JP6943220B2 - Inverter - Google Patents

Description

The present invention relates to an inverter.

The inverter for driving the motor includes a plurality of switching elements. When this switching element is switched, DC power is converted 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 due to the fluctuation of the load of the motor, the switching signal (pulse pattern) changes, and the switching element is controlled according to the modulation factor.

Japanese Unexamined Patent Publication No. 2013-215041

In the inverter disclosed in Patent Document 1, when the step of the modulation factor is coarse and the modulation factor changes slightly, the switching signal may not change even though the modulation factor has 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 according to a modulation factor.

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

According to this, a switching signal is generated by comparing a modulated wave in which a correction wave is added to a voltage command with a carrier wave. The correction wave is derived so that a target switching signal is generated according to the modulated wave. Therefore, the modulated wave obtained by adding the correction wave to the voltage command and the switching signal generated from the carrier wave correspond to the modulation rate. That is, it is possible to output a switching signal according to the modulation factor.

For the inverter, the division period may be shorter than the period of the carrier wave.
According to this, it is possible to finely respond to fluctuations in the rotation speed of the motor and fluctuations in the torque of the motor.

According to the present invention, a switching signal according to the modulation factor 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 the d, q / u, v, w conversion circuit. The figure for demonstrating the derivation method of a correction wave. The figure for demonstrating the derivation method of a correction wave. The schematic diagram which shows the NT 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 showing 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 the present 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. A switching element Q1 forming the u-phase upper arm and a switching element Q2 forming the u-phase lower arm are connected in series between the positive electrode bus Lp and the negative electrode bus Ln. A switching element Q3 forming a v-phase upper arm and a switching element Q4 forming a v-phase lower arm are connected in series between the positive electrode bus Lp and the negative electrode bus Ln. A switching element Q5 forming the w-phase upper arm and a switching element Q6 forming the w-phase lower arm are connected in series between the positive electrode bus Lp and the negative electrode bus Ln. Diodes D1 to D6 are connected in antiparallel 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. You can do it. The motor 60 is a three-phase AC motor in which three coils U, V, and W are star-connected. The 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 detection unit 61 that detects the electric 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 supply. It includes a voltage sensor 64 that detects the voltage Vdc.

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

The speed calculation unit 41 calculates the speed ω from the electric angle θ detected by the position detection unit 61. The subtraction unit 33 calculates the 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 the d-axis current command value Id * and the 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 the 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 is performed.

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 electric 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 subtraction unit 36 calculates the difference ΔId between the d-axis current command value Id * and the d-axis current Id. The subtraction unit 37 calculates the 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 inputs the electric 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 of is output to the drive circuit 31.

As shown in FIG. 2, the d, q / u, v, w conversion circuit 39 is derived from the d, q / u, v, w conversion unit 50, the modulation factor calculation unit 51, and the correction wave output unit 52. A unit 54, a carrier wave output unit 55, and a comparison unit 56 are provided.

The d, q / u, v, w conversion unit 50 sets the d-axis voltage command value Vd * and the q-axis voltage command value Vq * based on the electric angle θ which is the angle information (rotor position) u, Coordinate conversion is performed to the voltage command value of the v and w phases. In this embodiment, only the u-phase voltage command value Vu * is shown. The d, q / u, v, w conversion unit 50 is a calculation unit that calculates the voltage command value for each phase. The voltage command value Vu * has a sinusoidal waveform. The wave indicating the voltage command value Vu * is defined as the voltage command VW.

The modulation rate calculation unit 51 calculates the modulation rate 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 the ratio of 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 electric angle θ and the modulation factor Keu. In the present embodiment, the case where the correction wave RW of the u phase is output will be described, but the correction wave RW is also output for the v phase and the w phase. The correction wave RW of each phase is out of phase by 120 °. The inverter control device 30 includes a memory 53. The correction wave RW is stored in the memory 53 as a result of Fourier transforming the map, the approximate expression, or 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 electric angle θ and the modulation factor Keu.

The derivation unit 54 is an addition 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 the present embodiment can be said to be a triangular wave comparison type inverter. The carrier wave CW is output for each phase. The carrier waves CW of each phase are out of phase by 120 °.

The comparison unit 56 generates the switching signal SW1 by comparing the modulated wave MW output from the derivation unit 54 with the carrier wave CW output from the carrier wave output unit 55. The switching signal SW1 is a pulsed signal. The high level signal is an ON instruction signal for instructing the ON of the upper arm switching elements Q1, Q3, and Q5. The Low level signal is an off instruction signal for instructing the upper arm switching elements Q1, Q3, and Q5 to be turned off. By outputting the switching signal SW1 according to the modulation factor Keu and the electric angle θ, the switching elements Q1 to Q6 are switched according to the modulation factor Keu and the electric angle θ.

The switching signal SW1 is predetermined in association with the modulation factor Keu and the electric angle θ. The switching signal SW1 is defined so that, for example, a switching operation is performed so as to minimize the harmonic loss.

Next, a method of 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 electric angle θ. The target switching signal SW2 can be said to be a switching signal to be output to the comparison unit 56.

As shown in FIG. 3, when deriving the correction wave RW, 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 is the same cycle as the cycle of the carrier wave CW.

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 electric angle. This waveform W1 is a waveform that matches the modulated wave MW output from the comparison unit 56. That is, the modulated wave MW required to generate 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 in the reverse procedure of 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 electric angle θ, and the correction wave RW is derived so that the generated switching signal SW1 becomes the target switching signal SW2. Therefore, 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 in the modulation factor Keu, and the voltage corresponding to 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 differs depending on the position. In FIG. 7, the correction wave RW is constant within the range A indicated by the 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 factor Keu is the minimum in the range A 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 larger modulation factor Keu than the point P1.

As can be seen from FIGS. 6 and 7, it can be seen that the amplitude of the voltage command VW increases as the modulation factor 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 electric angle θ can be output.

If the switching signal SW1 is generated from a map in which the modulation factor Keu and the electric angle θ are associated with each other, 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 with each modulation factor Keu, at least the switching information at the point P1 is generated. , Switching information at point P2 is required. If you want to improve the accuracy further, you need a more detailed map.

On the other hand, when the switching signal SW1 is generated by 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 demand for the modulated wave MW can be satisfied by increasing the voltage command VW as the modulation factor Keu increases, and the correction wave RW does not have to be changed little by little as the modulation factor Keu increases. In other words, the same correction wave RW can be used for a modulation factor Keu in a certain range.

When the switching signal SW1 is generated from the map in which the modulation factor Keu and the electric angle θ are associated with each other, it is necessary to consider the voltage command value Vu *, whereas the correction wave RW considers the voltage command value Vu *. It is set without. The amount of data can be reduced by the amount that the voltage command value Vu * is not taken into consideration.

The effect 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 so as to generate a target switching signal SW2 associated with the modulation factor Keu and the electric angle θ. Therefore, the switching signal SW1 corresponds to the modulation factor 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 according to a slight change in the modulation factor by making the step of the modulation factor finer. However, in this case, the amount of data in the map increases, which puts pressure on the memory capacity. On the other hand, the inverter 10 of the present embodiment generates the modulated wave MW by adding the correction wave RW to the voltage command VW, and generates the switching signal SW1 from the comparison between the modulated wave MW and the carrier wave CW. There is. The amount of data can be reduced in the case of storing the correction wave RW as compared with the case of storing the map in which the modulation factor Keu and the electric angle θ are associated with each other in the memory 53, and the storage capacity of the memory 53 is less likely to be compressed.

The embodiment can be modified and implemented as follows. Each embodiment and the following modifications 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 rotation speed of the motor 60 fluctuates or the torque of the motor 60 fluctuates, the voltage command VW changes. By shortening the division cycle T1, it is possible to finely respond to fluctuations in the rotation speed of the motor 60 and fluctuations in the torque of the motor 60.

○ Any one of the three-phase modulation rates may be used as the common modulation factor for the three phases. For example, the modulation factor Keu may be a modulation factor common to all three phases. Moreover, 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 ... derivation unit, 55 ... carrier wave output unit, 56 ... comparison Unit, 60 ... Motor, 61 ... Position detection unit.

Claims (2)

An inverter that drives a motor by converting DC power into AC power.
A position detection unit that detects the electrical angle of the motor,
Inverter circuit with multiple switching elements and
An inverter control device for controlling the switching element is provided.
The inverter control device is
A calculation unit that calculates the voltage command value for each phase from the electric angle of the motor,
Modulation rate calculation unit that calculates the modulation rate, and
A correction wave output unit that outputs a correction wave for each phase according to the electric angle and the modulation factor,
A derivation unit that derives a modulated wave by adding the voltage command indicating the voltage command value and the correction wave, and
A comparison unit for generating a switching signal for controlling the switching element by comparing the modulated wave with a carrier wave is provided.
The correction wave in the correction wave output unit is
The electric angle 1 of the motor obtained by dividing the target switching signal associated with the electric angle and the modulation factor into 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 the waveform for a period. The inverter according to claim 1, wherein the division period is shorter than the period of the carrier wave.

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