Motor drive device and motor drive method

Abstract

A motor drive device according to an embodiment includes: a power conversion circuit configured by connecting a plurality of legs in parallel, the plurality of legs being configured from a series circuit of positive and negative semiconductor switching elements, and driving a motor; a control unit that generates and outputs an ON / OFF signal for each semiconductor switching element constituting the power conversion circuit by means of PWM control; a current detection unit that detects a current flowing through the power conversion circuit; a current limiting unit that stops the operation of the control unit when the current reaches a threshold value; and a position estimation unit that estimates the rotational position of the motor using a motor current and a motor voltage, the position estimation unit correcting the motor voltage used for estimating the rotational position in a carrier period of the PWM control in which the operation of the control unit is stopped.

Description

Technical Field

[0001] An embodiment of the present invention relates to a device for driving a motor. Background Art

[0002] For example, a power conversion device for driving a three-phase brushless motor is configured to have a three-phase half-bridge circuit connected in parallel between positive and negative DC power lines. The half-bridge circuit is composed of a pair of semiconductor switching elements connected in series between the DC power lines, and a freewheeling diode connected in reverse parallel to each of these semiconductor switching elements. In the power conversion device configured as above, the drive of each semiconductor switching element is controlled by PWM (Pulse Width Modulation). As a result, the DC power provided from the DC power line is converted into three-phase AC power, and current is passed to the windings of the motor.

[0003] In circuits driving brushless motors, sensor driving using position sensors is proposed, particularly in applications requiring starting torque. However, in order to achieve cost reduction and miniaturization, there is a demand for motor drive devices that control brushless motors without using position sensors.

[0004] For example, a method has been proposed in which the rotation position of the motor is detected by using the induced voltage generated in the motor winding instead of using a magnetic pole sensor such as a Hall element, and the motor voltage is output based on the induced voltage. In a 120-degree rectangular wave drive that outputs a rectangular wave voltage with a 120-degree energization angle of one phase, the induced voltage can be directly detected in the 60-degree interval where the output stops. However, compared with a 180-degree sine wave drive that outputs a sine wave voltage, the 120-degree rectangular wave drive has disadvantages in terms of noise and vibration.

[0005] Generally, there is a method of calculating an induced voltage based on a motor voltage equation and estimating a rotational position using the induced voltage in order to perform sinusoidal wave driving without using a position sensor, as disclosed in Japanese Patent Application Laid-Open No. 2004-072906, for example.

[0006] In addition, as a method for controlling a brushless motor with high precision, vector control can be used. In vector control, the three-phase AC current of the motor is converted into a q-axis current as a torque component of DC and a d-axis current as a magnetic flux component. By independently and finely controlling the two, it is possible to achieve high efficiency, low vibration operation, and an expanded range of operation. For controlling the current, it is necessary to detect the motor current, and generally more than two current sensors are used. However, similar to the position sensor, in order to achieve low cost and miniaturization, sometimes an expensive current transformer is not used as a current sensor, but a cheap shunt resistor is used. In addition, in order to make the system cost lower, a 1-shunt current detection method is adopted in which the number of shunt resistors is reduced from three to one.

[0007] If an excessive current flows through the brushless motor, it may cause the magnet of the brushless motor to be demagnetized or the semiconductor switching element to be damaged. Therefore, in order to limit the motor current, as disclosed in Japanese Patent Application Laid-Open No. 2007-089332, a function of cutting off the gate signal is used when the voltage of the shunt resistor arranged on the ground line of the inverter becomes above a threshold value.

[0008] However, since the gate signal is cut off during current limiting, not only the output voltage is lower than the command, but also the motor current cannot be accurately detected when the motor current is detected based on the gate signal. In position estimation control that realizes low cost of the motor system and does not use a rotation position detector, the position estimation accuracy during current limiting may be reduced because the output voltage command and the motor current are used. Summary of the invention

[0009] Therefore, a motor drive device is provided that can prevent a decrease in the estimation accuracy of the rotational position during current limiting.

[0010] The motor drive device of the embodiment includes: a power conversion circuit configured by connecting a plurality of bridge arms formed by series circuits of positive-side and negative-side semiconductor switching elements in parallel, and driving a motor;

[0011] A control unit that generates and outputs an on / off signal for each semiconductor switch element constituting the power conversion circuit through PWM control;

[0012] a current detection unit for detecting a current flowing through the power conversion circuit;

[0013] a current limiting unit, which stops the operation of the control unit when the current reaches a threshold value; and

[0014] a position estimating unit that estimates a rotational position of the motor using the motor current and the motor voltage,

[0015] The position estimating unit corrects the motor voltage used for estimating the rotational position during a carrier cycle of the PWM control in which the operation of the control unit is stopped.

[0016] In the motor driving method of the embodiment, when driving the motor via a power conversion circuit formed by connecting a plurality of bridge arms formed by series circuits of positive-side and negative-side semiconductor switching elements in parallel,

[0017] Generate and output an on / off signal for each semiconductor switch element constituting the power conversion circuit through PWM control,

[0018] detecting a current flowing through the power conversion circuit,

[0019] When the current reaches the threshold, the output of the conduction cutoff signal is stopped.

[0020] using the motor current and the motor voltage to infer the rotational position of the motor,

[0021] In a carrier cycle of the PWM control in which output of the on / off signal is stopped, the motor voltage used for estimating the rotational position is corrected. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a diagram showing the configuration of a motor drive device according to an embodiment.

[0023] Figure 2 This is a diagram showing the internal structure of a gate driver.

[0024] Figure 3 The diagram shows a carrier waveform in PWM control and an output waveform of a gate signal of each phase when current limitation occurs.

[0025] Figure 4 This is a diagram showing the relationship between the d-axis induced voltage Ed and the estimation axis during position estimation for the case of (Ed>0).

[0026] Figure 5 This is a diagram showing the relationship between the d-axis induced voltage Ed and the estimation axis during position estimation for the case of (Ed<0).

[0027] Figure 6 This is a diagram showing simulation results of position estimation in a case where there is no current restriction.

[0028] Figure 7 It is a diagram showing the simulation results of position estimation in the case of current limitation.

[0029] Figure 8This is a diagram for explaining a period during which a current cannot be detected in the case of a single-shunt current detection method.

[0030] Fig. 9 This is a diagram for explaining three conditions when the d-axis voltage is corrected based on the timing of generating the current limit and the output timing of the gate signal of each phase.

[0031] Fig.10 This is a diagram showing an example of current on dq axis coordinates when current limitation occurs.

[0032] Fig.11 : is a flowchart showing the position estimation process.

[0033] Fig.12 FIG. 1 is a diagram showing simulation results of position estimation when current limitation occurs without position estimation correction.

[0034] Fig.13 FIG. 1 is a diagram showing simulation results of position estimation in the case where position estimation correction is performed when current limitation occurs. DETAILED DESCRIPTION

[0035] An implementation method is described below. Figure 1 As shown, an inverter 2 as a power conversion device is connected to the motor 1. The inverter 2 is a structure in which a three-phase half-bridge circuit 4 corresponding to a bridge arm is connected in parallel between positive and negative DC power lines 3a and 3b. The half-bridge circuit 4 is composed of a pair of semiconductor switching elements 5 connected in series between the DC power lines 3a and 3b, and a freewheeling diode 6 connected in reverse parallel to the semiconductor switching element 5. For example, when the semiconductor switching element is an N-channel MOSFET, the freewheeling diode 6 is a parasitic diode.

[0036] A DC power source 7, a smoothing capacitor 8, and a series circuit of resistors 9a and 9b are connected in parallel between the DC power lines 3a and 3b. A resistor 10 as a current detection unit is inserted between the resistor 9b and the DC power line 3b. A so-called 1-shunt current detection method is adopted in which the motor current is detected by the terminal voltage of the resistor 10. The motor current is converted into a dq axis current on a rotating coordinate by a current coordinate conversion unit 12 of a control unit 11. In addition, the voltage detection point of the resistor 10 is connected to the input terminal of the current limiting unit 13.

[0037] The speed command is inputted from the outside to the speed control unit 14 and the position estimation unit 15 of the control unit 11. The speed control unit 14, which functions as a current command value determination unit, performs PI (Proportional Integral) control on the difference between the speed command and the estimated speed calculated by the position estimation unit 15 to generate a q current command.

[0038] In the position estimation unit 15, the d-axis induced voltage is calculated based on the motor parameters, the dq-axis current, and the d-axis voltage. PI control is performed so that the d-axis induced voltage becomes zero, and the speed is calculated based on the result and the speed command. In addition, the speed is integrated to calculate the angle, which is used for coordinate transformation. The d-axis current command is set to zero when the weak magnetic control is not performed in the surface magnet type motor. The current control unit 16 performs PI control on the difference between the dq current command and the dq-axis current to generate the dq-axis voltage command.

[0039] The output coordinate conversion unit 17 performs coordinate conversion on the dq axis voltage command to generate a three-phase voltage command. The common connection point of the resistor elements 9a and 9b is connected to the input terminal of the duty cycle calculation unit 18. The duty cycle calculation unit 18 detects the voltage after dividing the voltage of the DC power supply 7, and calculates the duty cycle value of each phase in the PWM control according to the three-phase voltage command and the power supply voltage. The duty cycle value of each phase is input to the gate driver 19. The gate driver 19 generates a gate signal supplied to each semiconductor switch element 5 constituting the inverter 2 as a PWM signal and outputs it.

[0040] If the terminal voltage of the resistor element 10 exceeds the current limiting threshold, the current limiting unit 13 outputs a pulsed current limiting trigger (see Fig. 9 ). If the gate driver 19 is triggered by the input current limit, it cuts off the output of the gate signal from that moment until the end of one cycle of the PWM carrier to prevent a large current from flowing through the motor 1. This state is sometimes called "current limit". Figure 2 As shown, the gate driver 19 includes a basic carrier generation unit 21 , a carrier waveform conversion unit 22 , comparators 23U to 23W, and a energization control unit 24 .

[0041] like Figure 3 As shown, the basic carrier generator 21 has a carrier counter that simply increases, and generates a sawtooth wave as the basic carrier. The carrier waveform converter 22 has a carrier counter that performs subtraction in the first half cycle of the basic carrier and addition in the second half cycle, and generates a triangular wave as the PWM carrier. The trough of the triangular wave becomes the center point for generating the PWM signal of each phase. The comparators 23U~23W compare the PWM carrier waveform data with the duty cycle of each phase, and output the comparison result to the power-on control unit 24. In the power-on control unit 24, the dead time for short-circuit prevention is given to the upper and lower semiconductor switch elements 5, and the gate signal as the PWM signal is output to each semiconductor switch element 5.

[0042] If the current limiting trigger is input from the current limiting unit 13, the power control unit 24 cuts off the output of the gate signal. The basic carrier generation unit 21 has a built-in data latch equivalent to a data holding unit, which holds the count value of the basic carrier at the time of generating the current limiting trigger as the limiting timing OVVDATA and outputs it to the outside. The method of using OVVDATA will be described later. In addition, Figure 3 The detection current shown is an image, and is different from the voltage when the shunt current is detected by the resistor element 10. The gate signal is cut off in the middle of output, which means that the voltage following the voltage command is not output.

[0043] Here, a basic formula for position estimation is shown.

[0044] Ed=Vd-R·Id+ω·Lq·Iq…(1)

[0045] Ed: d-axis induced voltage, Vd: d-axis voltage, Id: d-axis current, Iq: q-axis current, R: winding resistance, ω: (angular) velocity, Lq: q-axis inductance.

[0046] exist Figure 4 as well as Figure 5 , the relationship between the d-axis induced voltage Ed and the estimated axis during position estimation is shown. Figure 4 As shown, when Ed>0, the estimated axis, in other words, the position estimation is ahead of the actual axis, as shown in Figure 5 As shown, when Ed<0, the position estimation is in a delayed state.

[0047] Next, two issues in the case of current limitation are described. The first issue is that the voltage that follows the voltage command is not output. Since the output of the gate signal is cut off midway, it is considered that the amplitude of the d-axis voltage Vd becomes smaller. When the motor 1 is driven, Vd is usually less than 0 and the d-axis induced voltage Ed becomes larger, so it is expected that the position estimation is advanced.

[0048] Figure 6 as well as Figure 7 The effect of simulated current limitation on position estimation is shown. Figure 6 is the position estimation error without current limitation, Figure 7 This is the position estimation error when there is current limitation (= actual position - estimated position). Position estimation starts after 0.5s. Based on the results, it can be confirmed that the position estimation is advanced due to current limitation, and the estimation accuracy is reduced, which is consistent with the above expectation.

[0049] The second problem is that when current limiting occurs, the gate signal is cut off, so the 1-shunt current detection method cannot detect accurate current. Figure 8The gate signal and current detection timing during current limiting are shown. In the 1-shunt current detection method, the current is detected when one or both gate signals are ON; high level. Therefore, if the gate signal is cut off due to current limiting, no current flows through the resistor element 10, the terminal voltage becomes zero, and the accurate current cannot be detected.

[0050] Next, the countermeasures for the above two problems are described. First, the countermeasure for the first problem, that is, the method of correcting the d-axis voltage used in position estimation according to the current limit generation timing, is described. Fig. 9 As shown, according to the timing of the gate signal being cut off and the limiting timing, it is classified into three conditions. Condition (1) is the case where the gate signal is cut off before the gate signal is output, in other words, the gate signal is completely cut off, condition (2) is the case where the gate signal is cut off in the middle of the output, and condition (3) is the case where the gate signal is cut off after the output of the gate signal is completed, in other words, the gate signal is output as is.

[0051] If a current limit generation trigger is generated, the count value of the basic carrier at that moment is held as the limit timing data OVVDATA. OVVDATA can be read out in the next carrier cycle where current limit is generated. The correction value for correcting the voltage of each phase is obtained as follows based on OVVDATA, the start timing START of each phase gate signal, the end timing END of each phase gate signal, and the duty cycle DUTY of each phase for the above three conditions.

[0052] Condition (1): OVVDATA<calibration value at START=0

[0053] Condition (2): START<OVVDATA<END

[0054] Correction value = (OVVDATA - START) / DUTY

[0055] Condition (3): When END<OVVDATA, the correction value=1

[0056] In the figure, conditions (1) to (3) are indicated by circled numbers.

[0057] For example, when DUTY = 0.75, the start timing START becomes 0.125 of the maximum value of the basic carrier. If the current limit generation trigger is generated at a timing of 0.75 of the carrier cycle, it is condition (2) and the correction value is:

[0058] 0.833=(0.75-0.125) / 0.75.

[0059] If DUTY is corrected by the correction value, it is:

[0060] 0.75×0.833≒0.625.

[0061] Next, the d-axis correction voltage used for position estimation is obtained as follows using the correction value of each phase.

[0062] Correction voltage of each phase = duty cycle of each phase × correction value of each phase × power supply voltage…(2)

[0063] α-axis correction voltage = {U-phase correction voltage - (V-phase correction voltage + W-phase correction voltage) /

[0064] 2}×2 / 3…(3)

[0065] β-axis correction voltage = (V-phase correction voltage - W-phase correction voltage) / √3…(4)

[0066] d-axis correction voltage = α-axis correction voltage × COSθ + β-axis correction voltage × SINθ (5)

[0067] As SINθ and COSθ, the values ​​used in the output coordinate conversion unit 15 can be used.

[0068] Next, a method for solving the second problem, that is, a method for calculating the dq axis current used for position estimation using the current limit value and the previous dq axis current, will be described. Fig.10 As shown in FIG. 1 , the occurrence of current limitation means that the motor current amplitude Iamp reaches the current limitation value. Using the current limitation value as the motor current amplitude, the dq axis current correction value used for position estimation is obtained as follows.

[0069] d-axis current correction value = -current limit value × SIN {current phase (previous value)}…(6)

[0070] q-axis current correction value = current limit value × COS {current phase (previous value)} ... (7)

[0071] The current phase (previous value) is obtained as follows.

[0072] Current phase (previous value) = ATAN (d-axis current (previous value) / q-axis current (previous value))

[0073] …(8)

[0074] Here, the current limit value and the previous dq axis current are used, but it is also possible to consider using only the previous dq axis current, or using the dq axis current instruction, the current limit value, the previous dq axis current, and the limit timing as a method of using the dq axis current correction value used in position estimation.

[0075] Fig.11This is a flowchart showing the position estimation process. When current limitation does not occur (S1; N), the current phase (S2) used for correction when current limitation occurs next time is calculated according to equation (8). If current limitation occurs (S1; Y), the correction current (S5) is calculated using equations (6) and (7). Next, the three-phase correction voltage, the 2-axis correction voltage, and the d-axis correction voltage are calculated according to equations (2) to (5) (S6 to S8).

[0076] After executing step S2 or S8, the d-axis induced voltage Ed is obtained according to formula (1), and PI control is performed in such a way that the d-axis induced voltage Ed becomes zero, and the speed is obtained based on the result and the speed command. In addition, the speed is integrated to obtain the angle for position estimation calculation (S3). Then, for the next calibration, the dq-axis current, the three-phase duty ratio, and the sine / cosine values ​​used in the output coordinate axis conversion are stored in a memory equivalent to the current value storage unit, etc. (S4).

[0077] exist Fig.12 as well as Fig.13 2 shows the simulation results when current limitation occurs. Fig.12 In the case of no position estimation correction, Fig.13 This is the case with position estimation correction. In the case without position estimation correction, the rotation stops due to the decrease in position estimation accuracy. In the case with position estimation correction, the drive can be continued while maintaining the position estimation accuracy. Based on the above, it is confirmed that by performing position estimation correction when current limitation occurs, the rotation stop of the motor 1 caused by loss of step can be avoided. In addition, this embodiment can be applied to a motor control microcomputer and a driver IC.

[0078] As described above, according to the present embodiment, the inverter 2 for driving the motor 1 is configured by connecting the three-phase half-bridge circuit 4 composed of a series circuit of a pair of semiconductor switch elements 5 on the positive side and the negative side in parallel, the control unit 11 for generating and outputting an on / off signal for each semiconductor switch element 5 by PWM control, the resistor element 10 as a current detection unit for detecting the current flowing through the inverter 2, the current limiting unit 13 for stopping the operation of the control unit 11 when the current reaches a threshold value, and the position estimation unit 15 for estimating the rotation position of the motor 1 using the motor current and the motor voltage. The position estimation unit 15 corrects the motor voltage used for estimating the rotation position in the carrier cycle of the PWM control in which the operation of the control unit 11 is stopped. Thus, the rotation position of the motor 1 can be estimated with high accuracy even during the period of current limitation.

[0079] In addition, if the detected current exceeds the threshold value, the current limiting unit 13 outputs a trigger signal, and the gate driver 19 holds the count value OVVDATA in the carrier cycle in the PWM control at the time when the trigger signal is output as the current limit generation timing data. In addition, the position estimation unit 15 uses the current limit generation timing data to correct the motor voltage. The current limit generation timing data is output by the gate driver 19 at a timing synchronized with the carrier cycle, in other words, at the next cycle of the carrier cycle in which the trigger signal is output. Therefore, the position estimation unit 15 can grasp at which timing in the carrier cycle the current limit is generated.

[0080] In addition, the position estimation unit 15 determines the correction value of the motor voltage by comparing one or both of the start count value START at the time when the output of each phase PWM signal starts and the end count value END at the time when the output ends with the data OVVDATA. That is, the correction value can be determined according to three conditions according to the output state of each phase gate signal and the timing of the output trigger signal.

[0081] Furthermore, if the data OVVDATA is larger than the count value START and smaller than the count value END, the position estimation unit 15 determines the correction value by dividing the difference between the data OVVDATA and the count value START by the duty cycle predetermined to be output in the cycle. Thus, even in the case of condition (2) where a trigger signal is output during the output of the gate signal, the correction value can be appropriately determined.

[0082] In addition, the resistor element 10 as the current detection unit is a single-shunt resistor disposed in the DC power supply unit, and the position estimation unit 15 uses the current value or current command value stored in the carrier cycle before the operation of the control unit 11 stops in estimating the rotational position. Therefore, even if a period occurs in which the current cannot be detected by the single-shunt current detection method, the rotational position can be estimated with high accuracy.

[0083] (Other embodiments)

[0084] The current detection method is not limited to the 1-shunt method, and may be a 3-shunt method. In this case, the rotation position does not need to be estimated using the stored current value or current command value.

[0085] The PWM signal does not necessarily need to be generated in both directions from the center phase of the carrier cycle.

[0086] The semiconductor switch element is not limited to the N-channel MOSFET.

[0087] Although several embodiments of the present invention have been described, these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the subject matter of the invention. These embodiments and their variations are included in the scope and subject matter of the invention, and are included in the invention described in the claims and the scope of their equivalents.

Claims

1. A motor drive device, comprising: A power conversion circuit is formed by connecting in parallel a plurality of bridge arms formed by series circuits of positive-side and negative-side semiconductor switching elements, and drives the motor; A control unit that generates and outputs an on / off signal for each semiconductor switch element constituting the power conversion circuit through PWM control; a current detection unit for detecting a current flowing through the power conversion circuit; a current limiting unit, which stops the operation of the control unit when the current reaches a threshold value; as well as a position estimating unit that estimates a rotational position of the motor using the motor current and the motor voltage, The position estimating unit corrects the motor voltage used for estimating the rotational position during a carrier cycle of the PWM control in which the operation of the control unit is stopped.

2. The motor drive device according to claim 1, The current limiting unit outputs a trigger signal when the current exceeds the threshold value, The motor drive device includes a data holding unit that holds a count value within a carrier cycle in the PWM control at a time when the trigger signal is output as current limit generation timing data. The position estimating unit corrects the motor voltage using the current limit generation timing data.

3. The motor drive device according to claim 2, The current limit generation timing data is outputted from the data holding unit at a timing synchronized with the carrier cycle.

4. The motor drive device according to claim 3, The current limit generation timing data is outputted from the data holding unit in a cycle next to the carrier cycle in which the trigger signal is outputted.

5. The motor drive device according to claim 4, The position estimation unit determines the correction value of the motor voltage by comparing one or both of a start count value at a time when output of each phase PWM signal starts and a stop count value at a time when the output ends with the current limit generation timing data.

6. The motor drive device according to claim 5, When the current limit generation timing data is larger than the start count value and smaller than the end count value, the position estimation unit determines the correction value by dividing the difference between the current limit generation timing data and the start count value by a duty ratio scheduled to be output in the cycle.

7. The motor drive device according to any one of claims 1 to 6, The current detection unit is a shunt resistor configured in the DC power supply unit. The motor drive device includes a current value storage unit for storing the current value detected by the current detection unit. The position estimating unit uses the current value stored in the carrier cycle before the operation of the control unit stops, in estimating the rotational position.

8. The motor drive device according to any one of claims 1 to 6, The current detection unit is a shunt resistor configured in the DC power supply unit. The motor drive device comprises: a current command value determination unit for current control, which determines the current command value according to a speed command inputted from the outside; and A command value storage unit stores a current command value. The position estimating unit uses the current command value stored in the carrier cycle before the operation of the control unit stops, in estimating the rotational position.

9. A method for driving a motor, wherein the motor is driven via a power conversion circuit, wherein the power conversion circuit is formed by connecting in parallel a plurality of bridge arms formed by series circuits of positive and negative semiconductor switching elements, and when driving the motor, Generate and output an on / off signal for each semiconductor switch element constituting the power conversion circuit through PWM control, detecting a current flowing through the power conversion circuit, When the current reaches the threshold, the output of the conduction cutoff signal is stopped. using the motor current and the motor voltage to infer the rotational position of the motor, In a carrier cycle of the PWM control in which output of the on / off signal is stopped, the motor voltage used for estimating the rotational position is corrected.

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