JP2005204404A - Motor drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive having a short acceleration/deceleration time capable of operating a switching element in a safety operating region under any operating condition and capable of feeding a current to the maximum within a rated current range. <P>SOLUTION: A first state performing forward torque drive and a second state performing reverse torque drive are divided according to the relation of a reference voltage ECR and a command signal EC. A first limit value Flim is set for a torque command signal Vecl in the first state and a second limit value Rlim is set for the second state. The first limit value Flim and the second limit value Rlim are altered depending on a speed detection signal VD from a speed detector 46. A difference signal Vec corresponding to the difference between the reference voltage ECR and the command signal EC is limited by the first limit value Flim and the second limit value Rlim to produce the torque command signal Vecl and a motor 5 is driven. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a motor driving device driven by pulse width modulation (PWM).

  In a motor drive device, an excessive current may cause deterioration or breakage of the switching element of the inverter, and the temperature rise due to the excessive current increases the influence on peripheral circuits. Therefore, it is necessary to limit the switching element of the inverter so that a current higher than the rated current does not flow (that is, operates within the safe operation region).

  When the motor is braked, the value of the flowing current is increased due to the influence of the back electromotive force compared to the forward rotation. Therefore, there is a method of setting a limit value so that a current higher than the rated current does not flow through the switching element of the inverter during braking in which a larger current flows (so as to operate within a safe operation region). However, if the limit value is set on the basis of the braking operation time, it is set low during normal operation. Therefore, the current flowing through the switching element of the inverter during forward rotation is limited to a current value smaller than the rated current.

  Therefore, the limit value is set to a different value during forward rotation and braking, and the drive is switched. That is, the driving is performed with the limit value at the time of braking set smaller than that at the time of forward rotation. Specifically, a first limit value is set such that the current flowing through the inverter switching element during forward rotation is a value equal to or lower than the rated current, and during braking, the first limit value is set to be positive when braking based on the same current command. A value divided by the ratio of the current flowing through the switching element of the inverter during the rotation is set as the second limit value. In this way, by switching the limit value and driving, it is possible to flow the current to the maximum in the rated current range through the switching element of the inverter regardless of the operating state (being able to operate in the safe operation area). .

As described above, for example, Patent Document 1 discloses a method of driving by switching the limit value during forward rotation and during braking.
Japanese Patent No. 1964376

However, the above conventional configuration has the following problems.
When the first limit value and the second limit value are set and driven as described above, it is possible to suppress the current flowing through the switching element of the inverter below the rated current. However, comparing the case of braking with a braking command from medium speed operation and the case of braking with a braking command from high speed operation, in both cases, current exceeding the rated current does not flow, but the former is limited in current. The maximum current can not flow within the rated current range. That is, the braking time becomes longer compared to a case where the maximum current can flow within the rated current range. Especially when used for applications where the specification of the braking time is strict, in order to shorten the braking time as much as possible, a configuration in which the current flows as much as possible within the rated current range in any operating condition (the inverter switching element is within the safe operating range). It is required to operate with

  In addition, when comparing acceleration from low speed with acceleration command and acceleration from medium speed with acceleration command, current exceeding the rated current does not flow, but the former is limited in current and rated current range The maximum current can not flow in the. In other words, the acceleration time becomes longer than that in the case where the current can flow to the maximum within the rated current range. In particular, when used in applications where acceleration time specifications are strict, in order to shorten the acceleration time as much as possible, a configuration in which current flows to the maximum within the rated current range in any operating state (the inverter switching element is within the safe operating range). It is required to operate with

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to operate the switching element in a safe operation region in any operating state and to flow the current to the maximum within the rated current range. An object of the present invention is to provide a motor drive device that can achieve a short acceleration / deceleration time.

A motor driving device having a configuration of the present invention includes a power supply unit that supplies power to a motor, a current detection unit that detects a current of the power supply unit, a torque command unit that outputs a torque command signal, a torque command signal, and a current Switching control means for controlling energization of the power supply means in accordance with the difference between the current detection signals of the detection means. The torque command means includes differential means for outputting a signal corresponding to the difference between the command signal and the reference voltage, and limiting means for restricting the output of the differential means and outputting it as a torque command signal. In particular, the limiting means sets the state where the command signal is small relative to the reference voltage as the first state, sets the state where the command signal is large as compared to the reference voltage as the second state, and sets the upper limit of the output of the differential means as the first state. Limiting with the first limit value, and limiting with the second limit value in the second state. Further, the limiting means changes at least one of the first limit value and the second limit value according to the motor rotation speed.
By configuring in this way, the first limit value and the second limit value can be made variable in response to the speed detection signal. Therefore, the switching element is operated in the safe operation region in any operating state, and within the rated current range. It is possible to flow the current as much as possible. Furthermore, since the current can flow as much as possible within the rated current range regardless of the rotational speed of the motor, the acceleration / deceleration time can be shortened.

  According to the motor drive device of the present invention, it is possible to operate the switching element in the safe operation region in any operation state, to allow the maximum current to flow in the rated current range, and to shorten the acceleration / deceleration time. it can.

  Embodiments of a motor drive device according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows the overall configuration of a motor drive device according to the present invention. The motor 5 is composed of a rotor having a field portion made of a permanent magnet and a stator in which a three-phase coil is Y-connected.

  The motor drive device includes a power supply device 20, a switching control circuit 30, a torque command device 40, and a current detector 50.

  The power supply 20 is configured by a bridge by three upper power transistors 21, 22, 23 and three lower power transistors 25, 26, 27, and supplies power from the DC power supply 1 to the motor 5. The upper power transistors 21, 22, and 23 are connected to the upper power diodes 21d, 22d, and 23d in antiparallel, and the lower power transistors are connected to the lower power diodes 25d, 26d, and 27d in antiparallel. ing. The upper power transistors 21, 22, 23 and the lower power transistors 25, 26, 27 are N-type field effect transistors, and the upper power diodes 21d, 22d, 23d and the lower power diodes 25d, 26d, 27d are parasitic diodes. You may comprise using.

  A current detector 50 is connected between the power supply unit 20 and GND, and the current detector 50 detects a current flowing through the current supply unit 20 and outputs the current detection signal Vcs to the switching control circuit 30.

  FIG. 2 shows a basic configuration diagram of the current detector 50, and FIG. 3 shows a timing chart for explaining the operation of each part of the current detector 50. As shown in FIG. 2, the current detector 50 includes a current detection resistor 51 and a filter 55 including a resistor 52 and a capacitor 53. The current detection resistor 51 detects a current flowing through the power supply 20 and the filter. The current detection signal Vcs is output via 55. As shown in FIG. 3, the signal Rcs detected by the current detection resistor 51 has a pulse waveform because it is PWM-driven as will be described later. Further, the current detection signal Vcs is substantially an average DC voltage of the current flowing through the power supplier 20. The current detection means is not limited to the current detection resistor, and may be constituted by a current sensor or the like.

  Returning to FIG. 1, the torque command device 40 includes a command signal input terminal 41, a power supply ECR that supplies a reference voltage (ECR), a differential circuit 42, a comparator 43, and a limiter 44 that limits the upper limit of the torque command signal. And a speed detector 46. The command signal EC is input from the command signal input terminal 41 and is input to one input terminal of each of the differential circuit 42 and the comparator 43. The reference voltage ECR is input to the other input terminals of the differential circuit 42 and the comparator 43, respectively.

  The differential circuit 42 outputs a differential signal Vec (= K * | ECR−EC | (K is a constant gain)), which is a differential absolute value output of the command signal EC and the reference voltage ECR, to the limiter 44. On the other hand, the comparator 43 compares the command signal EC with the reference voltage ECR and outputs a forward / reverse signal FR. The forward / reverse signal FR becomes “H” level (hereinafter, this state is referred to as “first state”) when the command signal EC <the reference voltage ECR. The “first state” is a positive torque drive section of the motor 5. Conversely, when the command signal EC> the reference voltage ECR, the forward / reverse signal FR is at the “L” level (hereinafter, this state is referred to as “second state”). The “second state” is a reverse torque drive section of the motor 5. The forward torque drive section and the reverse torque drive section will be described later.

  FIG. 4 is a timing chart for explaining the operation of each part of the differential circuit 42 and the comparator 43. 4A shows the relationship between the reference voltage ECR and the command signal EC, FIG. 4B shows the forward / reverse signal FR from the comparator 43, and FIG. 4C shows the differential from the differential circuit 42. Signal Vec is shown.

  In a region where the command signal EC is smaller than the reference voltage ECR (first state), as shown in FIG. 4B, the forward / reverse signal FR of the comparator 43 outputs “H” level, and conversely to the reference voltage ECR. On the other hand, in the region where the command signal EC is large (second state), the forward / reverse signal FR of the comparator 43 outputs the “L” level. The differential signal Vec from the differential circuit 43 shown in FIG. 4C is a signal obtained by multiplying the absolute value of the difference between the reference voltage ECR and the command signal EC by K (K is a gain).

  The differential signal Vec from the differential circuit 42 is input to the limiter 44. FIG. 5 shows a circuit configuration diagram of the limiter 44. FIG. 6 shows an operational characteristic diagram of the speed detector 46. As shown in FIG. 6, the speed detector 46 outputs a speed detection signal VD corresponding to (for example, proportional or substantially proportional) the rotational speed of the motor 5. In the figure, the horizontal axis is the rotational speed, and V5 is the maximum rotational speed of the motor 5 determined by the motor constant. At the rotational speed V5 or higher, the speed detection signal VD is saturated.

  Referring to FIG. 5, the limiter 44 includes a limit output unit 47 and a storage 48. The storage 48 receives the speed detection signal VD and the forward / reverse signal FR from the speed detector 46, and stores information (approximation formula, table, etc.) regarding the first limit value Flim and the second limit value Rlim. . The storage 48 calculates the first limit value Flim and the second limit value Rlim based on the speed detection signal VD, and selects either the first limit value Flim or the second limit value Rlim based on the forward / reverse signal FR. And output to the limit output unit 47. The limit output unit 47 limits the differential signal Vec from the differential circuit 43 with the first limit value Flim in the first state and the second limit value Rlim in the second state, and outputs it as the torque command signal Vecl. To do. The torque command signal Vecl output in a limited manner is indicated by a solid line in FIG.

  As described above, the torque command device 40 outputs the torque command signal Vecl that is limited and output by the first limit value Flim and the second limit value Rlim based on the difference between the command signal EC and the reference voltage ECR. The detailed operation of the torque command device 40 will be described later.

  The forward / reverse signal FR and the torque command signal Vecl of the torque command device 40 are input to the switching control circuit 30. The switching control circuit 30 outputs upper power transistor control signals UU, VU, WU and lower power transistor control signals UL, VL, WL in response to the difference between the torque command signal Vecl and the current detection signal Vcs from the current detector 50. It outputs to the power supply device 20. Here, the basic configuration of the switching control circuit 30 will be described.

  FIG. 8 shows a basic configuration diagram of the switching control circuit 30. The switching control circuit 30 includes a differential amplifier circuit 60, multipliers 31, 32, 33, a sine wave generator 34, a triangular wave generator 35, comparators 36, 37, 38, and a gate drive circuit 39. .

  The torque command signal Vecl from the torque command device 40 is input to one input terminal of the differential amplifier circuit 60, and the current detection signal Vcs is input to the other input terminal. The differential amplifier circuit 60 amplifies the difference between the torque command signal Vecl and the current detection signal Vcs, and outputs the difference signal Vr to the multipliers 31, 32, and 33. The sine wave generator 34 outputs three-phase sine wave signals SIN1 to SIN3 having a constant amplitude and a phase shifted by an electrical angle of 120 degrees. The three-phase sine wave signals SIN1 to SIN3 of the sine wave generator 34 may be created by analog processing of signals obtained from a magnetic sensor such as a Hall element or by digital processing. Good. Moreover, it is good also as a format input from the outside by a microcomputer etc.

  Multipliers 31, 32, and 33 multiply the three-phase sine wave signals SIN1 to SIN3 by the differential signal Vr of the differential amplifier circuit 60, and output input command signals Vuin, Vvin, and Vwin. Therefore, the input command signals Vuin, Vvin, Vwin are three-phase sine wave signals having an amplitude proportional to the magnitude of the difference signal Vr. The input command signals Vuin, Vvin, Vwin are input to one input terminal of the comparators 36, 37, 38, and the high-frequency triangular wave signal Vtri from the triangular wave generator 35 is input to the other input terminal. The triangular wave signal Vtri is set to a frequency outside the audible range (for example, 20 kHz to 200 kHz), and has a frequency that is about three orders of magnitude higher than the input command signals Vuin, Vvin, and Vwin. The triangular wave signal Vtri input to the comparators 36, 37, and 38 is not limited to a triangular wave, and may be a sawtooth wave or the like.

  Comparators 36, 37, and 38 compare the input command signals Vuin, Vvin, and Vwin with the triangular wave Vtri, and perform pulse width modulation. The pulse width modulated PWM signals PWMU, PWMV, and PWMW are input to the gate drive circuit 39. The gate drive circuit 39 responds to the PWM signals PWMU, PWMV, and PWMW, and outputs upper power transistor control signals UU, VU, and WU that control the gates of the upper power transistors 21, 22, and 23 of the power supply 20, and lower Lower power transistor control signals UL, VL, WL for controlling the gates of the power transistors 25, 26, 27 are output.

  FIG. 9 shows a basic configuration diagram of the gate drive circuit 39 (U phase only), and FIG. 10 shows a timing diagram (U phase only) for explaining the operation of each part of the gate drive circuit 39. FIG. 9 is a configuration diagram of only the U phase, but since the same applies to the other two phases, the description thereof is omitted here.

  In FIG. 9, the gate drive circuit 39 includes a delay circuit 61, a logical product gate 62, a logical sum inversion gate 63, and a switching circuit 64. The PWM signal PWMU is a pulse width modulation result of the input command signal Vuin and the triangular wave Vtri by the comparator 36. The PWM signal PWMU is delayed by a predetermined time Td by a delay circuit 61 composed of, for example, an RC circuit. The delay signal PWMUd is input to one input terminal of the AND gate 62 and one input terminal of the OR gate 63, respectively. The PWM signal PWMU is input to the other input terminal.

  The AND gate 62 performs an AND operation on the PWM signal PWMU and the delay signal PWMUd and outputs a UUin signal to the switching circuit 64. The logical sum inversion gate 63 performs a logical sum inversion operation of the PWM signal PWMU and the delay signal PWMUd, and outputs a ULin signal to the switching circuit 64.

  The switching circuit 64 outputs the upper power transistor control signal UU and the lower power transistor control signal UL based on the forward / reverse signal FR of the torque command device 40. Specifically, when the forward / reverse signal FR is at “H” level (first state), the switching circuit 64 outputs the UUin signal as the upper power transistor control signal UU and the ULin signal as the lower power transistor control signal UL. . At this time, the switching circuit 64 operates as a through circuit, and the motor 5 is driven with a positive torque.

  Conversely, when the forward / reverse signal FR is at the “L” level (second state), the switching circuit 64 outputs the ULin signal as the upper power transistor control signal UU and the UUin signal as the lower power transistor control signal UL. At this time, the switching circuit 64 operates as a circuit for switching inputs. That is, since the upper power transistor control signal and the lower power transistor control signal are interchanged to drive the motor 5, reverse torque driving is performed.

  The upper power transistor control signal UU and the lower power transistor control signal UL perform gate control of the U-phase upper and lower power transistors 21 and 25 of the power supply 20 and supply power to the U-phase of the motor 5. The delay time Td by the delay circuit 61 is a dead time for preventing penetration due to simultaneous turning on of the upper and lower power transistors of the power supply 20.

  As described above, each power transistor of the power supplier 20 performs an on / off operation in response to the upper power transistor control signals UU, VU, WU and the lower power transistor control signals UL, VL, WL of the gate drive circuit 39, and Supply power and drive.

  As described above, the amplitude control of the input command signals Vuin, Vvin, and Vwin is performed in response to the difference between the torque command signal Vecl and the current detection signal Vcs, the pulse width is modulated by comparison with the triangular wave Vtri, and the motor 5 is driven. To do.

The torque command device 40 will be described in detail below.
FIG. 11 is a diagram for explaining the operation of the torque command device 40. The broken line in FIG. 11 represents the differential signal Vec from the differential circuit 42, and the solid line represents the torque command signal Vecl from the limiter 44. As described above, the limiter 44 limits the differential signal Vec with the first limit value Flim in the first state (ECR-EC <0), and the second limit value in the second state (ECR-EC> 0). Restrict with Rlim. In the present embodiment, since the first state is the positive torque drive section and the second state is the reverse torque drive section, the relationship between the first limit value Flim and the second limit value Rlim is the first limit value Flim>. This is the second limit value Rlim. This is due to the following reason.

  When the command signal EC is too small or too large with respect to the reference voltage ECR, the absolute value of the differential signal Vec becomes large, and as a result, the difference signal Vr between the torque command signal Vecl and the current detection signal Vcs also becomes a large value. . Therefore, it is necessary to set a limit value. That is, when the difference signal Vr becomes a large value, the amplitudes of the input command signals Vuin, Vvin, and Vwin increase in proportion to the difference signal Vr, and an excessive current may flow through the coil of the motor 5. At this time, if each power transistor of the power supply device 20 is operating outside the safe operation region, the device will be deteriorated or damaged, and it may cause abnormal heat generation. Therefore, it is necessary to limit the maximum value of the drive current flowing through the coil of the motor 5 to be within the rated current range (each power transistor of the power supply 20 operates within the safe operation region). Further, in the motor drive device of the present embodiment, the drive current flowing in the coil of the motor 5 is greater in the latter when the positive torque drive is performed with the same rotational speed and the same torque command signal Vecl and when the reverse torque drive is performed. growing. This is because the phase of the counter electromotive voltage induced in the coil of the motor 5 with respect to the input command signal in the positive torque drive is substantially in phase, while that in the coil of the motor 5 with respect to the input command signal in the reverse torque drive. This is because the phase of the induced back electromotive force is almost opposite. As described above, the same limit value is not set in the first state (positive torque drive section) and the second state (reverse torque drive section), and the second limit value Rlim is set smaller than the first limit value Flim.

  The state where the drive current becomes the largest is a case where the reverse torque drive (deceleration) is suddenly performed with full torque from the state where the rotor is rotating at the maximum rotation speed. It is necessary to set the second limit value Rlim so as to operate within the safe operation region. Further, in the first state, the drive current becomes the largest when the positive torque is driven (accelerated) with full torque at the time of start-up, and each power transistor of the power supplier 20 operates within the safe operation region even in this state. Thus, it is necessary to set the first limit value Flim.

  Here, when the first limit value Flim and the second limit value Rlim are set to fixed values, each power transistor of the power supply device 20 is always maintained in the safe operation region, but from the low rotational speed. In the reverse torque drive (deceleration), the positive torque drive (acceleration) from the middle rotational speed, etc., the ratio limited by the first limit value Flim and the second limit value Rlim increases, and the drive current becomes small. That is, there is a problem that the driving torque is reduced and the deceleration time and acceleration time are lengthened. In general, in the drive control of information equipment motors, it is desired that start-up time, acceleration time, and deceleration time be as short as possible, especially chasing playback as in a DVD recorder (playback operation performed immediately after recording). In a device that performs the above, shortening the acceleration / deceleration time makes it possible to reduce the buffer memory for storing data, which can contribute to cost reduction of the device. Therefore, when the motor 5 is driven with the limit value as a fixed value as described above, the drive current is limited, which is not effective in terms of acceleration / deceleration time.

Therefore, in the motor drive device of the present embodiment, the limiter 44 of the torque command device 40 receives the speed detection signal VD from the speed detector 46, and responds to the speed control signal VD to the first limit value Flim and the second limit value. The limit value Rlim is varied. That is, in this embodiment, the counter electromotive voltage induced in the coil is proportional to the rotation speed, so that the first limit value Flim is increased and the second limit is increased as the speed detection signal VD is larger (the rotation speed is faster). On the contrary, the limit value is changed so that the first limit value Flim is decreased and the second limit value Rlim is increased as the speed detection signal VD is smaller (lower rotation speed). The relationship between the speed during control and the limit value to be set can be summarized as follows.

  In FIG. 11, a solid line is a figure when the rotational speed of a rotor is A (rpm), for example, and a dashed-dotted line is a figure when the rotational speed of a rotor is B (rpm) smaller than A, for example. Thus, when the rotation speed decreases from A (rpm) to B (rpm), the first limit value is reduced from Flim to Flim2, and the second limit value is increased from Rlim to Rlim2. As described above, this is because the counter electromotive voltage induced in the coil becomes small because the rotational speed is slow. That is, by making the limit value variable according to the rotation speed, it becomes possible to flow the current to the maximum within the rated current range. Therefore, it is possible to shorten the start-up time, the acceleration time, and the deceleration time compared to the case where the limit value is a fixed value.

  Next, a method for setting the first limit value Flim and the second limit value Rlim will be described. FIG. 12A is a diagram showing the relationship of the first limit value Flim with respect to the speed detection signal VD, and FIG. 12B is a diagram showing the relationship of the second limit value Rlim with respect to the speed detection signal VD. The horizontal axis in FIG. 12 indicates the rotational speed 0 to V5 (rpm) (maximum rotational speed) of the motor 5, and the vertical axis indicates the first limit value Flim and the second limit value Rlim, respectively.

  In FIG. 12B, as described above, when the reverse torque drive (deceleration) is performed with the full torque from the maximum rotation speed V5 (rpm), the current flowing through the coil of the motor 5 is the largest, so the rotation speed The second limit value Rlim at V5 (rpm) is the smallest value Rlim5. When the rotation speed is 0 rpm (no back electromotive force), the limit value is relaxed, and the limit value at which the maximum current flows within the rated current range is set to the largest Rlim0. The second limit values Rlim0 and Rlim5 are obtained by numerical analysis such as simulation or experiments. A function obtained by connecting these two points with a straight line is a function Flimf of the second limit value with respect to the speed detection signal VD. In the above description, a limit value is obtained for two motor speeds, and a function that gives the limit value is obtained by linear approximation. You may approximate. In addition, limit values for many motor speeds may be obtained discretely and stored in the storage 48 as a table.

  On the other hand, in FIG. 12A as well, when the positive torque drive (acceleration) is performed with the full torque from the rotation speed 0 (rpm), the current flowing through the coil of the motor 5 becomes the largest, so the rotation speed 0 ( rpm), the first limit value Flim is set to the smallest value Flim0. Further, a limit value at which the current flows to the maximum within the rated current range in the middle rotation speed range (for example, the rotation speed V3 (rpm)) is Flim3. A function obtained by connecting these two points with a straight line is a function Flimf of the first limit value with respect to the speed detection signal VD. The first limit value Flim0 in FIG. 12A and the second limit value Rlim0 in FIG. 12B are set to the same value.

  As described above, the first limit value function Flimf and the second limit value function Rlimf are set, and the information is stored in the storage 48 of the limiter 44. The storage 48 may store information on approximate expressions of the functions Flimf and Rlimf, or may store a table for giving function values. The storage 48 outputs a limit value (first limit value Flim or second limit value Rlim) according to the speed detection signal VD according to these functions. For example, when reverse torque driving is performed from the state of driving at the rotational speed V4 (rpm), the storage 48 outputs the second limit value Rlim4 corresponding to V4 (rpm) to the limit output unit 47 according to FIG. To do.

  Instead of continuously changing and outputting the first limit value Flim and the second limit value Rlim according to the speed detection signal VD, the storage 48 changes stepwise as shown in the functions Flimfs and Rlimfs in FIG. You may let them. That is, at each rotational speed (0, V1, V2, V3, V4, V5), limit values (Flim0-5, Rlim0-5) determined by the first limit value function Flimf and the second limit value function Rlimf are obtained. The limit value may be set stepwise so as not to exceed the functions Flimf and Rlimf. For example, in FIG. 13B, when reverse torque driving (deceleration) is performed from the state of driving at the rotational speed V4 (rpm), the second limit value Rlim4 is reduced until the rotational speed is reduced to V3 (rpm). When the speed is reduced from the rotational speed V3 (rpm) to the rotational speed V2 (rpm), Rlim3 is set as the second limit value. In this case, the rotational speeds (0, V1, V2, V3, V4, V5) to be set are rotational speeds corresponding to a plurality of threshold values (X1 to X5) as shown in FIG.

  Further, as shown in FIGS. 14A and 14B, the limit values are obtained for each predetermined speed from the functions Flimf and Rlimf, and values obtained by shifting these values downward by a predetermined amount are used. Limit values Flimfd and Rlimfd that change automatically may be set.

  The advantage of continuously outputting the first limit value Flim and the second limit value Rlim in response to the speed detection signal VD is that the maximum current can always flow within the rated current range. It is possible to perform acceleration / deceleration in a short time. For example, as shown in FIG. 15, at the rotational speed x, the limit value Flimx set by the function Flimf is reduced by Δlim (= Flimx−Flim2) with respect to the limit value Flim2 limited in a stepwise manner. , The increase in current leads to shortening of acceleration / deceleration.

  On the other hand, the advantage of changing the first limit value Flim and the second limit value Rlim in a step-like manner in response to the speed detection signal VD is, for example, the storage 48 as compared with the configuration in which the variable output is continuously variable. Is configured with software such as a microcomputer, the number of interrupts can be reduced, and when the storage 48 is configured with hardware such as an analog circuit, the circuit scale is reduced.

  As described above, the storage 48 outputs the first limit value Flim and the second limit value Rlim in response to the speed detection signal VD according to the set functions Flimf and Rlimf.

  In the present embodiment, the function Flimf of the first limit value and the function Rlimf of the second limit value are each set by first obtaining two points and connecting them with a straight line. It is better to obtain a limit value according to, and set it as the functions Flimf and Rlimf. Functions approximated by a linear expression so as not to exceed the functions Flimf and Rlimf obtained for the function to be set may be set as the functions Flimf and Rlimf.

  As shown in FIG. 16, the storage 48 may include an external input terminal 49. The storage 48 receives the first limit value Flim and the second limit value Rlim corresponding to the speed detection signal VD from the external terminal 49, and the input first limit value Flim and second limit value Rlim are directly input to the limit output unit 47. Output to. Further, a gain signal may be input from the external input terminal 49, and the gain may be adjusted and output by a gain signal to which the first limit value Flim and the second limit value Rlim are input. With this configuration, the first limit value Flim and the second limit value Rlim can be adjusted according to the speed detection signal VD.

  Further, in the present embodiment, both the first limit value Flim and the second limit value Rlim are made variable by the speed detection signal VD, but only the first limit value Flim or only the second limit value Rlim is variable. Needless to say, it may be allowed to be allowed to.

  Various other modifications can be made without changing the spirit of the present invention, and it goes without saying that such a configuration is included in the present invention.

  The motor drive device according to the present invention operates the switching element in a safe operation region in any operating state, and allows the maximum current to flow within the rated current range, so that the acceleration / deceleration time can be shortened. And is useful as a motor drive device that is driven by pulse width modulation (PWM).

It is a figure showing the whole motor drive unit composition concerning the present invention. It is a circuit block diagram of the current detector of a motor drive device. It is a timing diagram for demonstrating operation | movement of each part of a current detector. It is a figure for demonstrating operation | movement of each part of the differential circuit in a torque command device, and a comparator. It is a circuit block diagram of a limiter. It is a figure explaining the operating characteristic of a speed detector. It is a figure explaining a mode that a torque command signal is restricted by limit values Flim and Rlim in the 1st state (forward torque drive state) and the 2nd state (reverse torque drive state). It is a circuit block diagram of a switching control circuit. It is a circuit block diagram of a gate drive circuit. It is a timing diagram for explaining the operation of each part of the gate drive circuit. It is a figure explaining a mode that a torque command signal is restricted by limit values Flim and Rlim which are variable according to speed. It is a figure explaining a mode that the 1st limit value Flim and the 2nd limit value Rlim which are variable according to rotation speed are calculated by linear approximation. It is a figure explaining the 1st limit value Flimfs and the 2nd limit value Rlimfs which change in steps according to rotation speed. It is the figure explaining the 1st limit value Flimfd and the 2nd limit value Rlimfd which change in steps according to rotation speed. It is a figure for demonstrating the advantage of continuously variable-outputting the 1st limit value Flim and the 2nd limit value Rlim. It is the figure which showed the storage provided with the external input terminal for inputting 1st limiting value Flim, 2nd limiting value Rlim, etc. according to a speed detection signal.

Explanation of symbols

1: DC power supply 5: Motor 20: Power supply device 30: Switching control circuit 40: Torque command device 42: Differential circuit 43: Comparator 44: Limiter
46: Speed detector 50: Current detector

Claims (14)

Power supply means for supplying power to the motor;
Current detection means for detecting the current of the power supply means;
Torque command means for outputting a torque command signal;
Switching control means for controlling energization of the power supply means according to the difference between the torque command signal and the current detection signal of the current detection means,
The torque command means includes differential means for outputting a signal corresponding to the difference between the command signal and a reference voltage, and limiting means for limiting the output of the differential means and outputting it as a torque command signal.
The limiting means sets the state where the command signal is small relative to the reference voltage as a first state, sets the state where the command signal is large as compared to the reference voltage as a second state, and sets the upper limit of the output of the differential means. The first state is limited by a first limit value, the second state is limited by a second limit value, and at least one of the first limit value and the second limit value is changed according to the motor rotation speed. A motor drive device characterized by being made to cause.   The motor drive device according to claim 1, wherein a positive torque drive is performed in the first state and a reverse torque drive is performed in the second state.   The torque command means further includes speed detection means for detecting a motor speed and outputting a speed detection signal substantially proportional to the motor speed, and the first and second limit values are determined according to the speed detected by the speed detection means. The motor driving device according to claim 1, wherein at least one of them is changed.   4. The motor driving apparatus according to claim 3, wherein the torque command means sets the first limit value to be larger as the motor speed indicated by the speed detection signal becomes larger.   4. The motor drive apparatus according to claim 3, wherein the torque command means sets the second limit value to be smaller as the motor speed indicated by the speed detection signal is larger.   6. The motor driving apparatus according to claim 4, wherein the torque command means changes at least one of the first limit value and the second limit value in a step shape according to the motor speed. .   6. The motor driving apparatus according to claim 4, wherein the torque command means continuously changes at least one of the first limit value and the second limit value according to the motor speed. .   2. The motor driving apparatus according to claim 1, wherein the torque command means sets at least one of the first and second limit values for each of a plurality of predetermined motor speeds.   The torque command means obtains an approximate expression using the set first and second limit values, and according to the approximate expression, at least one of the first limit value and the second limit value according to the motor speed. 9. The motor driving apparatus according to claim 8, wherein one of them is continuously changed.   The motor driving apparatus according to claim 9, wherein the approximate expression is a linear expression.   10. The motor driving apparatus according to claim 9, wherein the approximate expression is obtained so that a limit value calculated by the approximate expression does not exceed the set first limit value and second limit value. .   A first limit value and a second limit value that change stepwise at each predetermined speed interval are set using values lower than the first limit value and the second limit value obtained by the approximate expression at each predetermined speed interval. The motor driving device according to claim 11, wherein   The torque command means further includes storage means for storing the approximate expression, and the limit means reads the first limit value and the second limit value according to the motor speed from the storage means. The motor drive device according to any one of claims 8 to 12. The motor driving apparatus according to claim 1, wherein the first limit value and the second limit value can be input from the outside.

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