JP2021168581A - Power conversion device - Google Patents

Abstract

To provide a power conversion device which can reduce distortion of input current to be caused by overmodulation.SOLUTION: A power conversion device comprises: a converter; and a control part. The converter has: a plurality of diodes connected with a three-phase AC power supply; and a plurality of switch elements connected in parallel with the diodes, performs DC conversion of voltage of the AC power supply and boosts the voltage by switching. The control part performs sine-wave modulation of the switching of the converter so that DC voltage output by the converter becomes a target value, and input currents to the converter become sine waves, respectively, and controls the target value so that distortion of the input currents to the converter become minimum in an operation area of the converter in which the sine-wave modulation becomes a state of overmodulation.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power conversion device including a converter that converts and boosts the voltage of a three-phase AC power supply to DC.

Power conversion that converts the voltage of a three-phase AC power supply into DC with a converter (PWM converter), boosts the voltage, converts the DC voltage into an AC voltage of a predetermined frequency with an inverter, and outputs the AC voltage as drive power for a load such as a motor. The device is known.

This power converter detects the phase of the power supply voltage (zero cross point), the DC voltage of the converter, and the input current to the converter, so that the DC voltage output by the converter becomes the target value and the input current to the converter. The converter switching is sinusoidally modulated so that is sinusoidal (so that harmonics can be suppressed). That is, in the sinusoidal modulation for driving the converter, the sinusoidal duty command value whose voltage level changes according to the target value is pulse width modulated (PWM modulation; voltage comparison) with a triangular wave-shaped carrier signal of a predetermined frequency. As a result, a driving signal for switching whose pulse width (on / off duty) is determined according to the above target value is generated.

Further, the power conversion device switches the inverter so that the speed of the motor, which is a load, becomes the target speed required for its operation.

In sinusoidal modulation for driving a converter, when the DC voltage of the converter is 2 / √3 times (about 1.15 times) or less of the DC voltage at no load due to non-switching, the duty command value exceeds the voltage level of the carrier signal. It becomes the state of. By setting this overmodulation state, it is possible to reduce the power loss due to the switching of the converter.

Japanese Unexamined Patent Publication No. 2018-88741

When the sinusoidal modulation for driving the converter is in the overmodulated state, the input current to the converter is distorted. This distortion becomes a harmonic and is transmitted to the power supply side, which adversely affects the operation of other equipment.

An object of the present embodiment is to provide a power conversion device capable of reducing distortion of an input current caused by overmodulation.

The power conversion device according to claim 1 includes a converter and a control unit. The converter has a plurality of diodes connected to an AC power supply and a plurality of switch elements connected in parallel to these diodes, and converts and boosts the voltage of the AC power supply by switching. The control unit performs sine wave modulation of the switching of the converter so that the DC voltage output by the converter becomes a target value and the input current to the converter becomes a sine wave, and the sine wave modulation performs the sine wave modulation. The target value is controlled so that the distortion of the input current to the converter is minimized in the operating region of the converter in the overmodulated state.

The block diagram which shows the structure of one Embodiment. The figure which shows the specific structure of the sine wave modulation part in one Embodiment. The figure which shows the sine wave modulation with respect to the PWM converter in one Embodiment. The figure which shows the relationship between the distortion of an input current and the step-up ratio of a converter when each phase voltage of a three-phase AC power source is in a balanced state in one Embodiment. The figure which shows the relationship between the distortion of an input current, and the step-up ratio of a converter when the voltage of each phase of a three-phase AC power source is not in equilibrium state in one Embodiment. The figure which shows the example of the effective value of the power supply voltage, the target value, and the effective value of an input current when each phase voltage of a three-phase AC power source is in a balanced state in one embodiment. The flowchart which shows the control of the control part in one Embodiment.

Hereinafter, one embodiment will be described with reference to the drawings.
As shown in FIG. 1, a converter (also referred to as a PWM converter) 4 is connected to a three-phase AC power supply 1 via an LC filter 2 and reactors 3r, 3s, 3t, and a smoothing capacitor 5 is connected to the output end of the converter 4. Has been done. Then, an inverter 6 is connected to the smoothing capacitor 5, and each phase winding of a load, for example, a three-phase brushless DC motor (referred to as a motor) 7 is connected to the output end of the inverter 6.

The converter 4 has a bridge circuit of a plurality of diodes Tad to Tfd, and switch elements (for example, IGBTs) Ta to Tf connected in parallel to these diodes Tad to Tfd, and boosts and converts the voltage of the three-phase AC power supply 1 into DC. .. For example, a 200V three-phase AC voltage Vc is converted into a DC voltage of about 280V. The diodes Tad to Tfd are freewheeling diodes.

The bridge circuit of the diodes Tad to Tfd is an R-phase series circuit in which the diodes Tad and Tbd are connected in series and the interconnection points of both diodes are connected to the R phase of the 3-phase AC power supply 1, and the diodes Tcd and Tdd are connected in series. The interconnection point of the diode is connected to the S phase of the 3-phase AC power supply 1. The S-phase series circuit, the diodes Ted and Tfd are connected in series, and the interconnection point of both diodes is connected to the T phase of the 3-phase AC power supply 1. It is configured by bridging a T-phase series circuit.

The inverter 6 connects the switch elements (for example, IGBT) T1 and T2 in series, and connects the switch elements T3 and T4 in series, which is a U-phase series circuit in which the interconnection point of both switch elements is connected to the U-phase winding of the motor 7. A V-phase series circuit in which the interconnection points of both switch elements are connected to the V-phase winding of the motor 7, the switch elements T5 and T6 are connected in series, and the interconnection points of both switch elements are connected to the W-phase winding of the motor 7. The W-phase series circuit is included, and the voltage of the smoothing capacitor 5 is converted into a 3-phase AC voltage of a predetermined frequency by switching of each switch element, and this is output as the drive power of the motor 7. The switch elements T1 to T6 have freewheeling diodes T1d to T6d.

The motor 7 is composed of a stator having three phase windings connected in a star shape and a rotor having a permanent magnet, and operates by the output of the inverter 6.

Current sensors 11r and 11s that detect the input currents Ir and Is to the converter 4 are arranged on the R-phase and S-phase energization lines between the three-phase AC power supply 1 and the reactors 3r and 3s. Current sensors 12u and 12v for detecting the current flowing through the U-phase / V-phase windings of the motor 7 so-called motor current are arranged in the energizing path between the output end of the inverter 6 and the motor 7. The detection results of these current sensors 11r, 11s, 12u, 12v are supplied to the control unit 10.

The control unit 10 is composed of a microcomputer and its peripheral parts, and the converter 4 has a DC voltage Vdc of the converter 4 as a target value Vdct and input currents Ir, Is, and It to the converter 4 as sine waves. In addition to sine wave modulation of the switching, the distortion δ (%) of the input currents Ir, Is, and It to the converter 4 is minimized in the operating region of the converter 4 in which the sine wave modulation is in the overmodulated state. The target value Vdct is controlled.

As a specific means of this control, the control unit 10 is a phase detection unit 21 that detects a zero cross point of the phase voltage Vr, Vs, Vt of the three-phase AC power supply 1, and a detection current of the current sensors 11r, 11s ( Input current) A coordinate conversion unit 22 that converts Ir and Is into an invalid component current Iq and an active component current Id, and a subtraction for obtaining the deviation ΔIq between the invalid component current Iq obtained by the coordinate conversion unit 22 and the invalid component current target value Iqref. Unit 23, the subtraction unit 24 for obtaining the deviation ΔId between the active component current Id obtained by the coordinate conversion unit 22 and the active component current target value Idref supplied from the PI control unit 33 described later, and these subtraction units 23 and 24. PI control to obtain the invalid component (q-axis component) Vq and active component (d-axis component) Vd of the DC voltage Vdc to be output from the converter 4 by calculating the deviations ΔIq and ΔId respectively in proportion and integral control (PI control). Units 25 and 26, coordinate conversion unit 27 for setting sinusoidal AC voltage command values Er, Es, Et at a level corresponding to the invalid component Vq and the active component Vd obtained by the PI control units 25 and 26, this coordinate conversion. The sine wave modulation unit 28 that generates drive signals Sr, Ss, St for switching to the switch elements Ta to Tf of the converter 4 by sine wave modulation based on the AC voltage command values Er, Es, Et set in the unit 27 is included.

Specifically, as shown in FIG. 2, the sine wave modulation unit 28 provides a division unit 28d for normalizing each AC voltage command value Er, Es, Et, and a carrier signal (triangle wave signal) Eo having a predetermined frequency. It is composed of a carrier signal generation unit 28a to be output, a comparison unit 28b, and an inversion unit (NOT circuit) 28c that inverts the output of the comparison unit 28b. Each AC voltage command value Er, Es, Et is divided by the DC voltage Vdc to be output by the converter 4 by the dividing unit 28d, and is normalized as the duty command values Dr, Ds, Dt. The duty command values Dr, Ds, and Dt determine the on-time of the switch elements Ta to Tf of the converter 4, that is, the duty. The duty command values Dr, Ds, and Dt are compared with the carrier signal Eo output from the Yaria signal generation unit 28a in the comparison unit 28b, respectively. Here, the carrier signal Eo is a triangular wave that changes in a width of "+1" to "-1". The carrier signal may be a sawtooth wave, which is a kind of triangular wave. Each comparison unit 28b compares the carrier signal Eo with the normalized duty command values Dr, Ds, and Dt, and outputs "1" or "0" depending on the magnitude relationship thereof.

The output of each comparison unit 28b is divided into two, one of which becomes the drive signals Sa, Sc, and Se of the upper switching elements Ta, Tb, and Tc as they are, and the other output is logically inverted by the inversion unit 28c to switch to the lower side. The drive signals Sb, Sd, Sf of the elements Tb, Td, and Tf. At this time, the signal of "1" becomes an on signal of each switching element Ta to Tf, and the signal of "0" becomes an off signal of each switching element Ta to Tf. In the actual driving of the switching element, a delay is provided in the on signal so that the upper and lower switching elements, for example, the switching element Ta and the switching element Tb do not turn on at the same time.

FIG. 3 shows the output waveform of each part. In this sinusoidal modulation, when the DC voltage Vdc of the converter 4 is 2 / √3 times (about 1.15 times) or less of the DC voltage Vdc (st) at no load due to non-switching, it is normalized as shown by the broken line in FIG. The duty command value Dr (Ds, Dt) is overmodulated to exceed the voltage level of the carrier signal Eo. When the load is low and it is not necessary to increase the output voltage Vdc of the converter 4, the power loss due to the switching of the converter 4 can be reduced by setting this overmodulation state.

Further, the control unit 10 includes a voltage detection unit 31, a subtraction unit 32, a PI control unit 33, a target value setting unit 40, a harmonic detection unit 41, and a motor control unit 50. The voltage detection unit 31 detects the DC voltage (voltage of the smoothing capacitor 5) Vdc of the converter 4. The subtraction unit 32 obtains a deviation ΔVdc between the detection voltage Vdc of the voltage detection unit 31 and the target value Vdct set by the target value setting unit 40. The PI control unit 33 obtains the active ingredient current target value Idref with respect to the active ingredient current Id by performing proportional / integral control (PI control) calculation on the deviation ΔVdc obtained by the subtraction unit 32.

The target value setting unit 40 sets the target value Vdct with respect to the DC voltage Vdc of the converter 4 based on the instruction from the motor control unit 50. Further, the target value setting unit 40 distorts the input currents Ir, Is, and It from the harmonics detected by the harmonic detection unit 41 in the operating region of the converter 4 in which the sine wave modulation is overmodulated. %) Is detected (calculated), and the target value Vdct set above is corrected so that the detected distortion δ (%) becomes the minimum value in the change of the valley described later.

The harmonic detection unit 41 Fourier-expands the changes in the input currents It obtained from the detection currents Ir and Is of the current sensors 11r and 11s and the detection currents Ir and Is, and thereby includes the harmonics included in the input currents Ir, Is and It. Detect wave components.

The motor control unit 50 estimates the speed of the motor 7 from the detected currents (motor currents) of the current sensors 12u and 12v, and the inverter so that this estimated speed becomes the target speed required for the load of the motor 7, for example, the operation of the compressor. The motor 7 is controlled to the target speed by operating 6 in a predetermined switching operation. FIG. 4 shows the relationship between the distortion δ of the input currents Ir, Is, and It when the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are in substantially the same equilibrium state with each other and the step-up ratio α of the converter 4. Since the distortions δ of the input currents Ir, Is, and It almost coincide with each other, only the distortion δ of the input currents of one phase is shown.

The boost ratio α is the ratio of the DC voltage of the converter 4 when the switching of the converter 4 is stopped, that is, the DC voltage Vdc (st) at no load, and the DC voltage Vdc of the converter 4 obtained by switching the converter 4. be.

歪みδは、入力電流Ｉｒ，Ｉｓ，Ｉｔのそれぞれｎ次高調波成分をＩｎとすると、次式で算出することができる。

Distortion δ can be calculated by the following equation, where In is the nth harmonic component of each of the input currents Ir, Is, and It.

昇圧比αが“1.15”未満の範囲にあるとき、正弦波変調が過変調の状態となる。この過変調の運転領域において、歪みδは、昇圧比αの上昇方向の変化に伴い、一旦下降してから上昇に転じて谷間を形成し、その谷間から山なりに上昇して再び下降していく。その後、歪みδは、過変調領域から脱したところで、上記谷間の最小値より十分に低い値で安定する。

When the boost ratio α is in the range of less than “1.15”, the sinusoidal modulation becomes overmodulated. In this overmodulated operating region, the strain δ descends once, then turns upward to form a valley, rises in a mountainous manner from the valley, and then falls again as the boost ratio α changes in the upward direction. go. After that, the strain δ stabilizes at a value sufficiently lower than the minimum value of the valley when the strain δ is removed from the overmodulation region.

If the open loop control is such that the AC voltage command value of the ideal sine wave waveform is input to the sine wave modulation unit 28 without the feedback control of the coordinate conversion unit 27 from the phase detection unit 21, the distortion δ is , The step-up ratio α = “0.97” is the minimum value of the change in the valley, and the step-up ratio α = “1.03” is the maximum value of the change in the peak.

When there is feedback control from the phase detection unit 21 to the coordinate conversion unit 27 and the control gain is “1”, the distortion δ is smaller than in the case of open loop control, and the valley is around the boost ratio α = “0.97”. It becomes the minimum value of change, and becomes the maximum value of mountainous change around the boost ratio α = “1.03”. Similarly, when there is feedback control and the control gain is “2”, the distortion δ is smaller than when the control gain is “1”, and becomes the minimum value of the change in the valley around the boost ratio α = “0.98”. The maximum value of the mountainous change is reached around the boost ratio α = “1.03”.

FIG. 5 shows an example of the relationship between the distortion δ of the input currents Ir, Is, and It when the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are not in equilibrium and the boost ratio α of the converter 4. The strain δ of each of the input currents Ir, Is, and It is shown by three lines. When the boost ratio α is in the range of less than “1.15”, the sinusoidal modulation becomes overmodulated.

In this overmodulated operating region, the distortion δ of the input current Ir rises in a mountain from the valley after temporarily falling and then turning to rise as the boost ratio α changes in the rising direction. It will descend again. The distortion δ of the input current Is continuously decreases without forming a valley as the boost ratio α changes in the ascending direction. The distortion δ of the input current It becomes flat once in the middle of the descent as the boost ratio α changes in the rising direction, and then falls again from there. That is, the distortion δ of the input current Ir has the minimum value of the change in the valley, but the distortion δ of the input currents Is and It does not have the minimum value of the change in the valley.

As described above, the distortion characteristics of the input currents Ir, Is, It differ depending on the control gain of the feedback control, and also differ depending on the equilibrium state of the phase voltages Vr, Vs, Vt of the three-phase AC power supply 1.

Here, regarding the values ν of the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1, the amplitudes of the duty command values Dr, Ds, and Dt obtained by normalizing the AC voltage command values Er, Es, and Et of sinusoidal modulation. It can be estimated from the relationship between D and the amplitude (voltage level) of the carrier signal Eo. In the normal operation region of the converter 4 in which the sinusoidal modulation does not become overmodulated, the values ν of the phase voltages Vr, Vs, and Vt are expressed by the following equations. The amplitude D of each of the duty command values Dr, Ds, and Dt is an internal calculation variable of the microcomputer constituting the control unit 10, and is a value that the control unit 10 can recognize by itself.

したがって、直接的な検出手段を要することなく、相電圧Ｖｒ，Ｖｓ，Ｖｔの値νを推定することができる。

Therefore, the values ν of the phase voltages Vr, Vs, and Vt can be estimated without requiring direct detection means.

When the sinusoidal modulation is in the overmodulated state, the trapezoidal wavy fundamental wave component γ of the duty command values Dr, Ds, and Dt contributes, so the values ν of the phase voltages Vr, Vs, and Vt are given by the following equation. It is represented by.

ただし、上式はオープンループ制御時に成立するもので、デューティ指令値Ｄｒ，Ｄｓ，Ｄｔの波形に変形を加えるフィードバック制御においては上式が必ずしも成立しない。このため、フィードバック制御がある場合は相電圧Ｖｒ，Ｖｓ，Ｖｔの値νを推定することが難しい。

However, the above equation holds during open loop control, and the above equation does not necessarily hold in feedback control that deforms the waveforms of duty command values Dr, Ds, and Dt. Therefore, when there is feedback control, it is difficult to estimate the values ν of the phase voltages Vr, Vs, and Vt.

When the converter 4 is operated by overmodulation in order to reduce the power loss due to the switching of the converter 4, the boost ratio α is searched so that the distortion δ of each of the input currents Ir, Is, and It becomes the minimum value of the change in the above valley. However, as described above, the minimum value of the change in the valley of the distortion δ differs depending on the control gain, and when the phase voltages Vr, Vs, and Vt are not in the equilibrium state, the distortion δ of the input current does not change in the valley. It is difficult to search for the boost ratio α because it may descend continuously.

Therefore, the target value setting unit 40 is provided on the condition that the speed (estimated speed) of the motor 7 is kept constant in the operating region of the converter 4 in which the sinusoidal modulation is in the overmodulated state (motor load). It is determined whether or not the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are in substantially the same equilibrium state with each other (provided that there is no change in the input current due to the fluctuation of the above).

The determination of the equilibrium state is performed using at least one of the comparison of the amplitude D of the duty command values Dr, Ds, and Dt of each phase and the comparison of the input currents Ir, Is, and It. For example, as shown in FIG. 6, when the phase voltages Vr, Vs, and Vt are in substantially the same equilibrium state, the peak values of the amplitudes D of the duty command values Dr, Ds, and Dt are substantially the same, and the input current Ir , Is, It are almost the same as each other. On the other hand, in an unbalanced state in which the phase voltage Vt deviates from the phase voltages Vr and Vs by a predetermined value or more, the amplitude D of the duty command value Dr deviates from the amplitude D of the duty command values Ds and Dt by a predetermined value or more, respectively. The state is set, and the input currents Ir, Is, and It are also deviated from each other by a predetermined value or more.

When in the equilibrium state, the target value setting unit 40 determines that the distortion δ will change in the valley, and detects the distortion δ sequentially by calculation from the harmonics, and the distortion δ is in the valley. The target value Vdct is increased or decreased by a predetermined value ΔV with an upper limit of 1.03 times the no-load DC voltage Vdc (st) so as to be within the minimum value of change. 1.03 times is the step-up ratio α when the strain δ is at the maximum value of the above-mentioned peak change. If the target value Vdct exceeds 1.03 times the unloaded DC voltage Vdc (st) when searching for distortion δ, the search for distortion δ cannot be returned to the minimum value side of the change in the valley. The upper limit of the distortion search is set to a value of 1.03 times the no-load DC voltage Vdc (st) so that In addition, by setting this upper limit, it is possible to prevent an unnecessary increase in the boost ratio α and, by extension, reduce power loss due to unnecessary switching.

If it is not in an equilibrium state, the target value setting unit 40 determines that the distortion δ may not change in the valley, and sequentially detects the distortion δ by calculation from the harmonic In. The target value Vdct is increased or decreased by a predetermined value ΔV so that the strain δ falls within the predetermined set value δs.

The control executed by the target value setting unit 40 will be described with reference to the flowchart of FIG.

The target value setting unit 40 is on the condition that the speed (estimated speed) of the motor 7 is kept constant in the operating region of the converter 4 in which the sinusoidal modulation is in the overmodulated state (motor load fluctuation). Initially set the no-load DC voltage Vdc (st) as the target value Vdct (provided that there is no change in the input current due to the above) (S1), and compare the amplitudes D of the duty command values Dr, Ds, and Dt with each other. (S2). If there is no deviation of a predetermined value or more in this comparison, the target value setting unit 40 determines that the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are in substantially the same equilibrium state with each other (YES in S3). If there is a deviation of a predetermined value or more in the above comparison, the target value setting unit 40 determines that the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are not in an equilibrium state (NO in S3).

When in the equilibrium state (YES in S3), the target value setting unit 40 detects the strain δ as “δ1” (S4) and adds a predetermined value ΔV to the target value Vdct (S6). Subsequently, the target value setting unit 40 detects the strain δ as “δ2” (S11) on condition that the boost ratio α is equal to or less than the upper limit of the strain search “1.03” (NO in S6), and the strain δ is detected as “δ2” (S11). The strain δ2 and the previously detected strain δ1 are compared (S12). When the strain δ2 detected later is smaller than the strain δ1 detected earlier (YES in S12), the target value setting unit 40 replaces the strain δ2 detected later with “δ1” (S14). When the strain δ2 detected later is the same as or larger than the strain δ1 detected earlier (NO in S12), the target value setting unit 40 inverts the predetermined value ΔV from the + value up to that point to the − value (S13). .. Then, the target value setting unit 40 replaces the distortion δ2 detected later with “δ1” (S14), and compares the amplitudes D of the duty command values Dr, Ds, and Dt with each other (S15). If there is no deviation of a predetermined value or more in this comparison, the target value setting unit 40 returns to the above S5 and adds a predetermined value ΔV to the target value Vdct based on the determination that the equilibrium state is reached (NO in S16). S5). After that, the processing of S11 to S16 is repeated on condition that the step-up ratio α is equal to or less than the upper limit of the strain search “1.03” (NO in S6). By repeating this, the strain δ decreases toward the minimum value of the change in the valley.

In the above determination of S6, when the boost ratio α is larger than the upper limit of the distortion search “1.03” (YES in S6), the target value setting unit 40 targets a value 1.03 times the no-load DC voltage Vdc (st). Set as the value Vdct (S7). Subsequently, the target value setting unit 40 detects the strain δ as “δ1” (S8), sets the predetermined value ΔV to a − value (S9), and adds it to the target value Vdct (S10). Then, the target value setting unit 40 detects the strain δ as “δ2” (S11), and compares the strain δ2 with the strain δ1 detected in the above S8 (S12). After that, the same process as described above is repeated. By repeating this, the strain δ decreases toward the minimum value of the change in the valley.

When the equilibrium state is not reached in the determination of S3 or the determination of S16 (NO in S3 or YES in S16), the target value setting unit 40 adds a predetermined value ΔV to the target value Vdct (S17). Subsequently, the target value setting unit 40 detects the strain δ (S18) and compares the strain δ with the set value δs (S19). When the strain δ is larger than the set value δs (YES in S19), the target value setting unit 40 repeats the process from S2. When the strain δ is the same as or smaller than the set value δs (YES in S19), the target value setting unit 40 inverts the predetermined value ΔV from the previous + value or − value (S20), and processes from the above S2. repeat. By repeating this, the strain δ decreases toward the set value δs.

As described above, regardless of whether the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are in the equilibrium state, the distortion δ caused by overmodulation is surely set to the minimum value or the set value δs of the change in the valley. It can be reduced.

In the above embodiment, the case where the load is a three-phase brushless DC motor has been described as an example, but the load is not limited and can be applied to various electric devices.

The above embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. This novel embodiment and modification can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the gist of the invention. These embodiments and modifications are included in the gist of the invention as well as in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... 3-phase AC power supply, 4 ... converter, 6 ... inverter, 7 ... 3-phase brushless DC motor, 11r, 11s ... current sensor, 21 ... phase detector, 28 ... sine wave modulator, 31 ... voltage detector, 40 ... target value setting unit, 41 ... harmonic detection unit, 50 ... motor control unit

Claims (3)

A converter having a plurality of diodes connected to a three-phase AC power supply, a plurality of switch elements connected in parallel to these diodes, and DC conversion and boosting of the AC power supply by switching.
The switching of the converter is sinusoidally modulated so that the DC voltage of the converter becomes a target value and the input current to the converter becomes a sine wave, and the sinusoidal modulation becomes an overmodulated state. A control unit that controls the target value so that the distortion of the input current to the converter is minimized in the operating region of the converter.
A power conversion device characterized by comprising. The control unit
By sine-wave-modulating a sinusoidal duty command value whose voltage level changes according to the target value with a carrier signal having a predetermined period, a drive signal for switching to the converter is generated.
In the operating region of the converter in which the sine wave modulation is in the overmodulated state, when the respective phase voltages of the AC power supply are in the balanced state, the target value is set to the unloaded DC so that the distortion of the input current is within the minimum value. The target value is increased or decreased by a predetermined value with a predetermined multiple of the voltage as the upper limit, and when the voltage of each phase of the AC power supply is not in the equilibrium state, the target value is increased or decreased by a predetermined value so that the distortion of the input current becomes a set value.
The power conversion device according to claim 1. An inverter that converts the DC voltage output by the converter into an AC voltage of a predetermined frequency and outputs it as drive power for the motor.
With more
The control unit
Whether each phase voltage of the AC power supply 1 is in a balanced state in the operating region of the converter in which the sinusoidal modulation is in a state of overmodulation and on condition that the speed of the motor is kept constant. Judge whether or not.
The power conversion device according to claim 1 or 2, wherein the power conversion device is characterized by the above.

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