JP5593253B2 - Reactive power compensator - Google Patents

Description

  The present invention relates to a reactive power compensator. More specifically, the present invention relates to a self-excited reactive power compensator for a power system.

  The self-excited reactive power compensator is connected to the power system and is used for adjusting the system voltage and improving the stability by generating or consuming reactive power.

  As a conventional self-excited reactive power compensator for a distribution system, for example, there is one using a cascade converter as shown in FIG. This self-excited reactive power compensator has a single-phase full-bridge converter module called a cell (indicated as “con.” In FIG. 19) as one element, and AC terminals of a plurality of cells are connected in series (this is referred to as a cascade connection). High voltage can be output. For example, when six stages of cells (references con. 1 to con. 6) in which the voltage of the DC capacitor of each cell (hereinafter also referred to as a DC voltage) is set to 1 [kV] are connected in series at 25 levels, 7 [ kV] (= 1 [kV] x 6 stages x √ (3/2)) AC voltage waveform can be output and connected to a 6.6 [kV] three-phase high-voltage distribution system without using a transformer (Non-Patent Document 1).

  However, in the self-excited reactive power compensator of Non-Patent Document 1, all the cells may have the same configuration, but in order to increase the number of levels of the waveform of the output voltage, the number of cells proportional to the number of levels is connected. There is a need. The output voltage of the above converter takes a discrete value to form a stepped waveform, and the number of steps of the stepped waveform is referred to as the number of levels.

Therefore, a hybrid configuration has been proposed as a method for increasing the number of levels of the waveform of the output voltage with a small number of series in the cascade converter. A hybrid cascade converter to which this is applied obtains a necessary output voltage by connecting cells in which DC voltages are set to different values in series and synthesizing those DC voltages according to a predetermined logic. Single-phase full-bridge converter constituting the cell, it is possible to select the three output voltages of -1, 0, 1, a DC voltage of 1: 3: 9: ...: maximum is set to a ratio of 3 ⁿ The number of output levels can be obtained. In addition, other voltage ratios may be used to reduce the number of times of switching or to perform voltage control with redundancy in switching.

  As a conventional self-excited reactive power compensator for a distribution system using the hybrid cascade converter described above, for example, as shown in FIG. 20, the DC voltage is set to 3.2 [kV], 1.6 [kV], 0.8, respectively. By connecting the cells set to [kV] in cascade, it is possible to output a voltage of 29 levels between three lines in series, and to directly connect to a 6.6 kV distribution system (non-patent document) 2).

Specifically, three single-phase full-bridge converters having AC terminals connected in series are linked to a three-phase AC distribution system via a reactor. As a hybrid cascade converter system, there is a single-phase converter having a voltage ratio of 4: 2: 1 such as 4Vc _N [V], 2Vc _N [V], and Vc _N [V]. Those connected in series are used. The reference DC voltage Vc _N is a voltage width of one step in the stepped waveform of the output voltage, and the magnitude of the reference DC voltage Vc _N [V] is appropriately determined according to the application. For example, when applied to a three-phase 6.6 kV system without a transformer, the reference DC voltage Vc _N is set to about 0.8 [kV], and the reference values of the DC capacitor voltage are Vc _H = 3.2 [kV], Vc _M = 1.6 [kV ], Vc _L = 0.8 [kV].

In the apparatus of Non-Patent Document 2, the ratio of the capacitor voltages Vc _H and Vc _M of the single-phase converter whose DC voltage reference values are 4Vc _N [V] and 2Vc _N [V] is always maintained at 4: 2. As a result, the two output patterns of the two single-phase converters (= Vs _H + Vs _M ) are set to two timings at the timing of ± 2Vc _N [V], and the capacitor charged with each pattern is discharged. The capacitor is different. On the other hand, the single-phase converter with the DC voltage reference value Vc _N [V] is the sum of the output voltages of the single-phase converter with the reference value 4Vc _N [V] and the single-phase converter with the reference value 2Vc _N [V] and the target voltage. Therefore, the switching pattern is uniquely determined with respect to the output voltage. Therefore, it is impossible to adjust charging / discharging like the capacitor of the single-phase converter whose reference values are 4Vc _N [V] and 2Vc _N [V]. For this reason, a single-phase converter with a reference value of Vc _N [V] requires an auxiliary power source such as an AC-DC converter instead of a DC capacitor.

Ken Yoshii, Shigenori Inoue, Yasufumi Akagi “6.6kV Transformerless Cascade PWM STATCOM -Operation Verification with Three-phase 200V 10kVA Mini-model”, IEEJ Transactions D, Vol.127, No.8, pp.781-788, 2007 Nobuhiko Haneda, Yukimori Kishida, Akihiko Iwata “Self-excited reactive power compensator using gradation control converter”, IEEJ Transactions D, Vol. 127, No. 8, pp.789-795, 2007

As described above, in the self-excited reactive power compensator of Non-Patent Document 2, the cell that outputs the lowest voltage (that is, the single-phase converter with the DC voltage reference value Vc _N [V]) controls the DC voltage. Therefore, in order to keep the DC voltage at a predetermined value, it is necessary to supply power to the DC unit, and an additional insulation DC power source as an additional auxiliary power source is required. For this reason, i) the cost of the DC power supply is increased, ii) the device configuration becomes complicated, and iii) a high voltage equivalent to the distribution line voltage (ie, 6.6 [kV]) is applied between the input and output. Due to the need for high insulation performance, there is a problem that the overall volume of the apparatus is increased and the cost is increased. It is hard to say that it is expensive.

  Therefore, an object of the present invention is to provide a self-excited reactive power compensator using a hybrid cascade converter that can be operated without requiring a DC power supply as an additional auxiliary power supply.

To achieve the above object, the reactive power compensator according to claim 1, wherein the three-Ai交 flow a reactive power compensator of self-excited to be interconnection to the power system of the reactive power compensator is the output voltage comprising a line right wing hybrid type cascaded converter control waveform, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said clusters, each single-phase full-bridge converter Including a high voltage cell, a medium pressure cell, and a low voltage cell connected in series, V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , and V _CLy is the low voltage _Assuming that the voltage of the DC capacitor of the cell is V _dc is a reference DC voltage, and the subscript y is one of the phases (u, v, w) of the three-phase AC, 3V _CMy ≧ V _CHy > V _CMy > V _CLy > 0.5 V _{CM y} and V _CLy > V _dc , and in order to control V _CHy , V _CMy and V _CLy , the output voltage of the high-voltage cell that it or advancing delaying a pulse waveform in part, as well as by or advancing delaying the pulses of the output voltage waveform of the medium pressure cell partially, the high pressure cell, the medium pressure cells, and the low-pressure cells and so as to generate exchanges of power between cells.

  According to this reactive power compensator, in the hybrid cascade converter, by adjusting the output voltage pulse of each cell, the same phase is configured (in other words, the same cluster) enables power interchange between cells. There is no need to connect a DC power source as an additional auxiliary power source to each cell.

Further, the reactive power compensation device according to claim 2 is a reactive power compensator of self-excited to be interconnection to the power system of the three Ai交 flow, the reactive power compensation device, the row control of the output voltage of the waveform comprising a right-wing hybrid type cascade converter, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said cluster, high pressure cell, the medium each containing a single-phase full-bridge converter It is composed of a series connection of a pressure cell and a low voltage cell, V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , and V _CLy is the voltage of the DC capacitor of the low voltage cell. voltage, a reference DC voltage V _{dc, 'the} voltage deviation for the causes energy transfer between the high pressure cell and the low-pressure cells, ΔV _MLy' ΔV _hLy previous The voltage deviation for causing energy transfer between the medium pressure cell and the low-pressure cell, the output current of the i _y from the cluster, the subscript y is each phase of the three-phase alternating current (u, v, w when a represents any of the), along with a _{3V CMy ≧ V CHy> V CMy} > V CLy> 0.5 V CM y, a _{V CLy> V dc, further,} V _{CHy, V CMy,} In order to control V _CLy , a boundary value for switching the output voltage mode of the high voltage cell , the medium voltage cell , and the low voltage cell for controlling the waveform of the output voltage from the cluster is set to i _y ≧ 0 [Delta] V _hly 'and adds ΔV _hLy'> 0 and ΔV _MLy '> 0 and is [Delta] V _hly' and [Delta] V _MLY ', when the _i y <0 is ΔV _hLy' <0 and ΔV _MLy '<0 when adding ΔV _MLy ' By Rukoto, the high pressure cell, and so as to generate the exchange of power between the cells in said pressure cells, and the low-pressure cells.

Moreover, reactive power compensation apparatus according to the third aspect, a reactive power compensator of self-excited to be interconnection to the power system of the three Ai交 flow, the reactive power compensation device, the row control of the output voltage of the waveform comprising a right-wing hybrid type cascade converter, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said cluster, high pressure cell, the medium each containing a single-phase full-bridge converter It is composed of a series connection of a pressure cell and a low voltage cell, V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , and V _CLy is the voltage of the DC capacitor of the low voltage cell. voltage, a reference DC voltage V _{dc, 'the} voltage deviation for the causes energy transfer between the medium pressure cell and the high pressure cell, ΔV _hLy' ΔV _HMy previous The voltage deviation for causing energy transfer between the high pressure cell and the low-pressure cell, the output current of the i _y from the cluster, each phase of the subscript y is the three-phase alternating current (u, v, w) when a representative of one of, with a _{3V CMy ≧ V CHy> V CMy} > V CLy> 0.5 V CM y, a _{V CLy> V dc, further,} V _{CHy, V CMy,} V _{In order} to control _CLy , when the boundary value of switching the output voltage mode of the high voltage cell , the medium voltage cell , and the low voltage cell for controlling the waveform of the output voltage from the cluster is i _y ≧ 0 ΔV _HMy '> 0 and ΔV _HLy '> 0 and ΔV _HMy 'and ΔV _HLy ' are added, and when i _y <0, ΔV _HMy '<0 and ΔV _HLy '<0 , ΔV _HMy 'and ΔV adding the _HLy ' By Rukoto, the high pressure cell, and so as to generate the exchange of power between the cells in said pressure cells, and the low-pressure cells.

Moreover, reactive power compensation apparatus according to claim 4, there is provided a reactive power compensator of self-excited to be interconnection to the power system of the three Ai交 flow, the reactive power compensation device, the row control of the output voltage of the waveform comprising a right-wing hybrid type cascade converter, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said cluster, high pressure cell, the medium each containing a single-phase full-bridge converter It is composed of a series connection of a pressure cell and a low voltage cell, V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , and V _CLy is the voltage of the DC capacitor of the low voltage cell. voltage, a reference DC voltage V _{dc, 'the} voltage deviation for the causes energy transfer between the medium pressure cell and the high pressure cell, ΔV _MLy' ΔV _HMy previous The voltage deviation for causing energy transfer between the medium pressure cell and the low-pressure cell, the output current of the i _y from the cluster, the subscript y is each phase of the three-phase alternating current (u, v, w when a represents any of the), along with a _{3V CMy ≧ V CHy> V CMy} > V CLy> 0.5 V CM y, a _{V CLy> V dc, further,} V _{CHy, V CMy,} In order to control V _CLy , a boundary value for switching the output voltage mode of the high voltage cell , the medium voltage cell , and the low voltage cell for controlling the waveform of the output voltage from the cluster is set to i _y ≧ 0 [Delta] V _HMy 'and adds ΔV _HMy'> 0 and ΔV _MLy '> 0 and is [Delta] V _HMy' and [Delta] V _MLY ', when the _i y <0 is ΔV _HMy' <0 and ΔV _MLy '<0 when adding ΔV _MLy ' By Rukoto, the high pressure cell, and so as to generate the exchange of power between the cells in said pressure cells, and the low-pressure cells.

Moreover, reactive power compensator of claim 5, any one is used of the methods of energy transfer according to claims 2 to 4 for each phase of the three-phase alternating current, the three-phase AC phase In all or at least some of them, the method of energy transfer is different from the other phases.

  According to these reactive power compensators, in the hybrid cascade converter, the voltage of the cell that outputs the lowest voltage is slightly increased from the reference DC voltage, and at the same time, the same phase is configured by adjusting the output voltage pulse of each cell. Since power interchange is possible between cells (in other words, in the same cluster), there is no need to connect a DC power source as an additional auxiliary power source to each cell.

According to a sixth aspect of the present invention, in the reactive power compensator according to any one of the second to fifth _aspects , the voltage V _CHy of the DC capacitor of the high-voltage cell and the voltage V of the DC capacitor of the medium-pressure cell _{When CMy} and the voltage V _CLy of the DC capacitor of the low-voltage cell are 1 <k <2, V _CHy : V _CMy : V _CLy = 6: 2: k . According to a seventh aspect of the present invention, in the reactive power compensator according to any one of the second to fifth _aspects , the voltage V _CHy of the DC capacitor of the high-voltage cell and the voltage V of the DC capacitor of the medium-pressure cell _{When CMy} and the voltage V _CLy of the DC capacitor of the low-voltage cell are 1 <k <2, V _CHy : V _CMy : V _CLy = 4: 2: k . In these cases, the ratio of the output voltage of each cell becomes appropriate, and the waveform of the output voltage from the cluster corresponding to each phase of the three-phase alternating current becomes good.

The invention of claim 8 is the reactive power compensator according to claim 6 or 7, wherein the value before Symbol k is as is 1.01 to 1.3. In this case, the magnitude of the voltage V _CLy of the DC capacitor of the low-voltage cell becomes appropriate in relation to the reference DC voltage V _dc, and the waveform of the output voltage from the cluster corresponding to each phase of the three-phase AC is Even better.

  According to the reactive power compensator of the present invention, there is no need to connect a DC power source as an additional auxiliary power source to each cell. Therefore, the reactive power compensator is simpler, smaller in size and lower in cost than the prior art. The versatility of the reactive power compensator can be improved.

It is a figure which shows the system configuration | structure of an example of embodiment of the reactive power compensation apparatus of this invention. It is a control system block diagram of an example of an embodiment of a reactive power compensator of the present invention. It is a figure which shows the waveform of the output voltage of each cell at the time of voltage ratio 6: 2: k when the conditions of Table 1 are applied. It is a figure which shows waveforms, such as inflow electric power of each cell at the time of applying the control using the conditions of Table 1 to a self-excited reactive power compensation apparatus. It is a figure which shows waveforms, such as inflow electric power of each cell in the case of moving energy from the high voltage | pressure cell to the low voltage | pressure cell in the reactive power compensator of embodiment. It is a figure which shows waveforms, such as inflow electric power of each cell in the case of moving energy from the medium pressure cell to a low voltage cell in the reactive power compensation apparatus of embodiment. It is a figure which shows waveforms, such as inflow electric power of each cell in the case of moving energy from the high voltage | pressure cell to a medium pressure cell in the reactive power compensation apparatus of embodiment. It is an image figure of DC voltage ratio control between steps in the reactive power compensator of an embodiment. (A) is an image diagram when voltage deviation ΔV _HLy ′ and voltage deviation ΔV _MLy ′ are added simultaneously. (B) is an image diagram when voltage deviation ΔV _HMy 'and voltage deviation ΔV _HLy ' are added simultaneously. (C) is an image diagram when voltage deviation ΔV _HMy 'and voltage deviation ΔV _MLy ' are added simultaneously. It is a block diagram of active / reactive power control in the reactive power compensator of the embodiment. It is a block diagram of DC voltage balance control between phases in the reactive power compensator of the embodiment. It is a block diagram of interstage direct-current voltage ratio control in the reactive power compensator of the embodiment. It is a figure which shows an example of the other pattern of the DC voltage ratio control between steps in the reactive power compensation apparatus of this invention. It is a figure which shows waveforms, such as inflow electric power of each cell when there is no energy control between cells in Example 1. FIG. It is a figure which shows waveforms, such as inflow electric power of each cell at the time of performing energy control of the high voltage | pressure cell in Example 1. FIG. It is a figure which shows waveforms, such as inflow electric power of each cell at the time of performing energy control of the medium pressure cell in Example 1. FIG. It is a figure which shows waveforms, such as inflow electric power of each cell at the time of using together the energy control of the high voltage | pressure cell and intermediate pressure cell in Example 1. FIG. It is a figure which shows the simulation result at the time of starting of the hybrid cascade converter in Example 1. FIG. It is a figure which shows the simulation result at the time of invalidating voltage control during the steady operation in Example 1. FIG. It is a figure which shows the system configuration | structure of the self-excited reactive power compensation apparatus for the conventional power distribution systems using a cascade converter. It is a figure which shows the system configuration | structure of the self-excited reactive power compensation apparatus for the conventional power distribution systems using a hybrid cascade converter.

  Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

1 to 11 show an example of a reactive power compensator according to an embodiment of the present invention. This reactive power compensator is a self-excited reactive power compensator linked to a three-phase (u, v, w phase) AC power system, each of which is constituted by a single-phase full-bridge converter. A hybrid having clusters 1u, 1v, and 1w corresponding to each phase of a three-phase alternating current configured to control a waveform of an output voltage, which is configured by connecting a high voltage cell 1 _Hy , a medium pressure cell 1 _My , and a low voltage cell 1 _Ly in series. comprising a shape cascade converters, voltage V _CHy of the DC capacitor of the high pressure cell 1 _Hy, voltage V _CMy of the DC capacitor of the intermediate pressure cell 1 _My, low pressure cell 1 _Ly voltage V _CLy is 3V _CMy ≧ V _CHy of the DC capacitor of> V _CMy > V _CLy > 0.5V _CMy (where the subscript y represents one of the three phases u, v, and w), and the voltage V _CLy of the DC capacitor of the low voltage cell 1 _Ly is the reference DC voltage V greater than _dc, cluster 1u, 1v, 1w High pressure cell 1 _Hy for controlling the waveform of al the output voltage, medium-pressure cell 1 _My, the boundary value of the switching of the output voltage mode of the low pressure cell 1 _Ly, between the high pressure cell 1 _Hy and the low-pressure cell 1 _Ly 'voltage deviation [Delta] V _MLY for causing energy transfer between and intermediate pressure cell 1 _My and the low-pressure cell 1 _Ly' (although voltage deviation [Delta] V _hly for causing energy transfer, cluster 1u, 1 v, 1 w as the output current i _y from, when the i _y ≧ 0 adds <0) ΔV _hLy '<0 and [Delta] V _MLY' when the ΔV _hLy '> 0 and _{ΔV MLy'> 0, i y} <0 As a result, power is exchanged between the high-pressure cell 1 _{Hy, the} medium-pressure cell 1 _My, and the low-pressure cell 1 _Ly , and the voltages V _CHy , V _CMy , V _CLy of the DC capacitors of the cells 1 _Hy , 1 _My , 1 _Ly are _obtained . I try to control it. In this embodiment, the voltages V _CHy and V _CMy of the DC capacitors of the cells 1 _Hy , 1 _My , and 1 _Ly due to the exchange of electric power among the high-pressure cell 1 _{Hy, the} medium-pressure cell 1 _My, and the low-pressure cell 1 _Ly. , V _CLy is specifically controlled by flowing out (in other words, discharging) or flowing (in other words, charging) power from the high-pressure cell 1 _Hy and the medium-pressure cell 1 _My to flow into the low-pressure cell 1 _Ly. Or let it flow out.

  Here, in the following description, the subscript y is used to mean any of the three phases u, v, and w of the three-phase alternating current, and the subscript x is one of the high pressure H, the intermediate pressure M, and the low pressure L. Used to mean either. The symbol * is used to mean a command value.

(1) Circuit Configuration FIG. 1 shows a configuration of an embodiment of a self-excited reactive power compensator of the present invention using a hybrid cascade converter. Specifically, one phase component is constructed by connecting three cells (high-pressure cell 1 _Hy , medium-pressure cell 1 _My , low-pressure cell 1 _Ly ) composed of a single-phase full-bridge converter in series (hereinafter referred to as three-phase). The one corresponding to the u phase is referred to as cluster 1u, the one corresponding to the v phase is referred to as cluster 1v, and the one corresponding to the w phase is referred to as cluster 1w). In this embodiment, the three cells 1 _Hy , 1 _My , 1 _Ly have a DC capacitor (capacitance C _x ) voltage (ie, DC voltage) ratio of V _CHy : V _CMy : V _CLy = 6: 2. : K (where 1 <k <2). Then, by synthesizing the output voltage waveforms of the three cells 1 _Hy , 1 _My , and 1 _Ly constituting the same cluster, a sinusoidal output voltage waveform is obtained as each cluster 1 u, 1 v, 1 w.

When connecting to a high-voltage distribution system, the line voltage Vs of the power source is 6.6 [kV], and the DC voltages of the cells 1 _Hy , 1 _My , 1 _Ly are assumed to be k = 1.2 in this embodiment. V _CHy = 3.6 [kV] in the high voltage cell 1 _Hy having the highest voltage, V _CMy = 1.2 [kV] in the medium voltage cell 1 _My having the next highest voltage, and V _CLy = 0.72 in the low voltage cell 1 _Ly having the lowest voltage. [KV]. The ratio k of the DC capacitor voltage V _CLy of the low voltage cell 1 _Ly may be 1 <k <2 in order to make the ratio of the output voltage V _Cxy of each cell 1 _xy appropriate. In order to make the waveform of the output voltage from the clusters 1u, 1v, 1w corresponding to each phase of the three-phase alternating current good with few harmonics, it is preferable to make the value as small as possible. Specifically, for example, it is considered that the value of k is preferably in the range of about 1.01 to 1.3 in order to achieve the effect of the present invention and to improve the waveform of the output voltage.

(2) Control system The control method for the conventional cascade converter, which consists of cells of the same voltage, is composed of three layers: active / reactive power control, interphase DC voltage balance control, and interstage DC voltage balance control. (For example, non-patent document 1 mentioned above, Shigenori Inoue et al. "6.6kV transformerless power storage system using cascade PWM converter and secondary battery -200V, 10kW, 3.6kWh mini model) "Experimental verification", see IEEJ Transactions D, Vol.129, No.1, pp.67-76, 2009 (hereinafter referred to as non-patent document 3)).

  In the active / reactive power control, the three clusters 1u, 1v, 1w constituting the three phases are collectively regarded as one three-phase converter, and the active power / reactive power flowing into the entire converter is controlled.

  In interphase DC voltage balance control, each of the clusters 1u, 1v, and 1w is regarded as a single-phase converter, and the power is adjusted between the three-phase clusters 1u, 1v, and 1w to adjust the power between the clusters 1u, 1v, and 1w. Equalize stored energy.

In the interstage DC voltage balance control, the stored energy of each cell 1 _Hy , 1 _My , 1 _Ly is controlled to a predetermined value by adjusting the power between the cells 1 _Hy , 1 _My , 1 _Ly constituting the same cluster. .

  In the hybrid cascade converter, the configuration inside the cluster is different from that of the conventional cascade converter, but the upper configuration from the cluster can be regarded as the same. Therefore, methods similar to those in the past can be applied to active / reactive power control and interphase DC voltage balance control. On the other hand, conventional interstage DC voltage balance control cannot be applied to voltage control in the same cluster. For this reason, in the present invention, a newly developed interstage DC voltage ratio control is used to implement this.

  FIG. 2 shows a control block diagram of the self-excited reactive power compensator of the present invention using a hybrid cascade converter.

In the active / reactive power control, a voltage command value v _y ^* necessary for the operation of the self-excited reactive power compensator is generated from the power supply voltage v _Sy and the output current i _y (reference numeral 2 in FIG. 2; using FIG. 9). Will be detailed later). At this time, the reactive power is controlled to follow the command value q ^* , and at the same time, the total energy E _C of the entire converter is controlled to coincide with the command value E _C ^* . The reactive power command value q ^* is given by a host control system or an operator so as to appropriately control the voltage of the power system.

In the interphase DC voltage balance control, the _zero phase voltage v ₀ ^* is superimposed on the voltage command value v _y ^* of the converter so that the accumulated energy E _Cy is uniform between the clusters 1u, 1v, 1w constituting each phase. The output voltage command value v _out-y ^* is generated (same reference numeral 3; detailed description will be given later using FIG. 10).

In the interstage DC voltage ratio control, voltage level deviations ΔV _HLy , ΔV _MLy , ΔV _HMy are generated so that the stored energy E _Cxy of each cell constituting the same cluster matches the command value (same reference numeral 4; FIG. 11). And will be described in detail later).

Here, the voltage level deviations ΔV _HLy , ΔV _MLy , ΔV _HMy in the present invention are _expressed as (k) based on the reference DC voltage V _dc and the ratio k of the voltage V _CLy of the DC capacitor of the low voltage cell 1 _Ly described above. −1) × V _dc [V] or less is required.

Finally, from the output voltage command value v _out-y ^* and the voltage level deviations ΔV _HLy , ΔV _MLy , ΔV _HMy (voltage deviations ΔV _HLy ', ΔV _MLy ', ΔV _HMy 'considering polarity), Table 2 The output voltage command value v _xy ^* for each cell 1 _xy is determined based on the voltage distribution rule shown in FIG.

In the control of the DC voltage of each cell 1 _xy , an average value V _Cxy obtained by applying a low-pass filter (symbol LPF in FIG. 2) to the detected voltage v _Cxy of the DC capacitor and a known capacitor capacitance C _x are used. The accumulated energy E _Cxy of the DC capacitor is calculated by Equation 1 (reference numeral 5 in FIG. 2), and feedback control is configured so that this follows the command value.

Even if the DC voltage V _Cxy of each cell 1 _xy and the capacitor capacitance C _x are different as in the hybrid cascade converter, the sum of the stored energy can be easily calculated, and a plurality of cells can be combined. The system configuration can be easily controlled.

In the interphase DC voltage balance control, the total energy E _Cy in each cluster 1u, 1v, 1w is obtained from the accumulated energy E _CHy , E _CMy , E _CLy of each cell of high pressure, medium pressure, and low pressure by Equation 2, and this accumulation is performed. The energy E _Cy is controlled to be uniform between the three phases u, v, and w.
( _Equation 2) E _Cy = E _CHy + E _CMy + E _CLy

Further, the active and reactive power control, the total sum E _C stored energy of the transducer according to Equation 3, and controls so that the total sum E _C matches the stored energy instruction value E _C ^* of the entire converter.
(Equation 3) E _C = E _Cu + E _Cv + E _Cw

Here, the stored energy command value E _Cx ^* of each cell 1 _xy is determined by Equation 4 from the voltage command value V _Cx ^* of each cell of high pressure, medium pressure, and low pressure. The voltage command value V _Cx ^* of each cell 1 _xy is determined and given by the converter designer or the driver so that the converter can output the power line voltage Vs of the AC system. Specifically, for example, the circuit designer first determines the reference DC voltage V _dc and the DC voltage ratio (6: 2: k in this embodiment), and then V _CH ^* = 6 V _dc and V _CM ^* = 2 V. The voltage command value V _Cx ^* of each cell is determined and given so that _dc , V _CL ^* = kV _dc .

The stored energy command value E _C ^* of the entire converter is determined by Equation 5.
(Equation 5) E _C ^* = 3 (E _CH ^* + E _CM ^* + E _CL ^* )

(3) Output voltage of each cell of the hybrid cascade converter Table 1 shows the DC voltage ratio V _CH ^* : V _CM ^* : V _CL ^* = 6: 2: k (1 ≦ k) by the conventional hybrid cascade converter. The relationship of the output voltage of each cell in the case of <2) is shown. Using a reference DC voltage V _dc , V _CH ^* = 6 V _dc , V _CM ^* = 2 V _dc , V _CL ^* = kV _dc . The magnitude of the reference DC voltage V _dc [V] is appropriately determined according to the application.

When the output voltage command value v _out ^* is given, the output voltage v _H of the high voltage cell 1 _Hy (v _Hy when considered for each phase), the medium voltage cell 1 _My The output voltage v _M (v _My when considered for each phase) is uniquely determined. The output voltage v _L of the low-voltage cell 1 _Ly (v _Ly when considered for each phase) is given by Equation 6, which is output by pulse width modulation.
(Equation 6) v _L = v _out ^* −v _H −v _M

At this time, the output voltage v _L given by Expression 6 has a waveform that satisfies Expression 7, and the DC voltage of the low-voltage cell 1 _Ly may be equal to or higher than the reference DC voltage V _dc , that is, 1 ≦ k.
(Expression 7) −V _dc ≦ v _L ≦ V _dc

FIG. 3 shows an output voltage waveform when a sine wave having an amplitude of 9 V _dc is given as the output voltage command value v _out ^* . In this example, the high-pressure cell 1 _Hy outputs one pulse for each positive and negative power supply period, and the medium-pressure cell 1 _My outputs five positive and negative pulses for one power supply period. A deviation obtained by subtracting the output voltage v _H of the high voltage cell and the output voltage v _{M of the} medium voltage cell from the output voltage v _out is calculated, and the low voltage cell 1 _Ly outputs a voltage corresponding to the deviation.

FIG. 4 shows the voltage waveform v _x and inflow power v _x · i of each cell 1 _xy when the hybrid cascade converter using the operation rules shown in Table 1 is applied to the self-excited reactive power compensator. Show.

When operating as a self-excited reactive power compensator, the output voltage v _out and the output current i form a phase angle of 90 degrees. In addition, since the AC side of the high-pressure cell 1 _Hy , the medium-pressure cell 1 _My, and the low-pressure cell 1 _Ly are connected in series, the AC terminal current of all the cells is equal to i (i _y when considered for each phase). Therefore, the power flowing into each cell is the product of the output voltages v _H , v _M , v _{L of} each cell and i.

  When this power is averaged over the power supply cycle, in principle, it becomes zero. As an average value, no effective power flows into each cell and the DC voltage does not change. However, the active power may actually flow into each cell due to non-periodic current at the time of transition or variations in element switching characteristics, and the DC voltage ratio of each cell deviates from 6: 2: k. There is. When the DC voltage ratio deviates from the predetermined value, the waveform of the output voltage is distorted. Therefore, it is necessary to maintain the DC voltage ratio by some method.

In general, when the ratio of the DC voltages of the three cells 1 _Hy , 1 _My , 1 _Ly is controlled for each cluster 1u, 1v, 1w, two degrees of freedom are required for the control. In the present invention, by adjusting the output voltage phase of each cell, the exchange of stored energy between the high pressure cell 1 _Hy and the low pressure cell 1 _Ly and the storage between the medium pressure cell 1 _My and the low pressure cell 1 _Ly are performed. Realize energy exchange at the same time. As a result, two degrees of freedom of control can be obtained, and the DC voltage ratio can be kept constant. By doing so, in the present invention, it is not necessary to connect a power source to any of the DC portions of the three cells 1 _Hy , 1 _My , and 1 _Ly .

Table 2 shows the output voltage of each cell in the hybrid cascade converter of the present invention for enabling energy transfer between the cells.

Voltage deviation ΔV _HL '(ΔV _HLy ' when considering each phase), medium to make the energy transfer between the high voltage cell 1 _Hy and the low voltage cell 1 _Ly to the boundary value for switching the output voltage mode of each cell Voltage deviation ΔV _ML ′ (ΔV _MLy ′ for each phase) for energy transfer between pressure cell 1 _My and low pressure cell 1 _Ly , between high pressure cell 1 _Hy and medium pressure cell 1 _My By adding the voltage deviation ΔV _HM '(ΔV _HMy ' considering each phase) in a predetermined combination to change the output voltage mode, the energy transfer between cells is changed. Occurs. Note that when ΔV _HL ′, ΔV _ML ′, and ΔV _HM ′ are set to 0, Table 2 matches Table 1, and energy transfer between the cells does not occur.

In the present invention, for example, i) energy transfer between the high-pressure cell 1 _Hy and the low-pressure cell 1 _Ly and ii) the medium-pressure cell 1 _My are omitted in order to eliminate the connection of the power supply to the DC parts of the three cells. and utilizing energy transfer between the low pressure cell 1 _Ly, or, iii) and energy transfer and i) high pressure cell 1 _Hy and the low-pressure cell 1 _Ly between the high pressure cell 1 _Hy and medium pressure cell 1 _My Or iii) energy transfer between the high pressure cell 1 _Hy and the medium pressure cell 1 _My and ii) energy between the medium pressure cell 1 _My and the low pressure cell 1 _Ly. Use movement. Here, the following processing is basically performed for each of the three phases u, v, and w of the three-phase alternating current. In the following description, for each of the three phases u, v, and w (in other words, for each cluster 1u, 1v, and 1w). ) Is basically omitted, and the suffix y meaning any one of the three phases u, v, and w is omitted as appropriate.

In the following, first, i) energy transfer between the high pressure cell 1 _Hy and the low pressure cell 1 _Ly , ii) energy transfer between the medium pressure cell 1 _My and the low pressure cell 1 _Ly, and iii) a high pressure cell. Each energy transfer between 1 _Hy and the medium pressure cell 1 _My will be described. Thereafter, the method of using the present invention i) and ii), the method of using iii) and i), and the method of using iii) and ii) of the present invention for omitting the connection of the power source to the DC part of the three cells. Each will be described.

i) Energy transfer between the high pressure cell and the low pressure cell First, energy transfer between the high pressure cell 1 _Hy and the low pressure cell 1 _Ly will be described. In order to allow power to be exchanged between the high voltage cell 1 _Hy and the low voltage cell 1 _Ly , the output voltage of each cell is changed by manipulating the voltage level deviation ΔV _HL . Based on the voltage level deviation ΔV _HL and the output current i, the polarity of ΔV _HL ′ is selected as shown in Equation 8. When the voltage level deviation ΔV _HL is increased (made larger than zero), the electric power moving from the high voltage cell 1 _Hy to the low voltage cell 1 _Ly can be increased.

FIG. 5 shows voltage / power waveforms of each cell when the voltage level deviation ΔV _HL is increased. In FIG. 5, a thin line is a waveform when control is not performed with ΔV _HL = 0, and a thick line is a waveform when control is performed with ΔV _HL > 0. In either case, ΔV _ML = ΔV _HM = 0.

When control is applied, the phase of the output voltage v _H of the high voltage cell 1 _Hy is delayed. As a result, the inflow power P _H (= v _H · i) of the high voltage cell 1 _Hy changes. The difference ΔP _H between the inflow power P _H before and after the application of the control is generated with negative polarity at all four locations of the waveform of the ΔP _H. Therefore, electric power flows out from the high voltage cell 1 _Hy .

On the other hand, the output voltage v _M of the medium voltage cell 1 _My is delayed in the switching of the high voltage cell 1 _{Hy and in} the switching immediately before and after. As a result, the difference ΔP _M before and after the control application of the inflow power P _M (= v _M · i) of the intermediate pressure cell 1 _My is 4 times with positive polarity and 8 times with negative polarity in the waveform of ΔP _M. However, when averaged over one power supply cycle, it becomes almost zero. Therefore, almost no electric power flows into the intermediate pressure cell 1 _My .

Further, the output voltage v _L of the low voltage cell 1 _Ly is determined based on the above-described Equation 6 in conjunction with the output voltage v _H of the high voltage cell 1 _Hy and the output voltage v _M of the medium voltage cell 1 _My . At this time, the output voltage v _L of the low voltage cell 1 _Ly can take a range represented by Equation 9.
(Equation 9) −V _dc − | ΔV _HL | ≦ v _L ≦ V _dc + | ΔV _HL |

Then, to be able to output a voltage of the entire region where the output voltage v _L of the low pressure cell 1 _Ly is expressed by Equation 9, a low pressure cell 1 _Ly DC voltage (i.e., voltage of the DC capacitor) V _CL formula 10 must be set to satisfy. Therefore, the DC voltage V _CL is set higher than the reference DC voltage V _dc .
(Equation 10) V _CL ≧ V _dc + | ΔV _HL |

The difference ΔP _L before and after the control application of the inflow power P _L (= v _L · i) of the low-pressure cell 1 _Ly is 12 positive pulses in the ΔP _L waveform, and the average value is positive. Become. That is, power flows into the low-pressure cell 1 _Ly . This can cause energy transfer from the high pressure cell 1 _Hy to the low pressure cell 1 _Ly .

ii) Energy transfer between the medium pressure cell and the low pressure cell Next, energy transfer between the medium pressure cell 1 _My and the low pressure cell 1 _Ly will be described. In order to allow power to be exchanged between the medium pressure cell 1 _My and the low pressure cell 1 _Ly , the output voltage of each cell is changed by manipulating the voltage level deviation ΔV _ML . Also in this case, the polarity of ΔV _ML ′ is selected by the output current i as shown in Expression 11. When the voltage level deviation ΔV _ML is increased (made larger than zero), the electric power moving from the intermediate pressure cell 1 _My to the low pressure cell 1 _Ly can be increased.

FIG. 6 shows voltage / power waveforms of each cell when the voltage level deviation ΔV _ML is increased. In FIG. 6, the thin line is a waveform when control is not performed with ΔV _ML = 0, and the thick line is a waveform when control is performed with ΔV _ML > 0. In any case, ΔV _HL = ΔV _HM = 0.

In this control, the output voltage v _H of the high-pressure cell 1 _Hy does not change, there is no power flow of the high pressure cell 1 _Hy. On the other hand, the intermediate voltage cell 1 _My operates so that the phase of the output voltage v _M is delayed, and power flows out from the intermediate voltage cell 1 _My .

Since the low voltage cell 1 _Ly changes the output voltage v _L in conjunction with the medium voltage cell 1 _My , power flows into the low voltage cell 1 _Ly . Thereby, the energy transfer from the medium pressure cell 1 _My to the low pressure cell 1 _Ly can be caused.

Further, the output voltage v _L of the low voltage cell 1 _Ly is determined based on the above-described Equation 6 in conjunction with the output voltage v _H of the high voltage cell 1 _Hy and the output voltage v _M of the medium voltage cell 1 _My . At this time, the output voltage v _L of the low voltage cell 1 _Ly can take a range represented by Expression 12.
(Equation 12) −V _dc − | ΔV _ML | ≦ v _L ≦ V _dc + | ΔV _ML |

Then, to be able to output a voltage of the entire region where the output voltage v _L of the low-pressure cell 1 _Ly is represented by Equation 12, the low pressure cell 1 _Ly DC voltage (i.e., voltage of the DC capacitor) V _CL formula 13 needs to be set to satisfy. Therefore, the DC voltage V _CL is set higher than the reference DC voltage V _dc .
(Equation 13) V _CL ≧ V _dc + | ΔV _ML |

iii) Energy transfer between the high-pressure cell and the medium-pressure cell Next, energy transfer between the high-pressure cell 1 _Hy and the medium-pressure cell 1 _My will be described. In order to allow power to be exchanged between the high-pressure cell 1 _Hy and the intermediate-pressure cell 1 _My , the output voltage of each cell is changed by manipulating the voltage level deviation ΔV _HM . Also in this case, the polarity of ΔV _HM ′ is selected according to the output current i as shown in Expression 14. When the voltage level deviation ΔV _HM is increased (made larger than zero), the electric power moving from the high pressure cell 1 _Hy to the intermediate pressure cell 1 _My can be increased.

FIG. 7 shows voltage / power waveforms of the respective cells when the voltage level deviation ΔV _HM is increased. In FIG. 7, a thin line is a waveform when control is not performed with ΔV _HM = 0, and a thick line is a waveform when control is performed with ΔV _HM > 0. In any case, ΔV _HL = ΔV _ML = 0 is set.

The output voltage v _H at the control application high pressure cell 1 _Hy is delayed in phase, the power flows out from the high pressure cell 1 _Hy. Further, the output voltage v _M medium pressure cell 1 _My also changed, flows power P _M of the medium pressure cell _{1 My (= v M · i} ) is changed. The difference [Delta] P _M of the inflow power P _M of the before and after the control application occurs four times in the positive polarity. Accordingly, power flows into the medium pressure cell 1 _My . As a result, energy can be transferred from the high-pressure cell 1 _Hy to the medium-pressure cell 1 _My .

The low voltage cell 1 _Ly changes the output voltage v _L in conjunction with the medium pressure cell 1 _My , but the difference ΔP _L before and after the application of the control of the inflow power P _L (= v _L · i) of the low voltage cell 1 _Ly. Occurs four times with a positive polarity and four times with a negative polarity in the waveform of ΔP _L , and on average, no power exchange occurs.

Further, the output voltage v _L of the low voltage cell 1 _Ly is determined based on the above-described Equation 6 in conjunction with the output voltage v _H of the high voltage cell 1 _Hy and the output voltage v _M of the medium voltage cell 1 _My . At this time, the output voltage v _L of the low voltage cell 1 _Ly can take a range represented by Equation 15.
(Equation 15) −V _dc − | ΔV _HM | ≦ v _L ≦ V _dc + | ΔV _HM |

Then, to be able to output a voltage of the entire region where the output voltage v _L of the low-pressure cell 1 _Ly is represented by the equation 15, a low pressure cell 1 _Ly DC voltage (i.e., voltage of the DC capacitor) V _CL formula 16 needs to be set to satisfy. Therefore, the DC voltage V _CL is set higher than the reference DC voltage V _dc .
(Equation 16) V _CL ≧ V _dc + | ΔV _HM |

A) Method using i and ii above In this case, voltage deviation ΔV _HLy ′ and voltage deviation ΔV _MLy ′ are added at the same time in order to perform voltage control of both high voltage cell 1 _Hy and medium pressure cell 1 _My simultaneously. To do. FIG. 8A shows an image diagram of interstage DC voltage ratio control in this case. In FIG. 8, the arrows in the figure indicate the state of energy exchange between cells, in other words, the presence or absence of energy exchange between cells. Further, in the description of the present specification, when it is necessary to specify, the method A is assumed instead of the method B and the method C described below.

In this case, the output voltage v _L of the low-voltage cell 1 _Ly can take the range of Expression 17 in addition to Expression 9 and Expression 12. Further, the DC voltage of the low-voltage cell 1 _Ly (that is, the voltage of the DC capacitor) so that the output voltage v _L of the low-voltage cell 1 _Ly can output the voltages in all three regions of Equations 9, 12, and 17. V _CL needs to be set so as to satisfy the three equations 18-1, 18-2, and 18-3.
( _Equation 17) −V _dc − | ΔV _HLy + ΔV _MLy | ≦ v _L ≦ V _dc + | ΔV _HLy + ΔV _MLy |
( _Equation 18-1) V _CL ≧ V _dc + | ΔV _HLy |
( _Equation 18-2) V _CL ≧ V _dc + | ΔV _MLy |
( _Equation 18-3) V _CL ≧ V _dc + | ΔV _HLy + ΔV _MLy |
B) Method using iii and i above In this case, the voltage deviation ΔV _HMy ′ and the voltage deviation ΔV _HLy ′ are added simultaneously. FIG. 8B shows an image diagram of the interstage DC voltage ratio control in this case.

In this case, the output voltage v _L of the low voltage cell 1 _Ly can take the range of Formula 19 in addition to Formula 15 and Formula 9. Further, the DC voltage of the low-voltage cell 1 _Ly (that is, the voltage of the DC capacitor) so that the output voltage v _L of the low-voltage cell 1 _Ly can output the voltages in all three areas of Equations 9, 15, and 19. V _CL needs to be set so as to satisfy the three equations 20-1, 20-2, and 20-3.
( _Equation 19) −V _dc − | ΔV _HMy + ΔV _HLy | ≦ v _L ≦ V _dc + | ΔV _HMy + ΔV _HLy |
( _Equation 20-1) V _CL ≧ V _dc + | ΔV _HMy |
( _Equation 20-2) V _CL ≧ V _dc + | ΔV _HLy |
( _Equation 20-3) V _CL ≧ V _dc + | ΔV _HMy + ΔV _HLy |
C) Method using iii and ii In this case, voltage deviation ΔV _HMy 'and voltage deviation ΔV _MLy ' are added at the same time in order to perform voltage control of both high voltage cell 1 _Hy and medium pressure cell 1 _My simultaneously. To do. FIG. 8C shows an image diagram of interstage DC voltage ratio control in this case.

In this case, the output voltage v _L of the low voltage cell 1 _Ly can take the range of Formula 21 in addition to Formula 15 and Formula 12. Furthermore, the DC voltage of the low-voltage cell 1 _Ly (that is, the voltage of the DC capacitor) so that the output voltage v _L of the low-voltage cell 1 _Ly can output the voltages in all three areas of the equations 12, 15, and 21. V _CL needs to be set so as to satisfy three equations 22-1, 22-2 and 22-3.
( _Equation 21) −V _dc − | ΔV _HMy + ΔV _MLy | ≦ v _L ≦ V _dc + | ΔV _HMy + ΔV _MLy |
( _Equation 22-1) V _CL ≧ V _dc + | ΔV _HMy |
( _Equation 22-2) V _CL ≧ V _dc + | ΔV _MLy |
( _Equation 22-3) V _CL ≧ V _dc + | ΔV _HMy + ΔV _MLy |

In the present invention, the voltage v _Cxy of each cell 1 _xy of the detected DC capacitor, there may be a case where the electric power from the low-pressure cell 1 _Ly even when power to the low-pressure cell 1 _Ly flowing flows. That is, the cluster 1u, 1 v, a DC voltage v _Cxy of some cells with the DC voltage v _Cxy of small variations in part due to the cell characteristics between the cells 1 _xy every 1w rises decreases In the present invention, control is performed so that power flows into the low voltage cell 1 _{Ly when} the DC voltage v _CLy of the low voltage cell 1 _Ly is lower than the default value. work, on the other hand, acts to control so that power from the low-pressure cell 1 _Ly flowing in the DC voltage V _CLy low pressure cell 1 _Ly is higher than the default value conditions. In the high-pressure cell 1 _Hy and the intermediate-pressure cell 1 _My , power can flow in and out similarly.

(4) Control Method of Self-Excited Reactive Power Compensation Device Hereinafter, a control method of the self-excited reactive power compensation device of the present invention will be described.

(4-1) Active / Reactive Power Control A conventional method can be used as a method of active / reactive power control in the present invention (see FIG. 9; see, for example, Non-Patent Document 1 above).

Specifically, the control is performed by regarding the clusters 1u, 1v, and 1w constituting the three phases as one three-phase grid connection converter. The output current i _y and the power supply voltage v _Sy are respectively converted into a d-axis component i _d , a q-axis component i _q , and a d-axis component v _{Sd of} the power supply voltage by dq conversion (reference numerals 9a and 9b in FIG. 9), The non-interfering current control is applied on the dq coordinate by separating the q-axis component v _Sq .

Deviation between the total energy E _C of the three-phase cascade converter and the command value E _C ^* is taken (same sign 10), and the feedback controller (same sign 11; K _C is the controller) The instantaneous active power p ^* flowing into the entire converter is calculated by the following equation. Using the instantaneous active power p ^* and the instantaneous reactive power command value q ^* , current command values i _d ^* and i _q ^* are obtained so that the converter outputs them (same reference numerals 12a and 12b).

Then, the deviation between the current command values i _d ^* , i _q ^* and the actual output currents i _d , i _q is taken (same reference numerals 13a, 13b), and current feedback control is configured using a proportional integral controller (same as above). Reference numerals 14a and 14b; K ₁ is a proportional gain of the current controller, s is a Laplace operator (differential operator), and T ₁ is an integration time constant of the current controller). The sum of the term for canceling the voltage drop in the AC reactor and the feed forward term of the power supply voltage is taken (same reference numerals 15a and 15b), and the inverse dq transformation is performed to obtain the three-phase voltage command values v _u ^* , v _v ^* , v _w ^* is output (reference numeral 16). In FIG. 9, ω represents the angular frequency of the power supply voltage, and in FIGS. 9 and 1, L _AC represents the inductance of the AC reactor.

(4-2) Interphase DC voltage balance control The conventional method can also be used as the method of interphase DC voltage balance control in the present invention (see FIG. 10; for example, see Non-Patent Document 3 above).

In general, in a three-phase power converter that outputs a three-phase balanced current, if the fundamental zero-phase voltage v ₀ ^* is superimposed on the three-phase voltage command values v _u ^* , v _v ^* , v _w ^* , the power between the phases Is delivered. The magnitude of the power to be transferred between the phases is determined by the amplitude of the superimposed zero-phase voltage v ₀ ^* , and the power flows into a cluster that outputs a voltage having the same phase as the phase φ ₀ .

In the inter-phase DC voltage balance control, the fundamental zero-phase voltage v ₀ ^* is calculated by using feedback control so that the power between the clusters 1u, 1v, 1w constituting the three phases is uniform (reference numeral 20 in FIG. 10). To 21). In FIG. 10, ΔE _Cα and ΔE _Cβ are α-axis and β-axis components obtained by subjecting the energy deviations ΔE _Cu , ΔE _Cv and ΔE _{Cw of} each cluster to three-phase to two-phase transformation, and K ₀ is interphase energy control. , ₀ represents the phase of the zero-phase voltage v ₀ ^* , ω represents the angular frequency of the power supply voltage, and t represents time.

Then, by superimposing the fundamental wave zero-phase voltage v ₀ ^* on the three-phase voltage command values v _u ^* , v _v ^* , v _w ^* determined by the above-described active / reactive power control (see FIG. 2), The electric power among the clusters 1u, 1v, 1w is adjusted, and the accumulated energy E _{Cy of} each cluster is kept uniform.

(4-3) Interstage DC voltage ratio control On the other hand, for the interstage DC voltage ratio control, a method unique to the present invention is used. First, when the voltage distribution conditions shown in Table 2 are applied, the stored energy of each cell can be adjusted by giving voltage deviations ΔV _HLy ′, ΔV _MLy ′, and ΔV _HMy ′. In the present invention, this is used to apply the feedback control to the stored energy E _Cxu , E _Cxv , E _Cxw of the cells 1 _xu , 1 _xv , 1 _xw in the clusters 1 u, 1 v, 1 w to obtain the DC voltage ratio. Control.

In the inter-stage DC voltage ratio control according to the present invention, as shown in FIG. 11A, the stored energy command value E _CHy ^* to be shared by the high voltage cell 1 _Hy is _calculated from the stored energy E _{Cy of the} entire cluster by the equation 23. Calculate (reference numeral 30a in FIG. 11A).

Then, a deviation between the stored energy command value E _CHy ^* and the actual accumulated energy E _CHy calculated by detecting the voltage is calculated (same as 31a), and the deviation is multiplied by the gain K _CH to obtain a voltage level deviation ΔV _HLy. (Same reference numeral 32a). The voltage level deviation ΔV _MLy is also obtained for the intermediate pressure cell 1 _{My in} the same procedure (same symbols 30b, 31b, 32b).

In the case of the present embodiment, the voltage deviations ΔV _HLy ′ and ΔV _MLy ′ based on the voltage level deviations ΔV _HLy and ΔV _MLy obtained as described above are reflected in the voltage distribution conditions shown in Table 2 so that the high voltage cell 1 _Hy , The stored energy E _CHy , E _CMy , E _CLy between the medium pressure cell 1 _My and the low pressure cell 1 _Ly is controlled to a predetermined value, and the DC voltage ratio of the cells constituting the same cluster is kept at 6: 2: k. Can do.

When the interstage DC voltage ratio control is performed by exchanging energy between cells as shown in FIG. 8A as in the present embodiment, the voltage level deviation ΔV _HLy and the variable and procedure shown in FIG. prompts the voltage level difference [Delta] V _MLY, the voltage level difference [Delta] V _HMy by the variable and procedure shown in FIG. 11 (B) in the case of exchanging interstage DC voltage ratio control by the energy between the cells shown in FIG. 8 (B) And the voltage level deviation ΔV _HLy is obtained, and when the interstage DC voltage ratio control is performed by exchanging energy between the cells shown in FIG. _{8C, the} voltage level deviation ΔV is obtained by the variables and procedures shown in FIG. _HMy and voltage level deviation ΔV _MLy are determined.

  According to the reactive power compensator of the present invention having the above configuration, the voltage of the cell that outputs the lowest voltage in the hybrid cascade converter is slightly increased from the reference DC voltage, and the output voltage pulse of each cell is adjusted at the same time. This enables power interchange between cells that make up the same phase (in other words, in the same cluster), eliminating the need to connect a DC power source as an additional auxiliary power source to each cell. Thus, a reactive power compensator having a simple device configuration, a small size, and a low cost can be configured, and versatility as a reactive power compensator can be improved.

In addition, although the above-mentioned form is an example of the suitable form of this invention, it is not limited to this, A various deformation | transformation implementation is possible in the range which does not deviate from the summary of this invention. For example, in the above-described embodiment, as shown in FIG. 8, the interstage DC voltage ratio control is performed by the same method in any of the u, v, and w phases. The interstage DC voltage ratio control may be performed by a method different in w phase. As an example, for example, as shown in FIG. 12A, in cluster 1u (that is, u phase), energy transfer between high pressure cell 1 _Hy and low pressure cell 1 _Ly and medium pressure cell 1 _My Energy transfer between the low-pressure cell 1 _Ly and the energy transfer between the high-pressure cell 1 _Hy and the medium-pressure cell 1 _My and the high-pressure cell 1 _Hy and the low-pressure cell 1 in the cluster 1 v (ie, v phase). _In the cluster 1w (ie, the w phase), energy transfer between the high pressure cell 1 _Hy and the intermediate pressure cell 1 _My and the intermediate pressure cell 1 _My and the low pressure cell 1 _Ly are utilized. Energy transfer between the high-pressure cell 1 _Hy and the low-pressure cell 1 _Ly and the intermediate-pressure cell 1 _My in the cluster 1u as shown in FIG. Energy transfer with low-pressure cell 1 _Ly In cluster 1v and cluster 1w, energy transfer between the high pressure cell 1 _Hy and the medium pressure cell 1 _My and energy transfer between the high pressure cell 1 _Hy and the low pressure cell 1 _Ly are used. You may do it. As described above, even if the inter-stage DC voltage ratio control is performed by different methods for the u, v, and w phases, the control operates independently for each phase, so that a predetermined operation is performed. The effect is demonstrated. In FIG. 12, the arrows in the figure represent the state of energy exchange between cells, in other words, the presence or absence of energy exchange between cells.

In the above-described embodiment, the voltage ratio of the DC capacitors of the high-pressure cell 1 _Hy , the medium-pressure cell 1 _My , and the low-pressure cell 1 _Ly is V _CHy : V _CMy : V _CLy = 6 V _dc : 2 V _dc : kV _dc (where 1 <K <2; V _dc is a reference DC voltage), but the voltage ratio of the DC capacitor is not limited to this. Specifically, for example, V _CHy : V _CMy : V _CLy = 4 V _dc : 2 V _dc : kV _dc (where 1 <k <2), and further speaking, 3V _CMy ≧ V _CHy > V _CMy > V _CLy As _{long as} the relationship> 0.5V _CMy is established, V _CHy : V _CMy : V _CLy may be any value.

Furthermore, in the above-described embodiment, as shown in Table 2, the phase of the output voltage pulse of each cell 1 _xy is changed by adding the voltage deviations ΔV _HMy 'and ΔV _MLy ' to the boundary value for switching the output voltage mode. Enables energy transfer between cells, but operates a self-excited reactive power compensator using a hybrid cascade converter without the need for a DC power supply as an additional auxiliary power, which is the main point of the present invention The method for making it not limited is the method of adding the voltage deviation. That is, the main point of the present invention can be realized by outputting a pulse train in which the voltage phase is changed as shown in FIGS.

Specifically, first, the DC voltage v _Cxy of each of the high-voltage, medium-pressure, and low-voltage cells 1 _xy is detected, and the stored energy E _Cxy of each cell 1 _xy is obtained by Equation 1, and the accumulated energy command obtained by Equation 4 is obtained. Compare with the value E _Cx ^* . Then, for example, when the actually stored energy E _CHy of the high pressure cell is larger than the stored energy command value E _CH ^* , the same as FIG. 5 as shown in FIG. 5 in order to release energy from the high pressure cell 1 _Hy . What is necessary is just to delay a pulse train so that only the output voltage pulse of a part may change. Further, when the actually stored energy E _CHy of the high pressure cell is smaller than the stored energy command value E _CH ^* , the pulse train may be advanced in the opposite direction to that of FIG. 5 in order to flow the energy into the high pressure cell 1 _Hy . . When the actually stored energy E _CMy of the medium pressure cell is larger than the stored energy command value E _CM ^* , as shown in FIG. 6 in order to release energy from the medium pressure cell 1 _My , the same as FIG. What is necessary is just to delay a pulse train so that only the output voltage pulse of a part may change. In addition, when the measured stored energy E _CMy of the intermediate pressure cell is smaller than the stored energy command value E _CM ^* , the pulse train can be advanced in the opposite direction to that of FIG. 6 in order to flow the energy into the intermediate pressure cell 1 _My . It ’s fine. The magnitude of advancing or delaying the pulse train may be proportional to the difference between the actually measured stored energy E _Cxy and the stored energy command value E _Cx ^* , or may be a fixed value set in advance. May be.

In the case of using the above concept, as a whole, there are two _types of stored energy E _CHy and stored energy command value E _CH ^* of the high-pressure cell: E _CH ^* ≧ E _CHy and E _CH ^* <E _CHy , Measured stored energy E _CMy and stored energy command value E _CM ^{* of the} medium pressure cell E _CM ^* ≧ E _Cmy and E _CM ^* <E _CMy and measured stored energy E _CLy and stored energy of the low pressure cell With respect to the command value E _CL ^* , all eight possible combinations of E _CL ^* ≧ E _Cly and E _CL ^* <E _CLy are output using the methods A, B, C, etc. in the above-described embodiment. By investigating in advance which part of the voltage pulse should be shifted and storing in the storage device how to shift the output voltage pulse, the measured value and command value of the stored energy of each cell What kind of relationship Power of the interaction between even if each cell that Tsu is performed.

Then, by changing the phase of the output voltage pulse according to the above-described concept, power is exchanged between the high voltage cell 1 _{Hy, the} medium voltage cell 1 _My and the low voltage cell 1 _Ly to control the voltage of the DC capacitor. Also good. Specifically, for example, power is allowed to flow out from the high-pressure cell 1 _Hy and the medium-pressure cell 1 _{My so as} to flow into the low-pressure cell 1 _Ly , or power can be flowed out from the high-pressure cell 1 _Hy to cause the medium-pressure cell 1 _My to flow out. In addition, power is allowed to flow into the low-pressure cell 1 _Ly , or power is drained from the high-pressure cell 1 _Hy to cause power to flow into the medium-pressure cell 1 _My , while power is drained from the medium-pressure cell 1 _My to cause the low-pressure cell 1 _Ly to flow out. The power may be allowed to flow into the low-pressure cell 1 _Ly by causing the power to flow into the low-pressure cell 1 _Ly . In this case, the DC voltage V _CHy of the high voltage cell, the DC voltage V _{CMy of} the medium voltage cell, and the DC voltage V _{CLy of} the low voltage cell _satisfy V _CHy > V _CMy > V _CLy and the DC voltage V of the low voltage cell. _CLy is larger than the reference DC voltage _Vdc .

That is, in the present invention, the “voltage” in FIG. 2 for realizing the gist of operating the self-excited reactive power compensator using the hybrid cascade converter without requiring a DC power supply as an additional auxiliary power supply. The method of “distribution” is not limited to the method of adding the voltage deviations ΔV _HMy ′ and ΔV _MLy ′ to the boundary value for switching the output voltage mode as shown in Table 2 described in the above embodiment. Any method may be used as long as it outputs a pulse train having a changed voltage phase.

Here, in the present invention, the method of outputting a pulse train in which the voltage phase for partially delaying or advancing the pulse train of the waveform of the output voltage from each cell is not limited to a specific method. Further, since there is a known method for outputting a pulse train with the voltage phase changed, the details are omitted. As an example, specifically, for example, i) when the pulse train is not operated, ii) when the pulse train is delayed, iii) when the pulse train is advanced, the high pressure cell 1 _Hy and the medium pressure cell 1 _My It is conceivable that the output voltage waveform is stored in a high-speed storage device such as a semiconductor memory and switched in synchronization with the cycle of the power supply. Note that the output voltage v _L of the low voltage cell 1 _Ly is calculated and determined from time to time based on Equation 6 above in conjunction with the output voltage v _H of the high voltage cell 1 _Hy and the output voltage v _M of the medium voltage cell 1 _My. The

  Further, in the above-described embodiment, one cluster is configured by three-stage cells using three cells of high pressure, medium pressure, and low pressure, but the configuration of the cluster is not limited to this, For example, a cell having a voltage three times that of the high voltage cell of the above-described embodiment is further added to form a four-stage configuration (in this case, the voltage ratio of the DC capacitor is set to 18: 6: 2: k, for example) The high voltage cell may have four stages to form a six-stage configuration (in this case, the voltage ratio of the DC capacitors is, for example, 6: 6: 6: 6: 2: k).

  Note that the reactive power compensator of the present invention is not limited to being used by being connected to a power distribution system, and can be used by being connected to a power transmission system by using, for example, a transformer. .

  The simulation results performed to verify the operational suitability of the self-excited reactive power compensator using the hybrid cascade converter to which the configuration of the reactive power compensator of the present invention is applied will be described with reference to FIGS. . In the following description, the suffix y meaning any one of the three phases u, v, and w is omitted as appropriate.

In this example, the circuit model shown in FIG. 1 was constructed, and the operational suitability was verified by computer simulation. Table 3 shows circuit constants used in the simulation of this example.

In this embodiment, in order to apply the interstage DC voltage ratio control, the DC voltage ratio of each cell 1 _H , 1 _M , 1 _L is set to V _CH ^* : V _CM ^* : V _CL ^* = 6: 2: 1.2. did. As a result, the DC voltage of the low voltage cell 1 _L becomes 4 [V] higher than the reference DC voltage V _dc, so | ΔV _HL |, | ΔV _ML |, | ΔV _HL + ΔV _ML | is 4 [V] or less. Set by range.

(1) Verification of energy control between in-phase cells Various operation simulations using the voltage distribution conditions shown in Table 2 are performed, and the output voltages of the respective cells 1 _H , 1 _M , 1 _L are synthesized, thereby producing a circuit shown in FIG. The result shown in FIG. 16 was obtained. Specifically, FIG. 13 to FIG. 16 show the output voltage v _out-u , output current i _u , high voltage cell output voltage v _Hu , medium voltage cell output voltage v _Mu , and low voltage cell output voltage v _Lu of the u-phase cluster. , High voltage cell DC voltage v _CHu , medium voltage cell DC voltage v _CMu , and low voltage cell DC voltage v _CLu .

First, a simulation was performed in the case where ΔV _HLu = ΔV _MLu = 0 [V] and energy control between cells was not performed, and the result shown in FIG. 13 was obtained. From this result, as each cell 1 _Hu , 1 _Mu , 1 _Lu outputs the voltage v _Hu , v _Mu , v _Lu , the DC voltage v _CHu , v _CMu , of each cell 1 _Hu , 1 _Mu , 1 _Lu is _output . Although ripple occurred in v _CLu , it was confirmed that the voltage returned to the original voltage after one cycle of power supply (= 20 [ms]) and no voltage deviation occurred. From this, it was confirmed that no energy transfer occurred between the cells 1 _Hu , 1 _Mu , 1 _Lu during one power cycle.

Next, simulation was performed when ΔV _HLu = 4 [V] and ΔV _MLu = 0 [V] and control was performed so that power was discharged from the high-pressure cell 1 _Hu , and the result shown in FIG. 14 was obtained. . This result is possible DC voltage v _CLu of the DC voltage v _CHu low cell while decreases 1 _Lu of the high pressure cell 1 _Hu has risen was confirmed after the power cycle. On the other hand, it was confirmed that the DC voltage v _CMu of the medium pressure cell 1 _Mu did not change. From these, it was confirmed that energy was exchanged between the high pressure cell 1 _Hu and the low pressure cell 1 _Lu .

Further, a simulation was performed in which ΔV _HLu = 0 [V] and ΔV _MLu = 4 [V] were set to control power to flow out from the intermediate pressure cell 1 _Mu , and the result shown in FIG. 15 was obtained. . From this result, it was confirmed that the DC voltage _vCMu of the low-pressure cell 1 _Lu increased while the DC voltage _vCMu of the medium-pressure cell 1 _Mu decreased after one cycle of the power source. On the other hand, it was confirmed that the DC voltage v _CHu of the high voltage cell 1 _Hu did not change. From these, it was confirmed that energy was exchanged between the medium pressure cell 1 _Mu and the low pressure cell 1 _Lu .

Furthermore, a _{simulation is performed} when ΔV _HLu = −4 [V] and ΔV _MLu = 4 [V] are set so that power flows into the high-pressure cell 1 _Hu and power flows out from the medium-pressure cell 1 _Mu. The results shown in FIG. 16 were obtained. From this result, in the case of adjusting the high pressure cell 1 _Hu and medium pressure cell 1 _Mu simultaneously, to reduce the DC voltage v _CMu medium pressure cell 1 _Mu with increasing DC voltage v _CHu the high pressure cell 1 _Hu It was confirmed that

From the above results, it was confirmed that exchange of stored energy can be realized between the cells 1 _H , 1 _M , and 1 _L by applying energy control between the cells to the voltage distribution of the hybrid cascade converter.

(2) Verification of operation of self-excited reactive power compensator Next, a simulation when starting the hybrid cascade converter was performed. In this simulation, the DC capacitors of the cells 1 _H , 1 _M , and 1 _L were started with the initial charging circuit charged to 90% of the rated value, and a reactive power command of 5 [kVA] was given simultaneously with the starting. .

A simulation when starting the hybrid cascade converter under the above-described conditions was performed, and the results shown in FIG. 17 were obtained. From this result, it was confirmed that the DC voltage v _Cxy of each cell 1 _{xy coincided} with a predetermined voltage command value (see Table 3) after 50 [ms] from the start. In addition, it was confirmed that a current that is 90 degrees out of phase from the power supply voltage flows, and that reactive power compensation can be realized.

Next, a simulation was performed when the interstage DC voltage ratio control was disabled during steady operation. In this simulation, a resistor for simulating a voltage non-uniformity factor was connected in parallel with the DC capacitor of each cell 1 _xy .

A simulation was performed when the interstage DC voltage ratio control was disabled during steady operation under the above-described conditions, and the results shown in FIG. 18 were obtained. From this result, while the interstage DC voltage ratio control is applied, the DC voltage v _Cxy of each cell 1 _{xy operates} in accordance with a predetermined voltage command value (see Table 3), while the stage 1 It was confirmed that the DC voltage v _Cxy of each cell 1 _xy becomes non-uniform when the inter-current DC voltage ratio control is disabled.

  From the above results, it is confirmed that the interstage DC voltage ratio control contributes to maintaining the DC voltage of the hybrid cascade converter at a predetermined value, and can operate properly as a self-excited reactive power compensator. confirmed.

1 _Hy high pressure cell (y phase)
1 _My medium pressure cell (y phase)
1 _Ly low pressure cell (y phase)

Claims (8)

A reactive power compensation apparatus of the self-excited to be interconnection to the power system of the three Ai交 stream,
The reactive power compensation device, the control of the output voltage waveform includes a line right wing hybrid type cascade converter, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said cluster Consists of a series connection of a high pressure cell, a medium pressure cell, and a low pressure cell, each containing a single phase full bridge converter,
V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , V _CLy is the voltage of the DC capacitor of the low voltage cell , V _dc is the reference DC voltage, and the suffix y Is one of the phases (u, v, w) of the three-phase alternating current,
3V _CMy ≧ V _CHy > V _CMy > V _CLy > 0.5 V _{CM y} and V _CLy > V _dc , and in order to control V _CHy , V _CMy and V _CLy , delaying it or proceed with the pulse of the output voltage of the waveform partially and by or advancing delaying the pulses of the output voltage waveform of the medium pressure cell partially, the high pressure cell, the medium pressure cells, and the and wherein the generating the power exchange between the low pressure cell cells, reactive power compensator. A reactive power compensation apparatus of the self-excited to be interconnection to the power system of the three Ai交 stream,
The reactive power compensation device, the control of the output voltage waveform includes a line right wing hybrid type cascade converter, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said cluster Consists of a series connection of a high pressure cell, a medium pressure cell, and a low pressure cell, each containing a single phase full bridge converter,
V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , V _Cly is the voltage of the DC capacitor of the low voltage cell , V _dc is the reference DC voltage, ΔV _HLy 'Is a voltage deviation for causing energy transfer between the high pressure cell and the low pressure cell, and ΔV _MLy ' is a voltage for causing energy transfer between the medium pressure cell and the low pressure cell. When the deviation _y represents the output current from the cluster and the suffix y represents one of the phases (u, v, w) of the three-phase alternating current,
3V _CMy ≧ V _CHy > V _CMy > V _CLy > 0.5 V _{CM y} and V _CLy > V _dc , and further from the cluster to control V _CHy , V _CMy , V _CLy When i _y ≧ 0, ΔV _HLy '> 0 and ΔV _MLy '> are set as boundary values for switching the output voltage modes of the high voltage cell , the medium voltage cell , and the low voltage cell for controlling the waveform of the output voltage. by adding [Delta] V _hly 'and [Delta] V _MLY' is 0, by the time _i y <0 for adding the [Delta] V _hly '<0 and [Delta] V _MLY' <0 and is [Delta] V _hly 'and [Delta] V _MLY', the high pressure cell , and wherein the generating the exchange of power between the cells in said pressure cells, and the low-pressure cells, the reactive power compensator. A reactive power compensation apparatus of the self-excited to be interconnection to the power system of the three Ai交 stream,
The reactive power compensation device, the control of the output voltage waveform includes a line right wing hybrid type cascade converter, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said cluster Consists of a series connection of a high pressure cell, a medium pressure cell, and a low pressure cell, each containing a single phase full bridge converter,
V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , V _Cly is the voltage of the DC capacitor of the low voltage cell , V _dc is the reference DC voltage, ΔV _HMy 'Is a voltage deviation for causing energy transfer between the high pressure cell and the medium pressure cell, and ΔV _HLy ' is a voltage for causing energy transfer between the high pressure cell and the low pressure cell. When the deviation _y represents the output current from the cluster and the suffix y represents one of the phases (u, v, w) of the three-phase alternating current,
3V _CMy ≧ V _CHy > V _CMy > V _CLy > 0.5 V _{CM y} and V _CLy > V _dc , and further from the cluster to control V _CHy , V _CMy , V _CLy When i _y ≧ 0, ΔV _HMy ′> 0 and ΔV _HLy ′> are set as boundary values for switching the output voltage mode of the high voltage cell , the medium voltage cell , and the low voltage cell for controlling the waveform of the output voltage. by adding [Delta] V _HMy 'and [Delta] V _hly' is 0, by the time _i y <0 for adding the [Delta] V _HMy '<0 and [Delta] V _hly' <0 and is [Delta] V _HMy 'and [Delta] V _hly', the high pressure cell , and wherein the generating the exchange of power between the cells in said pressure cells, and the low-pressure cells, the reactive power compensator. A reactive power compensation apparatus of the self-excited to be interconnection to the power system of the three Ai交 stream,
The reactive power compensation device, the control of the output voltage waveform includes a line right wing hybrid type cascade converter, the hybrid cascade converter has a cluster corresponding to each phase of the three-phase AC, said cluster Consists of a series connection of a high pressure cell, a medium pressure cell, and a low pressure cell, each containing a single phase full bridge converter,
V _CHy is the voltage of the DC capacitor of the high voltage cell , V _CMy is the voltage of the DC capacitor of the medium voltage cell , V _Cly is the voltage of the DC capacitor of the low voltage cell , V _dc is the reference DC voltage, ΔV _HMy 'Is a voltage deviation for causing energy transfer between the high pressure cell and the medium pressure cell, and ΔV _MLy ' is for causing energy transfer between the medium pressure cell and the low pressure cell. When the voltage deviation is represented by i _y indicating the output current from the cluster, and the subscript y represents one of the phases (u, v, w) of the three-phase alternating current,
3V _CMy ≧ V _CHy > V _CMy > V _CLy > 0.5 V _{CM y} and V _CLy > V _dc , and further from the cluster to control V _CHy , V _CMy , V _CLy The boundary value for switching the output voltage mode of the high voltage cell , the medium voltage cell , and the low voltage cell for controlling the waveform of the output voltage is set to ΔV _HMy '> 0 and ΔV _MLy '> when i _y ≧ 0. by adding [Delta] V _HMy 'and [Delta] V _MLY' is 0, by the time _i y <0 for adding the [Delta] V _HMy '<0 and [Delta] V _MLY' <0 and is [Delta] V _HMy 'and [Delta] V _MLY', the high pressure cell , and wherein the generating the exchange of power between the cells in said pressure cells, and the low-pressure cells, the reactive power compensator. Any one is used of the methods of energy transfer according to claims 2 to 4 for each phase of the three-phase alternating current, the method of energy transfer in all or at least some of the phases of the three-phase alternating current A reactive power compensator characterized by being different from other phases. The voltage _{V CHy} of the DC capacitor of the high pressure cell, the voltage _{V CMy} of the DC capacitor in said pressure cell, and the voltage _{V CLy} of the DC capacitor of the low-pressure cells, 1 <k <V _CHy when a 2: _{V CMy} The reactive power compensator according to claim 2, _wherein : V _CLy = 6: 2: k . The voltage _{V CHy} of the DC capacitor of the high pressure cell, the voltage _{V CMy} of the DC capacitor in said pressure cell, and the voltage _{V CLy} of the DC capacitor of the low-pressure cells, 1 <k <V _CHy when a 2: _{V CMy} The reactive power compensator according to claim 2, _wherein : V _CLy = 4: 2: k . Reactive power compensator according to claim 6 or 7, wherein the value before Symbol k is 1.01 to 1.3.

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