Motor control system and motor control method

Abstract

To suppress the degradation of accuracy in motor PWM control while employing an internal clock that generates a low-precision clock signal. [Solution] The time duration of the period of the PWM signal from the higher-level system 60, measured using the clock signal generated by the control device 30's internal clock, is compared with time data indicating a specified time duration for the PWM signal period. Based on the comparison result, the period error calculation unit 36 ​​calculates the error in the clock signal generated by the internal clock as a period error. Then, based on the calculated error, a time-corrected PWM signal is generated and output to the switching element of the inverter 20.

Description

Technical Field

[0001] The present disclosure relates to a motor control system and a motor control method for PWM controlling a motor via an inverter.

Background Art

[0002] Patent Document 1 describes a blower motor control device that suppresses a detection error of an actual rotation speed and enables a rotation operation with little variation even when the blower motor control device has an operation clock with low accuracy.

[0003] The blower motor control device of Patent Document 1 is given a target rotation speed from an upper system using a PWM signal duty ratio. The blower motor control device calculates a cycle error of a PWM signal from the upper system, and performs speed control by multiplying and correcting the rotor rotation speed calculated from a position detection sensor based on the cycle error.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, when the control device adopts an internal clock that generates a clock signal with low accuracy in order to reduce costs and PWM controls the motor, errors may occur in the period and dead time of the PWM signal due to the error of the clock signal generated by the internal clock. For example, if the period of the PWM signal becomes long due to the error of the clock signal generated by the internal clock, the current ripple becomes large. As a result, the loss increases, leading to a decrease in efficiency in motor control. In addition, an increase in the current ripple may cause a problem that the drive torque of the motor fluctuates and the vibration and drive noise of the motor increase.

[0006] This disclosure has been made in view of the above-mentioned points, and aims to provide a motor control system and motor control method that can suppress a decrease in the accuracy of PWM control of a motor while employing an internal clock that generates a low-accuracy clock signal. [Means for solving the problem]

[0007] To achieve the above objective, the motor control system (10) according to this disclosure is a motor control system (10) that PWM controls a motor (50) via an inverter (20), A receiving unit (32) that receives a reference signal having a predetermined time length from another system (60), A measurement unit (34) measures the duration of a reference signal using a clock signal generated by an internal clock, An error calculation unit (36) compares the time length measured by the measurement unit with time data representing a predetermined time length, and calculates the error of the clock signal generated by the internal clock based on the comparison result. The system includes an output unit (48) that generates a time-corrected PWM signal to reduce the effect of the error based on the error calculated by the error calculation unit and outputs it to the switching element of the inverter.

[0008] Furthermore, the motor control method according to this disclosure is a motor control method that controls a motor (50) via an inverter (20) using PWM, Receiving a reference signal having a predetermined time length from another system (60) (S100), The duration of the reference signal is measured using the clock signal generated by the internal clock (S110). The measured time length is compared with time data representing a predetermined time length, and based on the comparison result, the error of the clock signal generated by the internal clock is calculated (S160), and The system includes generating a time-corrected PWM signal based on the calculated error to reduce the effects of the error, and outputting it to the switching element of the inverter (S210).

[0009] In the motor control system and motor control method disclosed herein, a time length measured using a clock signal generated by an internal clock is compared with time data indicating a predetermined time length. Based on the comparison result, the error of the clock signal generated by the internal clock is calculated. Then, based on the calculated error, a time-corrected PWM signal is generated and output to the switching element of the inverter.

[0010] As described above, the motor control system and motor control method according to this disclosure generate a time-corrected PWM signal based on the error in the clock signal generated by the internal clock, thereby reducing the effect of the error. Therefore, the motor's PWM control can be performed using a PWM signal that reduces the effect of the error in the clock signal generated by the internal clock. This makes it possible to suppress a decrease in the accuracy of the motor's PWM control.

[0011] The reference numbers in parentheses above are merely examples of correspondences with specific configurations in embodiments described later, in order to facilitate understanding of this disclosure, and are not intended to limit the scope of this disclosure in any way.

[0012] Furthermore, technical features described in each claim of the patent claims, other than those described above, will become clear from the description of the embodiments and the accompanying drawings, which will be discussed later. [Brief explanation of the drawing]

[0013] [Figure 1] This is a configuration diagram showing an example of the configuration of a motor control system according to the embodiment. [Figure 2] This is a block diagram showing the various functional components of the control unit, represented by blocks. [Figure 3] This figure shows an example of PWM signals for the upper and lower switching elements of the U-phase, V-phase, and W-phase, respectively, generated based on a comparison between the corresponding sinusoidal and triangular waves. [Figure 4] This diagram illustrates how, when the frequency of the clock signal generated by the control device's internal clock is higher than the normal frequency, the period and dead time of the PWM signal become smaller than their respective specified values. [Figure 5] This diagram illustrates how, when the frequency of the clock signal generated by the control device's internal clock is lower than the normal frequency, the period and dead time of the PWM signal will be greater than their respective specified values. [Figure 6] This figure shows that the current ripple is relatively small when the period and dead time of the PWM signal are at their respective specified values. [Figure 7] This diagram shows that when the period or dead time of a PWM signal exceeds its respective specified value, the current ripple becomes relatively larger. [Figure 8] This figure shows the time relationship between the switching of the upper U-phase switching element from on to off and the switching of the lower U-phase switching element from off to on. [Figure 9] Figure 8 shows the state of the upper and lower switching elements of the U-phase, and the current flow state, during periods A, B, and C, respectively. [Figure 10] This flowchart shows an example of the process that a control device performs to control a motor using PWM. [Modes for carrying out the invention]

[0014] Hereinafter, embodiments of a motor control system and a motor control method according to the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiments, and various modifications described hereinafter are also included in the technical scope of the present disclosure. Furthermore, various changes can be made and implemented without departing from the gist of the present disclosure other than those described below. The embodiments and various modifications can be implemented in appropriate combination as long as there is no technical contradiction. In the following description, the same or similar configurations may be given the same reference numerals in a plurality of drawings, and the description may be omitted. In addition, when only a part of the configuration is mentioned, the description described elsewhere can be applied to other parts.

[0015] (First Embodiment) FIG. 1 is a configuration diagram showing an example of the configuration of a motor control system 10 according to the present embodiment. As shown in FIG. 1, the motor control system 10 includes a DC power supply 12, an inverter 20, a control device 30, and the like. The motor control system 10 performs PWM control on the motor 50 via the inverter 20.

[0016] The motor 50 to be controlled by the motor control system 10 is, for example, a three-phase brushless motor. The three-phase brushless motor includes, for example, a stator having three-phase (U-phase, V-phase, W-phase) windings 50U, 50V, 50W connected in Y, and a rotor to which a permanent magnet is attached. The motor 50 is provided with a rotation position sensor using, for example, a hall element or a resolver in order to detect the rotation position of the rotor. However, the rotation position of the rotor may be detected based on the induced voltage induced in the winding of the phase that is not energized among the three-phase windings 50U, 50V, 50W.

[0017] The inverter 20 is supplied with a DC power supply voltage by the DC power supply 12. The inverter 20 is a DC-AC conversion circuit that converts DC voltage to AC voltage. The inverter 20 converts the DC voltage to a three-phase AC voltage by switching elements 24H and 24L on and off according to the switching control (PWM control) by the control device 30. The converted AC voltage is output to the motor 50. This drives the motor 50 to rotate.

[0018] The inverter 20 is equipped with three phase upper and lower arm circuits 22U, 22V, and 22W. Each upper and lower arm circuit 22U, 22V, and 22W includes an upper arm circuit 22H and a lower arm circuit 22L. Each upper arm circuit 22H and lower arm circuit 22L is connected in series between the high-potential line 14 and the low-potential line 16, with the upper arm circuit 22H on the high-potential line 14 side and the lower arm circuit 22L on the low-potential line 16 side. A smoothing capacitor 18 is also connected between the high-potential line 14 and the low-potential line 16 to smooth the power supply voltage supplied by the DC power supply 12.

[0019] The upper arm circuit 22H has a high-potential side switching element 24H and a high-potential side freewheeling diode 26H, respectively. In the following description, the "high-potential side" may be referred to as the "upper stage". The lower arm circuit 22L has a low-potential side switching element 24L and a low-potential side freewheeling diode 26L, respectively. In the following description, the "low-potential side" may be referred to as the "lower stage".

[0020] In addition, the number of high-potential switching elements 24H and low-potential switching elements 24L in the upper arm circuit 22H and the lower arm circuit 22L is not particularly limited; there may be one or multiple. When multiple switching elements are provided, the multiple switching elements may be connected in parallel with each other. The multiple switching elements connected in parallel may then be driven on and off at the same timing by a common gate drive signal.

[0021] The high-potential switching element 24H and the low-potential switching element 24L illustrated in Figure 1 are both n-channel type MOSFETs. MOSFET is an abbreviation for Metal Oxide Semiconductor Field Effect Transistor. As shown in Figure 1, the drain of the MOSFET in the upper arm circuit 22H is connected to the high-potential line 14. The source of the MOSFET in the lower arm circuit 22L is connected to the low-potential line 16. The source of the MOSFET in the upper arm circuit 22H and the drain of the MOSFET in the lower arm circuit 22L are then interconnected.

[0022] The high-potential freewheeling diode 26H is connected in antiparallel to the high-potential switching element 24H. That is, the anode of the high-potential freewheeling diode 26H is connected to the source of the corresponding high-potential switching element 24H, which is a MOSFET, and its cathode is connected to the drain. The low-potential freewheeling diode 26L is also connected in antiparallel to the low-potential switching element 24L. The high-potential freewheeling diode 26H and the low-potential freewheeling diode 26L may be parasitic diodes (body diodes) of the high-potential switching element 24H and the low-potential switching element 24L, respectively, or they may be external diodes.

[0023] Note that the high-potential switching element 24H and the low-potential switching element 24L are not limited to MOSFETs. For example, IGBTs may be used as the high-potential switching element 24H and the low-potential switching element 24L. IGBT is an abbreviation for Insulated Gate Bipolar Transistor. Even when IGBTs are used, freewheeling diodes are connected in antiparallel to the high-potential switching element 24H and the low-potential switching element 24L, respectively.

[0024] In each of the upper and lower arm circuits 22U, 22V, and 22W, the connection point between the upper arm circuit 22H and the lower arm circuit 22L, i.e., the midpoint of the upper and lower arm circuits 22U, 22V, and 22W, is connected to the corresponding phase windings 50U, 50V, and 50W of the motor 50 via output lines 28U, 28V, and 28W, respectively. More specifically, among the upper and lower arm circuits 22U, 22V, and 22W, the midpoint of the upper and lower arm circuit 22U corresponding to the U phase of the motor 50 is connected to the U phase winding 50U of the motor 50 via output line 28U. The midpoint of the upper and lower arm circuit 22V corresponding to the V phase of the motor 50 is connected to the V phase winding 50V of the motor 50 via output line 28V. The midpoint of the upper and lower arm circuit 22W corresponding to the W phase of the motor 50 is connected to the W phase winding 50W of the motor 50 via output line 28W.

[0025] The control device 30 may be composed of, for example, a computer having a processor and memory. The control device 30 performs various functions by having the processor execute a program stored in memory. When performing various functions, the control device 30 operates with reference to a clock signal generated by an internal clock. The control device 30 has a CR oscillator circuit, an LC oscillator circuit, or a ceramic oscillator as its internal clock. Compared to a crystal oscillator, the CR oscillator circuit, LC oscillator circuit, or ceramic oscillator has the advantage of being low-cost. On the other hand, the CR oscillator circuit, LC oscillator circuit, or ceramic oscillator has the disadvantage that the frequency accuracy of the clock signal is lower compared to a crystal oscillator. The control device 30 also has hardware such as an AD converter and an I / F circuit.

[0026] In this embodiment, as described above, in order to reduce the cost of the motor control system 10, the control device 30 has a low-cost CR oscillator circuit, LC oscillator circuit, or ceramic oscillator as its internal clock. However, when a CR oscillator circuit, LC oscillator circuit, or ceramic oscillator is used as the internal clock, the frequency accuracy of the generated clock signal is lower than that of a clock signal generated by a crystal oscillator. Therefore, if the control device 30 uses a clock signal with low frequency accuracy as a reference to perform PWM control of the motor 50, the problems described below may occur.

[0027] For example, when the control device 30 drives the motor 50 by 180-degree sinusoidal current control, sinusoidal signals shifted by 120 degrees are generated, corresponding to the U-phase, V-phase, and W-phase, respectively. The generated sinusoidal signals corresponding to the U-phase, V-phase, and W-phase are compared with triangular waves by a comparator as the U-phase comparison signal, V-phase comparison signal, and W-phase comparison signal, respectively, as shown in Figure 3. The triangular waves can be generated using a timer in the control device 30. For example, the triangular waves can be generated by the timer in the control device 30 counting up until it has counted half the period T of the PWM signal, and then counting down after it has reached half the period of the PWM signal.

[0028] The timer in the control device 30 operates based on a clock signal generated by the control device 30's internal clock. As shown in Figure 3, the period from the beginning to the end of one triangular wave corresponds to one period T of the PWM signal. The length of one period T of the PWM signal is affected by the deviation (error) if the frequency of the internal clock signal deviates from the normal frequency. In the following explanation, one period T of the PWM signal may be referred to as the PWM period T.

[0029] Then, based on the comparison result from the comparator, the control device 30 generates and outputs PWM signals for each switching element, as shown in Figure 3, such that if the sine wave signal, which is the comparison signal, is larger than the triangular wave, it turns on the upper switching element (upper MOSFET) of the corresponding phase and turns off the lower switching element (lower MOSFET).

[0030] When the sine wave signal, which is the comparison signal, changes from a state where it is larger than a triangular wave to a state where it is smaller, the control device 30 generates and outputs a PWM signal that turns the upper switching element of the corresponding phase from on to off, as shown in Figure 3. At this time, a PWM signal is not immediately generated for the lower switching element to turn it from off to on. This is to prevent a short circuit (high current flow) caused by the simultaneous turning on of the lower and upper switching elements. As shown in Figure 3, the control device 30 outputs a PWM signal to the lower switching element to turn the upper switching element from on to off, and then, after a specified dead time DT has elapsed, generates and outputs a PWM signal to turn the lower switching element from off to on. The dead time DT is counted based on the clock signal generated by the internal clock. Therefore, the dead time DT is also affected by the error in the clock signal generated by the internal clock.

[0031] Then, when the sine wave signal, which is the comparison signal, changes from a state smaller than the triangular wave to a state larger than the triangular wave, the control device 30 generates and outputs a PWM signal that turns the lower switching element of the corresponding phase from on to off, as shown in Figure 3. Furthermore, the control device 30 outputs a PWM signal to the upper switching element that turns the lower switching element from on to off, and then, after a specified dead time DT has elapsed, generates and outputs a PWM signal that turns the upper switching element from off to on.

[0032] As described above, the PWM period T and dead time DT are affected by errors in the clock signal generated by the internal clock of the control device 30. For example, if the frequency of the clock signal generated by the internal clock is higher than the normal value (regular frequency), the PWM signal period and dead time will become smaller than the specified values ​​T and DT, respectively (T1 and DT1), as shown in Figure 4. In this case, because the dead time becomes smaller than the specified value DT (DT1), sufficient dead time cannot be secured between the switching of one switching element from on to off and the switching of the other switching element from off to on, increasing the likelihood of a short circuit occurring.

[0033] Furthermore, for example, if the frequency of the clock signal generated by the internal clock is lower than the normal value, the period and dead time of the PWM signal will become larger than their respective specified values ​​T and DT, T2 and DT2, as shown in Figure 5. In this case, the current ripple of the current flowing through the motor 50 will increase as a result of the period and dead time of the PWM signal becoming larger than their respective specified values ​​T and DT, as shown in Figures 6 and 7. Note that Figure 6 shows that the current ripple is relatively small when the period and dead time of the PWM signal are at their respective specified values ​​T and DT. On the other hand, Figure 7 shows that the current ripple becomes relatively large when the period and dead time of the PWM signal become larger than their respective specified values ​​T and DT, T2 and DT2.

[0034] As shown in Figure 7, when the current ripple increases, losses increase, leading to a decrease in the efficiency of the PWM control of the motor 50. In addition, when the current ripple increases, the driving torque of the motor 50 fluctuates, which can also lead to problems such as increased motor vibration and driving noise.

[0035] Furthermore, if the dead time becomes a value DT2 greater than the specified value DT, losses increase, which can lead to a decrease in the efficiency of the PWM control of the motor 50. This point will be explained below with reference to Figures 8 and 9.

[0036] Figure 8 shows the temporal relationship between the switching of the upper U-phase switching element from on to off and the switching of the lower U-phase switching element from off to on. Figure 9 shows the state of the upper and lower U-phase switching elements and the current flow state during periods A, B, and C in Figure 8.

[0037] As shown in Figures 8 and 9, during period B, which corresponds to the dead time when both the upper and lower switching elements are turned off, a freewheeling current due to the inductance component of the motor 50 flows through the freewheeling diode. The voltage drop across the freewheeling diode at this time is greater than the voltage drop due to the on-resistance of the lower switching element when the freewheeling current flows through the lower switching element during period C. Therefore, the longer period B, which corresponds to the dead time, the greater the power consumption and the lower the efficiency of the PWM control of the motor 50.

[0038] Therefore, the control device 30 according to this embodiment is configured to have the functional units shown in Figure 2 in order to suppress the decrease in accuracy of the motor's PWM control while employing an internal clock that generates a low-accuracy clock signal. Each of the functional units shown in Figure 2 can be built into the control device 30 by software and / or hardware.

[0039] As shown in Figure 2, the control device 30 has as functional units a PWM signal receiving unit 32, a PWM signal period measurement unit 34, a period error calculation unit 36, an output PWM signal period correction unit 38, a dead time correction unit 40, a duty cycle measurement unit 42, a target rotation speed calculation unit 44, an output voltage calculation unit 46, and an output processing unit 48.

[0040] The PWM signal receiving unit 32 receives a PWM signal with a fixed period transmitted from the higher-level system 60. In other words, in this embodiment, the PWM signal transmitted from the higher-level system 60 is used as a reference signal with a predetermined time length. The duty cycle of the PWM signal transmitted from the higher-level system 60 indicates the target rotational speed, which is the control target value of the motor 50. The higher-level system 60 has an internal clock, such as a crystal oscillator, which has higher frequency accuracy than the internal clock of the control device 30. Therefore, the accuracy of the period of the PWM signal transmitted by the higher-level system 60 based on its high-precision internal clock is also high.

[0041] The PWM signal period measurement unit 34 measures the time between rising edges of a fixed-period PWM signal received by the PWM signal receiving unit 32 as the period of the PWM signal, based on a clock signal generated by the internal clock of the control device 30. For example, the PWM signal period measurement unit 34 includes a free-run counter that repeatedly counts up or down within a predetermined count range. The counting up or counting down by the free-run counter is performed based on a clock signal generated by the internal clock of the control device 30. The PWM signal period measurement unit 34 detects the rising edge of the PWM signal and stores the count value of the free-run counter at that time. Then, the PWM signal period measurement unit 34 can measure the period of the PWM signal from the difference between the count value of the free-run counter when the rising edge of the PWM signal is detected and the previously stored count value at the rising edge of the PWM signal.

[0042] As described above, the PWM signal period measurement unit 34 measures the period of the PWM signal based on the clock signal generated by the internal clock of the control device 30. Therefore, the period of the PWM signal measured by the PWM signal period measurement unit 34 includes the effect of the error in the clock signal generated by the internal clock of the control device 30. For example, suppose the period of the PWM signal transmitted by the host system 60 is 2ms and the error in the clock signal generated by the internal clock of the control device 30 is -1%. A specific example of a clock signal error of -1% is when the frequency of the specified clock signal is 40MHz, but the actual frequency of the clock signal generated by the internal clock of the control device 30 is 39.6MHz, which is 1% lower than 40MHz. In this case, the PWM signal period measurement unit 34 measures 1.98ms as the period T of the PWM signal.

[0043] Furthermore, when the PWM signal receiving unit 32 receives signals using circuits such as capacitors and resistors, the rising edge of the PWM signal may not rise sharply. For example, the waveform of the PWM signal may become distorted just before it reaches its peak. In such cases, it is preferable for the PWM signal period measurement unit 34 to set a threshold value at the level before the waveform of the PWM signal becomes distorted, and to detect the rising edge of the PWM signal when the PWM signal exceeds the threshold value. This allows the PWM signal period measurement unit 34 to reduce the effect of waveform distortion and accurately measure the period T of the PWM signal.

[0044] The period error calculation unit 36 ​​calculates the error in the period of the PWM signal measured by the PWM signal period measurement unit 34. For example, the period error calculation unit 36 ​​compares the period of the PWM signal measured by the PWM signal period measurement unit 34 with time data indicating the time length of a specified period of the PWM signal, and calculates the difference based on the time data. Then, the period error calculation unit 36 ​​calculates the error in the period of the PWM signal measured by the PWM signal period measurement unit 34 as a percentage by dividing the calculated difference by the time data indicating the time length of a specified period of the PWM signal. For example, as in the example above, if the PWM signal period measurement unit 34 measures 1.98 ms as the period of the PWM signal, the difference based on 2 ms, which is the time data indicating the time length of a specified period of the PWM signal, is -0.02 ms, and the error (error rate) expressed as a percentage is -1%.

[0045] The output PWM signal period correction unit 38 calculates a correction period by correcting the specified period of the PWM signal to be output to the motor 50 based on the error calculated by the period error calculation unit 36. The calculated correction period is provided to the output processing unit 48. For example, suppose the specified period of the PWM signal is set to 50 μs. And, as in the example above, suppose the period error calculation unit 36 ​​calculates an error (error rate) of -1%. In this case, the output PWM signal period correction unit 38 calculates a correction period of 49.5 μs by subtracting -1% from the specified period of the PWM signal, which is 50 μs. This correction period is provided to the output processing unit 48.

[0046] The dead time correction unit 40 calculates a corrected dead time by correcting the specified dead time based on the error calculated by the periodic error calculation unit 36. The calculated corrected dead time is provided to the output processing unit 48. For example, suppose the specified dead time is set to 2 μs. And, as in the example above, suppose the periodic error calculation unit 36 ​​calculates an error (error rate) of -1%. In this case, the dead time correction unit 40 calculates a corrected dead time of 1.98 μs by subtracting -1% from the specified dead time of 2 μs. This corrected dead time is provided to the output processing unit 48.

[0047] The duty cycle measurement unit 42 measures the duty cycle of the received PWM signal from the ratio of the on time and off time of the PWM signal received by the PWM signal receiving unit 32. For example, the duty cycle measurement unit 42 measures the time from the rising edge to the falling edge of the PWM signal received by the PWM signal receiving unit 32 as the on time of the PWM signal, based on the clock signal generated by the internal clock of the control device 30. Furthermore, the duty cycle measurement unit 42 measures the time from the falling edge to the rising edge of the PWM signal received by the PWM signal receiving unit 32 as the off time of the PWM signal, based on the clock signal generated by the internal clock of the control device 30. Then, the duty cycle measurement unit 42 measures the duty cycle of the received PWM signal from the ratio of the measured on time and off time. In this way, since the duty cycle of the PWM signal is measured from the ratio of the on time and off time of the PWM signal, it is not affected by errors in the clock signal generated by the internal clock of the control device 30.

[0048] The target rotational speed calculation unit 44 calculates the target rotational speed of the motor 50 based on the duty cycle of the PWM signal measured by the duty cycle measurement unit 42. The correspondence between the duty cycle and the target rotational speed is predetermined. The target rotational speed calculation unit 44 provides the calculated target rotational speed to the output voltage calculation unit 46. The output voltage calculation unit 46 calculates the applied voltage to be output to the motor 50 based on the difference between the target rotational speed calculated by the target rotational speed calculation unit 44 and the actual rotational speed based on the rotational position of the rotor detected by a rotational position sensor or the like. The output voltage calculation unit 46 provides the calculated applied voltage to the motor 50 to the output processing unit 48.

[0049] The output processing unit 48 generates a time-corrected PWM signal to reduce the effects of errors, based on the correction period calculated by the output PWM signal period correction unit 38, the corrected dead time calculated by the dead time correction unit 40, and the applied voltage of the motor 50 calculated by the output voltage calculation unit 46, and outputs it to each switching element of the inverter 20.

[0050] For example, the output processing unit 48 uses a correction period to generate a triangular wave using a timer. For instance, if the specified period of the PWM signal is 50 μs and the correction period is 49.5 μs, the output processing unit 48 sets the time from the start to the end of generation of one triangular wave to the correction period of 49.5 μs. This makes the actual period time 50 μs.

[0051] Furthermore, the output processing unit 48 generates a sinusoidal wave signal with an amplitude corresponding to the applied voltage of the motor 50 calculated by the output processing unit 48. For example, the output processing unit 48 generates a sinusoidal wave signal with a larger amplitude as the applied voltage of the motor 50 increases, and compares it with a triangular wave. This generates a PWM signal with a duty cycle corresponding to the magnitude of the applied voltage of the motor 50 calculated by the output processing unit 48.

[0052] Furthermore, the output processing unit 48 generates and outputs a PWM signal that switches one of the upper and lower switching elements from on to off, then, after a correction dead time has elapsed, switches the other of the upper and lower switching elements from off to on.

[0053] In this manner, the output processing unit 48 generates and outputs a time-corrected PWM signal for each switching element of the inverter 20, based on the error in the clock signal generated by the internal clock, in order to reduce the effect of the error. Therefore, according to the motor control system 10 of this embodiment, the PWM control of the motor 50 can be performed with a PWM signal that reduces the effect of the error in the clock signal generated by the internal clock. This makes it possible to suppress a decrease in the accuracy of the PWM control of the motor 50.

[0054] Next, an example of the process performed in the control device 30 of this embodiment to control the motor 50 using PWM will be described with reference to the flowchart in Figure 10. The process shown in the flowchart in Figure 10 is executed repeatedly at regular intervals. The motor control method of this disclosure is executed when the control device 30 executes the process shown in the flowchart in Figure 10.

[0055] In step S100, the control device 30 receives a PWM signal with a fixed period transmitted from the higher-level system 60. The duty cycle of this PWM signal indicates the target rotational speed, which is the control target value for the motor 50.

[0056] In step S110, the control device 30 measures the period of the received fixed-period PWM signal based on the clock signal generated by the internal clock. In step S120, the control device 30 determines whether the measured period of the PWM signal falls within a predetermined period range. In other words, in step S120, the control device 30 determines whether the correct period of the PWM signal has been measured. For example, if the period of the PWM signal cannot be measured correctly due to the influence of noise or other factors, and the control device 30 determines that the measured period of the PWM signal does not fall within the predetermined period range, the control device 30 proceeds to step S130. On the other hand, if the period of the PWM signal is measured correctly and the control device 30 determines that the measured period of the PWM signal falls within the predetermined period range, the control device 30 proceeds to step S160.

[0057] In step S130, the control device 30 detects the duration for which the PWM signal period is abnormal. Then, in step S140, the control device 30 determines whether the duration for which the PWM signal period is abnormal is longer than a predetermined period. If it is determined to be longer than the predetermined period, the control device 30 proceeds to the process in step S150. On the other hand, if it is determined to be shorter than the predetermined period, the control device 30 terminates the process shown in the flowchart of Figure 10.

[0058] If the period of time during which the PWM signal period is abnormal exceeds a predetermined period, it is possible that there is some kind of malfunction in the control device 30, rather than the PWM signal period being temporarily abnormal due to noise or the like. Therefore, in step S150, the control device 30 stops outputting the PWM signal for driving the motor 50. As a result, each switching element of the inverter 20 is turned off, and the motor 50 is stopped.

[0059] In step S160, the control device 30 calculates the error in the period of the measured PWM signal. For example, the control device 30 compares the period of the measured PWM signal with time data indicating the time length of a specified period of the PWM signal and calculates a difference based on the time data. Then, the control device 30 calculates the error in the period of the PWM signal as a percentage by dividing the calculated difference by the time data indicating the time length of a specified period of the PWM signal.

[0060] In step S170, the control device 30 measures the duty cycle of the received PWM signal from the ratio of the on-time to the off-time of the received PWM signal. Then, in step S180, the control device 30 calculates the target rotational speed of the motor 50 based on the measured duty cycle of the PWM signal. The relationship between the duty cycle and the target rotational speed is predetermined. In step S190, the control device 30 calculates the voltage to be applied to the motor 50 based on the difference between the calculated target rotational speed and the actual rotational speed based on the rotational position of the rotor detected by a rotational position sensor or the like.

[0061] In step S200, the control device 30 calculates a correction period by correcting the error in the calculated PWM signal period to the specified period of the PWM signal to be output to the motor 50. In step S210, the control device 30 calculates a correction dead time by correcting the error in the calculated PWM signal period to the specified dead time.

[0062] In step S220, the control device 30 generates a time-corrected PWM signal to reduce the effects of errors, based on the applied voltage to the motor 50 calculated in step S180, the correction period calculated in step S200, and the correction dead time calculated in step S210, and outputs it to each switching element of the inverter 20.

[0063] (modified version) While preferred embodiments of this disclosure have been described above, this disclosure is not limited in any way to the embodiments described above and can be implemented in various modified forms without departing from the spirit of this disclosure.

[0064] For example, in the embodiment described above, the error in the clock signal generated by the internal clock of the control device 30 was always calculated as the periodic error of the PWM signal. However, the error in the clock signal generated by the internal clock does not change significantly. Therefore, the control device 30 may calculate the error in the clock signal generated by the internal clock only for a predetermined period of time from the start of the motor control system 10.

[0065] Furthermore, the error in the clock signal generated by the internal clock may change with temperature. Therefore, the control device 30 may, for example, repeatedly calculate the error in the clock signal generated by the internal clock at predetermined intervals.

[0066] In the embodiment described above, an example was described in which a constant-period PWM signal received from a higher-level system 60 is used as a reference signal having a predetermined time length from another system. However, the system may be configured to receive a signal other than a PWM signal having a predetermined time length as a reference signal from the higher-level system 60 or from another system.

[0067] In the embodiments described above, the motor control system 10 was described in an example in which the motor 50 is PWM controlled by 180-degree sinusoidal current application. However, the motor control system 10 according to this disclosure is also applicable when 120-degree square wave current application is performed. In 120-degree square wave current application, the magnitude of the current supplied to the motor 50 can be controlled by performing PWM control during the current application period of each switching element. By applying the motor control system 10 according to this disclosure to this PWM control, the error in the PWM period can be reduced.

[0068] In the embodiment described above, an example was explained in which the duty cycle of the PWM signal from the higher-level system 60 indicates the target rotational speed of the motor 50. However, the target rotational speed is just one example of a control target value; for example, the target torque that the motor 50 should generate may be used as the control target value. In this case, since the torque generated by the motor 50 is correlated with the current, the applied voltage to be output to the motor 50 can be calculated based on the difference between the target current corresponding to the target torque and the actual current.

[0069] Furthermore, for example, the control device 30 and its method described in this disclosure may be implemented by a dedicated computer comprising a processor programmed to execute one or more functions embodied by a computer program. The control device 30 and its method described in this disclosure may also be implemented using dedicated hardware logic circuits. The control device 30 and its method described in this disclosure may also be implemented by one or more dedicated computers comprising a combination of a processor that executes a computer program and one or more hardware logic circuits. The processor may be any arithmetic core, such as a CPU, MPU, GPU, or DFP (Data Flow Processor). Some or all of the functions of the processor may be implemented by hardware. For example, some or all of the functions of the processor may be implemented using a system-on-a-chip (SoC), integrated circuit (IC), or field-programmable gate array (FPGA). [Explanation of Symbols]

[0070] 10: Motor control system, 12: DC power supply, 14: High potential line, 16: Low potential line, 18: Smoothing capacitor, 20: Inverter, 22H: Upper arm circuit, 22L: Lower arm circuit, 22U, 22V, 22W: Upper and lower arm circuits, 24H: High potential side switching element, 24L: Low potential side switching element, 26H: High potential side freewheel diode, 26L: Low potential side freewheel diode, 28U, 28V, 28W: Output lines, 30: Control device, 32: PWM signal receiving unit, 34: PWM signal period measurement unit, 36: Period error calculation unit, 38: Output PWM signal period correction unit, 40: Dead time correction unit, 42: Duty ratio measurement unit, 44: Target rotation speed calculation unit, 46: Output voltage calculation unit, 48: Output processing unit, 50: Motor, 60: Higher-level system

Claims

1. A motor control system (10) that controls a motor (50) using PWM via an inverter (20), A receiving unit (32) that receives a reference signal having a predetermined time length from another system (60), A measuring unit (34) measures the time length of the reference signal using a clock signal generated by an internal clock, An error calculation unit (36) compares the time length measured by the measurement unit with time data indicating a predetermined time length, and calculates the error of the clock signal generated by the internal clock based on the comparison result, A motor control system comprising: an output unit (48) that generates a time-corrected PWM signal to reduce the effect of the error based on the error calculated by the error calculation unit and outputs it to the switching element of the inverter.

2. The motor control system according to claim 1, wherein the generation of a time-corrected PWM signal by the output unit includes correcting the time length of the period of the PWM signal based on the calculated error.

3. The motor control system according to claim 2, wherein the output unit generates a time-corrected PWM signal to be output to the switching element of the inverter from the period of the corrected PWM signal and the control target value of the motor.

4. The generation of a time-corrected PWM signal by the output unit includes correcting the dead time between the on-to-off switching of one of the high-potential-side switching elements and low-potential-side switching elements in the inverter and the off-to-on switching of the other, based on the error. The motor control system according to any one of claims 1 to 3, wherein the output unit outputs a PWM signal for turning on the other of the high-potential-side switching element and the low-potential-side switching element as a time-corrected PWM signal after the corrected dead time has elapsed.

5. The motor control system according to any one of claims 1 to 3, wherein the error calculation unit calculates the error of the clock signal generated by the internal clock for a predetermined period of time from the start of the motor control system.

6. The motor control system according to any one of claims 1 to 3, wherein the error calculation unit calculates the error of the clock signal generated by the internal clock each time a predetermined amount of time has elapsed.

7. The motor control system is provided with a target control value for the motor using the duty cycle of a PWM signal with a fixed period transmitted from a higher-level system. The motor control system according to any one of claims 1 to 3, wherein the reference signal is the PWM signal transmitted from the higher-level system.

8. The motor control system according to any one of claims 1 to 3, wherein the error calculation unit determines whether the time length of the reference signal measured by the measurement unit falls within a predetermined time length range, and if it determines that it falls within the predetermined time length range, calculates the error of the clock signal generated by the internal clock based on the time length measured by the measurement unit.

9. The motor control system according to claim 8, wherein, in the error calculation unit, if a predetermined period of time is determined to be outside a predetermined time length range, the output unit stops outputting a PWM signal to the switching element of the inverter.

10. A motor control method that controls a motor (50) using PWM via an inverter (20), Receiving a reference signal having a predetermined time length from another system (60) (S100), The duration of the reference signal is measured using a clock signal generated by an internal clock (S110). The measured time length is compared with time data indicating the predetermined time length, and based on the comparison result, the error of the clock signal generated by the internal clock is calculated to reduce the influence of the error (S160), and A motor control method comprising generating a time-corrected PWM signal to reduce the effect of the error based on the calculated error, and outputting it to the switching element of the inverter (S210).

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