Converter controller

Abstract

To provide a converter controller that suppresses increases in switching loss of a semiconductor switching element of a converter and loss due to a voltage drop of an AC reactor, and also suppresses a drop in DC voltage of a converter in power running to suppress reduction in output torque of a motor.SOLUTION: A converter controller 1 comprises a converter circuit 2 which converts AC power from a three-phase power supply 100 into DC power, a converter control part 10 which controls switching of the converter circuit 2, and an AC reactor ACL which is arranged between the three-phase AC power supply 100 and converter circuit 2. The converter control part 10 has a current controller 41 which generates an energization command from the difference between a current command and a DC current of the converter circuit 2, and a gate controller 42.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a converter control device. [Background technology]

[0002] A motor control device with a power regeneration function consists of an AC reactor, a converter, a smoothing capacitor, and an inverter. When operating the motor in powered mode, the converter converts AC power to DC power, and the inverter converts the DC power back into AC power to drive the motor. When operating the motor in regenerative mode, the inverter converts the AC power generated by the motor back into DC power, and the converter converts the DC power back into AC power, which is then regenerated into the power supply.

[0003] Converters for power regeneration often use the 120° energization method for cost reasons. In this method, when the DC voltage is higher by a predetermined voltage than the peak value of the full-wave rectified voltage of the power supply voltage, the regenerative operation is performed. The upper and lower semiconductor switching elements of the converter for each phase are turned on in the 120° section of the phase with the highest voltage in the three-phase AC power supply and in the 120° section of the phase with the lowest voltage in the three-phase AC power supply, thereby regenerating current to the power supply. Furthermore, when the motor is powered, the upper and lower semiconductor switching elements of the converter are turned off, and full-wave rectification is performed using diodes.

[0004] Converter control devices without a power regeneration function do not have an AC reactor, and the converter is composed of diodes, which perform full-wave rectification when the motor is in power running mode. In contrast, converter control devices with a power regeneration function are equipped with an AC reactor, so the DC voltage drops when the motor is in power running mode due to the voltage drop across the AC reactor. Figure 5 shows a graph of the DC voltage when the motor is accelerated in a converter control device with a power regeneration function according to the prior art. As shown in the bottom part of Figure 5, the DC voltage before the motor is driven decreases from 280V to approximately 250V as the motor accelerates. Therefore, when the DC voltage decreases during motor acceleration, the voltage output from the inverter also decreases, reducing the torque output from the motor and lengthening the acceleration time, which is a problem.

[0005] For example, Patent Document 1 discloses a motor control device that includes a converter that converts AC voltage into DC voltage, a converter control unit that boosts the DC voltage to the target value when the detected DC voltage value is lower than the target DC voltage value, and a boost command means that sends a boost command to the converter control unit when a powering state detection signal from a powering detection means, an excess rotation speed detection signal from a rotation speed detection means, and an excess torque detection signal from a torque detection means are all input; the motor is controlled by supplying the DC voltage to an inverter and controlling the operation of the inverter based on a position command and a torque command calculated from the position detection value; and the converter control unit boosts the DC voltage to the voltage of a boost reference power supply when a boost command is input. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-287474 Summary of the Invention [Problem to be solved by the invention]

[0007] The motor control device disclosed in Patent Document 1 uses a PWM converter to determine the operating state of a motor, issue a boost command to boost the DC voltage to a boost reference voltage, and drive the motor. This PWM converter outputs a current command corresponding to the difference between the boost command and the DC voltage, amplifies the difference between the current command and the detected current value using an amplifier, and controls the current using PWM control. However, with this configuration, a high voltage control response is required to control the DC voltage in response to sudden acceleration of the motor. This requires a current control response several times greater than the voltage control response, necessitating a PWM frequency several times higher than the current control response. PWM control amplifies the current deviation and pulse-width modulates it, applying voltage to an AC reactor based on the average on-off duty ratio to generate current. Therefore, a high PWM frequency is required to improve the current control response. Patent Document 1 discloses a method for reducing switching losses in semiconductor switching elements due to high PWM frequencies by determining when the motor is rotating at high speed and outputting large torque, and issuing a boost command to shorten the boost time. However, in motors with a wide field-weakening region and constant output range, such as spindle motors, the voltage rise time during motor acceleration is long, which poses the problem of not being able to achieve sufficient loss reduction.In addition, increasing the PWM frequency also poses the problem of increased loss in the AC reactor.

[0008] Therefore, an object of the present invention is to provide a converter control device that suppresses the switching loss of the semiconductor switching elements of the converter and the increase in loss of the AC reactor due to switching, suppresses the drop in DC voltage during power running operation, and suppresses the reduction in motor output torque. [Means for solving the problem]

[0009] A converter control device according to one aspect of the present invention includes: a converter circuit for converting AC power from a three-phase AC power source into DC power; a converter control unit that controls switching of the converter circuit; an AC reactor disposed between the three-phase AC power supply and the converter circuit; Equipped with The converter control unit a current controller that generates a current command based on a difference between a current command and a DC current of the converter circuit; a gate controller; and the current controller has a hysteresis characteristic that controls the energization command to be on when the difference is equal to or greater than a first threshold, and controls the energization command to be off when the difference is equal to or less than a second threshold that is lower than the first threshold, The gate controller controls the lower switching semiconductor of the converter circuit based on the energization command in a 120° section of the phase of the three-phase AC power supply where the voltage is maximum. [Effects of the Invention]

[0010] The DC current flowing from the converter circuit to the smoothing capacitor is estimated, and a current control system is constructed using a hysteresis comparator to directly control the semiconductor switching elements of the converter circuit based on the instantaneous value of the DC current. A voltage control system is also constructed to control the DC voltage of the smoothing capacitor to the peak value of the power supply voltage during power running, so that the DC voltage of the smoothing capacitor remains constant. This makes it possible to provide a converter control device that does not require a current detector to detect the DC current, can lower the switching frequency, suppresses increases in cost and switching losses, suppresses a drop in DC voltage during power running, and suppresses a decrease in motor output torque. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram of a motor control device according to an embodiment of the present invention; [Figure 2] 10A and 10B are diagrams illustrating a power supply voltage, a current selection signal, a power supply current selected based on the current selection signal, and a DC current of a converter circuit. [Figure 3] FIG. 10 is a diagram showing waveforms of a voltage boosting operation when the motor is accelerated. [Figure 4] FIG. 4 is a diagram showing the waveform of a gate signal in FIG. 3. [Figure 5] 10 is a graph showing the DC voltage of a converter circuit when a motor is accelerated in a converter control device with a power regeneration function according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For the sake of convenience, the description of components having the same reference numerals as components already described in the description of the embodiments will be omitted.

[0013] [Embodiment] FIG. 1 is a block diagram of a motor control device 1 according to an embodiment of the present invention. 1, the motor control device 1 includes an AC reactor ACL, a converter circuit 2, a smoothing capacitor 3, an inverter circuit 4, a current detection unit 5, and a converter control unit 10. The motor control device 1 is connected to a three-phase AC power supply 100 on the input side and a motor M on the output side.

[0014] The converter circuit 2 is composed of three upper diodes and three lower semiconductor switching elements. The semiconductor switching elements are composed of, for example, IGBTs. When the motor M is in power running mode, the converter circuit 2 converts the three-phase AC input from the three-phase AC power supply 100 into DC. Here, the upper diodes and lower semiconductor switching elements refer to the diodes arranged on the upper side and the semiconductor switching elements arranged on the lower side in the circuit diagram, respectively.

[0015] The smoothing capacitor 3 is, for example, an electrolytic capacitor, and smoothes the direct current output from the converter circuit 2.

[0016] The inverter circuit 4 is a three-phase (u-phase, v-phase, w-phase) full-bridge circuit and is composed of six semiconductor switching elements. The semiconductor switching elements are composed of, for example, IGBTs. The inverter circuit 4 converts the direct current from the smoothing capacitor 3 or the direct current output by the converter circuit 2 into three-phase alternating current for driving the motor M and supplies it to the motor M.

[0017] The current detection unit 5 detects the power supply current of each phase flowing between the three-phase AC power supply 100 and the converter circuit 2.

[0018] The motor control device 1 supplies power from the three-phase AC power supply 100 to the motor M by energizing the semiconductor switching elements of the converter circuit 2 using a gate signal from the converter control unit 10 during the 120° section of the phase of the three-phase AC power supply where the voltage is greatest.

[0019] Converter control unit 10 has a voltage control unit 20, a DC current estimating unit 30, a current control unit 40, and a boost operation determining unit 50. Voltage control unit 20 has a voltage command calculator 21, a voltage controller 22, a limiter 23, and a filter 24. DC current estimating unit 30 has a phase detector 31, a current selection signal generating unit 32, and a selector 33. Current control unit 40 has a current controller 41 and a gate controller 42. Boost operation determining unit 50 has a boost start detector 51 and a boost stop detector 52.

[0020] A voltage command calculator 21 detects a peak value Vp of the power supply voltage, generates a voltage command Vc that is a value higher than the peak value Vp by a predetermined value Vs1, and outputs the voltage command Vc. A voltage controller 22 is configured, for example, as a proportional-integral controller, and generates and outputs a current command Ic from the difference between the voltage command Vc and a DC voltage Vd applied to the smoothing capacitor 3. A limiter 23 limits the current command Ic so as to restrict the range of the powering current, and a filter 24 removes ripple components from the current command Ic limited by the limiter 23.

[0021] The phase detector 31 detects the phase of a 120° section where the voltage of each phase of the three-phase AC power supply is maximum and the phase of a 120° section where the voltage of each phase of the three-phase AC power supply is minimum, and outputs a phase signal. The current selection signal generator 32 generates an AC current selection signal for current selection based on the phase signal. The AC current selection signal is generated so as to select the power supply current of the phase where the voltage increases or decreases, out of the two phases through which current flows.

[0022] The process of selecting an AC current will now be described in detail with reference to Fig. 2. Fig. 2 is a diagram showing the power supply voltage, the current selection signal, the power supply current (AC current) selected based on the current selection signal, and the DC current of the converter circuit 2 in an embodiment of the present invention. For example, in the first 60° section of the 120° section in which the R-phase voltage is maximum, indicated by reference numeral 32a, power supply currents for the R and S phases flow, and the R-phase voltage is increasing, so the R-phase is selected. Also, in the second 60° section of the 120° section in which the R-phase voltage is maximum, indicated by reference numeral 32b, power supply currents for the R and T phases flow, and the T-phase voltage is increasing in the negative direction, so the T-phase power supply current is selected with its sign inverted.

[0023] Returning to the explanation of Fig. 1, the selector 33 selects the power supply current detected by the current detection unit 5 based on the AC current selection signal from the current selection signal generation unit 32, and outputs the selected power supply current to the current control unit 40 and the boost operation determination unit 50. Here, the selection of the power supply current by the selector 33 is equivalent to AC-DC conversion, and a positive current value is output during power running.

[0024] In this way, the DC current estimation unit 30 detects the phase of the AC power in which the voltage is maximum, and selects the current of one of the phases of the AC power based on the detected phase, thereby making it possible to estimate with high accuracy the DC current Id of the converter circuit 2 during powering operation.

[0025] The current controller 41 is configured by, for example, a hysteresis comparator, and generates a conduction command Ci from the difference between the current command Ic from the voltage controller 20 and the estimated value of the DC current Id from the DC current estimator 30, and outputs the generated conduction command Ci to the gate controller 42. Specifically, the current controller 41 has a hysteresis characteristic, and controls the conduction command Ci to be turned on when the difference becomes equal to or greater than a first threshold value Th1, and controls the conduction command Ci to be turned off when the difference becomes equal to or less than a second threshold value Th2 that is lower than the first threshold value Th1.

[0026] The boost start detector 51 compares the DC voltage Vd applied to the smoothing capacitor 3 with the peak value Vp of the power supply voltage, detects that the DC voltage Vd is lower than the peak value Vp of the power supply voltage by a predetermined value or more, and outputs a boost start signal to the gate controller 42. Here, since it is only necessary to detect that the DC voltage Vd has dropped, the predetermined value may be set to a very small value. The boost stop detector 52 outputs a boost stop signal to the gate controller 42 when it detects that the current command has been 0 for a certain period of time.

[0027] The gate controller 42 generates a gate signal based on the energization command Ci from the current controller 41, the boost start signal from the boost start detector 51, and the boost stop signal from the boost stop detector 52. The gate controller 42 also outputs the gate signal to the converter circuit 2 to control the semiconductor switching elements of the converter circuit 2.

[0028] Specifically, when the gate controller 42 receives a boost start signal from the boost start detector 51, it starts the boost operation, and generates a gate signal that controls the semiconductor switching element of the corresponding lower phase based on the energization command Ci in the 120° section of the phase in which the 120° period phase signal from the phase detector 31 is at its maximum.

[0029] 3 is a diagram showing waveforms of a voltage step-up operation when accelerating the motor M. When the value obtained by subtracting the estimated value of the DC current Id from the current command Ic is equal to or greater than a first threshold value Th1 (45 A in the example of FIG. 3), the energization command Ci is controlled to be turned on, and when the value obtained by subtracting the estimated value of the DC current Id from the current command Ic is equal to or less than a second threshold value Th2 (5 A in the example of FIG. 3) that is lower than the first threshold value Th1, the energization command Ci is controlled to be turned off.

[0030] As shown in Figure 3, DC voltage Vd applied to smoothing capacitor 3 has ripples of about 10 V, but is stable at about 280 V. The ripples are of a magnitude that does not affect motor control. Furthermore, because motor control device 1 controls DC current Id using the hysteresis characteristics of current controller 41, ripples occur in DC current Id, but the frequency of energization command Ci is suppressed to about 500 Hz, suppressing switching losses in AC reactor ACL and semiconductor switching elements.

[0031] A specific process for generating the gate signal by the gate controller 42 will be described with reference to Fig. 4. Fig. 4 is a diagram showing the waveform of the gate signal in Fig. 3.

[0032] 4, in the 120° section of the phase in which the voltage of the three-phase AC power supply is maximum, that is, when the upper phase signal is on, the gate signal of the lower switching semiconductor of the corresponding phase is generated based on the energization command Ci. Therefore, when the energization command Ci is on, the lower gate signal of the corresponding phase is on, and when the energization command Ci is off, the lower gate signal of the corresponding phase is off.

[0033] As described above, in the embodiment of the present invention, the DC current flowing from the converter circuit to the smoothing capacitor is estimated, and a hysteresis comparator is used to immediately drive the switching semiconductor when the difference between the current command and the DC current is equal to or greater than the first threshold, and to immediately stop the switching semiconductor when the difference between the current command and the DC current is equal to or less than the second threshold.

[0034] In this way, the current is controlled by directly driving the switching semiconductor based on the instantaneous value of the DC current in the converter circuit, which allows for extremely fast current response. In addition, by providing a hysteresis width, the switching frequency of the switching semiconductor can be lowered.

[0035] The voltage command calculator 21 may generate and output a voltage command Vc that is a constant value higher than the peak value Vp of the power supply voltage. In this case, the switching frequency of the switching semiconductor increases, but the field weakening of the motor is reduced, the output torque of the motor M is increased, and the acceleration time can be shortened. Also, the upper side of the converter circuit 2 may be configured with a switching semiconductor instead of a diode.

[0036] Although the embodiments of the present invention have been described above, it goes without saying that the technical scope of the present invention should not be construed as being limited by the description of the present embodiments. The present embodiments are merely examples, and it will be understood by those skilled in the art that various modifications of the embodiments are possible within the scope of the invention described in the claims. The technical scope of the present invention should be determined based on the scope of the invention described in the claims and its equivalents. [Explanation of symbols]

[0037] 1: Motor control device 2: Converter circuit 3: Smoothing capacitor 4: Inverter circuit 5: Current detection section 10: Converter control section 20: Voltage control section 21: Voltage command calculator 22: Voltage controller 23: Limiter 24: Filter 30: DC current estimation section 31: Phase detector 32: Current selection signal generator 33: Selector 41: Current controller 42: Gate controller 50: Boost operation determination unit 51: Boost start detector 52: Boost stop detector 100: Three-phase AC power supply M: Motor ACL: AC reactor

Claims

1. A converter control device, a converter circuit for converting AC power from a three-phase AC power source into DC power; a converter control unit that controls switching of the converter circuit; an AC reactor disposed between the three-phase AC power supply and the converter circuit; Equipped with The converter control unit a current controller that generates a current command based on a difference between a current command and a DC current of the converter circuit; a gate controller; and the current controller has a hysteresis characteristic that controls the energization command to be on when the difference is equal to or greater than a first threshold, and controls the energization command to be off when the difference is equal to or less than a second threshold that is lower than the first threshold, the gate controller controls a lower switching semiconductor of the converter circuit based on the energization command in a 120° section of a phase of the three-phase AC power supply in which a voltage is maximum.

2. the converter control unit further includes a DC current acquisition unit that acquires the DC current; The converter control device according to claim 1 , wherein the DC current acquisition unit is configured by a DC current estimation unit or a DC current detector.

3. 3. The converter control device according to claim 2, wherein the DC current estimation unit detects a phase of the three-phase AC power supply in which a voltage is maximum and a phase of the three-phase AC power supply in which a voltage is minimum, and selects a current of any one of the phases of the three-phase AC power supply based on the detected phase, and estimates the DC current.

4. the converter control unit further includes a voltage control unit, The converter control device according to claim 1 , wherein the voltage control unit generates the current command from a difference between a voltage command and a DC voltage of the DC power.

5. 5. The converter control device according to claim 4, wherein the voltage command is a value that is set based on a peak value of a voltage of the three-phase AC power supply.

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