Overcurrent control method and system for alternating-current parallel hybrid converter and converter

Abstract

The invention discloses an over-current control method and system for an alternating-current parallel hybrid converter and the converter, and relates to the technical field of high-voltage direct-current power transmission. The over-current control method comprises the following steps: controlling the voltage source converter to perform first temporary locking under the condition that the bridge arm current of at least one phase of the voltage source converter is detected to be greater than a first current threshold value and lasts for a first time threshold value; and / or under the condition that the bridge arm current of at least one phase of the voltage source converter is detected to be greater than a second current threshold value and lasts for a second time threshold value, controlling the voltage source converter to be secondarily temporarily locked, and controlling the current source converter to switch a bypass pair and / or shift phase. When the bridge arm current of the voltage source converter exceeds the device limit value, the voltage source converter is controlled to be temporarily locked, and meanwhile, the current source converter is controlled to switch the bypass pair and / or the phase shift, so that the current flowing into the voltage source converter from the current source converter is quickly inhibited, and the bridge arm current of the voltage source converter is inhibited from continuously increasing; and the reliability of the converter is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current transmission, in particular to an overcurrent control method and system for an AC parallel hybrid converter and the converter. BACKGROUND

[0002] A high-voltage direct current transmission system adopts a current source converter such as a line commutated converter (LCC). Since the LCC adopts a thyristor semi-controlled device, it cannot control turn-off, and thus consumes a large amount of reactive power and generates a large amount of harmonics during operation. Therefore, the LCC needs to be configured with an AC filter and a reactive power compensation device.

[0003] In order to improve the flexibility of reactive power control and reduce the floor area, a voltage source converter such as a static var generator can be configured to replace the traditional AC filter and reactive power compensation device for reactive power compensation and harmonic suppression. The voltage source converter can be connected in parallel with the current source converter at the valve side and connected to the AC system through a converter transformer or a reactor. This type of converter is referred to as an AC parallel hybrid converter (topology for series compensation with FB arms connected in parallel at the ac side of the LCC, PAC topology) or a self-adaption STATCOM and Line Commutated Converter (SLCC).

[0004] However, when the AC system fails, the voltage source converter will overcurrent, and if permanent blocking is taken, it will lead to failure of AC fault ride-through, resulting in blocking of the high-voltage direct current transmission system and thus threatening the safe operation of the power system. Therefore, it is necessary to control the overcurrent of the converter. SUMMARY

[0005] The present application provides an overcurrent control method and system for an AC parallel hybrid converter and the converter to realize overcurrent control of the converter.

[0006] Technical solution: The overcurrent control method for an AC parallel hybrid converter provided by the present application includes a current source converter and a voltage source converter, the current source converter and the voltage source converter are connected in parallel by phase, and the method includes:

[0007] In the case where it is detected that the bridge arm current of at least one phase of the voltage source converter is greater than a first current threshold and lasts for a first time threshold, the voltage source converter is controlled to be temporarily blocked; and / or,

[0008] In a case where it is detected that the bridge arm current of at least one phase of the voltage source converter is greater than the second current threshold and lasts for a second time threshold, the second temporary blocking of the voltage source converter is controlled, and the current source converter is controlled to throw a bypass pair and / or to shift phase.

[0009] In some embodiments, the AC parallel hybrid converter overcurrent control method further comprises:

[0010] In a case where it is detected that the bridge arm current of at least one phase of the voltage source converter is greater than the second current threshold and lasts for a third time threshold, the voltage source converter and the current source converter are controlled to be blocked.

[0011] In some embodiments, the method for controlling the temporary blocking of the voltage source converter comprises:

[0012] The switching device of the bridge arm or all bridge arms of the voltage source converter in which overcurrent is controlled to be turned off and lasts for a fourth time threshold.

[0013] In some embodiments, the current source converter comprises three phases, and each phase comprises an upper bridge arm and a lower bridge arm; the method for controlling the current source converter to throw a bypass pair comprises:

[0014] The upper bridge arm and the lower bridge arm of at least one phase of the current source converter are controlled to be turned on.

[0015] In some embodiments, the method for controlling the current source converter to shift phase comprises:

[0016] The firing angle of the current source converter is controlled to be greater than 110 degrees.

[0017] In some embodiments, the first current threshold is less than the second current threshold; the first current threshold ranges from 1.0 times to 4.0 times the rated current of the device; and the second current threshold ranges from 1.5 times to 6.0 times the rated current of the device.

[0018] In some embodiments, the first time threshold ranges from 0 μs to 1 ms; and the second time threshold has the same range as the first time threshold.

[0019] In some embodiments, the third time threshold ranges from 50 μs to 2 ms.

[0020] Correspondingly, the embodiments of the present application also provide an AC parallel hybrid converter overcurrent control system for executing the AC parallel hybrid converter overcurrent control method as described above; the system comprises a current source converter control device and a voltage source converter valve control device.

[0021] The voltage source converter valve control device is configured to control a first temporary blocking of the voltage source converter if it is detected that a bridge arm current of at least one phase of the voltage source converter is greater than a first current threshold for a first time threshold; and / or control a second temporary blocking of the voltage source converter if it is detected that the bridge arm current of at least one phase of the voltage source converter is greater than a second current threshold for a second time threshold.

[0022] The current source converter control device is configured to control a bypass pair throw-in and / or phase shift of the current source converter if it is detected that the bridge arm current of at least one phase of the voltage source converter is greater than the second current threshold for the second time threshold, or a second temporary blocking is received from the voltage source converter valve control device.

[0023] In some embodiments, the AC parallel hybrid converter overcurrent control system further comprises a voltage source converter control device;

[0024] The voltage source converter control device is configured to control a third temporary blocking of the voltage source converter if it is detected that the bridge arm current of at least one phase of the voltage source converter is greater than the first current threshold for the first time threshold; and / or

[0025] The voltage source converter control device is configured to control a fourth temporary blocking of the voltage source converter if it is detected that the bridge arm current of at least one phase of the voltage source converter is greater than the second current threshold for the second time threshold.

[0026] In some embodiments, the second temporary blocking of the voltage source converter valve control device is transmitted to the voltage source converter control device first, and then to the current source converter control device.

[0027] In some embodiments, the voltage source converter control device comprises:

[0028] A first detection unit configured to detect a first parameter of the voltage source converter;

[0029] A first control unit configured to control a temporary blocking of the voltage source converter according to the first parameter of the voltage source converter.

[0030] In some embodiments, the current source converter control device comprises:

[0031] A second detection unit configured to detect a second parameter of the current source converter;

[0032] A second control unit configured to control a bypass pair throw-in and / or phase shift of the current source converter according to the second parameter of the current source converter.

[0033] In some embodiments, the voltage source converter valve control device comprises:

[0034] a third detection unit configured to detect a third parameter of the voltage source converter;

[0035] a third control unit configured to control the voltage source converter to temporarily shut down according to the third parameter of the voltage source converter.

[0036] Correspondingly, the application also provides an AC parallel hybrid converter, which comprises the AC parallel hybrid converter overcurrent control system as described above.

[0037] Advantages: Compared with the prior art, the application provides an AC parallel hybrid converter overcurrent control method, system and converter, which comprises: controlling the voltage source converter to temporarily shut down in the case that the bridge arm current of at least one phase of the voltage source converter is greater than a first current threshold and lasts for a first time threshold; and / or controlling the voltage source converter to temporarily shut down and controlling the current source converter to throw bypass pairs and / or to shift phase in the case that the bridge arm current of at least one phase of the voltage source converter is greater than a second current threshold and lasts for a second time threshold. The overcurrent control method provided by the application controls the voltage source converter to temporarily shut down when the bridge arm current of the voltage source converter exceeds the device limit, and controls the current source converter to throw bypass pairs and / or to shift phase at the same time, so as to quickly inhibit the current flowing from the current source converter to the voltage source converter, inhibit the bridge arm current of the voltage source converter from continuing to increase, prevent the AC parallel hybrid converter from shutting down or being damaged, and effectively improve the reliability of the AC parallel hybrid converter. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort.

[0039] Figure 1 is a main circuit schematic diagram of an AC parallel hybrid converter provided in the embodiments of the application;

[0040] Figure 2 is a main circuit schematic diagram of another AC parallel hybrid converter provided in the embodiments of the application;

[0041] Figure 3 is a main circuit schematic diagram of another AC parallel hybrid converter provided in the embodiments of the application;

[0042] Figure 4 is a full-bridge submodule structure schematic diagram of a modular multilevel structure voltage source converter provided in an embodiment of the present application;

[0043] Figure 5 is a flow chart of an overcurrent control method of an AC parallel hybrid converter provided in an embodiment of the present application;

[0044] Figure 6 is a main circuit schematic diagram of a double six-pulse circuit composed of an AC parallel hybrid converter provided in an embodiment of the present application;

[0045] Figure 7a is a test waveform schematic diagram during an A-phase ground fault of an AC system provided in an embodiment of the present application;

[0046] Figure 7b is a test waveform schematic diagram during A-phase and B-phase short-circuit faults of an AC system provided in an embodiment of the present application;

[0047] Figure 8 is a structure schematic diagram of an overcurrent control system of an AC parallel hybrid converter provided in an embodiment of the present application.

[0048] Reference signs:

[0049] 1-current source converter; 2-voltage source converter; 3-converter transformer; 4-fourth reactor; 11-first current source converter; 12-first voltage source converter; 13-first converter transformer; 21-second current source converter; 22-second voltage source converter; 23-second converter transformer; 500-overcurrent control system of an AC parallel hybrid converter; 510-current source converter control device; 520-voltage source converter valve control device; 530-voltage source converter control device; 511-second detection unit; 512-second control unit; 521-third detection unit; 522-third control unit; 531-first detection unit; 532-first control unit. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative work fall within the scope of protection of the present application.

[0051] It should be understood that although the terms first, second, etc., may be used herein to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another. Therefore, the first component discussed below may be referred to as the second component without departing from the teachings of this application. As used herein, the term "and / or" includes all combinations of any and more of the associated listed items.

[0052] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments and may not be to scale. The modules or processes shown in the drawings are not necessarily essential for implementing this application and therefore should not be used to limit the scope of protection of this application.

[0053] Figure 1 This is a schematic diagram of the main circuit of an AC parallel hybrid converter provided in an embodiment of this application. For an example, please refer to... Figure 1 The AC parallel hybrid converter includes a current source converter 1 and a voltage source converter 2, with the AC sides of the current source converter 1 and the voltage source converter 2 connected in parallel according to phase.

[0054] The current source converter 1 is a six-pulse bridge circuit with six arms: three upper arms and three lower arms. Phases A, B, and C of the current source converter 1 each include upper and lower arms. Taking the inverter operation of the current source converter 1 as an example, the upper arm of phase A includes the fourth valve V4, the upper arm of phase B includes the sixth valve V6, and the upper arm of phase C includes the second valve V2. The lower arm of phase A includes the first valve V1, the lower arm of phase B includes the third valve V3, and the lower arm of phase C includes the fifth valve V5. The DC bus voltage connected to the upper arm of each phase is higher than the DC bus voltage connected to the lower arm of the same phase.

[0055] Among them, voltage source converter 2 is a three-phase star-connected circuit with three bridge arms. These three bridge arms include the seventh valve V7, the eighth valve V8, the ninth valve V9, the first reactor LSA1, the second reactor LSB1, and the third reactor LSC1.

[0056] For example, the voltage source converter 2 can also adopt a three-phase delta-connected circuit, which can be set according to the actual situation, and no specific limitation is made here.

[0057] Figure 2 This is a schematic diagram of the main circuit of another AC parallel hybrid converter provided in this embodiment. For an example, please refer to... Figure 2The AC parallel hybrid converter includes a current source converter 1, a voltage source converter 2, and a converter transformer 3. The current source converter 1 and voltage source converter 2 are connected in parallel phase by phase and then connected to the secondary side of the converter transformer 3. The connection points of the three phases on the secondary side of the converter transformer 3 are the first connection point U, the second connection point V, and the third connection point W. The voltages at the first connection point U, the second connection point V, and the third connection point W are u... Va u Vb u Vc The AC side currents of current source converter 1 are i V1a i V1b i V1c The bridge arm currents of voltage source converter 2 are i V2a i V2b i V2c The combined currents of current source converter 1 and voltage source converter 2 are i V3a i V3b i V3c .

[0058] Figure 3 This is a schematic diagram of the main circuit of another AC parallel hybrid converter provided in this embodiment. For an example, please refer to... Figure 3 The AC parallel hybrid converter includes a current source converter 1, a voltage source converter 2, and a fourth reactor 4. The current source converter 1 and the voltage source converter 2 are connected in parallel phase by phase and then connected to the fourth reactor 4. The three-phase connection points of the fourth reactor 4 are the first connection point U, the second connection point V, and the third connection point W, respectively. The voltages at the first connection point U, the second connection point V, and the third connection point W are u... Va u Vb u Vc The AC side currents of current source converter 1 are i V1a i V1b i V1c The bridge arm currents of voltage source converter 2 are i V2a i V2b i V2c The combined currents of current source converter 1 and voltage source converter 2 are i V3a i V3b i V3c .

[0059] In some embodiments, the current source converter 1 includes a line commutated converter (LCC), a controllable line commutated converter (CLCC), a hybrid line commutated converter (HLCC), or a hybrid commutated converter (HCC). The voltage source converter 2 includes at least one of a modular multilevel structure, a hybrid multilevel structure, a two-level cascaded structure, and a stacked two-level structure.

[0060] Among them, grid-commutated converters include semi-controlled devices, while controlled-commutated converters, controlled-commutated hybrid converters, and hybrid-commutated converters include fully controlled devices and / or semi-controlled devices, respectively. The fully controlled devices of controlled-commutated converters (CLCC) and controlled-commutated hybrid converters (HLCC) include, but are not limited to, insulated-gate bipolar transistors (IGBTs) and integrated-gate commutated thyristors (IGCTs). The fully controlled devices of hybrid-commutated converters (HCC) include, but are not limited to, integrated-gate commutated thyristors. In a controllable commutated converter (CLCC), each bridge arm uses a parallel full control valve and a semi control valve. In a controllable commutated hybrid converter (HLCC), the three upper bridge arms or the three lower bridge arms share a single full control valve, and semi control valves are connected to the bridge arms separately. In a hybrid commutated converter (HCC), reverse-resistance type IGCT devices are used instead of thyristors. All three types of converters have the function of suppressing commutation failure during AC transient faults.

[0061] For example, current source converter 1 is a grid-commutated converter, and voltage source converter 2 is a static var generator (SVG).

[0062] For example, the voltage source converter is a static var compensator (SVC) or a static synchronous compensator (STATCOM).

[0063] Figure 4 This is a schematic diagram of a full-bridge submodule structure of a modular multilevel voltage source converter provided in an embodiment of this application. For an example, please refer to [link to example]. Figure 4The full-bridge submodule comprises four IGBT modules (IGBT module T1, IGBT module T2, IGBT module T3, and IGBT module T4) and one capacitor C1. When IGBT module T1 and IGBT module T4 are turned on, and IGBT module T2 and IGBT module T3 are turned off, the full-bridge submodule presents a positive voltage between port X1 and port X2. When IGBT module T1 and IGBT module T4 are turned off, and IGBT module T2 and IGBT module T3 are turned on, the full-bridge submodule presents a negative voltage between port X1 and port X2.

[0064] Figure 5 This is a flowchart illustrating an overcurrent control method for an AC parallel hybrid converter provided in an embodiment of this application. Please refer to... Figure 5 The method includes the following steps:

[0065] S110. If the arm current of at least one phase of the voltage source converter is detected to be greater than the first current threshold and continues for a first time threshold, the voltage source converter is controlled to be temporarily blocked.

[0066] The bridge arm current of the voltage source converter can be obtained in real time by current sensing elements such as current transformers.

[0067] The first current threshold value ranges from 1.0 to 4.0 times the device's rated current. For example, for a 3000A IGBT device, the first current threshold value is 4700A.

[0068] The first time threshold ranges from 0 μs to 1 ms, for example, a value of 50 μs.

[0069] In some embodiments, the method of controlling the temporary blocking of a voltage source converter includes: controlling the switching devices of the bridge arm or all bridge arms of the voltage source converter to turn off for a fourth time threshold.

[0070] The fourth time threshold ranges from 2ms to 100ms, for example, 6ms; the control switch is turned off by sending a low-level signal to the switch.

[0071] For example, with Figure 2 and Figure 3 For example, when the A-phase bridge arm current i of voltage source converter 2 is detected... V2aIf the current exceeds the first current threshold (e.g., 4700A) and lasts for the first time threshold (e.g., 50μs), the switching devices of all bridge arms of the voltage source converter 2 are turned off and last for the fourth time threshold (e.g., 6ms); alternatively, only the switching devices of the A-phase bridge arm of the voltage source converter 2 are turned off and last for the fourth time threshold.

[0072] S120. If the arm current of at least one phase of the voltage source converter is detected to be greater than the second current threshold and continues for a second time threshold, the voltage source converter is controlled to be temporarily blocked, and the current source converter is controlled to switch to bypass and / or phase shift.

[0073] The first current threshold is less than the second current threshold. The second current threshold ranges from 1.5 to 6.0 times the device's rated current. For example, for a 3000A IGBT device, the first current threshold is 5200A.

[0074] The second time threshold ranges from 0 μs to 1 ms, for example, a value of 20 μs.

[0075] It should be noted that the duration of the first temporary blocking and the second temporary blocking (i.e., the fourth time threshold) can be the same or different. The specific duration can be set according to the actual situation, and no specific limitation is made here.

[0076] In some embodiments, the method of controlling the bypass pair of a current source converter includes: controlling the upper arm and the lower arm of at least one phase of the current source converter to be turned on.

[0077] In some embodiments, the control current source converter bypass pair is activated either immediately or after a delay.

[0078] By controlling the bypass pair of the current source converter, the DC current of the current source converter can no longer flow into the voltage source converter, suppressing the continued increase of the bridge arm current of the voltage source converter, preventing the AC parallel hybrid converter from being locked out or damaged, and effectively improving the reliability of the AC parallel hybrid converter.

[0079] For example, with Figure 2 and Figure 3 Taking the AC parallel hybrid converter shown as an example, if the current source converter 1 is operating in inverter mode, when the A-phase bridge arm current i of the voltage source converter 2 is detected... V2aWhen the current exceeds the second current threshold (e.g., 5200A) and remains above the second time threshold (20μs), the switching devices of all bridge arms of the control voltage source converter 2 are turned off and remain above the fourth time threshold (e.g., 30ms). Simultaneously, the sixth valve V6 and the third valve V3 of phase B of the control current source converter 1 are turned on, preventing the DC current of the current source converter 1 from being inverted to the AC side. Instead, the DC current flows directly through the sixth valve V6 and the third valve V3, and the AC side current i... V1a The phase-to-phase follow current is reduced or decreased, thereby reducing the current flowing from the current source converter 1 into the seventh valve V7.

[0080] In some embodiments, the method for controlling the phase shift of a current source converter includes controlling the firing angle of the current source converter to be greater than 110 degrees.

[0081] For example, with Figure 2 and Figure 3 Taking the AC parallel hybrid converter shown as an example, if the current source converter 1 is operating in rectification mode, when the A-phase bridge arm current i of the voltage source converter 2 is detected... V2a When the current exceeds the second current threshold (e.g., 5200A) and remains above the second time threshold (20μs), the switching devices of all bridge arms of the voltage source converter 2 are turned off and remain off for the fourth time threshold (e.g., 30ms), and the current source converter 1 is phase-shifted (e.g., the firing angle is controlled to be 164 degrees), causing the AC side current i of the current source converter 1 to... V1a This reduces the current flowing from the current source converter 1 into the seventh valve V7.

[0082] Specifically, when the arm current of at least one phase of the voltage source converter is detected to be greater than a first current threshold and remain at a first time threshold, the voltage source converter is controlled to undergo a first temporary blocking; and / or, when the arm current of at least one phase of the voltage source converter is detected to be greater than a second current threshold and remain at a second time threshold, the voltage source converter is controlled to undergo a second temporary blocking, and the current source converter is controlled to switch to a bypass pair and / or phase shift. The first current threshold is less than the second current threshold, thereby allowing for graded overcurrent control based on the severity of the overcurrent phenomenon in the voltage source converter, improving the reliability of the AC parallel hybrid converter. For example, when a minor overcurrent phenomenon occurs in the voltage source converter (i.e., the arm current of the voltage source converter is greater than the first current threshold and remains at the first time threshold), controlling the first temporary blocking of the voltage source converter quickly suppresses the current flowing into the voltage source converter from the current source converter. When a large overcurrent occurs in the voltage source converter (i.e., the arm current of the voltage source converter is greater than the second current threshold and remains above the second time threshold), the second temporary blocking of the voltage source converter is controlled, and the bypass pair and / or phase shift of the current source converter are controlled, which quickly suppresses the current flowing from the current source converter into the voltage source converter and suppresses the continued increase of the arm current of the voltage source converter, effectively improving the reliability of the AC parallel hybrid converter.

[0083] In some embodiments, the AC parallel hybrid converter overcurrent control method further includes: controlling the voltage source converter and the current source converter to lock out when it is detected that the arm current of at least one phase of the voltage source converter is greater than a second current threshold and continues for a third time threshold.

[0084] The value of the third time threshold ranges from 100μs to 10ms, for example, a value of 1ms.

[0085] Controlling the blocking of voltage source converters and current source converters involves turning off and stopping the switching devices of all bridge arms of the voltage source converter.

[0086] Figure 6 This is a schematic diagram of the main circuit of a dual six-pulse circuit composed of an AC parallel hybrid converter, as provided in an embodiment of this application. For an example, please refer to... Figure 6 The dual six-pulse circuit includes two Y-bridge AC parallel hybrid converters, namely a first Y-bridge AC parallel hybrid converter and a second Y-bridge AC parallel hybrid converter. Each of the first and second Y-bridge AC parallel hybrid converters includes one current source converter, one voltage source converter, and one converter transformer, as described above. For example, the first Y-bridge AC parallel hybrid converter includes a first current source converter 11, a first voltage source converter 12, and a first converter transformer 13. The AC side current of the first current source converter 11 is i... VY1a i VY1b i VY1c The bridge arm currents of the first voltage source converter 12 are i VY2a i VY2b i VY2c The resultant current of the two is i VY3a i VY3b i VY3c The second Y-bridge AC parallel hybrid converter includes a second current source converter 21, a second voltage source converter 22, and a second converter transformer 23. The AC side currents of the second current source converter 21 are i... VD1a i VD1b i VD1c The bridge arm currents of the second voltage source converter 22 are i VD2a i VD2b i VD2c The resultant current of the two is i VD3a i VD3b i VD3c The grid-side voltages are u A1 u B1 u C1 and u A2 uB2 u C2 The grid-side currents are i A1 i B1 i C1 and i A2 i B2 i C2 The DC-side voltages are UDL1 and UDL2, and the DC-side currents are IDC1 and IDC2, respectively.

[0087] Figure 7a This is a schematic diagram of a test waveform during a phase A ground fault in an AC system, provided in an embodiment of this application. Figure 7b This is a schematic diagram of a test waveform during a two-phase short-circuit fault (phases A and B) in an AC system, as provided in an embodiment of this application. For example, Figure 7a , Figure 7b This is the overcurrent control waveform of the converter inverter during AC system fault operation in the embodiments of this application. Figure 6 The circuit structure shown has the following corresponding signal meanings: u A1 u B1 u C1 These represent the AC voltages of phases A, B, and C on the grid side, respectively; i VY1a i VY1b i VY1c These represent the three-phase AC currents of the Y-bridge current source converter; i VY2a i VY2b i VY2c These represent the three-phase currents of the Y-bridge voltage source converter; IDC1 represents the positive DC current; UDL1 represents the positive DC voltage; SVF1_OCP1_BLOCK represents the first temporary blockade; SVF1_OCP2_BLOCK represents the second temporary blockade; RETARD represents phase shift; BPPO represents the bypass pair.

[0088] For example, Figure 7a This is a test waveform from an embodiment of this application during a phase A ground fault in an AC system. Figure 7a As can be seen, the fault time is 120ms. During the fault period, the B-phase bridge arm current i of the voltage source converter... VY2b When the current exceeds 4700A, the first temporary blockade is triggered (SVF1_OCP1_BLOCK is set to high level), all bridge arms of the voltage source converter are blocked, the bridge arm current of the voltage source converter drops rapidly, and after the fourth time threshold (6ms), the voltage source converter is unlocked again, realizing reliable ride-through during AC faults. Figure 7b These are test waveforms from embodiments of this application during short-circuit faults in phases A and B of an AC system. Figure 7bAs can be seen, the fault time is 100ms, and during the fault period, the B-phase bridge arm current i of the voltage source converter... VY2b If the current exceeds 5200A, the first temporary block (SVF1_OCP1_BLOCK set high) and the second temporary block (SVF1_OCP2_BLOCK set high) are triggered, blocking all bridge arms of the voltage source converter. At the same time, the current source converter is bypassed (BPPO set high) and phase-shifted (RETARD set high). The bridge arm current of the voltage source converter drops rapidly, and the DC current of the current source converter flows through the bypass pair. The AC current continues under the action of the converter transformer but does not flow into the voltage source converter. After the fourth time threshold (30ms), the voltage source converter is unlocked again, realizing reliable ride-through during AC faults.

[0089] Figure 8 This is a schematic diagram of the overcurrent control system for an AC parallel hybrid converter provided in an embodiment of this application. Please refer to... Figure 8 The AC parallel hybrid converter overcurrent control system 500 includes: a current source converter control device 510 and a voltage source converter valve control device 520; the voltage source converter valve control device 520 is used to control the voltage source converter to temporarily lock out a first temporary current when it detects that the arm current of at least one phase of the voltage source converter is greater than a first current threshold and remains so for a first time threshold; and / or, to control the voltage source converter to temporarily lock out a second temporary current when it detects that the arm current of at least one phase of the voltage source converter is greater than a second current threshold and remains so for a second time threshold. The current source converter control device 510 is used to control the current source converter to switch to a bypass pair and / or shift phases when it detects that the arm current of at least one phase of the voltage source converter is greater than the second current threshold and remains so for a second time threshold, or when it receives the second temporary lockout from the voltage source converter valve control device.

[0090] The technical solution of this application embodiment provides an overcurrent control system for an AC parallel hybrid converter. By controlling the voltage source converter to temporarily lock out when the arm current of the voltage source converter exceeds the device limit, and simultaneously controlling the current source converter to switch to bypass and / or phase shift, the system quickly suppresses the current flowing from the current source converter to the voltage source converter, suppresses the continued increase of the arm current of the voltage source converter, and effectively improves the reliability of the AC parallel hybrid converter.

[0091] In some embodiments, the AC parallel hybrid converter overcurrent control system further includes a voltage source converter control device 530; the voltage source converter control device 530 is configured to control a third temporary blockade of the voltage source converter when it is detected that the arm current of at least one phase of the voltage source converter is greater than a first current threshold and remains at a first time threshold; and / or, to control a fourth temporary blockade of the voltage source converter when it is detected that the arm current of at least one phase of the voltage source converter is greater than a second current threshold and remains at a second time threshold.

[0092] In some embodiments, if the AC parallel hybrid converter overcurrent control system further includes a voltage source converter control device 530, the second temporary blocking of the voltage source converter valve control device 520 is first transmitted to the voltage source converter control device 530 and then to the current source converter control device 510.

[0093] In some embodiments, the voltage source converter control device 530 includes: a first detection unit 531 for detecting a first parameter of the voltage source converter; and a first control unit 532 for controlling the voltage source converter to temporarily lock out according to the first parameter of the voltage source converter.

[0094] The first parameter is the three-phase bridge arm current of the voltage source converter. The first detection unit 531 can be a current detection element such as a current transformer, and the specific configuration can be set according to the actual situation, without specific limitations here.

[0095] In some embodiments, the current source converter control device 510 includes: a second detection unit 511 for detecting a second parameter of the current source converter; and a second control unit 512 for controlling the current source converter to switch to bypass pairs and / or phase shift according to the second parameter of the current source converter.

[0096] The second parameter is the AC side current of the current source converter. The second detection unit 511 can be a current detection element such as a current transformer, and the specific configuration can be set according to the actual situation, without specific limitations here.

[0097] In some embodiments, the voltage source converter valve control device 520 includes: a third detection unit 521 for detecting a third parameter of the voltage source converter; and a third control unit 522 for controlling the temporary blocking of the voltage source converter according to the third parameter of the voltage source converter.

[0098] The third parameter is the bridge arm current of the voltage source converter. The third detection unit 521 can be a current sensing element such as a current transformer; the specific configuration can be determined based on actual conditions and is not limited here.

[0099] Accordingly, this application also provides an AC parallel hybrid converter, which includes the AC parallel hybrid converter overcurrent control system described in any embodiment of this application.

[0100] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0101] The above provides a detailed description of the AC parallel hybrid converter overcurrent control method, system, and converter provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for overcurrent control of an AC parallel hybrid converter, characterized in that, The AC parallel hybrid converter includes a current source converter and a voltage source converter, wherein the current source converter and the voltage source converter are connected in parallel in phase, and the method includes: If the arm current of at least one phase of the voltage source converter is detected to be greater than a first current threshold and remains greater than a first time threshold, the voltage source converter is controlled to undergo a first temporary blockout; and / or, If it is detected that the arm current of at least one phase of the voltage source converter is greater than the second current threshold and remains greater than the second time threshold, the voltage source converter is controlled to be temporarily blocked for a second time, and the current source converter is controlled to switch to bypass and / or shift phases.

2. The overcurrent control method for an AC parallel hybrid converter according to claim 1, characterized in that, Also includes: If the arm current of at least one phase of the voltage source converter is detected to be greater than the second current threshold and continues for a third time threshold, the voltage source converter and the current source converter are controlled to be locked out.

3. The overcurrent control method for an AC parallel hybrid converter according to claim 1, characterized in that, A method for controlling the temporary blocking of the voltage source converter includes: The switching devices of the voltage source converter that have an overcurrent in the bridge arm or all bridge arms are turned off and remain off for a fourth time threshold.

4. The overcurrent control method for an AC parallel hybrid converter according to claim 1, characterized in that, The current source converter includes three phases, and each phase includes an upper bridge arm and a lower bridge arm; the method for controlling the current source converter to switch on a bypass pair includes: Control the conduction of the upper and lower bridge arms of at least one phase of the current source converter.

5. The overcurrent control method for an AC parallel hybrid converter according to claim 1, characterized in that, The method for controlling the phase shift of the current source converter includes: The firing angle of the current source converter is controlled to be greater than 110 degrees.

6. The overcurrent control method for an AC parallel hybrid converter according to claim 1, characterized in that, The first current threshold is less than the second current threshold; the value range of the first current threshold is 1.0 to 4.0 times the rated current of the device; the value range of the second current threshold is 1.5 to 6.0 times the rated current of the device.

7. The overcurrent control method for an AC parallel hybrid converter according to claim 1, characterized in that, The first time threshold ranges from 0 μs to 1 ms; the second time threshold ranges from the same range as the first time threshold.

8. The overcurrent control method for an AC parallel hybrid converter according to claim 2, characterized in that, The value range of the third time threshold is 50μs to 2ms.

9. An overcurrent control system for an AC parallel hybrid converter, characterized in that, The system is used to perform the overcurrent control method for an AC parallel hybrid converter as described in any one of claims 1-8; the system includes a current source converter control device and a voltage source converter valve control device; The voltage source converter valve control device is used to control the voltage source converter to temporarily lock out when it detects that the arm current of at least one phase of the voltage source converter is greater than a first current threshold and continues for a first time threshold. And / or, if the arm current of at least one phase of the voltage source converter is detected to be greater than a second current threshold and remains greater than a second time threshold, the voltage source converter is controlled to undergo a second temporary blocking. The current source converter control device is used to control the current source converter to switch to a bypass pair and / or shift phases when it detects that the arm current of at least one phase of the voltage source converter is greater than the second current threshold and continues for the second time threshold, or when it receives the second temporary blockage issued by the voltage source converter valve control device.

10. The AC parallel hybrid converter overcurrent control system according to claim 9, characterized in that, It also includes a voltage source converter control device; The voltage source converter control device is configured to control a third temporary blockade of the voltage source converter when it detects that the arm current of at least one phase of the voltage source converter is greater than the first current threshold and remains so for the first time threshold; and / or, If the arm current of at least one phase of the voltage source converter is detected to be greater than the second current threshold and remains greater than the second time threshold, the voltage source converter is controlled to be temporarily blocked for the fourth time.

11. The AC parallel hybrid converter overcurrent control system according to claim 10, characterized in that, The second temporary lockout of the voltage source converter valve control device is first transmitted to the voltage source converter control device, and then to the current source converter control device.

12. The AC parallel hybrid converter overcurrent control system according to claim 10, characterized in that, The voltage source converter control device includes: The first detection unit is used to detect the first parameter of the voltage source converter; A first control unit is configured to temporarily lock out the voltage source converter based on the first parameter of the voltage source converter.

13. The AC parallel hybrid converter overcurrent control system according to claim 9, characterized in that, The current source converter control device includes: The second detection unit is used to detect the second parameter of the current source converter; The second control unit is used to control the current source converter to switch on bypass pairs and / or shift phases according to the second parameter of the current source converter.

14. The AC parallel hybrid converter overcurrent control system according to claim 9, characterized in that, The voltage source converter valve control device includes: The third detection unit is used to detect the third parameter of the voltage source converter; The third control unit is used to control the temporary blocking of the voltage source converter according to the third parameter of the voltage source converter.

15. An AC parallel hybrid converter, characterized in that, Including the AC parallel hybrid converter overcurrent control system as described in any one of claims 9-14.

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