Motor control device

Abstract

To provide a motor control device with which it is possible to secure the timing to detect a motor current using a single-shunt system by simple control, while reducing noises attributable to a carrier frequency.SOLUTION: A current acquisition unit 40 of a motor control device acquires a busbar current value in a current acquisition period that appears alternately in the first half and the second half of a carrier period. The current acquisition unit 40 acquires a busbar current value in a first period in which a first signal is on and second and third signals are off, and in a second period in which the first and second signals are on and the third signal is off during the current acquisition period. A PWM signal generation unit 80 outputs PWM signals Up, Vp, Wp in which at least one of the first, second and third signals is shifted in a time base direction, with respect to the reference position determined from a carrier wave Cw and voltage command values Vu*, Vv*, Vw*, so as to satisfy the condition that the first period is a specific length and the second period is the specific length or longer.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] For example, Patent Document 1 describes a control device that controls a switching circuit of an inverter that drives a motor based on a PWM (Pulse Width Modulation) signal. This control device includes modulation means for modulating a voltage command value with a carrier wave of a predetermined frequency to generate a pulse waveform, and waveform deformation means for moving and deforming the pulse waveform in the time axis direction while holding the duty ratio of the pulse waveform for each cycle, and generates a PWM signal based on the pulse waveform deformed by the waveform deformation means. By thus deforming the pulse waveform, this control device attempts to shift the frequency of the PWM signal (hereinafter, switching frequency) with respect to the frequency of the carrier wave (hereinafter, carrier frequency) and suppress noise caused by the carrier frequency.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, as a detection method for three-phase currents (hereinafter, motor currents) flowing through a motor driven by an inverter, a "one-shunt method" is known. In the one-shunt method, one shunt resistor connected between the inverter and the DC power supply is used to detect each of the three-phase motor currents at appropriate timings.

[0005] The technology described in Patent Document 1 uses a method that determines the travel distance for each period of the pulse waveform using random numbers, which makes the control method complex and may not ensure the timing for detecting the motor current in a single-shunt system.

[0006] This invention has been made in view of the above circumstances, and aims to provide a motor control device that can reduce noise caused by the carrier frequency while ensuring the detection timing of the motor current in a single-shunt system with simple control. [Means for solving the problem]

[0007] To achieve the above objective, the motor control device according to the present invention is A motor control device that controls the operation of a motor via an inverter that drives the motor using a DC voltage output from a DC power supply, A carrier wave generation means that generates a triangular wave with a predetermined period as a carrier wave, A PWM signal generation means generates a three-phase PWM signal based on the carrier wave and three-phase voltage command values ​​corresponding to each phase of the motor, and outputs the three-phase PWM signal to the inverter. The system includes a current acquisition means for acquiring the value of the current flowing between the DC power supply and the inverter during a current acquisition period that is repeated in a specific pattern, The aforementioned specific pattern is, If we define the period of one waveform of the carrier wave as the carrier period, one such carrier period as the first carrier period, and the carrier period following the first carrier period as the second carrier period, If the first half of the first carrier period is the current acquisition period and the second half of the first carrier period is not the current acquisition period, then the first half of the second carrier period is not the current acquisition period, and the second half of the second carrier period is the current acquisition period. If the first half of the first carrier period is not the current acquisition period, and the second half of the first carrier period is the current acquisition period, then the first half of the second carrier period is the current acquisition period, and the second half of the second carrier period is not the current acquisition period. If, among the three-phase PWM signals during the carrier period, the one with the longest ON period is designated as the first signal, the one with the second longest ON period is designated as the second signal, and the one with the longest OFF period is designated as the third signal, The current acquisition means acquires the value of the current during a first period in which the first signal is ON and the second and third signals are OFF, and a second period in which the first and second signals are ON and the third signal is OFF. The PWM signal generation means is The first signal, the second signal, and the third signal are determined according to the voltage command values ​​of the three phases. The First Career period and the aforementioned second career period The three-phase PWM signals are output with respect to a reference position determined from the carrier wave and the three-phase voltage command values, such that the duty cycles of each phase are maintained, the first period is a predetermined specific length, and the second period is greater than or equal to the specified length. At least one of the first signal, the second signal, and the third signal is shifted in the time axis direction.

[0008] The PWM signal generation means may output a three-phase PWM signal in which the third signal is not shifted relative to the reference position, and at least one of the first signal and the second signal is shifted relative to the reference position, so as to satisfy the above conditions.

[0009] The motor control device controls the inverter using a three-phase modulation method. The PWM signal generation means may output the three-phase PWM signal, each of which the first period and the second period have the specified length.

[0010] The motor control device further includes a shift amount calculation means that predicts the first period and the second period, and calculates a shift amount in the time axis direction relative to the reference position of at least one of the first signal, the second signal, and the third signal, in accordance with the prediction result, which satisfies the conditions. The PWM signal generation means is When the shift amount is calculated, an adjustment means for calculating a three-phase adjusted voltage command value obtained by adding or subtracting a value corresponding to the shift amount to the three-phase voltage command value, The system may also include an output means that generates and outputs a three-phase PWM signal by modulating the adjusted voltage command value of the three phases calculated by the adjustment means with the carrier wave. [Effects of the Invention]

[0011] According to the present invention, it is possible to reduce noise caused by the carrier frequency while ensuring the detection timing of the motor current in a single-shunt system with simple control. [Brief explanation of the drawing]

[0012] [Figure 1] A diagram showing the configuration of a motor control device according to one embodiment of the present invention. [Figure 2] A block diagram showing the main functions of the control circuit according to the above embodiment. [Figure 3] A diagram illustrating the current acquisition period according to the above embodiment. [Figure 4] This figure shows the relationship between the carrier wave and the three-phase PWM signal according to the same embodiment. [Figure 5] (a) and (b) are diagrams illustrating the shift amount and shift direction of the PWM signal according to the above embodiment. [Figure 6] (a) and (b) are diagrams illustrating the shift amount and shift direction of the PWM signal according to the above embodiment. [Figure 7] A diagram illustrating each area for the three-phase voltage command values ​​according to the above embodiment. [Figure 8]A diagram for explaining the shift amount and shift direction of the PWM signal of the U phase for each area shown in FIG. 7. [Figure 9] A diagram comparing the switching frequencies of the embodiments for each area shown in FIG. 7 with other examples. [Figure 10] (a) is a diagram showing the distribution of the switching frequency according to the comparative example, and (b) is a diagram showing the distribution of the switching frequency according to the embodiment. [Figure 11] (a) is a diagram showing the distribution of the switching frequency according to the comparative example, and (b) is a diagram showing the distribution of the switching frequency according to the embodiment.

Mode for Carrying Out the Invention

[0013] An embodiment of the present invention will be described with reference to the drawings.

[0014] As shown in FIG. 1, the motor control device 100 includes a DC power supply 3, an inverter 10 that drives a motor M1 for a compressor, a fan motor drive circuit 20 that drives a fan motor M2, a current detection circuit 21, and a control circuit 30.

[0015] The DC power supply 3 outputs a DC voltage to the inverter 10. The DC power supply 3 is composed of, for example, a converter that converts an AC voltage from an AC power supply such as a commercial power supply into a DC voltage and outputs it.

[0016] The inverter 10 includes a switching circuit 11 and a drive unit 12 that drives the switching circuit 11 according to a PWM (Pulse Width Modulation) signal (switching control signal) from the control circuit 30.

[0017] The switching circuit 11 has a pair of switching elements connected in series for the three phases U, V, and W. The switching circuit 11 has switching elements 1u, 1v, and 1w on the upper arm and switching elements 2u, 2v, and 2w on the lower arm. The pair of switching elements 1u and 2u correspond to the U phase. The pair of switching elements 1v and 2v correspond to the V phase. The pair of switching elements 1w and 2w correspond to the W phase. Freewheeling diodes D1u, D1v, and D1w are connected to both ends of each switching element 1u, 1v, and 1w on the upper arm. Freewheeling diodes D2u, D2v, and D2w are connected to both ends of each switching element 2u, 2v, and 2w on the lower arm. Note that known switching elements such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors) can be appropriately used, and the type is arbitrary.

[0018] The inverter 10 converts the DC voltage into three-phase output voltages U, V, and W by switching each switching element on and off according to the PWM signal output from the control circuit 30, and applies them to the three motor terminals of the compressor motor M1 that is to be driven. The inverter 10 is composed of, for example, an IPM (Intelligent Power Module).

[0019] Motor M1 is a three-phase brushless motor installed in the compressor unit 200 of the air conditioner. The compressor unit 200 comprises motor M1 and a compressor (not shown) driven by the rotation of motor M1.

[0020] The fan motor drive circuit 20 drives the fan motor M2, which rotates the fan of the air conditioner, using the DC voltage output by the DC power supply 3. The fan motor drive circuit 20 has a well-known configuration with three pairs of switching elements. For example, the fan motor M2 is a three-phase brushless motor.

[0021] The current detection circuit 21 has a shunt resistor R connected between the DC power supply 3 and the inverter 10, and uses the shunt resistor R to detect the bus current. The motor control device 100 uses this shunt resistor R to detect the motor current in a single-shunt manner. The three-phase currents Iu, Iv, and Iw, which are the motor current, and the bus current corresponding to the PWM signal flow through the shunt resistor R. At this time, a voltage drop occurs across the shunt resistor R. The current detection circuit 21 detects the bus current flowing through the shunt resistor R from the magnitude of this voltage drop and the resistance value of the shunt resistor R, and outputs a detection signal Si indicating the value of the bus current to the control circuit 30. The shunt resistor R is inserted, for example, in the DC line between the N side (- side) terminal of the DC power supply 3 and the inverter 10. Alternatively, the shunt resistor R may be inserted in the DC line between the P side (+ side) terminal of the DC power supply 3 and the inverter 10.

[0022] The control circuit 30 consists of a microcomputer that controls the operation of part or all of the air conditioner, and includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. The ROM pre-stores the CPU's processing procedures, as well as programs that enable the computer to function as the various parts described later, and various fixed data. The RAM temporarily stores various calculation results, etc.

[0023] As shown in Figure 2, the control circuit 30 includes, as its main functions, a current acquisition unit 40, a three-phase current calculation unit 50, a vector control unit 60, a carrier wave generation unit 70, a PWM signal generation unit 80, a shift amount calculation unit 90, and a current acquisition period specification unit 91.

[0024] The current acquisition unit 40 is configured to acquire the value of the current (bus current) flowing between the DC power supply 3 and the inverter 2 during the current acquisition period P described later. The current acquisition unit 40 includes an A / D (Analog to Digital) conversion unit 41 and an A / D conversion control unit 42.

[0025] The A / D conversion unit 41 converts the detection signal Si input from the current detection circuit 21 into a digital signal at a timing determined by the A / D conversion control unit 42. The A / D conversion unit 41 then outputs the digital signal to the three-phase current calculation unit 50.

[0026] The A / D conversion control unit 42 controls the timing of the A / D conversion performed by the A / D conversion unit 41. This timing is the first period P1 and the second period P2 within the current acquisition period P determined by the current acquisition period specification unit 91, which will be described later.

[0027] In other words, the A / D conversion unit 41 of the current acquisition unit 40 acquires the value of the current (bus current) flowing between the DC power supply 3 and the inverter 10 during the first period P1 and the second period P2 of the current acquisition period P. The A / D conversion unit 41 acquires the current of two phases out of the three phase currents Iu, Iv, and Iw during each of the first period P1 and the second period P2 of the current acquisition period P.

[0028] The three-phase current calculation unit 50 calculates (reproduces) the three-phase currents Iu, Iv, and Iw from the two-phase motor currents acquired by the A / D conversion unit 41 during the current acquisition period P, using Kirchhoff's first law.

[0029] The vector control unit 60 performs a well-known vector control calculation and calculates three-phase voltage commands Vu*, Vv*, Vw* based on the rotational speed command ω0 of the motor M1 given from an external source and the three-phase currents Iu, Iv, Iw calculated by the three-phase current calculation unit 50.

[0030] The vector control unit 60 can estimate the angle θ (rotational position) of the motor M1 based on the values ​​of the q-axis current Iq and d-axis current Id, and the q-axis voltage command value Vq and d-axis voltage command value Vd, which are described later. The angle θ corresponds to the magnetic pole position of the rotor of the motor M1. The vector control unit 60 can also obtain the maximum voltage, which is the upper limit of the terminal voltage of the motor M1, from a voltage sensor (not shown). Furthermore, the vector control unit 60 can estimate the rotational speed ω by differentiating the angle θ with respect to time.

[0031] The vector control unit 60 primarily comprises a current conversion unit 61, a dual-axis current command value calculation unit 62, and a voltage command value calculation unit 63.

[0032] The current conversion unit 61 converts the three-phase currents Iu, Iv, and Iw calculated by the three-phase current calculation unit 50 into two-phase q-axis current Iq and d-axis current Id based on the angle θ. The q-axis current Iq is the torque component of the motor M1, and the d-axis current Id is the magnetic flux component of the motor M1.

[0033] The dual-axis current command value calculation unit 62 calculates the q-axis current command value Iq* and the d-axis current command value Id*. For example, the dual-axis current command value calculation unit 62 performs feedback control to calculate the q-axis current command value Iq* so that the rotational speed ω (estimated value) of the motor M1 matches the rotational speed command ω0 of the motor M1 given from an external source. Then, the dual-axis current command value calculation unit 62 calculates the d-axis current command value Id* corresponding to the q-axis current command value Iq*. By setting the d-axis current command value Id* for the q-axis current command value Iq*, various controls become possible, such as maximum torque control, which controls the current vector so that the maximum torque can be obtained with the minimum current, and flux weakening control, which reduces the magnetic flux of the motor M1 to suppress the induced voltage of the motor M1 and increase the rotational speed of the motor M1. The dual-axis current command value calculation unit 62 calculates the d-axis current command value Id* based on the rotational speed ω, the maximum voltage, and data stored in the ROM beforehand (table data, data showing formulas according to the theories of maximum torque control and flux weakening control, etc.).

[0034] The voltage command value calculation unit 63 performs feedback control and calculates the q-axis voltage command value Vq to match the q-axis current Iq to the q-axis current command value Iq*, and the d-axis voltage command value Vd to match the d-axis current Id to the d-axis current command value Id*. This feedback control is, for example, PI control, but may also be PD control, PID control, etc. The same applies to the feedback control performed by the two-axis current command value calculation unit 62. The voltage command value calculation unit 63 then converts the q-axis voltage command value Vq and the d-axis voltage command value Vd into three-phase voltage command values ​​Vu*, Vv*, Vw* based on the angle θ. The time-dependent changes of each of the three-phase voltage command values ​​Vu*, Vv*, Vw* are sinusoidal, as shown in Figure 7.

[0035] The carrier wave generation unit 70 generates a triangular wave with a predetermined period as the carrier wave Cw, as shown in Figures 3 and 4, based on a clock of a predetermined frequency generated by the oscillation circuit. The frequency of the carrier wave Cw is, for example, 5 kHz (period is 200 μs). Hereinafter, the period of one waveform of the carrier wave Cw will be referred to as the carrier period Sc.

[0036] The PWM signal generation unit 80 generates a three-phase PWM signal corresponding to each phase of the motor M1 based on the carrier wave Cw generated by the carrier wave generation unit 70 and the three-phase voltage command values ​​Vu*, Vv*, Vw* corresponding to each phase of the motor M1, and outputs it to the inverter 10.

[0037] The PWM signal generation unit 80 includes a voltage command value adjustment unit 81 and a PWM signal output unit 82.

[0038] When the shift amount is calculated by the shift amount calculation unit 90 described later, the voltage command value adjustment unit 81 calculates the adjusted three-phase voltage command values ​​Vu1*, Vv1*, Vw1* by adding or subtracting a value corresponding to the shift amount to the three-phase voltage command values ​​Vu*, Vv*, Vw*.

[0039] The PWM signal output unit 82 generates and outputs three-phase PWM signals Up, Vp, and Wp by comparing the adjusted three-phase voltage command values ​​Vu1*, Vv1*, Vw1* with the level of the carrier wave Cw. If the command values ​​are not adjusted by the voltage command value adjustment unit 81, the PWM signal output unit 82 generates and outputs three-phase PWM signals Up, Vp, and Wp by comparing the three-phase voltage command values ​​Vu*, Vv*, Vw* with the level of the carrier wave Cw. The output PWM signals Up, Vp, and Wp have different duty cycles within the carrier period Sc so that the output voltage is a sinusoidal modulation of the average voltage of the inter-phase voltages of the UV, VW, and WU phases of the motor M1. The motor control device 100 in this embodiment controls the inverter 10 using a three-phase modulation method.

[0040] Here, the three-phase PWM signal generated and output by the PWM signal output unit 82 includes not only the three-phase PWM signals Up, Vp, and Wp for driving the upper arm (switching elements 1u, 1v, and 1w) of the inverter 10, but also the three-phase PWM signals Un, Vn, and Wn (not shown) for driving the lower arm (switching elements 2u, 2v, and 2w) of the inverter 10. Focusing on the U phase, the switching element 1u of the upper arm is turned on / off in accordance with the on / off status of Up, and the switching element 2u of the lower arm is turned on / off in accordance with the on / off status of Un. The same applies to the V and W phases. The PWM signals Un, Vn, and Wn for driving the lower arm are simply the PWM signals Up, Vp, and Wp for driving the upper arm with their polarities reversed and dead time added as needed. Therefore, in this disclosure, the PWM signals Up, Vp, and Wp for driving the upper arm are mainly treated as the three-phase PWM signals.

[0041] Figure 4 shows the three-phase PWM signals Up, Vp, Wp generated by modulating the three-phase voltage command values ​​Vu*, Vv*, Vw* with the carrier wave Cw when the command values ​​are not adjusted by the voltage command value adjustment unit 81. In this embodiment, the PWM signal output unit 82 generates three-phase PWM signals Up, Vp, Wp such that the PWM signal of one phase turns on when the value of the carrier wave Cw is greater than the voltage command value of that phase, and turns off when the value of the carrier wave Cw is smaller. Note that the frequency of the carrier wave Cw is sufficiently higher than the frequency of the three-phase voltage command values ​​Vu*, Vv*, Vw*, so in Figure 4, the three-phase voltage command values ​​Vu*, Vv*, Vw* are approximately represented linearly.

[0042] In the following, among the three-phase PWM signals Up, Vp, and Wp during a single carrier period Sc, the one with the longest ON period is designated as the first signal S1, the one with the second longest ON period is designated as the second signal S2, and the one with the longest OFF period is designated as the third signal S3. Figure 4 shows an example where the first signal S1 is Wp, the second signal S2 is Vp, and the third signal S3 is Up. In reality, the correspondence between the three-phase PWM signals Up, Vp, and Wp and the first to third signals S1 to S3 changes depending on the three-phase voltage command values ​​Vu*, Vv*, and Vw*.

[0043] Figure 4 also shows an example in which one current acquisition period P, repeated in a specific pattern described later, is in the latter half of the carrier period Sc. In the following, within one current acquisition period P, the period when the first signal S1 is ON and the second signal S2 and third signal S3 are OFF will be referred to as the first period P1, and the period when the first signal S1 and second signal S2 are ON and the third signal S3 is OFF will be referred to as the second period P2.

[0044] The current acquisition unit 40 acquires the bus current value in each of the first period P1 and the second period P2. In the first period P1 shown in Figure 4, only the switching element 1w is turned on in the upper arm. In this state, if the direction of current flow into the motor M1 is considered the positive direction of current, the bus current is Iw. In the second period P2 shown in Figure 4, only the switching element 2u is turned on in the lower arm. In this state, if the direction of current flow into the motor M1 is considered the positive direction of current, the bus current is -Iu. The remaining V phase can be calculated using Kirchhoff's first law: Iv = -(Iw - Iu). Using this method, the three-phase current calculation unit 50 calculates (reproduces) the three-phase currents Iu, Iv, and Iw (motor currents) from the two-phase motor currents acquired by the current acquisition unit 40 during one current acquisition period P.

[0045] Furthermore, in the following, when the command value is not adjusted by the voltage command value adjustment unit 81, the first signal S1, second signal S2, and third signal S3, which are generated by modulating the three-phase voltage command values ​​Vu*, Vv*, Vw* with the carrier wave Cw, will be specifically referred to as the first reference signal Sb1, second reference signal Sb2, and third reference signal Sb3. In the example in Figure 4, the first signal S1 and the first reference signal Sb1 coincide, the second signal S2 and the second reference signal Sb2 coincide, and the third signal S3 and the third reference signal Sb3 coincide.

[0046] Furthermore, the reference position Bt is defined as the position in the time axis direction determined by the carrier wave Cw and the three-phase voltage command values ​​Vu*, Vv*, and Vw*, whose command values ​​are not adjusted. The reference position Bt indicates the reference when shifting the PWM signal in the time axis direction, as described later. It can be set arbitrarily as long as it is a position within the carrier period Sc, but in order to facilitate understanding of the explanation, in this embodiment it is set to the center position of the carrier period Sc. In other words, the reference position Bt is the center position in the time axis direction of the first reference signal Sb1, the second reference signal Sb2, and the third reference signal Sb3.

[0047] The current acquisition period identification unit 91 identifies the current acquisition period P for the PWM signal generated for each carrier period Sc, based on a specific pattern which is the appearance pattern of the current acquisition period P predetermined in ROM and the carrier period Sc of the carrier wave Cw. Based on the identified current acquisition period P, the A / D conversion control unit 42 of the current acquisition unit 40 controls the timing of the A / D conversion by the A / D conversion unit 41 (the timing of the first period P1 and the second period P2 within the current acquisition period P). In other words, at that timing, the current acquisition unit 40 acquires the value of the bus current.

[0048] The specific pattern, as shown in Figure 3, is one in which, if the first half of one carrier period Sc is the current acquisition period P, then the second half of the following carrier period Sc is also set as the current acquisition period P, and if the second half of one carrier period Sc is the current acquisition period P, then the first half of the following carrier period Sc is also set as the current acquisition period P.

[0049] In the example shown in Figure 4, the "Λ" shaped waveform, which occurs between the minimum values ​​of the carrier wave Cw and the next minimum value, represents one wave of the carrier wave Cw. Note that, depending on the settings of the control circuit 30, the method of comparing the carrier wave Cw and the voltage command value may be reversed. In this case, if the value of the carrier wave Cw is smaller than the voltage command value of one phase, the PWM signal of that phase is turned on, and if the value of the carrier wave Cw is larger, the PWM signal of that phase is turned off. In this case, where the comparison relationship is reversed from the example in Figure 4, the "V" shaped waveform from when the carrier wave Cw shows its maximum value to when it shows its next maximum value can be considered as one waveform of the carrier wave Cw. In either case, within the carrier period Sc, which is the period of one waveform of the carrier wave Cw, a three-phase PWM signal with one period of duty cycle corresponding to the voltage command value is generated.

[0050] The shift amount calculation unit 90 calculates the shift amount when shifting at least one of the first signal S1 and the second signal S2 in the time axis direction from the three-phase PWM signal for one period, such that the following conditions are met.

[0051] (conditions) The aforementioned conditions are that the duty cycles of the first signal S1, the second signal S2, and the third signal S3, which are determined according to the three-phase voltage command values ​​Vu*, Vv*, and Vw*, are maintained, and that the first period P1 and the second period P2 each have a predetermined specific length. This specific length is pre-stored in ROM as the time during which the current acquisition unit 40 can stably acquire the bus current value, and in this embodiment, it is 10 μs. This value of 10 μs is set as the sum of the A / D conversion and calculation time of the control circuit 30 (5 to 6 μs), the time until the bus current stabilizes (1 to 2 μs), and a margin. In other words, the current acquisition unit 40 acquires the bus current at a timing of 6 to 8 μs elapsed from the start of each of the first period P1 and the second period P2. Note that the specific length is not limited to 10 μs and can be set arbitrarily as long as it is the time during which the current acquisition unit 40 can stably acquire the bus current value.

[0052] Specifically, the shift amount calculation unit 90 predicts the first period P1 and the second period P2, which are determined from the carrier wave Cw and the three-phase voltage command values ​​Vu*, Vv*, Vw*, before the PWM signal for one cycle of the shift target is output (for example, the cycle before the said PWM signal). More specifically, the shift amount calculation unit 90 predicts the first period P1 and the second period P2, which are determined from the first reference signal Sb1, the second reference signal Sb2, and the third reference signal Sb3.

[0053] The shift amount calculation unit 90 calculates the shift amount and direction of the first signal S1 relative to the reference position Bt in order to satisfy the above conditions. In other words, the first signal S1 can be considered to be the first reference signal Sb1 shifted by this shift amount and direction. Similarly, the shift amount calculation unit 90 calculates the shift amount and direction of the second signal S2 relative to the reference position Bt in order to satisfy the above conditions. In other words, the second signal S2 can be considered to be the second reference signal Sb2 shifted by this shift amount and direction. In this embodiment, even when the PWM signal is shifted, the third signal S3 is not shifted. In other words, the third signal S3 in this embodiment is always synonymous with the third reference signal Sb3. Note that when the shift amount calculation unit 90 does not calculate a shift amount, it may include cases where the shift amount calculation unit 90 calculates the shift amount as "0 (zero)".

[0054] Next, referring to Figures 5 and 6, we will explain the concepts of shift amount and shift direction by considering different cases. Note that the rectangular regions in Figures 5 and 6 indicate the period during which the PWM signal is ON.

[0055] In the following, among the U, V, and W phases, the phase corresponding to the first signal S1 will be referred to as the "first phase," the phase corresponding to the second signal S2 as the "second phase," and the phase corresponding to the third signal S3 as the "third phase," and the symbols will be defined as follows. an: The difference between the time when the second reference signal Sb2 turns from on to off and the time when the third reference signal Sb3 turns from on to off, or the difference between the time when the second reference signal Sb2 turns from off to on and the time when the third reference signal Sb3 turns from off to on. bn: The difference between the time when the first reference signal Sb1 turns from on to off and the time when the second reference signal Sb2 turns from on to off, or the difference between the time when the first reference signal Sb1 turns from off to on and the time when the second reference signal Sb2 turns from off to on. cn: Shift amount of the second phase PWM signal dn: Shift amount of the first phase PWM signal

[0056] In the above symbols, the index n is 1 or 2, where index n of a PWM signal for a certain period is 1, and index n of the PWM signal for the following period is 2. Also, bn and an are called "phase differences". Specifically, bn is the phase difference between the first and second phases, and an is the phase difference between the second and third phases. Furthermore, when explaining the shift direction, the direction in which time advances is referred to as the "right" or "+" side, and the opposite direction is referred to as the "left" or "-" side. Correspondingly, obtaining the bus current value in the latter half of a carrier period Sc is sometimes called "right-side acquisition", and obtaining the bus current value in the first half of a carrier period Sc is sometimes called "left-side acquisition".

[0057] (When the phase difference is less than 10 μs) First, let's explain the case where the phase difference is less than 10 μs. That is, when bn and an are less than a certain length (bn < 10 μs, an < 10 μs). In this case, it corresponds to a case where the voltage command value is relatively small.

[0058] Figure 5(a) shows an example in the specific pattern shown in Figure 3 where the latter half of one carrier period Sc is the current acquisition period P, and the first half of the following carrier period Sc is also the current acquisition period P. In other words, this is an example where the "left-side acquisition" period appears immediately after the "right-side acquisition" period. In the example shown in Figure 5(a), for the PWM signal on the left side of the figure to satisfy the above conditions, d1 = 10 - b1 + c1 and c1 = 10 - a1 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the right by d1 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where the second reference signal Sb2 (or reference position Bt) is shifted to the right by c1. In the PWM signal on the right side of the figure, in order to satisfy the above conditions (P1=10μs, P2=10μs), d2=10-b2+c2 and c2=10-a2 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the left by d2 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where it is shifted to the left by c2 with respect to the second reference signal Sb2 (or reference position Bt).

[0059] In the state shown in Figure 5(a), if we let T be the period of the first to third reference signals Sb1 to Sb3, and T1 be the period of the first signal S1 and the second signal S2 in the resulting PWM signal, then the following equation holds. Period T1 of the first signal S1: T1 = T - d1 - d2 Period T1 of the second signal S2: T1 = T - c1 - c2 Therefore, the frequency of the adjacent first signal S1 in Figure 5(a) is 1 / (T-d1-d2), and the frequency of the adjacent second signal S2 in Figure 5(a) is 1 / (T-c1-c2). Note that the period T of the first to third reference signals Sb1 to Sb3 is the same length as the period of the carrier wave Cw and the carrier period Sc.

[0060] Figure 5(b) shows an example in the specific pattern shown in Figure 3 where the first half of one carrier period Sc is the current acquisition period P, and the second half of the following carrier period Sc is also the current acquisition period P. In other words, it is an example in which a "left-side acquisition" period is followed by a "right-side acquisition" period. In the example shown in Figure 5(b), for the PWM signal on the left side of the figure to satisfy the above conditions, d1 = 10 - b1 + c1 and c1 = 10 - a1 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the left by d1 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where it is shifted to the left by c1 with respect to the second reference signal Sb2 (or reference position Bt). In the PWM signal on the right side of the figure, in order to satisfy the above conditions, d2 = 10 - b2 + c2 and c2 = 10 - a2 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the right by d2 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where the second reference signal Sb2 (or reference position Bt) is shifted to the right by c2.

[0061] In the state shown in Figure 5(b), if we let T be the period of the first to third reference signals Sb1 to Sb3, and T1 be the period of the first signal S1 and the second signal S2 in the resulting PWM signal, then the following equation holds. Period T1 of the first signal S1: T1 = T + d1 + d2 Period T1 of the second signal S2: T1 = T + c1 + c2 Therefore, the frequency of the adjacent first signal S1 in Figure 5(b) is 1 / (T+d1+d2), and the frequency of the adjacent second signal S2 in Figure 5(b) is 1 / (T+c1+c2).

[0062] (When the phase difference is 10 μs or more) Next, we will explain the case where the phase difference is 10 μs or more. That is, when bn and an are greater than a certain length (bn ≥ 10 μs, an ≥ 10 μs). In this case, the voltage command value is relatively large. Note that in this case, at least one of dn and cn may also be 0.

[0063] Figure 6(a) shows an example in the specific pattern shown in Figure 3 where the latter half of one carrier period Sc is the current acquisition period P, and the first half of the following carrier period Sc is also the current acquisition period P. In other words, this is an example where the "left-side acquisition" period appears immediately after the "right-side acquisition" period. In the example shown in Figure 6(a), for the PWM signal on the left side of the figure to satisfy the above conditions, d1 = b1 - 10 + c1 and c1 = a1 - 10 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the left by d1 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where it is shifted to the left by c1 with respect to the second reference signal Sb2 (or reference position Bt). In the PWM signal on the right side of the figure, in order to satisfy the above conditions, d2 = b2 - 10 + c2 and c2 = a2 - 10 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the right by d2 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where the second reference signal Sb2 (or reference position Bt) is shifted to the right by c2.

[0064] In the state shown in Figure 6(a), if we let T be the period of the first to third reference signals Sb1 to Sb3, and T1 be the period of the first signal S1 and the second signal S2 in the resulting PWM signal, then the following equation holds. Period T1 of the first signal S1: T1 = T + d1 + d2 Period T1 of the second signal S2: T1 = T + c1 + c2 Therefore, the frequency of the adjacent first signal S1 in Figure 6(a) is 1 / (T+d1+d2), and the frequency of the adjacent second signal S2 in Figure 6(a) is 1 / (T+c1+c2).

[0065] Figure 6(b) shows an example in the specific pattern shown in Figure 3 where the first half of one carrier period Sc is the current acquisition period P, and the second half of the following carrier period Sc is also the current acquisition period P. In other words, it is an example in which a "right-side acquisition" period appears following a "left-side acquisition" period. In the example shown in Figure 6(b), for the PWM signal on the left side of the figure to satisfy the above conditions, d1 = b1 - 10 + c1 and c1 = a1 - 10 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the right by d1 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where the second reference signal Sb2 (or reference position Bt) is shifted to the right by c1. In the PWM signal on the right side of the figure, in order to satisfy the above conditions, d2 = b2 - 10 + c2 and c2 = a2 - 10 must hold. In this case, the output PWM signal will have a waveform where the first signal S1 is shifted to the left by d2 with respect to the first reference signal Sb1 (or reference position Bt), and the second signal S2 will have a waveform where the second reference signal Sb2 (or reference position Bt) is shifted to the left by c2.

[0066] In the state shown in Figure 6(b), if we let T be the period of the first to third reference signals Sb1 to Sb3, and T1 be the period of the first signal S1 and the second signal S2 in the resulting PWM signal, then the following equation holds. Period T1 of the first signal S1: T1 = T - d1 - d2 Period T1 of the second signal S2: T1 = T - c1 - c2 Therefore, the frequency of the adjacent first signal S1 in Figure 6(b) is 1 / (T-d1-d2), and the frequency of the adjacent second signal S2 in Figure 6(b) is 1 / (T-c1-c2).

[0067] The shift amount calculation unit 90 calculates the shift amounts dn and cn necessary to satisfy the above conditions and identifies the shift direction. The voltage command value adjustment unit 81 calculates the adjusted three-phase voltage command values ​​Vu1*, Vv1*, Vw1* by adding or subtracting values ​​corresponding to the shift amount to the three-phase voltage command values ​​Vu*, Vv*, Vw* in order to realize the shift amount and identified shift direction calculated by the shift amount calculation unit 90. In other words, the PWM signal generation unit 80 modulates the adjusted three-phase voltage command values ​​Vu1*, Vv1*, Vw1* with the carrier wave Cw to generate and output the three-phase PWM signals Up, Vp, Wp which are shifted according to the shift amount.

[0068] Here, as shown in Figure 7, when considering the phase of one cycle of the three-phase voltage command values ​​Vu*, Vv*, Vw*, the areas (periods) that appear every 60° are denoted as A to F. With the areas defined in this way, Figure 8 summarizes the relationship between the shift amount and shift direction for the U-phase PWM signal Up in order to satisfy the above conditions. As can be understood from the figure, the PWM signal Up becomes the first signal S1 in areas A and B, the second signal S2 in areas C and F, and the third signal S3 in areas D and E. Although not shown in the figure, the PWM signal Vp becomes the first signal S1 in areas C and D, the second signal S2 in areas E and B, and the third signal S3 in areas F and A. Also, the PWM signal Wp becomes the first signal S1 in areas E and F, the second signal S2 in areas A and D, and the third signal S3 in areas B and C.

[0069] Figure 9 is a table showing the switching frequencies according to the above embodiment (example) for each area shown in Figure 7, along with other examples (no shift, comparative example). In the "no shift" example, the carrier frequency is the same as the switching frequency. The "comparative example" is an example in which the current acquisition period P is set in the latter half of each carrier period Sc, and the PWM signal is shifted to the right to satisfy the above conditions. In other words, the "comparative example" is an example in which the interval between adjacent current acquisition periods P in the time axis direction is always constant. Referring to the table in Figure 9, it can be seen that the "example" is able to intentionally change the instantaneous switching frequency compared to the "comparative example".

[0070] Figures 10(a) and (b) show the simulation results for the comparative example and the embodiment described in Figure 9. In Figures 10(a) and (b), a carrier wave Cw with a frequency of 5 kHz was used, and a sine wave with a peak of ±5 V was used as the voltage command value. This voltage command value corresponds to the case where the phase difference bn,an is less than 10 μs. Although these simulation results are for the U phase, the same considerations can be applied to the V phase and W phase.

[0071] In the comparative example shown in Figure 10(a), the switching frequency hardly changes with respect to time, and the frequency of switching frequency occurrences also shows that it does not change much from the frequency of the carrier wave Cw. On the other hand, in the embodiment shown in Figure 10(b), the switching frequency changes instantaneously repeatedly, and the frequency of switching frequency occurrences shows that a variable range of approximately 4500 to 5700 Hz can be achieved.

[0072] Figures 11(a) and (b) show the simulation results for a comparative example and an example, using a carrier wave Cw with a frequency of 5 kHz and a sine wave with a peak of ±30 V as the voltage command value. This voltage command value corresponds to a case where the phase difference bn,an is 10 μs or more. Although these simulation results are for the U phase, the same considerations can be applied to the V phase and W phase.

[0073] In the comparative example shown in Figure 11(a), the switching frequency hardly changes with time, and the frequency of switching frequency occurrences also shows that it does not change much from the frequency of the carrier wave Cw. On the other hand, in the embodiment shown in Figure 11(b), the switching frequency changes instantaneously repeatedly, and the frequency of switching frequency occurrences shows that a variable range of approximately 3700 to 7400 Hz can be achieved.

[0074] As described above, the motor control device 100 of this embodiment ensures the detection timing of the motor current in a single-shunt system while instantaneously changing the frequency (switching frequency) of the resulting PWM signal. This reduces noise caused by the carrier frequency. Furthermore, since the calculation required to achieve this is as simple as described above, control by the motor control device 100 is straightforward.

[0075] The present invention is not limited to the embodiments and drawings described above. Modifications (including the deletion of components) can be made as appropriate without altering the essence of the invention.

[0076] The above example shows how to control the inverter 10 using a three-phase modulation method, but the motor control device 100 may also control the inverter 10 using a two-phase modulation method. In the case of a two-phase modulation method, the third signal S3 during one carrier period Sc is always off (duty cycle is 0). In this case, the shift amount calculation unit 90 only needs to calculate the shift amount when shifting at least one of the first signal S1 and the second signal S2 in the time axis direction of the three-phase PWM signal for one period, such that the duty cycles of the first signal S1, the second signal S2, and the third signal S3, which are determined according to the three-phase voltage command values ​​Vu*, Vv*, Vw*, are maintained, and the conditions that the first period P1 is a predetermined specific length (for example, 10 μs) and the second period P2 is a specific length or longer are met.

[0077] In the above example, the third signal S3 is not shifted from the reference position Bt, and the third signal S3 and the third reference signal Sb3 are always synonymous. However, the example is not limited to this. The first signal S1, the second signal S2, and the third signal S3 may be shifted relatively in the time axis direction to output a PWM signal that satisfies the above conditions. In other words, the PWM signal generation unit 80 may output a three-phase PWM signal in which at least one of the first signal S1, the second signal S2, and the third signal S3 is shifted in the time axis direction with respect to the reference position Bt to satisfy the above conditions. In this case, the shift amount calculation unit 90 only needs to calculate the shift amount in the time axis direction of at least one of the first signal S1, the second signal S2, and the third signal S3 to satisfy the above conditions, and specify the direction of the shift.

[0078] The above example shows how the voltage command value adjustment unit 81 adds or subtracts voltage command values ​​to generate and output a three-phase PWM signal that satisfies the above conditions, but it is not limited to this. The PWM signal generation unit 80 may first generate a reference PWM signal as a PWM signal obtained by modulating the three-phase voltage command values ​​Vu*, Vv*, Vw* directly with the carrier wave Cw, and then generate PWM signals Up, Vp, Wp by shifting the generated reference PWM signal in the time axis direction to satisfy the above conditions, and output them to the inverter 10.

[0079] Furthermore, it is not necessary to constantly calculate the shift amount and output a PWM signal that is shifted in the time axis direction. When the rotational speeds of the air conditioner's compressor motor M1 and fan motor M2 are relatively high, the user will relatively become less bothered by the noise caused by the carrier frequency. Taking this characteristic into consideration, if at least one of the following conditions is met—that the rotational speed of motor M1 is above a certain threshold and that the rotational speed of fan motor M2 is above a certain threshold—the shift amount calculation unit 90 may not calculate the shift amount, and the PWM signal generation unit 80 may output a PWM signal (i.e., a PWM signal that is not shifted as described above) obtained by modulating the three-phase voltage command values ​​Vu*, Vv*, Vw* directly with the carrier wave Cw. For example, if the conditions are met that the rotational speed of motor M1 is above a certain threshold and the rotational speed of fan motor M2 is above a certain threshold, the PWM signal generation unit 80 may output a PWM signal that is not shifted as described above. The control circuit 30 can obtain the rotational speed (rotational velocity) of motor M1 and fan motor M2 as estimated or measured values ​​using a well-known method. Furthermore, the threshold values ​​for motor M1 and fan motor M2 may be the same or different.

[0080] In the above description, it is assumed that the program that implements the above operations is pre-stored in the ROM of the control circuit 30, but it may be distributed and provided on a removable recording medium. Furthermore, the program may be downloaded from other devices connected to the control circuit 30. Also, the control circuit 30 may execute each process according to the program by exchanging various data with other devices via a telecommunications network or the like.

[0081] In the above explanation, explanations of known technical matters have been omitted as appropriate in order to facilitate understanding of the present invention.

[0082] While embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0083] 100...Motor control device, 3...DC power supply 10...Inverter, M1...Motor 20...Fan motor drive circuit, M2...Fan motor 21...Current detection circuit, R...Shunt resistor, Si...Detection signal 30...Control circuit 40...Current acquisition unit, 41...A / D conversion unit, 42...A / D conversion control unit 50…Three-phase current calculation section 60…Vector control unit 61...Current conversion unit, 62...Two-axis current command value calculation unit, 63...Voltage command value calculation unit 70...Carrier wave generation section, Cw...Carrier wave, Sc...Carrier period 80...PWM signal generation section 81...Voltage command value adjustment unit, 82...PWM signal output unit 90... Shift amount calculation unit 91…Current acquisition period specification part S1...1st signal, S2...2nd signal, S3...3rd signal Sb1...first reference signal, Sb2...second reference signal, Sb3...third reference signal P...Current acquisition period, P1...First period, P2...Second period, Bt...Reference position

Claims

1. A motor control device that controls the operation of a motor via an inverter that drives the motor using a DC voltage output from a DC power supply, A carrier wave generation means that generates a triangular wave with a predetermined period as a carrier wave, A PWM signal generation means generates a three-phase PWM signal based on the carrier wave and three-phase voltage command values ​​corresponding to each phase of the motor, and outputs the three-phase PWM signal to the inverter. The system includes a current acquisition means for acquiring the value of the current flowing between the DC power supply and the inverter during a current acquisition period that is repeated in a specific pattern, The aforementioned specific pattern is, If we define the period of one waveform of the carrier wave as the carrier period, and define one such carrier period as the first carrier period, and define the carrier period following the first carrier period as the second carrier period, If the first half of the first carrier period is the current acquisition period and the second half of the first carrier period is not the current acquisition period, then the first half of the second carrier period is not the current acquisition period, and the second half of the second carrier period is the current acquisition period. If the first half of the first carrier period is not the current acquisition period, and the second half of the first carrier period is the current acquisition period, then the first half of the second carrier period is the current acquisition period, and the second half of the second carrier period is not the current acquisition period. If, among the three-phase PWM signals during the carrier period, the one with the longest ON period is designated as the first signal, the one with the second longest ON period is designated as the second signal, and the one with the longest OFF period is designated as the third signal, The current acquisition means acquires the value of the current during a first period in which the first signal is ON and the second and third signals are OFF, and a second period in which the first and second signals are ON and the third signal is OFF. The PWM signal generation means is The three-phase PWM signals are output with respect to a reference position determined from the carrier wave and the three-phase voltage command values, such that the duty cycles of the first, second, and third signals during the first and second carrier periods are maintained according to the voltage command values ​​of the three phases, and that the first period is of a predetermined specific length and the second period is greater than or equal to the specified length. Motor control device.

2. The PWM signal generation means outputs a three-phase PWM signal in which the third signal is not shifted relative to the reference position, and at least one of the first signal and the second signal is shifted relative to the reference position, so as to satisfy the above conditions. The motor control device according to claim 1.

3. The motor control device controls the inverter using a three-phase modulation method. The PWM signal generation means outputs the three-phase PWM signal, each of which has a specific length, the first period and the second period. The motor control device according to claim 1 or 2.

4. The system further includes a shift amount calculation means for predicting the first period and the second period, and calculating a shift amount in the time axis direction relative to the reference position of at least one of the first signal, the second signal, and the third signal, in accordance with the prediction results, which satisfies the conditions, The PWM signal generation means is When the shift amount is calculated, an adjustment means for calculating a three-phase adjusted voltage command value obtained by adding or subtracting a value corresponding to the shift amount to the three-phase voltage command value, The system includes an output means that generates and outputs a three-phase PWM signal by modulating the adjusted voltage command value of the three phases calculated by the adjustment means with the carrier wave. A motor control device according to any one of claims 1 to 3.

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