JP2007020384A - Power conversion apparatus and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion apparatus for suppressing secondary harmonics vibration of transmission power which occurs due to asymmetrical accident, and stably supplying electric power. <P>SOLUTION: The apparatus is provided with a first transformer converting three phase AC power supplied from one three phase power system into independent first to third single phase AC powers, first to third AC/DC/AC conversion means which independently convert first to third single phase AC powers into DC power, and converting DC power into fourth to sixth single phase AC powers, a second transformer converting fourth to sixth single phase AC powers into three phase AC power and supplying it to the other three phase power system and a control means for controlling the first to third AC/DC/AC conversion means so that transmission current suppressing secondary harmonics vibration is supplied to respective phases in the other three phase power system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

 The present invention relates to a power conversion device and a control method.

For example, Japanese Patent Application Laid-Open No. 07-200084 discloses a technique relating to a method for controlling a power converter (AC / DC converter) when an asymmetrical system fault such as a one-wire ground fault occurs in a three-phase power system. . In the technique disclosed in Japanese Patent Laid-Open No. 07-200084, a three-phase AC voltage of a three-phase power system is measured by dividing it into a real part and an imaginary part, and the phase of the positive phase is calculated by an instantaneous symmetric coordinate method. Even if one of the phases is grounded and the transmission voltage becomes zero, the phase is detected accurately, and the operation is continued without stopping the power conversion device by controlling the power conversion device based on the phase. It is what makes it possible.
Japanese Patent Application Laid-Open No. 07-200084

  By the way, when a one-line ground fault occurs in the three-phase power system, if power is supplied with the remaining two healthy phases, the transmission power vibrates due to the second harmonic component of the three-phase power system frequency. Therefore, a problem that stable power cannot be supplied has been known. In addition, such second harmonic vibration is not limited to a one-line ground fault, but may occur in the same way even when three-phase power is unbalanced due to other asymmetrical accidents.

 In the above prior art, it is possible to continue the operation of the power converter when a one-wire ground fault occurs, but no countermeasure is taken for the suppression of the second harmonic vibration as described above, and the operation is stable. Therefore, there is a limit to supplying power. In order to suppress the second harmonic vibration due to such unbalance of the three-phase power system and to supply more stable power, the present inventor has three-phase AC balanced conditions (three-phase voltage) as in the prior art. Alternatively, the present invention is filed on the assumption that it is difficult as long as it is a power conversion device in which the sum of currents is always limited to zero.

    The present invention has been made in view of the above-described circumstances, and an object of the present invention is to suppress the second harmonic vibration of transmission power caused by an asymmetrical accident or the like and to supply stable power.

In order to achieve the above object, according to the present invention, as the first solving means related to the power converter, the first to third single-phase alternating currents obtained by independently converting the three-phase alternating current power supplied from one of the three-phase power systems. A first transformer that converts power and the first to third single-phase AC powers are independently converted to DC power, and the DC power is converted to fourth to sixth single-phase AC powers. First to third AC / DC / AC conversion means, a second transformer for converting the fourth to sixth single-phase AC power into three-phase AC power and supplying the same to the other three-phase power system; A control means for controlling the first to third AC / DC / AC conversion means so that a transmission current that suppresses second-order harmonic vibration is supplied to each phase in the other three-phase power system; The means of comprising is adopted.

Further, as a second solving means related to the power conversion device, in the first solving means, the control means has an effective value V _{1 of} the a-phase transmission voltage serving as a reference phase, the effective value V ₂ and the phase φb of the transmission voltage becomes b-phase, and the effective value V ₃ and the phase φc of the transmission voltage of c-phase is the next phase to the b-phase, the transmission current of the c-phase before the control the following conditional expression relating to a phase .theta.c (12), (17), the transmission current having a power current to a phase, the effective value _{I 2} and the phase θb having an effective value _{I 1} and phase θa satisfying the (18) the b-phase, and the effective value I ₃ and the phase .theta.c (where the phase .theta.c control value before) the first to third AC / DC / AC converting means as transmission current with a is supplied to the c-phase It is characterized by controlling.

Further, as a third solving means related to the power converter, the control means comprises the ground fault detecting means for detecting the occurrence of a one-line ground fault in the other three-phase power system in the first solving means. Is the effective value Vf and phase φf of the first healthy phase transmission voltage that is the next phase to the ground fault phase, and the second healthy phase transmission voltage that is the next phase to the first healthy phase. A transmission current having an effective value If and a phase θf that satisfies the following conditional expressions (39), (42), and (43) with respect to the effective value Vs and the phase φs becomes the first healthy phase, and the effective value Is and the phase The first to third AC / DC / AC converters are controlled so that a transmission current having θs is supplied to the second healthy phase.

In addition, as a fourth means for solving the power conversion apparatus, first to third DC / AC conversions for independently converting DC power supplied from a DC power source into first to third single-phase AC powers, respectively. Means, a transformer that converts the first to third single-phase AC powers into three-phase AC powers and supplies them to a three-phase power system, and suppresses second-order harmonic vibrations in the three-phase power system And a control means for controlling the first to third DC / AC conversion means so that a proper transmission current is supplied to each phase.

Further, as a fifth solving means related to the power conversion device, in the fourth solving means, the control means has an effective value V _{1 of} the a-phase transmission voltage serving as a reference phase, the effective value V ₂ and the phase φb of the transmission voltage becomes b-phase, and the effective value V ₃ and the phase φc of the transmission voltage of c-phase is the next phase to the b-phase, the transmission current of the c-phase before the control the condition concerning the phase .theta.c (12), (17), the transmission current having a power current to a phase, the effective value _{I 2} and the phase θb having an effective value _{I 1} and phase θa satisfying the (18) the b-phase, and the effective value I ₃ and the phase .theta.c (where phase .theta.c the value before control) controls said first to third DC / AC conversion unit so transmitting current with a is supplied to the c-phase It is characterized by doing.

Further, as a sixth solving means related to the power conversion device, in the fourth solving means, a ground fault detecting means for detecting occurrence of a one-line ground fault in the three-phase power system is provided, and the control means includes: The effective value Vf and phase φf of the first healthy phase transmission voltage that is the next phase to the ground fault phase, and the effective value of the second healthy phase transmission voltage that is the next phase to the first healthy phase A transmission current having an effective value If and a phase θf that satisfies the above conditional expressions (39), (42), and (43) with respect to Vs and the phase φs becomes the first healthy phase, and the effective value Is and the phase θs. The first to third DC / AC converters are controlled such that the transmitted current is supplied to the second healthy phase.

 On the other hand, as a first solving means related to the power control method, a first step of converting three-phase AC power supplied from one three-phase power system into independent first to third single-phase AC powers; A second step of converting each of the first to third single-phase AC powers into DC power independently and converting the DC power into fourth to sixth single-phase AC powers; A third step of converting six single-phase AC power into three-phase AC power and supplying it to the other three-phase power system, and a transmission current that suppresses second-order harmonic vibration in the other three-phase power system And a fourth step of controlling the second step so that is supplied to each phase.

Further, as a second solving means related to the power control method, in the first solving means, in the fourth step, the effective value V _{1 of} the a-phase transmission voltage serving as a reference phase is compared with the a-phase. rms V ₂ and the phase φb of transmission voltage of b phase that provides the Tsugisho, the effective value V ₃ and the phase φc of the transmission voltage of c-phase is the next phase to the b-phase, transmission of c-phase before the control A power transmission current having an effective value I ₁ and a phase θa that satisfies the above conditional expressions (12), (17), and (18) with respect to the phase θc of the current is a power transmission having an effective value I ₂ and a phase θb. current to b-phase, and the effective value I ₃ and the phase .theta.c (where the phase .theta.c value before control) and wherein the transmission current having to control the second step to be supplied to the c-phase To do.

Further, as a third solution means related to the power control method, the first solution means includes a fifth step of detecting occurrence of a one-line ground fault in the other three-phase power system, In step 4, the effective value Vf and phase φf of the transmission voltage of the first healthy phase that is the next phase to the ground fault phase, and the second healthy phase that is the next phase to the first healthy phase. A transmission current having an effective value If and a phase θf that satisfies the conditional expressions (39), (42), and (43) with respect to the effective value Vs and the phase φs of the transmitted voltage is the first healthy phase and the effective value. The second step is controlled such that a transmission current having Is and phase θs is supplied to the second healthy phase.

 Further, as a fourth solving means related to the power control method, a first step of independently converting direct current power supplied from a direct current power source into first to third single-phase alternating current power; A second step of converting the third single-phase AC power into the three-phase AC power and supplying the three-phase AC power to the three-phase power system; And a third step of controlling the first step so as to be supplied to the phase.

Further, as a fifth solving means related to the power control method, in the fourth solving means, in the third step, the effective value V _{1 of} the a-phase transmission voltage serving as a reference phase is compared with the a-phase. rms V ₂ and the phase φb of transmission voltage of b phase that provides the Tsugisho, the effective value V ₃ and the phase φc of the transmission voltage of c-phase is the next phase to the b-phase, transmission of c-phase before the control A power transmission current having an effective value I ₁ and a phase θa that satisfies the above conditional expressions (12), (17), and (18) with respect to the phase θc of the current is a power transmission having an effective value I ₂ and a phase θb. current to b-phase, and the effective value I ₃ and the phase .theta.c (where the phase .theta.c value before control) and wherein the transmission current having to control the first step to be supplied to the c-phase To do.

Further, as a sixth solving means relating to the power control method, the fourth solving means includes a fourth step of detecting the occurrence of a one-wire ground fault in the three-phase power system, In the process, the effective value Vf and phase φf of the first healthy phase transmission voltage that is the next phase to the ground fault phase, and the second healthy phase transmission voltage that is the next phase to the first healthy phase. A transmission current having an effective value If and a phase θf that satisfies the above conditional expressions (39), (42), and (43) with respect to the effective value Vs and the phase φs of the first effective phase, and the effective value Is and The first step is controlled such that a transmission current having a phase θs is supplied to the second healthy phase.

  According to the present invention, the first transformer for converting the three-phase AC power supplied from one of the three-phase power systems into independent first to third single-phase AC powers not restricted by the three-phase AC balance condition; , First to third AC / DC / AC conversion means for independently converting the first to third single-phase AC powers into fourth to sixth single-phase AC powers; 6 is provided with a second transformer that converts single-phase AC power into three-phase AC power and supplies it to the other three-phase power system, so that the transmission current of each phase is not restricted by the three-phase AC equilibrium condition. Each can be controlled independently. Therefore, it is also possible to supply a transmission current that satisfies the conditional expressions (12), (17), (18) or (39), (42), (43). As a result, it is possible to suppress the second harmonic vibration of the transmission power that occurs when an unbalance such as an asymmetrical accident occurs, and to supply a stable power.

The power converter of the present invention converts DC power supplied from a DC power source into single-phase AC power independently by three DC / AC converters, and converts it into three-phase AC power by a transformer. Thus, a configuration for supplying to the three-phase power system can be employed. Therefore, by using a DC power source such as a fuel cell or a storage battery as a power converter that converts three-phase AC power, an unbalance such as an asymmetrical accident is occurring in a power system in which the DC power source and the three-phase power system are linked It is possible to suppress the second-order harmonic vibration and to supply stable power.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a power conversion apparatus according to an embodiment of the present invention. In FIG. 1, the present power conversion device R links the first power system A and the second power system B.

 The power converter R converts, for example, three-phase AC power having a system frequency of 60 Hz (that is, three-phase AC power of the first power system A) into three-phase AC power having a system frequency of 50 Hz (that is, three-phase AC of the second power system B). AC power). The power converter R includes, as its constituent elements, a first transformer R1, a first converter circuit R2, a second converter circuit R3, a third converter circuit R4, smoothing capacitors R5, R6, R7, first Inverter circuit R8, second inverter circuit R9, third inverter circuit R10, second transformer R11, first zero-phase current transformer R12, first measurement transformer R13, first measurement Current transformer R14, first power control unit R15, first PWM signal generation circuit R16, second zero-phase current transformer R17, second measurement transformer R18, second measurement current transformer R19 The second power control unit R20 and the second PWM signal generation circuit R21 are provided.

 In the first transformer R1, the primary side coil and the secondary side coil are Y-Δ connected, but the secondary side Δ connection is each phase like a general three-phase transformer. The end of the coil is not connected to the start of the next phase coil in sequence, and the coils of each phase are completely independent of the other phases. That is, the first transformer R1 is independent of the three-phase AC power input from the first power system A to the primary coil without being restricted by the three-phase AC balance condition in the secondary coil. It converts to three single-phase AC power. Thus, the first transformer R1 includes the first single-phase AC power Pa corresponding to the supply power of each phase (a phase, b phase, c phase) of the first power system A from the secondary coil. Are output to the first converter circuit R2, the second single-phase AC power Pb is output to the second converter circuit R3, and the third single-phase AC power Pc is output to the third converter circuit R4. The neutral point of the Y connection of the primary coil is grounded through resistance.

 The first converter circuit R2, the second converter circuit R3, and the third converter circuit R4 are configured by a plurality of semiconductor switching elements, for example, bridge circuits of IGBTs (Insulated Gate Bipolar Transistors). Each single-phase AC power is converted into DC power by controlling (Pulse Width Modulation). In other words, the first converter circuit R2 converts the first single-phase AC power Pa input from the first transformer R1 into the first DC power Pa1, and converts it into the smoothing capacitor R5 and the first inverter circuit R8. Output. Similarly, the second converter circuit R3 converts the second single-phase AC power Pb input from the first transformer R1 into the second DC power Pb1, thereby converting the smoothing capacitor R6 and the second inverter circuit R9. Output to. Further, the third converter circuit R4 converts the third single-phase AC power Pc input from the first transformer R1 into the third DC power Pc1, and supplies the third DC power Pc1 to the smoothing capacitor R7 and the third inverter circuit R10. Output.

 The smoothing capacitors R5, R6, and R7 are provided to reduce the AC components included in the first to third DC powers Pa1 to Pc1.

 The first inverter circuit R8, the second inverter circuit R9, and the third inverter circuit R10 are composed of a plurality of IGBT bridge circuits, and each of the DC powers is single-phased by PWM control of the IGBT. It converts to AC power. That is, the first inverter circuit R8 converts the first DC power Pa1 input from the first converter circuit R2 into the fourth single-phase AC power Pa2 and outputs the fourth single-phase AC power Pa2 to the second transformer R11. Similarly, the second inverter circuit R9 converts the second DC power Pb1 input from the second converter circuit R3 into a fifth single-phase AC power Pb2 and outputs the fifth single-phase AC power Pb2 to the second transformer R11. The third inverter circuit R10 converts the third DC power Pc1 input from the third converter circuit R4 into the sixth single-phase AC power Pc2 and outputs the sixth single-phase AC power Pc2 to the second transformer R11. The fourth to sixth single-phase AC powers Pa2 to Pc2 are converted to the same frequency as the system frequency (50 Hz) of the second power system B.

 Similarly to the secondary coil of the first transformer R1, the second transformer R11 is wired such that the coils of each phase are completely independent of the other phases, as in the secondary coil of the first transformer R1. The fourth to sixth single-phase AC powers Pa2 to Pc2 input to the coil are converted into three-phase AC power in the secondary coil (Y connection) and output to the second power system B. The neutral point of the Y connection of the secondary coil is grounded by resistance.

 The first zero-phase current transformer R12 is connected to each phase of the second power system B, and detects a zero-phase current generated when a ground fault occurs in any of the phases. The occurrence of a ground fault is detected, and a ground fault detection signal indicating the occurrence of the ground fault is output to the first power control unit R15. The first measurement transformer R13 is connected to each phase of the second power system B, and converts the transmission voltage of each phase, which is a large voltage value, into a measurable voltage value. The effective value and phase of the voltage are measured and output to the first power control unit R15. The first measuring current transformer R14 is connected to each phase of the second power system B, and converts the transmission current of each phase, which is a large current value, into a measurable current value. The effective value and phase of the transmission current are measured and output to the first power control unit R15.

 When an unbalance due to an asymmetrical accident or the like occurs in the second power system B, the first power control unit R15 performs the measurement result of the transmission voltage by the first measurement transformer R13 and the first measurement current transformer. Based on the measurement result of the transmission current by the instrument R14, a transmission current that suppresses the second harmonic vibration caused by an asymmetrical accident or the like is obtained by a predetermined calculation process, and the transmission current obtained by the calculation process is An unbalanced power control signal for controlling the first PWM signal generation circuit R16 is output to the first PWM signal generation circuit R16 so as to be supplied to the phase.

 Further, the first power control unit R15 is configured such that when a one-line ground fault occurs in the second power system B, that is, when a ground fault detection signal is input from the first zero-phase current transformer R12. The ground fault phase is determined based on the measurement result of the transmission current by the first measurement current transformer R14, and the one-wire ground fault is caused based on the measurement result of the transmission voltage by the first measurement transformer R13. First, the transmission current that suppresses the second harmonic vibration generated in the healthy phase of the remaining two wires due to the predetermined calculation processing is obtained, and the transmission current obtained by the calculation processing is supplied to the healthy phase. A ground fault power control signal for controlling the PWM signal generation circuit R16 is output to the first PWM signal generation circuit R16. Further, the first power control unit R15 outputs a gate block signal for stopping the power supply to the ground fault phase to the first PWM signal generation circuit R16.

  The first power control unit R15 outputs a normal power control signal for normal operation when an imbalance (including a one-wire ground fault) such as an asymmetrical accident has not occurred in the second power system B. This is output to the first PWM signal generation circuit R16.

 The first PWM signal generation circuit R16 generates a PWM signal for controlling on / off of the gate of the IGBT, and is an unbalanced power control signal input from the first power control unit R15, a ground fault. A PWM signal is generated based on the hour power control signal, the gate block signal, and the normal hour power control signal, and is output to the first inverter circuit R8, the second inverter circuit R9, and the third inverter circuit R10.

 On the other hand, the second zero-phase current transformer R17 is connected to each phase of the first electric power system A, and detects a zero-phase current generated when a ground fault occurs in any one of the phases. Thus, the occurrence of a ground fault is detected, and a ground fault detection signal indicating the occurrence of the ground fault is output to the second power control unit R20. The second measurement transformer R18 is connected to each phase of the first electric power system A, and converts the transmission voltage of each phase, which is a large voltage value, into a measurable voltage value. The effective value and phase of the voltage are measured and output to the second power control unit R20. The second measuring current transformer R19 is connected to each phase of the first electric power system A, and converts the transmission current of each phase, which is a large current value, into a measurable current value. The effective value and phase of the transmission current are measured and output to the second power control unit R20.

 When an unbalance such as an asymmetrical accident occurs in the first power system A, the second power control unit R20 performs the measurement result of the transmission voltage by the second measurement transformer R18 and the second measurement current transformer. Based on the measurement result of the transmission current by the device R19, a transmission current that suppresses the second harmonic vibration caused by an asymmetrical accident or the like is obtained by a predetermined calculation process, and the transmission current obtained by the calculation process is An unbalanced power control signal for controlling the second PWM signal generation circuit R21 is output to the second PWM signal generation circuit R21 so as to be supplied to the phase.

 Further, the second power control unit R20 is configured such that when a one-wire ground fault occurs in the first power system A, that is, when a ground fault detection signal is input from the second zero-phase current transformer R17. The ground fault phase is determined based on the measurement result of the transmission current by the second measurement current transformer R19, and the one-wire ground fault is caused based on the measurement result of the transmission voltage by the second measurement transformer R18. The transmission current that suppresses the second harmonic vibration that occurs in the sound phases of the remaining two wires due to this is obtained by a predetermined calculation process, and the second so that the transmission current obtained by the calculation process is supplied to the sound phase. The ground fault power control signal for controlling the PWM signal generation circuit R21 is output to the second PWM signal generation circuit R21. The second power control unit R20 outputs a gate block signal for stopping the power supply to the ground fault phase to the second PWM signal generation circuit R21.

  Note that the second power control unit R20 generates a normal power control signal for normal operation when an unbalance (including a one-wire ground fault) such as an asymmetrical accident has not occurred in the first power system A. This is output to the second PWM signal generation circuit R21.

 The second PWM signal generation circuit R21 generates a PWM signal for controlling on / off of the gate of the IGBT, and is an unbalanced power control signal input from the second power control unit R20. A PWM signal is generated based on the hour power control signal, the gate block signal, and the normal hour power control signal, and is output to the first converter circuit R2, the second converter circuit R3, and the third converter circuit R4.

 Among the above components, the first converter circuit R2, the smoothing capacitor R5, and the first inverter circuit R8 constitute a single-phase AC / DC / single-phase AC converter, and similarly, the second converter The circuit R3, the smoothing capacitor R6, and the second inverter circuit R9 also constitute a single-phase AC / DC / single-phase AC converter, and the third converter circuit R4, the smoothing capacitor R7, and the third inverter circuit R10 are also single-phase. An AC / DC / single-phase AC converter is configured. That is, the power conversion device R includes three single-phase AC / DC / single-phase AC converters, and three single-phase AC powers output from the first transformer R1 are converted into the single-phase AC / DC. / Power conversion is performed by independently controlling the single-phase AC converter. This is the greatest feature of the configuration of the power converter R.

 Next, operation | movement of this power converter device R of the above structures is demonstrated. In the following description, it is assumed that power is supplied from the first power system A to the second power system B.

[Unbalanced due to asymmetrical accidents, etc.]
First, a case where an unbalance due to an asymmetrical accident or the like occurs in the second power system B and second-order harmonic vibration occurs in three-phase AC power will be described.
FIG. 2 is an operation flowchart of the first power control unit R15. First, the first power control unit R15 obtains in advance the phase θ _c of the c-phase transmission current before the occurrence of unbalance due to an asymmetrical accident or the like (before control) from the first measurement transformer R13 (step S1). ). Then, the first power control unit R15 determines whether there is an asymmetrical accident or the like based on the measurement result of the transmission voltage by the first measurement transformer R13 or the measurement result of the transmission current by the first measurement current transformer R14. It is determined whether equilibrium has occurred (step S2). In this step S2, when “NO”, that is, when an unbalance due to an asymmetrical accident or the like has not occurred, the first power control unit R15 outputs a normal power control signal for performing normal operation (frequency conversion) as the first power control signal. To the PWM signal generating circuit R16 (step S3).

 The first PWM signal generation circuit R16 outputs a PWM signal generated based on the normal power control signal to the first inverter circuit R8, the second inverter circuit R9, and the third inverter circuit R10. On the other hand, the second power control unit R20 also outputs a normal power control signal to the second PWM signal generation circuit R21, and the second PWM signal generation circuit R21 generates based on the normal power control signal. The PWM signal thus output is output to the first converter circuit R2, the second converter circuit R3, and the third converter circuit R4. These converter circuits and inverter circuits perform power conversion based on the PWM signal, and normal operation is performed.

In Step S2, when “YES”, that is, when an unbalance due to an asymmetrical accident or the like occurs in the second power system B, the first power control unit R15 receives the asymmetrical accident from the first measuring transformer R13. The effective value V ₁ of the a-phase (reference phase) transmission voltage, the effective value V ₂ and the phase φ _{b of the b-} phase transmission voltage, and the effective value V ₃ and the phase φ _c of the c-phase transmission voltage are acquired. (Step S4).

The first power control unit R15 includes the effective value V _{1 of the} a-phase transmission voltage, the effective value V ₂ and the phase φ _{b of} the b-phase transmission voltage, the effective value V ₃ and the phase of the c-phase transmission voltage. and phi _c, on the basis of the phase theta _c of the transmission current of the c-phase before unbalanced generated by asymmetric accidents, the following conditional expression (12), (17), the effective value I ₁ and which satisfy (18) transmitting current of the a-phase having a phase theta _a, transmission current b phase having an effective value I ₂ and the phase theta _b, also effective value I ₃ and the phase theta _{c (where} the phase theta _c imbalance occurs due to the asymmetric accidents The c-phase transmission current having the previous value is calculated (step S5).
Note that the phase θ _c of the c-phase transmission current before the occurrence of unbalance due to an asymmetrical accident or the like is stored in advance in the internal memory of the first power control unit R15 by the operation of step S1.

The first power control unit R15 outputs an unbalanced power control signal to the first PWM signal generation circuit R16 so that the transmission current calculated as described above is generated by the inverter circuit corresponding to each phase. (Step S6). In the conditional expression (12), the constant G can be increased as much as possible to supply larger electric power. Therefore, the effective value I _{1 of the} a-phase transmission current, the effective value I ₂ of the b-phase transmission current, and the effective value I ₃ of the c-phase transmission current are as large as possible within a range that satisfies the conditional expression (12). It is desirable to set it to a value.

   The first PWM signal generation circuit R16 generates a PWM signal based on the unbalanced power control signal, and outputs the PWM signal to the primary side coil of the second transformer R11 corresponding to each phase. The AC power is output to the inverter circuits (first inverter circuit R8, second inverter circuit R9, and third inverter circuit R10). These inverter circuits switch the IGBT based on the PWM signal, thereby transmitting the transmission current having the effective value and phase determined in step S4 to the second electric power system B via the second transformer R11. Supply.

 When a transmission current that satisfies the conditional expressions (12), (17), and (18) as described above is supplied to each phase, the second harmonic vibration of the second power system B when an unbalance occurs due to an asymmetrical accident or the like is generated. It becomes possible to suppress. The principle will be described in detail below.

First, a phase of the second electric power system B, b-phase, instantaneous voltage _v a of the transmission voltage of _c-phase, v b, _v and _c, the instantaneous current _i a of the transmission _current, i b, a _{i c} below (1 ) To (6).

In the above (1) to _(6), V _1, V 2, _{V 3} is the effective value of each phase of the transmission voltage, respectively, _also, I _1, I 2, _{I 3} is the phase of the transmission current, respectively Effective value. On the other hand, as shown in the vector diagram of FIG. 3 (a), phi _b v is the phase of v _b on the basis vectors _a, is the phase of similarly phi _c also v v _a was used as a reference vector _c . Further, a phase of θ _a, θ _b, θ _c is _i a on the basis vectors _{v a respective,} i b, _{i c.} ω is an angular frequency (2π · f), and f is a system frequency (50 Hz) of the second power system B. t is time.

Further, the instantaneous power p of the three-phase AC power of the second power system B is expressed by the following equation (7).

 By substituting the equations (1) to (6) into the equation (7), the following equation (8) is obtained.

   When only the 2ω (second harmonic) term is extracted in the above equation (8), the following equation (9) is obtained.

   The 2ω component of the instantaneous power p expressed by the above equation (9) is a cause of generating second harmonic vibration in the three-phase AC power when an unbalance occurs due to an asymmetrical accident or the like. Therefore, in order to suppress the second harmonic vibration, the coefficients of cos2ωt and sin2ωt in the above equation (9) may be set to zero. That is, the following equations (10) and (11) are obtained.

From the above expressions (10) and (11), a conditional expression such as the following expression (12) is obtained. In addition,
In the following formula (12), G is a constant.

When φ _b + θ _b = α and φ _c + θ _c = β, the above expressions (10) and (11) are expressed as the following expressions (13) and (14).

    The sum of the squared expression (13) and the squared expression (14) gives the following expression (15).

    When the above equation (15) is expanded, the following equation (16) is obtained.

From the above equation (16), it can be seen that α−β = φ _b + θ _b −φ _c −θ _c = ± 120 °, and from this, regarding the phase θ _b of the b-phase current, The following conditional expression is obtained.

Similarly, for the phase θa of the _a- phase current, a conditional expression such as the following expression (18) is obtained.

As described above, it can be seen that the equations (12), (17), and (18) are conditional equations for suppressing the second harmonic vibration when an unbalance occurs due to an asymmetrical accident or the like. The transmission voltage of each phase during an unbalanced occurrence due to an asymmetrical accident or the like is almost determined by the accident condition and the like. Therefore, the phase θ _c of the c-phase transmission current before the occurrence of unbalance due to an asymmetrical accident or the like is stored in advance, and the effective value of the phase θ _c and the a-phase transmission voltage during the occurrence of unbalance due to the asymmetrical accident or the like is stored. Substituting V ₁ , effective value V ₂ and phase φ _{b of} the b-phase transmission voltage, and effective value V ₃ and phase φ _c of the c-phase transmission voltage into the above equations (12), (17), and (18) A-phase transmission current having an effective value I ₁ and phase θ _a satisfying these conditional expressions, b-phase transmission current having effective value I ₂ and phase θ _b , effective value I ₃ and phase θ _c (θ _(c is a value before occurrence of unbalance due to an asymmetrical accident or the like) c-phase transmission current to suppress the second harmonic vibration of the three-phase AC power during the occurrence of unbalance due to an asymmetrical accident or the like Is possible.

  Further, in order to supply a transmission current that satisfies the conditional expressions (12), (17), and (18) to the second power system B, it is necessary to perform current control independently for each phase. In the conventional three-phase power converter, the above-described independent control is difficult because the three-phase AC balance condition is limited. However, in the present power conversion device R, as described above, the three-phase AC power of the first power system A is once converted into three single-phase AC powers not restricted by the three-phase AC equilibrium condition, and these are converted into three single-phase powers. The AC / DC / single-phase AC converter controls the power independently to convert the power, and the second transformer R11 converts the power into three-phase AC power and supplies it again. Therefore, even when an unbalance due to an asymmetrical accident or the like occurs, the transmission current supplied to each phase can be controlled independently. As a result, the conditional expressions (12), (17), (18) By controlling the transmission current so as to satisfy the above, the second harmonic vibration of the three-phase AC power can be suppressed.

[At the time of 1-line ground fault]
Next, a case where a one-wire ground fault occurs and second harmonic vibration occurs in the healthy phases of the remaining two wires will be described.
FIG. 4 is an operation flowchart of the first power control unit R15 at the time of a one-line ground fault. First, the first power control unit R15 determines whether or not a ground fault detection signal is input from the first zero-phase current transformer R12 (step S10). In this step S10, when “NO”, that is, when a ground fault has not occurred, the first power control unit R15 generates a normal power control signal for performing normal operation (frequency conversion) as a first PWM signal. Output to the circuit R16 (step S11).

 The first PWM signal generation circuit R16 outputs a PWM signal generated based on the normal power control signal to the first inverter circuit R8, the second inverter circuit R9, and the third inverter circuit R10. On the other hand, the second power control unit R20 also outputs a normal power control signal to the second PWM signal generation circuit R21, and the second PWM signal generation circuit R21 generates based on the normal power control signal. The PWM signal thus output is output to the first converter circuit R2, the second converter circuit R3, and the third converter circuit R4. These converter circuits and inverter circuits perform power conversion based on the PWM signal, and normal operation is performed.

 On the other hand, in Step S10, when “YES”, that is, when a one-line ground fault occurs, the first power control unit R15 detects the ground fault phase based on the measurement result of the first current transformer R14, A gate block signal for stopping the power supply to the ground fault phase is output to the first PWM signal generation circuit R16 (step S12). The first PWM signal generation circuit R16 applies PWM to the inverter circuit that supplies single-phase AC power to the primary coil of the second transformer R11 corresponding to the ground fault phase based on the gate block signal. Stop signal output. That is, since the IGBT of the inverter circuit does not perform a switching operation, power supply to the ground fault phase is stopped.

 Then, the first power control unit R15 includes the effective value Vf and the phase φf of the transmission voltage of the first healthy phase that is the next phase to the ground fault phase from the first measurement transformer R13, and the first The effective value Vs and phase φs of the transmission voltage of the second healthy phase that is the next phase to the healthy phase are acquired (step S13). The effective value Vf and phase φf of the first healthy phase transmission voltage and the effective value Vs and phase φs of the second healthy phase transmission voltage may be different from the values before the occurrence of the ground fault. It is necessary to detect the value after the occurrence of the fault.

 Next, the first power control unit R15 obtains the effective value Vf and phase φf of the first healthy phase transmission voltage and the effective value Vs and phase φs of the second healthy phase transmission voltage acquired as described above. Are substituted into the following conditional expressions (39), (40), (41), and the first healthy phase transmission current (effective value If, phase θf) and second A healthy phase transmission current (effective value Is, phase θs) is calculated (step S14). The first power control unit R15 outputs a ground fault power control signal to the first PWM signal generation circuit R16 so that the transmission current calculated as described above is generated by the inverter circuit corresponding to each healthy phase. (Step S15).

 In the conditional expression (39), a larger electric power can be supplied by increasing the constant K as much as possible. Therefore, it is desirable to set the effective values If and Is as large as possible within a range that satisfies the conditional expression (39).

 The first PWM signal generation circuit R16 generates a PWM signal based on the ground fault power control signal as described above, and the second PWM signal corresponds to the first healthy phase and the second healthy phase. Output to the inverter circuit (any one of the first inverter circuit R8, the second inverter circuit R9, or the third inverter circuit R10) that supplies single-phase AC power to the primary coil of the transformer R11. . The inverter circuit corresponding to the above switches the IGBT based on such a PWM signal, so that the transmission current obtained in step S14 is supplied to the first power system B of the second power system B via the second transformer R11. To the healthy phase and the second healthy phase.

 When a current that satisfies the above equations (39), (40), and (41) is supplied to the healthy phase, it is possible to suppress the second-order harmonic vibration of the healthy phase at the time of a one-wire ground fault. The principle will be described in detail below.

 Considering the case where a ground fault occurs in the a phase and the power supply of the a phase is stopped, the above equation (7) becomes the following equation (19).

  Substituting the above equations (1) to (6) into the above equation (19), the following equation (20) is obtained.

Substituting the formula of trigonometric function cos ² ωt = (cos2ωt + 1) / 2, sin ² ωt = (1−cos2ωt) / 2, and cosωt · sin ωt = sin2ωt / 2 into the above formula (20) become that way.

  If only the 2ω (second harmonic) term is extracted in the above equation (21), the following equation (22) is obtained.

  The 2ω component of the instantaneous power p expressed by the above equation (22) is a cause of generating second harmonic vibration when power is supplied in the remaining healthy phase at the time of ground fault. Therefore, in order to suppress the second harmonic vibration, the coefficients of cos2ωt and sin2ωt in the above equation (22) may be set to zero. That is, the following formulas (23) and (24) are obtained.

 From the above equations (23) and (24), a conditional expression such as the following equation (25) is obtained. In the following equation (25), K is a constant.

  From the above equation (25), the above equations (23) and (24) are expressed as follows.

  Further, a conditional expression such as the following expression (28) is obtained from the expressions (26) and (27).

 Expressions (25) and (28) as described above are conditional expressions for removing the second harmonic vibration, and the second harmonic vibration is removed from the expressions (21), (26) and (27). The instantaneous power p at this time is expressed by the following equation (29).

 As can be seen from the above equation (29), the instantaneous value p when the second harmonic vibration is removed is a constant value regardless of the time t. Substituting the above expression (28) into such an expression (29) yields the following expression (30).

  From the above equation (30), the following conditions are necessary to maximize the instantaneous power p.

 Further, when the above expression (31) is substituted into the above expression (28), the following conditional expression is obtained.

 The conditional expressions (31) and (32) are conditional expressions for maximizing the instantaneous power p when the second harmonic vibration is removed. In other words, by supplying a transmission current that satisfies the equations (25), (31), and (32) to the healthy phase, the second harmonic vibration that occurs at the time of a one-wire ground fault is suppressed, and the maximum power is reduced. It becomes possible to supply.

On the other hand, when the b-phase is grounded, as shown in FIG. 3B, the phase φ _c of the c-phase instantaneous voltage v _{c and the} a-phase instantaneous voltage are set using the b-phase instantaneous voltage v _b as a reference vector. v _a phase phi _a, also, defining the phase theta _a instantaneous current i _a phase theta _c, a phase of the instantaneous current i _c of c-phase, as in the case where a phase as described above was ground The following conditional expressions (33) to (35) can be obtained.

Also, if the c-phase is grounded, as shown in FIG. 3 (c), as a reference vector instantaneous voltage v _c of c-phase, phase phi _a, b-phase instantaneous voltage of the instantaneous voltage v _a a-phase v _b of the phase phi _b also, by defining the phase theta _b of the instantaneous current _{i b} of the phase theta _a, b-phase instantaneous current _{i a} of a phase, as well as the following conditional expression (36) - (38) Can be requested.

 As can be seen from the above, using the instantaneous voltage of the ground fault phase as a reference vector, the effective value of the transmission voltage of the first healthy phase as the next phase is Vf and the phase is φf, the effective value of the transmission current is If and the phase is θf And defining the effective value of the transmission voltage of the second healthy phase that is the next phase of the first healthy phase as Vs and the phase as φs, the effective value of the transmission current as Is and the phase as θs, The conditional expression can be generalized as follows.

 That is, the first power control unit R15 causes the ground fault power control signal to be sent to the first PWM signal generation circuit R16 so that a transmission current that satisfies the conditional expressions (39), (40), and (41) is generated. Is output.

  As described above, in order to supply a transmission current that satisfies the conditional expressions (39), (40), and (41) to the second power system B, current control is performed independently for each healthy phase. Although it is necessary, the conventional three-phase power converter is restricted by the three-phase AC balance condition, and thus the above independent control is difficult. However, in the power conversion device R, as described above, it is possible to independently control the transmission current supplied to each phase, and as a result, the conditional expressions (39), (40), (41) By controlling the transmission current of the healthy phase so as to be satisfied, it is possible to suppress second-order harmonic vibrations, and it is possible to secure as much supply power as possible with the healthy phase of two wires.

  Note that the above equations (40) and (41) do not necessarily have to be satisfied, and the phase θf of the transmission current of the first healthy phase and the second healthy phase are within a range such as the following equations (42) and (43). Even if the phase θs of the transmission current is set, it is possible to obtain the effects of suppressing the second harmonic vibration and supplying a large amount of power. However, since this effect is greatest when the above expressions (40) and (41) are satisfied, it is desirable to use the expressions (40) and (41).

  In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.

(1) In the above embodiment, the case where power is supplied from the first power system A to the second power system B and the case where an unbalance due to an asymmetrical accident or the like occurs in the second power system B has been described. However, the present invention is not limited to this, and even if power is supplied from the second power system B to the first power system A and an unbalance due to an asymmetrical accident or the like occurs in the first power system A, the second power system B The same effect can be obtained by performing current control of each phase on the first power system A side by the power control unit 20. When power is supplied from the second power system B to the first power system A in this way, the functions of the inverter circuit and the converter circuit are reversed.

(2) In the above embodiment, the power conversion device that interconnects two three-phase AC power systems has been described. However, the present invention is not limited to this, and for example, a DC power source such as a fuel cell or a storage battery is converted into three-phase AC power. It can also be configured as a power converter. That is, this power conversion device includes three inverter circuits that each independently convert DC power supplied from a DC power source into single-phase AC power, and converts these single-phase AC power into three-phase AC power to generate three-phase power. Power control unit that controls transmission current so as to suppress secondary harmonic vibration caused by asymmetrical accidents (including 1-wire ground faults) in transformers to be supplied to the system and three-phase power systems And a PWN signal generation circuit that controls the inverter circuit under the control of the power control unit. According to the power conversion device configured in this way, even when an unbalance due to an asymmetrical accident or the like occurs in a power system in which a DC power supply and a three-phase power system are linked, second harmonic vibration can be suppressed. , Stable power supply can be performed.

(3) In the above embodiment, the power conversion device R is used for frequency conversion. However, the present invention is not limited to this, and for example, between different power systems such as between Hokkaido and Honshu is linked by DC power transmission. It can also be used as a power conversion device.

(4) In the above embodiment, the IGBT is used as the semiconductor switching element. However, the present invention is not limited to this, and other semiconductor switching elements may be used.

1 is a schematic configuration diagram of a power conversion device R according to an embodiment of the present invention. It is an operation | movement flowchart figure of 1st electric power control part R15 at the time of the unbalance generation | occurrence | production by the asymmetrical accident etc. which concern on one Embodiment of this invention. It is a vector diagram for demonstrating the suppression principle of the 2nd harmonic vibration which concerns on one Embodiment of this invention. It is an operation | movement flowchart figure of 1st electric power control part R15 at the time of 1 line | wire ground fault accident which concerns on one Embodiment of this invention.

Explanation of symbols

     A ... 1st electric power system, B ... 2nd electric power system, R ... Power converter, R1 ... 1st transformer, R2 ... 1st converter circuit, R3 ... 2nd converter circuit, R4 ... 3rd Converter circuit, R5, R6, R7 ... smoothing capacitor, R8 ... first inverter circuit, R9 ... second inverter circuit, R10 ... third inverter circuit, R11 ... second transformer, R12 ... first Zero-phase current transformer, R13 ... first measurement transformer, R14 ... first measurement current transformer, R15 ... first power control unit, R16 ... first PWM signal generation circuit, R17 ... second Zero-phase current transformer, R18 ... second measurement transformer, R19 ... second measurement current transformer, R20 ... second power control unit, R21 ... second PWM signal generation circuit

Claims (12)

A first transformer for converting three-phase AC power supplied from one three-phase power system into independent first to third single-phase AC power;
The first to third AC / DC / AC that converts the first to third single-phase AC powers independently into DC power and converts the DC power to fourth to sixth single-phase AC powers. Conversion means;
A second transformer for converting the fourth to sixth single-phase AC powers into three-phase AC powers and supplying the other three-phase power systems;
Control means for controlling the first to third AC / DC / AC conversion means so that a transmission current that suppresses second-order harmonic vibration is supplied to each phase in the other three-phase power system; A power converter characterized by comprising. The control means includes an effective value V ₁ of the a-phase transmission voltage serving as the reference phase, an effective value V ₂ of the b-phase transmission voltage serving as the next phase to the a phase, the phase φb, and the b phase. the effective value V ₃ and the phase φc of the transmission voltage of c phase to be Tsugisho, the following conditional expression relating to a phase θc of the transmission current of the c-phase before the control (12), (17), that satisfies (18) the transmission current a phase having an effective value I ₁ and phase .theta.a, the transmission current b phase having an effective value I ₂ and phase .theta.b, also effective value I ₃ and the phase .theta.c (where phase .theta.c control value before 2. The power conversion device according to claim 1, wherein the first to third AC / DC / AC converters are controlled such that a transmission current having a power source is supplied to the c-phase.

A ground fault detection means for detecting the occurrence of a one-line ground fault in the other three-phase power system;
The control means includes an effective value Vf and a phase φf of the transmission voltage of the first healthy phase that is the next phase to the ground fault phase, and a second healthy phase that is the next phase to the first healthy phase. A transmission current having an effective value If and a phase θf that satisfies the following conditional expressions (39), (42), and (43) regarding the effective value Vs and the phase φs of the transmitted voltage is the first healthy phase and the effective value: 2. The power converter according to claim 1, wherein the first to third AC / DC / AC converters are controlled so that a transmission current having Is and a phase θs is supplied to the second healthy phase. .

First to third DC / AC conversion means for independently converting DC power supplied from a DC power source into first to third single-phase AC power;
A transformer for converting the first to third single-phase AC power into a three-phase AC power and supplying the three-phase power system;
Control means for controlling the first to third DC / AC conversion means so that a transmission current that suppresses second-order harmonic vibration is supplied to each phase in the three-phase power system. The power converter characterized by this. The control means includes an effective value V ₁ of the a-phase transmission voltage serving as the reference phase, an effective value V ₂ of the b-phase transmission voltage serving as the next phase to the a phase, the phase φb, and the b phase. the effective value V ₃ and the phase φc of the transmission voltage of c phase to be Tsugisho, the condition concerning the phase θc of the transmission current of the c-phase before the control (12), (17), that satisfies (18) the transmission current a phase having an effective value I ₁ and phase .theta.a, the transmission current b phase having an effective value I ₂ and phase .theta.b, also effective value I ₃ and the phase .theta.c (where phase .theta.c control value before 5. The power conversion device according to claim 4, wherein the first to third DC / AC converters are controlled such that a transmission current having a power source is supplied to the c-phase. A ground fault detecting means for detecting occurrence of a one-line ground fault in the three-phase power system;
The control means includes an effective value Vf and a phase φf of the transmission voltage of the first healthy phase that is the next phase to the ground fault phase, and a second healthy phase that is the next phase to the first healthy phase. A transmission current having an effective value If and a phase θf that satisfies the conditional expressions (39), (42), and (43) with respect to the effective value Vs and the phase φs of the transmitted voltage is the first healthy phase and the effective value. 5. The power converter according to claim 4, wherein the first to third DC / AC converters are controlled so that a transmission current having Is and a phase θs is supplied to the second healthy phase. A first step of converting three-phase AC power supplied from one of the three-phase power systems into independent first to third single-phase AC powers;
A second step of independently converting each of the first to third single-phase AC powers into DC power and converting the DC power into fourth to sixth single-phase AC powers;
A third step of converting the fourth to sixth single-phase AC powers into three-phase AC powers and supplying them to the other three-phase power system;
And a fourth step of controlling the second step so that a transmission current that suppresses second-order harmonic vibration is supplied to each phase in the other three-phase power system. Method. In the fourth step, the effective value V ₁ of the a-phase transmission voltage serving as the reference phase, the effective value V ₂ of the b-phase transmission voltage serving as the next phase to the a phase, the phase φb, and the b phase satisfy the effective value V ₃ and the phase φc of the transmission voltage of c phase of the next phase, the condition concerning the phase θc of the transmission current of the c-phase before the control (12), (17), (18) for The transmission current having the effective value I ₁ and the phase θa is in the a phase, the transmission current having the effective value I ₂ and the phase θb is in the b phase, and the effective value I ₃ and the phase θc (where the phase θc is before the control) The control method according to claim 7, wherein the second step is controlled such that a transmission current having a value of (5) is supplied to the c-phase. A fifth step of detecting the occurrence of a one-line ground fault in the other three-phase power system;
In the fourth step, the effective value Vf of the transmission voltage of the first healthy phase that is the next phase to the ground fault phase
And the phase φf and the conditional expressions (39), (42), and (43) relating to the effective value Vs and phase φs of the transmission voltage of the second healthy phase that is the next phase to the first healthy phase are satisfied The second step is controlled so that the transmission current having the effective value If and the phase θf is supplied to the first healthy phase, and the transmission current having the effective value Is and the phase θs is supplied to the second healthy phase. The control method according to claim 7, wherein: A first step of converting DC power supplied from a DC power source into first to third single-phase AC power independently of each other;
A second step of converting the first to third single-phase AC powers into three-phase AC powers and supplying them to a three-phase power system;
And a third step of controlling the first step so that a transmission current that suppresses second-order harmonic vibration is supplied to each phase in the three-phase power system. . In the third step, the effective value V ₁ of the a-phase transmission voltage serving as the reference phase, the effective value V ₂ of the b-phase transmission voltage serving as the next phase to the a phase, the phase φb, and the b phase satisfy the effective value V ₃ and the phase φc of the transmission voltage of c phase of the next phase, the condition concerning the phase θc of the transmission current of the c-phase before the control (12), (17), (18) for the transmission current a phase having an effective value I ₁ and phase θa as, the transmission current b phase having an effective value I ₂ and phase .theta.b, also effective value I ₃ and the phase .theta.c (where phase .theta.c control before The control method according to claim 10, wherein the first step is controlled such that a transmission current having a value of (5) is supplied to the c-phase. A fourth step of detecting the occurrence of a one-line ground fault in the three-phase power system;
In the third step, the effective value Vf of the transmission voltage of the first healthy phase that is the next phase to the ground fault phase
And the phase φf and the conditional expressions (39), (42), and (43) relating to the effective value Vs and phase φs of the transmission voltage of the second healthy phase that is the next phase to the first healthy phase are satisfied The first step is controlled such that the transmission current having the effective value If and the phase θf is supplied to the first healthy phase, and the transmission current having the effective value Is and the phase θs is supplied to the second healthy phase. The control method according to claim 10.

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