Power conversion device, power conversion method, and computer program

Abstract

To provide a power conversion device that prevents influences of mixing of a switching noise and a measurement error due to a time error of a detection timing, and calculates an average value of an output current value with higher accuracy.SOLUTION: A power conversion device includes: a voltage conversion circuit having a switching element; a control circuit performing switching control of the voltage conversion circuit; and a current detection circuit detecting current output from the voltage conversion circuit. The control circuit calculates an average value of the current output from the voltage conversion circuit based on a first current value detected in a first switching state where output of current increases, a second current value detected in a second switching state where output of current decreases and a modulation ratio related to switching control of voltage conversion; and controls operation of the voltage conversion circuit based on a calculated average value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device, a power conversion method, and a computer program. [Background technology]

[0002] 2. Description of the Related Art Photovoltaic power generation systems and distributed power supply systems in which large-capacity storage batteries mounted on electric vehicles are interconnected to a grid have become widespread as emergency power sources during long-term power outages caused by disasters and as systems to compensate for power supply shortages during peak power periods in summer and winter.

[0003] The distributed power system is equipped with a power conditioner that converts the DC power of the distributed power source into AC power. The power conditioner performs AD / AC conversion by controlling the switching of the inverter. The power conditioner detects the output current in accordance with the switching timing of the inverter, calculates the output average current, and performs various controls (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 58-190281 [Patent Document 2] JP 2014-060851 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the above-mentioned output average current is affected by measurement errors resulting from mixing of switching noise and time errors in the detection timing, there has been a problem in that an accurate output current value cannot be calculated.

[0006] An object of the present invention is to provide a power conversion device, a power conversion method, and a computer program that can suppress the influence of measurement errors due to the inclusion of switching noise and time errors in detection timing, and calculate the average value of the output current with higher accuracy. [Means for solving the problem]

[0007] A power conversion device according to one embodiment of the present disclosure includes a voltage conversion circuit having a switching element, a control circuit for controlling the switching of the voltage conversion circuit, and a current detection circuit for detecting a current output from the voltage conversion circuit, wherein the control circuit calculates an average value of the current output from the voltage conversion circuit based on a first current value detected in a first switching state in which the current output increases, a second current value detected in a second switching state in which the current output decreases, and a modulation factor related to the switching control of the voltage conversion, and controls the operation of the voltage conversion circuit based on the calculated average value.

[0008] A power conversion method according to one embodiment of the present disclosure is a power conversion method using a voltage conversion circuit having a switching element, which includes switching control of the voltage conversion circuit, detecting a current output from the voltage conversion circuit, calculating an average value of the current output from the voltage conversion circuit based on a first current value detected in a first switching state in which the current output increases, a second current value detected in a second switching state in which the current output decreases, and a modulation factor related to the switching control of the voltage conversion, and controlling the operation of the voltage conversion circuit based on the calculated average value.

[0009] A computer program according to one embodiment of the present disclosure is a computer program that causes a computer to calculate a process related to power conversion using a voltage conversion circuit having a switching element, the computer executing a process of controlling the switching of the voltage conversion circuit, detecting a current output from the voltage conversion circuit, calculating an average value of the current output from the voltage conversion circuit based on a first current value detected in a first switching state in which the current output increases, a second current value detected in a second switching state in which the current output decreases, and a modulation factor related to the switching control of the voltage conversion, and controlling the operation of the voltage conversion circuit based on the calculated average value. Effect of the Invention

[0010] According to the above, it is possible to suppress the influence of measurement errors due to mixing of switching noise in the power conversion device and time errors in the detection timing, and to calculate the average value of the output current with higher accuracy. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a configuration example of a grid interconnection system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a circuit diagram showing an inverter and its peripheral circuits. [Diagram 3] FIG. 2 is a block diagram showing a configuration example of a control circuit; [Figure 4] 4 is a flowchart showing a processing procedure of a control circuit. [Diagram 5] 4 is a timing chart for explaining a method of calculating an average output current. [Figure 6] 4 is a timing chart for explaining a method of calculating an average output current. [Figure 7] 4 is a timing chart for explaining a method of calculating an average output current. [Figure 8] 10 is a timing chart for explaining a method of calculating an average output current according to the second embodiment. [Figure 9]13 is a timing chart for explaining a method of calculating an average output current according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A power conversion device, a power conversion method, and a computer program according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is intended to include all modifications within the meaning and scope of the claims as indicated by the claims. In other words, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

[0013] (Embodiment 1) Fig. 1 is a block diagram showing a configuration example of a grid interconnection system 1 according to the present embodiment 1. The grid interconnection system 1 includes a power grid 2, a distributed power source 3 interconnected with the power grid 2, and a power conditioner 4 disposed between the power grid 2 and the distributed power source 3. A load 8 such as a general home appliance is connected between the power conditioner 4 and the power grid 2 via a distribution board.

[0014] The distributed power sources 3 are solar power generators, wind power generators, fuel cells, cogeneration systems, storage batteries, etc., and are power sources that output DC power. The distributed power sources 3 include storage batteries and generators mounted on vehicles. The distributed power sources 3 output the DC power to the power conditioner 4.

[0015] <Circuit configuration of power conditioner 4> The power conditioner 4 is a device that converts DC power output from the distributed power source 3 into AC power and supplies the converted AC power to the load 8 and the power system 2. The power conditioner 4 includes a DC / DC converter 5, a power conversion device 6, and a switch 7.

[0016] The DC / DC converter 5 is a circuit that converts the voltage of the DC power output from the distributed power source 3 into a predetermined voltage. The DC / DC converter 5 outputs the voltage-converted DC power to the power conversion device 6.

[0017] The power conversion device 6 includes a control circuit 60, an inverter (voltage conversion circuit) 61, a filter circuit 62, a current detection circuit 63, and a voltage detection circuit 64.

[0018] The switch 7 is a relay for connecting or disconnecting the distributed power source 3 to the power grid 2. The opening and closing of the switch 7 is controlled by a control circuit 60. When the switch 7 is switched to a conductive state (parallel state), the distributed power source 3 is connected to the power grid, and when the switch 7 is switched to a non-conductive state (disconnected state), the distributed power source 3 is disconnected from the power grid 2.

[0019] The inverter 61 is a circuit that converts the DC power output from the DC / DC converter 5 into AC power by system interconnection control so as to follow fluctuations in the power system 2. The inverter 61 outputs the converted AC power to the filter circuit 62.

[0020] The filter circuit 62 is a circuit that cuts high-frequency components contained in the AC power output from the inverter 61 and outputs the AC power to the load 8 and the power system 2. The filter circuit 62 includes, for example, an inductor 62a connected in series to the inverter 61 and a capacitor 62b connected in parallel to the inverter 61.

[0021] FIG. 2 is a circuit diagram showing the inverter 61 and its peripheral circuit. The inverter 61 is a full bridge circuit consisting of two legs connected in parallel. The first leg is a circuit formed by connecting a high-side switching element 61a and a low-side switching element 61b in series. Similarly, the second leg is a circuit formed by connecting a high-side switching element 61c and a low-side switching element 61d in series. The high-side switching elements 61a, 61c and the low-side switching elements 61b, 61d are, for example, N-channel MOSFETs. Hereinafter, the high-side switching elements 61a, 61c and the low-side switching elements 61b, 61d are appropriately collectively referred to as each switching element. The control circuit 60 outputs a PWM signal to the gate of each switching element to PWM-control the on-off state of each switching element. In particular, in the first embodiment, an example will be described in which the control circuit 60 PWM-controls the on-off state of each switching element in a bipolar manner.

[0022] One end of an inductor 62a is connected to the midpoint where the high-side switching element 61a and the low-side switching element 61b are connected, and the other end of the inductor 62a is connected to one end of a capacitor 62b. The other end of the capacitor 62b is connected to the midpoint where the high-side switching element 61c and the low-side switching element 61d are connected.

[0023] The current detection circuit 63 is a current sensor that detects the current value of the AC power output from the inverter 61 and outputs a current value signal indicating the detected current value to the control circuit 60. The control circuit 60 acquires the current value signal output from the current detection circuit 63 by AD conversion into digital current value data.

[0024] The voltage detection circuit 64 is a voltage sensor circuit that detects the voltage value of the AC power output from the inverter 61, and outputs a voltage value signal indicating the detected voltage value to the control circuit 60. The control circuit 60 acquires the voltage value signal output from the voltage detection circuit 64 by AD conversion into digital voltage value data.

[0025] The control circuit 60 is a computer that controls the operation of the power conditioner 4. 3 is a block diagram showing an example of the configuration of the control circuit 60. The control circuit 60 is a computer, and includes a calculation unit 60a, a storage unit 60b, an input unit 60c, and an output unit 60d.

[0026] The storage unit 60b includes, for example, a main storage unit and an auxiliary storage unit. The main storage unit is a temporary storage area such as a static random access memory (SRAM), a dynamic random access memory (DRAM), or a flash memory, and temporarily stores data required for the arithmetic unit 60a to execute arithmetic processing. The auxiliary storage unit is a storage device such as an electrically erasable programmable ROM (EEPROM). The auxiliary storage unit stores a computer program 91 executed by the arithmetic unit 60a and various data required for other processing.

[0027] The computer program 91 may be written into the auxiliary storage unit during the manufacturing stage of the power conversion device 6, or may be distributed by an external computer and acquired by the power conditioner 4 through communication and stored in the auxiliary storage unit. The computer program 91 may be recorded in a readable manner on a recording medium 9 such as a magnetic disk, an optical disk, or a semiconductor memory, or may be read from the recording medium 9 by a reading device and stored in the auxiliary storage unit.

[0028] The input unit 60c is a circuit that inputs a current value signal and a voltage value signal output from the current detection circuit 63 and the voltage detection circuit 64, respectively. The input unit 60c has, for example, an AD conversion circuit, and converts the input current value signal into digital current value data. The input unit 60c also converts the input voltage value signal into digital voltage value data. The calculation unit 60a acquires the current value data and voltage value data via the input unit 60c at a predetermined monitoring timing, and stores each acquired data in the memory unit 60b.

[0029] The calculation unit 60a is a calculation circuit such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The calculation unit 60a controls the operation of each component by executing a computer program 91 stored in the storage unit 60b. The calculation unit 60a executes processing in accordance with the computer program 91, thereby controlling the operation of the control circuit 60, calculating the average value of the output current with high accuracy, and controlling the operation of the power conversion device 6. In the present embodiment, the control circuit 60 realizes various functional units in the form of software. However, some or all of the various functional units may be configured with dedicated hardware such as a semiconductor integrated circuit.

[0030] The output unit 60d outputs a PWM signal for PWM-controlling the inverter 61 to the inverter 61 under the control of the calculation unit 60a. The output unit 60d also outputs a signal to the switch 7 for opening and closing the switch 7.

[0031] <Calculation method of the inverter 61 output average current> FIG. 4 is a flowchart showing the processing procedure of the control circuit 60, and FIGS. 5 to 7 are timing charts for explaining a method of calculating the average output current.

[0032] 5 to 7, the square waves in the top rows show the time changes in the on / off states of the high-side switching element 61a and the low-side switching element 61d, and the square waves in the middle rows show the time changes in the on / off states of the high-side switching element 61c and the low-side switching element 61b. The switching control shown in FIGS. 5 to 7 is an inverter system. The bottom rows show the time changes in the current output from the inverter 61. The black circles show the timing of current detection, i.e., the timing of current value data acquisition by the control circuit 60.

[0033] The control circuit 60 PWM controls the inverter 61 with a modulation factor m according to the state in order to convert the DC power output from the distributed power sources 3 into AC power (step S11). The modulation factor m is the ratio of the output voltage (effective value) of the inverter 61 to the input voltage to the inverter 61. The modulation factor has a value between -1 and 1.

[0034] Next, the control circuit 60 detects the current output from the inverter 61 (step S12). The control circuit 60 acquires current value data every time switching of the full bridge circuit constituting the inverter 61 is performed. Specifically, the control circuit 60 acquires current value data at the timing when the high-side switching element 61a and the low-side switching element 61d are in the ON state and the timing when they are in the OFF state. More specifically, as shown in FIG. 5, the control circuit 60 acquires current value data at the center point (Ta / 2) of the ON period Ta of the high-side switching element 61a and the low-side switching element 61d. The ON state of the high-side switching element 61a and the low-side switching element 61d is a switching state (first switching state) in which the current output of the inverter 61 increases. In addition, the control circuit 60 acquires current value data at the center point (Tb / 2) of the OFF period Tb of the high-side switching element 61a and the low-side switching element 61d. The off state of the high-side switching element 61a and the low-side switching element 61d is a switching state (second switching state) in which the current output of the inverter 61 decreases.

[0035] Then, the control circuit 60 calculates a weighted average value of the output current using a weighting coefficient based on the modulation factor m related to the PWM control (step S13), and executes a predetermined process based on the calculated average value of the output current (step S14). The predetermined process is, for example, a process of changing the dead time of the PWM control.

[0036] Specifically, the control circuit 60 calculates the average value of the current output from the inverter 61 based on the following formula (1).

[0037]

number

[0038] The technical meaning of the above formula (1) will be explained. When the modulation factor m is small, as shown in FIG. 6, the ON period Ta of the high-side switching element 61a and the low-side switching element 61d becomes short, so that the measurement point and the switching point become closer. Switching noise occurs at the switching point, and ringing may continue for a certain period of time due to interaction with parasitic elements. Therefore, the closer the switching point is, the more susceptible it is to the influence of switching noise. Therefore, if weighted averaging is performed as in (1) above, the shorter the ON period Ta is, the lower the weighting for the first current value Ia, and the influence of noise can be reduced. Similarly, when the OFF period Tb of the high-side switching element 61a and the low-side switching element 61d is short, the weighting for the second current value Ib becomes lower, and the influence of noise can be reduced.

[0039] On the other hand, if the output current can be detected at the midpoint of the on-period Ta and the midpoint of the off-period Tb, both the first current value Ia and the second current value Ib will be equal to or close to the output average current value I. However, there is always an error in the measurement timing of the output current. The measurement error in the measurement timing is an error that occurs due to the performance and characteristics of the control circuit 60. When the time error in the measurement timing is ΔT, the measured first current value Ia and second current value Ib are respectively expressed by the following equations (2) and (3).

[0040]

number

[0041] In this case, the average value of the first current value Ia and the second current value Ib is expressed by the following formula (4).

[0042]

number

[0043] The second term in the above equation (4) is an error term, and the error term increases as the modulation factor m deviates from 0 and as the time error ΔT increases.

[0044] Therefore, if the weighted average expressed by the above formula (1) is used instead of the arithmetic average, the error term can be cancelled out.

[0045] As described above, according to the first embodiment, it is possible to suppress the influence of measurement errors due to mixing of switching noise in the power conversion device 6 and time errors in the detection timing, and to calculate the average value of the output current of the inverter 61 with higher accuracy.

[0046] The average current of the inverter 61 is expressed by only the variables of the modulation factor m, the first current value Ia, and the second current value Ib, and does not include any error terms related to the detection timing from the center point in the on-period and off-period of the switching element. Therefore, the average current of the inverter 61 can be accurately calculated by only these three variables without being affected by the detection timing error.

[0047] The right-hand side of the above formula (1) consists of multiple current value variables, and the average current value is calculated by setting the ratio (weight) of each of these variables. In other words, the modulation factor m is an important parameter that determines this weight.

[0048] In this embodiment, the unidirectional DC / DC converter 5 and inverter 61 have been described, but the power conditioner 4 according to this embodiment may be configured using a bidirectional DC / DC converter 5 and inverter 61.

[0049] (Embodiment 2) The grid interconnection system 1 according to the second embodiment is different from the first embodiment in that the control circuit 60 uses a unipolar method to PWM-control the on / off state of each switching element, and in the method of calculating the output average current of the inverter 61. Since the other configurations of the grid interconnection system 1 are similar to those of the grid interconnection system 1 according to the first embodiment, the same reference numerals are used for similar parts, and detailed descriptions thereof will be omitted.

[0050] Fig. 8 is a timing chart for explaining a method of calculating an average output current according to the second embodiment. Fig. 8A shows unipolar switching control when the modulation factor is equal to or greater than 0, and Fig. 8B shows unipolar switching control when the modulation factor is less than 0. Figs. 8A and 8B show, from top to bottom, the changes over time in the on / off states of the high-side switching element 61a, the low-side switching element 61b, the high-side switching element 61c, and the low-side switching element 61d. The bottommost part shows the changes over time in the current output from the inverter 61 and the timing of acquiring the current value data, as in the first embodiment.

[0051] The control circuit 60 according to the second embodiment performs unipolar PWM control of the switching elements, and measures the current output from the inverter 61 in the same manner as in the first embodiment.

[0052] When the modulation rate is 0 or more, the control circuit 60 controls the high-side switching element 61c to be in the OFF state and the low-side switching element 61d to be in the ON state, and acquires current value data at the timing when the high-side switching element 61a is in the ON state (the low-side switching element 61b is in the OFF state) and at the timing when the high-side switching element 61a is in the OFF state. More specifically, as shown in FIG. 8A, the control circuit 60 acquires current value data at the center point (Ta / 2) of the ON period Ta of the high-side switching element 61a. The state in which the high-side switching element 61a is ON and the low-side switching element 61b is OFF is a switching state (first switching state) in which the current output of the inverter 61 increases. The control circuit 60 also acquires current value data at the center point (Tb / 2) of the OFF period Tb of the high-side switching element 61a. The state in which the high-side switching element 61a is OFF and the low-side switching element 61b is ON is a switching state (second switching state) in which the current output of the inverter 61 decreases.

[0053] When the modulation rate is less than 0, the control circuit 60 controls the high-side switching element 61a to be in the OFF state and the low-side switching element 61b to be in the ON state, and acquires current value data at the timing when the high-side switching element 61c is in the ON state (the low-side switching element 61d is in the OFF state) and at the timing when the high-side switching element 61c is in the OFF state. More specifically, as shown in FIG. 8A, the control circuit 60 acquires current value data at the center point (Ta / 2) of the OFF period Ta of the high-side switching element 61c. The state in which the high-side switching element 61c is OFF and the low-side switching element 61d is ON is a switching state (first switching state) in which the current output of the inverter 61 increases. The control circuit 60 also acquires current value data at the center point (Tb / 2) of the ON period Tb of the high-side switching element 61c. The state in which the high-side switching element 61c is ON and the low-side switching element 61d is OFF is a switching state (second switching state) in which the current output of the inverter 61 decreases.

[0054] Then, the control circuit 60 calculates a weighted average value of the output current using a weighting coefficient based on the modulation factor m related to the PWM control. Specifically, when the modulation factor is equal to or greater than 0, the control circuit 60 calculates the average value of the current output from the inverter 61 based on the following formula (5).

[0055]

number

[0056] When the modulation factor is less than 0, the control circuit 60 calculates the average value of the current output from the inverter 61 based on the following formula (6).

[0057]

number

[0058] Thus, according to the second embodiment, as in the first embodiment, it is possible to suppress the influence of switching noise in the power conversion device 6 controlled by the unipolar method and the influence of measurement errors due to time errors in the detection timing, and to calculate the average value of the output current of the inverter 61 with higher accuracy.

[0059] (Embodiment 3) The grid interconnection system 1 according to the third embodiment is different from the first embodiment in that the control circuit 60 PWM controls the on / off state of each switching element in a totem pole system and in the method of calculating the output average current of the inverter 61. Since the other configurations of the grid interconnection system 1 are similar to those of the grid interconnection system 1 according to the first embodiment, the same reference numerals are used for similar parts and detailed description will be omitted.

[0060] Fig. 9 is a timing chart for explaining a method of calculating an average output current according to the third embodiment. Fig. 9A shows switching control of the totem pole system when the modulation rate is equal to or greater than 0, and Fig. 9B shows switching control of the totem pole system when the modulation rate is less than 0. Figs. 9A and 9B show, from top to bottom, the changes over time in the on / off states of the high-side switching element 61a, the low-side switching element 61b, the high-side switching element 61c, and the low-side switching element 61d. The bottommost part shows the changes over time in the current output from the inverter 61 and the timing of acquiring the current value data, as in the first embodiment.

[0061] The control circuit 60 according to the third embodiment performs PWM control of the switching elements by the totem pole method, and measures the current output from the inverter 61 in the same manner as in the first embodiment.

[0062] When the modulation rate is 0 or more, the control circuit 60 controls the high-side switching element 61c to be in the OFF state and the low-side switching element 61d to be in the ON state, and acquires current value data at the timing when the high-side switching element 61a is in the ON state (the low-side switching element 61b is in the OFF state) and at the timing when the high-side switching element 61a is in the OFF state. More specifically, as shown in FIG. 9A, the control circuit 60 acquires current value data at the center point (Ta / 2) of the ON period Ta of the high-side switching element 61a. The state in which the high-side switching element 61a is ON and the low-side switching element 61b is OFF is a switching state (first switching state) in which the current output of the inverter 61 increases. The control circuit 60 also acquires current value data at the center point (Tb / 2) of the OFF period Tb of the high-side switching element 61a. The state in which the high-side switching element 61a is OFF and the low-side switching element 61b is ON is a switching state (second switching state) in which the current output of the inverter 61 decreases.

[0063] When the modulation rate is less than 0, the control circuit 60 controls the high-side switching element 61c to be in an on state and the low-side switching element 61d to be in an off state, and acquires current value data at the timing when the high-side switching element 61a is in an on state (the low-side switching element 61b is in an off state) and at the timing when the high-side switching element 61a is in an off state. More specifically, as shown in FIG. 9B, the control circuit 60 acquires current value data at a central time point (Ta / 2) of the on-period Ta of the high-side switching element 61a. The state in which the high-side switching element 61a is on and the low-side switching element 61b is off is a switching state (first switching state) in which the current output of the inverter 61 increases. The control circuit 60 also acquires current value data at a central time point (Tb / 2) of the off-period Tb of the high-side switching element 61a. The state in which the high-side switching element 61a is off and the low-side switching element 61b is on is a switching state (second switching state) in which the current output of the inverter 61 decreases.

[0064] Then, the control circuit 60 calculates a weighted average value of the output current using a weighting coefficient based on the modulation factor m related to the PWM control. Specifically, similar to the second embodiment, when the modulation factor is 0 or more, the control circuit 60 calculates the average value of the current output from the inverter 61 based on the above formula (5). When the modulation factor is 0 or more, the control circuit 60 calculates the average value of the current output from the inverter 61 based on the above formula (6).

[0065] Thus, according to the third embodiment, as in the first embodiment, it is possible to suppress the influence of switching noise in the power conversion device 6 controlled by the totem pole method and the influence of measurement errors due to time errors in the detection timing, and to calculate the average value of the output current of the inverter 61 with higher accuracy.

[0066] (Embodiment 4) The grid interconnection system 1 according to the fourth embodiment differs from the first embodiment in that the power conversion device 6 includes a step-down chopper circuit instead of the inverter 61 and the filter circuit 62, and the control circuit 60 calculates the output average current of the step-down chopper circuit. Since the other configurations of the grid interconnection system 1 are similar to those of the grid interconnection system 1 according to the first embodiment, the same reference numerals are used for the similar parts, and detailed description thereof will be omitted.

[0067] The step-down chopper circuit includes a switching element, an inductor, a diode, and a capacitor. The switching element and the inductor are connected in series from the high potential side to the low potential side, and the cathode of the diode is connected to the connection point of the switching element and the inductor, and the anode is grounded. The capacitor is connected in parallel to the low potential side.

[0068] The control circuit 60 according to the fourth embodiment controls the switching of the step-down chopper circuit, and obtains current value data when the switching element of the step-down chopper circuit is in the on state and when it is in the off state. More specifically, the control circuit 60 obtains current value data at the center of the on-state period and the center of the off-state period. The on-state of the switching element is a switching state (first switching state) in which the current output of the step-down chopper circuit increases, and the off-state of the switching element is a switching state (second switching state) in which the current output of the step-down chopper circuit decreases.

[0069] Then, the control circuit 60 calculates a weighted average value of the output current using a weighting coefficient based on the step-down ratio α. The step-down ratio α is a type of modulation factor. Specifically, the control circuit 60 performs the calculation based on the following formula (7).

[0070]

number

[0071] As described above, according to the fourth embodiment, it is possible to suppress the influence of measurement errors due to mixing of switching noise in the power conversion device 6 and time errors in the detection timing, and to calculate the average value of the output current of the step-down chopper circuit with higher accuracy.

[0072] (Embodiment 5) The grid interconnection system 1 according to the fifth embodiment differs from the first embodiment in that the power conversion device 6 includes a boost chopper circuit instead of the inverter 61 and the filter circuit 62, and the control circuit 60 calculates the output average current of the boost chopper circuit. Since the other configurations of the grid interconnection system 1 are similar to those of the grid interconnection system 1 according to the first embodiment, the same reference numerals are used for the similar parts, and detailed description thereof will be omitted.

[0073] The boost chopper circuit includes a switching element, an inductor, a diode, and a capacitor. The inductor and the diode are connected in series from the high potential side to the low potential side, one end of the switching element is connected to the connection point of the inductors, and the other end of the switching element is grounded. The capacitor is connected in parallel to the low potential side.

[0074] The control circuit 60 according to the fifth embodiment controls the switching of the boost chopper circuit, and obtains current value data when the switching element of the boost chopper circuit is in the on state and when it is in the off state. More specifically, the control circuit 60 obtains current value data at the center of the on state period and the center of the off state period. The on state of the switching element is a switching state (first switching state) in which the current output of the boost chopper circuit increases, and the off state of the switching element is a switching state (second switching state) in which the current output of the boost chopper circuit decreases.

[0075] Then, the control circuit 60 calculates a weighted average value of the output current using a weighting coefficient based on the step-up ratio α. The step-up ratio α is a type of modulation factor. Specifically, the control circuit 60 performs the calculation based on the following formula (8).

[0076]

number

[0077] As described above, according to the fifth embodiment, it is possible to suppress the influence of measurement errors due to mixing of switching noise in the power conversion device 6 and time errors in the detection timing, and to calculate the average value of the output current of the boost chopper circuit with higher accuracy. [Explanation of symbols]

[0078] 1: Grid-connected system 2: Power system 3: Distributed power supply 4: Power conditioner 5: DC / DC converter 6: Power conversion device 7: Switch 8: Load 9: Recording media 60: Control circuit 61: Inverter 62: Filter circuit 62a: Inductor 62b: Capacitor 63: Current detection circuit 64: Voltage detection circuit 91: Computer Programs

Claims

1. a voltage conversion circuit having a switching element; a control circuit for controlling switching of the voltage conversion circuit; a current detection circuit that detects a current output from the voltage conversion circuit; Equipped with The control circuit includes: calculating an average value of a current output from the voltage conversion circuit based on a first current value detected in a first switching state in which the output of the current increases, a second current value detected in a second switching state in which the output of the current decreases, and a modulation factor related to switching control of the voltage conversion; The operation of the voltage conversion circuit is controlled based on the calculated average value. Power conversion equipment.

2. The control circuit includes: A weighted average of the first current value and the second current value is calculated using a weighting coefficient based on the modulation factor. The power conversion device according to claim 1 .

3. The voltage conversion circuit includes: An inverter having a circuit in which two switching elements are connected in series, The control circuit includes: The voltage conversion circuit is PWM controlled by a bipolar method, The average value of the current output from the voltage conversion circuit is calculated based on the following formula: The power conversion device according to claim 1 or 2. I=Ia×(1+m) / 2+Ib×(1-m) / 2 however, I: Average value of the current output from the voltage conversion circuit Ia: the first current value Ib: the second current value m: the modulation factor

4. The voltage conversion circuit includes: An inverter having a circuit in which two switching elements are connected in series, The control circuit includes: The voltage conversion circuit is PWM-controlled by a unipolar method or a totem pole method, The average value of the current output from the voltage conversion circuit is calculated based on the following formula: The power conversion device according to claim 1 or 2. I = m x Ia + (1-m) x Ib (when m ≥ 0) I = (m + 1) x Ia - m x Ib (when m < 0) however, I: Average value of the current output from the voltage conversion circuit Ia: the first current value Ib: the second current value m: the modulation factor

5. A power conversion method using a voltage conversion circuit having a switching element, Switching control of the voltage conversion circuit; Detecting a current output from the voltage conversion circuit; calculating an average value of a current output from the voltage conversion circuit based on a first current value detected in a first switching state in which the output of the current increases, a second current value detected in a second switching state in which the output of the current decreases, and a modulation factor related to switching control of the voltage conversion; The operation of the voltage conversion circuit is controlled based on the calculated average value. Power conversion methods.

6. A computer program for causing a computer to calculate a process related to power conversion using a voltage conversion circuit having a switching element, Switching control of the voltage conversion circuit; Detecting a current output from the voltage conversion circuit; calculating an average value of a current output from the voltage conversion circuit based on a first current value detected in a first switching state in which the output of the current increases, a second current value detected in a second switching state in which the output of the current decreases, and a modulation factor related to switching control of the voltage conversion; The operation of the voltage conversion circuit is controlled based on the calculated average value. A computer program that causes the computer to execute a process.

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