JP2019054649A - AC inverter - Google Patents

Abstract

To provide an AC inverter which can output stable AC voltage to load even when an actual value of AC current flowing through the load fluctuates.SOLUTION: An AC inverter has an insulation type DCDC conversion portion 11, a control portion 13, a DCAC conversion portion 15, and a control portion 16. The insulation type DCDC conversion portion 11 converts DC power into AC power by making a switching element SWdc ON/OFF according to a duty ratio of a control signal Sdc, transmits the same from primary coil of a transformer to secondary coil, and rectifies and smooths the AC power transmitted to the secondary coil to be converted into the DC power. The control portion 13 obtains the duty ratio of the control signal Sdc based on input voltage vin, and corrects the duty ratio based on at least input current Iin. The DCAC conversion portion 15 converts the DC power outputted from the insulation type DCDC conversion portion 11 into commercial AC power.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an AC inverter.

Some existing AC inverters include, for example, an insulation type DCDC converter and a DCAC converter.
The insulation type DCDC converter converts the input DC power into AC power by turning on and off the switching element, and transmits the AC power from the primary coil to the secondary coil of the transformer. It is converted into DC power by rectifying and smoothing.

  The DCAC converter converts, for example, DC power output from the isolated DCDC converter into AC power and outputs the AC power to a load by turning on and off switching elements connected in an H-bridge shape.

  Further, in the above-described existing AC inverter, as the effective value of the alternating current output to the load increases, the output voltage output from the isolated DCDC converter decreases due to the voltage drop due to the resistance component in the AC inverter. Accordingly, the duty ratio of the control signal for controlling the on / off of the switching element of the DCAC converter is increased to suppress the decrease in the effective value of the AC voltage output to the load.

  See, for example, Patent Document 1 as related technology.

JP 2013-219982 A

  However, in the above-described existing AC inverter, when the output voltage of the insulation type DCDC converter fluctuates due to the voltage drop due to the resistance component in the AC inverter with the fluctuation of the effective value of the alternating current output to the load, the control signal Since the duty ratio also fluctuates, the waveform of the AC voltage output to the load becomes unstable, and the load may not be driven stably.

  Further, in the above-described existing AC inverter, when the effective value of the alternating current output to the load increases, the output voltage of the insulation type DCDC converter decreases due to the voltage drop due to the resistance component in the AC inverter. The maximum value (crest value) of the output AC voltage may be smaller than the maximum value of the AC voltage necessary for driving the load, and the load may not be driven.

  An object of one aspect of the present invention is to provide an AC inverter that can output an AC voltage having a stable waveform to a load even if the effective value of the AC current flowing to the load varies.

  An AC inverter according to one embodiment of the present invention is an AC inverter that is mounted on a vehicle and converts input DC power into commercial AC power, and includes an insulated DCDC converter, a controller, and a DCAC converter. With.

  The insulation type DCDC converter converts the DC power into AC power by turning on and off the switching element, transmits the AC power from the primary coil of the transformer to the secondary coil, and rectifies the AC power transmitted to the secondary coil. Converts to DC power by smoothing.

  The control unit obtains a duty ratio of a control signal for controlling on / off of the switching element based on an input voltage input to the isolated DCDC converter, and the duty ratio is input to at least the isolated DCDC converter. Correction based on the input current.

  The DCAC converter converts the DC power output from the isolated DCDC converter into commercial AC power.

  According to the present invention, even if the effective value of the alternating current flowing from the AC inverter to the load fluctuates, an alternating voltage having a stable waveform can be output to the load.

It is a figure which shows the AC inverter of embodiment. It is a flowchart which shows an example of operation | movement of a control part. It is a figure showing an example of information memorized by a storage part.

Hereinafter, embodiments will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating an AC inverter according to an embodiment.
The AC inverter shown in FIG. 1 is mounted on a vehicle such as a plug-in hybrid vehicle or an electric vehicle, converts DC power output from the battery B into commercial AC power, and supplies the commercial AC power to a load Lo such as a personal computer or a game machine. . For example, the commercial AC power is a rectangular wave AC power having the same frequency as the AC power of the commercial power source.

The AC inverter shown in FIG. 1 includes an insulation type DCDC conversion unit 11, a current detection unit 12, a control unit 13, a storage unit 14, a DCAC conversion unit 15, and a control unit 16.
The isolated DCDC converter 11 includes a switching element SWdc, a transformer T, a diode D1, a diode D2, an inductor L, and a capacitor C.

  The switching element SWdc is, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The source terminal of the switching element SWdc is connected to the negative terminal of the battery B. The positive terminal of the battery B is connected to one end of the primary coil of the transformer T via the current detection unit 12. The other end of the primary coil of the transformer T is connected to the drain terminal of the switching element SWdc. One end of the secondary coil of the transformer T is connected to the anode terminal of the diode D1. The cathode terminal of the diode D1 is connected to the cathode terminal of the diode D2 and one end of the inductor L. The other end of the inductor L is connected to one end of the capacitor C. The other end of the capacitor C is connected to the other end of the secondary coil of the transformer T and the anode terminal of the diode D2. Note that the circuit configuration of the insulation type DCDC converter 11 is not limited to the circuit configuration shown in FIG.

  The insulation type DCDC conversion unit 11 converts the DC power output from the battery B and input to the insulation type DCDC conversion unit 11 into AC power by switching the switching element SWdc on and off, and from the primary coil of the transformer T. The AC power transmitted to the secondary coil is rectified by the diodes D1 and D2 and smoothed by the inductor L and the capacitor C to be converted to DC power.

The current detection unit 12 includes, for example, a shunt resistor or a Hall element, and detects an input current Iin of the isolated DCDC conversion unit 11.
The control unit 13 includes, for example, a CPU (Central Processing Unit) or a programmable device (FPGA (Field Programmable Gate Array), PLD (Programmable Logic Device), etc.).

  In addition, the control unit 13 controls the duty ratio of the control signal Sdc for controlling on / off of the switching element SWdc, so that the output voltage Vout of the isolated DCDC converter 11 with respect to the input voltage Vin of the isolated DCDC converter 11 is controlled. The step-up ratio or step-down ratio is controlled.

  Further, the control unit 13 obtains a duty ratio of the control signal Sdc based on the input voltage Vin. In this way, an insulating element such as a photocoupler for feeding back the output voltage Vout to the control unit 13 is AC compared to a configuration in which the duty ratio of the control signal Sdc is obtained based not only on the input voltage Vin but also on the output voltage Vout. Since it is not necessary to provide the inverter, the manufacturing cost of the AC inverter can be reduced.

  Further, the control unit 13 corrects the duty ratio of the control signal Sdc based on at least the input current Iin (current value detected by the current detection unit 12) input to the isolated DCDC conversion unit 11. For example, the effective value of the alternating current output from the AC inverter to the load Lo increases, that is, the input current Iin increases, and the voltage drop due to the resistance component in the AC inverter increases, so the duty ratio of the control signal Sdc is increased. By increasing the output voltage Vout, the fluctuation of the output voltage Vout accompanying the fluctuation of the effective value of the alternating current output from the AC inverter to the load Lo can be suppressed. Thereby, the fluctuation | variation of the duty ratio of control signals Sac1-Sac4 accompanying the fluctuation | variation of the output voltage Vout can be suppressed. Moreover, it can suppress that the maximum value (peak value) of the alternating voltage output from the AC inverter to the load Lo due to the decrease in the output voltage Vout decreases. Accordingly, since an AC voltage having a stable waveform can be output to the load Lo, the load Lo can be driven stably.

The storage unit 14 is configured by, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory).
The DCAC conversion unit 15 includes switching elements SWac1 to SWac4.

  Each of the switching elements SWac1 to SWac4 is, for example, a MOSFET. The drain terminal of the switching element SWac1 is connected to one end of the capacitor C and the drain terminal of the switching element SWac2, and the source terminal of the switching element SWac1 is connected to the drain terminal of the switching element SWac3 and one input terminal of the load Lo. The source terminal of the switching element SWac3 is connected to the other end of the capacitor C and the source terminal of the switching element SWac4. The drain terminal of the switching element SWac4 is connected to the source terminal of the switching element SWac2 and the other input terminal of the load Lo. The circuit configuration of the DCAC conversion unit 15 is not limited to the circuit configuration illustrated in FIG. The switching element SWac1 is controlled to be turned on / off by a control signal Sac1, the switching element SWac2 is controlled to be turned on / off by a control signal Sac2, and the switching element SWac3 is controlled to be turned on / off by a control signal Sac3. SWac4 is controlled to be turned on / off by a control signal Sac4.

  In the DCAC converter 15, the switching element SWac1 and the switching element SWac4 are turned on, the switching element SWac2 and the switching element SWac3 are turned off, the switching element SWac1 and the switching element SWac4 are turned off, and the switching element SWac2 and the switching element SWac3 are turned on. By repeating the turn-on, the DC power output from the insulated DCDC converter 11 is converted into commercial AC power.

The control part 16 is comprised by CPU or a programmable device, for example.
Further, the control unit 16 is insulated so that the effective value of the AC voltage output from the DCAC conversion unit 15 to the load Lo is within the allowable range of the effective value of the AC voltage that can drive the load Lo. Based on the output voltage Vout of the DCDC converter 11, the duty ratio of the control signal Sac1 to the control signal Sac4 is obtained.

FIG. 2 is a flowchart illustrating an example of the operation of the control unit 13. In addition, the control part 13 shall perform the process of S21-S26 shown in FIG. 2 for every control timing, for example.
First, the control unit 13 acquires the input voltage Vin (S21) and acquires the input current Iin (S22).

Next, the control unit 13 obtains the duty ratio of the control signal Sdc based on the input voltage Vin (S23).
For example, as shown in FIG. 3A, the control unit 13 refers to the input voltage-duty ratio correspondence information D1 indicating the relationship between the input voltage Vin and the duty ratio Duty of the control signal Sdc, and acquires it in S21. The duty ratio Duty corresponding to the input voltage Vin is obtained as the duty ratio of the control signal Sdc at the current control timing.

  The magnitude relationship between the input voltage Vin1 to the input voltage Vin3 shown in FIG. 3A is the input voltage Vin1 <input voltage Vin2 <the input voltage Vin3, and the magnitude relationship between the duty ratio Duty1 to the duty ratio Duty3 shown in FIG. , Duty ratio Duty1 <duty ratio Duty2 <duty ratio Duty3. That is, as the input voltage Vin increases, the duty ratio of the control signal Sdc decreases.

  As a result, the duty ratio of the control signal Sdc can be reduced as the input voltage Vin increases, so that it is possible to suppress the output voltage Vout from fluctuating with the fluctuation of the input voltage Vin. It is assumed that the input voltage-duty ratio correspondence information D1 shown in FIG. 3A is obtained in advance, for example, through experiments or simulations, and stored in the storage unit 14.

  Next, in the flowchart shown in FIG. 2, the control unit 13 obtains a correction value Duty + based on at least the input current Iin (S24), and based on the obtained correction value Duty +, the control signal Sdc obtained in S23. The duty ratio is corrected (S25).

  For example, as illustrated in FIG. 3B, the control unit 13 refers to the input current-correction value correspondence information D2 indicating the relationship between the input current Iin and the correction value Duty +, and at S22 of the current control timing. The correction value Duty + corresponding to the acquired input current Iin is acquired as the correction value Duty + at the current control timing, and the acquired correction value Duty + is added to the duty ratio Duty obtained in S23, whereby the control signal Sdc Correct the duty ratio.

  The magnitude relationship between the input current Iin1 to the input current Iin3 shown in FIG. 3B is set such that the input current Iin1 <the input current Iin2 <the input current Iin3. The magnitude relationship between the correction value Duty + 1 to the correction value Duty + 3 shown in FIG. 3B is correction value Duty + 1 <correction value Duty + 2 <correction value Duty + 3. That is, the correction value Duty + increases as the input current Iin increases.

  Accordingly, the correction value Duty + increases as the input current Iin increases, that is, as the effective value of the AC current output from the AC inverter to the load Lo increases. Therefore, the AC current output from the AC inverter to the load Lo increases. As the effective value increases, the duty ratio of the control signal Sdc increases. Therefore, as the effective value of the alternating current output from the AC inverter to the load Lo increases, the voltage drop due to the resistance component in the AC inverter increases, so the duty ratio of the control signal Sdc is increased and the output voltage Vout is increased. Thus, fluctuations in the output voltage Vout accompanying fluctuations in the effective value of the alternating current output from the AC inverter to the load Lo can be suppressed. Therefore, it is possible to suppress the variation in the duty ratio of the control signals Sac1 to Sac4 due to the variation in the output voltage Vout. Moreover, it can suppress that the maximum value (peak value) of the alternating voltage output from the AC inverter to the load Lo due to the decrease in the output voltage Vout decreases. Accordingly, since an AC voltage having a stable waveform can be output to the load Lo, the load Lo can be driven stably.

  As shown in FIG. 3C, the control unit 13 refers to the input current-input voltage-correction value correspondence information D3 indicating the relationship among the input current Iin, the input voltage Vin, and the correction value Duty +. The correction value Duty + corresponding to the input current Iin acquired at S22 of the current control timing and the input voltage Vin acquired at S21 is acquired as the correction value Duty + at the current control timing, and the acquired correction value Duty + is acquired at S23. The duty ratio of the control signal Sdc may be corrected by adding to the duty ratio obtained in step (1).

  The magnitude relationship between the input current Iin1 to the input current Iin3 shown in FIG. 3C is set such that the input current Iin1 <the input current Iin2 <the input current Iin3. The magnitude relationship between the input voltage Vin1 to the input voltage Vin3 shown in FIG. 3C is set such that the input voltage Vin1 <the input voltage Vin2 <the input voltage Vin3. The magnitude relationship between the correction values Duty + 1 to the correction value Duty + 5 shown in FIG. 3C is correction value Duty + 1 <correction value Duty + 2 <correction value Duty + 3 <correction value Duty + 4 <correction value Duty + 5. In other words, the correction value Duty + increases as the input current Iin and the input voltage Vin increase.

  As described above, when the correction value Duty + is obtained with reference to the input current-input voltage-correction value correspondence information D3 shown in FIG. 3C, the input current-duty ratio correspondence information D2 shown in FIG. As compared with the case of obtaining the correction value Duty +, the correction value Duty + can be obtained more accurately in consideration of the fluctuation of the voltage drop due to the resistance component in the AC inverter accompanying the fluctuation of the input voltage Vin. The output voltage Vout can be further stabilized, and the waveform of the AC voltage output from the AC inverter to the load Lo can be further stabilized.

  Note that the input current-duty ratio correspondence information D2 shown in FIG. 3B or the input current-input voltage-correction value correspondence information D3 shown in FIG. It is preliminarily obtained by performing a simulation or the like. Further, the magnitude relationship between the input voltage Vin1 to the input voltage Vin3 of the input current-input voltage-correction value correspondence information D3 is not limited to the magnitude relationship shown in FIG.

In the flowchart shown in FIG. 2, the control unit 13 controls on / off of the switching element SWdc by the corrected control signal Sdc (S26).
In addition, this invention is not limited to the above embodiment, A various improvement and change are possible within the range which does not deviate from the summary of this invention.

DESCRIPTION OF SYMBOLS 11 Insulation type DCDC conversion part 12 Current detection part 13 Control part 14 Storage part 15 DCAC conversion part 16 Control part

Claims (3)

An AC inverter that is mounted on a vehicle and converts input DC power into commercial AC power,
When the switching element is turned on / off, the DC power is converted into AC power and transmitted from the primary coil of the transformer to the secondary coil, and the AC power transmitted to the secondary coil is rectified and smoothed to generate direct current. An insulated DCDC converter that converts power into power,
A duty ratio of a control signal for controlling on / off of the switching element is obtained based on an input voltage input to the isolated DCDC converter, and the duty ratio is input to at least the isolated DCDC converter. A controller for correcting based on the input current;
A DCAC converter that converts DC power output from the isolated DCDC converter into the commercial AC power;
An AC inverter comprising: The AC inverter according to claim 1,
A storage unit for storing input current-correction value correspondence information in which the input current is associated with a correction value;
The control unit obtains a correction value corresponding to the input current input to the insulation type DCDC conversion unit with reference to the input current-correction value correspondence information, and obtains the correction value based on the input voltage. An AC inverter characterized by correcting the duty ratio of the control signal by adding to the duty ratio. The AC inverter according to claim 1,
A storage unit for storing input current-input voltage-correction value correspondence information in which the input current, the input voltage, and the correction value are associated;
The controller refers to the input current-input voltage-correction value correspondence information, and corrects the input current input to the isolated DCDC converter and the input voltage input to the isolated DCDC converter. An AC inverter characterized by correcting a duty ratio of the control signal by obtaining a value and adding the correction value to a duty ratio obtained based on the input voltage.

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