JP2013162568A - Motor drive control system - Google Patents

Abstract

A motor drive control system capable of suppressing malfunction due to erroneous detection of current flowing in an H-bridge circuit is provided.
A motor drive control system includes a backflow detection circuit that outputs a backflow detection signal when a current flows in a coil load in a second direction opposite to the first direction in the high-speed decay mode. Prepare. The PWM control circuit shifts the state of the H bridge circuit from the high-speed attenuation mode to the low-speed attenuation mode in accordance with the backflow detection signal.
[Selection] Figure 1

Description

The present invention relates to a motor drive control system.

  Conventionally, when an inductive load such as a motor coil is current-driven by an H-bridge circuit, in order to perform an ideal drive, a variable ability to change the drive current to a predetermined value along with driving stability (constant current control) (Variable current control) is required.

  In order to efficiently perform such constant current control and variable current control, pulse width modulation (PWM) control is often used.

  PWM control is a commonly used method for controlling the amount of power by switching a reactance load (inductive load or capacitive load). Constant current control is performed by repeating (attenuation).

JP 2002-204150 A

  Provided is a motor drive control system capable of suppressing malfunction due to erroneous detection of current flowing in an H-bridge circuit.

  The motor drive control system according to the embodiment includes a first switch element having one end connected to a power source and the other end connected to one end of a coil load of the motor, one end connected to ground, and the other end connected to the first switch. A second switch element connected to the other end of one switch element; a third switch element having one end connected to the power supply and the other end connected to the other end of the coil load; and one end to the ground And a fourth switch element having the other end connected to the other end of the third switch element. The motor drive control system compares a detection value corresponding to the current flowing in the H bridge circuit between the power source and the ground with a reference voltage, and outputs a first detection signal corresponding to the comparison result. A first current detection comparator is provided. The motor drive control system controls the switching of the first to fourth switch elements by a pulse width modulation signal so that the current flowing in the coil load in the first direction increases in the state of the H bridge circuit. A current increasing mode in which a voltage is applied between one end and the other end of the coil load, a slow decay mode in which both ends of the coil load are short-circuited so that a current flowing in the first direction is attenuated to the coil load, or The current increase mode can be set to any one of a fast decay mode in which a voltage is applied between one end and the other end of the coil load so that a current flowing in the first direction to the coil load is attenuated. If the first detection signal indicates that the detected value exceeds the reference voltage at the time, the state of the H-bridge circuit is changed to the slow decay mode or the fast decay. Select a mode, and a PWM control circuit for controlling the current flowing through the coil load. The motor drive control system includes a backflow detection circuit that outputs a backflow detection signal when a current flows in the coil load in a second direction opposite to the first direction in the high-speed decay mode.

  The PWM control circuit shifts the state of the H-bridge circuit from the fast decay mode to the slow decay mode in response to the backflow detection signal.

FIG. 1 is a circuit diagram illustrating an example of a configuration of a motor drive control system 100 according to the first embodiment. FIG. 2 is a circuit diagram showing an example of the circuit configuration of the H-bridge circuit 101 shown in FIG. FIG. 3 is a diagram showing an example of a current setting value for setting the current supplied to the coil load L shown in FIG. FIG. 4 is a waveform diagram showing an example of the waveform of each timing pulse output from the PWM reference generation circuit 23 shown in FIG. FIG. 5 is a diagram showing the state of each switch element and the current flowing through the coil load L when the state of the H-bridge circuit 101 shown in FIG. 6 is a diagram showing the state of each switch element and the current flowing through the coil load L when the state of the H-bridge circuit 101 shown in FIG. FIG. 7 is a diagram showing the state of each switch element and the current flowing through the coil load L when the state of the H-bridge circuit 101 shown in FIG. FIG. 8 is a diagram showing the state of each switch element and the state where the current flowing through the coil load L flows backward from the state of FIG. 5 when the state of the H-bridge circuit 101 shown in FIG. 2 is the current increase mode. FIG. 9 is a diagram showing the state of each switch element and the state where the current flowing through the coil load L flows backward from the state of FIG. 7 when the state of the H-bridge circuit 101 shown in FIG. 2 is the high-speed decay mode. FIG. 10 is an example of controlling the current flowing through the coil load L by combining three operation modes. FIG. 11 is an example of controlling the current flowing through the coil load L by combining three operation modes. FIG. 12 is a circuit diagram showing an example of a specific configuration of the PWM control circuit 10 shown in FIG. FIG. 13 is a diagram showing an example of the current of the coil load L and the waveform of each signal when the motor drive control system 100 is operated under the condition that the current set value is near 0 and a reverse flow occurs in the coil load L. It is. FIG. 14 is a circuit diagram showing an example of the configuration of the motor drive control system 200 according to the second embodiment. FIG. 15 is a diagram showing an example of the current of the coil load L and the waveform of each signal when the motor drive control system 200 is operated under the condition that the current set value is near 0 and a reverse flow occurs in the coil load L. It is. FIG. 16 is a diagram illustrating an example of a current setting value for setting a current to be supplied to the coil load L illustrated in FIG. FIG. 17 is a circuit diagram showing an example of a specific configuration of the PWM control circuit 10 according to the third embodiment. FIG. 18 is a diagram illustrating an example of the control at point A, the current of the coil load L, and the waveform of each signal when the current control shown in FIG. 16 is performed in the forward rotation direction in the motor drive control system 100. FIG. 19 is a circuit diagram showing another example of a specific configuration of the PWM control circuit 10 according to the third embodiment. FIG. 20 is a diagram illustrating an example of the control at point B, the current of the coil load L, and the waveform of each signal when the current control shown in FIG. 16 is performed in the forward rotation direction in the motor drive control system 100.

  Hereinafter, embodiments will be described with reference to the drawings.

First embodiment

  FIG. 1 is a circuit diagram illustrating an example of a configuration of a motor drive control system 100 according to the first embodiment.

  As shown in FIG. 1, the motor drive control system 100 includes a PWM control circuit 10, a detection resistor 17, a current setting circuit 20, a first current detection comparator 22, a backflow detection circuit 26, and an H bridge circuit 101. And comprising.

  As illustrated in FIG. 1, the H bridge circuit 101 includes, for example, a first switch element 11, a second switch element 12, a third switch element 13, and a fourth switch element 14.

  The first switch element 11 has one end connected to the power supply V and the other end connected to one end (node 15) of the coil load L of the motor.

  The second switch element 12 has one end connected to the ground and the other end connected to the other end of the first switch element 11 (one end of the coil load L).

  The third switch element 13 has one end connected to the power source V and the other end connected to the other end (node 16) of the coil load L.

  The fourth switch element 14 has one end connected to the ground and the other end connected to the other end of the third switch element 12 (the other end of the coil load L).

  The coil load L is, for example, a stepping motor coil or a DC motor coil.

  Here, FIG. 2 is a circuit diagram showing an example of the circuit configuration of the H-bridge circuit 101 shown in FIG.

  As shown in FIG. 2, the first and third switch elements 11 and 13 are high-side pMOS transistors. The sources of the pMOS transistors 11 and 13 on the high side are connected to the power supply V in common.

  The second and fourth switch elements 12 and 14 are low-side nMOS transistors. The sources of the nMOS transistors 12 and 14 on the low side are connected to the ground via the detection resistor 17.

  In addition, each MOS transistor has a diode formed in a parasitic manner in parallel, and this diode is a counter electromotive force generated when the high-side and low-side MOS transistors connected in series are turned off simultaneously. Plays the function of absorbing.

  As shown in FIG. 1, the detection resistor 17 has one end connected to one end (node 18) of the second and fourth switch elements 12 and 14, and the other end connected to the ground.

  The detection resistor 17 converts the current of the coil load L when the voltage is applied in the direction in which the current increases across the coil load L into a voltage. That is, the detection value Vm is a value based on the voltage drop of the detection resistor 17. The voltage at one end of the detection resistor 17 is supplied to the first current detection comparator 22 as the detection value Vm.

  The detection resistor 17 may have one end connected to one end (node 19) of the first and third switch elements 13 and the other end connected to the power supply V.

  As shown in FIG. 1, the current setting circuit 20 generates the reference voltage Vref.

  Here, FIG. 3 is a diagram showing an example of a current setting value for setting the current supplied to the coil load L shown in FIG.

  When the coil load L is, for example, a stepping motor coil or a brushless DC motor coil, the current flowing through the coil load L needs to be controlled in a sine wave shape. Therefore, as shown in FIG. 3, the current setting value for setting the current to be supplied to the coil load L is set so as to change stepwise in a pseudo sine wave form. The current flowing through the coil load L is controlled using this current set value as a target value. In this case, the current setting path 20 changes the reference voltage Vref stepwise in a pseudo sine wave shape corresponding to the current setting value shown in FIG.

  Further, the first current detection comparator 22 compares the detection value Vm corresponding to the current flowing through the H bridge circuit 101 between the power supply V and the ground with the reference voltage Vref, and the first current detection comparator 22 according to the comparison result. The detection signal COMP1 is output.

  For example, when the detection value Vm is higher than the reference voltage Vref, the first detection signal COMP1 is at “High” level, and when the detection value Vm is lower than the reference voltage Vref, the first detection signal COMP1 is “Low”. "Become level.

  The PWM reference generation circuit 23 supplies the PWM control circuit 10 with each timing pulse (start pulse signal START, switching signal DECay, detection pulse signal SD) that serves as a reference for PWM control.

  FIG. 4 is a waveform diagram showing an example of the waveform of each timing pulse output from the PWM reference generation circuit 23 shown in FIG.

  As shown in FIG. 4, the PWM reference generation circuit 23 periodically outputs a start pulse signal START, a switching signal DECay, and a detection pulse signal SD with a certain period T.

  The start pulse signal START is a signal for starting control of the switch element of the H bridge circuit 101 in the direction in which the current of the coil load L increases.

  In addition, the switching signal DECay is a low-speed decay mode in which both ends of the coil load L are set at the same potential when the current is attenuated, or the current is attenuated at a low speed, or the voltage of the power supply V is applied at a high speed in the direction of decreasing the current This is a signal for instructing switching of a high-speed attenuation mode for attenuating current. In the embodiment, it is assumed that the “Low” level indicates the low-speed attenuation mode, and the “High” level indicates the high-speed attenuation mode.

  The detection pulse signal SD is a signal that instructs the backflow detection circuit 26 to detect whether or not the current flowing through the coil load L is backflowing. In the embodiment, the backflow detection circuit 26 performs the detection operation in response to the rising edge of the detection pulse signal SD.

  Further, as shown in FIG. 1, the backflow detection circuit 26 receives the detection pulse signal SD, the signal SC indicating whether or not the H bridge circuit 101 is in the high-speed decay mode, and the first detection signal COMP1. In response to these signals, a backflow detection signal SID is output.

  The backflow detection circuit 26 performs a detection operation in response to the rising edge of the detection pulse signal SD in the high-speed decay mode, and when the current flowing through the coil load L flows back, the backflow detection signal SID (here, “ High "level) is output.

  Here, the backflow detection circuit 26 detects whether or not a current flows in the coil load L in the reverse direction (second direction) based on the signal SC and the first detection signal COMP.

  For example, the backflow detection circuit 26 determines that the first current detection signal COMP1 is generated at the rising edge of the detection pulse signal SD even though the signal SC indicates that the state of the H bridge circuit 101 is the fast decay mode. When the level is “High” (the detection value Vm is higher than the reference voltage Vref), it is determined that the current is flowing backward. Then, the backflow detection circuit 26 outputs a backflow detection signal SID (here, “High” level) so as to control the PWM control circuit 10 in the low-speed decay mode.

  The PWM control circuit 10 receives the start pulse signal START, the switching signal DECAY, the first detection signal COMP1, and the backflow detection signal SID from the PWM reference generation circuit 23. Based on these signals, the first to fourth The switching elements 11 to 14 are controlled to be switched by a pulse width modulation signal. That is, the PWM control circuit 10 applies the voltage of the power source V to both ends of the coil load L by controlling on / off of the first to fourth switch elements 11 to 14 and changes the time and direction thereof. . Thereby, the amount and direction of the current flowing through the coil load L are controlled to a pseudo sine wave current that changes stepwise so as to approach the current setting value shown in FIG.

  As described above, the current setting circuit 20 outputs the reference voltage Vref that changes stepwise in a pseudo sine wave form to the first current detection comparator 22. At this time, a signal SP for switching the polarity of the current flowing through the coil load L is sent to the PWM control circuit 10. In response to this signal SP, the PWM control circuit 10 switches whether the current flowing through the coil load L flows from the node 15 side or from the node 16 side.

  The PWM control circuit 100 switches the first to fourth switch elements 11 to 14 with a pulse width modulation signal to change the state of the H bridge circuit 101 forward to the coil load L (first direction). Current increasing mode in which a voltage is applied between one end and the other end of the coil load L so that the current flowing through the coil load increases, and both ends of the coil load L are short-circuited so that the forward current flowing through the coil load L is attenuated. It can be set to either the low-speed attenuation mode or the high-speed attenuation mode in which a voltage is applied between one end and the other end of the coil load L so that the current flowing in the forward direction to the coil load L is attenuated.

  When the first detection signal COMP indicates that the detection value Vm has exceeded the reference voltage Vref in the current increase mode, the PWM control circuit 10 sets the state of the H bridge circuit 101 to the low-speed attenuation mode or the high-speed attenuation. By switching to the mode, the value of the current flowing through the coil load L is controlled.

  Further, the PWM control circuit 10 shifts the state of the H bridge circuit 101 from the high-speed attenuation mode to the low-speed attenuation mode in accordance with the backflow detection signal SID.

  As described above, the PWM control circuit 10 performs PWM control on the gates of the first to fourth switch elements 11 to 14 and normally combines the following three operation modes when performing current control in each step. Executes control (Mixed Decay Mode).

  Here, the three operation modes will be described.

  FIG. 5 is a diagram showing the state of each switch element and the current flowing through the coil load L when the state of the H-bridge circuit 101 shown in FIG. FIG. 6 is a diagram showing the state of each switch element and the current flowing through the coil load L when the state of the H-bridge circuit 101 shown in FIG. FIG. 7 is a diagram showing the state of each switch element and the current flowing through the coil load L when the state of the H-bridge circuit 101 shown in FIG.

  In the current increase mode (Charge Mode) shown in FIG. 5, the first and fourth switch elements 11 and 14 are controlled to be turned on, and the second and third switch elements 12 and 13 are controlled to be turned off. A power supply V is applied to L. Thereby, a current flows from the node 15 to the node 16 (in the forward direction with respect to the coil load L).

  In the slow decay mode shown in FIG. 6, the second and fourth switch elements 12 and 14 are controlled to be on and the first and third switch elements 11 and 13 are controlled to be off. The current is circulated between the second and fourth switch elements 12 and 14 and the coil load L. In this case, due to the back electromotive force of the coil load L, a current flows from the node 15 to the node 16 (in the forward direction with respect to the coil load L). However, since the amount of current includes the parasitic resistance of the coil load L and the ON resistances of the second and fourth switch elements 12 and 14, the current flowing through the coil load L gradually decreases.

  In the fast decay mode (Fast Decay Mode) shown in FIG. 7, the second and third switch elements 12 and 13 on the opposite side to the current increasing mode are controlled to be in the on state, and the coil in which the back electromotive force is generated is generated. Since the current is returned from the load L to the power source V, the current rapidly decreases. Also in this case, a current flows from the node 15 to the node 16 (in the forward direction with respect to the coil load L).

  In the above three operation modes, normally, a current flows through the coil load L in the same forward direction.

  However, when the current set value is in the vicinity of zero, the current flowing through the coil load L flows from the forward direction to the reverse direction even if the switch elements are in the same ON / OFF state. Here, FIG. 8 is a diagram showing a state in which the state of each switch element and the current flowing through the coil load L are reversed from the state of FIG. 5 when the state of the H-bridge circuit 101 shown in FIG. 2 is the current increase mode. It is. FIG. 9 is a diagram illustrating a state in which the state of each switch element and the current flowing through the coil load L are reversed from the state of FIG. 7 when the state of the H-bridge circuit 101 illustrated in FIG. is there.

  For example, in the current increase mode, when the current set value is near zero, when time elapses from the state in which current flows in the forward direction through the coil load L shown in FIG. 5, as shown in FIG. A current flows through L in the opposite direction.

  For example, in the case of the high-speed decay mode, when the current set value is in the vicinity of zero, when time elapses from a state in which current flows in the forward direction through the coil load L shown in FIG. 7, as shown in FIG. A current flows through L in the opposite direction.

  Note that the backflow detection circuit 26 determines that the first current detection signal COMP1 is generated at the rising edge of the detection pulse signal SD although the signal SC indicates that the state of the H-bridge circuit 101 is the fast decay mode. When the level is “High” (the detection value Vm is higher than the reference voltage Vref), it is determined that the current flows backward in the reverse direction of FIG. 9 instead of FIG. Then, the backflow detection circuit 26 outputs a backflow detection signal SID (here, “High” level) so as to control the PWM control circuit 10 in the low-speed decay mode.

  Here, FIGS. 10 and 11 are examples of controlling the current flowing through the coil load L by combining three operation modes.

  In the examples of FIGS. 10 and 11, the control for switching in the order of the current increase mode → the low-speed attenuation mode → the high-speed attenuation mode is repeatedly executed at a fixed period.

  At this time, switching between the low-speed attenuation mode and the high-speed attenuation mode is performed at a fixed timing (a period during which the switching signal DECay in FIG. . On the other hand, as described above, switching from the current increase mode is performed by detecting whether the current flowing through the coil load L has reached the set current value in the current increase mode by converting it into a voltage using the detection resistor 17. Perform when the current value is the same or larger.

  Therefore, as shown in FIG. 11, when the current setting value increases and the switching timing exceeds the switching timing from the low-speed attenuation mode to the high-speed attenuation mode, the low-speed attenuation mode is skipped and the mode is switched to the high-speed attenuation mode. Further, when the switching timing is delayed, the processing is performed beyond the PWM cycle.

  On the other hand, if the current value of the coil load L exceeds the set value at the timing when the current set value falls and the current increase mode starts (rising edge of the start pulse signal START in FIG. 10), there is almost no current increase mode period. Switch to slow decay mode.

  By these processes, the average current flowing through the coil load L is stably controlled with respect to the current set value, and can follow the change of the set value at high speed.

  However, when the current set value is controlled so as to be a pseudo sine wave as shown in FIG. 3, the current set value is low in the vicinity where the current direction is reversed. For this reason, the current of the coil load L flowing from the node 15 to the node 16 starts to flow backward from the node 16 to the node 15 in the high-speed decay mode as shown in FIG. Then, in the next current increase mode, the operation of returning the current direction to the original forward direction is repeated.

  When the current flowing through the coil load L starts to flow backward in the high-speed decay mode, the current flows to the ground side via the detection resistor 17. For this reason, the current detection voltage (node 18 in FIG. 1) has a positive value. When the current value Vm increases and exceeds the reference voltage Vref, the first detection signal COMP1 becomes “High” level.

  When the current increase mode is entered in this state, the current flowing through the detection resistor 17 is inverted, the detection value Vm becomes a negative value, and the first detection signal COMP1 becomes the “Low” level. However, since the current detection comparator 22 has a low comparison voltage, the ability to set the output to the “Low” level is reduced, and a delay occurs.

  FIG. 12 is a circuit diagram showing an example of a specific configuration of the PWM control circuit 10 shown in FIG.

  As shown in FIG. 12, the PWM control circuit 10 includes inverters 41, 45, 56, AND circuits 42, 50, NAND circuits 53, 54, multiplexers 43, 44, D-flip flops 40, 52, Have

  The D-flip flop 40 generates a PWM signal for controlling the switch elements 11 to 14 in the direction of increasing the current of the coil load L, and the Q output becomes “1” at the rising edge of the start pulse signal START. When the first detection signal COMP1 becomes “1” (“High” level), the Q output becomes “0”.

  The NAND circuit 42 generates a PWM signal for attenuating the current of the coil load L at high speed, and the PWM signal for increasing the current of the coil load L by using the inverted output QN of the D-flip flop 40 as the switching signal DECay. Is masking the period in which “1” is “1”.

  The multiplexers 43 and 44 select whether to switch the current of the coil load L from the node 15 side or from the node 16 side.

  The D flip-flop 52 is an element for storing the backflow detection result, and the first detection signal COMP1 is “1” when the current of the coil load L is attenuated at high speed (the output of the AND circuit 42 is “1”). In the case of (“High” level), the output of the AND circuit 50 becomes “1”, the inverted output QN becomes “0” at the rise of the detection pulse signal SD, and the NAND circuits 53 and 54 cause the H bridge circuit 101 to 2. The fourth switch elements 12 and 14 are turned on, the first and third switch elements 11 and 13 are turned off, and both ends of the coil load L are fixed at the same potential so that the current decreases at a low speed. Is controlling.

  The D flip-flop 52 is reset when the start pulse signal START is input, the QN output becomes “1”, and the normal operation is resumed.

  Next, a description will be given of a case where the motor drive control system 100 is operated under the condition that the current set value is near 0 and the coil load L generates a backflow.

  FIG. 13 is a diagram showing an example of the current of the coil load L and the waveform of each signal when the motor drive control system 100 is operated under the condition that the current set value is near 0 and a reverse flow occurs in the coil load L. It is.

  Note that the first detection signal COMP1 is not reflected in the operation of the PWM control circuit 10 while the mask pulse is at the “High” level.

  At point A in FIG. 13, the current flowing through the coil load L starts to flow backward. However, the current flowing through the coil load L has not reached the current set value. Therefore, the first detection signal COMP1 is “0” (“Low” level). For this reason, the backflow detection signal SID is not output ("Low" level), and the transition from the fast decay mode to the slow decay mode does not occur.

  Thereafter, since the current of the coil load L exceeds the current value setting, the first detection signal COMP1 becomes “1” (“High” level), and the operation of the first current detection comparator 22 is performed when the current increase mode is entered. Due to this delay, malfunction occurs and the reverse current starts to increase.

  As a result, at point B, the current of the coil load exceeds the set current value, so the first detection signal COMP1 is “1” (“High” level), and the backflow detection signal SID is output. (“High” level), a transition from the fast decay mode to the slow decay mode occurs.

  As a result, the first detection signal COMP1 can be “0” (“Low” level) before shifting to the current increase mode, and the normal operation in which the current of the coil load L increases to the set current value is restored. .

  As described above, according to the motor drive control system according to the present embodiment, it is possible to suppress malfunction due to erroneous detection of the current flowing through the H bridge circuit.

Second embodiment

  FIG. 14 is a circuit diagram showing an example of the configuration of the motor drive control system 200 according to the second embodiment. In FIG. 14, the same reference numerals as those in FIG. 1 indicate the same configurations as those in the first embodiment.

  As illustrated in FIG. 14, the motor drive control system 200 further includes a second current detection comparator 29 as compared with the motor drive control system 100 illustrated in FIG. 1.

  The second current detection comparator 29 compares the detection value Vm corresponding to the current flowing in the H bridge circuit 101 between the power supply V and the ground with the ground voltage, and the second detection signal corresponding to the comparison result. COMP2 is output.

  The backflow detection circuit 26 detects whether or not a current has flowed in the coil load L in the reverse direction (second direction) based on the second detection signal COMP2.

  In other words, the motor drive control system 200 is a type in which backflow detection is performed by a second current detection comparator 29 different from the first current detection comparator 22. The second current detection comparator 29 determines a reverse flow if the voltage at the node 18 is a positive value.

  For this reason, the motor drive control system 200 increases the number of circuits, but the reliability is improved because the backflow can be detected at an early stage.

  Other configurations of the motor drive control system 200 are the same as those of the motor drive control system 100 shown in FIG.

  Here, a description will be given of a case where the motor drive control system 200 is operated under the condition that the current set value is near 0 and the coil load L generates a backflow.

  FIG. 15 is a diagram showing an example of the current of the coil load L and the waveform of each signal when the motor drive control system 200 is operated under the condition that the current set value is near 0 and a reverse flow occurs in the coil load L. It is.

  At point A in FIG. 15, the current flowing through the coil load L starts to flow backward. For this reason, the second detection signal COMP2 is “1” (“High” level), and unlike the case of FIG. 13, a transition from the fast decay mode to the slow decay mode occurs.

  Thus, the first detection signal COMP1 can be set to “0” (“Low” level) before shifting to the current increase mode. That is, normal operation in which the current of the coil load L increases to the set current value can be continued in the current increasing mode without increasing the backflow current.

  As described above, according to the motor drive control system according to the present embodiment, it is possible to suppress malfunction due to erroneous detection of the current flowing through the H bridge circuit.

Third embodiment

  In the third embodiment, a case where further control is applied to the configuration of the motor drive control system 100 shown in FIG. 1 will be described. However, the following control is performed separately from the control of the first embodiment. May be executed.

  FIG. 16 is a diagram illustrating an example of a current setting value for setting a current to be supplied to the coil load L illustrated in FIG. As shown in FIG. 16, the current setting value for setting the current supplied to the coil load L is set so as to change stepwise in a pseudo sine wave shape. That is, as in the first embodiment, the reference voltage Vref changes stepwise into a pseudo sine wave.

  In the motor drive system 100 according to the above-described first embodiment, the average current flowing through the coil load L is stably controlled with respect to the current set value, and can follow the change of the set value at high speed. . Since the average current value is controlled to a low value with a fixed offset relative to the current set value, the current set value is controlled to be a pseudo sine wave as shown in FIG. Will cause distortion at the point where the direction of the current reverses.

  In particular, in the actual control, since the control polarity exists even when the current set value is zero, the average current flowing through the coil load L does not become zero, and the step is small at point A in FIG. Causes phase distortion.

  Therefore, when the reference voltage Vref is a value corresponding to zero (ie, the current setting value is zero), the PWM control circuit 10 changes the state of the H bridge circuit 101 to the low-speed decay mode. To do.

  For example, when the backflow detection circuit 26 receives from the current value setting circuit 20 a signal indicating that the current setting is zero (current setting 0 signal), the signal SC becomes H at the rising edge of the detection pulse signal SD shown in FIG. In the case where the first current detection signal COMP1 is at “High” level (the detection value Vm is higher than the reference voltage Vref) even though the state of the bridge circuit 101 indicates that it is the fast decay mode. It is determined that the current is flowing backward. Then, the backflow detection circuit 26 outputs a backflow detection signal SID (here, “High” level) so as to control the PWM control circuit 10 in the low-speed decay mode.

  Then, the PWM control circuit 10 determines the H bridge circuit when the reference voltage Vref is a value corresponding to zero (that is, the current set value is zero) according to the backflow detection signal SID. The state 101 is set to the slow decay mode.

  FIG. 17 is a circuit diagram showing an example of a specific configuration of the PWM control circuit 10 according to the third embodiment.

  As shown in FIG. 17, the PWM control circuit 10 includes inverters 41 and 45, AND circuits 42 and 50, NAND circuits 53 and 54, an OR circuit 51, multiplexers 43 and 44, a D-flip flop 40, 52.

  In the PWM control circuit 10 shown in FIG. 17, the reference voltage Vref is controlled to change in synchronization with the start pulse signal START of PWM control.

  That is, the D-flip-flop 40 generates a PWM signal for controlling the switch element in the direction of increasing the current of the coil load L, the Q output becomes “1” at the rising edge of the start pulse signal START, When the output of the detection signal COMP1 of 1 becomes “1”, the Q output becomes “0”.

  The NAND circuit 42 generates a PWM signal for attenuating the current of the coil load L at high speed. The PWM signal increases the current of the coil load L by using the inverted output QN of the D-flip flop 40 as the switching signal DECay. The period during which the signal is “1” is masked.

  The multiplexers 43 and 44 select whether to switch the current of the coil load L from the node 15 side or from the node 16 side.

  The D-flip flop 52 is an element that stores a backflow detection result. When the first detection signal COMP1 is “1” when the current of the coil load L is attenuated at a high speed (the output of the AND circuit 42 is “1”), the D-flip flop 52 is an AND circuit 50. Becomes “1”, and the inverted output QN becomes “0” at the rising edge of the detection pulse signal SD. Then, the second and fourth switch elements 12 and 14 are turned on and the first and third switch elements 11 and 13 are turned off by the NAND circuits 53 and 54 to control the low-speed decay mode.

  The OR circuit 51 is an element for preventing the detection pulse signal SD from being inverted to “0” when the Q output of the D-flip flop 52 becomes “1”. This OR circuit 51 holds the state when the current setting 0 signal is “1”, and when the current setting 0 signal becomes “0”, the state is cleared and the QN output becomes “1” and returns to the normal PWM control. .

  FIG. 18 is a diagram illustrating an example of the control at point A, the current of the coil load L, and the waveform of each signal when the current control shown in FIG. 16 is performed in the forward rotation direction in the motor drive control system 100.

  As shown in FIG. 18, when the current setting value becomes 0, the current polarity is inverted from the node 15 to the node 16, so that the node 16 → node 15. For this reason, it is controlled that a negative current flows through the coil.

  For this reason, the H-bridge circuit 101 operates in the current increase mode (Charge Mode) until the current becomes zero, and thereafter increases the current in the negative direction in the fast decay mode and returns the current to 0 in the current increase mode. Repeated.

  In the low-speed decay mode, the current remains zero because both ends of the load are at the same potential. Since the current flows during the high-speed decay mode and the current increase mode, the average current of the coil does not become zero, and an offset is added in the opposite direction to that before the current setting becomes zero. It becomes smaller as shown in.

  FIG. 19 is a circuit diagram showing another example of the specific configuration of the PWM control circuit 10 according to the third embodiment.

  The PWM control circuit 10 shown in FIG. 19 is not controlled such that the reference voltage Vref changes in synchronization with the PWM control start pulse.

  The difference from FIG. 17 is that the change of the current setting 0 signal is synchronized with the rising edge of the start pulse signal START by the D-flip flop 55.

  FIG. 20 is a diagram illustrating an example of the control at point B, the current of the coil load L, and the waveform of each signal when the current control shown in FIG. 16 is performed in the forward rotation direction in the motor drive control system 100.

  In the example shown in FIG. 20, since the current polarity is not reversed, control is performed assuming that a positive current flows through the coil. For this reason, the current increase mode ends immediately after the start, the current of the coil load L decreases by the low-speed attenuation mode and the high-speed attenuation mode, and a negative current flows by the high-speed attenuation mode. The operation of increasing the current in the negative direction in the fast decay mode and returning the current to 0 in the current increase mode is repeated.

  Since the current hardly changes in the low-speed decay mode, the offset value is slightly smaller, but an offset occurs in the same direction as before the current setting becomes 0. Therefore, the step at the B point is different from the A point. The difference between the two becomes distortion.

  In order to solve this, it is only necessary to fix to the slow decay mode in which the current does not change when the current becomes 0. However, when the current setting becomes 0, the mode is fixed to the slow decay mode. As indicated by the one-dot broken line 19, the current gradually decreases, and the responsiveness deteriorates.

  In the reverse current detection circuit 26, when the voltage of the node 18 converted into a voltage by the detection resistor 17 is a negative voltage when the current of the coil load L starts to reverse when the current of the coil load L starts to flow backward, When the reference voltage Vref is 0, using the fact that the first detection signal is “1” when starting reverse flow, the reverse flow prevention signal is set to “1” (“High” level) and the output of the PWM control circuit 10 Is fixed to the slow decay mode.

  As a result, as indicated by the two-dot broken line in FIGS. 18 and 20, the current of the coil load L is rapidly attenuated to 0 and then fixed in the low-speed decay mode, and the offset current is converged to 0. Accordingly, the average current of the coil indicated by the dotted line in FIG. 16 is equal to the solid line that is the current setting value only when the current setting is 0, and the steps at the point A and the point B are also equal, thereby reducing the phase distortion.

  If current setting switching is not synchronized with PWM control, backflow may be detected immediately after the current setting is switched to 0. Therefore, the backflow prevention function is activated until the current increase mode starts. Do not.

  As described above, according to the motor drive control system according to the present embodiment, it is possible to suppress malfunction due to erroneous detection of the current flowing through the H bridge circuit.

  In addition, embodiment is an illustration and the range of invention is not limited to them.

100, 200 Motor drive control system 101 H bridge circuit

Claims (11)

A first switch element having one end connected to a power source and the other end connected to one end of a coil load of the motor; one end connected to ground and the other end connected to the other end of the first switch element; A second switch element; a third switch element having one end connected to the power supply and the other end connected to the other end of the coil load; and one end connected to the ground and the third switch element A fourth switch element having the other end connected to the other end, and an H bridge circuit,
A first current detection comparator that compares a detection value corresponding to a current flowing in the H-bridge circuit between the power source and the ground with a reference voltage and outputs a first detection signal corresponding to the comparison result; ,
The first to fourth switching elements are controlled to be switched by a pulse width modulation signal, and the state of the H bridge circuit is set to one end of the coil load so that a current flowing in the first direction of the coil load increases. A current increasing mode in which a voltage is applied to the other end, a slow decay mode in which both ends of the coil load are short-circuited so that a current flowing in the first direction to the coil load is attenuated, or the coil load is It can be set to any one of fast decay modes in which a voltage is applied between one end and the other end of the coil load so that the current flowing in the first direction is attenuated. When the first detection signal indicates that the reference voltage has been exceeded, the state of the H-bridge circuit is switched to the slow decay mode or the fast decay mode, A PWM control circuit for controlling the current flowing through the yl load,
A backflow detection circuit that outputs a backflow detection signal when a current flows in the coil load in a second direction opposite to the first direction in the fast decay mode,
The PWM control circuit shifts the state of the H-bridge circuit from the high-speed attenuation mode to the low-speed attenuation mode according to the backflow detection signal. The motor drive control system according to claim 1, wherein the backflow detection circuit detects whether or not a current flows in the coil load in a second direction based on the first detection signal. A second current detection comparator that compares a detection value corresponding to a current flowing through the H-bridge circuit between the power source and the ground with a ground voltage and outputs a second detection signal corresponding to the comparison result. In addition,
The motor drive control system according to claim 1, wherein the backflow detection circuit detects whether or not a current flows in the coil load in a second direction based on the second detection signal.   4. The motor drive control system according to claim 1, wherein the reference voltage changes stepwise in a pseudo sine wave form. 5. The PWM control circuit sets the state of the H bridge circuit to the low-speed decay mode when the reference voltage is a value corresponding to zero of the current flowing through the coil load. The motor drive control system described. A first switch element having one end connected to a power source and the other end connected to one end of a coil load of the motor; one end connected to ground and the other end connected to the other end of the first switch element; A second switch element; a third switch element having one end connected to the power supply and the other end connected to the other end of the coil load; and one end connected to the ground and the third switch element An H-bridge circuit having a fourth switch element having the other end connected to the other end;
A first current detection comparator that compares a detection value corresponding to a current flowing in the H-bridge circuit between the power source and the ground with a reference voltage and outputs a first detection signal corresponding to the comparison result. When,
The first to fourth switching elements are controlled to be switched by a pulse width modulation signal, and the state of the H bridge circuit is set to one end of the coil load so that a current flowing in the first direction of the coil load increases. A current increasing mode in which a voltage is applied to the other end, a slow decay mode in which both ends of the coil load are short-circuited so that a current flowing in the first direction to the coil load is attenuated, or the coil load is It can be set to any one of fast decay modes in which a voltage is applied between one end and the other end of the coil load so that the current flowing in the first direction is attenuated. When the first detection signal indicates that the reference voltage has been exceeded, the state of the H-bridge circuit is switched to the slow decay mode or the fast decay mode, A PWM control circuit for controlling the current flowing through the yl load,
A backflow detection circuit that outputs a backflow detection signal when a current flows in the coil load in a second direction opposite to the first direction in the fast decay mode,
The reference voltage changes stepwise in a pseudo sine wave form,
The PWM control circuit sets the state of the H bridge circuit to the low-speed decay mode when the reference voltage is a value corresponding to zero in the current flowing through the coil load. . A detection resistor having one end connected to one end of the second and fourth switch elements and the other end connected to the ground;
The motor drive control system according to claim 1, wherein the detection value is a value based on a voltage drop of the detection resistor. A detection resistor having one end connected to one end of each of the first and third switch elements and the other end connected to the power source;
The motor drive control system according to claim 1, wherein the detection value is a value based on a voltage drop of the detection resistor.   The motor drive control system according to claim 7 or 8, wherein the detection value is a voltage at one end of the detection resistor.   The motor drive control system according to claim 1, further comprising a current setting circuit that generates the reference voltage.   The motor drive control system according to any one of claims 1 to 10, wherein the coil load is a coil of a stepping motor or a coil of a DC motor.

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