

[0007] Optionally, the calculation of the switching frequency compensation amount of the input series output parallel resonant converter sub-module includes: acquiring physical characteristics of the input series output parallel resonant converter; determining the switching frequency compensation amount of the input series output parallel resonant converter sub-module based on the physical characteristics and the first system real-time electrical parameter detection item.

[0008] Optionally, the physical characteristics of the input series output parallel resonant converter are obtained according to internal characteristics of the input series output parallel resonant converter.

[0009] Optionally, the determination of the switching frequency compensation amount of the input series output parallel resonant converter sub-module based on the physical characteristics and the first system real-time electrical parameter detection item includes: determining a steady-state switching frequency in a stable operation state before a fault and a fault switching frequency in a transient process after the fault based on the physical characteristics and the first system real-time electrical parameter detection item; determining the switching frequency compensation amount of the input series output parallel resonant converter sub-module based on the steady-state switching frequency in the stable operation state before the fault and the fault switching frequency in the transient process after the fault.

[0010] Optionally, determining the switching signal of the input-series-output-parallel resonant converter submodule switching transistor based on the switching frequency compensation amount includes: Based on the aforementioned switching frequency compensation amount, the compensation switching frequency of the input-series-output-parallel resonant converter submodule is determined. Based on the compensated switching frequency, the switching signals of the switching transistors in the input-series-output-parallel resonant converter submodule are determined.

[0011] Optionally, if the judgment result of step S106 is yes, only conventional frequency conversion control is performed.

[0012] The present invention has the following beneficial effects: The method proposed in this invention effectively fills the technological gap in this field and significantly improves the stability of the submarine DC power supply system during transient processes. Attached Figure Description

[0013] Figure 1 A flowchart illustrating a method for improving the transient stability of a submarine DC power supply system based on frequency compensation, provided in an embodiment of the present invention. Figure 2 A structural diagram of a submarine DC power supply system provided in an embodiment of the present invention; Figure 3 The overall structure diagram of the input-series-output-parallel resonant converter (ISOP-LLC) provided in the embodiment of the present invention is shown below. Figure 4 A schematic diagram illustrating the physical characteristics of an input-series-output-parallel resonant converter (ISOP-LLC) provided in an embodiment of the present invention; Figure 5 The diagram shows a stable boost control structure based on frequency compensation of a submodule of an input-series-output parallel resonant converter (ISOP-LLC) provided in an embodiment of the present invention. Figure 6 The graph shows a comparison of the transient stability improvement effect when using the method provided by this invention and when not using the method provided by this invention. Detailed Implementation

[0014] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0015] To solve the above-mentioned technical problems, the present invention proposes the following... Figure 1 The transient stability improvement method for a frequency-compensated submarine DC power supply system shown includes: Step S101: Collect real-time electrical parameter detection items of the first system; The structure of the submarine DC power supply system used in this invention is as follows: Figure 2As shown, the whole system is composed of a modular multilevel converter (MMC), a submarine transmission cable, an input-series output-parallel LLC resonant converter (ISOP-LLC) and a constant power load (CPL), the system realizes the conversion and transmission of 4083V AC to 375V DC through a multi-level converter, wherein, is the input voltage of the ISOP-LLC, is the output voltage of the ISOP-LLC, is the output voltage of the MMC, is the current flowing through the submarine cable. is the large capacitor of the DC bus, is the submarine cable capacitor, is the submarine cable inductance, is the submarine cable resistance. The overall structure of the input-series output-parallel LLC resonant converter (ISOP-LLC) is shown in Figure 3 , wherein, is the input voltage of the ISOP-LLC, is the output voltage of the ISOP-LLC, is the output voltage of the MMC, is the excitation inductance, is the resonant inductance, is the input side capacitor, S 1 , S 2 , S 3 , S 4 is the power switch tube, is the resonant capacitor, is the high-frequency transformer, is the excitation current, is the resonant current, is the resonant voltage, n:1 represents the turns ratio of the primary winding and the secondary winding, D 5 , D 6 , D 7 , D 8 is the rectifier diode, is the current after the rectifier bridge, is the output filter capacitor.

[0016] The present application needs to collect the first system real-time electrical parameter detection item, i.e. the first system real-time electrical parameter detection item, including the first system load power The first current flowing through the submarine cable The first input voltage of the input-series-output-parallel resonant converter and first output voltage The system collects real-time electrical parameter data for subsequent assessments of system stability and whether stable operation has been restored.

[0017] Step S102: Based on the collected real-time electrical parameter detection items of the first system, determine whether the system load power is within the power range required for transient stable operation conditions; If not, proceed to step S103; First of all Figure 2 The theoretical model of the submarine DC power supply system can be obtained by theoretical analysis and modeling. Based on the theoretical model, the hybrid function method is used to analyze the theoretical model of the submarine DC power supply system, and the transient stable operating conditions of the system can be determined, as shown in formula (1): (1) In the formula, and These represent the DC-side equivalent resistance and inductance of the MMC, respectively. For submarine cable inductance, This refers to the resistance of the submarine cable. The input-output voltage transfer ratio of the input-series-output parallel resonant converter (ISOP-LLC) is given by formula (2). It can be calculated from the input-output voltage ratio of ISOP-LLC. It is the load power. For the large capacitor of the DC bus, The current flowing through the submarine cable, This is the input voltage for ISOP-LLC. This represents the DC component of the total voltage across the MMC submodule capacitors. Because the MMC submodule capacitors have large capacitance values, they possess extremely strong voltage regulation capabilities. It can be regarded as an unchanging constant: (2) In the formula, This is the input voltage for ISOP-LLC. This refers to the output voltage of the ISOP-LLC. This indicates the number of cascaded submodules in ISOP-LLC. This indicates the transformer winding ratio for each LLC submodule.

[0018] The first system real-time electrical parameter detection item collected is substituted into formula (1), so as to determine whether the system transient stable operation condition is met, that is, if the load power of the system Within the range required by formula (1), it represents that the system is in a stable operation stage at this time, and adjustment is not required, and only the physical characteristics of the input series output parallel type resonant converter sub-module are calculated and stored to calculate and store the steady-state switching frequency of the sub-module If the load power of the system Exceeds the range required by formula (1), it represents that the system has a risk of instability, and the subsequent step 103 is performed.

[0019] Step S103: Calculate the switching frequency compensation amount of the input series output parallel type resonant converter sub-module; According to the physical characteristics of the input series output parallel type resonant converter and the first system real-time electrical parameter detection item, the switching frequency compensation amount of the input series output parallel type resonant converter sub-module The specific process is as follows: According to the internal characteristics of the input series output parallel type resonant converter (ISOP-LLC), the voltage transmission ratio The relationship between the switching frequency The load power Is shown in formula (3), and the physical characteristics of the ISOP-LLC shown in formula (2) can be obtained according to formula (3): Figure 4 (3) In the formula, The ratio of the excitation inductance And the resonant inductance In the LLC sub-module resonant cavity is represented, The switching frequency of the LLC sub-module is represented. The resonant frequency can be calculated by formula (4), which is a constant. The resonant inductance is represented, The resonant capacitance is represented, The load power is represented: (4) It should be noted that the voltage transmission ratio ​The value of , and the physical characteristics of ISOP-LLC shown in formula (3) are inherent characteristics and will not change with the change of operating conditions. In other words, during steady-state or transient operation, the real-time switching frequency of the submodule can be calculated by substituting the relevant real-time electrical parameter detection items into (3). Specifically, in the case of a fault, based on the collected real-time electrical parameter detection items, the fault switching frequency of the submodule during the transient process after the fault can be obtained based on formula (3). Similarly, during the stable operation before the fault occurs, the steady-state switching frequency of the submodule in step S102... The collected steady-state real-time electrical parameters are obtained and stored by substituting them into formula (3) so that step S103 can further determine the frequency compensation required to maintain the transient stable operation of the system. Then, the steady-state switching frequency under the stable operating state before the fault is... and the fault switching frequency during the transient process after the fault Substituting into formula (5), the corresponding frequency compensation amount can be obtained. : (5) During stable operation, considering the large power demand of submarine power supply and the fact that ISOP-LLC operates in the zero-voltage switching region (ZVS), Approaching the resonant frequency ISOP-LLC's input-output voltage transfer ratio Approaching 1. Therefore, for transient instability caused by a sudden increase in load power, even if the amount of the load increase is uncertain, it will... Limited to the original steady-state switching frequency Effectively prevent The transient decrease can also help the system recover to a stable operating state after the fault is cleared.

[0020] Step S104: Based on the switching frequency compensation amount, determine the switching signal of the switching transistor of the input-series-output-parallel resonant converter submodule; like Figure 5 As shown, As the output voltage reference value, this step determines the switching signals of the switching transistors of the input-series-output-parallel resonant converter submodule based on the switching frequency compensation. The specific process is as follows: Based on the compensation amount of the switching frequency and the fault switching frequency of the LLC submodule (Right now Figure 5 In Adding the two together determines the compensation switching frequency of the input-series-output-parallel resonant converter submodule. After frequency compensation, the switching frequency of the submodule increases to And through the modulation link shown in equation (6), the PWM switching signal of the input series output parallel resonant converter submodule switch is determined to control the submodule switch on and off: (6) In the formula, S _ PWM PWM signal of the switch Figure 3 1 and S 4 in the control S , Figure 3 PWM signal of the switch S 2 and S 3 and the PWM signal of the switch S 1 and S 4 are opposite. The switching frequency of the LLC submodule after frequency compensation is represented.

[0021] Step S105: Collect the second system real-time electrical parameter detection item; After frequency compensation, the second system real-time electrical parameter detection item is collected again, that is, the second system load power, the second current flowing through the submarine cable, the second input voltage and the second output voltage of the input series output parallel resonant converter, which is used to judge whether the system resumes stable operation.

[0022] Step S106: Based on the second system real-time electrical parameter detection item, judge whether the system load power is within the power range required by the transient stable operation condition; If not, execute step S101.

[0023] Substitute the second system real-time electrical parameter detection item into equation (1). If the load power of the system is not within the range required by equation (1), execute step S01 to continue the frequency compensation control. If the load power of the system is within the range required by equation (1), it means that the fault is removed, and the frequency compensation method is stopped, and the conventional variable frequency control shown in equation (7) is adopted. The PWM wave generation method is the same as shown in equation (6), except that the switching frequency of the ISOP-LLC submodule is represented by (7) In the formula, , respectively represent the proportional and integral coefficients of the variable frequency control, is the output voltage of ISOP-LLC, is the standard value of the output voltage of ISOP-LLC.

[0024] Simulation experiment To verify the correctness and feasibility of the above method, the proposed method is implemented in the submarine DC power supply system as shown in Figure 2 The proposed method is implemented in the submarine DC power supply system as shown in Figure 2 The proposed method is implemented in the submarine DC power supply system as shown in Figure 5 The proposed method is implemented in the submarine DC power supply system as shown in The proposed method is implemented in the submarine DC power supply system as shown in The proposed method is implemented in the submarine DC power supply system as shown in The proposed method is implemented in the submarine DC power supply system as shown in Figure 6 The proposed method is implemented in the submarine DC power supply system as shown in

[0025] In summary, the proposed method of the present application effectively fills the technical gap in this field by combining system stability boundary analysis of input series output parallel resonant converter (ISOP-LLC) and real-time detection and calculation technology, significantly improving the stability of submarine DC power supply system in transient process.

[0026] The above embodiments are the preferred implementation of the present application, in addition to this, the present application can be implemented in other ways, without departing from the technical scheme concept of the present application, any obvious substitution is within the protection scope of the present application.

[0027] In order to make the ordinary skilled in the art more convenient to understand the improvement of the present application over the prior art, some drawings and descriptions of the present application have been simplified, and some other elements have been omitted in the present application file for the sake of clarity, and the ordinary skilled in the art should realize that these omitted elements can also constitute the content of the present application.

Claims

1. A method for improving the transient stability of a submarine DC power supply system based on frequency compensation, wherein the submarine DC power supply system includes an input-series-output parallel resonant converter, characterized in that, include: Step S101: Collect real-time electrical parameter detection items of the first system; Step S102: Based on the real-time electrical parameter detection items of the first system, determine whether the system load power is within the power range required for transient stable operation conditions; If not, proceed to step S103; Step S103: Calculate the switching frequency compensation amount of the input-series-output-parallel resonant converter submodule; Step S104: Based on the switching frequency compensation amount, determine the switching signal of the switching transistor of the input-series-output-parallel resonant converter submodule; Step S105: Collect real-time electrical parameter detection items of the second system; Step S106: Based on the real-time electrical parameter detection items of the second system, determine whether the system load power is within the power range required for transient stable operation conditions; If not, proceed to step S101.

2. The method according to claim 1, characterized in that, The process for determining the transient stable operating conditions of the system is as follows: Obtain the theoretical model of the submarine DC power supply system; The theoretical model of the submarine DC power supply system was analyzed using the mixed potential function method to determine the transient stable operating conditions of the system.

3. The method according to claim 1, characterized in that, The real-time electrical parameter detection items of the first system include the first system load power, the first current flowing through the submarine cable, and the first input voltage and first output voltage of the input-series-output-parallel resonant converter.

4. The method according to claim 1, characterized in that, The switching frequency compensation amount of the input-series-output-parallel resonant converter submodule includes: Obtain the physical characteristics of an input-series-output parallel resonant converter; Based on the physical characteristics and the real-time electrical parameter detection items of the first system, the switching frequency compensation amount of the input-series-output-parallel resonant converter submodule is determined.

5. The method according to claim 4, characterized in that, The physical characteristics of the input-series-output-parallel resonant converter can be obtained from the internal characteristics of the input-series-output-parallel resonant converter.

6. The method according to claim 5, characterized in that, Based on the aforementioned physical characteristics and the real-time electrical parameter detection items of the first system, the switching frequency compensation amount of the input-series-output-parallel resonant converter submodule is determined, including: Based on the physical characteristics and the real-time electrical parameter detection items of the first system, the steady-state switching frequency under the stable operating state before the fault and the fault switching frequency under the transient process after the fault are determined. Based on the steady-state switching frequency under the stable operating state before the fault and the fault switching frequency during the transient process after the fault, the switching frequency compensation amount of the input-series-output-parallel resonant converter submodule is determined.

7. The method according to claim 6, characterized in that, The determination of the switching signals of the input-series-output-parallel resonant converter submodule switching transistors based on the switching frequency compensation amount includes: Based on the aforementioned switching frequency compensation amount, the compensation switching frequency of the input-series-output-parallel resonant converter submodule is determined. Based on the compensated switching frequency, the switching signals of the switching transistors in the input-series-output-parallel resonant converter submodule are determined.

8. The method according to claim 1, characterized in that, When the judgment result of step S106 is yes, only conventional frequency conversion control is performed.

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