JP6159271B2 - Power converter and control method of power converter - Google Patents

Description

  The present invention relates to a power conversion device and a method for controlling the power conversion device.

  In recent years, the introduction of distributed power sources using natural energy, such as solar power generation devices and wind power generation devices, has progressed. A distributed power source using natural energy converts electric power generated by natural energy into a system frequency by a self-excited power converter and transmits it to the power system. In general, the output power of such a distributed power source varies depending on the climate, and there is a risk of impairing the stability of the interconnected power system. Under such circumstances, for the purpose of stabilizing the power system, the introduction of a power storage system including power storage means represented by a storage battery and a self-excited power converter is progressing mainly in small systems.

  If a power system breaker is opened due to an accident detection or system switching when a distributed power source or storage system using natural energy is connected to the power system, the distributed power source connected to the subordinate system of the circuit breaker If the generated power of the power storage system matches the power consumption of the load connected to the lower system, the voltage of the lower system may be maintained for a long time. This state in which supply and demand is balanced is referred to as an isolated operation state.

  If an islanding condition occurs, it will hinder maintenance of the power system. Therefore, according to the grid interconnection technical requirement guidelines in Japan and IEC62116 overseas, the self-excited power converter for distributed power sources and the power converter for power storage system have a function of detecting isolated operation, and after detecting isolated operation. It is stipulated that a function to quickly disconnect from the system is provided. In particular, the grid connection regulations in Japan stipulate that for a distributed power source connected to a low-voltage system, the isolated operation is detected within 0.1 s after the occurrence of the isolated operation, and the operation is stopped. Isolated operation detection is necessary.

  As an isolated operation detection method, Patent Document 1 discloses a method of detecting an isolated operation by generating reactive power using a frequency change rate as a trigger.

  As another isolated operation detection method, a method for detecting a phase jump of the interconnection point voltage and a method for detecting a change in system impedance due to harmonic injection are known.

JP 2013-099230 A

  However, when the power consumed by the load and the power output from the self-excited power converter completely match, it is impossible to detect an isolated operation by phase jump. In addition, when testing the isolated operation detection function using an R-L-C parallel circuit having a large-capacity capacitor as a load as described in IEC62116, the method using harmonic injection absorbs harmonic components by the capacitor. This makes it difficult to detect an isolated operation.

  In order to solve the above-described problem, a power conversion device according to an aspect of the present invention includes an inverter that converts direct current into alternating current and outputs the alternating current to a power system, and a direct current voltage detection unit that detects a direct current voltage input to the inverter. An output current detection unit for detecting an output current from the inverter, a connection point voltage detection unit for detecting a connection point voltage at a connection point between the inverter and the power system, and an interconnection based on the connection point voltage A phase calculation unit for calculating a point voltage phase, an effective current command value calculation unit for calculating an effective current command value indicating an effective current to be output to the inverter based on a DC voltage, and a connection point voltage and an output current A reactive current command value calculation unit for calculating a reactive current command value indicating a reactive current to be output to the inverter, and an input based on the output current, the connection point voltage phase, the active current command value, And a control unit that changes the phase of the output voltage of the inverter at predetermined time intervals by controlling the inverter, and the isolated operation state of the power converter is detected based on the change of the interconnection point voltage phase. An independent operation detection unit.

  According to one embodiment of the present invention, the isolated operation state can be detected even when the output power of the power converter matches the power consumption of the load or when the load includes a capacitor.

The structure of the power converter device of Example 1 is shown. The structure of the load 200 is shown. The structure of the main circuit of the power converter device 1 is shown. The structure of the controller 100 of Example 1 is shown. The configuration of the phase calculator 1004 is shown. The configuration of the isolated operation detector 1005 is shown. An example of the output voltage vector of the inverter 10 is shown. It is a time chart which shows the operation | movement of an isolated operation detection. The structure of the power converter device of a 1st modification is shown. The structure of the power converter device of a 2nd modification is shown. The structure of the power converter device 2 of Example 2 is shown. The structure of the controller 100 of Example 2 is shown. The input / output characteristics of the upper and lower limiter 1077 are shown.

  Embodiments of the present invention will be described below with reference to the drawings.

  A present Example demonstrates the power converter device 1 for solar power generation.

  FIG. 1 illustrates the configuration of the power conversion apparatus according to the first embodiment.

  A solar panel 30 is connected to the DC circuit of the power conversion device 1. The power conversion device 1 converts the DC power generated by the solar panel 30 into AC power having the system frequency of the power system 300. The AC power is supplied to the power system 300 and the load 200. In the power converter 1, the connection point on the power system 300 side is called a connection point (system connection point).

  The power conversion apparatus 1 and the load 200 are connected in parallel to the power system 300 via the circuit breaker 400. The circuit breaker 400 is opened and closed by the operator of the power system 300 when a system fault is detected and for system maintenance.

  The power converter 1 includes a DC voltage sensor 71PT for detecting a DC circuit voltage connected to the solar panel 30, an inverter 10, a harmonic filter 20 for removing harmonics of the output of the inverter 10, and a connection point with the inverter 10. Contactor 40 that opens and closes, output current sensors 72CTu and 72CTw for detecting the output current of the power converter 1, linkage point voltage sensors 70PTuv and 70PTvw for detecting linkage point voltages, detected currents and voltages And a controller 100 that calculates a gate signal GateUP to WN (GateUP, GateVP, GateWP, GateUN, GateVN, GateWN) of the inverter 10 and a contactor control signal CTTctl that controls ON / OFF of the contactor 40.

  In the inverter 10, the solar panel 30 is connected to the DC circuit terminals P and N, and the harmonic filter 20 is connected to the AC terminals U, V, and W. The inverter 10 converts the DC power output from the solar panel 30 into three-phase AC power and outputs it. The harmonic filter 20 smoothes the pulse waveform output from the inverter 10 and allows the fundamental wave component to pass therethrough, thereby reducing harmonics flowing out from the inverter 10 to the power system 300.

  FIG. 2 shows the configuration of the load 200.

  A load 200 is connected in parallel to the interconnection point of the power conversion device 1. The electric characteristics of the load 200 are indicated by a parallel circuit of a resistor, a reactor, and a capacitor.

  FIG. 3 shows the configuration of the main circuit of the power conversion device 1.

  This figure includes a DC voltage sensor 71PT, an inverter 10, a harmonic filter 20, output current sensors 72CTu and 72CTw, a contactor 40, and interconnection point voltage sensors 70PTuv and 70PTvw in the power conversion device 1.

  The inverter 10 includes an IGBT module 10k, 10l, 10p, 10m, 10n, 10o, 10p, and a DC capacitor 10C in which a diode and a self-extinguishing semiconductor switching device such as an IGBT (Insulated Gate Bipolar Transistor) are connected in reverse parallel. including. The harmonic filter 20 includes two three-phase reactors 20L1 and 20L2 and a three-phase capacitor 20C. Current sensors 72CTu and 72CTw detect the U-phase current and the W-phase current of the output current of the harmonic filter 20, respectively. The connection point voltage sensors 70PTuv and 70PTvw measure the U-phase and V-phase line voltages vsuv and the V-phase and W-phase line voltages vsvw at the connection point, respectively.

  FIG. 4 shows a configuration of the controller 100 of the first embodiment.

  Line voltages vsuv and vsvw at connection points detected by the connection point voltage sensors 70PTuv and 70PTvw are input to the controller 100. Output current detection values isu and isw detected by the output current sensors 72CTu and 72CTw are input to the controller 100. A DC voltage detection value vdc detected by the DC voltage sensor 71PT is input to the controller 100. Based on the input voltage and current, the controller 100 sets the IGBT module 10k, 10l, 10p, 10m, 10n, the target of matching the voltage command value and the instantaneous average value of the inverter output voltage, as will be described later. The 10o and 10p gate signals GateUP, GateVP, GateWP, GateUN, GateVN, and GateWN are calculated, respectively. The controller 100 further calculates a contactor control signal CTTctl based on the input voltage and current.

  The controller 100 includes an interconnection point voltage phase detection unit 100a, a DC voltage control unit 100b, a reactive power control unit 100c, a current control unit 100d, and an isolated operation control unit 100e.

  First, the interconnection point voltage phase detection unit 100a will be described.

  The connection point voltage phase detection unit 100a detects a connection point voltage phase that is a phase of the connection point voltage. The interconnection point voltage phase detection unit 100a includes a phase voltage calculator 1001, an α-β converter 1002, a dq converter 1003, a phase calculator 1004, a cos table 1006, and a sin table 1007.

  The phase voltage calculator 1001 sets the phase voltage of the zero phase component to zero, and calculates the phase voltages vsu, vsv, vsw based on the line voltages vsuv, vsvw according to Equation 1.

  The α-β converter 1002 performs α-β conversion on the phase voltages vsu, vsv, vsw according to Equation 2, thereby calculating vs_alp, which is the α component of the connection point voltage in the fixed coordinate system, and vs_bet, which is the β component. To do.

  The d-q converter 1003 performs d-q conversion on vs_alp and vs_bet according to Equation 3 based on a cos table output value cos and a sin table output value sin, which will be described later, thereby connecting the interconnection point voltage in the rotating coordinate system. The d component vsd and q component vsq are calculated.

  The phase calculator 1004 calculates the connection point voltage phase theta and the angular frequency omega based on the q component vsq of the connection point voltage.

  FIG. 5 shows the configuration of the phase calculator 1004.

  The phase calculator 1004 includes a PI controller 10041, an adder 10042, and a time integrator 10043.

  The PI controller 10040 calculates del_omeg which is a correction angular frequency based on vsq.

  The adder 10044 adds the corrected angular frequency del_omeg and the rated angular frequency Omega0, and outputs the sum omega to the time integrator 10034.

  The time integrator 10043 calculates the interconnection point voltage phase theta by time integrating the angular frequency omega.

  When the connection point voltage phase theta calculated by the controller 100 matches the phase of the connection point voltage, the q component vsq of the connection point voltage is zero. On the other hand, when the connection point voltage phase theta and the connection point voltage phase do not match, the q component vsq of the connection point voltage becomes non-zero. Therefore, the connection point voltage phase can be detected by the configuration of the phase calculator 1004 described above.

  The interconnection point voltage phase theta is input to the cos table 1006 and the sin table 1007. The cos table 1006 and the sin table 1007 calculate cos and sin corresponding to the interconnection point voltage phase theta. The dq converter 1003 described above performs dq conversion on the interconnection point voltage α component vs_alp and β component vs_bet using the calculated cos and sin.

  The angular frequency omega output from the phase calculator 1004 is output to the isolated operation detector 1005 of the isolated operation detection unit 100e. The d component vsd and the q component vsq of the interconnection point voltage are output to the reactive power calculator 1070 of the reactive power control unit 100c.

  Next, the DC voltage control unit 100b will be described.

  The DC voltage control unit 100b controls the DC voltage in order to adjust the amount of power from the solar panel 30. The DC voltage control unit 100b includes a subtracter 1050 and a DC voltage controller 1051.

  The subtractor 1050 calculates a difference by subtracting the voltage command value Vdc_ref from the DC voltage detection value vdc detected by the DC voltage sensor 71PT, and outputs the difference to the DC voltage controller 1051. The DC voltage controller 1051 is composed of a PI controller, and performs a PI operation on the difference between the DC voltage command value calculated by the subtractor 1050 and the DC voltage detection value, and the result is used as an effective current command value. The result is output to the subtracter 1013.

  Next, the reactive power control unit 100c will be described.

  The reactive power control unit 100c calculates a reactive current command value for causing the reactive power to follow the reactive power command value of the target value. The reactive power control unit 100c includes a reactive power calculator 1070, a subtracter 1071, a reactive power controller 1072, a reactive current correction signal calculator 1073, and an adder 1074.

  The reactive power calculator 1070 outputs the reactive power to the power system 300 side of the power conversion device 1 based on the interconnection point voltages vsd and vsq and the active current isd and reactive current isq described later according to Equation 4. And the result is output to the subtractor 1071 as the reactive power calculation value Qfb.

  The subtractor 1071 calculates a difference between a predetermined reactive power command value Qref and Qfb output from the reactive power calculator 1070, and outputs the difference to the reactive power controller 1072.

  The reactive power controller 1072 is composed of a PI controller, and performs a PI control operation on the output of the subtractor 1071 to calculate a reactive current command value iqref of the power conversion device 1. Thereby, the reactive power from the power converter device 1 can be brought close to the target value.

  The adder 1074 calculates the sum of the reactive current command value iqref and a reactive current correction signal del_iqref output from the reactive current correction signal calculator 1073 described later, and uses the sum as a new reactive current command value iqref2 for current control. To the subtracter 1014 of the unit 100d.

  Next, the current control unit 100d will be described.

  The current control unit 100d corrects the output voltage based on the active current command value and the reactive current command value. The current control unit 100d includes a subtractor 1010, an α-β converter 1011, a dq converter 1012, a subtractor 1013, a subtractor 1014, a d-axis current controller 1015, a q-axis current controller 1016, an adder 1017, An inverse dq converter 1018, a two-phase to three-phase converter 1019, a carrier wave calculator 1020, and a PWM (Pulse Width Modulation) calculator 1021 are included.

  First, a method for calculating the d component isd and the q component isq of the output current will be described.

  The subtractor 1010 calculates the v-phase component isv from the u-phase component isu and the w-phase component isw of the output current detected by the output current sensors 72CTu and 72CTw, respectively. The α-β converter 1011 calculates an α component is_alp and a β component is_bet by performing α-β conversion on the u-phase component isu, the v-phase component isv, and the w-phase component isw of the output current. Since this α-β conversion is the same as that in Equation 2, duplicate description will be omitted.

  The dq converter 1012 performs dq conversion on the α component is_alp and the β component is_bet of the AC output current using cos output from the cos table 1006 and sin output from the sin table 1007. Thus, the d component isd and the q component isq of the output current are calculated. Since this dq conversion is the same as Equation 3, repeated description is omitted. The d component isd of the output current is output to the subtractor 1013, and the q component isq of the output current is output to the subtractor 1014.

  The subtractor 1013 calculates a deviation from the effective current command value output from the DC voltage controller 1051 by subtracting the d component isd of the output current, and outputs the deviation to the d-axis current controller 1015. The subtractor 1014 calculates a deviation from the reactive current command value iqref2 output from the adder 1074 by subtracting the q component isq of the output current, and outputs the deviation to the q-axis current controller 1016.

  The d-axis current controller 1015 and the q-axis current controller 1016 are composed of PI controllers, perform PI control calculations on the input deviation, and reduce the deviation by the d-axis voltage command value of the inverter 10 and q Calculate the shaft voltage command value.

  The adder 1017 calculates a new d-axis voltage command value vdref by adding Vd0, which is a preset fixed value, and the d-axis voltage command value output from the d-axis current controller 1015. Vd0 is a value at which the output voltage of the inverter 10 and the amplitude of the connection point voltage are equal when the amplitude of the connection point voltage is rated. By adding the d-axis voltage command value to Vd0, it is possible to prevent an excessive current from flowing into the power conversion device 1 from the power system 300 when the inverter 10 is gate-deblocked.

  The inverse dq converter 1018 includes a vdref output from the adder 1017, a q-axis voltage command value vqref output from the q-axis current controller 1016, a cos output from the cos table 1006, and a sine table 1007. Sin is output, and vdref and vqref are calculated as voltage vectors valp and vbet in a fixed coordinate system according to Equation 5.

  The two-phase / three-phase converter 1019 converts the valp and vbet output from the inverse dq converter 1018 into voltage command values vu_ref, vv_ref, and vw_ref for each phase of the inverter 10 according to Equation 6, and performs PWM calculation. Output to the device 1021.

  The carrier wave calculator 1020 outputs a carrier wave tri, which is a triangular wave having a frequency equal to the switching frequency of the inverter 10. The frequency of the carrier wave is several kHz, for example.

  The PWM calculator 1021 calculates the gate signals GateUP to WN by comparing the voltage command values vu_ref, vv_ref, and vw_ref of each phase with the carrier wave tri, and outputs the gate signals GateUP to WN to the inverter 10.

  A method for calculating the gate signals GateUP and GateUN will be described using the U phase as an example.

  When the voltage command value vu_ref is greater than or equal to the carrier wave tri, the PWM calculator 1021 turns on the gate signal GateUP of the IGBT module 10k and turns off the gate signal GateUN of the IGBT module 10n. Conversely, when the voltage command value vu_ref is smaller than the carrier wave tri, the PWM calculator 1021 turns off the gate signal GateUP of the IGBT module 10k and turns on the gate signal GateUN of the IGBT module 10n. As a result, a pulse voltage for making the instantaneous average voltage the voltage command value vu_ref is output to the AC output terminal U of the inverter 10. Since the PWM calculator 1021 calculates gate signals in the same way for the V phase and the W phase, a duplicate description is omitted.

  When the islanding detection state ISLANDING_FLG output from the islanding detector 1005 is 1, the PWM calculator 1021 does not depend on the magnitude relationship between each of the voltage command values vu_ref, vv_ref, and vw_ref and the carrier wave tri, and all the gates Turn off the signal. Thus, when the isolated operation is detected, the PWM computing unit 1021 can quickly stop the switching of the inverter 10 and avoid the isolated operation state.

  Next, the independent operation control unit 100e will be described.

  The isolated operation control unit 100e detects the isolated operation of the power conversion device 1 based on the angular frequency omega of the interconnection point voltage, and stops the isolated operation of the power conversion device 1 when the isolated operation is detected. The isolated operation control unit 100e includes an isolated operation detector 1005 and a contactor control signal calculator 1008.

  The isolated operation detector 1005 receives the angular frequency omega output from the phase calculator 1004 and calculates the isolated operation detection state ISLANDING_FLG. The isolated operation detector 1005 sets the value of ISLANDING_FLG to 1 when an isolated operation is detected, and sets the value of ISLANDING_FLG to 0 when normally connected.

  The contactor control signal calculator 1008 turns on the contactor control signal CTTctl when ISLANDING_FLG is 0, and turns off CTTctl when ISLANDING_FLG is 1. The contactor 40 is turned on when CTTctl is on, and is opened when CTTctl is off. Thereby, when the isolated operation is detected, the isolated operation control unit 100e opens the contactor 40 in addition to the gate block of the PWM computing unit 1021, and disconnects the power conversion device 1 from the power system 300 in the power failure. be able to.

  FIG. 6 shows the configuration of the isolated operation detector 1005.

  The isolated operation detector 1005 includes a low-pass filter 10051, 10052, a subtractor 10053, and a comparator 10054.

  The angular frequency omega of the connection point voltage is input to low pass filters 10051 and 10052 having different time constants. The time constant τ1 of the low-pass filter 10051 is shorter than the time constant τ2 of the low-pass filter 10052. The subtractor 10053 subtracts the output of the low pass filter 10052 from the output of the low pass filter 10051. The low-pass filters 10051 and 10052 and the subtractor 10053 constitute a band-pass filter and output BPF_omeg. Thereby, the direct current component and the high frequency component of the fluctuation of omega can be removed. This high frequency component is a harmonic based on the PWM signal of the inverter 10, and is sufficiently higher than the frequency of the reactive current correction signal. Malfunctions can be prevented by removing high frequency components.

  Comparator 10054 compares BPF_omeg output from the bandpass filter with each of upper limit determination value TH_H and lower limit determination value TH_L. When BPF_omeg is equal to or higher than TH_H, or when BPF_omeg is equal to or lower than TH_L, the comparator 10054 outputs 1 as the isolated operation detection state ISLANDING_FLG.

  By this calculation, the isolated operation detector 1005 sets ISLANDING_FLG to 1 when the angular frequency omega changes more than a predetermined value. When the phase jump or sudden phase change of the interconnection point voltage occurs, the band pass filter output BPF_omeg fluctuates greatly, so that ISLANDING_FLG can be set to 1 and the isolated operation state can be avoided.

  Next, the reactive current correction signal calculator 1073 in the reactive power control unit 100c will be described.

  The reactive current correction signal calculator 1073 generates a reactive current correction signal del_iqref. The reactive current command value iqref, which is the output of the reactive power controller 1072, is added to the reactive current correction signal del_iqref by the adder 1074, and the sum is output to the current control unit 100d as a new reactive current command value iqref2.

  The reactive current correction signal del_iqref is a rectangular wave having a predetermined correction signal period Tperiod. The correction signal period Tperiod is set to not more than twice the detection upper limit time that is the upper limit of the time required from the occurrence of the isolated operation state to the detection. The detection upper limit time is, for example, 0.1 s defined by the grid connection regulations. In this case, the correction signal period Tperiod is 0.2 s or less. Note that the waveform of the reactive current correction signal del_iqref is not limited to this shape, and may be a pulse shape or a step shape.

  Since the difference between the q component isq of the output current and the reactive current command value iqref2 increases at the rising or falling of the rectangular wave of the reactive current correction signal del_iqref, the q-axis current controller 1016 sets the q-axis voltage command value vqred. Change sharply. By making the reactive current correction signal del_iqref a rectangular wave having a period Tperiod, the output voltage of the inverter 10 can be changed in a stepwise manner at intervals of half the period Tperiod.

  FIG. 7 shows an example of the output voltage vector of the inverter 10.

  This figure shows the interconnection point voltage vector vs and the output voltage vector vinv of the inverter 10. When the q-axis voltage command value changes suddenly, the q component of the output voltage vector vinv changes, and the phase difference Δθ with respect to the interconnection point voltage changes.

  When power system 300 is normal and circuit breaker 400 is turned on, the connection point voltage is determined by the voltage of power system 300. Therefore, even if the power converter 1 fluctuates the output voltage vector phase of the inverter 10 by the reactive current correction signal, the phase fluctuation of the interconnection point voltage hardly occurs. Thereby, when it is not an independent operation state, there is almost no influence by adding the reactive current correction signal to the reactive current command value. On the other hand, in the isolated operation state in which the circuit breaker 400 is opened, there is no element that stabilizes the interconnection point voltage phase, so the phase change of the output voltage of the inverter 10 is changed to the secondary side (the power conversion device 1 The q-axis voltage command value periodically changes suddenly based on the reactive current correction signal, so that the isolated operation can be detected quickly.

  FIG. 8 is a time chart showing the operation of the isolated operation detection.

  This time chart shows the waveform of the reactive current correction signal del_iqref and the reactive current command value iqref2, the waveform of the linkage point voltage phase theta, the waveform of the angular frequency bandpass filter output BPF_omeg, the waveform of the isolated operation detection state ISLANDING_FLG, The waveform of the contactor control signal CTTctl is shown. Here, the waveform of the reactive current correction signal del_iqref is represented by a broken line, and the waveform of the reactive current command value iqref2 after correction is represented by a solid line.

  The reactive current correction signal del_iqref is a rectangular wave having a correction signal period Tperiod, and changes its value in steps at times t1, t2, and t4 every half period. Since current control unit 100d changes the voltage command value of inverter 10 to follow reactive current command value iqref2, the reactive current and reactive power output from power conversion device 1 change.

  When the reactive current command value iqref2 is changed to a rectangular waveform by del_iqref, the reactive current output from the inverter 10 substantially matches iqref2, although the delay of the current control system remains as an error. On the other hand, reactive power controller 1072 changes reactive current command value iqref so that the reactive power output from power conversion device 1 matches reactive power command value Qref. Since reactive power controller 1072 regards reactive current correction signal del_iqref as a disturbance and responds, reactive current command value iqref also varies in the same cycle as reactive current correction signal del_iqref.

  Therefore, the waveform of the reactive current command value iqref2 after correction is slightly different from the waveform of the reactive current correction signal del_iqref. The waveform of the reactive current output from the inverter 10 according to the reactive current command value iqref2 is not a rectangular wave itself of the reactive current correction signal del_iqref but a substantially rectangular wave shape due to a response delay of the current control unit 100d. Thereby, the periodic phase change of the output voltage of the inverter 10 based on the reactive current command value iqref2 is compared with the phase change of the voltage of the power system 300 (interconnection point voltage when the power conversion device is not in the single operation state). It becomes steep. In other words, the output voltage of the inverter 10 based on the reactive current command value iqref2 includes a higher frequency component than the voltage of the power system 300.

  It is assumed that the circuit breaker 400 is opened due to an accident in the power system 300 or the like at time t3. Here, it is assumed that the power output from the load 200 and the power conversion device 1 completely matches. In this case, as shown in the waveform of the connection point voltage phase theta, no deviation occurs in the connection point voltage phase theta.

  At time t4, which is the first change point of the reactive current correction signal del_iqref after time t3, the change in the reactive current correction signal del_iqref causes a pulsation in the interconnection point voltage phase theta, and the angular frequency also varies. Variations also occur in BPF_omeg. Here, BPF_omeg becomes equal to or lower than the lower limit determination value TH_L, and the isolated operation detector 1005 detects the isolated operation state. When the isolated operation detector 1005 detects the isolated operation state, the isolated operation detection state ISLANDING_FLG changes from 0 to 1, all the gate signals of the inverter 10 are turned off, and the contactor control signal CTTctl changes from ON to OFF.

  By changing the reactive current command value sharply periodically, a large fluctuation can be generated in BPF_omeg, so that it is possible to reliably detect an isolated operation. It is possible to change the angular frequency by changing the reactive power command value, but the reactive response of the reactive power controller 1072 having the current control system in the minor loop is slower than the response of the current control unit 100d. When the correction signal calculator 1073 changes the reactive current command value, it is possible to cause a large variation in BPF_omeg compared to changing the reactive power command value.

  By setting the correction signal period Tperiod to be not more than twice the upper limit time, the reactive current correction signal changes suddenly every less than the upper limit time. In other words, the timing at which the reactive current command value suddenly changes can be reached within the upper limit time from the occurrence of the single operation state. As a result, the time required to detect the isolated operation state is equal to or shorter than the upper limit time, and the grid connection regulations can be satisfied.

  According to the present embodiment, when the power conversion device 1 is in an isolated operation state, even when the output power of the power conversion device 1 matches the power consumption of the load 200 connected in parallel to the power conversion device 1, It becomes possible to detect the single operation state reliably and promptly, stop the power generation of the power conversion device 1, and disconnect from the power system 300.

  Hereinafter, modifications of the present embodiment will be described.

  FIG. 9 shows a configuration of the power conversion device of the first modification.

  The power conversion device 1 of the first modified example is a power conversion device for a power storage system. A storage battery 31 is connected to the DC circuit of this power storage system power converter. This power conversion device for a power storage system has the same effects as the power conversion device 1 for solar power generation described above.

  FIG. 10 shows a configuration of a power conversion device of a second modification.

  The power converter 1 of a 2nd modification is a power converter device for wind power generation systems. A wind power generation system is connected to the DC circuit of the wind power generation system power converter. The wind power generation system obtains rotational torque by receiving wind by the blade 32, transmits the rotational torque to the rotor of the permanent magnet generator 34 via the shaft 33, and the stator winding of the permanent magnet generator 34. The induced voltage generated in the line is rectified by the diode rectifier 35 to obtain DC power. This power conversion device for wind power generation systems has the same effect as the power conversion device 1 for solar power generation described above. The diode rectifier 35 that rectifies the electric power of the permanent magnet generator 34 may be a self-excited converter.

  According to the present embodiment, a steep phase change at the connection point can be generated only at the time of isolated operation without being generated at the time of system connection, and the isolated operation can be detected at an early stage. In addition, by setting the change period of the reactive current command value within 0.2 s, it becomes possible to detect an isolated operation within 0.1 s.

  The power converter of the present embodiment changes the amplitude of the reactive current correction signal according to the effective current output from the power converter. By this operation, the amount of change in the reactive current can be limited when the effective current is small, and the efficiency reduction of the power conversion device due to the excessive reactive current can be suppressed. Here, when the effective current is small and coincides with the consumed effective current of the load, it means that the capacity of the load is small (light load). When the effective current is small, even if the reactive current is small, the unbalance ratio of the reactive current is large, and the phase change of the interconnection point voltage can be increased. Therefore, it is possible to achieve both the detection of the single operation state and the suppression of the decrease in efficiency of the power converter at all times.

  FIG. 11 illustrates a configuration of the power conversion device 2 according to the second embodiment.

  Compared with the power conversion device 1 of the first embodiment, the power conversion device 2 of the present embodiment has a controller 101 instead of the controller 100. In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 12 illustrates a configuration of the controller 100 according to the second embodiment.

  Compared to the controller 100, the controller 101 includes a reactive power control unit 101c instead of the reactive power control unit 100c. The reactive power control unit 101c adjusts the reactive current correction signal del_iqref according to the active current command value output from the DC voltage controller 1051. The reactive power control unit 101c includes a multiplier 1076, an upper / lower limiter 1077, and a multiplier 1078 in addition to the elements of the reactive power control unit 100c.

  The multiplier 1076 multiplies the active current command value by a predetermined gain. The upper / lower limiter 1077 limits the output of the multiplier 1076 with 1.0 as the upper limit and the ratio of the reactive current command value necessary for detecting the single operation state at no load as the lower limit.

  FIG. 13 shows the input / output characteristics of the upper / lower limiter 1077.

  This figure shows the relationship between the DC current command value and the output of the upper / lower limiter 1077. The output of the upper / lower limiter 1077 has a monotonically increasing characteristic with respect to the DC current command value, and limits the output to a range between a preset lower limit value and upper limit value. Thus, the reactive current command value can maintain the minimum amplitude even when the load is lightened. Further, even when the ratio of reactive power to active power is limited, reactive power can be suppressed.

  The multiplier 1078 multiplies the output of the reactive current correction signal calculator 1073 by the upper / lower limiter 1077, thereby calculating the reactive current correction signal del_iqref.

  In this embodiment, the reactive current correction signal corresponding to the effective current can be output by using the output of the multiplier 1078 as the reactive current correction signal. Thereby, since the reactive current at the time of the light load of the power converter device 2 can be reduced, it is possible to suppress a reduction in efficiency due to the reactive current output and to output the reactive current necessary for detecting the independent operation state.

  According to the present embodiment, when the power converter 2 is in a single operation state, even when the output power from the power converter 2 matches the power consumption of the load 200 connected in parallel to the power converter 2. Thus, it is possible to detect the single operation state reliably and promptly, stop the output of the power conversion device 2, and disconnect from the power system 300.

  Further, by limiting the range of the reactive current correction signal and making the reactive current correction signal monotonically increasing with respect to the active current command value, the loss due to the reactive current output at light load of the power converter 2 is reduced, It becomes possible to suppress a decrease in efficiency.

  In the present embodiment, the example in which the power conversion device 2 is applied to the inverter for solar power generation has been described. However, the same applies to the inverter for power storage system and the inverter for wind power generation as in the modification of the first embodiment. Has an effect.

  Terms in one embodiment of the present invention will be described. The DC voltage detection unit corresponds to the DC voltage sensor 71PT and the like. The output current detection unit corresponds to the output current sensors 72CTu, 72CTw, and the like. The connection point voltage detection unit corresponds to the connection point voltage sensors 70PTuv, 70PTvw, and the like. The phase calculation unit corresponds to the interconnection point voltage phase detection unit 100a and the like. The direct current command value calculation unit corresponds to the direct current voltage control unit 100b and the like. The reactive current command value calculation unit corresponds to the reactive power control unit 100c and the like. The control unit corresponds to the current control unit 100d and the like. The isolated operation detection unit corresponds to the isolated operation control unit 100e and the like. The basic reactive current command value corresponds to the reactive current command value iqref and the like. The correction command value corresponds to the reactive current correction signal del_iqref and the like. The reactive current command value corresponds to iqref2 and the like.

  The present invention is not limited to the above embodiments, and can be modified in various other forms without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Power converter, 10 ... Inverter, 10k, 10l, 10m, 10n, 10o, 10p ... IGBT module, 10C ... Capacitor, 20 ... Harmonic filter, 20L1, 20L2 ... Reactor, 20C ... Capacitor, 30 ... Solar panel 31 ... Storage battery, 32 ... Blade, 33 ... Shaft, 34 ... Permanent magnet generator, 35 ... Diode rectifier, 40 ... Contactor, 70PTuv, 70PTvw ... Interconnection point voltage sensor, 71PT ... DC voltage sensor, 72CTu, 72CTw ... Output Current sensor, 100, 101 ... Controller, 200 ... Load, 300 ... Power system, 400 ... Circuit breaker

Claims (5)

An inverter that converts direct current to alternating current and outputs it to the power system;
A DC voltage detector for detecting a DC voltage input to the inverter;
An output current detector for detecting an output current from the inverter;
A connection point voltage detection unit for detecting a connection point voltage at a connection point between the inverter and the power system;
A phase calculation unit for calculating a connection point voltage phase based on the connection point voltage;
Based on the DC voltage, an effective current command value calculation unit that calculates an effective current command value indicating an effective current to be output to the inverter;
A reactive current command value calculation unit that calculates a reactive current command value indicating a reactive current to be output to the inverter based on the output current and the interconnection point voltage;
By controlling the inverter based on the output current, the interconnection point voltage phase, the active current command value, and the reactive current command value, the phase of the output voltage of the inverter is set at predetermined time intervals. A control unit to change,
Based on the change in the interconnection point voltage phase, the isolated operation detecting unit for detecting an islanding operation state of the power converter,
With
The phase change of the output voltage that occurs at each time interval is steeper than the phase change of the voltage in the power system,
The time interval is equal to or less than an upper limit time predetermined as an upper limit of time from occurrence to detection of the isolated operation state,
The reactive current output from the inverter changes periodically with a period of twice the time interval,
The reactive current command value calculating section, based on the output current and the interconnection point voltage, to calculate a basic reactive current command value indicating the reactive current by the control to approximate the reactive power from the power converter to a target value , Calculating a correction command value that changes at the time interval, calculating the reactive current command value by adding the correction command value to the basic reactive current command value,
The reactive current command value calculation unit increases the correction command value in accordance with an increase in the active current command value.
Power conversion device. The reactive current command value calculation unit outputs a multiplication value used for multiplication for calculating the correction command value according to the active current command value, and calculates the correction command value using the multiplication value. The power converter device described in 1. The power conversion device according to claim 2, wherein the multiplication value is a value between a predetermined lower limit value and a predetermined upper limit value. The reactive current command value calculation unit outputs a lower limit value as the multiplication value when the active current command value is smaller than a predetermined first value, and when the active current command value is larger than a predetermined second value. Outputs an upper limit value as the multiplication value, and when the effective current command value is in the range from the first value to the second value, the multiplication value becomes monotonous if the effective current command value increases. The power conversion device according to claim 3, wherein the multiplication value is output so as to increase. A method for controlling a power converter including an inverter that converts direct current into alternating current and outputs the power to the power system,
Detect DC voltage input to the inverter,
Detecting the output current from the inverter;
Detecting a connection point voltage at a connection point between the inverter and the power system;
Calculate the connection point voltage phase based on the connection point voltage,
Based on the DC voltage, an active current command value indicating an effective current to be output to the inverter is calculated,
Based on the interconnection point voltage and the output current, to calculate a reactive current command value indicating a reactive current to be output to the inverter,
By controlling the inverter based on the output current, the interconnection point voltage phase, the active current command value, and the reactive current command value, the phase of the output voltage of the inverter is set at predetermined time intervals. Change
Based on the change of the interconnection point voltage phase, to detect the single operation state of the power converter ,
The phase change of the output voltage that occurs at each time interval is steeper than the phase change of the voltage in the power system,
The time interval is equal to or less than an upper limit time predetermined as an upper limit of time from occurrence to detection of the isolated operation state,
The reactive current output from the inverter changes periodically with a period of twice the time interval,
The reactive current command value is calculated based on the output current and the interconnection point voltage, and a basic reactive current command value indicating a reactive current by a control for bringing reactive power from the power converter close to a target value is calculated. A correction command value that changes at intervals is calculated, calculated by adding the correction command value to the basic reactive current command value,
The correction command value is increased according to an increase in the active current command value.
Control method.

Images