JP2014124028A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC/DC conversion power converter which, while achieving the objective of DC voltage level conversion, is highly efficient and low cost due to a reduced facility capacity and a reduced loss.SOLUTION: The power converter comprises: a series compensation circuit unit 11 composed of a first phase leg and a second phase leg mutually connected in parallel, each configured with two series-connected circuits of phase arms 3b having one or more H bridge units 3 connected in series; a parallel compensation circuit unit 12 composed of a third phase leg and a fourth phase leg mutually connected in parallel, each configured with two series-connected circuits of phase arms 4b having one or more chopper units 4 connected in series; and a single-phase high-frequency insulation transformer TR1. DC terminals of the series compensation circuit unit 11 are connected to a non-grounded-side line between two DC power transmission networks, and DC terminals of the parallel compensation circuit unit 12 are connected to a non-grounded-side line of one of the DC power transmission networks, and to a common ground-side line. The primary side of the single-phase high-frequency insulation transformer TR1 is connected to UV AC terminals of the series compensation circuit unit 11, and the secondary side is connected to uv AC terminals of the parallel compensation circuit unit 12.

Description

  The present invention relates to a power conversion device that connects two DC power transmission networks by converting voltage levels.

  In recent years, the spread of renewable energy such as wind power generation, solar power generation, and solar thermal power generation has been promoted, but in order to supply higher power with renewable energy, offshore wind power generation, sunlight in the desert area, solar heat Power generation is being considered. In offshore wind power generation, the generated power is transmitted to the city where it is consumed using a submarine cable, or the power is generated over a long distance from the desert area in the back of Africa or China to a large city in Europe or the coastal area. It is necessary to transmit electricity with high efficiency. In order to meet such demands, direct current power transmission is more efficient than conventional three-phase alternating current power transmission, and it is possible to install it while suppressing costs. Therefore, construction of a direct current power transmission network has begun to be studied.

  In direct current power transmission, a power converter such as a converter that converts the generated alternating current power into direct current direct current power and an inverter that converts the transmitted direct current into alternating current in the city is required. A modular multilevel converter circuit that can output a voltage waveform close to a sine wave is being studied and put into practical use so that harmonics associated with switching of the converter and inverter do not flow into the AC system.

  When applied to long-distance high-power transmission, the DC power transmission system can be installed at a lower cost than the conventional AC power transmission system, and a high-efficiency system with less transmission loss can be constructed. There is a restriction that the size cannot be changed freely. This is because in an AC system, the voltage can be freely converted by the turns ratio of the transformer and tap control, whereas a transformer cannot be used in DC.

  When constructing a power transmission network, it is assumed that it is effective to determine the optimal voltage level determined by restrictions on the transmission capacity and insulation installation space at the right place in the transmission network. If there is a restriction that cannot be freely converted, it becomes impossible to construct a power transmission network at such an optimum voltage level.

  On the other hand, in the prior art, as shown in FIG. 8, direct current is once converted into high frequency alternating current by a modular multilevel inverter and then converted into direct current by an alternating current direct current conversion converter via a high frequency insulation transformer. There has been proposed a system for freely changing the size of. In this system, the voltage can be changed freely by setting the turns ratio of the high-frequency isolation transformer and the voltage control of the converter and inverter, and the voltage level can be freely optimized in the future DC transmission power network. It becomes possible.

Non-Patent Literature 2009 Cigre Paper Proceedings Paper 401: Multilevel Voltage-Sourced Converters for HVDC and FACTS Applications: Siemens AG

  However, the conventional circuit system as shown in FIG. 8 converts all the electric power to be transmitted from direct current to alternating current, and again converts from alternating current to direct current through the transformer. Since the power transmission efficiency is reduced due to the increase, there is a problem of high cost and large equipment.

  An object of the embodiment is to provide a high-efficiency and low-cost DC / DC conversion power converter that achieves the object of DC voltage level conversion while reducing facility capacity and loss.

  One embodiment is a power conversion device that connects two DC power transmission networks by converting voltage levels, and includes a first leg and a second leg each having two switching elements each having a self-extinguishing capability connected in series. When a component formed by connecting capacitors in parallel is an H bridge unit, a first phase leg and a second phase in which two or more phase arms in which one or more of the H bridge units are connected in series are connected in series A series compensation circuit unit in which legs are connected in parallel to each other, one DC terminal of the series compensation circuit unit is connected to a non-ground side line of one DC transmission network, and the other DC terminal is the other DC transmission A chopper comprising a third leg connected to the ungrounded line of the network and having two switching elements having a self-extinguishing capability connected in series, and a capacitor connected in parallel to the third leg A parallel compensation circuit unit in which a third phase leg and a fourth phase leg are connected in parallel with each other, each of which is connected in series with two or more phase arms each having one or more chopper units connected in series; One DC terminal of the compensation circuit unit is connected to a non-ground side line of the other DC transmission network, and the other DC terminal is connected to a common ground side line of the two DC transmission networks. A primary winding connected to the phase arm interconnection point of the first and second phase legs, and a secondary winding connected to the phase arm interconnection point of the third and fourth phase legs of the parallel compensation circuit unit And a single-phase high-frequency insulating transformer having a wire.

It is a figure which shows the structure of the power converter device which concerns on 1st Embodiment. It is a figure for demonstrating the relationship of the voltage current controlled in 1st Embodiment. It is a figure for demonstrating the control system of 1st Embodiment. It is a figure for demonstrating the other control system of 1st Embodiment. It is a figure which shows the circuit structure of 2nd Embodiment. It is a figure which shows the circuit structure of 3rd Embodiment. It is a figure for demonstrating the control system corresponding to the circuit structure of FIG. It is a figure which shows the structure of the conventional power converter device.

  Hereinafter, embodiments will be described with reference to the drawings.

[First embodiment]
First, a situation where the embodiment is applied will be described. In two power systems that receive power supply from different power companies and have different system DC voltages, when one power system has insufficient power and the other power system has sufficient power, When power is transmitted from one power system to one power system, or conversely, when one power system has sufficient power and the other power system has insufficient power, the other power system In some cases, power is transmitted from one to the other power system. The power conversion device according to the embodiment is a device applied in such a situation.

  FIG. 1 is a diagram illustrating a configuration of the power conversion device according to the first embodiment.

  The power conversion device according to the first embodiment is a system that transmits power from a DC power network 1 that is a first DC power transmission network to a DC power network 2 that is a second DC power transmission network, accompanied by DC voltage conversion. The compensation circuit unit 11, the parallel compensation circuit unit 12, and the high-frequency insulating transformer unit TR1 are included.

  The series compensation circuit unit 11 uses, as a converter unit, an H-bridge converter 3 formed by connecting two circuits of a leg 3a in which two switching elements Q1 having self-extinguishing capability are connected in series and a capacitor C1 in parallel. The phase arm 3b is formed by connecting N (N = 2 in this example) converter units in series.

  A structure in which two phase arms are connected in series is called a phase leg 3c, and both ends of a U-phase leg and a V-phase leg are connected to each other, and one end is connected to the positive terminal (ungrounded side) of the DC power network 1. Line) and the other end is connected to the positive terminal (non-grounded line) of the DC power network 2.

  The AC output U-phase and V-phase of the series compensation circuit unit 11 are connected to the UV phase of the primary winding of the high-frequency insulation transformer TR1, respectively. The negative terminals (ground side lines) of the DC power network 1 and the DC power network 2 are connected to each other.

  The parallel compensation circuit unit 12 includes a leg 4a in which two switching elements Q2 having a self-extinguishing capability are connected in series as one leg and a chopper bridge converter 4 formed by connecting a capacitor in parallel as a converter unit. A phase arm 4b in which M (M = 4 in this example) converter units are connected in series is configured.

  Two phase arms 4b connected in series are called a phase leg 4c. Both ends of the u-phase leg and the v-phase leg are connected to each other, and then one end is connected to the positive terminal of the DC power network 2. The other end is connected to the negative terminal of the DC power network 2. The AC output u phase and v phase of the parallel compensation circuit unit 12 are connected to the uv phase of the secondary winding of the high frequency insulation transformer TR1, respectively.

  Next, the relationship between the voltage and current controlled in the first embodiment will be described with reference to FIG. In FIG. 2, for simplicity of explanation, the phase arm of the series compensation circuit unit 11 is configured by one H-bridge converter (converter unit).

  In FIG. 2, it is assumed that the DC voltage Vdc1 of the DC power transmission network 1 is 100 kV and the DC voltage Vdc2 of the DC power transmission network is 80 kV. An example will be described in which the transmission power (Power1, Power2) from the DC power transmission network 1 to the DC power transmission network 2 is 100 MW.

  The direct current Idc1 of the DC power transmission network 1 is calculated by the following equation.

Idc1 = Power1 / Vdc1 = 1 kA
The direct current Idc2 of the DC power transmission network 2 is calculated by the following equation.

Idc2 = Power2 / Vdc2 = 1.25 kA
The direct current ΔIpc output from the parallel compensation circuit unit 12 is obtained as follows according to Kirchhoff's law in current.

ΔIpc = Idc2-Idc1 = 0.25 kA
Since the parallel compensation circuit unit 12 outputs ΔIpc and the voltage is Vdc2, the following power ΔPowerPC constantly flows out.

ΔPowerPC = Vdc2 × ΔIpc = 20 MW
The DC voltage ΔVsc across the series compensation circuit unit 11 is the difference voltage between Vdc1 and Vdc2 in a steady state.

ΔVsc = Vdc1−Vdc2 = 20 kV
The power 100 MW constantly flows into the series compensation circuit unit 11, and the following power ΔPowerSC flows out from the UV AC terminal.

ΔPowerSC = ΔVsc × Idc1 = 20 MW
The series compensation circuit unit 11 outputs an alternating current of 12.5 kV rms and 500 Hz as an alternating voltage between UVs, and performs alternating current control so that 20 MW flows out in synchronization with this. The series compensation circuit unit 11 transmits the direct current 80 MW to the direct current power network 2 without conversion.

  The high-frequency isolation transformer TR1 is designed with a turn ratio such that the secondary winding connected to the parallel compensation circuit unit 12 and the primary winding connected to the series compensation circuit unit 11 have a voltage ratio of 4: 1. Has been. That is, the primary and secondary winding ratio is 1: 4.

  The parallel compensation circuit unit 12 is applied with an AC voltage of 50 kVrms (= (50/4) × 12.5) and 500 Hz as an inter-uv AC voltage. As a result, 20 MW of electric power flows into the parallel compensation circuit unit 12 performing the AC voltage control, and the entire output can be stably operated in balance with the output power to the DC.

  When the power converter having the above-described configuration is used, the parallel compensation circuit unit, the series compensation circuit unit, and the high-frequency insulation transformer need only have a power capacity of 20 MW. On the other hand, in the conventional circuit configuration shown in FIG. 8, the DC / AC converter, the AC / DC converter, and the high-frequency insulation transformer all require a power capacity of 100 MW, which is a power transmission capacity. Therefore, in the present embodiment, the power can be changed by a device having a power capacity of 1/5 as compared with the prior art, and it is possible to achieve a reduction in cost and a reduction in loss and efficiency.

  Next, the control part which controls the power converter device of this embodiment is demonstrated. First, a control method in a configuration in which the parallel compensation circuit unit 12 performs AC voltage control and the series compensation circuit unit 11 performs AC current control will be described with reference to FIGS.

  The parallel compensation unit capacitor voltage constant control unit 30 is an average value of the capacitor voltage of a total of 16 parallel compensation unit converter units of the 4 series of the parallel compensation unit capacitor voltage command VdcCPref and the positive and negative phase arms of the u phase and the v phase. Using VdcCP_AVE as an input, a parallel compensator DC current command value ΔIpcRef is obtained and output by the following calculation.

ΔIpcRef = −G (s) × (VdcCPref−VdcCP_AVE)
s represents a Laplace operator, and G (s) represents proportional-integral control.

  The parallel compensator DC current controller 31 receives the parallel compensator DC current command value ΔIpcRef and the detected parallel compensator DC current actual value ΔIpc as input, and calculates and outputs the parallel compensator DC voltage command VdcPRef by the following calculation. .

VdcPRef = G (s) × (ΔIpcRef−ΔIpc) + Vdc2
(Vdc2 is the DC voltage detection value of the second DC power network)
The parallel compensator AC voltage command VacPref is an AC voltage command of 500 Hz, 50 kVrms, and each parallel compensation unit converter unit output voltage command (u-phase positive DC voltage command VcpUP, u-phase negative DC voltage command VcpUN, v-phase positive side) DC voltage command VcpVP, v-phase negative DC voltage command VcpVN) is obtained by the following calculation and output.

VcpUP = VdcPref / 2−VacPref / 2
VcpUN = VdcPref / 2 + VacPref / 2
VcpVP = VdcPref / 2 + VacPref / 2
VcpVN = VdcPref / 2−VacPref / 2
In the series compensation unit DC current control unit 32, the series compensation unit DC current command Idc1Ref, the series compensation unit DC current detection value Idc1, the DC voltage detection value Vdc1 of the first DC power network, and the DC voltage of the second DC power network. With the detection value Vdc2 as an input, the series compensation unit DC voltage output command ΔVscRef is obtained and output by the following calculation.

ΔVscRef = −H (s) × (Idc1Ref−Idc1)
+ Vdc1-Vdc2
(S is Laplace operator and H (s) is proportional integral control)
In the series compensation unit capacitor voltage constant control unit 33, the series compensation unit capacitor voltage command value VdcCSref and the average of the capacitor voltages of the four series compensation units H bridge units in series of the positive and negative phase arms of the U phase and V phase, respectively. With the value VdcCS_AVE and the AC voltage detection value VacS as inputs, the series compensation unit AC current command value Iac1Ref is obtained and output by the following calculation.

  First, the series compensation unit AC current command amplitude | Iac1Ref | is obtained.

| Iac1Ref | = J (s) × (VdcCSref−VdcCS_AVE)
An AC sine wave sin_VacS having the same phase as the AC voltage detection value VacS and an amplitude of 1 is obtained.

sin_VacS = VacS / | VacS |
(| VacS | is the amplitude of the sine wave of VacS)
Iac1Ref = | Iac1Ref | × sin_VacS
The AC current control unit 34 receives the AC current command value Iac1Ref, the AC current detection value Iac1, and the AC voltage detection value VacS as input and obtains and outputs the AC voltage command value VacSref by the following calculation.

VacSref = K (s) × (Iac1Ref−Iac1) + VacS
Series Compensator Each converter unit output voltage command (U phase positive DC voltage command VcsUP, U phase negative DC voltage command VcsUN, V phase positive DC voltage command VcsVP, V phase negative DC voltage command VcsVN) Obtained by calculation and output.
VcsUP = ΔVscRef / 2−VacSref / 2
VcsUN = ΔVscRef / 2 + VacSref / 2
VcsVP = ΔVscRef / 2 + VacSref / 2
VcsVN = ΔVscRef / 2−VacSref / 2
Next, a control method in a configuration in which the series compensation circuit unit 11 performs AC voltage control and the parallel compensation circuit unit 12 performs AC current control will be described with reference to FIGS.

  In the series compensation unit DC current control unit 50, the series compensation unit DC current command Idc1Ref, the series compensation unit DC current detection value Idc1, the DC voltage detection value Vdc1 of the first DC power network, and the DC voltage of the second DC power network. With the detection value Vdc2 as an input, the series compensation unit DC voltage output command ΔVscRef is obtained and output by the following calculation.

ΔVscRef = −H (s) × (Idc1Ref−Idc1)
+ Vdc1-Vdc2
(S is Laplace operator and H (s) is proportional integral control)
The series compensator AC voltage command VacSref is an AC voltage command of 500 Hz and 12.5 kVrms, and each converter unit output voltage command (U phase positive DC voltage command VcsUP, U phase negative DC voltage command VcsUN, V phase) The positive side DC voltage command VcsVP and the V phase negative side DC voltage command VcsVN) are obtained by the following calculation and output.

VcsUP = ΔVscRef / 2−VacSref / 2
VcsUN = ΔVscRef / 2 + VacSref / 2
VcsVP = ΔVscRef / 2 + VacSref / 2
VcsVN = ΔVscRef / 2−VacSref / 2
The parallel compensation unit capacitor voltage constant control unit 51 is an average value of the capacitor voltage of a total of 16 parallel compensation unit converter units of the 4 series of the parallel compensation unit capacitor voltage command VdcCPref and each of the u-phase v-phase positive and negative phase arms. Using VdcCP_AVE as an input, a parallel compensator DC current command value ΔIpcRef is obtained and output by the following calculation.

ΔIpcRef = −G (s) × (VdcCPref−VdcCP_AVE)
s represents a Laplace operator, and G (s) represents proportional-integral control.

  The parallel compensator DC current controller 52 receives the parallel compensator DC current command value ΔIpcRef and the detected parallel compensator DC current actual value ΔIpc as input, and calculates and outputs the parallel compensator DC voltage command VdcPref by the following calculation. .

VdcPref = G (s) × (ΔIpcRef−ΔIpc) + Vdc2
(Vdc2 is the DC voltage detection value of the second DC power network)
In the series compensation unit capacitor voltage constant control unit 53, the series compensation unit capacitor voltage command value VdcCSref and the average of the capacitor voltages of the four series compensation units H bridge units in series of the positive and negative phase arms of the U phase and V phase, respectively. Using the value VdcCS_AVE and the AC voltage detection value VacS as inputs, the parallel compensation unit AC current command value Iac2Ref is obtained and output by the following calculation.

  First, the parallel compensator AC current command amplitude | Iac2Ref | is obtained.

| Iac2Ref | = J (s) × (VdcCSref−VdcCS_AVE)
An AC sine wave sin_VacP having the same phase as the parallel compensation unit AC voltage detection value VacP and an amplitude of 1 is obtained.

sin_VacP = VacP / | VacP |
(| VacP | is the sinusoidal amplitude of VacP)
Iac2Ref = | Iac2Ref | × sin_VacP
The AC current control unit 54 receives the AC current command value Iac2Ref, the parallel compensation unit AC current detection value Iac2, and the AC voltage detection value VacP as input and obtains and outputs the AC voltage command value VacPref by the following calculation.

VacPref = −K (s) × (Iac2Ref−Iac2) + VacP
Parallel compensation unit Each converter unit output voltage command (U phase positive DC voltage command VcpUP, U phase negative DC voltage command VcpUN, V phase positive DC voltage command VcpVP, V phase negative DC voltage command VcpVN) Obtained by calculation and output.

VcpUP = VdcPref / 2−VacPref / 2
VcpUN = VdcPref / 2 + VacPref / 2
VcpVP = VdcPref / 2 + VacPref / 2
VcpVN = VdcPref / 2−VacPref / 2
Since the H-bridge converter 3 is used as the converter unit, the series compensation circuit unit 11 can operate even when the voltage levels of the DC power network 1 and the DC power network 2 are reversed during operation.

[Second Embodiment]
Next, FIG. 5 shows a circuit configuration of the second embodiment that can be applied to a system in which the DC voltage Vdc1 of the DC power transmission network 1 is always higher than the DC voltage Vdc2 of the DC power transmission network 2.

  The series compensation circuit unit 13 in the second embodiment is characterized in that it is composed of a chopper bridge converter 4. The other circuit configuration is the same as that of the first embodiment. Since the series compensation circuit unit 13 is configured not by the H-bridge converter 3 but by the chopper bridge converter 4, in this embodiment, the voltage of one DC power transmission network (the power transmission network 2 in this example) is the other power transmission network. Applies when the voltage is always higher than

  The positive side terminal of the series compensation circuit unit 13 is connected to the positive side terminal of the DC power transmission network 1, and the negative side terminal of the series compensation circuit unit 13 is connected to the positive side terminal of the DC power transmission network 2.

  Even if the power converter having the above configuration is used, the parallel compensation circuit unit 12, the series compensation circuit unit 13, and the high-frequency insulated TR1 transformer need only have a power capacity of 20 MW, and the cost and the loss are reduced as in the first embodiment. High efficiency can be achieved. Furthermore, since the number of switching elements having a self-extinguishing capability constituting the converter unit of the series compensation circuit section is halved compared to the H-bridge converter in the first embodiment, further cost reduction and lowering are achieved. Loss efficiency can be improved.

[Third embodiment]
Next, in a configuration in which three DC power transmission networks are connected at one place and DC power transmitted from one DC power transmission network is distributed and transmitted to two DC power transmission networks, the distribution ratio can be freely adjusted. The circuit configuration of the third embodiment is shown in FIG.

  One end of each of the series compensation circuit units 21 and 22 in the third embodiment is connected to the positive side terminals of the DC power transmission network 2 and the DC power transmission network 3, and the other end is connected together to the positive side terminal of the DC power transmission network 1. The transformer TR2 is a three-winding transformer, the primary winding w1 is connected to the u-phase and v-phase arm interconnection points of the parallel compensation circuit section 12, and the secondary winding w2 is the U-phase of the series compensation circuit section 21. The secondary winding w3 is connected to the V-phase phase arm interconnection point and the U-phase and V-phase phase arm interconnection point of the series compensation circuit unit 22. Note that the number of secondary windings is determined according to the number of DC power transmission networks to which power is distributed.

  The DC voltage ΔVsc2 output from the series compensation circuit unit 21 and the DC voltage ΔVsc3 output from the series compensation circuit unit 3 are set as follows according to a distribution ratio command k: 1 (supplied from an external device not shown).

ΔVsc2: ΔVsc3 = k: 1
The current ratio is determined corresponding to the voltage distribution ratio (k: 1), and as a result, the power distribution ratio for the power transmission networks 1 and 2 is k: 1. In other words, the voltage distribution ratio command is determined according to the power distribution ratio command. In reality, the distribution ratio changes depending on the DC resistance of the DC transmission network 2 and the DC transmission network 3 and the DC voltage at the connection point to the AC transmission network. According to the feedback value, ΔVsc2 and ΔVsc3 are corrected so that the distribution is adjusted to the command value.

  Even if the power converter having the above-described configuration is used, it is possible to achieve cost reduction and low loss and high efficiency in the parallel compensation circuit unit, the series compensation circuit unit, and the high-frequency insulation transformer. Furthermore, since current distribution control in a multi-terminal DC power transmission network can be performed freely, system control can be more stably performed.

  A control method corresponding to the circuit configuration of FIG. 6 will be described with reference to FIG.

  The parallel compensation unit capacitor voltage constant control unit 61 is an average value of the capacitor voltage of a total of 16 parallel compensation unit converter units of the 4 series of the parallel compensation unit capacitor voltage command VdcCPref and the positive and negative phase arms of the u phase and the v phase. Using VdcCP_AVE as an input, a parallel compensator DC current command value ΔIpcRef is obtained and output by the following calculation.

ΔIpcRe = −G (s) × (VdcCPref−VdcCP_AVE)
s represents a Laplace operator, and G (s) represents proportional-integral control.

  The parallel compensator DC current controller 62 receives the parallel compensator DC current command value ΔIpcRef and the detected parallel compensator DC current actual value ΔIpc as input, and calculates and outputs the parallel compensator DC voltage command VdcPref by the following calculation. .

VdcPref = G (s) × (ΔIpcRef−ΔIpc) + Vdc2
(Vdc2 is the DC voltage detection value of the second DC power network)
The parallel compensator AC voltage command VacPref is an AC voltage command of 500 Hz and 50 kVrms, and each parallel converter unit output voltage command (U phase positive DC voltage command VcpUP, U phase negative DC voltage command VcpUN, V phase positive side) DC voltage command VcpVP, V-phase negative DC voltage command VcpVN) is obtained by the following calculation and output.

VcpUP = VdcPref / 2−VacPref / 2
VcpUN = VdcPref / 2 + VacPref / 2
VcpVP = VdcPref / 2 + VacPref / 2
VcpVN = VdcPref / 2−VacPref / 2
In the DC current control unit 63 of the series compensation circuit unit 21, the series compensation unit DC current command Idc1Ref, the power distribution ratio m2: m3 to the DC power network 2 and the DC power network 3, and the DC current detection value of the series compensation circuit unit 2 The Idc2, the DC voltage detection value Vdc1 of the first DC power network, and the DC voltage detection value Vdc2 of the second DC power network are input and the series compensation unit DC voltage output command ΔVscRef is obtained and output by the following calculation.

Idc2Ref = Idc1 × m2 / (m2 + m3)
ΔVscRef2 = H (s) × (Idc2Ref−Idc2)
+ Vdc2−Vdc1
(S is Laplace operator and H (s) is proportional integral control)
In the capacitor voltage constant control unit 64 of the series compensation circuit unit 21, the capacitor voltage of the series compensation unit capacitor voltage command value VdcCS2ref and one series of each of the U phase V phase positive and negative legs in total of four series compensation units H bridge. The average value VdcCS2_AVE and the AC voltage detection value VacS2 are input, and the series compensation unit AC current command value Iac2Ref is obtained and output by the following calculation.

  First, a series compensation unit AC current command amplitude | Iac2Ref | is obtained.

| Iac2Ref | = J (s) × (VdcCS2ref−VdcCS2_AVE)
An AC sine wave sin_VacS2 having the same phase as the AC voltage detection value VacS2 and an amplitude of 1 is obtained.

sin_VacS2 = VacS2 / | VacS2 |
(| VacS2 | is the sine wave amplitude of VacS2)
Iac2Ref = | Iac2Ref | × sin_VacS2
The AC current control unit 65 receives the AC current command value Iac2Ref, the AC current detection value Iac2, and the AC voltage detection value VacS2 as input and obtains and outputs the AC voltage command value VacS2ref by the following calculation.

VacS2ref = K (s) × (Iac2Ref−Iac2) + VacS2
Each converter unit output voltage command of the series compensation circuit unit 21 (U-phase positive DC voltage command VcsUP2, U-phase negative DC voltage command VcsUN2, V-phase positive DC voltage command VcsVP2, V-phase negative DC voltage command VcsVN2) Is obtained by the following calculation and output.

VcsUP2 = ΔVscRef2 // 2−VacS2ref / 2
VcsUN2 = ΔVscRef2 / 2 + VacS2ref / 2
VcsVP2 = ΔVscRef2 / 2 + VacS2ref / 2
VcsVN2 = ΔVscRef2 // 2−VacS2ref / 2
In the DC current control unit 66 of the series compensation circuit unit 22, the series compensation unit DC current command Idc1Ref, the power distribution ratio m2: m3 to the DC power network 2 and the DC power network 3, and the DC current detection value of the series compensation circuit unit 2 The Idc2, the DC voltage detection value Vdc1 of the first DC power network, and the DC voltage detection value Vdc3 of the second DC power network are inputted and the series compensation unit DC voltage output command ΔVscRef is obtained and output by the following calculation.

Idc3Ref = Idc1 × m3 / (m2 + m3)
ΔVscRef3 = H (s) × (Idc3Ref−Idc3)
+ Vdc3-Vdc1
(S is Laplace operator and H (s) is proportional integral control)
In the capacitor voltage constant control unit 67 of the series compensation circuit unit 22, a series compensation unit capacitor voltage command value VdcCS3ref and a series of four series compensation units H bridge capacitors in each of the U phase V phase positive and negative phase arms. The average voltage value VdcCS3_AVE and the AC voltage detection value VacS3 are input, and the series compensation unit AC current command value Iac3Ref is obtained and output by the following calculation.

  First, a series compensation unit AC current command amplitude | Iac3Ref | is obtained.

| Iac3Ref | = J (s) × (VdcCS3ref−VdcCS3_AVE)
An AC sine wave sin_VacS3 having the same phase as the AC voltage detection value VacS3 and an amplitude of 1 is obtained.

sin_VacS3 = VacS3 / | VacS3 |
(| VacS3 | is the sine wave amplitude of VacS3)
Iac3Ref = | Iac3Ref | × sin_VacS3
The AC current control unit 68 receives the AC current command value Iac3Ref, the AC current detection value Iac3, and the AC voltage detection value VacS3 as input and obtains and outputs the AC voltage command value VacS3ref by the following calculation.

VacS3ref = K (s) × (Iac3Ref−Iac3) + VacS3
Each converter unit output voltage command of the series compensation circuit unit 3 (U-phase positive DC voltage command VcsUP3, U-phase negative DC voltage command VcsUN3, V-phase positive DC voltage command VcsVP3, V-phase negative DC voltage command VcsVN3) Is obtained by the following calculation and output.

VcsUP3 = ΔVscRef3 / 2−VacS3ref / 2
VcsUN3 = ΔVscRef3 / 2 + VacS3ref / 2
VcsVP3 = ΔVscRef3 / 2 + VacS3ref / 2
VcsVN3 = ΔVscRef3 / 2−VacS3ref / 2
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1, 2 ... DC power network, 3 ... H bridge converter, 3a ... Leg, 4 ... Chopper bridge converter, 4a ... Leg, 11, 13, 21, 22 ... Series compensation circuit part, 12 ... Parallel compensation circuit part,

Claims (5)

A power conversion device for connecting two DC power grids by converting voltage levels,
When the first and second legs each having two switching elements each having a self-extinguishing capability are connected in series and a capacitor connected in parallel is an H-bridge unit,
A series compensation circuit unit in which a first phase leg and a second phase leg in which two or more phase arms each having one or more H bridge units connected in series are connected in series are connected in parallel;
One DC terminal of the series compensation circuit unit is connected to a non-ground side line of one of the DC transmission networks, and the other DC terminal is connected to a non-ground side line of the other DC transmission network,
When a chopper unit is composed of a third leg in which two switching elements having a self-extinguishing capability are connected in series and a capacitor connected in parallel to the third leg,
A parallel compensation circuit unit in which a third phase leg and a fourth phase leg are connected in parallel with each other, each of which includes two or more phase arms each having one or more chopper units connected in series;
One DC terminal of the parallel compensation circuit unit is connected to a non-ground side line of the other DC transmission network, and the other DC terminal is connected to a common ground side line of the two DC transmission networks,
A primary winding connected to the phase arm interconnection point of the first and second phase legs of the series compensation circuit unit, and a phase arm interconnection point of the third and fourth phase legs of the parallel compensation circuit unit A single-phase high-frequency isolation transformer having a secondary winding to be connected;
A power conversion device comprising: A power conversion device that connects three or more DC power transmission networks by converting voltage levels,
When the first and second legs each having two switching elements each having a self-extinguishing capability are connected in series and a capacitor connected in parallel is an H-bridge unit,
A plurality of series compensation circuit units each including a first phase leg and a second phase leg in which two or more phase arms each having one or more H bridge units connected in series are connected in series; and
One DC terminal of the plurality of series compensation circuit units is connected to a non-grounded side line of each DC power transmission network excluding a specific DC power transmission network of the plurality of DC power transmission networks, and the other DC terminal is connected to the specific DC terminal Connect together to the ungrounded line of the power grid,
When a chopper unit is composed of a third leg in which two switching elements having a self-extinguishing capability are connected in series and a capacitor connected in parallel to the third leg,
A parallel compensation circuit unit in which a third phase leg and a fourth phase leg are connected in parallel with each other, each of which includes two or more phase arms each having one or more chopper units connected in series;
One DC terminal of the parallel compensation circuit unit is connected to a non-ground side line of the specific DC transmission network, and the other DC terminal is connected to a ground side line of the specific DC transmission network,
Single-phase high-frequency insulation having a primary winding connected to the phase arm interconnection point of the parallel compensation circuit section and a plurality of secondary windings respectively connected to the phase arm interconnection points of the plurality of series compensation circuit sections With a transformer,
A power conversion device comprising:   The power converter according to claim 1 or 2, wherein one of the series compensation circuit unit and the parallel compensation circuit unit performs AC voltage control, and the other compensation circuit unit performs AC current control.   The series compensation circuit unit outputs a DC voltage based on a voltage difference command value of two DC transmission networks, and an AC current so that a time average value of a sum of capacitor voltages constituting the H bridge unit becomes a constant value. The power converter according to claim 1 which performs control.   3. The power converter according to claim 2, wherein DC voltage outputs of the plurality of series compensation circuit units are determined based on a power distribution command of the plurality of DC power transmission networks.

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