JP6024245B2 - Inverter control device - Google Patents

Description

  The present invention relates to an inverter control device including an inverter for driving a three-phase motor.

  An inverter composed of switching elements such as a plurality of transistors and diodes is a circuit that converts a DC voltage into an AC voltage by PWM modulation. Inverters are widely used in the fields of compressors, OA equipment, home appliances, and vehicle motors for driving non-commutator motors such as synchronous motors and induction motors.

  In driving a three-phase motor using such an inverter, it is necessary to accurately control the output current of the inverter in order to obtain a designated three-phase motor rotational speed. For this purpose, the value of the motor current for three phases (hereinafter referred to as phase current) is detected, and feedback control of the inverter output voltage command value (hereinafter referred to as voltage command value) is performed.

  The simplest method for detecting the phase current value for the three phases is to provide a current sensor for each phase of the three-phase motor to be detected and detect the value of the phase current for the three phases by the current detection circuit. It is used as.

  However, providing a plurality of current sensors in the inverter device causes an increase in cost. For this reason, a single shunt system is proposed in which a shunt resistor is used for the current sensor and the shunt resistor is provided only between the inverter and the DC power source 3 (hereinafter referred to as a DC link unit).

  In the one shunt method, the value of the DC link current flowing through the DC link unit is detected twice or more every predetermined control cycle. And it is a system which calculates the value of the phase current for 3 phases from the detected value of the DC link current detected at a plurality of timings. That is, phase currents for three phases are acquired for each control cycle. In addition, the DC link current is detected by comparing the ON state and the OFF state of the PWM signal that is the drive signal of the switching element of each phase of the inverter, and based on the comparison result, only the phase current for one phase is DC. It is decided to detect at the timing when it flows on the link.

Further, in PWM control, in order to expand the inverter output under a constant input voltage, the voltage command value for one phase out of the three phases is a duty ratio of 100% which is the same value as the amplitude of the reference triangular wave, or In some cases, two-phase modulation is used in which the voltage command value is fixed to a minimum value of 0% duty ratio. Furthermore, in order to expand the inverter output, the output of the inverter is controlled by setting the modulation rate represented by the following formula (1) to 1 or more (hereinafter referred to as overmodulation).
Modulation rate = Voltage command value / Reference triangle wave (1)
In addition, in the case of detecting the phase current for three phases by the one shunt method in the two-phase modulation, the value of the phase current for two phases out of the three phases is detected during a predetermined control cycle, and the remaining one phase is detected. The current value of the minute phase current is calculated. As a result, a method of acquiring the phase current values for three phases has been proposed (for example, Patent Document 1 below).

  Also, in 2-phase modulation, if the modulation rate is made larger than 1 to further increase the inverter output, the voltage command value for 2 phases out of 3 phases is fixed at a duty ratio of 100% or a duty ratio of 0%. It may become a state to be. When this state is longer than the predetermined control period, according to the one shunt method, only the phase current value for one phase can be detected during the predetermined control period. Therefore, a method for detecting a phase current value for two phases by decreasing one of the two phase voltage command values having the same voltage command value or shifting one phase. Has been proposed (for example, Patent Document 2 below).

JP 2005-192358 A JP 2006-42454 A

When acquiring phase current values for three phases for each predetermined control cycle as in Patent Document 2, one of the two-phase voltage command values having the same voltage command value for each control cycle is reduced. Or shifting one of the phases. In this case, the modulation rate decreases and the inverter output decreases.
The present invention provides an inverter control device capable of improving a modulation rate and performing motor drive control with high accuracy in a one-shunt inverter control device.

In order to solve the above-described problems and achieve the object, an inverter control device according to the present invention includes an inverter that drives a motor by outputting a three-phase alternating current having different phases by turning on and off a plurality of switching elements, respectively. One shunt resistor through which the three-phase alternating current flows, a control circuit for controlling on / off of each of the plurality of switching elements by PWM control or rectangular wave control, and a three-phase current flowing through the shunt resistor A current detection circuit for detecting a current value of a two-phase current in a predetermined cycle, and a calculation for calculating a current value of the remaining one-phase current based on the two-phase current value detected by the current detection circuit and a section, an inverter control device for controlling the inverter based on the detected current value and the calculated current value, are connected to the inverter The shunt resistor is only one, the current detection circuit, said detects only the current value of the current flowing to the shunt resistor during PWM control, the control circuit, the when the rectangular wave control is performed, in advance Switching control for switching from the rectangular wave control to the PWM control that allows the current detection circuit to detect the current value of the two-phase current among the three-phase current flowing through the shunt resistor when the determined fixed time has elapsed. It is characterized by performing.

  According to the present invention, in a one-shunt inverter control device, the modulation factor can be improved and the motor drive control can be performed with high accuracy.

It is a block diagram of the inverter control apparatus of embodiment. It is a circuit diagram for demonstrating the detection of the phase current of embodiment. It is a figure which shows the relationship of the state of the switching element of the inverter of embodiment, and the detected phase current. It is a figure which shows the current detection by the conventional rectangular wave control. It is a figure which shows the switching waveform of PWM control by the sine wave drive of embodiment, and rectangular wave control. It is a figure which shows the switching waveform of PWM control by the trapezoid wave drive of embodiment, and rectangular wave control. It is a figure which shows the waveform of the PWM control by the conventional trapezoidal wave drive. It is a figure which shows the shift waveform of the PWM control by the conventional trapezoidal wave drive. It is a flowchart which shows the electric current detection operation | movement of the inverter control apparatus of embodiment. It is a figure which shows the switching waveform of PWM control by the sine wave drive of embodiment, and rectangular wave control.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Moreover, in the following description, the case where embodiment of this invention is applied to a three-phase motor is described as an example. Even in a multi-phase motor, the current value of each phase can be detected by applying the embodiment of the present invention.
[Embodiment]
FIG. 1 is a configuration diagram of an inverter control device according to an embodiment.

  The inverter control device 1 includes an inverter 2, a DC power supply 3, a control unit 4, and a shunt resistor 5, and performs drive control of the three-phase motor 6. For example, the three-phase motor 6 is a non-commutator motor such as a synchronous motor or an induction motor.

  The inverter 2 is configured by, for example, switching elements 21 to 26 made of IGBT (Insulated Gate Bipolar Transistor) or the like being bridge-connected to each other. Specifically, the drains of the switching elements 21 to 23 that are switching elements for the upper arms of the U phase, the V phase, and the W phase are connected to the plus terminal of the DC power supply 3. The sources of the switching elements 21 to 23 are connected to the drains of the switching elements 24 to 26 that are switching elements for the lower arm of the U phase, the V phase, and the W phase. The sources of the switching elements 24 to 26 are connected to each other and connected to one end of the shunt resistor 5. The other end of the shunt resistor 5 is connected to the negative terminal of the DC power supply 3. Furthermore, the connection part of the switching element 21 and the switching element 24, the connection part of the switching element 22 and the switching element 25, and the connection part of the switching element 23 and the switching element 26 serve as output terminals of the inverter 2, respectively. Connected to the phase.

The DC power supply 3 is not particularly limited, but is, for example, a vehicle-mounted battery.
The control unit 4 includes a current detection circuit 41, a recording unit 42, a calculation unit 43, a control switching unit 44, a PWM control unit 47, a rectangular wave control unit 48, and a drive unit 49, and drives the switching elements 21 to 26 of the inverter 2. Drive signal to output. Moreover, the operation | movement of each component of the control part 4 is performed by being controlled by CPU, DSP, and a programmable device which are not shown in figure, for example.

  The shunt resistor 5 is, for example, a resistor having a small resistance value. Then, by detecting the voltage applied to the shunt resistor 5, the value of the flowing current can be detected. In the present invention, since it is connected to the DC link part of the inverter control device, the DC link current can be detected by detecting the voltage of the shunt resistor 5.

  The three-phase motor 6 is connected to the output terminal of the inverter 2 controlled by the control unit 4 and is driven by an alternating current (U phase, V phase, W phase) output from the output terminal of the inverter 2. Accordingly, the compressor, the OA device, the home appliance, the vehicle driving electric motor, and the like are operated.

Furthermore, each component of the control unit 4 will be described with reference to FIG.
The current detection circuit 41 is a circuit that detects the voltage of the shunt resistor 5. That is, the value of the DC link current flowing through the shunt resistor 5 is detected. Then, by detecting the DC link current at a predetermined timing, the phase current values for two phases or more are detected during a predetermined control cycle. In addition, the detected phase current value (analog signal) is converted into a digital signal using an A / D converter and output to the calculation unit 43. Details of the detection of the phase current by the current detection circuit 41 will be described later.

  The recording unit 42 is a memory such as a ROM or a RAM, and records a program and data for controlling the three-phase motor 6. For example, a rotational speed table representing the relationship between the rotational speed of the three-phase motor 6 and the value of the phase current flowing in each phase is stored. More specifically, the rotation speed table is a table in which the rotation speed of the three-phase motor 6 and the value of the phase current flowing in each phase are recorded in association with each other, and obtained for each three-phase motor 6 through an experiment. It is created using the value of the phase current.

  The calculation unit 43 receives from each external device a signal (hereinafter referred to as an “operation status signal”) representing the operation status of an external device driven by the three-phase motor 6 such as a compressor, OA device, home appliance, or vehicle driving motor. Receive. Based on the received operation status signals, the required number of rotations of the three-phase motor 6 (hereinafter referred to as the required number of rotations) is calculated. Further, the calculation unit 43 refers to the rotation speed table, and acquires the value of the phase current (hereinafter referred to as “required current”) of each phase corresponding to the required rotation speed. That is, the calculation unit 43 refers to the rotation number column of the rotation number table recorded in the recording unit 42 and acquires the necessary current by extracting the phase current value corresponding to the same rotation number as the necessary rotation number. . In addition, the calculation unit 43 obtains a difference (hereinafter referred to as a correction difference value) between the value of the phase current flowing in each phase of the three-phase motor 6 acquired by the current detection circuit 41 and the value of the required current of each phase. . Furthermore, the calculation unit 43 corrects the voltage command value so as to eliminate the correction difference value. Then, the calculation unit 43 outputs the obtained voltage command value to the control switching unit 44. The calculation unit 43 appropriately corrects the voltage command value according to the driving status of each external device by performing feedback control that repeats the above operation while the three-phase motor 6 is driven. Note that a method for correcting the voltage command value from the detected current value of each phase in the calculation unit 43 is known, and the voltage command value can be corrected as appropriate in addition to the method using the rotation speed table described above. A method may be used.

  When the voltage command value generated and corrected by the calculation unit 43 is input, the control switching unit 44 drives the inverter 2 based on the voltage command value, either the PWM control unit 47 or the rectangular wave control unit 48. Determine whether to use. The control switching unit 44 controls the three-phase motor 6 by the PWM control unit 47 when the rotation speed of the three-phase motor 6 is in the low speed range, and is rectangular when the rotation speed of the three-phase motor 6 is in the high speed range. The wave control unit 48 performs switching control for controlling the three-phase motor 6. In addition, when the rectangular wave control using the rectangular wave control unit 48 is performed, the control switching unit 44 performs switching control to switch to PWM control when a predetermined time has elapsed.

  As an example, the control switching unit 44 calculates the modulation rate of the voltage command value input from the calculation unit 43. When the calculated modulation rate is equal to or lower than the upper limit modulation rate, the control switching unit 44 causes the inverter 2 to perform PWM control using the PWM control unit 47. Further, when the calculated modulation rate is larger than the upper limit modulation rate, the control switching unit 44 controls the inverter 2 using the rectangular wave control unit 48 in the rectangular wave control. Further, when the rectangular wave control is continued, the control switching unit 44 uses the PWM control unit 47 for every predetermined time even when the calculated modulation rate is larger than the upper limit modulation rate. Is PWM controlled.

  The PWM control unit 47 controls the output of the inverter 2 by switching on / off of the switching elements 21 to 26 by PWM control based on the voltage command value input from the calculation unit 43 via the control switching unit 44. The drive signal is output to the drive unit 49. Note that a method of generating a drive signal using a voltage command value and a reference triangular wave is common, but this PWM control is known and will not be described here.

  The rectangular wave control unit 48 switches on / off of the switching elements 21 to 26 by rectangular wave control based on the voltage command value input from the calculation unit 43 via the control switching unit 44 and outputs the output of the inverter 2. A drive signal to be controlled is output to the drive unit 49. Note that a drive signal is generated using a rectangular wave as the voltage command value, but this rectangular wave control is publicly known and will not be described here.

The drive unit 49 turns on / off the switching elements 21 to 26 of the inverter 2 by a drive signal input from the PWM control unit 47 or the rectangular wave control unit 48.
FIG. 2 is a circuit diagram for explaining phase current detection according to the embodiment. The detection of the phase current of the current detection circuit 41 will be described with reference to FIG.

  In the example shown in FIG. 2A, the switching element 21 is on and the switching elements 22 and 23 are off (at this time, the switching element 24 is off and the switching element 25, 26 is on).

  In this case, the current flows in the order of the DC power supply 3, the switching element 21, the U-phase coil of the three-phase motor 6, the V-phase / W-phase coil of the three-phase motor 6, the switching elements 25 and 26, the shunt resistor 5, and the DC power supply 3. It flows in. Therefore, the current flowing through shunt resistor 5 corresponds to U-phase current Iu of three-phase motor 6. That is, the value of the U-phase current Iu can be detected from the voltage across the shunt resistor 5.

  In the example shown in FIG. 2B, the switching elements 21 and 22 are on and the switching element 23 is off (at this time, the switching elements 24 and 25 are off and the switching element 26 is on).

  In this case, the current flows in the order of the DC power supply 3, the switching elements 21 and 22, the U-phase / V-phase coil of the three-phase motor 6, the W-phase coil of the three-phase motor 6, the switching element 26, the shunt resistor 5, and the DC power supply 3. It flows in. Therefore, the current flowing through the shunt resistor 5 corresponds to the W-phase current −Iw of the three-phase motor 6. That is, the value of the W-phase current −Iw can be detected from the voltage across the shunt resistor 5.

In the above description, the direction from the inverter 2 to the three-phase motor 6 is positive, and the direction from the three-phase motor 6 to the inverter 2 is negative.
Thus, when the states of the switching elements 21 to 26 of the inverter 2 are determined, the phase currents (U phase, V phase, W phase) flowing through the shunt resistor 5 are uniquely determined. That is, the detectable phase current is uniquely determined by the states of the switching elements 21 to 26.

FIG. 3 is a diagram showing the relationship between the state of each switching element of the inverter 2 and the detectable phase current.
The detected current table 301 shows the phase current detected by the current detection circuit 41 corresponding to the state of each switching element. The U phase, the V phase, the W phase, the U phase, the V phase, and the W phase are respectively a switching element 21, a switching element 22, a switching element 23, a switching element 24, a switching element 25, It is the switching element 26. The phase current that can be detected using the shunt resistor 5 is a phase current that flows through the shunt resistor 5 corresponding to the state of the switching elements 21 to 26 of the inverter 2.

Here, the timing at which the current detection circuit 41 detects the current will be described.
The on / off states of the switching elements 21 to 26 are switched by driving signals of the switching elements 21 to 26. Therefore, the DC link current is detected by comparing the drive state of the PWM signal that is the drive signal of the switching elements 21 to 26 of each phase of the inverter, and based on the comparison result and the relationship of FIG. It is decided to detect at the timing when it flows on the link. And the timing which can detect the value of the phase current more than two phases during a predetermined control cycle is extracted. The drive signal used when the current detection circuit 41 determines the current detection timing may be obtained by feedback from the actual operation state of the inverter 2, or the voltage command value calculated by the calculation unit 43 may be used. A drive signal created based on this may also be used.

Next, the inverter control of the embodiment using the rectangular wave control unit 48 will be described with reference to FIGS.
FIG. 4 is a diagram showing current detection by the conventional rectangular wave control.

  Focusing on the rectangular wave period surrounded by the broken line frame of the rectangular wave control waveform 401, the voltage command values for the V phase and U phase are always “1” during the rectangular wave period, and the voltage command value for the W phase is Since it is always “0”, only the value of −Iw can be detected. Therefore, in the case of rectangular wave control, it can be seen that the phase current values for three phases cannot be acquired. Note that even in another rectangular wave period, the state of the switching element of each phase is constant within the rectangular wave period, and therefore, when the one-shunt method is used, the phase current value for three phases cannot be detected.

  Therefore, FIG. 5 and FIG. 6 show control waveforms of the inverter using the control switching unit 44 of the present invention that can improve the modulation rate and improve the drive control of the three-phase motor 6. FIG. 5 is a diagram showing a switching waveform between PWM control and rectangular wave control by sinusoidal driving according to the embodiment. FIG. 6 is a diagram illustrating a switching waveform between PWM control and rectangular wave control by trapezoidal wave driving according to the embodiment.

  A PWM control waveform 501 shown in FIG. 5 shows a relationship between a voltage command value represented by a sine wave with a modulation factor of 0 ≦ a ≦ 1 input from the calculation unit 43 to the PWM control unit 47 and a reference triangular wave. The period (1) of the PWM control waveform 501 is a control period for performing PWM control when the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48.

  The rectangular control waveform 502 indicates the relationship between the voltage command value input from the calculation unit 43 to the rectangular wave control unit 48 and the reference triangular wave. The period (2) of the rectangular control waveform 502 is a control period for performing rectangular wave control when the control switching between the PWM control unit 47 and the rectangular wave control unit 48 of the control switching unit 44 is performed.

  The control switching waveform 503 switches between PWM control and rectangular wave control when the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48 in the period (1) and the period (2). It is a control waveform of the inverter 2 at the time.

  Note that the rectangular wave waveforms of the rectangular wave control waveform 502 and the control switching waveform 503 are shown by shifting the positive and negative absolute values of the three phases so that they can be referred to as appropriate, but in reality, the three phases have the same amplitude. .

  A PWM control waveform 601 shown in FIG. 6 shows a relationship between a reference voltage and a voltage command value that is input from the calculation unit 43 to the PWM control unit 47 with a modulation factor of 1 <a <MV1 and is represented by a trapezoidal wave. The period (1) of the PWM control waveform 601 is a control period for performing PWM control when the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48.

Note that the modulation factor MV1 is a modulation factor corresponding to the maximum voltage command value (hereinafter, referred to as the upper limit modulation factor) among the three-phase currents that can be acquired by the single shunt method.
In addition, the upper limit modulation rate is such that the value of the two-phase phase current can be detected by changing the magnitude of one of the equal two-phase voltage command values or shifting one of the phases. May be included up to the modulation rate.

  Specifically, when the modulation rate is further increased as compared with the two-phase modulation waveform 701 shown in FIG. 7, the U-phase, V-phase, and W-phase voltages are represented as indicated by the broken line frame of the two-phase modulation waveform 702. A control cycle in which the command values are all solid-on within the PWM cycle is possible. Then, the switching element is not switched within the PWM cycle, and the phase current values for three phases cannot be acquired. In this case, the voltage command value is shifted as indicated by the two-phase modulation waveform 801 in FIG. Note that the period of FIG. 8 is the same period as the PWM cycle surrounded by the broken line frame of FIG.

  As a specific example of the shift of the voltage command value, as shown in the V-phase command value, one of the two-phase voltage command values having the same voltage command value is reduced. Alternatively, as shown in the U-phase command value, the phase of one electrical angle may be shifted to shift the phase of the electrical angle between the U-phase and the V-phase. And the control part 4 controls the drive part 49, and switches the switching elements 21-26 so that the phase current for two phases can be detected within the PWM cycle, thereby obtaining the phase current for three phases. Can be acquired. Thereby, even if the upper limit modulation rate is set larger, the control unit 4 can acquire phase currents for three phases.

  A rectangular control waveform 602 in FIG. 6 shows the relationship between the voltage command value input from the calculation unit 43 to the rectangular wave control unit 48 and the reference triangular wave. The period (2) of the rectangular control waveform 502 is a control period in which rectangular wave control is performed when control switching between the PWM control unit 47 and the rectangular wave control unit 48 is performed by the control switching unit 44.

  The control switching waveform 603 switches between PWM control and rectangular wave control when the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48 in the period (1) and the period (2). It is a control waveform of the inverter 2 at the time.

  Note that the rectangular wave waveforms of the rectangular wave control waveform 602 and the control switching waveform 603 are shown by shifting the positive and negative absolute values of the three phases so that they can be referred to as appropriate, but in reality, the three phases have the same amplitude. .

  The control switching unit 44 switches control between PWM control and rectangular wave control when the voltage command value calculated by the calculation unit 43 is higher than the upper limit modulation rate based on the input operation state signal. To decide. 5 and 6, the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48 so as to perform PWM control and rectangular wave control for each control cycle.

  The inverter control device 1 estimates the driving state of the three-phase motor 6 based on the current value of each phase detected by the current detection circuit 41, and performs feedback control to correct the voltage command value. Yes. If the error of the current value used for the control falls within the allowable range, the execution ratio of the rectangular wave control and the PWM control may be selected as appropriate. For example, every time PWM control is performed for two cycles, rectangular wave control may be performed for one cycle, and the like, which may be determined as appropriate based on required control accuracy and the output of the inverter 2. Also, PWM control may be performed only when it is desired to detect the phase current of each phase. Note that the modulation rate is improved and the output of the inverter 2 is increased as the period for performing the rectangular wave control is increased.

  In addition, when the control unit that uses the output voltage control circuit between the PWM control unit 47 and the rectangular wave control unit 48 is switched every control cycle, the current detection circuit 41 changes the rectangular wave control unit 48. In the period (2) to be used, the current value of each phase is not detected. Then, the current detection circuit 41 detects a current in a cycle (1) in which the PWM control unit 47 is used. That is, the current detection circuit 41 detects the current value every two control cycles, which is the sum of the cycle (1) and the cycle (2). Thereby, the current detection circuit 41 can detect phase currents for two or more phases and acquire phase currents for three phases. Note that the phase current may also be detected in the period (2) in which the rectangular wave control is performed as necessary.

Here, the average output of the inverter 2 obtained by switching the PWM control and the rectangular wave control every control cycle will be described.
The output of the inverter 2 is cycle (2)> cycle (1), and the average output of the inverter 2 when the PWM control and the rectangular wave control are switched every cycle is expressed by the following equation (2).
Average output = [output of period (1) + output of period (2)] / 2 (2)
Therefore, in the embodiment, the rectangular wave control and the PWM control based on the upper limit modulation rate are switched for the output of the inverter 2 that is driven and controlled using only the PWM control equal to or lower than the upper limit modulation rate. Thus, it can be seen that the output of the inverter 2 can be improved as a whole.

  In the embodiment, the PWM control and the rectangular wave control are switched and performed. Therefore, the phase current values for two phases or more are detected by using the timing for performing the PWM control, and the phase currents for the three phases are calculated. Can be acquired. As a result, in the one-shunt inverter control device, the modulation factor can be improved and the drive control of the motor can be performed with high accuracy.

FIG. 9 is a flowchart showing a current detection operation of the inverter device according to the embodiment.
The calculation unit 43 calculates a voltage command value from information recorded in the recording unit 42 (such as a rotation speed table), an operation status signal, and the obtained phase current values for three phases, and calculates the calculated voltage command. The value is output to the control switching unit 44. Then, the control switching unit 44 calculates the modulation rate by the following equation (3) based on the voltage command value input from the calculation unit 43 (S901).
Modulation rate = Voltage command value amplitude / Reference triangle wave amplitude (3)
That is, the modulation factor is calculated by dividing the amplitude of the voltage command value by the amplitude of the reference triangular wave.

The control switching unit 44 determines whether or not the calculated modulation rate is 1 or less (S902). If the determination result is a modulation factor of 1 or less, the process proceeds to step 903.
The control switching unit 44 outputs a sine wave voltage command value to the PWM control unit 47. The PWM control unit 47 outputs a drive signal for the inverter 2 to the drive unit 49 (S903).

  And each switching element 21-26 of the inverter 2 is driven by the drive part 49 based on a drive signal. The current detection circuit 41 acquires phase currents for three phases using a conventional one-shunt method. That is, the current detection circuit 41 detects a current value every control cycle. Thereby, feedback control using each phase current of the three-phase motor 6 is enabled (S904). Thereafter, when one control cycle elapses, the process proceeds to S905.

  When the next control cycle comes, the calculation unit 43 determines whether or not to stop the three-phase motor 6 based on the input operation status signal. If the determination result shows that the three-phase motor 6 is to be continuously driven, the process proceeds to S901 in order to control the inverter 2 in the next control cycle. Further, when the motor 5 is to be stopped based on the determination result, a series of operations is terminated (S905). An example of a case where the three-phase motor 6 is stopped includes a case where an ignition key OFF operation is detected when the three-phase motor 6 is provided in a vehicle.

If the determination result in S902 is greater than the modulation factor 1, the process proceeds to S906.
The control switching unit 44 determines whether or not the calculated modulation rate is equal to or lower than the upper limit modulation rate MV1 (S906). If the determination result is equal to or less than the upper limit modulation factor MV1, the process proceeds to step 907.

  The control switching unit 44 outputs a trapezoidal wave voltage command value having an upper limit modulation factor MV1 or less to the PWM control unit 47. Then, the PWM control unit 47 outputs a drive signal for the inverter 2 to the drive unit 49 (S907).

  And each switching element 21-26 of the inverter 2 is driven by the drive part 49 based on a drive signal. The current detection circuit 41 obtains phase currents for three phases using the conventional one shunt method (S908). Thereby, feedback control using each phase current of the three-phase motor 6 is enabled. Thereafter, when one control cycle elapses, the process proceeds to S905.

If the result of the determination in S906 is greater than the upper limit modulation factor MV1, the process proceeds to S909.
The control unit 4 determines whether the immediately preceding control cycle is the cycle (1) or the cycle (2) (S909). When the control unit 4 determines in S909 that the immediately preceding control cycle is cycle (1) (PWM control), the control unit 4 sets the current control cycle to cycle (2) (S910). When control is started and the immediately preceding cycle is neither cycle (1) nor cycle (2) (when neither PWM control nor rectangular wave control is performed), the control unit 4 sets the current control cycle to cycle (1). ) (S912) or cycle (2) (S910).

  When the current control cycle is set to cycle (2) (S910), the control switching unit 44 outputs a rectangular wave voltage command value to the rectangular wave control unit. And the rectangular wave control part 48 outputs the drive signal of the inverter 2 to the drive part 49 (S911).

  And each switching element 21-26 of the inverter 2 is driven by the drive part 49 based on a drive signal. In this case, the current detection circuit 41 does not detect a current. Thereafter, when one control cycle elapses, the process proceeds to S905.

  When the control unit 4 determines in S909 that the immediately preceding control cycle is not the cycle (1), the control unit 4 determines that the current control is the cycle (1) in S912. The case where the immediately preceding control cycle is not the cycle (1) during the driving of the three-phase motor 6 corresponds to the case where the control cycle is the cycle (2).

  Then, the control switching unit 44 outputs a voltage command value of a sine wave or a trapezoidal wave having an upper limit modulation factor MV1 or less to the PWM control unit 47. Then, the PWM control unit 47 outputs a drive signal for the inverter 2 to the drive unit 49 (S913). That is, the control switching unit 44 can detect the current value of the two-phase current out of the three-phase current flowing from the rectangular wave control to the shunt resistor 5 by the current detection circuit 41 when the control cycle has elapsed one cycle from the start of the rectangular wave control. Switch to PWM control.

  And each switching element 21-26 of the inverter 2 is driven by the drive part 49 based on a drive signal. The current detection circuit 41 obtains phase currents for three phases using the conventional one shunt method (S914). That is, the current detection circuit 41 acquires a current value when performing PWM control between two control cycles that are longer than one control cycle. Thereby, feedback control using each phase current of the three-phase motor 6 is enabled. Thereafter, when one control cycle elapses, the process proceeds to S905. Therefore, when the result of the determination in S906 continues to be greater than the upper limit modulation factor MV1, the control switching unit 44 switches from rectangular wave control to PWM control every control cycle, and every two control cycles. Thus, the current value of the phase current for three phases is acquired.

  According to the above-described embodiment, the PWM control and the rectangular wave control are appropriately switched, and the current value of the two-phase current is detected during the PWM control even when the single-shunt current detection circuit 5 is used. can do. As a result, the modulation factor can be improved and the drive control of the motor can be performed with high accuracy.

  Furthermore, by thinning out the period for performing rectangular wave control and inserting a period for performing PWM control capable of acquiring current values of currents for three phases, a plurality of phases using a single-shunt-type current detection circuit 41 is provided. The current value of the current is detected. Therefore, it is not necessary to provide the shunt resistor 5 for each phase of the three-phase motor 6. Furthermore, since it is not necessary to perform control for shifting the current command value in order to detect the current values of a plurality of phases of current, the configuration of the inverter control device can be simplified.

  In this embodiment, the rectangular wave control is switched to the PWM control every control cycle, and phase currents for three phases are acquired every two control cycles. However, as shown in FIG. Each period of the triangular wave is set to period (1) and period (2), switching from rectangular wave control to PWM control for each period of the reference triangular wave, and phase currents for three phases are acquired every two periods of the reference triangular wave. Also good.

FIG. 10 is a diagram illustrating a switching waveform between PWM control and rectangular wave control by sinusoidal drive according to the embodiment.
A PWM control waveform 101 shown in FIG. 10 shows a relationship between a voltage command value represented by a sine wave with a modulation factor of 0 ≦ a ≦ 1 input from the calculation unit 43 to the PWM control unit 47 and a reference triangular wave. The period (1) of the PWM control waveform 101 is a period for performing PWM control when the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48.

  The rectangular control waveform 102 indicates the relationship between the voltage command value input from the calculation unit 43 to the rectangular wave control unit 48 and the reference triangular wave. The period (2) of the rectangular control waveform 102 is a period for performing rectangular wave control when the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48.

  The control switching waveform 103 switches between PWM control and rectangular wave control when the control switching unit 44 switches between the PWM control unit 47 and the rectangular wave control unit 48 in the period (1) and the period (2). It is a control waveform of the inverter 2 at the time.

In addition, the rectangular wave waveforms of the rectangular wave control waveform 102 and the control switching waveform 103 are shown by shifting the positive and negative absolute values of the three phases so that they can be referred to as appropriate, but in reality, the three phases have the same amplitude. .
Further, instead of switching from rectangular wave control to PWM control every control cycle, switching may be performed every two control cycles. What is necessary is just to switch for every integral multiple of a control period. When switching every two control cycles, rectangular wave control is performed for two control cycles, switching to PWM control in the third cycle, and current values of phase currents for three phases are acquired in the third cycle. You may do it. Further, the rectangular wave control may be switched to the PWM control every two cycles of the reference triangular wave. You may make it switch from rectangular wave control to PWM control for every integral multiple of the period of a reference | standard triangular wave.

DESCRIPTION OF SYMBOLS 1 Inverter control apparatus 2 Inverter 3 DC power supply 4 Control part 5 Shunt resistor 6 Three-phase motor 21, 22, 23 Upper arm switching element 24, 25, 26 Lower arm switching element 41 Current detection circuit 42 Recording part 43 Calculation Unit 44 control switching unit 47 PWM control unit 48 rectangular wave control unit 49 drive unit 101 PWM control waveform 102 rectangular wave control waveform 103 control switching waveform 301 detection current table 401 rectangular wave control waveform 501 PWM control waveform 502 rectangular wave control waveform 503 control Switching waveform 601 PWM control waveform 602 Rectangular wave control waveform 603 Control switching waveform 701 Two-phase modulation waveform 702 Two-phase modulation waveform 801 Shift control waveform

Claims (4)

An inverter that drives a motor by outputting three-phase alternating currents having different phases by turning on and off each of a plurality of switching elements;
One shunt resistor through which the three-phase alternating current flows;
A control circuit for controlling on / off of each of the plurality of switching elements by PWM control or rectangular wave control;
A current detection circuit for detecting a current value of a two-phase current among the three-phase currents flowing through the shunt resistor at a predetermined period;
A calculation unit that calculates the current value of the remaining one-phase current based on the two-phase current value detected by the current detection circuit;
An inverter control device that controls an inverter based on the detected current value and the calculated current value,
The shunt resistor connected to the inverter is only one,
The current detection circuit detects only a current value of a current flowing through the shunt resistor during the PWM control,
When the rectangular wave control is performed, the control circuit can detect a current value of a two-phase current among the three-phase currents flowing through the shunt resistor by the current detection circuit when a predetermined time has elapsed. An inverter control device that performs switching control for switching from the rectangular wave control to the PWM control.   The inverter control device according to claim 1, wherein a control waveform of the PWM control is a sine wave or a trapezoidal wave.   The inverter control apparatus according to claim 1, wherein the control circuit changes a ratio of the PWM control and the rectangular wave control based on a required output of the inverter.   The inverter control device according to any one of claims 1 to 3, wherein in the PWM control, a modulation rate is changed based on a required output of the inverter.