Electric power system

Abstract

To enable detection of capacitance loss of a capacitor without providing a current sensor that detects current flowing through the capacitor.SOLUTION: An electric power system includes: an inverter that converts DC power into three-phase AC power and supplies the three-phase AC power to a three-phase load; a capacitor connected to a DC side of the inverter; and a control device that controls the inverter based on a d-axis voltage command and a q-axis voltage command obtained through current feedback control of a d-axis current based on a phase current of the three-phase load and a d-axis current command based on a phase voltage effective value command for the three-phase load and a rated capacitance of the capacitor. The control device determines a capacitance loss of the capacitor when a difference-related value related to the difference between the d-axis current command and the previous d-axis current when current feedback control is turned off is larger than a threshold value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to power systems. [Background technology]

[0002] A technology has been proposed in the past in which the capacitance of an electrolytic capacitor is calculated from the current flowing through the electrolytic capacitor and the terminal voltage applied to the electrolytic capacitor, and the life of the electrolytic capacitor is determined to be over when the calculated capacitance of the electrolytic capacitor becomes smaller than a specified value (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-157636 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned technology cannot determine whether or not a capacitance loss has occurred in an electrolytic capacitor unless a current sensor is provided to detect the current flowing through the electrolytic capacitor. Therefore, there is a need to devise a method for detecting capacitance loss in a capacitor without providing such a current sensor.

[0005] A main object of the power system of the present disclosure is to enable detection of capacitance loss in a capacitor without providing a current sensor that detects current flowing through the capacitor. [Means for solving the problem]

[0006] The power system of the present disclosure employs the following measures to achieve the above-mentioned main object.

[0007] The power system of the present disclosure includes: an inverter that converts DC power into three-phase AC power and supplies it to a three-phase load; a capacitor connected to the DC side of the inverter; a control device that controls the inverter based on a d-axis voltage command and a q-axis voltage command obtained by current feedback control of a d-axis current based on a phase current of the three-phase load, a phase voltage effective value command of the three-phase load, and a d-axis current command based on a rated capacitance of the capacitor; A power system comprising: The control device determines that capacitance loss of the capacitor has occurred when a difference-related value related to a difference between the d-axis current command and a previous d-axis current is greater than a threshold value when the current feedback control is turned off. The gist of this is as follows.

[0008] In the power system disclosed herein, the inverter is controlled based on a d-axis voltage command and a q-axis voltage command obtained by current feedback control of a d-axis current based on the phase current of a three-phase load, a d-axis current command based on a phase voltage effective value command of the three-phase load, and the rated capacitance of the capacitor. In this case, when the current feedback control is turned off, a difference-related value related to the difference between the d-axis current command and the d-axis current is greater than a threshold value. This makes it possible to detect capacitance loss in the capacitor without providing a current sensor that detects the current flowing through the capacitor. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a power system 20 according to an embodiment of the present disclosure. [Figure 2] 4 is a flowchart showing an example of a switching command calculation routine executed by an electronic control unit 50. [Figure 3] 3 is an explanatory diagram showing an example of a determination routine executed by the electronic control unit 50. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] A mode (embodiment) for carrying out the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a power system 20 according to an embodiment of the present disclosure. As shown in the figure, the power system 20 according to the embodiment is configured as a device that converts DC power from a power storage device 10 serving as a voltage source into three-phase AC power and supplies the power to a three-phase AC motor 12 serving as a three-phase load, and includes an inverter 24, a capacitor 26, and an electronic control unit 50. The power storage device 10 is connected to and disconnected from a power grid via an AC / DC converter or the like. The three-phase AC motor 12 has a rotor and a stator and is driven by three-phase AC.

[0011] The inverter 24 includes six transistors T11-T16 as switching elements and six diodes D11-D16 connected in parallel to the six transistors T11-T16, respectively. The transistors T11-T16 are arranged in pairs, two at a time, on the source side and two at the sink side of a positive line 22p and a negative line 22n to which the power storage device 10 is connected. The connection points of two transistors in each pair of the transistors T11-T16 are connected to power lines 28u, 28v, and 28w, respectively, to which the U-phase, V-phase, and W-phase of the three-phase AC motor 12 are connected. The inverter 24 converts DC power from the positive line 22p and the negative line 22n into three-phase AC power and outputs it to the power lines 28u, 28v, and 28w. A capacitor 26 is connected to the positive line 22p and the negative line 22n.

[0012] Coils 30u, 30v, 30w, resistive elements 32u, 32v, 32w, and coils 34u, 34v, 34w are provided on power lines 28u, 28v, 28w, respectively, from inverter 24 toward three-phase AC motor 12. One ends of capacitors 36u, 36v, 36w are connected between coils 30u, 30v, 30w and resistive elements 32u, 32v, 32w on power lines 28u, 28v, 28w, respectively. The other ends of capacitors 36u, 36v, 36w are connected to each other, thereby forming a neutral point.

[0013] The electronic control unit 50 includes a microcomputer having a CPU, ROM, RAM, flash memory, input / output ports, and communication ports. The electronic control unit 50 receives signals from various sensors. For example, the electronic control unit 50 receives the voltage Vc (voltage between the power line 28u and the neutral point) of the capacitor 36u from a voltage sensor 37 attached to both ends of the capacitor 36u, and the phase currents Iu, Iv, and Iw of the three-phase AC motor 12 from current sensors 38u, 38v, and 38w attached to the power lines 28u, 28v, and 28w, respectively. The electronic control unit 50 outputs various control signals. For example, the electronic control unit 50 outputs switching control signals to the transistors T11 to T16 of the inverter 24. The electronic control unit 50 virtually calculates the electrical angle θe corresponding to the desired output frequency.

[0014] Next, the operation of the power system 20 of the embodiment, and the operation when the three-phase AC motor 12 is operated in an autonomous mode (operated at a certain voltage and a certain frequency independent of the power grid), will be described. Fig. 2 is a flowchart showing an example of a switching command calculation routine executed by the electronic control unit 50. This routine is repeatedly executed when the three-phase AC motor 12 is operated in an autonomous mode.

[0015] 2 is executed, the electronic control unit 50 first inputs the phase voltage effective value command Vrms* of the three-phase AC motor 12, the electrical angle θe, the phase currents Iu, Iv, and Iw, and the voltage Vc of the capacitor 36u (step S100). Here, the phase voltage effective value command Vrms* is an effective value command (e.g., 100 V) of the phase voltage of the three-phase AC motor 12 for autonomous operation of the three-phase AC motor 12. The electrical angle θe is virtually calculated according to the desired output frequency (e.g., 60 Hz). The phase currents Iu, Iv, and Iw are input with the detected values ​​of the current sensors 38u, 38v, and 38w. The voltage Vc of the capacitor 36u (the voltage between the power line 28u and the neutral point) is input with the detected value of the voltage sensor 37.

[0016] Once the data is input in this manner, the phase voltage effective value Vrms of the three-phase AC motor 12 is calculated from the amplitude of the voltage Vc of the capacitor 36u (step S110), and the q-axis voltage command Vq* is calculated by voltage feedback control to cancel out the difference between the phase voltage effective value Vrms of the three-phase AC motor 12 and the phase voltage effective value command Vrms* (step S120).

[0017] Next, a d-axis current Id is calculated from the phase currents Iu, Iv, and Iw using the electrical angle θe through three-phase to two-phase conversion (step S130), and a d-axis current command Id* is calculated based on the phase voltage effective value command Vrms* (step S140). Here, the d-axis current command Id* can be calculated using equation (1) using the frequency f (e.g., 60 Hz) when the three-phase AC motor 12 is operating in a self-sustained manner, the rated capacitance Crv of the capacitor 26, and the phase voltage effective value command Vrms*.

[0018] Id*=-2·π·f·Crv·Vrms* (1)

[0019] After calculating the d-axis current Id and the d-axis current command Id* in this way, the routine calculates a d-axis voltage command Vd* by current feedback control to cancel the difference between the d-axis current Id and the d-axis current command Id* (step S150). Then, by two-phase to three-phase conversion, the routine calculates the phase voltage commands Vu*, Vv*, and Vw for each phase from the q-axis voltage command Vq* and the d-axis voltage command Vd* using the electrical angle θe (step S160). The calculated phase voltage commands Vu*, Vv*, and Vw for each phase are compared with a carrier wave (triangular wave) to calculate switching commands (PWM commands) for transistors T11 to T16 of inverter 24 (step S170), and the routine ends.

[0020] Once the switching commands for the transistors T11 to T16 are calculated in this manner, the calculated switching commands for the transistors T11 to T16 are used to control the switching of the transistors T11 to T16. In this embodiment, in order to reduce low-order harmonics that occur due to dead times in the switching of the transistors T11 to T16, a d-axis voltage command Vd* is calculated by current feedback control and used to control the inverter 24. In this way, power distortion is suppressed and power quality is ensured.

[0021] Next, a process for determining whether capacitance loss (a drop in actual capacitance greater than a threshold value relative to the rated capacitance) has occurred in capacitor 26 will be described. FIG. 3 is an explanatory diagram showing an example of a determination routine executed by electronic control unit 50. This routine executes the processes of steps S130 and S140 in the switching command calculation routine of FIG. 2, but is executed when a value of 0 is used as d-axis voltage command Vd* instead of the value of step S150 (the value calculated by current feedback control), i.e., when current feedback control is turned off. Note that current feedback control may be turned off when a predetermined condition is met, for example, when three-phase AC motor 12 is operating in no-load mode, or may be turned off periodically for executing this routine.

[0022] When this routine is executed, the electronic control unit 50 inputs the d-axis current command Id* and the d-axis current Id (step S200), and calculates the difference ΔId (=|Id*-Id|) between the input d-axis current command Id* and the d-axis current Id (step S210). Next, it is determined whether the difference ΔId is greater than a threshold value ΔIdref (step S220), and if the difference ΔId is equal to or less than the threshold value ΔIdref, the routine ends. On the other hand, if the difference ΔId is greater than the threshold value ΔIdref, it is determined that capacitance loss has occurred in the capacitor 26 (step S230), and the routine ends.

[0023] Here, the threshold value ΔIdref is determined in advance through experiments, analysis, etc. The inventors have confirmed through experiments and analysis that when capacitance loss occurs in the capacitor 26, the difference ΔId increases. This is thought to be because when capacitance loss occurs in the capacitor 26, the d-axis current Id based on the actual capacitance of the capacitor 26 decreases, and the deviation between the d-axis current Id and the d-axis current command Id* tends to increase. In this way, by determining whether the difference ΔId is greater than the threshold value ΔIdref, it is possible to determine whether capacitance loss has occurred in the capacitor 26 without providing a current sensor that detects the current flowing through the capacitor 26.

[0024] In the power system 20 according to the embodiment described above, the transistors T11 to T16 of the inverter 24 are controlled based on a d-axis voltage command Vd* and a q-axis voltage command Vq* obtained by current feedback control of a d-axis current Id based on the phase currents Iu, Iv, and Iw of each phase of the three-phase AC motor 12, and a d-axis current command Id* based on the phase voltage effective value command Vrms* of the three-phase AC motor 12 and the rated capacitance Crv of the capacitor 26. In this case, when the current feedback control is turned off, a difference ΔId between the d-axis current command Id* and the d-axis current Id is greater than a threshold ΔIdref, and capacitance loss of the capacitor 26 is determined. This makes it possible to detect capacitance loss of the capacitor 26 without providing a current sensor for detecting the current flowing through the capacitor 26.

[0025] In the above-described embodiment, capacitance loss of the capacitor 26 is determined when the difference ΔId between the d-axis current command Id* and the d-axis current Id is greater than the threshold value ΔIdref. However, this is not limiting. For example, capacitance loss of the capacitor 26 may be determined when a processed value ΔIds obtained by performing smoothing, rate processing, moving average processing, or the like on the difference ΔId is greater than the threshold value ΔIdref. Alternatively, capacitance loss of the capacitor 26 may be determined when a state in which the difference ΔId or the processed value ΔIds is greater than the threshold value ΔIdref continues for a predetermined time.

[0026] In the above-described embodiment, a power storage device is used as the voltage source, but this is not limiting. For example, a fuel cell or the like may be used as the voltage source.

[0027] In the above-described embodiment, the three-phase AC motor 12 is used as the three-phase load, but the present invention is not limited to this.

[0028] The correspondence between the main elements of the embodiment and the main elements of the invention described in the "Means for Solving the Problems" section will be explained below. In the embodiment, the inverter 24 corresponds to the "inverter," the capacitor 26 corresponds to the "capacitor," and the electronic control unit 50 corresponds to the "control device."

[0029] The correspondence between the main elements of the embodiments and the main elements of the invention described in the "Means for Solving the Problem" section does not limit the elements of the invention described in the "Means for Solving the Problem" section, since the embodiments are examples for specifically explaining the mode for implementing the invention described in the "Means for Solving the Problem" section. In other words, the interpretation of the invention described in the "Means for Solving the Problem" section should be based on the description in that section, and the embodiments are merely specific examples of the invention described in the "Means for Solving the Problem" section.

[0030] The above describes the forms for implementing the present disclosure using embodiments, but the present disclosure is not limited to these embodiments in any way, and it goes without saying that the present disclosure can be implemented in various forms within the scope that does not deviate from the gist of the present disclosure. [Industrial Applicability]

[0031] The present disclosure is applicable to the power system manufacturing industry and the like. [Explanation of symbols]

[0032] 10 storage device, 12 three-phase AC motor, 20 power system, 22n negative line, 22p positive line, 24 inverter, 26 capacitor, 28u power line, 30u coil, 32u resistive element, 34u coil, 36u capacitor, 37 voltage sensor, 38u, 38v, 38w current sensors, 40 electronic control unit, 50 electronic control unit, D11 to D16 diodes, T11 to T16 transistors.

Claims

[Claim 1] an inverter that converts DC power into three-phase AC power and supplies it to a three-phase load; a capacitor connected to the DC side of the inverter; a control device that controls the inverter based on a d-axis voltage command and a q-axis voltage command obtained by current feedback control of a d-axis current based on the phase currents of the three-phase load, a phase voltage effective value command of the three-phase load, and a d-axis current command based on the rated capacitance of the capacitor; A power system comprising: The control device determines that capacitance loss of the capacitor has occurred when a difference-related value related to a difference between the d-axis current command and a previous d-axis current is greater than a threshold value when the current feedback control is turned off. Power system.

Images