Motor control device, motor system, and motor control method

Abstract

This motor control method includes: generating PWM signals of respective phases with duty ratios each having the same value, the PWM signals including, in one cycle, a first period in which a part of an arm in an inverter is turned on in a first energization pattern during idling of a rotor and a second period in which a part of the arm in the inverter is turned on in a second energization pattern during the idling; detecting a first current value of a first phase flowing in the first period and a second current value of the first phase flowing in the second period with a current detector provided on the DC side of the inverter; and deriving an offset current value of the first phase by calculation using one of the first current values detected in the first period or a plurality of the first current values detected in each of the first periods, and a plurality of the second current values detected in each of the second periods.

Description

Motor control device, motor system, and motor control method

[0001] The present disclosure relates to a motor control device, a motor system, and a motor control method.

[0002] Conventionally, there has been known a motor control device that includes a current detector connected to the DC side of an inverter, a generation unit that generates PWM signals for each phase with the same duty ratio, each PWM signal having a first period during which some arms of the inverter are turned on with a first current pattern while the motor rotor is idling, and a second period during which some arms of the inverter are turned on with a second current pattern while the motor rotor is idling, and a current detection unit that derives an offset current value for the first phase by subtracting half the sum of a first current value of the first phase that flows through the current detector during the first period and a second current value of the first phase that flows through the current detector during the second period from the first current value or the second current value.

[0003] The current detector derives a detected current value of the first phase current by subtracting, for each cycle of the PWM signal, the pre-derived first phase offset current value from the current value of the first phase current detected for each cycle of the PWM signal. As a result, the current detector corrects the detected value of the first phase current flowing through the current detector when the inverter is rotating the rotor, according to the pre-derived first phase offset current value. This reduces an error in the detected value of the first phase current (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2021-164281

[0005] However, when the offset current value is derived using the detected value of the current flowing through the current detector while the rotor is idling, the error in the derived offset current value may become larger as the rotor idling speed increases.

[0006] An object of the present disclosure is to reduce errors in an offset current value derived using a detection value of a current flowing through a current detector while a rotor is idling.

[0007] A motor control device according to one aspect of the present disclosure includes: an inverter that energizes a motor having a rotor; a current detector provided on the DC side of the inverter; a generation unit that generates PWM signals for each phase, each PWM signal having the same duty ratio, the PWM signals including, in one cycle, a first period during which some arms of the inverter are turned on with a first current pattern while the rotor is idling and a second period during which some arms of the inverter are turned on with a second current pattern while the rotor is idling; and a current detection unit that detects a first current value of the first phase flowing through the current detector during the first period and a second current value of the first phase flowing through the current detector during the second period, wherein the current detection unit derives an offset current value of the first phase by performing a calculation using one of the first current values ​​detected during the first period or a plurality of the first current values ​​detected for each of the first periods and a plurality of the second current values ​​detected for each of the second periods.

[0008] A motor control method according to another aspect of the present disclosure is a motor control method for energizing a motor having a rotor using an inverter, the method comprising: generating PWM signals for each phase, each PWM signal having a first period during which some arms of the inverter are turned on with a first current pattern while the rotor is idling, and a second period during which some arms of the inverter are turned on with a second current pattern while the rotor is idling, with the same duty ratio; detecting a first current value of the first phase flowing during the first period with a current detector provided on the DC side of the inverter, and a second current value of the first phase flowing during the second period with the current detector; and deriving an offset current value of the first phase by calculation using one of the first current values ​​detected during the first period or multiple first current values ​​detected for each of the first periods, and multiple second current values ​​detected for each of the second periods.

[0009] According to the present disclosure, it is possible to reduce errors in the offset current value derived using the detection value of the current flowing in the current detector while the rotor is idling.

[0010] 6 is a diagram showing an example of the configuration of a motor system according to a first embodiment. FIG. 7 is an enlarged view showing an example of the current waveform of a U-phase current flowing in a current detector by turning on some of all the arms of the inverter in accordance with PWM signals for each phase, all of which have a duty ratio of 50%. FIG. 8 is a view showing an example of the waveform of a PWM signal when detecting the current value of a current flowing in a current detector before the inverter rotates the rotor. FIG. 9 is a view showing a switching state in which a negative U-phase current "-Iu" flows in a current detector. FIG. 10 is a view showing a switching state in which a positive U-phase current "+Iu" flows in a current detector. FIG. 11 is a waveform diagram showing an example of a process for calculating a U-phase offset current value for 10 periods of a PWM signal during rotor idling. FIG. 12 is an enlarged view of the portion surrounded by a dotted line frame shown in FIG. 6. FIG. 13 is a schematic view of an example of the waveform of a current flowing in a current detector while the rotor is stopped. FIG. 14 is a schematic view of an example of the waveform of a current flowing in a current detector during rotor idling. FIG. 15 is a view for explaining an example of a first calculation method for deriving an offset current value for one phase by calculation using a detected value of a current flowing in a current detector during rotor idling. 12 is a diagram for explaining an example of a second calculation method for deriving an offset current value for one phase by calculation using a detection value of a current flowing in a current detector while the rotor is spinning freely. FIG. 13 is a diagram for explaining in more detail the second calculation method shown in FIG. 11. FIG. 14 is a diagram for explaining an example of a third calculation method for deriving an offset current value for one phase by calculation using a detection value of a current flowing in a current detector while the rotor is spinning freely. FIG. 15 is a diagram for explaining in more detail the third calculation method shown in FIG. 13. FIG. 16 is a diagram for explaining a first example of a method for outputting a PWM signal while the rotor is spinning freely. FIG. 17 is a diagram for explaining a second example of a method for outputting a PWM signal while the rotor is spinning freely.

[0011] Hereinafter, a motor control device, a motor system, and a motor control method according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0012] Fig. 1 is a diagram showing an example of the configuration of a motor system according to the first embodiment. The motor system 201 shown in Fig. 1 controls the rotational operation of a motor 4. Devices in which the motor system 201 is installed include, but are not limited to, copy machines, personal computers, refrigerators, and pumps. The motor system 201 includes at least a motor 4 and a motor control device 101.

[0013] The motor 4 is a permanent magnet synchronous motor having multiple coils. The motor 4 has, for example, three-phase coils including a U-phase coil, a V-phase coil, and a W-phase coil. A specific example of the motor 4 is a three-phase brushless DC motor. The motor 4 has a rotor in which at least one permanent magnet is disposed, and a stator disposed around the rotor axis. The motor 4 is a sensorless motor that does not use a position sensor to detect the angular position (magnetic pole position) of the rotor magnet. The motor 4 is, for example, a fan motor that rotates a blower fan.

[0014] The motor control device 101 drives a motor via an inverter that converts direct current into three-phase alternating current by controlling a plurality of switching elements connected in a three-phase bridge to be on or off in accordance with a current pattern including a three-phase PWM signal. The motor control device 101 includes an inverter 23, a current detector 24, a current detection unit 27, a drive circuit 33, and a generation unit 35.

[0015] The inverter 23 is a circuit that converts the DC 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 to rotate the rotor of the motor 4. The inverter 23 drives the motor 4 based on a plurality of current patterns (more specifically, three-phase PWM signals) generated by a generation unit 35. PWM stands for Pulse Width Modulation.

[0016] The inverter 23 has a plurality of arms Up, Vp, Wp, Un, Vn, and Wn connected in a three-phase bridge. The upper arms Up, Vp, and Wp are high-side switching elements connected to the positive side of the DC power supply 21 via a positive-side bus 22a. The lower arms Un, Vn, and Wn are low-side switching elements connected to the negative side (specifically, the ground side) of the DC power supply 21. The plurality of arms Up, Vp, Wp, Un, Vn, and Wn are each turned on or off in accordance with a corresponding one of a plurality of drive signals supplied from a drive circuit 33 based on a PWM signal included in the above-described current conduction pattern. Hereinafter, the plurality of arms Up, Vp, Wp, Un, Vn, and Wn may be simply referred to as arms unless otherwise specified.

[0017] The connection point between the U-phase upper arm Up and the U-phase lower arm Un is connected to one end of the U-phase coil of the motor 4. The connection point between the V-phase upper arm Vp and the V-phase lower arm Vn is connected to one end of the V-phase coil of the motor 4. The connection point between the W-phase upper arm Wp and the W-phase lower arm Wn is connected to one end of the W-phase coil of the motor 4. The other ends of the U-phase coil, the V-phase coil, and the W-phase coil are connected to each other.

[0018] Specific examples of the arm include an N-channel metal oxide semiconductor field effect transistor (MOSFET) and an insulated gate bipolar transistor (IGBT), but the arm is not limited to these.

[0019] The current detector 24 is provided on the DC side of the inverter 23 and outputs a detection signal Sd corresponding to the current value of the current flowing on the DC side of the inverter 23. The current detector 24 shown in FIG. 1 is connected to the negative bus 22b on the DC side of the inverter 23 and 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 shunt resistor inserted in the negative bus 22b. The 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.

[0020] The current detection unit 27 detects the phase currents Iu, Iv, and Iw by acquiring the detection signal Sd based on the plurality of current conduction patterns (more specifically, three-phase PWM signals) generated by the generation unit 35. More specifically, the current detection unit 27 detects the phase currents Iu, Iv, and Iw by acquiring the detection signal Sd at acquisition timings synchronized with the plurality of current conduction patterns (more specifically, three-phase PWM signals).

[0021] For example, the current detection unit 27 inputs an analog voltage detection signal Sd generated by the current detector 24 into an AD (Analog to Digital) converter at acquisition timings set in accordance with a plurality of current conduction patterns. The AD converter is provided in the current detection unit 27. The current detection unit 27 then AD converts the input analog detection signal Sd into a digital detection signal Sd and digitally processes the AD-converted digital detection signal Sd to detect phase currents Iu, Iv, and Iw of the U, V, and W phases of the motor 4. The detection values ​​of the phase currents Iu, Iv, and Iw of each phase detected by the current detection unit 27 are supplied to the generation unit 35.

[0022] The generation unit 35 generates a pattern for energizing the inverter 23 (energization pattern of the inverter 23). The energization pattern of the inverter 23 may also be referred to as a pattern for energizing the motor 4 (energization pattern of the motor 4). The energization pattern of the inverter 23 includes three-phase PWM signals for energizing the inverter 23. The generation unit 35 generates three-phase PWM signals for energizing the inverter 23 so as to rotate the motor 4, based on the detection values ​​of the phase currents Iu, Iv, and Iw of the motor 4 detected by the current detection unit 27.

[0023] The functions of the current detection unit 27 and the generation unit 35 are realized, for example, by a processor of a CPU (Central Processing Unit) operating according to a program stored in a readable manner in a storage device (not shown). These functions are realized, for example, by cooperation between hardware and software in a microcomputer including the processor.

[0024] The drive circuit 33 outputs drive signals that switch the six arms Up, Vp, Wp, Un, Vn, and Wn included in the inverter 23 in accordance with the current pattern including the PWM signal provided from the generation unit 35. This causes a three-phase AC drive current to be supplied to the motor 4, causing the rotor of the motor 4 to rotate.

[0025] Even when the inverter 23 is not rotating the rotor with three-phase AC current, the rotor may be spinning freely due to external disturbances such as wind, etc. In particular, rotors that rotate rotating bodies such as fans with relatively small frictional resistance are prone to spinning freely.

[0026] The current detection unit 27 detects the phase currents Iu, Iv, and Iw using a method of detecting a plurality of phase currents from one current detector 24 (so-called one-shunt current detection method).

[0027] In the one-shunt current detection method, the current of each phase flowing through the current detector 24 by turning on some of the arms of the inverter 23 in accordance with the PWM signals of each phase, all of which have the same duty ratio (for example, 50%), may be defined as the offset current of each phase. The value of the offset current (offset current value) corresponds to the offset error (detection error) included in the current detection value.

[0028] 2 is an enlarged view showing an example of the current waveform of the U-phase current flowing to the current detector 24 when some of the arms of the inverter 23 are turned on in accordance with PWM signals for each phase, each of which has a duty ratio of 50%. In FIG. 2, the upper waveform shows the state when the rotor is stopped, and the lower waveform shows the state when the rotor is idling. FIG. 2 illustrates the waveforms of approximately 16 cycles of the PWM signal. Both waveforms are offset vertically with almost no change, and this offset is due to the induced voltage generated in the coils of each phase of the motor 4 due to the rotor idling.

[0029] FIG. 3 shows an example of a waveform of a PWM signal when the current detector 24 detects the current value of a current flowing through it before the inverter 23 rotates the rotor of the motor 4 (when the rotor is stopped or spinning freely). The inverter 23 energizes the motor 4 having a rotor by turning on a different portion of all arms for each current conduction pattern. The generator 35 generates PWM signals for each phase with the same duty ratio. One cycle of the PWM signal for each phase includes a first period in which some of the arms are turned on with a first current conduction pattern while the rotor is spinning freely (or stopped), a second period in which some of the arms are turned on with a second current conduction pattern while the rotor is spinning freely (or stopped), and a third period in which all of the upper arms or all of the lower arms are turned on with a third current conduction pattern while the rotor is spinning freely (or stopped). Driving the motor 4 in accordance with the PWM signals for each phase results in the switching states of the arms shown in FIG. 3 . FIG. 3 illustrates an example in which the duty ratio of the PWM signals for each phase is 50%.

[0030] The first current detection interval P1 (a period including the timing of the first detection) in which some arms are in the ON state in the first current conduction pattern is an example of a first period. The second current detection interval P2 (a period including the timing of the second detection) in which some arms are in the ON state in the second current conduction pattern is an example of a second period. The non-current conduction interval P3 in which all upper arms are in the ON state and all lower arms are in the OFF state is an example of a third period. In this example, the third period exists between the first period and the second period.

[0031] During a first current detection interval P1 (an example of a first period), the upper arm Up and the lower arms Vn and Wn are in the ON state according to the first current conduction pattern, and therefore a negative U-phase current "-Iu" flowing in from the U-phase terminal of the motor 4 flows to the current detector 24 (see FIG. 4). During a second current detection interval P2 (an example of a second period), the lower arm Un and the upper arms Vp and Wp are in the ON state according to the second current conduction pattern, and therefore a positive U-phase current "+Iu" flowing out from the U-phase terminal of the motor 4 flows to the current detector 24 (see FIG. 5). The current detection unit 27 detects a first current value of the first phase flowing in the current detector 24 during the first period and a second current value of the first phase flowing in the current detector 24 during the second period. In this example, the first current value is the current value of the negative U-phase current "-Iu (= Iv + Iw)," and the second current value is the current value of the positive U-phase current "+Iu."

[0032] The current detection unit 27 utilizes the fact that the phase currents of the first phase detected within one cycle of the PWM signal are paired, and detects the difference between zero and half the sum of the first current value and the second current value of the first phase as the influence of the induced voltage. The current detection unit 27 then subtracts the influence of the detected induced voltage from the first current value or second current value detected at the first or second detection timing to derive the offset current value of the first phase. The current detection unit 27 can also derive the offset current value of the second or third phase other than the first phase using the same calculation method, whether the rotor is stopped or spinning.

[0033] Fig. 6 is a waveform diagram showing an example of a process for calculating a U-phase offset current value for 10 periods (e.g., 400 μs) of a PWM signal when the rotor is spinning freely. Fig. 7 is an enlarged view of the portion surrounded by the dotted line in Fig. 6, and is a waveform diagram showing an example of a process for calculating a U-phase offset current value for one period (e.g., 40 μs) of a PWM signal when the rotor is spinning freely. The U-phase is an example of the first phase.

[0034] The current detection unit 27 can derive the influence component e due to the induced voltage by calculating half the sum of the first U-phase current value (-ΔIu+e) flowing through the current detector 24 at the first detection in the first period and the second U-phase current value (ΔIu+e) flowing through the current detector 24 at the second detection in the second period. The current detection unit 27 can derive the U-phase offset current value ΔIu by subtracting the influence component e from the U-phase second current value (ΔIu+e) at the second detection. Similarly, the current detection unit 27 can derive the V-phase offset current value ΔIv and the W-phase offset current value ΔIw.

[0035] In other words, the current detection unit 27 can derive the U-phase offset current value ΔIu by calculating half the difference between the first U-phase current value (−ΔIu+e) flowing through the current detector 24 in the first period and the second U-phase current value (ΔIu+e) flowing through the current detector 24 in the second period. Similarly, the current detection unit 27 can derive the V-phase offset current value ΔIv or the W-phase offset current value ΔIw.

[0036] Since the sum of the phase currents of the three phases is zero (iu + iv + iw = 0), the current detection unit 27 may derive the offset current value of the first phase and the offset current value of the second phase, and then derive the remaining offset current value of the third phase from these derived results.

[0037] The current detection unit 27 stores the derived three-phase offset current values ​​in memory. The motor control device 101 starts the motor 4 by the inverter 23 using the three-phase offset current values ​​stored in advance in memory, and causes the inverter 23 to rotate the rotor of the motor 4.

[0038] The current detection unit 27 detects the current values ​​of each of the three phase currents by performing current detection at least twice while the inverter 23 is rotating the rotor. The current detection unit 27 calculates the current detection values ​​of each of the three phase currents Iu, Iv, and Iw by subtracting the three-phase offset current values ​​stored in advance in memory from the current values ​​of each of the three phase currents detected for each cycle of the PWM signal. As a result, the current detection unit 27 corrects the phase currents of each phase flowing through the current detector 24 when the inverter 23 is rotating the rotor according to the offset current value of each phase, thereby removing detection errors from the current detection values ​​of each of the three phase currents Iu, Iv, and Iw. The PWM signal generating unit 32 uses the corrected current detection values ​​of the three phase currents Iu, Iv, and Iw, from which detection errors have been removed, to generate three-phase PWM signals when the inverter 23 is rotating the rotor, thereby enabling the inverter 23 to control the rotation of the motor 4 with high precision.

[0039] Fig. 8 is a schematic diagram of an example of the waveform of the current flowing through the current detector 24 while the rotor is stopped. Fig. 9 is a schematic diagram of an example of the waveform of the current flowing through the current detector 24 while the rotor is spinning freely. The current detection unit 27 calculates the offset current value by detecting the current as shown in Fig. 8 or 9 while the rotor is stopped or spinning freely.

[0040] According to the above calculation method for deriving the offset current value, the current detection unit 27 calculates ΔI1 or ΔI2 as the offset current value. However, the faster the rotor's idling speed, the greater the effect of the induced voltage generated in the coils of each phase of the motor 4 on the current flowing through the current detector 24. Therefore, as shown in FIG. 9 , the waveform of the current flowing through the current detector 24 is inclined overall due to the induced voltage. In this case, the slope of the current waveform becomes steeper in the non-energized section P3, where all upper arms are on and all lower arms are off. As a result, the error in the offset current value ΔI2 derived using the detected value of the current flowing through the current detector 24 during rotor idling may become larger as the rotor's idling speed increases.

[0041] For example, in FIG. 3 , the current detection unit 27 detects the current flowing through the current detector 24 when a predetermined delay time td1 has elapsed since one phase of the PWM signal transitions to a different logic level from the other two phases (e.g., timing t1 when the U-phase PWM signal transitions from the same level as the V-phase and W-phase to a different level from the V-phase and W-phase). This allows the current detection unit 27 to detect the negative U-phase current "-Iu" flowing through the current detector 24 in the first current detection interval P1. Meanwhile, the current detection unit 27 detects the current flowing through the current detector 24 when a predetermined delay time td2 has elapsed since one phase of the PWM signal transitions to a different logic level from the other two phases (e.g., timing t2 when the U-phase PWM signal transitions from the same level as the V-phase and W-phase to a different level from the V-phase and W-phase). This allows the current detection unit 27 to detect the positive U-phase current "+Iu" flowing through the current detector 24 in the second current detection interval P2.

[0042] However, if the delay time td1 or the delay time td2 is a fixed value, as shown in Figure 9, the faster the rotor's idling speed, the larger the error in the offset current value ΔI2 derived using the detection value of the current flowing in the current detector 24 while the rotor is idling may become.

[0043] 10 is a diagram illustrating an example of a first calculation method for deriving the offset current value ΔI3 for one phase by calculation using the detected value of the current flowing through the current detector 24 while the rotor is idling. As described above, the current detection unit 27 may detect the current flowing through the current detector 24 when the delay time td1 or the delay time td2 has elapsed.

[0044] The current detection unit 27 detects a first current value A of the first phase flowing through the current detector 24 during a first period and a second current value B of the first phase flowing through the current detector 24 during a second period. The current detection unit 27 derives an offset current value ΔI3 of the first phase by calculation using one first current value A detected during the first period or multiple first current values ​​A detected during each first period and multiple second current values ​​B detected during each second period. Because one offset current value ΔI3 is derived by calculation using detected values ​​of multiple current values ​​(one or multiple first current values ​​A and multiple second current values ​​B) detected at different times, an error in the derived offset current value ΔI3 is reduced.

[0045] The current detection unit 27 derives one offset current value ΔI3 by substituting the plurality of current values ​​(one or more first current values ​​A and multiple second current values ​​B) having different timings into a predetermined calculation formula as described below, thereby easily deriving one offset current value ΔI3 with reduced error.

[0046] The current detection unit 27 may detect a first specific current value Aa, which is the value of the current flowing through the current detector 24 at the first timing ta, by using one first current value A detected in the first period or a plurality of first current values ​​A detected for each first period. The first specific current value Aa is calculated by dividing the first specific current value Aa by the plurality of first current values ​​A detected for each first period. １ ~A ５ In this example, the first current value A １ ~A ５ The first specific current value Aa is the average value of the plurality of first current values ​​A １ ~A ５ For example, the detection timing may be the first current value A １ and the detection timing is the last first current value A ５ It may be an intermediate value between

[0047] For example, the current detection unit 27 detects a plurality of first current values ​​A of the U-phase current flowing in each first current detection section P1. １ ~A ５ The detected first current value A １ ~A ５The current detection unit 27 detects the first specific current value Aa by averaging the first specific current value A １ ~A ５ By averaging the first A １ Detection timing and the last A ５ The first specific current value Aa can be estimated at a first timing ta that is intermediate (more specifically, approximately in the middle) between the detection timings of the first current values ​​A and the second current values ​​A. １ ~A ５ is the arithmetic mean of

[0048] Similarly, the current detection unit 27 may use the plurality of second current values ​​B detected for each second period to detect a second specific current value Ba, which is the value of the current flowing through the current detector 24 at the first timing ta. The second specific current value Ba may be, for example, １ ~B ４ In this example, the representative value of the second current value B １ ~B ４ The second specific current value Ba is the average value of the plurality of second current values ​​B １ ~B ４ For example, the detection timing may be the first second current value B １ and the detection timing is the last second current value B ４ It may be an intermediate value between

[0049] For example, the current detection unit 27 detects a plurality of second current values ​​B of the U-phase current flowing in the current detector 24 for each second current detection interval P2. １ ~B ４ The detected second current value B １ ~B ４ The current detection unit 27 detects the second specific current value Ba by averaging the second specific current value B １ ~B ４ By averaging the first B １ Detection timing and the last B ４ The second specific current value Ba can be estimated at a first timing ta that is intermediate (more specifically, approximately in the middle) between the detection timings of the second current values ​​B １ ~B ４ is the arithmetic mean of

[0050] The current detection unit 27 derives the first-phase offset current value ΔI3 by performing a calculation using the first specific current value Aa and the second specific current value Ba. For example, the current detection unit 27 derives the first-phase offset current value ΔI3 by calculating half the difference Δ between the first specific current value Aa and the second specific current value Ba.

[0051] It is considered that the influence of the induced voltage generated in the coils of each phase of the motor 4 on the detected current value is the same if the timing is the same. Therefore, the current detection unit 27 can reduce the error caused by the induced voltage in the offset current value ΔI3 of the first phase (e.g., U phase) by deriving the offset current value ΔI3 of the first phase using the first specific current value Aa and the second specific current value Ba at the same first timing ta. Similarly, the current detection unit 27 can derive the offset current value ΔI3 of the V phase or the offset current value ΔI3 of the W phase.

[0052] The first timing ta is not limited to a momentary time, but may be a time period having a predetermined duration. The duration of the first timing ta is, for example, shorter than half the period of the PWM signal, and preferably shorter than a quarter of the period of the PWM signal.

[0053] The first specific current value Aa is a sum of a plurality of adjacent first current values ​​A (in this example, A １ ~A ５ ), but also a plurality of non-adjacent first current values ​​A (for example, A １ and A ５ Similarly, the second specific current value Ba may be the average value of a plurality of adjacent second current values ​​B (in this example, B １ ~B ４ ), but also a plurality of non-adjacent second current values ​​B (for example, B １ and B ４ ) may also be the average value of

[0054] The first B １ In this example, the detection timing of the first A １However, as long as the first specific current value Aa and the second specific current value Ba can be detected at the same first timing ta, the detection timing of the first second current value B may be earlier than the detection timing of the first first current value A. Similarly, the detection timing of the last B ４ In this example, the detection timing of ５ However, as long as the first specific current value Aa and the second specific current value Ba can be detected at the same first timing ta, the detection timing of the last second current value B may be later than the detection timing of the last first current value A.

[0055] 10 illustrates an example in which the number of detected current values ​​required for one calculation of the offset current value ΔI3 is smaller than the number of second current values ​​B (four in this example) than the number of first current values ​​A (five in this example). However, the number of second current values ​​B may be greater than the number of first current values ​​A as long as the first specific current value Aa and the second specific current value Ba can be detected at the same first timing ta.

[0056] The number of first current values ​​A may be an integer other than 5. The number of second current values ​​B may be an integer other than 4. For example, the current detection unit 27 may detect one first current value A. ３ is detected as the first specific current value Aa (i.e., Aa=A ３ ), and two second current values ​​B ２ and B ３ The second specific current value Ba may be detected by averaging the above.

[0057] Although not shown in the figure, the current detection unit 27 detects two first current values ​​A ２ and A ３ The first specific current value Aa is detected by averaging the second specific current values ​​B ２ may be detected as a second specific current value Ba at the same timing as the first specific current value Aa (i.e., Ba=B ２ ).

[0058] When the number of first current values ​​A is odd, the number of second current values ​​B should be even, and when the number of first current values ​​A is even, the number of second current values ​​B should be odd. This allows the current detection unit 27 to make the first specific current value Aa and the second specific current value Ba approach the values ​​at the same first timing ta.

[0059] 11 is a diagram illustrating an example of a second calculation method for deriving the offset current value ΔI for one phase by calculation using the detected value of the current flowing through the current detector 24 while the rotor is idling. As described above, the current detection unit 27 may detect the current flowing through the current detector 24 when the delay time td1 or td2 has elapsed. As shown in FIG. 11 , the second calculation method is a method that can reduce errors in the offset current value even when the center line of the waveform of the current flowing through the current detector 24 forms an arc during the detection period of the offset current.

[0060] The current detection unit 27 derives an offset current value ΔI for one phase by performing a calculation using a plurality of first current values ​​A detected for each first period and a plurality of second current values ​​B detected for each second period. For example, the current detection unit 27 detects a plurality of first current values ​​A of the first phase flowing in the current detector 24 for each first period. １ , A ２ and a plurality of second current values ​​B of the first phase flowing in each second period are detected by the current detector 24. １ , B ２ Detect.

[0061] In the second calculation method, the current detection unit 27 derives the offset current value ΔI for one phase based on the following equation 1.

[0062] Equation 1 will be described below with reference to FIG.

[0063] In step S21, the current detection unit 27 detects A １ and A ２ The second current value B is calculated from the average value of １ (the first term in the numerator of Equation 1). １ and A ２By averaging these, it is possible to estimate the first specific current value Aa1 that flows at the same first timing ta1 as the second specific current value Ba1. １ That is, the first term in the numerator of Equation 1 is a term that calculates the difference Δa1 between the first specific current value Aa1 and the second specific current value Ba1.

[0064] In step S22, the current detection unit 27 detects A ２ From B １ and B ２ The current detection unit 27 subtracts the average value of B １ and B ２ By averaging these, it is possible to estimate the second specific current value Ba2 that flows at the same second timing ta2 as the first specific current value Aa2. ２ That is, the second term in the numerator of Equation 1 is a term that calculates the difference Δa2 between the first specific current value Aa2 and the second specific current value Ba2.

[0065] In step S23, the current detection unit 27 averages the difference Δa1 calculated in step S21 and the difference Δa2 calculated in step S22 (the "2" in one of the numerator and denominator of Equation 1), and divides the average value by 2 (the "2" in the other denominator of Equation 1). The average value of Δa1 and Δa2 corresponds to the average value of the difference Δ ( FIG. 10 ) at each point on the current waveform. Therefore, by dividing the average value of Δa1 and Δa2 by 2, the current detection unit 27 can derive the offset current value ΔI corresponding to the offset current value ΔI3 for one phase (see FIG. 10 ).

[0066] In this way, the current detection unit 27 detects the current in the above equation 1, "ΔI=(A １ +3A ２ -3B １ -B ２ The offset current value ΔI for one phase is calculated based on the second calculation method using "(phase offset) / 8".

[0067] Fig. 12 is a diagram for explaining in more detail the second calculation method shown in Fig. 11. As shown in Fig. 12, the current waveform shown in Fig. 11 can be divided into a ripple current component α that depends on the current conduction pattern of the PWM signal, and a central current component β that depends on the induced voltage generated by the rotor spinning.

[0068] Considering the central current component β, the first term in the numerator of Eq. １_ｅ and A ２_ｅ From the average value of B １_ｅ The second term in the numerator of Equation 1 is A ２_ｅ From B １_ｅ and B ２_ｅ Therefore, when each current value is detected in an arc portion as shown in the figure, the first term of the numerator will be a negative value and the second term of the numerator will be a positive value.

[0069] On the other hand, when considering the ripple current component α, the first term in the numerator of Equation 1 is A １_ｒ and A ２_ｒ From the average value of B １_ｒ The second term in the numerator of Equation 1 is A ２_ｒ From B １_ｒ and B ２_ｒ In other words, in the numerator of Equation 1, the difference Δ between the current waveforms is calculated twice, and the sum of these calculations is calculated. The two differences Δ are then averaged (the "2" in one of the numerator and denominator of Equation 1), and this averaged value is divided by 2 (the "2" in the other denominator of Equation 1), thereby making it possible to reduce the effect of the induced voltage on the error in the offset current value ΔI derived by Equation 1 close to zero.

[0070] 13 is a diagram illustrating an example of a third calculation method for deriving the offset current value ΔI for one phase by calculation using the detected value of the current flowing through the current detector 24 while the rotor is idling. As described above, the current detection unit 27 may detect the current flowing through the current detector 24 when the delay time td1 or td2 has elapsed. As shown in FIG. 13 , the third calculation method is a method that can reduce errors in the offset current value even when the center line of the waveform of the current flowing through the current detector 24 forms an arc during the detection period of the offset current.

[0071] The current detection unit 27 derives an offset current value ΔI for one phase by performing a calculation using a plurality of first current values ​​A detected for each first period and a plurality of second current values ​​B detected for each second period. For example, the current detection unit 27 detects a plurality of first current values ​​A of the first phase flowing in the current detector 24 for each first period. １ , A ２ , A ３ and a plurality of second current values ​​B of the first phase flowing in each second period are detected by the current detector 24. １ , B ２ Detect.

[0072] In the third calculation method, the current detection unit 27 derives the offset current value ΔI for one phase based on the following equation 2.

[0073] Equation 2 will be described below with reference to FIG.

[0074] In step S31, the current detection unit 27 detects A １ and A ２ The second current value B is calculated from the average value of １ (the first term in the numerator of Equation 2). １ and A ２ By averaging these, it is possible to estimate the first specific current value Aa1 that flows at the same first timing ta1 as the second specific current value Ba1. １ That is, the first term in the numerator of Equation 2 is a term that calculates the difference Δa1 between the first specific current value Aa1 and the second specific current value Ba1.

[0075] In step S32, the current detection unit 27 detects A ２ From B １ and B ２ The current detection unit 27 subtracts the average value of B １ and B ２ By averaging these, it is possible to estimate the second specific current value Ba2 that flows at the same second timing ta2 as the first specific current value Aa2. ２ That is, the second term in the numerator of Equation 2 is a term that calculates twice the difference Δa2 between the first specific current value Aa2 and the second specific current value Ba2.

[0076] In step S33, the current detection unit 27 detects A ２ and A ３ The second current value B is calculated from the average value of ２ (the third term in the numerator of Equation 2). ２ and A ３ By averaging these, it is possible to estimate the first specific current value Aa3 that flows at the same third timing ta3 as the second specific current value Ba3. ２ That is, the third term in the numerator of Equation 3 is a term that calculates the difference Δa3 between the first specific current value Aa3 and the second specific current value Ba3.

[0077] In step S34, the current detection unit 27 averages the difference Δa1 calculated in step S31, twice the difference Δa2 calculated in step S32, and the difference Δa3 calculated in step S33 (the "4" in the numerator and denominator of Equation 3), and divides the average by 2 (the "2" in the denominator of Equation 2). The average of Δa1, 2 × Δa2, and Δa3 corresponds to the average of the difference Δ ( FIG. 10 ) at each point on the current waveform. 2 × Δa2 represents the difference between two identical points. By doubling Δa2, an average value is calculated that weights the points with large curvature. Therefore, the current detection unit 27 can derive the offset current value ΔI corresponding to the offset current value ΔI3 for one phase (see FIG. 10 ) by dividing the average of Δa1, 2 × Δa2, and Δa3 by 2.

[0078] In this way, the current detection unit 27 calculates the current by the above formula 2 "(A １ +6A ２ +A ３ -4B １ -4B ２ The offset current value ΔI for one phase is calculated based on the third calculation method using "(1 / 16) / 16".

[0079] Fig. 14 is a diagram for explaining in more detail the third calculation method shown in Fig. 13. As shown in Fig. 14, the current waveform shown in Fig. 13 can be divided into a ripple current component α that depends on the current conduction pattern of the PWM signal, and a central current component β that depends on the induced voltage generated by the rotor spinning.

[0080] Considering the central current component β, the first term in the numerator of Equation 2 is A １_ｅ and A ２_ｅ From the average value of B １_ｅ The second term in the numerator of Equation 2 is A ２_ｅ From B １_ｅ and B ２_ｅ The average value of the two is subtracted and doubled, and the third term in the numerator of Equation 2 is A ２_ｅ and A ３_ｅ From the average value of B ２_ｅ Therefore, when each current value is detected in an arc portion as shown in the figure, the first term of the numerator will be a negative value, and the second and third terms of the numerator will be positive values.

[0081] On the other hand, when considering the ripple current component α, the first term in the numerator of Equation 1 is A １_r and A ２_r From the average value of B １_r The second term in the numerator of Equation 2 is A ２_ｒ From B １_ｒ and B ２_ｒ The average value of the two is subtracted and doubled, and the third term in the numerator of Equation 2 is A ２_r and A ３_r From the average value of B ２_r In other words, in the numerator of Equation 2, the difference Δ in the current waveforms is calculated four times and the sum is calculated. The four differences Δ are then averaged (the "4" in the numerator and denominator of Equation 2), and this averaged value is divided by 2 (the "2" in the denominator of Equation 2), thereby making it possible to reduce the effect of the induced voltage on the error in the offset current value ΔI derived by Equation 2 close to zero.

[0082] 15 is a diagram for explaining a first example of a method for outputting a PWM signal during rotor idling. Note that the order in which the offset current values ​​of the phases are detected is not limited to that shown in FIG.

[0083] The generator 35 outputs PWM signals for each phase used to detect offset currents with the same duty ratio (50% in this example). While the inverter 23 is operating at this duty ratio, the current detector 27 detects the U-phase offset current value ΔIu, and then detects the W-phase offset current value ΔIw (or the V-phase offset current value ΔIv). The waveforms of the phase currents Iu and Iw may form an arc as shown in FIG. 15 due to an induced voltage caused by rotor idling. The calculation method according to the present disclosure can detect the U-phase offset current value ΔIu and the W-phase offset current value ΔIw (or the V-phase offset current value ΔIv) even in the case of such arc-shaped waveforms. Note that the order in which the offset current values ​​of each phase are detected is not limited to this.

[0084] 16 is a diagram illustrating a second example of a method for outputting a PWM signal during rotor idle. The output method shown in FIG. 16 is an example of a method for reducing the effect of induced voltage due to rotor idle on the error in the offset current value. Note that the order in which the offset current value of each phase is detected is not limited to the case shown in FIG. 16.

[0085] The generator 35 outputs PWM signals for each phase used for offset current detection with the same duty cycle (50% in this example). The generator 35 stops outputting the PWM signals for each phase during the period from the end of the period during which the current detector 27 derives the U-phase offset current value ΔIu to the start of the period during which the current detector 27 derives the W-phase offset current value ΔIw. By temporarily stopping the output of the PWM signals for each phase before the start of the period during which the second W-phase offset current value ΔIw is derived, the influence of the induced voltage due to idling on the current Iw can be temporarily reduced to zero. This causes the slope of the waveform of the current Iw during the period during which the W-phase offset current value ΔIw is derived to approach a constant value, thereby reducing the influence of the induced voltage on the error in the W-phase offset current value ΔIw derived using the calculation method disclosed herein to approach zero.

[0086] The time from when the generator 35 starts outputting the PWM signals for each phase used for offset current detection until the current detector 27 starts detecting the current for deriving the offset current value is preferably short, while ensuring a predetermined waiting time. If the current detection for deriving the offset current value is completed before the current waveform becomes too curved, the influence of the induced voltage on the error in the W-phase offset current value ΔIw derived by the calculation method according to the present disclosure can be reduced to close to zero. The predetermined waiting time is set, for example, to the length of a predetermined period of the PWM signal (e.g., three periods).

[0087] The contents of the present disclosure are applicable to cases where the regularity and symmetry of a waveform over a certain period of time are lost.

[0088] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0089] For example, in the above-described embodiment, the first specific current value detected using one or more first current values ​​of the first phase flowing through the current detector during the first period is designated as Aa, and the second specific current value detected using multiple second current values ​​of the first phase flowing through the current detector during the second period is designated as Ba. However, this relationship may be reversed. That is, the first specific current value detected using one or more first current values ​​of the first phase flowing through the current detector during the first period may be designated as Ba, and the second specific current value detected using multiple second current values ​​of the first phase flowing through the current detector during the second period may be designated as Aa.

[0090] For example, the current detector that outputs a detection signal corresponding to the current value of the current flowing on the DC side of the inverter may be a current detector that outputs a detection signal corresponding to the current value of the current flowing on the positive bus. Also, the current detector may be a sensor such as a CT (Current Transformer).

[0091] This international application claims priority based on Japanese Patent Application No. 2024-001415, filed on January 9, 2024, the entire contents of which are incorporated herein by reference.

[0092] 4 Motor 21 DC power supply 22a Positive bus 22b Negative bus 23 Inverter 24 Current detector 27 Current detection unit 33 Drive circuit 35 Generation unit 101 Motor control device 201 Motor system Up, Vp, Wp, Un, Vn, Wn Arm

Claims

1. An inverter that energizes a motor having a rotor, a current detector provided on the DC side of the inverter, and a first period in which a part of the arms of the inverter is turned on in a first energization pattern during idling of the rotor and a second period in which a part of the arms of the inverter is turned on in a second energization pattern during the idling, and a generation unit that generates PWM signals for each phase including both in one cycle, all with the same duty ratio value, and a current detection unit that detects a first current value of a first phase flowing in the first period in the current detector and a second current value of the first phase flowing in the second period in the current detector, and the current detection unit derives an offset current value of the first phase by an operation using one of the first current values detected in the first period or a plurality of the first current values detected for each first period and a plurality of the second current values detected for each second period. A motor control device.

2. The current detection unit uses one of the first current values detected in the first period or a plurality of the first current values detected for each first period to detect a first specific current value that is the value of the current flowing in the current detector at a first timing, and uses a plurality of the second current values detected for each second period to detect a second specific current value that is the value of the current flowing in the current detector at the first timing, and derives the offset current value by an operation using the first specific current value and the second specific current value. The motor control device according to claim 1.

3. The current detection unit derives the offset current value using the difference between the first specific current value and the second specific current value. The motor control device according to claim 2.

4. The current detection unit derives the offset current value by calculating half of the difference. The motor control device according to claim 3.

5. The current detection unit detects the first specific current value by averaging a plurality of the first current values, or detects the second specific current value by averaging a plurality of the second current values. The motor control device according to claim 2.

6. The current detection unit detects the first specific current value by averaging a plurality of the first current values, and detects the second specific current value by averaging a plurality of the second current values. The motor control device according to claim 5.

7. The motor control device according to claim 2, wherein the first timing is between the detection timing of the first first current value and the detection timing of the last first current value among the plurality of first current values, or between the detection timing of the first second current value and the detection timing of the last second current value among the plurality of second current values.

8. The plurality of the first current values include A １ and A ２ and the plurality of the second current values include B １ and B ２ When the offset current value is ΔI, the current detection unit derives the offset current value based on ΔI = (A １ + 3A ２ - 3B １ - B ２ ) / 8. The motor control device according to claim 1 9. The plurality of the first current values are A １ and A ２ and A ３ and include, and the plurality of the second current values are B １ and B ２ and B ３ and include. When the offset current value is ΔI, the current detection unit derives the offset current value based on ΔI = (A １ + 6A ２ + A ３ - 4B １ - 4B ２ ) / 16. The motor control device according to claim 1 10. The motor control device according to claim 1, wherein the generation unit stops the output of the PWM signal of each phase in a period from when the period in which the current detection unit derives the offset current value of the first phase ends until the period in which the current detection unit derives the offset current value of the second phase starts.

11. A motor system comprising the motor control device according to any one of claims 1 to 10 and the motor.

12. A motor control method for energizing a motor having a rotor with an inverter, wherein PWM signals of each phase including a first period in which a part of an arm of the inverter is turned on with a first energization pattern during idling of the rotor and a second period in which the part of the arm of the inverter is turned on with a second energization pattern during the idling are generated with the same duty ratio value, a first current value of a first phase flowing in the first period is detected by a current detector provided on a DC side of the inverter, and a second current value of the first phase flowing in the second period is detected by the current detector, and an offset current value of the first phase is derived by an operation using one of the first current values detected in the first period or a plurality of the first current values detected for each first period and a plurality of the second current values detected for each second period.

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