JP2018174660A - Three-phase inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-phase inverter device in which current characteristics in response to a voltage command is improved so as not to have discontinuity positions due to a dead time.SOLUTION: A correction voltage generator 10 outputs correction voltages Zu, Zv, and Zw that is changed and repeated in three patterns in order of +Vc, -Vc, and 0 in each period Ts which is a half of the carrier signal period in synchronism with a signal of a triangular wave signal Wt from a carrier signal generating device 4. The correction voltages Zu, Zv, and Zw output a correction voltage value different in the period Ts at the same timing. The correction voltages Zu, Zv, and Zw are added to command voltages Vu, Vv, and Vw output from a current control part 3 in each of adders 11, 12, and 13, and are corrected to command voltages Vuc, Vvc, and Vwc. Thus, in a PWM converter 5, an on-off time of a PWM signal is corrected for the command voltages Vu, Vv, and Vw by a correction voltage repair.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a three-phase inverter device that performs three-phase current control of an electric motor.

  FIG. 7 is a block diagram showing a part of a conventional three-phase inverter device for an electric motor. In the figure, the inverter unit 2 is composed of three sets of switching elements in which switching elements Q1, Q2, Q3, Q4, Q5, and Q6 are bridge-connected. Each set of switching elements outputs a three-phase current of U phase, V phase, and W phase to the motor 1. The current detectors 14 and 15 detect U-phase and V-phase currents Iu and Iv, respectively, and the detected currents Iu and Iv are input to the current control unit 3. Inside the current control unit 3, the current command values Id, Iq in the orthogonal coordinate system from the previous stage are converted into three-phase command currents Iuc, Ivc, Iwc. Further, in the current control unit 3, a value obtained by adding Iu and Iv and changing the sign is set as a W-phase detection current Iw, and the detection currents Iu, Iv, and Iw are subtracted from the command currents Iuc, Ivc, and Iwc, respectively. Thus, current deviations Iud, Ivd, and Iwd are calculated. In the current control unit 3, the current deviations Iud, Ivd, and Iwd are converted into command voltages Vu, Vv, and Vw through the PID controllers of the respective phases and output. The command voltages Vu, Vv, and Vw are input to the PWM converter 5, and the triangular wave signal Wt from the carrier signal generator 4 that generates a triangular wave with the carrier frequency f is compared with the values of the command voltages Vu, Vv, and Vw. Command voltages Up, Un, Vp, Vn, Wp, Wn, which are PWM signals for changing the on / off width of the switching element, are generated. The command voltages Up, Un, Vp, Vn, Wp, Wn, which are PWM signals, are input to the inverter unit 2, and the switching elements Q1, Q2, Q3, Q4, Q5, Q6 are on / off controlled, respectively. Accordingly, the three-phase inverter device of FIG. 7 outputs a three-phase current of U phase, V phase, and W phase according to the command currents Iuc, Ivc, and Iwc to the electric motor 1. The PWM converter 5 compares the command voltages Vu, Vv, and Vw with the triangular wave signal Wt, and when Vu, Vv, and Vw are larger than the triangular wave signal Wt, the Up, Vp, and Wp are turned on, and Un, Vn and Wn are turned off. When Vu, Vv, and Vw are smaller than the triangular wave signal Wt, Up, Vp, and Wp are turned off, and Un, Vn, and Wn are turned on. However, since there is a delay in the response time until the upper and lower switching elements that are bridge-connected are turned on or off, there is a timing when the upper and lower switching elements of each set are simultaneously turned on, and the switching elements are short-circuited vertically. Problem to destroy. Therefore, the PWM converter 5 is provided with a dead time Td that prevents the other switching element from being turned on for a certain period of time immediately after one of the switching elements is turned off so that the bridge-connected upper and lower switching elements are not simultaneously turned on. The signals Up, Un, Vp, Vn, Wp, and Wn are output. During the dead time, both the upper and lower switching elements that are bridge-connected are turned off. However, in an electric motor having a winding that is an inductive load, the flowing current tends to flow even during the dead time period. Therefore, when a current flows in the positive direction, a current flows through a diode connected in parallel to the lower switching element even during the dead time period, and the lower switching element becomes the same as the ON state. Further, when a current flows in the negative direction, the current flows through a diode connected in parallel to the upper switching element even during the dead time period, and the upper switching element becomes the same as the ON state. For this reason, when the direction of the flowing current changes, the time width during which the upper and lower switching elements are turned on changes abruptly.

  Here, FIG. 5 shows a waveform diagram when the switching element is turned on and off by the command voltage shown in FIG. A broken line indicates the waveform of the conventional technique, and a solid line indicates the waveform of the embodiment.

  As described above, when the time width during which the switching element is turned on suddenly changes, the U-phase, V-phase, and W-phase voltages become discontinuous at the timing when the current flow direction is switched as shown by the broken line in FIG. As a result, the current waveform also becomes a distorted waveform as shown by the broken line in FIG. In this state, since the current of the motor cannot be faithfully controlled according to the command value, there is a problem that the rotational torque, rotational speed, or rotational position of the motor cannot be controlled with high accuracy.

  FIG. 8 is a block diagram showing an example of a three-phase inverter device in which a dead time compensator is added to the three-phase inverter device of FIG. The dead time compensator 6 detects the polarities of the command currents Iuc, Ivc, Iwc from the current control unit 3 and outputs dead time compensation voltages Du, Dv, Dw. Here, assuming that a voltage corresponding to half of the voltage change in which the U-phase, V-phase, and W-phase voltages change discontinuously and rapidly due to dead time is Vd, the dead time compensation voltages Du, Dv, and Dw correspond to each other. When the polarity of the command current is positive, it is + Vd, and when the polarity of the command current is negative, the corresponding phase compensation voltage is output as -Vd. In the adders 7, 8, and 9, the dead time compensation voltages Du, Dv, and Dw are added to the command voltages Vu, Vv, and Vw, respectively, and the dead time compensated command voltages Vu ′, Vv ′, and Vw ′ are PWMed. Output to the converter 5. By compensating for the dead time in this way, in the three-phase inverter device of FIG. 8, the U-phase, V-phase, and W-phase voltages and currents are normal as shown by the solid lines in FIGS. 5 (b) and 5 (c). Can be corrected to a simple waveform.

JP 09-084385 A

  In the above-described three-phase inverter device of FIG. 7, when a current is passed between the UV phases assuming a resistance load, the U-phase and V-phase current average currents with respect to the command voltages Vu and Vv are as shown by the broken lines in the graph of FIG. Characteristics. Since there is such a dead time, when the three phases are close to 0 voltage, there is no timing when the upper and lower sides of the six switching elements are simultaneously turned on, and a dead zone where no current flows in all phases is generated. Such characteristics are similar to those of the inductive load when the voltage and current are very small because the current flowing through the diode becomes 0 during the dead time period. Moreover, even if the electric current was somewhat distorted as the rotational speed of the electric motor increased, the inertial force acted, and even if the current distortion due to the dead time was large, the influence on the exercise performance was small. However, when the rotational speed is low, the inertial force does not work and the voltage applied to the windings of the motor is also small, so the performance of the motor is greatly deteriorated due to the dead time.

  However, in the three-phase inverter device to which the dead time compensator of FIG. 8 is added, the command voltage is instantaneously corrected to near the timing where the upper switching element and the lower switching element overlap with the dead time compensation voltage even near zero voltage. Therefore, there is no such problem in theory. However, since the switching element from OFF to ON or from ON to OFF does not change abruptly but changes gradually and switches, the dead time compensator 6 as shown in FIG. The effect could not be completely removed. In addition, since the response time until the switching element is turned on or off is also affected by element variation, temperature, and the like, the dead time is not always constant, and the optimum dead time compensation voltage value changes with time. Therefore, if the dead time compensation voltage is too small, a discontinuous characteristic in which the current hardly changes appears near the zero current as shown by the broken line in FIG. Further, if the dead time compensation voltage is too large, a portion near a discontinuity in which the current changes abruptly occurs as shown by a broken line in FIG. If it is a simple voltage-current characteristic with monotonous increase, current distortion can be removed by feedback from the current control unit. However, when discontinuous portions are formed as shown by broken lines in FIGS. 5C and 5D, it is difficult to reduce current distortion only by feedback. For the problem of changing the dead time, there is a method in which the dead time is directly measured and compensated in real time. However, the number of circuit elements increases and there is a problem of false detection due to the influence of noise and the like.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to improve a current characteristic with respect to a voltage command so that there is no discontinuous part due to dead time, and a three-phase inverter having a good current control characteristic. To provide an apparatus.

  The present invention relates to a three-phase inverter device that outputs three-phase current by turning on and off three sets of bridge-connected switching elements by a PWM signal having a carrier frequency, and is an integral multiple of a half cycle of the carrier frequency with a constant voltage Vc. The voltage of the PWM signal is corrected with a correction voltage of any of three values of + Vc, −Vc, 0 every period Ts, and the sum of the correction voltages of each phase is a period that is an integral multiple of 3 of the period Ts. In the three-phase inverter device, the correction amount of the voltage of the PWM signal for turning on and off the three sets of switching elements is + Vc and −Vc in at least two sets within the same timing period Ts.

  In the present invention, the on / off time by the PWM signal is corrected so as to correct the output voltage by the PWM within the cycle Ts with the voltage of any of the three patterns of + Vc, −Vc, 0 at the constant voltage Vc, and the same timing is obtained. Within the cycle Ts, at least two sets of correction voltages are + Vc and -Vc. For this reason, when the constant voltage | Vc | is larger than the optimum dead time compensation voltage Vd described with reference to FIG. 8, the upper switching element and the lower switching element are turned on even when the three-phase command voltages are all zero. Thus, there is always a timing for the current to flow on the motor side, and the dead zone of the current due to the dead time can be eliminated. In addition, since the sum of the correction voltages for each phase becomes 0 in a cycle that is an integral multiple of 3 of the cycle Ts, the applied average voltage or current becomes 0 in a cycle that is an integral multiple of 3 · Ts. In addition, when the cycle Ts is half of the carrier cycle and the condition of repeating + Vc → −Vc → 0, the frequency component applied by the correction voltage is a very high frequency of 2/3 times the carrier frequency. The adverse effect of the correction voltage on the motor can be ignored. Further, the discontinuous current characteristic due to the dead time can be improved by the dither effect by repeating the output voltage + Vc and −Vc.

  In addition, when the present invention is applied to a three-phase inverter device having a dead time compensator, even if the dead time compensation amount is made smaller than the optimum amount, the discontinuous current characteristic due to the dead time is improved by a dither effect. it can. For this reason, it is possible to eliminate the discontinuous portion due to the excessive amount of compensation while improving the linear characteristic of the current characteristic by dead time compensation. As a result, even if the switching element characteristics fluctuate due to temperature and element variations, the influence on the current characteristics can be suppressed to a small level. For this reason, highly accurate current control is possible even without a dead time measuring circuit or the like that increases costs.

It is a block diagram which shows the Example of the three-phase inverter apparatus of this invention. It is a block diagram which shows another Example of the three-phase inverter apparatus of this invention. It is a wave form diagram for operation | movement description of the three-phase inverter apparatus of this invention. It is a waveform diagram for explaining the operation of the conventional and three-phase inverter device of the present invention. It is a waveform diagram for explaining the operation of the conventional and three-phase inverter device of the present invention. It is a table | surface which shows the example of a pattern of the correction voltage of the three-phase inverter apparatus of this invention. It is a block diagram which shows the conventional three-phase inverter apparatus. It is a block diagram which shows the conventional three-phase inverter apparatus which added the dead time compensator.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1, the same functions and operations as those in FIG. 7 are denoted by the same reference numerals, and the description thereof is omitted.

  As described above, this embodiment includes the correction voltage generator 10 and the adders 11, 12, and 13 that are not included in the configuration of FIG. 7.

  The correction voltage generator 10 outputs correction voltages Zu, Zv, and Zw for the U, V, and W phases, which are supplied to adders 11, 12, and 13, where the U, V, and W phase command voltages Vu, It is added to Vv and Vw.

  Here, correction of the command voltages Vu, Vv, and Vw will be described with reference to FIG. In the current control unit 3, the triangular wave signal Wt of the carrier frequency is compared with the values of the command voltages Vu, Vv, Vw, and the command voltages Up, Un, which are PWM signals for changing the on / off width of the switching elements Q1 to Q6. Vp, Vn, Wp and Wn are generated and supplied to the adders 11, 12 and 13.

  The correction voltage generator 10 changes and repeats in three patterns in the order of + Vc, -Vc, 0 every period Ts that is half the carrier signal period in synchronization with the triangular wave signal Wt from the carrier signal generator 4. Correction voltages Zu, Zv, and Zw are output. That is, the correction voltage Zu is the command voltage Up, Un, the correction voltage Zv is the command voltage Vp, Vn, the correction voltage Zw is the command voltage Wp, Wn at the timing when the command voltage Wp, Wn is switched from on to off or off to on. The state of Vc, 0 is repeated in order. For this reason, the total sum of the correction voltages within a period three times the period Ts is zero. As shown in FIG. 3, the correction voltages Zu, Zv, and Zw output different correction voltage values within the same timing period Ts. For this reason, within the same timing period Ts, there are always two sets of phases in which the correction voltages are + Vc and -Vc. The correction voltages Zu, Zv, and Zw are added by the adders 11, 12, and 13, respectively, and the command voltages Vu, Vv, and Vw output from the current control unit 3 are added to be corrected to voltage commands Vuc, Vvc, and Vwc. As a result, the PWM converter 5 corrects the on / off time of the PWM signal by the correction voltage amount with respect to the command voltages Vu, Vv, and Vw.

  Thus, in the present embodiment, + Vc or −Vc is added as a correction voltage at the switching timing of the switch element three times. Therefore, when the constant voltage | Vc | is larger than the optimum dead time compensation voltage Vd described in FIG. 8, the upper switching element and the lower switching element are turned on even when the three-phase command voltages are all zero. Therefore, there is always a timing for current to flow to the motor side. Thereby, the dead zone of the current due to the dead time can be eliminated. In addition, since the sum of the correction voltages of each phase becomes 0 in a cycle that is an integral multiple of 3 of the cycle Ts, there is no adverse effect on the applied average voltage or current.

  In the three-phase inverter device of FIG. 1, when a current is passed between the UV phases assuming a resistance load, the characteristics of the average current of the U-phase and V-phase currents with respect to the command voltages Vu and Vv are indicated by the solid line in the graph of FIG. Thus, discontinuous characteristics near 0V due to dead time can be improved. Further, the voltage applied to the winding of the motor is as shown by the broken line in FIG. 5E, and the current is also free from discontinuous portions due to dead time as shown by the broken line in FIG. 5F. However, the characteristic of the broken line portion is a waveform when the feedback loop gain of the current control unit is low, and when the feedback loop gain is high, the waveform is a waveform as shown by the solid lines in FIGS.

  Further, as shown in FIG. 2, the dead time compensator 6 shown in FIG. 8 may be added to the three-phase inverter device of the present invention shown in FIG. In this case, if the compensation voltage Vd by the dead time compensator 6 is set below the optimum dead time compensation amount, and if | Vc | + | Vd | In addition to improving the waveform distortion as shown by the broken lines in FIGS. 5 (e) and 5 (f) without increasing the feedback loop gain, the voltage and current do not become discontinuous even if the dead time compensation amount is slightly deviated. A current waveform faithful to the command can be realized by feedback of the current control unit.

  FIG. 1 shows a pattern in which the half cycle of the carrier frequency is a period Ts and the correction voltages Zu, Zv, and Zw repeat at 3Ts. Other correction voltage patterns as shown in the table of FIG. 6 are also conceivable. As a pattern of the correction voltage, the correction voltage is one of three values of + Vc, −Vc, 0, and the sum of the correction voltages of each phase is 0 in a cycle that is an integral multiple of 3 of the cycle Ts. The present invention can be realized if the correction voltages of the three sets of switching elements are patterns in which at least two sets are + Vc and −Vc within the period Ts of the same timing.

  DESCRIPTION OF SYMBOLS 1 Electric motor, 2 Inverter part, 3 Current control part, 4 Carrier signal generator, 5 PWM converter, 6 Dead time compensator, 7, 8, 9, 11, 12, 13 Adder, 10 Correction voltage generator, 14 , 15 Current detector.

Claims (2)

In a three-phase inverter device that turns on and off three sets of switching elements connected in a bridge by a PWM signal of a carrier frequency and outputs a three-phase current,
The constant voltage is Vc, the voltage of the PWM signal is corrected with a correction voltage of any one of three values of + Vc, −Vc, and 0 every period Ts that is an integral multiple of a half cycle of the carrier frequency, and the correction of each phase The sum of the voltages becomes 0 in a cycle that is an integral multiple of 3 of the cycle Ts, and the correction amount of the voltage of the PWM signal that turns on and off the three sets of switching elements is + Vc in at least two sets within the cycle Ts of the same timing. And a three-phase inverter device characterized by being -Vc.   It has a dead time compensator that compensates the voltage of the PWM signal corresponding to the phase by −Vd or + Vd according to the polarity of the command current or the detection current of each phase of the three-phase current, and the compensation voltage Vd is the optimum dead time compensation. The three-phase inverter device according to claim 1, wherein the three-phase inverter device is set to be equal to or less than an amount, and the | Vc | + | Vd | is equal to or greater than an optimum dead time compensation amount.

Images