JP5699912B2 - Inverter for electric vehicle - Google Patents

Description

  The present invention relates to an inverter for an electric vehicle provided with an electric motor (motor) for driving wheels. The “electric vehicle” in the present specification includes a fuel cell vehicle and a hybrid vehicle including both a wheel driving motor and an engine.

  In an electric vehicle including a wheel driving motor, it is preferable that the motor can be driven and driven as much as possible even if a problem occurs. This is because the vehicle can be moved to a safe place. Patent Document 1 discloses an inverter that can drive a motor with the remaining two phases even if one of the switching circuits of the inverter that drives the motor has a problem and one of the AC three-phase outputs becomes uncontrollable. Is disclosed.

  According to the technique disclosed in Patent Document 1, the inverter is connected in series between the positive electrode line and the negative electrode line on the DC input side (the input side of the six switching circuit groups generating three-phase AC current). Two capacitors are provided. The connection point between the two capacitors is called the “neutral point”. When a failure occurs in any of the three-phase arms, the inverter connects the arm where the failure has occurred to a neutral point, and drives the motor with the remaining two normal phases.

  When the technique of Patent Document 1 is applied to an electric vehicle, it is possible to travel even if one phase of the inverter UVW three-phase output fails.

Japanese Patent Laid-Open No. 2004-120883

  In the technique of Patent Document 1, one faulty phase is connected to a neutral point on the inverter input side. Since the neutral point is a connection point between two capacitors connected in series between the positive electrode line and the negative electrode line, the neutral point voltage (reference potential) is generated by the normal two-phase AC output of the inverter. The potential of the neutral point) with respect to. When the voltage at the neutral point fluctuates, normal two-phase AC output (output current waveform) is disturbed, and the drive efficiency of the motor is reduced. In Patent Document 1, a reduction in motor driving efficiency due to voltage fluctuation at the neutral point is suppressed by adding correction considering the voltage fluctuation at the neutral point to the motor driving signal.

  The present specification provides a technique capable of suppressing a decrease in motor driving efficiency without adding a special correction to a motor driving signal as in Patent Document 1 by directly suppressing a voltage fluctuation at a neutral point. To do.

  The inverter disclosed in the present specification is a device that converts DC power of a battery into AC power and supplies it to a wheel driving motor. The inverter includes first and second capacitors connected in series between a positive electrode line and a negative electrode line on the input side of six switching circuit groups that generate a three-phase alternating current. The switching circuit is, for example, a transistor such as an IGBT. The switching circuit group corresponds to a main circuit of an inverter that outputs a three-phase alternating current. In addition to the transistor, the switching circuit may be accompanied by other elements such as a freewheeling diode connected in reverse parallel to the transistor. The first and second capacitors preferably have the same capacity. The inverter further includes a relay for switching the connection destination of each UVW three-phase motor wire coming out of the motor. The relay individually connects each connection destination of each motor wire to the corresponding output terminal (UVW each of the inverters). Switch from the phase output end) to the connection point (neutral point) between the first and second capacitors. The relay usually has a motor wire connected to the inverter output terminal.

  In the inverter controller disclosed in this specification, when any of the switching circuit groups fails, the connection destination of the motor wire connected to the failed switching element among the motor wires of the UVW three-phase motor is neutral. The relay is controlled so as to switch to, and a predetermined drive signal for driving the motor in two phases is given to a switching element that has not failed. When the motor is a PWM drive type, the drive signal to the motor is a PWM signal. When the motor is a PAM drive type, the drive signal is a PAM signal. For an example of a drive signal for driving a motor in two phases (in the case of a PWM type), refer to Patent Document 1.

  The inverter disclosed in this specification further includes a power adjustment circuit. The power adjustment circuit includes two input terminals and three output terminals. The input end is connected to a battery, and the three output ends are connected to a positive electrode line, a negative electrode line, and a neutral point. When the voltage difference between the voltage across the first capacitor and the voltage across the second capacitor exceeds a predetermined voltage difference allowable range, the power adjustment circuit returns the voltage difference to the voltage difference allowable range. When the capacities of the first and second capacitors are equal, the power adjustment circuit operates so that the divided voltages of both capacitors are equal. In the above inverter, even if the remaining two normal phases output an alternating current, the power adjustment circuit maintains the neutral point potential (potential with respect to the reference potential), so that the motor efficiency does not decrease.

  An example of the power adjustment circuit is as follows. The power adjustment circuit connects the positive electrode of the battery to the positive electrode line of the inverter and connects the negative electrode of the battery to the negative electrode line of the inverter. Two switching circuits are connected in series between the positive electrode line and the negative electrode line. The midpoint of the two switching circuits is connected to the neutral point via the reactor.

  By the way, a malfunction occurs in one phase of the inverter output during traveling of the automobile, and when switching from the three-phase control to the two-phase control, the motor is rotating, and thus back electromotive force is generated. At this time, if the switching circuit of the upper arm of the inverter has a short-circuit fault (a state in which the switching circuit does not move with the switching circuit turned on), a current from the battery is also added, and a large current flows in the phase in which the malfunction occurred. Accordingly, a relay that switches the connection destination of the motor line is required to have a capacity that can withstand a large current. If the capacity is small, an arc may occur at the time of switching and the relay may be damaged. The battery for driving the motor has a large output, and the motor for driving the wheel is a large output type, so that the back electromotive force is large. Therefore, if a relay having a capacity that can withstand the maximum current that can be assumed is employed, the cost increases. Therefore, it is preferable that the controller operates as follows so that a large current does not flow when the relay of the failed phase is switched. That is, the controller immediately outputs a relay switching signal when the failure of the switching circuit is an open failure. The open failure is typically a disconnection or a state where the switching element remains OFF. In the case of an open failure, no current flows through the failed arm, so the relay may be switched immediately. On the other hand, in the case of a short-circuit failure, the controller measures the current flowing through the short-circuited switching element after holding all the non-failed switching circuits in the ON state. The current flowing through the switching element has an AC component (inductive current component) due to the back electromotive force. The controller measures the change over time of the AC component and specifies the zero cross timing. Then, the controller outputs a relay switching signal so that the timing at which the relay is actually switched coincides with the zero cross timing of the induced current. In other words, the controller considers the delay time from when the relay switching signal is output until the relay is actually driven, and outputs the relay switching signal at a timing preceding the zero cross timing of the induced current by the delay time. . By performing such processing, it is possible to prevent a large current from flowing through the relay when the relay is switched. Conversely, a relay with a small capacity can be employed.

  A preferred example of a controller that considers the delay time is as follows. The inverter includes a voltage sensor that measures a voltage for driving the relay, and the controller specifies a delay time from the relay switching signal output until the relay is actually switched based on the voltage measured by the voltage sensor. Based on the specified delay time, the controller outputs a relay switching signal so that the timing at which the relay actually switches matches the zero cross timing of the induced current.

  One of the technologies disclosed in this specification suppresses a decrease in motor drive efficiency when a problem occurs in one phase of the three-phase outputs and the motor is driven with the remaining two phases. Further, another technique disclosed in the present specification prevents a large current from flowing through the relay when the connection destination of the motor wire corresponding to the failed arm is switched to the neutral point.

It is a circuit diagram of the inverter of an Example. It is a flowchart figure of the process which a controller performs when a failure is detected. It is a flowchart figure of the process which switches a relay when the heavy current is not flowing. It is a graph of the current waveform which flows into each phase at the time of a U-phase upper arm short circuit fault (other switching circuits are in an OFF state) It is a graph of the current waveform which flows into each phase at the time of U-phase upper arm short circuit failure (all switching circuits are in ON state) It is a graph which shows the relationship between an electric current waveform, a relay switching signal, and actual relay operation | movement. It is a flowchart figure of the process which switches a relay when the heavy current is not flowing (modified example). It is a graph which shows an example of the relationship between the excitation voltage which drives a relay, and delay time.

  FIG. 1 shows a circuit diagram of an inverter 100 according to the embodiment. The inverter 100 is a device that is mounted on an electric vehicle and supplies AC power to the wheel driving motor 6 using the DC power of the battery 9. The inverter 100 includes a power adjustment circuit 3, an inverter main circuit 4, a relay circuit 5, two capacitors (a first capacitor Cp and a second capacitor Cn), and a controller 2 as main components. In addition, the inverter 100 includes a voltage sensor 12 and a current sensor 13.

  The circuit configuration of the inverter 100 will be described in detail. The inverter main circuit 4 includes six switching circuits Sw1 to Sw6. That is, here, six switching circuit groups that generate three-phase AC power from the DC power of the battery 9 are referred to as the inverter main circuit 4. Each of the switching circuits Sw1 to Sw6 has a circuit configuration in which an IGBT and a diode (freewheeling diode) are connected in antiparallel. In order to configure a switching circuit that allows a large current with an IGBT having a small allowable current value, a single switching circuit may be configured by connecting a plurality of IGBTs in parallel.

  In the inverter main circuit 4, three sets in which two switching circuits are connected in series are connected in parallel, and an inverter output line extends from the connection point of the two switching circuits in series to the motor. The outputs of the inverter main circuit 4 are three UVWs, and the three output lines are connected to each UVW line (motor line 14) of the motor through the relay circuit 5. Each of the three output lines and a set of switching circuits corresponding to the output lines are called “arms”.

  The relay circuit 5 is a switch for switching the connection destination of each UVW three-phase motor wire 14 coming out of the motor from a corresponding output end of the inverter to a neutral point Np (described later). The relay circuit 5 includes three relays 5a, 5b, and 5c, and the connection destination of each line of the motor line 14 can be individually switched from the inverter output to the neutral point. The controller 2 instructs which relay to switch. Each relay connects the motor line 14 to the output line of the inverter when power is not supplied. When a predetermined voltage is applied to the coil of the relay, the connection destination of the motor line is switched to the neutral point Np.

  The relay circuit 5 is provided with a voltage sensor 12. The voltage sensor 12 is provided for measuring a voltage (excitation voltage) supplied to the electromagnetic coil of the relay when the relay is driven. The voltage sensor 12 is illustrated in FIG. 1 for explaining a modification of the present embodiment.

  In addition, a current sensor 13 that measures the current flowing through each line of the motor line 14 and a rotation speed sensor 15 that measures the rotation speed of the motor are provided as sensors. The sensor data of the voltage sensor 12, the current sensor 13, and the rotation speed sensor 15 are sent to the controller 2. Although not shown, the inverter 100 is also provided with a voltage sensor that measures the voltage Vcp across the first capacitor Cp and the voltage Vcn across the second capacitor Cn.

  The input terminal of the inverter main circuit 4 is connected to the battery 9 through the power adjustment circuit 3. In FIG. 1, the upper line of the battery 9 is the positive electrode line 10a, and the lower line is the negative electrode line 10b.

  On the input side of the inverter main circuit 4 (input side of the switching circuit group), two capacitors Cp and Cn are connected in series between the positive electrode line and the negative electrode line. The capacitances of the two capacitors Cp and Cn are equal. These two capacitors Cp and Cn are inserted in order to suppress the pulsation of the input current due to the influence of the switching operation of the switching circuit group (inverter main circuit 4). Therefore, the capacitors Cp and Cn are sometimes called smoothing capacitors.

  A connection point between the two capacitors Cp and Cn corresponds to the neutral point Np. Since the two capacitors Cp and Cn have the same capacity, the potential of the neutral point Np is half of the voltage of the battery 9 when the inverter main circuit 4 is not operating. On the other hand, when viewed from the output side of the inverter main circuit 4, the potential at the neutral point Np corresponds to the average voltage in the AC voltage output from the inverter main circuit 4.

  The power adjustment circuit 3 is connected between the capacitors Cp and Cn and the battery 9. The input terminal of the power adjustment circuit 3 is connected to the battery 9, and the three output terminals are connected to the positive electrode line 10a, the negative electrode line 10b, and the neutral point Np. More specifically, the power adjustment circuit 3 includes two switching circuits Swa and Swb and a reactor L. Both the switching circuits Swa and Swb have the same configuration as the switching circuit in the inverter main circuit 4, and are configured by an antiparallel circuit of IGBT and diode. The two switching circuits Swa and Swb are connected in series between the positive electrode line 10 a and the negative electrode line 10 b of the battery 9. A connection point Mp between the two switching circuits Swa and Swb is connected to one end of the reactor L, and the other end of the reactor L is connected to the neutral point Np.

  The power adjustment circuit 3 prevents a problem in one phase of the three-phase output of the inverter main circuit 4 and prevents the motor drive efficiency from being lowered when driving the motor with the remaining two phases. The function will be described. When one of the switching circuits of the inverter main circuit 4 fails and a failure occurs in one of the UVW three phases, the controller 2 sets the connection destination of the motor line connected to the inverter output where the failure occurs to a neutral point. Then, AC power is supplied to the motor 6 in the remaining two normal phases, and the motor 6 is driven. Since the normal two phases are connected to the neutral point via the switched relay, the neutral point potential fluctuates due to the influence of the AC power flowing in the normal two phases. Conversely, if the potential at the neutral point on the downstream side of the current changes, the waveform of the alternating current flowing through the motor 6 is disturbed, and the drive efficiency of the motor decreases. Therefore, the power adjustment circuit 3 operates so as to keep the neutral point potential constant, thereby preventing a reduction in the driving rate of the motor.

  The power adjustment circuit 3 operates according to the difference between the voltages at both ends of the capacitors Cp and Cn. The power adjustment circuit 3 is controlled by the controller 2. The operation of the power adjustment circuit 3 will be outlined. The voltage across the capacitor Cp is represented by “Vcp”, and the voltage across the capacitor Cn is represented by “Vcn”. Although not shown, a voltage sensor for measuring the voltage Vcp across the capacitor Cp and a voltage sensor for measuring the voltage Vcn across the capacitor Cn are provided, and data of these voltage sensors are also sent to the controller 2. For example, in the case of Vcp> Vcn, the controller 2 turns on the upper switching circuit Swa in FIG. 1 (the lower switching circuit Swb is kept off). Then, the electric charge stored in the first capacitor Cp flows through the switching circuit Swa, and electric energy is stored in the reactor L. When the controller 2 switches the upper switching circuit Swa to OFF, the electrical energy accumulated in the reactor L is transferred to the second capacitor Cn by the action of the freewheeling diode inserted in the lower switching circuit Swb. The controller 2 can adjust the amount of charge transferred from the first capacitor Cp to the second capacitor Cn by adjusting the ON time of the switching circuit Swa. Thus, the charge of the first capacitor Cp moves to the second capacitor Cn, and the voltage difference is corrected. In other words, the unbalance between the capacity stored in the capacitor Cp and the capacity stored in Cn is eliminated, and the divided voltages Vcp and Vcn of the two capacitors are kept substantially equal. The same applies to the case of Vcp <Vcn. The divided voltages Vcp and Vcn of the two capacitors may not be completely equal, and the power adjustment circuit 3 only needs to maintain the voltage difference | Vcp−Vcn | within a predetermined voltage difference allowable range Vth. That is, when the voltage difference | Vcp−Vcn | exceeds a predetermined voltage difference allowable range Vth, the voltage adjustment circuit 3 operates to return the voltage difference to the voltage difference allowable range Vth. The allowable voltage difference range Vth may be determined in advance according to the characteristics of the individual vehicle system, such as the capacitance of the capacitor and the degree of motor output reduction with respect to the magnitude of the voltage difference.

  Next, a process when a failure occurs in the switching circuit of the inverter main circuit 4 that generates AC power will be described in detail. FIG. 2 shows a flowchart of processing executed by the controller 2 when a failure occurs in any of the switching circuits. The failure can be detected from, for example, pulsation of the rotation speed of the motor or sensor data of the current sensor 13. When the pulsation width (amplitude) of the motor rotational speed exceeds a predetermined amplitude upper limit value, or when the current flowing in any phase (arm) of the UVW3 phase is out of the predetermined current range, the controller 2 Judge that a failure has occurred. Alternatively, each switching circuit may be provided with a failure detector (specifically, for example, a temperature sensor).

  When the controller 2 detects a failure in any of the switching circuits in the switching circuit group (when one of the three phases becomes uncontrollable), the relay of the uncontrollable phase among the three relays of the relay circuit 5 And the motor wire of the phase is connected to the neutral point Np (S2). Next, the controller 2 drives the motor using the remaining two normal phases (S3). Regarding the control for driving the motor in two of the three phases, for example, Japanese Patent Application Laid-Open No. 2004-120883 (Patent Document 1), Japanese Patent Application Laid-Open No. 2008-067429, or Japanese Patent Application Laid-Open No. 2004-028007. Therefore, the detailed description is omitted here.

  The controller 2 performs two-phase motor control until the vehicle stops (S4: NO). The controller 2 monitors whether or not the voltage difference dV = | Vcp−Vcn | between the voltage Vcp across the first capacitor Cp and the voltage Vcn across the second capacitor Cn is within a predetermined voltage difference allowable range Vth (S5). ). If the voltage difference dV is the voltage difference allowable range Vth, the controller 2 continues the motor control in two phases as it is (S5: YES, S3). On the other hand, when the voltage difference dV is outside the voltage difference allowable range Vth, the controller 2 drives the power adjustment circuit 3 to reduce the voltage difference dV (S5: NO, S6). The operation of the power adjustment circuit is as described above.

  If the voltage difference dV is within the voltage difference allowable range Vth by the action of the power adjustment circuit 3, the controller 2 continues the motor control in two phases (S7: YES, S3). On the other hand, if the voltage difference dV does not fall within the voltage difference allowable range Vth even by the power adjustment circuit 3, the controller 2 limits the output of the inverter (normal two-phase output current magnitude) (S8). This is because if the output of the inverter is limited, the fluctuation of the potential at the neutral point Np is also reduced, and the voltage difference dV is reduced.

  With the above processing, the inverter 100 can continue to drive the motor 6 with the normal two-phase output even if one of the three phases becomes uncontrollable. Since the motor is driven by two of the three phases, the original torque cannot be output, but a torque that allows the vehicle to travel slowly can be output. If the vehicle can be moved even at low speeds, it can be moved to a safe place. The inverter 100 can drive the motor as efficiently as possible by suppressing the potential fluctuation at the neutral point when the motor is driven in two phases by the action of the power adjustment circuit 3.

  When the vehicle is traveling, that is, when the motor 6 is driven from the axle side, a counter electromotive force is generated, and an alternating current (inductive current) due to the counter electromotive force flows through the motor line 14. At this time, if the switching circuit of the upper arm (any of Sw1, Sw3, and Sw5 in FIG. 1) causes a short-circuit fault (a state in which the switching circuit does not move while being ON), current also flows from the battery 9. A large current flows in the failed phase. Therefore, if the relay circuit 5 is switched while the motor is rotating, the switched relay may be damaged. For example, if the relay is switched while a large current is flowing, an arc may be generated and the contact may be burned. Adopting a relay with a large capacity to avoid damage increases the cost. Next, a technique for suppressing the current flowing when the relay is switched will be described.

  FIG. 3 shows a flowchart of processing for switching the relay at a timing when a large current is not flowing. The process of FIG. 3 is executed prior to the process of FIG.

  When a failure is found in any of the switching circuit groups, the controller 2 first stops the inverter main circuit 4 (S12). That is, all switching circuits are turned off. Here, if a current flows through the faulty phase, it is found that the fault is a short-circuit fault (a state in which the faulty switching circuit remains on). On the other hand, if no current flows in the failed phase, it is determined that the failure is an open failure (a state in which the failed switching circuit remains in an OFF state). The controller 2 monitors the current of each phase with the current sensor 13 and determines the type of failure (S13). When the failure is an open failure, there is no possibility that a large current flows through the relay circuit 5, and therefore the relay circuit 5 is controlled so that the connection destination of the motor line of the failed phase is immediately switched to the neutral point Np. That is, in the case of an open failure, the process proceeds to step S2 in FIG. 2 (S13: open failure). Subsequent processing is as described above.

  On the other hand, if the failure is a short-circuit failure, the controller 2 waits until the motor rotational speed (that is, the vehicle speed) falls below a predetermined rotational speed threshold (S14). This is to wait until the frequency of the alternating current (inductive current) caused by the counter electromotive force becomes a predetermined value or less. This is because when the frequency of the alternating current is high, the accuracy of the timing when the relay is operated at a timing when a large current is not flowing is lowered.

  When the motor rotational speed is equal to or lower than the rotational speed threshold, the controller 2 turns on all the switching circuits (Sw1 to Sw6) of the inverter main circuit 4 (S15). The reason for turning on all the switching circuits will be described. FIG. 4 shows that when the U-phase upper arm switching circuit (Sw1 in FIG. 1) causes a short-circuit failure and other switching circuits are open (switching circuit OFF), each phase is caused by the back electromotive force. It is the waveform of the alternating current which flows. Since the current from the battery 9 is applied to the U-phase upper arm, the current value increases. In the example of FIG. 4, 150 [A] is the contribution of the battery 9, and the AC component of ± 75 [A] is the current (inductive current) due to the back electromotive force. On the other hand, in the V phase and the W phase, the direct current component is shifted to the negative side as opposed to the U phase. In the case of the example of FIG. 4, there is a possibility that a current of 200 [A] or more flows through the relay 5a (see FIG. 1) for switching the U phase.

  When all the switching circuits of the inverter main circuit 4 are switched ON, the current waveform flowing in each phase is as shown in FIG. The currents of all phases are averaged, and an alternating current that swings positive and negative around a current value of zero is obtained. Thus, the current flowing in the short-circuited phase can be suppressed by simply turning on all the switching circuits. The inverter of this embodiment further reduces the current that flows when the relay is switched.

  In general, a relay applies a current to an electromagnetic coil to drive a contact. For this reason, there is a delay time Trd from when the switching signal is output to the relay until the relay actually operates. If the mechanical characteristics of the relay and the magnitude of the voltage for driving the coil are known, the delay time Trd can also be specified. The controller 2 stores a predetermined delay time Trd.

  Returning to FIG. 3, the description will be continued. The controller 2 specifies the frequency and phase of the alternating current resulting from the back electromotive force (S16). They are obtained from the sensor data of the current sensor 13 (see FIG. 1). FIG. 6A shows an example of the specified U-phase current waveform. FIG. 6B shows the output timing Ts of the relay switching signal, and FIG. 6C shows the timing Tx at which the relay actually operates. As shown in FIG. 5, since all the switching circuits are turned on, the alternating current flowing through the U phase also becomes a sine wave that swings positively and negatively around zero. The controller 2 detects the zero cross point Zx from the sensor data of the current sensor 13 and specifies the frequency f and phase (timing of the zero cross point Zx) of the current.

  If the relay 5a can be switched at the zero cross point Zx of the sine wave, the relay can be switched when the flowing current is zero (or very small). Therefore, the controller 2 outputs a relay switching signal at time Ts preceding the timing Tx by the delay time Trd so that the relay 5a operates at the timing Tx when the zero cross point Zx is reached. More specifically, the controller 2 calculates a current phase Ph (= 2π × Trd / f) corresponding to the delay time Trd from the identified frequency f of the current. The controller 2 determines the time when the phase (2π−Ph) has elapsed from the zero cross point Zx as the relay switching timing (S17). The controller 2 detects the zero cross point Zx from the sensor data of the current sensor 13, and outputs a relay switching signal at a timing (ie, relay switching timing Ts) when the phase (2π−Ph) has elapsed from the zero cross point Zx (S18, FIG. 6). (B)). Then, since the relay 5a operates with a delay of the delay time Trd (phase is Ph), the relay 5a is switched at the next zero cross point Zx (timing Tx). That is, the flowing current becomes almost zero at the timing when the relay 5a is switched. After switching the relay, the process may be shifted to step 3 in FIG. In other words, the relay switching timing Ts corresponds to the time after the elapse of time (1 / f-Trd) from the zero cross timing.

  For example, when the motor rotates at 6000 [rpm], the current frequency f is 100 [Hz], and the cycle is 10 [msec]. Therefore, if the relay switching timing cannot be specified on the order of 1 [msec], the effect is small. The delay time Trd depends on the voltage (excitation voltage) for driving the relay, and the excitation voltage depends on the voltage situation of the entire circuit. Therefore, in order to specify the relay switching timing more accurately, it is preferable that the delay time Trd, that is, the magnitude of the excitation voltage can be specified in real time. As an improvement of the process of FIG. 3, FIG. 7 shows a process of measuring the excitation voltage in real time and specifying the relay switching timing based on the result.

  The process of FIG. 7 is obtained by adding steps S21 and S22 between steps S16 and S17 of the process of FIG. The controller 2 measures the excitation voltage Vex based on the sensor data of the voltage sensor 12 provided in the relay circuit 5 (S21). There is a specific relationship between the excitation voltage Vex and the delay time Trd. An example is shown in FIG. As a tendency, the larger the excitation voltage Vex, the smaller the delay time. Since this relationship can be specified in advance, the controller 2 stores the graph of FIG. 8 (or a relational expression corresponding to the graph) in advance. The controller 2 specifies the delay time Trd in real time from the relationship between the measured excitation voltage Vex and FIG. 8 (S22). If the delay time Trd is specified, a relay switching signal is output in accordance with the processing of steps S17 and S18 described above. According to the process of FIG. 7, the relay can be switched at a timing closer to the zero cross point of the current than the process of FIG.

  In the inverter 100 having the processing of FIG. 3 or FIG. 7, the current flowing through the relay is small when switching the relay of the failed phase. Therefore, the inverter 100 has an advantage that the possibility that the relay circuit 5 is damaged is small.

  Points to note about the inverter 100 of the embodiment will be described. The motor 6 of the example is a PWM drive type, and the motor drive signal output from the inverter 100 is a PWM signal. The motor is not limited to the PWM drive type. For example, it may be a PAM drive type or another drive type. Moreover, the inverter 100 of the Example was an apparatus for 1-motor electric vehicles. The technology disclosed in this specification is also preferably applied to a hybrid vehicle including a motor that drives wheels and an engine. It should be noted that the circuit configuration of the power adjustment circuit 3 illustrated in FIG. 1 is an example, and other circuit configurations may be used as the power circuit configuration.

  In the embodiment, several flowcharts have been described. The order of processing in the flowchart may be changed within a range not exceeding the technical idea disclosed in the present specification. For example, in the flowchart of FIG. 3, after stopping the main circuit of the inverter (S12), the type of failure is determined (S13). Instead of such processing order, the main circuit of the inverter may be stopped after determining the type of failure. In this case, it should be noted that the flowchart of FIG. 3 is modified so that the inverter main circuit is stopped regardless of whether the failure type is an open failure or a short-circuit failure.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Controller 3: Power adjustment circuit 4: Inverter main circuit (switching circuit group)
5: Relay circuit 5a, 5b, 5c: Relay 6: Motor 9: Battery 10a: Positive line 10b: Negative line 12: Voltage sensor 13: Current sensor 14: Motor line 15: Speed sensor 100: Inverter Cp: First capacitor Cn: second capacitor L: reactor Np: neutral point Sw: switching circuit

Claims (3)

It is an inverter that converts the DC power of the battery into AC power and supplies it to the wheel drive motor,
A first capacitor and a second capacitor connected in series between a positive electrode line and a negative electrode line on an input side of a switching circuit group that outputs a three-phase alternating current;
A relay for switching the connection destination of each UVW three-phase motor wire coming out of the motor. The connection destination of each motor wire is individually connected to the connection point between the first and second capacitors from the corresponding output terminal of the inverter ( A relay to switch to the neutral point)
When one of the switching circuit groups fails, the relay is controlled to switch the connection destination of the motor line connected to the failed switching circuit among the UVW three-phase motor lines of the motor to the neutral point. And a controller that provides a drive signal for driving the motor in two phases to a switching circuit that has not failed,
The input terminal is connected to the battery, and the three output terminals are connected to the positive line, the negative line, and the neutral point, and the voltage difference between the voltage across the first capacitor and the voltage across the second capacitor A power adjustment circuit that operates to return the voltage difference to the allowable voltage difference when the voltage difference exceeds a predetermined allowable voltage difference;
Equipped with a,
The controller
If the switching circuit failure is an open failure, immediately output a relay switching signal,
In the case of a short-circuit failure, after all of the non-failed switching circuits are held in the ON state, the current flowing through the short-circuit failure switching circuit is measured, and the timing at which the relay actually switches matches the zero-cross timing of the current. electric vehicle inverter, wherein also be output from the relay switching signal as. A voltage sensor for measuring a voltage for driving the relay;
The controller
Based on the voltage measured by the voltage sensor, specify the delay time from the relay switching signal output until the relay actually switches,
2. The electric vehicle inverter according to claim 1 , wherein a relay switching signal is output based on the specified delay time so that a timing at which the relay is actually switched coincides with the zero cross timing. The power adjustment circuit includes:
Connect the positive electrode of the battery to the positive line of the switching circuit group and connect the negative electrode of the battery to the negative line of the switching circuit group,
Two switching circuits are connected in series between the positive line and the negative line,
Connecting the midpoint of the two switching circuits to the neutral point;
Electric vehicle inverter according to claim 1 or 2, characterized in that it has a structure.

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