JP6766583B2 - Power conversion system - Google Patents

Description

The present invention relates to a power conversion system that converts battery power, and more particularly to a power conversion system capable of determining an abnormality of a current sensor in the power conversion system.

Vehicles that use a rotating electric machine as a drive source, such as electric vehicles and hybrid vehicles, are equipped with a battery that is a DC power source. A power conversion system is provided between the battery and the rotating electric machine. The power conversion system includes, for example, a buck-boost DC / DC converter. The buck-boost DC / DC converter raises the battery voltage when the rotary electric machine is powered, and lowers the voltage applied from the rotary electric machine when the rotary electric machine is regenerated.

The buck-boost DC / DC converter includes a switching element such as an IGBT, and the step-up ratio and the step-down ratio are controlled via the duty ratio given to the switching element. The duty ratio is also called the flow rate and represents the ratio of the on-time to the switching cycle.

For example, at the time of boosting, 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. Further, 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 feedforward control and the duty ratio Duty_FB (FB duty ratio) based on feedback control are added to generate the final duty ratio command Duty *.

A smoothing capacitor that suppresses voltage fluctuations is provided on the secondary side (high voltage side, load side), and the voltage across the smoothing capacitor is used as the secondary side actual voltage VH for feedback control. 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. A current sensor that measures the current flowing through the smoothing capacitor is used to calculate the current value.

If a detection abnormality occurs in this current sensor, for example, if a fixed value (for example, 0 [A]) is output regardless of the actual current, the input of the feedback loop will be out of order, resulting in a malfunction 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. Due to high-period, large-amplitude hunting, a current containing high-frequency components may flow into the battery, leading to overheating.

Therefore, for example, in Patent Document 1, in addition to the value of the current sensor, the value of the voltage sensor that measures the voltage before boosting (primary side voltage) is monitored. If the fluctuation of the detected value of the current sensor is less than the predetermined value but the fluctuation of the detected value of the voltage sensor is larger than the predetermined value, it is determined that the current sensor has failed.

Japanese Unexamined Patent Publication No. 2015-139236

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 as the capacitance thereof increases, the fluctuation range of the voltage across the smoothing capacitor becomes smaller, and it becomes difficult to determine an 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 fluctuation of a detected value of a voltage sensor as a determination means.

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

According to the present invention, the presence / absence of abnormality of the current sensor is determined by monitoring the duty ratio, and the presence / absence of abnormality of the current sensor can be determined without using the fluctuation of the detected value of the voltage sensor as the determination means.

It is a figure which illustrates the structure of the vehicle including the power conversion system which concerns on 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 the occurrence of an abnormality of a current sensor to the power limitation. It is a figure which shows another example of the time chart from the occurrence of an abnormality of a current sensor to the power limitation.

FIG. 1 illustrates the configuration of the power conversion system according to the present embodiment and the vehicle on which the system is mounted. In addition, in order to simplify the illustration, in FIG. 1, the configuration which is not related to the power conversion system according to the present embodiment is omitted as appropriate. The arrow lines represent signal lines.

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

The DC power output from the main battery 10 is boosted by the buck-boost DC / DC converter 12. The boosted DC power is orthogonally converted by the inverter 14. The converted AC power is supplied to at least one of the rotary electric machines MG1 and MG2. Since the power transmission path from the rotary electric machines MG1 and MG2 to the wheel 20 via the power distribution mechanism 18 is known, the description thereof will be omitted here.

At the time of regeneration of the rotary electric machines MG1 and MG2, the regenerative power is AC / DC converted by the inverter 14. The converted DC power is stepped down by the buck-boost 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, a battery cell is composed of a square battery or a cylindrical battery (cylindrical battery) such as a lithium ion secondary battery or a nickel hydrogen secondary battery. The main battery 10 is configured by including a laminated body in which a plurality of these battery cells are laminated. For example, a plurality of battery packs including a plurality of battery cells connected in parallel are connected in series to the main battery 10.

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

In the buck-boost DC / DC converter 12, a reactor 26 is provided on the high-voltage path 24, and a lower arm, that is, a switching element 32 and a diode 34 are provided on the reference electric circuit 30 side from the contact 28 beyond the reactor 26. The switching element 32 has the reference electric circuit 30 side in the forward direction, and the diode 34 is connected in antiparallel 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 antiparallel to this direction.

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

The inverter 14 converts DC power and AC power (orthogonal conversion and AC / DC conversion). The inverter 14 is, for example, a three-phase AC inverter, and converts the DC power boosted by the buck-boost DC / DC converter 12 into three-phase AC power and supplies it to the rotary electric machines MG1 and MG2.

Further, a filter capacitor CL is provided between the primary side of the buck-boost DC / DC converter 12 and the system main relay SMR. Further, a smoothing capacitor CH is provided between the secondary side of the buck-boost 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 buck-boost 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 across the filter capacitor CL and outputs this as the primary side voltage to the control unit 16. Further, a secondary voltage sensor 42 is provided in parallel with the smoothing capacitor CH. The secondary side voltage sensor 42 measures the actual voltage VH across the smoothing capacitor CH and outputs this as the secondary side voltage to the control unit 16. Further, battery voltage sensors 44 are provided at both ends of the main battery 10, and battery current sensors 46 are provided at the positive end or the negative end 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, and as is clear 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 the reactor current sensor 48 is used for feedback control in the control unit 16 as a current value flowing through the smoothing capacitor CH. As described above, in the present embodiment, the measured value of the reactor current sensor 48 is used for applications other than the monitoring of the reactor 26. Hereinafter, the reactor current sensor 48 will be referred to as an IL current sensor.

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

The control unit 16 controls various devices in the vehicle. For example, PWM control is performed on a switching element (not shown) of the buck-boost DC / DC converter 12 and the inverter 14. The rotation speed and torque of the rotary electric machines MG1 and MG2 are controlled via PWM control.

Upon 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 buck-boost DC / DC converter 12 as an example, the control unit 16 controls the step-up rate and the step-down rate through the generation of the duty ratio.

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 is configured with a functional unit as shown in FIG. 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 primary side actual voltage VL acquired from the primary side voltage sensor 40 and the secondary side command voltage VH * are input to the feedforward control unit 54. The secondary command voltage VH * is generated based on, for example, an output request calculated from an accelerator stroke sensor (not shown), a speed sensor, or the like.

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

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

The addition / subtraction unit 64, the division unit 66, and the PI calculation unit 68 calculate the energy deficient in the smoothing capacitor CH. The secondary side command voltage VH * and the secondary side actual voltage VH acquired from the secondary side voltage sensor 42 are input to the addition / subtraction unit 64. In the addition / subtraction unit 64, the insufficient energy ΔW [J] is obtained from the following mathematical formula (1).

Subsequently, the division unit 66 divides the capacitance C of the smoothing capacitor CH from the above ΔW. 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, in the addition / subtraction unit 70, the actual current measured value IL is subtracted 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 measured 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 addition unit 58, the FF duty ratio Duty_FF and the FB duty ratio Duty_FB are added together to generate the 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 buck-boost DC / DC converter 12 is boost-driven, the 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 measured value IL deviates from the actual current, the feedback control using the actual current measured value IL as an input value becomes unsuccessful. 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 occur. Hunting that fluctuates in a high cycle occurs.

For example, when the measured value of the actual current is lower than the actual current, the current difference ΔIL obtained by the addition / subtraction unit 70 is higher than the current difference ΔIL based on the actual current. As a result, the secondary side actual voltage VH according to the duty ratio command Duty * becomes higher (overcharge) than the secondary side command voltage VH *. On the other hand, when the actual current measured 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 that in the normal state of the IL current sensor 48. Feedback control functions to compensate for this difference, resulting in hunting of the FB duty ratio Duty_FB and duty ratio command Duty *.

FIG. 3 illustrates changes in the actual current measured 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 (0 failure), the duty ratio command Duty * and the FB duty ratio Duty_FB are hunted. Comparing this amplitude (change amount), the average duty * ave_A of the change amount of the duty ratio command Duty * when the IL current sensor 48 fails is the duty ratio command Duty * when the IL current sensor 48 is normal (before failure). It is understood that the amount of change is clearly larger than the average duty * ave_N. Similarly, the average change amount of the FB duty ratio Duty_FB when the IL current sensor 48 fails is clearly larger than the average change amount 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 or not the IL current sensor 48 has an abnormality based on the acquisition amount.

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

The IL sensor abnormality determination unit 60 determines whether or not the time counter t exceeds 1. (S10). When 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 the predetermined duty threshold value Duty_FBth (S14). As shown in FIG. 3, the duty threshold value Duty_FBth is set to a value larger than the average change amount Duty_FBave_N when the IL current sensor 48 is normal and equal to or less than the average change amount Duty_FBave_A when the IL current sensor 48 fails. Since the duty ratio takes a value of 0 (0%) or more and 1.0 (100%) or less, 0.2 (20%) may be set as the duty threshold value Duty_FBth, for example.

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

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

Next, it is determined whether or not the abnormality counter n exceeds a predetermined abnormality counter threshold value 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 value Duty_FBth is continued for a predetermined period. The upper limit of this predetermined period is determined based on the heat resistance of the main battery 10. Further, the lower limit of the predetermined period is determined based on the response speed to the output request to the vehicle. For example, as a predetermined period, a value of 1.0 [sec] or more and 5.0 [sec] or less is set.

If the abnormality counter n is equal to or less than a predetermined abnormality counter threshold value n_th, the process proceeds to step S18. If the vehicle start button (power switch) 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 value n_th, the IL sensor abnormality determination unit 60 determines that the IL current sensor 48 has an abnormality 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 (power running power) are limited (reduced to the 0 side). In addition, the IL sensor abnormality message is displayed on the vehicle display or the like (S30). For example, display a message on the display recommending inspection at the dealer.

FIG. 5 shows a time chart of the abnormality determination flow of the IL current sensor 48 according to the present embodiment. From the top, FIG. 5 shows 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. The time change of the side actual voltage VH, the duty ratio command Duty *, and the FB duty ratio Duty_FB is shown. The horizontal axis represents time, and both graphs are synchronized.

When an abnormality occurs in the IL current sensor 48 at time t0 and a 0 failure that continues to output a fixed value 0 [A] occurs, hunting occurs in the duty ratio command Duty * and the FB duty ratio Duty_FB, and as a result, the main battery 10 The voltage and current fluctuate.

When the abnormality determination of FIG. 4 is executed during this hunting period and the IL current sensor 48 is determined to have an abnormality, the input power upper limit value Win and the output power upper limit value Wout are reduced to 0 at time t1. As a result, the buck-boost of the buck-boost DC / DC converter 12 is interrupted, and hunting is eliminated.

In addition, in FIGS. 2 and 4, the FB duty ratio Duty_FB was selected as the duty ratio to be monitored, but instead, the duty ratio command Duty * may be the monitoring target. As shown in FIG. 3, since hunting also occurs in the duty ratio command Duty * with the occurrence of an abnormality in the IL current sensor 48, it is possible to determine the occurrence of an abnormality in the IL current sensor 48 by catching this.

Further, in FIGS. 4 and 5, the input power upper limit Win and the output power upper limit Wout are limited as so-called fail-safe means, but instead of this, the buck-boost is interrupted due to the so-called diagnosis (fault diagnosis). You may order. FIG. 6 illustrates a time chart of the abnormality determination flow of the IL current sensor 48 using the diagnostic.

From the top, FIG. 6 shows 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 *, and FB. The duty ratio Duty_FB and the time change of the diagnosis value are shown. The horizontal axis represents time, and both graphs are synchronized.

As shown at time t2 in FIG. 6, when the IL sensor abnormality determination unit 60 outputs an abnormality signal indicating that there is an abnormality in the IL current sensor 48, a failure (not shown) of the control unit 16 is shown in the lowermost part of FIG. In response to this, the diagnostic unit switches the diagnostic value from 0 to 1 (sets the diagnostic flag). Along with this, the duty ratio command Duty * generation itself is interrupted. As a result, hunting is eliminated.

10 Main battery, 12 buck-boost DC / DC converter, 16 control unit, 32 switching element, 40 primary side voltage sensor, 42 secondary side voltage sensor, 48 IL current sensor, 54 feed forward control unit, 56 feedback control unit, 60 IL sensor abnormality judgment unit, 62 timer, CH smoothing capacitor, CL filter capacitor.

Claims (1)

A power converter consisting of a chopper-type buck-boost DC / DC converter equipped with upper and lower arms and a reactor,
A smoothing capacitor provided on the secondary side with a higher voltage than the power converter,
A current sensor that measures the current flowing through the reactor, and
A feedback control unit that obtains the duty ratio of the upper and lower arms to the switching element using the difference between the command voltage on the secondary side and the actual voltage across the smoothing capacitor and the 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 value continues for a predetermined period.
A power conversion system characterized by being equipped with.