JP4907982B2 - Grid-connected inverter device - Google Patents

Description

  The present invention relates to a grid-connected inverter device, and more particularly to a technique for reducing switching loss in the inverter circuit.

  In recent years, a power generation system using a fuel cell, a solar cell, or the like that has little influence on the environment has been actively developed from the viewpoint of protecting the global environment. In such a power generation system, the generated DC power is converted into AC power having a commercial frequency by a grid-connected inverter device, and is supplied to a load linked to the commercial power system.

  FIG. 12 is a configuration example of a conventional grid-connected inverter device used for such a purpose. A grid interconnection inverter device 101 shown in FIG. 12 includes a DC / DC conversion circuit 102, an inverter main circuit 103, a filter circuit 104, and an inverter control circuit 105.

  DC power supplied from a DC power source 110 such as a fuel cell or a solar cell is converted into DC power transformed by the DC / DC conversion circuit 102 and supplied to the inverter main circuit 103. The inverter main circuit 103 switches the DC power supplied under the control of the inverter control circuit 105 and performs pulse width modulation, so that the phase of the system voltage Vac of the commercial power system 111 is substantially changed from the filter circuit 104 connected to the load side. The current Iac having the matched phase is output.

  Since it is necessary to output the current Iac against the system voltage Vac, a DC voltage Vdc higher than the peak voltage of the system voltage is supplied to the inverter main circuit 103 of the conventional system interconnection inverter device 101. Is always supplied by.

  By the way, when the high DC voltage Vdc is constantly supplied to the inverter main circuit 103 as described above, the input DC voltage Vdc and the system voltage Vac of the inverter main circuit 103 are low when the voltage of the system voltage Vac changing in a sine wave is low. The voltage difference from the instantaneous value of increases. The switching operation of the inverter main circuit 103 in a state where the voltage difference is large causes a large switching loss.

  As described above, the conventional control method has a problem that a high switching loss is generated at a timing when the instantaneous value of the system voltage Vac is low. Also, when outputting a low current, the filter circuit 104 receives a pulse current having a voltage higher than the peak value of the system voltage Vac. For this reason, there is a problem that a large high-frequency loss is generated in the reactor 106 of the filter circuit N104.

As a prior art related to such a problem in the grid-connected inverter device, there are techniques disclosed in Patent Documents 1 and 2, for example. However, since these disclosed technologies change the supply voltage to the inverter main circuit in accordance with the change in the peak voltage of the system voltage, the effect is limited.
Japanese Patent Application No. 2003-274061 Japanese Patent Laid-Open No. 10-14112

  The present invention has been made to solve such problems of the prior art, and an object thereof is to reduce the switching loss of the inverter main circuit in the grid-connected inverter device.

In order to achieve the above object, the invention according to claim 1 is a grid-connected inverter device that converts DC power supplied from the outside into AC power and links the commercial power system (12) to a load. A DC / DC conversion circuit (2) for converting the voltage of the DC power, an inverter main circuit (3) for switching the DC power output from the DC / DC conversion circuit into AC power, An inverter control circuit (4) for controlling the switching operation of the inverter main circuit, and a filter circuit (5) for removing harmonic components from the alternating current output from the inverter main circuit, wherein the DC / DC conversion circuit comprises: the commercial power system constructed in so as to output a voltage value obtained by adding a constant voltage predetermined to the absolute value of the instantaneous value of the system voltage, constant voltage the predetermined is specified magnitude of the current System interconnection inverter device system interconnection characterized by having a value not less than the sum of the instantaneous maximum value of the voltage drop in the filter circuit when flowing and the maximum value of the voltage drop in the switching element of the inverter circuit It is an inverter device.

According to such a configuration, a voltage having a value obtained by adding a predetermined constant voltage to the absolute value of the instantaneous value of the system voltage is applied to the inverter main circuit. Therefore, by adjusting a predetermined constant voltage, the switching voltage when the switching element in the inverter main circuit performs the switching operation can be set to a low value without distorting the output current waveform. As a result, the switching loss of the inverter main circuit is reduced.
In addition, a low voltage can be supplied to the inverter main circuit within a range where the output current waveform is not distorted. Therefore, the switching loss of the inverter main circuit can be reduced.

The invention described in claim 2 is a grid-connected inverter device that converts DC power supplied from the outside into AC power and supplies it to a load linked to a commercial power system, the voltage of the DC power being A DC / DC conversion circuit that converts the DC power, an inverter main circuit that switches the DC power output from the DC / DC conversion circuit into AC power, an inverter control circuit that controls the switching operation of the inverter main circuit, A filter circuit that removes harmonic components from the alternating current output from the inverter main circuit, and the DC / DC conversion circuit is a constant voltage predetermined to an absolute value of an instantaneous value of a system voltage of the commercial power system. The inverter control circuit is configured to output a voltage having a value equal to the phase of the grid voltage and a current whose amplitude matches a specified value. Controlling said inverter main circuit so as to be output from the filter circuit to the commercial power system, a constant voltage the predetermined, the value of .omega.t when showing the waveform of the system voltage in Vacp · sin (ωt) is n Is a first positive constant voltage in the range of nπ to (n + 1/2) π, and in the range of (n + 1/2) π to (n + 1) π, the first positive constant voltage. A grid-connected inverter device having a small second positive constant voltage.

According to such a configuration, a voltage having a value obtained by adding a predetermined constant voltage to the absolute value of the instantaneous value of the system voltage is applied to the inverter main circuit. Therefore, by adjusting a predetermined constant voltage, the switching voltage when the switching element in the inverter main circuit performs the switching operation can be set to a low value without distorting the output current waveform. As a result, the switching loss of the inverter main circuit is reduced.
Since power is output from the grid-connected inverter device at a power factor of 1.0, power can be efficiently output to the commercial power system. The same effect as that of the first aspect of the invention can also be obtained.
Furthermore , compared with the invention according to claim 1 , the switching loss can be further reduced when the value of ωt is in the range of (n + 1/2) π to (n + 1) π.

The invention according to claim 3 is a grid-connected inverter device that converts DC power supplied from the outside into AC power and supplies the load to the commercial power grid, the voltage of the DC power being A DC / DC conversion circuit that converts the DC power, an inverter main circuit that switches the DC power output from the DC / DC conversion circuit into AC power, an inverter control circuit that controls the switching operation of the inverter main circuit, A filter circuit that removes harmonic components from the alternating current output from the inverter main circuit, and the DC / DC conversion circuit is a constant voltage predetermined to an absolute value of an instantaneous value of a system voltage of the commercial power system. The inverter control circuit is configured to output a voltage having a value equal to the phase of the grid voltage and a current whose amplitude matches a specified value. Controlling said inverter main circuit so as to be output to the commercial power system from the filter circuit, the DC / DC converter circuit, the system voltage is equal phase amplitude to the nominal amplitude of the actual system voltage having the same phase And the filter circuit has a predetermined constant voltage as the absolute value of the instantaneous voltage at the input end of the filter circuit when a current of a specified magnitude in phase with the system voltage flows through the filter circuit. It is comprised so that the voltage of the value which added may be output, It is the grid connection inverter apparatus characterized by the above-mentioned.

According to such a configuration, a voltage having a value obtained by adding a predetermined constant voltage to the absolute value of the instantaneous value of the system voltage is applied to the inverter main circuit. Therefore, by adjusting a predetermined constant voltage, the switching voltage when the switching element in the inverter main circuit performs the switching operation can be set to a low value without distorting the output current waveform. As a result, the switching loss of the inverter main circuit is reduced.
Since power is output from the grid-connected inverter device at a power factor of 1.0, power can be efficiently output to the commercial power system. The same effect as that of the first aspect of the invention can also be obtained.
Furthermore , a low voltage that does not distort the output current waveform can be supplied to the inverter main circuit. Accordingly, when the switching element in the inverter main circuit performs the switching operation, the switch voltage becomes a lower value, so that the switching loss can be further reduced.

  Hereinafter, an embodiment of a grid-connected inverter device according to the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of the grid-connected inverter device 1 with a block diagram.

  The grid-connected inverter device 1 converts DC power supplied from a DC power source 11 such as a fuel cell or a solar cell into AC power, and connects to the commercial power system 12 to load connected to the commercial power system 12. It supplies power. The grid-connected inverter device 1 of this embodiment includes a DC / DC conversion circuit 2, an inverter main circuit 3, an inverter control circuit 4, and a filter circuit 5.

  The DC / DC conversion circuit 2 includes a high-frequency inverter main circuit 7, a high-frequency transformer 8, a rectifier circuit 9, a smoothing circuit 10, and a DC / DC conversion control circuit 13. The high-frequency inverter main circuit 7 is a switching circuit composed of four switching elements configured in a full bridge. Under the control of the DC / DC conversion control circuit 13, the DC power supplied from the DC power supply 11 is switched and converted to high-frequency AC power.

  The high frequency transformer 8 transforms the voltage of the high frequency AC power output from the high frequency inverter main circuit 7 and supplies it to the rectifier circuit 9. Depending on the relationship between the voltage of the DC power supply 11 and the system voltage of the commercial power system 12, the high-frequency transformer 8 may be a step-up transformer or a step-down transformer.

  The rectifier circuit 9 is a rectifier circuit composed of a diode bridge, and rectifies the high-frequency current output from the high-frequency transformer 8 to return it to DC power. The smoothing circuit 10 smoothes the current and voltage of the output DC power. The smoothing circuit 10 includes a reactor L1 and a capacitor C1, and the capacitor C1 is connected to the output side. Both ends of the capacitor C1 are output terminals of the DC / DC conversion circuit 2, and the voltage Vdc between them is the output voltage Vdc of the DC / DC conversion circuit 2.

  The output voltage Vdc and the system voltage Vac of the commercial power system 12 are input to the DC / DC conversion control circuit 13. The DC / DC conversion control circuit 13 determines a target value Vdcs of the output voltage Vdc based on the system voltage Vac and later-described logic and circuit configuration, and the high-frequency inverter main circuit so that the output voltage Vdc matches the target value Vdcs. 7 is controlled.

  The DC power output from the DC / DC conversion circuit 2 is supplied to the inverter main circuit 3. The inverter main circuit 3 is a switching circuit composed of four switching elements. Under the control of the inverter control circuit 4, the DC power supplied from the DC / DC conversion circuit 2 is switched and converted into PWM-modulated AC power. . The fundamental frequency of the PWM-modulated AC power is controlled to be equal to the frequency of the commercial power system 12.

  The PWM-modulated alternating current is supplied to the filter circuit 5. The filter circuit 5 is a low-pass filter including a reactor L2 and a capacitor C2, and attenuates and removes harmonic currents included in the current output from the inverter main circuit 3, and supplies the attenuated harmonic current to the commercial power system 12.

  The inverter control circuit 4 includes an output current Iinv of the inverter main circuit 3, an amplitude target value Iacps of the output current Iac output to the commercial power system 12, and a phase difference target value θs between the output current Iac and the system voltage Vac of the commercial power system 12. Is entered. The phase difference target value θs is often zero, and an output current Iac that matches the phase of the system voltage Vac is output to the commercial power system 12. The output current Iinv of the inverter main circuit 3 is detected by a current transformer 15 attached to the input side of the filter circuit 5.

  The inverter control circuit 4 controls the waveform of the output current Iinv by adjusting the switching operation of the inverter main circuit 3. The target waveform changes in a sine wave shape at the same frequency as the frequency of the system voltage Vac, the amplitude is equal to the amplitude target value Iacps, and the phase difference from the system voltage Vac is a waveform that matches the phase difference target value θs.

  A configuration example of the inverter control circuit 4 for performing such control is shown in a block diagram in FIG. The system voltage Vac is input to the zero-cross detection circuit 21 and the timing when the voltage becomes zero (hereinafter referred to as zero-cross timing) is detected. The detected zero-cross timing signal is input to the PLL oscillation circuit 22. A phase difference target value θs given from the outside is also input to the PLL oscillation circuit 22. The PLL oscillation circuit 22 generates a sine wave sin (ωt + θs) having a unit amplitude whose phase is advanced from the system voltage Vac by the phase difference target value θs based on the input zero-cross timing.

  The unit sine wave sin (ωt + θs) is multiplied by the output current amplitude target value Iacps given from the outside by the multiplication circuit 23 to generate the output current target value Iinvs (= Iacps · sin (ωt + θs)). This output current target value Iinvs is compared with the output current Iinv of the inverter main circuit 3 in the subtraction circuit 24, and a deviation ΔI is calculated. The deviation ΔI is subjected to proportional-integral calculation by the PI calculation circuit 25, and a substantially sinusoidal voltage is output as the calculation result.

  The substantially sine wave output voltage is compared with the high frequency triangular wave voltage output from the triangular wave generating circuit 28 in the first and second PWM comparison circuits 26 and 27. The first PWM comparison circuit 26 compares the triangular wave that swings in the positive direction. From the output, a signal obtained by PWM modulating the waveform of the positive voltage portion of the approximately sine wave voltage is output. In the second PWM comparison circuit 27, a comparison is made with a triangular wave that swings in the negative direction. From the output, a signal obtained by PWM-modulating the waveform of the negative voltage portion of the approximately sine wave voltage is output. The output signal of the first PWM comparison circuit 26 is voltage level converted to drive the switching elements Q5 and Q8 in the inverter main circuit 3. The output signal of the second PWM comparison circuit 27 is voltage level converted to drive the switching elements Q6 and Q7 in the inverter main circuit 3.

  The inverter main circuit 3 switches the DC voltage Vdc that is the input voltage in accordance with such a drive signal output from the inverter control circuit 4. As a result, a substantially sinusoidal output voltage Vinv that is PWM-modulated is output from the inverter main circuit 3 and input to the filter circuit 5. By applying a substantially sine wave voltage Vinv to the filter circuit 5, a substantially sine wave current Iinv (which is also an output current of the inverter main circuit 3) flows through the filter circuit 5.

  As can be seen from the block diagram of FIG. 2, the output current Iinv of the inverter main circuit 3 is feedback-controlled so as to coincide with the output current target value Iinvs (= Iacps · sin (ωt + θs)) which is a sine wave. Therefore, the output current Iinv should be a sine wave. However, since the output voltage Vinv of the inverter main circuit 3 is a PWM-modulated voltage, it does not have a clean sine waveform but a substantially sine waveform including harmonic components. However, since feedback control is performed, the output current Iinv has a basic angular frequency that matches the angular frequency ω (= 2πf, f is the frequency of the system voltage Vac) of the system voltage Vac, and the amplitude is substantially equal to the output current amplitude target value Iacps. In addition, the phase difference with respect to the system voltage Vac has a waveform that substantially matches the phase difference target value θs.

  Next, operations unique to the grid interconnection inverter device 1 of the present embodiment will be described. As described in “Background Art”, in the conventional grid-connected inverter device, the value of the input DC voltage Vdc supplied to the inverter main circuit 3 is controlled to a constant voltage higher than the amplitude of the system voltage Vac. On the other hand, in the grid-connected inverter device 1 of the present embodiment, the value of the input DC voltage Vdc is dynamically changed in accordance with the fluctuation within one cycle of the system voltage Vac, thereby switching loss in the inverter main circuit 3. To reduce

  As described above, the output current Iinv flowing through the filter circuit 5 includes harmonic components, but the harmonic components are attenuated and removed by the filter circuit 5. Only the current of the fundamental wave component (the sine wave whose frequency is equal to the frequency f of the system voltage Vac) component is supplied to the commercial power system 12 as the output current Iac of the system interconnection inverter device 1. Normally, the fundamental current component flowing through the capacitor C2 of the filter circuit 5 is designed to be small, so that value is ignored. Then, the fundamental wave current included in the output current Iinv of the inverter main circuit 3 and the output current Iac of the grid interconnection inverter device 1 become a current that matches.

The input terminal voltage of the filter circuit 5 when only the fundamental wave current Iac having the frequency f flows through the filter circuit 5 is Vdac (the output voltage of the inverter main circuit 3 including the harmonics is Vinv). The resistance of reactor L2 is neglected because it is small, and its inductance is L. Then, the input voltage Vdac of the filter circuit 5 when only the fundamental wave current Iac flows is calculated as follows.
Vdac = Vac + jωL · Iac (1) jωL · Iac (j is a complex number) on the right side of the equation is a voltage drop in the reactor L2, and the phase is advanced by π / 2 with respect to the fundamental current Iac.

When the phase of the fundamental wave current Iac is controlled so as to coincide with the phase of the system voltage Vac, formula (1) is converted into a vector diagram as shown in FIG. The input voltage Vdac of the filter circuit 5 with respect to the fundamental current Iac is a voltage whose phase is advanced by θ from the system voltage Vac. The phase difference θ is calculated by the following equation from FIG.
θ = arctan (ωL · Iacp / Vacp) (2) where Iacp is the amplitude of the fundamental current (output current of the grid-connected inverter device 1) Iac, and Vacp is the amplitude of the system voltage Vac.

  The instantaneous value of the system voltage Vac is expressed as Vacp · sin (ωt). When the phase of the fundamental wave current Iac is made to coincide with the phase of the system voltage Vac, the waveforms of the voltage drops jωL · Iac and Vdac in the reactor L2 are drawn as shown in (1) of FIG.

  When the fundamental wave current Iac is passed through the filter circuit 5, the input terminal voltage Vdac of the filter circuit 5 calculated by the equation (1) changes as shown by a curve Vdac in (1) of FIG. In other words, when a voltage changing as shown by the curve Vdac in the figure is applied to the input terminal of the filter circuit 5, the fundamental current Iac shown in the figure flows in the filter circuit 5, and the current is connected to the grid connection. It means that the output current Iac of the inverter device 1 flows into the commercial power system 12. That is, in order to supply the output current Iac to the commercial power system 12, a voltage that changes as shown by the curve Vdac in the figure may be applied to the input terminal of the filter circuit 5.

  However, the curve Vdac in (1) of FIG. 4 is a voltage waveform when the commercial power system 12 outputs the output current Iac having the same phase as the system voltage Vac, and the voltage Vdac when outputting a current not in phase is shown in the figure. The amplitude and phase are slightly different from the curve Vdac of 4 (1). The voltage Vdac in such a case is also calculated by equation (1).

  The voltage Vdac needs to be generated as the output voltage of the inverter main circuit 3. When outputting a positive voltage to the output of the inverter main circuit 3, the switching elements Q5 and Q8 are turned on, and Q6 and Q7 are turned off. When outputting a negative voltage, the switching elements Q5 and Q8 are turned off and Q6 and Q7 are turned on. Therefore, a positive DC voltage may be supplied to the inverter main circuit 3 at any time.

  The minimum value of the voltage that must be applied to the inverter main circuit 3 in order to output the voltage Vdac shown in (1) of FIG. 4 satisfying the expression (1) from the inverter main circuit 3 is the switching element Q5. Assuming that the voltage drop at Q8 is zero, the voltage is as shown in (2) of FIG. The curve (2) in FIG. 4 is a curve representing the absolute value | Vdac | of the instantaneous value of the voltage Vdac shown in (1) in FIG.

  A voltage | Vdac | which changes as shown in (2) of FIG. 4 is applied to the inverter main circuit 3, and switching is performed when the voltage Vdac is positive, for example, during a period of angular frequency (−θ) to (π−θ). Elements Q5 and Q8 are turned on, and Q6 and Q7 are turned off. The switching elements Q5 and Q8 are turned off and Q6 and Q7 are turned on during a period when the voltage Vdac is negative, for example, during a period of angular frequency (π−θ) to (2π−θ). If operated in this way, the inverter main circuit 3 outputs a voltage Vdac that changes as indicated by the curve Vdac in FIG. When such a voltage Vdac is input to the filter circuit 5, a sine wave current Iac that changes as indicated by a curve Iac in FIG. Then, the current is supplied to the commercial power system 12 as the output current Iac.

  The above is an explanation of the ideal state assuming that the current of the frequency f component flowing in the capacitor C2, the DC resistance of the reactor L2, and the conduction resistances of the switching elements Q5 to Q8 are all zero. In an actual circuit, it is necessary to consider the influence of these currents, DC resistance, and conduction resistance. Therefore, the value of the DC voltage Vdc applied to the inverter main circuit 3 is a value obtained by adding a positive constant voltage ΔV predetermined in consideration of such a voltage drop to the voltage | Vdac | of the waveform shown in (2) of FIG. | Vdac | + ΔV), or a value slightly higher than that. The value of the constant voltage ΔV is, for example, the sum of the instantaneous maximum value of the voltage drop in the filter circuit 5 and the maximum value of the voltage drop in the switching element of the inverter main circuit 3 when an output current Iac having a specified magnitude flows. The value shall not be less than.

In that way, the output current target value Iinvs of the inverter main circuit 3 is determined and given to the inverter control circuit 4 as follows. A value of Iacps, θs = 0 is given as a target value.
Iinvs = Iac = Iacps · sin (ωt + θs) (3) Expression Iacps is an amplitude target value, and θs is a phase difference target value with respect to the system voltage Vac, which is often zero. In this case, Iac is a target current output to the commercial power system 12. When the values of Iacps and θs are given as target values, the inverter control circuit 4 performs feedback control so that the output current Iinv of the inverter main circuit 3 matches the target current Iinvs = Iac by the control logic shown in FIG.

  By the way, if the predetermined constant voltage ΔV in the DC voltage Vdc = (| Vdac | + ΔV) applied to the inverter main circuit 3 is larger than the instantaneous value of the actual voltage drop in the filter circuit 5 and the inverter main circuit 3, the output current Iinv tends to be larger than the target current Iinvs = Iac. Then, the inverter control circuit 4 detects this by current feedback, and starts the switching operation for PWM-modulating the input DC voltage Vdc in the inverter main circuit 3 to suppress the output current Iinv from deviating from the target current Iinvs = Iac. . When the inverter main circuit 3 starts a switching operation for PWM modulation, the output voltage Vinv of the inverter main circuit 3 becomes a substantially sine wave voltage including harmonics. Therefore, the current Iinv that is the output current of the inverter main circuit 3 and the input current of the filter circuit 5 is a substantially sinusoidal current including harmonics.

  Thus, the inverter control circuit 4 tries to make the output current Iinv coincide with the sine wave target current Iinvs = Iac by feedback control. However, since the operation of the inverter main circuit 3 is a switching operation for PWM modulation, the output current Iinv Includes a harmonic component. The harmonic component in the output current Iinv is removed by the filter circuit 5, and the sine wave current Iac, which is the fundamental wave component of the output current Iinv and is also the target current, is output to the commercial power system 12.

  Here, the harmonic current component removed by the filter circuit 5 generates a voltage at both ends of the reactor L2. Therefore, the value of the constant voltage ΔV in the DC voltage Vdc = (| Vdac | + ΔV) given to the inverter main circuit 3 needs to consider the voltage generated at both ends of the reactor L2 due to the harmonic current component.

  The DC voltage Vdc = (| Vdac | + ΔV) applied to the inverter main circuit 3 is generated by the DC / DC conversion circuit 2. The output voltage Vdc of the DC / DC conversion circuit 2 is controlled by feedback control by the DC / DC conversion control circuit 13. Control is accompanied by delay and advancement. Accordingly, the output voltage target value Vdcs given to the DC / DC conversion circuit 2 that generates the DC voltage Vdc needs to be given a value that also takes into account control delay and advancement.

  For this reason, in addition to the voltage drop considered when determining the value of ΔV, the DC / DC conversion circuit 2 has a voltage drop in the reactor L2 due to the harmonic current component described above, control delay / advance, and other controls. In consideration of errors and the like, it is necessary to give a voltage represented by the following equation as the output voltage target value Vdcs.

Output voltage target value Vdcs = (| Vdac | + ΔV1) However, ΔV1> ΔV (4) Equation (4) The DC / DC conversion circuit 2 is operated so that the voltage Vdcs calculated by the equation (4) is output. When the inverter control circuit 4 is operated with the current of the expression (3) as a target value, the target sine wave current Iinvs = Iac can be output to the commercial power system 12. In that case, the fundamental wave component in the output voltage Vinv of the inverter main circuit 3 becomes equal to the system voltage Vac.

  Incidentally, the voltage | Vdac | in the equation (4) is a voltage that changes as shown in (2) of FIG. 4, for example. The value changes with time, and the amplitude changes with voltage fluctuation of the system voltage Vac. Further, there is a phase difference with respect to the system voltage Vac, and the phase difference also changes slightly due to voltage fluctuation. Therefore, it is not easy to generate the output voltage target value Vdcs calculated by the equation (4) by strictly calculating it.

  Therefore, in an actual circuit, the value of | Vdac | is obtained by approximate calculation. Instead, the value of ΔV1 is determined taking into account the error due to the approximate calculation. The two values thus determined and added are added to determine the output voltage target value Vdcs that is not less than the value strictly calculated by equation (4). The high-frequency inverter main circuit 7 is controlled by the DC / DC conversion control circuit 13 so that the output voltage Vdc of the DC / DC conversion circuit 2 matches the value.

  Hereinafter, a practical control method for adopting such approximate calculation to control the output voltage Vdc of the DC / DC conversion circuit 2 and to output the target sine wave current Iinvs = Iac to the commercial power system 12 will be described. This will be explained separately.

(First embodiment)
The voltage Vdac in the equation (4) for calculating the output voltage target value Vdcs of the DC / DC conversion circuit 2 is calculated by the equation (1). Since the efficiency is poor if the voltage drop of the reactor L2 due to the target sine wave output current Iac is large, the voltage drop jωL · Iac is designed to be smaller than the system voltage Vac. The value of ωL · Iacp (Iacp is the amplitude of the output current Iac) is normally about 3% of the amplitude Vacp of the system voltage Vac. Therefore, the equation (1) is approximated as follows.
Vdac≈Vac (5) Equation (4) becomes as follows.
Output voltage target value Vdcs≈ (| Vac | + ΔV1) (6)

Vdcs is determined as follows in consideration of errors due to approximation so that the value of Vdcs calculated by equation (6) does not fall below Vdcs calculated by equation (4).

Output voltage target value Vdcs = | Vac | + ΔV2> | Vdac | + ΔV1 (7) The value of the equation ΔV2 can be determined by calculation or experimentally. If the value of ΔV2 is too large, the effect of reducing the switching loss is reduced, so the value is determined as small as possible.

  FIG. 5 is a configuration example of the DC / DC conversion control circuit 13 for realizing the control using the equation (7). The system voltage Vac is rectified by the rectifier circuit 30 to generate a voltage | Vac |. Next, the adder 31 adds a predetermined constant voltage ΔV2 to the voltage | Vac | to calculate the output voltage target value Vdcs of the equation (7). Thereafter, feedback control is performed so that the output voltage Vdc matches the target value Vdcs.

  In the feedback control, first, the subtractor 32 calculates a deviation ΔV between the target value Vdcs and the output voltage Vdc. The deviation ΔV is input to the PI calculation circuit 33 to perform proportional integration calculation. The PWM gate drive signal generation circuit 34 generates a PWM-modulated gate drive signal for driving the switching elements Q1 to Q4 in the high-frequency inverter main circuit 7 based on the calculation result thus obtained. The switching elements Q1 to Q4 in the high-frequency inverter main circuit 7 are controlled by the output gate drive signal. By such control, the output voltage Vdc of the DC / DC conversion circuit 2 coincides with the output voltage target value Vdcs calculated by the equation (7).

On the other hand, the inverter control circuit 4 performs feedback control so that the output current Iinv of the inverter main circuit 3 matches the target sine wave current Iinvs = Iac. The control is to set the target current Iinvs,
Iinvs = Iac = Iacps · sin (ωt + θs) It is determined as shown in the equation (8), and the amplitude target value Iacps and the phase difference target value θs may be input to the inverter control circuit 4 shown in FIG. The phase difference target value θs may be an arbitrary value, but is often set to zero.

  6 shows the absolute value | Vac | of the system voltage Vac when the phase difference target value θs is zero, the output current Iac controlled according to the equation (8), the absolute value of Vdac | Vdac | according to the equation (1), 7 shows the waveform of the output voltage (input DC voltage of the inverter main circuit 3) Vdc of the DC / DC conversion circuit 2 controlled by the output voltage target value Vdcs of the equation (7).

  As apparent from FIG. 6, the difference voltage between the input DC voltage Vdc of the inverter main circuit 3 and the absolute value | Vac | of the system voltage Vac applies a constant voltage higher than the peak voltage of the system voltage Vac to the inverter main circuit 3. Compared to the case of the prior art, it is significantly smaller. The small difference voltage means that the voltage applied to the switching element when the switching elements Q5 to Q8 in the inverter main circuit 3 are turned on / off is low. If the applied voltage at the time of switching is small, the power loss that occurs when switching is also reduced. For this reason, the grid interconnection inverter device 1 of the present embodiment has an effect of greatly reducing the switching loss.

(Second Embodiment)
This embodiment is an embodiment limited to the case where the phase of the output current Iac output from the grid interconnection inverter device 1 to the commercial power system 12 is matched with the phase of the system voltage Vac. In order to match the phases, the inverter control circuit 4 shown in FIG. 2 controls the output current Iac by giving zero as the phase difference target value θs and giving the target amplitude value as the amplitude Iacps of the output current Iac.

  In the control method described in the first embodiment, when the phase difference target value θs is zero, the absolute value | Vac | of the system voltage Vac, the output current Iac, and the absolute value of Vdac | Vdac | The waveform of the input DC voltage Vdc of the inverter main circuit 3 controlled by the equation 7) is shown in FIG. In the waveform of FIG. 6, the phase of the absolute value | Vdac | of Vdac is advanced by θ from the phase of the absolute value | Vac | of system voltage Vac. The waveform of the DC voltage Vdc is in phase with | Vac | because it is based on a value obtained by adding a constant value ΔV2 to | Vac |. Therefore, the phase of the absolute value | Vdac | is advanced by θ with respect to the DC voltage Vdc. For this reason, the difference voltage between the DC voltage Vdc and the absolute value | Vdac | is small in the first half (for example, the angular frequency is in the range of 0 to π / 2) of the one-cycle waveform of | Vac | In the range of π / 2 to π).

  In the first embodiment, the equality equation (7) is used to control the DC voltage Vdc to be (| Vac | + ΔV2). However, as shown by the inequality equation (7), The DC voltage Vdc may be larger than (| Vdac | + ΔV1). Accordingly, the control method of the first embodiment is modified, and the value of ΔV2 is set to the second half of the one-period waveform of the absolute value | Vac | on the condition that the inequality expression of the expression (7) always holds. The value of the DC voltage Vdc may be controlled to a value smaller than the first half of the one-cycle waveform.

  In this embodiment, in order to perform such control, the value of ΔV2 is determined to be ΔV21 in the first half of the one-cycle waveform of | Vac | and ΔV22 in the second half so that ΔV21> ΔV22. Then, the control is performed with the output voltage target value Vdcs being (| Vac | + ΔV21) in the first half of the one-cycle waveform of | Vac |, and (| Vac | + ΔV22) in the second half. With such control, it is possible to reduce the switching loss in the second half of the one-cycle waveform compared to the case where the value of ΔV2 is set to a constant value of ΔV21. The waveform of the input DC voltage Vdc of the inverter main circuit 3 in such a control is shown by a curve Vdc in FIG.

  FIG. 8 shows a configuration example of the DC / DC conversion control circuit 13 for outputting the DC voltage Vdc having the waveform shown by the curve Vdc in FIG. In the DC / DC conversion control circuit 13 a, the system voltage Vac is first input to the rectifier circuit 41, the absolute value | Vac | is taken out, and is input to the adder 31. At the same time, in order to generate a signal for identifying the first half and the second half of one period waveform of the absolute value | Vac |, the absolute value | Vac | Next, the differential value is compared with zero V by the comparison circuit 43. Then, from the output of the comparison circuit 43, a rectangular wave having a positive voltage in the first half of the one-period waveform of the absolute value | Vac | and zero V in the second half is output.

  The analog switch 44 is opened / closed by the output of the comparison circuit 43, and when the output is a positive voltage, the voltage of ΔV 21 is input to the adder 31. On the other hand, the analog switch 45 is opened / closed by a signal obtained by inverting the output of the comparison circuit 43 by the inverter circuit 46, and when the output is zero V, the voltage of ΔV 22 is input to the adder 31. By switching between ΔV21 and ΔV22 in this way, the voltage from the adder 31 is (| Vac | + ΔV21) in the first half of the one-cycle waveform of the absolute value | Vac |, and (| Vac | + ΔV22) in the second half. Is output.

  Thereafter, (| Vac | + ΔV21) and (| Vac | + ΔV22) are set as target voltages, and the output voltage Vdc of the DC / DC conversion circuit 2 is set to the target voltage by feedback control with the same circuit configuration as in the first embodiment. Match the voltage. In this way, the DC / DC conversion circuit 2 can output the DC voltage Vdc having the waveform shown by the curve Vdc in FIG. If such control is performed, the difference between the DC voltage Vdc and the absolute value | Vac | of the system voltage Vac in the latter half of the one-period waveform of the absolute value | Vac | Switching loss can be reduced compared to the case where the constant value ΔV21 is maintained.

(Third embodiment)
In the first and second embodiments, without considering the phase difference θ (see FIG. 3) between the system voltage Vac and the voltage Vdac calculated by the expression (1), the voltage Vdac becomes the system voltage Vac as in the expression (5). Approximate to be equal. The error caused by such approximation is taken into account when determining the value of ΔV1 in the equation (6) so that the error due to approximation does not affect the output current Iac.

  On the other hand, in the present embodiment, the DC voltage Vdc is controlled according to the equations (1) and (4) without approximating the equation (5). However, the constant value ΔV1 is determined in consideration of the voltage drop in the filter circuit 5 due to the above-described harmonic current component, the delay or advance of control in the DC / DC conversion circuit 2, and other control errors. Further, the phase of the output current Iac is assumed to match the phase of the system voltage Vac as in the case of the second embodiment.

  Such control will be described with reference to the waveform diagram. This means that the output voltage Vdc is changed like a curve Vdc obtained by translating the curve | Vdac | shown in FIG. 9 upward by a constant voltage ΔV1. By changing in this way, the voltage applied to the switching elements when the switching elements Q5 to Q8 of the inverter main circuit 3 are switched can be made smaller than in the first and second embodiments, and the switching loss is further reduced. Can be made. A configuration example of the DC / DC conversion control circuit 13 for performing such control is shown in FIG.

In the DC / DC conversion control circuit 13b of the present embodiment, the vector calculator 51 is used to calculate | Vdac | based on the equation (1), and the amplitude Vdacp of the voltage Vdac and the phase θ with respect to the system voltage Vac are first determined. Calculate. The vector calculator 51 receives the target amplitude value Iacp of the output current Iac and the rated amplitude value Vacp of the system voltage Vac. As the amplitude rating value Vacp, a maximum amplitude value expected in consideration of fluctuations may be used. The vector calculator 51 calculates the amplitude Vdacp of the voltage Vdac and the phase θ with respect to the system voltage Vac from the relationship of the expression (1). The phase θ can be calculated by the above equation (2), and the amplitude Vdacp can be calculated by the following equation.
Vdacp = (Vacp ² + (ωL · Iacp) ² ) ^1/2 Equation (9)

  On the other hand, the actual system voltage Vac is detected and input to the zero cross detection circuit 52, and the zero cross timing at which the voltage becomes zero is detected. The detected zero-cross timing signal is input to the PLL oscillation circuit 53. The phase θ calculated by the vector calculator 51 is also input to the PLL oscillation circuit 53. The PLL oscillation circuit 53 generates a sine wave sin (ωt + θ) having a unit amplitude that is advanced by the phase θ from the system voltage Vac based on the input zero-cross timing.

  Next, the unit sine wave sin (ωt + θ) and the amplitude Vdacp calculated by the vector calculator 51 are multiplied by the multiplication circuit 23 to generate a voltage Vdac (= Vdacp · sin (ωt + θ)). This voltage Vdac is rectified by the rectifier circuit 55 to generate | Vdac |. Next, the adder 56 adds a constant voltage ΔV1 in which an error is expected to generate an output voltage target value Vdcs of the DC / DC conversion circuit 2 according to the equation (4). After that, feedback control is performed with the same circuit configuration as in the first and second embodiments using the Vdcs as a target voltage, and the output voltage Vdc of the DC / DC conversion circuit 2 is made to coincide with the target value Vdcs. By controlling in this way, the DC / DC conversion circuit 2 can output the DC voltage Vdc shown by the curve Vdc in FIG. And if it controls in this way, the switching loss of the inverter main circuit 3 can be reduced as mentioned above.

(Other embodiments)
The DC / DC conversion circuit 2 used in the above embodiment may be modified as follows.
(1) The output voltage Vdc of the DC / DC conversion circuit 2 in each of the above embodiments is controlled by feedback control by the DC / DC conversion control circuit 13. For this reason, the charging voltage of the capacitor C1 in the smoothing circuit 10 is constantly changing, and the need for voltage smoothing by the capacitor C1 is lower than that of the conventional circuit. Therefore, the capacity of the capacitor C1 may be reduced. For this reason, it is preferable to use a highly reliable film capacitor having better frequency characteristics than the electrolytic capacitor for the capacitor C1.
(2) A capacitor C3 having good frequency characteristics may be connected in series to the primary winding of the high-frequency transformer 8 as shown in FIG. Such a capacitor C3 blocks a minute direct current flowing out from the high-frequency inverter main circuit 7. Accordingly, it is possible to prevent the DC bias of the high-frequency transformer 8.

It is a structural example of a grid connection inverter apparatus. 3 is a configuration example of an inverter control circuit 4. It is a vector diagram which shows the relationship between system voltage Vdac, output current Iac, and reactor voltage drop jωL · Iac. 4 is a waveform diagram of each part of the grid-connected inverter device 1. FIG. 1 is a configuration diagram of a DC / DC conversion control circuit 13 according to a first embodiment. FIG. It is explanatory drawing of the control method of the DC / DC conversion control circuit. It is explanatory drawing of the control method of the DC / DC conversion control circuit 13a which concerns on 2nd Embodiment. It is a block diagram of the DC / DC conversion control circuit 13a. It is explanatory drawing of the control method of the DC / DC conversion control circuit 13b which concerns on 3rd Embodiment. It is a block diagram of the DC / DC conversion control circuit 13b. 3 is an example of a circuit that prevents the high frequency transformer 8 from being demagnetized. FIG. 2 is a view corresponding to FIG.

Explanation of symbols

  In the drawings, 1 is a grid-connected inverter device, 2 is a DC / DC conversion circuit, 3 is an inverter main circuit, 4 is an inverter control circuit, 5 is a filter circuit, 7 is a high-frequency inverter main circuit, 8 is a high-frequency transformer, 9 Is a rectifier circuit, 10 is a smoothing circuit, 11 is a DC power supply, 12 is a commercial power system, 13 is a DC / DC conversion control circuit, C1 and C3 are capacitors, and L2 is a reactor.

Claims (3)

A grid-connected inverter device that converts DC power supplied from the outside into AC power and links the commercial power system (12) to a load,
A DC / DC conversion circuit (2) for converting the voltage of the DC power;
An inverter main circuit (3) for switching the DC power output from the DC / DC conversion circuit into AC power;
An inverter control circuit (4) for controlling the switching operation of the inverter main circuit;
A filter circuit (5) for removing harmonic components from the alternating current output from the inverter main circuit,
The DC / DC conversion circuit is configured to output a voltage having a value obtained by adding a predetermined constant voltage to an absolute value of an instantaneous value of the system voltage of the commercial power system, and the predetermined constant voltage is specified. A system characterized in that the value is not less than the sum of the instantaneous maximum value of the voltage drop in the filter circuit and the maximum value of the voltage drop in the switching element of the inverter circuit when a current of a specified magnitude flows. Interconnected inverter device. A grid-connected inverter device that converts DC power supplied from the outside into AC power and links it to a commercial power system and supplies it to a load,
A DC / DC conversion circuit for converting the voltage of the DC power;
An inverter main circuit for switching the DC power output from the DC / DC conversion circuit to convert it into AC power;
An inverter control circuit for controlling the switching operation of the inverter main circuit;
A filter circuit that removes harmonic components from the alternating current output by the inverter main circuit,
The DC / DC conversion circuit is configured to output a voltage having a value obtained by adding a predetermined constant voltage to an absolute value of an instantaneous value of a system voltage of the commercial power system,
The inverter control circuit controls the inverter main circuit so that a current whose phase matches the phase of the system voltage and whose amplitude matches a specified value is output from the filter circuit to the commercial power system,
The predetermined constant voltage is the first positive constant voltage when the waveform of the system voltage is expressed as Vacp · sin (ωt) and the value of ωt is in the range of nπ to (n + 1/2) π where n is an integer. And a second positive constant voltage smaller than the first positive constant voltage in the range of ωt between (n + 1/2) π and (n + 1) π . A grid-connected inverter device that converts DC power supplied from the outside into AC power and links it to a commercial power system and supplies it to a load,
A DC / DC conversion circuit for converting the voltage of the DC power;
An inverter main circuit for switching the DC power output from the DC / DC conversion circuit to convert it into AC power;
An inverter control circuit for controlling the switching operation of the inverter main circuit;
A filter circuit that removes harmonic components from the alternating current output by the inverter main circuit,
The DC / DC conversion circuit is configured to output a voltage having a value obtained by adding a predetermined constant voltage to an absolute value of an instantaneous value of a system voltage of the commercial power system,
The inverter control circuit controls the inverter main circuit so that a current whose phase matches the phase of the system voltage and whose amplitude matches a specified value is output from the filter circuit to the commercial power system,
In the DC / DC conversion circuit, the system voltage has an amplitude equal to its rated amplitude and a phase in phase with the actual system voltage, and the filter circuit has a specified magnitude of the same phase as the system voltage. A system characterized in that a voltage having a value obtained by adding a predetermined constant voltage to the absolute value of the instantaneous voltage at the input end of the filter circuit when the current is flowing is output. Interconnected inverter device.

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