Flexible DC power transmission system starting loop based on negative temperature characteristic resistor

Abstract

The invention relates to a flexible direct current power transmission system starting loop based on a negative temperature characteristic resistor. The flexible direct current power transmission system starting loop comprises a transformer, a charging switch, the negative temperature characteristic resistor, an upper bridge arm and a lower bridge arm, one end of the transformer is connected with an alternating current side, the other end of the transformer is connected with one end of the charging switch, the other end of the charging switch is connected with one end of the negative temperature characteristic resistor, and the other end of the negative temperature characteristic resistor is connected with one end of the upper bridge arm and one end of the lower bridge arm; each of the upper bridge arm and the lower bridge arm consists of a plurality of converter valves which are connected in series, and bridge arm reactors are arranged at the joints of the upper bridge arm and the negative temperature characteristic resistor as well as the joints of the lower bridge arm and the negative temperature characteristic resistor; when the converter valve capacitor begins to be charged, charging current flows through the negative temperature characteristic resistor to enable the temperature to rise, the resistance value of the negative temperature characteristic resistor is reduced, and the charging current is gradually increased; and detecting the capacitance parameter of the converter valve, and when the capacitance parameter of the converter valve reaches a preset threshold value, completing the starting of the flexible DC power transmission system.

Description

Technical Field

[0001] The invention relates to a flexible direct current power transmission system starting circuit based on a negative temperature characteristic resistor, belonging to the technical field of power systems. Background Art

[0002] During the startup process of a traditional flexible DC transmission system, a fixed resistor is usually used to limit the charging current of the converter valve during startup.

[0003] Since the converter valve is equivalent to a short-circuit state in the initial charging stage, if the current is not limited, a huge impact current will be generated, which may not only damage the electrical components in the system, but also cause serious disturbances to the power grid.

[0004] Therefore, at the initial stage of startup, a fixed resistor is connected to the circuit. After the converter valve is charged to a certain level and the startup is basically completed, the fixed resistor is bypassed through the isolation switch to allow the system to enter normal operation.

[0005] However, this traditional solution has some obvious disadvantages:

[0006] On the one hand, the resistance of a fixed resistor is fixed. In order to effectively limit the current at the initial startup, its resistance is often large, which leads to slow charging of the capacitor and a long startup process, reducing the operating efficiency of the system. On the other hand, the use of an isolating switch for resistor bypass operation increases the complexity and cost of the system. At the same time, the isolating switch has a limited number of operations. Frequent operation will reduce its reliability, and it is easy to generate arcing and other problems at the moment of operation, affecting the stability and safety of the system. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the present invention proposes a flexible direct current transmission system starting circuit based on a negative temperature characteristic resistor.

[0008] The technical solution of the present invention is as follows:

[0009] On the one hand, the present invention provides a flexible direct current transmission system starting circuit based on a negative temperature characteristic resistor, comprising a transformer, a charging switch, a negative temperature characteristic resistor, an upper bridge arm and a lower bridge arm;

[0010] One end of the transformer is connected to the AC side, the other end of the transformer is connected to one end of the charging switch, the other end of the charging switch is connected to one end of the negative temperature characteristic resistor, and the other end of the negative temperature characteristic resistor is respectively connected to one end of the upper bridge arm and one end of the lower bridge arm;

[0011] The upper bridge arm and the lower bridge arm are both composed of a plurality of converter valves connected in series, and bridge arm reactors are provided at the connection points between the upper bridge arm and the lower bridge arm and the negative temperature characteristic resistor.

[0012] On the other hand, the present invention also provides a method for starting a flexible direct current transmission system based on a negative temperature characteristic resistor, comprising the following steps:

[0013] When the flexible DC transmission system is started, the voltage of the converter valve capacitor is zero. At this time, the resistance value of the negative temperature characteristic resistor remains unchanged and plays a current limiting role.

[0014] The converter valve capacitor starts to charge, and the charging current flows through the negative temperature characteristic resistor to increase its temperature, the resistance value of the negative temperature characteristic resistor decreases, and the charging current gradually increases;

[0015] The converter valve capacitance parameters are detected. When the converter valve capacitance parameters reach a preset threshold, the flexible DC transmission system is started.

[0016] As a preferred embodiment of the present invention, when the flexible DC power transmission system is started, the calculation formula of the initial resistance value of the negative temperature characteristic resistor is:

[0017]

[0018] Where: R0 represents the initial resistance value of the negative temperature characteristic resistor when the flexible DC transmission system is started; U s Indicates the effective value of the AC line voltage; I max Indicates the maximum starting current of the flexible DC transmission system.

[0019] As a preferred embodiment of the present invention, the calculation formula of the starting current of the flexible DC power transmission system is:

[0020]

[0021] Where: i s (t) represents the starting current at time t; f represents the AC side voltage frequency; t represents the starting time; τ0 represents the time constant; R represents the resistance value of the negative temperature characteristic resistor.

[0022] As a preferred embodiment of the present invention, the calculation formula of the time constant is:

[0023] τ0=12RC

[0024] Where: C represents the equivalent capacitance value of any bridge arm.

[0025] As a preferred embodiment of the present invention, a charging current constraint condition is set, which is specifically shown in the following formula:

[0026]

[0027] Where: I represents the charging current.

[0028] As a preferred embodiment of the present invention, when the converter valve capacitor is charged, the instantaneous power calculation formula of the negative temperature characteristic resistor is specifically shown as follows:

[0029] P R =i s (t)·i s (t)·R

[0030] Where: P R It represents the instantaneous power of the negative temperature characteristic resistor when the flexible DC transmission system is started.

[0031] As a preferred embodiment of the present invention, when the converter valve capacitor is charged, the energy consumption value of the negative temperature characteristic resistor is calculated as follows:

[0032] W R =∫P R dt=c×m×ΔT

[0033] Where: W R It represents the energy consumption value of the negative temperature characteristic resistor when the flexible DC transmission system is started; c represents the specific heat capacity of the negative temperature characteristic resistor material; m represents the mass of the negative temperature characteristic resistor material; ΔT represents the temperature rise of the negative temperature characteristic resistor material.

[0034] As a preferred embodiment of the present invention, when the converter valve capacitor is charged, the resistance value calculation formula of the negative temperature characteristic resistor is:

[0035] R=f1(T d )

[0036] Where: R represents the resistance value of the negative temperature characteristic resistor; f1 represents the relationship function between temperature and resistance; T d Indicates the temperature of a negative temperature characteristic resistor;

[0037] T d =ΔT+T

[0038] Where: T represents the initial temperature of the negative temperature characteristic resistor.

[0039] The present invention has the following beneficial effects:

[0040] 1. The resistance value of the negative temperature characteristic resistor adopted in the present invention decreases as its own temperature increases. When the system is just started, the temperature of the negative temperature characteristic resistor is low, and its resistance value is large at this time, which can effectively limit the charging current of the converter valve, avoid excessive impact current, and protect system components and grid stability; as the startup process proceeds, the current continues to flow through the negative temperature characteristic resistor, and the resistor heats up due to the Joule heating effect, and its resistance value decreases accordingly. The reduction in resistance value gradually reduces the equivalent resistance of the charging circuit, and then the charging current of the converter valve can increase at a faster rate, so that the entire charging process of the converter valve can be completed at a faster speed, which greatly shortens the startup time and improves the startup efficiency of the system.

[0041] 2. The negative temperature characteristic resistor used in the present invention generates heat during the startup process and eventually reaches a stable operating temperature. At this time, its resistance value is only a few tenths of an ohm. The voltage drop generated by this resistance in a normally operating DC circuit is extremely small and almost negligible, and will not have a negative impact on the normal operation of the system. Therefore, the resistor does not need to be cut off after the startup is completed like a traditional fixed resistor, and can continue to work in the circuit. This not only simplifies the structure of the system, reduces a series of problems caused by the isolating switch and its operation, reduces costs, but also improves the reliability and stability of the system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a circuit diagram of the present invention. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0045] It should be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0046] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0047] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0048] Embodiment 1:

[0049] See also Figure 1 , a startup circuit of a flexible direct current transmission system based on a negative temperature characteristic resistor, comprising a transformer, a charging switch, a negative temperature characteristic resistor, an upper bridge arm and a lower bridge arm;

[0050] One end of the transformer is connected to the AC side, the other end of the transformer is connected to one end of the charging switch, the other end of the charging switch is connected to one end of the negative temperature characteristic resistor, and the other end of the negative temperature characteristic resistor is respectively connected to one end of the upper bridge arm and one end of the lower bridge arm;

[0051] The upper bridge arm and the lower bridge arm are both composed of a plurality of converter valves connected in series, and bridge arm reactors are provided at the connection points between the upper bridge arm and the lower bridge arm and the negative temperature characteristic resistor;

[0052] The other end of the upper bridge arm is connected to the positive pole of the DC bus, and the other end of the lower bridge arm is connected to the negative pole of the DC bus;

[0053] In the design of the starting circuit of the flexible DC transmission system, a suitable negative temperature characteristic resistor is selected. Its key parameters, such as the initial resistance value at room temperature, need to be accurately calculated and selected based on the rated voltage, the capacitance value of the converter valve, and the expected starting current.

[0054] The selected negative temperature characteristic resistor is connected in series to the flexible DC starting circuit, and is connected with other necessary electrical components, such as bridge arm inductors, current transformers, etc. according to a reasonable circuit topology to form a complete flexible DC starting circuit.

[0055] Embodiment 2:

[0056] A method for starting a flexible direct current transmission system based on a negative temperature characteristic resistor comprises the following steps:

[0057] When the flexible DC transmission system is started, the voltage of the converter valve capacitor is zero. At this time, the resistance value of the negative temperature characteristic resistor remains unchanged and plays a current limiting role.

[0058] The converter valve capacitor starts to charge, and the charging current flows through the negative temperature characteristic resistor to increase its temperature. The resistance value of the negative temperature characteristic resistor decreases, and the charging current gradually increases. The decrease in resistance value causes the equivalent resistance of the charging circuit to gradually decrease, and then the charging current of the converter valve can increase at a faster rate, so that the charging process of the entire converter valve can be completed at a faster speed, which greatly shortens the startup time and improves the startup efficiency of the system;

[0059] The converter valve capacitance parameters (current, voltage, etc.) are detected. When the converter valve capacitance parameters reach the preset threshold, the flexible DC transmission system is started.

[0060] As a preferred implementation of this embodiment, when the flexible DC power transmission system is started, the calculation formula of the initial resistance value of the negative temperature characteristic resistor is:

[0061]

[0062] Where: R0 represents the initial resistance value of the negative temperature characteristic resistor when the flexible DC transmission system is started; U s Indicates the effective value of the AC line voltage; I max Indicates the maximum starting current of the flexible DC transmission system.

[0063] As a preferred implementation of this embodiment, the calculation formula of the starting current of the flexible DC power transmission system is:

[0064]

[0065] Where: i s (t) represents the starting current at time t; f represents the AC side voltage frequency; t represents the starting time; τ0 represents the time constant; R represents the resistance value of the negative temperature characteristic resistor.

[0066] As a preferred implementation of this embodiment, the calculation formula of the time constant is:

[0067] τ0=12RC

[0068] Where: C represents the equivalent capacitance value of any bridge arm.

[0069] As a preferred implementation of this embodiment, a charging current constraint condition is set, which is specifically shown in the following formula:

[0070]

[0071] Where: I represents the charging current.

[0072] As a preferred implementation of this embodiment, when the converter valve capacitor is charged, the instantaneous power calculation formula of the negative temperature characteristic resistor is specifically shown as follows:

[0073] P R =i s (t)·i s (t)·R

[0074] Where: P R It represents the instantaneous power of the negative temperature characteristic resistor when the flexible DC transmission system is started.

[0075] As a preferred implementation of this embodiment, when the converter valve capacitor is charged, the energy consumption value of the negative temperature characteristic resistor is calculated as follows:

[0076] W R =∫P R dt=c×m×ΔT

[0077] Where: W R It represents the energy consumption value of the negative temperature characteristic resistor when the flexible DC transmission system is started; c represents the specific heat capacity of the negative temperature characteristic resistor material; m represents the mass of the negative temperature characteristic resistor material; ΔT represents the temperature rise of the negative temperature characteristic resistor material.

[0078] As a preferred implementation of this embodiment, when the converter valve capacitor is charged, the resistance value calculation formula of the negative temperature characteristic resistor is:

[0079] R=f1(T d )

[0080] Where: R represents the resistance value of the negative temperature characteristic resistor; f1 represents the relationship function between temperature and resistance; T d Indicates the temperature of a negative temperature characteristic resistor;

[0081] In this embodiment, the relationship function between temperature and resistance is shown as follows:

[0082]

[0083] Where: B represents negative temperature coefficient;

[0084] T d =ΔT+T

[0085] Where: T represents the initial temperature of the negative temperature characteristic resistor.

[0086] Embodiment three:

[0087] This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method described in any embodiment of the present invention when executing the program.

[0088] Embodiment 4:

[0089] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the method described in any embodiment of the present invention is implemented.

[0090] In the embodiments of the present application, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c can be represented by: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, c can be single or multiple.

[0091] Those of ordinary skill in the art will appreciate that the various units and algorithm steps described in the embodiments disclosed herein can be implemented in a combination of electronic hardware, computer software, and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0092] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0093] In several embodiments provided in the present application, if any function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory; hereinafter referred to as: ROM), random access memory (Random Access Memory; hereinafter referred to as: RAM), disk or optical disk, and other media that can store program codes.

[0094] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A starting circuit of a flexible direct current transmission system based on a negative temperature characteristic resistor, characterized in that: It includes a transformer, a charging switch, a negative temperature characteristic resistor, an upper bridge arm and a lower bridge arm; One end of the transformer is connected to the AC side, the other end of the transformer is connected to one end of the charging switch, the other end of the charging switch is connected to one end of the negative temperature characteristic resistor, and the other end of the negative temperature characteristic resistor is respectively connected to one end of the upper bridge arm and one end of the lower bridge arm; The upper bridge arm and the lower bridge arm are both composed of a plurality of converter valves connected in series, and bridge arm reactors are provided at the connection points between the upper bridge arm and the lower bridge arm and the negative temperature characteristic resistor.

2. A method for starting a flexible direct current transmission system based on a negative temperature characteristic resistor, used in a starting circuit of a flexible direct current transmission system based on a negative temperature characteristic resistor as claimed in claim 1, characterized in that: The following steps are involved: When the flexible DC transmission system is started, the voltage of the converter valve capacitor is zero. At this time, the resistance value of the negative temperature characteristic resistor remains unchanged and plays a current limiting role. The converter valve capacitor starts to charge, and the charging current flows through the negative temperature characteristic resistor to increase its temperature, the resistance value of the negative temperature characteristic resistor decreases, and the charging current gradually increases; The converter valve capacitance parameters are detected. When the converter valve capacitance parameters reach a preset threshold, the flexible DC transmission system is started.

3. The method for starting a flexible direct current transmission system based on negative temperature characteristic resistance according to claim 2, characterized in that: When the flexible DC transmission system is started, the calculation formula for the initial resistance value of the negative temperature characteristic resistor is: Where: R0 represents the initial resistance value of the negative temperature characteristic resistor when the flexible DC transmission system is started; U s Indicates the effective value of the AC line voltage; I max Indicates the maximum starting current of the flexible DC transmission system.

4. The method for starting a flexible direct current transmission system based on negative temperature characteristic resistance according to claim 3 is characterized in that: The calculation formula of the starting current of the flexible DC transmission system is: Where: i s (t) represents the starting current at time t; f represents the AC side voltage frequency; t represents the starting time; τ0 represents the time constant; R represents the resistance value of the negative temperature characteristic resistor.

5. The method for starting a flexible direct current transmission system based on negative temperature characteristic resistance according to claim 4, characterized in that: The calculation formula of the time constant is: τ0=12RC Where: C represents the equivalent capacitance value of any bridge arm.

6. The method for starting a flexible direct current transmission system based on negative temperature characteristic resistance according to claim 4, characterized in that: Set the charging current constraint conditions, as shown in the following formula: Where: I represents the charging current.

7. The method for starting a flexible direct current transmission system based on negative temperature characteristic resistance according to claim 4, characterized in that: When the converter valve capacitor is charged, the instantaneous power calculation formula of the negative temperature characteristic resistor is specifically shown as follows: P R =i s (t)·i s (t)·R Where: P R It represents the instantaneous power of the negative temperature characteristic resistor when the flexible DC transmission system is started.

8. The method for starting a flexible direct current transmission system based on negative temperature characteristic resistance according to claim 4, characterized in that: When the converter valve capacitor is charged, the energy consumption value of the negative temperature characteristic resistor is calculated as follows: w R =∫P R dt=c×m×ΔT Where: W R It represents the energy consumption value of the negative temperature characteristic resistor when the flexible DC transmission system is started; c represents the specific heat capacity of the negative temperature characteristic resistor material; m represents the mass of the negative temperature characteristic resistor material; ΔT represents the temperature rise of the negative temperature characteristic resistor material.

9. The method for starting a flexible direct current transmission system based on negative temperature characteristic resistance according to claim 4, characterized in that: When the converter valve capacitor is charged, the resistance value of the negative temperature characteristic resistor is calculated as follows: R=f1(T d ) Where: R represents the resistance value of the negative temperature characteristic resistor; f1 represents the relationship function between temperature and resistance; T d Indicates the temperature of a negative temperature characteristic resistor; T d =ΔT+T Where: T represents the initial temperature of the negative temperature characteristic resistor.

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