JPH0470879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a drive circuit for a three-phase bidirectional current-carrying brushless DC motor.

BACKGROUND TECHNOLOGY AND PROBLEMS As a method of reducing torque ripple in brushless DC motors, conventionally, the rotor magnet used to form the field is made into a trapezoidal wave-like magnetization pattern, and the magnetic flux linkage of the coil in the energized area is kept almost constant. The following method is used. However, with this method, it is difficult to make the flux linkage completely constant in the energized area, and a drop in torque occurs near the shoulder of the trapezoidal wave, resulting in torque ripple. Further, by forming a trapezoidal wave-like magnetization pattern, the effective magnetic flux may be reduced, and the output of the motor may be reduced.

As a method to obtain a constant torque that is independent of the field waveform, the coil flux linkage B is detected and a drive current proportional to 1/B is applied to generate the torque (linkage flux x current).
A driving method has been proposed that keeps the constant. As a method for detecting coil linkage magnetic flux, a method using a magnetically sensitive detection element such as a Hall element, and a method in which a detection coil is wound overlappingly with a motor drive coil are generally used. These methods have a problem in that the number of coupling wires between the motor and the drive circuit increases by the number of detection elements or detection coils. Note that when detecting with a detection element such as a Hall element, it is conceivable to use the detection element that detects the rotational position of the rotor and obtains the energization switching signal of the drive coil of each phase and the coil flux linkage detection element. Due to the timing of energization switching, the rotor position detection element and the drive coil are rarely arranged in the same phase, and therefore, it is often substantially difficult to detect the interlinkage magnetic flux of the drive coil.

In addition, when detecting magnetic flux linkage with a Hall element, etc.,
The output of the detection element includes DC offset and drift, which requires a means to correct them in a circuit, and since it is point detection, it has a predetermined area facing the rotor magnet (coil area). It is difficult to accurately represent the flux linkage of the coil.

On the other hand, when detecting interlinkage magnetic flux with a detection coil wound over the motor drive coil, there are problems in that the winding structure of the motor becomes complicated and the winding space of the drive winding decreases, resulting in a decrease in efficiency.

Purpose of the Invention The present invention solves the above-mentioned problems by detecting a signal extremely close to the actual interlinkage flux of each drive coil and applying a current proportional to the reciprocal of the signal to each coil without providing any special detection element or detection coil. The purpose of this is to obtain constant torque without torque ripple.

SUMMARY OF THE INVENTION The present invention provides a three-phase bidirectional current-carrying brushless motor in which two current-carrying phases overlap each other. A circuit that obtains an approximate signal of the composite flux linkage of two energized phases by adding integral signals of two energized phases and subtracting a signal with twice the level of the integral signal of a non-energized phase from the added signal. , and a circuit for causing a drive current proportional to the reciprocal of the approximate signal to flow through the energized phase.

Embodiments Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the principle of a brushless motor drive circuit according to the present invention. In FIG. 1, the drive current i of the motor 1 is controlled by a series control transistor 2. In FIG. The current of this transistor 2 is detected by a minute resistor R, and the detection voltage iR
is fed back to the voltage-current conversion circuit 3, so that a current i=V _c /R corresponding to the input control voltage V _c of the voltage-current conversion circuit 3 is caused to flow. On the other hand, the induced voltage of the drive coil of the motor 1 is detected by the induced voltage detection circuit 4, and the flux linkage approximation circuit 5 generates the flux linkage approximation signal E of the energized phase based on the detection output. This approximate signal E is given to a multiplier 6 and multiplied by the drive current detection voltage iR. The multiplication result, iRE, is given to the operational amplifier 7 and compared with the torque command voltage V (for example, speed servo voltage), and the control voltage V _c , that is, the current i (=V _c /R) is controlled so that V = iRE. Ru.

As a result, a current i=V/RE flows that is inversely proportional to the interlinkage magnetic flux of the energized phase and proportional to the torque command voltage V, and a constant torque (current x magnetic flux) that is unrelated to the interlinkage flux waveform is obtained.

Next, Fig. 2 is a circuit diagram of a brushless motor drive circuit that can be considered when embodying the principle circuit shown in Fig. 1, and Figs. 3, 4, and 5 show the operation of the circuit shown in Fig. 2. They are a waveform diagram and a vector diagram for explanation.

This motor is a three-phase bidirectional current-carrying brushless motor, and the three-phase coils 11 to 13 are Y-connected and driven by push-pull connected switching transistors 14, 14', 15, 15', 16, 16'. be done. Figures 3a to 3c show the interlinkage magnetic fluxes Ba, Bb, and Bc of each phase. Each phase is energized alternately in the positive and negative directions, as shown by the shaded areas in Figure 3 a, b, and c, for each 120°C interval centered on the maximum positive and negative positions of its interlinkage magnetic flux. . Therefore, the conduction angles of each phase overlap each other by 60 degrees, current is always passed through the coils of the two phases, and a composite torque of the two phases is generated sequentially. For example, in FIG. 2, when transistors 16 and 14' are on, current flows through A-phase coil 11 and B-phase coil 12. At this time, the C-phase coil 13 is not energized.

Each switching transistor 14, 14'-1
The switching signals applied to 6 and 16' are formed in a switch circuit 18 based on the output of a rotor position detector 17, such as a Hall element.

Assuming that the field waveform generated by the rotor magnet is a sine wave, the composite vector of the flux linkages of the energized phases (for example, A phase and B phase) is B ₁ for the fundamental wave component, as shown in the vector diagram of Fig. 4a. a−B ₁ b＝B ₁ ab
Therefore, a torque proportional to the product of this magnetic flux B ₁ ab and the drive current i is generated.

As is clear from FIG. 4a, the composite flux linkage (B ₁ ab) of the energized phase is 90° ahead of the flux linkage (B _c ) of the non-energized phase. That is, if the interlinkage magnetic fluxes of the energized phase are sin θ and sin (θ+120°), the combined magnetic flux is 3 sin (θ+240°+90°). θ+240° matches the phase of the non-energized phase. Therefore, the composite interlinkage flux of the two energized phases involved in torque generation can be approximated by a signal obtained by detecting the induced voltage of the non-energized phase coil and advancing the phase by 90 degrees.

In FIG. 2, the induced voltages in the coils 11-13 of each phase are derived via switches 19-21.
These switches 19 to 21 are the switch circuit 18
, and only the switch corresponding to the non-energized phase is closed. As a result, the induced voltage waveform of the non-energized phase shown in FIG. 3d is obtained from the common connection output of each switch 19-21. This waveform corresponds to the magnetic flux waveforms other than the shaded areas in FIGS. 3a to 3c, which are sequentially extracted.

The detected induced voltage waveform is given to the differentiating circuit 23 via the operational amplifier 22, and the fine powder (90° phase advance) is
be done. The output of the differentiating circuit 23 (FIG. 3e) is rectified by the full waveform rectifying circuit 24 as shown in FIG. 3c. This rectified output corresponds to the composite flux linkage of the energized phase, as described above. The output of the full-wave rectifier circuit 24 is given to the multiplier 6 as the flux linkage approximation signal E. By controlling the multiplier 6 and the operational amplifiers 7 and 3, a motor drive current that is inversely proportional to the magnetic flux and proportional to the torque command voltage V as shown in FIG. 3g is caused to flow.

However, in the brushless motor shown in Figure 2,
The field waveforms generated by the rotor magnet are shown in Figure 3a,
If the waveform is not a perfect sine wave like b and c, but is close to a trapezoidal wave, for example, harmonic components are included in the interlinkage magnetic flux of the coils of each phase. Considering the third harmonic, which has the largest spectrum among the harmonic components, as shown in Figure 4b, the A-phase interlinkage magnetic flux B ₃ a = sin3θ
, the B-phase and C-phase interlinkage flux is B ₃ b=sin3
(θ+120°)=sin3θ, B ₃ c=sin3(θ+240°)=sin
3θ
Therefore, they are each in phase. Therefore, the third harmonic component (B ₃ ab) of the composite flux linkage of the energized phases (for example, A and B phases) is always zero. That is, even if the third harmonic is included in the interlinkage bundle of each phase, this component is essentially not included in the generated torque.

On the other hand, regarding the flux linkage approximation signal E obtained by advancing the induced voltage of the non-energized phase by 90°, for example, when the non-energized layer is in phase C, its fundamental wave component E is as shown in Fig. 5a. ₁ c is in phase with the composite interlinkage flux of the two energized phases (for example, A phase and B phase) as described above.
However _, the third harmonic component E ₃ c leads the harmonic component E 3 c which is in phase with the harmonic components E ₃ a and E ₃ b of the A phase and B phase by 90 degrees, as shown in Fig. 5b. It is something that has been done,
This does not become zero and is also different in phase from the fundamental wave component E′ ₁ c. On the other hand, the third harmonic component B ₃ ab of the combined interlinkage flux of the A phase and B phase is zero as described above.
Therefore, a third harmonic component is included in the drive current proportional to the reciprocal of the flux linkage approximation signal E, causing distortion in the generated torque.

Next, FIG. 6 is a drive circuit diagram of a three-phase bidirectionally energized brushless motor according to an embodiment of the present invention that solves the above-mentioned problems. In FIG. 6, the same parts as in FIG. 2 are given the same reference numerals.

In FIG. 6, the induced voltages Ea, Eb, and Ec of the coils 11-13 of each phase are integrated by operational amplifiers 26-28 and integration circuits 29-31. These integrating circuits 29 to 31 correspond to the differentiating circuit 23 in FIG.
It has the function of shifting the phase of ~Ec by 90°.

The outputs E'a, E'b, and E'c of the integrating circuits 29 to 31 are selected by the switch circuit 25 and outputted to the inverting multiplier 32 and the adder 33. The switch circuit 25 includes three switches 19a to 19 for each phase.
c, 20a to 20c, 21a to 21c..., and by a control signal from the switch circuit 18,
The switch a, the switch b, or the switch c corresponding to the non-energized phase is closed simultaneously for each phase. As a result, the induced voltage of the non-energized phase is reduced by the inverting multiplier 32.
The induced voltages of the two energized phases are respectively derived to an adder 33 and added to each other. For example, when the C phase is a non-energized phase, the induced voltage E'c is applied to the inverting multiplier 3 through the switch 21c.
The induced voltages E'a and E'b of the energized phase are derived to the adder 33 through switches 19c and 20c.

Note that the induced voltage of the energized phase has a component of drive current x coil impedance superimposed on it, so although it is not strictly the coil linkage flux itself, it can be considered to approximately represent the linkage flux.

The outputs of the inverting multiplier 32 and the adder 33 are added by an adder 34, and further rectified by a full-wave rectifier circuit 24 to form an approximate signal E corresponding to the composite flux linkage of the energized phase. Based on this approximate signal, the multiplier 6 and operational amplifiers 7 and 3 cause a drive current i proportional to the reciprocal of the interlinkage flux to flow, as in FIG. 2.

7a and 7b are vector diagrams showing signal processing (arithmetic) operations from the integrating circuits 29 to 31 to the adder 34 in FIG. 6, and FIGS. 8a to 8c are frequency spectrum diagrams of the processed signals. Operational amplifier 26 in Figure 6
The induced voltage (for example, Ec) of the non-energized phase detected by 28 has a fundamental wave f ₁ , a harmonic wave f 3 , and a harmonic wave f ₃ as shown in FIG.
It has f ₅ ... components. These harmonic components pass through integration circuits 29-31 and are attenuated as shown in FIG. 8b. The harmonic components of the induced voltage in the energized phase are similarly attenuated by integration, but at this time, the distortion components in the induced voltage detection signal that exhibits a discontinuous waveform due to switching energization are As a result, a substantially sinusoidal induced voltage detection output is obtained.

Out of the outputs of the integrating circuits 29 to 31, the non-energized phase signal is multiplied by -2 by an inverting multiplier 32, the two energized phase signals are added together in an adder 33, and these are further added together in an adder 34. . As a result, for the fundamental wave component, ∫{(E ₁ a + E ₁ b) −
2E _1c }dt is performed to obtain an approximate signal E that is in phase with the composite flux linkage belt B ₁ ab shown in FIG. 4a. Note that although the integration and addition and subtraction are each performed separately, it is clear from the distribution law of integration that a result equivalent to integrating the result of addition and subtraction can be obtained as shown in the above equation.

Third-order high wave component of induced voltage of each phase E ₃ a, E ₃ b,
As mentioned above, E ₃ c appears in phase as shown in FIG. 7b. However, the calculation for these in-phase components∫
Since {(E ₃ a+E ₃ b)−2E ₃ c}dt is performed, the third harmonic component of the flux linkage approximation signal E becomes zero as shown in FIG. 8C. As a result, for the third harmonic component, both the composite interlinkage flux of the energized phase and the flux approximation signal E approximated from the induced voltage become zero. Therefore, an approximation signal that is extremely close to the actual combined magnetic flux linkage can be obtained, so that the distortion component of the generated torque is significantly reduced, and a constant torque with little fluctuation can be obtained.

In the embodiment shown in FIG. 6 described above, a divider may be provided to perform a reciprocal calculation of the flux linkage approximation signal E, and a drive current proportional to the division output 1/E may be caused to flow. Alternatively, instead of controlling the current using the series control transistor 2, a current control signal and a switching signal may be applied to the switching transistors 14 to 16, 14' to 16' so that the current is controlled at the same time as the current is switched. good.

Effects of the Invention As described above, the present invention detects the induced voltage of the three-phase coil, integrates it (90° phase shift), and subtracts the signal at twice the level of the non-energized phase from the signal obtained by adding the two energized phases. Since the structure is configured to obtain an approximate signal corresponding to the composite flux linkage of two energized phases, the third harmonic component included as an in-phase signal in the induced voltage of each phase generates an approximate signal. It disappears. Therefore,
Since an approximation signal extremely close to the actual composite flux linkage of the drive coil can be obtained without providing a special magnetic flux detection element or detection coil, the structure of the motor does not become complicated. In addition, by passing a drive current proportional to the reciprocal of the approximate signal to the coil of the energized phase,
It is possible to obtain a constant torque that is unrelated to rotational angle fluctuations of the field waveform, and even when the field waveform is not a sine wave, it is possible to obtain a rotational torque that is less affected by its distortion components.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the principle configuration of a brushless motor drive circuit according to the present invention, FIG. 2 is a circuit diagram showing an example of a motor drive circuit embodying the principle configuration of FIG. 1, and FIG. FIG. 4 a, b and FIG. 5 a, b are vector diagrams to explain the operation of FIG. 3. FIG. 6 is a three-phase diagram showing an embodiment of the present invention. A drive circuit diagram of a bidirectional energizing brushless motor, Fig. 7 a, b is a vector diagram showing the signal calculation process of Fig. 6, Fig. 8 a, b, c
is a frequency spectrum diagram of the processed signal. In addition, in the symbols used in the drawings, 1... motor, 2... series control transistor, 3...
Voltage-current conversion circuit, 4...Induced voltage detection circuit,
5...Flux linkage approximation circuit, 6...Multiplier, 7...
Operational amplifier, 11, 12, 13...Coil, 19
a, 19b, 19c... switch, 20a, 20
b, 20c...Switch, 21a, 21b, 21
c...Switch, 29, 30, 31... Integrating circuit, 32... Inverting multiplier.

Claims (1)

[Claims] 1. In a three-phase bidirectional current-carrying brushless motor in which two current-carrying phases overlap each other,
a circuit that detects the induced voltage of each of the three-phase coils;
By integrating the detected signal, adding together the integrated signals of the two energized phases, and subtracting from the added signal a signal that is twice the level of the integrated signal of the non-energized phase,
A drive circuit for a three-phase bidirectionally energized brushless motor, comprising a circuit that obtains an approximate signal of a composite flux linkage of two energized phases, and a circuit that causes a drive current proportional to the reciprocal of the approximate signal to flow through the energized phases.