JP2014068417A - Inverter control device - Google Patents

Abstract

The present invention relates to an inverter control device, and an object of the present invention is to prevent the on / off of upper and lower arms from returning to the original state near 0% or 100% of a PWM command duty ratio in PWM control.
An inverter control device generates an AC power supplied to a plurality of phases of an AC motor, and includes an inverter having a pair of switching elements corresponding to each phase and a phase current of each phase of the AC motor. Current detecting means for detecting the switching current, a switching control means for controlling on / off of the pair of switching elements based on a voltage comparison result between the PWM command signal based on the phase current and a carrier signal of a predetermined period, and an AC motor Current zero-cross determination means for determining the vicinity of the zero-cross of the phase current of each phase, and the PWM command signal when the PWM command duty ratio based on the phase current is near 0% or 100% in the vicinity of the zero-cross in PWM control Voltage command correction means for increasing or decreasing the voltage than usual.
[Selection] Figure 1

Description

  The present invention relates to an inverter control device, and in particular, an inverter suitable for controlling an inverter having a pair of switching elements corresponding to each phase for generating AC power supplied to a multi-phase AC motor. The present invention relates to a control device.

  2. Description of the Related Art Conventionally, a control device that controls an inverter having a pair of switching elements (that is, an upper arm and a lower arm) corresponding to each phase for driving and controlling a multi-phase AC motor is known (for example, a patent) Reference 1). This inverter control device generates AC power supplied to an AC motor by turning on / off a pair of switching elements for each phase in accordance with pulse width modulation (PWM) control of the inverter.

  As PWM control, there are at least a sine wave mode and an overmodulation mode that can realize higher rotation and higher torque of the AC motor than the sine wave mode. The sine wave mode controls on / off of the switching element so that the input voltage changes in a sine wave form within a predetermined period by comparing the voltage between a sine wave voltage command value and a carrier (for example, a triangular wave). It is. In the overmodulation mode, the PWM command duty ratio is quickly reduced to 0 by performing voltage comparison between a stepped voltage command value in which a high level value and a low level value are alternately generated and a carrier (for example, a triangular wave). % Or 100% is controlled to turn on / off the switching element.

  By the way, in order to prevent a short circuit by the upper and lower arms of the inverter, it is common to provide a short-circuit prevention time (dead time) in which both the upper and lower arms are turned off. Moreover, the phase current of each phase fluctuates near the zero cross due to the influence of noise and current ripple. When both the upper and lower arms are turned off near the zero cross of the phase current due to the dead time, the output voltage moves up and down, and the time change of the output voltage becomes slower than usual. In this regard, there may occur a situation in which the upper and lower arms are not properly switched due to fluctuations in the output voltage change during the dead time near the current zero cross.

  Therefore, in order to avoid unauthorized switching of the upper and lower arms due to fluctuations in the output voltage, the time change (dv / dt) of the output voltage is detected, and the output voltage changes relatively quickly, and the time change dv / It is conceivable that the switching command for the upper and lower arms is not masked during the period when dt is large, while the switching command for the upper and lower arms is masked during the period when the output voltage changes relatively slowly and the time change dv / dt is small. (See, for example, Patent Document 2). According to such a configuration, it is possible to prevent the upper and lower arms from being illegally switched when the output voltage moves up and down relatively slowly, and as a result, it is possible to appropriately perform inverter control. It becomes.

JP 2012-023885 A JP 2000-252809 A

  On the other hand, in the overmodulation mode, switching that continues to be turned on (or off) for several carrier cycles can be performed. However, when the PWM command duty ratio is near 100% or near 0%, Since the voltage magnitude relationship between the voltage command value and the carrier may change within a short time at the peak or valley point, the switching command is (a) on → (b) off → (c) in a short time. There may be a situation where the switching occurs in the order of ON or vice versa (that is, generation of a short pulse). Even in the sine wave mode, when high rotation and high torque of the AC motor is realized, the PWM command duty ratio reaches near 100% or near 0%. Since the voltage magnitude relationship between the value and the carrier may change within a short time, the above short pulse can be generated.

  In this regard, when the mask process for masking the switching command of the upper and lower arms is executed as described above during the dead time near the current zero cross in the sine wave mode and overmodulation mode of the PWM control, the switching element of the short pulse is changed. If the ON or OFF duration is shorter than the mask time, there may occur a situation where the second switching change command (for example, the ON command in (c) above) is masked, and thereafter the second switching change command. There is a risk that the switching of the upper and lower arms based on the above will not be performed.

  The present invention has been made in view of the above points, and it is possible to prevent the on / off of the upper and lower arms from returning to the original state in the vicinity of 0% or 100% of the PWM command duty ratio in the PWM control. It is an object to provide a simple inverter control device.

  The above object is to detect an inverter having a pair of switching elements corresponding to each phase for generating AC power supplied to the AC motor of a plurality of phases, and a phase current of each phase of the AC motor. On / off of the pair of switching elements based on a voltage comparison result between a current detection unit, a PWM command signal generated based on the phase current detected by the current detection unit, and a carrier signal having a predetermined period. Switching control means for controlling off, current zero cross determination means for determining the vicinity of the zero cross of each phase current of the AC motor, and the phase current detected by the current detection means in the vicinity of the zero cross in PWM control The PWM command signal when the PWM command duty ratio based on is near 0% or near 100% It is achieved by the inverter control device comprising: a voltage command correction means for voltage raising or voltage drop, the than normal.

  According to the present invention, it is possible to prevent the on / off of the upper and lower arms from returning to the original state when the PWM command duty ratio in the PWM control is near 0% or near 100%.

1 is an overall configuration diagram of a system including an inverter control device according to an embodiment of the present invention. It is a block block diagram of the principal part of the inverter control apparatus of a present Example. It is a figure showing the situation where the output voltage of an up-and-down arm moves up and down during the short-circuit prevention time (dead time) in which both upper and lower arms are turned off near the current zero cross. It is a figure showing the relationship between the detection timing of the phase current using the current sensor in the inverter control apparatus of a present Example, and the determination timing of the electric current zero cross vicinity. It is a figure showing the control mode which controls an inverter in the inverter control apparatus of a present Example. 6 is an example of an operation time chart in an overmodulation PWM control mode. It is a figure for demonstrating the inconvenience accompanying performing mask processing which masks a switching command during the dead time near the zero cross in overmodulation mode. It is an example of the operation | movement time chart in the overmodulation PWM control mode in the inverter control apparatus of a present Example.

  Hereinafter, specific embodiments of an inverter control device according to the present invention will be described with reference to the drawings.

  FIG. 1 shows an overall configuration diagram of a system including an inverter control device 10 according to an embodiment of the present invention. FIG. 2 is a block diagram of a main part of the inverter control device 10 of this embodiment. The inverter control device 10 according to the present embodiment is a device that controls the inverter 12 for generating AC power from a DC power source.

  The inverter 12 generates, for example, torque for driving driving wheels of an electric vehicle or a hybrid vehicle, or AC power supplied to a motor 14 that starts the engine as an electric motor for a vehicle engine, such as a lithium ion battery or a nickel metal hydride battery. It is the apparatus for generating using the direct-current power of the battery 16. The motor 14 is a three-phase synchronous AC motor, and has a configuration in which one end of three coils of a U phase, a V phase, and a W phase is commonly connected to a neutral point.

  The inverter 12 is interposed between the battery 16 and the motor 14. A boost converter may be provided between the inverter 12 and the battery 16 to boost the DC voltage of the battery 16 by turning on / off the pair of switching elements by using the energy storage action of the reactor. The inverter 12 has upper and lower arms 20, 22, 24 corresponding to each phase of the motor 14. The U-phase upper and lower arms 20, the V-phase upper and lower arms 22 and the W-phase upper and lower arms 24 are connected in parallel between the positive power source and the negative power source.

  The U-phase upper and lower arms 20 include a switching element 20a that is an upper arm element and a switching element 20b that is a lower arm element. The V-phase upper and lower arms 22 include a switching element 22a that is an upper arm element and a switching element 22b that is a lower arm element. The W-phase upper and lower arms 24 include a switching element 24a that is an upper arm element and a switching element 24b that is a lower arm element. The upper arm element and the lower arm element of the upper and lower arms 20, 22, 24 of each phase are connected in series between the positive power source and the negative power source. An intermediate point between the upper arm element and the lower arm element of the upper and lower arms 20, 22, 24 of each phase is connected to the other end of the coil of the phase of the motor 14. Each switching element is a power transistor such as an IGBT.

  The inverter 12 converts the DC voltage into an AC voltage and outputs it by alternately turning on / off the upper arm element and the lower arm element of the upper and lower arms 20, 22, 24 for each phase. ON / OFF of each switching element which is an upper arm element and a lower arm element is controlled by a control signal from the inverter control device 10. Anti-parallel diodes Du and Dd are connected in parallel to these switching elements.

  The inverter control device 10 has an electronic control unit (ECU) 18 mainly composed of a microcomputer, and by software processing by executing a program stored in advance by the CPU and / or hardware processing by an electronic circuit, The operation of the inverter 12 is controlled.

  The ECU 18 of the inverter control device 10 is connected to a current sensor 26 and a resolver 28. The current sensor 26 outputs a signal corresponding to the phase current of each phase of the motor 14. The ECU 18 detects a phase current flowing in each phase of the motor 14 based on a signal output from the current sensor 26. Since the sum of instantaneous values of the three-phase phase currents iu, iv, iw is zero, the current sensor 26 outputs a signal corresponding to the phase current for two phases, and the remaining one-phase current is It is good also as calculating | requiring by calculation (for example, iu =-(iv + iw)). The resolver 28 outputs a signal corresponding to the rotor rotation angle θ of the motor 14. The ECU 18 detects the rotor rotation angle θ of the motor 14 based on the signal output from the resolver 28.

  The ECU 18 includes a dq axis current converter 30 connected to the current sensor 26. Information on the phase currents iu, iv, and iw of each phase of the motor detected using the current sensor 26 is supplied to the dq-axis current conversion unit 30. The dq-axis current conversion unit 30 converts the three-phase phase currents iu, iv, and iw of the motor 14 input from the current sensor 26 into a two-phase d-axis current id and a q-axis current iq, thereby converting the three-phase. The d-axis current id and the q-axis current iq are calculated based on the phase currents iu, iv and iw.

  The ECU 18 receives a d-axis current command value id * and a q-axis current command value iq * corresponding to the torque command value of the motor 14 according to a predetermined map or the like. The ECU 18 includes a feedback calculation unit 32. The feedback calculation unit 32 includes a deviation Δid (= id * −id) between the command value id * of the d-axis current and the actual value id, and a deviation Δiq between the command value iq * of the q-axis current and the actual value iq ( = Iq * -iq).

  The ECU 18 includes a rotation speed calculation unit 34 connected to the resolver 28. Information on the rotor rotation angle θ of the motor 14 detected using the resolver 28 is supplied to the rotation speed calculation unit 34. The rotation speed calculation unit 34 calculates the rotation speed N of the motor 14 based on the rotor rotation angle θ of the motor 14.

  The rotation speed calculation unit 34 is connected to the feedback calculation unit 32 described above. Information on the rotational speed N of the motor 14 calculated by the rotational speed calculator 34 is supplied to the feedback calculator 32. The feedback calculation unit 32 uses the rotational speed N of the motor 14 so that the d-axis current deviation Δid and the q-axis current deviation Δiq converge to zero so that the d-axis voltage command values vd and q-axis are converged to zero. The voltage command value vq is calculated.

  The ECU 18 includes a dq axis voltage conversion unit 36 connected to the feedback calculation unit 32. Information on the dq-axis voltage command values vd and vq calculated by the feedback calculation unit 32 is supplied to the dq-axis voltage conversion unit 36. The resolver 28 is also connected to the dq axis voltage converter 36. Information on the rotor rotation angle θ of the motor 14 detected using the resolver 28 is supplied to the dq axis voltage converter 36. The dq axis voltage conversion unit 36 converts the input dq axis voltage command values vd and vq into the three-phase reference voltage command values Vu, Vv and Vw by using the rotor rotation angle θ of the motor 14. The three-phase reference voltage command values Vu, Vv, Vw are calculated based on the dq axis voltage command values vd, vq. The three-phase reference voltage command values Vu, Vv, and Vw are signals that have the same amplitude and are out of phase by an electrical angle of 120 °.

  The ECU 18 includes a PWM command correction unit 40 connected to the dq axis voltage conversion unit 36. Information on the three-phase reference voltage command values Vu, Vv, and Vw calculated by the dq-axis voltage conversion unit 36 is supplied to the PWM command correction unit 40. The PWM command correction unit 40 corrects the input three-phase reference voltage command values Vu, Vv, and Vw as will be described in detail later, and calculates the three-phase voltage command values U, V, and W to be output.

  The ECU 18 also includes a PWM output unit 42 connected to the PWM command correction unit 40. Information on the three-phase voltage command values U, V, and W calculated by the PWM command correction unit 40 is supplied to the PWM output unit 42. A carrier signal having a predetermined cycle Tc is input to the PWM output unit 42. This carrier signal is a carrier wave formed in a triangular wave shape, for example, and has a predetermined amplitude substantially the same as the amplitude of the three-phase voltage command values U, V, and W. The PWM output unit 42 compares the input voltage command values U, V, W with the carrier signal in each phase, and controls the on / off of the upper and lower arms 20, 22, 24 of the inverter 12. Is output to the upper and lower arms 20, 22, and 24.

  Next, the operation of the inverter control device 10 according to the present embodiment will be described with reference to FIGS.

  FIG. 3 shows that the output voltages of the upper and lower arms 20, 22, and 24 move up and down during the short-circuit prevention time (dead time) in which both the upper and lower arms of the upper and lower arms 20, 22, and 24 are turned off near the current zero cross. The figure showing the situation to do is shown. 3A shows a circuit diagram, and FIG. 3B shows an operation time chart. FIG. 4 is a diagram showing a control mode for controlling the inverter 12 in the inverter control apparatus 10 of the present embodiment. FIG. 6 shows an example of an operation time chart in the overmodulation PWM control mode in the inverter control apparatus 10 of the present embodiment. FIG. 7 is a diagram for explaining inconveniences associated with the execution of the mask process for masking the switching command during the dead time near the zero cross in the overmodulation PWM control mode.

  In this embodiment, the upper and lower arms 20, 22, 24 of the inverter 12 are respectively connected in series between a positive power source and a negative power source, and from an upper arm element and a lower arm element that are alternately turned on / off. Become. In such a structure, when the ECU 18 controls on / off of each switching element of the inverter 12, the upper arm element and the lower arm element are both connected to prevent the upper arm element and the lower arm element from being short-circuited. A short-circuit prevention time (dead time) for turning off is provided. Further, the phase currents iu, iv, iw of the motor phases fluctuate near the zero cross due to the influence of noise and current ripple. When the upper and lower arms are turned off by the dead time when the phase currents iu, iv and iw of the motor 14 reach the vicinity of the zero cross, the output voltage Vce of the upper and lower arms 20, 22 and 24 becomes the phase current iu, It moves up and down according to iv and iw, and the time change of the output voltage Vce becomes gentler than usual (see FIG. 3). In this regard, there may occur a situation in which the upper and lower arms 20, 22, and 24 are not properly switched due to fluctuations in the output voltage change during the dead time near the current zero cross.

  On the other hand, in the inverter control device 10 of the present embodiment, the ECU 18 includes a current zero cross determination unit 44. Information on the phase currents iu, iv, and iw of each phase of the motor detected using the current sensor 26 is input to the current zero cross determination unit 44, and the rotation speed of the motor 14 calculated by the rotation speed calculation unit 34 is input. N information is input. The current zero cross determination unit 44 determines whether or not the phase currents iu, iv, and iw of the motor phases reach the vicinity of the zero cross.

  The ECU 18 compares the three-phase voltage command values U, V, and W with the carrier signal to generate a control signal to the inverter 12, and generates the vertex timing of the carrier signal (for example, the peak and valley points of the triangular wave). In both cases, the phase currents iu, iv, iw from the current sensor 26 are monitored (see FIG. 4). Then, at the next apex timing of the apex timing (for example, when the phase current is monitored at the peak of the triangular wave, at the next trough, and when the phase current is monitored at the trough of the triangular wave, the next peak The PWM command to the inverter 12 is performed.

  In determining the vicinity of the current zero cross, the current zero cross determination unit 44 first determines the apex timing t_n as shown in the following equation (1) based on the phase current i_n monitored at the apex timing t_n of the carrier signal. The phase current i_n + 1 generated at the next vertex timing t_n + 1 is estimated. However, Tc is the period of the carrier signal, and α is the gradient when the phase current changes with time, and is a value that varies according to the rotational speed of the motor 14.

i_n + 1 = i_n + α × Tc / 2 (1)
Then, when the phase current i_n + 1 generated at the next vertex timing t_n + 1 is estimated as described above, the current zero cross determination unit 44 determines whether or not the phase current i_n + 1 is in the vicinity of the zero cross. The determination of whether or not it is in the vicinity of the zero cross may be made based on whether or not the phase current i_n + 1 belongs to a predetermined vertical range centering on the current zero.

  When the ECU 18 determines that the phase current i_n + 1 is close to the zero cross at the next vertex timing t_n + 1 as described above, the dead time when both the upper arm element and the lower arm element are turned off near the vertex timing t_n + 1 is determined. It is determined whether or not it occurs, that is, whether or not on / off switching to the upper and lower arms is performed. This determination may be made based on whether or not the time change of the output voltage of the upper and lower arms is detected and whether the time change is larger than the threshold value.

  When the ECU 18 determines that the upper and lower arms are switched on and off with dead time in the vicinity of the current zero cross, the PWM command is set so that the PWM command to the inverter 12 at the vertex timing t_n + 1 is masked. A mask process for a predetermined period is performed. The predetermined period may be set to a time during which the vertical movement of the output voltage Vce of the upper and lower arms 20, 22, 24 continues at least. According to such a mask process, the vertical movement of the output voltage Vce of the upper and lower arms 20, 22, and 24 continues for a long time in the vicinity of the current zero cross during the dead time. It can be avoided that the ON command and the OFF command for 24 are illegally performed, and it can be prevented that the switching is not appropriately performed.

  Further, in the motor control device 10 of the present embodiment, as shown in FIG. 5, the ECU 18 performs sine wave PWM (Pulse Width Modulation) control, overmodulation PWM control, and rectangular wave as control modes for controlling the inverter 12. The control mode has three control modes, and one of the three control modes is selected, and the inverter 12 is controlled.

  In the sine wave PWM control, a PWM signal whose pulse width is modulated is generated by comparing a voltage between a sine wave voltage command value and a carrier signal, and the upper and lower arms 20, 22,. The on / off of the switching element in 24 is controlled. Then, a first period in which the upper arm switching element is turned on and the lower arm switching element is turned off and a second period in which the upper arm switching element is turned off and the lower arm switching element is turned on are alternately repeated. The duty ratio of each switching element is controlled so that the voltage output from the inverter 12 and input to the motor 14 in a period changes in a sine wave shape. When the inverter 12 performs power conversion according to the PWM signal by the above sine wave PWM control, the voltage waveform input to the motor 14 is substantially sinusoidal. According to such sine wave PWM control, torque control can be easily performed even when the motor 14 is driven to rotate in a relatively low rotation range, and smooth rotation can be obtained.

  Further, as shown in FIG. 6, for example, the overmodulation PWM control is performed by a high level value (for example, a value near the voltage value of the positive power supply), a low level value (for example, a value near the voltage value of the negative power supply), or A PWM signal whose pulse width is modulated is generated by comparing the voltage between the stepped voltage command value for generating the intermediate value and the carrier signal, and the PWM command duty ratio is quickly 0% or The on / off states of the switching elements in the upper and lower arms 20, 22, 24 of each phase of the motor 14 are controlled so as to reach 100%. When the inverter 12 performs power conversion according to the PWM signal by the overmodulation PWM control, the voltage waveform input to the motor 14 immediately becomes a high level or a low level. According to such overmodulation PWM control, even if the motor 14 is driven to rotate in a relatively high rotation range, high torque can be generated.

  Further, the rectangular wave control generates a rectangular wave signal corresponding to the rotational position of the motor 14 and controls on / off of switching elements in the upper and lower arms 20, 22, 4 of each phase of the motor 14 by the rectangular wave signal. Is. Then, an ON period and an OFF period of each switching element are set so that the voltage output from the inverter 12 and input to the motor 14 within a predetermined period becomes a rectangular wave, that is, one pulse of the rectangular wave is input to the motor 14. Are controlled on a one-to-one basis, and a half cycle (electrical angle 180 °) of each phase of the motor is output as one pulse. In the rectangular wave control, the amplitude of the voltage output from the inverter 12 is fixed, and the output control of the motor 14 is realized by changing the phase of the output voltage of the inverter 12. When the inverter 12 performs power conversion according to the rectangular wave signal by the rectangular wave control described above, the voltage waveform input to the motor 14 becomes a rectangular wave shape according to the rotational position. According to such rectangular wave control, the ratio of the amplitude of the input voltage to the motor 14 with respect to the input voltage to the inverter 12 can be increased as compared with the above PWM control. Even if it is rotationally driven in a high torque range, it can be controlled easily. Further, compared to PWM control that performs field weakening control or the like, it is possible to suppress the occurrence of iron loss in the motor 14 and improve energy efficiency, and it is possible to reduce the number of times of switching in the inverter 12. Switching loss can be suppressed.

  In this embodiment, the ECU 18 determines the torque to be output by the motor 14 based on the accelerator operation amount, the motor rotation speed, etc., obtains a torque command value corresponding to the torque, and switches the inverter 12 according to the torque command value. A signal to be supplied to the element is generated. The ECU 18 switches the control mode of the inverter 12 between sine wave PWM control, overmodulation PWM control, and rectangular wave control in accordance with the motor rotation speed N, the motor torque T, and the like.

  The ECU 18 obtains the d-axis current command value id * and the q-axis current command value iq * on the dq-axis coordinates from the torque command value obtained as described above, and from the motor current actually flowing in each phase of the motor 14. The d-axis current id and the q-axis current iq are obtained. In the sine wave PWM control mode, the sinusoidal dq axis voltage command values vd and vq are obtained based on the deviation between the command value and the actual value of these currents. On the other hand, in the overmodulation PWM control mode, Based on the deviation between the command value and the actual value, rectangular wave-shaped dq-axis voltage command values vd and vq are obtained. Next, the voltage command values vd and vq obtained as described above are subjected to two-phase → three-phase coordinate conversion, and the corrected voltage command values U, V, and Q are compared with the carrier signal, and the pulse A width-modulated PWM signal is generated.

  Further, in the rectangular wave control mode, the ECU 18 obtains the d-axis current id and the q-axis current iq from the motor current actually flowing in each phase of the motor 14, and obtains the torque generated in the motor 14 from the current value. Then, the torque is compared with the torque command value to determine the phase of the rectangular wave, and the phase is added to the rotor angle to generate a rectangular wave signal.

  By the way, in the above-described overmodulation PWM control mode, switching that continues to be turned on (or off) for several times of the carrier cycle Tc can be performed, but the PWM command duty ratio is near 100% or near 0%. In some cases, the voltage magnitude relationship between the voltage command value and the carrier signal may change within a short time at the peak or valley point of the carrier signal, so that the switching command is (a) on → (b) in a short time. There is a possibility of switching from OFF to (c) ON or vice versa (that is, generation of a short pulse).

  In this regard, as shown in FIG. 7, in the situation where the voltage command value in the overmodulation PWM control mode is near the high level value (PWM command duty ratio 100%) or the low level value (PWM command duty ratio 0%), When the mask processing for masking the switching command of the upper and lower arms is executed during the dead time near the current zero crossing as described above, when the switching element is continuously turned on or off with a short pulse is shorter than the mask time, There may be a situation where the second switching change command (for example, the ON command in (c) above) is masked, and there is a possibility that the upper and lower arms are not switched based on the second switching change command. .

  FIG. 8 shows an example of an operation time chart in the overmodulation PWM control mode in the inverter control apparatus 10 of the present embodiment. In FIG. 8, the waveform of the voltage command value in the present embodiment is indicated by a solid line, and the waveform of the voltage command value in comparison with the present embodiment is indicated by a broken line.

  Therefore, in the inverter control device 10 of the present embodiment, the above-described PWM command correction unit 40 is connected to the current zero cross determination unit 44. The determination result in the current zero cross determination unit 44 is supplied to the PWM command correction unit 40. In the PWM command correction unit 40, the control mode is the overmodulation PWM control mode, and the voltage command value is in the vicinity of the high level value (PWM command duty ratio 100%) or the low level value (PWM command duty ratio 0%). In the situation, if it is determined that the phase current i_n + 1 is close to the zero cross at the next vertex timing t_n + 1 based on the determination result of the current zero cross determination unit 44, the voltage command value is changed from the normal value.

  Specifically, in a situation where the voltage command value is close to the high level value, the voltage command value is increased from the normal (= proportional) voltage so that it is near the peak and valley points of the carrier signal. Then, change is made so as not to generate a short pulse (see FIG. 8). Also, in a situation where the voltage command value is near the low level value, the voltage command value is lowered from the normal (= proportional) voltage so that a short pulse is generated near the peak and valley points of the carrier signal. Change so that does not occur.

  When such a change in the voltage command value is performed, the time for which the switching element is continuously turned on or off with a short pulse will not be shorter than the mask time, and a short time near the peak and valley points of the carrier signal. Generation of pulses is suppressed. In this case, in the overmodulation PWM control mode, the PWM command duty ratio is reliably maintained at 100% or 0% even when the carrier signal reaches the vicinity of the peak and valley points near the current zero cross. There is no dead time in which both are turned off, and it is avoided that the mask process for masking the switching command due to the existence of the dead time is performed.

  Therefore, according to the present embodiment, in the overmodulation PWM control mode, in the situation where the voltage command value is near the high level value or the low level value and the PWM command duty ratio is near 100% or near 0%, Even when the carrier signal reaches the vicinity of the peak point and the valley point in the vicinity, it is possible to eliminate the situation where the switching of the upper and lower arms based on the switching change command is not performed due to the execution of the mask processing described above. It is possible to prevent the upper and lower arms from being turned on / off by masking.

  In the above-described embodiment, the upper and lower arms 20, 22, and 24 correspond to “a pair of switching elements” recited in the claims. Further, the ECU 18 detects a phase current flowing in each phase of the motor 14 based on a signal output from the current sensor 26, whereby the “current detection means” described in the claims is input with a voltage command. The values U, V, and W are compared with a carrier signal having a predetermined period, and a control signal for commanding on / off of the upper and lower arms 20, 22, and 24 of the inverter 12 is generated. The “switching control means” determines whether or not the current zero cross determination unit 44 reaches the vicinity of the zero cross for each of the phase currents iu, iv, iw of each phase of the motor. In the vicinity of the current zero cross in the overmodulation PWM control mode in the PWM command correction unit 40 based on the phase currents iu, iv, iw. When the M command duty ratio is close to 0% or close to 100%, the voltage command value for each phase is increased or decreased more than usual by the “voltage command correction means” described in the claims. Are realized.

  By the way, in the above embodiment, in the situation where the voltage command value is in the vicinity of the high level value or the low level value and the PWM command duty ratio is in the vicinity of 100% or 0%, the carrier signal has a peak near the current zero cross. The control mode is the overmodulation PWM control mode at the timing to eliminate the situation where the switching of the upper and lower arms based on the switching change command is not performed due to the execution of the mask processing when reaching the point and the vicinity of the valley point. Sometimes we are going to limit it. However, the present invention is not limited to this, and the same situation can occur when the control mode is the sine wave PWM control mode. The control mode may be limited to the mode, or the control mode may be limited to the overmodulation PWM control mode or the sine wave PWM control mode.

DESCRIPTION OF SYMBOLS 10 Inverter control apparatus 12 Inverter 14 Motor 18 ECU
20, 22, 24 Upper and lower arms 20a, 20b, 22a, 22b, 24a, 24b Switching element 26 Current sensor 28 Resolver 40 PWM command correction unit 42 PWM output unit 44 Current zero cross determination unit

Claims (1)

An inverter having a pair of switching elements corresponding to each phase for generating AC power supplied to a multi-phase AC motor;
Current detecting means for detecting a phase current of each phase of the AC motor;
Switching for controlling on / off of the pair of switching elements based on a voltage comparison result between a PWM command signal generated based on the phase current detected by the current detection means and a carrier signal having a predetermined period Control means;
Current zero cross determining means for determining the vicinity of the zero cross of the phase current of each phase of the AC motor;
In the vicinity of the zero cross in the PWM control, when the PWM command duty ratio based on the phase current detected by the current detection means is near 0% or near 100%, the voltage of the PWM command signal is increased more than usual or Voltage command correction means for lowering the voltage;
An inverter control device comprising:

Images