JP2013255305A - Motor driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a switching loss while simplifying a control configuration in a motor driving device which controls an inverter according to a PWM switching system.SOLUTION: A motor driving circuit comprises an inverter bridge circuit and a motor control circuit which performs PWM control on a switching element of the inverter bridge circuit in such a manner that a three-phase current that flows in a three-phase motor becomes a sinusoidal three-phase current waveform. The motor control circuit performs the control by switching a three-phase control system and a two-phase control system at intervals of 60°. According to the three-phase control system, an on interval and an off interval are set to phases of upper and lower arms. According to the two-phase control system, an always-on interval is set to one of U, V and W phases in any one of the upper and lower arms and an always-off interval is set to the one phase in the other arm. When switching the three-phase control system and the two-phase control system, the on interval and the always-on interval are controlled to be continued and the off interval and the always-off interval are controlled to be continued.

Description

  The present invention relates to a motor drive device that controls an inverter by a PWM switching method.

  As this type of motor drive device, one having an inverter bridge circuit composed of a U phase, a V phase, and a W phase is known. As shown in FIG. 12, the inverter bridge circuit 11 is configured by providing diodes Da-Df in parallel with the switching element Ta-Tc on the upper arm side and the switching element Td-Tf on the lower arm side, respectively. The inverter bridge circuit 11 receives a PWM signal for switching the on / off state of the switching element Ta-Tf from the motor control circuit 12. The inverter bridge circuit 11 converts the DC power into AC power by switching the switching element Ta-Tf by PWM control, and supplies necessary power to the three-phase motor 13.

  By the way, in order to suppress the power loss in the inverter bridge circuit, PWM control for reducing the switching loss has been proposed (for example, see Patent Document 1). In the PWM control described in Patent Document 1, a two-phase control method is used in which only the two-phase switching elements are switched among the three-phase switching elements on the upper arm side and the lower arm side. By reducing the number of times of switching for one phase using the two-phase control method, the power loss due to the switching loss is reduced compared to the three-phase control method.

JP 2010-200412 A

  By the way, the three-phase motor is driven by a sinusoidal three-phase current waveform obtained by shifting the phase of the three-phase current by 120 °. In this three-phase current waveform, the current value of any one phase becomes 0 near the current phase 60 °, 120 °, 180 °, 240 °, 300 °, 360 ° of each phase (see FIG. 2). Such control is difficult in the above-described two-phase control method. For this reason, it is necessary to perform control such that the current phase of each phase is temporarily switched to the three-phase control method in the vicinity of 60 °, 120 °, 180 °, 240 °, 300 °, and 360 ° and then returned to the two-phase control method again. It was. For this reason, the PWM control described in Patent Document 1 has a problem in that although the switching loss can be reduced, the control configuration becomes complicated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a motor drive device that can reduce the switching loss while facilitating the control configuration.

  The motor drive device of the present invention is composed of an upper arm and a lower arm having U-phase, V-phase, and W-phase switching elements, respectively, and converts the direct current supplied from the power source side to alternating current by the on / off operation of the switching elements. The inverter bridge circuit that outputs to the three-phase motor, and the switching element so that the U-phase current, the V-phase current, and the W-phase current that flow through the three-phase motor each have a sinusoidal current waveform shifted by 120 °. A control circuit that performs PWM control of an ON section or an OFF section of the upper arm and the lower arm, and the control circuit sets an ON section and an OFF section for each phase of the upper arm and the lower arm, and the upper section In either one of the arm and the lower arm, an always on section is set for one of the U phase, the V phase, and the W phase, and either the upper arm or the lower arm On the other hand, the two-phase control method for setting the always-off interval for the one phase is controlled by switching every 60 °, and at the switching timing between the three-phase control method and the two-phase control method, Control is performed so that the on-section and the always-on section are continuous, and the off-section and the always-off section are continuous.

  According to this configuration, since the control is performed by switching between the three-phase control method and the two-phase control method, switching frequency is reduced by reducing the number of times of switching compared with the configuration in which the inverter bridge circuit is controlled only by the three-phase control method. Can be reduced. Also, switching loss can be reduced because switching is performed so as not to occur at the switching timing (seam) between the three-phase control method and the two-phase control method. Furthermore, since the two-phase control method and the three-phase control method are switched every 60 °, the control configuration does not become complicated. Therefore, power loss due to switching loss can be reduced with a simple control configuration.

  In the motor drive device of the present invention, the control circuit may be configured such that, in the three-phase control method and / or the two-phase control method, the section having the shortest on section among the U phase, the V phase, and the W phase is set as the off section. Set. According to this configuration, by setting the section with the shortest ON section as the OFF section, the ON section is shortened, so that the saturation loss can be reduced. At this time, the section with the shortest ON section is a commutation section in which no current flows through the three-phase motor.

  In the motor drive device of the present invention, the control circuit sets an ON interval of one pulse or a plurality of pulses immediately before the current value of the current waveform of each phase becomes 0 in the three-phase control method as an OFF interval. To do. According to this configuration, by setting the ON period of one pulse or several pulses immediately before the current value becomes 0 as the OFF period, the number of switchings can be further reduced, and the switching loss can be reduced. Further, since the ON section of the switching element is shortened, the saturation loss can be reduced. At this time, since the value of the current flowing through the three-phase motor becomes 0 in the ON period immediately before the current value becomes 0, the motor driving is not affected even if the current value is set to the OFF period.

  Another motor driving device of the present invention is composed of an upper arm and a lower arm each having a switching element of U phase, V phase, and W phase, and direct current supplied from the power source side by the on / off operation of the switching element is changed to alternating current. Inverter bridge circuit that outputs to the three-phase motor and the U-phase current, V-phase current, and W-phase current flowing through the three-phase motor, respectively, so as to have a sinusoidal current waveform shifted by 120 °. A control circuit that performs PWM control of an ON section or an OFF section of the switching element, and the control circuit sets an ON section of one pulse or a plurality of pulses immediately before the current value of the current waveform of each phase becomes 0 as an OFF section. It is characterized by setting to.

  According to this configuration, by setting the ON period of one pulse or several pulses immediately before the current value becomes 0 as the OFF period, the number of times of switching can be reduced and the switching loss can be reduced. Further, since the ON section of the switching element is shortened, the saturation loss can be reduced. At this time, since the value of the current flowing through the three-phase motor becomes 0 in the ON period immediately before the current value becomes 0, the motor driving is not affected even if the current value is set to the OFF period.

  According to the present invention, switching loss can be reduced while facilitating the control configuration by switching between the two-phase control method and the three-phase control method every 60 ° and suppressing the occurrence of switching at this switching timing. .

It is a block diagram of the motor drive device concerning this embodiment. It is a figure which shows the three-phase current waveform which flows into the three-phase motor which concerns on this Embodiment. It is a figure which shows an example of the PWM signal waveform of a three-phase control system. It is a figure which shows an example of the PWM signal waveform of a two-phase control system. It is a figure which shows another example of the PWM signal waveform of a two-phase control system. It is a figure which shows an example at the time of the switching of the PWM control pattern of a two-phase control system. It is a figure which shows another example at the time of the switching of the PWM control pattern of a two-phase control system. It is a figure which shows an example of the PWM signal waveform which concerns on this Embodiment. An example of the PWM signal waveform which made the commutation area which concerns on this Embodiment the OFF area is shown. It is a figure which shows another example of the PWM signal waveform which concerns on this Embodiment. It is a circuit diagram used in simulation. It is a block diagram of a general motor drive device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of a motor drive device according to the present embodiment. FIG. 1 shows an example, and the present invention is not limited to this configuration, and any configuration including a three-phase inverter bridge circuit may be used.

  As shown in FIG. 1, the motor driving device converts a direct current from a three-phase AC power source (power supply) 1 into a direct current, and converts a direct current from the rectifier 2 into an alternating current and outputs the alternating current to the three-phase motor 3. An inverter bridge circuit 4 and a motor control circuit (control circuit) 5 that performs PWM control of the inverter bridge circuit 4 are provided. A smoothing capacitor 6 that smoothes the output (DC voltage) of the rectifier 2 is connected in parallel to the output terminal of the rectifier 2. The inverter bridge circuit 4 has a half-bridge circuit 7 for three phases connected in parallel to the output terminal of the rectifier 2.

  The U-phase half-bridge circuit 7u includes an upper arm (high-side) switching element T1 and a lower arm (low-side) switching element T4 connected in series, and a free-wheeling diode D1, It is configured by connecting D4 in parallel. Similarly, the V-phase half-bridge circuit 7v has an upper arm switching element T2 and a lower arm switching element T5 connected in series, and freewheeling diodes D2 and D5 are connected in parallel to the switching elements T2 and T5, respectively. Connected and configured.

  The W-phase half-bridge circuit 7w includes an upper arm switching element T3 and a lower arm switching element T6 connected in series, and freewheeling diodes D3 and D6 connected in parallel to the switching elements T3 and T6, respectively. Composed. The connection points of the U-phase switching elements T1 and T4, the connection points of the V-phase switching elements T2 and T5, and the connection points of the W-phase switching elements T3 and T6 are the three-phases (not shown) of the three-phase motor 3, respectively. Are mutually connected via an exciting coil.

  The PWM signal is input from the motor control circuit 5 to the three-phase half-bridge circuits 7u-7w. An input line from the motor control circuit 5 is connected to the gates of the switching elements T1 to T6. The switching elements T1 to T6 are switched between an on state and an off state when a PWM signal is applied from the motor control circuit 5. The U-phase current, V-phase current, and W-phase current flowing through the three-phase motor 3 are controlled by turning on / off the switching elements T1-T6. In the present embodiment, PWM control is performed so as to draw a sinusoidal three-phase current waveform (see FIG. 2) in which the U-phase current, the V-phase current, and the W-phase current are each shifted by 120 °.

  When the three-phase motor 3 is driven, a power running operation for supplying power from the inverter bridge circuit 4 to the three-phase motor 3 and a regenerative operation for returning power from the three-phase motor 3 to the inverter bridge circuit 4 are repeated. It is. In the case of power running operation, rapid acceleration is required for the three-phase motor 3, and the power consumption in the inverter bridge circuit 4 also increases. On the other hand, in the case of regenerative operation, the regenerative current returning from the three-phase motor 3 to the smoothing capacitor 6 via the inverter bridge circuit 4 increases as the speed decreases rapidly from high speed rotation.

  In addition, although switching element T1-T6 of this Embodiment was comprised with the power transistor, it is not limited to this structure. The switching element may be a current-voltage control element that can control the current voltage. For example, the switching element may be an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), or a bipolar transistor. The free-wheeling diodes D1 to D6 may be elements that constitute a path for the regenerative current, and a parasitic diode built in the power transistor can also be used.

  Next, PWM control by the motor control circuit will be described. Here, a case where a three-phase current waveform is formed by a three-phase control method and a case where a three-phase current waveform is formed by a two-phase control method will be individually described. FIG. 2 is a diagram showing a three-phase current waveform flowing in the three-phase motor. FIG. 3 is a diagram illustrating an example of a PWM signal waveform of a three-phase control method. FIG. 4 is a diagram illustrating an example of a PWM signal waveform of the two-phase control method. FIG. 5 is a diagram illustrating another example of the PWM signal waveform of the two-phase control method.

  FIG. 6 is a diagram illustrating an example when switching the PWM control pattern of the two-phase control method. FIG. 7 is a diagram illustrating another example when switching the PWM control pattern of the two-phase control method. In FIG. 2, a solid line U indicates a change in U-phase current, a broken line V indicates a change in V-phase current, and an alternate long and short dash line W indicates a change in W-phase current. 3 to 7, U, V, and W indicate the upper arm U-phase, V-phase, and W-phase, respectively, U-lower, V-lower, and W-lower indicate the U-phase and V-phase of the lower arm. , W phase is shown respectively.

  As shown in FIG. 2, the three-phase current waveform is formed by shifting a U-phase current, a V-phase current, and a W-phase current that change in a sine wave shape by 120 °. Using the U-phase current as a reference, the current value of the U-phase current becomes 0 near the phase 0 °, the current value of the V-phase current becomes 0 near the phase 120 °, and the current of the W-phase current near the phase 240 °. The value becomes 0. Thus, in the three-phase current waveform obtained by shifting the current phase of each phase by 120 °, the current value of any one phase changes to 0 every 60 °. This three-phase current waveform is formed by a PWM signal input to the inverter bridge circuit 4.

  The three-phase control method will be described with reference to FIG. In the three-phase control method, an ON section and an OFF section are set for each of the three phases of the U phase, the V phase, and the W phase, and the switching of the three-phase switching element T is generated within the pulse period, thereby generating a three-phase current. This is a control method for forming a waveform. For example, the vicinity of the phase 120 ° of the three-phase current waveform indicated by P1 in FIG. 2 is formed by switching based on the PWM signal waveform shown in FIG. In the vicinity of 120 ° phase, the upper arm U phase, V phase, and W phase duty ratios are set to 50%, 50%, and 50% or lower, respectively, and the lower arm U phase, V phase, and W phase duty ratios. Are set to 50% or less, 50%, or 50% or more, respectively.

  In step A, the PWM signals for all three phases U, V, and W of the upper arm are set to Low, and the PWM signals for all three phases U, V, and W of the lower arm are set to High. Set to Therefore, the switching elements T1-T3 are controlled to the off state, and the switching elements T4-T6 are controlled to the on state. As a result, the current flowing through the three-phase motor 3 is commutated to the switching element T6, the return diode D4, the three-phase motor 3, or the switching element T6, the return diode D5, and the three-phase motor 3. Note that commutation indicates a flow from one path to another path, and in this embodiment, a flow that does not affect the driving of the three-phase motor 3.

  In the section of Step B, in the upper arm, one of the U-phase, V-phase, and W-phase PWM signals is set to High, and the remaining two-phase PWM signals are set to Low. In the lower arm, the one-phase PWM signal set to High in the upper arm is set to Low, and the remaining two-phase PWM signals set to Low in the upper arm are set to High. In FIG. 3, the U-phase PWM signal of the upper arm, the V-phase and W-phase of the lower arm are set to High, and the PWM signal of the V-phase, W-phase and U-phase of the lower arm are set to Low. Yes. Therefore, the switching elements T1, T5, and T6 are controlled to be in the on state, and the switching elements T2 to T4 are controlled to be in the off state. As a result, current flows from the switching element T1 of the upper arm through the three-phase motor 3 toward the switching elements T5 and T6 of the lower arm, and the three-phase motor 3 is driven.

  In Step C, in the upper arm, any two-phase PWM signal of U phase, V phase, and W phase is set to High, and the remaining one-phase PWM signal is set to Low. In the lower arm, the two-phase PWM signal set to High in the upper arm is set to Low, and the remaining one-phase PWM signal set to Low in the upper arm is set to High. In FIG. 3, the upper arm U-phase, V-phase, and lower-arm W-phase PWM signals are set to High, and the upper-arm W-phase, lower-arm U-phase, and V-phase PWM signals are set to Low. Yes. Accordingly, the switching elements T1, T2, and T6 are controlled to be in the on state, and the switching elements T3 to T5 are controlled to be in the off state. As a result, current flows from the switching elements T1 and T2 on the upper arm through the three-phase motor 3 toward the switching element T6 on the lower arm, and the three-phase motor 3 is driven.

  In step D, the PWM signals of the upper arm U-phase, V-phase, and W-phase are all set to High, and the lower-arm U-phase, V-phase, and W-phase PWM signals are all low. Set to Therefore, the switching elements T1-T3 are controlled to be in the on state, and the switching elements T4-T6 are controlled to be in the off state. As a result, the current flowing through the three-phase motor 3 is commutated to the switching element T1, the three-phase motor 3, the return diode D2, or the switching element T1, the three-phase motor 3, and the return diode D3. As described above, the three-phase control method is controlled by a combination of processes from Step A to Step D.

  As shown in FIG. 3, processing is performed in the order of step A, step B, step C, step D, step D, step C, step B, and step A in the vicinity of the phase 120 ° of the three-phase current waveform. At this time, the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw flowing through the three-phase motor 3 have a tendency as shown in the lower half of FIG. In this three-phase control method, since the switching elements T of all three phases are switched on and off, the number of switching is large and the switching loss is large. For this reason, a two-phase control method that can reduce the number of times of switching compared to a three-phase control method has been proposed.

  Subsequently, the two-phase control method will be described with reference to FIGS. 4 and 5. In the two-phase control method, one of the upper arm and the lower arm sets a normally on section for one of the U phase, V phase, and W phase, and the other arm sets a normally off section for the one phase. . That is, the two-phase control method is a control method that forms a three-phase current waveform by two-phase control by eliminating the switching of the switching element T of any one of the U-phase, V-phase, and W-phase. For example, the vicinity of the phase of 90 ° of the three-phase current waveform indicated by P2 in FIG. 2 is formed by switching based on the PWM signal waveform shown in FIG. Further, the vicinity of the phase 270 ° of the three-phase current waveform shown at P3 in FIG. 2 is formed by switching based on the PWM signal waveform shown in FIG.

  As shown in FIGS. 4 and 5, the two-phase control method is controlled by a combination of Step B and Step D described above or a combination of Step A and Step C described above. In the combination of Step B and Step D, any one of the U-phase, V-phase, and W-phase PWM signals is set to High for one pulse period in the upper arm, and this one-phase PWM signal is 1 in the lower arm. Set to Low over the pulse period. In the combination of Step A and Step C, the PWM signal of any one of the U phase, V phase, and W phase is set to Low for one pulse period in the upper arm, and this one-phase PWM signal is set in the lower arm. Is set to High for one pulse period.

  As shown in FIG. 4, processing is performed in the order of Step B, Step D, Step D, and Step B in the vicinity of the phase of 90 ° of the three-phase current waveform. Here, the U-phase PWM signal of the upper arm is set to High for one pulse period, and the U-phase PWM signal of the lower arm is set to Low for one pulse period. Therefore, a constantly on section is set for the U-phase switching element T1, and a normally off section is set for the U-phase switching element T4. At this time, the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw flowing through the three-phase motor 3 have a tendency as shown in the lower half of FIG.

  As shown in FIG. 5, processing is performed in the order of step A, step C, step C, and step A in the vicinity of the phase 270 ° of the three-phase current waveform. Here, the U-phase PWM signal of the upper arm is set to Low for one pulse period, and the U-phase PWM signal of the lower arm is set to High for one pulse period. Therefore, a normally-off section is set for the U-phase switching element T1, and a normally-on section is set for the U-phase switching element T4. At this time, the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw flowing through the three-phase motor 3 have a tendency as shown in the lower half of FIG.

  By the way, although the number of times of switching can be reduced by using the two-phase control method, the current value becomes 0 like the phase of the three-phase current waveform in the vicinity of 60 °, 120 °, 180 °, 240 °, 300 °, 360 °. There is a problem that it is difficult to apply to the phase. For example, as shown in FIG. 6, the first PWM control pattern is repeated for two phases from phase 60 ° to phase 120 °, and the second PWM control pattern is repeated from phase 120 ° to phase 180 °. Two-phase control. In the vicinity of a phase of 120 ° where the switching of the PWM control pattern occurs, the pulse width (output voltage command value) changes abruptly. Therefore, the two-phase control method cannot be appropriately controlled.

  In this case, a configuration in which the three-phase control PWM control pattern is temporarily sandwiched between the two-phase control PWM control pattern switching portions is conceivable. For example, as shown in FIG. 7, the first PWM control pattern is repeatedly controlled in two phases from around 60 ° to around 120 °, and the second PWM control pattern from around 120 ° to around 180 °. Are repeated to perform two-phase control, and at a phase of 120 °, three-phase control is performed with the third PWM control pattern. With such a configuration, a sudden change in the pulse width at the time of switching the PWM control pattern is suppressed, and it is possible to cope with a phase where the current value of the three-phase current waveform becomes zero.

  However, in such a configuration, since it is necessary to frequently switch the control method in the vicinity of the phase of 120 °, there is a problem that the control configuration becomes complicated. Further, at the time of switching from the first PWM control pattern to the third PWM control pattern, as shown by the broken line S, switching occurs and the switching loss increases. The present applicant has arrived at the present invention in order to improve the above-mentioned problems caused by the combination of the two-phase control method and the three-phase control method. Hereinafter, the PWM control by the motor control circuit 5 of the present invention will be described in detail.

  FIG. 8 is a diagram illustrating an example of a PWM signal waveform according to the present embodiment. FIG. 9 shows an example of a PWM signal waveform in which the commutation section according to the present embodiment is an off section. 8 and 9, U, V, and W indicate the U-phase, V-phase, and W-phase of the upper arm, respectively, and U-lower, V-lower, and W-lower indicate the U-phase and V-phase of the lower arm, respectively. , W phase is shown respectively.

  In the PWM control according to the present embodiment, control is performed such that the above-described three-phase control method and two-phase control method are switched every 60 °. For example, as shown in FIG. 8, three-phase control is performed up to a phase of 60 ° -120 °, and two-phase control is performed up to a phase of 120 ° -180 °. Therefore, in the three-phase control up to the phase 60 ° -120 °, the process is repeated in the order of step A, step B, step C, step D, step D, step C, step B, and step A. On the other hand, in the two-phase control up to the phase 120 ° -180 °, the process is repeated in the order of step A, step C, step C, and step A.

  Accordingly, when switching from the three-phase control method to the two-phase control method, step A of the three-phase control method and step A of the two-phase control method are continuous. For this reason, control is performed such that the ON section of the three-phase control method and the always-on section of the two-phase control method are continuous, and the OFF section of the three-phase control method and the always-OFF section of the two-phase control method are continuous. Therefore, the switching frequency at the time of switching between the three-phase control method and the two-phase control method is reduced, and the switching loss is reduced. In the PWM control according to the present embodiment, the phases 60 ° -120 °, 180 ° -240 °, and 300 ° -360 ° of the three-phase current waveform are controlled by the three-phase control method, and the phase of the three-phase current waveform is 0 °. By controlling −60 °, 120 ° -180 °, and 240 ° -300 ° by the two-phase control method, Step A can be continued when the control method is switched.

  In addition, the phase 0 ° -60 °, 120 ° -180 °, 240 ° -300 ° of the three-phase current waveform is controlled by the three-phase control method, and the phase 60 ° -120 °, 180 ° -240 °, 300 °- It is also possible to control 360 ° by a two-phase control method. In this case, when the control method is switched, the step D is continued, so that the three-phase control method ON section and the two-phase control method always-on section are continuous, the three-phase control method OFF section and the two-phase control method always-on. It is controlled so that the off period is continuous. Therefore, the switching frequency at the time of switching between the three-phase control method and the two-phase control method is reduced, and the switching loss is reduced. In the PWM control according to the present embodiment, since the control method is switched every 60 °, only the section that cannot be controlled by the two-phase control method is temporarily switched to the three-phase control method, and the two-phase control is performed again. The control configuration does not become complicated as compared with the configuration returned to the system.

  Next, with reference to FIG.1 and FIG.8, the three-phase control to phase 60 degrees -120 degrees is demonstrated. In step A, the PWM signals for all three phases U, V, and W of the upper arm are set to Low, and the PWM signals for all three phases U, V, and W of the lower arm are set to High. Set to Therefore, the switching elements T1-T3 are controlled to the off state, and the switching elements T4-T6 are controlled to the on state. As a result, the current flowing through the three-phase motor 3 is commutated to the switching element T6, the return diode D4, the three-phase motor 3, or the switching element T6, the return diode D5, and the three-phase motor 3.

  Next, in step B, the upper arm U-phase, lower arm V-phase, and W-phase PWM signals are set to High, and the upper arm V-phase, W-phase, and lower-arm U-phase PWM signals are set to high. It is set to Low. Therefore, the switching elements T1, T5, and T6 are controlled to be in the on state, and the switching elements T2 to T4 are controlled to be in the off state. As a result, current flows from the switching element T1 of the upper arm through the three-phase motor 3 toward the switching elements T5 and T6 of the lower arm, and the three-phase motor 3 is driven.

  Next, in the section of step C, the U-phase, V-phase, and W-phase PWM signals of the upper arm are set to High, and the upper-arm W-phase, lower-arm U-phase, and V-phase PWM signals are set to high. It is set to Low. Accordingly, the switching elements T1, T2, and T6 are controlled to be in the on state, and the switching elements T3 to T5 are controlled to be in the off state. As a result, current flows from the switching elements T1 and T2 on the upper arm through the three-phase motor 3 toward the switching element T6 on the lower arm, and the three-phase motor 3 is driven.

  Next, in the section of Step D, the PWM signals of the U-phase, V-phase, and W-phase of the upper arm are all set to High, and the PWM signals of all three phases of the U-phase, V-phase, and W-phase of the lower arm are set. The signal is set to Low. Therefore, the switching elements T1-T3 are controlled to be in the on state, and the switching elements T4-T6 are controlled to be in the off state. As a result, the current flowing through the three-phase motor 3 is commutated to the switching element T1, the three-phase motor 3, the return diode D2, or the switching element T1, the three-phase motor 3, and the return diode D3. Subsequently, processing is performed in the order of Step D, Step C, Step B, and Step A. The process is repeated with these 8 steps as one cycle.

  Next, two-phase control up to a phase of 120 ° to 180 ° will be described. In step A, the PWM signals for all three phases U, V, and W of the upper arm are set to Low, and the PWM signals for all three phases U, V, and W of the lower arm are set to High. Set to Therefore, the switching elements T1-T3 are controlled to the off state, and the switching elements T4-T6 are controlled to the on state. As a result, the current flowing through the three-phase motor 3 is commutated to the switching element T6, the return diode D4, the three-phase motor 3, or the switching element T6, the return diode D5, and the three-phase motor 3.

  Next, in the section of step C, the U-phase, V-phase, and W-phase PWM signals of the upper arm are set to High, and the upper-arm W-phase, lower-arm U-phase, and V-phase PWM signals are set to high. It is set to Low. Accordingly, the switching elements T1, T2, and T6 are controlled to be in the on state, and the switching elements T3 to T5 are controlled to be in the off state. As a result, current flows from the switching elements T1 and T2 on the upper arm through the three-phase motor 3 toward the switching element T6 on the lower arm, and the three-phase motor 3 is driven. Subsequently, processing is performed in the order of step C and step A. Then, the process is repeated with these four steps as one cycle.

  Thus, in the PWM control according to the present embodiment, the three-phase control method and the two-phase control method are switched every 60 °, and the occurrence of switching at this switching timing is suppressed, thereby facilitating the control configuration. Switching loss is reduced.

  In the PWM control described above, the shortest ON section among the U phase, the V phase, and the W phase is set as a commutation section that does not affect the driving of the three-phase motor 3. As shown in FIG. 9, this commutation section can be set as an off section. Therefore, the switching frequency can be reduced and the switching loss can be further reduced without affecting the driving of the three-phase motor 3. In addition, since the ON period (operation time) of the switching element T is reduced, saturation loss can be reduced. Note that all commutation sections may be set as off sections, or only a part of the commutation sections may be set as off sections.

  By the way, when the phase of the three-phase current waveform is around 60 °, 120 °, 180 °, 240 °, 300 °, 360 °, any of the U-phase current Iu, V-phase current Iv, and W-phase current Iw is 0. Three-phase control is performed so as to approach. For example, as shown in FIG. 3, near the phase of 120 ° of the three-phase current waveform, the current value of the V-phase current Iv is controlled to approach 0 (see FIG. 2). The phase current Iv does not flow. Therefore, as shown in FIG. 10, even if the ON section immediately before the current value of the V-phase current Iv approaches 0 is set as the OFF section, the driving of the three-phase motor 3 is not affected. Therefore, the switching frequency can be reduced and the switching loss can be further reduced without affecting the driving of the three-phase motor 3.

  The ON phase of the V phase of one pulse (one pulse period) immediately before the current value of the three-phase current waveform becomes 0 may be set as the OFF interval, or the current value of the three-phase current waveform becomes 0. The immediately preceding V-pulse ON section of several pulses (several pulse periods) may be set as the OFF section. In addition, since the ON period (operation time) of the switching element T is reduced, saturation loss can be reduced. At this time, the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw flowing through the three-phase motor 3 have a tendency as shown in the lower half of FIG. 10, and as shown in the lower half of FIG. Therefore, a temporary increase / decrease in the V-phase current Iv can be suppressed, and a wasteful current can be suppressed.

  In addition, in the configuration in which the three-phase control method and the two-phase control method are switched every 60 °, the ON interval of one pulse or a plurality of pulses immediately before the current value of any phase of the three-phase current waveform becomes 0 is the OFF interval. Although the configuration to be set is applied, it is not limited to this configuration. It is also possible to apply a configuration in which the ON section of one pulse or a plurality of pulses immediately before the current value of one phase of the three-phase current waveform becomes 0 is set as the OFF section to the normal three-phase control method.

  With reference to FIG. 11, a simulation result of the above-described PWM control will be described. FIG. 11 is a circuit diagram used in the simulation. In the following simulation, three PWM control patterns were implemented. The first PWM control pattern is normal PWM control using only the three-phase control method. The second PWM control pattern is PWM control in which the commutation section is set to the off section in the two-phase control method. The third PWM control pattern is PWM control in which the one phase where the current value of the three-phase current waveform is 0 in the three-phase control method is set as the off section.

  That is, the first PWM control pattern assumes normal control as shown in FIG. The second PWM control pattern assumes a state where the three-phase control method is switched to the two-phase control method as shown in the right half of FIG. As shown in FIG. 10, the third PWM control pattern assumes a state in which an off section is always set for the V phase in the three-phase control method.

  The simulation circuit shown in FIG. 11 corresponds to the overall configuration diagram shown in FIG. In this simulation circuit, the power supply V1 is set to 280 [V], and IGBTs are used as the switching elements T1-T6. The low level of the gate drive voltage of the IGBT is −5 [V], and the High level is 15 [V]. Further, the gate resistances R1-R6 for driving each IGBT were set to 30 [Ω]. Furthermore, the inductance components L1-L3 of the three-phase motor 3 were set to 1500 [μH], and the internal resistances R7-R9 of the three-phase motor 3 were set to 1.03 [Ω].

  Also, PWM_U_UP, PWM_V_UP, PWM_W_UP, PWM_U_DOWN, PWM_V_DOWN, and PWM_W_DOWN in the figure indicate PWM signal sources, respectively. With the above configuration, one pulse period of the PWM signal was set to 90 [μs], and two periods were observed, and an average value of switching losses of the switching elements T1 to T6 was calculated. Here, in the first PWM control pattern, the ON times of the switching elements T1 to T6 are set to 55 [μs], 33 [μs], 33 [μs], 57 [μs], 35 [μs], and 35 [μs], respectively. μs]. As a result, the average switching loss of the first PWM control pattern was 5.43 [W].

  In the second PWM control pattern, the ON times of the switching elements T1, T2, and T5 are set to 18 [μs], 8 [μs], and 10 [μs], and the switching elements T3 and T4 are always set to OFF. The switching element T6 was always turned on. As a result, the average switching loss of the second PWM control pattern was 4.22 [W], which was reduced by about 1.2 [W] in two cycles compared to the first PWM control pattern. Therefore, it has been confirmed that the control method in which the three-phase control method and the two-phase control method are switched every 60 ° reduces the switching loss as a whole as compared with the configuration in which only the three-phase control is applied.

  In the third PWM control pattern, the ON times of the switching elements T1, T3, T4, and T6 are set to 53 [μs], 33 [μs], 55 [μs], and 35 [μs], and the switching elements T2, T5 was always set to off. As a result, the average switching loss of the third PWM control pattern was 5.42 [W], which was reduced by about 0.1 [W] in two cycles as compared with the first PWM control pattern. Therefore, in the three-phase control method, in the control method in which one phase where the current value of the three-phase current waveform is 0 is set as the off section, the switching loss as a whole is reduced as compared with the normal three-phase control configuration. Was confirmed.

  In addition, since this simulation result measured the switching loss for 2 periods, it is assumed that an effect becomes large when PWM control is repeated by the increase in the drive time of the three-phase motor 3. FIG.

  As described above, according to the motor drive device according to the present embodiment, since the control is performed by switching between the three-phase control method and the two-phase control method, compared with the configuration in which the PWM control is performed only by the three-phase control method. Switching loss can be reduced by reducing the number of times of switching. Also, switching loss can be reduced because switching is performed so as not to occur even when switching between the three-phase control method and the two-phase control method. Furthermore, since the two-phase control method and the three-phase control method are switched every 60 °, the control configuration does not become complicated. Therefore, power loss due to switching loss can be reduced with a simple control configuration.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in the above-described embodiment, the DC voltage is supplied from the three-phase AC power source 1 to the inverter bridge circuit 4 via the rectifier 2, but the present invention is not limited to this configuration. Any configuration may be used as long as a DC voltage is supplied to the inverter bridge circuit 4, and a DC power source may be provided instead of the three-phase AC power source 1 and the rectifier 2.

  As described above, the present invention has an effect that switching loss can be reduced while facilitating the control configuration, and is particularly useful for a motor drive device that controls an inverter by a PWM switching method.

1 Three-phase AC power supply
2 Rectifier 3 Three-phase motor 4 Inverter bridge circuit 5 Motor control circuit (control circuit)
6 Smoothing capacitor 7u-7w Half bridge circuit T1-T6 Switching element D1-D6 Reflux diode

Claims (4)

Consists of an upper arm and a lower arm each having U-phase, V-phase, and W-phase switching elements, and converts the direct current supplied from the power supply side to alternating current by the on / off operation of the switching elements and outputs it to a three-phase motor. An inverter bridge circuit to
A control circuit that performs PWM control of the ON section or the OFF section of the switching element so that the U-phase current, the V-phase current, and the W-phase current flowing through the three-phase motor each have a sinusoidal current waveform shifted by 120 °. Prepared,
The control circuit includes a three-phase control method for setting an on section and an off section for each phase of the upper arm and the lower arm, and in any one of the upper arm and the lower arm, a U phase, a V phase, A two-phase control method in which a constantly on section is set for one phase of the W phase and a normally off section is set for the one phase in either one of the upper arm and the lower arm is set every 60 °. To switch to
The switching timing between the three-phase control method and the two-phase control method is controlled so that the on-section and the always-on section are continuous, and the off-section and the always-off section are continuous. A motor drive device.   2. The control circuit according to claim 1, wherein in the three-phase control method and / or the two-phase control method, the section having the shortest on section among the U phase, the V phase, and the W phase is set as an off section. The motor drive device described in 1.   2. The control circuit according to claim 1, wherein, in the three-phase control method, the on period of one pulse or a plurality of pulses immediately before the current value of the current waveform of each phase becomes 0 is set as an off period. The motor drive device according to claim 2. Consists of an upper arm and a lower arm each having U-phase, V-phase, and W-phase switching elements, and converts the direct current supplied from the power supply side to alternating current by the on / off operation of the switching elements and outputs it to a three-phase motor. An inverter bridge circuit to
A control circuit that performs PWM control of the ON section or the OFF section of the switching element so that the U-phase current, the V-phase current, and the W-phase current flowing through the three-phase motor each have a sinusoidal current waveform shifted by 120 °. Prepared,
The control circuit sets an ON section of one pulse or a plurality of pulses immediately before the current value of the current waveform of each phase becomes 0 as an OFF section.

Images