Current source type converter valve and current source type converter valve system

Abstract

The utility model provides a current source type converter valve and a current source type converter valve system, and the current source type converter valve comprises a plurality of bridge arms, each bridge arm comprises a plurality of converter modules connected in series, the plurality of converter modules comprise a first converter module, the first converter module comprises a plurality of first converter units connected in series, and the first converter units comprise a plurality of second converter units connected in series; the first commutation unit comprises a full-control device and a voltage-sharing module, the voltage-sharing module is connected in parallel to two ends of the full-control device, the voltage-sharing module comprises a charging unit and a discharging unit, the charging unit and the discharging unit share a target capacitor, and the charging unit comprises a first thyristor connected in series with the target capacitor; the discharging unit comprises a second thyristor connected with the target capacitor in series, the first end of the first thyristor is the first end of the charging unit, the second end of the second thyristor is the first end of the discharging unit, and the second end of the target capacitor is the second end shared by the charging unit and the discharging unit. The problem that a current source type converter valve is prone to phase commutation failure under the fault condition in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current transmission, in particular to a current source converter and a current source converter system. BACKGROUND

[0002] As a high-efficiency and stable power transmission mode, high-voltage direct current (HVDC) has been widely applied and developed in recent years. The traditional scheme mainly adopts a grid commutation converter based on a half-controlled device (such as a thyristor), and the biggest disadvantage of the traditional scheme is that the device cannot be self-turn-off, and when a system fault occurs, the commutation failure is easily caused due to insufficient turn-off angle, thereby threatening the safety of the grid. CONTENT OF THE UTILITY MODEL

[0003] The main purpose of the embodiments of the present application is to provide a current source converter and a current source converter system, so as to at least solve the problem that the current source converter is prone to commutation failure in a fault condition in the related art.

[0004] In order to achieve the above-mentioned purpose, according to one aspect of the embodiments of the present application, a current source converter is provided, comprising: a plurality of bridge arms, the bridge arm comprising a plurality of series-connected converter modules, the plurality of converter modules comprising a first converter module, the first converter module comprising a plurality of series-connected first converter units, the first converter unit comprising a fully-controlled device and a voltage balancing module, the voltage balancing module being connected in parallel at both ends of the fully-controlled device, the voltage balancing module comprising a charging unit and a discharging unit, the charging unit and the discharging unit sharing a target capacitor, the charging unit comprising a first thyristor connected in series with the target capacitor, the discharging unit comprising a second thyristor connected in series with the target capacitor, a first end of the first thyristor being a first end of the charging unit, a second end of the second thyristor being a first end of the discharging unit, the first end of the charging unit being electrically connected with a first end of the fully-controlled device and a first end of the discharging unit respectively, a second end of the first thyristor being electrically connected with a first end of the second thyristor, a second end of the target capacitor being a shared second end of the charging unit and the discharging unit, and the shared second end of the charging unit and the discharging unit being electrically connected with a second end of the fully-controlled device.

[0005] Optionally, the voltage balancing module comprises: a first target voltage balancing unit and a second target voltage balancing unit, the first target voltage balancing unit being connected in parallel at both ends of the fully-controlled device, and the second target voltage balancing unit being electrically connected with the first target voltage balancing unit.

[0006] Optionally, the second target voltage-sharing unit comprises a charging unit and a discharging unit, wherein a first end of the charging unit is electrically connected to the first end of the first target voltage-sharing unit, and a second end of the charging unit is electrically connected to the second end of the first target voltage-sharing unit; a first end of the discharging unit is electrically connected to the first target voltage-sharing unit, and a second end of the discharging unit is electrically connected to the second end of the first target voltage-sharing unit.

[0007] Optionally, the first target voltage-sharing unit comprises a first resistor, a first diode and a second capacitor, wherein the first resistor is connected in parallel with the first diode, the second capacitor is connected in series with a parallel branch of the first resistor and the first diode, a first end of the first resistor is electrically connected to the first end of the full-control device and the first end of the second target voltage-sharing unit respectively, and a second end of the second capacitor is electrically connected to the second end of the full-control device and the second end of the second target voltage-sharing unit respectively.

[0008] Optionally, the plurality of converter modules further comprises a second converter module, the second converter module comprises a plurality of second converter units connected in series, the second converter unit comprises a semi-control device and a third target voltage-sharing unit, the second converter module is connected in series with the first converter module, and the third target voltage-sharing unit is connected in parallel with the semi-control device.

[0009] Optionally, the third target voltage-sharing unit comprises a third capacitor and a second resistor connected in series.

[0010] Optionally, the third target voltage-sharing unit comprises a third capacitor, a second resistor and a second diode, the second resistor is connected in parallel with the second diode, and the third capacitor is connected in series with a parallel branch of the second resistor and the second diode.

[0011] Optionally, the full-control device comprises an IGCT and an IGBT.

[0012] Optionally, the semi-control device comprises a thyristor.

[0013] According to another aspect of the embodiments of the present application, a current source type converter valve system is provided, comprising the current source type converter valve.

[0014] The technical scheme of the embodiment of the application is applied to the first commutation unit in the current source type converter valve, wherein the full-controlled device and the voltage sharing module are connected in parallel, the voltage sharing module comprises a charging unit and a discharging unit, the charging unit and the discharging unit share a target capacitor, the charging unit comprises a first thyristor, the discharging unit comprises a second thyristor, the first thyristor is connected in series with the target capacitor and the second thyristor, and the second thyristor is connected in series with the target capacitor. When the full-controlled device is actively turned off, the charging unit bears the positive voltage drop generated by the turning off, the first thyristor is turned on, the overvoltage is transmitted to the target capacitor, and the voltage of the target capacitor gradually rises to form a positive commutation voltage, so that the active commutation is better realized. The overvoltage generated in the active turning off process of the full-controlled device is absorbed by the voltage sharing module, and the active commutation voltage is effectively formed. The active commutation voltage can quickly and reliably complete the active turning off in the system fault, resist the commutation failure, and enhance the fault ride-through capability of the converter valve, so that the problem that the converter valve is prone to commutation failure in the power system fault is solved. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The present application is not limited by the accompanying drawings.

[0016] Figure 1 A structure schematic diagram of a first current source type converter valve provided in an embodiment of the present application is shown;

[0017] Figure 2 A structure schematic diagram of a second current source type converter valve provided in an embodiment of the present application is shown;

[0018] Figure 3 A structure schematic diagram of a third current source type converter valve provided in an embodiment of the present application is shown;

[0019] Figure 4 A structure schematic diagram of a fourth current source type converter valve provided in an embodiment of the present application is shown;

[0020] Figure 5 A structure schematic diagram of a fifth current source type converter valve provided in an embodiment of the present application is shown;

[0021] Figure 6 A structure schematic diagram of a sixth current source type converter valve provided in an embodiment of the present application is shown.

[0022] In the above drawings, the following reference signs are used:

[0023] 10, commutation module; 11, first commutation module; 12, first commutation unit; 13, fully controlled device; 14, voltage equalization module; 141, charging unit; 142, discharging unit; 143, first target voltage equalization unit; 144, second target voltage equalization unit; 15, second commutation module; 16, second commutation unit; 17, semi-controlled device; 171, third target voltage equalization unit. DETAILED DESCRIPTION

[0024] It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict. The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0025] In order for those skilled in the art to better understand the present application, 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 a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0026] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0027] As introduced in the background, the related art mainly uses a grid commutation converter based on a semi-controlled device (such as a thyristor). When a system fails, it is easy to cause commutation failure due to insufficient turn-off angle, which threatens the safety of the grid. To solve the problem that the current source type commutation valve in the related art is prone to commutation failure under fault conditions, the embodiments of the present application provide a current source type commutation valve and a current source type commutation valve system.

[0028] 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.

[0029] According to an aspect of the present application, a current source type commutation valve is provided, such as Figures 1 to 3As shown, the current source type converter includes a plurality of bridge arms, each bridge arm including a plurality of series-connected converter modules 10, the plurality of converter modules 10 including a first converter module 11, the first converter module 11 including a plurality of series-connected first converter cells 12, the first converter cell 12 including a unidirectional device 13 and a voltage balancing module 14, the voltage balancing module 14 being connected in parallel across the unidirectional device 13, the voltage balancing module 14 including a charging unit 141 and a discharging unit 142, the charging unit 141 and the discharging unit 142 sharing a target capacitor C1, the charging unit 141 including a first thyristor T1 connected in series with the target capacitor C1, the discharging unit 142 including a second thyristor T2 connected in series with the target capacitor C1, a first end of the first thyristor T1 being a first end of the charging unit 141, a second end of the second thyristor T2 being a first end of the discharging unit 142, the first end of the charging unit 141 being electrically connected to a first end of the unidirectional device 13 and the first end of the discharging unit 142 respectively, a second end of the first thyristor T1 being electrically connected to a first end of the second thyristor T2, a second end of the target capacitor C1 being a shared second end of the charging unit 141 and the discharging unit 142, the shared second end of the charging unit 141 and the discharging unit 142 being electrically connected to a second end of the unidirectional device 13.

[0030] By providing the unidirectional device and the voltage balancing module in parallel in the first converter cell in the current source type converter of the application, the voltage balancing module includes the charging unit and the discharging unit, the charging unit and the discharging unit share the target capacitor, the charging unit includes the first thyristor, the discharging unit includes the second thyristor, the first thyristor is connected in series with the target capacitor and the second thyristor respectively, and the second thyristor is connected in series with the target capacitor. When the unidirectional device is actively turned off, the charging unit bears the forward voltage drop generated by the turn-off, the first thyristor is turned on, the overvoltage is transmitted to the target capacitor, and the voltage of the target capacitor gradually rises to build a forward commutation voltage, which better realizes active commutation. By absorbing the overvoltage generated during the active turn-off of the unidirectional device through the voltage balancing module, the active commutation voltage is effectively built, which can quickly and reliably complete the active turn-off during system failure, resist commutation failure, and enhance the fault ride-through capability of the converter valve. In this way, the problem of commutation failure of the converter valve under power system fault is solved.

[0031] The valve arm is composed of dozens or even hundreds of high-voltage and high-power devices in series. Due to the slight differences in reverse recovery charge characteristics, junction capacitance, and driving signal delay of each device, a huge dynamic voltage distribution imbalance will occur during high-speed turn-off, which will easily cause individual devices to break down first due to overvoltage, triggering a chain reaction and causing the entire valve arm to fail. The voltage balancing module of the application forcibly balances the dynamic voltage of the unidirectional device during turn-off, overcoming the insufficient voltage balancing capability of traditional voltage balancing circuits under high-frequency and large-current turn-off, and also solving the problem of dynamic voltage distribution imbalance between series-connected devices, significantly improving the operation reliability and device safety of the converter valve.

[0032] In the above embodiment, the structure of the current source type converter valve can be a three-phase six-bridge arm circuit including a, b and c three phases, each phase is connected with an alternating current power supply, the alternating current power supply is connected with a transformer, and the transformer can transform the current provided by the alternating current power supply, so that the power devices in the converter module can normally operate. The three-phase six-bridge arm circuit topology can realize current commutation and voltage control in high voltage direct current transmission, and is the core of the operation of the converter valve.

[0033] When the current source type converter valve is normally operated, the converter valve needs to receive a trigger pulse signal after the natural commutation point (line voltage zero crossing point) to perform commutation. At this time, due to the decrease of the external circuit voltage (AC grid line voltage), the on-state current of the power devices of the converter module flowing through the bridge arm slowly decreases, and the power devices can work in the continuous small current off state. The above voltage balancing module can passively balance and actively balance the power devices in the converter module. The passive balancing is that during the small current off process of the series bridge arm, the difference between the parameters and performances of the power devices will cause the inconsistent off actions of the devices, so that some off devices bear excessive voltage, and the passive balancing can be realized through the buffer circuit in the parallel voltage balancing module.

[0034] When the fault occurs, when the receiving end AC grid voltage is in the rated range (1±0.15p.u.), the current source type converter valve adopts the phase control operation mode. The active balancing is that when the AC grid voltage drops due to the fault of the AC grid, the voltage balancing module parallelly connected with the first converter unit in the bridge arm can enter the circuit to construct the commutation voltage in time, effectively resist the commutation failure, protect the voltage imbalance damage of the all-controllable devices caused by the large current impact, and improve the reliability and fault ride-through capability of the whole converter valve system.

[0035] And the first converter unit is used for active balancing in the embodiment of the present application, and multiple active off can be realized. Compared with the voltage balancing scheme in the related art, in which the MOV is set as the off voltage balancing circuit, the MOV is used to limit the voltage stress of the active commutation converter valve during the active commutation, but the MOV cannot realize continuous multiple active off due to the upper limit of the energy.

[0036] In the above embodiment, the multiple converter modules include the first converter module, which can be all the converter modules, or part of the converter modules, and the other part of the converter modules is the second converter module, wherein the types of the power devices in the first converter module and the second converter module are different, so that the current source type converter valve can simultaneously integrate the characteristics of two different power devices, and can have the functions of high voltage resistance and controllable commutation. By reasonably configuring the proportion of the first converter module and the second converter module, the current source type converter valve can have economy and reliability.

[0037] In some alternative implementations, such as Figure 2 As shown, the voltage equalization module 14 includes a first target voltage equalization unit 143 and a second target voltage equalization unit 144. The first target voltage equalization unit 143 is connected in parallel across the two ends of the fully controlled device 13, and the second target voltage equalization unit 144 is electrically connected to the first target voltage equalization unit 143. The first target voltage equalization unit 143 is used to equalize the voltage between adjacent fully controlled devices 13, and the second target voltage equalization unit 144 is used to absorb the voltage generated by the fully controlled device 13 during active shutdown. The first target voltage equalization unit 143 is a passive voltage equalization unit in the voltage equalization module 14. Its parallel connection across the two ends of the fully controlled device 13 allows for passive voltage equalization when the shutdown actions of multiple fully controlled devices 13 are inconsistent, preventing overvoltage in the fully controlled device 13. The second target voltage equalization unit 144 is an active voltage equalization unit in the voltage equalization module 14. During normal operation of the current source converter valve, the second target voltage equalization unit 144 does not participate in the operation of the current source converter valve, thus reducing the daily operating losses of the current source converter valve. When a current-source converter valve experiences an AC fault and the fully controlled device 13 is actively shut down, the second target voltage equalization unit 144 enters the current-source converter valve to actively equalize voltage. This absorbs the excess voltage (overvoltage) generated in the faulty bridge arm (also known as the bridge arm to be deactivated) due to the active shutdown of the fully controlled device 13. This achieves both voltage equalization and the establishment of a commutation voltage, preventing voltage imbalance damage to the fully controlled device 13 caused by large current surges. By employing the aforementioned circuit that integrates autonomous commutation voltage construction and voltage equalization, commutation voltage is effectively established during bridge arm faults, preventing commutation failure and significantly improving system reliability.

[0038] The second target voltage equalization unit includes a charging process and a discharging process during the active shutdown process. In some optional implementations, such as... Figure 2 As shown, the second target voltage equalization unit 144 includes a charging unit 141 and a discharging unit 142. The first end of the charging unit 141 is electrically connected to the first end of the first target voltage equalization unit 143, and the second end of the charging unit 141 is electrically connected to the second end of the first target voltage equalization unit 143. The first end of the discharging unit 142 is electrically connected to the first target voltage equalization unit 143, and the second end of the discharging unit 142 is electrically connected to the second end of the first target voltage equalization unit 143. The charging unit 141 is used to actively shut off the redundant commutation current generated by the fully controlled device 13 under high current conditions when a bridge arm fault occurs, and then send it to the target capacitor for storage to construct the commutation voltage. The discharging unit 142 is used to discharge the charge stored in the target capacitor in the charging unit 141 to the fully controlled device 13 after successful commutation, avoiding charge accumulation. Through the dynamic linkage control of the charging unit 141 and the discharging unit 142, the autonomous switching of the second target voltage equalization unit 144 under different operating conditions is realized, improving the flexibility and effectiveness of voltage equalization.

[0039] Specifically, in the case of an AC fault, the full-controlled device actively turns off in the case of a large current generated when the bridge arm fails, and the voltage balancing module bears a forward voltage drop when the full-controlled device turns off, and the charging unit is turned on. At this time, the target capacitor in the charging unit and the element storing charge in the first sub-voltage balancing module are connected in parallel, thereby increasing the capacity of the stored charge in the voltage balancing module, effectively relieving the overvoltage of the device caused by the large current turning off, and the redundant commutation current generated by the active turn-off is injected into the target capacitor and the element storing charge in the first sub-voltage balancing module, so that the voltage of the target capacitor and the element storing charge is raised. After the target capacitor of the charging unit is charged, a forward voltage is formed to turn on the commutation module of the target commutation bridge arm. When the full-controlled device of the original fault bridge arm is turned on again after the current source type commutation valve resumes normal operation after successfully resisting commutation failure by using the full-controlled device to perform active turn-off, the forward voltage drop disappears, the charging unit is turned off, and the discharging unit is turned on. At this time, the target capacitor and the element storing charge in the first sub-voltage balancing module are discharged at the same time to the full-controlled device on the fault bridge arm, avoiding charge accumulation.

[0040] As shown in Figure 2 and Figure 3 , the first capacitor C1 is used to absorb the voltage generated by the full-controlled device 13 during active turn-off. When the full-controlled device 13 actively turns off, the charging unit bears a forward voltage drop, the first thyristor T1 is turned on, the overvoltage is transmitted to the first capacitor C1, the voltage of the first capacitor C1 gradually rises, a forward commutation voltage is formed, and the first capacitor C1 and the charge storage unit in the first target voltage balancing unit 143 are connected in parallel to store more electric energy and form a higher commutation voltage, better achieving active commutation. After the first capacitor C1 is charged, a forward voltage is formed to turn on the power device of the target commutation bridge arm (also called the valve bridge arm), and a negative voltage is formed across the first thyristor T1, the first thyristor T1 is turned off, a forward voltage is formed across the second thyristor T2 in the discharging unit, the second thyristor T2 is turned on, and the first capacitor C1 discharges the stored electric energy after the current source type commutation valve resumes normal operation, releases the stored energy, avoids charge accumulation, and ensures the long-term stability of the first capacitor C1. And the second target voltage balancing unit 144 only works when the current source type current valve fails, which can also reduce the aging speed of the first capacitor C1.

[0041] Specifically, when the fully controlled device performs a high-current active turn-off, the voltage equalization module experiences a positive voltage drop during turn-off. This positive voltage drop causes the first thyristor in the charging unit to turn on. At this time, the second target voltage equalization unit enters the current-source commutator valve and begins the active turn-off process. The first target voltage equalization unit operates continuously within the current-source commutator valve. The charge storage unit in the first target voltage equalization unit is connected in parallel with the first capacitor, which increases the capacity of the charge storage unit in the voltage equalization module, effectively mitigating the device overvoltage caused by the high turn-off current. The redundant commutation current generated by the active turn-off is injected into the charge storage unit and the first capacitor in the first target voltage equalization unit, causing the voltage to rise. After the first capacitor is charged, it will construct a positive voltage to force the power device in the target commutation bridge arm (also known as the entry valve bridge arm) to conduct. At the same time, a negative voltage is constructed across the first thyristor, and a positive voltage is constructed across the second thyristor in the discharge unit. The first thyristor is turned off, providing the conditions for the second thyristor to conduct during the subsequent discharge process.

[0042] Specifically, when the large current active shutdown is successfully performed using a fully controlled device, and when the current source converter valve resumes normal operation and the original faulty bridge arm device is turned on again, a negative voltage is constructed across the first thyristor, and a positive voltage is constructed across the second thyristor in the discharge unit to turn on the second thyristor. At this time, the first capacitor and the capacitor in the first target voltage equalization unit can simultaneously discharge the fully controlled device on the bridge arm through the damping resistor in the second target voltage equalization unit to avoid charge accumulation.

[0043] In some alternative implementations, such as Figure 3 As shown, the first target voltage equalization unit 143 includes a first resistor R1, a first diode D1, and a second capacitor C2. The first resistor R1 is connected in parallel with the first diode D1, and the second capacitor C2 is connected in series with the parallel branch of the first resistor R1 and the first diode D1. The first terminal of the first resistor R1 is electrically connected to the first terminal of the fully controlled device 13 and the first terminal of the second target voltage equalization unit 144, respectively. The second terminal of the second capacitor C2 is electrically connected to the second terminal of the fully controlled device 13 and the second terminal of the second target voltage equalization unit 144, respectively. The first resistor R1 can suppress the inrush current generated by the discharge of the first capacitor C1 to the fully controlled device 13 at the moment of its turn-on, while the first diode D1 enables the first capacitor C2 to conduct unidirectionally during charging, preventing reverse energy flow and thus protecting the fully controlled device 13, improving the stability and reliability of the voltage equalization circuit. This circuit can fine-tune the voltage stress across each fully controlled device 13, achieving voltage equalization of the series devices under normal operation and fault conditions, reducing the impact of voltage unevenness on device safety.

[0044] When the converter system is in normal operation, the full-controlled device works in continuous small-current off mode. At this time, only the second capacitor is involved in the work, providing voltage clamping and energy absorption for the full-controlled device in the off process, and realizing basic dynamic voltage sharing. The first resistor is used to suppress the impact current generated by the discharge of the second capacitor to the full-controlled device at the moment of turning on.

[0045] When the converter system fails (large-current off and commutation voltage construction): the full-controlled device actively turns off, and the forward voltage generated thereby will construct a forward voltage across the first thyristor, causing it to turn on. The turning on of the first thyristor causes the first diode to be short-circuited, and the first capacitor is connected in parallel to the second capacitor. At this time, the first capacitor and the second capacitor together form a larger-capacitance voltage-sharing capacitor group, providing strong voltage absorption and clamping capability for the large-current off of the full-controlled device, forcing the voltage of all the full-controlled devices in series to be evenly distributed, and actively constructing sufficient commutation voltage to ensure reliable off.

[0046] After the failure of the converter system, the charge discharge and reset mechanism: after the off process of the full-controlled device ends, a negative voltage is constructed across the first thyristor, and a positive voltage is constructed across the second thyristor in the discharge unit, causing the second thyristor to turn on. The turning on of the second thyristor provides a discharge circuit for the first capacitor and the second capacitor through the first resistor, safely discharging the charge stored therein, thereby preparing for the next off action and avoiding the problem of charge accumulation leading to capacitor failure or voltage sharing effect degradation.

[0047] In order to enable the current source type converter valve to simultaneously have the functions of high withstand voltage and controllable commutation, and to enable a single bridge arm of the converter valve to simultaneously have the commutation modules of two different power devices, in some optional embodiments, as shown in Figure 4 and Figure 5 the plurality of commutation modules further include a second commutation module 15, the second commutation module 15 includes a plurality of second commutation units 16 in series, the second commutation unit 16 includes a semi-controlled device 17 and a third target voltage sharing unit 171, the second commutation module 15 is in series with the first commutation module 11, and the third target voltage sharing unit 171 is in parallel with the semi-controlled device 17. In this way, the single bridge arm of the converter valve can simultaneously have the controllable commutation capability of the full-controlled device and the high withstand voltage capability of the semi-controlled device, improving the flexibility and reliability of the overall current source type converter valve. In this way, a kind of "functionally graded" hybrid valve arm can be formed.

[0048] In order to make the overall use of the current source converter more cost-effective, in some optional embodiments, the cost lower semi-controlled device (which can be a thyristor) can be responsible for the basic voltage withstand and current carrying task, and the cost higher fully-controlled device can include any one of integrated gate-commutated thyristor (IGCT) and insulated gate bipolar transistor (IGBT). The fully-controlled device can provide the "high-order function" of active turn-off and commutation voltage construction at critical moments (such as at the time of failure). By precisely configuring the number ratio of the two, the required performance indicators can be achieved at the lowest cost.

[0049] Specifically, the above semi-controlled device can be a thyristor, the fully-controlled device adopts a small current active turn-off mode in a steady state working condition, and the semi-controlled device is in a natural turn-off mode, which can avoid the inconsistency of reverse recovery of the fully-controlled device and the semi-controlled device in the related art. The fully-controlled device adopts a large current turn-off when a commutation failure is about to occur under an AC fault, and a large capacitor is used to construct a commutation voltage.

[0050] The sub-voltage equalization module in parallel with the above fully-controlled and semi-controlled devices passively equalizes the voltage for the devices in the operation of the current source current valve. In some optional embodiments, as shown in Figure 5 The third target voltage equalization unit 171 includes a third capacitor C3 and a second resistor R2 in series. In the second commutation module formed by cascading a plurality of thyristors, each thyristor is provided with an RC damping circuit for suppressing the turn-off overvoltage and voltage unevenness caused by reverse recovery of the thyristor itself.

[0051] Alternatively, in some optional embodiments, as shown in Figure 6 Each thyristor can also be provided with an RCD voltage equalization circuit, and the third target voltage equalization unit 171 includes a third capacitor C3, a second resistor R2 and a second diode D2. The second resistor R2 is connected in parallel with the second diode D2, and the third capacitor C3 is connected in series with the parallel branch of the second resistor R2 and the second diode D2. The second diode D2 is added to the RC circuit, and the function of the second diode D2 can be to limit the reverse flow of energy during the turn-off process, so as to ensure that the third capacitor C3 can effectively absorb the overvoltage. This active and passive voltage equalization circuit design can better adapt to the characteristics of the semi-controlled device 17, achieve more accurate voltage control, reduce the threat of voltage unevenness to the safety of the semi-controlled device 17, and improve the fault ride-through capability and reliability of the current source converter.

[0052] Specifically, for the half-controlled device or full-controlled device that is turned off in advance, the freewheeling current will flow into the parallel sub-voltage equalization module, the third capacitor in the sub-voltage equalization module performs unbalanced voltage suppression on the adjacent half-controlled device or adjacent full-controlled device, the greater the capacitance value of the third capacitor, the higher the degree of voltage imbalance that can be suppressed. When the original fault bridge arm is re-conducted, the third capacitor parallel to the half-controlled device or full-controlled device is discharged through the second resistor to avoid charge accumulation, wherein the second resistor is used to suppress the current peak value of the third capacitor when the half-controlled device or full-controlled device is turned on.

[0053] Specifically, the capacitance value of the first capacitor is greater than that of the second capacitor, and in normal operation of the converter valve, the second capacitor of the first target voltage equalization unit and the third capacitor in the third target voltage equalization unit are sufficient for conventional voltage equalization, but in a fault condition, such as a sudden drop in AC grid voltage, the large current turn-off of the full-controlled device on the trigger bridge arm is needed, the large capacitance value of the first capacitor can store more charges. When the full-controlled device is turned off, the parallel connection of the first capacitor and the second capacitor can be quickly charged and build enough commutation voltage to help the full-controlled device maintain voltage equalization in a large current environment and prevent device damage or commutation failure caused by uneven voltage distribution. And in continuous multiple fault events, the first capacitor has higher energy storage capacity, which can build commutation voltage by discharging energy from the first capacitor without relying on external power supply, thereby ensuring voltage clamping of the full-controlled device after large current turn-off, which can avoid the limitation of continuous turn-off capacity due to the limited capacity of the arrester (MOV). And the switching capacitor used in the present application does not have the problem of heat accumulation, and through the mutual cooperation between the charging unit and the discharging unit, it can support unlimited times of turn-off operation, thereby significantly improving the ability of the system to cope with continuous faults.

[0054] According to another aspect of the embodiments of the present application, a current source type converter valve system is provided, including the current source type converter valve.

[0055] The technical features of the above embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present disclosure.

[0056] It is also important to note that the terms "comprising", "containing", or any other similar term as used herein are intended to allow for a number of implementations of the present application. For example, a process, method, composition or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such process, method, composition or apparatus. Where no further limitation is mentioned, the use of the term "comprising" should not be interpreted as excluding the presence of elements that are identical than, equivalent to, or similar to those already provided.

[0057] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:

[0058] 1) The first commutation unit in the current source type converter valve of the embodiments of the present application is provided with a parallel full-controlled device and a voltage balancing module, the voltage balancing module includes a charging unit and a discharging unit, the charging unit and the discharging unit share a target capacitor, the charging unit includes a first thyristor, the discharging unit includes a second thyristor, the first thyristor is connected in series with the target capacitor and the second thyristor respectively, and the second thyristor is connected in series with the target capacitor. When the full-controlled device is actively turned off, the charging unit bears the forward voltage drop generated by the turning off, the first thyristor is turned on, the overvoltage is transmitted to the target capacitor, and the voltage of the target capacitor gradually rises to build a forward commutation voltage, thereby better achieving active commutation. The overvoltage generated during the active turning off of the full-controlled device is absorbed by the voltage balancing module, and the active commutation voltage is effectively built, which can quickly and reliably complete active turning off during system failure, resist commutation failure, and enhance the fault ride-through capability of the converter valve, thereby solving the problem of commutation failure of the converter valve under power system failure.

[0059] 2) The first commutation module and the second commutation module with different types of devices are connected in series on a single bridge arm of the current source type converter valve of the embodiments of the present application, so that the single bridge arm of the converter valve can simultaneously have the controllable commutation capability of the full-controlled device and the high withstand voltage capability of the half-controlled device, thereby improving the flexibility and reliability of the overall current source type converter valve.

[0060] 3) The charging unit of the current source type converter valve of the embodiments of the present application is used to store the redundant commutation current generated by the turning off of the full-controlled device when large current active turning off is performed, and to build a commutation voltage; the above-mentioned discharging unit is used to output the charge stored in the charging unit to the full-controlled device after successful commutation, thereby avoiding charge accumulation. Through the dynamic linkage control of the charging unit and the discharging unit, intelligent switching of the second target voltage balancing unit under different working conditions is realized, and the flexibility and effectiveness of voltage balancing are improved.

[0061] The above descriptions are only the preferred embodiments of the present application, and are not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A current source type converter valve, characterized in that, The device includes multiple bridge arms, each bridge arm comprising multiple series-connected converter modules. Each converter module includes a first converter module, which in turn includes multiple series-connected first converter units. Each first converter unit includes a fully controllable device and a voltage equalization module. The voltage equalization module is connected in parallel across the fully controllable device. Each voltage equalization module includes a charging unit and a discharging unit. The charging unit and the discharging unit share a target capacitor. Each charging unit includes a first thyristor connected in series with the target capacitor. Each discharging unit includes a second thyristor connected in series with the target capacitor. The first terminal of the first thyristor is the first terminal of the charging unit, and the second terminal of the second thyristor is the first terminal of the discharging unit. The first terminal of the charging unit is electrically connected to the first terminal of both the fully controllable device and the first terminal of the discharging unit. The second terminal of the first thyristor is electrically connected to the first terminal of the second thyristor. The second terminal of the target capacitor is a shared second terminal of both the charging unit and the discharging unit, and this shared second terminal is electrically connected to the second terminal of the fully controllable device.

2. The current source type converter valve according to claim 1, characterized in that, The voltage equalization module includes: a first target voltage equalization unit and a second target voltage equalization unit, wherein the first target voltage equalization unit is connected in parallel across the two ends of the fully controllable device, and the second target voltage equalization unit is electrically connected to the first target voltage equalization unit.

3. The current source type converter valve according to claim 2, characterized in that, The second target voltage equalization unit includes: the charging unit and the discharging unit, wherein, The first end of the charging unit is electrically connected to the first end of the first target voltage equalization unit, and the second end of the charging unit is electrically connected to the second end of the first target voltage equalization unit. The first end of the discharge unit is electrically connected to the first target voltage equalization unit, and the second end of the discharge unit is electrically connected to the second end of the first target voltage equalization unit.

4. The current source type converter valve according to claim 2, characterized in that, The first target voltage equalization unit includes a first resistor, a first diode, and a second capacitor. The first resistor is connected in parallel with the first diode, and the second capacitor is connected in series with the parallel branch of the first resistor and the first diode. The first end of the first resistor is electrically connected to the first end of the fully controllable device and the first end of the second target voltage equalization unit, respectively. The second end of the second capacitor is electrically connected to the second end of the fully controllable device and the second end of the second target voltage equalization unit, respectively.

5. The current source type converter valve according to claim 1, characterized in that, The plurality of converter modules further include a second converter module, which includes a plurality of second converter units connected in series. Each second converter unit includes a semi-controlled device and a third target voltage equalization unit. The second converter module is connected in series with the first converter module, and the third target voltage equalization unit is connected in parallel with the semi-controlled device.

6. The current source type converter valve according to claim 5, characterized in that, The third target voltage equalization unit includes a third capacitor and a second resistor connected in series.

7. The current source type converter valve according to claim 5, characterized in that, The third target voltage equalization unit includes a third capacitor, a second resistor, and a second diode. The second resistor and the second diode are connected in parallel, and the parallel branch of the third capacitor, the second resistor, and the second diode is connected in series.

8. The current source type converter valve according to claim 1, characterized in that, The fully controllable devices include IGCT and IGBT.

9. The current source type converter valve according to claim 5, characterized in that, The semi-controlled device includes a thyristor.

10. A current source type converter valve system, characterized in that, The current source type converter valve includes any one of claims 1 to 9.

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