CN108701998B - Control system and method for line commutation converter of high-voltage direct-current system - Google Patents
Control system and method for line commutation converter of high-voltage direct-current system Download PDFInfo
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Abstract
The invention provides a control system and a control method thereof for an LCC of an HVDC system. The control system includes: a first measurement unit (20) configured to provide a current measurement value indicative of a DC current magnitude of the HVDC system; and a controller (21) configured to increase a first arc-quench angle at which the controlled LCC operates to a second arc-quench angle in response to the current measurement value exceeding the current reference level to avoid a commutation failure of the controlled LCC. By using the solution of the HVDC system, the chance of commutation failure caused by a fast rise of the DC current of the HVDC system can be reduced as the arc-extinguishing angle of the LCC increases. Reliability and stability of the entire AC and DC power system are improved.
Description
Technical Field
The present invention relates to control of a Line Commutated Converter (LCC) for a High Voltage Direct Current (HVDC) system, and more particularly to preventing commutation faults of the LCC of the HVDC system.
Background
HVDC systems are commonly used to connect high voltage AC grids or remote power stations to AC grids. Such a system usually consists of two converter stations interconnected by DC transmission lines or cables. At the generating or transmitting end, the converter comprises a rectifier for converting alternating current power into direct current and voltage, while at the receiving end the converter comprises an inverter for transmitting power from a DC transmission line to an AC grid.
A typical HVDC system may comprise a monopolar transmission line or a bipolar transmission line. Fig. 1A and 1B show block diagrams of a bipolar HVDC system and a monopolar HVDC system. As shown in fig. 1A, in a bipolar HVDC system, if one pole in the bipolar system fails, this current path will switch to the earth return, allowing the system to continue to operate at reduced capacity and reducing the likelihood of the pole failure causing a bipolar interruption. Typically these earth return paths are only used for a very short duration until the fault is largely back up to service. The ground current in this solution can flow in either direction and the electrodes must be designed to be reversible and can operate as either anodes or cathodes. In a three-phase AC system, each phase feeding and receiving an AC grid is connected to positive and negative DC transmission lines through two pairs of valves facing forward. As shown in fig. 1B, in a monopolar HVDC system, the DC transmission line permanently carries DC current. Each phase feeding and receiving the AC grid is connected to the DC transmission line and ground through a valve towards the forward direction. The valve is actuated by a trigger control system which provides gating signals to the valve in a predetermined timed sequence to effect the transfer or commutation of current from phase to phase.
It is known that HVDC systems of either type may contain converters comprising bridges based on thyristors or mercury arc valves. Such a valve bridge (valve bridge) allows converting three-phase alternating voltages and currents into direct voltages and currents or vice versa. The valve (e.g. thyristor) only conducts current in the forward direction from the anode to the cathode only when the forward voltage across the valve is positive and the valve receives a control pulse. Once the valve begins to conduct, the magnitude of the current is determined solely by the main circuit outside the valve and is not affected by the elimination of the gate pulse. The current through the valve continues to flow until it decreases due to external influences and tries to become negative. Because the valve is reverse biased, reverse current flow is prevented, causing current to dissipate through it. In the forward direction, the valve will block current flow until a control pulse is applied to the gate. Due to these characteristics, the operation cycle of the valve is divided into a forward blocking interval, a conduction interval, and a reverse blocking interval.
When the valve is operated in inverter mode, the dc voltage is negative when the current direction is concerned. This means that the voltage across the valve is positive most of the time before the trigger pulse is applied. In order to establish the forward blocking voltage, the charge established during conduction must be removed. Therefore, the valve needs to have a time interval of negative valve voltage between the end of the on period and the application of the positive voltage. The electrical angle corresponding to this time period is called commutation margin or arc-extinguishing angle.
In typical inverter operation, with one valve conducting, there is sufficient time before the next zero crossing to trigger the next subsequent valve, at which time the phase-to-phase voltage will become positive. Therefore, the commutation from the valve to be shut off to the valve to be turned on must be terminated in time to ensure a sufficient commutation margin. If for some reason the commutation is not completed when the voltage across the shut-off valve is either made positive or the commutation margin is so small that the valve has no time to regain sufficient forward blocking capability, there is a transient disturbance in the inverter operation, referred to as commutation failure.
As described above, to establish the forward blocking capability of the valve, the charge built up during the on-time interval is eliminated by providing a negative valve voltage during the time interval corresponding to the commutation time. This is not a problem in rectifier operation, as rectifiers typically operate at firing angles of less than 90 degrees in electrical angle. However, such commutation failures are a concern for inverter operation, since it is desirable to keep the arc-extinguishing angle as small as possible to maximize power transfer.
Conventional inverter firing angle control systems typically attempt to prevent commutation failure by increasing commutation margin in response to a decrease in AC grid voltage. This method of reducing commutation failure is disclosed in "a new method for mitigating commutation failure in an HVDC system", Lidong Zhang, Lars
PowerCon 2002, Kunming, China, 10 months, 13 days-17 days in 2002. According to this article, classical HVDC systems are easily reversedThe phase change failure occurs at the substation. This is because successful thyristor turn-off depends on the external AC grid voltage. Existing solutions to this problem use the external AC grid voltage as its critical input and, if necessary, temporarily increase the inverter extinction angle to avoid commutation failure.
It is known that in a monopolar HVDC system, if the rectifier AC voltage rises rapidly, the DC current also rises rapidly until the rectifier current controller drops the measured DC current to its ordered value. The inverter overlap angle (voltage time area) will increase before the rectifier reduces the DC current. Due to the increase of the voltage time area, the inverter may fail in commutation. For a bipolar HVDC system, there will be inductive mutual coupling between the two DC transmission lines. Once the DC current changes rapidly in one pole, the other pole will also change. This phenomenon can cause a failed commutation of an already operating pole when the other pole is restarted after clearing the DC transmission line fault. Therefore, there is still a need for improved adjustment of the arc-quenching angle in order to better reduce commutation failures when the DC current in the DC transmission line rises.
Disclosure of Invention
According to an aspect of the invention, there is provided a control system for an LCC of an HVDC system, comprising: a first measurement unit configured to provide a current measurement value indicative of a DC current magnitude of the HVDC system; and a controller configured to increase a first arc-out angle at which the controlled LCC operates to a second arc-out angle in response to the current measurement value exceeding the current reference level to avoid a commutation failure of the controlled LCC.
According to another aspect of the invention, there is provided a control method for an LCC of an HVDC system, comprising: providing a current measurement value indicative of a DC current magnitude of the HVDC system; and in response to the current measurement value exceeding the current reference level, increasing the first arc-quenching angle at which the controlled LCC operates to a second arc-quenching angle to avoid a commutation failure of the controlled LCC.
By using the solution according to the invention, the chance of commutation failure caused by a rapid rise of the DC current of the HVDC system can be reduced as the arc-extinguishing angle of the LCC increases. Reliability and stability of the entire AC and DC power system are improved.
Preferably, the controller is further configured to predict an overlap angle of the controlled LCC required for more than a minimum successful commutation in view of the amperage measurements; and decreasing the firing angle of the controlled LCCs to achieve an increase of the first arc-quenching angle to the second arc-quenching angle and the predicted overlap angle of the controlled LCCs. With respect to this method, considering current measurement values, it is preferred to include a step of predicting that the controlled LCC overlap angle exceeds the minimum required for successful commutation; wherein: decreasing a firing angle of the controlled LCC to effect increasing the first arc-quenching angle to the second arc-quenching angle and a predicted overlap angle of the controlled LCC. The firing angle of the LCC can thereby be reduced, thereby allowing room for an increase in the first arc-quenching angle and increasing the voltage-time area of the controlled LCC. The first arc-quench angle at which the controlled LCC operates may be increased to a second arc-quench angle in response to the current measurement value of the DC current exceeding a current reference level by adjusting a firing angle of a valve to avoid a commutation failure of the controlled LCC. The voltage time area a may also be adjusted beyond the minimum required for successful commutation.
Especially if the HVDC system is a bipolar HVDC system comprising a first pole HVDC transmission line and a second pole HVDC transmission line, wherein there is inductive mutual coupling therebetween; a DC side of the controlled LCC is coupled to the first pole HVDC transmission line; a first measurement unit configured to provide a current measurement value indicative of the amount of DC current in the second pole HVDC transmission line of the HVDC system; and during the period when said second pole restarts until it resumes normal operation, the current reference level is set to substantially zero. Once the DC current in the second pole HVDC transmission line changes rapidly, the DC current in the first pole HVDC transmission line will also change due to the inductive mutual coupling. This phenomenon may cause a commutation failure of the already active first pole when the second pole is restarted after clearing the DC line fault. A first measurement unit of the control system continuously measures the DC current in said second pole HVDC transmission line. When the rectifier of the second pole resumes DC power transmission again, a DC current will flow in the second pole HVDC transmission line. Once the first measurement unit of the control system measures a sufficiently high DC current, it will temporarily increase its arc-quenching angle as described above to avoid a commutation failure.
Preferably, the controller is further configured to decrease from the second arc-quenching angle to a substantially minimum first arc-quenching angle required for successful commutation within the period. By keeping the extinction angle at the minimum angle required for successful commutation, this may satisfy the desire to adjust the extinction angle as small as possible to maximize power transfer.
Especially if the HVDC system is a monopolar HVDC system; the DC side of the controlled LCC is coupled to the HVDC transmission line; a first measurement unit configured to provide a current measurement value indicative of the amount of DC current in the HVDC transmission line of the HVDC system; and the current reference level is set to a steady state value formed by low pass filtering the amount of DC current in normal operation. Once the first measurement unit of the control system measures a sufficiently high DC current, it will temporarily increase its arc-quenching angle as described above to avoid a commutation failure. In addition, preferably, the control system further includes: a second measurement unit configured to provide a voltage quantity measurement value indicative of a DC voltage quantity of the HVDC system; wherein: the controller is further configured to increase a first arc-quenching angle to a second arc-quenching angle to avoid a commutation failure of the controlled LCC in response to the voltage measurement exceeding a voltage reference level; and the voltage reference level is set to a steady state value formed by low pass filtering the DC voltage amount in normal operation.
Drawings
The subject matter of the invention will be explained in more detail hereinafter with reference to preferred exemplary embodiments shown in the drawings, in which:
fig. 1A and 1B show block diagrams of a bipolar HVDC system and a monopolar HVDC system;
fig. 2A and 2B show block diagrams of a control system for operation of an LCC and control system of an HVDC system, respectively, according to an embodiment of the present invention;
fig. 2C shows a commutation process of an LCC according to an embodiment of the invention.
Fig. 3A shows a block diagram of a bipolar HVDC system using a control system according to an embodiment of the present invention;
fig. 3B shows an increment of the arc-quenching angle and a waveform of the DC current in a second pole HVDC transmission line according to an embodiment of a bipolar HVDC system;
fig. 4A shows a block diagram of a monopolar HVDC system using a control system according to an embodiment of the present invention; and
fig. 4B shows an increment of the arc-quenching angle and a waveform of the DC current in the HVDC transmission line according to an embodiment of the monopolar HVDC system.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular circuits, circuit components, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods and programming procedures, devices, and circuits are omitted so as not to obscure the description of the present invention with unnecessary detail.
Fig. 2A and 2B show block diagrams of a control system for operation of an LCC and control system of an HVDC system, respectively, according to an embodiment of the invention. Fig. 2C shows a commutation process of an LCC according to an embodiment of the invention.
As shown in fig. 2A, the control system 2 includes a first measurement unit 20 and a controller 21. In this embodiment, the first measurement unit 20 may be a shunt resistor, a hall effect current sensor transducer and a transformer, the current detection part of which is coupled to the DC transmission line of the HVDC system. The first measurement unit 20 can provide a current measurement value IDC_M，IDC_MIndicating DC current I of HVDC systemDCThe amount of (c). The detection is based on instantaneous current values, which ensure a fast response of the control system when a relatively fast rise of the DC current occurs. Because the LCC transformer is electrifiedThe inductance, and therefore the transformer current, cannot change immediately. The limited rate of change of current means that the transfer of current from one valve to another requires a limited commutation time.
As shown in fig. 2C, the rectified current is derived from the DC current of the HVDC system. For example, before a phase change, when only valves 1 and 2 are conductive, the DC voltage is formed by two-phase voltages of the three-phase voltages. During the overlapping period of time when the current I (indicated by the arrow) commutates from valve 1 (output valve) to valve 3 (input valve), a DC voltage develops from all three-phase voltages. The higher the commutation current, the larger the voltage time area a. Typical full load values for the overlap angle μ are in the range of 20 to 30 electrical degrees under normal steady state operation. A phenomenon in thyristor valves is that the internal stored charge generated during the forward conduction interval must be eliminated before the valve can establish the forward voltage blocking capability. This time is called the de-ionization time of the valve and the time from the moment when the valve current becomes zero to the moment when the voltage between the lines is zero is defined as the arc-extinguishing angle γ. If the thyristor becomes positively biased before de-ionization is completed, the thyristor will resume current flow.
As shown in fig. 2B, state I represents normal steady-state operation without control of the control system 2 to prevent commutation failure, while state II represents transient operation with commutation failure prevention applied. The flip, overlap and extinction angles for states I and II are represented by α 1, μ 1, γ 1 and α 2, μ 2, γ 2, respectively. The arc-extinguishing angles γ 1, γ 2 are represented in fig. 2B as the remaining voltage-time area of the commutation voltage after commutation, the commutation being the time from the end of the voltage-time area to the moment when the voltage across the valve changes sign, i.e. from reverse to blocking voltage. This indicates that a successful commutation requires a minimum voltage time area rather than a fixed time interval.
It is well known that commutation requires an electrical angle of the voltage time area a, i.e. the overlap angle μ. The overlap angle mu is related to the commutation current flowing through the valve at commutation. Since the overlap angle μ increases with increasing DC current, a relatively large overlap angle μ is required to complete the commutation. The arc-extinguishing angle γ is represented in fig. 2B as a horizontally shaded area and is calculated by the controller 21 according to the following equation:
180°＝α+μ+γ (1)
wherein: α is the firing angle of the oncoming valve, μ is the overlap angle related to the oncoming and off valves, and γ is the extinction angle of the off valve. Too small an arc-extinguishing angle γ due to a rapid rise in DC current is one of the fundamental reasons for commutation failure. In order to maintain a sufficiently large gamma for the valve to be shut off, the controller 21 should give an early trigger moment when a DC current disturbance is detected, while leaving room for an increase in the voltage time area a to complete the de-ionization of the valve to be shut off. The voltage time area a is related to the commutation current flowing through the valve at commutation, and it can be predicted that the voltage time area a exceeds the minimum value required for a successful commutation, taking into account that the current measurement value provided by the first measurement unit 20 indicates the amount of DC current of the HVDC system. As shown in fig. 2B, in normal steady state operation I, there will be an edge area. However, if the firing angle α is not sufficient to maintain a sufficient voltage time area a and arc-quenching angle γ due to a rapid rise in DC current, the firing angle calculation module 211 of the controller 20 will decrease the firing angle α, e.g., from α 1 to α 2, or in other words, the firing angle α will decrease such that the voltage time area a and arc-quenching angle γ between firing and zero-crossing points will increase, e.g., from μ 1 to μ 2 and from γ 1 to γ 2.
As mentioned above, the voltage time area a may exceed the minimum required for successful commutation. The overlap angle μmay be predicted by the overlap angle prediction module 210 of the controller 21 from the following equation:
wherein: i isdIs a measured DC current, IdNIs a nominal DC current, UdioNIs a nominal unloaded DC voltage, and UdioIs the measured unloaded DC voltage. Furthermore, the horizontal shaded area in fig. 2B is typically set between 17 and 18 electrical degrees, which will result in commutation under normal conditions. To ensure that a successful valve commutation occurs, the trigger control signal must be 180 degrees minus 17 to 18 electrical degrees minus the overlap angle or moreA small angle pattern is delivered to the valve.
In this embodiment, following the numerical relationship defined in equation (1), the firing angle calculation module 211 of the controller 21 is configured to reduce the firing angle α of the valve of the controlled LCC, thereby enabling an increase in the first extinction angle γ and an increase in the voltage time area a of the controlled LCC. By adjusting the firing angle α of the valve, the first arc-quench angle γ 1 during operation of the controlled LCC can be increased to the second arc-quench angle γ 2 in response to the current measurement value of the DC current exceeding the current reference level to avoid a commutation failure of the controlled LCC. The voltage time area a may also be adjusted beyond the minimum required for successful commutation.
By using the solution according to an embodiment of the invention, the chance of a commutation failure caused by a fast rise of the DC current of the HVDC system can be reduced. Reliability and stability of the entire AC and DC power system are improved.
Fig. 3A shows a block diagram of a bipolar HVDC system using a control system according to an embodiment of the present invention. Fig. 3B shows an increment of the arc-quenching angle and a waveform of the DC current in a second pole HVDC transmission line according to an embodiment of the bipolar HVDC system.
As shown in fig. 3A, the bipolar HVDC system 3 comprises a first pole HVDC transmission line 30, a second pole HVDC transmission line 31 and a control system 2. The first pole HVDC transmission line 30 and the second pole HVDC transmission line 31 are each at a high potential with respect to ground, with opposite polarity. They are coupled between two stations A, B consisting of LCC R1, R2, I1, I2, LCC R1, I1 and a first pole HVDC transmission line 30 constituting a first pole, where LCC R1 operates as a rectifier and LCC I1 operates as an inverter, and LCC R2, I2 and a second pole HVDC transmission line 31 constituting a second pole, where LCC R2 operates as a rectifier and LCC I2 operates as an inverter. There is an inductive mutual coupling L between the first pole HVDC transmission line 30 and the second pole HVDC transmission line 31.
As shown in fig. 3A, in this embodiment the DC side of the LCC I1 is coupled to the first pole HVDC transmission line 30, which is placed under the control of the control system 2 in order to prevent commutation failures. Control system 2 may be coupled to the valves of LCC I1 to adjust their firing angle α. The first measurement unit 20 of the control system 2 is arranged outside the second pole HVDC transmission line 31 for providing a current measurement value indicative of the amount of DC current in the second pole HVDC transmission line 31 of the HVDC system. Once the DC current changes rapidly in the second pole HVDC transmission line 31, the DC current in the first pole HVDC transmission line 30 will also change due to the inductive mutual coupling L. This phenomenon may cause a failed commutation of the already active first pole when the second pole is restarted after clearing the DC line fault. The first measurement unit 20 of the control system 2 continuously measures the DC current in the second pole HVDC transmission line 31. When the rectifier R2 of the second pole resumes DC power transmission again, DC current will flow into the second pole HVDC transmission line 31. Once the first measuring unit 20 of the control system 2 measures a sufficiently high direct current, it will temporarily increase its extinction angle γ as described above to avoid a commutation failure. In case of a restart of the second pole, a fast rise of the DC current from substantially zero occurs in the first pole HVDC transmission line 30 at the beginning of the rise of the DC current in the second pole HVDC transmission line 31. To identify this, the current reference level may be set to substantially zero during the period when the second pole restarts until it resumes normal operation. As shown in fig. 3B, the DC current in the second pole HVDC transmission line 31 becomes flatter as it approaches the value of normal steady state operation. As a result, the DC current generated from the inductive mutual coupling L in the first pole HVDC transmission line 30 is reduced from the restart of the second pole to normal operation. In this embodiment, the controller 2 is further configured to gradually decrease from the second arc-extinguishing angle γ 2 to the first arc-extinguishing angle γ 1 during the second pole restart period until normal operation is resumed. The adjustment of the second extinction angle γ 2 can be expressed as a step response following an exponential decay, according to the following formula:
N(t)＝N0*e(-λt) (3)
wherein: n (t) is the increased extinction angle gamma 2 minus gamma 1, N0Is the increased arc-quenching angle upon restarting the second pole, and λ is the decay time constant.
By keeping the arc-quenching angle at the minimum angle required for successful commutation, this may satisfy the desire to adjust the arc-quenching angle as small as possible to maximize power transfer.
Fig. 4A shows a block diagram of a monopolar HVDC system using a control system according to an embodiment of the present invention. Fig. 4B shows an increment of the arc-quenching angle and a waveform of the DC current in the HVDC transmission line according to an embodiment of the monopolar HVDC system.
As shown in fig. 4A, the monopolar HVDC system 4 comprises a DC current transmission line 40 and a control system 2. The DC current transmission line 40 is coupled between two stations A, B consisting of LCCs R, I, the LCCs R operating as rectifiers and the LCCs I operating as inverters.
As shown in fig. 4A, in this embodiment the DC side of the LCC I is coupled to the HVDC transmission line 40 and to ground, which is placed under the control of the control system 2 to prevent commutation failures. For example, the control system 2 may be coupled to the valves of the LCC I to adjust their firing angle α. The first measurement unit 20 of the control system 2 is arranged outside the HVDC transmission line 40 for providing a current measurement value indicative of the amount of DC current in the HVDC transmission line 40 of the HVDC system. A HVDC system fault such as a sharp rise of the AC voltage at the LCC R may cause a rapid change in the DC current in the HVDC transmission line 40. This phenomenon can cause a commutation failure of LCC I operating as an inverter. Once the first measurement unit 20 of the control system 2 measures a sufficiently high DC current, it will temporarily increase its extinction angle γ as described above to avoid a commutation failure. To identify this, the current reference level may be set to a steady-state value formed by low-pass filtering the DC current amount in normal operation.
In this embodiment, the control system 2 may further comprise a second measurement unit 22 configured to provide a voltage quantity measurement value indicative of a DC voltage quantity of the HVDC system. The second measuring unit 22 may be, for example, a voltmeter, potentiometer or oscilloscope, and it may be arranged in the station housing the LCC I, with its detection terminal coupled between the DC transmission line and ground. The controller 21 is further configured to increase the first arc-extinguishing angle γ 1 to the second arc-extinguishing angle γ 2 in response to the voltage measure exceeding the voltage reference level to avoid a commutation failure of the controlled LCC. The voltage reference level is set to a steady-state value formed by low-pass filtering the DC voltage amount in normal operation. A key advantage of also including the DC voltage measurement criteria is to avoid false identification by the DC current criteria only.
If the DC current and DC voltage increase above their respective reference levels at the same time, commutation failure prevention may proceed as shown in FIG. 4B. In this embodiment, the controller 2 is further configured to gradually decrease from the second arc-extinguishing angle γ 2 to the first arc-extinguishing angle γ 1 during the DC transmission resumes normal operation. According to equation (3), the adjustment of the second extinction angle γ 2 can be expressed as a step response, which follows an exponential decay.
In each embodiment of the present invention, the increment value of the second extinction angle γ 2 with respect to the first extinction angle γ 1 ranges from 10 to 15 electrical degrees. This provides room for an increase in the overlap angle μ and the ability of the valve to recover its ability to withstand a positive voltage after conducting current.
Although the present invention has been described based on some preferred embodiments, those skilled in the art should understand that these embodiments should not limit the scope of the present invention in any way. Any variations and modifications of the embodiments should be within the purview of one of ordinary skill in the art without departing from the spirit and intended concept of the invention and, therefore, fall within the scope of the invention as defined by the appended claims.
Claims (12)
1. A control system for an LCC of an HVDC system, comprising:
a first measurement unit configured to provide a current measurement value indicative of a DC current magnitude of the HVDC system; and
a controller configured to increase a first arc-extinguishing angle at which a controlled LCC operates to a second arc-extinguishing angle to avoid a commutation failure of the controlled LCC in response to the current measurement value exceeding a current reference level, and configured to decrease the second arc-extinguishing angle to the first arc-extinguishing angle during a DC transmission resuming normal operation, wherein,
the controller is further configured to:
predicting an overlap angle of the controlled LCC that exceeds a minimum required for successful commutation, taking into account the amperage measurements; and
decreasing a firing angle of the controlled LCC to effect increasing the first arc-quenching angle to the second arc-quenching angle and the predicted overlap angle of the controlled LCC.
2. The control system of claim 1, wherein:
the HVDC system is a bipolar HVDC system comprising a first pole HVDC transmission line and a second pole HVDC transmission line, wherein there is inductive mutual coupling between them;
a DC side of the controlled LCC is coupled to the first pole HVDC transmission line;
the first measurement unit is configured to provide the amperage measurement value indicative of the DC amperage in the second pole HVDC transmission line of the HVDC system; and
during the period when the second pole restarts until it resumes normal operation, the current reference level is set to substantially zero.
3. The control system of claim 2, wherein:
the controller is further configured to decrease from the second arc-quenching angle to the substantially minimum first arc-quenching angle required for successful commutation during the period.
4. The control system of claim 1, wherein:
the HVDC system is a monopolar HVDC system;
the DC side of the controlled LCC is coupled to an HVDC transmission line;
the first measurement unit is configured to provide the amperage measurement value indicative of the DC amperage in the HVDC transmission line of the HVDC system; and
the current reference level is set to a steady state value formed by low pass filtering the amount of DC current in normal operation.
5. The control system of claim 4, further comprising:
a second measurement unit configured to provide a voltage quantity measurement value indicative of a DC voltage quantity of the HVDC system;
wherein:
the controller is further configured to increase the first arc-quenching angle to the second arc-quenching angle to avoid commutation failure of the controlled LCC in response to the voltage measurement exceeding a voltage reference level; and
the voltage reference level is set to a steady state value formed by low pass filtering the DC voltage amount in normal operation.
6. The control system of claim 1, wherein:
the second arc-quenching angle is incremented by an amount in the range of 10 to 15 electrical degrees with respect to the first arc-quenching angle.
7. A method of controlling an LCC for an HVDC system, comprising:
providing a current measurement value indicative of a DC current magnitude of the HVDC system;
in response to the current measurement value exceeding a current reference level, increasing a first arc-quenching angle at which a controlled LCC operates to a second arc-quenching angle to avoid a commutation failure of the controlled LCC, and decreasing the second arc-quenching angle to the first arc-quenching angle during a DC transmission resuming normal operation;
predicting an overlap angle of the controlled LCC that exceeds a minimum required for successful commutation, taking into account the amperage measurements; and
decreasing a firing angle of the controlled LCC to effect increasing the first arc-quenching angle to the second arc-quenching angle and the predicted overlap angle of the controlled LCC.
8. The control method according to claim 7, wherein:
the HVDC system is a bipolar HVDC system comprising a first pole HVDC transmission line and a second pole HVDC transmission line, wherein there is inductive mutual coupling between them;
a DC side of the LCC is coupled to the first pole HVDC transmission line;
the current magnitude measurement is indicative of the amount of DC current in the second pole HVDC transmission line of the HVDC system; and
during the period when the second pole restarts until it resumes normal operation, the current reference level is set to substantially zero.
9. The control method according to claim 8, wherein:
gradually decreasing from the second arc-quenching angle to the first arc-quenching angle during the period.
10. The control method according to claim 7, wherein:
the HVDC system is a monopolar HVDC system;
the DC side of the LCC is coupled to an HVDC transmission line;
the current measurement value is indicative of the amount of DC current in the HVDC transmission line of the HVDC system; and
the current reference level is set to a steady state value formed by low pass filtering the amount of DC current in normal operation.
11. The control method according to claim 10, further comprising:
providing a voltage quantity measurement value indicative of a DC voltage quantity of the HVDC system;
wherein:
completing the increase of the first arc-quenching angle to the second arc-quenching angle in response to the voltage measurement exceeding a voltage reference level to avoid a commutation failure of the controlled LCC; and
the voltage reference level is set to a steady state value formed by low pass filtering the DC voltage amount in normal operation.
12. The control method according to claim 7, wherein:
the second arc-quenching angle is incremented by an amount in the range of 10 to 15 electrical degrees with respect to the first arc-quenching angle.
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| Application Number | Priority Date | Filing Date | Title |
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| PCT/CN2016/085264 WO2017210892A1 (en) | 2016-06-08 | 2016-06-08 | Line-commutated converter control system and method |
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| CN112865165B (en) | 2021-01-25 | 2024-03-19 | 华中科技大学 | Energy storage transient power coordination control method for inhibiting subsequent commutation failure |
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| CN103545835A (en) * | 2013-09-22 | 2014-01-29 | 国家电网公司 | Direct-current power system commutation failure judgment method |
| CN103730907A (en) * | 2014-01-26 | 2014-04-16 | 华北电力大学 | Defense method for commutation failures of direct-current transmission based on current limiting method |
| CN105071424A (en) * | 2015-07-24 | 2015-11-18 | 四川大学 | High voltage direct current system control method |
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| US20140146582A1 (en) * | 2012-11-29 | 2014-05-29 | General Electric Company | High voltage direct current (hvdc) converter system and method of operating the same |
| EP2773032A1 (en) * | 2013-03-01 | 2014-09-03 | GE Energy Power Conversion Technology Ltd | Current source converter with gate turn off semiconductor elements and a special commutation mode |
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| CN103545835A (en) * | 2013-09-22 | 2014-01-29 | 国家电网公司 | Direct-current power system commutation failure judgment method |
| CN103730907A (en) * | 2014-01-26 | 2014-04-16 | 华北电力大学 | Defense method for commutation failures of direct-current transmission based on current limiting method |
| CN105071424A (en) * | 2015-07-24 | 2015-11-18 | 四川大学 | High voltage direct current system control method |
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