JPH0527357B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that detects the rotor position of a brushless DC motor using the winding voltage of a stator winding.

Conventionally, various types of brushless DC motors have been proposed in which a rotor position detection signal is directly obtained from the winding voltage of a stator winding. An example of this will be explained with reference to FIG. 1 is a commercial AC power source (for example, AC 100 V, 60 Hz), 2 is a rectifier circuit that rectifies and smoothes the AC power source 1 and outputs it, and the anode of diode D ₁ and the cathode of diode D ₂ are
Connected to one end via reactor 3 for power factor improvement, and connected to the cathode of the diode _D1 above and the diode
Insert a circuit in which capacitors C ₁ and C ₂ are connected in series between the anode of D ₂ and a capacitor C ₃ in parallel, and connect the connection point of the capacitors C ₁ and C ₂ to the other end of AC power supply 1. They are connected to form a so-called voltage doubler rectifier circuit, and a DC output is sent out between the terminals of the capacitor _C3 . 4 is a brushless DC motor (hereinafter simply referred to as the motor),
It consists of a stator winding 5 and a rotor 6 connected in a three-phase star shape. Reference numeral 7 denotes a so-called 120° energization type pulse width control type inverter circuit (hereinafter simply referred to as an inverter circuit) connected to the output terminal of the rectifier circuit 2 to control energization of the stator winding 5 of the motor 4.
Then, six switching elements Q _u , Q _x , Q _v , Q _y , Q _w , Q _z consisting of transistors etc. are connected in series, two each (Q _u and Q _x , Q _v and Q _y , Q _w and Q _z ),
This is connected in a bridge shape and connected to the output end of the rectifier circuit ₂ , and each of _the stator windings 5 is The stator windings 5 are connected to the respective phases, and the stator winding 5 is energized for each phase by conducting each switching element. Buffer drivers BD are connected to the bases of the switching elements Q _u , Q _x , Q _v , Q _y , Q _w , and Q _z , respectively, so that the input side and the output side are isolated and the drive output is sent out. It has been done. 8 is a position detection circuit connected to each phase of the stator winding 8 to obtain a position detection signal of the rotor 6 from the stator winding voltage; one end of the capacitors C _u , C _v , C _w ; are the resistance R _u ,
The other ends of the capacitors C _u , _C v , C _w of the phase shifter consisting of a resistor and a capacitor connected to each phase of the stator winding 5 via R _v , R _w are connected in common to the neutral point. None, a comparator consisting of a star-connected phase shift circuit 9 which is grounded, and an operational amplifier at the output end of each phase shifter (connection point of the resistor and capacitor) of this phase shift circuit 9.
The non-inverting input terminals of CP _u , CP _v , and CP _w are connected, respectively, and the inverting input terminals of these comparators CP _u , CP _v , and CP _w are grounded (i.e., connected to the neutral point of the phase shift circuit 9). a phase shift circuit 9 which is formed from a comparison circuit 10 and receives the winding voltage of each phase of the stator winding 5 as a phase voltage in response to a change in the magnetic flux of the rotor 6 interlinked with the stator winding 5; The voltage is formed into a substantially triangular waveform with a 90° phase lag by integrating it with each phase shifter, and this is compared with the neutral point voltage using comparators CP _u , CP _v , and CP _w . Rectangular wave comparison signals U ₀ , V ₀ , W ₀ with a phase difference of 120° are obtained from the output terminals of the devices CP _u , CP _v , and CP _w at a duty ratio of 50%, and these are used as position detection signals. I'm getting older.
11 _is a _{combination of} logic circuits (e.g.
₀・W ₀ , U ₀・₀ , ₀・U ₀ , V ₀・₀ , ₀・V ₀ ,
W ₀・₀ ), the switching elements Q _u , Q _x , Q _v , Q _y , Q _w , Q _z of the inverter circuit 7 are sequentially turned on (for example, Q _u →Q _z →Q _v →Q _x →Q _w → _This is a distribution circuit designed to send open/close signals that cause Further, this distribution circuit 11 sends a switching signal to turn off the switching element of the inverter circuit 7 in response to a signal from a load current detection circuit 13 connected from a current detector 12 that detects the load current, thereby preventing an overload of the circuit. Current protection is provided, and when the motor 4 is started, a signal from the starting circuit 14 sends out an opening/closing signal that sequentially turns on and off the switching elements.

In such a rotor position detection device, when the speed control of the motor is performed by a pulse width control method (that is, a logical combination of the opening/closing signal of the distribution circuit 11 and the output signal of a pulse width modulation circuit (not shown) Detection of the position of the rotor in the case where the switching element of the inverter circuit 7 is pulse width modulated and switched will be explained with reference to FIG. Figure 2 shows the waveforms of the input/output of the phase shift circuit 9 and the output of the comparator circuit 10 in the position detection circuit 8 when the switching element is switched by pulse width modulation. The figures (b) and (c) show one phase at light load, heavy load, and overload, respectively. In addition, in the same figure, V _S1 is caused by the release of electromagnetic energy accumulated by the leakage inductance of the stator winding due to current interruption when switching the switching element (for example, when switching from Q _u to Q _v ). Reverse voltage generated (hereinafter referred to as spike voltage),
V _S2 is the reverse voltage (hereinafter referred to as cutting spike) generated by the release of electromagnetic energy due to the current interruption when the switching element switches with pulse width modulation, and V _I is the reverse voltage of the stator winding. The induced voltage and V _F indicate the phase voltages of the stator windings, respectively. During no-load and light-load conditions (Fig. 2 A), the ON period of the pulse-width modulated switching element is short and the stator winding current is small, so the electromagnetic energy is also small. The cutting spike V _S2 generated by this becomes linear, and after this occurs, an induced voltage V _I due to the rotation of the motor appears, and then the switching element turns on, resulting in a voltage waveform where the DC output of the rectifier circuit is applied (see Figure 2). (input in step 9). For this reason, the output of the phase shift circuit 9 has a waveform in which a triangular wave-like high frequency component due to the cutting spike V _S2 is superimposed (output of A9 in Fig. 2). The zero-crossing point of the output becomes unstable, and the rising and falling points of the rectangular wave of the comparison circuit 10 that compares these become unstable and unstable, and the phase voltage V _F
It becomes difficult to accurately obtain a signal with a 90° phase lag.

In addition, under heavy load (Figure 2 B), the on-period of the switching element is extended to maintain the stator winding voltage, so the stator winding current increases. , the electromagnetic energy due to the leakage inductance also increases, and the width of the cutting spike V _S2 generated by this emission also increases, and the pulse width modulated switching element turns on before the induced voltage V _I of the motor appears, causing a direct current The output is applied to the stator winding, resulting in a waveform that alternates between positive and negative at a so-called chopper frequency (input shown in FIG. 2, 9). Therefore, the ripple increases and the phase shift circuit 9
The zero-crossing point of the output waveform, which alternates between positive and negative in a substantially triangular waveform with a 90° phase lag, equivalently advances in phase, and the comparison signal of the comparator circuit 10 that compares this is the phase voltage.
As mentioned above, it becomes impossible to accurately obtain a signal with a 90° phase lag for V _F.

Furthermore, in the event of an overload (Fig. 2 C), the on-period of the switching element is controlled to be even longer (for example, fully conductive within a range of 120°), so the current further increases. The electromagnetic energy due to the leakage inductance also increases, and the width of the spike voltage _S1 generated when switching the switching element also increases (input 9 in FIG. 2C). Therefore, the zero-crossing point of the output waveform which alternates between positive and negative in a substantially triangular waveform due to the 90° phase lag of the phase shift circuit 9 becomes equivalently a large lead phase, and the comparison signal of the comparison circuit 10 that compares this also becomes , as described above, it becomes impossible to obtain a signal with an accurate 90° phase delay with respect to the phase voltage V _F.
As a result, the comparison signals U ₀ , V ₀ ,
This poses a problem in that W ₀ cannot be used as a rotor position detection signal, and if used as is, stable operation of the motor cannot be obtained.

The present invention has been made in view of the above points, and an object of the present invention is to enable accurate detection of the position of the rotor of an electric motor even when the switching element is controlled by pulse width modulation. Our mission is to provide what we believe in.

In order to achieve the above object, the present invention has been made so that even when the switching element is controlled by pulse width modulation, the switching element is not switched near the zero-crossing point of the phase voltage. Focusing on the fact that high frequency components are not superimposed, this system is configured to obtain a signal with the same phase or 180° phase difference from the phase voltage from the output of the phase shift circuit and use this as a rotor position detection signal. be.

Embodiments of the present invention will be described below with reference to FIGS. 3 and 4. Since the configuration is the same as that in Fig. 1 except for the position detection circuit, the same reference numerals are used.
I will explain this without repeating it. In FIG. 3, 100 is a position detection circuit for detecting the position of the rotor 6 of the electric motor 4, and a virtual neutral point circuit 1 is inserted in parallel with the inverter circuit 7 at the output end of the rectifier circuit 2.
01, and a voltage clamp circuit 1 in which clamp devices connected to each phase of the stator winding 5 are connected in a star shape.
02, a phase shift circuit 103 in which phase shifters connected to the output terminals of each clamper of this voltage clamp circuit 102 are connected in a star shape, and a stator winding from the output of each phase shifter of this phase shift circuit 103. Obtain a rectangular wave signal having the same phase or a 180° phase difference as each phase voltage of 5,
The comparator circuit 104 converts this into a substantially triangular waveform signal with a phase delay of 90 degrees, and obtains a position detection signal by comparing this phase-shifted output with a virtual neutral point voltage. . These circuits will be explained. The virtual neutral point circuit 101 includes two capacitors C ₄ and C ₅ between the output terminals of the rectifier circuit 2.
are inserted in series, resistors R ₁ and R ₂ are inserted between the terminals of these capacitors C ₄ and C ₅ , respectively, and the connection point of the above capacitors C ₄ and C ₅ is grounded as a virtual neutral point EN, and the rectification is performed. Always 1/2 of the output voltage of circuit 2
It is now possible to obtain a virtual neutral point voltage of . Therefore, the output of the rectifier circuit 2 which rectifies and smoothes the AC power supply 1, that is, each output terminal of the inverter circuit 7 connected in a bridge form to the DC power supply, is connected to each phase of the stator winding 5 of the three-phase star connection. As a result, the voltage at the neutral point that is not derived from the stator winding 5 is substantially obtained from the connection point (virtual neutral point EN) of the capacitors C ₄ and C ₅ , and the voltage at the neutral point is obtained from the virtual neutral point EN. It is becoming like a voltage. And the above capacitor C ₄ ,
C ₅ and resistors R ₁ and R ₂ have the same value (C ₄ = C ₅ ,
R ₁ = R ₂ ), and its value is such that the impedance of capacitors C ₄ and C ₅ is sufficiently lower than the leakage impedance of the switching element of the inverter circuit 7 when it is off, in order to sufficiently remove the induced voltage caused by the AC power source 1. The resistors R ₁ and R ₂ are selected to have a value sufficiently lower than the leakage resistance of the capacitors C ₄ and C ₅ , and the virtual neutral point voltage is set to the output voltage of the rectifier circuit 2. It is designed to reduce the voltage to 1/2 and to obtain a stable voltage with respect to the AC power supply 1. For example, it may be set so that C ₄ =C ₅ 10 μF, R ₁ =R ₂ 100KΩ. Voltage clamp circuit 102
is a pair of constant voltage diodes ZD ₁ whose anodes are connected to each phase of the stator winding 5 to form an anti-series connection.
The cathodes of the above voltage regulator diodes ZD ₁ , ZD ₃ , ZD ₅ of ZD ₂ , ZD 3 and ZD ₄ , ZD _{5 and ZD 6 are} resistors, respectively.
Connected through R ₃ , R ₄ , R ₅ and constant voltage diode
The cathodes of ZD ₂ , ZD ₄ , and ZD ₆ are commonly connected to form a neutral point, and this neutral point is connected to the above virtual neutral point to ground the circuit, and a clamp device consisting of a resistor and a pair of voltage regulator diodes is constructed. form a three-phase star-shaped connection, and use the connection point between the resistor of each clamper and the constant voltage diode (the connection point between R ₃ and ZD ₁ , R ₄ and ZD ₃ , and R ₅ and ZD ₅ ) as the output terminal. Outputs obtained by clamping each phase voltage of the stator winding 5 to a constant value determined from the Zener voltage V _Z are sent out from the output ends, respectively. The phase shift circuit 103 is the voltage clamp circuit 1 described above.
A capacitor C ₆ is connected to the output terminal of each clamp device of 02,
One ends of C ₇ and C ₈ are connected through resistors R ₆ , R ₇ , and R ₈ respectively, and the other ends of the capacitors C ₆ , C ₇ , and C ₈ are commonly connected to form a neutral point. A point is connected to the above virtual neutral point EN to ground the circuit, a phase shifter consisting of a resistor and a capacitor is formed into a three-phase star connection, and between the terminals of the above capacitors C ₆ , C ₇ and C ₈ , In order to prevent fluctuations in the time constant caused by variations in leakage resistance between the capacitors, bypass resistors R ₉ ,
By inserting R ₁₀ and R ₁₁ respectively, each phase shifter is connected to the connection point of the resistor and capacitor (R ₆ and C ₆ , R ₇ and C ₇ , R ₈ and
The connection point of _C8 ) is used as the output terminal to send out substantially triangular waveform output voltages, which are obtained by shifting the phase of the input to a phase delayed by 90°, as output signals U ₁ , V ₁ , and W ₁ , respectively. The comparison circuit 104 is the phase shift circuit 1
03 to output rectangular wave output signals U ₃ , V ₃ , W ₃ having a phase difference of approximately 180° from each phase voltage of the stator winding 5. The subtractive amplifying section 105 has an inverted output type, and the output signals U ₃ , V ₃ , W ₃ of this subtracting amplifying section 105 are phase-shifted by 90° to produce approximately triangular wave-like output signals U ₄ , V ₄ , W . The output of this integrating section 106 is AC-coupled with the integrating section 106, which is configured to send out ₄ , respectively, and is compared with the virtual neutral point voltage and inverted, and the result is calculated with respect to the phase voltage V _F.
The comparator 107 is configured to send out output signals U ₀ , V ₀ , and W ₀ with a 90° phase delay, respectively. Then, the subtraction amplification section 105
connects the inverting input terminals of operational amplifiers A ₁ , A ₂ , A ₃ to the output terminals of each phase shifter of the phase shift circuit 103 via resistors R ₁₂ , R ₁₃ , R ₁₄ respectively, and Connect the non-inverting input terminals of A ₁ , A ₂ , and A ₃ to resistors and capacitors (R ₁₅ and C ₉ , R ₁₆ and C ₁₀ , R ₁₇ and
C ₁₁ ), and feedback resistors R ₁₈ , R ₁₉ , and R ₂₀ are inserted between the inverting input terminals and output terminals of the operational amplifiers A ₁ , A ₂ , and A _{3 ,} respectively. The above resistors R ₁₂ , R ₁₃ , R ₁₄ and feedback resistor R ₁₈ ,
The relationship between R ₁₉ and R ₂₀ is R ₁₂ = R ₁₃ = R ₁₄ ≪ R ₁₈ = R ₁₉ =
R ₂₀ , the output terminals of the operational amplifiers A ₁ , A ₂ , A ₃ are phase-shifted from the output signals U ₂ , V ₂ , W ₂ sent from the output terminals _au , _av , aw of the delay _circuit . output signal U ₁ ,
Subtract V ₁ and W ₁ (U ₁ − U ₂ , V ₁ − V ₂ , W ₁ −
W ₂ ), this is inverted and amplified with a large amplification degree, and alternating square wave output signals U ₃ , V ₃ , W ₃ with a phase difference of approximately 180° with respect to the above-mentioned phase voltage V _F are sent out, respectively. I'm starting to do that. This subtraction amplifier circuit 1
The delay circuit in 05 is provided to accurately detect the inflection point at the peak of the output waveform of each phase shifter (i.e., the zero-crossing point of the phase voltage V _F ).
The CR time constant is set to about 10 μS to 100 μS to send out an output whose phase is slightly delayed from that of the phase shifter output, and the operational amplifiers A ₁ , A ₂ ,
Since the amplification degree of A ₃ is set large so that the relationship R ₁₂ = R ₁₃ = R ₁₄ ≪ R ₁₈ = R ₁₉ = R ₂₀ is established, the output signal is a rectangular wave with saturated ripples due to inversion amplification. It's becoming like that. The integrating section 106 _connects two resistors and capacitors (R ₂₁ , R ₂₂ and C ₁₂ , R _{23 , R 24} and C ₁₃ , R ₂₅ , R ₂₆ and
C ₁₄ ) in series, and the connection points of the above two resistors (R ₂₁ and R ₂₂ , R ₂₃ and R ₂₄ , R ₂₅ and R ₂₆
) are the output terminals, and the above two resistors are
When setting the relationship R ₂₁ = R ₂₃ = R ₂₅ ≫ R ₂₂ = R ₂₄ = R ₂₆ and integrating the output of the subtraction amplifier 105 with a 90° phase delay, the integral alternates between positive and negative in a substantially triangular waveform. so that the zero-crossing point of the waveform is slightly advanced in phase (i.e., the zero-crossing point of the integral waveform is the phase voltage V _F
Output signals U ₄ , V ₄ , and W ₄ (corresponding with a 90° phase delay with respect to the zero-crossing point of ) are sent out from each of the output terminals. The comparator 107 connects the inverting input terminals of comparators CP _u , CP _v , CP _w consisting of operational amplifiers to each output terminal of the integrator 106 via capacitors C ₁₅ , C ₁₆ , C ₁₇ , respectively. Insert resistors R ₂₇ , R ₂₈ , and R ₂₉ between the inverting input terminal and circuit ground, respectively, and connect the above comparator.
The non-inverting input terminals of CP _u , CP _v , CP _w are connected to the circuit ground, and each output of the integrating section 106 is inputted to the comparators CP _u , CP _v , CP _w via AC coupling, and the input terminals and the virtual Compare the sex point voltages and use comparators CP _u , CP _v , CP _w
Rectangular wave comparison signals U ₀ , V ₀ , and W ₀ having a phase difference of 120° from each other are sent from the output terminals to the distribution circuit 11 at a duty ratio of 50%.

Next, the position detection operation of the rotor 6 will be explained. The rectifier circuit 2 receives an AC power source 1 (for example, AC 100 V, 60 Hz) via a reactor 3, and supplies a DC output voltage obtained by rectifying and smoothing the AC power source 1 to a doubled voltage to an inverter circuit 7 and a virtual neutral point circuit 101.

Next, the electric motor 4 is started. As is well known, the distribution circuit 11 responds to the starting signal from the starting circuit 14, and the inverter circuit 7 is connected to the output terminal of the distribution circuit 11.
The switching elements Q _u , Q _x , Q _v , Q _y , Q _w , Q _z are sequentially sent open/close signals to their bases via the base driver BD, and the switching elements are
Conducting and disconnecting in the order of Q _u → Q _z → Q _v → Q _x → Q _w → Q _y , energizing each phase of the stator winding 5 in turn and starting the motor 4, the output frequency of the inverter circuit 7 gradually increase to a predetermined frequency (e.g. about 20Hz), and increase the rotation speed to a predetermined number (e.g.
The starting circuit 14 performs a so-called additional braking operation to increase the speed up to about 600 rpm. Thereafter, a so-called self-control operation is performed in which each switching element of the inverter circuit 7 is made conductive or disconnected as appropriate via the distribution circuit 11 in response to the position detection signal from the position detection circuit 100.

In this self-control operation, when the switching element is pulse-width-modulated and switched in order to control the speed of the motor 4, the winding voltage of each phase of the stator winding 5 changes depending on whether the switching element is turned on or off. When the output of the rectifier circuit 2 is applied, and looking at one phase, it has a cutting spice V _S2 that occurs during switching and a spike voltage V _S1 that occurs when switching the switching element, and the voltage is positive and negative around the virtual neutral point EN. This is shown as an alternating substantially trapezoidal voltage waveform, which is input as a phase voltage V _F to each clamper of the voltage clamp circuit 102 (input in FIG. 4 102). At this time, the virtual neutral point EN is such that the virtual neutral point circuit 101 always derives a voltage that is 1/2 of the output voltage of the rectifier circuit 2.
Shown as a stable virtual neutral point voltage. Then, the winding voltage of each phase of the stator winding 5 is determined as the phase voltage.
Each clamper of the voltage clamp circuit 102 received as _VF has a pair of constant voltage diodes (ZD ₁ and
Zener voltage V _Z of ZD ₂ , ZD ₃ and ZD ₄ , ZD ₅ and ZD ₆ )
The voltages are clamped to a constant value and output voltages of approximately rectangular waves are transmitted. At this time, the load on the motor increases and the ripples superimposed on the rectified and smoothed output increase, causing unbalance in the winding voltage of each phase of the stator winding 5, and the peak value of the phase voltage V _F of each phase. Even if unbalance occurs, phase voltages with stable peak values are output from each of the clamps (see Fig. 4, 10).
2 output). Each phase shifter of the phase shift circuit 103 receives the output of each clamper of the voltage clamp circuit 102, and integrates the input voltage using a resistor and a capacitor.
The output voltages, which are converted to approximately triangular waveforms with a 90° phase lag and alternate between positive and negative around the virtual neutral point EN, are sent out as output signals U ₁ , V ₁ , and W ₁ (output 103 in Figure 4). ). At this time, the neutral point of the voltage clamp circuit 102 and the phase shift circuit 103 connected in a three-phase star shape is the virtual neutral point EN of the virtual neutral point circuit 101.
The virtual neutral point circuit 101 has an impedance sufficiently low with respect to the power frequency of the AC power supply 1, and is set to an impedance sufficiently lower than the leakage impedance of each switching element of the inverter circuit 7 when it is off. Therefore, the voltage-clamped output is phase-shifted with a 90° phase lag without being affected by the induced voltage due to variations in leakage impedance when the switching element is off, and the output of each phase shifter is equal to the phase voltage. It becomes a nearly triangular wave shape with a peak at the zero cross point of V _F ,
This is a waveform that accurately captures the above zero-crossing point.
Further, when the electric motor 4 is used for a compressor, for example, and the load changes during one rotation of the electric motor 4,
A so-called wow and flutter phenomenon occurs that causes unevenness in the rotational speed during rotation, causing a phase imbalance in the winding voltage of each phase of the stator winding 5, resulting in a difference in the positive and negative charging times for the phase shifter capacitor. Even if the above phase shifter outputs a DC-shifted waveform with respect to the virtual neutral point EN, the phase voltage
The inflection point at the peak corresponding to the zero crossing point of V _F is accurately output without change. Then, the output signal of each phase shifter of the phase shift circuit 103 is
The subtraction amplification section 105 of the comparator circuit 104 that receives U ₁ , V ₁ , W ₁ outputs the output signals U ₁ , V ₁ , W ₁ of the phase shifter.
Then, the output signals U ₂ , V ₂ , W ₂ are obtained by delaying the output signals U ₁ , V ₁ , W ₁ by a time period determined by the CR time constant using a delay circuit (i.e., the above output signals U ₁ ,
The output signal obtained by slightly delaying the phase of V ₁ and W ₁ (point a in Fig. 4, 105) is subtracted (U ₁ - U ₂ ,
V ₁ −V ₂ , W ₁ −W ₂ ), the waveform is
As shown by the input difference of A in Figure 4 105, the phase voltage
At the zero-crossing point delayed by the phase with respect to the zero-crossing point of V _F , a substantially rectangular wave signal that alternates between positive and negative and has ripples is obtained, and this is transmitted to the resistors R ₁₂ , R ₁₃ , R ₁₄
By inverting and amplifying the large amplification determined by R ₁₈ , R ₁₉ , and R ₂₀ , the above ripple is saturated,
Output signals U ₃ , V ₃ , W ₃ which alternate between positive and negative with a rectangular wave having a phase difference of 180° with respect to the phase voltage V _F are output from the output terminals of operational amplifiers A ₁ , A ₂ , A ₃ with a delay of the phase. (output of 105 in FIG. 4). The integrating section 106 that receives the output signals U ₃ , V ₃ , W ₃ integrates the input signals U ₃ , V ₃ , W ₃ with a 90° phase lag, and outputs an output signal U having a substantially triangular waveform alternating between positive and negative. ₄ , _V4 ,
W ₄ respectively (output of 106 in FIG. 4).
At this time, the integrating section 106 connects two resistors (R ₂₁ and
R ₂₂ , R ₂₃ and R ₂₄ , R ₂₅ and R ₂₆ ) and capacitor C ₁₂ ,
The input signals U ₃ , V ₃ , and W ₃ are integrated by C ₁₃ and C ₁₄ respectively, and the output signals U ₄ , V ₄ , and W ₄ are sent out from the connection point (output end) between the two resistors. and two resistors R ₂₁ = R ₂₃ = R ₂₅ ≫ _{R 22} =
Since the relationship R ₂₄ = R ₂₆ is set, when the polarity of the input signals U ₃ , V ₃ , W ₃ is reversed, the voltage at the output terminal is the same as that of the input signals U ₃ , V ₃ , W _{3 .} Voltages V _u3 , V _v3 , V _W3 after polarity reversal and capacitors C ₁₂ , C ₁₃ ,
The charging voltage V _c12 immediately before the above input signal polarity reversal of C ₁₄ ,
The voltage V _d (for example, (V _u3 − V _c12 ) R ₂₂ /R ₂₁ + R ₂₂ ), which is the difference between V _c13 and V _c14 multiplied by the voltage division ratio of the two resistors, changes sharply toward zero voltage, and then The output waveform (fourth
106), the zero-crossing point of the output waveform of _the output signals _{U 4} , V ₄ , W ₄ of the integrating section 106 _is simply 90 It is slightly on the leading side (that is, on the leading side by the phase shift) of the zero-crossing point of the output waveform when integrated over the phase lag. That is, the phase shift with respect to the phase voltage V _F is corrected. As a result, even if the input signal is a signal with a phase difference of 180° that is delayed by the phase with respect to the phase voltage V _F , the integrating section 106 can set the zero-crossing point of its output waveform at 270° with respect to the zero-crossing point of the phase voltage V _F. This can be obtained by phase difference. The comparator CP _u of the comparator 107 that received this,
CP _v and CP _w are inputted by blocking the DC component through AC coupling by the capacitor and resistor (C ₁₅ and R ₂₇ , C ₁₆ and R ₂₈ , C ₁₇ and R ₂₉ ) provided at the inverting input terminal. , this input is compared with the input of _the non-inverting input terminal (virtual neutral point voltage) and inverted to produce a rectangular wave output signal U ₀ , V with a duty ratio of 50% that is 90° phase delayed with respect to the phase voltage V F ₀ and W ₀ are sent out from the output terminals of comparators CP _u , CP _v , and CP _w, respectively, with phases that are 120° different from each other.
The position detection circuit 100 sends these to the distribution circuit 11 as position detection signals U ₀ , V ₀ , and W ₀ of the rotor 6, respectively.

In the above position detection operation, the inverter circuit 7
Let T be the period of the output frequency of , and let td be the delay time of the delay circuit of the subtraction amplification section 105 , when the above output frequency is low ((i.e., when the rotational speed of the motor 4 is low)
Since the period T is long and the delay time td is constant, the phase shift determined by 2・td/T×2π is extremely small with respect to the period T. As the integration time becomes longer, the output of the section 106 becomes larger, and the amplitude of the output waveform that alternates between positive and negative in a substantially triangular waveform increases, and the ratio of the voltage V _d that suddenly changes when the polarity is reversed to this amplitude becomes smaller. If the zero-crossing point in the output waveform of is corrected to a smaller value on the advancing side, and if the output frequency becomes higher (that is, if the rotational speed of the electric motor 4 becomes higher), the period T becomes shorter, and the above relational expression 2. As can be understood from td/T×2π, the phase delay increases, but the integration time of the output from the integrating section 106 due to this decreases, and the amplitude of the alternating approximately triangular waveform decreases. , the ratio of the voltage V _d that suddenly changes at the time of polarity reversal to this amplitude increases, and the zero-crossing point in the output waveform of the integrating section 106 is greatly corrected to the advancing side. In other words, the zero-crossing point of the output waveform of the integrating section 106 is corrected to the leading side according to the magnitude of the phase shift that changes according to the output frequency (that is, according to the rotational speed), and the zero-crossing point of the phase voltage V _F is adjusted to the leading side. to the point
A zero-cross point signal having a 270° phase difference can be obtained from the integrating section 106, and this signal is sent to the comparing section 107.
By comparing and inverting at , it is possible to accurately obtain a signal with a phase delay of 90° with respect to the phase voltage V _F . This means that the position of the rotor 6 can be accurately detected without interfering with the operation of the electric motor 4 even when the rotation of the electric motor 4 ranges from low speed to high speed.

Furthermore, when the electric motor 4 is used as a compressor, the load fluctuates during one rotation, resulting in uneven rotational speed during one rotation, which is the so-called wow and flutter phenomenon, which causes the phase of the winding voltage of each phase of the stator winding 5 to change. When an unbalance occurs and a shift occurs in the integration time in the positive and negative polarity directions in each phase shifter of the phase shift circuit 103, the bypass resistors R ₉ , R ₁₀ , and R ₁₁ quickly discharge the DC current. In order to suppress the accumulation of charge that causes a shift, the output signals U ₁ , V ₁ , W ₁ of each phase shifter are AC-coupled via the subtraction amplification section 105 and the integration section 106 for comparison. Therefore, the comparison signal U ₀ ,
Preventing phase shift between V ₀ and W ₀ and adjusting for phase voltage V _F
This means that a position detection signal with a 90° phase delay can be obtained accurately.

In the above embodiment, the comparison circuit 104 of the position detection circuit 100 detects the phase voltage by the subtraction amplification section 105.
Output signals U ₃ , V ₃ , W ₃ alternating with rectangular waves having a phase difference of 180° delayed by the phase with respect to V _F are obtained, and these are compared with the virtual neutral point voltage via the integrating section 106. Although it has been explained that a position detection signal with a phase delay of 90° is obtained with respect to the phase voltage V _F , instead of this, as shown in FIG. The non-inverting input terminals of amplifiers A ₁ , A ₂ , and A ₃ are connected, and the inverting input terminal is connected to a delay circuit consisting of a resistor and a capacitor (R ₁₅ and C ₉ , R ₁₆ and C ₁₀ , R ₁₇ and C ₁₁ ). Connected through operational amplifier A ₁ ,
Feedback resistor between the inverting input terminal and output terminal of A ₂ and A ₃
By inserting R ₁₈ , R ₁₉ , and R ₂₀ respectively, the outputs U ₁ , V ₁ , and W ₁ of each of the above phase shifters are subtracted by the outputs delayed by the phase through the delay circuits, and this is done with a large amplification factor. A subtraction amplification unit 105' that amplifies and outputs alternating output signals U ₃ ′, V ₃ ′, and W ₄ ′ with rectangular waves having the same phase difference with respect to the phase voltage V _F with a slight phase delay and sends them out respectively. , an integrating section 106 formed in the same manner as described above, and a comparator at each output terminal of this section.
The non-inverting input terminals of CP _u , CP _v , CP _w are connected respectively, and the inverting input terminals of the comparators CP _u , CP _v , CP _w are connected to resistors and capacitors (R ₃₀ and C ₁₈ , R ₃₁
and C ₁₉ , R ₃₂ and C ₂₀ ), and the outputs U ₄ ′, V ₄ ′, W ₄ ′ of the integrating section 106 are averaged by the low-pass filter. Signals compared with the output U ₀ , V ₀ ,
Comparison unit 10 configured to send W ₀ respectively
7' is provided, and even if the output of each phase shifter of the phase shift circuit 103 includes a DC shift component, this is corrected by the above-mentioned low-pass filter, and the phase voltage V _F is On the other hand, comparison signals U ₀ , V ₀ , and W ₀ with a phase delay of 90° may be sent out as position detection signals.

According to the present invention, the rotor position is detected by forming a signal having the same phase or a 180° phase difference with respect to the phase voltage, with a slight phase shift, and transmitting the signal with respect to the phase voltage.
Since the position detection signal is obtained by comparing and detecting the integrated output with a 90° phase delay, even if the switching element of the inverter circuit is pulse width modulated and switches, it will not be affected by this. The position of the rotor can be detected accurately. Moreover, outputs with the same phase or a 180° phase difference are obtained by installing a low-impedance virtual neutral point circuit at the output end of the rectifier circuit that rectifies and smoothes the commercial AC power source, and outputs the output with the same phase or a 180° phase difference. The star-wired voltage clamp circuit of the clamper is connected to each phase of the star-wired stator winding at the power point, and the phase shifter connected to the output end of the clamper is star-wired. The neutral point of the phase shift circuit is connected to ground the circuit, thereby stabilizing the neutral point voltage and preventing the superposition of induced components due to variations in leakage impedance when the switching element is turned off. Since the output of the phase shifter and the output slightly delayed from the phase of the phase shifter are subtracted and amplified, it is possible to accurately detect the zero crossing point of the phase voltage, and the above slight phase delay is due to the difference between the two. A position detection signal with a phase delay of 90° relative to the phase voltage can be obtained by easily correcting the integration using a resistor and a capacitor, and switching can be performed over the entire motor speed range from low speed to high speed without the need for special correction means. The position of the rotor can be accurately detected even when the element is switched by pulse width modulation.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional example, and Fig. 2 is a voltage waveform diagram of each part explaining the operation of Fig. 1. Figure C shows the case of overload.
FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG.
This figure is a voltage waveform diagram of each part explaining the operation of FIG. 3, and FIG. 5 is a block diagram showing another embodiment of the comparison circuit of FIG. 4. 1: Commercial AC power supply, 2: Rectifier circuit, 4: Brushless DC motor, 5: Stator winding, 6: Rotor,
7: Inverter circuit, 100: Position detection circuit, 1
01: Virtual neutral point circuit, 102: Voltage clamp circuit, 103: Phase shift circuit, 104, 104': Comparison circuit, 105, 105': Subtraction amplifier section, 106:
Integration section, 107, 107': Comparison section.

Claims (1)

[Claims] 1. A brushless DC motor consisting of a star-connected stator winding and a rotor, and a plurality of switching elements connected to a commercial AC power source in a bridge shape via a rectifier circuit, and the output end of the stator winding connected to the stator winding. The switching element is equipped with an inverter circuit connected to each phase, and a position detection circuit that detects the rotor position from the winding voltage of the stator winding and sends a position detection signal that makes the switching element conductive or disconnected as appropriate. In a device in which each phase of the stator winding is sequentially energized, the position detection circuit has two terminals connected to the output end of the rectifier circuit.
A virtual neutral point circuit is created by connecting two capacitors in series, inserting a resistor between the terminals of each capacitor, and grounding the circuit by using the connection point between the capacitors as a virtual neutral point. There is a voltage clamp circuit in which a clamp device consisting of a resistor connected to each phase and a pair of voltage regulator diodes connected in anti-series is connected in a star shape, and the neutral point is connected to the above virtual neutral point. A phase shifter that outputs a substantially triangular wave voltage whose phase is shifted by 90° by integrating it with a resistor and a capacitor connected in series to the output terminal of each clamp device is star-wired and neutralized. a phase shift circuit whose point is connected to the virtual neutral point, and at the output end of each phase shifter of the phase shift circuit, the output of the phase shifter and this are slightly delayed in phase through a delay circuit. A subtraction amplification section consisting of an operational amplifier that operationally amplifies the output and outputs it, and the output of this is integrated to a 90° phase delay using two resistors and a capacitor connected in series, and the above two resistors are connected. A comparison circuit is provided, which consists of an integrating section that outputs from a point, and a comparing section that sends out a signal that compares the output of this with the virtual neutral point voltage. A rotor position detection device for a brushless DC motor, characterized in that a position detection signal is obtained from a signal having a phase or a 180° phase difference.