Power conversion device

Abstract

To provide a power conversion device that performs charge / discharge control with high accuracy without depending on an additional protection function or special equipment.SOLUTION: According to an embodiment, a power conversion device includes: a converter that is connected between a DC power supply and a power storage element, charges the power storage element, and outputs a power discharged from the power storage element to the DC power supply; and a control device that controls an operation of the converter. The control device generates a control signal based on an offset-compensated difference value obtained by subtracting an offset compensation value set to cancel an offset from a difference between a preset current command value and a current detection value detected by a current detector having the offset with respect to a detected current value and configured to detect a magnitude and a direction of a current flowing between the converter and the power storage element, and controls the converter.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a power conversion device that controls charging and discharging of a power storage element. [Background technology]

[0002] 2. Description of the Related Art There is a power conversion device that charges a large-capacity power storage element and discharges the charged power storage element to supply power to a grid.

[0003] Such a power conversion device for controlling charging and discharging is required to detect charging current and discharging current with high accuracy.

[0004] Current detectors that detect charge / discharge currents include those that use Hall elements, but when charging or discharging a large-capacity storage element, the range of currents to be detected is very wide, and if there is an offset in the current detector, the detection accuracy at low currents decreases. Because charging at low currents is often the final stage of charging or discharging, protection is required on the storage element side and the converter side to prevent overcharging or overdischarging of the storage element, and it is necessary to select specific current detectors with low offset.

[0005] There is a strong demand for highly accurate charge / discharge control without relying on additional protection functions or special equipment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-209246 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of an embodiment of the present invention is to provide a power conversion device that controls charging and discharging with high precision without relying on additional protection functions or special equipment. [Means for solving the problem]

[0008] A power conversion device according to an embodiment of the present invention includes a converter connected between a DC power source and a storage element, charging the storage element and outputting power discharged from the storage element to the DC power source, and a control device that controls the operation of the converter. The control device generates a control signal and controls the converter based on an offset-compensated difference value obtained by subtracting an offset compensation value set to offset a difference between a preset current command value and a current detection value detected by a current detector that is provided to detect the magnitude and direction of a current flowing between the converter and the storage element and has an offset with respect to the detected current value. [Effects of the Invention]

[0009] According to the embodiments of the present invention, it is possible to provide a power conversion device that controls charging and discharging with high precision without relying on additional protection functions or special equipment. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic block diagram illustrating a power conversion device according to an embodiment; [Figure 2] FIG. 2 is a schematic block diagram illustrating a control device according to the embodiment. [Figure 3] 3(a) and 3(b) are schematic diagrams showing examples of characteristics set in an offset generating unit that is part of the control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0012] FIG. 1 is a schematic block diagram illustrating a power conversion device according to an embodiment. FIG. 1 also shows a charging / discharging system 100 to which a power conversion device 10 according to the embodiment is applied. As shown in FIG. 1, the charging / discharging system 100 includes the power conversion device 10, a current detector 40, a power source 102, and a power storage element 104. The power conversion device 10 is connected between the power source 102 and the power storage element 104. The power source 102 is, for example, a DC power source. The DC power source may be a power system including a DC power source generated by renewable energy, or may be another DC power system. The power storage element 104 is, for example, a storage battery. The current detector 40 is provided between the power conversion device 10 and the power storage element 104. The current detector 40 is provided to detect a current flowing between the power conversion device 10 and the power storage element 104.

[0013] The power conversion device 10 converts a DC voltage supplied from a power source 102 and charges a power storage element 104. The power conversion device 10 outputs DC power supplied from the charged power storage element 104 to the power source 102. A current flowing from the power conversion device 10 to the power storage element 104 is a charging current, and a current flowing from the power storage element 104 to the power conversion device 10 is a discharging current.

[0014] The power conversion device 10 controls the charging current and discharging current according to the magnitude and direction of the current output from the current detector 40.

[0015] 1, the power conversion device 10 includes a converter 20 and a control device 30. The converter 20 has a conversion circuit 22 connected between a power source 102 and an energy storage element 104, and performs bidirectional power conversion. An appropriate circuit configuration, etc. of the conversion circuit 22 is selected depending on the magnitude of the power to be converted, the voltage value, etc.

[0016] Control device 30 is connected to current detector 40 and receives as input data of the current value detected by current detector 40. Although not shown, control device 30 detects the voltage of converter 20. When charging power storage element 104, control device 30 generates a control signal Vg so that the output voltage of converter 20 and the charging current detected by current detector 40 become desired current values, and when discharging power storage element 104, control device 30 generates a control signal Vg and outputs it to converter 20 so that the discharge current and the output voltage of converter 20 become desired values.

[0017] FIG. 2 is a schematic block diagram illustrating a control device according to the embodiment. As shown in FIG. 2 , the control device 30 includes an offset generation unit 32, a PI controller 34, and a PWM unit 36. In the example of FIG. 2 , the control device 30 further includes a protection function unit 38. The protection function unit 38 includes, for example, a protection function for the converter 20 and a protection function for the power storage element 104. For example, if the control device 30 determines that the output voltage of the converter 20 is an overvoltage or an overcurrent, it generates a gate block command GB to stop the operation of the converter 20. Note that the example of FIG. 2 shows elements related to charge control to the power storage element 104 and discharge control from the power storage element 104. The PI controller may be any other control method as long as it is a control element that configures feedback control. For example, a PID controller may be used instead of the PI controller. Furthermore, the PWM unit may also be any other control signal generation element as long as it can appropriately generate a control signal along with the components of feedback control.

[0018] A current detection value Is of the charging current to the power storage element 104 and the discharging current from the power storage element 104 (hereinafter also simply referred to as the current detection value) and a current command value Ic / d* of the charging current and the discharging current (hereinafter also simply referred to as the current command value) are input to the control device 30. The current detection value Is is a detection value of the charging / discharging current detected by the current detector 40. The current command value Ic / d* is a command value set in advance in the control device 30, or a command value set and output by a higher-level control device (not shown), etc.

[0019] In the control device 30, the current command value Ic / d* and the detected current value Is are processed as follows. That is, the control device 30 calculates the difference between the set current command value Ic / d* and the detected current value Is. The control device 30 calculates the difference between the difference between the current command value Ic / d* and the detected current value Is and the offset compensation value Ios output by the offset generation unit 32. The current deviation ΔI calculated from the current command value Ic / d*, the detected current value Is, and the offset compensation value Ios is the offset-compensated current deviation.

[0020] The offset-compensated current deviation ΔI is input to the PI controller 34. The PI controller 34 generates a modulation signal Vpwm so as to set the offset-compensated current deviation ΔI to zero, and outputs the signal to the PWM unit 36. The PWM unit 36 ​​generates and outputs a control signal Vg based on a carrier signal having, for example, a triangular wave, generated inside or outside the PWM unit 36, and the modulation signal Vpwm.

[0021] The offset generating unit 32 will now be described. 2, the offset generation unit 32 is configured to output the offset compensation value Ios in accordance with the voltage VBATT across the power storage element 104. The offset generation unit 32 determines whether the converter 20 is charging or discharging the power storage element 104, based on the voltage value of the voltage VBATT across the power storage element 104. The threshold voltage VB1 is set in advance and is, for example, a charging voltage when the power storage element 104 is subjected to constant voltage charging control.

[0022] 2, when voltage VBATT is lower than threshold voltage VB1, offset generation unit 32 determines that converter 20 is controlling discharge from power storage element 104. In this case, offset generation unit 32 outputs a positive offset compensation value +Ios1.

[0023] When voltage VBATT is equal to or greater than threshold voltage VB1, offset generator 32 determines that converter 20 is controlling charging of power storage element 104. In this case, offset generator 32 outputs a negative offset compensation value −Ios1. Note that the example in FIG. 2 shows a case where the discharge current is positive.

[0024] 3(a) and 3(b) are schematic diagrams showing examples of characteristics set in an offset generating unit that is part of the control device according to the embodiment. As shown in Figures 3(a) and 3(b), in the offset generation unit 32, the positive and negative offset compensation values ​​±Ios1 for the voltage VBATT may be set to different threshold voltages when determining the direction of the charging current and the direction of the discharging current.

[0025] In the example of Figure 3(a), the threshold voltage VB2 is lower than the threshold voltage VB3. In this example, a hysteresis is set in the threshold voltage, and the difference between the threshold voltages VB2 and VB3 is the hysteresis voltage. By providing the hysteresis voltage, it is possible to prevent erroneous detection near the threshold voltage.

[0026] In the example of FIG. 3(b), similar to the example of FIG. 2, the offset generation unit 32 determines that the direction of the current is the discharging direction when the voltage VBATT is lower than the threshold voltage VB1, and determines that the direction of the current is the charging direction when the voltage VBATT is equal to or higher than the threshold voltage.

[0027] When the voltage VBATT is lower than the threshold voltage VB4, the offset generation unit 32 outputs a constant offset compensation value +Ios1. When the voltage VBATT is in the range from the threshold voltage VB4 to VB1, the offset generation unit 32 outputs an offset compensation value that gradually decreases as the voltage VBATT increases.

[0028] When the voltage VBATT is equal to or greater than the threshold voltage VB5, the offset generation unit 32 outputs a constant offset compensation value −Ios1. When the voltage VBATT is in the range of the threshold voltages VB1 to VB5, the offset generation unit 32 outputs an offset compensation value that gradually decreases as the voltage VBATT increases.

[0029] By setting the output characteristics of the offset generating unit 32 to the examples shown in Figures 3(a) and 3(b), it is possible to prevent malfunctions when switching between charging and discharging, and it is possible to more reliably determine the current direction at low currents and perform offset compensation due to the occurrence of an offset in the current detector 40.

[0030] The operation and effects of the power conversion device 10 according to the embodiment will be described. The power conversion device 10 according to the embodiment includes a control device 30 having an offset generation unit 32. The offset generation unit 32 monitors the voltage VBATT of the power storage element 104 and determines the direction of charge / discharge current depending on whether the voltage VBATT is lower than the threshold voltage VB1 or equal to or higher than the threshold voltage VB1. Therefore, even for a current detected by a current detector 40 with a large offset, the direction of charge / discharge current can be determined accurately and reliably.

[0031] The offset generation unit 32 outputs an offset compensation value ±Ios1. The control device 30 subtracts the offset compensation value ±Ios1 from the difference between the current command value Ic / d* and the detected current value Is. This makes it possible to return the charge / discharge control to the correct direction even if an error occurs in the charge / discharge determination due to an offset specific to the current detector. This makes it possible to omit protection functions that take into account errors due to the offset of the current detector 40, thereby simplifying the configuration of the power conversion device and the power storage element.

[0032] In this way, a power conversion device that controls charging and discharging with high precision can be realized without relying on additional protection functions or special equipment.

[0033] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0034] 10...power conversion device, 20...converter, 22...conversion circuit, 30...controller, 32...offset generation unit, 34...PI controller, 36...PWM unit, 38...protection function unit, 40...current detector, 100...charge / discharge system, 102...power supply, 104...energy storage element

Claims

1. a converter connected between a DC power source and a power storage element, charging the power storage element and outputting power discharged from the power storage element to the DC power source; a control device for controlling the operation of the converter; Equipped with The control device generates a control signal and controls the converter based on an offset-compensated difference value obtained by subtracting an offset compensation value set to cancel out the offset from a difference between a preset current command value and a current detection value detected by a current detector that is configured to detect the magnitude and direction of a current flowing between the converter and the storage element and has an offset with respect to the detected current value.

2. the control device sets the offset compensation value based on the voltage across the storage element; 2. The power conversion device according to claim 1, wherein the offset compensation value has a positive value when the voltage across the terminals is lower than a predetermined first threshold voltage, and a negative value when the voltage across the terminals is equal to or higher than the first threshold voltage, or a negative value when the voltage across the terminals is lower than the first threshold voltage and a positive value when the voltage across the terminals is equal to or higher than the first threshold voltage.

3. the control device sets the offset compensation value based on the voltage across the storage element; 2. The power conversion device according to claim 1, wherein the offset compensation value has a negative value when the voltage across the terminals is equal to or greater than a predetermined second threshold voltage, and a positive value when the voltage across the terminals is lower than a predetermined third threshold voltage having a voltage value higher than the second threshold voltage, or a positive value when the voltage across the terminals is equal to or greater than the second threshold voltage, and a negative value when the voltage across the terminals is lower than a predetermined third threshold voltage having a voltage value higher than the second threshold voltage.

4. the offset compensation value has a positive constant value when the voltage across the terminals is lower than a predetermined fourth threshold voltage that is lower than the first threshold voltage; a positive value that decreases as the voltage across the terminals increases when the voltage across the terminals is equal to or higher than the fourth threshold voltage but lower than the first threshold voltage; a negative value that decreases as the voltage across the terminals increases when the voltage across the terminals is lower than a fifth threshold voltage that is equal to or higher than the first threshold voltage but higher than the first threshold voltage; a negative constant value when the voltage across the terminals is equal to or higher than the fifth threshold voltage; or a negative constant value when the voltage across the terminals is lower than the fourth threshold voltage; a negative value that increases as the voltage across the terminals increases when the voltage across the terminals is equal to or higher than the fourth threshold voltage but lower than the first threshold voltage; a positive value that increases as the voltage across the terminals increases when the voltage across the terminals is equal to or higher than the first threshold voltage;

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