Motor drive method

Abstract

To provide a motor drive method capable of improving a maximum output of a motor even if a dead time is secured by driving a three-phase DC brushless motor by overmodulation PWM control with a modulation factor in a predetermined range exceeding 100% in a sensor-less manner.SOLUTION: A control circuit 4 outputs a pulse signal having a duty ratio of 0% to an inverter circuit 2 when a predetermined minimum value is input as a modulation signal, outputs a pulse signal having a duty ratio of 100% to the inverter circuit 2 when a predetermined maximum value is input as the modulation signal, and outputs a pulse signal having a duty ratio of 100% to the inverter circuit 2 when an overmodulation signal having a maximum modulation degree, which is a ratio of a maximum value of the modulation signal relative to the predetermined maximum value, larger than 100% is input as the modulation signal and an overmodulation state occurs in which an instantaneous value of the modulation signal becomes larger than the predetermined maximum value.SELECTED DRAWING: Figure 30

Description

[Technical Field]

[0001] The present invention relates to a motor drive method for driving a three-phase DC brushless motor, for example for HVAC, in a sensorless manner using a pulse width modulation method to generate a sinusoidal wave. [Background technology]

[0002] When a three-phase DC brushless motor that does not use a Hall sensor for detecting the position of the permanent magnet field is driven by a sine wave using pulse width modulation control (PWM control), overmodulation control is not performed so as not to interfere with the position detection of the permanent magnet field. Also, although a method of superimposing harmonics on the fundamental wave of the sine wave is used, it is performed in a way that does not result in overmodulation.

[0003] Using sine wave drive, it is possible to reduce the noise and vibration of a three-phase DC brushless motor, but there are issues with this: two-phase modulation has a high maximum output but produces more noise and vibration than three-phase modulation, while three-phase modulation has lower noise and vibration than two-phase modulation but produces less maximum output. To solve these problems, a motor drive method has been proposed in which three-phase modulation is achieved by adding the same modulation period to all phases, including unmodulated phases, within a carrier cycle to the switching of two-phase modulation, which outputs a sinusoidal AC current, and by making the added modulation period half the non-energized period within the carrier cycle before the addition, thereby achieving both the high output of two-phase modulation and the low noise and vibration of three-phase modulation (Patent Document 1; Patent Publication No. 4581391). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4581391 Summary of the Invention [Problem to be solved by the invention]

[0005] When a three-phase DC brushless motor is driven using sine waves and PWM control without a sensor, dead time is used to detect the position of the permanent magnet field, making it difficult to actively use output with a duty ratio of 100%, which results in problems such as the inability to increase the maximum output of the motor, lowering the maximum rotation speed or maximum output for motors with high back electromotive force, and increasing the number of switching times of switching elements such as FETs provided in the inverter circuit of the motor drive device, resulting in increased heat generation from the switching elements. [Means for solving the problem]

[0006] The present invention has been made to solve the various problems mentioned above, and its purpose is to provide a motor drive method that can expect to improve the maximum output of the motor even while ensuring dead time by driving a three-phase DC brushless motor using overmodulation PWM control at a modulation degree exceeding 100% in a predetermined range without a sensor.

[0007] A motor drive method for driving a three-phase brushless motor using a pulse width modulation system, wherein the three-phase brushless motor comprises an inverter circuit having output elements for three phases, each having a pair of high-side and low-side arms, and outputting current to coils for each of the three phases of the three-phase brushless motor; and a control circuit that performs pulse width modulation to determine a duty ratio based on an input modulation signal and output a pulse signal, and controls the output of the pulse signal to the inverter circuit, wherein the control circuit outputs a pulse signal with a duty ratio of 0% to the inverter circuit when a predetermined minimum value is input as the modulation signal, outputs a pulse signal with a duty ratio of 100% to the inverter circuit when a predetermined maximum value is input as the modulation signal, and outputs a pulse signal with a duty ratio of 100% to the inverter circuit when an overmodulation signal having a maximum modulation degree greater than 100%, which is the ratio of the maximum value of the modulation signal to the predetermined maximum value, is input as the modulation signal, resulting in an overmodulation state in which the instantaneous value of the modulation signal exceeds the predetermined maximum value.

[0008] In this way, when an overmodulated signal having a maximum modulation degree, which is the ratio of the maximum value of the modulated signal to the predetermined maximum value, greater than 100% is input as a modulated signal, the control circuit outputs a pulse signal with a duty ratio of 100% to the inverter circuit when the instantaneous value of the modulated signal is greater than the predetermined maximum value, thereby achieving low noise and vibration, improving motor output, and reducing the number of switching operations to suppress heat generation in the switching elements.

[0009] The modulating signal may be a signal in which a sine wave of a predetermined frequency is superimposed on a sine wave of a frequency three times the predetermined frequency, and the modulation degree in the overmodulation state when using the signal as the modulating signal may be up to 130%. In this way, by setting the upper limit of the modulation degree in an overmodulation state to 130% when using a modulation signal in which a sine wave of a predetermined frequency is superimposed on a sine wave of a frequency three times the predetermined frequency, the maximum output of the motor can be improved with the modulation degree of 130% being the upper limit at which the motor output level peaks.

[0010] The three-phase brushless motor may be a sensorless motor. In this case, it is possible to ensure the dead time for detecting the position of the permanent magnet field while ensuring the accuracy of detecting the position of the permanent magnet field in sensorless driving.

[0011] The rotor position detection method for a sensorless motor may be either a one-shunt FOC sensorless detection method in which at least one phase is in a switching state during sensing to estimate the magnetic pole position, or a detection method in which sensing to estimate the magnetic pole position is performed during dead time, or both. In this way, by driving the sensorless motor in an overmodulation state within a specified range where the modulation degree exceeds 100%, it is possible to improve the maximum output of the motor even when the motor is rotating or stopped, while ensuring dead time in sensing for magnetic pole position estimation.

[0012] The control circuit has a three-phase modulation operation mode in which a pulse width modulation signal is output to the coils of each of the three phases of the three-phase brushless motor to drive the motor, a two-phase modulation operation mode in which a pulse width modulation signal is output to the coils of two of the three phases of the three-phase brushless motor to drive the motor, and a transition operation mode in which a transition modulation signal is output that gradually changes the mixed ratio of the pulse width modulation signal for each phase of the three-phase modulation operation mode and the pulse width modulation signal for each phase of the two-phase modulation operation mode to drive the motor, and the motor may be operated in the three-phase operation mode from start-up to a maximum output at which an overmodulation state occurs, or in the two-phase operation mode from start-up to a maximum output at which an overmodulation state occurs, or may be operated by starting in the three-phase operation mode and switching to the two-phase operation mode via the transition operation mode as the output increases and operating up to the maximum output at which an overmodulation state occurs. As a result, when a three-phase DC brushless motor is driven at low speeds, it is driven by a three-phase overmodulation PWM drive signal that has good controllability, and when it is driven at high speeds, high loads, or high temperatures, it is driven by a two-phase overmodulation PWM drive signal that has good energy utilization efficiency.This makes it possible to reduce vibration and noise at high output when driven at low speeds, and to reduce the number of switching times at high output at high speeds, high loads, and high temperatures, thereby reducing the amount of heat generated by the switching elements and contributing to energy savings. [Effects of the Invention]

[0013] By driving a three-phase DC brushless motor using overmodulation PWM control without a sensor at a modulation factor exceeding 100% within a predetermined range, it is possible to provide a motor drive method that can expect to improve the maximum output of the motor even while ensuring dead time. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a terminal voltage waveform diagram when the modulation signal applied to the motor coil in the three-phase modulation operation mode is a sine wave. [Figure 2] FIG. 2 is a diagram showing interphase voltage waveforms in the three-phase modulation operation mode of FIG. [Figure 3]FIG. 3 is a terminal voltage waveform diagram when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave in which a third harmonic is superimposed at 1 / 6 on the fundamental wave. [Figure 4] FIG. 4 is a diagram showing interphase voltage waveforms in the three-phase modulation operation mode of FIG. [Figure 5] FIG. 5 is a diagram showing terminal voltage waveforms when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave and the modulation degree is 100%. [Figure 6] FIG. 6 is a terminal voltage waveform diagram when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave and the modulation degree is 130%. [Figure 7] FIG. 7 is a terminal voltage waveform diagram when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave in which the third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 80%. [Figure 8] FIG. 8 is a diagram showing interphase voltage waveforms in the three-phase modulation operation mode of FIG. [Figure 9] FIG. 9 is a terminal voltage waveform diagram when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave in which the third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 100%. [Figure 10] FIG. 10 is a diagram showing interphase voltage waveforms in the three-phase modulation operation mode of FIG. [Figure 11] FIG. 11 is a terminal voltage waveform diagram when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave in which a third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 115%. [Figure 12] FIG. 12 is a diagram showing interphase voltage waveforms in the three-phase modulation operation mode of FIG. [Figure 13] FIG. 13 is a terminal voltage waveform diagram when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave in which a third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 130%. [Figure 14] FIG. 14 is a diagram showing interphase voltage waveforms in the three-phase modulation operation mode of FIG. [Figure 15]FIG. 15 is a terminal voltage waveform diagram when the modulation signal applied to each motor coil in the three-phase modulation operation mode is a sine wave in which a third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 180%. [Figure 16] FIG. 16 is a diagram showing interphase voltage waveforms in the three-phase modulation operation mode of FIG. [Figure 17] FIG. 17 shows the terminal voltage waveform of the modulation signal applied to each motor coil in the two-phase modulation operation mode, where the composite waveform of the switching phases is a sine wave in which the third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 80%. [Figure 18] FIG. 18 is a diagram showing interphase voltage waveforms in the two-phase modulation operation mode of FIG. [Figure 19] FIG. 19 shows the terminal voltage waveform of the modulation signal applied to each motor coil in the two-phase modulation operation mode, where the composite waveform of the switching phase is a sine wave in which the third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 100%. [Figure 20] FIG. 20 is a diagram showing interphase voltage waveforms in the two-phase modulation operation mode of FIG. [Figure 21] FIG. 21 shows the terminal voltage waveform of the modulation signal applied to each motor coil in the two-phase modulation operation mode, where the composite waveform of the switching phases is a sine wave in which the third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 115%. [Figure 22] FIG. 22 is a diagram showing interphase voltage waveforms in the two-phase modulation operation mode of FIG. [Figure 23] Figure 23 shows the terminal voltage waveform of the modulation signal applied to each motor coil in the two-phase modulation operation mode, where the composite waveform of the switching phases is a sine wave in which the third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 130%. [Figure 24] FIG. 24 is a diagram showing interphase voltage waveforms in the two-phase modulation operation mode of FIG. [Figure 25]Figure 25 shows the terminal voltage waveform of the modulation signal applied to each motor coil in the two-phase modulation operation mode, where the composite waveform of the switching phase is a sine wave in which the third harmonic is superimposed at 1 / 6 on the fundamental wave, and the modulation degree is 180%. [Figure 26] FIG. 26 is a diagram showing interphase voltage waveforms in the two-phase modulation operation mode of FIG. [Figure 27] FIG. 27 is a graph showing a torque curve at a modulation degree of 130%. [Figure 28] FIG. 28 is a graph showing a torque curve at a modulation degree of 180%. [Figure 29] FIG. 29 is a table showing the relationship between the inter-phase output ratio when the modulation index is changed. [Figure 30] FIG. 30 is a block diagram showing an example of a motor drive circuit. [Figure 31] FIG. 31 shows the concept of the interphase output in the present invention, and is a graph showing that the interphase output is the integral value of the absolute value of the interphase voltage waveform over one period. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of a motor driving method according to the present invention will be described with reference to the accompanying drawings. An example of a motor driving device will be described with reference to Fig. 30. To avoid complication, descriptions of a clock generating unit, a communication unit, a motor current detection circuit, etc. will be omitted. In addition, a three-phase brushless motor will be used as an example of a three-phase motor.

[0016] In FIG. 30, three-phase brushless motor 1 has, for example, a rotor equipped with a permanent magnet field, and a stator core with pole teeth arranged facing permanent magnets with a mechanical angle phase difference of 120°. A motor coil is wound around each pole tooth, and the U, V, and W phase ends are connected to inverter circuit 2. Inverter circuit 2 is supplied with power from DC power supply 2a. Note that the motor coil may be delta-connected, connecting adjacent phases and having no neutral point. Three-phase brushless motor 1 may be either an inner rotor type or an outer rotor type. Furthermore, the permanent magnet field may be either an interior permanent magnet (IPM) motor or a surface permanent magnet (SPM) motor.

[0017] The external command device 3 sends a rotation command (RUN) to the control circuit 4 (MPU). The control circuit 4 incorporates a logic circuit (LOGIC), a PWM controller, a current amplifier, an AD converter circuit, etc. (not shown). The logic circuit stores a conduction pattern for a 180° electrical angle. The PWM controller generates a PWM control signal based on the conduction pattern.

[0018] When the control circuit 4 receives a rotation command from the external command device 3, it generates a PWM control signal via a logic circuit (LOGIC) and a PWM controller. The PWM controller sends a DC gate signal to the gate driver 5. The gate driver 5 receives the gate signal and sends a voltage-amplified gate output to the inverter circuit 2. The gate driver 5 incorporates a charge pump circuit that boosts the gate output voltage and a through-current prevention circuit. The inverter circuit 2 is a three-phase half-bridge inverter circuit. When the gate output is input from the gate driver 5, the switching elements (FETs) of the high-side arm or low-side arm of each phase turn on, and the power-amplified coil voltage is output to the three-phase coils U, V, and W. FETs are used as switching elements and have built-in body diodes. The control circuit 4 also detects the position of the permanent magnet field based on the current and voltage values ​​obtained by sensing the three-phase coils.

[0019] Here, the modulation degree in the PWM modulation of the present invention will be explained with reference to the drawings. Figure 1 shows the waveform of a typical sinusoidal-wave PWM drive signal for three-phase modulation, illustrating the terminal voltages applied to each of the three-phase coils U, V, and W. The duty ratio is determined so that the short-term average value forms a sinusoidal wave relative to the rotor's electrical angle, and the PWM drive signal is PWM-modulated using this duty ratio and output to inverter circuit 2. In the claims, the term "modulation signal" refers to the curves of U-phase (solid line), V-phase (dotted line), and W-phase (dashed line) that determine the duty ratio of the terminal voltages applied to each of the three-phase coils, and the duty ratio of the voltages applied to each of the U-, V-, and W-phases is uniquely determined from the intersection with the modulation signal depending on the rotor's electrical angle (horizontal axis).

[0020] Figure 2 shows the relationship between the voltages (phase-to-phase voltages) between U, V, W, and WU and the rotor electrical angle in Figure 1. Like the terminal voltages mentioned above, these phase-to-phase voltages are also PWM-modulated and show the average values ​​over a short time period. The maximum value of the terminal voltage waveform in Figure 1 is 1.0 (duty ratio 100%), but in Figure 2, although the waveforms of the phase-to-phase voltages are sine waves, the maximum absolute value does not reach 1.0, so there is room for the output to increase with a PWM drive signal that is PWM modulated using only sine waves.

[0021] Figure 3 shows the terminal voltages applied to each of the three-phase coils U, V, and W when the three-phase modulation PWM drive signal is not a simple sine wave, but a superimposed sine wave that contains 1 / 6 of the third harmonic of the fundamental frequency signal. Figure 4 shows the relationship between the voltages (interphase voltages) between U, V, W, and WU and the rotor electrical angle in Figure 3. Like the terminal voltages mentioned above, these interphase voltages also show the average value over a short time period for PWM modulation. As the waveform in Fig. 4 shows, the phase-to-phase voltage waveform is a sine wave with a maximum value of 1.0. By using a PWM drive signal that is not simply a sine wave but a superimposed sine wave in which a third harmonic is superimposed on a fundamental wave in this way, the terminal voltage waveform becomes trapezoidal as shown in Fig. 3, improving the output density relative to the rotor's electrical angle and also improving the phase-to-phase voltage shown in Fig. 4, thereby improving the motor output overall. Such techniques are well known and commonly used.

[0022] 5 and 6 are waveform diagrams illustrating the concept of modulation degree. Figure 5 shows an example of a PWM drive signal that uses a sine wave with only the fundamental wave, and shows the terminal voltages applied to each of the three-phase coils U, V, and W. When the maximum value (= amplitude) of the PWM drive signal is 1.0 as shown in this figure, the maximum modulation degree is 100%, which means that, for example, at an electrical angle of 90 degrees, the U phase is PWM modulated with a modulation degree of 100% (= duty ratio of 100%).

[0023] Like Figure 5, Figure 6 shows an example in which a sine wave with only the fundamental wave is used as the PWM drive signal, showing the terminal voltages applied to each of the three-phase coils U, V, and W. As shown in this figure, when the maximum value (= amplitude) of the PWM drive signal is 1.3, the maximum modulation level is 130%. However, since the PWM duty ratio cannot be greater than 100%, the duty ratio is set to 100% in the electrical angle range where the amplitude of the PWM drive signal exceeds 1.0 (modulation level 100%). For example, at an electrical angle of 90 degrees, the modulation level for the U phase is 130%, but the duty ratio is PWM modulated at 100%. In this invention, "there is an electrical angle section in which the modulation degree of the PWM drive signal exceeds 100% and the duty ratio is set to 100% in that electrical angle section" is referred to as overmodulation.

[0024] Next, an example of a motor drive method using the motor drive device described above will be described. The control circuit 4 can execute a three-phase modulation operation mode in which it outputs a three-phase modulated PWM drive signal to the inverter circuit 2 to perform three-phase modulation as shown in FIG. 1 as a PWM drive signal. The duty ratio of the terminal voltage of the coils of each of the U, V, and W phases is set and output according to the electrical angle of the rotor. When the rotor starts to rotate, the electrical angle also changes, and the duty ratio of the terminal voltage of the coils of each of the U, V, and W phases is reset and output according to the changed electrical angle. By performing this process continuously, it is possible to sustain the rotation of the rotor using PWM control. The strength of the motor output can be adjusted by changing the amplitude of the curves of the U phase (solid line), V phase (dotted line), and W phase (dashed line) in Figure 1, which are the source of the PWM drive signal mentioned above.

[0025] Below, the terminal voltage waveform diagram and the interphase voltage waveform diagram in the three-phase modulation operation mode will be explained while changing the modulation index. Figure 7 shows the terminal voltage waveforms when the modulation signal (PWM drive signal) applied to each motor coil in three-phase modulation operation mode is a sine wave with a third harmonic superimposed at 1 / 6 on the fundamental wave, with a modulation depth of 80%. The solid line shows the U-phase coil voltage, the dotted line shows the V-phase coil voltage, and the dashed line shows the W-phase coil voltage. Figure 8 shows a phase-to-phase voltage waveform diagram in the three-phase modulation operation mode of Figure 7. The solid line indicates the UV phase-to-phase voltage, the dotted line indicates the VW phase-to-phase voltage, and the dashed line indicates the WU phase-to-phase voltage.

[0026] Figure 9 shows the terminal voltage waveforms when the modulation signal (PWM drive signal) applied to each motor coil in three-phase modulation operation mode is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, with a modulation depth of 100%. The solid line represents the U-phase coil voltage, the dotted line represents the V-phase coil voltage, and the dashed line represents the W-phase coil voltage. Fig. 10 shows a phase-to-phase voltage waveform diagram (sine wave waveform diagram) in the three-phase modulation operation mode of Fig. 9. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage.

[0027] Figure 11 shows the terminal voltage waveform when the modulation signal (PWM drive signal) applied to each motor coil in three-phase modulation operation mode is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, with a modulation depth of 115%. The solid line shows the U-phase coil voltage, the dotted line shows the V-phase coil voltage, and the dashed line shows the W-phase coil voltage. When the modulation depth exceeds 100%, the terminal voltage waveform has an amplitude exceeding 1.0, but with PWM control, there is no state in which the output exceeds 100%, so there are sections in the positive and negative terminal voltage waveforms where the maximum output is flat. Figure 12 shows a phase-to-phase voltage waveform (sine wave waveform) in the three-phase modulation operation mode of Figure 11. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage. The positive and negative phase-to-phase voltage waveforms have intervals where the maximum output is flat.

[0028] Figure 13 shows the terminal voltage waveform (trapezoidal waveform) when the modulation signal (PWM drive signal) applied to each motor coil in three-phase modulation operation mode is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, with a modulation depth of 130%. The solid line represents the U-phase coil voltage, the dotted line represents the V-phase coil voltage, and the dashed line represents the W-phase coil voltage. When the modulation depth exceeds 100%, the terminal voltage waveform has an amplitude greater than 1.0. However, with PWM control, there is no state in which the output exceeds 100%, so there is a section in the positive and negative terminal voltage waveforms where the maximum output is flat. The flat section is also wider than when the modulation depth is 115% (see Figure 11). Figure 14 shows a phase-to-phase voltage waveform diagram (trapezoidal waveform diagram) in the three-phase modulation operation mode of Figure 13. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage. The flat sections of the positive and negative phase-to-phase voltage waveforms, where maximum output is flat, are wider than when the modulation index is 115% (see Figure 12).

[0029] Figure 15 shows the terminal voltage waveform (trapezoidal waveform) when the modulation signal (PWM drive signal) applied to each motor coil in three-phase modulation operation mode is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, with a modulation depth of 180%. The solid line represents the U-phase coil voltage, the dotted line represents the V-phase coil voltage, and the dashed line represents the W-phase coil voltage. When the modulation depth exceeds 100%, the terminal voltage waveform has an amplitude greater than 1.0. However, with PWM control, there is no state in which the output exceeds 100%, so there is a section in the positive and negative terminal voltage waveforms where the maximum output is flat. The flat section is also slightly wider than when the modulation depth is 130% (see Figure 13). Figure 16 shows the phase-to-phase voltage waveforms in the three-phase modulation operation mode of Figure 15. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage. The flat sections of the positive and negative phase-to-phase voltage waveforms, where maximum output is flat, are wider than when the modulation index is 130% (see Figure 14).

[0030] Next, we will explain the terminal voltage waveform and interphase voltage waveform in two-phase modulation operation mode by sequentially changing the modulation index. Two-phase modulation (up / down method) is a method in which, during PWM control, the voltage of one phase is fixed high or low for a specific section within one cycle of the signal wave compared to the modulating wave, and the voltages of the other two phases are modulated. For example, in the section from 60 to 120 electrical degrees, the U-phase voltage is fixed high, and the V and W phases output signals that are delayed by 120 and 240 electrical degrees relative to the U-phase. Similarly, in the section from 120 to 180 electrical degrees, the V-phase voltage is fixed low, and the U and W phases output signals that are delayed by 120 and 240 electrical degrees relative to the V-phase.

[0031] Figure 17 shows the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode, and shows the terminal voltage (average voltage applied to the coil) waveform when the composite waveform of the switching phase is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave, with a modulation depth of 80%. The solid line shows the U-phase coil voltage, the dotted line shows the V-phase coil voltage, and the dashed line shows the W-phase coil voltage. The positive and negative terminal voltage waveforms have sections where the maximum output is flat. Fig. 18 shows a phase-to-phase voltage waveform diagram (sine wave waveform diagram) in the two-phase modulation operation mode of Fig. 17. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage.

[0032] Figure 19 shows the terminal voltage waveform of the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode, where the composite waveform of the switching phase is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, and the modulation level is 100%. The solid line shows the U-phase coil voltage, the dotted line shows the V-phase coil voltage, and the dashed line shows the W-phase coil voltage. The flat sections of the positive and negative terminal voltage waveforms, where maximum output is flat, are wider than when the modulation level is 80%. Fig. 20 shows a phase-to-phase voltage waveform diagram (sine wave waveform diagram) in the two-phase modulation operation mode of Fig. 19. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage.

[0033] Figure 21 shows the terminal voltage waveform of the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode, where the composite waveform of the switching phase is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, and the modulation level is 115%. The solid line shows the U-phase coil voltage, the dotted line shows the V-phase coil voltage, and the dashed line shows the W-phase coil voltage. The range in which the maximum output is flat on both the positive and negative terminal voltage waveforms is wider than when the modulation level is 100%. Figure 22 shows a phase-to-phase voltage waveform (sine wave waveform) in the two-phase modulation operation mode of Figure 21. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage. The positive and negative phase-to-phase voltage waveforms have intervals where the maximum output is flat.

[0034] Figure 23 shows the terminal voltage waveform (trapezoidal waveform diagram) of the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode, where the composite waveform of the switching phase is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, and the modulation level is 130%. The solid line represents the U-phase coil voltage, the dotted line represents the V-phase coil voltage, and the dashed line represents the W-phase coil voltage. The positive and negative terminal voltage waveforms have intervals where the maximum output is flat. Furthermore, the flat interval is wider than when the modulation level is 115% (see Figure 21). Figure 24 shows a phase-to-phase voltage waveform diagram (trapezoidal waveform diagram) in the two-phase modulation operation mode of Figure 23. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage. The flat sections of the positive and negative phase-to-phase voltage waveforms, where maximum output is flat, are wider than when the modulation index is 115% (see Figure 22).

[0035] Figure 25 shows the terminal voltage waveform (trapezoidal waveform) of the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode, where the composite waveform of the switching phase is a sine wave with a third harmonic superimposed at 1 / 6 of the fundamental wave, and the modulation level is 180%. The solid line represents the U-phase coil voltage, the dotted line represents the V-phase coil voltage, and the dashed line represents the W-phase coil voltage. The range in which the maximum output is flat on the positive and negative terminal voltage waveforms is slightly wider than when the modulation level is 130% (see Figure 23). Figure 26 shows the phase-to-phase voltage waveforms in the two-phase modulation operation mode of Figure 25. The solid line shows the UV phase-to-phase voltage, the dotted line shows the VW phase-to-phase voltage, and the dashed line shows the WU phase-to-phase voltage. The flat sections of the positive and negative phase-to-phase voltage waveforms, where maximum output is flat, are wider than when the modulation index is 130% (see Figure 24).

[0036] The above experimental results show that, in either three-phase modulation operation mode or two-phase modulation operation mode, when comparing phase-to-phase output (the integral value of one cycle of the absolute value of the phase-to-phase voltage waveform; see Figure 31), even if the modulation index is changed beyond a certain level, the phase-to-phase output remains almost constant once the modulation index exceeds a certain value. Specifically, it was found that there is no significant difference and the output remains constant even when the modulation index exceeds 130%. Figures 27 and 28 are graphs comparing torque curves at modulation indexes of 130% and 180% in three-phase modulation operation mode. While the 180% modulation index (Figure 28) provides slightly higher torque, this is only a small difference compared to the 130% modulation index.

[0037] Fig. 29 is a table showing the relationship between the inter-phase output ratio when the modulation index is changed in the three-phase modulation operation mode and the two-phase modulation operation mode. The inter-phase output ratio is a relative value where the inter-phase output at a modulation index of 100% is set to 100. As the modulation index increases, the inter-phase output also increases, but it can be seen that the inter-phase output remains unchanged up to a modulation index of 130%. Furthermore, when the modulation index exceeds 130%, the position detection interval (dead time) of the permanent magnet field becomes shorter in sensorless drive, reducing controllability. In this way, by setting the modulation degree of the overmodulated PWM drive signal to exceed 100% and setting the upper limit at 130%, it is possible to improve motor output with the upper limit set at 130% modulation degree, at which the motor output level peaks out, and ensure the position detection accuracy of the permanent magnet field in sensorless drive.

[0038] Even if the modulation degree of the overmodulated PWM drive signal is around 180%, it is possible to detect the position of the permanent magnet field using sensorless drive, but this reduces position detection accuracy and controllability, while not improving interphase output. Therefore, by using a modulation degree range that exceeds 100% and has an upper limit of 130%, which is expected to improve output while ensuring the sensing range (operating stability) of sensorless drive, it is possible to achieve both motor drive stability and improved output.

[0039] In the present invention, the sensorless drive method can be a one-shunt FOC sensorless detection method in which at least one phase of sensing for magnetic pole position estimation is in a switching state, or a method in which sensing for magnetic pole position estimation is performed during dead time, either individually or simultaneously.

[0040] Furthermore, in the present invention, the explanation has been given on the assumption that a "sine wave with a third harmonic superimposed on a fundamental wave" is used as the PWM drive signal, but a pure sine wave as shown in FIG. 1 can also be used, in which case the maximum modulation degree applicable as overmodulation is 200%.

[0041] Here, an example of a specific motor driving method for a three-phase DC brushless motor will be described. The control circuit 4 has a three-phase overmodulation operation mode in which a three-phase modulated PWM drive signal is output to the inverter circuit 2 as a PWM drive signal, a two-phase overmodulation operation mode in which a two-phase modulated PWM drive signal is output to the inverter circuit 2 as a PWM drive signal, and a transition operation mode in which a transition overmodulation signal in which the ratio of the three-phase overmodulated PWM drive signal and the two-phase overmodulated PWM drive signal is gradually changed is output to the inverter circuit 2. In the three-phase modulation operation mode and two-phase modulation operation mode, the modulation degree of the PWM drive signal is set to an overmodulation state of up to 130% as described above, but the modulation degree may be changed appropriately to adjust the output depending on the situation, such as starting from a stopped state, deceleration from a high rotation state, load fluctuations in a constant speed state, etc. Furthermore, the three-phase modulation operation mode has lower vibration and noise than the two-phase modulation operation mode, but is inferior in terms of efficiency, so either the three-phase modulation operation mode or the two-phase modulation operation mode should be selected depending on the load characteristics and application requirements. In the transition operation mode, the waveforms of three-phase modulation signals and two-phase modulation signals with modulation indices ranging from 0% to 100% are mixed, and the ratio between them changes gradually. The ratio of the three-phase modulation signal is decreased in increments of 60 electrical degrees, and the ratio of the two-phase modulation signal is increased. The motor may be started and operated in the three-phase modulation operation mode with a modulation indices ranging from 0% to 100%, then switched to the two-phase modulation operation mode with a modulation indices ranging from 0% to 100% via the transition operation mode, and then driven in the two-phase modulation operation mode with a modulation indices ranging from 100% to 130%.

[0042] As a result, when a three-phase DC brushless motor is driven at low speeds, it is driven by a three-phase modulated PWM drive signal that produces low noise and vibration, and when it is driven at high speeds, high loads, or high temperatures, it is driven by a two-phase modulated PWM drive signal that is advantageous in terms of heat generation in the switching elements and has good energy utilization efficiency.This makes it possible to reduce the amount of heat generated by the switching elements by achieving low vibration and low noise at high output when driven at low speeds, and by reducing the number of switching operations at high output when driven at high speeds, high loads, and high sounds, thereby contributing to energy savings.

[0043] The motor driving method described above is suitable for use in voltage-type inverter control systems such as inverter air conditioners, inverter home appliances, and compressors. [Explanation of symbols]

[0044] 1 Three-phase brushless motor 2 Inverter circuit 2a DC power supply 3 External command device 4 Control circuit 5 Gate driver

Claims

1. A motor driving method for driving a three-phase brushless motor using a pulse width modulation system, comprising: The three-phase brushless motor is an inverter circuit having output elements each having a pair of high-side arm and low-side arm for three phases, and outputting current to each of the three-phase coils of the three-phase brushless motor; a control circuit that determines a duty ratio based on an input modulation signal, performs pulse width modulation to output a pulse signal, and controls output of the pulse signal to the inverter circuit; The control circuit When a predetermined minimum value is input as the modulation signal, a pulse signal with a duty ratio of 0% is output to the inverter circuit, When a predetermined maximum value is input as the modulation signal, a pulse signal with a duty ratio of 100% is output to the inverter circuit, a motor driving method comprising: inputting an overmodulation signal as the modulation signal, the maximum modulation degree of which is the ratio of the maximum value of the modulation signal to the predetermined maximum value, greater than 100%, and outputting a pulse signal with a duty ratio of 100% to the inverter circuit when the instantaneous value of the modulation signal reaches an overmodulation state where it exceeds the predetermined maximum value.

2. 2. The motor drive method according to claim 1, wherein the modulation signal is a signal in which a sine wave of a predetermined frequency is superimposed on a sine wave of a frequency three times the predetermined frequency, and when the signal is used as the modulation signal, the modulation degree in the overmodulation state is up to 130%.

3. 3. The motor driving method according to claim 1, wherein the three-phase brushless motor is a sensorless motor.

4. 4. The motor driving method according to claim 3, wherein the rotor position detection method of the sensorless motor is either a one-shunt FOC sensorless detection method in which at least one phase is in a switching state during sensing for magnetic pole position estimation, or a detection method in which sensing for magnetic pole position estimation is performed during dead time, or both.

5. The control circuit a three-phase modulation operation mode in which a pulse width modulation signal is output to each of the coils of the three phases of the three-phase brushless motor to drive the motor; a two-phase modulation operation mode in which a pulse width modulation signal is output to coils of two of the three phases of the three-phase brushless motor to drive the motor; a transition operation mode in which a motor is driven by outputting a transition modulation signal that gradually changes a mixed ratio of a pulse width modulation signal for each phase of the three-phase modulation operation mode and a pulse width modulation signal for each phase of the two-phase modulation operation mode, 3. A motor driving method according to claim 1 or 2, wherein the motor is operated in the three-phase operation mode from start-up until the maximum output at which an overmodulation state occurs, or in the two-phase operation mode from start-up until the maximum output at which an overmodulation state occurs, or is started in the three-phase operation mode, and as the output increases, switches to the two-phase operation mode via the transition operation mode and operates until the maximum output at which an overmodulation state occurs.

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