JP2018068032A - Power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine an abnormality of a current sensor without using a fluctuation of a detected value of a voltage sensor as a determination means in a power conversion system including a feedback control unit for obtaining a duty ratio to a switching element 32 using a measured value of an IL current sensor. Make it possible. A power conversion system includes a feedback control unit 56 and an IL sensor abnormality determination unit 60. The feedback control unit 56 obtains the duty ratio Duty_FB to the switching element 32 by using the difference between the command voltage VH * on the secondary side and the actual voltage VH and the measured value IL of the IL current sensor 48. The IL sensor abnormality determination unit 60 determines that the IL current sensor 48 has an abnormality when the state in which the duty ratio change amount ΔDuty_FB exceeds the predetermined threshold value Duty_FBth continues for a predetermined period. [Selection diagram] Fig. 2

Description

  The present invention relates to a power conversion system that performs battery power conversion, and more particularly, to a power conversion system that can determine abnormality of a current sensor in the power conversion system.

  A vehicle that uses a rotating electrical machine as a drive source, such as an electric vehicle or a hybrid vehicle, is equipped with a battery that is a DC power source. A power conversion system is provided between the battery and the rotating electrical machine. The power conversion system includes a step-up / step-down DC / DC converter, for example. The step-up / step-down DC / DC converter boosts the battery voltage during powering of the rotating electrical machine, and steps down the voltage applied from the rotating electrical machine during regeneration of the rotating electrical machine.

  The step-up / step-down DC / DC converter includes a switching element such as an IGBT, and the step-up ratio and the step-down ratio are controlled through a duty ratio given to the switching element. The duty ratio is also called a conduction ratio and represents the ratio of the on time to the switching period.

  For example, at the time of boosting, a feed forward in which the duty ratio is determined based on the difference between the voltage VL on the battery side (primary side, low voltage side) and the command voltage VH * (target voltage) on the load side (secondary side, high voltage side). Control is executed. Furthermore, feedback control based on the difference between the actual secondary voltage VH (actual voltage) and the command voltage VH * is also executed. The duty ratio Duty_FF (FF duty ratio) based on the feedforward control and the duty ratio Duty_FB (FB duty ratio) based on the feedback control are added to generate a final duty ratio command Duty *.

  On the secondary side (high voltage side, load side), a smoothing capacitor that suppresses voltage fluctuation is provided, and the voltage across the smoothing capacitor is used for feedback control as the secondary side actual voltage VH. When there is a difference (ΔVH) between the secondary side actual voltage VH and the command voltage VH *, the FB duty ratio is obtained from I = C * dV / dt based on the current value. In calculating the current value, a current sensor for measuring the current flowing through the smoothing capacitor is used.

  When a detection abnormality occurs in the current sensor, for example, when a fixed value (for example, 0 [A]) is output regardless of the actual current, an error occurs in the input of the feedback loop, causing a problem in control. For example, hunting occurs in which the FB duty ratio Duty_FB and the duty ratio command Duty * fluctuate in a high cycle. High-frequency large-amplitude hunting may cause a current containing a high-frequency component to flow into the battery, resulting in overheating.

  Therefore, in Patent Document 1, for example, the value of the voltage sensor that measures the pre-boosting voltage (primary voltage) is monitored in addition to the value of the current sensor. If the fluctuation of the detection value of the voltage sensor is larger than the predetermined value even though the fluctuation of the detection value of the current sensor is less than the predetermined value, it is determined that the current sensor has failed.

JP2015-139236A

  By the way, the voltage sensor may be connected so as to measure the voltage across the smoothing capacitor. The smoothing capacitor is provided to suppress voltage fluctuation (ripple), and the larger the capacity, the smaller the fluctuation width of the voltage at both ends thereof, making it difficult to determine abnormality of the current sensor based on the voltage fluctuation. Therefore, an object of the present invention is to provide a power conversion system capable of determining an abnormality of a current sensor without using a detection value variation of a voltage sensor as a determination unit.

  The present invention relates to a power conversion system. The system includes a power converter including a switching element, a smoothing capacitor provided on a secondary side having a higher voltage than the power converter, a current sensor that measures a current flowing through the smoothing capacitor, a feedback control unit, and an abnormality. A determination unit is provided. The feedback control unit obtains a duty ratio to the switching element by using a difference between the command voltage on the secondary side and an actual voltage across the smoothing capacitor and a measured value of the current sensor. The abnormality determination unit determines that there is an abnormality in the current sensor when the state in which the amount of change in the duty ratio exceeds a predetermined threshold is continued for a predetermined period.

  According to the present invention, whether or not the current sensor is abnormal is determined by monitoring the duty ratio, and it is possible to determine whether or not the current sensor is abnormal without using the detection value fluctuation of the voltage sensor as a determination unit.

It is a figure which illustrates the composition of the vehicles containing the power conversion system concerning this embodiment. It is a figure which illustrates the functional block of a control part. It is a figure explaining the principle of abnormality determination of a current sensor. It is a figure which illustrates the current sensor abnormality determination flow which concerns on this embodiment. It is a figure which illustrates the time chart from an abnormality generation of a current sensor to performing electric power limitation. It is a figure which shows another example of the time chart from performing abnormality of a current sensor to performing electric power limitation.

  FIG. 1 illustrates the configuration of a power conversion system according to the present embodiment and a vehicle on which the system is mounted. In addition, in order to simplify illustration, in FIG. 1, about the structure with low relevance with the power conversion system which concerns on this embodiment, illustration is abbreviate | omitted suitably. Moreover, the arrow line represents the signal line.

  In the vehicle shown in FIG. 1, electric power is supplied from the main battery 10 to a load such as the rotating electrical machines MG1 and MG2 that are driving sources via the power conversion system. The power conversion system includes a step-up / step-down DC / DC converter 12, an inverter 14, a control unit 16, and various sensors described later (primary side voltage sensor 40, secondary side voltage sensor 42, battery voltage sensor 44, battery current sensor 46, reactor A current sensor 48).

  The DC power output from the main battery 10 is boosted by the step-up / step-down DC / DC converter 12. The boosted DC power is orthogonally converted by the inverter 14. The AC power after the conversion is supplied to at least one of the rotating electrical machines MG1 and MG2. Since the power transmission path from the rotating electrical machines MG1, MG2 to the wheels 20 via the power distribution mechanism 18 is known, the description thereof is omitted here.

  When the rotating electrical machines MG1 and MG2 are regenerated, the regenerative power is AC / DC converted by the inverter 14. The converted DC power is stepped down by the step-up / step-down DC / DC converter 12 and supplied to the main battery 10.

  The main battery 10 is composed of a plurality of battery cells. For example, the battery cell includes a prismatic battery or a cylindrical battery (cylindrical battery) such as a lithium ion secondary battery or a nickel hydride secondary battery. The main battery 10 is configured including a stacked body in which a plurality of these battery cells are stacked. For example, a plurality of battery packs composed of a plurality of battery cells connected in parallel are connected in series to the main battery 10.

  The step-up / step-down DC / DC converter 12 is a bidirectional power converter (two-quadrant chopper circuit) capable of stepping up and stepping down a DC voltage. The primary side (low voltage side) of the step-up / step-down DC / DC converter 12 is connected to the main battery 10, and the secondary side (high voltage side) is connected to a load such as the inverter 14 or the rotating electrical machines MG1, MG2.

  In the step-up / step-down DC / DC converter 12, a reactor 26 is provided on the high piezoelectric path 24, and further, a lower arm, that is, a switching element 32 and a diode 34 are provided on the reference electrical path 30 side from the previous contact 28. The switching element 32 has the reference electric circuit 30 side in the forward direction, and the diode 34 is connected in reverse parallel to this. Further, an upper arm, that is, a switching element 36 and a diode 38 are provided in series with the reactor 26. The switching element 36 has a forward direction toward the reactor 26, and the diode 38 is connected in reverse parallel to this.

  During boosting, the lower arm switching element 32 is mainly turned on / off according to the duty ratio. At the time of step-down, the switching element 36 of the upper arm is mainly turned on / off according to the duty ratio. Since these operations are already known, a description thereof will be omitted below.

  The inverter 14 performs conversion (orthogonal conversion and AC / DC conversion) between DC power and AC power. The inverter 14 is, for example, a three-phase AC inverter, and converts the DC power boosted by the step-up / step-down DC / DC converter 12 into three-phase AC power and supplies it to the rotating electrical machines MG1 and MG2.

  A filter capacitor CL is provided between the primary side of the step-up / step-down DC / DC converter 12 and the system main relay SMR. Further, a smoothing capacitor CH is provided between the secondary side of the step-up / step-down DC / DC converter 12 and the inverter 14. The filter capacitor CL and the smoothing capacitor CH mainly smooth the voltage fluctuation (ripple) accompanying the drive of the step-up / step-down DC / DC converter 12 and the inverter 14.

  A primary voltage sensor 40 is provided in parallel with the filter capacitor CL. The primary side voltage sensor 40 measures the actual voltage VL at both ends of the filter capacitor CL, and outputs this to the control unit 16 as the primary side voltage. A secondary side voltage sensor 42 is provided in parallel with the smoothing capacitor CH. The secondary side voltage sensor 42 measures the both-ends actual voltage VH of the smoothing capacitor CH, and outputs this to the control unit 16 as a secondary side voltage. Further, a battery voltage sensor 44 is provided at both ends of the main battery 10, and a battery current sensor 46 is provided at the positive terminal or the negative terminal of the main battery 10.

  Further, a reactor current sensor 48 is provided between the filter capacitor CL and the reactor 26. The reactor current sensor 48 is for measuring the current IL flowing through the reactor 26. As is apparent from the circuit diagram of FIG. 1, this current IL also flows through the smoothing capacitor CH. Therefore, as will be described later, the detected current value of reactor current sensor 48 is used for feedback control in control unit 16 as a current value flowing through smoothing capacitor CH. Thus, in this embodiment, the measured value of the reactor current sensor 48 is used for purposes other than the monitoring of the reactor 26. Hereinafter, the reactor current sensor 48 is referred to as an IL current sensor.

  The control unit 16 includes, for example, a computer and includes a CPU 50 that is an arithmetic circuit and a storage unit 52. The storage unit 52 includes a volatile memory such as an SRAM and a nonvolatile memory such as a ROM and a hard disk. The storage unit 52 stores a program for executing a later-described current sensor abnormality determination flow, a program for executing PWM control for performing on / off control of the switching element, and a setting value (initial value) used for these. Has been.

  The control unit 16 controls various devices in the vehicle. For example, PWM control is performed on switching elements (not shown) of the step-up / step-down DC / DC converter 12 and the inverter 14. The rotation speed and torque of the rotating electrical machines MG1 and MG2 are controlled via the PWM control.

  In PWM control of the switching element, the control unit 16 generates a duty ratio command Duty *. The duty ratio represents the ratio of the on-time to the switching cycle, and in short, determines the on-time of the switching element in the switching period. Taking the step-up / step-down DC / DC converter 12 as an example, the control unit 16 controls the step-up rate and step-down rate through generation of the duty ratio.

  2 is configured in the control unit 16 by executing the PWM control execution program and the current sensor abnormality determination program stored in the storage unit 52 of the control unit 16. The control unit 16 includes a feedforward control unit 54, a feedback control unit 56, an addition unit 58, a reactor current sensor abnormality determination unit 60 (hereinafter referred to as an IL sensor abnormality determination unit), and a timer 62.

  The feedforward control unit 54 receives the primary side actual voltage VL acquired from the primary side voltage sensor 40 and the secondary side command voltage VH *. The secondary side command voltage VH * is generated based on, for example, an output request calculated from an accelerator stroke sensor (not shown) and a speed sensor.

  The feedforward control unit 54 obtains a ratio VL / VH * of the primary side actual voltage VL to the secondary side command voltage VH *, and outputs this as a feedforward duty ratio (hereinafter referred to as FF duty ratio) Duty_FF.

  The feedback control unit 56 calculates a charge amount (current amount) for charging the smoothing capacitor CH to the secondary command voltage VH *, and based on this, a feedback duty ratio (hereinafter referred to as FB duty ratio) Duty_FB is calculated. Desired. The feedback control unit 56 includes addition / subtraction units 64 and 70, a division unit 66, and PI calculation units 68 and 72.

  The adder / subtractor 64, the divider 66, and the PI calculator 68 calculate the energy that is insufficient in the smoothing capacitor CH. The adder / subtractor 64 receives the secondary command voltage VH * and the secondary actual voltage VH acquired from the secondary voltage sensor 42. The adder / subtractor 64 obtains the shortage energy ΔW [J] from the following formula (1).

  Subsequently, the division unit 66 divides the capacitance C of the smoothing capacitor CH from ΔW. The capacitance C can be obtained in advance from tests and specifications. Subsequently, the PI calculation unit 68 converts the parameter (ΔW / C) acquired from the division unit 66 into the command current IL *.

  Further, the addition / subtraction unit 70 subtracts the actual current measurement value IL from the command current IL *. The actual current measurement value IL is sent from the IL current sensor 48. The current difference ΔIL obtained by subtracting the actual current measurement value IL from the command current IL * is sent to the PI calculation unit 72 to generate the FB duty ratio Duty_FB.

  In the adder 58, the FF duty ratio Duty_FF and the FB duty ratio Duty_FB are added to generate a duty ratio command Duty *. This duty ratio command Duty * is transmitted to the switching element, and its on / off operation is controlled. For example, when the step-up / step-down DC / DC converter 12 is boosted, a duty ratio command Duty * is sent to the switching element 32 of the lower arm.

  Here, when an abnormality such as a failure occurs in the IL current sensor 48 and the actual current measurement value IL deviates from the actual current, feedback control using the actual current measurement value IL as an input value becomes unstable. For example, when a so-called sticking failure occurs in which the IL current sensor 48 continues to output a fixed value (for example, 0 [A]) regardless of the actual current, the FB duty ratio Duty_FB and the duty ratio command Duty * reflecting this are obtained. Hunting that fluctuates in a high cycle occurs.

  For example, when the actual current measurement value is lower than the actual current, the current difference ΔIL obtained by the addition / subtraction unit 70 is higher than the actual current base current difference ΔIL. As a result, the secondary side actual voltage VH based on the duty ratio command Duty * becomes higher (overcharge) than the secondary side command voltage VH *. On the other hand, when the measured actual current value is higher than the actual current, the secondary side actual voltage VH is lower than the secondary side command voltage VH *.

  The difference (opening) between the secondary side command voltage VH * and the secondary side actual voltage VH is larger than when the IL current sensor 48 is normal. The feedback control functions to compensate for this difference, and as a result, the FB duty ratio Duty_FB and the duty ratio command Duty * are hunted.

  FIG. 3 illustrates changes in the actual current measurement value IL, the duty ratio command Duty *, and the FB duty ratio Duty_FB before and after the failure of the IL current sensor 48. When the IL current sensor 48 fails at time t0 (zero failure), the duty ratio command Duty * and the FB duty ratio Duty_FB are hunted. When this amplitude (amount of change) is compared, the amount of change Duty * ave_A of the duty ratio command Duty * when the IL current sensor 48 fails is equal to the duty ratio command Duty * when the IL current sensor 48 is normal (before the failure). It is understood that it is clearly larger than the variation average Duty * ave_N. Similarly, the change amount average Duty_FBave_A of the FB duty ratio Duty_FB when the IL current sensor 48 is faulty is clearly larger than the change amount average Duty_FBave_N of the FB duty ratio Duty_FB when the IL current sensor 48 is normal (before failure). Is understood.

  Therefore, the IL sensor abnormality determination unit 60 (see FIG. 2) acquires the FB duty ratio Duty_FB, obtains the amount of change thereof, and determines whether the IL current sensor 48 is abnormal based on this.

  FIG. 4 illustrates an abnormality determination flow of the IL current sensor 48 by the IL sensor abnormality determination unit 60. The flow is started when a start button (power switch) (not shown) of the vehicle is turned on and the system main relay SMR is switched from the disconnected state to the connected state. As initial values, a time counter t = 1 and an abnormality counter n = 0 are set.

  The IL sensor abnormality determination unit 60 determines whether or not the time counter t exceeds 1 (S10). If t ≦ 1, the process proceeds to step S20 and waits for a predetermined time. When the time counter t exceeds 1, the IL sensor abnormality determination unit 60 subtracts the previous FB duty ratio Duty_FB (t−1) from the current FB duty ratio Duty_FB (t), and the duty ratio change amount ΔDuty_FB (t ) Is obtained (S12).

  Further, the IL sensor abnormality determination unit 60 determines whether or not the absolute value of the duty ratio change amount ΔDuty_FB (t) exceeds a predetermined duty threshold Duty_FBth (S14). As shown in FIG. 3, the duty threshold Duty_FBth is set to a value that is larger than the change amount average Duty_FBave_N when the IL current sensor 48 is normal and equal to or less than the change amount average Duty_FBave_A when the IL current sensor 48 fails. Since the duty ratio takes a value between 0 (0%) and 1.0 (100%), for example, 0.2 (20%) may be set as the duty threshold Duty_FBth.

  When the absolute value of the duty ratio change amount ΔDuty_FB (t) is equal to or less than the duty threshold Duty_FBth, the IL sensor abnormality determination unit 60 resets the abnormality counter n to 0 (S16). Further, it is determined whether or not the start button (power switch) of the vehicle is turned off and the system main relay SMR is switched from the connected state to the disconnected state (S18). When the start button is turned off, this flow ends. If not turned off, the timer 62 is activated to measure the time. After waiting for a predetermined time (S20), the time counter t is incremented (S22), and the process returns to step S10.

  In step S14, if the absolute value of the duty ratio change amount ΔDuty_FB (t) exceeds the duty threshold Duty_FBth, whether this excess is normal due to a sudden change in the required output or whether the IL current sensor 48 is abnormal. Determined. First, the abnormality counter n is incremented (S24).

  Next, it is determined whether or not the abnormality counter n has exceeded a predetermined abnormality counter threshold n_th (S26). That is, it is determined whether or not the state in which the absolute value of the duty ratio change amount ΔDuty_FB (t) exceeds the duty threshold Duty_FBth is continued for a predetermined period. The upper limit of the predetermined period is determined based on the heat resistance of the main battery 10. The lower limit of the predetermined period is determined based on the response speed with respect to the output request to the vehicle. For example, a value of 1.0 [sec] or more and 5.0 [sec] or less is set as the predetermined period.

  When the abnormality counter n is equal to or smaller than the predetermined abnormality counter threshold n_th, the process proceeds to step S18. When the start button (power switch) of the vehicle is not turned off in step S18, the process proceeds to steps S20 and S22, and the time counter t is incremented. When the abnormality counter n exceeds a predetermined abnormality counter threshold n_th, the IL sensor abnormality determination unit 60 determines that the IL current sensor 48 is abnormal, and executes power limitation (S28). Specifically, the upper limit value Win of the input power (regenerative power) and the upper limit value Wout of the output power (powering power) are limited (lowered to 0 side). In addition, an IL sensor abnormality message is displayed on the vehicle display or the like (S30). For example, a message recommending inspection at a dealer is displayed on the display.

  FIG. 5 shows a time chart of an abnormality determination flow of the IL current sensor 48 according to the present embodiment. FIG. 5 shows from the top the measured value (actual current measured value) IL of the IL current sensor 48, the input power upper limit value Win and the output power upper limit value Wout, the current and voltage of the main battery 10, the primary side actual voltage VL, and the secondary voltage. A time change of the side actual voltage VH, duty ratio command Duty *, and FB duty ratio Duty_FB is shown. The horizontal axis represents time, and all graphs are synchronized.

  When an abnormality occurs in the IL current sensor 48 at time t0 and a 0 failure that continues to output the fixed value 0 [A] occurs, hunting occurs in the duty ratio command Duty * and the FB duty ratio Duty_FB. Voltage and current fluctuate.

  When the abnormality determination of FIG. 4 is executed during this hunting period and it is determined that the IL current sensor 48 is abnormal, the input power upper limit value Win and the output power upper limit value Wout are reduced to 0 at time t1. Thereby, the step-up / step-down voltage of the step-up / step-down DC / DC converter 12 is interrupted, and hunting is eliminated.

  In FIG. 2 and FIG. 4, the FB duty ratio Duty_FB is selected as the duty ratio to be monitored. Alternatively, the duty ratio command Duty * may be monitored. As shown in FIG. 3, since the hunting also occurs in the duty ratio command Duty * with the occurrence of an abnormality in the IL current sensor 48, the occurrence of the abnormality in the IL current sensor 48 can be determined by capturing this.

  In FIGS. 4 and 5, the input power upper limit value Win and the output power upper limit value Wout are limited as so-called fail-safe means. Instead, the step-up / step-down operation is interrupted in accordance with so-called diagnosis (fault diagnosis). You may order. FIG. 6 illustrates a time chart of an abnormality determination flow of the IL current sensor 48 using a diagnosis.

  FIG. 6 shows from the top the measured value (actual current measured value) IL of the IL current sensor 48, the current and voltage of the main battery 10, the primary side actual voltage VL and the secondary side actual voltage VH, the duty ratio command Duty *, FB. The duty ratio Duty_FB and the time change of the diagnosis value are shown. The horizontal axis represents time, and all graphs are synchronized.

  As shown at time t2 in FIG. 6, when an abnormality signal indicating that there is an abnormality is output to the IL current sensor 48 by the IL sensor abnormality determination unit 60, as shown in the lowermost part of FIG. The diagnosis unit receives this and switches the diagnosis value from 0 to 1 (sets a diagnosis flag). Accordingly, the generation of duty ratio command Duty * is interrupted. As a result, hunting is eliminated.

  DESCRIPTION OF SYMBOLS 10 Main battery, 12 Buck-boost DC / DC converter, 16 Control part, 32 Switching element, 40 Primary side voltage sensor, 42 Secondary side voltage sensor, 48 IL current sensor, 54 Feedforward control part, 56 Feedback control part, 60 IL sensor abnormality determination unit, 62 timer, CH smoothing capacitor, CL filter capacitor.

Claims (1)

A power converter comprising a switching element;
A smoothing capacitor provided on the secondary side of a higher voltage than the power converter;
A current sensor for measuring a current flowing through the smoothing capacitor;
A difference between the command voltage on the secondary side and the actual voltage across the smoothing capacitor, and a feedback control unit for obtaining a duty ratio to the switching element using a measured value of the current sensor;
An abnormality determination unit that determines that there is an abnormality in the current sensor when the state in which the amount of change in the duty ratio exceeds a predetermined threshold is continued for a predetermined period;
A power conversion system comprising: