JP2016144239A - Power conversion device and photovoltaic power generation system of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve operational continuity even in the case where voltage of AC system drops to 0% in a power conversion device which outputs power generated by a photovoltaic power generation panel to the AC system.SOLUTION: A power conversion device 1 which outputs power generated by a photovoltaic power generation panel 2 to an AC system, comprises: generated power control power converter 11 which controls generated power of a photovoltaic power generation panel to output DC power; a smoothing capacitor 14 connected to a DC power output side of the generated power control power converter; system connection power converter 13 which converts DC power to AC power to output the AC power; a voltage detector which detects a voltage magnitude of an AC system; and a control part 100 which turns off semiconductor switching elements 11m, 11n of the generated power control power converter when the voltage magnitude of the AC system sinks below a first criterion for determining and cancels turning-off of the semiconductor switching elements of the generated power control power converter when the voltage magnitude of the AC system exceeds the first criterion for determining.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device and a photovoltaic power generation system.

  In recent years, the introduction of a distributed power system such as a solar power generation system has been advanced. In an AC system to which many distributed power supplies are connected, if the distributed power system is disconnected when the system voltage drops, the power supply disappears, causing a further system voltage drop, which may cause a large-scale power outage. For this reason, the distributed power source is required to continue operation even when the system voltage drops.

  There are two types of power converters used in the solar power generation system, with a power converter for generating power control as a chopper and without a power converter for controlling generated power. In the case of a power converter without a power converter for power generation control, the power conversion efficiency is high because the input power from the photovoltaic power generation panel can be directly input to the grid-connected power converter, but the operation of the power converter The voltage range is narrower than that with a power converter for generating power control, and the input voltage cannot be output to the AC system unless the input voltage is equal to or higher than the predetermined minimum input voltage of the grid interconnection power converter.

  On the other hand, in the case of a power conversion device with a power converter for generated power control, the power conversion efficiency is inferior to that without a power converter for generated power control, but the operating voltage range of the power converter is a power converter for generated power control. There is an advantage that it is wider than the case without it.

  In a photovoltaic power generation system that uses a boost chopper as a power converter for generated power control, the DC voltage is boosted so that the generated power from the photovoltaic power generation panel is maximized, and the output of the power converter for sequential generated power control The power is being adjusted. The DC power that is the output of the power converter for generated power control is input to the grid interconnection power converter, and AC power is output according to the AC grid voltage.

  In general, the output current of the grid-connected power converter to the AC system is limited to a rated current or less. In this case, when the system voltage decreases, the maximum output power that is the product of the AC system voltage and the output current of the system interconnection power converter also decreases. At this time, if the output power of the power converter for generating power control that controls the output power of the photovoltaic power generation panel exceeds the output power of the grid-connected power converter that outputs power to the AC system, two power conversions There is a possibility that the power of the power converter for generated power control that exceeds the power that can be output to the AC system flows into the smoothing capacitor between the units, the DC voltage of the smoothing capacitor increases, and the smoothing capacitor may be damaged.

  Patent Document 1 is disclosed as protection against a smoothing capacitor between power converters. In Patent Document 1, when the voltage of the AC system decreases, the output current command upper limit value of the photovoltaic power generation panel is changed, and the output of the power converter for generating power control is limited to the power that can be output to the AC system. .

JP2013-66378

  When the AC grid voltage is reduced to 0% by the method of Patent Document 1, the power that can be output to the grid by the grid-connected power converter becomes zero. The output of the power converter for controlling generated power needs to be zero. In order to make the output of the power converter for generated power control zero, it is necessary to set the duty ratio of the semiconductor switching element of the power converter for generated power control to zero. However, if the duty ratio of the semiconductor switching element is too small, the semiconductor switching element may be damaged by a narrow pulse. Generally, in order to prevent damage to the semiconductor switching element, a lower limit must be set for the duty ratio. Don't be. As a result, even when the current command value is zero, the switching operation continues at the lower limit value of the duty ratio, and the power converter for generated power control outputs power even when the AC system voltage is 0%. Since power cannot be output to the AC system at AC system voltage 0%, the output power of the power converter for power generation control exceeds the power that can be output to the AC system, and power is input to the smoothing capacitor, which increases the voltage of the smoothing capacitor. In addition, the semiconductor switching element may be damaged.

  In view of the above circumstances, the present invention proposes a power converter that can suppress the above-described increase in DC voltage and continue operation, and a control method therefor.

  In order to solve the above problem, for example, a power conversion device that controls input power from a photovoltaic power generation panel and outputs it to an AC system, and generates power by controlling the generated power of the photovoltaic power generation panel and outputting DC power. A power converter for power control, a smoothing capacitor connected to the DC power output side of the power converter for generated power control, and a DC power converted to AC power by connecting to the power converter for generated power control and the smoothing capacitor. Power converter for grid connection to output, voltage detector for detecting voltage amplitude of AC system, and semiconductor switching of power converter for power generation control when voltage amplitude of AC system falls below first criterion A control unit that turns off the element and releases the semiconductor switching element of the power converter for generated power control when the voltage amplitude of the AC system exceeds the first criterion. That.

  According to the present invention, even if the voltage of the AC system decreases, the terminal voltage of the smoothing capacitor can be prevented from increasing, and the operation can be continued.

It is a block diagram which shows the structure of the power converter device in a present Example. It is a figure which shows the block of the controller 100 in the case of controlling the power converter 13 for system power control in a present Example. It is a figure which shows the block of the controller 100 in the case of controlling the power converter 11 for electric power generation control in a present Example. It is a flowchart of the electric power maximization controller which calculates an input voltage command value so that the input electric power from the photovoltaic power generation panel in this Example to the electric power converter for electric power generation control may become the maximum. The change of the AC system voltage drop flag, the switching of a semiconductor switching element, and the DC voltage between power converters accompanying the change of the AC system voltage in a present Example is shown. It is the figure shown about the hysteresis of the voltage amplitude detection value of the alternating current system in a present Example. It is a figure which shows the block of the controller 100 in the case of controlling the power converter 11 for electric power generation control in the present Example 2. FIG. The change of the AC system voltage drop flag, the DC voltage rise flag, switching of a semiconductor switching element, and the change of the DC voltage between power converters with the change of the AC system voltage in the present Example 2 is shown. It is the figure shown about the hysteresis of the voltage amplitude detection value of the alternating current system in the present Example 2.

    A first embodiment of the present invention will be described with reference to FIG.

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

  A photovoltaic power generation panel 2 is connected to the power conversion device 1, and a power converter 11 for controlling the generated power that controls the generated power from the photovoltaic power generation panel 2 of the power conversion device 1, and the power conversion for controlling the generated power A smoothing capacitor 12 connected to the output terminal of the generator 11, the power converter 11 for controlling the generated power and the DC power from the power converter 11 for controlling the generated power connected to the smoothing capacitor 12 is converted into AC power, A grid interconnection power converter 13 for outputting to the AC grid 3, a power converter 11 for controlling the generated power, and a controller 100 for controlling the outputs of the grid converter power converter 13 are provided. As described above, in the main circuit configuration of the present embodiment, the photovoltaic power generation panel 2 and the AC system 3 are connected to the power converter 1.

  The positive electrode of the photovoltaic power generation panel 2 is connected to the boost reactor 19 of the power converter 11 for power generation control. Boost reactor 19 is connected to input terminal 11A. The negative electrode of the photovoltaic power generation panel 2 is connected to the input terminal 11B of the power converter 11 for controlling the generated power.

  The power converter 11 for controlling generated power is a step-up chopper composed of semiconductor switching elements 11m and 11n, and the output voltage between the terminals 11A and 11B is PWM-controlled by a gate signal from the controller 100, and a photovoltaic power generation panel 2 is controlled, and the input power is output between the output terminals 11P-11N.

A smoothing capacitor 12 is connected between the output terminals 11P and 11N to smooth the output voltage of the power converter 11 for controlling generated power.
The grid interconnection power converter 13 is a three-phase inverter, and is composed of semiconductor switching elements 13m to 13r. The grid connection power converter 13 is PWM-controlled by the gate signal from the controller 100, and the DC input power from the power converter 11 for generated power control is converted from the output terminals 30U to 30W to AC power and output. Since the AC power includes harmonic components, the harmonic components are removed by the filter reactor 20 and output to the AC system 3.

  Next, functions of the sensor and the control unit 100 provided in the power conversion device 1 of the present embodiment will be described. First, various sensors provided in the power conversion device 1 will be described.

  The power converter 1 includes a voltage sensor 14 for detecting the voltage of the smoothing capacitor 12 between the two power converters, a current sensor 15 for detecting a current input to the power converter 11 for controlling the generated power, solar light A voltage sensor 16 for detecting the output voltage of the power generation panel 2, a voltage sensor 17 for detecting the voltage of the AC system 3, and a current sensor 18 for detecting the output current of the power converter 13 for grid connection, the output of the sensor Is input to the controller 100. The controller 100 calculates and outputs a gate signal for PWM control of the semiconductor switching elements of the generated power control power converter 11 and the grid interconnection power converter 13 according to the input of the sensor.

  Next, the control of the generated power control power converter 11 and the grid interconnection power converter 13 by the controller 100 will be described.

FIG. 2 is a diagram illustrating a block of the controller 100 when controlling the power converter 13 for system power control in the present embodiment. First, the AC system voltage detection values Vuv and Vvw detected from the voltage sensor 17 are input to the phase voltage calculator 1001, and the phase voltage calculator 1001 calculates the phase voltages Vu, Vv, and Vw. The phase voltages Vu, Vv, and Vw are input to an α-β converter 1002 and converted into an α component Vs_alp and a β component Vs_bet. The AC system voltage α component Vs_alp and β component Vs_bet are input to the DQ converter 1003. The DQ converter 1003 receives the Vs_alp, Vs_bet, a cos table output value cos described later, and a sin table output value sin, and calculates an AC system voltage D-axis component Vsd and a Q-axis component Vsq. The AC system voltage Q-axis component Vsq is output to the phase calculator 1004, and the phase calculator 1004 calculates the AC system phase theta. The AC system voltage phase theta is input to a cos table 1005 and a sin table 1006, and both tables calculate cos and sin according to the phase theta. The DQ converter 1003 DQ-converts the AC system voltage using the outputs of the cos table 1005 and the sin table 1006.

  The AC output currents isu and isw of the grid interconnection power converter 13 detected by the current sensor 18 are input to the subtractor 1007, and the subtracter 1007 calculates isv that is the v-phase current value. The U-phase current isu, V-phase current isv, and W-phase current isw are input to the α-β converter 1008 and converted to the α component Is_alp and β component Is_bet of the AC output current of the power converter 13 for grid interconnection. Is done. The α component Is_alp and β component Is_bet of the AC output current are output to the D-Q converter 1009. The D-Q converter 1009 calculates the output current D-axis component Isd and Q-axis component Isq of the grid interconnection power converter 13 using sin and cos which are outputs of the sin table 1005 and the cos table 1006. The D-axis component Isd and Q-axis component Isq, which are the outputs of the D-Q converter 1009, are output to the subtractor 1010 and the subtracter 1011, respectively.

  The terminal voltage vdc of the smoothing capacitor 12 detected by the voltage sensor 14 and a predetermined voltage command value vdc_ref are input to the subtractor 1012, and the difference vdc_def is output to the DC voltage control unit 1013. The DC voltage control unit 1013 is composed of a PI controller, and performs a PI operation on the difference between the DC voltage vdc between the two power converters calculated by the subtractor 1012 and a predetermined voltage command value vdc_ref. The active current command value idref is calculated and output to the subtractor 1010.

  The predetermined reactive power command value Qref and the output Qfb of the reactive power calculator 1014 are input to the subtractor 1015, and the difference Qdef is output to the reactive power controller 1016. The reactive power controller 1016 is configured by a PI controller, performs PI control calculation on the difference calculated by the subtractor 1015, calculates the reactive power command value iqref of the grid interconnection power converter 13, Output to the subtractor 1011.

  The subtractor 1010 calculates the difference between the effective current command value Idref and the D-axis component Isd of the output current of the grid interconnection power converter 13, and the difference is output to the D-axis current controller 1017. The subtractor 1011 calculates the difference between the reactive current command value Iqref and the output current Q-axis component Isq of the grid interconnection power converter 13, and the difference is output to the Q-axis current controller 1018. The D-axis current controller 1017 and Q-axis current controller 1018 are PI controllers, and PI control calculation is performed on the difference between the input command value and output current D-axis component, and the difference between the input command value and Q-axis component. In order to reduce the difference, the D-axis voltage command value vdref1 and the Q-axis voltage component vqref1 are calculated and output to the inverse DQ converter 1021.

  The Q-axis voltage command value vdref1 that is the output of the D-axis current controller 1017 is input to the adder 1019. The adder 1018 adds the D-axis voltage component Vsd and the D-axis voltage command value vdcref1, and calculates the D-axis voltage command value vdref2.

  The Q-axis voltage command value vqref1 that is the output of the Q-axis current controller 1018 is input to the adder 1020. The adder 1020 adds the Q-axis component Vsq of the phase voltage and the Q-axis voltage command value vqcref1, and calculates the Q-axis voltage command value vqref2.

  The D-axis voltage command value vqref2 output from the adder 1019 and the Q-axis voltage command value vqref2 output from the adder 1020 are input to the inverse D-Q converter 1021. The inverse D-Q converter 1021 calculates the voltage vectors valp and vbet of the fixed coordinate system from vdref and vqrwf using the output cos of the cos table 1005 and the output sin of the sin table 1006 in addition to vdref2 and vqref2.

The vlp and vbet that are the outputs of the inverse DQ converter 1021 are output to the 2-phase to 3-phase converter 1022, and the phase voltage output command values vu_ref, vv_ref, and vw_ref of the power converter 13 for system power control are calculated.
The phase voltage output command values vu_ref, vv_ref, and vw_ref are input to the PWM calculator 1023.
In addition to the voltage command value, the PWM calculator 1023 inputs the triangular wave tri that is the output of the carrier wave calculator 1024, compares the magnitude, and outputs the gate signals GatePm to rN to the IGBT module of the power converter 13 for system power control. Calculate and output to the power converter 13 for system power control.

  Next, a control block of the power converter 11 for generated power control will be described with reference to FIG.

  FIG. 3 is a diagram illustrating a block of the controller 100 when controlling the power converter 11 for controlling generated power in the present embodiment.

  The DC input current ichop from the photovoltaic power generation panel 2 detected by the current sensor 15 to the power converter 11 for generated power control and the power converter 11 for generated power control detected from the photovoltaic power panel 2 detected by the voltage sensor 16 The DC input voltage vchop to is input to the power maximization controller 1027. The power maximization controller 1027 calculates the input voltage command value vchop_ref1 so that the input power from the photovoltaic power generation panel 2 to the power converter 11 for controlling the generated power is maximized. The input voltage command value vchop_ref1 is input to a control block CHOP_CAL_NEW1, which will be described later, and an input voltage command value vchop_ref2 that is a calculation result is output. The voltage command value vchop_ref2 is input to the PWM calculator 1023. The PMW calculator 1023 compares the voltage command value vchop_ref2 with the magnitude of the triangular wave tri that is the output of the carrier wave calculator 1024, calculates the gate signal to the IGBT module of the power converter 11 for power generation control, and generates power control Output to the power converter 11. The carrier wave calculator 1024 calculates a triangular wave tri having a frequency equal to the switching frequency of the power converter 11 for controlling generated power. The control block CHOP_CAL_NEW1 which is a new point of the present embodiment will be described later.

  FIG. 4 is a flowchart of the power maximization controller that calculates the input voltage command value so that the input power from the photovoltaic power generation panel to the power converter for generated power control is maximized in the present embodiment.

  The power maximization controller 1027 calculates the current generated power P_now of the photovoltaic power generation panel 2 that is the product of the DC input current ichop and the DC input voltage vchop (step 4001). Next, the current generated power P_now and the previous value P_old of the generated power of the photovoltaic power generation panel 2 are compared (step 4002), and then the current value Ichop_now of the DC current detected by the current sensor 15 and its previous value Ichop_old. Are compared (step 4003 and step 4004). As a result of comparison, if P_now> P_old (YES in step 4002) and Ichop_now> Ichop_old (YES in step 4003), or P_now <P_old (NO in step 4002) and Ichop_now <Ichop_old (NO in step 4004), the input voltage command The value is increased by a predetermined value Δ from the previous value of the input voltage command value (step 4005). On the other hand, if P_old> P_now (NO in step 4002) and Ichop_old <Ichop_now (YES in step 4004), or P_old <P_now (YES in step 4002) and Ichop_old> Ichop_now (NO in step 4003), the input voltage command value is input. Decrease by a predetermined value Δ from the previous value of the voltage command value (step 4006). The values of the generated power and the direct current are updated (step 4007), and after a predetermined time has passed (step 4008), the calculation of STEP1 is repeated again. By repeating this calculation, the input voltage command value vchop_ref1 is calculated sequentially so that the input power from the photovoltaic power generation panel 2 to the power converter for generated power control is maximized.

  Next, a control operation when a system fault occurs, which is a feature of the present embodiment, will be described. A feature of the present embodiment is that when a voltage drop in the AC system 3 is detected, the semiconductor switching element of the power converter 11 for controlling generated power is turned off. Hereinafter, this control operation will be described.

  This control will be described using the control block CHOP_CAL_NEW1 in FIG. The AC system voltage detection values Vuv and Vvw detected by the voltage sensor 17 are converted into an α component V_alp and a β component V_bet as in the control block of the system power control power converter 13 and output to the amplitude calculator 1025. The amplitude calculator 1025 calculates the voltage amplitude Vs from the α component V_alp and the β component V_bet. The voltage amplitude Vs is output to the comparator 1026 and is compared with a predetermined voltage amplitude lower limit value vsdtmin. When the previous voltage amplitude Vs falls below the voltage amplitude lower value vsdtmin, the AC system low voltage flag lvdt is changed from 0 to 1, and the AC system low voltage flag lvdt = 1 is output. When AC system low voltage flag lvdt = 1 is output, AC system low voltage flag lvdt = 1 is input to PWM calculator 1006, and PWM calculator 1023 turns off the semiconductor switching element of power converter 11 for power generation control. Then, the output power of the power converter 11 for generated power control to the power converter 13 for system power control is set to zero.

  Further, in this embodiment, when the voltage amplitude of the AC system 3 falls below a predetermined value, the calculation of the power maximization controller 1027 is stopped, and the sunlight at the time when the voltage amplitude of the AC system 3 falls below the predetermined value. Calculation contents such as the input voltage command value vchop_ref1 that maximizes the input power from the power generation panel 2 to the power converter 11 for controlling the generated power are held. When the voltage amplitude of the AC system 3 exceeds the predetermined value, the calculation content of the power maximization controller 1027 held as the initial value is stored in the power maximization controller 1027 such as the input voltage command value vchop_ref1. Can also be resumed.

  As described above, the power maximizing converter 1027 is configured to convert the DC input current ichop detected by the current sensor 15 and the vchop detected by the voltage sensor 16 from the photovoltaic power generation panel 2 to the power converter 11 for controlling the generated power. Calculate the input voltage command value vchop_ref1 that maximizes the input power. The input voltage command value vchop_ref1 is input to the voltage command value holding unit 1028. When the voltage amplitude of the AC system 3 falls below a predetermined value, the AC system low voltage flag lvdt becomes 0 → 1, and the AC system low voltage flag lvdt = 1 is output. When the AC system low voltage flag lvdt = 1 is output to the voltage command value holding unit 1028, the switch of the voltage command value holding unit 1028 switches from 0 to 1, and the voltage amplitude of the AC system 3 falls below a predetermined value The input voltage command value vchop_ref1 and the calculation contents of the power maximization controller 1027 are held.

  The operation of the power conversion apparatus when a system fault occurs will be described with reference to FIG.

  FIG. 5 shows the AC system voltage drop flag, the switching of the semiconductor switching element, and the change of the DC voltage between the power converters according to the change of the AC system voltage in the present embodiment.

  The waveforms in FIG. 5 are, in order from the top, (a) AC system voltage, (b) AC system voltage drop flag, (c) Switching of semiconductor switching element of power converter 11 for power generation control, (d) Between power converters The time change of DC voltage is shown. When the AC grid voltage falls below the threshold A as shown in FIG. 5 (a), the AC grid voltage drop flag is set (see FIG. 5 (b)). When the AC system voltage drop flag is set, the PWM computing unit 1023 turns off the semiconductor switching element of the power converter 11 for controlling generated power (see FIG. 5 (c)).

  When the semiconductor switching element of the power converter 11 for generated power control is turned off, the inflow of power to the smoothing capacitor disappears, so that the rise in the terminal voltage of the smoothing capacitor 12 can be suppressed even when the residual voltage of the AC system is 0%. Yes (see FIG. 5 (d)).

  In addition, when the voltage amplitude of the AC system 3 falls below a predetermined value and the semiconductor switching element of the power converter 11 for generated power control is turned off, the power maximization controller 1027 stops the calculation and includes the input voltage command value vchop_ref1. The calculation contents of the maximization controller 1027 are held. When the voltage amplitude of the AC system 3 exceeds a predetermined value and the switching of the semiconductor switching element is resumed, the output of the photovoltaic power generation panel 3 before the AC system voltage drops is reduced by setting the hold value as the initial value of the input voltage command value. Since the state of the voltage, the input voltage to the power converter 11 for controlling generated power and the state of the input current can be restored, the power generation of the photovoltaic power generation panel 2 can be restarted promptly.

  In the present embodiment, the detected value of the voltage amplitude of the AC system 3 can be provided with hysteresis.

  Hereinafter, this control operation will be described.

  FIG. 6 is a diagram showing the hysteresis of the voltage amplitude detection value of the AC system.

  The threshold value C is a voltage value at which the AC system low voltage flag is output, and the threshold value D is a voltage value at which the AC system low voltage flag is not output. The magnitude relationship between the thresholds C and D is threshold C <threshold D. When the voltage amplitude of the AC system decreases, the AC system low voltage flag is output at threshold C, and when the voltage amplitude of the AC system increases, the AC system low voltage flag does not disappear at threshold C, and the AC system is low at threshold D. The voltage flag is not output.

  By providing a wide range for the detection value of the AC system low voltage flag and the detection value of the falling edge, fluctuations in the output power in the vicinity of the detection value without hysteresis can be eliminated, and unnecessary switching of the semiconductor switching element can be eliminated. Can improve efficiency.

  As described above, when the voltage amplitude of the AC system 3 to which the power converter 1 is connected falls below a predetermined value, the semiconductor switching element of the power converter 11 for power generation control is turned off, and the power converter 11 for power generation control 11 The output power to the grid interconnection power converter 13 can be made zero, and an increase in the terminal voltage of the smoothing capacitor 12 can be avoided. Further, when the voltage amplitude of the AC system 3 falls below a predetermined value, the generated power control power converter 11 holds the previous input voltage command value vchop_ref1, and the held voltage command value is used as the generated power control power converter. As the output voltage initial value of 11, when the voltage amplitude of the AC system 3 exceeds a predetermined value, the power generation of the photovoltaic power generation panel 2 can be restarted promptly. Further, the power converter 11 for controlling generated power can provide hysteresis to the detected value of the voltage amplitude of the AC system 3, and can eliminate unnecessary switching of the semiconductor switching element.

  Next, Example 2 of the present invention will be described. The main circuit configuration of the power conversion device according to the second embodiment is the same as that of the first embodiment. The same parts as those of the present invention and the first embodiment are denoted by the same symbols, and overlapping is omitted.

  The difference between the present embodiment and the first embodiment is that, in the first embodiment, only a decrease in the AC system voltage is detected and the semiconductor switching element of the power converter 11 for controlling generated power is turned off. The embodiment is that the semiconductor switching element of the power converter 11 for generated power control is turned off when a decrease in AC system voltage and a rise in the terminal voltage of the smoothing capacitor are detected at the same time.

  This control will be described using the control block CHOP_CAL_NEW2 in FIG.

  FIG. 7 is a diagram illustrating a block of the controller 100 when controlling the power converter 11 for controlling generated power in the second embodiment.

  The terminal voltage vdc of the smoothing capacitor 12 and the predetermined voltage upper limit determination value vdcup detected by the voltage sensor 14 are input to the comparator 1029. When the DC voltage vdc exceeds the voltage upper limit determination value vdcup, the DC voltage increase flag vdcmaxflg becomes 0 → 1. At the same time, when the same system voltage drop flag lvdt = 1 as in the first embodiment is output, the semiconductor switching element of the power converter 11 for generated power control is turned off.

  Further, in this embodiment, when the voltage amplitude of the AC system 3 falls below a predetermined value, and when the terminal voltage of the smoothing capacitor 12 exceeds a predetermined value, it is calculated by the power maximization controller 1027 immediately before the condition is satisfied. Holds the input voltage command value vchop_ref1. When the voltage amplitude of the AC system 3 exceeds a predetermined value or the terminal voltage of the smoothing capacitor 12 falls below a predetermined value, the operation of the power converter 11 for generating power control is performed with the held voltage command value vchop_ref1 as an initial value. You can also resume.

  The power maximizing converter 1027 maximizes the input power from the photovoltaic power generation panel 2 to the power converter 11 for controlling the generated power from the DC input current ichop detected by the current sensor 15 and the vchop detected by the voltage sensor 16. The input voltage command value vchop_ref1 is calculated as follows. The input voltage command value vchop_ref1 is input to the voltage command value holding unit 1028. When the voltage amplitude of the AC system 3 falls below a predetermined value and the terminal voltage of the smoothing capacitor 12 exceeds the predetermined value, the DC voltage rise flag vdcmaxflg becomes 0 → 1 and the AC low voltage flag lvdt becomes 0 → 1. The system low voltage flag lvdt = 1 is output. When the DC voltage rise flag vdcmaxflg 0 → 1 and the AC system low voltage flag lvdt = 1 are output to the voltage command value holding unit 1028, the switch of the voltage command value holding unit 1028 switches from 0 → 1, and the voltage of the AC system 3 The input voltage command value vchop_ref1 and the calculation content of the power maximization controller 1027 when the amplitude falls below a predetermined value are held.

  The operation of the power conversion apparatus when a system fault occurs will be described with reference to FIG. 8. FIG. 8 illustrates an AC system voltage drop flag, a flow voltage rise flag, a semiconductor switching according to a change in the AC system voltage in the second embodiment. The change of the element switching and the DC voltage between power converters is shown.

  The waveforms in FIG. 8 are, in order from the top, (a) AC system voltage, (b) AC voltage voltage drop flag, (c) DC voltage rise flag, and (d) switching of the semiconductor switching element of the power converter 11 for power generation control. (E) The time change of the DC voltage between power converters is shown. When the AC grid voltage falls below the threshold A as shown in FIG. 8A, an AC grid voltage drop flag is set (see FIG. 8B). On the other hand, since the terminal voltage of the smoothing capacitor 12 has not risen, the DC voltage rise flag is not raised. Therefore, the generated power control power converter 11 continues the switching operation (see FIGS. 8C and 8D). However, when the AC grid voltage is 0%, power cannot be output to the AC grid 3, so that power is input to the smoothing capacitor 12 and the terminal voltage of the smoothing capacitor 12 increases. When the DC voltage rises to the threshold value B, a DC voltage increase flag is set. When the DC voltage rise flag is set, the PWM calculator 1023 turns off the semiconductor switching element of the power converter 11 for generated power control, and makes the generated power of the power converter 11 for generated power control zero.

  In the first embodiment, even when output can be performed with an AC system voltage of 0% or more, when the voltage amplitude of the AC system 3 falls below a predetermined value, the semiconductor switching element of the power converter 11 for generated power control is turned off, and the generated power Since the output power to the grid interconnection power converter 13 of the control power converter 11 is made zero, if the output power zero time is long, the utilization rate of the photovoltaic power generation system decreases. However, in the present embodiment, the semiconductor switching element of the power converter 11 for controlling the generated power is turned off only when both the decrease in the voltage amplitude of the AC system 3 and the increase in the terminal voltage of the smoothing capacitor are detected. Compared with the case where the switching element of the power converter 11 for controlling generated power is turned off only by lvdt, the utilization rate of the photovoltaic power generation system can be improved.

  Further, when the voltage amplitude of the AC system 3 is lower than a predetermined value and the terminal voltage of the smoothing capacitor 12 exceeds a predetermined value, the power switching controller 1027 The calculation of the power maximization controller 1027 including the input voltage command value vchop_ref1 is held. When the voltage amplitude of the AC system 3 exceeds a predetermined value, or the terminal voltage of the smoothing capacitor 12 falls below a predetermined value and the switching of the semiconductor switching element is resumed, the holding value is set to the input voltage command value as an initial value. Since the output voltage of the photovoltaic power generation panel 3 before the AC system voltage drop, the input voltage to the power converter 11 for controlling the generated power and the state of the input current can be restored, the power generation of the photovoltaic power generation panel 2 must be resumed promptly. Can do.

  In this embodiment, in addition to the detected value of the voltage amplitude of the AC system 3, the detected value of the terminal voltage of the smoothing capacitor 12 can have hysteresis. Since the detection value of the voltage amplitude of the AC system 3 is the same as that in the first embodiment, it is omitted. The details of this control will be described below.

FIG. 9 is a diagram illustrating the hysteresis of the voltage amplitude detection value of the AC system in the second embodiment. The threshold value E is a voltage value at which the DC voltage increase flag is output, and the threshold value F is a voltage value at which the DC voltage increase flag is not output. The relationship between the thresholds E and F is threshold E> threshold F. When the DC voltage increases, the DC voltage increase flag is output at the threshold E, and when the DC voltage decreases, the DC voltage increase flag does not disappear at the threshold E and the DC voltage increase flag is not output at the threshold F.
By providing a wide range for the detection value and falling detection value of the AC system low-voltage flag, output power fluctuates in the vicinity of the detection value when there is no hysteresis, and unnecessary switching of the semiconductor switching element is eliminated. Can improve efficiency.

  As described above, when the voltage amplitude of the AC system 3 to which the power converter 1 is connected is lower than a predetermined value and the terminal voltage of the smoothing capacitor 12 exceeds a predetermined threshold, the semiconductor switching of the power converter 11 for power generation control is performed. By turning off the element, the output of the power converter 11 for generating power control can be made zero, and an increase in the terminal voltage of the smoothing capacitor 12 can be avoided. When the voltage amplitude of the AC system 3 is lower than a predetermined value and the terminal voltage of the smoothing capacitor 12 exceeds a predetermined value, the power converter 11 for generated power control is the input voltage command value vchop_ref1 immediately before satisfying the above condition. Hold. The held voltage command value is used as the output voltage initial value of the power converter 11 for generated power control. When the voltage amplitude of the AC system 3 exceeds a predetermined value, the power output is restarted promptly. In addition, since a predetermined value for detecting the voltage rise of the smoothing capacitor 12 can be provided with hysteresis, unnecessary switching of the semiconductor switching element can be eliminated.

DESCRIPTION OF SYMBOLS 1 ... Power converter 2 ... Photovoltaic power generation panel 3 ... AC system 11 ... Power converter 11A, 11B ... Power converter 11m for input power control 11n: Semiconductor switching element 11P, 11N: Output terminal of power converter for generated power control 12: Smoothing capacitor 13: Power converter for grid connection 13P, 13N: For grid connection Input terminals of power converters 13m, 13n, 13o, 13p, 13q, 13r ... Semiconductor switching elements 14, 16, 17 ... Voltage sensors 15, 18 ... Current sensors 19 ... Boosting reactors 20 ... -Filter reactor 30P, 30N ... Output terminal of power converter for grid connection 100 ... Control unit

Claims (7)

A power conversion device that controls input power from a photovoltaic power generation panel and outputs it to an AC system,
A power converter for controlling generated power for controlling the generated power of the photovoltaic power generation panel and outputting DC power; and
A smoothing capacitor connected to the DC power output side of the power converter for power generation control,
A grid interconnection power converter that is connected to the power converter for generated power control and the smoothing capacitor to convert the DC power into AC power and output the power converter,
A voltage detector for detecting a voltage amplitude of the AC system;
When the voltage amplitude of the AC system is lower than the first determination criterion, the semiconductor switching element of the power converter for generated power control is turned off, and the voltage amplitude of the AC system exceeds the first determination criterion A control unit for releasing off the semiconductor switching element of the power converter for power generation control,
A power conversion device comprising:
The power conversion device according to claim 1,
The controller is
A power maximization controller that calculates an input voltage command value of the power converter for generated power control so that the input power from the solar panel to the power converter for generated power control is maximized;
A voltage command value holding unit that holds the input voltage command value when the voltage amplitude of the AC system falls below the first determination criterion;
When the voltage amplitude of the AC system exceeds the first determination criterion, the held input voltage command value is used as the output voltage initial value to the grid interconnection power converter of the generated power control power converter. A power conversion device characterized by resuming computation of a power maximization control unit.
The power conversion device according to claim 1,
It has a voltage detector that detects the terminal voltage of the smoothing capacitor,
The control unit includes a comparison unit that detects that a terminal voltage of the smoothing capacitor exceeds a second determination criterion;
When it is detected that the voltage amplitude of the AC system has fallen below the first determination criterion, and when it has been detected that the terminal voltage of the smoothing capacitor has exceeded the second determination criterion, Turn off the semiconductor switching element of the power converter,
When the voltage amplitude of the AC system exceeds the first determination value or the terminal voltage of the smoothing capacitor falls below the second determination criterion, the switching operation of the semiconductor switching element of the power converter for power control is performed. A power conversion device comprising a control unit for restarting.
The power conversion device according to claim 3,
The voltage command value holding unit detects that the voltage amplitude of the AC system has fallen below the first determination criterion, and has detected that the terminal voltage of the smoothing capacitor has exceeded the second determination criterion. The input voltage command value at the time when the condition is satisfied,
The controller is
When the voltage amplitude of the AC system exceeds the first determination criterion, or when the terminal voltage of the smoothing capacitor falls below the second determination criterion, the held voltage command value is used as the power for controlling generated power. A power conversion device that restarts the operation of the power maximization control unit as an initial value of an output voltage to a power converter for grid interconnection of a converter.
The power conversion device according to claim 1 or 2,
The power converter according to claim 1, wherein the first determination criterion is a threshold value or has a predetermined determination value width.
The power conversion device according to claim 3 or 4,
The power conversion device according to claim 2, wherein the second determination criterion is a threshold value or has a predetermined determination value width.
A photovoltaic power generation system having a photovoltaic power generation panel and a power conversion device that controls input power from the photovoltaic power generation panel and outputs it to an AC system,
The power converter is
A power converter for controlling generated power for controlling the generated power of the photovoltaic power generation panel and outputting DC power; and
A smoothing capacitor connected to the DC power output side of the power converter for power generation control,
A grid interconnection power converter that is connected to the power converter for generated power control and the smoothing capacitor to convert the DC power into AC power and output the power converter,
A voltage detector for detecting a voltage amplitude of the AC system;
When the voltage amplitude of the AC system is lower than the first determination criterion, the semiconductor switching element of the power converter for generated power control is turned off, and the voltage amplitude of the AC system exceeds the first determination criterion A control unit for releasing off the semiconductor switching element of the power converter for power generation control,
A photovoltaic power generation system comprising: