Motor control device, motor system, and motor control method

Abstract

To reduce an error of an offset current value derived by using a detection value of a current flowing in a current detector during rotor idling.SOLUTION: With a motor control method, a PWM signal of each phase that includes a first period in which part of arms of an inverter is turned on with a first energizing pattern during rotor idling and a second period in which part of the arms of the inverter is turned on with a second energizing pattern during the rotor idling, is generated by a duty ratio of a same value. A current detector provided at a DC side of the inverter detects a first current value of a first phase flowing during the first period and a second current value of the first phase flowing during the second period. An offset current value of the first phase is derived by a calculation using the first current value of the first phase detected during the first period or a plurality of first current values detected for each first period and a plurality of second current values detected for each second period.SELECTED DRAWING: Figure 10

Description

Technical Field

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

Background Art

[0002] Conventionally, there is known a motor control device including a current detector connected to the DC side of an inverter, a generation unit that generates PWM signals of each phase including, in one cycle, a first period in which a part of an arm of the inverter is turned on with a first energization pattern during idling of a rotor of a motor 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, both with the same duty ratio, and a current detection unit that derives an offset current value of a first phase by subtracting half of the sum of a first current value of the first phase flowing through the current detector in the first period and a second current value of the first phase flowing through the current detector in the second period from the first current value or the second current value.

[0003] The current detection unit derives a current detection value of the phase current of the first phase by subtracting, for each cycle of the PWM signal, the offset current value of the first phase derived in advance from the current value of the phase current of the first phase detected for each cycle of the PWM signal. Thereby, the current detection unit corrects the detection value of the phase current of the first phase flowing through the current detector when the inverter rotates the rotor according to the offset current value of the first phase derived in advance. For this reason, the error included in the detection value of the phase current of the first phase is reduced (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when deriving the offset current value using the detected value of the current flowing during the idling of the rotor in the current detector, if the idling speed of the rotor increases, the error of the derived offset current value may increase.

[0006] An object of the present disclosure is to reduce the error of the offset current value derived using the detected value of the current flowing during the idling of the rotor in the current detector.

Means for Solving the Problems

[0007] A motor control device according to an 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 of each phase including, in one cycle, a first period in which a part of the arm of the inverter is turned on with a first energization pattern during the idling of the rotor and a second period in which a part of the arm of the inverter is turned on with a second energization pattern during the idling, with the same duty ratio for all; 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; The current detection unit derives the 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.

[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 with an inverter, generating PWM signals of each phase including, in one cycle, a first period in which a part of the arm of the inverter is turned on with a first energization pattern during the idling of the rotor and a second period in which a part of the arm of the inverter is turned on with a second energization pattern during the idling, with the same duty ratio for all, A current detector provided on the DC side of the inverter detects a first current value of a first phase flowing during the first period and a second current value of the first phase flowing during the second period in the current detector. An offset current value of the first phase is derived by an operation using one of the first current values detected during 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.

Advantages of the Invention

[0009] According to the present disclosure, an error in an offset current value derived using a detection value of a current flowing during idling of a rotor in a current detector can be reduced.

Brief Description of the Drawings

[0010]

Figure 1

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Figure 10

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Figure 16

Embodiments for Carrying Out the Invention

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

[0012] FIG. 1 is a diagram showing a configuration example of a motor system according to the first embodiment. The motor system 201 shown in FIG. 1 controls the rotational operation of the motor 4. The device on which the motor system 201 is mounted is, for example, a copying machine, a personal computer, a refrigerator, a pump, etc., but the device is not limited thereto. The motor system 201 includes at least the motor 4 and the motor control device 101.

[0013] The motor 4 is a permanent magnet synchronous motor having a plurality of coils. The motor 4 has, for example, a three-phase coil including a U-phase coil, a V-phase coil, and a W-phase coil. Specific examples of the motor 4 include a three-phase brushless DC motor and the like. The motor 4 has a rotor in which at least one permanent magnet is disposed, and a stator disposed around the axis of the rotor. The motor 4 is a sensorless type motor that does not use a position sensor for detecting the angular position (magnetic pole position) of the magnet of the rotor. The motor 4 is, for example, a fan motor that rotates a fan for ventilation.

[0014] The motor control device 101 drives the motor via an inverter that converts direct current into three-phase alternating current by controlling a plurality of three-phase bridge-connected switching elements to be turned on or off according to a conduction pattern including three-phase PWM signals. 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 direct current supplied from the DC power supply 21 into three-phase alternating current by switching a plurality of switching elements, and rotates the rotor of the motor 4 by flowing a three-phase alternating drive current through the motor 4. The inverter 23 drives the motor 4 based on a plurality of conduction patterns (more specifically, three-phase PWM signals) generated by the generation unit 35. PWM means Pulse Width Modulation.

[0016] The inverter 23 has a plurality of arms Up, Vp, Wp, Un, Vn, Wn connected in a three-phase bridge. The upper arms Up, Vp, Wp are high-side switching elements each connected to the positive side of the DC power supply 21 via the positive bus 22a. The lower arms Un, Vn, Wn are low-side switching elements each connected to the negative side (specifically, the ground side) of the DC power supply 21. The plurality of arms Up, Vp, Wp, Un, Vn, Wn are each turned on or off according to the corresponding drive signal among the plurality of drive signals supplied from the drive circuit 33 based on the PWM signals included in the energization pattern described above. Hereinafter, when the plurality of arms Up, Vp, Wp, Un, Vn, Wn are not particularly distinguished, they may simply be referred to as arms.

[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 type MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor). However, 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 through the DC side of the inverter 23. The current detector 24 shown in FIG. 1 is connected to the negative-side 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 through the negative-side bus 22b. The current detector 24 is, for example, a current detection element disposed on the negative-side bus 22b, and more specifically, a shunt resistor inserted into the negative-side bus 22b. The current detection element such as a shunt resistor generates a voltage signal corresponding to the current value of the current flowing through itself 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 a plurality of energization 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 an acquisition timing synchronized with a plurality of energization patterns (more specifically, three-phase PWM signals).

[0021] For example, the current detection unit 27 takes in the detection signal Sd of the analog voltage generated by the current detector 24 into an AD (Analog to Digital) converter at an acquisition timing set according to a plurality of energization patterns. The AD converter is provided in the current detection unit 27. Then, the current detection unit 27 AD-converts the taken-in analog detection signal Sd into a digital detection signal Sd and digitally processes the digital detection signal Sd after AD conversion to detect the phase currents Iu, Iv, and Iw of each of the U, V, and W phases of the motor 4. The detected 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 (the 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 (the 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 that the motor 4 rotates based on the detected values of the phase currents Iu, Iv, and Iw of the motor 4 detected by the current detection unit 27.

[0023] Each function of the current detection unit 27 and the generation unit 35 is realized, for example, by the operation of a processor of a CPU (Central Processing Unit) according to a program that is readably stored in a storage device (not shown). Each of these functions is realized, for example, by the cooperation of hardware and software in a microcomputer including a processor.

[0024] The drive circuit 33 outputs drive signals for switching the six arms Up, Vp, Wp, Un, Vn, and Wn included in the inverter 23 according to an energization pattern including the PWM signals given from the generation unit 35. Thereby, a three-phase alternating current drive current is supplied to the motor 4, and the rotor of the motor 4 rotates.

[0025] Even when the inverter 23 is not rotating the rotor with a three-phase alternating current, the rotor may rotate idly due to disturbances such as wind. In particular, a rotor that rotates a rotating body such as a fan with relatively low frictional resistance is likely to rotate idly.

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

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

[0028] FIG. 2 is an enlarged view showing an example of the current waveform of the U-phase current flowing through the current detector 24 by turning on some of the arms of all the arms of the inverter 23 according to the PWM signals of each phase with a duty ratio of 50% in each case. In FIG. 2, the upper waveform indicates the time when the rotor stops, and the lower waveform indicates the time when the rotor idles. FIG. 2 illustrates waveforms for approximately 16 cycles of the PWM signal. Both waveforms are shifted up and down with almost no change, and this vertical shift is caused by the induced voltage generated in the coils of each phase of the motor 4 due to the idling of the rotor.

[0029] FIG. 3 is a diagram showing an example of the waveform of the PWM signal when detecting the current value of the current flowing through the current detector 24 before the inverter 23 rotates the rotor of the motor 4 (when the rotor stops or idles). The inverter 23 energizes the motor 4 having a rotor by turning on some different arms for each energization pattern among all the arms. The generation unit 35 generates the PWM signals of each phase with the same duty ratio. One cycle of the PWM signal of each phase includes a first period in which some arms are turned on in the first energization pattern during the idling (or stopping) of the rotor, a second period in which some arms are turned on in the second energization pattern during the idling (or stopping) of the rotor, and a third period in which all the upper arms or all the lower arms are turned on in the third energization pattern during the idling (or stopping) of the rotor. By driving the motor 4 according to such PWM signals of each phase, the switching state of each arm as shown in FIG. 3 is obtained. FIG. 3 illustrates the case where the duty ratio of the PWM signal of each phase is 50% in each case.

[0030] A first current detection section P1 (a period including the first detection timing) in which some arms are in an on state with a first energization pattern is an example of a first period. A second current detection section P2 (a period including the second detection timing) in which some arms are in an on state with a second energization pattern is an example of a second period. A non-energization section P3 in which all upper arms are in an on state and all lower arms are in an 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] In the first current detection section P1 (an example of the first period), since the upper arm Up and the lower arms Vn, Wn are in an on state with the first energization pattern, a negative U-phase current "-Iu" flowing into the U-phase terminal of the motor 4 flows into the current detector 24 (see FIG. 4). In the second current detection section P2 (an example of the second period), since the lower arm Un and the upper arms Vp, Wp are in an on state with the second energization pattern, a positive U-phase current "+Iu" flowing out of the U-phase terminal of the motor 4 flows into the current detector 24 (see FIG. 5). The current detection unit 27 detects a first current value of the first phase flowing through the current detector 24 in the first period and a second current value of the first phase flowing through the current detector 24 in 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 half of the sum of the first current value of the first phase and the second current value of the first phase and zero as the influence component due to the induced voltage. Then, the current detection unit 27 derives the offset current value of the first phase by subtracting the detected influence component due to the induced voltage from the first current value or the second current value detected at the first or second detection timing. The current detection unit 27 can derive the offset current value even when the rotor is stopped or idling for the second phase or the third phase other than the first phase by the same calculation method.

[0033] FIG. 6 is a waveform diagram showing an example of a process of calculating the U-phase offset current value in 10 cycles (e.g., 400 μs) of the PWM signal during the no-load rotation of the rotor. FIG. 7 is an enlarged view of the portion surrounded by the dotted line frame shown in FIG. 6, and is a waveform diagram showing an example of a process of calculating the U-phase offset current value in 1 cycle (e.g., 40 μs) of the PWM signal during the no-load rotation of the rotor. 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 of 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 second U-phase 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 of 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 three-phase phase currents 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 derive the offset current value of the remaining third phase from the derived results.

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

[0038] When the inverter 23 rotates the rotor, the current detection unit 27 detects the current values of each of the three-phase phase currents by performing at least two current detections. The current detection unit 27 subtracts the three-phase offset current values pre-stored in the memory from the current values of each of the three-phase phase currents detected every one cycle of the PWM signal every one cycle of the PWM signal, thereby calculating the current detection values of each of the three-phase phase currents Iu, Iv, and Iw. As a result, when the inverter 23 rotates the rotor, the current detection unit 27 corrects the phase current of each phase flowing through the current detector 24 according to the offset current value of each phase, so that the detection error is removed from the current detection values of each of the three-phase phase currents Iu, Iv, and Iw. The PWM signal generation unit 32 generates three-phase PWM signals when the inverter 23 rotates the rotor by using the current detection values of the corrected three-phase phase currents Iu, Iv, and Iw from which the detection error has been removed, so that the rotation of the motor 4 can be controlled with high precision by the inverter 23.

[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 idling. The current detection unit 27 calculates the offset current value by detecting a current as shown in FIG. 8 or FIG. 9 while the rotor is stopped or idling.

[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 idling speed of the rotor, the greater the influence of the induced voltage generated in each phase coil of the motor 4 on the current flowing through the current detector 24. For this reason, as shown in FIG. 9, the waveform of the current flowing through the current detector 24 is inclined as a whole due to the induced voltage. In this case, the inclination of the current waveform in the non-conduction section P3 where all the upper arms are in the on state and all the lower arms are in the off state becomes large. As a result, the error of the offset current value ΔI2 derived using the detected value of the current flowing through the current detector 24 during the idling of the rotor may increase as the idling speed of the rotor increases.

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

[0042] However, if the delay time td1 or the delay time td2 is a fixed value, as shown in FIG. 9, the error of the offset current value ΔI2 derived using the detected value of the current flowing through the current detector 24 during the idling of the rotor may increase as the idling speed of the rotor increases.

[0043] FIG. 10 is a diagram for explaining an example of a first calculation method for deriving an offset current value ΔI3 for one phase by an operation using the detected value of the current flowing through the current detector 24 during the idling of the rotor. 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, as described above.

[0044] The current detection unit 27 detects a first current value A of the first phase flowing in the current detector 24 during the first period and a second current value B of the first phase flowing in the current detector 24 during the second period. The current detection unit 27 derives an offset current value ΔI3 of the first phase by performing an operation using one first current value A detected during the first period or 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. Since one offset current value ΔI3 is derived by performing an operation using detection values of a plurality of current values (one or a plurality of first current values A and a plurality of second current values B) with different timings, the error of the derived offset current value ΔI3 is reduced.

[0045] The current detection unit 27 derives one offset current value ΔI3 by substituting those plurality of current values (one or a plurality of first current values A and a plurality of second current values B) with different timings into a predetermined arithmetic expression as described below. Thereby, one offset current value ΔI3 with reduced error is easily derived.

[0046] The current detection unit 27 may detect a first specific current value Aa which is the value of the current flowing in the current detector 24 at the first timing ta, using one first current value A detected during the first period or a plurality of first current values A detected for each first period. The first specific current value Aa is a representative value of a plurality of first current values A1 to A5 detected for each first period, and in this example, it is the average value of the plurality of first current values A1 to A5. The first specific current value Aa does not have to be exactly equal to the average value of the plurality of first current values A1 to A5. For example, it may be an intermediate value between the first current value A1 with the earliest detection timing and the first current value A5 with the latest detection timing.

[0047] For example, the current detection unit 27 detects a plurality of first current values A1 to A5 of the U-phase flowing through the current detector 24 for each first current detection section P1, and detects a first specific current value Aa by averaging the detected first current values A1 to A5. By averaging the first current values A1 to A5, the current detection unit 27 can estimate the first specific current value Aa flowing at the first timing ta in the middle (more specifically, approximately in the center) between the detection timing of the first A1 and the detection timing of the last A5. The first specific current value Aa is, for example, the arithmetic mean of the plurality of first current values A1 to A5.

[0048] Similarly, the current detection unit 27 may detect a second specific current value Ba, which is the value of the current flowing at the first timing ta in the current detector 24, using a plurality of second current values B detected for each second period. The second specific current value Ba is, for example, a representative value of the plurality of second current values B1 to B4 detected for each second period, and in this example, it is the average value of the plurality of second current values B1 to B4. The second specific current value Ba does not have to be exactly equal to the average value of the plurality of second current values B1 to B4, and may be, for example, an intermediate value between the detection timing of the first second current value B1 and the detection timing of the last second current value B4.

[0049] For example, the current detection unit 27 detects a plurality of second current values B1 to B4 of the U-phase flowing through the current detector 24 for each second current detection section P2, and detects a second specific current value Ba by averaging the detected second current values B1 to B4. By averaging the second current values B1 to B4, the current detection unit 27 can estimate the second specific current value Ba flowing at the first timing ta in the middle (more specifically, approximately in the center) between the detection timing of the first B1 and the detection timing of the last B4. The second specific current value Ba is, for example, the arithmetic mean of the plurality of second current values B1 to B4.

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

[0051] If it is the same timing, it is considered that the influence of the induced voltage generated in the coils of each phase of the motor 4 on the current detection value is also the same. Therefore, the current detection unit 27 uses the first specific current value Aa and the second specific current value Ba at the same first timing ta to derive the offset current value ΔI3 of the first phase, thereby reducing the error occurring in the offset current value ΔI3 of the first phase (for example, the U phase) due to the induced voltage. 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 an instantaneous moment and may be a time zone having a predetermined time width. The time width of the first timing ta is, for example, shorter than the half cycle of the PWM signal, and preferably shorter than a quarter cycle of the PWM signal.

[0053] The first specific current value Aa is not limited to the average value of a plurality of adjacent first current values A (in this example, A1 to A5), and may be the average value of a plurality of non-adjacent first current values A (for example, A1 and A5). Similarly, the second specific current value Ba is not limited to the average value of a plurality of adjacent second current values B (in this example, B1 to B4), and may be the average value of a plurality of non-adjacent second current values B (for example, B1 and B4).

[0054] In this example, the detection timing of the first B1 is later than the detection timing of the first A1. However, if the first specific current value Aa and the second specific current value Ba at the same first timing ta can be detected, 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, in this example, the detection timing of the last B4 is earlier than the detection timing of the last A5. However, if the first specific current value Aa and the second specific current value Ba at the same first timing ta can be detected, 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] FIG. 10 illustrates a case where the number of the second current values B (in this example, four) is smaller than the number of the first current values A (in this example, five) as the number of current values to be detected for one operation of the offset current value ΔI3. However, if the first specific current value Aa and the second specific current value Ba at the same first timing ta can be detected, the number of the second current values B may be larger than the number of the first current values A.

[0056] The number of the first current values A may be an integer other than five. The number of the second current values B may be an integer other than four. For example, the current detection unit 27 may detect one first current value A3 as the first specific current value Aa (that is, Aa = A3), and detect the second specific current value Ba by averaging two second current values B2 and B3.

[0057] Although not particularly illustrated, the current detection unit 27 may detect the first specific current value Aa by averaging two first current values A2 and A3, and detect one second current value B2 as the second specific current value Ba at the same timing as the first specific current value Aa (that is, Ba = B2).

[0058] When the number of the first current values A is odd, the number of the second current values B is preferably even, and when the number of the first current values A is even, the number of the second current values B is preferably odd. Thereby, the current detection unit 27 can make the first specific current value Aa and the second specific current value Ba closer to the values at the same first timing ta.

[0059] FIG. 11 is a diagram for explaining an example of a second calculation method for deriving an offset current value ΔI for one phase by an operation using a detection value of a current flowing during idling of a rotor in the current detector 24. Similar to the 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 elapses. As shown in FIG. 11, the second calculation method is a method capable of reducing an error of the offset current value even when the center line of the waveform of the current flowing through the current detector 24 draws 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 an operation 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 A1, A2 of the first phase flowing through the current detector 24 for each first period, and detects a plurality of second current values B1, B2 of the first phase flowing through the current detector 24 for each second period.

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

[0062]

Equation

[0063] In step S21, the current detection unit 27 subtracts the second current value B1 from the value obtained by averaging A1 and A2 (the first term in the numerator of formula 1). By averaging A1 and A2, the current detection unit 27 can estimate the first specific current value Aa1 that flows at the same first timing ta1 as the second specific current value Ba1. The second specific current value Ba1 is equal to the second current value B1. That is, the first term in the numerator of formula 1 is the term for calculating 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 subtracts the value obtained by averaging B1 and B2 from A2 (the second term in the numerator of formula 1). By averaging B1 and B2, the current detection unit 27 can estimate the second specific current value Ba2 that flows at the same second timing ta2 as the first specific current value Aa2. The first specific current value Aa2 is equal to the first current value A2. That is, the second term in the numerator of formula 1 is the term for calculating 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 (one of the "2"s in the numerator and denominator of Equation 1), and divides the averaged value by 2 (the other "2" in the denominator of Equation 1). The average value of Δa1 and Δa2 corresponds to the average value of the difference Δ (FIG. 10) at each location of the current waveform. Therefore, by dividing the average value of Δa1 and Δa2 by 2, the current detection unit 27 can derive an offset current value ΔI corresponding to the offset current value ΔI3 (see FIG. 10) for one phase.

[0066] In this way, the current detection unit 27 derives the offset current value ΔI for one phase based on the second calculation method using the above Equation 1 "ΔI = (A1 + 3A2 - 3B1 - B2) / 8".

[0067] FIG. 12 is a diagram for explaining the second calculation method shown in FIG. 11 in more detail. As shown in FIG. 12, the current waveform shown in FIG. 11 can be divided into a ripple current component α depending on the energization pattern by the PWM signal and a center current component β depending on the induced voltage generated by the idling of the rotor.

[0068] Considering the center current component β, the first term in the numerator of Equation 1 subtracts B 1_e from the average value of A 2_e and A 1_e , and the second term in the numerator of Equation 1 subtracts the average value of B 2_e from A 1_e and B 2_e . Therefore, when each current value is detected in the arc portion as shown in the figure, the first term in the numerator becomes a negative value and the second term in the numerator becomes a positive value.

[0069] On the other hand, considering the ripple current component α, the first term in the numerator of Equation 1 subtracts B 1_r from the average value of A 2_r and A 1_r , and the second term in the numerator of Equation 1 subtracts the average value of B 2_r from A 1_r and B 2_rSubtract the averaged value. That is, in the numerator of Equation 1, the difference Δ of the current waveform is calculated twice, and the sum thereof is calculated. Then, the two differences Δ are averaged (one of the "2"s in the numerator and denominator of Equation 1), and the averaged value is divided by 2 (the other "2" in the denominator of Equation 1), so that the error of the offset current value ΔI derived from Equation 1 due to the induced voltage can be made close to zero.

[0070] FIG. 13 is a diagram for explaining an example of a third calculation method for deriving an offset current value ΔI for one phase by an operation using the detected value of the current flowing during the idling of the rotor in the current detector 24. Similar to the 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. As shown in FIG. 13, the third calculation method is a method capable of reducing the error of the offset current value even when the center line of the current waveform flowing through the current detector 24 draws 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 an operation 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 A1, A2, A3 of the first phase flowing through the current detector 24 for each first period, and a plurality of second current values B1, B2 of the first phase flowing through the current detector 24 for each second period.

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

[0073]

Equation

[0074] In step S31, the current detection unit 27 subtracts the second current value B1 from the value obtained by averaging A1 and A2 (the first term in the numerator of Equation 2). By averaging A1 and A2, the current detection unit 27 can estimate the first specific current value Aa1 that flows at the same first timing ta1 as the second specific current value Ba1. The second specific current value Ba1 is equal to the second current value B1. That is, the first term in the numerator of Equation 2 is the term for calculating 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 subtracts the value obtained by averaging B1 and B2 from A2 (the second term in the numerator of Equation 2). By averaging B1 and B2, the current detection unit 27 can estimate the second specific current value Ba2 that flows at the same second timing ta2 as the first specific current value Aa2. The first specific current value Aa2 is equal to the first current value A2. That is, the second term in the numerator of Equation 2 is the term for calculating 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 subtracts the second current value B2 from the value obtained by averaging A2 and A3 (the third term in the numerator of Equation 2). By averaging A2 and A3, the current detection unit 27 can estimate the first specific current value Aa3 that flows at the same third timing ta3 as the second specific current value Ba3. The second specific current value Ba3 is equal to the second current value B2. That is, the third term in the numerator of Equation 3 is the term for calculating 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 averaged value by 2 (the "2" in the denominator of Equation 2). The average value of Δa1, 2×Δa2, and Δa3 corresponds to the average value of the difference Δ (Figure 10) at each location of the current waveform. 2×Δa2 represents the difference for two portions at the same location. By doubling Δa2, an average value with weighted curvature portions is calculated. Therefore, the current detection unit 27 can derive an offset current value ΔI corresponding to the offset current value ΔI3 (see Figure 10) for one phase by dividing the average value of Δa1, 2×Δa2, and Δa3 by 2.

[0078] In this way, the current detection unit 27 derives the offset current value ΔI for one phase based on the third calculation method using the above Equation 2, "(A1 + 6A2 + A3 - 4B1 - 4B2) / 16".

[0079] Figure 14 is a diagram for explaining the third calculation method shown in Figure 13 in more detail. As shown in Figure 14, the current waveform shown in Figure 13 can be divided into a ripple current component α depending on the energization pattern by the PWM signal and a center current component β depending on the induced voltage generated by the idling of the rotor.

[0080] Considering the center current component β, the first term in the numerator of Equation 2 subtracts B 1_e from the average value of A 2_e and A 1_e ; the second term in the numerator of Equation 2 doubles the value obtained by subtracting the average value of B 2_e from A 1_e and B 2_e ; and the third term in the numerator of Equation 2 subtracts B 2_e from the average value of A 3_e and A 2_e For this reason, when each current value is detected in the arc portion as shown in the figure, the first term in the numerator becomes a negative value, and the second and third terms in the numerator become positive values.

[0081] On the other hand, considering the ripple current component α, the first term in the numerator of Equation 1 is A1_r and A 2_r Subtract B from the averaged value of 1_r The second term in the numerator of Equation 2 is obtained by subtracting B from the average value of A 2_r from A 1_r and B 2_r Subtract the averaged value of B and B from A, and multiply the result by 2. The third term in the numerator of Equation 2 is obtained by subtracting B from the average value of A and A 2_r and A 3_r Subtract B from the averaged value of 2_r That is, in the numerator of Equation 2, the difference Δ of the current waveform is calculated four times, and the sum is calculated. Then, the four differences Δ are averaged (the "4" in the numerator and denominator of Equation 2), and the averaged value is divided by 2 (the "2" in the denominator of Equation 2), so that the error of the offset current value ΔI derived from Equation 2 due to the induced voltage can be reduced to near zero

[0082] FIG. 15 is a diagram for explaining a first example of an output method of a PWM signal during idling of a rotor. Note that the order of detecting the offset current value of each phase is not limited to the case shown in FIG. 15

[0083] The generation unit 35 outputs the PWM signals of each phase for detecting the offset current with the same duty ratio (in this example, 50%). In the state where the inverter 23 is operating at the duty ratio, the current detection unit 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 draw arcs as shown in FIG. 15 due to the induced voltage caused by the idling of the rotor. 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 a waveform drawing such an arc. Note that the order of detecting the offset current value of each phase is not limited to this

[0084] FIG. 16 is a diagram for explaining a second example of an output method of a PWM signal during idling of a rotor. The output method shown in FIG. 16 is an example of a method for reducing the influence of the induced voltage caused by the idling of the rotor on the error of the offset current value. Note that the order of detecting the offset current value of each phase is not limited to the case shown in FIG. 16

[0085] The generation unit 35 outputs the PWM signals of each phase for offset current detection with the same duty ratio (50% in this example). The generation unit 35 stops outputting the PWM signals of each phase during the period from the end of the period when the current detection unit 27 derives the U-phase offset current value ΔIu to the start of the period when the current detection unit 27 derives the W-phase offset current value ΔIw. By once stopping the output of the PWM signals of each phase before the start of the derivation period of the second W-phase offset current value ΔIw, the influence of the induced voltage due to no-load rotation on the current Iw can be once set to zero. As a result, since the slope of the waveform of the current Iw approaches a constant value during the derivation period of the W-phase offset current value ΔIw, the error of the W-phase offset current value ΔIw derived by the calculation method according to the present disclosure can be made closer to zero from the influence of the induced voltage.

[0086] The time from when the generation unit 35 starts outputting the PWM signals of each phase for offset current detection to when the current detection unit 27 starts detecting the current for deriving the offset current value is preferably made short after securing a predetermined standby time. If the current detection for deriving the offset current value is completed before the degree of bending of the current waveform becomes too large, the error of the W-phase offset current value ΔIw derived by the calculation method according to the present disclosure can be made closer to zero from the influence of the induced voltage. The predetermined standby time is set to, for example, the length of a predetermined period of the PWM signal (for example, the length of 3 periods, etc.).

[0087] The content of the present disclosure is applicable when the regularity and symmetry of a certain period of the waveform are broken.

[0088] As described above, the embodiments have been explained. However, the above embodiments are presented as examples, and the present invention is not limited by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

[0089] For example, in the above-described embodiment, the first specific current value detected by using one or a plurality of first current values of the first phase flowing in the first period by the current detector is defined as Aa, and the second specific current value detected by using a plurality of second current values of the first phase flowing in the second period by the current detector is defined as Ba. However, this relationship may be reversed. That is, the first specific current value detected by using one or a plurality of first current values of the first phase flowing in the first period by the current detector may be defined as Ba, and the second specific current value detected by using a plurality of second current values of the first phase flowing in the second period by the current detector may be defined 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 output 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).

Explanation of Reference Numerals

[0091] 4 Motor 21 DC power supply 22a Positive bus 22b Negative bus 23 Inverter 24 Current detector 27 Current detection unit 29 Drive circuit 31 Generation unit 101 Motor control device 201 Motor system Up, Vp, Wp, Un, Vn, Wn Arms

Claims

1. 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 of each phase including, in one cycle, 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, with all having the same duty ratio; 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 detects a first specific current value, which is a value of a current flowing at a first timing in the current detector, 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 detects a second specific current value, which is a value of a current flowing at the first timing in the current detector, using a plurality of the second current values detected for each second period, 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 a 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 first timing is between the detection timing of the first current value among the plurality of first current values and the detection timing of the last first current value, or between the detection timing of the first second current value among the plurality of second current values and the detection timing of the last second current value. The motor control device according to claim 2.

8. The plurality of the first current values are A １ and A ２ include, The plurality of the second current values are B １ and B ２ include, 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 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 generation unit stops the output of the PWM signal of each phase in a period from the end of the period in which the current detection unit derives the offset current value of the first phase to the start of the period in which the current detection unit derives the offset current value of the second phase. The motor control device according to claim 1.

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, Generating 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 a part of the arm of the inverter is turned on with a second energization pattern during the idling, all with the same duty ratio value, Detecting a first current value of the first phase flowing in the first period in a current detector provided on the DC side of the inverter and a second current value of the first phase flowing in the second period in the current detector, A motor control method for deriving 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.

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