The disclosure of Japanese Patent Application No. 2012-053823 filed on Mar. 9, 2012 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
The present disclosure relates to electric vehicle inverter devices.
Conventionally, electric vehicle inverter devices are known which discharge electric charge stored in a main circuit capacitor (smoothing capacitor) by using a forced discharge circuit unit (see, e.g., Japanese Patent Application Publication No. 2010-193691 (JP 2010-193691 A)).
When vehicle collision, etc. occurs, the voltage at both ends of the smoothing capacitor of the inverter device needs to be reduced to a target voltage within a predetermined time. In this case, in the configuration in which the smoothing capacitor is merely electrically connected to a fast discharge resistor as in the configuration described in JP 2010-193691 A, power that is consumed by the fast discharge resistor exponentially decreases with time with a peak at the start of the electrical connection (at the start of fast discharge). Thus, a problem arises that a large resistive element having (steady) rated power that allows the resistive element to withstand the initial peak power is required as a fast discharge resistor.
It is an object of the present disclosure to provide an electric vehicle inverter device capable of implementing necessary discharge of a smoothing capacitor by a fast discharge resistor and achieving reduction in size of the fast discharge resistor.
According to one aspect of the present disclosure, an electric vehicle inverter device is provided which includes: an inverter and a smoothing capacitor which are connected in parallel with a high voltage power supply; a fast discharge resistor and a discharge switch element which are connected in parallel with the smoothing capacitor; and a control device that controls the discharge switch element. In the electric vehicle inverter device, the control device duty controls switching of the discharge switch element so that a duty ratio increases with a decrease in a voltage at both ends of the smoothing capacitor, in response to a fast discharge command.
According to the aspect of the present disclosure, an electric vehicle inverter device is provided which is capable of implementing necessary discharge of a smoothing capacitor by a fast discharge resistor and achieving reduction in size of the fast discharge resistor.
Embodiments will be described below with reference to the accompanying drawings.
As shown in
The high voltage battery 10 is any electricity storage device that stores electric power and outputs a direct current (DC) voltage, and may be formed by a nickel hydrogen battery, a lithium ion battery, or a capacitive element such as an electric double layer capacity. The high voltage battery 10 is typically a battery having a rated voltage exceeding 100 V, and the rated voltage may be, e.g., 288 V.
An inverter 30 is formed by U, V, and W-phase arms arranged in parallel between a positive electrode line and a negative electrode line. The U-phase arm is formed by series connection of switching elements (in this example, insulated gate bipolar transistors (IGBTs)) Q1, Q2, the V-phase arm is formed by series connection of switching elements (in this example, IGBTs) Q3, Q4, and the W-phase arm is formed by series connection of switching elements (in this example, IGBTs) Q5, Q6. Diodes D1 to D6 are placed between the collector and the emitter of the switching elements Q1 to Q6, respectively, so as to allow a current to flow from the emitter side to the collector side. The switching elements Q1 to Q6 may be switching elements other than the IGBTs, such as metal oxide semiconductor field-effect transistors (MOSFETs).
The drive motor 40 is a three-phase alternating current (AC) motor, and one end of each of the three coils of U, V, and W phases is connected to a common middle point. The other end of the U-phase coil is connected to a middle point M1 between the switching elements Q1, Q2, the other end of the V-phase coil is connected to a middle point M2 between the switching elements Q3, Q4, and the other end of the W-phase coil is connected to a middle point M3 between the switching elements Q5, Q6. A smoothing capacitor C is connected between the collector of the switching element Q1 and the negative electrode line.
The inverter control device 50 controls the inverter 30. The inverter control device 50 includes, e.g., a CPU, a ROM, a main memory, and the inverter control device 50 performs its various functions by reading a control program recorded on the ROM, etc. onto the main memory and performing the control program by the CPU. The inverter 30 can be controlled by any method, but is basically controlled such that the two switching elements Q1, Q2 of the U phase turn on/off in opposite phases to each other, the two switching elements Q3, Q4 of the V phase turn on/off in opposite phases to each other, and that the two switching elements Q5, Q6 of the W phase turn on/off in opposite phases to each other.
Although the motor drive system 1 has the single drive motor 40 in the example shown in
As shown in
The motor drive system 1 further includes a discharge circuit 20. As shown in
As shown in
The discharge switching element SW2 of the discharge circuit 20 is controlled by a fast discharge control device 60. The fast discharge control device 60 may be implemented by any hardware, software, firmware, or any combination thereof. For example, any part or all of the functions of the fast discharge control device 60 may be implemented by an application-specific integrated circuit (ASIC) or a field programmable gate array (FPGA). Alternatively, any part or all of the functions of the fast discharge control device 60 may be implemented by the inverter control device 50 or other control devices. A method of controlling the discharge switch element SW2 by the fast discharge control device 60 will be described in detail later.
As shown in
A discharge command is externally input to the power supply circuit 62. The discharge command is typically input when vehicle collision is detected or when it is determined that vehicle collision is unavoidable. The discharge command may be supplied from an air bag ECU, a pre-crash ECU, etc. that control a safety device (e.g., an air bag) of the vehicle. In response to the discharge command, the power supply circuit 62 generates a power supply voltage by using a voltage between both ends of the smoothing capacitor C (namely, electric charge stored in the smoothing capacitor C from the high voltage battery 10 before reception of the discharge command). The power supply voltage thus generated by the power supply circuit 62 is preferably used for operation of the variable duty generation circuit 64, the abnormality detection circuit 66, and the discharge SW control unit 68. This eliminates the need for interconnection from a low voltage battery, and thus can avoid inconvenience that is caused in the case of using the interconnection from the low voltage battery (e.g., the interconnection is disconnected upon vehicle collision, disabling the operation of the variable duty generation circuit 64, the abnormality detection circuit 66, and the discharge SW control unit 68). Basically (unless there is abnormality such as fixing of the cut-off switch SW1), in the case where the discharge command is generated, the cut-off switch SW1 is opened, quickly creating a state where the high voltage battery 10 is disconnected.
The variable duty generation circuit 64 generates an on/off signal (pulse signal) that turns on/off the discharge switch element SW2 by duty control. The variable duty generation circuit 64 may be a circuit that is activated in response to power supply from the power supply circuit 62. When an on signal is generated by the variable duty generation circuit 64 (i.e., in an on period of the on/off signal), the discharge switch element SW2 is turned on (electrically connected) via the discharge SW control unit 68, whereby discharge of the smoothing capacitor C by the fast discharge resistor R1 is implemented. When an off signal is generated (i.e., in an off period of the on/off signal), the discharge switch element SW2 is turned off via the discharge SW control unit 68, whereby discharge of the smoothing capacitor C by the fast discharge resistor R1 is not performed. The variable duty generation circuit 64 generates the on/off signal while varying the duty ratio (on time/one cycle of the pulse signal). In this case, the variable duty generation circuit 64 generates the on/off signal so that the duty ratio increases as the voltage at both ends of the smoothing capacitor C decreases. Such a variable duty can be generated by various methods, and any method can be used. For example, the variable duty generation circuit 64 may generate an on/off signal whose duty ratio is determined according to the voltage at both ends of the smoothing capacitor C, based on the fact that the voltage at both ends of the smoothing capacitor C gradually decreases as discharge of the smoothing capacitor C progresses after the start of fast discharge. Alternatively, the variable duty generation circuit 64 may generate an on/off signal whose duty ratio is determined according to the elapsed time since the start of fast discharge, based on the fact that the voltage at both ends of the smoothing capacitor C gradually decreases as discharge of the smoothing capacitor C progresses after the start of fast discharge. Some examples of a method for generating a variable duty (configuration examples of the variable duty generation circuit 64) will be described later.
The abnormality detection circuit 66 forcibly turns off the discharge switch element SW2 if a predetermined condition is satisfied after the start of discharge. For example, the predetermined condition may be the case where the voltage at both ends of the smoothing capacitor C has a predetermined value or more even after a predetermined time has passed since the start of fast discharge. This is assumed to occur when the cut-off switch SW1 is closed even though a discharge command has been generated due to any abnormality (e.g., the case where the cut-off switch SW1 has been fixed in the on state). In this case, even if the smoothing capacitor C is being discharged by the fast discharge resistor R1, the voltage at both ends of the smoothing capacitor C does not decrease because the high voltage battery 10 is kept in the connected state. Accordingly, the discharge switch element SW2 is forcibly turned off upon detection of such a state. This can prevent prolonged energy loss due to continued discharge of the smoothing capacitor C by the fast discharge resistor R1 (and continued unnecessary consumption of power from the high voltage battery 10) even if a discharge command is accidentally generated due to, e.g., noise. Alternatively, the predetermined condition may be, e.g., the case where a predetermined time has passed since the start of fast discharge. In this case, the predetermined time may correspond to the time it takes for the voltage at both ends of the smoothing capacitor C to decrease to a predetermined target voltage in the case where the cut-off switch SW1 is opened normally in response to a discharge command (or the sum of this time and a predetermined margin), and may be adapted by a test, etc. This can also avoid the above disadvantage in the case where a discharge command is accidentally generated due to noise, etc.
The discharge SW control unit 68 implements switching of the discharge switch element SW2 based on the on/off signal from the variable duty generation circuit 64.
In the present embodiment and the comparative example, the state at the start of fast discharge (the voltage at both ends of the smoothing capacitor C) is under the same conditions. In the present embodiment and the comparative example, the size of the fast discharge resistor R1 is determined so that the voltage at both ends of the smoothing capacitor C decreases to a predetermined target voltage before a predetermined time passes after the start of fast discharge. Each of the predetermined time and the predetermined target voltage may be a value that is determined according to a law, a regulation, etc.
The comparative example shown in
In addition to the (steady) rated voltage at which the resistive element can withstand continuous load, the resistive element has a rated pulse voltage at which the resistive element can withstand load only for a short time (e.g., about 10 ms). This rated pulse voltage is higher than the (steady) rated voltage, and the shorter the pulse duration is, the higher the value of the rated pulse voltage is. More specifically, the rated voltage E and the rated pulse voltage Ep can be represented by the following expressions.
E=√{square root over ((P·R))}
Ep=√{square root over ((P·R·T/τ)}
In the expressions, P represents rated power, R represents a rated resistance value, τ represents pulse duration, and T represents a pulse period (one cycle of the on/off signal).
In this regard, in the present embodiment, the discharge switch element SW2 is duty controlled during fast discharge, and the duty ratio in that case is set so as to increase as the voltage at both ends of the smoothing capacitor C decreases. Thus, as shown in
The power supply circuit 62A is connected in parallel with the smoothing capacitor C. The power supply circuit 62A generates a constant voltage (in this example, +15 V and Vcc of, e.g., +5 V) by using the voltage of the smoothing capacitor C (discharge from the smoothing capacitor C). The power supply circuit 62A includes a switching element MOS1 formed by a MOSFET, a Zener diode DZ, resistors R3, R4, and voltage regulators (3-terminal regulators) 621, 622. The drain of the switching element MOS1 is connected to the positive electrode side of the smoothing capacitor C via the resistor R4, and the source of the switching element MOS1 is connected to the ground via a capacitor C2. The gate of the switching element MOS1 is connected between the resistor R3 and the Zener diode DZ which are series connected between the positive electrode side and the ground. If a discharge command is generated, a constant voltage is applied to the gate of the switching element MOS1 by the Zener diode DZ, and the switching element MOS1 operates as a linear regulator. Thus, a voltage of, e.g., about 17 V is generated at input terminals of the voltage regulators 621, 622, and a constant voltage (in this example, +15 V and Vcc) is generated by the voltage regulators 621, 622. As shown in
The variable duty generation circuit 64A includes a CPU 641, resistors R5, R6, and a switching element MOS2. The voltage obtained by dividing the voltage at both ends of the smoothing capacitor C by the resistors R5, R6 is input to the CPU 641, The CPU 641 produces an on/off signal so that the duty ratio increases as the voltage Vc at both ends of the smoothing capacitor C (capacitor voltage Vc) decreases, based on the divided voltage value of the voltage at both ends of the smoothing capacitor C. In this example, the CPU 641 sets the duty ratio so that the duty ratio increases in inverse proportion to the square of the voltage Vc at both ends of the smoothing capacitor C. That is, the duty ratio ∝1/Vc2. The on/off signal (in this example, low/high level) is generated by using the power supply voltage Vcc generated in the power supply circuit 62A, and is applied to the gate of the switching element MOS2. The drain of switching element MOS2 is connected to the discharge SW control unit 68, and the source of the switching element MOS2 is connected to the ground. In the off period of the duty control, a high level voltage_is applied to the gate of the switching element MOS2, and the switching element MOS2 is turned on. In the on period of the duty control, a low level voltage_is applied to the gate of the switching element MOS2, and the switching element MOS2 is turned off. The CPU 641 may generate an on/off signal whose duty ratio increases as the voltage Vc at both ends of the smoothing capacitor C decreases in any manner. For example, the duty ratio may be set to increase in proportion to a decrease from the voltage Vi at both ends of the smoothing capacitor C at the start of fast discharge (Vi−Vc). That is, the duty ratio ∝a+b (Vi−Vc), where a and b represent predetermined coefficients.
The abnormality detection circuit 66 includes a comparator CM1, resistors R7, R8, R9, and a capacitor C3. The comparator CM1 has an open collector output. The voltage of the capacitor C3 that is charged via the resistor R9 by the power supply voltage of +15 V generated by the power supply circuit 62A is input to an inverting input terminal of the comparator CM1. The voltage obtained by dividing the power supply voltage of +15 V (the power supply voltage of +15 V generated by the power supply circuit 62A) by the resistors R7, R8 is input to a non-inverting input terminal of the comparator CM1. The comparator CM 1 uses as a single power source the power supply voltage of +15 V generated by the power supply circuit 62A. If a discharge command is generated, the power supply voltage of +15 V is generated by the power supply circuit 62A, and thus the voltage of the capacitor C3 increases according to an exponential curve that is determined by a time constant C3·R9. While the voltage of the capacitor C3 is lower than the voltage obtained by dividing the power supply voltage of +15 V by the resistors R7, R8, the output of the comparator CM1 is at a high level. If the voltage of the capacitor C3 becomes higher than the voltage obtained by dividing the power supply voltage of +15V by the resistors R7, R8, the output of the comparator CM1 falls to a low level. Accordingly, the output of the comparator CM1 changes from the high level to the low level when predetermined time passes after generation of the discharge command.
The discharge SW control unit 68 includes resisters R10, R10′ connected in series between the power supply voltage of +15 V that is generated by the power supply circuit 62A and the ground. The drain of the switching element MOS2 and the output of comparator CM1 are connected between the resistors R10, R10′, and the gate of the discharge switch element SW2 (in this example, MOSFET) is also connected between the resistors R10, R10′. When the switching element MOS2 is off and the output of the comparator CM1 is at the high level, the voltage obtained by dividing the power supply voltage of +15 V by the resistors R10, R10′ is applied to the gate of the discharge switch element SW2, and the discharge switch element SW2 is turned on. On the other hand, when the switching element MOS2 is on or the output of the comparator CM1 is at the low level, the gate of the discharge switch element SW2 has the ground potential (0 V), and the discharge switch element SW2 is turned off.
As described above, in the example shown in
As shown in
As shown in
The power supply circuit 62B is connected in parallel with the smoothing capacitor C. The power supply circuit 62B generates a constant voltage (in this example, +15 V) by using the voltage of the smoothing capacitor C. The power supply circuit 62B includes a switching element MOS1 formed by a MOSFET, a Zener diode DZ, resistors R3, R4, and a voltage regulator 621. The drain of the switching element MOS1 is connected to the positive electrode side of the smoothing capacitor C via the resistor R4, and the source of the switching element MOS1 is connected to the ground via a capacitor C2. The gate of the switching element MOS1 is connected between the resistor R3 and the Zener diode DZ which are series connected between the positive electrode side and the ground. If a discharge command is generated, a constant voltage is applied to the gate of the switching element MOS1 by the Zener diode DZ, and the switching element MOS1 operates as a linear regulator. Thus, a voltage of, e.g., about 17 V is generated at an input terminal of the voltage regulator 621, and a constant voltage (in this example, +15 V) is generated by the voltage regulator 621. As shown in
The variable duty generation circuit 64B includes a comparator CM2, resistors R11, R12, R13, R14, R15, R16, a capacitor C4, and a switching element MOS2. The resisters R11, R12 are connected in series between the positive electrode side of the smoothing capacitor C and the ground, and a non-inverting input terminal of the comparator CM2 is connected between the resistors R11, R12 via the resister R13. The comparator CM2 has an open collector output. A power supply voltage of +15 V is connected between the resister R13 and the non-inverting input terminal of the comparator CM2 via the resisters R14, R15. The resisters R15, R16 and the capacitor C4 are connected in series between the power supply voltage of +15 V and the ground. An inverting input terminal of the comparator CM2 is connected between the capacitor C4 and the resister R16. The output of the comparator CM2 is connected between the resisters R15, R16, and is connected to the gate of the switching element MOS2. As described below, the variable duty generation circuit 64B generates an on/off signal having a duty ratio that increases substantially in proportion to a decrease from the voltage Vi at both ends of the smoothing capacitor C at the start of fast discharge (Vi−Vc). That is, the duty ratio ∝a+b (Vi−Vc), where a and b represent predetermined coefficients. The on/off signal (in this example, low/high level) is generated by using the power supply voltage of +15 V that is generated in the power supply circuit 62B, and is applied to the gate of the switching element MOS2. The drain of the switching element MOS2 is connected to the discharge SW control unit 68, and the source of the switching element MOS2 is connected to the ground. During an off period of the duty control, a high level voltage is applied to the gate of the switching element MOS2, and the switching element MOS2 is turned on. During an on period of the duty control, a low level voltage is applied to the gate of the switching element MOS2, and the switching element MOS2 is turned off.
Principles of generating the on/off signal by the variable duty generation circuit 64B will be described below with reference to
First, when VrefH represents the voltage Vref at the non-inverting input terminal of the comparator CM2 when the output of the comparator CM2 is at a high level, and VrefL represents the voltage Vref at the non-inverting input terminal of the comparator CM2 when the output of the comparator CM2 is at the low level, VrefH and VrefL can be given by the following expressions.
V
refH=(Vc·R12·R14+15·Ry)/Rx (1)
V
refL
=Vc·R12·R14/Rx (2)
where Rx=R11·R12+(R13+R14)·(R11+R12) and Ry=R11·R12+R13(R11+R12). Accordingly, the difference Δref between VrefH and VrefL is given by the following expression.
Δref=15·Ry/Rx (3)
The expression (3) shows that Δref is constant regardless of the voltage Vc at both ends of the smoothing capacitor C. On the other hand, the expressions (1) and (2) show that VrefH and VrefL decrease with a decrease in the voltage Vc at both end of the smoothing capacitor C. The resistance values of R11 to R14 are set so that VrefH and VrefL satisfy the following expression even when the voltage Vc at both ends of the smoothing capacitor C is the maximum voltage Vi (the voltage at the start of fast discharge).
V
refL
<V
refH<15 (4)
When the output Vout of the comparator CM2 is at the high level, the voltage Vch at the inverting input terminal of the comparator CM2 increases according to an exponential curve that is determined by a time constant C4·R16. When the voltage Vch increases and reaches VrefH the output Vout of the comparator CM2 changes to the low level (0V), and the operation of discharging the capacitor C4 is performed. Accordingly, the voltage Vch decreases according to the exponential curve that is determined by the time constants C4·R16. When the voltage Vch decreases and reaches VrefL, the output Vout of the comparator CM2 changes to the high level (15V), and the operation of charging the capacitor C4 is performed. Accordingly, the voltage Vch increases according to the exponential curve that is determined by the time constants C4·R16. Such a repeated operation is shown by the waveforms of
As shown in, e.g.,
As shown in
Although the preferred embodiments are described in detail above, the present invention is not limited to the above embodiments, and various modifications and replacements can be made to the above embodiments without departing from the scope of the present invention.
For example, in the above embodiments, the variable duty generation circuit 64A generates a variable duty by using a microcomputer (CPU 641), and the variable duty generation circuit 6413 generates a variable duty by an analog circuit without using a microcomputer. However, a variable duty can be generated by various methods. For example, a similar variable duty may be generated by using a triangular wave. The function of the abnormality detection circuit 66 may be implemented by using a microcomputer.
In the above embodiments, as a preferred embodiment, the power supply circuit 64 generates power source by using the voltage Vc at both ends of the smoothing capacitor C. However, the power supply circuit 64 may generate necessary power source from a low voltage battery.
Number | Date | Country | Kind |
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2012-053823 | Mar 2012 | JP | national |