Motor driving method

Abstract

The invention provides a motor driving method, which drives a three-phase DC brushless motor through over-modulation PWM control under the condition of no sensor and with a modulation degree exceeding 100% in a specified range, thereby being expected to improve the maximum output of the motor even if dead time is ensured. The control circuit (4) outputs a pulse signal having a duty ratio of 0% to the inverter circuit (2) when a predetermined minimum value is input as a modulation signal, and outputs a pulse signal having a duty ratio of 100% to the inverter circuit (2) when a predetermined maximum value is input as a modulation signal. When an overmodulation signal in which the maximum modulation degree, which is the ratio of the maximum value of the modulation signal to a prescribed maximum value, is greater than 100%, is input as the modulation signal, and when the modulation signal is in an overmodulation state in which the instantaneous value of the modulation signal is greater than the prescribed maximum value, a pulse signal having a duty ratio of 100% is output to the inverter circuit (2).

Description

Technical Field

[0001] The present invention relates to a motor driving method for sinusoidally driving a three-phase DC brushless motor, such as one used in HVAC, using a sensorless pulse width modulation method. Background Art

[0002] When a three-phase DC brushless motor that does not use a Hall effect sensor for position detection with permanent magnet excitation is driven sinusoidally using pulse width modulation (PWM) control, overmodulation control is not performed to avoid hindering position detection by permanent magnet excitation. Furthermore, while a method of superimposing higher harmonics on the fundamental wave of the sine wave is used, this is done in a manner that does not result in overmodulation.

[0003] If a sine wave drive is used, it is possible to achieve low noise or low vibration in a three-phase DC brushless motor. However, there is a technical problem: although two-phase modulation has a larger maximum output, its noise and vibration are greater than those of three-phase modulation. Although the noise and vibration of three-phase modulation are lower than those of two-phase modulation, its maximum output is smaller. In order to solve these technical problems, a motor driving method is proposed, in which, in a two-phase modulated switch that outputs a sinusoidal AC current, the same modulation period is added to all phases including the non-modulated phase within a carrier cycle to set it as three-phase modulation, and the added modulation period is set to half of the non-energized period within the carrier cycle before the addition, thereby taking into account both the large output of two-phase modulation and the low noise and low vibration of three-phase modulation (Patent Document 1; Japanese Patent Gazette No. 4581391). Prior art literature Patent Literature

[0004] Patent Document 1: Japanese Patent No. 4581391 Summary of the Invention Technical problem to be solved by the invention

[0005] When a three-phase brushless DC motor is driven sinusoidally by PWM control without a sensor, it is difficult to actively use the output with a 100% duty cycle because dead time is used to detect the position of the permanent magnet excitation. As a result, there are problems such as the inability to increase the maximum output of the motor, a decrease in the maximum speed or maximum output for motors with high back electromotive force, an increase in the number of switching operations of switching elements such as FETs provided in the inverter circuit of the motor drive device, and an increase in the heat generated by the switching elements. Technical means for solving technical problems

[0006] The present invention is completed to solve the above-mentioned various technical problems, and its purpose is to provide a motor driving method that drives a three-phase DC brushless motor through overmodulation PWM control at a modulation index exceeding 100% of a specified range without a sensor, thereby being able to increase the maximum output of the motor even if the dead time is ensured.

[0007] A motor driving method for driving a three-phase brushless motor by pulse width modulation, characterized in that the three-phase brushless motor includes: an inverter circuit, the inverter circuit having a three-phase output element with a pair of high-side arms and a low-side arm, outputting current to the coil of each of the three phases of the three-phase brushless motor; and a control circuit, the control circuit performing pulse width modulation that determines the duty cycle based on an input modulation signal and outputs a pulse signal, controlling the output of the pulse signal to the inverter circuit, and when a specified minimum value is input as the modulation signal, the control circuit The control circuit outputs a pulse signal with a duty cycle of 0% to the inverter circuit. When a specified maximum value is input as the modulation signal, the control circuit outputs a pulse signal with a duty cycle of 100% to the inverter circuit. When an overmodulation signal in which the ratio of the maximum value of the modulation signal to the specified maximum value, that is, a maximum modulation degree greater than 100%, is input as the modulation signal, thereby being in an overmodulation state in which the instantaneous value of the modulation signal is greater than the specified maximum value, the control circuit outputs a pulse signal with a duty cycle of 100% to the inverter circuit.

[0008] In this way, when the ratio of the maximum value of the input modulation signal to the prescribed maximum value, that is, the overmodulation signal with a maximum modulation degree greater than 100%, is used as the modulation signal, when the instantaneous value of the modulation signal is greater than the overmodulation state of the prescribed maximum value, the control circuit outputs a pulse signal with a duty cycle of 100% to the inverter circuit, thereby not only achieving low noise and low vibration, but also improving the motor output and reducing the number of switching times, thereby suppressing the heating of the switching element.

[0009] The modulation signal may be a signal in which a sine wave having a frequency three times the predetermined frequency is superimposed on a sine wave having a predetermined frequency. When this signal is used as the modulation signal, the degree of modulation in the overmodulation state may be a maximum of 130%. In this way, when using a modulation signal in which a sine wave with a frequency three times the specified frequency is superimposed on a sine wave with a specified frequency, the modulation degree in the overmodulation state is upper limited to 130%, thereby making it possible to increase the maximum output of the motor by setting the modulation degree of 130% at which the output level of the motor reaches its peak as the upper limit.

[0010] The three-phase brushless motor may also be a sensorless motor. In this case, a dead time for position detection of permanent magnet excitation can be ensured, and position detection accuracy of permanent magnet excitation in sensorless driving can be ensured.

[0011] For the rotor position detection method of a sensorless motor, either or both of a 1-shunt FOC sensorless detection method in which at least one phase is in a switching state during the sensing for estimating the magnetic pole position, and a detection method in which sensing for estimating the magnetic pole position is performed during the dead time can be performed. In this way, by driving the sensorless motor in an overmodulation state where the modulation index exceeds a specified range of 100%, it is possible to increase the maximum output of the motor even when the motor is rotating or stopped and even when a dead time is ensured in the sensing for estimating the magnetic pole position.

[0012] The control circuit may also have: a three-phase modulation operation mode, which outputs pulse width modulated signals 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, which outputs pulse width modulated signals to the coils of two of the three phases of the three-phase brushless motor to drive the motor; and a transition operation mode, which outputs a transition modulation signal to drive the motor, wherein the transition modulation signal gradually changes the ratio of mixing the pulse width modulated signals of each phase of the three-phase modulation operation mode and the pulse width modulated signals of each phase of the two-phase modulation operation mode. The control circuit may also perform any of the following operations: operating in the three-phase operation mode from startup to the maximum output in the overmodulation state; operating in the two-phase operation mode from startup to the maximum output in the overmodulation state; starting in the three-phase operation mode, switching to the two-phase operation mode through the transition operation mode as the output increases, and operating until the maximum output in the overmodulation state is reached. Therefore, by using a three-phase overmodulation PWM drive signal with good controllability to drive the three-phase DC brushless motor during low-speed driving, and using a two-phase overmodulation PWM drive signal with good energy utilization efficiency to drive the three-phase DC brushless motor during high rotation, high load or high temperature, the number of switching times can be reduced with low vibration and low noise at high output during low-speed driving and high output during high rotation, high load and high temperature, thereby reducing the heat generated by the switching elements and contributing to energy saving. Effects of the Invention

[0013] A motor driving method can be provided that drives a three-phase DC brushless motor by overmodulation PWM control without a sensor at a modulation index exceeding a prescribed range of 100%, thereby expecting to increase the maximum output of the motor even while ensuring a dead time. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0015] Hereinafter, embodiments of the motor driving method according to the present invention will be described with reference to the accompanying drawings. Figure 30 An example of a motor drive device will be described. To avoid complication, the clock generator, communication unit, motor current detection circuit, etc. will be omitted. Furthermore, a three-phase brushless motor will be described as an example of a three-phase motor.

[0016] exist Figure 30 In the embodiment, the three-phase brushless motor 1 includes, for example, a permanent magnet excitation on the rotor, a stator core having a phase difference of 120° in mechanical angle and pole teeth arranged opposite to the permanent magnet on the stator, a motor coil wound on each pole tooth, and each phase end of the U phase, the V phase, and the W phase is connected to the inverter circuit 2. The inverter circuit 2 is powered by a DC power supply 2a. In addition, the motor coils can also be connected to adjacent phases to form a delta connection without a neutral point. The three-phase brushless motor 1 can be an inner rotor type or an outer rotor type. In addition, as a permanent magnet excitation, it can be any of an embedded permanent magnet (IPM) motor and a surface permanent magnet (SPM) motor.

[0017] External command device 3 sends a rotation command (RUN) to control circuit 4 (MPU). Control circuit 4 includes a built-in logic circuit (LOGIC), a PWM controller, a current amplifier, and an A / D converter circuit (not shown). The logic circuit stores a power-on pattern for energizing the motor at an electrical angle of 180°. The PWM controller generates a PWM control signal based on the power-on pattern.

[0018] When a rotation instruction is received from the external instruction device 3, the control circuit 4 generates a PWM control signal through a logic circuit (LOGIC) or 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 the gate output after voltage amplification to the inverter circuit 2. The gate driver 5 has a built-in charge pump circuit or a through-current prevention circuit that boosts the gate output voltage. The inverter circuit 2 is an inverter circuit with a three-phase half-bridge structure. When the gate output is input from the gate driver 5, the switching element (FET) of the high-side arm or low-side arm of each phase is turned on, and the coil voltage after power amplification is output to the three-phase coils U, V, and W. The switching element uses a FET with a built-in body diode. In addition, the control circuit 4 detects the position of the permanent magnet excitation based on the current value or voltage value obtained by sensing the three-phase coil.

[0019] Here, the modulation degree in PWM modulation of the present invention is described with reference to the drawings. Figure 1 This is the waveform of a PWM drive signal for a typical three-phase modulated sinusoidal drive, representing the terminal voltages applied to the three-phase coils U, V, and W. The duty cycle is determined so that the minute time average value forms a sinusoidal wave relative to the rotor's electrical angle. PWM modulation is performed at this duty cycle, and the PWM drive signal is output to inverter circuit 2. The "modulation signal" in this invention refers to the curves for the U-phase (solid line), V-phase (dotted line), and W-phase (dashed line) that determine the duty cycle of the terminal voltage applied to each phase of the three-phase coil. The duty cycle of the voltage applied to each phase U, V, and W is uniquely determined by the intersection of the modulation signal with the rotor's electrical angle (horizontal axis).

[0020] Figure 2 express Figure 1 The relationship between the voltages between UV, VW, and WU (phase-to-phase voltages) and the electrical angle of the rotor. This phase-to-phase voltage also shows a small time average value relative to the PWM drive signal after PWM modulation similar to the terminal voltage. Figure 1 The maximum value of the terminal voltage waveform is 1.0 (duty cycle 100%), but Figure 2 In the example, although the waveform of each phase voltage is a sine wave, the maximum absolute value is not 1.0. Therefore, in the PWM drive signal that is PWM modulated only by a sine wave, there is room for the output to rise.

[0021] Figure 3 It indicates that the three-phase modulated PWM drive signal is set to not only a sine wave, but also an overlapping sine wave containing 1 / 6 of the third harmonic of the fundamental frequency signal, and indicates the terminal voltages applied to the three-phase coils U, V, and W respectively when using this drive signal. Figure 4 express Figure 3 The relationship between the voltages between UV, VW, and WU (phase-to-phase voltages) and the electrical angle of the rotor. This phase-to-phase voltage also shows a small time average value relative to the PWM drive signal after PWM modulation similar to the terminal voltage. like Figure 4 As shown in the waveform of the phase-to-phase voltage, the waveform is a sine wave, and its maximum value is increased to 1.0. In this way, a PWM drive signal that uses a superimposed sine wave with the third harmonic superimposed on the fundamental wave instead of a simple sine wave is used, so that Figure 3 As shown, the terminal voltage waveform becomes trapezoidal, and the output density of the rotor relative to the electrical angle increases. Figure 4 The interphase voltage shown is also increased, so that the motor output can be improved as a whole. This method is a well-known and commonly used technique.

[0022] Figure 5 and Figure 6 This is a waveform diagram that explains the concept of modulation. Figure 5 This figure illustrates the case where only a fundamental sine wave is used as a PWM drive signal, indicating the terminal voltages applied to the three-phase coils U, V, and W. As shown in the figure, when the maximum value (= amplitude) of the PWM drive signal is 1.0, the maximum modulation index is 100%. This means, for example, that PWM modulation is performed with a modulation index of 100% (= duty cycle of 100%) with respect to the U phase at an electrical angle of 90 degrees.

[0023] Figure 6 and Figure 5 Similarly, this figure illustrates the case where only a fundamental sine wave is used as the PWM drive signal, showing the terminal voltages applied to the three-phase coils U, V, and W. As shown in the figure, when the maximum value (=amplitude) of the PWM drive signal is 1.3, the maximum modulation index is 130%. However, since the PWM duty cycle cannot exceed 100%, the duty cycle is set to 100% in the electrical angle interval where the PWM drive signal amplitude exceeds 1.0 (modulation index exceeds 100%). For example, at an electrical angle of 90 degrees, the modulation index for the U phase is 130%, but this duty cycle means that PWM modulation is performed at 100%. As described above, in the present invention, “an electrical angle interval in which the modulation degree of the PWM drive signal exceeds 100%, and the duty ratio is 100% in the electrical angle interval” is referred to as overmodulation.

[0024] Next, an example of a motor driving method using the above motor driving device will be described. The control circuit 4 can execute a three-phase modulation operation mode, which is to be performed Figure 1The three-phase modulation PWM drive signal shown is output as a PWM drive signal to inverter circuit 2. The duty ratio of the terminal voltage for each of the U, V, and W phase coils is set and output according to the rotor's electrical angle. As the rotor begins to rotate, the electrical angle also changes, and the duty ratio of the terminal voltage for each of the U, V, and W phase coils is reset and output according to the changed electrical angle. By continuously performing this operation, the rotor's rotation under PWM control can be sustained. By changing the PWM drive signal as the basis of the above Figure 1 The amplitude of the curves of U phase (solid line), V phase (dotted line) and W phase (dashed line) can adjust the strength of the motor output.

[0025] The following are the terminal voltage waveforms and phase-to-phase voltage waveforms in three-phase modulation operation mode. Figure 1 The following explanation is given while changing the modulation index. Figure 7 This diagram shows the terminal voltage waveform for an 80% modulation index when the modulation signal (PWM drive signal) applied to each motor coil in three-phase modulation operation mode is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave. 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. Figure 8 express Figure 7 The phase-to-phase voltage waveforms in the three-phase modulation operation mode are shown in Figure 1. The solid line represents the UV phase-to-phase voltage, the dotted line represents the VW phase-to-phase voltage, and the dashed line represents the WU phase-to-phase voltage.

[0026] Figure 9 This diagram 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 1 / 6 third harmonic superimposed on the fundamental wave, with a modulation index 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. Figure 10 express Figure 9 Phase-to-phase voltage waveform (sine wave waveform) in three-phase modulation operation mode. The solid line represents the UV phase-to-phase voltage, the dotted line represents the VW phase-to-phase voltage, and the dashed line represents the WU phase-to-phase voltage.

[0027] Figure 11This diagram shows the terminal voltage waveform for a 115% modulation index. The modulation signal (PWM drive signal) applied to each motor coil in three-phase modulation operation mode is a sinusoidal wave with a 1 / 6 third harmonic superimposed on the fundamental wave. 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 index exceeds 100%, the terminal voltage waveform exhibits an amplitude exceeding 1.0. However, in PWM control, there is no state where the output exceeds 100%, resulting in a range where the maximum output of the positive and negative terminal voltage waveforms is flat. Figure 12 express Figure 11 The phase-to-phase voltage waveform (sine wave waveform) in three-phase modulation operation mode is shown. The solid line represents the UV phase-to-phase voltage, the dotted line represents the VW phase-to-phase voltage, and the dashed line represents the WU phase-to-phase voltage. The positive and negative phase-to-phase voltage waveforms are flat in the range where maximum output is achieved.

[0028] Figure 13 The modulation signal (PWM drive signal) applied to each motor coil in the three-phase modulation operation mode is a sine wave with 1 / 6 of the third harmonic superimposed on the fundamental wave, and the terminal voltage waveform diagram (trapezoidal waveform diagram) when the modulation rate 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. When the modulation index exceeds 100%, the terminal voltage waveform becomes a waveform with an amplitude exceeding 1.0, but in PWM control, since there is no state where the output exceeds 100%, the maximum output of the terminal voltage waveform on the positive and negative sides is a flat interval. In addition, the flat interval is smaller than the case of 115% modulation index (refer to Figure 11 ) is further magnified. Figure 14 express Figure 13 The waveform of the phase voltage under the three-phase modulation operation mode (trapezoidal waveform). The solid line represents the UV phase voltage, the dotted line represents the VW phase voltage, and the dashed line represents the WU phase voltage. The maximum output of the positive and negative phase voltage waveforms is flat, and the flat range is flat compared to the case of 115% modulation degree (refer to Figure 12 ) is further magnified.

[0029] Figure 15The modulation signal (PWM drive signal) applied to each motor coil in the three-phase modulation operation mode is a sine wave with 1 / 6 of the third harmonic superimposed on the fundamental wave, and the terminal voltage waveform diagram (trapezoidal waveform diagram) when the modulation rate 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. When the modulation index exceeds 100%, the terminal voltage waveform becomes a waveform with an amplitude exceeding 1.0, but in PWM control, since there is no state where the output exceeds 100%, the maximum output of the terminal voltage waveform on the positive and negative sides is a flat interval. In addition, the flat interval is larger than the case of 130% modulation index (refer to Figure 13 ) should be slightly enlarged. Figure 16 express Figure 15 The phase-to-phase voltage waveform in the three-phase modulation operation mode is shown in FIG. The solid line represents the UV phase voltage, the dotted line represents the VW phase voltage, and the dashed line represents the WU phase voltage. The maximum output of the positive and negative phase voltage waveforms is flat. The flat range is 130% of the modulation degree (see Figure 14 ) is further magnified.

[0030] Next, the terminal voltage waveform and interphase voltage waveform in the two-phase modulation operation mode are explained by sequentially changing the modulation degree. The two-phase modulation method (upper and lower method) is a method in which, in PWM control, the voltage of one phase is fixed to high or low only in a specific interval in one cycle of the signal wave compared with the modulation wave, and the voltages of the other two phases are modulated. For example, in the interval of 60 degrees to 120 degrees of electrical angle, the U-phase voltage is fixed to high, and the V-phase and W-phase output signals with an electrical angle of 120 degrees and an electrical angle of 240 degrees delayed relative to the U-phase. Similarly, in the interval of 120 degrees to 180 degrees of electrical angle, the V-phase voltage is fixed to low, and the U-phase and W-phase output signals with an electrical angle of 120 degrees and an electrical angle of 240 degrees delayed relative to the V-phase.

[0031] Figure 17 This diagram shows the terminal voltage (average applied coil voltage) waveform for an 80% modulation index, representing the combined waveform of the switching phases of the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode. The waveform is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave. 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 are flat in the range where maximum output occurs. Figure 18 express Figure 17 Phase-to-phase voltage waveform (sine wave waveform) in two-phase modulation operation mode. The solid line represents the UV phase-to-phase voltage, the dotted line represents the VW phase-to-phase voltage, and the dashed line represents the WU phase-to-phase voltage.

[0032] Figure 19This is the terminal voltage waveform diagram for a 100% modulation index, representing the combined waveform of the switching phases of the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode. The waveform is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave. 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 flat regions of the positive and negative terminal voltage waveforms, where the maximum output is flat, are significantly larger than those for an 80% modulation index. Figure 20 express Figure 19 Phase-to-phase voltage waveform (sine wave waveform) in two-phase modulation operation mode. The solid line represents the UV phase-to-phase voltage, the dotted line represents the VW phase-to-phase voltage, and the dashed line represents the WU phase-to-phase voltage.

[0033] Figure 21 This diagram shows the terminal voltage waveform for a 115% modulation index, representing the combined waveform of the switching phases of the modulation signal (PWM drive signal) applied to each motor coil in two-phase modulation operation mode. The waveform is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave. 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 ranges where the maximum output of the positive and negative terminal voltage waveforms is flat are larger than those for a 100% modulation index. Figure 22 express Figure 21 The phase-to-phase voltage waveform (sine wave waveform) in two-phase modulation operation mode is shown. The solid line represents the UV phase-to-phase voltage, the dotted line represents the VW phase-to-phase voltage, and the dashed line represents the WU phase-to-phase voltage. The positive and negative phase-to-phase voltage waveforms are flat in the range where maximum output is achieved.

[0034] Figure 23 The composite waveform representing the switching phase of the modulation signal (PWM drive signal) applied to each motor coil in the two-phase modulation operation mode is a terminal voltage waveform diagram (trapezoidal waveform diagram) with a modulation index of 130% and a sine wave of 1 / 6 of the third harmonic superimposed on the fundamental wave. 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 produce a flat range with maximum output. In addition, the flat range is smaller than the case with a modulation index of 115% (see Figure 21 ) is further magnified. Figure 24 express Figure 23 The waveform of the phase voltage in the two-phase modulation operation mode (trapezoidal waveform). The solid line represents the UV phase voltage, the dotted line represents the VW phase voltage, and the dashed line represents the WU phase voltage. The maximum output of the positive and negative phase voltage waveforms is flat, and the flat range is flat compared to the case of 115% modulation degree (refer to Figure 22 ) is further magnified.

[0035] Figure 25 The composite waveform representing the switching phases of the modulation signal (PWM drive signal) applied to each motor coil in the two-phase modulation operation mode is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave, and a terminal voltage waveform (trapezoidal waveform) when the modulation index 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 maximum output of the positive and negative terminal voltage waveforms is flat in the range of 130% modulation index (see Figure 23 ) should be slightly enlarged. Figure 26 express Figure 25 The waveform of the phase-to-phase voltage in the two-phase modulation operation mode is shown in FIG. The solid line represents the UV phase voltage, the dotted line represents the VW phase voltage, and the dashed line represents the WU phase voltage. The maximum output of the positive and negative phase voltage waveforms is flat. The flat range is 130% of the modulation degree (see Figure 24 ) is further magnified.

[0036] According to the above experimental results, in either the three-phase modulation operation mode or the two-phase modulation operation mode, the phase output (the integral value of one cycle of the absolute value of the phase voltage waveform, refer to Figure 31 ), even when the modulation index is varied beyond a certain level, the interphase output remains approximately constant when the modulation index exceeds a certain value. Specifically, even when the modulation index exceeds 130%, there is no significant difference, and the interphase output remains constant. Figure 27 and Figure 28 This is a graph comparing the torque curves of 130% and 180% modulation in three-phase modulation operation mode. Figure 28 ) has a slightly higher torque, but this is only a slight difference compared to the 130% modulation.

[0037] in addition, Figure 29 This chart shows the relationship between the interphase output ratios when varying the modulation index in the three-phase modulation mode and the two-phase modulation mode. The interphase output ratio is a relative value, with the interphase output at a modulation index of 100% being 100. As can be seen, increasing the modulation index increases the interphase output, but it remains constant up to a modulation index of 130%. Furthermore, exceeding 130% modulation shortens the position detection period (dead time) for permanent magnet excitation in sensorless drive, reducing controllability. In this way, the modulation index of the modulated PWM drive signal exceeds 100% and is capped at 130%, so that the modulation index of 130% at which the output level of the motor reaches its peak can be set as the upper limit, thereby improving the motor output and ensuring the position detection accuracy of the permanent magnet excitation in sensorless drive.

[0038] Furthermore, even with an overmodulated PWM drive signal modulation factor of approximately 180%, position detection of permanent magnet excitation is possible for sensorless drive. However, position detection accuracy and controllability are reduced, and improved interphase output cannot be expected. Therefore, by maintaining the sensorless drive sensing range (operation stability) while using a modulation factor exceeding 100%, which is expected to improve output, and capped at 130%, a balance can be achieved between motor drive stability and output improvement.

[0039] In the present invention, as sensorless driving methods, the following methods can be used individually or simultaneously: a 1-shunt FOC sensorless detection method in which at least one phase of sensing for estimating the magnetic pole position is in a switching state; and a sensing method for estimating the magnetic pole position during the dead time.

[0040] In addition, in the present invention, the description is given on the premise that "a sine wave having a third harmonic superimposed on a fundamental wave" is used as the PWM drive signal, but it is also possible to use a sine wave having a third harmonic superimposed on a fundamental wave. Figure 1 The ideal sine wave shown in this example has a maximum modulation depth of 200% that can be used as overmodulation.

[0041] Here, an example of a specific motor driving method for a three-phase brushless DC motor is described. The control circuit 4 has a three-phase overmodulation operation mode, which outputs a three-phase overmodulated PWM drive signal as a PWM drive signal to the inverter circuit 2; a two-phase overmodulation operation mode, which outputs a two-phase overmodulated PWM drive signal as a PWM drive signal to the inverter circuit 2; and a transition operation mode, which outputs a transition overmodulation signal to the inverter circuit 2, wherein the transition overmodulation signal gradually changes the ratio of the mixing of the three-phase overmodulated PWM drive signal and the two-phase overmodulated PWM drive signal. In the three-phase overmodulation operation mode or the two-phase overmodulation operation mode, the modulation degree of the PWM drive signal is performed in the above-mentioned maximum overmodulation state of 130%, but the modulation degree can also be appropriately changed to adjust the output according to conditions such as starting from a stopped state, deceleration from a high rotation state, or load changes in a constant speed state. In addition, the three-phase modulation operation mode has lower vibration and noise than the two-phase modulation operation mode, but is inferior in efficiency. Therefore, the choice of three-phase modulation operation mode or two-phase modulation operation mode depends on the characteristics of the load and the requirements of the application. Furthermore, in the transition mode, waveforms of three-phase and two-phase modulation signals with modulation intensities ranging from 0% to 100% are mixed, and their ratio gradually changes. This change occurs so that the ratio of the three-phase modulation signal decreases and the ratio of the two-phase modulation signal increases in 60-degree increments of the electrical angle. Alternatively, the motor can be started in the three-phase modulation mode with a modulation intensity between 0% and 100%, then switched to the two-phase modulation mode after the transition mode, and then driven again with the modulation in the two-phase modulation mode set to between 100% and 130%.

[0042] Thus, by using a three-phase modulated PWM drive signal with low noise and low vibration to drive the three-phase DC brushless motor during low-speed driving, and using a two-phase modulated PWM drive signal that is more advantageous in terms of heat generation of the switching element and has good energy utilization efficiency to drive the three-phase DC brushless motor during high rotation, high load or high temperature, the number of switching times can be reduced with low vibration and low noise at high output during low-speed driving and high output during high rotation, high load and high temperature. This can reduce the heat generated by the switching element and contribute to energy saving.

[0043] The motor driving method is applicable to voltage-type inverter control systems such as inverter air conditioners, inverter home appliances, and compressors.

Claims

1. A motor driving method for driving a three-phase brushless motor by pulse width modulation, wherein: The three-phase brushless motor comprises: an inverter circuit having a three-phase output element with a pair of high-side arms and a low-side arm, and outputting current to a coil of each of the three phases of the three-phase brushless motor; as well as a control circuit that performs pulse width modulation to output a pulse signal by determining a duty ratio based on an input modulation signal, and controls output of the pulse signal to the inverter circuit; When a prescribed minimum value is input as the modulation signal, the control circuit outputs a pulse signal with a duty cycle of 0% to the inverter circuit. When a prescribed maximum value is input as the modulation signal, the control circuit outputs a pulse signal with a duty cycle of 100% to the inverter circuit. When an overmodulation signal whose maximum value of the modulation signal is input as the ratio of the maximum value to the prescribed maximum value, that is, a maximum modulation degree greater than 100%, is used as the modulation signal, so that the instantaneous value of the modulation signal is greater than the prescribed maximum value and is in an overmodulation state, the control circuit outputs a pulse signal with a duty cycle of 100% to the inverter circuit.

2. The motor driving method according to claim 1, wherein: The modulation signal is a signal in which a sine wave having a frequency three times the predetermined frequency is superimposed on a sine wave having a predetermined frequency. When this signal is used as the modulation signal, the degree of modulation in the overmodulation state is a maximum of 130%.

3. The motor driving method according to claim 2, wherein: The three-phase brushless motor is a sensorless motor.

4. The motor driving method according to claim 3, wherein: For the position detection method of the rotor of the sensorless motor, either or both of a 1-shunt FOC sensorless detection method in which at least one phase is in a switching state during the sensing for magnetic pole position estimation and a detection method in which sensing for magnetic pole position estimation is performed during a dead time are performed.

5. The motor driving method according to claim 1 or 2, wherein: The control circuit has: A three-phase modulation operation mode, in which a pulse width modulated signal is output to the coil of each of the three phases of the three-phase brushless motor to drive the motor; A two-phase modulation operation mode, in which pulse width modulation signals are output to coils of two phases among the three phases of the three-phase brushless motor to drive the motor; as well as a transition operation mode that outputs a transition modulation signal to drive the motor, the transition modulation signal gradually changing a ratio of mixing the pulse width modulation signal of each phase of the three-phase modulation operation mode and the pulse width modulation signal of each phase of the two-phase modulation operation mode; The control circuit performs any of the following operations: operating in the three-phase operation mode from startup to the maximum output in the overmodulation state; operating in the two-phase operation mode from startup to the maximum output in the overmodulation state; starting in the three-phase operation mode, switching to the two-phase operation mode through the transition operation mode as the output increases, and operating until the maximum output in the overmodulation state is achieved.

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