JP7155076B2 - Controller and power conversion system - Google Patents

Description

TECHNICAL FIELD Embodiments of the present invention relate to control devices and power conversion systems.

2. Description of the Related Art There is a power converter that includes a separately-commutated power converter that uses a separately-commutated switching element such as a thyristor, and a control device that controls the operation of the separately-commutated power converter. A power conversion device is used, for example, in a power conversion system that converts AC power into DC power and converts DC power back into AC power.

The power conversion system includes, for example, a direct current power transmission (HVDC: High Voltage Direct Current) that transmits power with direct current power, a frequency converter (FC: Frequency Converter) that performs frequency conversion, or two alternating currents without frequency conversion It is used for BTB (Back-To-Back) that interconnects electric power systems.

A power conversion system includes two power converters. The controllers of the two power converters communicate with each other and perform cooperative control. For example, when an accident occurs in one of the externally-commutated power converters, protective shutdown is performed while the faulty end and healthy end cooperate.

For example, the control device at the fault end performs a gate block (GB) operation to stop the gate pulse given to the separately-commutated power converter, and the control device at the sound end is a gate that releases the energy of the DC circuit to the AC side. A shift (GS: Gate Shift) operation is performed. As a result, by removing the DC current from the DC circuit and generating a current zero point, protective shutdown can be performed without causing breakdowns in devices such as circuit breakers and filters.

However, if there is a communication failure (communication equipment failure or communication delay) between the control devices, the failure end can shift to GB operation, but the sound end cannot immediately detect the occurrence of an accident. Therefore, the operating state is continued. Moreover, in the externally-commutated power converter, even after performing the GB operation, a specific switching element continues to conduct. In this case, the DC current may not be removed from the DC circuit and a current zero may not be created. As a result, there is a concern that a state of direct current interruption, in which the circuit breaker is interrupted while the direct current is flowing, may cause equipment failure.

Therefore, in a control device that cooperatively controls two separately-commutated power converters together with another control device, and in a power conversion system using the same, even if a communication failure occurs with another control device, It is desirable to be able to safely shut down two separately commutated power converters.

JP-A-54-54234

In the embodiment, when the two separately-commutated power converters are cooperatively controlled together with another control device, the two separately-commutated power converters can be safely controlled even when a communication failure occurs with the other control device. Provided is a control device capable of protective shutdown and a power conversion system using the same.

A control device according to an embodiment connects a first separately-commutated power converter connected to a first AC power system and a second separately-commutated power converter connected to a second AC power system through a DC circuit. By connecting, it is used in a power conversion system that interconnects the first AC power system and the second AC power system , controls the operation of the first separately-commutated power converter, and controls the operation of the second separately-commutated power converter. Controlling the operations of the first separately-commutated power converter and the second separately-commutated power converter in cooperation with the another control device by communicating with another control device that controls the operation of the power converter. a constant current control unit for calculating a control angle for controlling the DC current flowing in the DC circuit to match the current reference; and the control angle calculated by the constant current control unit a phase control unit for controlling the operation of the first separately-commutated power converter by generating a control pulse based on the generated control pulse and inputting the generated control pulse to the first separately-commutated power converter; a current minimum value calculation unit that predicts and calculates a minimum value of the DC current flowing through the DC circuit when an operation for stopping input of the control pulse to the excitation type power converter is performed; and the first separately-commutated power converter. When a protection stop request for protective stop of the power converter is input, the control to the first separately-commutated power converter is performed based on the minimum value of the DC current calculated by the current minimum value calculation unit. a transition determination unit that determines whether or not to instantaneously transition to an operation of stopping the input of the pulse.

In this embodiment, when cooperatively controlling two separately-commutated power converters together with another control device, the two separately-commutated power converters can be controlled even when a communication failure occurs with the other control device. A controller capable of safe protective shutdown and a power conversion system using the same are provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which represents typically the power conversion system which concerns on 1st Embodiment. It is a block diagram showing typically the 1st power converter concerning a 1st embodiment. It is a block diagram showing typically the 1st control device concerning a 1st embodiment. 4 is a block diagram schematically showing a transition determination unit according to the first embodiment; FIG. It is a block diagram which represents typically the 2nd control apparatus which concerns on 2nd Embodiment. FIG. 11 is a block diagram schematically showing an invalidation unit according to the second embodiment; FIG. It is a block diagram which represents typically the modification of the 2nd control apparatus which concerns on 2nd Embodiment. FIG. 7 is a block diagram schematically showing a time constant setting section according to a second embodiment; FIG. It is a block diagram which represents typically the modification of the 2nd control apparatus which concerns on 2nd Embodiment. FIG. 7 is a block diagram schematically showing a limiter according to a second embodiment; FIG. It is a block diagram which represents typically the 1st power converter device which concerns on 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between portions, and the like are not necessarily the same as the actual ones. Also, even when the same parts are shown, the dimensions and ratios may be different depending on the drawing.
In addition, in the present specification and each figure, the same reference numerals are given to the same elements as those described above with respect to the previous figures, and detailed description thereof will be omitted as appropriate.

(First embodiment)
FIG. 1 is a block diagram schematically showing the power conversion system according to the first embodiment.
As shown in FIG. 1 , the power conversion system 10 includes a first power conversion device 11, a second power conversion device 12, and a DC circuit 14. The first power converter 11 includes a first separately-commutated power converter 21 and a first controller 31 . The second power conversion device 12 includes a second externally-commutated power conversion device 22 and a second control device 32 .

The DC circuit 14 is provided between the first power converter 11 and the second power converter 12 . More specifically, DC circuit 14 is provided between first separately-commutated power converter 21 and second separately-commutated power converter 22 . DC circuit 14 connects first separately-commutated power converter 21 and second separately-commutated power converter 22 .

The first separately-commutated power converter 21 is connected to the first AC power system 2 a and the DC circuit 14 . The second separately-commutated power converter 22 is connected to the second AC power system 2 b and the DC circuit 14 . That is, the first separately-commutated power converter 21 and the second separately-commutated power converter 22 are connected to each other via the DC circuit 14 .

The first separately-commutated power converter 21 converts the AC power supplied from the first AC power system 2 a into DC power, and supplies the DC power to the DC circuit 14 . The second separately-commutated power converter 22 converts the DC power supplied from the DC circuit 14 into AC power, and supplies the AC power to the second AC power system 2b.

The AC power of each AC power system 2a, 2b is, for example, three-phase AC power. Each separately-commutated power converter 21, 22 performs, for example, conversion from three-phase AC power to DC power and conversion from DC power to three-phase AC power. The AC power of each AC power system 2a, 2b may be single-phase AC power or the like.

Thus, in the power conversion system 10, the AC power of the first AC power system 2a is converted into DC power, converted back to AC power, and supplied to the second AC power system 2b. Moreover, in the power conversion system 10, contrary to the above, power can be supplied from the second AC power system 2b side to the first AC power system 2a side. In other words, the power conversion system 10 interconnects the AC power systems 2a and 2b via the separately-commutated power converters 21 and 22, respectively. However, power is supplied only in one direction from the first separately-commutated power converter 21 to the second separately-commutated power converter 22 or from the second separately-commutated power converter 22 to the first separately-commutated power converter 21. It's okay.

The DC circuit 14 has a positive DC bus 14p, a negative DC bus 14n, a DC reactor 14x, and a DC reactor 14y. DC reactor 14x and DC reactor 14y are provided on positive side DC bus 14p.

The power conversion system 10 is used for DC power transmission, for example. In this case, the positive DC bus 14p is, for example, a DC cable such as a submarine cable. The negative DC bus 14n may be a cable return line, an earth return line, a seawater return line, or the like. That is, the negative side DC bus 14n is provided as required and can be omitted. The DC reactors 14x and 14y are provided, for example, on the positive DC bus 14p and suppress harmonics of the current flowing through the positive DC bus 14p (DC circuit 14).

The power conversion system 10 includes a frequency converter, BTB, or the like that directly connects the DC side of the first separately-commutated power converter 21 and the DC side of the second separately-commutated power converter 22 without a power transmission cable or the like. It's okay. In this case, for example, a wiring member such as a bus bar that connects the DC side of the first separately-commutated power converter 21 and the DC side of the second separately-commutated power converter 22 may be used as the DC circuit 14 . In this case, one of the DC reactors 14x and 14y can be omitted. Either of the DC reactors 14x and 14y may be provided in the DC circuit 14 as required.

The first controller 31 is connected to the first separately-commutated power converter 21 via a signal line 31a. The first controller 31 controls power conversion by the first separately-commutated power converter 21 . The first separately-commutated power converter 21 has, for example, a plurality of bridge-connected separately-commutated switching elements. The first controller 31, for example, is connected to each switching element of the first separately-commutated power converter 21 via a signal line 31a, and inputs a control pulse to each switching element to control the ON timing of each switching element. Control. In this way, the first controller 31 controls power conversion by the first separately-commutated power converter 21 by controlling the ON timing of each switching element of the first separately-commutated power converter 21 .

The first control device 31 also acquires various data (feedback values) necessary for control from the first separately-commutated power converter 21 . The first control device 31, for example, measures the AC voltage value of each phase of the first AC power system 2a, the DC voltage value of the DC circuit 14, the DC current value of the DC circuit 14, etc. Get from

The second controller 32 is connected to the second separately-commutated power converter 22 via a signal line 32a. Similarly to the first control device 31, the second control device 32 acquires various data from the second separately-commutated power converter 22 and controls the ON timing of each switching element of the second separately-commutated power converter 22. Thus, power conversion by the second separately-commutated power converter 22 is controlled.

The first control device 31 and the second control device 32 are connected to each other via a network 34 or the like. The first control device 31 and the second control device 32 cooperatively control the operations of the first separately-commutated power converter 21 and the second separately-commutated power converter 22 by communicating with each other. For example, when a failure occurs in the first separately-commutated power converter 21 or the second separately-commutated power converter 22, the first separately-commutated power converter 31 and the second controller 32 cooperate with each other. The device 21 and the second separately-commutated power converter 22 are stopped for protection.

FIG. 2 is a block diagram schematically showing the first power converter according to the first embodiment.
As shown in FIG. 2 , the first separately-commutated power converter 21 of the first power converter 11 includes a main circuit section 40, transformers 41 and 42, a circuit breaker 43, and a DC reactor 44. .

The configuration of the second separately-commutated power converter 22 of the second power converter 12 is substantially the same as the configuration of the first separately-commutated power converter 21, except that the AC side is connected to the second AC power system 2b. are the same. Therefore, the configuration of the first separately-commutated power converter 21 will be described below, and the detailed description of the configuration of the second separately-commutated power converter 22 will be omitted.

The main circuit section 40 has converters 51 and 52 . The converter 51 has six switch units 61u, 61v, 61w, 61x, 61y, and 61z connected in a three-phase bridge. Similarly, the converter 52 has six switch sections 62u, 62v, 62w, 62x, 62y, 62z connected in a three-phase bridge. Hereinafter, for the sake of convenience, the switch units 61u, 61v, 61w, 61x, 61y, and 61z are collectively referred to as the "switch unit 61". Similarly, the switch units 62u, 62v, 62w, 62x, 62y, and 62z are collectively referred to as the "switch unit 62".

Each switch section 61 has a switching element 61s. Similarly, each switch section 62 has a switching element 62s. Separately-excited switching elements such as thyristors are used for the switching elements 61s and 62s, for example. Each switch unit 61 has, for example, a plurality of switching elements 61s connected in series. Each switch section 62 has, for example, a plurality of switching elements 62s connected in series. Each of the switch units 61 and 62 is, for example, a thyristor valve.

Each of the transformers 41, 42 has a primary winding 41a, 42a and a secondary winding 41b, 42b. Primary windings 41 a and 42 a of transformers 41 and 42 are connected to first AC power system 2 a via circuit breaker 43 . The circuit breaker 43 is connected to the first control device 31 . Closing and opening of the circuit breaker 43 are switched by the first control device 31 .

A secondary winding 41 b of transformer 41 is connected to the AC connection point of converter 51 . A secondary winding 42 b of transformer 42 is connected to the AC node of converter 52 . As a result, the AC power transformed by the transformers 41 and 42 is supplied to the AC connection points of the converters 51 and 52, respectively.

In this example, transformers 41, 42 are three-phase transformers. A primary winding 41a of the transformer 41 is Y-connected. A secondary winding 41b of the transformer 41 is delta-connected. A primary winding 42a of the transformer 42 is Y-connected. A secondary winding 42b of the transformer 42 is Y-connected. Therefore, the phase of the AC voltage supplied to the converter 52 is the same as the phase of the AC voltage of the first AC power system 2a, but the phase of the AC voltage supplied to the converter 51 is the phase of the first AC power system 2a. 30° out of phase with the AC voltage.

A positive side DC output point of the converter 51 is connected to a DC reactor 44 , and is connected to the positive side DC bus 14 p of the DC circuit 14 via the DC reactor 44 . The positive DC output point of converter 52 is connected to the negative DC output point of converter 51 . That is, the DC output points of converters 51 and 52 are connected in series with each other. A negative DC output point of the converter 52 is connected to the negative DC bus 14 n of the DC circuit 14 .

That is, in this example, the main circuit section 40 is a so-called 12-phase AC/DC conversion circuit. The main circuit unit 40 and the first control device 31 convert the AC power supplied from the first AC power system 2a into DC power by controlling the ON timings of the respective switch units 61 and 62 . The main circuit section 40 applies a DC voltage between the positive DC bus 14p and the negative DC bus 14n.

The first control device 31 inputs a control pulse to each of the switches 61 and 62 and controls the ON timing of each of the switches 61 and 62 so that the main circuit 40 converts AC power to DC power. Control conversion. The on-timings of the switches 61 and 62 are also called control angles. Further, the first control device 31 controls the voltage value of the DC voltage applied to the DC circuit 14 by controlling the control angle of the control pulse (firing pulse) input to each of the switches 61 and 62. do.

The main circuit section 40 is not limited to a 12-phase AC/DC conversion circuit, and may be a 6-phase AC/DC conversion circuit. Further, an AC/DC conversion circuit with more phases such as 24 phases, 36 phases, 48 phases, etc. may be used. Also, the AC power of the first AC power system 2a may be, for example, single-phase AC power. In this case, the main circuit section 40 may be a single-phase bridge circuit.

The first separately-commutated power converter 21 further includes voltage detectors 72 a , 72 b , 72 c , a current detector 74 and a voltage detector 75 .

The voltage detectors 72 a , 72 b , 72 c detect the AC voltage of each phase of the first AC power system 2 a and input the detected value of the AC voltage to the first controller 31 .

The first control device 31 detects the detected values from the voltage detectors 72a, 72b, and 72c, and, though not shown, the transformers 41 and 42 obtained from the tap position signals of the transformers 41 and 42. Using the ratio, the AC voltage on the converter 51, 52 side is calculated. Since the tap positions of the transformers 41 and 42 are always controlled to be the same, the converter-side AC voltages of the transformers 41 and 42 are substantially equal.

A current detector 74 detects the direct current output from each converter 51 , 52 . In other words, the current detector 74 detects the DC current flowing through the DC circuit 14 . The current detector 74 inputs the detected value of the DC current to the first controller 31 .

A voltage detector 75 detects the DC voltage output from each converter 51 , 52 . In other words, voltage detector 75 detects the DC voltage of DC circuit 14 . The voltage detector 75 inputs the detected value of the DC voltage to the first controller 31 .

The first control device 31 controls the on-timings of the switches 61 and 62 based on the detection values of the input AC current, AC voltage, DC current, and DC voltage. For example, in the normal operation mode, the first control device 31 obtains the voltage phase signal from the detected values of the AC voltage of the first AC power system 2a detected by the voltage detectors 72a, 72b, and 72c. Since the transformer 51 is out of phase by 30° due to the transformer 41 , the first controller 31 adjusts the voltage phase signal used for controlling the transformer 52 connected to the transformer 42 in consideration of this.

FIG. 3 is a block diagram schematically showing the first control device according to the first embodiment.
As shown in FIG. 3, the first control device 31 includes a phase detection unit 100, a constant voltage control unit 102, a constant current control unit 104, a minimum value selection unit 106, a phase control unit 108, a current minimum value It has a calculation unit 110 and a transition determination unit 112 .

The phase detection unit 100 receives the detected values of the AC voltage of the first AC power system 2a detected by the voltage detectors 72a, 72b, and 72c. Phase detector 100 inputs to phase controller 108 a voltage phase signal obtained from the detected value of the AC voltage of first AC power system 2a detected by voltage detectors 72a, 72b, and 72c.

The constant voltage control unit 102 receives the DC voltage detection value detected by the voltage detector 75 and the voltage reference of the DC voltage. The voltage reference may be a predetermined value set in advance, an input value input from a host controller or the like, or an input value manually input by an operator via an operation unit or the like.

The constant voltage control unit 102 calculates the control angle of the control pulse to be input to each of the switch units 61 and 62 of the main circuit unit 40 based on the input detected value of the DC voltage and the voltage reference. That is, the constant voltage control unit 102 calculates a control angle for controlling the DC voltage to match the voltage reference. Constant voltage control section 102 inputs the calculated control angle to minimum value selection section 106 .

The constant current control unit 104 receives the DC current detection value detected by the current detector 74 and the current reference of the DC current. The current reference may be a predetermined value set in advance, an input value input from a host controller or the like, or an input value manually input by an operator via an operation unit or the like.

The constant current control unit 104 calculates the control angle of the control pulse to be input to each of the switch units 61 and 62 of the main circuit unit 40 based on the input detection value of the direct current and the current reference. That is, the constant current control unit 104 calculates a control angle for controlling the DC current to match the current reference. Constant current control section 104 inputs the calculated control angle to minimum value selection section 106 .

The minimum value selection unit 106 selects the smaller one of the control angle input from the constant voltage control unit 102 and the control angle input from the constant current control unit 104, and inputs the selected control angle to the phase control unit 108. do.

The first control device 31 and the second control device 32 communicate and cooperate with each other to operate one of the first separately-commutated power converter 21 and the second separately-commutated power converter 22 as a forward converter, The other is operated as an inverse converter. At this time, the first control device 31 and the second control device 32 perform constant current control on the forward converter side and constant voltage control on the reverse converter side. The setting of constant current control and constant voltage control can be switched by setting the voltage reference and current reference.

As described above, the current reference on the inverter side is set smaller than the current reference on the forward converter side so that the constant voltage control is selected as the control on the inverter side. By doing so, the output of constant current control on the inverter side becomes large, and the output of constant voltage control is selected by the minimum value selection circuit. However, if for some reason the DC current becomes smaller and becomes smaller than the current reference on the inverter side, the output of the constant current control on the inverter side will decrease and the constant current control will be selected, resulting in intermittent DC current. can be suppressed.

Based on the voltage phase signal input from the phase detection unit 100 and the control angle input from the minimum value selection unit 106, the phase control unit 108 generates control pulses for the switches 61 and 62 of the main circuit unit 40. to generate The phase controller 108 generates a control pulse, for example, when the voltage phase and the control angle match. The phase control section 108 inputs the generated control pulse to each of the switch sections 61 and 62 . Thereby, constant voltage control by the constant voltage control unit 102 or constant current control by the constant current control unit 104 can be performed.

The current minimum value calculation unit 110 predicts and calculates the minimum value of the DC current flowing through the DC circuit 14 when the gate block operation is performed to stop the input of the control pulse to the main circuit unit 40 . When the gate block operation is performed, in other words, when the state in which the main circuit section 40 is operated under constant current control or constant voltage control is switched to the state in which the operation of the main circuit section 40 is stopped. Current minimum value calculation unit 110 inputs the calculated minimum value of DC current to transition determination unit 112 .

The current minimum value calculator 110 stores the AC voltage on the secondary side of the transformers 41 and 42 calculated from the voltage detectors 72a to 72c and the transformation ratio of the transformers 41 and 42, and the DC voltage detected by the current detector 74. A current detection value and an operating parameter of the first separately-commutated power converter 21 are input.

Transition determination unit 112 receives the minimum DC current value calculated by minimum current value calculation unit 110 and a protection stop request for protectively stopping first separately-commutated power converter 21 . The protection stop request may be input from a host controller or converter protective device, etc., or may be input manually by an operator via an operation unit, etc. It may be generated inside the control device 31 . The first control device 31 may further include an abnormality determination unit that inputs a protection stop request to the transition determination unit 112, for example, when the current or voltage detected by each detector exceeds a predetermined value. .

FIG. 4 is a block diagram schematically showing a transition determination unit according to the first embodiment;
As shown in FIG. 4 , when the protection stop request is input, the transition determination unit 112 mainly determines the minimum value of the DC current calculated by the minimum current value calculation unit 110 and the detection result of the communication failure. Switching between instantaneous transition to gate block operation (GB operation) for stopping input of control pulses to circuit unit 40 and transition to gate block operation after performing control to reduce energy in DC circuit 14 .

The shift determination unit 112 monitors communication failure with the second control device 32 during operation, and changes the mode of protection interlocking at the time of protection stop request based on the monitoring result. The shift determination unit 112 determines whether or not the communication state with the second control device 32 is normal. For example, the transition determination unit 112 transmits a predetermined confirmation signal to the second control device 32, and if there is a response from the second control device 32 within a predetermined time, the state of communication with the second control device 32 is normal, and if there is no response from the second control device 32 within a predetermined time, it is determined that the communication state with the second control device 32 is bad. It should be noted that the determination of whether or not the communication state with the second control device 32 is normal may be performed by a part other than the transition determination section 112 , and only the communication failure detection result may be input to the transition determination section 112 .

When the communication state with the second control device 32 is normal, the shift determination unit 112 determines to shift to the gate block operation instantaneously, and transmits a request for protection interlocking operation to the second control device 32 .

When the shift determination unit 112 determines that the gate block operation is to be performed instantaneously, it instructs the phase control unit 108 to perform the gate block operation. The phase control unit 108 stops inputting the control pulse to the main circuit unit 40 when instructed by the transition determination unit 112 to perform the gate block operation.

When the second control device 32 receives the protection interlocking operation request, it performs control to reduce the energy in the DC circuit 14, and then performs the gate blocking operation. As a result, when the communication state is normal, the DC current is made substantially zero, and the respective switch units 61 and 62 of the first separately-commutated power converter 21 and the second separately-commutated power converter 22 are turned off. can be done. The first control device 31 and the second control device 32 open the circuit breaker 43 after the direct current becomes substantially zero. Thereby, when the communication state is normal, the first separately-commutated power converter 21 and the second separately-commutated power converter 22 can be safely stopped for protection.

Transition determination unit 112 determines whether communication with second control device 32 is normal, and whether the minimum value of the DC current calculated by minimum current value calculation unit 110 is greater than zero.

The transition determination unit 112 determines that the gate block operation is instantaneously performed when communication with the second control device 32 is normal and the minimum value of the DC current calculated by the minimum current value calculation unit 110 is equal to or less than zero. judge. Then, when communication with the second control device 32 is abnormal, or when the minimum value of the DC current calculated by the current minimum value calculation unit 110 is greater than zero, control is performed to reduce the energy in the DC circuit 14. After that, it shifts to gate block operation.

The control for reducing the energy in the DC circuit 14 is, for example, a gate shift operation that releases the energy in the DC circuit 14 to the AC side. Below, the control for reducing the energy in the DC circuit 14 will be described as a gate shift operation. However, the control for reducing the energy in the DC circuit 14 is not limited to the gate shift operation, and any control capable of reducing the energy in the DC circuit 14 may be used.

When the transition determination unit 112 determines that the gate block operation is to be instantaneously performed, the transition determination unit 112 instructs the phase control unit 108 to perform the gate block operation, and stops inputting the control pulse to the main circuit unit 40 . As a result, the DC current can be made substantially zero, and the switch units 61 and 62 of the first separately-commutated power converter 21 and the second separately-commutated power converter 22 can be turned off.

On the other hand, when the transition determination unit 112 determines to perform the gate shift operation, it instructs the phase control unit 108 to perform the gate shift operation. When instructed by the transition determination unit 112 to perform the gate shift operation, the phase control unit 108 inputs a control pulse corresponding to the gate shift operation to the main circuit unit 40 . The phase control section 108 operates the main circuit section 40 as an inverse converter to release the energy of the DC circuit 14 to the AC side.

After performing the gate shift operation, the transition determination unit 112 causes the phase control unit 108 to perform the gate block operation when, for example, the minimum value of the DC current calculated by the minimum current value calculation unit 110 becomes zero or less. direct to. For example, the transition determination unit 112 may instruct the phase control unit 108 to perform the gate block operation after the direct current becomes zero after performing the gate shift operation. As a result, the DC current can be made substantially zero, and the switch units 61 and 62 of the first separately-commutated power converter 21 and the second separately-commutated power converter 22 can be turned off. The first control device 31 and the second control device 32 open the circuit breaker 43 after the direct current becomes substantially zero. As a result, even when the communication state is poor, the first separately-commutated power converter 21 and the second separately-commutated power converter 22 can be safely stopped for protection.

Next, an example of prediction calculation of the minimum value of the direct current by the current minimum value calculation unit 110 will be described.
Here, the circuit to be analyzed is the circuit shown in FIGS. 1 and 2 (a 12-phase AC/DC conversion circuit). Let the 1st power converter 11 be the forward converter side, and let the 2nd power converter 12 be the inverter side. Constant current control is performed in the first power conversion device 11 of the forward converter, and constant voltage control is performed in the second power conversion device 12 of the inverse converter. Then, the DC current behavior when the gate block operation is performed on the rectifier side is analyzed, and the DC current minimum value is calculated.

（１）式において、Ｌｄｃは、直流回路１４のインダクタンスである。この例において、直流回路１４のインダクタンスＬｄｃは、例えば、直流リアクトル１４ｘのインダクタンスＬｄｃｘと直流リアクトル１４ｙのインダクタンスＬｄｃｙとの和（Ｌｄｃ＝Ｌｄｃｘ＋Ｌｄｃｙ）である。Ｉｄｃは、直流回路１４に流れる直流電流である。Ｖ_Ｒ（ｔ）は、第１他励式電力変換器２１から出力される直流電圧である。Ｖ_Ｉ（ｔ）は、第２他励式電力変換器２２に入力される直流電圧である（いずれも図１参照）。 The voltage of the DC reactor 14x of the DC circuit 14 can be expressed by the following equation (1).

(1), Ldc is the inductance of the DC circuit 14 . In this example, the inductance Ldc of the DC circuit 14 is, for example, the sum of the inductance Ldcx of the DC reactor 14x and the inductance Ldcy of the DC reactor 14y (Ldc=Ldcx+Ldcy). Idc is a direct current flowing through the direct current circuit 14 . V _R (t) is the DC voltage output from the first separately-commutated power converter 21 . V _I (t) is the DC voltage input to the second separately-commutated power converter 22 (see FIG. 1 for both).

（２）式において、ｖ_ＨＩ（ｔ）は、変換器５１の直流電圧である。ｖ_ＬＯＷ（ｔ）は、変換器５２の直流電圧である。Ｖ_２ｎは、変圧器４１、４２の直流巻線側（二次側）の線間電圧の実効値である（いずれも図２参照）。Ｖ_２ｎは、換言すれば、電圧検出器７２ａ～７２ｃと変圧器４１、４２の変圧比から計算した変圧器４１、４２の二次側の交流電圧である。ωは、角周波数である。αは、ゲートブロック動作時の各スイッチ部６１、６２の制御角である。 On the rectifier side, specific switch sections 61 and 62 continue to conduct after the gate block operation. The DC voltage V _R (t) of the forward converter (first separately-commutated power converter 21) can be expressed by the following equation (2).

In equation (2), v _HI (t) is the DC voltage of converter 51 . v _LOW (t) is the DC voltage of converter 52; V _2n is the effective value of the line voltage on the DC winding side (secondary side) of transformers 41 and 42 (see FIG. 2 for both). V _2n is, in other words, the AC voltage on the secondary side of the transformers 41 , 42 calculated from the voltage detectors 72 a - 72 c and the transformation ratios of the transformers 41 , 42 . ω is the angular frequency. α is the control angle of each of the switch units 61 and 62 during the gate block operation.

（３）式において、ｘ_ｔは、変圧器４１、４２のリアクタンスＸをｐｕ換算したものである。 It is assumed that the inverter side (second separately-commutated power converter 22 side) performs constant voltage control at the rated voltage and rated current immediately before the gate block operation. In this case, the DC voltage V _I (t) of the inverter can be expressed by the following equation (3).

In the equation (3), _xt is the reactance X of the transformers 41 and 42 converted to pu.

各スイッチ部６１、６２がターンオフするかを判別するためには、（４）式の第１極小値を調べればよい。極小値においては、ｄＩｄｃ／ｄｔ＝０であるため、（４）式の積分中の中括弧内が零になる必要がある。すなわち、以下の（６）式の条件が必要となる。

（６）式により、直流電流最小値に達する時刻ｔ’を算出し、時刻ｔ’を（５）式に代入することで、直流電流最小値を計算することができる。この直流電流最小値が零以下となった場合には、直流電流の電流零点が生成されるため、瞬時にゲートブロック動作を行っても良いと考えることができる。 When the time response of the current value is calculated from the formulas (1), (2), and (3), it can be expressed by the following formulas (4) and (5). In equation (4), Id is the DC current during gate block operation. Id is, in other words, the detected value of the direct current detected by the current detector 74 . The operating parameters of the first separately-commutated power converter 21 are, for example, the inductance Ldc of the DC circuit 14, the reactance _xt of the transformers 41 and 42, the angular frequency ω, and the control angle α.

In order to determine whether the switches 61 and 62 are turned off, the first minimum value of equation (4) should be checked. At the local minimum, dIdc/dt=0, so the brackets in the integration of equation (4) must be zero. That is, the condition of the following formula (6) is required.

The DC current minimum value can be calculated by calculating the time t' at which the DC current reaches the minimum value using the equation (6) and substituting the time t' into the equation (5). When the DC current minimum value becomes zero or less, the current zero point of the DC current is generated, so it can be considered that the gate block operation may be performed instantaneously.

As described above, in the power conversion system 10, the first power conversion device 11, and the first control device 31 according to the present embodiment, when the current minimum value calculation unit 110 performs the gate block operation, the direct current The minimum value of the DC current flowing through the circuit 14 is predicted and calculated, and when the minimum value of the DC current is zero or less, the gate block operation is performed, and when the minimum value of the DC current is greater than zero, After performing control to reduce the energy in the DC circuit 14, the gate block operation is performed.

As a result, in the power conversion system 10, the first power conversion device 11, and the first control device 31 according to the present embodiment, even when the communication state with the second control device 32 is poor, the direct current is substantially , the switch units 61 and 62 of the first separately-commutated power converter 21 and the second separately-commutated power converter 22 are turned off, and the first separately-commutated power converter 21 and the second separately-commutated power converter 22 are turned off. You can safely stop the protection.

(Second embodiment)
FIG. 5 is a block diagram schematically showing the second control device according to the second embodiment.
It should be noted that the same reference numerals are given to elements that are substantially the same as those of the first embodiment in terms of function and configuration, and detailed description thereof will be omitted.
As shown in FIG. 5, the second control device 32 of the second power conversion device 12 includes a phase detection unit 200, a constant voltage control unit 202, a constant current control unit 204, a minimum value selection unit 206, and a phase control It has a section 208 , a current minimum value calculation section 210 , a transition determination section 212 , and an invalidation section 214 .

The phase detection unit 200, constant voltage control unit 202, constant current control unit 204, minimum value selection unit 206, phase control unit 208, current minimum value calculation unit 210, and transition determination unit 212 are the same as those in the first embodiment. substantially the same as the phase detection unit 100, the constant voltage control unit 102, the constant current control unit 104, the minimum value selection unit 106, the phase control unit 108, the current minimum value calculation unit 110, and the transition determination unit 112 described above. Therefore, detailed description is omitted.

The nullification section 214 is provided between the constant current control section 204 and the minimum value selection section 206 . The control angle for the constant current control calculated by the constant current control unit 204 and the minimum DC current calculated by the minimum current value calculation unit 210 are input to the nullifying unit 214 .

FIG. 6 is a block diagram schematically showing an invalidation unit according to the second embodiment.
As shown in FIG. 6, the control angle ACR-α for constant current control calculated by the constant current control unit 204 is input to the nullifying unit 214, and the maximum value αmax of the control angle α is set. It is

In addition, the minimum value of the DC current calculated by the current minimum value calculation unit 210 is input to the invalidation unit 214, and the detection result of the communication failure with the first control device 31 and the second separately-commutated power conversion and a signal indicating whether or not the converter 22 is in the inverter operating state. The communication failure detection result may be input from the outside or generated inside the invalidation unit 214 as described with respect to the transition determination unit 112 .

When the second separately-commutated power converter 22 is in the inverter operating state and the minimum value of the DC current calculated by the minimum current value calculation unit 210 is greater than zero, the nullification unit 214 sets the control angle The maximum value αmax of α is input to the minimum value selection section 206 as the control angle ACR-α′.

Further, even when the second separately-commutated power converter 22 is in the inverter operating state and a communication failure is detected, the invalidation unit 214 sets the maximum value αmax of the control angle α to the control angle ACR-α. ' is input to the minimum value selection unit 206 .

When the second separately-commutated power converter 22 is in the forward converter operating state, and when the second separately-commutated power converter 22 is in the inverter operating state, the disabling unit 214 determines that the communication state is normal, and When the minimum value of the DC current calculated by the current minimum value calculator 210 is less than or equal to zero, the control angle ACR-α is input to the minimum value selector 206 as the control angle ACR-α′.

When the maximum value αmax of the control angle α is input to the minimum value selection unit 206 as the control angle ACR-α′, the minimum value selection unit 206 always selects the control angle calculated by the constant voltage control unit 202. become. Therefore, when the second separately-commutated power converter 22 is in the inverter operating state and the minimum value of the DC current calculated by the current minimum value calculating section 210 is greater than zero, or when the second separately-commutated power converter 22 is in the inverter operating state and communication failure is detected, the second separately-commutated power converter 22 operating as an inverter switches from constant voltage control to constant current control. can be suppressed. That is, the constant current control on the inverter side can be substantially disabled.

For example, when the rectifier side performs a gate block operation and stops the current supply to the DC circuit 14, if the inverter side shifts from constant voltage control to constant current control, the inverter side will stop the DC current. I try to keep it. Therefore, even if the forward converter side performs gate block operation or gate shift operation, there is a possibility that the current zero point of the DC current cannot be generated.

On the other hand, in the second power conversion device 12 and the second control device 32 according to the present embodiment, the second separately-commutated power converter 22 is in the inverter operating state, and the current minimum value calculation unit 210 calculates When the minimum value of the DC current is greater than zero, or when the second separately-commutated power converter 22 is in the inverter operating state and communication failure is detected, the maximum value αmax of the control angle α is input to the minimum value selection unit 206 as the control angle ACR-α' to prevent the second separately-commutated power converter 22 operating as an inverter from switching from constant voltage control to constant current control.

In the second power conversion device 12 and the second control device 32 according to the present embodiment, the phase control unit 208 determines that the second separately-commutated power converter 22 is in the inverter operating state, and the current minimum value calculation unit 210 When the calculated minimum value of the direct current is greater than zero, or when the second separately-commutated power converter 22 is in the inverter operating state and communication failure with the first control device 31 is detected , even when the DC current drops, a control pulse is generated based on the control angle calculated by the constant voltage control unit 202, and constant voltage control is performed, so that the DC from the second separately-commutated power converter 22 The operation of the second separately-commutated power converter 22 is controlled so as to suppress the supply of energy to the circuit 14 .

As a result, the current zero point of the direct current can be generated more reliably when the forward converter side performs the gate block operation or the gate shift operation. Therefore, the first separately-commutated power converter 21 and the second separately-commutated power converter 22 can be protected and stopped more safely.

The maximum value αmax is, for example, about 160°. However, the maximum value αmax is not limited to about 160°, and may be any control angle that allows selection of the control angle calculated by the constant voltage control unit 202 .

Note that the configuration of the invalidation unit 214 is not limited to the above. The invalidation unit 214 may be configured, for example, to be provided on the input side of the constant current control unit 204 and switch the current reference input to the constant current control unit 204 .

For example, when the second separately-commutated power converter 22 is in the forward converter operating state, and when the second separately-commutated power converter 22 is in the inverter operating state, the communication state is normal, and When the minimum value of the DC current calculated by the current minimum value calculator 210 is less than or equal to zero, the normal current reference for constant current control is input to the constant current controller 204 .

Then, for example, when the second separately-commutated power converter 22 is in the inverter operating state and the minimum value of the DC current calculated by the current minimum value calculation unit 210 is greater than zero, Alternatively, when the second separately-commutated power converter 22 is in the inverter operating state and a communication failure with the first control device 31 is detected, the current reference input to the constant current control unit 204 is normally is made smaller than the current reference, the selection of the control angle calculated by the constant current control section 204 in the minimum value selection section 206 is invalidated.

Thus, even when the current reference is reduced, it is possible to prevent the second separately-commutated power converter 22 operating as an inverter from switching from constant voltage control to constant current control. For example, by setting the current reference to substantially zero, it is possible to prevent the second separately-commutated power converter 22 operating as an inverter from switching from constant voltage control to constant current control.

FIG. 7 is a block diagram schematically showing a modification of the second control device according to the second embodiment.
As shown in FIG. 7 , in this example, the invalidation section 214 is replaced with a time constant setting section 216 .

FIG. 8 is a block diagram schematically showing a time constant setting section according to the second embodiment.
As shown in FIG. 8, the time constant setting unit 216 communicates when the second separately-commutated power converter 22 is in the forward converter operating state and when the second separately-commutated power converter 22 is in the inverter operating state. When the state is normal and the minimum value of the DC current calculated by the minimum current value calculator 210 is less than or equal to zero, the control angle ACR-α calculated by the constant current controller 204 is changed to the control angle ACR- is input to the minimum value selection unit 206 as α'.

On the other hand, when the second separately-commutated power converter 22 is in the inverter operating state and the minimum value of the DC current calculated by the current minimum value calculation unit 210 is greater than zero, or , when the second externally-commutated power converter 22 is in the inverter operation state and a communication failure is detected, the fluctuation of the control angle ACR-α calculated by the constant current control unit 204 is moderated. A time constant is set, and the control angle ACR-α after setting the time constant is input to the minimum value selection unit 206 as the control angle ACR-α′.

The time constant setting unit 216, for example, inputs the control angle ACR-α to a first-order lag transfer function represented by 1/(1+sT), and converts the control angle ACR-α output from the transfer function to the control angle ACR-α. ' is input to the minimum value selection unit 206 .

Thus, in this example, by providing the first-order lag to the control angle ACR-α, fluctuations in the control angle ACR-α due to the occurrence of an accident or the like are moderated. As a result, the influence of the constant current control on the inverter side can be suppressed, and the current zero point of the direct current can be generated more reliably when the forward converter side performs the gate block operation or the gate shift operation.

Thus, even when the time constant setting unit 216 is provided, the phase control unit 208 determines that the second separately-commutated power converter 22 is in the inverter operating state and the current minimum value calculated by the current minimum value calculating unit 210 When the minimum value of the DC current is greater than zero, or when the second separately-commutated power converter 22 is in the inverter operating state and communication failure with the first control device 31 is detected, the first The operation of the second separately-commutated power converter 22 can be controlled so as to suppress the supply of energy from the second separately-commutated power converter 22 to the DC circuit 14 .

Therefore, the first separately-commutated power converter 21 and the second separately-commutated power converter 22 can be protected and stopped more safely. The time constant T may be appropriately set in consideration of, for example, the follow-up speed necessary for suppressing current intermittence in constant current control on the inverter side.

FIG. 9 is a block diagram schematically showing a modification of the second control device according to the second embodiment.
As shown in FIG. 9, in this example, a limiter 218 is newly provided in place of the invalidation section 214 and the time constant setting section 216 .

Limiter 218 is provided between minimum value selection section 206 and phase control section 208 . The control angle output from the minimum value selection unit 206 is input to the limiter 218 . The limiter 218 limits the control angle input from the minimum value selection unit 206 to the range between the upper limit value and the lower limit value so that the control angle does not exceed the upper limit value and does not fall below the lower limit value. In addition, the minimum value of the DC current calculated by the current minimum value calculation section 210 is input to the limiter 218 .

FIG. 10 is a block diagram schematically showing a limiter according to the second embodiment.
As shown in FIG. 10, the limiter 218 limits the control angle α to the upper limit value when the control angle α input from the minimum value selection unit 206 is equal to or greater than the upper limit value, and finally sets the upper limit value to is input to the phase control unit 208 as a control angle α'. Further, when the control angle α input from the minimum value selection unit 206 is equal to or less than the lower limit value, the limiter 218 limits the control angle α to the lower limit value, and uses the lower limit value as the final control angle α′. Input to the phase control unit 208 .

A limiter 218 is set with a first lower limit value αmin1 and a second lower limit value αmin2 of the control angle α. The second lower limit value αmin2 is set to a value larger than the first lower limit value αmin1. The second lower limit αmin2 is set to a value greater than 90°.

The limiter 218 operates when the second separately-commutated power converter 22 is in the forward converter operating state and when the second separately-commutated power converter 22 is in the inverter operating state, the communication state is normal, and the current minimum value is calculated. If the minimum value of the DC current calculated by the unit 210 is less than or equal to zero, the first lower limit αmin1 is set.

On the other hand, the limiter 218 operates when the second separately-commutated power converter 22 is in the inverter operating state and the minimum value of the DC current calculated by the minimum current value calculation unit 210 is greater than zero, or when the second When externally-commutated power converter 22 is in the inverter operating state and communication failure is detected, second lower limit value αmin2 is set.

When the second separately-commutated power converter 22 is operating as an inverter, constant current control is performed and energy is supplied from the inverter side to the DC circuit 14 side by the control angle α falling below 90°. be. Therefore, even if the constant current control is selected, the energy on the DC circuit 14 side can be reduced by preventing the control angle α from falling below 90°.

In this example, when the minimum value of the DC current calculated by the current minimum value calculator 210 is greater than zero, or when communication failure is detected, the second lower limit value αmin2 greater than 90° is set. do. As a result, when the constant current control is selected, the operation can be performed while the final control angle α' remains at the second lower limit value αmin2. Even though the final control angle α' reaches the second lower limit value αmin2, the second lower limit value αmin2 is greater than 90°, so the energy of the DC circuit 14 can continue to be reduced.

Thus, even when the limiter 218 is provided, the phase control unit 208 controls the DC current calculated by the minimum current value calculation unit 210 when the second separately-commutated power converter 22 is in the inverter operation state. When the minimum value is greater than zero, or when the second separately-excited power converter 22 is in the inverter operating state and a communication failure with the first control device 31 is detected, the second separately-excited power converter The operation of the second separately-commutated power converter 22 can be controlled so as to suppress the supply of energy from the power converter 22 to the DC circuit 14 .

Therefore, the influence of the constant current control on the inverter side can be suppressed, and the current zero point of the direct current can be generated more reliably when the forward converter side performs gate block operation or gate shift operation. The first separately-commutated power converter 21 and the second separately-commutated power converter 22 can be protected and stopped more safely.

(Third embodiment)
FIG. 11 is a block diagram schematically showing the first power conversion device according to the third embodiment. As shown in FIG. 11, in this example, the transformer 42 and the converter 52 of the main circuit section 40 are omitted, and the negative DC output point of the converter 51 is connected to the negative DC bus 14n of the DC circuit 14. It is That is, in this example, the main circuit section 40 is a so-called six-phase AC/DC conversion circuit.

また、６相構成の主回路部４０の場合、第２他励式電力変換器２２を逆変換器として定格電圧、定格電流で定電圧制御させた場合の直流電圧Ｖ_Ｉ（ｔ）は、以下の（８）式で表すことができる。

（１）、（７）、（８）式から電流値の時間応答を計算すると、以下の（９）式及び（１０）式で表すことができる。

各スイッチ部６１、６２がターンオフするかを判別するためには、（９）式の第１極小値を調べればよい。極小値においては、ｄＩｄｃ／ｄｔ＝０であるため、（９）式の積分中の中括弧内が零になる必要がある。すなわち、以下の（１１）式の条件が必要となる。

（１１）式により、直流電流最小値に達する時刻ｔ’を算出し、時刻ｔ’を（１０）式に代入することで、直流電流最小値を計算することができる。この直流電流最小値が零以下となった場合には、直流電流の電流零点が生成されるため、瞬時にゲートブロック動作を行っても良いと考えることができる。 In the case of the main circuit section 40 having a six-phase configuration, the DC voltage V _R (t) when the first separately-commutated power converter 21 is operated as a forward converter can be expressed by the following equation (7).

In the case of the main circuit section 40 having a six-phase configuration, the DC voltage V _I (t) when the second separately-commutated power converter 22 is used as an inverse converter and subjected to constant voltage control at the rated voltage and rated current is as follows: (8) can be expressed by the formula.

Calculating the time response of the current value from the equations (1), (7), and (8) can be expressed by the following equations (9) and (10).

In order to determine whether the switches 61 and 62 are turned off, the first minimum value of equation (9) should be checked. At the local minimum, dIdc/dt=0, so the brackets in the integration of equation (9) must be zero. That is, the condition of the following equation (11) is required.

The DC current minimum value can be calculated by calculating the time t' at which the DC current reaches the minimum value using the equation (11) and substituting the time t' into the equation (10). When the DC current minimum value becomes zero or less, the current zero point of the DC current is generated, so it can be considered that the gate block operation may be performed instantaneously.

In this way, even when the main circuit section 40 has a six-phase configuration, the minimum current value calculation sections 110 and 210 can calculate the secondary voltage of the transformer 41 from the voltage detectors 72a to 72c and the transformer 41 transformation ratio. side AC voltage, the DC current detection value detected by the current detector 74, and the operating parameters of the first separately-commutated power converter 21 or the second separately-commutated power converter 22, the DC current A minimum value can be calculated predictively.

Although several embodiments of the invention have been described above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included within the scope and spirit of the invention, and are included within the scope of the invention described in the claims and equivalents thereof. Moreover, each of the above-described embodiments can be implemented in combination with each other.

2a first AC power system 2b second AC power system 10 power conversion system 11 first power converter 12 second power converter 14 DC circuit 14n negative DC bus 14p positive DC bus 14x , 14y DC reactor, 21 first separately-commutated power converter, 22 second separately-commutated power converter, 31 first control device, 32 second control device, 34 network, 40 main circuit section, 41 transformer, 42 transformer , 43 circuit breaker, 44 DC reactor, 51 converter, 52 converter, 61 switch section, 61s switching element, 62 switch section, 62s switching element, 72a, 72b, 72c voltage detector, 74 current detector, 75 voltage detection 100 phase detector 102 constant voltage controller 104 constant current controller 106 minimum value selector 108 phase controller 110 current minimum value calculator 112 shift determination unit 200 phase detector 202 constant voltage Control unit 204 Constant current control unit 206 Minimum value selection unit 208 Phase control unit 210 Current minimum value calculation unit 212 Transition determination unit 214 Invalidation unit 216 Time constant setting unit 218 Limiter

Claims (12)

By connecting the first separately-commutated power converter connected to the first AC power system and the second separately-commutated power converter connected to the second AC power system via a DC circuit, the first Used in a power conversion system that interconnects an AC power system and the second AC power system , and controls the operation of the first separately-commutated power converter and the operation of the second separately-commutated power converter. A control device that cooperatively controls operations of the first separately-commutated power converter and the second separately-commutated power converter together with the another control device by communicating with another control device,
a constant current controller that calculates a control angle for controlling the direct current flowing in the direct current circuit to match a current reference;
By generating a control pulse based on the control angle calculated by the constant current control unit and inputting the generated control pulse to the first separately-commutated power converter, a phase control unit that controls the operation;
a current minimum value calculation unit that predicts and calculates the minimum value of the DC current flowing through the DC circuit when an operation of stopping the input of the control pulse to the first separately-commutated power converter is performed;
When a protection stop request for protectively stopping the first separately-commutated power converter is input, the first separately-commutated power converter is calculated based on the minimum value of the direct current calculated by the current minimum value calculation unit. a transition determination unit that determines whether or not to instantaneously transition to an operation of stopping the input of the control pulse to the power converter;
control device with The current minimum value calculation unit, based on the AC voltage input to the first separately-commutated power converter, the DC current of the DC circuit, and the operating parameters of the first separately-commutated power converter, 2. The control device according to claim 1, wherein said minimum value of said DC current is predicted and calculated. When the minimum value of the direct current calculated by the minimum current value calculation unit is equal to or less than zero, the transition determination unit determines to instantaneously transition to an operation of stopping the input of the control pulse. 3. The control device according to claim 1 or 2, which instructs the phase control section to execute an operation to stop the input of the pulse. When the minimum value of the DC current calculated by the current minimum value calculation unit is greater than zero, or when a communication failure with the other control device is detected, the transition determination unit determines whether the DC 4. The control device according to any one of claims 1 to 3, which instructs the phase control section to execute control for reducing energy in the circuit. By connecting the first separately-commutated power converter connected to the first AC power system and the second separately-commutated power converter connected to the second AC power system via a DC circuit, the first Used in a power conversion system that interconnects an AC power system and the second AC power system , and controls the operation of the second separately-commutated power converter and the operation of the first separately-commutated power converter. A control device that cooperatively controls operations of the first separately-commutated power converter and the second separately-commutated power converter together with the another control device by communicating with another control device,
a constant voltage control unit that calculates a control angle for controlling the DC voltage of the DC circuit to match a voltage reference;
a constant current controller that calculates a control angle for controlling the direct current flowing in the direct current circuit to match a current reference;
When the DC current is during normal operation, a control pulse is generated based on the control angle calculated by the constant voltage control unit, and when the DC current decreases, the control pulse calculated by the constant current control unit is generated. a phase control unit that controls the operation of the second separately-commutated power converter by generating a control pulse based on the control angle and inputting the generated control pulse to the second separately-commutated power converter;
a current minimum value calculation unit that predicts and calculates the minimum value of the DC current flowing through the DC circuit when an operation of stopping the input of the control pulse to the second separately-commutated power converter is performed;
with
When the second separately-commutated power converter is in an inverter operating state and the minimum value of the direct current calculated by the minimum current value calculation unit is greater than zero, or When the second separately-commutated power converter is in a reverse converter operation state and a communication failure with the other control device is detected, a line from the second separately-commutated power converter to the DC circuit is A control device that controls the operation of the second separately-commutated power converter so as to suppress the supply of energy. When the second separately-commutated power converter is in an inverter operating state and the minimum value of the direct current calculated by the minimum current value calculation unit is greater than zero, or When the second separately-commutated power converter is in an inverter operation state and a communication failure with the another control device is detected, the constant voltage control is performed even when the DC current decreases. generating a control pulse based on the control angle calculated by the unit, and performing constant voltage control to suppress supply of energy from the second separately-commutated power converter to the DC circuit; 6. The control device according to claim 5, which controls the operation of a two-externally-commutated power converter. selecting a smaller one of the control angle calculated by the constant voltage control unit and the control angle calculated by the constant current control unit, and selecting a minimum value for inputting the selected control angle to the phase control unit; Department and
When the second separately-commutated power converter is in an inverter operating state and the minimum value of the direct current calculated by the current minimum value calculation unit is greater than zero, or the second separately-commutated power When the converter is in the inverter operating state and a communication failure with the other control device is detected, the control angle calculated by the constant current control unit is set to the maximum value and the minimum value is set. an invalidation unit for invalidating selection of the control angle calculated by the constant current control unit in the minimum value selection unit by inputting to the value selection unit;
7. The controller of claim 6, further comprising: selecting a smaller one of the control angle calculated by the constant voltage control unit and the control angle calculated by the constant current control unit, and selecting a minimum value for inputting the selected control angle to the phase control unit; Department and
When the second separately-commutated power converter is in an inverter operating state and the minimum value of the direct current calculated by the current minimum value calculation unit is greater than zero, or the second separately-commutated power By decreasing the current reference input to the constant current control unit when the converter is in an inverter operation state and a communication failure with the other control device is detected, the constant current an invalidation unit that invalidates selection of the control angle calculated by the control unit in the minimum value selection unit;
7. The controller of claim 6, further comprising: selecting a smaller one of the control angle calculated by the constant voltage control unit and the control angle calculated by the constant current control unit, and selecting a minimum value for inputting the selected control angle to the phase control unit; Department and
When the second separately-commutated power converter is in an inverter operating state and the minimum value of the direct current calculated by the current minimum value calculation unit is greater than zero, or the second separately-commutated power When the converter is in the inverse converter operating state and a communication failure with the another control device is detected, a time constant is set to moderate fluctuations in the control angle calculated by the constant current control unit. a time constant setting unit configured to input the control angle after setting the time constant to the minimum value selection unit;
6. The controller of claim 5, further comprising: a minimum value selection unit that selects the smaller one of the control angle calculated by the constant voltage control unit and the control angle calculated by the constant current control unit;
provided between the minimum value selection unit and the phase control unit for limiting the control angle input from the minimum value selection unit to a range between the upper limit value and the lower limit value; a limiter that inputs the control angle in the range between the value to the phase control unit;
further comprising
The limiter operates when the second separately-commutated power converter is in an inverter operation state and the minimum value of the DC current calculated by the minimum current value calculation unit is greater than zero, or the second 6. The control device according to claim 5, wherein the lower limit value is made larger than 90 degrees when the two separately-commutated power converter is in an inverter operation state and a communication failure with the another control device is detected. . a first separately-commutated power converter connected to the first AC power system;
a second separately-commutated power converter connected to a second AC power system;
a DC circuit connecting the first separately-commutated power converter and the second separately-commutated power converter;
a first control device that controls the operation of the first separately-commutated power converter by inputting a control pulse;
By inputting a control pulse to control the operation of the second separately-commutated power converter and by communicating with the first control device, the first separately-commutated power converter and the first separately-commutated power converter together with the first control device a second control device that cooperatively controls operations with the second separately-commutated power converter;
with
The first control device predicts and calculates a minimum value of a DC current flowing through the DC circuit when an operation of stopping the input of the control pulse to the first separately-commutated power converter is performed. stopping the input of the control pulse to the first separately-commutated power converter based on the minimum value of the DC current when a protection stop request for protectively stopping the separately-commutated power converter is input; A power conversion system that determines whether to switch to operation instantaneously. The second control device predicts and calculates a minimum value of the DC current flowing through the DC circuit when an operation of stopping the input of the control pulse to the second separately-commutated power converter is performed. the second separately-commutated power converter is in inverter operation state and the minimum value of the direct current is greater than zero, or the second separately-commutated power converter is in inverter operation state, and When a communication failure with the first control device is detected, the second separately-commutated power converter is controlled so as to suppress energy supply from the second separately-commutated power converter to the DC circuit. 12. The power conversion system of claim 11 for controlling operation.

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