Motor control device and motor system

Abstract

This motor control device, on the basis of the rotational speed of the motor, switches current detection methods between a first method and a second method that differ in how the duty ratio is adjusted. With the first method, for the PWM signal of each phase, the signal level varies over the entire period of a single cycle at arbitrary points in time that differ from each other, and the current of a current detector is detected over the entire period. With the second method, a single cycle of the PWM signal of each phase includes a first period and a second period, and for the PWM signal of each phase, the signal level varies at points in time that are according to an established duty ratio in the first period, while in the second period, the signal level varies at fixed points in time that differ from each other and the order in which the PWM signal of each phase is replaced is fixed regardless of the set value of the duty ratio, and the current of the current detector is detected during the second period.

Description

Motor control device and motor system

[0001] The present invention relates to a motor control device and a motor system.

[0002] Conventionally, a technique for controlling a three-phase motor has been known in which a single shunt resistor inserted in a DC section of an inverter circuit is used to detect the currents of the U, V, and W phases. For example, a common technique for detecting all three phases of current involves generating pulse width modulation (PWM) signals (energization patterns) for each phase so that currents of two or more phases can be detected within one cycle of the PWM signal (carrier) for driving the motor. The order in which the levels of the PWM signals for each phase are switched is then changed depending on the energization pattern, and the current is detected (see, for example, Patent Document 1).

[0003] However, when the phase of the PWM signal is changed using the above method, distortion occurs in the current flowing through the DC bus when the order in which the signal levels of the PWM signals for each phase change, resulting in a waveform that appears to have a large amount of noise superimposed on it, which can cause noise.

[0004] Therefore, Patent Document 2 proposes a technique for adjusting the phase of PWM by providing, in one PWM cycle, a first period in which the signal level changes at a timing according to a set duty ratio, and a second period in which the signal level changes at fixed timing different from the first period and in which the current is detected. With this technique, the order in which the signal levels of the PWM signals change is fixed without sudden changes, thereby suppressing distortion of the motor current and preventing noise.

[0005] JP 2015-84632 A JP 2021-19458 A

[0006] However, although the noise can be eliminated by constantly using the PWM control method described in the above-mentioned document 2, there is a risk that the required control amount will not be output if the motor rotation speed becomes high or the calculated modulation rate exceeds a certain range.

[0007] Therefore, the present invention provides a motor control device that can output a required control amount while suppressing noise.

[0008] A motor control device according to a representative embodiment of the present invention includes a control unit that generates PWM signals corresponding to each phase of a motor having coils for multiple phases, an inverter circuit that drives the coils of each phase based on the PWM signals, and a current detector connected in series to a DC line of the inverter circuit, wherein the control unit includes a current detection unit that detects a current of the current detector, a duty ratio setting unit that sets a duty ratio of the PWM signal for each phase based on a detection result of the current detection unit, a PWM signal generation unit that generates the PWM signal for each phase based on the duty ratio set by the duty ratio setting unit, and a speed monitoring unit that monitors the rotational speed of the motor for each PWM period, and the duty ratio setting unit switches a current detection method between a first method and a second method that differ in how the duty ratio is adjusted. a switching unit, wherein in the first method, the signal level of the PWM signal of each phase changes at arbitrary timings that are different from each other throughout one cycle, and the current detection unit detects the current of the current detector throughout the entire period; and in the second method, one cycle of the PWM signal of each phase includes a first period and a second period, the signal level of the PWM signal of each phase changes during the first period at a timing according to the set duty ratio, and during the second period, the signal level changes at fixed timings that are different from each other, and the order in which the PWM signals of each phase are switched is fixed regardless of the set value of the duty ratio, and the current detection unit detects the current of the current detector during the second period; and the current detection method switching unit switches between the first method and the second method based on the rotational speed of the motor.

[0009] The motor control device according to the present invention can output a required control amount while suppressing noise.

[0010] 1 is a diagram showing an example of the configuration of a motor system according to a first embodiment. FIG. 2 is a diagram showing an overview of a phase current detection method of a first method by the motor control device according to the first embodiment. FIG. 3 is a diagram showing an overview of a phase current detection method of a first method by the motor control device according to the first embodiment. FIG. 4 is a diagram showing an overview of a phase current detection method of a second method by the motor control device according to the first embodiment. FIG. 5 is a diagram for explaining the principle of PWM signal generation of a second method by the motor control device according to the first embodiment. FIG. 6 is a flowchart showing the flow of motor drive control processing by the motor control device according to the embodiment. FIG. 7 is a diagram showing a motor current waveform when the motor is driven by a PWM signal generated while detecting current by the first method according to the first embodiment. FIG. 8 is a diagram showing a motor current waveform when the motor is driven by a PWM signal generated while detecting current by the second method according to the first embodiment. FIG. 9 is a diagram showing a noise level when the motor is driven by a PWM signal generated while detecting current by the first method or the second method according to the first embodiment. FIG. 10 is a flowchart of method switching determination for each PWM period according to the first embodiment. FIG. 11 is a diagram explaining the motor rotation speed and the control variables of the first method and the second method used in method switching determination according to the first embodiment. FIG. 12 is a diagram showing an example of the configuration of a motor system according to a second embodiment. 10 is a flowchart of a method switching determination for each PWM period according to embodiment 2. FIG. 11 is a diagram illustrating the sum of three duty start setting values ​​and a switching threshold value between the first method and the second method according to embodiment 2. FIG. 12 is a diagram illustrating detection timings of PWM signals and phase currents in a modified example of the second method in the motor control devices according to embodiments 1 and 2.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes embodiments of the present invention with reference to the accompanying drawings. In the following drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0012] <First Embodiment> Fig. 1 is a diagram showing an example of the configuration of a motor system according to a first embodiment. The motor system 1 shown in Fig. 1 controls the rotational operation of a motor 4. The motor system 1 is installed in devices such as, but not limited to, a copy machine, a personal computer, and a refrigerator. The motor system 1 includes at least a motor 4 and a motor control device 100.

[0013] The motor 4 has a plurality of coils. The motor 4 has, for example, three-phase coils including a U-phase coil Lu, a V-phase coil Lv, and a W-phase coil Lw. A specific example of the motor 4 is a three-phase brushless motor. The U-phase coil Lu, the V-phase coil Lv, and the W-phase coil Lw are connected to each other, for example, by star connection.

[0014] The motor control device 100 converts direct current into three-phase alternating current and drives the motor by controlling the on / off (ON / OFF) of multiple switching elements connected in a three-phase bridge according to a current pattern including a three-phase PWM signal.

[0015] Specifically, the motor control device 100 includes an inverter circuit 23 , a control unit 20 , and a current detector 24 .

[0016] The inverter circuit 23 is a circuit that converts DC power supplied from the DC power supply 21 into three-phase AC by switching a plurality of switching elements, and passes the three-phase AC drive current through the motor 4, thereby rotating the rotor of the motor 4. The inverter circuit 23 drives the motor 4 based on a plurality of current conduction patterns (more specifically, three-phase PWM signals generated by a PWM signal generation unit 32 in the current conduction pattern generation unit 35) generated by a current conduction pattern generation unit 35 described below.

[0017] The inverter circuit 23 includes a plurality of switching elements 25U+, 25V+, 25W+, 25U-, 25V-, and 25W- connected in a three-phase bridge configuration. The switching elements 25U+, 25V+, and 25W+ are high-side switching elements (upper arms) connected to the positive side of the DC power supply 21 via the positive bus 22a. The switching elements 25U-, 25V-, and 25W- are low-side switching elements (lower arms) connected to the negative side (specifically, the ground side) of the DC power supply 21. The switching elements 25U+, 25V+, 25W+, 25U-, 25V-, and 25W- are each turned on or off in response to a corresponding one of a plurality of drive signals supplied from the drive circuit 33 based on a PWM signal included in the above-described conduction pattern. Hereinafter, the multiple switching elements 25U+, 25V+, 25W+, 25U-, 25V-, and 25W- may be simply referred to as switching elements when no particular distinction is made.

[0018] The connection point between switching element 25U+ and switching element 25U- is connected to one end of the U-phase coil of motor 4. The connection point between switching element 25V+ and switching element 25V- is connected to one end of the V-phase coil of motor 4. The connection point between switching element 25W+ and switching element 25W- is connected to one end of the W-phase coil of motor 4. The other ends of the U-phase coil, V-phase coil, and W-phase coil are connected to each other.

[0019] Specific examples of the switching element include an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor), but the switching element is not limited to these.

[0020] The current detector 24 outputs a detection signal Sd corresponding to the current value of the current flowing on the DC side of the inverter circuit 23. The current detector 24 shown in FIG. 1 generates a detection signal Sd corresponding to the current value of the current flowing on the negative bus 22b. The current detector 24 is, for example, a current detection element disposed on the negative bus 22b, and more specifically, a resistor (shunt resistor) inserted on the negative bus 22b. A current detection element such as a shunt resistor generates a voltage signal corresponding to the current value of the current flowing therethrough as the detection signal Sd. Note that the current detector 24 may be any element that outputs a detection signal corresponding to the current value of the current flowing on the negative bus 22b, and may be a sensor such as a current transformer (CT).

[0021] The control unit 20 generates a plurality of PWM signals corresponding to each phase of the motor 4. The control unit 20 is, for example, a program processing device (e.g., a microcontroller) having a configuration in which a processor such as a CPU, various storage devices such as RAM and ROM, and peripheral circuits such as a counter (timer), an A / D conversion circuit, a D / A conversion circuit, and an input / output I / F circuit are connected to one another via a bus. In this embodiment, the control unit 20 is packaged as an IC (integrated circuit), but is not limited to this.

[0022] The control unit 20 generates a PWM signal so that the motor 4 operates appropriately, based on, for example, a rotation speed command ωref for the motor 4 input from a higher-level device (not shown) and the phase current of each phase of the motor 4 based on the detection signal Sd of the current detector 24.

[0023] The control unit 20 has a current detection unit 27, a current detection timing adjustment unit 34, a drive circuit 33, a current pattern generation unit 35, a clock generation unit 36, and a carrier generation unit 37 as functional blocks for generating PWM signals for each phase.

[0024] The energization pattern generating unit 35 includes a duty ratio setting unit 39 , a PWM signal generating unit 32 , and a speed monitoring unit 38 .

[0025] The duty ratio setting unit 39 is a functional unit for generating PWM signals as signals that specify the current conduction pattern of the inverter circuit 23. The duty ratio setting unit 39 sets the duty ratios of the three-phase PWM signals based on the current detection results obtained by the current detection unit 27. The duty ratio setting unit 39 includes, for example, a vector control unit 30 and a duty ratio calculation unit 31.

[0026] The duty ratio calculation unit 31 according to this embodiment includes a duty ratio / duty start setting value calculation unit 311 , a current detection method switching unit 312 , and a PWM limit detection unit 313 .

[0027] The motor control device 100 according to this embodiment switches between two current detection methods, which differ in the way they shift the phase of the PWM signal used for current detection (how they adjust the duty ratio). Specific examples of the two current detection methods will be described using Figures 2A, 2B, and 3. A specific configuration for generating three-phase PWM signals and a specific method and entity for detecting phase currents in the control unit 20 of the motor control device 100 shown in Figure 1 will be described later after the description of Figures 2A, 2B, and 3.

[0028] 2A and 2B are diagrams illustrating a pulse phase adjustment method according to a first method for adjusting the phase of a PWM signal for each phase in order to detect the phase current of a three-phase brushless motor. As shown in FIGS. 2A and 2B , in the pulse phase adjustment method according to the first method, the phase of the PWM signal for each phase is adjusted so that the center points of the PWM signal waveforms for each phase are aligned.

[0029] 2A , the duty ratio Udu of the U-phase PWM signal U is higher than the duty ratio Vdu of the V-phase PWM signal V. That is, in FIG. 2A , the U-phase PWM signal U changes at change point t4, and the V-phase PWM signal V changes at change point t5. On the other hand, in FIG. 2B , the duty ratio Udu of the U-phase PWM signal U is lower than the duty ratio Vdu of the V-phase PWM signal V. That is, in FIG. 2B , the V-phase PWM signal changes at change point t4, and the U-phase PWM signal changes at change point t5.

[0030] 2A , in one cycle of the PWM signal, motor control device 100 measures the current flowing through current detector (shunt resistor) 24 during period T21 between timing t4 when U-phase PWM signal U switches and timing t5 when V-phase PWM signal V switches. Motor control device 100 also measures the current flowing through current detector (shunt resistor) 24 during period T22 between timing t5 when V-phase PWM signal V switches and timing t6 when W-phase PWM signal W switches.

[0031] 2A, the current measured during a period T21 represents the U-phase current Iu, and the current measured during a period T22 represents the sum of the U-phase current Iu and the V-phase current Iv.

[0032] Here, the U-phase, V-phase, and W-phase currents Iu, Iv, and Iw have a relationship of "Iu+Iv+Iw=0." That is, there is a relationship of "Iw=-(Iu+Iv)."

[0033] 2A, the W-phase current Iw can be calculated from the above relational expression and the measurement value of the sum (Iu + Iv) of the U-phase and V-phase currents measured during the period T22. Furthermore, the V-phase current Iv can be calculated from the measurement value of the U-phase phase current Iu detected during the period T21 and the measurement value of the W-phase phase current Iw detected during the period T22.

[0034] As described above, in FIG. 2A, motor control device 100 measures the currents of the U-phase, V-phase, and W-phase by detecting the current of current detector 24 during periods T21 and T22 of the PWM cycle.

[0035] 2B , in one cycle of the PWM signal, motor control device 100 measures the current flowing through current detector (shunt resistor) 24 during period T21 between timing t4 when V-phase PWM signal V switches and timing t5 when U-phase PWM signal U switches. Motor control device 100 also measures the current flowing through current detector (shunt resistor) 24 during period T22 between timing t5 when U-phase PWM signal U switches and timing t6 when W-phase PWM signal W switches.

[0036] 2B, the current measured during a period T21 represents the V-phase current Iv, and the current measured during a period T22 represents the sum of the U-phase current Iu and the V-phase current Iv.

[0037] 2B, the W-phase current Iw can be calculated from the above relational expression and the measurement value of the sum (Iu + Iv) of the U-phase and V-phase currents measured during the period T22. Furthermore, the U-phase current Iu can be calculated from the measurement value of the V-phase current Iv detected during the period T21 and the measurement value of the W-phase current Iw detected during the period T22.

[0038] As described above, in FIG. 2B, motor control device 100 measures the currents of the U-phase, V-phase, and W-phase by detecting the current of current detector 24 during periods T21 and T22 of the PWM cycle.

[0039] 2A and 2B , the order in which the PWM signals for each phase are switched varies depending on the set value of the duty ratio, so that the signal levels change at different timings throughout one cycle of the PWM signals for each phase. The current detection unit 27 detects the current of the current detector (shunt resistor) 24 during periods T21 and T22, the timing of which varies throughout one cycle of the PWM signals.

[0040] <Current Detection Method: Second Method> FIG. 3 is a diagram for explaining an overview of a phase current detection method according to the second method performed by the motor control device 100 according to the first embodiment.

[0041] More specifically, in the motor control device 100 according to the second technique of the first embodiment shown in FIG. 3, two types of carriers C1 and C2 are used as the carriers C of the PWM signals U, V, and W.

[0042] Carrier C1 is a sawtooth carrier (carrier wave signal) whose level increases in a cycle corresponding to first period A in the PWM cycle. Carrier C2 is a sawtooth carrier whose level increases in a cycle corresponding to second period B in the PWM cycle.

[0043] As shown in FIG. 3, the carrier C1 and the carrier C2 are generated alternately, and one period (PWM period) of the PWM signals U, V, and W is determined by a pair of consecutive carriers C1 and C2.

[0044] The PWM signals U, V, and W corresponding to each phase are generated so that the high and low levels are inverted at the timing when the carriers C1 and C2 match a threshold calculated based on the duty ratios Udu, Vdu, and Wdu described below.

[0045] The timing at which the multiple PWM signals U, V, and W change from low level to high level is slightly delayed from the timing at which the carrier C matches a threshold based on the duty ratios Udu, Vdu, and Wdu of each phase. This is because a dead time is required to prevent short circuits between the upper and lower arms. For ease of explanation, the dead time is not shown in Figures 2A, 2B, and 3. Hereinafter, when the multiple PWM signals U to W are not distinguished from one another, they may be referred to as "PWM signals."

[0046] The PWM signals U, V, and W according to the second technique have their signal levels switched at timings according to the duty ratio during a first period A from time t0 to time t4 determined by the carrier C1, and their signal levels switched at mutually different fixed timings during a second period B from time t4 to time t8 determined by the carrier C2.

[0047] For example, the signal level of the U-phase PWM signal U switches from low to high at timing (time) t1 in the first period A, and switches from high to low at timing t5 in the second period B. The signal level of the V-phase PWM signal V switches from low to high at timing (time) t2 in the first period A, and switches from high to low at timing t6 in the second period B. The signal level of the W-phase PWM signal V switches from low to high at timing (time) t3 in the first period A, and switches from high to low at timing t7 in the second period B.

[0048] In the first period A, the timing at which the signal levels of the PWM signals U, V, and W are switched varies according to the duty ratios Udu, Vdu, and Wdu set by the duty ratio calculation unit 31 .

[0049] On the other hand, during the second period B, the timing at which the signal levels of the PWM signals U, V, and W change (switch) is fixed regardless of the set value of the duty ratio. In other words, the order in which the signal levels of the PWM signals U, V, and W switch during the second period B is fixed. For example, as shown in FIG. 3 , during the second period B, the signal levels of the PWM signals U, V, and W switch in the order of U phase, V phase, and W phase, and this order does not change during the drive control of the motor. Note that the order in which the signal levels of the PWM signals U, V, and W switch is not limited to the above example.

[0050] 3 , during second period B, motor control device 100 measures the current flowing through current detector (shunt resistor) 24 during period Tu between timing t5 when U-phase PWM signal U switches and timing t6 when V-phase PWM signal V switches. Motor control device 100 also measures the current flowing through current detector (shunt resistor) 24 during period Tuv between timing t6 when V-phase PWM signal V switches and timing t7 when W-phase PWM signal W switches.

[0051] The current measured during the period Tu represents the U-phase current Iu, and the current measured during the period Tuv represents the sum of the U-phase current Iu and the V-phase current Iv.

[0052] Here, the U-phase, V-phase, and W-phase currents Iu, Iv, and Iw have a relationship of "Iu+Iv+Iw=0." That is, there is a relationship of "Iw=-(Iu+Iv)."

[0053] Therefore, the W-phase current Iw can be calculated from the above relational expression and the measurement value of the sum (Iu + Iv) of the U-phase and V-phase currents measured during the period Tuv. Furthermore, the V-phase current Iv can be calculated from the measurement value of the U-phase phase current Iu detected during the period Tu and the measurement value of the W-phase phase current Iw detected during the period Tuv.

[0054] In this way, motor control device 100 measures the currents of the U-phase, V-phase, and W-phase by detecting the currents of current detector 24 during periods Tu and Tuv within the second period of the PWM cycle.

[0055] That is, in the second technique, in order to prevent distortion of the current of the motor 4, the PWM period is divided into a first period A for adjusting the duty ratio and a second period B for detecting the phase current of each phase. The control unit 20 generates a PWM signal for each phase so that the signal level of the PWM signal for each phase switches at a timing corresponding to the duty ratio in the first period A and switches at predetermined timings that are different from each other in the second period B. The control unit 20 then measures the phase current at a predetermined timing within the second period B of the PWM period. Furthermore, in the second period B, the order in which the PWM signals for each phase switch is fixed regardless of the set value of the duty ratio.

[0056] Returning to FIG. 1, a specific configuration for generating PWM signals for each phase and a specific configuration for detecting phase currents in motor control device 100 will be described in detail.

[0057] The current detection unit 27 detects the phase currents Iu, Iv, Iw of the U, V, and W phases flowing through the motor 4 by acquiring the detection signal Sd based on the plurality of current conduction patterns (more specifically, three-phase PWM signals) generated by the current conduction pattern generation unit 35. More specifically, the current detection unit 27 detects the phase currents Iu, Iv, Iw of the U, V, and W phases flowing through the motor 4 by acquiring the detection signal Sd at acquisition timings synchronized with the plurality of current conduction patterns (more specifically, three-phase PWM signals). The acquisition timing of the detection signal Sd is set by the current detection timing adjustment unit 34.

[0058] For example, the current detection unit 27 captures the analog voltage detection signal Sd generated by the current detector 24 into an analog-to-digital (A / D) converter at the acquisition timing set by the current detection timing adjustment unit 34. The A / D converter is provided in the current detection unit 27. The current detection unit 27 then AD-converts the captured analog detection signal Sd into a digital detection signal Sd, and measures the phase currents Iu, Iv, Iw of the U, V, W phases of the motor 4 by digitally processing the AD-converted digital detection signal Sd.

[0059] The measured values ​​of the phase currents Iu, Iv, and Iw of each phase measured by the current detection unit 27 are supplied to the current pattern generation unit 35. The clock generation unit 36 ​​generates a clock of a predetermined frequency using an internal oscillation circuit and outputs the generated clock to the carrier generation unit 37. Note that the clock generation unit 36 ​​starts operating, for example, at the same time as the motor control device 100 is powered on.

[0060] The current pattern generation unit 35 determines the rotor position of the motor 4 based on the measured values ​​of the phase currents Iu, Iv, and Iw of the motor 4 measured by the current detection unit 27, and generates a signal specifying a pattern for energizing the inverter circuit 23 (current pattern of the inverter circuit 23) so that the rotor of the motor 4 follows the determined rotor position.

[0061] Here, the energization pattern of the inverter circuit 23 may be rephrased as a pattern for energizing the motor 4 (energization pattern of the motor 4). The signal specifying the energization pattern of the inverter circuit 23 includes, for example, a three-phase PWM signal for energizing the inverter circuit 23 so as to rotate the motor 4.

[0062] In this embodiment, the current conduction pattern generation unit 35 generates the current conduction pattern of the inverter circuit 23 by vector control. Note that the method for generating the current conduction pattern of the inverter is not limited to vector control, and may be a method for determining the phase voltage of each phase using VF control or the like.

[0063] The speed monitoring unit 38 of the current conduction pattern generation unit 35 monitors the rotation speed of the motor 4. For example, the speed monitoring unit 38 calculates and monitors the rotation speed of the motor 4 based on the measured values ​​of the phase currents Iu, Iv, and Iw of the motor 4 measured by the current detection unit 27.

[0064] The vector control unit 30 of the energization pattern generation unit 35 calculates the phase difference between the rotor position and the command value from the induced voltage obtained by the extended induced voltage observer in the speed monitoring unit 38, and generates a torque current command Iqref and an excitation current command Idref based on this. The vector control unit 30 calculates the torque current Iq and the excitation current Id by vector control calculation using the rotor position θ based on the measured values ​​of the phase currents Iu, Iv, and Iw by the current detection unit 27. It is also possible to obtain a measured value of the rotational speed of the motor 4 by a sensor without using the extended induced voltage observer, and generate the torque current command Iqref and the excitation current command Idref based on the difference between the measured rotational speed value and the rotational speed command.

[0065] The vector control unit 30 performs, for example, a PI control calculation on the difference between the torque current command Iqref and the torque current Iq to generate a voltage command Vq. The vector control unit 30 performs, for example, a PI control calculation on the difference between the excitation current command Idref and the excitation current Id to generate a voltage command Vd.

[0066] The vector control unit 30 converts the voltage commands Vq and Vd into phase voltage commands Vu*, Vv*, and Vw* for the U, V, and W phases, respectively, using the rotor position θ. The phase voltage commands Vu*, Vv*, and Vw* for the respective phases are supplied to a duty ratio setting unit 39.

[0067] The duty ratio setting unit 39 of the energization pattern generating unit 35 is a functional unit for generating a PWM signal as a signal that specifies the energization pattern of the inverter circuit 23 .

[0068] The duty ratio setting unit 39 calculates the duty ratios of the three-phase PWM signals based on the current detection results by the current detection unit 27, sets a current detection method, and then sets the duty ratios according to the method. The duty ratio refers to the ratio of the H (high level) period to the total period of the H (high level) and L (low level) periods in the PWM signal of each phase.

[0069] The duty ratio / duty start setting value calculation unit 311 in the duty ratio calculation unit 31 calculates the duty ratios (setting values ​​of the duty ratios of each phase) Udu, Vdu, and Wdu for generating three-phase PWM signals based on the input phase voltage commands Vu*, Vv*, and Vw* of each phase.

[0070] Here, a specific example of a method for calculating the duty ratios Udu, Vdu, and Wdu of each phase will be described. The duty ratios Udu, Vdu, and Wdu of each phase are calculated based on the modulation factors modU, modV, and modW, as shown in the following equations (1) to (3).

[0071] The duty ratios Udu, Vdu, and Wdu of the respective phases obtained based on the following equations (1) to (3) have sinusoidal waveforms with phase differences of, for example, 120 degrees each. Examples of the waveforms of the duty ratios Udu, Vdu, and Wud of the respective phases will be described later.

[0072] Udu=modU×(carrier upper limit value) (1) Vdu=modV×(carrier upper limit value) (2) Wdu=modW×(carrier upper limit value) (3)

[0073] The duty ratio / duty start set value calculation unit 311 further calculates, for each PWM period, duty start set values ​​(Tsu, Tsv, Tsw) that are the time periods from the start of the PWM interval until the three-phase PWM signals change to H for the next PWM period based on the duty ratio. While this example illustrates an example in which the PWM signals change from L to H at t1, t2, and t3, the PWM signals may also change from H to L at t1, t2, and t3. That is, the duty start set values ​​(Tsu, Tsv, Tsw) are the time periods from the start of the PWM interval until the three-phase PWM signals change from the first level to the second level for the next PWM period. In the examples of FIGS. 2 to 4 , the first level indicates the L state, and the second level indicates the H state.

[0074] In detail, in the first technique, in FIG. 2A , the time period T03 from t0 (= ta) to t3 is the duty start setting value Tsu of the PWM signal U. The time period T02 from t0 (= ta) to t2 is the duty start setting value Tsv of the PWM signal V. The time period T01 from t0 (= ta) to t1 is the duty start setting value Tsw of the PWM signal W. In FIG. 2B , the time period T02 from t0 (= ta) to t2 is the duty start setting value Tsu of the PWM signal U. The time period T01 from t0 (= ta) to t1 is the duty start setting value Tsv of the PWM signal V. The time period T03 from t0 (= ta) to t3 is the duty start setting value Tsw of the PWM signal W.

[0075] 3 of the second technique, the time period T01 from t0 to t1 is the duty start setting value Tsu of the PWM signal U. The time period T02 from t0 to t2 is the duty start setting value Tsv of the PWM signal V. The time period T03 from t0 to t3 is the duty start setting value Tsw of the PWM signal W.

[0076] The PWM limit detection unit 313 detects the setting limit of the PWM according to the second method calculated by the duty ratio / duty start setting value calculation unit 311. The PWM limit detection unit 313 can also detect the setting limit of the PWM according to the first method calculated by the duty ratio / duty start setting value calculation unit 311.

[0077] The current detection method switching unit 312 switches the current detection method between a first method and a second method, which differ in how the duty ratio is adjusted. In this embodiment, the current detection method switching unit 312 selects and switches between the first method and the second method based on the rotation speed and control amount of the motor 4. Then, the current detection method switching unit 312 outputs a duty ratio according to the selected method.

[0078] The PWM signal generating unit 32 generates three-phase PWM signals U, V, and W as energization pattern signals based on the duty ratios Udu, Vdu, and Wdu of each phase set by the duty ratio setting unit 39 and the carriers C1 and C2. As described above, the carriers C1 and C2 are carrier wave signals whose levels periodically increase and decrease.

[0079] The PWM signal generating unit 32 generates three-phase PWM signals U, V, and W based on the results of comparison between the carriers C1 and C2 and threshold values ​​based on the duty ratios Udu, Vdu, and Wdu of the respective phases.

[0080] FIG. 4 is a diagram for explaining the principle of generating a PWM signal according to the second method by the motor control device according to the first embodiment.

[0081] 4 , the PWM signal generator 32 determines the timing at which the signal level of the PWM signal for each phase switches during the first period A based on the result of comparing the level of the first carrier C1 with first thresholds (Udu1, Vdu1, Wdu1) set based on the duty ratio. The PWM signal generator 32 also determines the timing at which the signal level of the PWM signal for each phase switches during the second period B based on the result of comparing the level of the second carrier C2 with second thresholds (Udu2, Vdu2, Wdu2), which are fixed values.

[0082] The two switching elements constituting the upper and lower arms of the U, V, and W phases respectively perform complementary on / off operations in response to changes in the levels of the PWM signals U, V, and W. However, there is a slight time difference between the timing of the complementary on / off operations; for example, the off operation precedes the on operation.

[0083] 4, however, the complementary on / off times are not taken into consideration due to the slight difference, and the duty ratio is defined as the time from when the upper arm turns on to when the upper arm turns off. Therefore, in FIG. 4, the time period T01 from t0 to t1 when the upper arm of the U-phase PWM signal turns on is the duty start set value Tsu for the U-phase. Similarly, for the V-phase and W-phase, the time periods T02 and T03 from t0 to t2 and t3 when the upper arms turn on based on the V-phase and W-phase PWM signals are the duty start set values ​​Tsv and Tsw.

[0084] The drive circuit 33 outputs drive signals that switch the six switching elements 25U+, 25V+, 25W+, 25U-, 25V-, and 25W- included in the inverter circuit 23 in accordance with a current pattern including the applied PWM signal. As a result, a three-phase AC drive current is supplied to the motor 4, causing the rotor of the motor 4 to rotate.

[0085] The current detection timing adjustment unit 34 determines the acquisition timing for the current detection unit 27 to detect the phase currents of two of the three phases within one period of the PWM signal based on the interrupt signal generated by the PWM signal generation unit 32.

[0086] The current detection unit 27, the current pattern generation unit 35, and the current detection timing adjustment unit 34 are realized by a processor (e.g., a CPU (Central Processing Unit)) performing various calculations in accordance with a program stored in a readable manner in a storage device (not shown). For example, each of these functions is realized by cooperation between hardware and software in a microcomputer including the CPU.

[0087] <Overall Control> Here, a description will be given of the flow of the motor drive control process performed by the motor control device 100 according to this embodiment. Fig. 5 is a flowchart showing the flow of the motor drive control process performed by the motor control device 100 according to this embodiment.

[0088] For example, when a rotation speed command ωref for the motor 4 is input from a higher-level device (not shown), the motor control device 100 starts drive control of the motor 4 .

[0089] First, motor control device 100 starts the process of generating a current conduction pattern for driving motor 4 (step S1). Specifically, duty ratio setting unit 39 sets initial values ​​for duty ratios Udu, Vdu, and Wdu for the U, V, and W phases, respectively, carrier generation unit 37 generates carriers C1 and C2, and PWM signal generation unit 32 generates a PWM signal based on carriers C1 and C2 and the set duty ratios Udu, Vdu, and Wdu using the method described above, and provides the PWM signal to motor 4.

[0090] Next, the motor control device 100 measures the phase currents Iu, Iv, and Iw of the U, V, and W phases (step S2). For example, the current detection unit 27 acquires the detection signal Sd using an AD converter at times t4, t5, and t6 during the second period B of the PWM cycle and stores the acquired value (Iu) of the detection signal Sd in a first acquisition register (not shown). The current detection unit 27 also acquires the detection signal Sd using an AD converter at time tuv during the second period B of the PWM cycle and stores the acquired value (Iu + Iw) of the detection signal Sd in a second acquisition register (not shown). The current detection unit 27 calculates the phase currents Iu, Iv, and Iw using the method described above based on the measured values ​​of the detection signal Sd stored in the first and second acquisition registers, respectively.

[0091] Next, the vector control unit 30 performs current control such as PI control based on the current calculation values ​​of the three-phase currents Iu, Iv, and Iw detected by the current detection unit 27 in step S2 (step S3), and calculates phase voltage commands Vu*, Vv*, and Vw* (control variables) for each phase (step S4).

[0092] Next, in step S5, the duty ratio setting unit 39 calculates the duty ratios and duty start set values ​​(Tsu, Tsv, Tsw) for each of the three phases based on the phase voltage commands Vu*, Vv*, and Vw* for each phase calculated in step S4, and sets the current detection method for the next period (step S5). Note that if the current detection method is switched from the current method to another method in the next PWM period, the duty ratios and duty start set values ​​(Tsu, Tsv, and Tsw) for each of the three phases are recalculated as necessary. Details of the conditions for performing the recalculation will be described later with reference to FIGS. 8 and 11.

[0093] In step S6, the PWM signal generating unit 32 generates a PWM signal based on the duty ratio and duty start setting value set by the method designed in step S5.

[0094] Thereafter, motor control device 100 determines whether a command to stop the motor has been input from a higher-level device (step S7). If a command to stop the motor has been input, motor control device 100 stops generating the PWM signal and stops driving motor 4.

[0095] On the other hand, if a command to stop the motor has not been input, motor control device 100 proceeds to step S2 and repeats the above-described processing (S1 to S6) until a command to stop the motor is input.

[0096] In addition, the general configuration of the motor control device 100 other than the duty ratio calculation unit 31 and the speed monitoring unit 38, and the specific aspects of the carrier wave using the carrier generation unit and the PWM signal generation unit, can be applied by incorporating the configuration and control behavior of the motor control device 100 described in Japanese Patent Application No. 2019-134650 (WO 2021 / 014947) previously filed by the applicant. Therefore, in this specification, the contents of the specification and drawings of the previous application, Japanese Patent Application No. 2019-134650 (WO 2021 / 014947), are incorporated by reference, and the contents of the specification and drawings of the previous application are deemed to be described in this specification.

[0097] <Current Ripple and Noise> Figures 6A and 6B show motor current waveforms when the motor is driven by a PWM signal. Specifically, Figure 6A shows the current waveform when the motor is driven while detecting the current using the first method, and Figure 6B shows the current waveform when the motor is driven while detecting the current using the second method. In Figures 6A and 6B, the horizontal axis represents frequency, and the vertical axis represents current. In Figures 6A and 6B, the solid line represents the U-phase current, and the dashed line represents the V-phase current.

[0098] In Figure 6A, as indicated by the arrows, large ripple currents are present in both the U and V phases. For example, when the conduction pattern changes from the state shown in Figure 2A to the state shown in Figure 2B, the time-series order of the timing at which the multiple PWM signals change suddenly changes. Therefore, in the first method, distortion of the motor current occurs at the timing at which the order in which the PWM signals for each phase change level suddenly changes.

[0099] In contrast to this, in FIG. 6B, a small amount of ripple current is generated in the V phase, but almost no ripple current is generated in the U phase.

[0100] Therefore, by comparing FIG. 6A and FIG. 6B, it can be seen that the second method causes less distortion of the current than the first method.

[0101] Fig. 7 shows the noise level when a motor is driven by a PWM signal while detecting current using the first or second method. In Fig. 7, the horizontal axis represents frequency and the vertical axis represents noise level (dB). In Fig. 7, the thin line represents the noise level when using the first method, and the thick line represents the noise level when using the second method.

[0102] Generally, the greater the amount of distortion in the current, the greater the noise level. As shown in Figure 7, the second method produces less noise across all frequency bands than the first method. Also, as shown in Figure 7, the overall average noise level is also lower with the second method than with the first method, at 49.52 dB for the first method and 37.30 dB for the second method.

[0103] Therefore, it is preferable to drive the motor using a PWM signal while detecting the current using the second method, but because the second method has a lower limit control amount than the first method, if the second method is executed all the time, it may not be possible to output the appropriate control amount, which could cause problems with the motor.

[0104] Therefore, in the motor control device 100 according to this embodiment, the current detection method switching unit 312 switches the current detection method between a first method and a second method, which differ in how the duty ratio is adjusted. More specifically, when the duty ratio adjustment method is switched, the method (algorithm) for shifting the phase of the PWM signal in one-shunt vector PWM control is switched. The switching method is described in detail below.

[0105] <Control Method 1> In this control method, the current detection method switching unit 312 selects either method 1 or method 2 based on the rotation speed and control amount of the motor. The switching of the current detection method will be described below with reference to Figures 8 and 9, along with a determination flow executed for each PWM cycle.

[0106] Fig. 8 is a flowchart of the method switching determination for each PWM period according to embodiment 1. Fig. 9 is a diagram illustrating the motor rotation speed and the control amounts of the first and second methods used in the method switching determination according to embodiment 1.

[0107] 8, in step S101, if the current detection method in the current PWM cycle is the first method, the determinations in steps S102 to S104 are performed. If it is the second method, the process proceeds to a loop in S105.

[0108] In step S102, the immediately preceding switching speed is subjected to Schmitt trigger processing to set the range of application of the second method. More specifically, in the case of a transition from low speed to high speed, when the limit of the PWM setting is detected using the second method, the current detection method is switched to the first method, and the switching speed at that time is stored.

[0109] On the other hand, when transitioning from high speed to low speed, the current detection method is switched from the first method to the second method in the PWM cycle following the cycle in which it is detected that the predetermined speed is lower than the immediately preceding switching speed. That is, as shown in Figure 9, the application range of the second method is set so that the first method is switched to the second method when the speed becomes sufficiently low, which is preset with respect to the switching speed from the second method to the first method.

[0110] In this embodiment, two variable thresholds with hysteresis are set as the speed for switching the current detection method. That is, the threshold for switching from the second method to the first method when the speed increases is an upper threshold that changes depending on the situation when the setting limit is detected, and the threshold for switching from the first method to the second method when the speed decreases is a lower threshold that is a predetermined speed lower than the upper threshold.

[0111] Then, in step S103, it is determined whether the detected speed is within the range applicable to the second method, that is, whether it is equal to or less than the lower threshold set in step S102.

[0112] If the detected speed is within the range applicable to the second method in step S103, the method is switched in the next PWM period in step S104, and the second current detection method is set to be applied, and the process enters a LOOP in step S105.

[0113] In step S103, if the detected speed is greater than the applicable range of the second method, the process skips step S104 and enters a loop in step S105 while remaining in the state of the first method.

[0114] In step S106, it is determined whether or not there was an output setting retry in the immediately preceding LOOP. If there was no retry setting, the process proceeds to step S107. If there was a retry, this will be described later.

[0115] In step S107, based on the current detection results, the duty ratio and duty start setting values ​​(Tsu, Tsv, Tsw), which are the time periods from the start of the PWM interval until each of the three-phase PWM signals becomes H, are calculated for the next PWM cycle.

[0116] Then, in step S108, if the current detection method for the current PWM cycle is the second method, or if the method was switched in step S104 and the second method is set for the next PWM cycle, the process proceeds to step S109. On the other hand, if the first method is selected and step S104 has not been executed, the process proceeds to step S113.

[0117] In step S109, it is determined whether the current detection method is the second method and PWM expression is not possible in the next PWM cycle. Here, "PWM expression is not possible" refers to a state in which, when the PWM setting of the duty ratio / duty start setting value calculation unit (microcomputer) 311 is derived from the control variable calculated by the vector control unit 30, it becomes a value that cannot be set. Figure 9 shows a state in which the control variable at speed Sa has reached a value that cannot be set.

[0118] If the result of step S109 is not expressible, the first method is applied to the next PWM cycle in step S110, and a retry of the PWM output setting is set in step S111. Since the second method is greater than the first method for the control amount, if the result of step S109 is not expressible, the first method is used.

[0119] On the other hand, if it is not impossible to express in step S109, the second method is set to be maintained in the next PWM period in step S112.

[0120] If step S108 determines that the current detection method for the current PWM cycle is the first method and S104 has not been executed, step S113 determines whether the current detection method for the next PWM cycle is the first method and PWM expression is not possible. Here, "PWM expression not possible" refers to a state in which, when a PWM setting is derived from the control variable calculated by the vector control unit 30, a value that cannot be set is obtained. If the control variable is not possible to express using the first method because the second method is lower than the first method, the process proceeds to step S114 and adjustment is performed within the range of the first method.

[0121] In step S114, the limit output of the first method is determined, and the control amount is adjusted to the maximum control amount that can be set in the microcomputer. More specifically, in step S113, it is clear that the control amount calculated by the microcomputer exceeds the settable range, so it is determined to be the limit output. Even if the limit is reached, current detection must be performed using the first method in the next PWM cycle, so the input control amount is adjusted to the maximum control amount that can be set in the microcomputer, as shown in FIG. 9.

[0122] Then, at the end point of the LOOP in step S115, it is checked whether there is a retry of the PWM output setting, and if there is no retry, the flow proceeds to step S117, where the microcomputer register is set, and the flow ends.

[0123] In this control example, a retry of step S111 is set after step S110, so that the LOOP is repeated only when it is determined that the current detection method should be switched from the second method to the first method.

[0124] Then, in the second loop, an output setting retry was performed in the loop immediately preceding S106 (YES), so the flow proceeds to step S116, where the current actual speed is used as the threshold for the switching speed. Since the first method is confirmed during the second loop, the flow skips steps S107 to S110 and moves from step S116 to step S113. After that, the flow reaches step S115, and since there is no retry for the third time, the microcomputer register is set in step S117, and the flow ends.

[0125] In the flow of Fig. 8, when switching from the second method to the first method, executing the loop twice means that the duty ratio / duty start setting value (2) is recalculated in step S5 of the overall flow of Fig. 5. In this control example, when switching from the first method to the second method, the method switch is determined based on the motor speed before the duty ratio / duty start setting calculation, so the loop is executed only once, and the recalculation of (2) is not executed in step S5 of the overall flow of Fig. 5, and only the second method after the method switch is calculated.

[0126] By performing such control, in this embodiment, while the rotation speed of the motor 4 is increasing by controlling the rotation of the motor while detecting the current using the second method, when PWM expression is not possible in step S109, i.e., when the limit of the PWM setting is detected, the current detection method is switched to the first method.

[0127] The speed at which the limit of the PWM setting is detected varies depending on the application, temperature, and other conditions, for example.

[0128] Then, in step S116, while the rotation speed of the motor 4 is increasing, the rotation speed of the motor when the current detection method is switched from the second method to the first method is stored as the switching speed.

[0129] On the other hand, when transitioning from high speed to low speed, if it is detected in step S103 that the motor speed has become lower than the stored previous switching speed by a predetermined speed, i.e., that the motor speed has entered the range in which the second method is applicable, then in the next PWM period, the current detection method is switched from the first method to the second method.

[0130] This determination method allows switching from the first method to the second method at a speed that has a predetermined buffer relative to the switching speed from the second method to the first method, thereby preventing frequent switching between the first and second current detection methods.

[0131] With this type of control, the motor control device of this embodiment can appropriately switch between two current detection methods that use different methods of PWM phase adjustment, thereby suppressing noise while outputting the required control amount without increasing the control amount excessively.

[0132] 10 is an overall view of a motor control system according to embodiment 2. Only the differences from embodiment 1 will be described below.

[0133] In this embodiment, the duty ratio calculation unit 31A includes a duty ratio / duty start setting value calculation unit 311A, a current detection method switching unit 312A, a setting impossibility detection unit 314, a start setting value summation unit 315, and a total maximum value discrete determination unit 316. Also, no speed monitoring unit is provided.

[0134] The duty ratio / duty start setting value calculation unit 311A ​​calculates, for each PWM period, the duty ratio and duty start setting value, which is the time period from the start of the PWM interval until each of the three-phase PWM signals becomes H, for the next PWM period, based on the detection result of the current detection unit 27.

[0135] In this embodiment, the current detection method switching unit 312A switches between the first method and the second method based on a duty start setting value, which is the time period from the start of the PWM period until each of the three-phase PWM signals becomes H.

[0136] The setting failure detection unit 314 detects whether any one of the three duty start setting values ​​calculated for the next PWM period is a value that cannot be set.

[0137] When all three duty start set values ​​are settable values, the start set value summing unit 315 calculates the sum of the three duty start set values ​​(Tsu, Tsv, Tsw) for each PWM period.

[0138] The sum of the three duty start setting values ​​changes, repeatedly taking maximum and minimum values ​​for each PWM period. The sum maximum value discrete determination unit 316 determines whether the discrete maximum value of the sum of the three duty start setting values ​​exceeds the switching threshold value a predetermined number of times in succession.

[0139] Next, the determination of switching of the PWM current detection method according to this embodiment will be described with reference to FIGS. 11 and 12. FIG.

[0140] Fig. 11 is a flowchart of PWM method determination according to embodiment 2. Fig. 12 shows the sum of three duty start set values ​​according to embodiment 2 and a threshold value for switching between the first method and the second method.

[0141] 11 is executed for each PWM period. More specifically, the flow is executed for each PWM period to determine the current detection method to be set for the next PWM period.

[0142] In the method determination of FIG. 11, a loop is immediately entered in step S201.

[0143] Then, in step S202, the duty ratio / duty start setting value calculation unit 311A ​​calculates, for each PWM period, based on the detection result of the current detection unit 27, the duty ratios of the three phases and the duty start setting values, which are the time periods from the start of the PWM interval until each of the PWM signals of the three phases becomes H, for the next PWM period.

[0144] Steps S203 to S210 are an example of software-implemented microcomputer control that is used to detect whether the duty start setting value for the next PWM cycle will be an unsettable value. Other methods may be used as long as it is possible to detect that even one of the three-phase duty start setting values ​​calculated for the next PWM cycle will be an unsettable value.

[0145] In step S203, if the duty start setting value Tsu<0, that is, if the calculation result shows that any of the values ​​t1, t2, and t3 corresponding to the U phase is before the start of the PWM period (t0), proceed to step S204 and set the sign state variable a=1.

[0146] In step S203, if Tsu≧0, that is, if the calculation result shows that any one of the values ​​of t1, t2, and t3 corresponding to the U phase is the same as or after the start of the PWM period, the process proceeds to step S205.

[0147] Similarly, if the duty start set value Tsv<0 in step S205, the process proceeds to step S206, where the code state variable b is set to 1. On the other hand, if Tsv≧0 in step S205, the process proceeds to step S207.

[0148] If the duty start setting value Tsw<0 in step S207, the process proceeds to step S208, where the C language code state variable c is set to 1. On the other hand, if Tsw≧0 in step S205, the process proceeds to step S209. If the variable a is a local variable, it is assumed that it is initialized (=0) when declared outside the loop, and therefore the process of setting it to 0 is not necessary.

[0149] In step S209, the variables a, b, and c are converted to bitOR, where bitOR is the original variable.

[0150] Then, in step S210, it is determined whether bitOR is 0. More specifically, the variable bitOR = a|b|c| is calculated, and a case where bitOR is other than 0 indicates a state where at least one 1 appears in the three numerical values ​​a, b, and c. More specifically, when a=0, b=1, 0|1=1...bitOr=1, c=0, bitOr=1, 0|1=1...bitOr=1, 0|0=0, 1|1=1, and the determination in step S210 intends a state where at least one of the duty start setting values ​​(Tsu, Tsv, Tsw) for the next PWM cycle is an unsettable value.

[0151] In this case, that is, if the answer is NO in step S210, the process proceeds to step S212, where the current detection method for the next PWM period is set to method 1. Then, in step S213, a PWM output setting retry is set.

[0152] On the other hand, if bitOR is 0 in step S210, that is, if the three numerical values ​​of the sign state variables a, b, and c are all 0 and the time periods of the three duty start setting values ​​to be set in the next PWM cycle can all be set, proceed to step S211.

[0153] Then, in S211, Σt=T01+T02+T03 is calculated. Specifically, the sum Σt of the duty start set values ​​Tsu+Tsv+Tsw is calculated (added up).

[0154] Then, in step S214, it is determined whether the sum Σt is equal to or greater than the switching threshold value. If the sum Σt is less than the switching threshold value, the process proceeds to step S212, where the current detection method for the next PWM period is set to the first method.

[0155] On the other hand, if the sum Σt is equal to or greater than the switching threshold (YES in S214), the process proceeds to step S215 for discrete determination of maximum values.

[0156] The sum of the three duty start set values ​​and the maximum value discrete determination will now be described in detail with reference to Fig. 12. In Fig. 12, the horizontal axis represents time (seconds) and the vertical axis represents Σt = T01 + T02 + T03.

[0157] 12 is a value before the PWM setting of duty ratio / duty start setting value calculation unit 311A ​​becomes impossible to set when the PWM setting is derived from the control amount calculated by vector control unit 30. For example, when the value at which the control amount becomes impossible to set is 1, the value is 0.6 to 0.95, and more preferably, 0.7 to 0.9.

[0158] 12, the sum Σt of the three duty start setting values ​​alternates between maximum and minimum peak values. The maximum value of the sum Σt is larger in the second method.

[0159] In step S216, it is determined whether the number of times it has been determined that the maximum value of the sum has exceeded the switching threshold is equal to or greater than a given number (determination threshold).

[0160] If the number of times that the maximum value of the sum Σt is determined to have continuously exceeded the switching threshold is equal to or greater than a predetermined number (YES in S216), proceed to step S217 and set the second method to be applied in the next PWM period.

[0161] On the other hand, if the maximum value of the sum Σt continuously exceeds the switching threshold less than the predetermined number of times (No in S216), proceed to step S212 and set the first method to be applied in the next PWM period.

[0162] Then, in step S218, it is determined whether or not the PWM output setting is to be retried. If it is not necessary, the flow is ended, and if it is necessary to retry, a retry is performed.

[0163] In more detail, if the current PWM cycle is the second method and it is determined in step S216 that the next cycle will also be set to the second method, or if the current PWM cycle is the first method and it is determined in step S216 that the next cycle will be set to the second method, the loop from steps S201 to S218 will be repeated only once.

[0164] On the other hand, if the current PWM cycle is the first method and it is determined in any of S210, S214, and S216 that the next cycle will also be the first method, or if the current PWM cycle is the second method and it is determined in step S210 that the next cycle will be set to the first method, the loop from S201 to S218 is executed twice in one PWM cycle. Executing the loop twice means that the recalculation of (2) is executed in step S5 of the overall flow in FIG. 5.

[0165] By switching the current detection method in this way, when the current detection method is switched from the second method to the first method, if it becomes impossible to set the duty start setting value in S210, the transition occurs immediately, so there is no shortage of control amount. Furthermore, thereafter, calculation of the sum or discrete determination of the maximum value is not performed, so the amount of processing can be minimized.

[0166] On the other hand, when switching the current detection method from the first method to the second method, (1) in S210, for each PWM period, the duty ratio and the duty start setting value, which is the time period from the start of the PWM interval until each of the three-phase PWM signals becomes H, are calculated for the next PWM period, and values ​​that can be set for all three duty start setting values ​​(time periods) are detected; (2) in S211, the sum of each of the three duty start setting values ​​is calculated; and (3) in S214, it is determined whether the maximum value of the sum exceeds the switching threshold, and if the maximum value of the sum exceeds the switching threshold, and in S216 the number of times that discrete maximum values ​​have exceeded the switching threshold is equal to or greater than an arbitrary number of times, the method finally transitions to the second method when these three conditions are met.

[0167] In other words, even if all three duty start setting values ​​are settable in S210, the sum Zt of the three calculated duty start setting values ​​is calculated, and if the maximum value of the sum Zt does not exceed the switching threshold in S215, the current detection method for the next PWM period is maintained as the first method.

[0168] Furthermore, even if all three duty start setting values ​​are settable in S210 and the maximum value of the calculated sum Zt exceeds the switching threshold in S215, if the number of times that the discrete maximum values ​​of the sum Zt continuously exceed the switching threshold is less than an arbitrary number of times, the current detection method for the next PWM period will be maintained as the first method.

[0169] In this control, by using such a determination method, it is possible to prevent frequent switching between the first method and the second method for detecting the current.

[0170] With this type of control, the motor control device according to this embodiment can appropriately switch between two current detection methods that use different methods for adjusting the PWM phase, thereby suppressing noise while outputting the required control amount without making the control amount excessive.

[0171] <<Modification of the Second Method>> In the above example, as an example of the second method, the current detection method for adjusting the PWM phase shown in Fig. 3 has been described. However, other waveform control may be used as long as the behavior is such that "one cycle of the PWM signal of each phase includes a first period and a remaining second period, the signal level of the PWM signal of each phase changes at a timing according to a set duty ratio in the first period, and the signal level changes at fixed timings different from each other in the second period, and the current detection unit detects the current of the current detector in the second period."

[0172] FIG. 13 is a diagram for explaining detection timings of the PWM signal and the phase current in the motor control device according to the first and second embodiments, in a modification of the second technique.

[0173] In this technique, a carrier generator generates a triangular-wave carrier (C) whose level increases in a cycle corresponding to a first period A and decreases in a cycle corresponding to a second period B. The PWM signal generator determines the timing at which the signal level of the PWM signal for each phase changes during the first period based on the result of comparing the level of the carrier C with first thresholds (Udu1, Vdu1, Wdu1) set based on the duty ratio. The PWM signal generator also determines the timing at which the signal level of the PWM signal for each phase changes during the second period based on the result of comparing the level of the carrier C with second thresholds (Udu2, Vdu2, Wdu2), which are fixed values. Furthermore, during the second period B, the order in which the PWM signals for each phase change is fixed regardless of the set value of the duty ratio.

[0174] The motor control according to the modified example of the second technique shown in Fig. 13 can suppress distortion of the motor current compared to the pulse phase adjustment control according to the first technique shown in Fig. 2A and Fig. 2B, similar to the motor control shown in Fig. 3. This makes it possible to prevent noise caused by distortion of the current in the motor 4.

[0175] Therefore, even when the control method of FIG. 8 or the control method 1 of FIG. 11 is realized using the second method of this modified example, by appropriately switching between the two types of PWM control methods, it is possible to suppress noise while adjusting the control amount so that it is not excessive.

[0176] In addition, as a specific aspect of the carrier generating unit and the PWM signal generating unit for realizing the control related to the modified example of the second method, the configuration and control behavior of the motor control device 100A described in Japanese Patent Application No. 2019-134650 (International Publication No. 2021 / 014947) previously filed by the present applicant can be incorporated and applied. Therefore, in this specification, the contents of the specification and drawings of the previous application, Japanese Patent Application No. 2019-134650 (International Publication No. 2021 / 014947), are incorporated by reference, and the contents of the specification and drawings of the previous application are deemed to be described in this specification.

[0177] <<Extending the Embodiments>> The invention made by the present inventors has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

[0178] For example, in the above embodiment, the current conduction pattern of each phase (duty ratio of the PWM signal of each phase) is updated and the phase current is measured every two PWM cycles, but this is not limiting. For example, the current conduction pattern of each phase (duty ratio of the PWM signal of each phase) may be updated and the phase current may be measured every one PWM cycle (n=1).

[0179] Furthermore, the above-described flowcharts are merely examples for explaining the operation, and are not intended to be limiting. That is, the steps shown in each diagram of the flowchart are specific examples, and the present invention is not limited to these flows. For example, the order of some processes may be changed, other processes may be inserted between processes, or some processes may be performed in parallel.

[0180] This international application claims priority based on Japanese Patent Application No. 2024-030123, filed on February 29, 2024, the entire contents of which are incorporated herein by reference.

[0181] 1...motor system, 4...motor, 20, 20A...control unit, 21...DC power supply, 22a...positive side bus, 22b...negative side bus, 23...inverter circuit, 24...current detector (shunt resistor), 25U, 25U-, 25V, 25V-, 25W, 25W-...switching element, 27...current detection unit, 30...vector control unit, 31, 31A...duty ratio calculation unit, 32...PWM signal generation unit, 33...drive circuit, 34...current detection timing adjustment unit, 35, ...energization pattern generation unit, 36...clock generation unit , 37...carrier generation unit, 38...speed monitoring unit, 39...duty ratio setting unit, 100, 100A...motor control device, 311, 311A...duty ratio / duty start setting value calculation unit (duty start setting value calculation unit), 312, 312A...current detection method switching unit, 313...PWM limit detection unit, 314...setting impossible detection unit, 315...start setting value summation unit, 316...sum maximum value discrete judgment unit, A...first period, B...second period, C, C1, C2...carrier, Udu, Vdu, Wdu...duty ratio.

Claims

1. A motor having coils for multiple phases, comprising: a control unit that generates PWM signals corresponding to each phase of the motor; an inverter circuit that drives the coils of each phase based on the PWM signals; and a current detector connected in series to a DC line of the inverter circuit, wherein the control unit has: a current detection unit that detects the current of the current detector; a duty ratio setting unit that sets the duty ratio of the PWM signal of each phase based on the detection result of the current detection unit; a PWM signal generation unit that generates the PWM signal of each phase based on the duty ratio set by the duty ratio setting unit; and a speed monitoring unit that monitors the rotation speed of the motor for each PWM period, wherein the duty ratio setting unit has a current detection method switching unit that switches the current detection method between a first method and a second method that differ in how the duty ratio is adjusted, wherein in the first method, the signal level of the PWM signal of each phase changes at arbitrary timings that are different from each other throughout one period, and the current detection unit detects the current of the current detector throughout the entire period, In the second method, one cycle of the PWM signal of each phase includes a first period and a second period, the signal level of the PWM signal of each phase changes in the first period at a timing according to the set duty ratio, and the signal level changes in the second period at fixed timings different from each other, and the order in which the PWM signals of each phase are switched is fixed regardless of the set value of the duty ratio, the current detection unit detects the current of the current detector in the second period, and the current detection method switching unit switches between the first method and the second method based on the rotational speed of the motor.

2. The motor control device according to claim 1, wherein the current detection method switching unit stores the motor rotation speed when the current detection method is switched from the second method to the first method while the rotation speed of the motor is increasing as a switching speed, and thereafter, while the rotation speed is decreasing, when the rotation speed becomes lower than the stored switching speed by a predetermined speed, switches from the first method to the second method.

3. The motor control device according to claim 2, wherein the current detection method switching unit switches the current detection method from the first method to the second method in the PWM period following the period in which the speed monitoring unit detects that the current has become lower than the stored immediately previous switching speed by a predetermined speed.

4. A motor control device as described in claim 2, wherein the duty ratio setting unit has a limit detection unit that detects the setting limit of PWM using the second method, and when the limit detection unit detects the limit of the PWM setting while the motor speed is increasing by controlling the rotation of the motor while detecting the current using the second method, the current detection method switching unit switches the current detection method for the next PWM period to the first method, and the speed at which the limit of the PWM setting is detected is variable depending on the situation.

5. A motor having three coils, comprising: a control unit that generates PWM signals corresponding to each phase of the motor; an inverter circuit that drives the coils of each phase based on the PWM signals; and a current detector connected in series to a DC line of the inverter circuit, wherein the control unit comprises: a current detection unit that detects the current of the current detector; a duty ratio setting unit that sets the duty ratio of the PWM signal of each phase based on the detection result of the current detection unit; and a PWM signal generation unit that generates the PWM signal of each phase based on the duty ratio set by the duty ratio setting unit, wherein the duty ratio setting unit has a current detection method switching unit that switches the current detection method between a first method and a second method that differ in how the duty ratio is adjusted, wherein in the first method, the signal level of the PWM signal of each phase changes at mutually different arbitrary timings throughout the entire period of one cycle, and the current detection unit detects the current of the current detector throughout the entire period, In the second method, one cycle of the PWM signal for each phase includes a first period and a second period, the signal level of the PWM signal for each phase changes in the first period at a timing according to the set duty ratio, and changes in the second period at fixed timings that are different from each other, the current detection unit detects the current of the current detector in the second period, and the current detection method switching unit switches between the first method and the second method based on a duty start setting value that is a time period from the start of a PWM interval to when each of the three-phase PWM signals changes from a first level to a second level.

6. The motor control device according to claim 5, wherein the duty ratio setting unit comprises: a duty start setting value calculation unit that calculates, for each PWM period, a duty start setting value that is the time period from the start of a PWM interval until each of the three-phase PWM signals changes from the first level to the second level for the next PWM period based on the detection result of the current detection unit and the calculated duty ratio; an unsettable detection unit that detects whether any one of the three duty start setting values ​​calculated for the next PWM period is an unsettable value; and a sum maximum value discrete determination unit that, if all three duty start setting values ​​are settable, calculates the sum of the three duty start setting values ​​for each PWM period and determines whether the discrete maximum value of the sum of the three duty start setting values, which changes while repeatedly taking maximum and minimum values, exceeds a switching threshold a predetermined number of times in a row.

7. The motor control device according to claim 6, wherein the current detection method switching unit switches the current detection method for the next PWM period from the second method to the first method when the setting failure detection unit detects that at least one of the three duty start setting values ​​calculated for the next PWM period is an unsettable value while the motor speed is increasing by controlling the rotation of the motor while detecting the current using the second method.

8. The motor control device according to claim 6, wherein the current detection method switching unit, when controlling the rotation of the motor while detecting current using the first method, if the non-setting detection unit detects that all of the three calculated duty start setting values ​​are settable values, the sum maximum value discrete determination unit calculates the sum of the three duty start setting values ​​for each PWM period if all of the three duty start setting values ​​are settable values, and if the discrete maximum value of the sum of the three duty start setting values, which changes while repeatedly changing between maximum and minimum values, does not exceed a switching threshold, maintains the first method as the current detection method for the next PWM period.

9. The motor control device according to claim 6, wherein the current detection method switching unit, while detecting the current using the first method and controlling the rotation of the motor, if the non-setting detection unit detects that all three duty start setting values ​​calculated for the next PWM period are settable values, the sum maximum value discrete determination unit calculates the sum of the three duty start setting values ​​for each PWM period if all three duty start setting values ​​are settable values, and if the discrete maximum value of the sum of the three duty start setting values, which changes while repeatedly changing between maximum and minimum values, exceeds a switching threshold value less than a predetermined number of times, maintains the first method as the current detection method for the next PWM period.

10. The motor control device according to claim 6, wherein the current detection method switching unit, while detecting the current using the first method and controlling the rotation of the motor, if the non-setting detection unit detects that all three duty start setting values ​​calculated for the next PWM period are settable values, the sum maximum value discrete determination unit calculates the sum of the three duty start setting values ​​for each PWM period if all three duty start setting values ​​are settable values, and switches the current detection method for the next PWM period from the first method to the second method if the discrete maximum value of the sum of the three duty start setting values, which changes while repeatedly changing between maximum and minimum values, exceeds a switching threshold value a predetermined number of times in a row.

11. A motor control device according to claim 9, wherein the duty ratio setting unit further comprises a vector control unit that calculates a phase voltage command for each phase and a control amount that is the sum of the phase voltage commands based on the calculated current values ​​of the three-phase currents detected by the current detection unit, and the switching threshold for the maximum value of the sum of the three duty start setting values ​​is a value before it becomes impossible to set a PWM setting when derived from the calculated control amount.

12. A motor system comprising: a motor control device according to any one of claims 1 to 11; and the motor.

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