JP2008160915A - Inverter controller for driving motor and apparatus employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter controller for driving a motor satisfactorily by reducing impact of ambient temperature variation thereby enhancing precision in detecting a phase current of the motor. <P>SOLUTION: In an inverter for driving a motor by inverting a DC voltage into an AC three-phase voltage, offset voltage of a DC current detector outputting a voltage according to a current flowing through an inverter bus is regulated when all the PWM signals for controlling the upper arm switching elements of an inverter are entirely turned on or off during driving of the motor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vector control inverter device for an induction motor and a DC motor provided with an inverter circuit, and more specifically to a method for detecting a motor current in the device.

  In an inverter control apparatus for driving a motor that performs variable speed driving such as an AC motor, an output waveform whose pulse width is modulated to reduce harmonics is generally used. FIG. 12 shows a conventional inverter control device for driving a motor using a pulse width modulation system. The inverter 2 generates and outputs a drive voltage to be supplied to the DC power source 1 and the brushless motor 3, and a control unit 19 that controls the inverter 2 is provided. Have.

  The DC current detector 11 detects a DC current flowing through the inverter bus, and the phase current conversion unit 7 detects each of the DC current detected by the DC current detector 11 and the PWM signal output by the PWM signal generation unit 9. From the phase duty, a U-phase motor current Iu, a V-phase motor current Iv, and a W-phase motor current Iw flowing through the motor 3 are detected.

  Based on the detected motor currents Iu, Iv, and Iw and a speed command ω * given from the outside, the PWM signal generation unit 9 generates a PWM signal for controlling the inverter 2.

  FIG. 13 shows the PWM signal (only the upper arm of the inverter 2) output from the PWM signal generator 9, the motor applied voltage generated thereby, and the current of each phase flowing through the motor.

  FIG. 14 shows details of the period T in FIG. Upper arm U phase switching element control signal, upper arm V phase switching element control signal, upper arm W phase switching element control signal, lower arm U phase switching element control signal, lower arm V phase switching element control signal, lower arm W A phase switching element control signal and a direct current flowing through the inverter bus. A phase current of the motor appears on the inverter bus and is converted into motor currents Iu, Iv, and Iw in the phase current converter 7 using the duty information of the PWM signal output from the PWM signal generator 9.

A method for obtaining the motor currents Iu, Iv, Iw from the current flowing through the inverter bus is described in detail in Patent Document 1.
Japanese Patent No. 2712470

  Usually, in the system configuration as shown in FIG. 12, most of the direct current flowing through the direct current detector 11 flows in the direction from the inverter side to the direct current power supply side. However, when the inductance component of the motor 3 is large, the direct current is applied. A phenomenon occurs in which the phase of the current flows with respect to the voltage, and in such a case, depending on the output timing of the PWM signal, the direction of the direct current flowing through the direct current detector 11 may change from the direct current power supply side to the inverter side.

  In order to drive the motor 3 by vector control, instantaneous and accurate motor current detection is indispensable, and assuming the above-described state, the DC current detector 11 must be capable of detecting bidirectional current.

  When the bidirectional current detection value is output by the DC current detector 11, an offset voltage is applied when the detected current value is zero, and if a current flows in the forward direction, a voltage greater than the offset voltage is set according to the magnitude. If a current flows in the opposite direction, a device or circuit that outputs a voltage smaller than the offset voltage in a linear line is used according to the magnitude of the current.In calculating the detected current value, the difference from the offset voltage is used. A method of multiplying the conversion coefficient after obtaining is used.

  However, the output value of the offset voltage varies depending on the temperature due to the characteristics of the devices and components in the circuit. For this reason, if the offset voltage when the phase current is not flowing, such as when the motor is stopped, is used for the current value calculation, when the motor 3 is continuously driven for a long time, an error occurs in the detected current value as the ambient temperature changes. As a result, the driving performance of the motor 3 is deteriorated.

  The present invention solves such a conventional problem, and reduces the influence of changes in ambient temperature to improve the detection accuracy of the phase current of the motor, thereby enabling a motor drive inverter capable of good motor drive. An object is to provide a control device.

  In order to solve the above problems, an inverter control apparatus for driving a motor of the present invention has an upper arm switching element and a lower arm switching element corresponding to each phase of phase current, and converts DC power into three-phase AC power. When an inverter, a PWM signal generation unit that generates a PWM signal for driving the inverter, and a voltage corresponding to the magnitude of the current flowing through the bus of the inverter are output, and no current appears on the bus of the inverter A DC current detector that outputs an offset voltage, a first timing that receives the PWM signal, and that the upper arm switching elements of the inverter are all off or all on, and a second timing that a phase current flows through the bus of the inverter And a data acquisition unit for sampling the output voltage of the DC detector, and the data acquisition unit A phase current converter that reproduces the phase current while adjusting the offset voltage based on a sampled voltage, and a drive circuit that drives the upper arm switching element and the lower arm switching element according to the PWM signal. Is.

  An object of the present invention is to maintain a good motor drive by reducing a detection error of a motor phase current due to a change in ambient temperature.

  The inverter control device for motor drive according to the present invention reduces the detection error of the motor phase current by periodically adjusting the offset voltage in the DC current detector while the motor is driven even when the ambient temperature changes. As a result, good motor drive can be maintained.

A first invention includes an upper arm switching element and a lower arm switching element corresponding to each phase of a phase current, an inverter that converts DC power into three-phase AC power, and a PWM signal for driving the inverter A PWM signal generator for generating, a DC current detector for outputting a voltage corresponding to the magnitude of the current flowing through the bus of the inverter, and outputting an offset voltage when no current appears on the bus of the inverter; and the PWM Data that receives the signal and samples the output voltage of the DC detector at the first timing when all the upper arm switching elements of the inverter are all off or on and the second timing when the phase current flows through the bus of the inverter The offset voltage is adjusted based on the voltage sampled by the acquisition unit and the data acquisition unit. Said phase current phase current converting portion to reproduce while, in which a drive circuit for driving the upper arm switching element and lower arm switching elements in response to the PWM signal.

  As a result, even when the ambient temperature changes, it is possible to reduce the detection error of the motor phase current by adjusting the offset voltage in the DC current detector periodically during motor driving. It is possible to maintain a stable motor drive.

  According to a second aspect of the invention, in particular, in the first aspect of the invention, the data acquisition unit sets a sampling period for sampling the output voltage of the DC detector at the first timing from a sampling period at the second timing. Is also set longer. Thereby, the processing time can be shortened.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of the motor drive inverter control apparatus according to the first embodiment of the present invention. The motor drive inverter control device includes a DC power source 1, an inverter 2 that generates and outputs a drive voltage to be supplied to the brushless motor 3, and a control unit 6 that controls the inverter 2.

  The brushless motor 3 includes a stator 4 to which three-phase windings 4u, 4v, 4w Y-connected around a neutral point are attached, and a rotor 5 to which a magnet is attached. The U-phase terminal 8u is connected to the non-connected end of the U-phase winding 4u, the V-phase terminal 8v is connected to the non-connected end of the V-phase winding 4v, and the W-phase terminal 8w is connected to the non-connected end of the W-phase winding 4w. Has been.

  The inverter 2 has a half-bridge circuit composed of a pair of switching elements for three phases for the U phase, the V phase, and the W phase. The pair of switching elements of the half-bridge circuit are connected in series between the high-voltage side end and the low-voltage side end of the DC power supply 1, and a DC voltage output from the DC power supply 1 is applied to the half-bridge circuit.

  The U-phase half-bridge circuit includes a switching element 12u on the high voltage side (upper arm) and a switching element 12x on the low voltage side (lower arm). The V-phase half-bridge circuit includes a high-voltage side switching element 12v and a low-voltage side switching element 12y. The W-phase half-bridge circuit includes a high-voltage side switching element 12w and a low-voltage side switching element 12z. In addition, free wheel diodes 14u, 14v, 14w, 14x, 14y, and 14z are connected in parallel with the respective switching elements.

  Terminals 8u, 8v, and 8w of the brushless motor 3 are connected to an interconnection point between the switching element 12u and the switching element 12x in the inverter 2, an interconnection point between the switching element 12v and the switching element 12y, and an interconnection point between the switching element 12w and the switching element 12z. Are connected to each other.

  The DC power applied to the inverter 2 is converted into three-phase AC power by the switching operation of the switching element in the inverter 2 described above, and the brushless motor 3 is thereby driven. A DC current detector 11 is provided on the bus of the inverter 2.

  The control unit 6 includes a PWM signal generation unit 9, a base driver 10, a phase current conversion unit 7, a data acquisition unit 15, a phase estimation unit 17, and a rotor speed estimation unit 18.

  The PWM signal generation unit 9 drives each switching element of the inverter 2 in order to output an output voltage obtained by calculation from an error between the current speed and the target speed in order to realize a target speed given from the outside. PWM signal is generated. The generated PWM signal is converted by the base driver 10 into a drive signal for electrically driving the switching element. Each switching element operates in accordance with the drive signal.

  The data acquisition unit 15 acquires data of the current flowing through the DC current detector 11 (hereinafter referred to as “inverter bus current”), and the phase current conversion unit 7 converts the result into the phase current of the brushless motor 3. The phase current converter 7 actually detects the current only for a predetermined period from when the inverter bus current changes.

  The phase estimation unit 17 outputs the phase current of the brushless motor 3 converted by the phase current conversion unit 7, the output voltage calculated by the PWM signal generation unit 9, and the inverter 2 detected by the inverter input voltage detection unit 16. The phase of the brushless motor 3 is estimated based on the information on the applied voltage.

  Further, the rotor speed estimation unit 18 estimates the speed of the brushless motor 3 from the estimated phase. Based on the information on the estimated rotor magnetic pole position, the PWM signal generator 9 generates a PWM signal for driving the brushless motor 3. At that time, the PWM signal generation unit 9 controls the PWM signal so that the rotor speed becomes the target speed based on deviation information between the estimated speed of the rotor 5 and the target speed given from the outside.

  In order to realize the target speed ω *, the PWM signal generation unit 9 calculates the voltage V * to be output by PI calculation or the like based on the difference Δω between the target speed ω * and the estimated speed ωm. From the voltage value V *, a voltage V * s to be output to each phase (s represents a phase u, v, or w) is obtained.

  Further, the PWM signal for each switching element for outputting the obtained voltage V * s is output to the base driver 10. Each switching element is driven according to a respective PWM signal to generate sinusoidal AC power.

  Thus, in the present embodiment, the sine wave drive of the brushless motor 3 is realized by flowing a sine wave phase current.

  The control unit 6 includes an AD conversion function for acquiring a voltage value as digital data, and a DA conversion function for outputting a gate pulse signal of a switching element based on a PWM signal that is digital data. All the functions are realized by a one-chip system LSI having a microprocessor and a memory.

  Here, the state where the phase current of the brushless motor 3 appears in the current flowing through the inverter bus will be described with reference to FIGS.

  FIG. 2 shows the state of the phase current flowing in each phase winding of the brushless motor 3 (FIG. 2A) and the direction of the current flowing in each phase winding in each section of the electrical angle every 60 °. It is a figure (FIG.2 (b)-(g)). Referring to FIG. 2, in the section where the electrical angle is 0 to 60 °, the U-phase winding 4u and the W-phase winding 4w are neutral from the unconnected end to the neutral point, and the V-phase winding 4v is neutral. Current flows from the point toward the non-connected end (FIG. 2B).

Further, in the section of electrical angle of 60 to 120 °, the U-phase winding 4u is connected from the non-connection end toward the neutral point, and the V-phase winding 4v and the W-phase winding 4w are not connected from the neutral point. A current flows toward the end (FIG. 2C). Hereinafter, in FIGS. 2D to 2G, the state of the phase current flowing through the windings of each phase is changed every 60 ° electrical angle.

  For example, consider a case in FIG. 2 where the PWM signal for one carrier period generated by the PWM signal generator 9 when the electrical angle is 30 ° changes as shown in FIG. In FIG. 3, the signal “U” indicates the upper arm switching element 12u, the signal “V” indicates the upper arm switching element 12v, the signal “W” indicates the upper arm switching element 12w, and the signal “X” indicates the lower arm. The switching element 12x, the signal “Y” indicates the lower arm switching element 12y, and the signal “Z” indicates the signal for operating the lower arm switching element 12z. These signals operate active high.

  In this case, at the timing (1), no current appears on the inverter bus as shown in FIG. 4A, and at the timing (2), the current flows through the W-phase winding 4w as shown in FIG. 4B. (W-phase current) appears, and at timing (3), a current (V-phase current) flowing through the V-phase winding 4v appears as shown in FIG. 4 (c).

  As another example, consider a case where the PWM signal of one carrier cycle generated by the PWM signal generation unit 9 changes as shown in FIG. 5 when the electrical angle is 30 ° in FIG. In this case, as shown in FIG. 6 (a), no current appears in the inverter bus at timing (1), and as shown in FIG. 6 (b), current flowing in the U-phase winding 4u at timing (2) ( U-phase current) appears, and current (V-phase current) flowing through the V-phase winding 4v appears at timing (3) as shown in FIG. 6C.

  As yet another example, consider a case where the PWM signal of one carrier cycle generated by the PWM signal generator 9 changes as shown in FIG. 7 when the electrical angle is 30 ° in FIG. In this case, as shown in FIG. 8 (a), no current appears on the inverter bus at timing (1), and flows to the U-phase winding 4u at timing (2) as shown in FIG. 8 (b). Current (U-phase current) appears, and as shown in FIG. 8C, the current (W-phase current) flowing through the W-phase winding 4w at the timing (3) is different from the DC power supply side to the inverter side. Appears in the direction.

  As described above, if the phase current of the brushless motor 3 appears on the inverter bus in accordance with the state of each switching element of the inverter 2, the current for two phases can be determined at close timing within one carrier cycle. The currents iu, iv, and iw of the three phases are obtained from the relationship of the following formula (1).

iu + iv + iw = 0 (1)
Timing (4) and timing (5) are dead time periods for preventing the inverter upper and lower arms from being short-circuited due to the operation delay of the switching element. The current flowing through the inverter bus in this period is It is indefinite depending on the direction of current flow.

  Next, the direct current detector 11 will be described. FIG. 9 shows an example of the characteristics of the DC current detector 11. When the detected current value is zero, an offset voltage of 2.5V is output, and if a current of 20A flows in the forward direction, 5V is output. This indicates that the 20 A current outputs 0 V in the reverse direction, and this characteristic is necessary to detect the phase current of the brushless motor 3 appearing on the inverter bus described above in both directions.

  FIG. 10 shows the relationship between the PWM signal of one carrier cycle generated by the PWM signal generation unit 9, the current flowing through the inverter bus, and the output voltage of the DC current detector 11 when the electrical angle is 30 ° in FIG.

Here, if the characteristics of the DC current detector 11 are as shown in FIG. 9, at the timing (1), no current flows through the inverter bus (that is, the inverter bus current is 0 A),
In this case, if the output voltage of the DC current detector 11 is 2.5 V and the U-phase current appearing on the inverter bus at timing (2) is 10 A, the output voltage of the DC current detector 11 is 3.75 V, and the timing ( If the W-phase current appearing on the inverter bus in 3) is −5 A, the output voltage of the DC current detector 11 is 1.875V.

  That is, in the case of the DC current detector 11 having the characteristics as shown in FIG. 9, the value of the current flowing through the inverter bus can be obtained by the equation (2).

Detection current = (Output voltage-Offset voltage) x Conversion coefficient
= (Output voltage -2.5) x 8 (2)
The offset voltage in the characteristic as shown in FIG. 9 is obtained from the specifications of the device or circuit used as the DC current detector 11, but there is an individual difference, resulting in variations in each product.

  In order to eliminate this variation, the output voltage of the DC current detector 11 is reduced when the brushless motor 3 is stopped and no phase current flows, that is, when the current flowing through the inverter bus is constantly zero. In general, a method of measuring and using the value at this time as an offset voltage used for detection current calculation is generally performed.

  However, since the offset voltage of the DC current detector 11 has a characteristic that is influenced by fluctuations in the ambient temperature, the offset voltage when the brushless motor 3 is stopped as described above and the brushless motor 3 have a certain level of effect. There will be an error in the offset voltage when the ambient temperature changes after continuous operation.

  For example, as shown in FIG. 11, assuming that the offset voltage changes from 2.5 V to 2.8 V because the ambient temperature changes when the brushless motor 3 operates for a certain period of time, An error of plus 2.4A is generated for the detected current, and an error of minus 2.4A is generated for the detected current in the reverse direction.

  This error in the phase current value is a factor that impedes optimal driving in vector control of the brushless motor 3, and causes an increase in power consumption, a decrease in rotational torque, noise and vibration.

  Therefore, the data acquisition unit 15 does not stop the DC current detector 11 during timing (1) in FIG. 10, that is, during a period in which all PWM signals for controlling the upper arm switching elements of the inverter 2 are OFF, even during driving of the motor. Is sampled and the value is set as the offset voltage. Even if the data acquisition unit 15 performs data sampling at the timing when all the PWM signals for controlling the upper arm switching elements are on, the same effect can be obtained.

  As described above, according to the motor drive inverter control apparatus of the present invention, even when the ambient temperature changes by adjusting the offset voltage in the DC current detector periodically during motor drive, Current detection errors can be reduced, and as a result, good motor drive can be maintained.

  As described above, two phase currents of the three phase currents are sampled at timings (2) and (3) in FIG. 10, and the remaining one phase current is the sampled two phase currents. The data sampling period in the data acquisition unit 15, that is, the time interval for adjusting the offset voltage of the DC current detector 11, is calculated by sampling two phase currents. There is no practical problem even if it is longer than the period.

  This is because, in general, the carrier frequency of the PWM signal that controls the switching element of the inverter 2 is several kHz to several tens of kHz, and the frequency of phase current detection and calculation is several thousand to several tens of thousands of times per second. However, the temperature around the device does not change so rapidly.

  Therefore, it is sufficient to adjust the offset voltage once every several seconds. By increasing the data sampling period of the offset voltage, it is possible to reduce the processing load of a control device such as a microcomputer.

  Moreover, the motor drive inverter control device of the present invention is a motor drive that drives an motor using an inverter circuit such as an air conditioner, a refrigerator, an electric washing machine, an electric dryer, a vacuum cleaner, a blower, and a heat pump water heater. In any case, it can contribute to the realization of a highly reliable product.

  As described above, the motor drive inverter control device according to the present invention constantly adjusts the output offset value of the DC current detector that detects the DC current flowing through the inverter bus, thereby causing a phase current detection error of the motor due to a temperature change. The system reliability can be improved, so not only when a speed sensor such as a pulse generator cannot be used, such as a compressor drive motor in an air conditioner, but also in a servo drive, etc. The present invention can be applied even when a speed sensor can be provided.

The block diagram which shows the system configuration | structure of the inverter control apparatus for motor drive which shows Embodiment 1 of this invention. An example of the temporal change of the phase current state of the motor and a diagram showing the current state in each phase winding of the motor in each section of the electrical angle The figure showing an example of the PWM signal in 1 carrier cycle The figure showing the current state which flows into a motor and an inverter at the time of the drive by a PWM signal in FIG. The figure showing an example of the PWM signal in 1 carrier cycle The figure showing the current state which flows into a motor and an inverter at the time of the drive by a PWM signal in FIG. The figure showing an example of the PWM signal in 1 carrier cycle The figure showing the current state which flows into a motor and an inverter at the time of the drive by a PWM signal in FIG. The figure showing an example of the output characteristic of the direct current detector 11 The figure showing the relationship between the PWM signal of 1 carrier period, the electric current which flows into an inverter bus, and the output voltage of the direct current detector 11 The figure showing an example of the output characteristic at the time of the temperature change of the direct current detector 11 having the characteristic shown in FIG. Block diagram showing the configuration of a conventional motor drive inverter control device Waveform diagram showing the operation of a conventional motor drive inverter control device Operation waveform diagram of T section in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Inverter 3 Brushless motor 4 Stator 4u-4w Winding 5 Rotor 6 Control part 7 Phase current conversion part 8u-8w Terminal 9 PWM signal generation part 10 Base driver 11 DC current detector 12u-12w Upper arm switching Element 12x-12z Lower arm switching element 14u-14w, 14x-14z Free wheel diode 15 Data acquisition part 16 Inverter input voltage detection part 17 Phase estimation part 18 Rotor speed estimation part

Claims (3)

An inverter having an upper arm switching element and a lower arm switching element corresponding to each phase of the phase current, and converting DC power to three-phase AC power;
A PWM signal generator for generating a PWM signal for driving the inverter;
A DC current detector that outputs a voltage according to the magnitude of the current flowing through the bus of the inverter, and outputs an offset voltage when no current appears on the bus of the inverter;
In response to the PWM signal, the output voltage of the DC detector is sampled at a first timing when all of the upper arm switching elements of the inverter are off or all on and a second timing when a phase current flows through the bus of the inverter. A data acquisition unit to
A phase current converter that reproduces the phase current while adjusting the offset voltage based on the voltage sampled by the data acquisition unit;
A drive circuit for driving the upper arm switching element and the lower arm switching element according to the PWM signal;
An inverter control device for driving a motor. 2. The motor drive inverter according to claim 1, wherein the data acquisition unit sets a sampling period for sampling the output voltage of the DC detector at the first timing longer than a sampling period at the second timing. Control device. The apparatus which has a motor and drives the said motor using the motor drive inverter control apparatus of Claim 1 or 2.

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