JP2005176456A - Position detecting circuit of brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position detecting circuit of a brushless motor, which detects the position accurately without causing erroneous operation even when a single power supply is employed in which the number of components is decreased, the driver is reduced in size, and the advantage of using a single power supply is utilized. <P>SOLUTION: The position detecting circuit 8 comprises comparators CPu, CPv and CPw operating with a single power supply and comparing induced voltages Vu, Vv and Vw with a reference voltage Vb, an offset voltage creating section 81 for applying an offset voltage Vo to the inverted input terminals of the comparators CPu, CPv and CPw receiving the induced voltages Vu, Vv and Vw, and a section 82 for creating the reference voltage Vb corresponding to the offset voltage Vo and applying it to the non-inverted input terminal of the comparators CPu, CPv and CPw. Advantage of using a single power supply that a negative voltage can be prevented from being inputted, as a comparison input, to the comparators CPu, CPv and CPw operating with a single power supply by applying the offset voltage Vo and the driver can be reduced in size, is utilized thereby. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a position detection circuit for a brushless motor that detects the position of a rotor from an induced voltage of a stator winding.

  Conventionally, an electric tool using a brushless motor has been provided (see, for example, Patent Document 1).

  In the brushless motor driving apparatus described in Patent Document 1, a magnet is used to detect the position of the rotor. However, the position is detected by using the induced voltage of the open-phase stator winding without using such a magnet. A driving device using a detection circuit is also provided.

  FIG. 3 shows a circuit configuration of this conventional driving apparatus. The driving circuit 1 is a speed setting value set by a speed setting circuit 2 that sets the rotation speed of the brushless motor M by the operation amount of the operating means such as a trigger volume. The adjustment of the voltage applied to the stator windings 3u, 3v, and 3w of the brushless motor M and the switching of energization to the stator windings 3u, 3v, and 3w of each phase are performed through the inverter circuit 4 in response to The drive circuit 5 of the circuit 4 includes a control circuit 6 for outputting a command voltage signal corresponding to the applied voltage and a position detection circuit 8 for detecting the position of the rotor 7 having the permanent magnet of the brushless motor M, and a direct current as a power source A power supply 9 is connected.

  Here, the inverter circuit 4 includes six switching elements Q1 to Q6 that are bridge-connected as shown in the figure. The inverter circuit 4 is controlled by the drive circuit 5 based on the command voltage signal so as to be commutated. A current flows through the stator windings 3u, 3v, 3w of each phase at a predetermined timing, and the rotor 7 rotates. The drive circuit 5 adjusts the voltage applied to the stator windings 3u, 3v, 3w by PWM control of the switching elements Q1-Q6.

The position detection circuit 8 compares the induced voltage of the open-phase stator winding 3 that is not energized with a reference voltage, detects the magnetic pole position of the rotor 7, and outputs a position detection signal to the control circuit 6. It is. As shown in FIG. 4, the control circuit 6 includes a speed detection circuit 60 that detects the rotational speed of the rotor 7, that is, the rotational speed of the brushless motor M based on the position detection signal from the position detection circuit 8, and the speed setting circuit 2. Based on the command speed setting circuit 61 that receives the speed setting value and sets the command speed value, the command speed value, and the detected speed value of the speed detection circuit 60, the command voltage value is obtained so that the deviation between the two becomes zero. A speed control circuit 62 that performs calculation and a voltage control circuit 63 that outputs a command voltage signal applied to the drive circuit 5 of the inverter circuit 7 based on the command voltage value, and commutates with a predetermined phase delay from the position detection. As described above, the speed control is performed so that the function of rotating the rotor 7 by controlling the inverter circuit 4 and the actual rotational speed obtained from the position detection interval of the rotor 7 coincide with the set speed. And a function of obtaining the applied voltage by performing a calculation. Note that a brushless motor drive device having a similar position detection circuit is also provided (for example, Patent Document 2).
JP 2003-199310 A (refer to the left column on page 1) JP-A-7-308092 (see FIG. 1)

  By the way, the conventional position detection circuit 8 used in the driving device 1 shown in FIG. 3 is generally designed as a circuit using two power sources using a positive power source + V and a negative power source -V.

  Therefore, the induced voltage of the open-phase stator winding 3u or 3v or 3w which is not energized is generated symmetrically with respect to 0V, so that as shown in FIGS. 5A to 5C, the rotor 7 Are the intersections of the induced voltages Vu, Vv, Vw and 0V of the fixed windings 3u, 3v, 3w. However, when the DC power source 9 is a single power source such as a secondary battery, a plasma and an invert dual power source circuit must be added for the position detection circuit 8, which increases the number of components and reduces the size of the drive device. There was a problem that was not suitable.

  Therefore, when the position detection circuit is configured using a comparator that uses a single power supply, the induced voltage of the stator winding that is positive with respect to the ground is input to the comparator as shown in FIG. Therefore, a voltage corresponding to the 0 level of the induced voltage is input to the comparator as the reference voltage Vb.

  However, the position detection circuit 8 using such a single power source has the following problems. That is, as shown in FIG. 7A, for example, the switching element Q2 of the inverter circuit 7 and the switching element Q4 are turned on to switch the switching element Q2, the V-phase stator winding 3v, and the U-phase stator winding 3u. When the current Ia flows through the path of the switching element Q4, no induced voltage Vv is generated in the stator winding 3v, but when commutation is performed so that only the switching element Q5 is turned on, FIG. Due to the induced voltage Vw generated in the W-phase stator winding 3w at the time of (a), as shown in FIG. 7 (b), it is connected in reverse parallel to the switching elements Q4, Q5, Q6. A free-wheeling current Ib flows through the diode (parasitic diode) as shown in the figure, so that the open-phase voltage is equal to or lower than the ground by the forward voltage of the free-wheeling diode. For example, although the induced voltage Vu of the U-phase stator winding 3v changes as shown in FIG. 6 due to commutation, the forward voltage of the free-wheeling diode is equal to or less than the ground as shown in FIG. It becomes. That is, a negative voltage is input to the comparator as a comparison input, which causes a problem that the comparator malfunctions.

  The present invention has been made in view of the above points. The object of the present invention is to realize position detection with high accuracy without occurrence of malfunction even when a single power supply is used, and to reduce the number of components and downsizing the driving device. It is an object of the present invention to provide a position detection circuit for a brushless motor that can take advantage of the use of a single power source to enable the above-mentioned.

  In order to achieve the above object, a brushless motor having a rotor having a permanent magnet and a three-phase stator winding is used to switch a DC voltage supplied from an external power source by an inverter circuit. This is used in a drive device that is driven by switching the energization state of each phase stator winding, and by comparing the induced voltage generated in the open phase stator winding with the reference voltage as the rotor rotates. In a position detection circuit of a brushless motor that detects the rotational position of a rotor, a comparator that operates with a single power source and compares the induced voltage with a reference voltage, and an offset voltage with respect to one input terminal of the comparator to which the induced voltage is input An offset voltage generating unit that applies voltage and a reference voltage generating unit that generates a reference voltage corresponding to the offset voltage and inputs the reference voltage to the other input terminal of the comparator Characterized by comprising a.

  According to the present invention, it is possible to prevent a negative voltage from being input as a comparison input to a comparator that operates with a single power supply. Therefore, even if a single power supply is used, the position can be detected with high accuracy without causing malfunction, and the number of parts is reduced. The advantage of using a single power source that enables downsizing of the driving device can be utilized.

  According to a second aspect of the present invention, in the first aspect of the invention, the offset voltage creating unit creates an offset voltage equal to or higher than a forward voltage of a semiconductor switching element constituting the inverter circuit.

  According to the present invention, it is possible to prevent a negative voltage from being input as a comparison input to a comparator that operates with a single power supply. Therefore, even if a single power supply is used, the position can be detected with high accuracy and the number of parts is reduced. There is an effect that it is possible to take advantage of the use of a single power source that enables downsizing of the driving device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the drive device using the position detection circuit according to the present invention is suitable for various electric devices (for example, electric tools) using a brushless motor as a power source.

  The position detection circuit 8 of the present embodiment has a configuration as shown in FIG. 1, and, as in the conventional example, induced voltages Vu and Vv generated at both ends of the stator winding 3u or 3v or 3w that are in an open phase. , Vw outputs a position detection signal when it detects a midpoint, and operates with a single power source to compare the induced voltages Vu, Vv, Vw with the reference voltage Vb, and comparators CPu, CPv, CPw, and the induced voltage Vu. , Vv, Vw are input to the inverting input terminals of the comparators CPu, CPv, CPw, an offset voltage generator 81, and a reference voltage Vb corresponding to the offset voltage Vo is generated to generate the comparators CPu, CPv. , CPw and a non-inverting input terminal of the reference voltage generating unit 82.

  The reference voltage creating unit 82 creates the reference voltage Vb by dividing the DC voltage Vm substantially the same as the applied voltage of the inverter circuit 7 with a voltage dividing circuit including resistors R5 and R6. The offset voltage generator 81 divides the DC voltage Vm by a voltage dividing circuit composed of resistors R3 and R4, amplifies the divided output by an amplifier AP to obtain an offset reference voltage Vr1, and this offset reference voltage. The offset voltage Vb is applied by applying Vr1 to the inverting input terminals of the comparators CPu, CPv, and CPw via the resistors R1u to R1w and R2u to R2w. Each of the comparators CPu, CPv, CPw is provided with a Schmitt trigger circuit Tu, Tv, Tw for inputting the respective outputs and outputting them as corresponding phase position detection signals. The operation power supply of the amplifier AP, comparators CPu, CPv, CPw, and Schmitt trigger circuits Tu, Tv, Tw is obtained from a power supply voltage V1 output from a power supply circuit (not shown).

  Here, since each phase is the same, the voltage of each part in the position detection circuit 8 for the U phase will be described.

First, the voltage Vui input to the inverting input terminal of the comparator CPu is
Vui = (R2u / (R1u + R2u)) × (Vu−Vr1) + Vr1 (1)
It is expressed. That is, the voltage Vui is a voltage obtained by adding the offset voltage Vo based on the offset reference voltage Vr1 output from the amplifier AP. As shown in FIG. 2, even if the input voltage Vui is reduced by the forward voltage of the freewheeling diode (which may be a parasitic diode) connected in reverse parallel to the switching element of the inverter circuit 7 as described above. The resistance values of the resistors R1u and R2u are set so as to be larger than 0V.

  On the other hand, the reference voltage Vb input to the non-inverting input terminal of the comparator CPu may be a voltage for detecting that the induced voltage Vu becomes Vm / 2. That is, this means that the midpoint of the induced voltage Vu becomes half (= Vm / 2) of the power supply voltage Vm applied to the inverter circuit 7.

  Therefore, the resistance values of the resistors R1u to R1w, R2u to R2w, and R3 to R6 may be set so as to satisfy the above formula (1) and the following formulas (2) to (4) from these conditions.

Vo = (R2u / (R1u + R2u)) × (Vm / 2−Vr1) + Vr1 (2)
Vr1 = (R4 / (R3 + R4)) × Vm (3)
Vb = (R6 / (R5 + R6)) × Vm (4)
Thus, as described above, the offset voltage Vo is added to the induced voltages Vu, Vv, and Vw input to the comparators CPu, CPv, and CPw. Therefore, the advantage of using a single power supply is that there is no malfunction even if a single power supply is used, the position can be detected accurately, the number of parts is small, and the drive device can be downsized. You can save it.

It is a circuit diagram which shows the position detection circuit of this invention. It is a wave form diagram of an induced voltage in the same as the above. It is a schematic circuit block diagram which shows the drive device of the brushless motor using the conventional position detection circuit which uses 2 power supply circuits. It is a block diagram which shows the control circuit in the same as the above. It is a wave form diagram of an induced voltage in the same as the above. It is a wave form diagram for operation | movement description of the conventional position detection circuit which comprises the comparator of a single power supply. It is operation | movement explanatory drawing same as the above.

Explanation of symbols

8 Position detection circuit 81 Offset voltage generator 82 Reference voltage generator CPu, CPv, CPw Comparator

Claims (2)

  A brushless motor with a rotor having a permanent magnet and a three-phase stator winding is switched by a DC voltage supplied from an external power supply by an inverter circuit to switch the energization state of each phase stator winding. In a position detection circuit for a brushless motor, which is used in a drive device driven by the motor, and detects the rotational position of the rotor by comparing the induced voltage generated in the open-phase stator winding with the reference voltage as the rotor rotates. A comparator that operates with a single power source and compares the induced voltage with a reference voltage; an offset voltage generator that applies an offset voltage to one input terminal of the comparator to which the induced voltage is input; and the offset voltage A brushless motor comprising a reference voltage generation unit that generates a reference voltage and inputs the reference voltage to the other input terminal of the comparator.置検 out circuit.   2. The position detection circuit for a brushless motor according to claim 1, wherein the offset voltage creation unit creates an offset voltage that is equal to or higher than a forward voltage of a semiconductor switching element constituting the inverter circuit.

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