JP2019193545A - Inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter capable of outputting a switching signal according to a modulation rate. In an inverter, a d, q / u, v, w conversion circuit includes a d, q / u, v, w conversion unit, a modulation factor calculation unit, a correction wave output unit, a derivation unit, and a carrier wave output. And a comparison unit. The correction wave output unit outputs a correction wave according to the electrical angle modulation rate. When deriving the correction wave, first, the target switching signal SW2 is divided at the division period T1. Next, the duty is calculated for each division cycle T1. The waveform W1 can be obtained by calculating the duty for one cycle of the electrical angle. Next, the voltage command is subtracted from the waveform W1. Thereby, the correction wave can be derived. [Selection diagram] Fig. 3

Description

  The present invention relates to an inverter.

An inverter for driving a motor includes a plurality of switching elements. The switching element is switched to convert DC power into AC power.
The inverter disclosed in Patent Document 1 controls a switching element by a map in which a modulation factor and a speed are associated with a switching signal. When the modulation factor fluctuates as the motor load fluctuates, the switching signal (pulse pattern) changes, and the switching element is controlled according to the modulation factor.

JP 2013-215041 A

  In the inverter disclosed in Patent Document 1, when the modulation rate is rough and the modulation rate slightly changes, the switching signal may not change even though the modulation rate is changed. As a result, an appropriate voltage may not be output to the motor.

  An object of the present invention is to provide an inverter capable of outputting a switching signal corresponding to a modulation rate.

  An inverter that solves the above problems is an inverter that drives a motor by converting DC power into AC power, a position detection unit that detects an electrical angle of the motor, an inverter circuit having a plurality of switching elements, An inverter control device that controls the switching element, wherein the inverter control device calculates a voltage command value for each phase from an electrical angle of the motor, a modulation rate calculation unit that calculates a modulation rate, A correction wave output unit that outputs a correction wave for each phase according to the electrical angle and the modulation factor, a derivation unit that derives a modulation wave by adding the voltage command indicating the voltage command value and the correction wave, and A comparison unit that generates a switching signal for controlling the switching element by comparing the modulated wave and a carrier wave, and the correction in the correction wave output unit Is obtained by dividing the target switching signal associated with the electrical angle and the modulation rate with a division period equal to or less than the period of the carrier wave, and calculating the duty for each division period. It is derived by subtracting the voltage command from the waveform for one angular period.

  According to this, the switching signal is generated by comparing the modulated wave obtained by adding the correction wave to the voltage command and the carrier wave. The correction wave is derived so that a target switching signal is generated according to the modulation wave. Therefore, the modulation wave obtained by adding the correction wave to the voltage command and the switching signal generated from the carrier wave are in accordance with the modulation rate. That is, a switching signal corresponding to the modulation rate can be output.

In the inverter, the division period may be shorter than the period of the carrier wave.
According to this, it is possible to finely cope with fluctuations in the rotational speed of the motor and fluctuations in the torque of the motor.

  According to the present invention, a switching signal corresponding to the modulation rate can be output.

The block diagram which shows the motor and the inverter which drives a motor. The block diagram which shows the structure of d, q / u, v, and w conversion circuit. The figure for demonstrating the derivation | leading-out method of a correction wave. The figure for demonstrating the derivation | leading-out method of a correction wave. The schematic diagram which shows NT area | region. The figure which shows the relationship between a voltage command, a correction wave, and a modulation wave. The figure which shows the relationship between a voltage command, a correction wave, and a modulation wave. Schematic which shows a map.

Hereinafter, an embodiment of the inverter will be described.
As shown in FIG. 1, the inverter 10 includes an inverter circuit 20 and an inverter control device 30. The inverter control device 30 includes a drive circuit 31 and a control unit 32. The inverter 10 of this embodiment is for driving the motor 60.

  The inverter circuit 20 includes six switching elements Q1 to Q6 and six diodes D1 to D6. IGBTs are used as the switching elements Q1 to Q6. Between positive electrode bus Lp and negative electrode bus Ln, switching element Q1 constituting the u-phase upper arm and switching element Q2 constituting the u-phase lower arm are connected in series. Between positive electrode bus Lp and negative electrode bus Ln, switching element Q3 that constitutes the v-phase upper arm and switching element Q4 that constitutes the v-phase lower arm are connected in series. Between the positive electrode bus Lp and the negative electrode bus Ln, a switching element Q5 constituting a w-phase upper arm and a switching element Q6 constituting a w-phase lower arm are connected in series. Diodes D1 to D6 are connected in reverse parallel to the switching elements Q1 to Q6. A battery B is connected to the positive electrode bus Lp and the negative electrode bus Ln via a smoothing capacitor C.

  The switching element Q1 and the switching element Q2 are connected to the u-phase terminal of the motor 60. The switching element Q3 and the switching element Q4 are connected to the v-phase terminal of the motor 60. The switching element Q5 and the switching element Q6 are connected to the w-phase terminal of the motor 60. The inverter circuit 20 having the switching elements Q1 to Q6 constituting the upper and lower arms can convert the DC voltage, which is the voltage of the battery B, into an AC voltage and supply it to the motor 60 in accordance with the switching operation of the switching elements Q1 to Q6. It can be done. The motor 60 is a three-phase AC motor in which three coils U, V, and W are star-connected. Motor 60 may be a three-phase AC motor in which coils U, V, and W are delta-connected.

  A drive circuit 31 is connected to the gate terminals of the switching elements Q1 to Q6. The drive circuit 31 switches the switching elements Q1 to Q6 of the inverter circuit 20 based on the switching signal SW1.

  The inverter 10 includes a position detector 61 that detects the electrical angle θ of the motor 60, a current sensor 62 that detects the u-phase current Iu of the motor 60, a current sensor 63 that detects the v-phase current Iv of the motor 60, and a power source. And a voltage sensor 64 for detecting the voltage Vdc.

  The control unit 32 is configured by a microcomputer. The control unit 32 includes a subtraction unit 33, a torque control unit 34, a torque / current command value conversion unit 35, subtraction units 36 and 37, a current control unit 38, and a d, q / u, v, and w conversion circuit. 39, a coordinate conversion unit 40, and a speed calculation unit 41.

  The speed calculator 41 calculates the speed ω from the electrical angle θ detected by the position detector 61. The subtraction unit 33 calculates a difference Δω between the command speed ω * and the speed ω calculated by the speed calculation unit 41. The torque control unit 34 calculates the torque command value T * from the difference Δω of the speed ω.

  The torque / current command value conversion unit 35 converts the torque command value T * into a d-axis current command value Id * and a q-axis current command value Iq *. For example, the torque / current command value conversion unit 35 uses a table in which the target torque stored in advance in a storage unit (not shown) is associated with the d-axis current command value Id * and the q-axis current command value Iq *. Torque / current command value conversion.

  The coordinate conversion unit 40 obtains the w-phase current Iw of the motor 60 from the u-phase current Iu and the v-phase current Iv by the current sensors 62 and 63, and based on the electrical angle θ detected by the position detection unit 61, the u-phase current Iu, v-phase current Iv and w-phase current Iw are converted into d-axis current Id and q-axis current Iq. The d-axis current Id is a current vector component for generating a field in the current flowing through the motor 60, and the q-axis current Iq is a current vector component for generating torque in the current flowing through the motor 60. .

  The subtractor 36 calculates a difference ΔId between the d-axis current command value Id * and the d-axis current Id. The subtraction unit 37 calculates a difference ΔIq between the q-axis current command value Iq * and the q-axis current Iq. The current control unit 38 calculates the d-axis voltage command value Vd * and the q-axis voltage command value Vq * based on the difference ΔId and the difference ΔIq.

  The d, q / u, v, w conversion circuit 39 receives the electrical angle θ, the d-axis voltage command value Vd *, the q-axis voltage command value Vq *, and the power supply voltage Vdc and inputs the switching elements Q1 to Q6. The switching signal SW1 is output to the drive circuit 31.

  As shown in FIG. 2, the d, q / u, v, w conversion circuit 39 includes a d, q / u, v, w conversion unit 50, a modulation factor calculation unit 51, a correction wave output unit 52, and a derivation. Unit 54, carrier wave output unit 55, and comparison unit 56.

  The d, q / u, v, w converter 50 converts the d-axis voltage command value Vd * and the q-axis voltage command value Vq * to u, u based on the electrical angle θ that is angle information (rotor position). Coordinates are converted to voltage command values for v and w phases. In the present embodiment, only the u-phase voltage command value Vu * is illustrated. The d, q / u, v, w conversion unit 50 is a calculation unit that calculates a voltage command value for each phase. The voltage command value Vu * has a sinusoidal waveform. A wave indicating the voltage command value Vu * is defined as a voltage command VW.

  The modulation factor calculator 51 calculates the modulation factor Keu based on the voltage command value Vu * and the power supply voltage Vdc. The modulation factor calculation unit 51 is a value obtained by dividing the voltage command value Vu * by the power supply voltage Vdc, and is a ratio between the voltage command value (voltage amplitude) Vu * and the power supply voltage Vdc.

  The correction wave output unit 52 outputs a correction wave RW corresponding to the electrical angle θ and the modulation factor Keu. In the present embodiment, the case where the u-phase correction wave RW is output will be described. However, the correction wave RW is similarly output for the v-phase and the w-phase. The correction wave RW of each phase is shifted in phase by 120 °. The inverter control device 30 includes a memory 53. The correction wave RW is stored in the memory 53 as a map, an approximate expression, or the result of Fourier transforming the correction wave RW. That is, the correction wave RW is derived in advance, and the derived correction wave RW is stored in the memory 53 associated with the electrical angle θ and the modulation factor Keu.

The deriving unit 54 is an adding unit that derives the modulated wave MW by adding the voltage command VW and the correction wave RW. The derivation unit 54 outputs the modulated wave MW to the comparison unit 56.
The carrier wave output unit 55 outputs the carrier wave CW to the comparison unit 56. The carrier wave CW of this embodiment is a triangular wave. The inverter 10 of this embodiment can be said to be a triangular wave comparison type inverter. The carrier wave CW is output for each phase. The phase of the carrier wave CW of each phase is shifted by 120 °.

  The comparison unit 56 compares the modulated wave MW output from the derivation unit 54 with the carrier wave CW output from the carrier wave output unit 55, thereby generating the switching signal SW1. The switching signal SW1 is a pulse signal. The high level signal is an on instruction signal for instructing to turn on the upper arm switching elements Q1, Q3, and Q5. The low level signal is an off instruction signal instructing to turn off the upper arm switching elements Q1, Q3, and Q5. Since the switching signal SW1 is output according to the modulation factor Keu and the electrical angle θ, the switching elements Q1 to Q6 are switched according to the modulation factor Keu and the electrical angle θ.

  The switching signal SW1 is determined in advance in association with the modulation rate Keu and the electrical angle θ. For example, the switching signal SW1 is determined so that a switching operation is performed so that the harmonic loss is minimized.

Next, a method for deriving the correction wave RW will be described.
The correction wave RW is derived from the target switching signal SW2 associated with the modulation factor Keu and the electrical angle θ. It can be said that the target switching signal SW2 is a switching signal to be output to the comparison unit 56.

  As shown in FIG. 3, when the correction wave RW is derived, first, the target switching signal SW2 is divided by the division period T1. The division period T1 is a period equal to or less than the period of the carrier wave CW. The division cycle T1 of the present embodiment is the same cycle as the minimum switching cycle and the same cycle as the carrier wave CW.

  Next, the duty is calculated for each division period T1. The waveform W1 can be obtained by calculating the duty for one electrical angle cycle. This waveform W1 is a waveform that matches the modulated wave MW output from the comparison unit 56. That is, the modulation wave MW necessary for generating the switching signal SW1 that matches the target switching signal SW2 can be derived.

  Next, as shown in FIG. 4, the voltage command VW is subtracted from the waveform W1 described above. Since the modulated wave MW is a waveform obtained by adding the voltage command VW and the correction wave RW, the correction wave RW can be derived by subtracting the voltage command VW from the waveform W1.

  As described above, the correction wave RW can be derived from the target switching signal SW2 by a procedure reverse to the procedure for generating the switching signal SW1 from the voltage command VW and the modulated wave MW.

The operation of the embodiment will be described.
The correction wave RW is derived from the target switching signal SW2. The target switching signal SW2 corresponds to the modulation factor Keu and the electrical angle θ, and the correction wave RW is derived so that the generated switching signal SW1 becomes the target switching signal SW2. For this reason, the switching signal SW1 obtained by comparing the modulated wave MW and the carrier wave CW corresponds to the modulation factor Keu. That is, when the modulation factor Keu changes slightly, the switching signal SW1 changes according to the slight change of the modulation factor Keu, and a voltage in accordance with the modulation factor Keu is output.

  As shown in FIG. 5, in the NT region defined by the torque T of the motor 60 and the rotation speed N of the motor 60, the modulation factor Keu varies depending on the position. In FIG. 7, the correction wave RW is constant within a range A indicated by a broken line. For example, when the torque T and the rotation speed N are within the range A, the correction wave RW1 when the modulation rate Keu in the range A is minimum is output.

  FIG. 6 shows the voltage command VW1 at the position indicated by the point P1 in the range A. FIG. 7 shows the voltage command VW2 at the position indicated by the point P2 in the range A. The point P2 has a higher modulation factor Keu than the point P1.

  As can be understood from FIGS. 6 and 7, it can be seen that the amplitude of the voltage command VW increases as the modulation rate Keu increases. It can be seen that even if the correction wave RW1 is the same, the modulation wave MW1 changes to the modulation wave MW2 due to the change in the amplitude of the voltage command VW, and the modulation wave MW corresponding to the modulation factor Keu and the electrical angle θ can be output.

  If the switching signal SW1 is generated from a map in which the modulation factor Keu is associated with the electrical angle θ, switching information of the switching elements Q1 to Q6 is required for each modulation factor Keu. For example, as shown in FIG. 8, when the switching signal SW1 is generated using a map in which the ON period and the OFF period of the switching elements Q1 to Q6 are associated for each modulation factor Keu, the switching information at least at the point P1 The switching information at the point P2 is necessary. In order to further improve the accuracy, a more detailed map is required.

  On the other hand, when the switching signal SW1 is generated using the correction wave RW as in the present embodiment, the duty increases as the amplitude of the voltage command VW increases as the modulation factor Keu increases. Therefore, the request for the modulation wave MW can be satisfied by increasing the voltage command VW as the modulation rate Keu increases, and the correction wave RW does not need to be changed in small increments as the modulation rate Keu increases. In other words, the same correction wave RW can be used for a certain range of modulation factor Keu.

  When the switching signal SW1 is generated from the map in which the modulation factor Keu and the electrical angle θ are associated with each other, the voltage command value Vu * needs to be considered, whereas the correction wave RW takes the voltage command value Vu * into consideration. It is stipulated. The amount of data can be reduced by the amount not considering the voltage command value Vu *.

The effects of the embodiment will be described.
(1) The switching signal SW1 is generated by comparing the modulated wave MW obtained by adding the correction wave RW to the voltage command VW and the carrier wave CW. The correction wave RW is derived such that a target switching signal SW2 associated with the modulation factor Keu and the electrical angle θ is generated. Therefore, the switching signal SW1 is in accordance with the modulation rate Keu. That is, the switching signal SW1 corresponding to the modulation factor Keu can be output.

  (2) In Patent Document 1, the switching signal can be changed in accordance with a slight change in the modulation rate by making the step of the modulation rate finer. However, in this case, the amount of data in the map increases, and the capacity of the memory is compressed. On the other hand, the inverter 10 of the present embodiment generates the modulation wave MW by adding the correction wave RW to the voltage command VW, and generates the switching signal SW1 from the comparison between the modulation wave MW and the carrier wave CW. Yes. Compared to storing the map in which the modulation factor Keu and the electrical angle θ are associated with each other in the memory 53, the amount of data can be reduced when the correction wave RW is stored, and the storage capacity of the memory 53 is less likely to be compressed.

The embodiment can be implemented with the following modifications. Each embodiment and the following modification examples can be implemented in combination with each other within a technically consistent range.
The division period T1 may be shorter than the period of the carrier wave CW. When the rotational speed of the motor 60 or the torque of the motor 60 changes, the voltage command VW changes. By shortening the division period T1, it is possible to respond finely when the rotational speed of the motor 60 or the torque of the motor 60 changes.

○ Any of the three-phase modulation rates may be used as the three-phase modulation rate. For example, the modulation factor Keu may be a modulation factor common to three phases. Also, the modulation factor may be individual in three phases.
The carrier wave CW may be a sawtooth wave.

  CW ... carrier wave, MW ... modulated wave, RW ... correction wave, SW1 ... switching signal, SW2 ... target switching signal, Q1 to Q6 ... switching element, VW ... voltage command, 10 ... inverter, 20 ... inverter circuit, 30 ... Inverter control device, 50... D, q / u, v, w conversion unit (calculation unit), 51... Modulation rate calculation unit, 52... Correction wave output unit, 54. Part, 60 ... motor, 61 ... position detection part.

Claims (2)

An inverter that drives a motor by converting DC power into AC power,
A position detector for detecting an electrical angle of the motor;
An inverter circuit having a plurality of switching elements;
An inverter control device for controlling the switching element,
The inverter control device
A calculation unit for calculating a voltage command value for each phase from the electrical angle of the motor;
A modulation rate calculation unit for calculating the modulation rate;
A correction wave output unit that outputs a correction wave for each phase according to the electrical angle and the modulation rate;
A derivation unit for deriving a modulated wave by adding the voltage command indicating the voltage command value and the correction wave;
A comparison unit that generates a switching signal for controlling the switching element by comparing the modulated wave and a carrier wave, and
The correction wave in the correction wave output unit is
The electrical angle 1 of the motor obtained by dividing the target switching signal associated with the electrical angle and the modulation rate by a division period equal to or less than the period of the carrier wave and calculating the duty for each division period An inverter derived by subtracting the voltage command from a waveform for a period.   The inverter according to claim 1, wherein the division period is shorter than the period of the carrier wave.