JP3951759B2 - Inverter device and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inverter device and a control method thereof.
[0002]
[Prior art]
The inverter device is a device that converts an applied DC link voltage into an AC voltage, and is particularly used for driving an induction motor. Such an inverter device converts the applied DC link voltage into an AC voltage by performing pulse width control or the like. The output voltage is determined by the voltage value of the applied DC link voltage, the on-duty in the pulse width control, and the like.
[0003]
Also, an inverter device having an output capacity corresponding to the rating of the induction motor is used. The output capacity of the inverter device is determined by the output voltage and the output current, and the rating of the element used for the inverter device is also determined by the output capacity. In particular, some VVVF (variable voltage variable frequency output) inverters for driving an induction motor can be operated with an output capacity larger than that.
[0004]
[Problems to be solved by the invention]
However, if the rated current is output when the output voltage of the inverter device is high, the output capacity of the inverter device increases. When the output capacity of the inverter device increases, it is necessary to use the element built in the inverter device according to the output capacity. For this reason, the element with a rating that is one rank higher is used. Will have to do. In addition, a fan having a large heat dissipation effect is required, which increases the size of the inverter device and increases the cost.
[0005]
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an inverter device and a control method thereof that can prevent an increase in size and cost.
[0006]
[Means for Solving the Problems]
In order to achieve this object, an inverter device according to the first aspect of the present invention provides:
An inverter device provided between a DC power source and a load, and setting a rated current of an output current to the load according to a voltage value of a DC voltage supplied from the DC power source,
A voltage converter that converts the DC voltage into an AC voltage based on a control signal and supplies the AC voltage to the load;
A control unit that generates the control signal and supplies the control signal to the voltage conversion unit,
The controller is
When the voltage value of the DC voltage is less than or equal to a first threshold value, the output capacity of the voltage conversion unit can be kept below a preset maximum output capacity to enable continuous operation of the voltage conversion unit. Set the current value to the rated current,
When the voltage value of the DC voltage exceeds the first threshold and is equal to or less than the second threshold, the output capacity of the voltage converter is less than or equal to the maximum output capacity to enable continuous operation of the voltage converter. Set the current value obtained by performing control to maintain a constant value of
When the voltage value of the DC voltage exceeds the second threshold value, a second current lower than the first current value is used for a short time operation in order to enable a short time operation of the voltage conversion unit. Set the value to the rated current,
The control signal is generated so that the output current of the voltage conversion unit is equal to or less than each of the rated currents, and is supplied to the voltage conversion unit .
[0012]
The control method of the inverter device according to the second aspect of the present invention is:
A control method for an inverter device, which is provided between a DC power supply and a load, and sets a rated current of an output current to the load according to a voltage value of a DC voltage supplied from the DC power supply,
The inverter device includes a voltage conversion unit that converts the DC voltage into an AC voltage based on a control signal and supplies the AC voltage to the load.
When the voltage value of the DC voltage is less than or equal to a first threshold value, the output capacity of the voltage conversion unit can be kept below a preset maximum output capacity to enable continuous operation of the voltage conversion unit. Set the current value to the rated current,
When the voltage value of the DC voltage exceeds the first threshold and is equal to or less than the second threshold, the output capacity of the voltage converter is less than or equal to the maximum output capacity to enable continuous operation of the voltage converter. Set the current value obtained by performing control to maintain a constant value of
When the voltage value of the DC voltage exceeds the second threshold value, a second current lower than the first current value is used for a short time operation in order to enable a short time operation of the voltage conversion unit. Setting the value to the rated current;
Generating the control signal such that an output current of the voltage converter is equal to or less than the rated current and supplying the control signal to the voltage converter;
It is characterized by including .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an inverter device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of the inverter device according to the present embodiment.
The inverter device according to the present embodiment is a voltage source inverter whose output voltage is a square wave, and includes a DC smoothing capacitor 11, a voltage converter 12, a U-phase current detector 13, and a V-phase current detector 14. A rotor position detector 15, a DC link voltage detector 16, and a control unit 17.
[0014]
The DC smoothing capacitor 11 is for smoothing the DC voltage of the DC power supply 18.
[0015]
The voltage converter 12 converts the DC link voltage smoothed by the DC smoothing capacitor 11 into an AC voltage based on the voltage command value supplied from the controller 17, and includes transistors Q1 to Q6 and diodes D1 to D1. D6. In addition, IGBT (Injection Enhanced Gate Transistor) etc. are used for these transistors Q1-Q6.
[0016]
The transistors Q <b> 1 to Q <b> 6 are switching elements that switch based on the pulse signal supplied from the control unit 17, and the collectors of the transistors Q <b> 1, Q <b> 3, and Q <b> 5 are connected to the positive electrode of the DC smoothing capacitor 11. The collectors of the transistors Q2, Q4, and Q6 are connected to the emitters of the transistors Q1, Q3, and Q5, respectively, and the emitters are connected to the negative electrode of the DC smoothing capacitor 11, respectively.
[0017]
A U-phase winding of the induction motor 19 is connected to a connection point between the emitter of the transistor Q1 and a collector of the transistor Q2, and a V-phase winding is connected to a connection point between the emitter of the transistor Q3 and the collector of the transistor Q4. A W-phase winding is connected to a connection point between the emitter of the transistor Q5 and the collector of the transistor Q6.
[0018]
The diodes D1 to D6 are diodes for commutating the output current when the transistors Q1 to Q6 are turned off. The cathodes of the diodes D1 to D6 are connected to the collectors of the transistors Q1 to Q6, respectively, and the anodes are connected to the emitters of the transistors Q1 to Q6, respectively.
The voltage converter 12 applies the converted AC voltage to a three-phase induction motor (denoted as “IM” in the figure) 19.
[0019]
The U-phase current detector 13 and the V-phase current detector 14 detect current values Iu and Iw of currents supplied to the U-phase and W-phase primary windings (stator windings) of the induction motor 19, respectively. .
[0020]
The rotor position detector 15 detects the rotation angle of the rotor shaft with respect to the winding axis of the stator of the induction motor 19 (for example, the U-phase winding axis is used as a reference axis).
[0021]
The DC link voltage detector 16 detects the voltage value Vdc of the DC voltage smoothed by the DC smoothing capacitor 11.
[0022]
The control unit 17 acquires current values Iu and Iv from the U-phase current detector 13 and the V-phase current detector 14, respectively, and controls the voltage conversion unit 12 based on the acquired current values Iu and Iv. In the present embodiment, vector control is used as the control method.
[0023]
When performing vector control, the control unit 17 calculates three-phase voltage command values Vu *, Vv *, and Vw *. In the case of the VVVF inverter, the control unit 17 sets a frequency based on the voltage command values Vu *, Vv *, Vw *, and generates a pulse signal based on this frequency. Then, the control unit 17 outputs this pulse signal to the voltage conversion unit 12.
[0024]
Further, the control unit 17 performs control so that the output power of the inverter device does not exceed the maximum output capacity (maximum output power). As described above, the output capacity of the inverter device is obtained based on the output voltage and the output current. Since it is difficult to detect the output voltage, the control unit 17 can continuously operate so that the output power of the inverter device does not exceed the maximum output capacity (maximum output power) based on the voltage value Vdc of the DC link voltage. Control is performed so that the output capacity is constant over a wide range.
[0025]
In order to perform such control, threshold values Vdc1 and Vdc2 are set to the voltage value of the DC link voltage Vdc. The threshold value Vdc1 is a threshold value corresponding to the maximum output capacity of the inverter device, and is a threshold value for switching to constant capacity control. The threshold value Vdc2 is a threshold value indicating a range in which continuous operation is possible. The control unit 17 includes a memory and stores threshold values Vdc1 and Vdc2 in this memory in advance.
[0026]
Next, the operation of the inverter device according to the present embodiment will be described.
The DC smoothing capacitor 11 smoothes the DC voltage of the DC power supply 18. The DC link voltage smoothed by the DC smoothing capacitor 11 is applied to the transistors Q1 to Q6 of the voltage converter 12. The DC link voltage detector 16 detects the voltage value Vdc of the DC link voltage.
[0027]
When the transistors Q1 to Q6 are turned on and off, an alternating voltage is generated, and a current flows through each of the U, V, and W phase windings of the induction motor 19. The U-phase current detector 13 and the V-phase current detector 14 detect current values Iu and Iv of currents flowing in the U and V phase windings of the induction motor 19, respectively.
[0028]
When performing vector control, the control unit 17 acquires the current values Iu and Iv from the U-phase current detector 13 and the V-phase current detector 14, and acquires the rotor position from the rotor position detector 15. . The current value Iw of the W-phase current is calculated from the current value Iu and the current value Iv based on the condition of three-phase equilibrium.
[0029]
The controller 17 uses the rotor position to perform coordinate conversion of the current values Iu, Iv, and Iw of the stationary coordinate system with the stator axis as the observation coordinate, and excites the rotary coordinate system with the rotor axis as the observation coordinate. A current value Id and a torque current value Iq are obtained.
[0030]
When the current command value Id * of the excitation current and the current command value Iq * of the torque current are set, the control unit 17 determines the deviation ed between the current command value Id * of the excitation current and the excitation current value Id, A deviation eq between the torque command value Iq * and the torque current value Iq is obtained.
[0031]
When determining the deviations ed and eq, the control unit 17 performs a PI (proportional integration) operation or the like of the obtained deviations ed and eq, and outputs voltage command values Vd * and Vq * such that the deviations ed and eq become zero, respectively. Ask.
[0032]
Then, the control unit 17 performs coordinate conversion of the voltage command values Vd * and Vq * into the stationary coordinate system based on the rotor position, and obtains three-phase voltage command values Vu *, Vv *, and Vwu *.
When performing PWM (Pulse Width Modulation) control, the control unit 17 generates a pulse signal based on the obtained voltage command values Vu *, Vv *, and Vwu *, and the pulse signal is converted into the transistor Q1 of the voltage conversion unit 12. Output to the base of ~ Q6.
[0033]
The transistors Q1 to Q6 are turned on and off based on the pulse signal supplied from the control unit 17.
When the transistors Q1 and Q6 are turned on and the transistors Q2 to Q5 are turned off, the DC smoothing capacitor 11 is connected to the positive electrode of the DC smoothing capacitor 11 via the transistor Q1, the U-phase winding and the W-phase winding of the induction motor 19, and the transistor Q6. Current flows to the negative electrode.
[0034]
When the transistors Q3, Q6 are turned on and the transistors Q1, Q2, Q4, Q5 are turned off, the positive electrode of the DC smoothing capacitor 11 passes through the transistor Q3, the V-phase winding of the induction motor 19, the W-phase winding, and the transistor Q6. Thus, a current flows to the negative electrode of the DC smoothing capacitor 11. In this way, an AC voltage is generated, and an AC current flows through each of the U, V, and W phase windings of the induction motor 19.
[0035]
Further, the control unit 17 sets the current value of the rated current Ir based on the voltage value of the DC link voltage Vdc detected by the DC link voltage detector 16 so that the output capacity of the inverter device does not exceed the maximum output capacity. . Here, the rated current refers to the design limit of the output current of the inverter device.
[0036]
The operation of the controller 17 is shown in the flowchart of FIG.
The control unit 17 takes out the threshold values Vdc1 and Vdc2 from the memory (step S11).
Based on the current value Iu acquired from the U-phase current detector 13, the control unit 17 performs voltage drop compensation on the threshold values Vdc1 and Vdc2 extracted from the memory (step S12). This voltage drop compensation is for compensating a drop voltage caused by a switching element such as an IGBT.
The controller 17 first calculates the drop voltage Vdrop based on the following equation (1).
[0037]
[Expression 1]
Vdrop = kd × Iout + b (1)
In equation (1), kd is a device voltage drop coefficient resulting from the loss of a switching element such as an IGBT, and is obtained from the relationship between the current and voltage of the switching element as shown in FIG. Iout is the value of the output current output from the voltage converter 12, and is obtained based on the current values detected by the U-phase current detector 13 and the V-phase current detector 14. b is a bias.
[0038]
Further, the control unit 17 performs voltage drop compensation of the threshold values Vdc1 and Vdc2 based on the obtained drop voltage Vdrop, and obtains the threshold values Vdc11 and Vdc12 based on the following equations (2) and (3), respectively.
[Expression 2]
Vdc11 = Vdc1 + Vdrop (2)
[Equation 3]
Vdc12 = Vdc2 + Vdrop (3)
[0039]
Next, the control unit 17 acquires the voltage value of the DC link voltage Vdc from the DC link voltage detector 16 (step S13).
The control unit 17 compares the threshold values Vdc11 and Vdc12 for which voltage drop compensation has been performed with the voltage value Vdc acquired from the DC link voltage detector 16 (step S14).
[0040]
The controller 17 determines whether or not the voltage value Vdc exceeds the threshold value Vdc11 (step S15).
[0041]
If the voltage value Vdc does not exceed the threshold value Vdc11 (Vdc ≦ Vdc11), the maximum output capacity of the inverter device will not be exceeded even if the rated current flows through the induction motor 19. Therefore, when it is determined that the voltage value Vdc does not exceed the threshold value Vdc11 (No in step S15), the control unit 17 sets the rated current Ir to a constant value Iref (step S16).
[0042]
When it is determined that the voltage value Vdc exceeds the threshold value Vdc11 (Yes in step S15), the control unit 17 determines whether or not the voltage value Vdc is equal to or less than the threshold value Vdc12 (step S17).
[0043]
When the voltage value Vdc is less than or equal to the threshold value Vdc12 (Vdc11 <Vdc ≦ Vdc12), even if the inverter device can be continuously operated, if the current of the current value Iref flows through the inverter device, the maximum output capacity is exceeded. Therefore, when the control unit 17 determines that the voltage value Vdc is equal to or less than the threshold value Vdc12 (Yes in step S17), the rated current Ir is set so that the output capacity of the inverter device becomes a constant value based on the voltage value Vdc. Is reduced from the current value Iref (step S18).
[0044]
In order to obtain the rated current Ir, the controller 17 first obtains a current value Ia that is reduced from the current value Iref based on the following equation (4).
[Expression 4]
Ia = Iref × (Pout / (Vdc11 × k)) (4)
In Expression (4), Pout represents the maximum output capacity, and k represents a capacity coefficient set according to the output capacity (0 ≦ k ≦ 1). In the case of three phases, the value obtained by multiplying the power of each phase by the square root of 3 is the maximum output capacity Pout.
[0045]
And the control part 17 calculates | requires rated current Ir from which output capacity becomes fixed based on following Formula (5).
[Equation 5]
Ir = Iref−Ia (5)
[0046]
Next, when the voltage value Vdc exceeds the threshold value Vdc12 (Vdc12 <Vdc), even if the current value of the rated current Ir is reduced, when the inverter device is continuously operated, the output power of the inverter device is the maximum output capacity. Will be exceeded. Therefore, when it is determined that the voltage value Vdc exceeds the threshold value Vdc12 (No in step S17), the control unit 17 sets the rated current Ir to a constant value Idec for discontinuous operation. (Step S19).
[0047]
When performing the vector control, the control unit 17 sets the current command value Id * of the excitation current and the current command value Iq * of the torque current so as not to exceed the rated current Ir set in Steps S16, 18, and 19. .
The control unit 17 performs such control, so that the inverter device has characteristics as shown in FIG.
[0048]
When Vdc ≦ Vdc11 (denoted by (1) in the figure), the rated current Ir is set to the current value Iref. Even if the current of the current value Iref flows through the induction motor 19, the output capacity of the inverter device does not exceed the maximum output capacity.
[0049]
In the case of Vdc11 <Vdc ≦ Vdc12 (denoted by (2) in the figure), the rated current Ir is reduced according to the equation (5) according to the voltage value Vdc, and the output capacity of the inverter device does not exceed the maximum output capacity. It becomes like this.
[0050]
In the case of Vdc12 <Vdc (denoted by (3) in the figure), the rated current Ir becomes the current value Idec, so continuous operation cannot be performed, and the inverter device is operated discontinuously.
[0051]
If the voltage value Vdc is up to the voltage limit value Vsv, the inverter device can be operated in a short time, and the range in which the inverter device can be operated is up to the maximum voltage value Vov even in discontinuous operation. .
[0052]
As described above, according to the present embodiment, the control unit 17 sets the rated current based on the DC link voltage Vdc so that the output power of the inverter device does not exceed the maximum output capacity, and the voltage conversion unit 12 To control.
[0053]
Therefore, even if the voltage value Vdc is higher than the rated voltage, the switching elements such as the transistors Q1 to Q6 should be less than the output capacity of the inverter device and protect the inverter device. However, the same characteristics as the conventional one can be obtained. Further, it is not necessary to use a heat sink, a fan, or the like that is larger than the output capacity of the inverter device, so that the device can be prevented from being increased in size and cost. Further, the heat loss and temperature rise of the apparatus can be reduced, and the reliability can be improved.
[0054]
In addition, since only existing software is changed, such control can be performed without changing hardware.
[0055]
In carrying out the present invention, various forms are conceivable and the present invention is not limited to the above embodiment.
For example, the inverter device is not limited to a voltage source inverter, and can also be applied to a current source inverter in which an output current is a square wave.
[0056]
In the present embodiment, control is performed such that the capacity is constant based on the current value Vdc. However, if the output voltage can be detected, the constant capacity control is performed based on the output voltage. Can do. Further, it is not always necessary to make the capacity constant, and it is only necessary to control so as not to exceed the maximum output capacity.
[0057]
Moreover, a transistor, FET (field effect transistor), a thyristor, etc. can be used for the transistors Q1-Q6 of the voltage conversion part 12 according to electric power capacity.
[0058]
Further, the induction motor 19 is not limited to a three-phase one but may be a two-phase one or a multi-phase one exceeding three phases. Furthermore, a motive motor can be used instead of the induction motor.
Further, the speed control of the induction motor is not limited to vector control, and primary frequency control, voltage / frequency control, and the like can also be used.
[0059]
【The invention's effect】
As described above, according to the present invention, an increase in size and cost can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an inverter device according to an embodiment of the present invention.
FIG. 2 is a flowchart showing the operation of the control unit of FIG.
FIG. 3 is an explanatory diagram showing the contents of coefficients used for calculation.
4 is an explanatory diagram showing an operation of the inverter device of FIG. 1; FIG.
[Explanation of symbols]
12 Voltage conversion unit 13 U phase current detector 14 V phase current detector 16 DC link voltage detector 17 Control unit 19 Induction motor

Claims (2)

An inverter device provided between a DC power source and a load, and setting a rated current of an output current to the load according to a voltage value of a DC voltage supplied from the DC power source,
A voltage converter that converts the DC voltage into an AC voltage based on a control signal and supplies the AC voltage to the load;
A control unit that generates the control signal and supplies the control signal to the voltage conversion unit,
The controller is
When the voltage value of the DC voltage is less than or equal to a first threshold value, the output capacity of the voltage conversion unit can be kept below a preset maximum output capacity to enable continuous operation of the voltage conversion unit. Set the current value to the rated current,
When the voltage value of the DC voltage exceeds the first threshold and is equal to or less than the second threshold, the output capacity of the voltage converter is less than or equal to the maximum output capacity to enable continuous operation of the voltage converter. Set the current value obtained by performing control to maintain a constant value of
When the voltage value of the DC voltage exceeds the second threshold value, a second current lower than the first current value is used for a short time operation in order to enable a short time operation of the voltage conversion unit. Set the value to the rated current,
An inverter device, wherein the control signal is generated so that an output current of the voltage conversion unit is equal to or less than the rated currents and is supplied to the voltage conversion unit . A control method for an inverter device, which is provided between a DC power supply and a load, and sets a rated current of an output current to the load according to a voltage value of a DC voltage supplied from the DC power supply,
The inverter device includes a voltage conversion unit that converts the DC voltage into an AC voltage based on a control signal and supplies the AC voltage to the load.
When the voltage value of the DC voltage is less than or equal to a first threshold value, the output capacity of the voltage conversion unit can be kept below a preset maximum output capacity to enable continuous operation of the voltage conversion unit. Set the current value to the rated current,
When the voltage value of the DC voltage exceeds the first threshold and is equal to or less than the second threshold, the output capacity of the voltage converter is less than or equal to the maximum output capacity to enable continuous operation of the voltage converter. Set the current value obtained by performing control to maintain a constant value of
When the voltage value of the DC voltage exceeds the second threshold value, a second current lower than the first current value is used for a short time operation in order to enable a short time operation of the voltage conversion unit. Setting the value to the rated current;
Generating the control signal such that an output current of the voltage converter is equal to or less than the rated current and supplying the control signal to the voltage converter;
Control method for an inverter device which comprises a.

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