JP2015136273A - Motor driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and reliably start a brushless DC motor.SOLUTION: A motor driving device has a brushless DC motor 1, an inverter 2, a bootstrap power source 6 for driving a high-voltage side switching element of the inverter 2, and a charge pump power source 7 serving a driving power source of a switching element 6a of the bootstrap power source 6. A capacitor of the charge pump power source is charged when a low-voltage side switching element of the inverter is turned off, so that an on-time of the low-voltage side switching element is not longer than a predetermined time. Therefore, a charge pump power source for driving a switch part of the bootstrap power source can secure a stable electric potential, reliably drive the switch part of the bootstrap power source, and reliably control the high-voltage switching element of the inverter 2, so as to stably and reliably drive the brushless DC motor.

Description

  The present invention relates to a motor drive device by inverter control.

Conventionally, this type of motor drive device uses a bootstrap power supply composed of a diode, a resistor, and a capacitor for the high voltage side switching element drive part of the inverter circuit, and when the motor is started, the low voltage side switching element of the inverter circuit is turned on / off. The capacitor of the bootstrap power supply is charged to a stable potential. (For example, see Patent Document 1)
FIG. 4 shows a conventional motor drive device described in Patent Document 1, which is one phase (U phase) of a motor drive device that drives a three-phase motor, and includes an inverter, a drive circuit, and a bootstrap circuit. The connection relationship is shown.

  FIG. 4 shows one phase of an inverter that drives a three-phase motor. The inverter 102 that drives the three-phase motor has a three-phase full bridge configuration using six circuits in which switching elements and diodes are connected in antiparallel.

  The drive circuits 104 and 105 respectively perform on / off control of the high-voltage side switching element 102a and the low-voltage side switching element 102b according to the states of the input signals Up and Un.

  The U-phase bootstrap circuit 106 is constituted by a series connection of a DC power supply 106a of about 15 V, a diode 106b, a resistor 106c, and a capacitor 106d. The negative potential side of the capacitor 106d is connected to the negative potential side of the drive circuit 104, and the switching element Commonly connected to the emitter terminal 102a. The positive terminal of the capacitor 106 d is connected to the power supply terminal of the drive circuit 104.

  Immediately before starting the motor, the switching element 102b is intermittently energized with an on / off duty of 50%, whereby the capacitor 106d is initially charged from the DC power source 106a via the diode 106b and the resistor 106c during the ON period of the switching element 102b. As a result, the power supply of the high-voltage side drive circuit 104 is secured, and the high-voltage side switching element is in a drivable state.

  Next, PWM control is performed on the high-voltage side switching element 102a when the motor starts rotating. In the charging operation of the bootstrap circuit 106, when the high-voltage side switching element 102a is turned off, the accumulated energy of the inductance of the motor 5 flows as a regenerative current through the low-voltage side diode 102h. Becomes close to the GND level of the inverter circuit 102 and is charged.

  Therefore, since the battery is charged when the low voltage side switching element 102b is turned on and when the high voltage side switching element 102a is turned on / off, the bootstrap potential has a stable potential.

JP 2000-23484 A

  However, in the above-described conventional configuration, the diode of the bootstrap circuit can be turned on / off at high speed, and a high-speed diode having a relatively large current rating that can inject charging charge into the capacitor in a short time, and the charging current of the capacitor as a diode A current limiting resistor is required to keep it below the rated value. Furthermore, a bootstrap circuit is required for three phases, and it is necessary to maintain an insulation distance according to safety regulations between phases having different potentials, resulting in an increase in circuit area. Therefore, in recent years, the bootstrap circuit diode is replaced with a MOSFET capable of high-speed switching, and the gate drive of the MOSFET is performed by charging the charge pump power supply synchronized with the low-voltage side switching element drive signal. It has been proposed to reduce the number of circuit components and reduce the size by using an element in which a part is integrated into a single chip. However, in the conventional configuration, in the low-speed drive region immediately after start-up, the low-voltage side switching element is continuously energized, the potential of the charge pump power supply for driving the MOSFET gate is lowered, thereby turning off the switch part of the bootstrap power supply and the motor There was a problem that start-up failure would occur.

  In order to solve the above-described conventional problems, a motor driving device according to the present invention includes a brushless DC motor including a stator and a rotor having a permanent magnet, an inverter that converts a DC voltage into an AC voltage, and a high voltage of the inverter. A bootstrap power supply composed of a capacitor that is a driving voltage of the switching element connected to the side and a switch element, and a charge pump power supply that drives the switch element of the bootstrap power supply, and the capacitor of the charge pump power supply includes: It is charged when a predetermined switching element of the inverter is turned off so that the ON time of the switching element does not become longer than a predetermined time.

  As a result, the charge pump power supply that drives the bootstrap power supply switch element can stably secure a potential above a certain level even during low-speed drive such as immediately after the motor is started, so that the bootstrap power supply switch element can be turned on reliably and stably. Will be able to. Therefore, the drive circuit power supply of the high-voltage side switching element of the inverter can be stably secured and a potential higher than a certain level can be ensured, and the high-voltage side switching element can be reliably controlled on / off.

  The motor drive device of the present invention can realize a reliable and stable motor start-up, reduce the circuit size and cost, and reduce the number of components.

1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention. Timing chart at motor start-up in Embodiment 1 of the present invention Timing chart at the time of positioning in the first embodiment of the present invention Circuit diagram for one phase of a conventional motor drive device

In the first invention, a brushless DC motor including a stator and a rotor having a permanent magnet, two switching elements are connected in series, and a pair of switching elements connected in series are connected in parallel to three pairs. An inverter that inputs a DC voltage to both ends and outputs an AC voltage; a bootstrap power supply configured by a capacitor and a switch element for driving each switching element connected to the high-voltage side of the inverter; and a switch of the bootstrap power supply The charge pump power supply capacitor is charged when the switching element connected to the low voltage side of the inverter is turned off, and the on time of the switching element connected to the low voltage side is a predetermined time. It is designed not to be longer. As a result, the charge pump power supply capacitor is periodically charged, and the charge pump power supply voltage can stably hold a predetermined voltage. Therefore, since the switching part of the bootstrap power supply can be turned on reliably, the high-voltage side switching element of the inverter can be reliably driven. In other words, this allows the brushless motor to be driven stably.

  In the second invention, when the brushless DC motor is started according to the first invention, the inverter is turned on when an arbitrary stator winding is energized to fix the rotation position of the rotor to a predetermined position. The low-voltage side switching element is turned off at an arbitrary frequency to charge the charge pump power supply capacitor. As a result, even when positioning the rotor that needs to be energized for a relatively long time, the charge pump power supply capacitor is always charged, and the charge pump power supply can maintain a predetermined voltage. Therefore, since the switching element of the bootstrap power supply can be reliably turned on, the high voltage side switching element of the inverter can be reliably driven. That is, the brushless motor can be started stably.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by this embodiment.

(Embodiment 1)
FIG. 1 is a block diagram of a motor driving apparatus according to an embodiment of the present invention.
In FIG. 1, a brushless DC motor (hereinafter referred to as a motor) 1 is constituted by a stator having a three-phase winding and a rotor having a permanent magnet.

  The inverter 2 is configured as a three-phase full bridge by connecting three circuits in parallel in which six switching elements are connected in series. A diode (2h to 21) is connected to each switching element in antiparallel.

  The brushless DC motor 1 includes a rotor 1a having a permanent magnet and a stator having a three-phase winding, and each end of the three-phase winding is connected to a connection point of series connection of switching elements of the inverter 2. .

  The drive circuit 3 is a drive circuit for the switching element of the inverter 2, and the high voltage side switching element 2 a connected to the high voltage side is driven by the high voltage side element driving unit 4 in response to the Hin signal and connected to the ground side. The side de-switching element 2b is driven by the low voltage side element driving unit 5 in accordance with the Lin signal.

  The bootstrap power supply 6 is a power supply for the high-voltage side element drive unit 4 and includes a diode 6a, a switch unit 6b, and a capacitor 6c, and serves as a drive voltage for the switch unit 6b. Note that the switch unit 6b is actually a semiconductor element switch element and uses a MOSFET.

  The switch drive unit is configured as a charge pump power supply 7 by the diode 7a, the capacitor 7b, and the drive unit 7c, and turns on / off the switch unit 6b by supplying a voltage to the switch unit 6b. Since the drive unit 7c receives the drive signal Lin for the low-voltage side switching element 2b, the drive unit 7c is driven in synchronization with the low-voltage side switching element.

  In the bootstrap circuit, a high-speed diode is generally used for the series circuit portion of the diode 6a and the switch portion 6b. However, in the present invention, a MOSFET capable of high-speed switching is used, and the charge charge VCC of the capacitor is obtained. A diode 6b is inserted in series so as to prevent backflow to the side.

  Further, by using the switch unit 6b as a MOSFET, the high-voltage side drive unit 4, the low-voltage side drive unit 5, the diode 6a, the MOSFET 6b, and the charge pump power supply 7 can be configured as a one-chip integrated circuit, and the number of components of the drive circuit 3 can be reduced. It is possible to reduce the size and cost.

  Here, the operation of the bootstrap power supply 6 will be described.

  In FIG. 1, the capacitor 6c of the bootstrap power supply is connected to VCC when the switch unit 6b is turned on, and is charged when the potential difference between the VCC potential and the capacitor 6c potential is larger than the forward voltage of the diode 6a.

  In addition, there are two paths for charging the capacitor 6c. When the low-voltage side switching element 2b is energized (first charging mode), and immediately after the high-voltage side switching element 2a is energized (transition from on to off), the low-voltage side At the time of recirculation to the diode 2h (second charge mode).

  First, in the first charging mode, when the switching element 2b is turned on, the potential at the connection point A (shown in FIG. 1) drops to near GND, and the capacitor from the power supply VCC through the diode 6a and the switch unit 6b. 6c is charged.

  Next, in the second charging mode, when the high-voltage side switching element 2a is switched from the energized state to the off state, the energy stored in the motor winding 1b is released in the reflux mode via the diode 2h. Accordingly, the potential at the connection point A drops below the GND level, and the capacitor 6c is charged from the power supply VCC.

  The operation of the charge pump power supply 7 which is a switch driving unit will be described. While the low signal is input to the Lin terminal, the low-voltage side element driving unit 5 outputs a low signal, and the low-voltage side switching element 2b is in the off state. At the same time, a low signal is input to the drive element 7c of the drive unit, and a low signal is output. As a result, the driving element 7c connection side terminal of the capacitor 7b becomes a potential near GND, and is charged from VCC via the diode 7a. As a result, the drive voltage of the switch unit 6b is a voltage obtained by subtracting the ON voltage of the diode 7a from VCC. When the potential difference between this voltage and the bootstrap capacitor 6c is greater than or equal to a predetermined potential difference, the switch unit 6b is turned on. That is, when the voltage of the capacitor 6c is lower than a certain level, the switch unit 6b is turned on.

  Next, when the Lin terminal changes from a low signal to a high signal, the output of the drive element 7c becomes VCC, and the potential of the capacitor 7b rises to a potential obtained by subtracting the forward voltage of the diode 7a from twice the VCC voltage. At this time, when the potential of the capacitor 6c of the bootstrap power supply 6 is near VCC, the switch unit 6b is turned on.

  FIG. 2 shows driving signals of the switching elements when the brushless DC motor 1 is started. In FIG. 2, the shaded area indicates the timing when the switching element is turned on.

  Control at startup will be described with reference to FIG. When the brushless DC motor 1 is in a stopped state, a low signal is input to Lin (Un, Vn, Wn in FIG. 2) (section A), and the drive element 7c is in an output state close to the GND level. The capacitor 7b is charged near the VCC voltage.

A section B is an initial charging section of the capacitor 6d of the bootstrap circuit. When a driving command for the brushless DC motor 1 is generated, the driving signals Lin (Un, Vn, Wn) of all three-phase low-voltage side switching elements are high. A signal is input. Thereby, the low voltage side switching elements 2b, 2d, and 2f are turned on. At this time, a high signal is output from the drive element 2c of the charge pump power supply 7, and the capacitor potential becomes a potential that is reduced by the voltage drop of the diode 7a from twice Vcc, and the switch element 6b of the bootstrap power supply 6 is turned on. At this time, since the low voltage side switching element is in the ON state, the connection side terminal of the capacitor 6d of the bootstrap circuit with the switching element is at a potential close to the GND level. Accordingly, the capacitor of the bootstrap circuit is charged with the charge injected from VCC, so that the power supply voltage of the high-voltage side element driving unit 4 is secured and the high-voltage side switching element can be driven.

  In section C, when the high-voltage side switching element is energized in section D, the upper and lower switching elements in the same phase (W-phase high-pressure side element 2e and W-phase low-pressure side element 2f in FIG. 2) are provided so as not to be energized simultaneously. However, this is not necessary when using elements that logically prohibit simultaneous energization of the upper and lower sides by a half-bridge gate driver or the like.

  Section D is a “positioning control” section in which the rotor rotation position is fixed at a predetermined position by energizing an arbitrary phase of the stator winding of the brushless DC motor 1. The side switching element Un is in the on state.

  By determining the magnetic pole position of the rotor to a predetermined position in this way, the motor is stably started by switching the driving pattern of the switching element (that is, the winding for starting energization) determined in advance in section E. To do.

  When the energization of the winding of the brushless DC motor 1 is a rectangular wave drive with an electrical angle of 150 degrees or less, the brushless DC motor is switched by switching either the upper or lower switching element at an arbitrary frequency at an arbitrary on / off ratio. The voltage applied to 1 is adjusted (PWM control).

  While the high-voltage side switching element is on, the capacitor voltage decreases due to the consumption of the charge of the capacitor 6c of the bootstrap power supply 6. Therefore, when the continuous energization time of the high-voltage side switching element is long, a large capacity capacitor is required (upsizing of parts and cost increase). Therefore, in the embodiment of the present invention, the high-voltage side switching elements (2a, 2c, 2e) ) Is turned on / off by PWM control.

  However, if the ON time of the low-voltage side switching element becomes longer, the non-charging period of the capacitor of the charge pump power supply 7 becomes longer, and the voltage decreases due to the influence of internal leakage current or the like.

  Therefore, in the present embodiment, the “on-time control period of the stator” and the “low-speed driving period after startup” in which the on-time of the low-voltage side switching element (that is, the non-charging period of the capacitor 7b of the charge pump power supply 7) is particularly long. In this case, a charging period for the charge pump power supply capacitor 7b is provided so that the switching element for the high-voltage energized phase and the switching element for the low-voltage energized phase are turned on / off at a predetermined interval.

  FIG. 3 is a timing chart of the switching element in the energized phase (current flows from the W-phase winding to the U-phase winding) during positioning in the first embodiment, where Wp is the W-phase high-voltage side switching element, and Un is The drive signal of a U-phase low voltage | pressure side switching element is shown.

  In FIG. 3, time T is a PWM cycle, section D1 is an ON section of the W-phase high-voltage side switching element, and section D2 is an OFF section of the U-phase low-voltage side switching element.

In FIG. 3, since the Lin signal in FIG. 1 becomes L in the section D2, the output signal of the drive element 7c of the charge pump power supply 7 is also output as the L signal. Thereby, since the capacitor 7b is charged from VCC, a stable voltage can be secured even during positioning control. Therefore, a stable voltage can be secured for the drive power supply of the switch element of the bootstrap power supply, and the switching element of the bootstrap power supply can be reliably turned on / off. Therefore, since the reliable ON state of the high voltage side switching element in the positioning control can be ensured, the stator can be reliably fixed at a predetermined position in the positioning control at the time of activation. That is, it is possible to secure a stable starting performance of the motor.

  In FIG. 3, the ON / OFF cycle of the U-phase low-voltage side switching element is made to coincide with the PWM cycle of the W-phase high-voltage side, but it can be arbitrarily set as the time when the charge of the capacitor 7b of the charge pump power supply is discharged. I do not care.

  As described above, in the embodiment of the present invention, a brushless DC motor including a stator and a rotor having a permanent magnet, two switching elements are connected in series, and the pair of switching units connected in series are connected. A bootstrap power supply composed of an inverter in which three pairs of elements are connected in parallel and DC voltage is input to both ends to output an AC voltage, and a capacitor and a switch element for driving each switching element connected to the high voltage side of the inverter And a charge pump power source for driving a switch of the bootstrap power source, and the capacitor of the charge pump power source is charged when the switching element connected to the low voltage side of the inverter is turned off, and the switching connected to the low voltage side The on-time of the element is prevented from becoming longer than a predetermined time.

  As a result, the charge pump power source that drives the switch element of the bootstrap power supply can stably secure a potential of a certain level or more, so that the switch element of the bootstrap power supply can be turned on reliably and stably. Therefore, since the drive circuit power supply of the high-voltage side switching element of the inverter can be stably secured and a potential higher than a certain level can be secured, the high-voltage side switching element can be reliably controlled on / off. Therefore, a MOSFET capable of high-speed switching is used as the bootstrap circuit diode, and the gate drive of the MOSFET is performed by charging the charge pump power supply synchronized with the low-voltage side switching element drive signal. Can be used as a single-chip integrated circuit, and the number of circuit components can be reduced, the size can be reduced, and the cost can be reduced.

  In addition, when the brushless DC motor is activated, when the arbitrary stator winding is energized to fix the rotational position of the rotor, the low-voltage switching element on which the inverter is turned off is turned off at an arbitrary frequency, and the charge pump The power capacitor is charged. As a result, even when positioning the rotor that needs to be energized for a relatively long time, the charge pump power supply capacitor is always charged, and the charge pump power supply can maintain a predetermined voltage. Therefore, since the switching element of the bootstrap power supply can be reliably turned on, the high voltage side switching element of the inverter can be reliably driven. That is, the brushless motor can be stably started by this.

  As described above, the motor driving device according to the present invention can stably start the motor while reducing the number of circuit components, reducing the size and cost, and is therefore a device for driving a three-phase brushless DC motor by inverter control. Applicable to all uses.

1 Brushless DC motor 2 Inverter 6 Bootstrap power supply 7 Charge pump power supply

Claims (2)

A brushless DC motor comprising a stator and a rotor having a permanent magnet, two switching elements are connected in series, and a DC voltage is applied to both ends of the three pairs of switching elements connected in parallel. An inverter that inputs and outputs an AC voltage, a bootstrap power supply configured by a capacitor and a switch element for driving each switching element connected to the high-voltage side of the inverter, and a charge pump that drives a switch of the bootstrap power supply And a capacitor of the charge pump power supply is charged when the switching element connected to the low voltage side of the inverter is turned off so that the ON time of the switching element connected to the low voltage side is not longer than a predetermined time. Motor drive. When the brushless DC motor is started, an arbitrary stator winding is energized to fix the rotor magnetic pole position to a predetermined position, and the switching element on the low voltage side where the inverter is turned on is turned off at an arbitrary frequency. The motor driving device according to claim 1, wherein the charge pump power supply capacitor is charged.

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