JP2005110335A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter in which the distortion of an output current of each phase is removed by correcting a voltage variation and a large smoothing capacitor is not required. <P>SOLUTION: The power converter comprises a polyphase inverter where each phase is formed of at least one unit inverter 1 obtaining an AC single phase output from a DC power supply through a smoothing capacitor, a means 3 for controlling the output by imparting a voltage command to the polyphase inverter, a means for detecting each DC voltage of the unit inverter 1 directly or indirectly, and a means 4 for correcting the voltage command of each phase of the polyphase inverter. The voltage command correcting means 4 comprises a means for operating a variation in the DC voltage of each phase of the polyphase inverter using a signal obtained from the detecting means, and the power converter is arranged to correct the voltage command of the polyphase inverter based on operation results from the operating means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power converter, and more particularly to a power converter that obtains multiphase AC power by configuring each phase with a single-phase output of a unit inverter.

  In a power converter that outputs three-phase power, a plurality of windings are provided from the three-phase AC power source to the secondary side in order to increase the capacity and voltage of the power converter and to improve the output waveform. The three-phase AC power is supplied to multiple unit inverters via a transformer with a power supply, the unit inverters are divided into three groups, and the single-phase outputs of each group are connected in series, and the series connected A method of supplying three-phase AC power to an AC motor by connecting one end of each group as a neutral point and connecting the other end to each phase of a three-phase AC motor is known (for example, a patent) Reference 1).

In this case, the main circuit of the unit inverter described above converts the power from the secondary winding of the transformer into DC power with a converter and a DC smoothing capacitor, and this DC power is AC with an arbitrary frequency and voltage by the inverter. It is configured to convert to electric power. Therefore, the DC link part of this power converter has an independent configuration for each phase of the output of the power converter.
Japanese Patent Laid-Open No. 11-122943 (page 14, FIG. 1)

  However, in such a power conversion device in which single-phase outputs of unit inverters having independent DC power supplies are connected in multiples, DC voltage fluctuations occur due to fluctuations in the instantaneous power of each phase, and the output current is a sine wave. Distorted from. This principle will be described below.

The output voltage and current of each phase at the time t of the three-phase inverter are expressed as follows, where the angular frequency is ω and the power factor angle is θ:
Vu = √2 · | V | · cos (ωt)
Vv = √2 · | V | · cos (ωt−2π / 3)
Vw = √2 · | V | · cos (ωt + 2π / 3)
Iu = √2 · | I | · cos (ωt−θ)
Iv = √2 · | I | · cos (ωt−2π / 3−θ)
Iw = √2 · | I | · cos (ωt + 2π / 3−θ)
Can be described. Here, | V | and | I | are the effective values of the phase voltage and phase current, respectively. Therefore, the instantaneous power of each phase is as follows.

Pu = | V | · | I | · {cos (2ωt−θ) + cosθ}
Pv = | V | · | I | · {cos (2ωt−2π / 3−θ) + cos θ}
Pw = | V | · | I | · {cos (2ωt + 2π / 3−θ) + cos θ}
The total power of all phases is the sum of these.

P = Pu + Pv + Pw = 3 · | V | · | I | · cos θ
That is, the total power has no time-dependent fluctuation component, but focusing on the instantaneous power of each phase, the first term is equivalent to reactive power, and the phase difference of twice the output frequency and half the power factor angle. It has a sine wave. The DC voltage varies according to this reactive power.

  FIG. 8 is an operation explanatory diagram of the power conversion device disclosed in Patent Document 1, and shows the waveforms of the output voltage, output current, and output instantaneous power of each phase with reference to the output voltage phase of the U phase. The U phase, V phase, and W phase of the output voltage of the power converter have a phase difference of 120 degrees. The output current of each phase is output with a certain phase difference with respect to the output voltage of each phase. The instantaneous output power of each phase is obtained by the product of the voltage and current of each phase. The output instantaneous power of each phase varies greatly depending on the output voltage phase as shown in FIG.

  If the power converter is a normal power converter with a common DC link, the output instantaneous power of the entire power converter, which is the sum of the output instantaneous power for each phase, is constant. The power to be supplied is constant regardless of the output voltage phase.

  However, in the case of the power conversion device shown in Patent Document 1, since it is composed of unit inverters having independent DC link portions for each phase, the output instantaneous power of the unit inverters constituting each phase is The output instantaneous power of the single-phase inverter supplied from the secondary winding of the transformer via the converter and the DC link unit varies greatly depending on the output voltage phase.

  In the PWM control circuit that assumes that the DC voltage is the same in each phase, the output current is distorted due to the fluctuation of the DC voltage. In order to suppress this current distortion, a large smoothing capacitor has been conventionally required. However, such a large smoothing capacitor has a problem in terms of appearance and economy.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power conversion device that reduces distortion of output current of each phase by correcting voltage fluctuation and does not require a large smoothing capacitor. And

  In order to achieve the above object, the power converter of the first invention of the present invention forms each phase with the output of at least one unit inverter that obtains a single-phase AC output from a DC power source through a smoothing capacitor. A multi-phase inverter configured as described above, a control means for giving a voltage command to the multi-phase inverter to control its output, a detection means for directly or indirectly detecting each DC voltage of the unit inverter, and the multi-phase inverter Voltage command correction means for correcting the voltage command of each phase of the multi-phase inverter using the signal detected by the detection means. It has a calculating means for obtaining, and the voltage command of each phase of the multiphase inverter is corrected by the calculation result of the calculating means.

  The power conversion device according to the second aspect of the present invention is a polyphase that is configured so that each phase is formed by an output of at least one unit inverter that obtains a single-phase AC output from a DC power source through a smoothing capacitor. An inverter, a control means for giving a voltage command to the multi-phase inverter to control the output, a detection means for directly or indirectly detecting each output voltage and output current of the unit inverter, and the multi-phase inverter Voltage command correction means for correcting the voltage command of each phase, and the voltage command correction means corresponds to the variation of the DC voltage of each phase of the multiphase inverter using the signal obtained by the detection means And calculating a reactive power, and correcting a voltage command for each phase of the multi-phase inverter based on a calculation result of the calculation means.

  According to the present invention, since the voltage command of each phase is corrected with the proportional component of the DC voltage or reactive power of each phase, the distortion of the output current of each phase is reduced, and a large smoothing capacitor is required. It is possible to provide a power conversion device that does not.

  Embodiments of the present invention will be described below with reference to the drawings.

  Below, the power converter concerning Example 1 of the present invention is explained with reference to Drawing 1 thru / or Drawing 3. FIG. 1 is a circuit configuration diagram of a power converter according to the present invention.

  The unit inverters 1U, 1V, and 1W are single-phase output inverters. The outputs of the unit inverters 1U, 1V, and 1W are Y-connected to form a three-phase inverter, and supply three-phase AC power to the AC motor 2. The unit inverters 1U, 1V and 1W are controlled so as to output a voltage having a desired frequency component according to a voltage command from the main control circuit 3 which will be described in detail later. Further, the voltage command correction circuit 4 obtains a variation in the DC voltage of each unit inverter 1U, 1V, and 1W, and outputs a voltage correction command for correcting the voltage command from the main control circuit 3. The corrected voltage command controls the unit inverters 1U, 1V and 1W via a PWM control circuit (not shown).

  The internal circuit configuration of the unit inverter 1 is shown in FIG. The output of the DC power supply 11 is supplied through a smoothing capacitor 12 to a single-phase inverter circuit composed of switching elements 13AP, 13AN, 13BP, and 13BN. A flywheel diode is connected to each switching element 13 in antiparallel. An AC output is obtained from the output terminals A and B of the single-phase inverter circuit. The DC power source 11 may use a battery as shown in FIG. 2, but the AC power source may be rectified using a converter.

  Next, the detailed configuration of the main control circuit 3 will be described.

  The torque reference T * given by the torque setting device 5 is divided by the excitation command Φ * set by the magnetic flux setting device 6 and converted into a torque current reference Iq *. Further, the excitation command Φ * is converted into an excitation current reference Id * by calculation.

  On the other hand, the three-phase to two-phase converter 9 orthogonally converts the currents of the respective phases of the AC motor 2 detected by the current detectors 8A, 8B and 8C to obtain a feedback torque current Iq and a feedback excitation current Id. These feedback currents Iq and Id are compared with the above-described torque current reference Iq * and excitation current reference Id *, respectively, and the current controllers 7A and 7B are connected to the q-axis and d-axis voltages so that the respective deviations become zero. References Vq * and Vd * are controlled. The q-axis and d-axis voltage references Vq * and Vd * obtained here are converted into three-phase voltage references Vu *, Vv * and Vw * by the two-phase / three-phase converter 10.

  Further, the slip angular frequency ωs is obtained by calculation from the torque reference T * and the excitation command Φ *, and the output angular frequency ω1 of the power converter is determined by adding the feedback angular velocity ωm thereto. The output phase reference θ1 obtained by integrating the output angular frequency ω1 is used as the phase reference of the three-phase two-phase converter 9 described above, and the three-phase voltage references Vu * and Vv from the two-phase three-phase converter 10. * And Vw * are used as phase references.

  Next, details of the voltage command correction circuit 4 will be described. FIG. 3 shows a block diagram of the voltage command correction circuit 4. The average value of the DC voltage values VDCu, VDCv and VDCw of the unit inverters 1U, 1V and 1W is obtained by the average value circuit 41, and is proportional to the difference between the obtained average value and the DC voltage values VDCu, VDCv and VDCw. The corrected eu, ev, and ew are used as correction amounts for the voltage command, and are added to the original voltage commands Vu *, Vv *, and Vw * for correction. The voltage command corrected in this way is converted into a gate pulse by a PWM control circuit (not shown) and supplied to the switching element 13 of the unit inverter 1 as described above.

  The operational effects of the first embodiment will be described below.

Normally, PWM control is to control the time average voltage. Therefore, when the two-level inverter shown in FIG. 2 is applied, assuming that the DC voltage is Vdc and the on-time ratio is Ton,
The average value Vout of the output voltage is as follows.

Vout = Ton · Vdc (1)
Since the on-time ratio Ton is proportional to the voltage command V * given to the PWM circuit, the proportional coefficient α is used,
Vout = α · V * · Vdc (2)
It can be expressed.

  On the other hand, the control amount on the d and q axes is treated as a direct current amount, and each voltage and current is treated as an average value of effective values of each phase. In the equation (2), it is assumed that Vdc is constant, but the actual PWM output Vout ^ is determined by the changing instantaneous DC voltage, and when this instantaneous DC voltage is rewritten as Vdc ^, It becomes an expression.

Vout ^ = α · V * · Vdc ^ (3)
Accordingly, the shortage of the actual voltage is expressed by the following equation from equations (2)-(3).

Vout−Vout ^ = α · V * · (Vdc−Vdc ^) (4)
Here, what is obtained by dividing equation (4) by (α · Vdc ^) is a voltage reference for correction.
e = {(Vdc−Vdc ^) / Vdc} · V * (5)
Therefore, Vout to be output using e is described as follows.

Vout = α · (V * + e) · Vdc ^ (6)
As described above, by correcting the voltage reference according to the varying DC voltage Vdc ^ of each single-phase inverter, the voltage to be output can be obtained correctly, and the distortion of the current due to the voltage fluctuation is reduced. It becomes possible.

  In the first embodiment, the voltage and current command values are given by so-called vector control, but the same effect can be obtained in other control systems that give the voltage and current commands by V / F control, for example. .

  Further, in this embodiment, an example in which a three-phase inverter is configured by using three unit inverters 1 is shown, but the inverter may be a multi-phase inverter, and each phase of the multi-phase inverter is a single phase of the unit inverter 1. A plurality of outputs may be connected in series.

  As described above, according to the present invention, the voltage command of each phase is corrected by the proportional component of the DC voltage of each phase, so that distortion of output current can be reduced and the capacity of the smoothing capacitor can be reduced. It becomes possible.

  FIG. 4 is a block diagram of a voltage command correction circuit of the power conversion apparatus according to the second embodiment of the present invention. The same parts as those in the block configuration diagram of the voltage command correction circuit of the power conversion apparatus according to the first embodiment shown in FIG. The second embodiment is different from the first embodiment in that time average circuits 42U, 42V and 42W for calculating time average values of the respective DC voltage values VDCu, VDCv and VDCw are provided instead of the average value circuit 41 of FIG. It is a point that each provided.

  In the voltage command correction circuit 4A of FIG. 4, the time average of each phase is used in this way, but considering the state in which the DC voltage of each phase is balanced, the output of the average value circuit 41 of FIG. The outputs of 42V and 42W are basically the same. Accordingly, the obtained correction voltage commands eu, ev, and ew are equal to those obtained in the first embodiment, and it is possible to suppress current distortion caused by fluctuations in DC voltage.

  As a method for obtaining the time average, there are a method using a low-pass filter that removes a frequency higher than the frequency of fluctuation, a method for obtaining an average by memorizing a DC voltage value of a past fixed time, and the like.

  FIG. 5 is a circuit configuration diagram of a power conversion apparatus according to Embodiment 3 of the present invention. In each part of the third embodiment, the same components as those in the circuit configuration diagram of the power conversion apparatus according to the first embodiment shown in FIG. The third embodiment differs from the first embodiment in that instead of the voltage command correction circuit 4 that receives the DC voltage values VDCu, VDCv, and VDCw, the voltage command values Vu *, Vv *, and Vw * for each phase, and The point that the voltage command correction circuit 4B that receives the current command values Iu *, Iv *, and Iw * is provided, and the d-axis and q-axis current references Id * and Iq * are the current references Iu * and Iv * for each phase. And a two-phase / three-phase converter 14 for converting to Iw *.

  FIG. 6 shows a block diagram of the voltage command correction circuit 4B. The voltage command correction circuit 4B adds and averages the product of the voltage and current command values of each phase by the adder circuit 43, and calculates an amount proportional to the difference between the added average amount and the instantaneous power of each phase for each phase. Output as voltage reference correction commands eu, ev and ew.

  The fluctuation of the DC voltage of each phase is proportional to the reactive power of each phase. The amount obtained by averaging as described above is active power, and the amount obtained by subtracting this active power from the instantaneous power of each phase is reactive power. Accordingly, by correcting the voltage command in proportion to the reactive power, the same effect as in the first embodiment can be obtained.

  In the third embodiment, the instantaneous power is calculated using the voltage and current commands. However, the output voltage or output current of each phase may be directly detected, or the output detected directly from the command value. The same effect can be obtained even when the instantaneous power is calculated using a combination of current or voltage.

  In Example 3, the effective power was obtained by adding the instantaneous power of the three phases. However, as in Example 2, the active power of each phase can be obtained using the time average of each phase. good.

  As described above, even if the voltage command of each phase is corrected with the proportional component of the reactive power amount of each phase instead of the proportional component of the DC voltage of each phase, the distortion of the output current can be reduced, and the smoothing capacitor Capacity can be reduced.

  FIG. 7 is a block diagram of the voltage command correction circuit of the power conversion apparatus according to the fourth embodiment of the present invention. The same parts as those in the block configuration diagram of the voltage command correction circuit of the power conversion device according to the third embodiment shown in FIG. The fourth embodiment is different from the third embodiment in that a reactive power of each phase is input and a square average circuit 44 that calculates a mean square of all phases, and a reactive power that is an output of the mean square circuit 44 is added. The tangent angle calculation circuit 45 for obtaining the power factor from the active power obtained by the averaging by the circuit 43, and the output of the square average circuit 44, the value of 1/2 of the power factor angle, and twice the output angular frequency A three-phase sine wave circuit 46 that adds an output corresponding to the sine wave reactive power amount of each phase with the frequency as an input is added.

  In the voltage command correction circuit 4C, as in the third embodiment, the active power is obtained by the sum of products of the voltage and current commands, and the reactive power of each phase is obtained by the difference between the active power and the instantaneous power of each phase. The average value of the effective values of the reactive power of each phase can be obtained by calculating the following equation by the square average circuit 44. In addition, Qu, Qv, and Qw represent the reactive power of each phase, and Q represents the average value of the effective value of the reactive power.

Q = {(Qu ² + Qv ² + Qw ² ) / 3} ^1/2 (7)
The tangent angle calculation circuit 45 obtains the tangent angles of the active power and the reactive power, and the three-phase sine wave circuit 46 determines the voltage command correction amount for each phase by the following equation.

eu = G · Q · cos (ωet−θe) (8)
ev = G · Q · cos (ωet−2π / 3−θe) (9)
ew = G · Q · cos (ωet + 2π / 3−θe) (10)
However, G is a proportionality constant, θe is a value ½ of the tangent angle, and ωe = 2ω1.

  In the above formulas (8) to (10), the reactive power is expressed not by an instantaneous value but by an amplitude and a phase. Therefore, according to the fourth embodiment, the same effect as that of the third embodiment in which the voltage reference is corrected using the instantaneous reactive power can be obtained.

  In the fourth embodiment, the instantaneous power is calculated with the voltage and current commands. However, the output voltage or output current of each phase may be directly detected, or the command value and the directly detected output current or Even if the instantaneous power is calculated using a combination with the voltage, the same effect can be obtained.

  In the fourth embodiment, the effective power is obtained by adding the instantaneous power of the three phases. However, as in the second embodiment, the active power of each phase may be obtained using the time average of each phase.

Furthermore, in Example 4, the reactive power of each phase was obtained from the difference between the average power per phase of the total power and the instantaneous power of each phase. For example, for the U phase,
Pu = | V | · | I | · {cos (2ωt−θ) + cosθ}
The obtained average power per phase corresponds to | V | · | I | · cos θ. By dividing this average power by the power factor cos θ, the apparent power | V | · | I | is obtained, and this is used as the amplitude, and the reactive power having a frequency twice the voltage command and a power factor angle of 1/2 is obtained. You may ask.

  When the power conversion device used in the first to fourth embodiments described above is used for motor control, the total power is not calculated by the product of the voltage command and the current command, but is obtained by the product of the voltage command and the torque component current. However, the same effect can be obtained. In addition, the same effect can be obtained by using a motor induced voltage obtained by the product of the motor magnetic flux or excitation current and the motor speed as the voltage command in this case.

  Further, the same effect can be obtained by using the directly detected output voltage and current of each phase instead of the voltage and current commands.

The circuit block diagram of the power converter device which concerns on Example 1 of this invention. The circuit block diagram of a unit inverter. The block block diagram of the voltage command correction circuit of the power converter device which concerns on Example 1 of this invention. The block block diagram of the voltage command correction circuit of the power converter device which concerns on Example 2 of this invention. The circuit block diagram of the power converter device which concerns on Example 3 of this invention. The block block diagram of the voltage command correction circuit of the power converter device which concerns on Example 3 of this invention. The block block diagram of the voltage command correction circuit of the power converter device which concerns on Example 4 of this invention. Operation | movement explanatory drawing of a power converter device.

Explanation of symbols

1, 1U, 1V, 1W Unit inverter 2 AC motor 3 Main control circuit 4, 4A, 4B, 4C Voltage command correction circuit 5 Torque setting device 6 Magnetic flux setting device 7A, 7B Current controller 8A, 8B, 8C Current detector 9 Three-phase two-phase converter 10 Two-phase three-phase converter 11 DC power supply 12 Smoothing capacitor 13, 13AP, 13AN, 13BP, 13BN Switching element 41 Average value circuit 42U, 42V, 42W Time average circuit 43 Adder circuit 44 Square average circuit 45 Tangent angle calculation circuit 46 Three-phase sine wave circuit

Claims (10)

A multi-phase inverter configured to form each phase with the output of at least one unit inverter that obtains a single-phase AC output from a DC power source through a smoothing capacitor;
Control means for controlling the output by giving a voltage command to the multi-phase inverter;
Detecting means for directly or indirectly detecting the DC voltage of each of the unit inverters;
Voltage command correction means for correcting the voltage command of each phase of the multi-phase inverter,
The voltage command correction means includes
Using a signal obtained by the detection means, calculating means for obtaining a variation in the DC voltage of each phase of the multi-phase inverter,
A power conversion device, wherein the voltage command of each phase of the multiphase inverter is corrected based on the calculation result of the calculation means. The computing means is
An average value of DC voltages of all phases of the multi-phase inverter;
The power conversion device according to claim 1, wherein a difference from a DC voltage of each phase of the multiphase inverter is obtained. The computing means is
For each phase of the multiphase inverter,
The power converter according to claim 1, wherein a difference between the DC voltage and the time average value of the DC voltage is obtained. A multi-phase inverter configured to form each phase with the output of at least one unit inverter that obtains a single-phase AC output from a DC power source through a smoothing capacitor;
Control means for controlling the output by giving a voltage command to the multi-phase inverter;
Detecting means for directly or indirectly detecting the output voltage and output current of each of the unit inverters;
Voltage command correction means for correcting the voltage command of each phase of the multi-phase inverter,
The voltage command correcting means is
Using arithmetic means for obtaining reactive power corresponding to the variation of the DC voltage of each phase of the multiphase inverter using the signal obtained by the detection means;
A power conversion device, wherein the voltage command of each phase of the multiphase inverter is corrected based on the calculation result of the calculation means. The computing means is
Average value per phase of instantaneous power obtained by adding the product of the output voltage and output current of the unit inverter for all phases;
The power converter according to claim 4, wherein a difference from the instantaneous power of each phase is obtained. The computing means is
Obtained by averaging the average of the instantaneous power per phase obtained by adding the product of the output voltage and output current of the single-phase inverter for all phases and the instantaneous power of each phase for all phases. Amplitude to be
Twice the frequency of the output voltage or output current of each phase;
5. The power conversion according to claim 4, wherein sine wave reactive power having an output voltage of each phase and a phase difference of half of the power factor angle obtained from the output current is obtained by converting each phase. apparatus. The computing means is
The amplitude obtained by dividing the average value per phase of instantaneous power obtained by adding the product of the output voltage and output current of the single-phase inverter for all phases, by the power factor;
Twice the frequency of the output voltage or output current of each phase;
5. The power conversion according to claim 4, wherein sine wave reactive power having an output voltage of each phase and a phase difference of half of the power factor angle obtained from the output current is obtained by converting each phase. apparatus. A multi-phase inverter configured to form each phase with the output of at least one unit inverter that obtains a single-phase AC output from a DC power source through a smoothing capacitor;
AC motor driven by this multi-phase inverter,
Control means for controlling the output by giving a voltage command to the multi-phase inverter;
Detection means for directly or indirectly detecting the output voltage and output current of each unit inverter;
Voltage command correction means for correcting the voltage command of each phase of the multi-phase inverter,
The voltage command correction means includes
Using a signal obtained by the detecting means, and calculating means for obtaining reactive power corresponding to the fluctuation of the DC voltage of each phase of the multi-phase inverter,
A power conversion device, wherein the voltage command of each phase of the multiphase inverter is corrected based on the calculation result of the calculation means. The computing means is
The amplitude obtained by dividing the average value per phase of instantaneous power obtained from the product of the output voltage of the single-phase inverter and the torque component current of the AC motor by the power factor;
Twice the frequency of the output voltage or output current of each phase;
9. The power conversion device according to claim 8, wherein a sine wave reactive power having an output voltage of each phase and a phase difference of half of the power factor angle obtained from the output current is obtained by converting each phase. Among the detection means, the detection means for detecting the output voltage is:
9. The power conversion device according to claim 8, wherein the power conversion device is based on a motor-induced voltage obtained from a product of a magnetic flux or magnetic flux component current command of the AC motor and a speed of the AC motor.

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