JP2015142432A - Motor control device and motor control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor control device and a motor control method that can prevent erroneous detection of overcurrent caused by linking and suppress increase of motor current occurring due to delay of a filter circuit.SOLUTION: A control device (8) of a motor control device (1) has an overcurrent determining unit (80) for determining, every carrier period of pulse width modulation, a time when filtered motor current from which a high frequency component is reduced by a filter circuit (6) falls into an overcurrent state that the filtered motor current exceeds a permissible value of the motor current, a carrier frequency switching unit (82) for comparing a carrier frequency used for pulse width modulation with a carrier frequency at the time when the overcurrent state is determined by the overcurrent determining unit (80), and switching the carrier frequency to a low-period carrier frequency, and a duty ratio setting unit (83) for setting a duty ratio to a smaller value than a target duty ratio set according to an output required to the motor (3) when the overcurrent state is determined by the overcurrent determining unit (80).

Description

  The present invention relates to a motor control device and a motor control method capable of determining an overcurrent state of a motor current.

  As an example of the motor control device, there are the inventions described in Patent Documents 1 and 2. The invention described in Patent Document 1 limits the duty ratio of the PWM signal according to the detected motor current when an overcurrent flows through the motor. The invention described in Patent Document 1 attempts to continue driving the motor while suppressing the motor current by controlling opening and closing of the semiconductor element of the motor drive circuit based on the limited duty ratio.

  On the other hand, in the invention described in Patent Document 2, a filter circuit (low-pass filter) is provided at the output of a resistor that detects a motor current. The invention described in Patent Document 2 compares the output of the filter circuit with the overcurrent level, and stops driving the switching element when the output of the filter circuit exceeds the overcurrent level. As a result, the invention described in Patent Document 2 attempts to prevent erroneous detection of overcurrent due to linking.

JP 2005-199899 A JP 2004-312955 A

  However, the invention described in Patent Document 2 detects an overcurrent using the output of the filter circuit. Since the output of the filter circuit is delayed compared to the actual motor current, the motor current continues to flow until an overcurrent is detected. Therefore, when the motor current is large, such as when the motor is started or when the motor is locked, there is a possibility that the motor current will continue to increase beyond the current value that is originally desired to be limited.

  The present invention has been made in view of such circumstances, and a motor control device capable of preventing an erroneous detection of an overcurrent due to linking and suppressing an increase in motor current caused by a delay of a filter circuit. It is another object of the present invention to provide a motor control method.

  The motor control device according to claim 1 is provided between the DC power source and the motor, and converts the DC power of the DC power source into AC power by opening and closing a switching element, and supplies the motor with power. A motor current detection circuit for detecting a motor current flowing in the armature winding of the motor; a filter circuit for reducing a high frequency component contained in the detection signal of the motor current; and a duty ratio varied by a pulse width modulation method. A control device that controls opening and closing of the switching element based on a duty ratio, and the control device is an overcurrent in which a filtered motor current in which a high frequency component is reduced by the filter circuit exceeds an allowable value of the motor current. An overcurrent discrimination unit that discriminates when the state is reached for each carrier period of the pulse width modulation, and the overcurrent discrimination unit A carrier frequency switching unit that switches a carrier frequency used for the pulse width modulation to a carrier frequency having a lower period than the carrier frequency at the time of the determination when it is determined that the current state is in a flow state, and the overcurrent determination unit A duty ratio setting unit that sets the duty ratio to be smaller than a target duty ratio that is set in accordance with an output required for the motor when it is determined that the overcurrent state has occurred.

  The control device of the motor control device according to claim 1 includes an overcurrent determination unit. The overcurrent determination unit determines, for each carrier period of pulse width modulation, when the filtered motor current whose high-frequency component has been reduced by the filter circuit is in an overcurrent state exceeding the allowable value of the motor current. Therefore, the motor control device according to claim 1 can prevent erroneous detection of overcurrent due to linking.

  The control device also includes a carrier frequency switching unit and a duty ratio setting unit. When it is determined that an overcurrent state has occurred, the carrier frequency switching unit switches the carrier frequency used for pulse width modulation to a carrier frequency having a lower period than the carrier frequency at the time of the determination. The duty ratio setting unit sets the duty ratio to be smaller than the target duty ratio set in accordance with the output required for the motor when it is determined that the overcurrent state has occurred. Therefore, the motor control device according to the first aspect can reduce the number of times the switching element transitions to the open state and the switching element open time when an overcurrent is detected. As a result, the motor control device according to the first aspect can suppress an increase in motor current caused by the delay of the filter circuit.

  A motor control device according to a second aspect is the motor control device according to the first aspect, wherein an allowable value of the motor current is set in accordance with a rated current of the motor. Thus, the overcurrent determination unit can determine the overcurrent state using an allowable value set in accordance with the rated current of the motor. Therefore, the motor control device according to claim 2 can perform an appropriate overcurrent detection in accordance with the physique of the motor.

  The motor control device according to claim 3 is the motor control device according to claim 1 or 2, wherein the carrier frequency switching unit continuously enters the overcurrent state over a plurality of cycles of the carrier cycle. When determined, the carrier frequency is switched to the low cycle carrier frequency. As a result, the motor control device according to claim 3 can prevent the frequency of the carrier frequency used for the pulse width modulation from being frequently switched when the motor current changes in the vicinity of the allowable value in the overcurrent state. , Control stability is improved.

  The motor control device according to claim 4 is the motor control device according to any one of claims 1 to 3, wherein when the carrier frequency switching unit is determined to be in the overcurrent state, The carrier frequency used for the pulse width modulation is switched to the carrier frequency of the low cycle step by step. Thus, the motor control device according to the fourth aspect can prevent the carrier frequency used for the pulse width modulation from being suddenly switched to the carrier frequency having a low cycle, and the control stability is improved.

  The motor control device according to claim 5 is the motor control device according to any one of claims 1 to 4, wherein the filter circuit performs the switching when the switching element transitions from a closed state to an open state. The time constant is set so that the overshoot of the motor current generated by the current response of the element and the inductance of the armature winding can be reduced. Thus, the motor control device according to the fifth aspect can efficiently reduce the high-frequency component included in the motor current detection signal.

  A motor control device according to a sixth aspect is the motor control device according to any one of the first to fifth aspects, wherein when the overcurrent state is determined, the switching element is closed from the open state. The timing of transition to the state is set according to the detection delay of the motor current by the filter circuit. As a result, the motor control device according to the sixth aspect can set the time for which the switching element is open when it is determined that the overcurrent state is set to the minimum necessary time. Therefore, the motor control device according to claim 6 can further suppress an increase in motor current caused by delay of the filter circuit.

  The motor control method according to claim 7 is provided between the direct current power source and the motor, and converts the direct current power of the direct current power source into alternating current power by opening and closing a switching element to supply the motor, A motor current detection circuit for detecting a motor current flowing in the armature winding of the motor; a filter circuit for reducing a high frequency component contained in the detection signal of the motor current; and a duty ratio varied by a pulse width modulation method. And a control device that controls opening and closing of the switching element based on a duty ratio, and a motor control method for controlling the motor, wherein the motor current after filtering in which a high-frequency component is reduced by the filter circuit is the motor current Overcurrent detection step for determining for each carrier period of the pulse width modulation when an overcurrent state exceeding the allowable value is reached. And when it is determined in the overcurrent determination step that the overcurrent state has been reached, the carrier frequency used to switch the carrier frequency used for the pulse width modulation to a carrier frequency having a lower period than the carrier frequency at the time of the determination The duty ratio is set smaller than the target duty ratio set according to the output required for the motor when it is determined by the switching step and the overcurrent determination step that the overcurrent state has been reached. A duty ratio setting step.

  The motor control method according to claim 7 includes an overcurrent determination step. The overcurrent discrimination step discriminates every pulse width modulation carrier period when the filtered motor current in which the high frequency component is reduced by the filter circuit is in an overcurrent state exceeding the allowable value of the motor current. Therefore, the motor control method according to claim 1 can prevent erroneous detection of overcurrent due to linking.

  According to a seventh aspect of the present invention, the motor control method includes a carrier frequency switching step and a duty ratio setting step. In the carrier frequency switching step, when it is determined that an overcurrent state has occurred, the carrier frequency used for pulse width modulation is switched to a carrier frequency having a lower period than the carrier frequency at the time of determination. The duty ratio setting step sets the duty ratio to be smaller than the target duty ratio set according to the output required for the motor when it is determined that an overcurrent state has occurred. Therefore, the motor control method according to claim 7 can reduce the number of times the switching element transitions to the open state and the switching element open time when an overcurrent is detected. As a result, the motor control method according to claim 7 can suppress an increase in the motor current caused by the delay of the filter circuit.

1 is a configuration diagram illustrating an example of a motor control device 1. FIG. It is a block diagram which shows an example of a control block. It is a timing chart which shows an example of the motor current when not changing carrier frequency at the time of overcurrent detection, an overcurrent detection output, and a motor drive output. It is a timing chart which shows an example of a motor current at the time of changing a carrier frequency into a low cycle carrier frequency at the time of overcurrent detection, an overcurrent detection output, and a motor drive output. It is a flowchart which shows an example of the change procedure of a carrier frequency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each figure is a conceptual diagram and does not define the dimensions of the detailed structure.

<Motor control device 1>
FIG. 1 is a configuration diagram illustrating an example of a motor control device 1. As shown in the figure, the motor control device 1 of this embodiment includes a power conversion device 4 provided between a DC power supply 2 and a motor 3, a motor current detection circuit 5, a filter circuit 6, and a comparison circuit 7. And a control device 8.

  The DC power supply 2 is a power supply device that supplies DC power. For example, a known lead storage battery (battery), a lithium ion battery, an electric double layer capacitor, or the like can be used. The DC power source 2 is not limited to the above embodiment as long as it can supply DC power. For example, the DC power can be generated by smoothing the AC power of the AC power source with a smoothing circuit. Note that the DC power supply 2 can be connected in parallel with a smoothing capacitor, and can reduce the ripple voltage.

  The motor 3 is an object to be controlled by the motor control device 1, and for example, a known brushless motor can be used. The motor 3 includes a stator 31 in which armature windings 32U to 32W are Y-connected, and a rotor (not shown). The armature windings 32U to 32W constitute a U-phase winding, a V-phase winding, and a W-phase winding in this order. One end side of the U-phase armature winding 32U is connected to the U-phase terminal 33U, and the other end side of the U-phase armature winding 32U is connected to the neutral point 33N. The same applies to the V phase and the W phase.

  The armature windings 32U to 32W can be wound by a known method such as concentrated winding or distributed winding. Further, a plurality of permanent magnets corresponding to predetermined magnetic poles are embedded in the rotor core. Note that the number of poles and the number of slots of the stator 31 are not limited. Further, the armature windings 32U to 32W may be Δ-connected.

  The power converter 4 converts the DC power of the DC power source 2 into AC power and supplies the motor 3 with power by opening and closing the switching elements 41UU to 41WL. The power conversion device 4 is provided between the DC power supply 2 and the motor 3, and for example, a three-phase bridge circuit can be used. As shown in the figure, in the three-phase bridge circuit, six switching elements 41UU, 41UL, 41VU, 41VL, 41WU, and 41WL are bridge-connected. In addition, the power converter device 4 is not limited to a three-phase bridge circuit, For example, a well-known H type bridge circuit can also be used.

  As the switching elements 41UU to 41WL, for example, known field effect transistors (FETs) can be used. As shown in the figure, the switching elements 41UU to 41WL are provided with free-wheeling diodes. As the free wheel diode, the body diode (parasitic diode) of the switching elements 41UU to 41WL can be used. The reflux diode can be provided separately and can be connected in parallel to the switching elements 41UU to 41WL.

  As shown in the figure, a U-phase positive switching element 41UU and a U-phase ground switching element 41UL are connected in series between the positive terminal 2U and the ground terminal 2L of the DC power supply 2. A U-phase output terminal 42U is provided between the switching elements 41UU and 41UL. The same applies to the V phase and the W phase. The first subscripts U, V, and W of the switching elements 41UU to 41WL indicate phases, the second subscript U indicates the positive side, and L indicates the ground side.

  The U-phase output terminal 42U is connected to the U-phase terminal 33U of the stator 31 by a power line 43U. Similarly, the V-phase output terminal 42V is connected to the V-phase terminal 33V of the stator 31 by a power line 43V. The W-phase output terminal 42W is connected to the W-phase terminal 33W of the stator 31 by a power line 43W.

  Switching elements 41UU to 41WL are independently controlled to be in an open state or a closed state by control signals 8UU to 8WL transmitted from control device 8. In the figure, the control signal for the switching element 41UU is indicated by a control signal 8UU, and the control signal for the switching element 41UL is indicated by a control signal 8UL. The same applies to the V phase and the W phase. Each of the phase terminals 33U, 33V, 33W of the stator 31 has three states depending on whether the switching elements 41UU to 41WL are open or closed.

  U-phase terminal 33U is constrained to power supply voltage VBAT when U-phase positive switching element 41UU is open and U-phase ground switching element 41UL is closed. U-phase terminal 33U is constrained to 0 voltage when U-phase positive side switching element 41UU is closed and U-phase ground side switching element 41UL is open. U-phase terminal 33U is in a high-impedance state when U-phase positive switching element 41UU and U-phase ground switching element 41UL are both closed. The same applies to the V-phase terminal 33V and the W-phase terminal 33W.

  The control device 8 can perform various motor drive controls including 120 ° energization control and vector control. In the 120 ° energization control, the energized phases are sequentially switched at a 60 ° electrical angle pitch according to the rotational position of the rotor. For example, when the control device 8 opens the U-phase positive side switching element 41UU and the V-phase ground side switching element 41VL, a motor current flows through the armature windings 32U and 32V.

  When the rotor rotates 60 degrees in electrical angle, control device 8 opens U-phase positive side switching element 41UU and W-phase ground side switching element 41WL. At this time, a motor current flows through the armature windings 32U and 32W. That is, the U-phase armature winding 32U is energized 120 ° in electrical angle. The same applies to the V phase and the W phase. The control device 8 can also perform wide-angle energization control that overlaps energization to a plurality of phases exceeding the electrical angle of 120 °. The rotational position of the rotor can be detected using a position detector such as a hall sensor. The rotational position of the rotor may be estimated based on an induced voltage generated when the phase terminals 33U, 33V, and 33W are in a high impedance state.

  In the vector control, the three-phase motor current is divided into direct current components (field component and torque component) in two directions and controlled. As a result, the control device 8 can perform smoother sine wave drive, and can achieve higher efficiency, lower vibration, lower noise, and the like compared to rectangular wave drive such as 120 ° energization control. . In addition, the control device 8 can variably control the duty ratio in order to adjust the output torque. In the present embodiment, the control device 8 varies the duty ratio by a pulse width modulation (PWM) method, and controls the switching elements 41UU to 41WL to open and close based on the duty ratio.

  The target duty ratio DF1 is instructed by a control device (not shown) of the control device 8. The target duty ratio DF1 is set in advance according to the output (for example, electric power, motor rotational speed, etc.) required for the motor 3. For example, the target duty ratio DF1 can be derived based on the number of revolutions of the motor 3, the motor current, the power supply voltage VBAT, and the like, and is stored in the memory of the host controller by a map, a table, a relational expression, and the like. .

  In this specification, for convenience of explanation, the motor current when the U-phase positive side switching element 41UU and the V-phase ground side switching element 41VL are opened will be described. However, other switching elements are opened. The same applies to the motor current in this case. Further, the pulse width modulation can be performed by the positive side switching elements 41UU, 41VU, 41WU, and can also be performed by the ground side switching elements 41UL, 41VL, 41WL.

  The motor current detection circuit 5 detects the motor current flowing through the armature windings 32U to 32W of the motor 3. The motor current detection circuit 5 can use a resistor 51, for example. As shown in the figure, the resistor 51 is provided between the ground side switching elements 41UL, 41VL, 41WL and the ground side terminal 2L of the DC power supply 2.

  A motor current output terminal 52 is provided between the ground side switching elements 41UL, 41VL, 41WL and the resistor 51. A voltage obtained by multiplying the motor current value by the resistance value of the resistor 51 is output to the motor current output terminal 52. That is, the motor current detection circuit 5 can calculate the motor current based on the voltage drop by the resistor 51. The resistance value of the resistor 51 is set as small as possible in order to reduce the loss in the resistor 51.

  The filter circuit 6 reduces high frequency components contained in the motor current detection signal. As the filter circuit 6, for example, a low-pass filter having a resistor 61 and a capacitor 62 can be used. The filter circuit 6 can use, for example, a high-order low-pass filter such as a second-order low-pass filter, or an active filter using an operational amplifier, in addition to the above form.

  As shown in the figure, the resistor 61 and the capacitor 62 are connected in series, and one end side of the resistor 61 is connected to the motor current output terminal 52 by a signal line 53. A filter output terminal 63 is provided on the other end side of the resistor 61. The filter output terminal 63 outputs a motor current with reduced high frequency components. In this specification, the motor current whose high frequency component is reduced by the filter circuit 6 is referred to as a post-filter motor current.

  The time constant of the filter circuit 6 can be expressed by a multiplication value obtained by multiplying the resistance value of the resistor 61 and the capacitance of the capacitor 62. The motor current overshoot is generated by the current response of the switching elements 41UU and 41VL when the switching elements 41UU and 41VL transition from the closed state to the open state, and the inductance of the armature windings 32U and 32V. Therefore, it is preferable that the time constant of the filter circuit 6 is set to a time constant capable of reducing motor current overshoot. Thereby, the filter circuit 6 can reduce the high frequency component contained in the detection signal of the motor current efficiently. Note that the time constant of the filter circuit 6 is preferably derived in advance for the motor 3 and the power conversion device 4 by simulation, measurement by an actual machine, or the like.

  The comparison circuit 7 compares the motor current after filtering with the allowable value of the motor current. As the comparison circuit 7, for example, a known comparator 71 can be used. As shown in the figure, the positive input terminal (+) of the comparator 71 is connected to the filter output terminal 63 by a signal line 64. A reference voltage is input to the negative input terminal (−) of the comparator 71. The reference voltage is generated by dividing the power supply voltage VBAT of the DC power supply 2 by the resistors 72 and 73. The reference voltage corresponds to an allowable value of the motor current when determining when the overcurrent state occurs. In the configuration shown in FIG. 1, the reference voltage is set to a multiplication value obtained by multiplying the allowable value of the motor current by the resistance value of the resistor 51 of the motor current detection circuit 5.

  The comparator 71 compares the voltage input to the positive input terminal (+) with the reference voltage input to the negative input terminal (−). When the voltage input to the positive input terminal (+) is equal to or lower than the reference voltage, the output of the comparator 71 is at a low level (Lo). On the other hand, when the voltage input to the positive input terminal (+) exceeds the reference voltage, the output of the comparator 71 becomes high level (Hi). That is, the control device 8 determines that the overcurrent state is not allowed (allowable current) when the output of the comparator 71 is low level (Lo), and when the output of the comparator 71 is high level (Hi), It can be determined that the current is in an overcurrent state. Note that the control device 8 can also compare the size of the filtered motor current and the allowable value of the motor current.

  The control device 8 has a known microcomputer 8M. The microcomputer 8M includes a CPU 8M1, a memory 8M2, an input / output interface 8M3, and a driver circuit 8M4, which are bus-connected so that various data and control signals can be transmitted and received. The CPU 8M1 is a central processing unit and can perform various calculations. The memory 8M2 is a readable / writable storage device and can store various electronic information. The control device 8 can perform the above-described motor drive control by executing the drive program stored in the memory 8M2.

  The input / output interface 8M3 can control input / output with an external device. For example, the output of the comparator 71 is input to the control device 8 via the input / output interface 8M3. The driver circuit 8M4 is a known motor driver, and generates control signals 8UU to 8WL based on the carrier frequency and the duty ratio. Then, the driver circuit 8M4 applies a control voltage to the control electrodes of the switching elements 41UU to 41WL based on the control signals 8UU to 8WL. As a result, the driver circuit 8M4 can control opening and closing of the switching elements 41UU to 41WL.

  FIG. 2 is a block diagram illustrating an example of a control block. When viewed as a control block, the control device 8 includes an overcurrent determination unit 80, a carrier frequency generation unit 81, a carrier frequency switching unit 82, and a duty ratio setting unit 83.

  The overcurrent discriminating unit 80 discriminates for each carrier period of the pulse width modulation when the motor current after filtering is in an overcurrent state exceeding the allowable value of the motor current. When the output of the comparison circuit 7 transitions from a low level (Lo) to a high level (Hi), the overcurrent determination unit 80 determines that an overcurrent state has occurred. Then, the overcurrent determination unit 80 holds the determination result in one of the carrier cycles when it is determined that the overcurrent state is reached, and clears the determination result at the timing when the next carrier cycle starts. As a result, the overcurrent determination unit 80 can determine when an overcurrent state occurs for each carrier period of pulse width modulation.

  Note that the allowable value of the motor current is preferably set in accordance with the rated current of the motor 3. As a result, the overcurrent determination unit 80 can determine the overcurrent state using an allowable value set in accordance with the rated current of the motor 3. Therefore, the motor control device 1 of the present embodiment can perform appropriate overcurrent detection according to the physique of the motor 3.

  The carrier frequency generation unit 81 generates a plurality of pulse width modulation carrier frequencies having different periods. The carrier frequency can be generated, for example, by dividing the high frequency reference frequency generated by the crystal oscillator by a known frequency dividing circuit. Further, the carrier frequency of the pulse width modulation can be easily changed by changing the frequency division ratio of the carrier frequency.

  FIG. 3 is a timing chart showing an example of the motor current, the overcurrent detection output, and the motor drive output when the carrier frequency is not changed when the overcurrent is detected. A curve L11 indicates the motor current. A curve L12 indicates an overcurrent detection output that represents a determination result by the overcurrent determination unit 80. A curve L13 indicates the motor drive output. The vertical axis in the curve L11 indicates the motor current value, and the allowable value of the motor current is indicated by the overcurrent detection threshold OC1. The vertical axis in the curve L12 indicates that the overcurrent detection output is high level (Hi) or low level (Lo). The vertical axis in the curve L13 indicates that the switching elements 41UU and 41VL are in the open state (On) or the closed state (Off). In the figure, the horizontal axis represents the time axis.

  Times T11, T13, T15, T17, T19, T21, T23, and T25 indicate the beginning or end of the carrier period Tc1 of pulse width modulation. The overcurrent discriminating unit 80 discriminates when the overcurrent state is entered using the filtered motor current. Therefore, the overcurrent detection output transitions from the low level (Lo) to the high level (Hi) with a delay of the period Tf1 after the motor current exceeds the overcurrent detection threshold OC1. The overcurrent detection output is maintained at a high level (Hi) state in one cycle of the carrier cycle Tc1 when the overcurrent determination unit 80 determines that the overcurrent state has been reached, and at the timing when the next carrier cycle Tc1 starts. Transition from level (Hi) to low level (Lo).

  Further, when it is determined by the overcurrent determination unit 80 that the overcurrent state has occurred, the control device 8 sets the duty ratio to be smaller than the target duty ratio DF1. For example, before time T11, the duty ratio is set to the target duty ratio DF1, but after time T11, the duty ratio is set to be smaller than the target duty ratio DF1. As a result, as shown in the figure, the time of the open state (On) of the switching elements 41UU and 41VL after the time T11 is compared with the time of the open state (On) of the switching elements 41UU and 41VL before the time T11. It is getting shorter.

  However, when the switching elements 41UU and 41VL transition to the open state (On), the motor current continues to increase beyond the overcurrent detection threshold OC1 as indicated by the curve L11. This is because the provision of the filter circuit 6 causes a delay in detection of the motor current (period Tf1), and the motor current continues to increase beyond the overcurrent detection threshold OC1 depending on the inductance of the armature windings 32U and 32V. It is shown that.

  Therefore, in this embodiment, the carrier frequency switching unit 82 compares the carrier frequency used for pulse width modulation with the carrier frequency at the time of the determination when the overcurrent determination unit 80 determines that the overcurrent state has occurred. Switch to a lower carrier frequency. The duty ratio setting unit 83 sets the duty ratio to be smaller than the target duty ratio DF1 when the overcurrent determination unit 80 determines that an overcurrent state has occurred. The target duty ratio DF1 is a duty ratio set according to the output required for the motor 3 described above.

  FIG. 4 is a timing chart showing an example of the motor current, the overcurrent detection output, and the motor drive output when the carrier frequency is changed to a low cycle carrier frequency when overcurrent is detected. In the figure, the motor current is indicated by a curve L31. The overcurrent detection output is indicated by a curve L32, and the motor drive output is indicated by a curve L33. The vertical axis and horizontal axis in the figure are the same as in FIG.

  Times T31, T33, T35, T37, and T39 indicate the start or end of the carrier periods Tc1 and Tc2 of the pulse width modulation. Similar to the case shown in FIG. 3, the overcurrent detection output transitions from the low level (Lo) to the high level (Hi) with a delay of a period Tf1 after the motor current exceeds the overcurrent detection threshold OC1. The overcurrent detection output maintains a high level (Hi) state in one cycle of the carrier cycles Tc1 and Tc2 when the overcurrent determination unit 80 determines that the overcurrent state is entered, and the next carrier cycle Tc1 and Tc2 starts. At the timing, the high level (Hi) transitions to the low level (Lo).

  When it is determined by the overcurrent determination unit 80 that the carrier current switching unit 82 is in an overcurrent state, the carrier frequency switching unit 82 sets the carrier frequency used for pulse width modulation to a carrier frequency having a lower period than the carrier frequency at the time of determination. Switch. For example, it is assumed that the overcurrent determination unit 80 determines that an overcurrent state has occurred at time T34. At this time, the carrier frequency switching unit 82 switches the carrier frequency used for the pulse width modulation to a carrier frequency (carrier period Tc2) having a lower period than the carrier frequency (carrier period Tc1) at the time of the determination. As a result, the time from time T33 to T35 is longer than the time from time T31 to T33. The same applies to times T36 and T38.

  The duty ratio setting unit 83 sets the duty ratio to be smaller than the target duty ratio DF1 when the overcurrent determination unit 80 determines that an overcurrent state has occurred. The duty ratio before time T33 is set to the target duty ratio DF1. For example, it is assumed that the overcurrent determination unit 80 determines that an overcurrent state has occurred at time T34. At this time, the duty ratio setting unit 83 sets the duty ratio to be smaller than the target duty ratio DF1. As a result, the duty ratio after time T33 is smaller than the target duty ratio DF1.

  In this way, in the present embodiment, the number of times that the switching elements 41UU and 41VL transition to the open state (On) when an overcurrent is detected and the time during which the switching elements 41UU and 41VL are open (On) are reduced. For example, when the curve L13 after the time T13 is compared with the curve L33 after the time T33, the number of times the switching elements 41UU and 41VL transition to the open state (On) is decreased from 6 times to 3 times. Moreover, the time of the open state (On) of switching element 41UU and 41VL is also reduced. As a result, the motor current indicated by the curve L31 is suppressed from increasing as compared with the motor current indicated by the curve L11.

  The control device 8 of this embodiment has an overcurrent determination unit 80. The overcurrent discriminating unit 80 discriminates for each carrier period of the pulse width modulation when the filtered motor current in which the high frequency component is reduced by the filter circuit 6 is in an overcurrent state exceeding the allowable value of the motor current. Therefore, the motor control device 1 of the present embodiment can prevent erroneous detection of overcurrent due to linking.

  The control device 8 includes a carrier frequency switching unit 82 and a duty ratio setting unit 83. When it is determined that an overcurrent state has occurred, the carrier frequency switching unit 82 compares the carrier frequency used for pulse width modulation with a carrier frequency having a lower cycle (carrier cycle Tc1) than the carrier frequency (carrier cycle Tc1) when determined. Switch to period Tc2). Further, when it is determined that an overcurrent state has occurred, the duty ratio setting unit 83 sets the duty ratio to be smaller than the target duty ratio DF1 set according to the output required for the motor 3. Therefore, the motor control device 1 of the present embodiment can reduce the number of times that the switching elements 41UU and 41VL transition to the open state (On) and the time during which the switching elements 41UU and 41VL are open (On) when overcurrent is detected. it can. As a result, the motor control device 1 of the present embodiment can suppress an increase in motor current caused by the delay of the filter circuit 6.

  FIG. 5 is a flowchart illustrating an example of a procedure for changing the carrier frequency. First, the carrier frequency switching unit 82 determines whether or not the overcurrent determination unit 80 determines that an overcurrent state has occurred (step S11). If it is not determined that the overcurrent state has occurred (in the case of No), the flowchart proceeds to step S12. Then, the carrier frequency switching unit 82 sets the carrier frequency used for pulse width modulation to the first carrier frequency (carrier period Tc1) (step S12). Then, the flowchart ends once.

  If it is determined in step S11 that an overcurrent state has occurred (Yes), the flowchart proceeds to step S13. Then, the carrier frequency switching unit 82 sets the carrier frequency used for the pulse width modulation to the second carrier frequency (carrier period Tc12) (step S13). The second carrier frequency (carrier cycle Tc12) is set to a low cycle compared to the first carrier frequency (carrier cycle Tc1).

  Next, the carrier frequency switching unit 82 determines whether or not the overcurrent determination unit 80 has determined that the overcurrent state has continued over the n cycles of the carrier cycle Tc12 (step S14). However, n is an arbitrary natural number. If it is determined that the overcurrent state has been continued over n periods of the carrier period Tc12 (in the case of Yes), the flowchart proceeds to step S15. Then, the carrier frequency switching unit 82 sets the carrier frequency used for pulse width modulation to the third carrier frequency (carrier period Tc2) (step S15). Then, the flowchart ends once. The third carrier frequency (carrier cycle Tc2) is set to a low cycle compared to the second carrier frequency (carrier cycle Tc12).

  If it is not determined in step S14 that the overcurrent state has continued for n periods of the carrier period Tc12 (in the case of No), the flowchart is temporarily terminated. That is, in this case, the carrier frequency used for pulse width modulation is set to the second carrier frequency (carrier cycle Tc12). Note that the steps shown in this flowchart are repeatedly executed at predetermined intervals.

  As described above, when it is determined that the carrier frequency switching unit 82 continues to be in an overcurrent state over a plurality of periods (n periods in the above example) of the carrier period Tc12, It is also possible to switch to the cycle Tc2). Thereby, the motor control device 1 can prevent the cycle of the carrier frequency used for the pulse width modulation from being frequently switched when the motor current changes in the vicinity of the allowable value in the overcurrent state, and the control stability is improved. improves.

  Also, the carrier frequency switching unit 82 can switch the carrier frequency used for the pulse width modulation stepwise to a low cycle carrier frequency (carrier cycle Tc2) when it is determined that an overcurrent state has occurred. As a result, the motor control device 1 can prevent the carrier frequency used for pulse width modulation from being sharply switched to a low-cycle carrier frequency (carrier cycle Tc2), thereby improving control stability.

  Furthermore, as shown in FIG. 4, when it is determined that the overcurrent state has occurred, the timing at which the switching elements 41UU and 41VL transition from the open state (On) to the closed state (Off) It is preferable that it is set in accordance with the detection delay (period Tf1). Thereby, the motor control device 1 can set the time required for the switching elements 41UU and 41VL to be in the open state (On) when it is determined that the overcurrent state has occurred to the minimum necessary time. Therefore, the motor control device 1 can further suppress an increase in motor current caused by the delay of the filter circuit 6.

<Motor control method>
The present invention can also be understood as a motor control method, and can also be understood as a motor control program for executing the motor control method by causing the microcomputer 8M to function. In the motor control method and the motor control program, the “XX portion” described in the motor control device 1 may be read as “XX step”. That is, the overcurrent determination unit 80 is replaced with an overcurrent determination step, and the carrier frequency generation unit 81 is replaced with a carrier frequency generation step. The carrier frequency switching unit 82 is read as a carrier frequency switching step, and the duty ratio setting unit 83 is read as a duty ratio setting step. Since the description of each step is the same as the above description, a duplicate description is omitted.

  The motor control method of this embodiment is a motor control method for controlling the motor 3 using the power conversion device 4, the motor current detection circuit 5, the filter circuit 6, and the control device 8. The motor control method according to the present embodiment includes an overcurrent determination step, a carrier frequency switching step, and a duty ratio setting step.

  The overcurrent determination step determines for each carrier period of the pulse width modulation when the filtered motor current in which the high frequency component is reduced by the filter circuit 6 is in an overcurrent state exceeding the allowable value of the motor current. Therefore, the motor control method of this embodiment can prevent erroneous detection of overcurrent due to linking.

  In the carrier frequency switching step, when it is determined by the overcurrent determination step that the overcurrent state has occurred, the carrier frequency used for the pulse width modulation is lower than the carrier frequency (carrier cycle Tc1) when determined. Switch to the carrier frequency (carrier cycle Tc2). The duty ratio setting step has a smaller duty ratio than the target duty ratio DF1 set according to the output required for the motor 3 when it is determined that the overcurrent state has occurred in the overcurrent determination step. Set. Therefore, the motor control method of the present embodiment can reduce the number of times that the switching elements 41UU and 41VL transition to the open state (On) and the time during which the switching elements 41UU and 41VL are open (On) when overcurrent is detected. . As a result, the motor control method of the present embodiment can suppress an increase in motor current caused by the delay of the filter circuit 6.

<Additional notes>
The following technical idea can also be grasped from the above description.
(Additional item 1)
8. The motor control method according to claim 7, wherein the carrier frequency switching step switches to the low-cycle carrier frequency when it is determined that the overcurrent state is continued over a plurality of the carrier cycles.
(Appendix 2)
2. The carrier frequency switching step according to claim 7, wherein the carrier frequency switching step switches the carrier frequency used for the pulse width modulation stepwise to the carrier frequency of the low cycle when it is determined that the overcurrent state has occurred. Motor control method.

<Others>
The present invention is not limited to the embodiment described above and shown in the drawings, and can be implemented with appropriate modifications within a range not departing from the gist. For example, in the above-described embodiment, the target duty ratio DF1 is generated by a higher-level control device of the control device 8, but the target duty ratio DF1 can also be generated by the control device 8. Moreover, the resistor 51 of the motor current detection circuit 5 can also be provided for each phase (U phase, V phase, W phase).

  In Step S11 of the flowchart shown in FIG. 5, when it is not determined that the overcurrent state has occurred (No), the flowchart proceeds to Step S12. The carrier frequency switching unit 82 sets the carrier frequency used for pulse width modulation to the first carrier frequency (carrier cycle Tc1). In this case, the carrier frequency switching unit 82 sets the carrier frequencies used for the pulse width modulation in the order of the third carrier frequency (carrier period Tc2), the second carrier frequency (carrier period Tc12), and the first carrier frequency (carrier period Tc1). It can also be set in stages. That is, the carrier frequency switching unit 82 can switch the carrier frequency used for pulse width modulation stepwise to the carrier frequency (carrier cycle Tc1) at the allowable current step by step when the overcurrent state disappears. As a result, the motor control device 1 can prevent the carrier frequency used for pulse width modulation from being sharply switched to the carrier frequency (carrier cycle Tc1) when the current is an allowable current, and control stability is improved.

1: motor control device,
2: DC power supply,
3: Motor, 32U to 32W: Armature winding,
4: Power converter, 41UU to 41WL: switching element,
5: Motor current detection circuit,
6: Filter circuit,
8: Control device,
80: Overcurrent determination unit, 82: Carrier frequency switching unit, 83: Duty ratio setting unit.

Claims (7)

A power conversion device that is provided between a DC power supply and a motor, converts DC power of the DC power supply into AC power by opening and closing a switching element, and feeds the motor;
A motor current detection circuit for detecting a motor current flowing in the armature winding of the motor;
A filter circuit for reducing a high-frequency component contained in the detection signal of the motor current;
A control device that varies the duty ratio by a pulse width modulation method and controls opening and closing of the switching element based on the duty ratio;
With
The control device determines, for each carrier period of the pulse width modulation, when a filtered motor current whose high frequency component has been reduced by the filter circuit is in an overcurrent state exceeding an allowable value of the motor current. A discriminator;
A carrier frequency switching unit that switches a carrier frequency used for the pulse width modulation to a carrier frequency having a lower period than the carrier frequency at the time of the determination when the overcurrent determination unit determines that the overcurrent state has occurred. When,
A duty ratio setting unit that sets the duty ratio to be smaller than a target duty ratio that is set according to the output required for the motor when the overcurrent determination unit determines that the overcurrent state has occurred. When,
A motor control device.   The motor control device according to claim 1, wherein the allowable value of the motor current is set in accordance with a rated current of the motor.   3. The motor control according to claim 1, wherein the carrier frequency switching unit switches to the low-cycle carrier frequency when it is determined that the overcurrent state has been continuously provided over a plurality of carrier cycles. 4. apparatus.   4. The carrier frequency switching unit according to claim 1, wherein, when it is determined that the overcurrent state has occurred, the carrier frequency used for the pulse width modulation is gradually switched to the low-cycle carrier frequency. The motor control device described in 1.   The filter circuit is capable of reducing a time constant that can reduce an overshoot of the motor current caused by a current response of the switching element when the switching element transitions from a closed state to an open state and an inductance of the armature winding. Is set, The motor control device according to any one of claims 1 to 4.   The timing at which the switching element transitions from an open state to a closed state when it is determined that the overcurrent state has been set is set in accordance with a detection delay of the motor current by the filter circuit. The motor control device according to any one of the above. A power conversion device that is provided between a DC power supply and a motor, converts DC power of the DC power supply into AC power by opening and closing a switching element, and feeds the motor;
A motor current detection circuit for detecting a motor current flowing in the armature winding of the motor;
A filter circuit for reducing a high-frequency component contained in the detection signal of the motor current;
A control device that varies the duty ratio by a pulse width modulation method and controls opening and closing of the switching element based on the duty ratio;
A motor control method for controlling the motor using
An overcurrent determination step of determining, for each carrier period of the pulse width modulation, when a filtered motor current in which a high-frequency component is reduced by the filter circuit is in an overcurrent state exceeding an allowable value of the motor current;
A carrier frequency switching step of switching the carrier frequency used for the pulse width modulation to a carrier frequency having a low period compared to the carrier frequency at the time of the determination when it is determined by the overcurrent determination step that the overcurrent state has been reached. When,
A duty ratio setting step for setting the duty ratio to be smaller than a target duty ratio set in accordance with the output required for the motor when it is determined that the overcurrent state has occurred in the overcurrent determination step. When,
A motor control method.

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