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 driving method for driving a three-phase DC brushless motor, such as for HVAC, sensorless and in a sine wave manner by pulse width modulation.

Background Art

[0002] When driving a three-phase DC brushless motor without using a hall sensor for detecting the position of a permanent magnet field in a sine wave manner by pulse width modulation control (PWM control), overmodulation control is not performed so as not to inhibit the detection of the position of the permanent magnet field. Also, a method of superimposing harmonics on the fundamental wave of a sine wave is used, but it is performed so as not to cause overmodulation.

[0003] When sine wave driving is used, the three-phase DC brushless motor can be made quieter and less vibratory. However, two-phase modulation has a larger maximum output but greater noise and vibration than three-phase modulation, and three-phase modulation has lower noise and vibration than two-phase modulation but has a smaller maximum output. To solve these problems, a motor driving method has been proposed in which, for the switching of two-phase modulation that outputs a sinusoidal alternating current, the same modulation period is added to all phases including the non-modulation phase within the carrier period to make it three-phase modulation, and the added modulation period is set to half of the non-conduction period within the carrier period before the addition, thereby achieving both the large output of two-phase modulation and the low noise and low vibration of three-phase modulation (Patent Document 1; Japanese Patent No. 4581391).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a three-phase DC brushless motor is driven sinusoidally by PWM control without sensors, there are several problems: it is difficult to actively use the 100% duty cycle output because dead time is used to detect the position of the permanent magnet field; the maximum output of the motor cannot be increased; the maximum rotational speed or maximum output becomes lower for motors with high back electromotive force; and the switching frequency of switching elements such as FETs in the inverter circuit of the motor drive device increases, leading to increased heat generation of the switching elements. [Means for solving the problem]

[0006] The present invention was made to solve the various problems described above, and its objective is to provide a motor driving method that can improve the maximum output of a three-phase DC brushless motor even while ensuring dead time, by driving the motor with sensorless, overmodulated PWM control at a predetermined modulation depth exceeding 100%.

[0007] A three-phase brushless motor is controlled using pulse width modulation. Sensorless motor A motor drive method comprising: an inverter circuit having output elements for each of the three phases, each equipped with a pair of high-side arms and low-side arms, which outputs current to each of the three phase coils of the three-phase brushless motor; and pulse width modulation which determines the duty cycle based on the input modulation signal and outputs a pulse signal. The modulated signal is a signal in which a sine wave of three times the frequency of a predetermined frequency is superimposed on a sine wave of a predetermined frequency, and the modulation degree in the overmodulated state when this signal is used as the modulated signal is a maximum of 130%. The inverter circuit comprises a control circuit that controls the output of a pulse signal to the inverter circuit, and the control circuit is Output control is performed in either a three-phase modulation operation mode, which drives the motor by outputting pulse-width modulated signals to the coils of each of the three phases of the three-phase brushless motor, or a two-phase modulation operation mode, which drives the motor by outputting pulse-width modulated signals to the coils of two of the three phases of the three-phase brushless motor. When a predetermined minimum value is input as the modulation signal, a pulse signal with a duty cycle 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 cycle of 100% is output to the inverter circuit. The modulation signal has a maximum modulation degree of 100%, which is the ratio of the maximum value of the modulation signal to the predetermined maximum value. ~130% range The device is characterized in that, when an overmodulated signal is input and the instantaneous value of the modulated signal becomes larger than the predetermined maximum value, an overmodulated state is reached, and a pulse signal with a duty cycle of 100% is output to the inverter circuit.

[0008] Thus, the control circuit sets the modulation signal to a maximum modulation index of 100%, which is the ratio of the maximum value of the modulation signal to a predetermined maximum value. ~130% range When an overmodulated signal is input, in an overmodulated state where the instantaneous value of the modulated signal exceeds the predetermined maximum value, a pulse signal with a duty cycle of 100% is output to the inverter circuit. This not only reduces noise and vibration but also improves motor output and reduces the number of switching cycles, thereby suppressing heat generation of the switching elements. In particular, by limiting the modulation degree of the overmodulated PWM drive signal to over 100% and 130%, the motor output can be increased with a modulation degree of 130% as the upper limit, while ensuring the accuracy of permanent magnet field position detection in sensorless drive while securing a dead time for detecting the position of the permanent magnet field. Furthermore, by limiting the modulation degree in an overmodulation state to 130% when using a modulated signal in which a sine wave of three times the frequency of a predetermined frequency is superimposed on a sine wave of a predetermined frequency, the maximum output of the motor can be increased, with a modulation degree of 130% as the upper limit at which the motor output level plateaus.

[0011] The rotor position detection method for a sensorless motor may be either a 1-shunt FOC sensorless detection method in which at least one phase is in a switching state for sensing to estimate the magnetic pole position, or a detection method in which sensing for estimating the magnetic pole position is performed during the dead time, or both. In this way, by driving the sensorless motor in an overmodulation state within a predetermined range where the modulation degree exceeds 100%, it is possible to improve the motor's maximum output even while ensuring a dead time in sensing for magnetic pole position estimation, whether the motor is rotating or stopped.

[0012] The aforementioned control circuit ,before The system has a transition operation mode that drives the motor by outputting a transition modulation signal that gradually changes the ratio in which 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 are mixed. The system may operate in one of the following ways: from startup to maximum output where an overmodulated state occurs, the system operates in the three-phase modulation operation mode; from startup to maximum output where an overmodulated state occurs, the system operates in the two-phase modulation operation mode; or the system starts in the three-phase modulation operation mode and, as the output increases, switches to the two-phase modulation operation mode via the transition operation mode and operates until the maximum output where an overmodulated state occurs. This allows a three-phase DC brushless motor to be driven by a three-phase overmodulated PWM drive signal with good controllability at low speeds, and by a two-phase overmodulated PWM drive signal with good energy utilization efficiency at high rotation speeds, high loads, or high temperatures. This reduces the amount of heat generated by the switching elements by reducing the number of switching cycles at high rotation speeds, high loads, and high temperatures, thereby contributing to energy saving. [Effects of the Invention]

[0013] By driving a three-phase DC brushless motor with sensorless overmodulation PWM control at a predetermined modulation depth exceeding 100%, it is possible to provide a motor drive method that can improve the motor's maximum output even while ensuring dead time. [Brief explanation of the drawing]

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

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

[0016] In Figure 30, the three-phase brushless motor 1 has, for example, a rotor equipped with a permanent magnet field, and a stator core in which pole teeth are arranged opposite the permanent magnets with a mechanical angle of 120° phase difference. Motor coils are wound around each pole tooth, and the phase ends of the U, V, and W phases are connected to the inverter circuit 2. The inverter circuit 2 is powered by a DC power supply 2a. The motor coils may be delta-connected, connecting adjacent phases and not having a neutral point. The 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 embedded 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 logic circuits (LOGIC), a PWM controller, a current amplifier, and an AD converter circuit, etc. (not shown). The logic circuit stores the energization pattern for energization at an electrical angle of 180°. The PWM controller generates a PWM control signal based on the energization pattern.

[0018] When the control circuit 4 receives a rotation command from the external command device 3, it generates a PWM control signal through 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 to boost 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 PWM drive signal for three-phase modulation, indicating the terminal voltages applied to each of the three-phase coils U, V, and W. The duty cycle is determined such that the minute time average value is sinusoidal with respect to the rotor's electrical angle, and the PWM drive signal is PWM modulated with this duty cycle and output to the inverter circuit 2. In the claims, "modulated signal" 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 voltages applied to each phase of the three-phase coil, and the duty cycle of the voltages applied to each of the U, V, and W phases is uniquely determined from the intersection with the modulated signal based on the rotor's electrical angle (horizontal axis).

[0020] Figure 2 shows the relationship between the voltages between U and V, V and W, and W and U (phase voltages) and the electrical angle of the rotor, as shown in Figure 1. These phase voltages, like the terminal voltages mentioned above, represent minute time averages for PWM-modulated voltages. The maximum value of the terminal voltage waveform in Figure 1 is 1.0 (100% duty cycle), but in Figure 2, although the waveforms of each phase voltage are sinusoidal, the maximum absolute value is not 1.0. Therefore, there is room for an increase in output in a PWM drive signal modulated with only sinusoidal waves.

[0021] Figure 3 shows the terminal voltages applied to each of the three-phase coils U, V, and W when the three-phase modulated PWM drive signal is not a simple sine wave, but a superimposed sine wave containing 1 / 6 of the third harmonic relative to the fundamental frequency signal. Figure 4 shows the relationship between the voltages between U and V, V and W, and W and U (phase voltages) and the electrical angle of the rotor, as shown in Figure 3. These phase voltages, like the terminal voltages mentioned above, represent minute time averages for PWM-modulated voltages. As shown in the waveform in Figure 4, the phase-to-phase voltage waveform is a sine wave, and its maximum value increases to 1.0. By using a superimposed sine wave, which is the fundamental wave superimposed with a third harmonic, instead of a simple sine wave for the PWM drive signal, the terminal voltage waveform becomes trapezoidal, as shown in Figure 3, improving the output density with respect to the rotor's electrical angle. As a result, the phase-to-phase voltage shown in Figure 4 also improves, thus improving the overall motor output. This method is well-known and a commonly used technique.

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

[0023] Figure 6, similar to Figure 5, shows an example where only the fundamental sine wave is used as the PWM drive signal, and illustrates 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 index is 130%. However, since the PWM duty cycle cannot be greater than 100%, the duty cycle is set to 100% in electrical angle intervals where the amplitude of the PWM drive signal exceeds 1.0 (modulation index of 100%). For example, at an electrical angle of 90 degrees, the modulation index for the U phase is 130%, but this means that the PWM modulation is performed with a duty cycle of 100%. In this invention, "having an electrical angle interval in which the modulation degree of the PWM drive signal exceeds 100%, and setting the duty cycle to 100% in that electrical angle interval," is referred to as overmodulation.

[0024] Next, an example of a motor drive method using the motor drive device described above will be explained. The control circuit 4 can execute a three-phase modulation operation mode by outputting a three-phase modulated PWM drive signal to the inverter circuit 2 in order to perform three-phase modulation as shown in Figure 1 as a PWM drive signal. The duty cycle of the terminal voltages of the U, V, and W phase coils 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 cycle of the terminal voltages of the U, V, and W phase coils is reset and output according to the changed electrical angle. By doing this continuously, the rotation of the rotor by PWM control can be sustained. Furthermore, the strength of the motor output can be adjusted by changing the amplitude of the U-phase (solid line), V-phase (dotted line), and W-phase (dashed line) curves in Figure 1, which are the basis for the aforementioned PWM drive signal.

[0025] The terminal voltage waveform diagrams and phase-to-phase voltage waveform diagrams in the three-phase modulation operation mode will be explained below while varying the modulation degree. Figure 7 shows the terminal voltage waveforms when the modulation signal (PWM drive 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 degree is 80%. 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 shows the phase-to-phase voltage waveforms in the three-phase modulation operation mode shown in Figure 7. 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 shows the terminal voltage waveforms when the modulation signal (PWM drive 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 degree is 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 shows the phase-to-phase voltage waveforms (sine wave waveforms) in the three-phase modulation operation mode shown in Figure 9. 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 11 shows the terminal voltage waveform when the modulation signal (PWM drive 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 degree is 115%. 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 degree exceeds 100%, the terminal voltage waveform becomes a waveform with an amplitude exceeding 1.0. However, in PWM control, there is no state where 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 the phase-to-phase voltage waveforms (sine wave waveforms) in the three-phase modulation operation mode shown in Figure 11. 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 have sections where the maximum output is flat.

[0028] Figure 13 shows the terminal voltage waveform diagram (trapezoidal waveform diagram) when the modulation signal (PWM drive 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 degree 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 degree exceeds 100%, the terminal voltage waveform becomes a waveform with an amplitude exceeding 1.0. However, in PWM control, there is no state where the output exceeds 100%, so there is a section in the positive and negative terminal voltage waveforms where the maximum output is flat. Furthermore, the flat section is wider than in the case of a modulation degree of 115% (see Figure 11). Figure 14 shows the phase-to-phase voltage waveform diagram (trapezoidal waveform diagram) in the three-phase modulation operation mode shown in Figure 13. 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 show an expanded flat section where the maximum output is flat compared to the case with a modulation degree of 115% (see Figure 12).

[0029] Figure 15 shows the terminal voltage waveform diagram (trapezoidal waveform diagram) when the modulation signal (PWM drive 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 degree 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 degree exceeds 100%, the terminal voltage waveform becomes a waveform with an amplitude exceeding 1.0. However, in PWM control, there is no state where the output exceeds 100%, so there is a section in the positive and negative terminal voltage waveforms where the maximum output is flat. Furthermore, the flat section is slightly wider than in the case of a modulation degree of 130% (see Figure 13). Figure 16 shows the phase-to-phase voltage waveforms in the three-phase modulation operation mode shown in Figure 15. 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 show an expanded flat section where the maximum output is flat compared to the case with a modulation degree of 130% (see Figure 14).

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

[0031] Figure 17 shows the terminal voltage (average applied voltage to the coils) waveform when the combined waveform of the switching phases is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave, and the modulation degree is 80%. 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 show a section where the maximum output is flat. Figure 18 shows the phase-to-phase voltage waveforms (sine wave waveforms) in the two-phase modulation operation mode shown in Figure 17. 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 19 shows the terminal voltage waveforms when the combined waveform of the switching phases is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave, and the modulation degree is 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. The positive and negative terminal voltage waveforms show an expanded flat section where the maximum output is flat compared to when the modulation degree is 80%. Figure 20 shows the phase-to-phase voltage waveforms (sine wave waveforms) in the two-phase modulation operation mode shown in Figure 19. 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 shows the terminal voltage waveforms when the combined waveform of the switching phases is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave, and the modulation index is 115%. 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 show an extended period where the maximum output is flat compared to when the modulation index is 100%. Figure 22 shows the phase-to-phase voltage waveform (sine wave waveform) in the two-phase modulation operation mode shown in Figure 21. 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 have sections where the maximum output is flat.

[0034] Figure 23 shows the terminal voltage waveform diagram (trapezoidal waveform diagram) when the combined waveform of the switching phases is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave, and the modulation degree 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 a section where the maximum output is flat. Furthermore, the flat section is wider than in the case of a modulation degree of 115% (see Figure 21). Figure 24 shows the phase-to-phase voltage waveform (trapezoidal waveform) in the two-phase modulation operation mode shown in Figure 23. 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 show an expanded flat section where the maximum output is flat compared to the case with a modulation degree of 115% (see Figure 22).

[0035] Figure 25 shows the terminal voltage waveform diagram (trapezoidal waveform diagram) when the combined waveform of the switching phases is a sine wave with a 1 / 6 third harmonic superimposed on the fundamental wave, and the modulation degree 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 positive and negative terminal voltage waveforms show a slightly wider interval where the maximum output is flat compared to when the modulation degree is 130% (see Figure 23). Figure 26 shows the phase-to-phase voltage waveforms in the two-phase modulation operation mode shown in Figure 25. 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 show an expanded flat section where the maximum output is flat compared to the case with a modulation degree of 130% (see Figure 24).

[0036] From the experimental results above, it was found that, in both the three-phase modulation operation mode and the two-phase modulation operation mode, when comparing the inter-phase output (the integral of the absolute value of the inter-phase voltage waveform over one period, see Figure 31), the inter-phase output becomes almost constant once the modulation level exceeds a certain value, even when the modulation level is changed beyond a certain point. Specifically, it was found that there is no significant difference and it remains constant even when the modulation level exceeds 130%. Figures 27 and 28 are graphs comparing the torque curves at a modulation level of 130% and 180% in the three-phase modulation operation mode. The torque is slightly higher at a modulation level of 180% (Figure 28), but it can be seen that the difference is negligible compared to a modulation level of 130%.

[0037] Figure 29 is a table showing the relationship between the phase-to-phase output ratio when the modulation degree is changed in the three-phase modulation operation mode and the two-phase modulation operation mode. The phase-to-phase output ratio is a relative value when the phase-to-phase output at a modulation degree of 100% is set to 100. It can be seen that the phase-to-phase output increases as the modulation degree increases, but the phase-to-phase output does not change up to a modulation degree of 130%. Furthermore, when the modulation degree exceeds 130%, the position detection interval (dead time) of the permanent magnet field shortens in sensorless drive, and controllability decreases. In this way, by setting the modulation degree of the overmodulated PWM drive signal to exceed 100% and limiting it to 130%, the motor output can be improved with a modulation degree of 130% as the upper limit at which the motor output level plateaus, and the position detection accuracy of the permanent magnet field in sensorless drive can be ensured.

[0038] Furthermore, even if the modulation degree of the overmodulated PWM drive signal is around 180%, it is still possible to detect the position of the permanent magnet field using sensorless drive. However, this will reduce the accuracy of position detection and controllability, while not improving the inter-phase output. Therefore, by using a modulation degree range exceeding 100% and with an upper limit of 130%, which allows for improved output while ensuring the sensing range (operational stability) of sensorless drive, it is possible to achieve both motor drive stability and improved output.

[0039] In the present invention, as a sensorless drive method, it is possible to use individually or simultaneously a 1-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 the dead time.

[0040] Furthermore, while the present invention has been described on the premise that a "sine wave obtained by superimposing a third harmonic on the fundamental wave" is used as the PWM drive signal, it is also possible to use a pure sine wave as shown in Figure 1, in which case the maximum modulation degree that can be applied as overmodulation is 200%.

[0041] Herein, we will describe an example of a specific motor drive method for a three-phase DC brushless motor. The control circuit 4 has a three-phase overmodulation operation mode in which it outputs a three-phase modulated PWM drive signal as a PWM drive signal to the inverter circuit 2, a two-phase overmodulation operation mode in which it outputs a two-phase modulated PWM drive signal as a PWM drive signal to the inverter circuit 2, and a transition operation mode in which it outputs a transition overmodulation signal to the inverter circuit 2 in which the ratio of the three-phase overmodulated PWM drive signal and the two-phase overmodulated PWM drive signal is gradually changed. In three-phase and two-phase modulation operation modes, the modulation degree of the PWM drive signal is set to the above-mentioned maximum of 130% in an overmodulated state. However, the modulation degree may be appropriately changed to adjust the output depending on the situation, such as starting from a standstill, decelerating from a high rotational speed state, or load fluctuations in a constant speed state. Furthermore, while the three-phase modulation operation mode is less vibrational and noisy than the two-phase modulation operation mode, it is less efficient. Therefore, the choice between the three-phase and two-phase modulation operation mode should be made according to the load characteristics and application requirements. Furthermore, in the transition mode, the waveforms of three-phase and two-phase modulated signals with modulation levels ranging from 0% to 100% are mixed, and their ratio gradually changes. At this time, the ratio of the three-phase modulated signal is decreased and the ratio of the two-phase modulated signal is increased in units of 60-degree electrical angle intervals. Alternatively, the motor may be started in three-phase modulated mode with a modulation level between 0% and 100%, then switched to two-phase modulated mode via the transition mode with a modulation level between 0% and 100%, and then the motor may be driven in two-phase modulated mode with a modulation level between 100% and 130%.

[0042] This allows a three-phase DC brushless motor to be driven by a low-noise, low-vibration three-phase modulated PWM drive signal at low speeds, and by a two-phase modulated PWM drive signal that is advantageous in terms of heat generation of the switching elements and has good energy utilization efficiency when the motor is driven at high speeds, high loads, or high temperatures. This reduces the amount of heat generated by the switching elements by reducing the number of switching cycles at high speeds, high loads, and high temperatures, thereby contributing to energy saving.

[0043] The motor drive method described above is suitably used 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 drive method for driving a sensorless motor using a pulse width modulation method with a three-phase brushless motor, The aforementioned three-phase brushless motor is An inverter circuit having output elements for each of the three phases, each equipped with a pair of high-side arms and low-side arms, and outputting current to each of the three-phase coils of the three-phase brushless motor, The system includes a control circuit that controls the output of a pulse signal to an inverter circuit, wherein pulse width modulation is performed by determining the duty cycle based on the input modulation signal and outputting a pulse signal, the modulation signal being a signal in which a sine wave of three times the frequency of a predetermined frequency is superimposed on a sine wave of a predetermined frequency, and the modulation degree in the overmodulation state when this signal is used as the modulation signal is a maximum of 130%. The control circuit performs output control in either a three-phase modulation operation mode, which drives the motor by outputting pulse-width modulated signals to the coils of each of the three phases of the three-phase brushless motor, or a two-phase modulation operation mode, which drives the motor by outputting pulse-width modulated signals to the coils of two of the three phases of the three-phase brushless motor. When a predetermined minimum value is input as the modulation signal, a pulse signal with a duty cycle 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 cycle of 100% is output to the inverter circuit. A motor driving method characterized in that, as the modulated signal, an overmodulated signal having a maximum modulation degree in the range of 100% to 130%, which is the ratio of the maximum value of the modulated signal to the predetermined maximum value, is input, and when an overmodulated state is reached in which the instantaneous value of the modulated signal becomes larger than the predetermined maximum value, a pulse signal with a duty cycle of 100% is output to the inverter circuit.

2. The motor drive method according to Claim 1, 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 for sensing for magnetic pole position estimation, or a detection method in which sensing for magnetic pole position estimation is performed during the dead time, or both.

3. The control circuit has a transition operation mode that drives the motor by outputting a transition modulation signal that gradually changes the ratio in which 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 are mixed, A motor driving method according to claim 1 or claim 2, wherein the motor is operated in one of the following ways: from startup to the maximum output at which an overmodulation state occurs, in the three-phase modulation operation mode; from startup to the maximum output at which an overmodulation state occurs, in the two-phase modulation operation mode; or the motor is started in the three-phase modulation operation mode and, as the output increases, switches to the two-phase modulation operation mode via the transition operation mode and operates until the maximum output at which an overmodulation state occurs.

Images