JP2014230382A - Motor drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor drive device capable of properly driving a motor by surely reading a current flowing to phase coils of the motor without distorting an output current of an inverter and also without varying an effective value of the output current of the inverter.SOLUTION: A current flowing to a motor is detected, a speed of the motor is estimated from the detected current, and a command value is generated of which the level is changed in accordance with a difference between the estimated speed and a target speed and which has the same effective value as the case where there is no correction bias, while including the correction bias required for detecting the current. A pulse width modulation signal based on the command signal is generated as a drive signal for a switching element of an inverter.

Description

  Embodiments described herein relate generally to a motor driving apparatus that drives a permanent magnet synchronous motor.

  There is known a permanent magnet synchronous motor (also referred to as a brushless DC motor) including a stator having a plurality of phase windings and a rotor having a plurality of permanent magnets. The motor drive device that drives the permanent magnet synchronous motor includes an inverter that outputs drive power to the motor, detects the current flowing through each phase winding of the motor, and based on the detected current, the motor speed (rotor speed) ; Angular velocity) is estimated, and so-called sensorless vector control is performed to control switching of the inverter so that the estimated speed becomes the target speed.

  During inverter switching control, a two-phase modulated wave signal for two-phase energization (or a three-phase sine wave signal for three-phase energization) whose level changes according to the difference between the estimated speed and the target speed is generated as a command signal Then, based on the comparison between the level of the command signal and the level of the triangular wave signal (carrier signal), a PWM (Pulse Width Modulation) signal for on / off driving of the switching element of the inverter is generated.

  As the current detecting means, for example, a shunt resistor is provided in the inverter, and a voltage generated in the shunt resistor is subjected to analog / digital conversion (A / D conversion) and read as a current value.

JP 2010-68653 A

  In the single shunt current detection method in which the current of each phase winding is detected by one shunt resistor, when the motor load is low, the ON period of the PWM signal is shortened and the motor current is read in a low current level region. The timing at which the current can be detected is short, the time for A / D conversion sampling and A / D conversion for reading the current value cannot be secured, and as a result, a period in which the motor current cannot be detected occurs. If the current value cannot be read, it is difficult to drive the motor properly.

  As a countermeasure, a constant correction bias is added to the command signal so as to lengthen the ON period of the PWM signal. However, if this is done, distortion occurs in the output current of the inverter or the effective value of the output current of the inverter fluctuates. There is a problem of end up.

  An object of an embodiment of the present invention is to read the current flowing through each phase winding of the motor without causing distortion in the output current of the inverter and without changing the effective value of the output current of the inverter. It is providing the motor drive device which can drive appropriately.

  The motor drive apparatus according to claim 1 includes an inverter and a control unit. The inverter has a plurality of switching elements, and outputs driving power to the motor when these switching elements are turned on and off. The control unit detects the current flowing through the motor, estimates the speed of the motor from the detected current, the level changes according to the difference between the estimated speed and the target speed, and correction necessary for detecting the current A command signal having the same effective value as that in the case of including the bias but without the correction bias is generated, and a pulse width modulation signal based on the command signal is generated as a drive signal for the switching element.

The figure which shows the structure of the control circuit of 1st Embodiment. The figure which shows the waveform of the 1st command signal (two-phase modulated wave signal) in 1st Embodiment. The figure which shows the waveform of the PWM signal obtained by the comparison with the 1st command signal and triangular wave signal of 1st Embodiment, and the electric current which flows through a bus-line. The figure which shows the waveform of the 2nd command signal (two-phase modulated wave signal) in 1st Embodiment in contrast with the waveform of a 1st command signal. The figure which shows the waveform of the PWM signal and bus current which are obtained by the comparison with the 2nd command signal and triangular wave signal of 1st Embodiment. The figure for demonstrating how to obtain | require the correction gain in 1st Embodiment. The figure which shows the waveform of the command signal when the 1st and 2nd command signal in 1st Embodiment is a three-phase sine wave signal as a modification. The figure which shows the structure of the control circuit of 2nd Embodiment. The figure which shows the waveform of the 1st command signal (three-phase sine wave signal) in 2nd Embodiment.

[1] A first embodiment will be described below with reference to the drawings.
As shown in FIG. 1, an AC voltage of a commercial AC power supply 1 is converted into a DC voltage by a rectifier circuit 4 including a diode bridge 2 and a smoothing capacitor 3. The DC voltage is converted into an AC voltage having a predetermined frequency by switching of the switching circuit 10, and the AC voltage is supplied to the permanent magnet synchronous motor 20 as driving power. The rectifier circuit 4 and the switching circuit 10 constitute an inverter.

  The switching circuit 10 includes a series circuit of a pair of U-phase switching elements 11a and 11b that are in an upstream and downstream relationship along a DC voltage application direction, and an upstream side and a downstream side along a DC voltage application direction. A series circuit of a pair of switching elements 12a, 12b for V-phase that has the relationship of, and a series circuit of a pair of switching elements 13a, 13b for W-phase that have an upstream and downstream relationship along the direction in which the DC voltage is applied The interconnection point of each switching element in these series circuits is an output terminal. A shunt resistor 14 is inserted and connected as a current detecting means to the bus line (negative line) of the switching circuit 10. As the switching element, for example, MOSFET or IGBT is used.

  The permanent magnet synchronous motor 20 includes an input terminal 21, a stator (armature) 22 having a plurality of phase windings Lu, Lv, and Lw, and a rotor (rotor) 23 in which a plurality of, for example, four permanent magnets are embedded as four poles. . One end of each of the phase windings Lu, Lv, Lw is connected to the three output terminals of the switching circuit 10 via the input terminal 21, and the other end of the phase windings Lu, Lv, Lw is interconnected as a neutral point. .

  The position of the rotor 23 can be represented by a position of 0 degrees to 360 degrees (= 0 degrees) of the electrical angle reference or the first to sixth sections of the space vector. A position with an electrical angle of 90 to 150 degrees corresponds to the first section (0 to 60 degrees) of the space vector. The position of the electrical angle of 150 degrees to 210 degrees corresponds to the second section (60 degrees to 120 degrees) of the space vector. The position of electrical angle 210 degrees to 270 degrees corresponds to the third section (120 degrees to 180 degrees) of the space vector. The position of electrical angle 270 to 330 degrees corresponds to the fourth section (180 to 240 degrees) of the space vector. The electrical angle of 330 to 30 degrees corresponds to the fifth section (240 to 300 degrees) of the space vector. The position of the electrical angle of 30 degrees to 90 degrees corresponds to the sixth section (300 degrees to 360 degrees) of the space vector.

  The sensorless vector control unit 30 detects the current flowing through the phase windings Lu, Lv, Lw of the permanent magnet synchronous motor 20 from the voltage generated in the shunt resistor 14, and based on the detected current, the speed of the permanent magnet synchronous motor 20 ( Rotor speed (angular speed) is estimated, and so-called sensorless vector control is performed to control switching of the switching circuit 10 so that the estimated speed becomes a target speed. The current detection unit 31, the speed estimation unit 32, and the speed control unit 33 , A PWM signal generator 34 is provided.

  The current detection unit 31 detects the current (bus current) flowing through the phase windings Lu, Lv, and Lw by reading the voltage generated in the shunt resistor 14 by analog / digital conversion (A / D conversion).

  The speed estimation unit 32 estimates the speed (rotor speed; angular speed) of the permanent magnet synchronous motor 20 by calculation based on the current detected by the current detection unit 31.

The speed control unit 33 includes the following means (1) to (3) as main functions.
(1) A determination unit that determines whether the load of the permanent magnet synchronous motor 20 is greater than or equal to a predetermined value or less than a predetermined value from the detected current of the current detection unit 31.

  (2) When the determination result of the determination means is equal to or greater than a predetermined value, the frequency changes according to the detection current of the current detection unit 31, and the difference between the estimated speed of the speed estimation unit 32 and the target speed input from the outside First generation means for generating first command signals I1u, I1v, I1w whose levels change in response.

  (3) When the determination result of the determination means is less than a predetermined value, the frequency changes according to the current detected by the current detector 31 and the level depends on the difference between the estimated speed of the speed estimator 32 and the target speed. A second generation that generates second command signals I2u, I2v, and I2w having the same effective value as the case where the correction bias Ibias necessary for current detection of the current detection unit 31 is included on the low level side and there is no correction bias. means. The second command signals I2u, I2v, I2w are predetermined in consideration of conditions for adding the correction bias Ibias to the first command signals I1u, I1v, I1w and having the same effective value as before adding the correction bias Ibias. Can be obtained by correcting with the correction gain Gain_hosei (= I2 / I1). Note that I1 is a maximum value of the inverter output based on the first command signals I1u, I1v, I1w, and I2 is a correction bias Ibias that is a fixed value from the maximum value of the inverter output based on the second command signals I2u, I2v, I2w. It represents the value after subtraction.

  The PWM signal generation unit 34 uses a pulse width modulation based on a comparison between the level of the first or second command signal generated by the speed control unit 33 and the level of the triangular wave signal (carrier signal) to generate a switching circuit. Pulse width modulation signals (referred to as PWM signals) for on / off driving for each of the ten switching elements are generated.

  The operation will be described.

  When the load of the permanent magnet synchronous motor 20 is equal to or greater than a predetermined value, the speed control unit 33 changes the frequency according to the detection current of the current detection unit 31 and the estimated speed of the speed estimation unit 32 and the target speed input from the outside. The first command signals (two-phase modulated wave signals) I1u, I1v, and I1w that change in level according to the difference are generated.

  The first command signals I1u, I1v, and I1w are obtained by modulating a three-phase sine wave signal. As shown in FIG. 2, 1/3 of the period (= 2π) of the three-phase sine wave signal (= A period corresponding to 2π / 3) has a waveform that maintains a zero level as a switching pause period, and is a signal whose phase angle is shifted by 120 degrees.

  As shown in FIG. 3, the PWM signal generation unit 34 performs each of the switching circuit 10 by pulse width modulation based on a comparison between the levels of the first command signals I1u, I1v, I1w and the level of the triangular wave signal (carrier signal) Io. A U-phase PWM signal, a V-phase PWM signal, and a W-phase PWM signal for on / off driving of the switching element are generated.

  In response to these PWM signals, the switching elements of the switching circuit 10 are turned on and off. Thereby, a current flows through the phase windings Lu, Lv, Lw of the permanent magnet synchronous motor 20. This current passes through the shunt resistor 14 of the switching circuit 10, and a voltage is generated in the shunt resistor 14.

  The current detector 31 detects the current (bus current) flowing through the phase windings Lu, Lv, Lw by A / D converting and reading the voltage generated in the shunt resistor 14. In this case, as indicated by a broken line in FIG. 3, the A / D conversion (processing time tx) for current detection sufficiently follows the change in the current level. Therefore, the current flowing through the phase windings Lu, Lv, Lw can be reliably detected.

  However, in the case of the one shunt current detection method in which the current of the phase windings Lu, Lv, and Lw is detected by one shunt resistor 14, when the load of the permanent magnet synchronous motor 20 is less than a predetermined value, the current level is low (see FIG. 2), that is, the position at an electrical angle of 90 degrees (the boundary between the sixth section and the first section of the space vector), the position at the electrical angle of 210 degrees (the boundary between the second section and the third section of the space vector), At the position of the electrical angle of 330 degrees (the boundary between the second section and the third section of the space vector), the A / D conversion for current detection cannot follow the change in the current level, and the current value cannot be read. If reading is not possible, it becomes difficult to drive the motor properly.

  Therefore, when the load of the permanent magnet synchronous motor 20 is low and less than the predetermined value, the speed control unit 33 changes the frequency according to the detection current of the current detection unit 31 and inputs the estimated speed of the speed estimation unit 32 from the outside. The second command having the same effective value as the state in which the level changes according to the difference from the target speed and the correction bias Ibias necessary for the current detection of the current detection unit 31 is included on the low level side but the correction bias Ibias is not present. Signals (two-phase modulated wave signals) I2u, I2v, and I2w are generated.

  The second command signals I2u, I2v, and I2w are corrected with a predetermined correction gain Gain_hosei (= I2 / I1) that adds the correction bias Ibias to the first command signals I1u, I1v, and I1w and considers the same effective value condition. As shown in FIG. 4, a region having a low current level (a region indicated by dots), that is, a position at an electrical angle of 90 degrees (a boundary between the sixth section and the first section of the space vector) and an electrical angle 210. Correction bias Ibias was added on the low level side at the position of degrees (boundary between the second section and the third section of the space vector) and the position of electrical angle 330 degrees (boundary between the second section and the third section of the space vector) Has a waveform. The waveforms of the second command signals I2u, I2v, I2w are such that the upper limit level is lower than the upper limit level of the first command signals I1u, I1v, I1w, and the lower limit level is the lower limit level of the first command signals I1u, I1v, I1w. Higher than.

  As shown in FIG. 5, the PWM signal generation unit 34 performs each of the switching circuit 10 by pulse width modulation based on a comparison between the level of the second command signals I2u, I2v, I2w and the level of the triangular wave signal (carrier signal) Io. A U-phase PWM signal, a V-phase PWM signal, and a W-phase PWM signal for on / off driving of the switching element are generated.

  In response to these PWM signals, the switching elements of the switching circuit 10 are turned on and off. Thereby, a current flows through the phase windings Lu, Lv, Lw of the permanent magnet synchronous motor 20. This current passes through the shunt resistor 14 of the switching circuit 10, and a voltage is generated in the shunt resistor 14.

  In this case, since the PWM signal is generated by the second command signals I2u, I2v, and I2w including the correction bias Ibias on the low level side, even if the load of the permanent magnet synchronous motor 20 is as low as less than a predetermined value, the current The A / D conversion (processing time tx) for detecting the current of the detection unit 31 can sufficiently follow the change in the current level as indicated by a broken line in FIG. Therefore, the current flowing through the phase windings Lu, Lv, Lw can be reliably detected, and the permanent magnet synchronous motor 20 can be driven appropriately.

  The value of the correction bias Ibias is, for example, 10% to 20% of the amplitude of the first command signals I1u, I1v, I1w, and the current detection unit 31 performs A / D conversion (processing time tx) for current detection. A value that can sufficiently follow the level change is selected after checking in advance.

  In addition, since the second command signals I2u, I2v, I2w have the same effective value as the first command signals I1u, I1v, I1w without the correction bias Ibias, even if the correction bias Ibias is added, The output current is not distorted, and the effective value of the output current of the switching circuit 10 is not changed. Since distortion does not occur in the output current, generation of unpleasant periodic sounds can be avoided. Although the upper limit levels of the second command signals I2u, I2v, and I2w are lower than the upper limit levels of the first command signals I1u, I1v, and I1w, since the effective values are the same, the motor drive performance is not deteriorated.

  One of the correction gain Gain_hosei and the correction bias Ibias is determined in advance, and as shown in FIG. 6, the effective value and the correction bias Ibias for one cycle of the first command signal to be output by the original inverter are obtained. In addition, the other is calculated so that the effective value of the newly generated second command signal is the same.

  Although the case where the first and second command signals are two-phase modulated wave signals has been described as an example, the case where the first and second command signals are three-phase sine wave signals shown in FIG.

  Here, how to obtain the correction gain Gain_hosei or the correction bias Ibias will be described.

  (1) In the case where the command signal is a two-phase modulated wave signal, the electrical angle of 90 degrees to 210 degrees is considered as a representative.

  (1-a) When determining the correction bias Ibias after determining the correction gain Gain_hosei (= I2 / I1) first; I1 is determined by the value to be output from the inverter when the first command signal is generated . The output of the inverter based on the signal obtained by subtracting the correction bias Ibias from the first command signal and the second command signal is assumed to be a sine wave.

The effective values (left side) of the first command signals I1u, I1v, I1w without the correction bias Ibias are set equal to the effective values (right side) of the second command signals I2u, I2v, I2w with the correction bias Ibias added.

Next, square both sides of the above equation and expand and arrange them using the addition theorem.

When the left side of the formula 2 is expanded, the following is obtained. In the following formulas, the capital letter “C” represents an integral constant.

Similarly, the right side of Equation 2 is

Incorporating Equation 3 and Equation 4 on both sides and moving the left side to the right side,

The coefficients a, b, c in the quadratic equation of the correction bias Ibias shown in the last equation of Formula 5 are

When Equation 5 is solved by a quadratic equation formula, Ibias is obtained from the condition that the correction bias Ibias> 0. Here, since the correction gain Gain_hosei (= I2 / I1) is determined in advance, the correction bias Ibias can be obtained by calculating each coefficient of the equation (6).

The formulas used when transforming each mathematical formula are shown below.

(1-b) When the correction gain Gain_hosei (= I2 / I1) is obtained after the correction bias Ibias is determined first; both sides of the formula 5 are divided by the square of I1.

Since the last equation of Equation 9 is a quadratic equation of the correction gain Gain_hosei (I2 / I1), the correction gain Gain_hosei is as follows from the formula of the solution of the quadratic equation and Gain_hosei> 0. Here, the coefficients of the quadratic equation (I2 / I1) are a, b, and c.

  (2) Subsequently, the relationship between the correction bias Ibias and the correction gain Gain_hosei (= I2 / I1) when the original command signal, that is, the first command signal I1 to which the correction bias Ibias is not added is a three-phase sine wave signal. To consider.

(2-a) The effective value (left side) of the first command signals I1u, I1v, I1w without the correction bias Ibias, and the effective value (right side) of the second command signals I2u, I2v, I2w with the correction bias Ibias added Are equal. The correction bias Ibias is for raising the waveform in both positive and negative directions, and is added so that the first command signal I1 is + in the positive range and-in the negative range.

Next, square both sides of the above formula and make them equal.

Here, the left side of the equation (12) is

Next, the first term on the right side is

Also, the two terms on the right side are

Since the right side = 1 term on the right side + 2 terms on the right side,

Since the right side = left side,

It becomes. Subsequently, the correction gain Gain_hosei (= I2 / I1) or the correction bias Ibias is obtained using the above equation.

(2-b) When determining the correction bias Ibias after determining the correction gain Gain_hosei (= I2 / I1) first;
When the above equation is arranged by the correction bias Ibias, the quadratic equation of the correction bias Ibias shown in the following equation is obtained.

The correction bias Ibias is as follows from the formula of the solution of the quadratic equation.

From the condition of Ibias> 0, Ibias is determined by the following equation.

(2-c) When determining the correction gain Gain_hosei (= I2 / I1) after determining the correction bias Ibias first; dividing both sides of the first expression of Equation 18 by the square of I2,

If each coefficient a, b, c is

The correction gain Gain_hosei is expressed by the following equation based on the formula of the solution of the quadratic equation and the condition of the correction gain Gain_hosei> 0.

  As described above, the correction bias Ibias in which the effective value when the correction bias Ibias is not added and the effective value when the correction bias Ibias is added is the same regardless of which of the three-phase modulation and the two-phase modulation methods is used. And the correction gain Gain_hosei. Accordingly, if one of the necessary correction bias Ibias and the correction gain Gain_hosei is determined, the other can be calculated.

  [2] A second embodiment will be described.

  In this embodiment, a shunt resistor for current detection is provided for each winding of the motor. As shown in FIG. 8, in the switching circuit 10, a shunt resistor 14u is inserted and connected as a current detecting means between the series circuit of the U-phase switching elements 11a and 11b and the bus (negative side line). A shunt resistor 14v is inserted and connected as a current detecting means between the connection of the series circuit of switching elements 12a and 12b and the bus (negative line), and the series circuit of the W-phase switching elements 13a and 13b and the bus (negative) The shunt resistor 14w is inserted and connected as a current detecting means between the connection to the side line).

  The current detection unit 31 reads the voltages generated in the shunt resistors 14u, 14v, and 14w by analog / digital conversion (A / D conversion), respectively, thereby reading currents (bus currents) flowing through the phase windings Lu, Lv, and Lw. Detect each.

The speed control unit 33 includes the following means (11) to (13) as main functions.
(11) A determination unit that determines from the detected current of the current detection unit 31 whether the load of the permanent magnet synchronous motor 20 is greater than or equal to a predetermined value.

  (12) When the determination result of the determination means is less than the predetermined value, the frequency changes according to the detection current of the current detection unit 31, and the difference between the estimated speed of the speed estimation unit 32 and the target speed input from the outside First generation means for generating first command signals I1u, I1v, I1w whose levels change in response.

  (13) When the determination result of the determination means is equal to or greater than a predetermined value, the frequency changes according to the detection current of the current detection unit 31, and the level changes according to the difference between the estimated speed of the speed estimation unit 32 and the target speed. A second generation that generates second command signals I2u, I2v, and I2w having the same effective value as the case where the correction bias Ibias necessary for current detection of the current detection unit 31 is included on the low level side and there is no correction bias. means. The second command signals I2u, I2v and I2w can be obtained by correcting the first command signals I1u, I1v and I1w with a predetermined correction gain Gain_hosei (= I2 / I1).

  Other configurations are the same as those of the first embodiment.

  The operation will be described.

  When the load of the permanent magnet synchronous motor 20 is as low as less than a predetermined value, the speed controller 33 changes the frequency according to the detected current of the current detector 31 and the estimated speed of the speed estimator 32 and the target input from the outside. First command signals (three-phase sine wave signals) I1u, I1v, and I1w whose levels change according to the difference from the speed are generated. The waveforms of the first command signals I1u, I1v, I1w are shown in FIG.

  In the three-shunt current detection method in which the currents of the phase windings Lu, Lv, and Lw are detected by a plurality of shunt resistors 14u, 14v, and 14w, when the load of the permanent magnet synchronous motor 20 is equal to or greater than a predetermined value, In each of the negative high areas (areas indicated by dots in FIG. 9), A / D conversion for current detection cannot follow the change in the current level, and the current value cannot be read.

  Therefore, when the load of the permanent magnet synchronous motor 20 is as high as a predetermined value or higher, the speed control unit 33 changes the frequency according to the detection current of the current detection unit 31 and inputs the estimated speed of the speed estimation unit 32 from the outside. The level changes according to the difference from the target speed and the correction bias Ibias necessary for the current detection of the current detection unit 31 is included on the higher side of the positive level and the negative level, but the correction bias Ibias is not present. Second command signals (three-phase modulated wave signals) I2u, I2v, and I2w having the same effective value are generated.

  Specifically, the second command signals I2u, I2v, and I2w are obtained by correcting the first command signals I1u, I1v, and I1w with a predetermined correction gain Gain_hosei (= I2 / I1).

  As described above, since the PWM signal is generated by the second command signals I2u, I2v, and I2w including the correction bias Ibias, even if the load of the permanent magnet synchronous motor 20 is high as a predetermined value or higher, the current detection unit 31 The A / D conversion (processing time tx) for current detection sufficiently follows the change in the current level. Therefore, the current flowing through the phase windings Lu, Lv, Lw can be reliably detected, and the permanent magnet synchronous motor 20 can be driven appropriately.

  In addition, since the second command signals I2u, I2v, I2w have the same effective value as the first command signals I1u, I1v, I1w without the correction bias Ibias, even if the correction bias Ibias is added, The output current is not distorted, and the effective value of the output current of the switching circuit 10 is not changed.

  In addition, although the case where the first and second command signals are three-phase sine wave signals has been described as an example, the case where the first and second command signals are two-phase modulated wave signals can be similarly implemented.

[Modification]
In the above embodiment and the modification, the motor speed is estimated from the current flowing through the motor, and the command signal whose level changes according to the difference between the estimated speed and the target speed is generated. The command signal may be generated in consideration of not only the difference between the estimated speed and the target speed but also the magnitude of the target speed.

  Moreover, the said embodiment and modification are shown as an example and are not intending limiting the range of invention. These novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the spirit of the invention. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalent scope thereof.

  DESCRIPTION OF SYMBOLS 1 ... Commercial AC power source, 2 ... Diode bridge, 3 ... Smoothing capacitor, 4 ... Rectifier circuit, 10 ... Switching circuit, 11a, 11b, 12a, 12b, 13a, 13b ... Switching element), 20 ... Permanent magnet synchronous motor, 21 ... input terminal, 22 ... stator, Lu, Lv, Lw ... phase winding, 23 ... rotor, 23a ... rotor shaft, M1, M2 ... permanent magnet, 31,32,33 ... current sensor, 40 ... control unit, 41 ... Main control unit, 42 ... storage unit, 50 ... sensorless vector control unit, 51 ... current detection unit, 52 ... speed estimation calculation unit, 53 ... integration unit, 54 ... subtraction unit, 55 ... speed control unit, 56 ... calculation unit , 57, 58..., Subtraction unit, 61... Current control unit, 62... Current control unit, 63.

Claims (5)

An inverter that has a plurality of switching elements, and outputs driving power to the motor by turning these switching elements on and off;
The current flowing through the motor is detected, the speed of the motor is estimated from the detected current, the level changes according to the difference between the estimated speed and the target speed, and the correction bias necessary for detecting the current is included. A control unit that generates a command signal having the same effective value as that without the correction bias, and generates a pulse width modulation signal based on the command signal as a drive signal for the switching element;
A motor drive device comprising: The control unit corrects a command signal whose level changes according to a difference between the estimated speed and the target speed and does not include the correction bias with a predetermined correction gain, thereby obtaining the estimated speed and the target speed. Generating a command signal having the same effective value as that in the case where the level changes according to the difference and includes the correction bias necessary for the detection of the current but without the correction bias.
The motor driving apparatus according to claim 1. The control unit calculates the correction gain based on an effective value of the generated command signal or an effective value of the detected current.
The motor driving apparatus according to claim 2, wherein One shunt resistor provided in the inverter;
The control unit detects a current flowing through the motor from a voltage generated in the shunt resistor, estimates a speed of the motor from the detected current, and when the load of the motor is equal to or greater than a predetermined value, the estimated speed and the target Generating a first command signal whose level changes according to the difference from the speed, and when the load of the motor is less than the predetermined value, the level changes according to the difference between the estimated speed and the target speed; and A second command signal having the same effective value as that in the case where the correction bias necessary for detecting the current is included on the low level side and there is no correction bias is generated, and a pulse width modulation signal based on the first or second command signal is generated. Generating a drive signal for the switching element;
The motor driving apparatus according to claim 1. A plurality of shunt resistors provided in the inverter;
The control unit detects a current flowing through the motor from a voltage generated in each shunt resistor, estimates a speed of the motor from the detected current, and when the load of the motor is less than a predetermined value, the estimated speed and the A first command signal whose level changes according to a difference from a target speed is generated, and when the load of the motor is equal to or greater than the predetermined value, the level changes according to the difference between the estimated speed and the target speed, and the A second command signal having the same effective value as that in the case where the correction bias necessary for detecting the current is included on the high level side but without the correction bias is generated, and a pulse width modulation signal based on the first or second command signal is generated. Generating a drive signal for the switching element;
The motor driving apparatus according to claim 1.

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