JP5491809B2 - Grid-connected inverter device - Google Patents

Description

  The present invention relates to a grid-connected inverter device that converts the output of a DC power source such as a solar cell or a fuel cell into an AC power source and outputs the AC power source.

  As shown in FIG. 16, this type of grid-connected inverter device 1 includes a booster circuit 3 that boosts a DC output from a DC power source (not shown) to a desired voltage, and an AC output from the DC output of the booster circuit 3. And an inverter circuit 4 for converting to a power conversion circuit. FIG. 16 shows an example in which the booster circuit 3 boosts DC power to a voltage that allows reverse power flow to the commercial power system, and the inverter circuit 4 performs reverse power flow to the commercial power system 2.

  Further, the system interconnection inverter device 1 is provided with a boost control unit 5 having a voltage detection means 56, a target setting means 57 and a control means 51 for controlling the boost circuit 3, and controls the inverter circuit 4. The output control unit 6 having an output calculation means 68 and a control means 63 is provided. The booster circuit 3 is feedback-controlled by the control means 51 so as to maintain the output voltage (hereinafter referred to as boosted voltage) V2 detected by the voltage detection means 56 at a constant voltage set by the target setting means 57. The inverter circuit 4 is controlled so that the output current is calculated by the output calculating means 68 so that a desired output power is obtained, and the calculated output current is output.

  As the booster circuit 3, for example, a resonant booster circuit 3 having a configuration as shown in FIG. The booster circuit 3 includes switching elements Q1 to Q4 connected in a full bridge between input terminals Tin, an output transformer T1 in which a primary winding is connected between output terminals of the switching elements Q1 to Q4, and an output transformer T1. And a rectifier circuit 32 connected to the secondary winding via a resonance circuit 31. The switching elements Q1 to Q4 are a full bridge in which a series circuit of two switching elements Q1 and Q2 and a series circuit of the other two switching elements Q3 and Q4 are connected in parallel between the input terminals Tin of the booster circuit 3. Connected. The primary winding of the output transformer T1 is connected between the connection point of the switching elements Q1 and Q2 and the connection point of the switching elements Q3 and Q4. The resonance circuit 31 is composed of a series circuit of an inductor L1 and a capacitor C3, and the rectifier circuit 32 is configured by a diode bridge. Note that snubber capacitors C11 to C14 are connected in parallel to the switching elements Q1 to Q4, respectively.

  The booster circuit 3 is driven under the condition that the switching frequency is matched with the resonance frequency of the resonance circuit 31 (see FIG. 6), so that the load current flowing through the secondary winding of the output transformer T1 is zero. Switching elements Q1 to Q4 can be turned on and off, and a partial resonance operation by the primary side excitation current of output transformer T1 and capacitors C11 to C14 can be realized relatively easily. Therefore, it is used as a power source with high efficiency and low noise. In particular, since it can operate with high efficiency even at a relatively high boost ratio due to the insulating structure, it is used as a booster circuit 3 for a power supply having low voltage / large current characteristics (see, for example, Patent Document 1).

  By the way, a direct current power source such as a solar cell or a fuel cell has a relatively large output impedance, and as shown in FIG. 3, the output current decreases as the output voltage increases, and the output voltage decreases with a certain voltage as a peak. Alternatively, it has a voltage power characteristic in which the output power decreases as it increases. In addition, these voltage-current characteristics and voltage-power characteristics vary greatly depending on fluctuations in the operating conditions of the DC power supply (for example, the amount of solar radiation with respect to solar cells). Therefore, in order to extract desired power from the DC power source, the load state of the DC power source is changed in accordance with the operating conditions of the DC power source, so that the power becomes a voltage that becomes the desired power on the voltage power characteristics of the DC power source. It is necessary to perform control for adjusting the input voltage (= the output voltage of the DC power supply) of the booster circuit 3. For this reason, the booster circuit 3 of the grid-connected inverter device 1 that uses a solar cell or a fuel cell as a DC power source is required to have high efficiency and low noise for a relatively wide range of input voltages. The

  Here, as a method of adjusting the input voltage (= output voltage of the DC power supply) of the grid-connected inverter device when using the above-described resonance type booster circuit 3, the switching frequency of the booster circuit 3 is changed and the booster circuit 3 is adjusted. It is conceivable to change the load state of the DC power supply by changing the input impedance. In this case, as shown in FIG. 17, the boosting ratio is generally lowered by shifting the switching frequency to a higher frequency side than the resonance frequency of the resonance circuit 31. In FIG. 17, the on / off states of the switching elements Q1, Q4 are shown in (a), the on / off states of the switching elements Q2, Q3 are shown in (b), and the load current flowing through the secondary winding of the output transformer T1 is expressed as (c). ).

JP 2005-304289 A

  However, when the switching frequency of the booster circuit 3 deviates from the resonance frequency of the resonance circuit 31, the switching elements Q1 to Q4 are turned on and off at a timing when the load current flowing through the secondary winding of the output transformer T1 is not zero, and the switching loss And switching noise increases. Furthermore, problems such as increased loss of the resonant inductor L1, heat generation, and increased noise due to a steep current change occur. Further, if the input voltage of the booster circuit 3 is increased, the switching frequency is shifted to the high frequency side, the loss is increased, and the on-time of the switching elements Q1 to Q4 is shortened, so that a sufficient excitation current cannot be obtained. On the primary side of the output transformer T1, the partial resonance condition cannot be satisfied and hard switching is performed, leading to a further reduction in efficiency.

  The present invention has been made in view of the above-described reasons, and an object thereof is to provide a grid-connected inverter device capable of realizing high efficiency and low noise while allowing adjustment of an input voltage from a DC power supply. .

According to the first aspect of the present invention, a booster circuit that boosts a DC voltage output from a DC power source, a power converter circuit having an inverter circuit that converts the output of the booster circuit into AC, and an output current output from the inverter circuit are controlled. and an output control unit which, step-up circuit is formed of switching power supply; and a resonant circuit for implementing the output transformer and the resonant behavior of an isolated, the output control unit, by varying the output current The input impedance of the entire power conversion circuit is changed.

  According to this configuration, the input impedance of the power conversion circuit as a whole changes by changing the output current of the inverter circuit, not the switching frequency of the booster circuit. The voltage can be boosted by the ratio. For this reason, switching at a timing when the load current is zero and partial resonance operation can be maintained, and there is an advantage that switching loss is reduced and high efficiency and low noise can be realized. Moreover, since the output control unit can adjust the input impedance of the entire power conversion circuit by changing the output current, the input voltage from the DC power supply can be adjusted, for example, when a solar cell is used as the DC power supply. In addition, maximum power tracking control can be realized.

  According to a second aspect of the present invention, in the first aspect of the present invention, the output control unit includes first detection means for detecting a voltage corresponding to the output voltage of the booster circuit, and the detection voltage of the first detection means is previously set. The input voltage of the power conversion circuit is adjusted by adjusting the input impedance of the entire power conversion circuit by controlling the output current so as to coincide with a set target voltage.

  According to this configuration, the input voltage from the DC power supply is adjusted so that the voltage corresponding to the output voltage of the booster circuit matches the target voltage. The output voltage of the booster circuit can be controlled.

  According to a third aspect of the present invention, in the second aspect of the present invention, the DC power supply has an output characteristic in which output power changes in relation to an output voltage, and the output control unit supplies power corresponding to the output power of the DC power supply. A second detecting means for detecting, judging the output characteristic of the DC power supply from the tendency of change in the detected power of the second detecting means when the target voltage is changed, and setting the target voltage based on the output characteristic; It is characterized by doing.

  According to this configuration, even when a DC power source having a different output power depending on the output voltage such as a solar cell or a fuel cell is used, desired power can be output from the DC power source.

  According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the output control unit ensures that the output voltage of the inverter circuit secures a minimum voltage necessary for reverse power flow to the commercial power system. A lower limit value of the target voltage is set, and when the target voltage is equal to or lower than the lower limit value, the target voltage is fixed to the lower limit value.

  According to this configuration, since the output voltage of the minimum necessary level for the reverse power flow to the commercial power system is maintained in the inverter circuit, the reverse generated when the output voltage of the inverter circuit falls below the magnitude. The distortion of the tidal current can be prevented, and the reverse tidal current with a low distortion rate can be stably achieved.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the output control unit includes a third detection unit that detects the voltage of the commercial power system, and according to a peak value of the detection voltage of the third detection unit. The lower limit value of the target voltage is changed.

  According to this configuration, since the lower limit value of the target voltage is determined according to the peak value of the voltage of the commercial power system, the inverter circuit ensures that the output voltage of the minimum necessary level for reverse power flow to the commercial power system is ensured. By maintaining it, a reverse flow with a lower distortion rate becomes possible. Moreover, since at least a certain difference can be secured between the peak value of the voltage of the commercial power system and the output voltage of the inverter circuit, it is not necessary to have a likelihood in the output voltage of the inverter circuit, and the lower limit value of the target voltage is set. It can be set as low as possible, improving the conversion efficiency. If the lower limit value of the target voltage is lowered, the input voltage from the DC power supply can be lowered, and the input voltage can be adjusted in a wider range.

  The invention according to claim 6 is the invention according to claim 4, wherein the output control unit has a distortion rate calculating means for calculating a distortion rate of the output current flowing backward to the commercial power system, and the target voltage is calculated. The distortion rate calculated by the distortion rate calculation means when it is lowered is compared with a specified value, and the target voltage when the distortion rate becomes equal to or higher than the specified value is set as the lower limit value.

  According to this configuration, the lower limit value of the target voltage can be set even lower than when the lower limit value of the target voltage is determined according to the peak value of the voltage of the commercial power system.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the fourth detection means for detecting a current corresponding to the current flowing through the resonance circuit, and the detection current of the fourth detection means is zero. And a step-up control unit that sets a switching frequency of the step-up circuit so that the switching element of the step-up circuit is turned off.

  According to this configuration, since the switching frequency is set so that the switching element is turned off when the load current flowing through the switching element of the booster circuit is zero, even if the circuit constant of the resonance circuit varies, the load current is Switching at zero timing and partial resonance operation can be maintained, and high efficiency and low noise can be realized.

According to an eighth aspect of the present invention, in any one of the first to sixth aspects, the fifth detection means for detecting the input power of the power conversion circuit and the sixth detection means for detecting the output power of the power conversion circuit. And an efficiency calculating means for calculating the conversion efficiency from the ratio of the detected power of the sixth detecting means to the detected power of the fifth detecting means, and changing the switching frequency of the booster circuit within a predetermined range and calculating by the efficiency calculating means And a step-up control unit that resets the switching frequency so that the conversion efficiency is maximized.

  According to this configuration, by switching the switching frequency so that the conversion efficiency is maximized, switching and partial resonance operation can be maintained when the load current is zero even if the circuit constants of the resonance circuit vary. Therefore, high efficiency and low noise can be realized. The means for detecting the input power and output power of the power conversion circuit is also required for other functions of the grid-connected inverter device, and the fifth detection means and the sixth detection means can be used for other functions. There is also.

  According to a ninth aspect of the present invention, in the eighth aspect of the invention, the step-up control unit includes a temperature sensor that detects a temperature of a component that contributes to a resonance frequency of the resonance circuit, and the temperature change of the temperature detected by the temperature sensor is changed. The switching frequency is reset when a predetermined threshold value is exceeded.

  According to this configuration, even if the resonance frequency of the resonance circuit may fluctuate due to the temperature of the component that contributes to the resonance frequency of the resonance circuit, the switching frequency is reset to match the resonance frequency after the fluctuation. Switching and partial resonance operation at the timing when the load current is zero can be maintained.

According to a tenth aspect of the present invention, in the second or third aspect of the present invention, when the booster circuit is a normal mode in which the switching frequency of the booster circuit is fixed when the target voltage is equal to or lower than a preset upper limit value. in work, when the target voltage exceeds the upper limit value, the target voltage is fixed to the upper limit value, to change the input impedance of the entire power conversion circuit by lowering the boost ratio changing said switching frequency It operates in a restricted mode.

  According to this configuration, the target voltage is prevented from exceeding the upper limit value by the limit mode. For example, even when the output voltage of the booster circuit increases when the DC power supply operates near the open circuit voltage, the target voltage is limited. By shifting to the mode, the output voltage of the booster circuit is limited. Therefore, the breakdown voltage of the circuit component can be kept low. Therefore, it is possible to reduce the size and cost of the circuit components while accommodating a relatively wide range of input voltages.

  According to an eleventh aspect of the present invention, in the booster circuit according to the tenth aspect, a series circuit of a pair of switching elements and a series circuit of another pair of switching elements are connected in parallel between the output terminals of the DC power supply. And a full bridge circuit in which the primary winding of the output transformer is connected between the connection points of each pair of switching elements. In the limit mode, the length of the on-time of each pair of switching elements is fixed, By setting the length of the off time of the switching elements to be longer than the on time, a dead time for turning off all the switching elements is provided, and the switching frequency is adjusted by adjusting the length of the dead time. It is characterized by adjusting in a range lower than the frequency.

  According to this configuration, the dead time is provided so that the switching element can be turned on while the current flowing through the switching element is zero, so that a sharp change does not occur in the current flowing through the switching element and the surge voltage of the switching element is suppressed. However, the boost ratio of the booster circuit can be reduced. Therefore, it is possible to maintain high efficiency and low noise even in the limited mode.

  According to a twelfth aspect of the present invention, in the eleventh aspect of the invention, the booster circuit includes a seventh detection unit that detects a voltage across the switching element, and the voltage across the switching element is equal to or less than a predetermined value in the limit mode. The switching element is turned on at the timing as follows.

  According to this configuration, even when a resonance voltage is generated between both ends of the switching element due to the stray capacitance or wiring inductance in the circuit during the period when all the switching elements are off, the resonance voltage is a predetermined value. When the switching element is turned on at the following timing, switching loss can be reduced, and high efficiency and low noise can be realized.

  The present invention makes it possible to adjust the input voltage from the DC power supply, while maintaining the switching frequency constant and maintaining the partial resonance operation when the load current is zero in the booster circuit, thereby reducing the switching loss. Thus, there is an advantage that high efficiency and low noise can be realized.

It is a schematic block diagram of Embodiment 1 of the present invention. It is a schematic circuit diagram of a booster circuit same as the above. It is explanatory drawing of the output characteristic of the solar cell used for the same as the above. It is explanatory drawing of operation | movement of a booster circuit same as the above. It is explanatory drawing of operation | movement of a booster circuit same as the above. It is a time chart which shows operation | movement of a booster circuit same as the above. It is a schematic block diagram which shows the other structural example same as the above. It is a schematic block diagram which shows the other structural example same as the above. It is a schematic block diagram of Embodiment 2 of the present invention. It is a schematic block diagram which shows the other structural example same as the above. It is a schematic block diagram of Embodiment 3 of the present invention. It is explanatory drawing of operation | movement of a booster circuit same as the above. It is a time chart which shows operation | movement of a booster circuit same as the above. It is a time chart which shows operation | movement of a booster circuit same as the above. It is a time chart which shows operation | movement of a booster circuit same as the above. It is a schematic block diagram which shows a prior art example. It is a time chart which shows operation | movement same as the above.

(Embodiment 1)
As shown in FIG. 1, the grid-connected inverter device 1 of this embodiment includes a booster circuit 3 that boosts an input voltage to a voltage that can flow backward to the commercial power system 2, and a DC output of the booster circuit 3 is an AC output. An inverter circuit 4 that converts and reversely flows into the commercial power system 2 is provided as a power conversion circuit.

  A DC power supply (not shown) that outputs a DC voltage is connected to the input terminal Tin of the booster circuit 3. In this embodiment, it is assumed that a solar cell is used as a DC power source as an example, but the DC power source is not limited to a solar cell, and may be a fuel cell, for example. Note that smoothing capacitors C1 and C2 are connected between the input terminal Tin and the output terminal Tout (see FIG. 2) of the booster circuit 3, respectively.

  As shown in FIG. 2, the booster circuit 3 includes switching elements Q <b> 1 to Q <b> 4 connected in a full bridge between input terminals Tin, and an insulation type in which a primary winding is connected between output terminals of the switching elements Q <b> 1 to Q <b> 4. The switching power supply includes an output transformer T1 and a rectifier circuit 32 connected to a secondary winding of the output transformer T1 via a resonance circuit 31.

  The switching elements Q1 to Q4 are a full bridge in which a series circuit of two switching elements Q1 and Q2 and a series circuit of the other two switching elements Q3 and Q4 are connected in parallel between the input terminals Tin of the booster circuit 3. Connected. The primary winding of the output transformer T1 is connected between the connection point of the switching elements Q1 and Q2 and the connection point of the switching elements Q3 and Q4. The resonance circuit 31 is composed of a series circuit of an inductor L1 and a capacitor C3, and the rectifier circuit 32 is configured by a diode bridge. Note that the snubber capacitors C11 to C14 are connected in parallel to the switching elements Q1 to Q4, respectively. However, when the output capacities of the switching elements Q1 to Q4 are substituted, these capacitors C11 to C14 can be omitted. is there.

  In order to drive the booster circuit 3, the grid-connected inverter device 1 is provided with a boost control unit 5 including a control means 51 that controls on / off of the switching elements Q1 to Q4 by a boost gate signal. Here, the boost control unit 5 sets the switching element Q1 and the switching element Q4 as one set, and sets the switching element Q2 and the switching element Q3 as one set, and sets each switching element Q1 at the switching frequency described later. ˜Q4 are turned on alternately.

  According to the above configuration, since the resonance circuit 31 is provided on the secondary side of the output transformer T1, the output voltage of the booster circuit 3 becomes maximum when the switching frequency matches the resonance frequency of the resonance circuit 31. Therefore, in this embodiment, the switching frequency is fixedly set so as to coincide with the resonance frequency of the resonance circuit 31, and boosting is always performed at the maximum boosting ratio. Therefore, the output voltage V2 (hereinafter referred to as boosted voltage) V2 of the booster circuit 3 increases with a certain slope as the input voltage V1 increases. When the switching frequency is made to coincide with the resonance frequency in this way, the ON / OFF timing of the switching elements Q1 to Q4 can be made to coincide with the zero cross point of the resonance current flowing through the resonance circuit 31. As a result, the switching elements Q1 to Q4 can be turned on / off in a state where the load current flowing through the secondary winding of the output transformer T1 is zero. Here, even when the load current is zero, the exciting current (primary excitation current) flows through the primary winding of the output transformer T1, so that the current flowing through the switching elements Q1 to Q4 does not become zero. Switching loss is significantly reduced compared to when the load current is turned on and off at a timing other than zero.

  As a result, it is possible to prevent the occurrence of switching loss and switching noise that occur when the switching elements Q1 to Q4 are turned on and off. Further, a steep current change is suppressed also on the secondary side of the output transformer T1, and loss, heat generation, noise increase, and the like of the inductor L1 constituting the resonance circuit 31 can be prevented. Furthermore, the soft switching condition is satisfied, and the partial resonance operation by the primary side excitation current of the output transformer T1 and the capacitors C11 to C14 can be maintained in a wide range.

  On the other hand, the inverter circuit 4 includes four switching elements (not shown) connected in a full-bridge manner between the two ends of the capacitor C2 connected to the output stage of the booster circuit 3 in the same manner as the switching elements Q1 to Q4 of the booster circuit 3. A full bridge type inverter circuit. The inverter circuit 4 includes a filter circuit (not shown) that includes an inductor and a capacitor and allows the frequency component of the commercial power system 2 to pass therethrough.

  The grid interconnection inverter device 1 is provided with an output control unit 6 that performs on / off control of the switching element of the inverter circuit 4 by an output gate signal. Here, the output control unit 6 performs on / off control of each pair of switching elements at a high frequency so that a current having a power factor of 1 and a desired effective value is output to the commercial power system 2 as a reverse flow current. The inverter circuit 4 is controlled.

  Thus, the output of the DC power source is boosted to a voltage necessary for reverse power flow by the booster circuit 3 and then converted to alternating current having a frequency that allows reverse power flow by the inverter circuit 4, and the reverse power flow to the commercial power system 2. Will be.

  By the way, a solar cell as a DC power supply has a relatively large output impedance, and as shown in FIG. 3, the output current becomes smaller as the output voltage becomes higher ("A" in the figure), and a certain voltage is peaked. It has a voltage power characteristic (“B” in the figure) in which the output power decreases as the output voltage decreases or increases. In addition, these voltage-current characteristics and voltage-power characteristics vary greatly due to variations in operating conditions such as variations in solar radiation with respect to the solar cell. Therefore, in order to extract the maximum power from the DC power supply, the booster circuit 3 has a voltage that maximizes the power on the voltage power characteristics of the DC power supply by changing the load state of the DC power supply in accordance with the operating conditions of the DC power supply. It is necessary to perform maximum power tracking control (MPPT control) for adjusting the input voltage (= output voltage of the DC power supply) V1.

  Here, as described in the background art section, the maximum power follow-up control method changes the load state of the DC power supply by changing the switching frequency of the booster circuit 3 and changing the input impedance of the booster circuit 3. It is possible to make it However, in this embodiment, since the switching frequency of the booster circuit 3 is fixedly set to coincide with the resonance frequency as described above, the input impedance of the booster circuit 3 is changed by changing the switching frequency of the booster circuit 3. This method of changing cannot be adopted.

  Therefore, the grid interconnection inverter device 1 of the present embodiment performs maximum power tracking control by adopting the following configuration.

  That is, in this embodiment, the output impedance of the inverter circuit 4 is changed by the output control unit 6 to change the input impedance (the load state of the DC power supply) as the entire power conversion circuit including the booster circuit 3 and the inverter circuit 4. Thus, the input voltage V1 of the booster circuit 3 is controlled. Specifically, if the output power determined by the reverse flow current (effective value) controlled by the output control unit 6 and the voltage of the commercial power system 2 increases, the input impedance decreases, and the load state of the DC power supply becomes heavy. It becomes a load and the output current of the DC power supply increases. On the other hand, when the output power decreases, the input impedance increases, the load state of the DC power supply becomes light, and the output current of the DC power supply decreases.

  Here, since the solar cell as the DC power source has a voltage-current characteristic in which the output voltage decreases as the output current increases as shown in FIG. 3, the output of the DC power source is eventually increased if the input impedance of the inverter circuit 4 is increased. When the voltage rises and the input impedance is reduced, the output voltage of the DC power supply is lowered. In this way, by changing the input impedance of the inverter circuit 4 by the output control unit 6, it becomes possible to adjust the input voltage (= output voltage of the DC power supply) V1 of the booster circuit 3, and the maximum power tracking control described above. It can be performed.

  More specifically, the output control unit 6 includes a first detection unit 61 that detects the boosted voltage V2 from the voltage across the capacitor C2 connected to the output stage of the booster circuit 3, and a detection voltage of the first detection unit 61. And a comparator 62 for comparing a target voltage described later. Further, the output control unit 6 detects the reverse flow current output from the inverter circuit 4 and drives the switching element of the inverter circuit 4 so that the detection result matches the command value output from the comparator 62. The control means 63 which outputs the output gate signal for performing is provided. The comparator 62 determines the magnitude of the command value so that the detection voltage of the first detection means 61 matches the target voltage. If the detection voltage is lower than the target voltage, the comparator 62 decreases the command value to reduce the reverse flow current. If the detection voltage is higher than the target voltage, the command value is increased to increase the reverse flow current. Here, since the boosting ratio of the booster circuit 3 is constant, as a result, the input voltage (= output voltage of the DC power supply) V1 of the booster circuit 3 is 1 / N (with respect to the target voltage as shown in FIG. N is determined on a one-to-one basis with a slope of the boost ratio of the booster circuit 3.

  Further, the output control unit 6 is based on the second detection means 64 for detecting the input power (= output power of the DC power supply) of the booster circuit 3 and the detection power of the second detection means 64 as shown in FIG. Target calculation means 65 for determining the target voltage is provided. The target calculation means 65 sets the input voltage of the booster circuit 3 (= the output of the DC power supply) to the voltage (hereinafter referred to as the optimum output voltage) that maximizes the power on the voltage power characteristics of the DC power supply in accordance with the operating conditions of the DC power supply. The target voltage value is determined so that the maximum power follow-up control for adjusting the voltage (V1) is performed.

  In short, the DC power supply has a voltage power characteristic in which the output power decreases as the output voltage decreases or increases with the optimum output voltage as a peak, so in order to extract the maximum power from the DC power supply, It is necessary to adjust the output voltage to the optimum output voltage. Therefore, the target calculation means 65 has a point that the detected power of the second detection means 64 becomes maximum when the input voltage (= output voltage of the DC power supply) V1 of the booster circuit 3 is changed by changing the target voltage. An optimum output voltage is set, and a voltage N times the optimum output voltage (N is a boost ratio of the booster circuit 3) is set as a target voltage. That is, if the detected power increases when the target voltage is lowered, the input voltage V1 of the booster circuit 3 at that time is determined to be in the negative characteristic region α higher than the optimum output voltage as shown in FIG. The electric power taken out from the DC power source is increased by lowering the target voltage. On the other hand, if the detected power increases when the target voltage is raised, it is determined that the input voltage V1 of the booster circuit 3 at that time is in the positive characteristic region β lower than the optimum output voltage, and the target voltage is raised. This increases the power extracted from the DC power supply.

  In this way, the process of finding the optimum output voltage by changing the target voltage in the target calculation means 65 is periodically executed. As a result, even if the operating condition of the DC power supply (irradiation with respect to the solar cell) fluctuates, The target voltage is periodically adjusted according to the characteristics after the fluctuation. Therefore, even when the operating conditions of the DC power supply fluctuate, the maximum power can be extracted from the DC power supply, and the grid-connected inverter device 1 can be operated in the most efficient state. The second detection unit 64 may be any unit that detects power corresponding to the output power of the DC power supply. For example, the second detection unit 64 may be configured to detect power on the rear stage side of the booster circuit 3.

  According to the configuration described above, the output control unit 6 controls the inverter circuit 4 so that the output power of the DC power supply is maximized in a state where the switching frequency of the booster circuit 3 is fixed. Maximum power tracking control for adjusting the input voltage V1 can be performed. Therefore, by making the switching frequency of the booster circuit 3 coincide with the resonance frequency of the resonance circuit 31, the switching elements Q1 to Q4 can always be turned on and off at the timing when the load current is zero. As a result, the current flowing through the primary winding of the output transformer T1 can be made sinusoidal without distortion as shown in FIG. 6, and the partial resonance operation can be maintained. Generation of switching noise can be prevented, and the grid-connected inverter device 1 with high efficiency and low noise can be realized. In FIG. 6, the on / off states of the switching elements Q1, Q4 are shown in (a), the on / off states of the switching elements Q2, Q3 are shown in (b), and the load current flowing through the secondary winding of the output transformer T1 is expressed as (c). ). Here, FIG. 6C shows a waveform when the output power of the DC power supply is large (a larger amplitude) and a waveform when the output power of the DC power supply is small (a smaller amplitude).

  By the way, in order to perform a reverse power flow from the grid-connected inverter device 1 to the commercial power system 2, it is necessary to maintain the output voltage of the inverter circuit 4 higher than the voltage of the commercial power system 2. Therefore, in this embodiment, a lower limit value is set for the target voltage, and the target voltage is prevented from falling below the lower limit value, so that the output voltage of the inverter circuit 4 is maintained at a level that allows reverse flow. In short, the target calculation means 65 sets the target voltage so that the detection power of the second detection means 64 is maximized in principle. However, if the target voltage is equal to or lower than the lower limit value, the target voltage is exceptionally applied. Fix to the lower limit. Thereby, since the output voltage of the inverter circuit 4 is maintained at a level higher than the minimum necessary for the reverse power flow, it is possible to prevent the reverse power current from being distorted when the output voltage of the inverter circuit 4 falls below the size. It is possible to perform a reverse flow with a low distortion rate stably.

  Here, the lower limit value of the target voltage is determined according to the peak voltage of the commercial power system 2, for example. In this case, as shown in FIG. 7, the output control unit 6 is provided with the third detection means 66 for detecting the voltage V3 of the commercial power system, and the target calculation means 65 sets the peak value of the detection voltage of the third detection means 66. Set the lower limit of the target voltage accordingly. As a result, the inverter circuit 4 can reliably maintain the output voltage having the minimum required level for the reverse power flow to the commercial power system 2 and can achieve a low distortion reverse power flow. Further, if the target voltage is set to be larger than the peak voltage of the commercial power system 2 by a predetermined difference, the output voltage of the inverter circuit 4 does not need to have likelihood, and the lower limit value of the target voltage is set. It can be set as low as possible. As a result, the maximum power follow-up control can be performed corresponding to a relatively wide range of input voltages V1, and there is an advantage that the power conversion efficiency is improved.

  In addition to this configuration, it is also conceivable to set the lower limit value of the target voltage to a value that can suppress the distortion rate of the reverse flow current to a specified value or less. In this case, as shown in FIG. 8, a distortion rate calculation means 67 for calculating the distortion rate of the reverse flow current output from the inverter circuit 4 is provided in the output control unit 6, and the target calculation means 65 gradually decreases the target voltage. When the distortion rate is calculated, the distortion rate calculated by the distortion rate calculation means 67 is compared with a specified value, and the target voltage when the distortion rate becomes equal to or higher than the specified value is set as the lower limit value. As a result, the lower limit value of the target voltage can be set lower as compared with the case where the lower limit value is determined according to the peak voltage of the commercial power system 2 as described above, and as a result, it corresponds to a wider range of the input voltage V1. Maximum power tracking control can be performed.

(Embodiment 2)
The grid interconnection inverter device 1 of the present embodiment is different from the grid interconnection inverter device 1 of the first embodiment in that the switching frequency of the booster circuit 3 is automatically set.

  That is, since the resonance frequency of the resonance circuit 31 is determined by circuit constants such as the inductance of the inductor L1 and the capacitor C3 and the output transformer T1 constituting the resonance circuit 31, the circuit constant varies due to individual differences between these circuit elements. The resonance frequency may also vary. Therefore, in the present embodiment, the switching frequency of the booster circuit 3 is not fixedly determined in advance, but the switching frequency is automatically corrected in a state where the system interconnection inverter device 1 is actually operated. adopt.

  Specifically, as shown in FIG. 9, fourth detection means 52 for detecting a load current flowing through the primary winding of the output transformer T1 of the booster circuit 3 is added to the boost controller 5, and the boost controller 5 The control means 51 controls the drive timing of the switching elements Q1 to Q4 so that the switching elements Q1 to Q4 are turned off when the detection current of the fourth detection means 52 is zero. As a result, the switching frequency of the booster circuit 3 matches the resonance frequency of the resonance circuit 31. The fourth detection means 52 is not limited to directly detecting the current flowing through the primary side of the output transformer T1, and detects the current flowing through the resonance circuit 31 connected to the secondary side of the output transformer T1 as a load current. You may do.

  As another configuration example of the present embodiment, as shown in FIG. 10, efficiency calculation means 53 for calculating the power conversion efficiency in the booster circuit 3 and the inverter circuit 4 is provided in the booster control unit 5, and the conversion efficiency is A configuration in which the switching frequency is adjusted by the boost control unit 5 so as to be maximized is also conceivable. In this case, fifth detection means 54 for detecting the input power of the booster circuit 3 and sixth detection means 55 for detecting the output power of the inverter circuit 4 are provided, and the efficiency calculation means 53 is detected power of the fifth detection means 54. The conversion efficiency is calculated from the ratio (detected power Wo / detected power Wi) of the detected power Wo of the sixth detecting means 55 to Wi. Then, the boost control unit 5 changes the switching frequency of the booster circuit 3 within a predetermined range, and sets the frequency at which the conversion efficiency calculated by the efficiency calculating unit 53 is maximized as a new switching frequency.

  As a result, the switching frequency is set based on the conversion efficiency. Therefore, even if the circuit constants of the resonance circuit 31 vary, the switching frequency is matched with the resonance frequency of the resonance circuit 31 and the conversion in the booster circuit 3 is performed. Efficiency can be maximized. In the grid-connected inverter device 1, the means for detecting input power and output power, such as the fifth detection means 54 and the sixth detection means 55, is an essential configuration for other functions. There is also an advantage that it is not necessary to add a dedicated circuit like the fourth detecting means 52 in FIG.

  When the configuration of FIG. 10 is adopted, the most recently set switching frequency is continuously used until the switching frequency is reset, but the resonance frequency of the resonance circuit 31 does not change. As long as there is no need to reset the switching frequency. Therefore, when the configuration of FIG. 10 is adopted, a thermistor (temperature sensor) for detecting the temperature of the components (inductor L1, capacitor C3, etc.) contributing to the resonance frequency of the resonance circuit 31 is provided in the boost control unit 5 and detected. It is desirable that the switching frequency be reset when the temperature change of the temperature exceeds a predetermined threshold. Thereby, even if the resonance frequency of the resonance circuit 31 may fluctuate depending on the operating temperature of the component, the switching frequency can be matched with the resonance frequency after the fluctuation by resetting the switching frequency. It can be avoided that a state in which the switching frequency deviates from the frequency continues for a long time.

  In FIGS. 9 and 10 shown in the present embodiment, the second detection means 64 is not shown. Other configurations and functions are the same as those of the first embodiment.

(Embodiment 3)
The grid-connected inverter device 1 according to the present embodiment sets an upper limit value for the target voltage, and in a normal mode in which the switching frequency of the booster circuit 3 matches the resonance frequency of the resonance circuit 31 when the target voltage is equal to or lower than the upper limit value. It is different from the grid-connected inverter device 1 of the first embodiment in that it operates and operates in a limit mode in which the target voltage is fixed to the upper limit value when the target voltage exceeds the upper limit value.

  That is, the operation in the normal mode is the same as that described in the first embodiment. However, in the limit mode, the boosting ratio of the booster circuit 3 is changed, so that the boosting voltage is increased regardless of the change of the input voltage V1 of the booster circuit 3. The boosted voltage V2 output from the circuit 3 is fixed to the upper limit value of the target voltage. In short, in the limited mode, the boosting ratio is lowered by shifting the switching frequency of the booster circuit 3 from the resonant frequency of the resonant circuit 31 so that the boosted voltage V2 is fixed to the upper limit value. Specifically, as shown in FIG. 11, the target calculation means 65 is configured to output a control signal to the boost control unit 5, and when the target voltage exceeds the upper limit value, the control signal indicates the boost circuit 3. Reduce the boost ratio. In addition, in FIG. 11, illustration of the 2nd detection means 64 is abbreviate | omitted.

  Thus, as shown in FIG. 12, in the range X where the input voltage V1 of the booster circuit 3 is not more than a certain boundary value, the switching frequency of the booster circuit 3 matches the resonance frequency and the boost ratio of the booster circuit 3 is constant. Since it is maintained, the boosted voltage V2 is proportional to the input voltage. On the other hand, in the range Y where the input voltage V1 exceeds the boundary value, the boosting voltage V2 is variably controlled by shifting the switching frequency of the boosting circuit 3 from the resonance frequency, so that the boosting voltage V2 is the upper limit value regardless of the input voltage V1. Maintained.

  According to the configuration described above, even when the input voltage V1 of the booster circuit 3 is increased, the boosted voltage V2 is suppressed to be equal to or lower than the upper limit value of the target voltage. It is never output. Therefore, the withstand voltage of the circuit components such as the booster circuit 3 and the inverter circuit 4 in the subsequent stage can be kept relatively low, and the circuit components can be reduced in size and cost while making the booster circuit 3 compatible with a wide range of input voltages. There is an advantage that can be achieved.

  By the way, in this embodiment, when reducing the step-up ratio of the booster circuit 3 in the limit mode, the length of the on time of each pair of switching elements Q1 to Q4 is fixed, and the off time of each pair of switching elements Q1 to Q4 is fixed. The dead time during which all the switching elements Q1 to Q4 are turned off is provided by increasing the length of the switching element Q as compared with the on time. Then, the boost control unit 5 adjusts the switching frequency of the booster circuit 3 in a range lower than the resonance frequency of the resonance circuit 31 by adjusting the length of the dead time.

  For example, in the normal mode, as shown in FIGS. 13A and 13B, the pair of switching elements Q1 and Q4 and the other pair of switching elements Q2 and Q3 have the same switching frequency as the resonance frequency. Therefore, the current flowing through the resonance circuit 31 becomes a sine wave without distortion as shown in FIG. 13 and 14 and 15, the voltage across switching elements Q 1 and Q 2 is shown in (a), the voltage across switching elements Q 2 and Q 3 is shown in (b), and the current flowing through the resonance circuit 31 is shown in (c). . Here, the period during which the switching elements Q2 and Q3 are on is represented by “Ton1”, the period during which the switching elements Q1 and Q4 are on is represented by “Ton2”, the dead time is represented by “Td”, and the reciprocal of the switching frequency (repetitive cycle of switching). Is represented by “Ta” or “Ta ′”.

  On the other hand, in the limited mode, as shown in FIGS. 14A and 14B, the switching elements Q1 and Q4 are turned off until the switching elements Q2 and Q3 are turned on, and the switching elements Q2 and Q3 are turned on. A dead time Td during which all the switching elements Q1 to Q4 are turned off is provided between the time when the switching elements Q1 and Q4 are turned on after the turning off. Therefore, as shown in FIG. 14C, the current flowing through the resonance circuit 31 flows in the opposite direction during the periods when the switching elements Q1, Q4 are on and the periods when the switching elements Q2, Q3 are on. However, since no current flows through the resonance circuit 31 during the dead time Td when all the switching elements Q1 to Q4 are turned off, a reverse current alternately flows intermittently through the resonance circuit 31.

  By providing the dead time Td in this manner, the load current flowing through the switching element can be turned on / off, so that the current flowing through the booster circuit 3 does not change sharply and the switching elements Q1 to Q1 are not changed. The surge voltage of Q4 and the core loss of the resonance reactor (inductor L1) can be suppressed. As a result, the grid-connected inverter device 1 can be operated with high efficiency and low noise even in the limited mode in which the switching frequency does not coincide with the resonance frequency of the resonance circuit 31.

  In the present embodiment, the booster circuit 3 is provided with seventh detection means (not shown) for detecting the voltage across the switching elements Q1 to Q4 (drain-source voltage). In the limiting mode, the switching elements Q1 to Q1 are provided. The timing at which Q4 is turned on is matched with the timing at which the voltage across the switching elements Q1 to Q4 becomes a predetermined value or less. In other words, in the dead time Td when all the switching elements Q1 to Q4 are turned off, the switching elements Q1 to Q4 as shown in FIGS. 14A and 14B due to the influence of stray capacitance and wiring inductance in the circuit. There is a possibility that a resonant voltage is generated between the drain and the source of the semiconductor. If the switching elements Q1 to Q4 are turned on in a state where a resonance voltage is generated between the drain and the source, a switching loss occurs, leading to a reduction in efficiency and generation of noise.

  Therefore, as shown in FIGS. 15A and 15B, switching loss is suppressed as much as possible by turning on the switching elements Q1 to Q4 at the timing when the voltage across the switching elements Q1 to Q4 becomes a predetermined value or less. . As a result, the booster circuit 3 can be made highly efficient and low noise. Strictly speaking, it is desirable to turn on the switching elements Q1 to Q4 at a timing at which the voltage between the drain and source of the switching elements Q1 to Q4 is minimized.

  Other configurations and functions are the same as those of the first embodiment.

DESCRIPTION OF SYMBOLS 1 Grid connection inverter apparatus 2 Commercial power system 3 Booster circuit 4 Inverter circuit 5 Boosting control part 6 Output control part 31 Resonance circuit 52 4th detection means 54 5th detection means 55 6th detection means 61 1st detection means 64 2nd Detection means 66 Third detection means 67 Distortion rate calculation means Q1 to Q4 Switching element T1 Output transformer Td Dead time V1 Input voltage V2 Boost voltage

Claims (12)

A booster circuit for boosting a DC voltage output from a DC power supply, a power converter circuit having an inverter circuit for converting the output of the booster circuit to AC, and an output control unit for controlling an output current output from the inverter circuit ,
Booster circuit comprises a switching power supply; and a resonant circuit for implementing the output transformer and the resonant behavior of an isolated, the output control unit, the input impedance of the entire power conversion circuit by changing the output current A grid-connected inverter device characterized by being changed.   The output control unit includes first detection means for detecting a voltage corresponding to the output voltage of the booster circuit, and the output current is set so that the detection voltage of the first detection means matches a preset target voltage. The grid-connected inverter device according to claim 1, wherein the input voltage of the power conversion circuit is adjusted by controlling the input impedance of the whole power conversion circuit by controlling the power.   The DC power supply has an output characteristic in which output power changes in relation to an output voltage, and the output control unit includes second detection means for detecting power corresponding to the output power of the DC power supply, and the target voltage is 3. The grid interconnection according to claim 2, wherein the output characteristic of the DC power supply is determined from the tendency of the change in the detected power of the second detection means when changed, and the target voltage is set based on the output characteristic. Inverter device.   The output control unit sets a lower limit value of the target voltage so that the output voltage of the inverter circuit secures a minimum voltage necessary for a reverse power flow to the commercial power system, and the target voltage becomes equal to or lower than the lower limit value. 4. The grid-connected inverter device according to claim 2, wherein the target voltage is fixed to a lower limit value.   The output control unit includes third detection means for detecting a voltage of the commercial power system, and changes a lower limit value of the target voltage according to a peak value of a detection voltage of the third detection means. The grid connection inverter apparatus of Claim 4.   The output control unit includes a distortion rate calculating unit that calculates a distortion rate of the output current that flows backward to the commercial power system, and the distortion calculated by the distortion rate calculating unit when the target voltage is lowered. 5. The grid-connected inverter device according to claim 4, wherein the rate is compared with a specified value, and the target voltage when the distortion rate is equal to or higher than the specified value is set as the lower limit value. A fourth detector for detecting a current corresponding to a current flowing through the resonant circuit; and a switching frequency of the booster circuit is set so that the switching element of the booster circuit is turned off when the detected current of the fourth detector is zero. A grid-connected inverter device according to any one of claims 1 to 6, further comprising: a step-up control unit that performs the operation. From the ratio of the detection power of the sixth detection means to the detection power of the fifth detection means for detecting the input power of the power conversion circuit, the sixth detection means for detecting the output power of the power conversion circuit, and the detection power of the fifth detection means and efficiency calculating means for calculating the conversion efficiency by changing the switching frequency of the boost circuit within a predetermined range, the step-up control unit which conversion efficiency calculated by the efficiency calculation means for re-setting the switching frequency so as to maximize The grid interconnection inverter device according to claim 1, further comprising a grid interconnection inverter device.   The step-up control unit includes a temperature sensor that detects a temperature of a component that contributes to the resonance frequency of the resonance circuit, and when the temperature change of the temperature detected by the temperature sensor exceeds a predetermined threshold, the switching frequency 9. The grid-connected inverter device according to claim 8, wherein resetting is performed. The booster circuit operates in a normal mode in which the switching frequency of the booster circuit is fixed when the target voltage is less than or equal to a preset upper limit value, and when the target voltage exceeds the upper limit value, the target voltage was fixed to the upper limit value, to claim 2 or claim 3, characterized in that operating in restricted mode to change the input impedance of the entire power conversion circuit by lowering the boost ratio changing said switching frequency The grid interconnection inverter apparatus of description.   In the booster circuit, a series circuit of a pair of switching elements and a series circuit of another pair of switching elements are connected in parallel between output terminals of the DC power supply, and a primary winding of an output transformer is connected to each pair of switching elements. In the restriction mode, the length of the on time of each pair of switching elements is fixed, and the length of the off time of each pair of switching elements is compared with the on time. A dead time in which all switching elements are turned off is provided by increasing the length, and the switching frequency is adjusted in a range lower than the resonance frequency of the resonance circuit by adjusting the length of the dead time. Item 15. The grid interconnection inverter device according to Item 10.   The booster circuit has a seventh detecting means for detecting a voltage across the switching element, and turns on the switching element at a timing when the voltage across the switching element becomes a predetermined value or less in the limit mode. The grid connection inverter apparatus of Claim 11.

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