JP7356395B2 - power converter - Google Patents

Description

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

Power conversion that converts and boosts the voltage of a three-phase AC power supply to DC using a converter (PWM converter), converts the DC voltage to AC voltage at a predetermined frequency using an inverter, and outputs the AC voltage as driving power for loads such as motors. The device is known.

This power conversion device detects the phase of the power supply voltage (zero cross point), the DC voltage of the converter, and the input current to the converter, and adjusts the input current to the converter so that the DC voltage output by the converter is the target value, and the input current to the converter is The switching of the converter is modulated in a sine wave so that it becomes a sine wave (so that harmonics can be suppressed). That is, in this sinusoidal modulation for driving the converter, a 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 carrier signal of a predetermined frequency. As a result, a switching drive signal whose pulse width (on/off duty) is determined according to the target value is generated.

Further, the power converter switches the inverter so that the speed of the motor, which is the load, reaches a target speed necessary for its operation.

In sinusoidal modulation for converter drive, when the converter DC voltage is 2/√3 times (approximately 1.15 times) or less the no-load DC voltage due to non-switching, overmodulation occurs where the duty command value exceeds the voltage level of the carrier signal. The state will be as follows. By creating this overmodulation state, power loss due to switching of the converter can be reduced.

JP2018-88741A

When the sinusoidal modulation for driving the converter is in an overmodulated state, distortion occurs in the input current to the converter. This distortion becomes harmonics that are transmitted to the power supply side and adversely affect the operation of other equipment.

The purpose of this embodiment is to provide a power conversion device that can reduce input current distortion caused by overmodulation.

A power conversion device according to a first aspect of the present invention includes a converter and a control section. The converter includes a plurality of diodes connected to a three-phase AC power supply and a plurality of switch elements connected in parallel to these diodes, and converts and boosts the voltage of the three-phase AC power supply to DC by switching. The control unit sinusoidally modulates 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 The target value is controlled so that distortion of the input current to the converter is minimized in an operating region of the converter in which overmodulation occurs. In particular, the control unit generates a switching drive signal for the converter by sinusoidally modulating a sinusoidal duty command value whose voltage level changes according to the target value with a carrier signal of a predetermined period; In the operating range of the converter where the sine wave modulation is in an overmodulated state, when each phase voltage of the three-phase AC power supply is in a balanced state, the target value is set to zero so that the distortion of the input current is kept to a minimum value. The target value is increased or decreased by a predetermined value with the upper limit being a predetermined multiple of the load DC voltage, and if each phase voltage of the three-phase AC power supply is not in a balanced state, the target value is increased or decreased by a predetermined value so that the distortion of the input current becomes the set value. do.

FIG. 1 is a block diagram showing the configuration of an embodiment. FIG. 3 is a diagram showing a specific configuration of a sine wave modulation section in one embodiment. FIG. 2 is a diagram illustrating sinusoidal modulation for a PWM converter in one embodiment. FIG. 3 is a diagram showing the relationship between input current distortion and converter step-up ratio when each phase voltage of a three-phase AC power source is in a balanced state in one embodiment. FIG. 3 is a diagram showing the relationship between input current distortion and converter step-up ratio when each phase voltage of a three-phase AC power supply is not in a balanced state in one embodiment. The figure which shows the example of the effective value of power supply voltage, target value, and effective value of input current when each phase voltage of a 3-phase AC power supply is in a balanced state, and when it is not in an equilibrium state in one embodiment. 5 is a flowchart showing control by a control unit 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, and 3t, and a smoothing capacitor 5 is connected to the output end of the converter 4. has been done. An inverter 6 is connected to the smoothing capacitor 5, and each phase winding of a load, such as 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, switch elements (eg, 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 to DC. . For example, a three-phase AC voltage Vc of 200V is converted to a DC voltage of about 280V. The diodes Tad to Tfd are freewheeling diodes.

The bridge circuit of diodes Tad to Tfd is an R-phase series circuit in which diodes Tad and Tbd are connected in series and the interconnection point of both diodes is connected to the R phase of three-phase AC power supply 1, and a bridge circuit in which diodes Tcd and Tdd are connected in series and both diodes are connected in series. An S-phase series circuit in which the interconnection point of the diodes is connected to the S phase of the three-phase AC power supply 1, diodes Ted and Tfd are connected in series, and the interconnection point of both diodes is connected to the T phase of the three-phase AC power supply 1. It is constructed by bridge-connecting T-phase series circuits.

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

The motor 7 includes a stator having three star-connected phase windings and a rotor having permanent magnets, and is operated by the output of the inverter 6.

Current sensors 11r and 11s that detect input currents Ir and Is to the converter 4 are arranged in 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 that detect currents flowing in the U-phase and V-phase windings of the motor 7, so-called motor currents, are arranged in a current-carrying path between the output end of the inverter 6 and the motor 7. The detection results of these current sensors 11r, 11s, 12u, and 12v are supplied to the control unit 10.

The control unit 10 is composed of a microcomputer and its peripheral parts, and controls the converter 4 so that the DC voltage Vdc of the converter 4 becomes the target value Vdct and the input currents Ir, Is, and It to the converter 4 each become a sine wave. The switching is sinusoidally modulated, and the distortions δ (%) of the input currents Ir, Is, It to the converter 4 are minimized in the operating range of the converter 4 where this sine wave modulation is in an overmodulation state. The target value Vdct is controlled.

As a specific means for this control, the control unit 10 includes a phase detection unit 21 that detects zero-crossing points of the phases of the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1, and a detection current ( A coordinate conversion unit 22 that converts input currents) Ir and Is into reactive component current Iq and active component current Id, and subtraction to determine the deviation ΔIq between the reactive component current Iq obtained by this coordinate conversion unit 22 and the reactive component current target value Iqref. A subtraction unit 24 that calculates a deviation ΔId between the active component current Id obtained by the coordinate conversion unit 22 and an active component current target value Idref supplied from the PI control unit 33, which will be described later. PI control that calculates the reactive 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 proportional-integral control (PI control) of the deviations ΔIq and ΔId, respectively. parts 25 and 26, a coordinate transformation part 27 that sets sinusoidal AC voltage command values Er, Es, and Et at levels corresponding to the reactive component Vq and active component Vd obtained by the PI control parts 25 and 26, and the coordinate transformation part 27; It includes a sine wave modulation section 28 that generates switching drive signals Sr, Ss, St for the switching 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 section 27.

Specifically, as shown in FIG. 2, the sine wave modulation unit 28 includes a division unit 28d for normalizing each AC voltage command value Er, Es, and Et, and a carrier signal (triangular wave signal) Eo of a predetermined frequency. It consists of a carrier signal generating section 28a that outputs, a comparing section 28b, and an inverting section (NOT circuit) 28c that inverts the output of the comparing section 28b. Each AC voltage command value Er, Es, Et is divided by the DC voltage Vdc to be output from the converter 4 by a dividing unit 28d, and normalized as duty command values Dr, Ds, Dt. Duty command values Dr, Ds, and Dt determine the on time of switch elements Ta to Tf of converter 4, that is, the duty. Each of the duty command values Dr, Ds, and Dt is compared with the carrier signal Eo outputted from the carrier signal generation section 28a in the comparison section 28b. Here, the carrier signal Eo is a triangular wave whose width varies from "+1" to "-1". Note that the carrier signal may be a sawtooth wave, which is a type of triangular wave. Each comparator 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.

The output of each comparator 28b is divided into two parts, one of which directly becomes the driving signals Sa, Sc, and Se for the upper switching elements Ta, Tb, and Tc, and the other output is logically inverted by the inverting part 28c and used as the driving signal for the lower switching element Ta, Tb, and Tc. These become drive signals Sb, Sd, and Sf for the elements Tb, Td, and Tf. At this time, a signal of "1" becomes an on signal for each switching element Ta to Tf, and a signal of "0" becomes an off signal for each switching element Ta to Tf. Note that in actual driving of the switching elements, a delay is provided to the ON signal so that the upper and lower switching elements, for example, the switching element Ta and the switching element Tb, are not turned on at the same time.

Figure 3 shows the output waveforms of each part. In this sine wave modulation, when the DC voltage Vdc of the converter 4 is 2/√3 times (approximately 1.15 times) or less the no-load DC voltage Vdc(st) due to non-switching, normalization is performed as shown by the broken line in Figure 3. A state of overmodulation occurs in which the duty command value Dr (Ds, Dt) exceeds the voltage level of the carrier signal Eo. By entering this overmodulation state during low load times when there is no need to increase the output voltage Vdc of the converter 4, power loss due to switching of the converter 4 can be reduced.

Further, the control section 10 includes a voltage detection section 31 , a subtraction section 32 , a PI control section 33 , a target value setting section 40 , a harmonic detection section 41 , and a motor control section 50 . Voltage detection section 31 detects the DC voltage of converter 4 (voltage of smoothing capacitor 5) Vdc. The subtraction unit 32 calculates the deviation ΔVdc between the detected 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 calculates the active component current target value Idref for the above-mentioned active component current Id by calculating the deviation ΔVdc determined by the subtraction unit 32 using proportional-integral control (PI control).

Target value setting section 40 sets a target value Vdct for DC voltage Vdc of converter 4 based on instructions from motor control section 50 . Further, the target value setting unit 40 detects distortions δ( %) is detected (calculated), and the set target value Vdct is corrected so that the detected distortion δ (%) becomes the minimum value in the valley change described later.

The harmonic detection unit 41 performs Fourier expansion on the detected currents Ir, Is of the current sensors 11r, 11s and the changes in the input current It found from the detected currents Ir, Is, thereby detecting the harmonics included in the input currents Ir, Is, 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 controls the inverter so that this estimated speed becomes the target speed necessary for operating the load of the motor 7, such as the compressor. The motor 7 is controlled to the target speed by performing a predetermined switching operation of the motor 6. FIG. 4 shows the relationship between the respective distortions δ of the input currents Ir, Is, It and the step-up ratio α of the converter 4 when the phase voltages Vr, Vs, Vt of the three-phase AC power supply 1 are in substantially the same equilibrium state. Since the distortions δ of the input currents Ir, Is, and It are almost the same, only the distortion δ of the input current of one phase is shown.

The step-up ratio α is the ratio between the DC voltage of the converter 4 when switching of the converter 4 is stopped, so-called no-load DC voltage Vdc(st), and the DC voltage 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 n-th 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 step-up ratio α is in a range less than “1.15”, the sine wave modulation becomes overmodulated. In this overmodulated operating region, the strain δ, as the step-up ratio α changes in the upward direction, once decreases, then begins to increase, forming a valley, and from that valley rises like a mountain and then decreases again. go. Thereafter, the distortion δ is stabilized at a value sufficiently lower than the minimum value of the valley after exiting the overmodulation region.

If the open-loop control is such that an ideal sinusoidal waveform AC voltage command value is input to the sine wave modulator 28 without feedback control from the phase detector 21 to the coordinate converter 27, the distortion δ is , the minimum value of the valley change occurs around the step-up ratio α=“0.97”, and the maximum value of the peak change occurs around the step-up ratio α=“1.03”.

When there is feedback control from the phase detection section 21 to the coordinate transformation section 27 and the control gain is "1", the distortion δ decreases compared to the case of open-loop control, and the distortion δ decreases at around the step-up ratio α = "0.97". The minimum value of the change is reached, and the maximum value of the change is reached around the step-up ratio α=“1.03”. Similarly, when there is feedback control and the control gain is "2", the distortion δ decreases compared to the case where the control gain is "1", and the valley change reaches the minimum value around the step-up ratio α = "0.98". The maximum value of the peak change occurs around the step-up ratio α=“1.03”.

FIG. 5 shows an example of the relationship between the distortions δ of the input currents Ir, Is, and It, respectively, and the step-up ratio α of the converter 4 when the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are not in a balanced state. The distortion δ of the input currents Ir, Is, and It is shown by three lines, respectively. When the step-up ratio α is in a range less than “1.15”, the sine wave modulation becomes overmodulated.

In this overmodulation operating region, the distortion δ of the input current Ir, as the step-up ratio α changes in the upward direction, once decreases and then begins to increase, forming a valley, and then rising from the valley in the form of a mountain. It goes down again. The distortion δ of the input current Is continuously decreases without forming a valley as the step-up ratio α changes in the upward direction. As the step-up ratio α changes in the upward direction, the distortion δ of the input current It temporarily becomes flat during the downward movement, and then decreases again. That is, the distortion δ of the input current Ir has a 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.

In this way, the distortion characteristics of the input currents Ir, Is, It vary depending on the control gain of the feedback control, and also vary depending on the balanced state of the phase voltages Vr, Vs, Vt of the three-phase AC power supply 1.

Here, for the values ν of the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1, the amplitudes of duty command values Dr, Ds, and Dt, which are normalized AC voltage command values Er, Es, and Et of sine wave modulation, are respectively It can be estimated from the relationship between D and the amplitude (voltage level) of the carrier signal Eo. In the normal operating range of the converter 4 in which the sine wave modulation does not become overmodulated, the values ν of the phase voltages Vr, Vs, and Vt are expressed by the following equation. The amplitude D of each of the duty command values Dr, Ds, and Dt is an internal calculation variable of the microcomputer that constitutes the control section 10, and is a value that the control section 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.

Note that when the sine wave modulation is in an overmodulated state, the trapezoidal 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 determined by the following equation. It is expressed as

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 true during open-loop control, and does not necessarily hold true during feedback control that deforms the waveforms of the 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 operating the converter 4 with overmodulation in order to reduce power loss due to switching of the converter 4, the step-up 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 between the above valleys. However, as mentioned above, the minimum value of the change in the valley of the strain δ varies depending on the control gain, and if the phase voltages Vr, Vs, and Vt are not in an equilibrium state, the input current distortion δ will not change in the valley. It is difficult to search for the step-up ratio α because it may drop continuously.

Therefore, the target value setting unit 40 sets the condition that the speed (estimated speed) of the motor 7 remains constant (motor load (on the condition that there is no change in the input current due to fluctuations in the input current), it is determined whether the phase voltages Vr, Vs, and Vt of the three-phase AC power supply 1 are in substantially the same equilibrium state.

This equilibrium state is determined using at least one of a comparison of the amplitudes D of the duty command values Dr, Ds, and Dt of each phase, and a 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, and It are also almost the same. On the other hand, in an unbalanced state where the phase voltage Vt deviates from the phase voltages Vr and Vs by more than a predetermined value, the amplitude D of the duty command value Dr deviates from the amplitude D of each of the duty command values Ds and Dt by more than a predetermined value. The input currents Ir, Is, and It also deviate from each other by a predetermined value or more.

When in an equilibrium state, the target value setting unit 40 determines that the distortion δ changes between the valleys, and sequentially detects the distortion δ by calculation from the harmonics, so that the distortion δ changes between the valleys. 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 stay within the minimum value of the change. 1.03 times is the boost ratio α when the strain δ is at the maximum value of the above-mentioned peak change. If the target value Vdct exceeds the value of 1.03 times the no-load DC voltage Vdc(st) when searching for the strain δ, it will not be possible to return the search for the strain δ to the minimum value side of the change in the valley. To prevent this from occurring, the upper limit of the distortion search is set to 1.03 times the no-load DC voltage Vdc(st). Further, by setting this upper limit, unnecessary increases in the step-up ratio α are prevented, and power loss due to unnecessary switching is reduced.

If the equilibrium state is not reached, the target value setting unit 40 determines that the distortion δ may not change between the valleys 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 distortion δ falls within a predetermined set value δs.

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

The target value setting unit 40 is set in the operating range of the converter 4 in which the sine wave modulation is in an overmodulated state, and on the condition that the speed (estimated speed) of the motor 7 remains constant (with no fluctuation in motor load). (on the condition that there is no change in the input current due to), the no-load DC voltage Vdc(st) is initialized as the target value Vdct (S1), and the amplitudes D of the duty command values Dr, Ds, and Dt are compared with each other. (S2). If there is no deviation of more than a predetermined value 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 (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 a balanced state (NO in S3).

When in the equilibrium state (YES in S3), the target value setting unit 40 detects the distortion δ as "δ1" (S4) and adds a predetermined value ΔV to the target value Vdct (S6). Next, the target value setting unit 40 detects the distortion δ as "δ2" (S11) on the condition that the boost ratio α is less than or equal to "1.03" which is the upper limit of the distortion search (NO in S6), and The distortion δ2 is compared with the previously detected distortion δ1 (S12). If the distortion δ2 detected later is smaller than the distortion δ1 detected earlier (YES in S12), the target value setting unit 40 replaces the distortion δ2 detected later with “δ1” (S14). If the distortion δ2 detected later is the same as or larger than the distortion 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 a - 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 more than the predetermined value in this comparison, the target value setting unit 40 determines that the equilibrium state is reached (NO in S16), returns to the above S5, and adds the predetermined value ΔV to the target value Vdct ( S5). Thereafter, the processes of S11 to S16 are repeated on the condition that the boost ratio α is equal to or less than "1.03" which is the upper limit of the distortion search (NO in S6). By repeating this process, the strain δ decreases toward the minimum value of the valley change.

In the determination in S6 above, if the step-up ratio α is larger than "1.03" which is the upper limit of the distortion search (YES in S6), the target value setting unit 40 sets the target value to a value that is 1.03 times the no-load DC voltage Vdc(st). The value is set as the value Vdct (S7). Subsequently, the target value setting unit 40 detects the distortion 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 distortion δ as “δ2” (S11), and compares the distortion δ2 with the distortion δ1 detected in S8 (S12). Thereafter, the same process as above is repeated. By repeating this process, the strain δ decreases toward the minimum value of the valley change.

If the equilibrium state is not determined in the determination in S3 or 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 distortion δ (S18), and compares the distortion δ with the set value δs (S19). If the distortion δ is larger than the set value δs (YES in S19), the target value setting unit 40 repeats the processing from S2. If the distortion 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 performs the processing from S2 above. repeat. By repeating this process, the distortion 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 equilibrium, the distortion δ caused by overmodulation can be reliably brought to the minimum value of the valley change or the set value δs. can be reduced.

In the above embodiment, the load is a three-phase brushless DC motor, but the load is not limited and the present invention can be applied to various electrical devices.

The embodiments and modifications described above are presented as examples and are not intended to limit the scope of the invention. This new embodiment and modification examples can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the gist of the invention. The scope of these embodiments and modifications is included in the gist of the invention, and is also included in the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 1... 3-phase AC power supply, 4... Converter, 6... Inverter, 7... 3-phase brushless DC motor, 11r, 11s... Current sensor, 21... Phase detection section, 28... Sine wave modulation section, 31... Voltage detection section, 40 ...Target value setting section, 41...Harmonic detection section, 50...Motor control section

Claims (2)

A converter that has a plurality of diodes connected to a three-phase AC power supply and a plurality of switch elements connected in parallel to these diodes, and converts the three-phase AC power supply into DC and boosts the voltage by switching,
The switching of the converter is modulated in a sine wave 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 sine wave modulation becomes an overmodulation state. a control unit that controls the target value so that distortion of the input current to the converter is minimized in the operating range of the converter;
Equipped with
The control unit includes:
generating a switching drive signal for the converter by sinusoidally modulating a sinusoidal duty command value whose voltage level changes according to the target value with a carrier signal of a predetermined period;
In the operating range of the converter where the sine wave modulation is in an overmodulated state, when each phase voltage of the three-phase AC power supply is in a balanced state, the target value is set to zero so that the distortion of the input current is kept to a minimum value. The target value is increased or decreased by a predetermined value with the upper limit being a predetermined multiple of the load DC voltage, and if each phase voltage of the three-phase AC power supply is not in a balanced state, the target value is increased or decreased by a predetermined value so that the distortion of the input current becomes the set value. do,
A power conversion device characterized by: an inverter that converts the DC voltage output by the converter into an AC voltage of a predetermined frequency and outputs it as driving power for the motor;
Furthermore,
The control unit includes:
In an operating range of the converter where the sine wave modulation is in an overmodulated state, and on the condition that the speed of the motor remains constant, the voltages of each phase of the three-phase AC power supply are in a balanced state. determine whether or not
The power conversion device according to claim 1 , characterized in that:

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