JP2019004651A - System interconnection electric power conversion system - Google Patents

Abstract

To provide a system interconnection electric power conversion system in which a continuation operation at low in a momentary voltage drop while achieving high conversion efficiency.SOLUTION: A system interconnection electric power conversion system A comprises: an inverter 5 that converts a DC power supplied to a DC bus into an AC power; a voltage measurement part that measures a system voltage; and a control part that controls a bus voltage of the DC bus. IN a normal operation mode, the control part controls the bus voltage on the basis of a first measurement voltage measured in the voltage measurement part before a second point that is backed from a predetermined first point by a predetermined time. On the other hand, in a voltage rising mode that a second measurement voltage measured in the voltage measurement part at the first point becomes larger than a predetermined threshold voltage than that of the first measurement voltage, the control part controls the bus voltage on the basis of the second measurement voltage.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a grid interconnection power conversion device used in linkage with a grid.

  In recent years, a power generation system that links power supplied from a distributed power source such as a solar power generation device via a power conversion device to a system, or a combination of a distributed power source and a power storage device is used. There is an increasing demand for so-called hybrid power generation systems linked to the grid. In these power generation systems, it is desired to increase the conversion efficiency of the power conversion device from the viewpoint of maximizing the use of natural energy. For example, Patent Document 1 discloses a technique for particularly improving the efficiency of a DC / DC converter for the purpose of improving the efficiency of a grid-connected inverter device.

  Further, regarding the power generation system as described above, “system interconnection provision JFEAC 9701-2012” requires that the system satisfy the operation continuation requirement at the time of an accident (hereinafter referred to as FRT requirement). In order to satisfy this FRT requirement, the power generation system needs to be configured to continue to operate for a predetermined period even when the system voltage is instantaneously reduced (hereinafter sometimes referred to as “instantaneous reduction”). is there.

  In Patent Document 2, the target value of the DC link voltage before and after the instantaneous drop of the system voltage is changed, and the link voltage between the DC / DC converter unit and the inverter device is reduced to an amount below a predetermined threshold. Accordingly, a technique for expanding the width of the pulse signal for driving the switching element is described. Further, Patent Document 3 holds the electric energy for eliminating the instantaneous voltage drop (voltage drop) in the capacitor, and is necessary from this capacitor when the commercial power system returns to the original voltage from the voltage drop (voltage drop). Technology that supplements electrical energy is described.

JP 2005-6383 A Japanese Unexamined Patent Publication No. 2016-32396 Japanese Patent Laid-Open No. 2015-2223038

  By the way, in the grid interconnection power converter, it is preferable to perform output power tracking control in order to improve the conversion efficiency. This is because the conversion efficiency of the power conversion device can be increased if the followability to the output power can be improved while suppressing distortion of the output current. On the other hand, when the followability to the output power is improved, the operation of the power conversion device may become unstable because it tries to follow a voltage drop such as an instantaneous drop. Therefore, measures for realizing stable continuous operation are necessary.

  Regarding the improvement of conversion efficiency, as disclosed in Patent Document 1, a method of increasing the efficiency of the entire inverter device by boosting DC power with a DC / DC converter at the maximum efficiency and reversely converting it with an inverter is as follows. When the commercial system voltage increases significantly, the duty ratio of the DC / DC converter may exceed the maximum allowable value, and the output current of the inverter may be distorted.

  In view of the above problems, an object of the present invention is to solve the above-described problems and to provide a power conversion device that ensures high conversion efficiency and ensures continuous operation at a sag.

  The grid interconnection power converter according to the first aspect of the present invention includes a DC bus, an inverter that converts DC power supplied to the DC bus into AC power, a voltage measurement unit that measures system voltage, A control unit that controls the bus voltage of the DC bus, and in the normal operation mode, the control unit is measured by the voltage measurement unit before a second time point that is a predetermined time backward from a predetermined first time point. In the voltage increase mode in which the bus voltage is controlled based on the first measurement voltage, and the second measurement voltage measured by the voltage measurement unit at the first time point is higher than the first measurement voltage by a predetermined threshold voltage or more. The bus voltage is controlled based on the second measurement voltage.

  According to this aspect, in the normal operation mode, the control unit controls the bus voltage of the DC bus based on the first measurement voltage measured before the second time point. By adopting such a configuration, when there is a change in the system voltage between the second time point and the first time point, it is possible to prevent the voltage change from affecting the control of the bus voltage. Thereby, for example, even when the system voltage drops rapidly, the operation can be continued without being influenced for a while. On the other hand, in the voltage increase mode, the bus voltage is controlled based on the second measurement voltage measured at the first time point, so that it is possible to realize an output follow-up type operation that quickly follows the increase in the system voltage. Conversion efficiency can be increased. Furthermore, when the system voltage rises, it is possible to prevent the output current of the power converter from being distorted due to a shortage of the DC bus voltage.

  The first measurement voltage may be an average value of the system voltage between the second time point and a third time point that is a predetermined period back from the second time point.

  As described above, by using the average value as the first measurement voltage, the influence of the voltage change occurring before the second time point can be reduced. Further, by using the averaged data, a highly stable operation can be realized.

  In the voltage increase mode, the control unit has a difference between the control value of the bus voltage based on the first measurement voltage and the control value of the bus voltage based on the second measurement voltage is less than a predetermined threshold value. The bus voltage may be controlled in the normal operation mode.

  According to this configuration, the difference in the control value of the bus voltage when shifting from the voltage increase mode to the normal operation mode can be reduced. For example, when the power converter is connected to the grid, the operation mode The influence on the system power supply voltage due to the change can be reduced.

  A storage unit storing a table indicating a relationship between a measurement voltage measured by the voltage measurement unit and a set value of the bus voltage; and the control unit includes the first measurement voltage and the second measurement voltage. The bus voltage may be controlled based on the reference value of the table corresponding to the above.

  By the way, with respect to the system voltage (measurement voltage), the set value of the bus voltage at which the conversion efficiency is maximized is a value determined to some extent at the stage of design and manufacture of the power converter. Therefore, by using the table method as in the above configuration, an optimum bus voltage can be set without performing complicated calculations.

  In the voltage increase mode, the control unit may pass a setting signal based on the second measurement voltage through a low-pass filter and control the bus voltage by the setting signal that has passed through the low-pass filter.

  According to this configuration, even if the variation of the second measurement voltage is large, the change in the setting signal can be made gentle according to the cutoff frequency of the low-pass filter. Thereby, it can prevent that a power converter device becomes an unstable factor of a commercial power system.

  The control unit fixes the bus voltage to an initial set value for a predetermined period from the activation of the power conversion device, and gradually increases the bus voltage toward a voltage based on the first measurement voltage after a predetermined period elapses. You may make it control so that it may approach.

  In this way, by adding a so-called soft start function that gradually brings the bus voltage closer to the voltage based on the first measurement voltage, the output voltage of the inverter can be prevented from changing suddenly and stably. Can be realized.

  When the voltage measurement unit detects an instantaneous voltage drop, the control unit reduces the output current of the inverter to a current value corresponding to the measurement voltage of the voltage measurement unit, and when the instantaneous voltage drop is resolved The bus voltage may be controlled to be the initial set value.

  By adopting such a configuration, it is possible to continue the operation without stopping the inverter even during a sag.

  Since the power conversion device according to the present invention performs bus voltage control based on measurement voltages measured at different times according to the system voltage, a voltage drop such as an instantaneous drop while realizing high conversion efficiency. Stable continuous operation at the time can be realized.

It is a schematic structure figure of a hybrid power generation system concerning this embodiment. It is a control block diagram of a control circuit. It is a block diagram of a DC bus voltage command value adjustment circuit. It is a flowchart which shows operation | movement of a hybrid electric power generation system. It is the figure which showed typically the operation state of the hybrid electric power generation system at the time of starting. It is the figure which showed typically the operation state of the hybrid electric power generation system at the time of system | strain voltage fluctuation | variation at the time of normal operation. FIG. 7 is a partially enlarged view of a DC bus voltage waveform, a system voltage waveform, and an output current waveform in FIG. 6. It is a figure for demonstrating a soft start. It is a figure for demonstrating the operation | movement at the time of a sag. It is a graph which shows the conversion efficiency of the hybrid electric power generation system which concerns on this embodiment. It is a schematic block diagram which shows the other example of the hybrid electric power generation system which concerns on this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

<Configuration of hybrid power generation system>
FIG. 1 is a schematic configuration diagram of a hybrid power generation system according to the present embodiment. As shown in FIG. 1, a hybrid power generation system 1 includes a solar cell 2 as a distributed power source, a storage battery 3 that stores power output from the solar cell 2, and a grid connection that links the solar cell 2 to a commercial power system. System power converter A (hereinafter simply referred to as power converter A). Incidentally, V _PV and I _PV in Figure 1, respectively, shows the output voltage of the solar cell 2, and the output current of the solar cell 2. Also, V _B and I _B in Figure 1, respectively, shows a charge-discharge current and discharge voltage of the battery 3.

The commercial power system 9 includes a commercial system power supply 10 and a system impedance. In FIG. 1, R _G and L _G indicate a resistance component and an inductive reactance component of the system impedance. Further, Z _L and i _L in FIG. 1, the AC load connected to a commercial power system 9 side (e.g., household load) shows a load current flowing in and AC load. In addition, e _{uw in} FIG. 1 is a voltage between distribution lines connecting the hybrid power generation system 1 and the commercial power system 9 (hereinafter referred to as a commercial system voltage e _uw ).

The power conversion device A includes a DC / DC converter 4a that receives the output of the solar battery 2 and performs DC / DC (Direct Current to Direct Current) conversion, and a bidirectional DC / DC converter 4b that performs charging and discharging of the storage battery 3. (Hereinafter simply referred to as a DC / DC converter 4b), an inverter 5 for converting DC power input from at least one of the solar cell 2 and the storage battery 3 into AC power, and control circuits 7a and 7b. A DC bus voltage V _dc that is an output voltage from the DC / DC converter 4a is _supplied to the inverter 5 via a capacitor C _dc for voltage smoothing. Furthermore, the power conversion apparatus A is provided with the connected LC filter 6 and the relay S _G for system interconnection to the subsequent inverter 5. Although not shown, the power converter A is provided with a voltmeter for measuring the DC bus voltage _Vdc , and the measured value is input to the control circuits 7a and 7b. In the following description, the DC bus voltage V _dc simply includes the measured value of the DC bus voltage V _dc . Further, _{S PV} in Figure 1 shows a switching element of the DC / DC converter 4a.

In the power conversion device A, the main parts of the inverter 5 and the DC / DC converter 4b are configured by an IPM (Intelligent Power Module) 8 for a three-phase inverter. Specifically, each phase of the IPM 8 for a three-phase inverter is configured by a half bridge circuit composed of two switching elements. Then, among the output lines of the three-phase in a three phase inverter for IPM8, connected to a commercial power system 9 of single-phase two-wire output line of the u-phase and w-phase via the relay S _G for LC filter 6 and the grid interconnection The v-phase output line is connected to the storage battery 3. FIG. 1 shows an example in which the switching elements S1 to S4 are used as switching elements for the inverter 5, and the switching elements S5 and S6 are used as switching elements for the DC / DC converter 4b. Further, the DC / DC converter 4b, between the intermediate node and the storage battery switching elements S5, S6, is provided DC reactor _{L B.} Incidentally, _{R B} in FIG. 1 is an internal resistance of the DC reactor _{L B.} The capacitor C _dc also serves as a capacitor necessary for DC / DC conversion of the DC / DC converter 4b. Further, e _inv and i _inv in FIG. 1 indicate the output voltage and output current of the inverter 5, respectively.

LC filter 6 is constituted by a pair of AC reactor L _i provided on the output line of the u-phase and w-phase, a capacitor C _i, which is connected between both output lines, harmonic component from the output of the inverter 5 ( Mainly, the carrier frequency of the PWM signal is removed. R _i and R _c in the figure indicate the internal resistance of the AC reactor L _{i and} the internal resistance of the capacitor C _i , respectively. In FIG. 1, i _c indicates a current flowing through the capacitor C _i (capacitor passing current), and i _sp indicates an output current output from the LC filter 6.

  The control circuits 7a and 7b are configured using, for example, a microcomputer, and mainly control the DC / DC converters 4a and 4b and the inverter 5.

The control circuit 7a in order to take full advantage of the power generated from the solar battery 2, based on power consumption information of the generated power and the AC load Z _L from the solar cell 2 through the DC / DC converter 4b Charge / discharge control of the storage battery 3 is performed. The control circuit 7 a includes the aforementioned DC bus voltage V _dc , the output current i _inv of the inverter 5, the load current i _L , the commercial system voltage e _uw , the output voltage e _inv of the inverter 5, the charge / discharge current I _B of the storage battery 3, and measurements of the voltage V _B of the battery 3 is provided as an input signal. In the following description of the control circuit 7a, there is a case where the description of the measured value is omitted with respect to each of the measured voltage and the measured current. Furthermore, the control circuit 7a, interruption control signal of the driving control signal, and a system interconnection relay S _G of the switching elements S1~S6 are output.

The control circuit 7b performs maximum power point tracking control (hereinafter referred to as MPPT (Maximum Power Point Tracking) control) of the solar cell 2 so that the output power from the solar cell 2 becomes maximum (optimum). Specifically, the input voltage from the solar cell 2 is adjusted by controlling the DC / DC converter 4a. In addition, when the commercial system voltage e _uw suddenly decreases (for example, during a momentary drop), the control circuit 7b determines that the absolute value of the output current of the active component from the inverter 5 is within the range of the output current limiter value I _lim . The DC / DC converter 4a is controlled so as to be suppressed within. Specifically, when the commercial system voltage e _uw suddenly drops, the control circuit 7b starts from the MPPT control in a CV (Constant Voltage) mode in which the DC output voltage of the DC / DC converter 4a is raised or lowered within a certain range. Switch to control (hereinafter referred to as CV mode control). The control circuit 7b, the DC bus voltage _{V dc,} the output voltage _{V PV} solar cell 2, and has an output current _{I PV} solar cell 2 is provided as an input signal, the switching element _{S PV} of the DC / DC converter 4a Output a control signal.

-Control circuit configuration-
FIG. 2 shows a control block diagram of the control circuit 7a. In FIG. 2, control blocks mainly related to constant control of the DC bus voltage V _dc (control to make the value of the DC bus voltage Vdc constant), reactive power control, and output current control of the inverter 5. Is shown.

In FIG. 2, a DC bus voltage control circuit 11 is a circuit that controls the value of the DC bus voltage V _dc to be constant. DC bus voltage control circuit 11, based on the difference between the feedback value of the DC bus voltage V _dc and (measurement), and the DC bus voltage command value V ^* _dc is a command value of the DC bus voltage V _dc, the inverter 5 The active current command value I ^* _p , which is the control target value of the output current of the active component of, is calculated and output to the output current limiter circuit 19 at the subsequent stage.

The output current limiter circuit 19 is based on a coefficient FRT _ratio obtained by an output current adjustment circuit 18 to be described later, an output current limiting command value I ^* _{lim, and the} like. I _lim is calculated. Then, the output current limiter circuit 19 outputs an effective component from the inverter 5 so that the absolute value of the effective current command value I ^* _p output from the DC bus voltage control circuit 11 does not exceed the output current limiter value I _lim. It has a function of suppressing current. Specifically, the limited effective current command value I ^* _p1 is output to the effective component generation circuit 12 at the subsequent stage.

When the remaining voltage of the commercial system voltage e _uw becomes 0% at the time of a momentary _drop or the like, the output current limiter circuit 19 is from when the state is detected until the commercial system voltage e _uw recovers, One of the following operations (1) and (2) is selected. (1) is an operation in which the limited effective current command value I ^* _p1 output to the active component generation circuit 12 is set to zero, the output current control of the inverter 5 is continued, and the operation of the inverter 5 is continued. (2) Is an operation of outputting a gate block signal to a PWM output control circuit 21 to be described later and stopping the inverter 5.

The effective component generation circuit 12 has a sine value sin (θ _uw ) of the phase angle θ _uw of the commercial system voltage e _uw output from the PLL _v 15 and the limited effective current command value I ^* _p1 received from the output current limiter circuit 19. Are multiplied to generate an instantaneous value of the current command value of the active component. Here, the PLL _v 15 is a circuit that receives the commercial system voltage e _uw as an input signal and generates a voltage signal synchronized with the phase angle θ _uw of the commercial system voltage e _uw . Specifically, by calculating the phase angle theta _uw and period _{T uw} of the commercial system voltage _{e uw,} and outputs. The period T _uw is supplied to an output voltage detection circuit 16 described later.

The invalid component generation circuit 14 multiplies the output value from the reactive current control circuit 13 by the cosine value cos (θ _uw ) of the phase angle θ _uw of the commercial system voltage e _uw output from the PLL _v 15 to be invalid. An instantaneous value of the current command value of the component is generated. Then, the output value from the effective component generation circuit 12 and the output value from the invalid component generation circuit 14 are added at the addition point SP1 to obtain the output current command value i ^* _{inv of} the inverter 5. This output current command value i ^* _inv is sent to the output current control circuit 20.

Here, the reactive current control circuit 13 includes a reactive component output current feedback value I _q output from the inverter 5, a reactive current command value I ^* _q that is a command value of the reactive component output current from the inverter 5, and Is a circuit that performs feedback control so that the output current of the reactive component from the inverter 5 becomes equal to the reactive current command value I ^* _q . In FIG. 2, PLL _i 22 is a circuit that generates a voltage signal synchronized with the phase angle θ _sp of the output current i _sp of the LC filter 6. The output current i _sp can be obtained by the following equation (1).

Further, the phase angle θ _uw output from the PLL _v 15 and the phase angle θ _sp output from the PLL _i 22 are subtracted at the subtraction point SP2 to generate a feedback value as a phase difference Δφ (θ _uw −θ _sp ). Supplied to the unit 23. The feedback value generation unit 23 is a circuit that obtains a tangent value tan (Δφ) from the phase difference Δφ. The multiplier 24 multiplies the tangent value tan (Δφ) of the phase difference Δφ by (2P _uw / E _uwm ) to obtain the feedback value I _q of the output current of the reactive component, and thereby the reactive current control circuit 13. The circuit that outputs to Note that P _uw used in this calculation is the effective output power of the hybrid power generation system 1, and E _uwm is the maximum value (amplitude value) of the commercial system voltage e _uw .

In the normal operation mode, which is an operation mode when normal power is supplied from the commercial power system 9, the output current control circuit 20 sets the output current i _inv value of the inverter 5 to the output current command value i ^* _inv . Feedback control based on the output current i _inv and the DC bus voltage V _dc is performed so as to follow, and the output duty ratio d _inv of the inverter 5 is calculated. This duty ratio d _inv is supplied to the PWM output control circuit 21.

Based on the output duty ratio d _inv received from the output current control circuit 20, the PWM output control circuit 21 generates a PWM signal having a pulse width corresponding to the output duty ratio d _inv . Based on the PWM signal, the switches SW1, SW2, SW3, SW4 of the inverter 5 are driven and controlled.

  Next, a circuit related to processing related to the operation continuation operation at the time of an accident (hereinafter referred to as FRT mode) at the time of a momentary drop in FIG. 2 will be described.

The output voltage detection circuit 16 acquires the commercial system voltage e _uw and outputs the amplitude value as the second measurement voltage E _uwm . E _uwm can be obtained by the following equation (2).

Further, the output voltage detection circuit 16 obtains the first measurement voltage E _uwa based on the following equation (3). In addition, z in Formula (3) is a sampling period for every half cycle.

In the above formula (3), x and y are measured values at the time point (corresponding to between the second time point and the third time point) that is the number of cycles back from the current time point (corresponding to the predetermined first time point). It is a positive integer indicating whether it is adopted as the measurement voltage, and is a value that can be arbitrarily set. The value satisfies the relationship y> x. For example, x and y can be determined based on the viewpoint of setting values that satisfy the FRT requirement. Specifically, the first measured voltage E _uwa shown in the equation (3) is based on the current time point (corresponding to the first time point) as the starting point before the y cycle (corresponding to the third time point) to the previous x cycle (at the second time point). The average value of the second measurement voltage E _um is shown in FIG. In other words, even if there is a change in the commercial system voltage e _uw between x cycles before and the present time, this change does not affect the value of the first measurement voltage E _uwa . Then, for example, by setting the time from x cycles before to the present time to a time that satisfies the FRT requirement (for example, 1 second) or more, even when a sag occurs, at least the time that satisfies the FRT requirement does not change. A measurement voltage (first measurement voltage E _uwa ) can be acquired.

The commercial voltage amplitude instantaneous value detection circuit 28 obtains an instantaneous value (hereinafter, referred to as “amplitude instantaneous value”) E _max of the commercial system voltage e _uw based on the commercial system voltage e _uw .

The voltage sag recovery detection circuit 17 _{generates a} voltage _{sag based on} the second measured voltage E _um received from the output voltage detection circuit 16 and the amplitude instantaneous value E _max received from the commercial voltage amplitude instantaneous value detection circuit 28. It is determined whether or not. For example, when the amplitude instantaneous value _Emax becomes less than a predetermined voltage sag determination voltage E _FRT , it is determined that a voltage sag has occurred. Furthermore, low restoration detection circuit 17 voltage instant, based on the second measurement voltage E _uwm and instantaneous amplitude E _max, that commercial system voltage e _uw has returned to instantaneous low to normal voltage value (normal operation mode) To detect. Note that the instantaneous drop determination voltage _EFRT is stored in advance in, for example, a memory (not shown) or the like mounted in the control circuits 7a and 7b or in the vicinity thereof.

The output current adjusting circuit 18 calculates a coefficient FRT _ratio and outputs the coefficient FRT _ratio to the output current limiter circuit 19 when a voltage sag is detected by the voltage sag return detection circuit 17. As a result, the output current value from the inverter 5 decreases to an output current value corresponding to the magnitude of the second measurement voltage E _uwm . The coefficient FRT _ratio is an adjustment coefficient for reducing the output current from the inverter 5 (decreasing the output current value) at the time of a sag (in the FRT mode).

  The charge / discharge stop instruction circuit 27 performs DC / DC on the charge / discharge power control circuit (not shown) when the voltage instantaneous drop recovery detection circuit 17 detects that the commercial power system 9 is in the instantaneous drop state. It is instructed not to charge / discharge the storage battery 3 by the converter 4b.

  FIG. 3 is a block diagram showing an example of the DC bus voltage command value adjustment circuit 26.

The DC bus voltage command value adjustment circuit 26 includes a changeover switch SW _Vdc having three inputs (SW0, SW1, SW2). Further, the DC bus voltage command value adjustment circuit 26 outputs, as input signals, a DC bus command reference value (hereinafter referred to as a reference command value V ^* _dc0 ) and an output voltage detection circuit 16 (see FIG. 2). The second measurement voltage E _uwm and the first measurement voltage E _uwa are input. Here, the reference command value V ^* _dc0 is arbitrarily set in advance based on the rated voltage or the like of the commercial power system 9, and is stored in, for example, a memory (not shown) or the like mounted on the control circuits 7a and 7b or the periphery thereof. Has been.

The reference command value V ^* _dc0 is supplied to the input terminal SW0 of the DC bus voltage command value adjustment circuit 26. The reference value of the lookup table LUT based on the first measurement voltage _Euwa is _supplied to the input terminal SW1 as the first DC bus voltage command value V ^* _dc1 . Similarly, the reference value of the lookup table LUT based on the second measurement voltage E _um is _supplied to the input terminal SW2 as the second DC bus voltage command value V ^* _dc2 via the low-pass filter LPF. As described above, by providing the low-pass filter LPF (cutoff frequency: fc), the second DC bus voltage command value V ^* _{dc2 is set} to the cut-off frequency fc even when the variation of the second measurement voltage E _um is large. It can be a gradual change. Thereby, it can prevent that the power converter device A becomes an unstable factor of the commercial power grid | system 9. FIG. Note that the cutoff frequency fc of the low-pass filter can be arbitrarily set.

Here, the lookup table LUT is a table in which the optimum DC bus voltage command value V ^* _dc is associated with the first measurement voltage E _uwa and the second measurement voltage E _uwm . For example, the lookup table LUT is created based on data measured in advance, simulation data, or the like, and is stored in advance in the control circuits 7a and 7b or a memory (not shown) mounted on the periphery thereof. Note that the lookup table LUT stored in the memory (for example, EPROM) may be configured to be rewritable from the outside of the power converter A.

<Operation of hybrid power generation system>
Next, the operation of the hybrid power generation system 1 will be specifically described with reference to FIGS. 4 to 9. FIG. 4 is a flowchart showing the operation of the hybrid power generation system 1. FIG. 5 is a diagram schematically showing the operating state of the hybrid power generation system 1 at the time of startup. FIG. 6 is a diagram schematically showing the operating state of the hybrid power generation system when the system voltage fluctuates during normal operation. 5 and 6, in order to facilitate the understanding of the invention, the portion that is the point of the invention and its peripheral portion are described exaggerated rather than actual voltage and current changes, or conversely weak. In some cases, voltage and current fluctuations are omitted. The same applies to FIG. 9 described later. In the following description of the operation, although not specified, it is assumed that the DC / DC converter 4a performs MPPT control of the solar cell 2.

-1. Normal operation (from startup to normal operation mode)-
First, the operation from the start of the hybrid power generation system 1 to the transition to the normal operation mode will be described.

  In step S10 of FIG. 4, when the hybrid power generation system 1 is activated, the soft start function is executed.

  A specific soft start will be described with reference to FIG.

First, when the hybrid power generation system 1 is activated, the control circuit 7a compares the DC bus voltage V _dc with the reference command value V ^* _dc0 . Then, as shown in (i) of FIG. 8, when the DC bus voltage V _dc at the time of start-up is higher than the reference command value V ^* _dc0 , the control circuit 7a performs soft start of the step-down operation. Specifically, the control circuit 7a (the DC bus voltage command value adjusting circuit 26) uses a DC bus voltage immediately after startup as a DC bus voltage command value V ^* _dc (hereinafter referred to as an initial command value V ^* _dcs ) immediately after startup. The bus voltage V _dc (a value greater than the reference command value V ^* _dc0 ) is used. Thereafter, the control circuit 7a causes the DC bus voltage command value adjustment circuit 26 and the DC bus voltage control circuit 11 to gradually _change the DC bus voltage command value V ^* _dc from the initial command value V ^* _dcs to the reference command value V ^* _dc0 . Control to get closer. The speed at which the initial command value V ^* _dcs approaches the reference command value V ^* _dc0 is determined based on a predetermined soft start time T _soft . The soft start time T _soft may be arbitrarily set based on a viewpoint that enables the hybrid power generation system 1 to be started smoothly and speedily. The same _applies when the DC bus voltage V _dc (initial command value V ^* _dcs ) at _startup is lower than the reference command value V ^* _dc0 . That is, as indicated by (ii) in FIG. 8, the control circuit 7a uses the DC bus voltage V _dc immediately after startup as the initial command value V ^* _dcs , and the DC bus voltage command value V ^* _dc is initial. Control is performed so that the command value V ^* _dcs gradually approaches the reference command value V ^* _dc0 . By adopting such a configuration, the difference between the value of the DC bus voltage V _dc and the DC bus voltage command value V ^* _dc can be reduced, and an increase in fluctuation of the output current i _sp can be prevented. . Furthermore, even when the step-up ratio of DC / DC converters 4a and 4b (step-up ratio for increasing DC bus voltage _Vdc by charging electrolytic capacitor _Cdc ) is low, hybrid power generation system 1 can be started. become. In FIG. 5, the period from time T10 to time T11 corresponds to the soft start period, and an example in which the soft start of the step-down operation is performed is shown as in (i) of FIG.

Returning to FIG. 4, when the soft start in step S11 is completed, the reference command value V ^* _dc0 value is set as the DC bus voltage command value V ^* _dc . At this time, the changeover switch SW _Vdc of the DC bus voltage command value adjustment circuit 26 is set to SW0. Thereby, the DC / DC converters 4a and 4b operate based on the reference command value V ^* _dc0 value. Specifically, the DC / DC converters 4a and 4b operate under control of the control circuit 7a so that the DC bus voltage V _dc becomes a voltage value corresponding to the reference command value V ^* _dc0 .

When the predetermined time TP1 elapses after setting the reference command value V ^* _dc0 in step S11, the flow proceeds to step S12, and the changeover switch SW _{Vdc of} the DC bus voltage command value adjustment circuit 26 is switched from SW0 to SW1 (FIG. 5 time T12). Here, the time T _s1 from the start to the time when the changeover switch SW _Vdc is switched to SW1 is given by the following equation, and is about several seconds, for example.

The predetermined time TP1 is preferably set longer than the time Ty required for the y cycle period. However, the predetermined time TP1 may be set shorter than the time Ty. In this case, for example, as an expression used for setting the first DC bus voltage command value V ^* _dc1 until the time Ty elapses, an expression that can calculate the set value in a time shorter than the expression (3) is adopted. That's fine.

By switching the switch SW _Vdc , the DC bus voltage command value adjustment circuit 26 outputs the first DC bus voltage command value V ^* _dc1 set based on the first measurement voltage E _uwa described above. (See FIG. 3). More specifically, in step S12, the reference value of the lookup table LUT based on the first measured voltage E _uwa is set as the first DC bus voltage command value V ^* _dc1 (see FIG. 5).

As described above, in the normal operation mode, as the first DC bus voltage command value V ^* _dc1 , “from the current cycle (corresponding to the first time point) to the start of the y cycle (corresponding to the third time point) to the previous x cycle (first time). The value selected based on the first measurement voltage E _uwa (refer to the equation (3)), which is the average value of the second measurement voltage E _uwm up to two time points) is used. As a result, during the period in which the changeover switch SW _Vdc is set to SW1, even if there is a change in the commercial system voltage between x cycles before and the present time, the setting of the DC bus voltage command value V ^* _dc is set. Can be prevented from being affected.

Note that, at time TP2 shown in FIG. 5, the output current i _sp is constant even though the DC bus voltage V _dc is decreasing, because the commercial system voltage e _uw is constant and the power converter A This is because the output power from is also constant. Further, as the DC bus voltage command value V ^* _dc is closer to the system voltage amplitude value e _uw , the upper and lower values of the duty ratio d _inv calculated in the output current control circuit 20 are closer to ± 1, and the inverter 5 Since the switching loss in the vicinity of the pick value of the output current i _inv is reduced, an improvement in conversion efficiency can be expected.

-2. Operation at the time of commercial system voltage drop (Amplitude instantaneous value E _max = Voltage drop judgment voltage E _FRT or more) −
Next, the operation when the commercial system voltage e _uw drops will be described with reference to FIGS. 4 and 6. In FIG. 6, it is assumed that the period TP1 up to time T21 is operating in the normal operation mode. That is, the commercial system voltage e _uw is constant, the changeover switch SW _{Vdc of} the DC bus voltage command value adjustment circuit 26 is set to SW1, and the first DC bus voltage command value V ^* _dc1 is set as the DC bus voltage command value V ^* _{dc .} Is set. Thereafter, the grid voltage _{e uw} is lowered from the time T21 toward T22, the grid voltage _{e uw} time T22 is assumed to be held until a time T26. Here, it is assumed that the instantaneous amplitude value E _max based on the commercial system voltage e _uw after the decrease is equal to or higher than the instantaneous drop determination voltage E _FRT .

In the period TP2 between T21 and T22 in FIG. 6, when the commercial system voltage e _uw decreases, the second measured voltage E _uwm decreases accordingly, and the second DC bus voltage command value V ^* _dc2 also decreases accordingly. On the other hand, the value of the output current i _sp is increasing. This is because the input power and output power of the inverter 5 are equal.

In the period TP3 between T21 and T23 in FIG. 6, the first measurement voltage E _uwa and the first DC bus voltage command value V ^* _dc1 are maintained up to the time T21. That is, when the commercial system voltage e _uw drops, a period is set in which the DC bus voltage command value V ^* _dc does not follow the change. Specifically, since the value of the first measurement voltage E _uwa based on the equation (2) does not change from the time T21 until the time corresponding to the x cycle elapses (see time TP2 in FIG. 5), The value of 1 DC bus voltage command value V ^* _dc1 is also not changed.

When a time corresponding to x cycles elapses from time T21, that is, when time T23 is _reached , the value of the first measurement voltage _Euwa gradually decreases, and the value of the first DC bus voltage command value V ^* _dc1 is accordingly increased. Decrease gradually.

Thus, in the present embodiment, the predetermined time period from the descent of the grid voltage e _uw is so as to control the DC bus voltage based on the past commercial system voltage e _{uw (first} measurement voltage E _UWA) Yes. That is, the inverter 5 is continuously operated without changing the DC bus voltage command value V ^* _dc according to the drop in the commercial system voltage _euw . As a result, continuous operation can be performed even when a short sag occurs and then returns immediately, or when intermittent sag occurs. The reason for such control is that if a drop in the commercial system voltage e _uw occurs, even if the DC bus voltage command value V ^* _dc is not changed, the commercial power system 9 It is because there is little possibility of making it unstable.

-3. Operation when the commercial system voltage rises-
Next, the operation when the commercial system voltage e _uw increases will be described with reference to FIGS. 4 and 6. 6 shows an example increases the commercial system voltage _{e uw} from the time T25 toward time T27, time T27 after which the commercial system voltage _{e uw} held at a constant voltage.

In the period TP4 from time T25 to time T28 in FIG. 6, when the commercial system voltage e _uw increases, the DC bus voltage command value V ^* _dc quickly follows the increase. The reason for promptly following the reason is that if the follow-up is delayed, the output current _isp is distorted due to a shortage of the DC bus voltage.

  This will be specifically described below.

When the commercial system voltage e _uw increases from time T25 to time T26 in FIG. 6, the second measurement voltage E _uwm and the second DC bus voltage command value V ^* _dc2 increase. At this time, the first measurement voltage E _uwa and the first DC bus voltage command value V ^* _dc1 hold the values so far. Therefore, the difference between the second measurement voltage E _uum and the first measurement voltage E _uwa gradually _increases . Between time T25 and time T26, the difference between the second measurement voltage E _uwm and the first measurement voltage E _uwa is less than or equal to a predetermined threshold voltage V _th1 (NO in step S13 in FIG. 4), so the DC bus voltage command value As V ^* _dc , the first DC bus voltage command value V ^* _dc1 is continuously set. The predetermined threshold voltage V _th1 is a value that can be arbitrarily set.

At time T26, when the difference between the second measurement voltage E _uum and the first measurement voltage E _uwa exceeds the threshold voltage V _th1 , a YES determination is made in step S13, and the flow proceeds to step S15. In step S15 (corresponding to the voltage increase mode), the control circuit 7a switches the changeover switch SW _Vdc from SW1 to SW2. As a result, the second DC bus voltage command value V ^* _dc2 is set as the DC bus voltage command value V ^* _dc . Since the second DC bus voltage command value V ^* _dc2 is set based on the second measured voltage E _uwm , the second DC bus voltage command value V ^* _dc2 increases according to the change in the commercial system voltage e _uw . As a result, the DC bus voltage command value V ^* _dc rises rapidly in response to changes in the commercial system voltage e _uw as compared to when the commercial system voltage e _uw drops. Thereby, output power followability can be improved.

Thus, in this embodiment, when the commercial system voltage e _uw increases, the output power follow-up property can be improved. Such control can prevent the output current _isp of the power converter A from being distorted.

  This point will be described more specifically below.

In the power converter A, the duty ratio d _{inv at} the output of the inverter 5 is operated in the range from −1 to 1, so that the switching loss can be reduced and the conversion efficiency can be improved. Specifically, as shown in the following formula (5), the output duty ratio d _inv of the inverter 5 is determined based on the ratio between the second measurement voltage E _uwm and the minimum value V _dcmin of the DC bus voltage V _dc. The As also shown in the following equation (5), the minimum value V _dcmin of the DC bus voltage V _dc is determined based on the sum of the second measurement voltage E _uwm and the voltage drop ΔE _inv of the AC reactor. .

In such a control form, when the commercial system voltage e _uw rises and the rise of the DC bus voltage command value V ^* _dc is slow, the output duty ratio d _{inv of the} inverter 5 expressed by the above equation (5) becomes ± It is conceivable that the waveform of the output current i _sp of the inverter is distorted due to the shortage of the DC bus voltage V _dc . On the other hand, as in the present embodiment, when the commercial system voltage e _uw increases, the waveform of the output current due to the shortage of the DC bus voltage V _dc is increased by quickly increasing the DC bus voltage command value V ^* _dc. Can prevent distortion.

Thereafter, when the increase of the commercial system voltage e _uw stops and becomes a constant voltage, and the difference between the second measurement voltage E _uwm and the first measurement voltage E _uwa becomes less than the predetermined threshold voltage V _th2 , a YES determination is made in step S16, The flow returns to step S12. Then, the control circuit 7a switches the changeover switch SW _Vdc from SW2 to SW1. As a result, the first DC bus voltage command value V ^* _dc1 is set as the DC bus voltage command value V ^* _dc .

FIG. 7 shows the DC bus voltage waveform (V _dc ), the system voltage waveform (e _uw ), and the output current waveform (i _sp ) of the power converter A in the period TP4. In Figure 7, the increase in the commercial system voltage e _uw, distortion of the output current i _sp due to lack of DC bus voltage is generated, after the peak value of the output current drops, are temporarily increased. However, after that, it can be seen that the DC bus voltage V _dc is stabilized in a short period of time, and the output current i _sp is also stabilized promptly. Note that the output current _isp is constant between the period TP3 and the period TP4 even though the DC bus voltage command value V ^* _dc is decreasing, because the commercial system voltage e _uw is constant. This is because the output power from the power converter A is also constant.

  Since the subsequent operation is the same as that described above, a detailed description thereof is omitted here.

In this way, by returning the changeover switch SW _Vdc to SW1 based on the difference between the second measurement voltage E _uwm and the first measurement voltage E _uwa , the inverter 5 again, regardless of the change in the commercial system voltage e _uw. Can be returned to the normal operation mode in which the operation can be continued. Further, since the adjusting the switching timing of the switch _{SW Vdc} with the threshold voltage _{V th2,} it is possible to reduce the influence on the system power supply voltage _{e uw} by the configuration change of the switch _{SW Vdc.}

-4. Operation during voltage sag (instantaneous amplitude value E _max = voltage sag determination voltage E less than _FRT ) −
Next, the operation in the case where the instantaneous drop occurs will be described with reference to FIG. FIG. 9 shows a case in which a sag occurs from the normal state, the sag continues for a while, and then returns to the normal state.

In this case, the control circuit 7a sets the output current i _inv of the inverter 5 within one cycle after the instantaneous amplitude value E _max becomes equal to or less than the threshold value for threshold voltage E _FRT (hereinafter referred to as the instantaneous voltage drop state). Perform processing to narrow down. Specifically, processing for decreasing the effective current command value I ^* _p is performed within one cycle after the instantaneous drop state. When the instantaneous amplitude _{E max} is restored from the state instantaneous drop determination threshold _{E FRT} in a high state or Delta] E _FRT than sag determination threshold _{E FRT,} the control circuit 7a, within one cycle from the return, Start the aforementioned soft start.

  The operation related to the above-described instantaneous drop will be described in detail with reference to FIG.

First, in the state operating in the normal operation mode (step S12) or in the state operating in the voltage increase mode (step S15), when an instantaneous drop occurs, that is, the instantaneous amplitude value E _max is used for determining the instantaneous drop. When the threshold value E _FRT or less is reached, step S14 is YES, and the flow proceeds to step S17. In FIG. 4, an arrow for transition of the flow from step S15 to step S14 is omitted.

In step S17, the control circuit 7a switches the control of the DC / DC converter 4a from MPPT control to CV mode control. In the CV mode control, as described above, the control circuit 7a performs a process of reducing the output current i _inv from the inverter 5 and controls the DC bus voltage V _dc so as to rise only to a certain threshold value.

When the instantaneous amplitude _{E max} returns from the state instantaneous drop determination threshold _{E FRT} in a high state or Delta] E _FRT than sag determination threshold _{E FRT,} the flow proceeds to S10, the soft-start is executed. In this soft start, the restored DC bus voltage V _dc is given as the DC bus voltage command value V ^* _dc , and the soft start is executed from that voltage. The soft start time T _{FRT at} this time is preferably set to a time shorter than the soft start time T _soft at the time of activation. By doing so, quick start-up from an instantaneous drop is realized. The basic soft-start operation is the same as that at the time of activation (description of FIG. 8), and detailed description thereof is omitted here.

Further, the upper part of FIG. 9 shows a change state of the setting of the changeover switch SW _Vdc of the DC bus voltage command value adjusting circuit 26 in this series of flows. Similarly to the above-mentioned “2. Operation at the time of system voltage drop”, the DC bus voltage command value V ^* _dc (first DC bus voltage command value) is applied for a predetermined period from the time of system voltage drop (here, when a voltage sag occurs). V ^* _dc1 ) does not change. On the other hand, the DC bus voltage V _dc increases as the amplitude instantaneous value E _max increases, and the soft start is started from a voltage in which the increase is taken into account.

Since the switch is operated in the CV mode during the sag period, the change-over switch SW _Vdc may be either SW0 or SW1. However, since it is necessary that the changeover switch SW _Vdc is set to SW0 at the time of soft start, in FIG. 9, when the process of lowering the active current command value I ^* _p is performed, the changeover switch SW _{Vdc is changed} to SW0. ing.

  By performing the processing as described above, it is possible to continue the operation of the power conversion device A even during a sag, and to prevent the power conversion device A from becoming an unstable factor of the commercial power system 9.

  FIG. 10 is a graph showing the conversion efficiency between the case where the DC bus voltage is fixed (described as DC bus voltage fixed in FIG. 10) and the configuration according to the present embodiment (described as variable DC bus voltage in FIG. 10). It is a thing. As shown in FIG. 10, the configuration according to the present embodiment can achieve high conversion efficiency compared to the case where the DC bus voltage is fixed. In particular, high conversion efficiency can be realized in a portion where the nominal voltage of the commercial power system is low, as compared with the DC bus voltage fixed control.

  The preferred embodiments of the present invention and the modifications thereof have been described above, but the technology according to the present disclosure is not limited thereto, and can be applied to embodiments that have been appropriately changed, replaced, and the like. Moreover, it is also possible to combine each component demonstrated by the said embodiment into a new embodiment.

For example, in the above embodiment, the DC bus voltage command value V ^* _dc is determined with reference to the lookup table LUT based on the first measurement voltage E _uwa and the second measurement voltage E _uwm . However, the present invention is not limited to this. Not. For example, the control circuit 7a may be provided with calculation means for calculating the DC bus voltage command value V ^* _dc .

  For example, although the hybrid electric power generation system 1 demonstrated the example provided with the storage battery 3 in the said embodiment, the storage battery 3 does not need to be. FIG. 11 shows an example in which the storage battery 3 is omitted. Also in the case of FIG. 11, it is possible to operate in the same manner as in the above-described embodiment, and it is possible to obtain the same operational effects. Moreover, in the said embodiment, although the solar cell 2 as a distributed power supply was illustrated, the distributed power supply is not limited to a solar cell, Other distributed power sources, such as a wind power generation, may be sufficient.

For example, in the above embodiment, the first measurement voltage E _uwa is calculated by using the average value of the second measurement voltage E _uwm from the y cycle before to the x cycle before the current time as a starting point, but this is not _limitative. not using x cycle previous value _E uwm (z-x), may be replaced with the value of the first measuring voltage _{E UWA,} with x cycle previous value _E uwm (z-x) The value passing through the low-pass filter may be replaced with the value of the first measurement voltage _Euwa through the low-pass filter.

In the above embodiment, the second DC bus voltage command value V ^* _dc2 is cut off even when the variation of the second measurement voltage E _ewm is large by interposing the low-pass filter LPF (cutoff frequency: fc). Although it is possible to make a gradual change according to the frequency fc, the present invention is not limited to this, and a low-pass filter may not be used due to control software limitations.

FIG. 5, FIG. 6, FIG. 8 and FIG. 9 describing the above embodiment are schematic diagrams showing waveforms obtained by removing the 2f component and the like in the DC bus voltage V _dc , and show the actual DC bus voltage V _dc . As shown in FIG. 7, the waveform includes a 2f component.

  INDUSTRIAL APPLICABILITY The present invention realizes high conversion efficiency operation and continuous operation at an instantaneous drop in the power conversion device, which is extremely useful.

A Power converter 5 Inverter 7a Control circuit (control unit)
16 Output voltage detection circuit (voltage measurement unit)
E _uwa first measurement voltage E _uwm second measurement voltage V _dc DC bus voltage (bus voltage)

Claims (7)

A power conversion device for grid connection used in connection with the grid,
DC bus,
An inverter that converts DC power supplied to the DC bus into AC power;
A voltage measurement unit for measuring the system voltage;
A controller for controlling the bus voltage of the DC bus,
The controller is
In the normal operation mode, the bus voltage is controlled based on the first measurement voltage measured by the voltage measurement unit before the second time point that is back by a predetermined time from the predetermined first time point.
In the voltage rising mode in which the second measurement voltage measured by the voltage measurement unit at the first time point is higher than the first measurement voltage by a predetermined threshold voltage or more, the bus voltage is controlled based on the second measurement voltage. A power conversion device for system interconnection characterized by that. In the grid connection power converter according to claim 1,
The first measurement voltage is an average value of the grid voltage between the second time point and a third time point that is a predetermined period after the second time point. . In the grid connection power converter according to claim 1,
In the voltage increase mode, the control unit has a difference between the control value of the bus voltage based on the first measurement voltage and the control value of the bus voltage based on the second measurement voltage is less than a predetermined threshold value. When this is the case, the power conversion device for grid connection is characterized in that the control of the bus voltage is set to the normal operation mode. In the grid connection power converter according to claim 1,
A storage unit storing a table indicating a relationship between the measurement voltage measured by the voltage measurement unit and the set value of the bus voltage;
The said control part controls the said bus voltage based on the reference value of the said table according to a said 1st measured voltage and a said 2nd measured voltage, The grid connection power converter device characterized by the above-mentioned. In the grid connection power converter according to claim 1,
In the voltage increase mode, the control unit passes a setting signal based on the second measurement voltage through a low-pass filter, and controls the bus voltage by the setting signal that has passed through the low-pass filter. System power converter. In the grid connection power converter according to claim 1,
The control unit fixes the bus voltage to an initial set value for a predetermined period from the activation of the power conversion device, and gradually increases the bus voltage toward a voltage based on the first measurement voltage after a predetermined period elapses. The power converter for grid connection is controlled so as to be close to In the grid connection power converter according to claim 6,
When the voltage measurement unit detects an instantaneous voltage drop, the control unit reduces the output current of the inverter to a current value corresponding to the measurement voltage of the voltage measurement unit, and when the instantaneous voltage drop is resolved A power interconnection device for grid connection is controlled so that the bus voltage is equal to the initial set value.

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