JP2015023737A - Dc voltage control device of power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC voltage control device of a power conversion device, with which even when there is a load current fluctuation, a DC voltage fluctuation is suppressed while reducing a deviation dv.SOLUTION: A current command Icmd(s) is generated at a PI arithmetic unit 2 on the basis of a deviation between a voltage command Vdc_cmd(s) and a voltage detection value Vdc_det(s), a voltage command value Vcmd(s) is generated at a current control unit ACR on the basis of the current command Icmd(s), and an output voltage Io(s) of a converter CNV is controlled through a PWM control unit PWM according to the voltage command value Vcmd(s). The current command Icmd(s) is pseudo-differentiated at a low-pass filter 5. At a current estimation unit 3, differentiation and pseudo-differentiation are performed by multiplying the voltage detection value Vdc_det(s) by synthetic electrostatic capacitances C(s) of capacitors C1 and C2, thereby obtaining a current estimation value. A deviation between an output of the low-pass filter 5 and an output of the current estimation unit 3 is superimposed on the current command Icmd(s) in reverse polarity as a disturbance estimation value D^(s).

Description

  The present invention relates to an operation method of a power converter using PWM (Pulse Width Modulation), and more particularly to disturbance response control of DC voltage control.

  FIG. 1 is a schematic diagram illustrating an example of a main circuit in a conventional power converter. As shown in FIG. 1, the power converter includes a converter CV connected to the system voltage via a reactor L, an inverter IV connected to the AC motor M side, and a DC circuit between the converter CV and the inverter IV. And connected capacitors C1 and C2. Here, the capacitance of the capacitor C1 is C1 [F], and the terminal voltage is Vdc1 [V]. The capacitance of the capacitor C2 for the inverter IV is C2 [F], and the terminal voltage is Vdc2 [V]. The power conversion apparatus is controlled using PWM control, and the PWM carrier frequency is Fc [Hz].

JP 2004-153978 A Japanese Patent Application No. 2012-35701

  As shown in FIG. 1, when the load is composed of an inverter IV and an electric motor M, when the output of the electric motor M changes suddenly, the DC voltage and the input current also change. At the time of the fluctuation, there is a risk that the operation is stopped due to a protection operation such as overvoltage protection or overcurrent protection of the power converter. In particular, when the electric motor M performs a regenerative operation, the DC voltage and the input current increase. If you want to use it in applications where the load fluctuates greatly, such as regenerative operation, it cannot be used normally unless the DC voltage can be controlled against disturbance. In addition, since direct current detection is difficult due to the influence of heat generation of the sensor depending on the attachment, direct current detection may not be possible.

  Therefore, it is desirable to operate the power conversion device while reducing the influence of disturbance on the DC voltage without providing a current detector in the DC circuit. Patent Document 1 discloses a mechanism that operates by estimating a direct current from a direct current voltage. This includes a current that is intended to be operated by a power conversion device and a current vibration that is generated by PWM. Since it is reproduced, the gain of the voltage controller cannot be increased.

  Patent Document 2 discloses a method for estimating only a disturbance except for a current that is intended to be operated by a power converter. In the method of Patent Document 2, the estimated disturbance value is estimated using the detected voltage value of the DC circuit. However, in the case of the configuration in which the converter CV and the inverter IV are combined, the capacitors C1 and C2 are provided respectively, and the DC section is provided. A characteristic impedance Z (s) exists in the wiring to be connected. Although the characteristic impedance Z (s) is very small, resistance and inductance exist. These have dead time and frequency response characteristics, and the method of Patent Document 2 does not take this into consideration, so there is a risk that an error will enter the high frequency band of the estimated disturbance value and will not be stable.

  Here, it is assumed that the DC voltage Vdc1 on the converter CV side and the DC voltage Vdc2 on the inverter side are as follows.

Vdc2 = Vdc1 + dv
In Patent Document 2, since there is only one voltage detection unit in the DC circuit, the compensation amount always has a deviation dv. If the deviation dv is reduced, the accuracy is improved. However, in order to eliminate the deviation dv, it is necessary to obtain the characteristic impedance Z (s). However, the characteristic impedance Z (s) of the wiring is difficult to estimate for each device because the shape of the metal conductor is often complicated when the wiring is a metal conductor. Therefore, there is a need for a method of simply increasing the accuracy while reducing the deviation dv.

  As described above, in the DC voltage control device of the power conversion device, it is a problem to suppress the fluctuation of the DC voltage even when the load current fluctuates while reducing the deviation dv.

  The present invention has been devised in view of the above-described conventional problems. One aspect of the present invention is to connect a converter that converts alternating current to direct current and an inverter that converts direct current to alternating current and supplies power to a load. In a power conversion device in which two capacitors are connected to a direct current circuit, a PI command unit generates a current command based on the deviation between the voltage command and the detected voltage value of the direct current circuit, and the current control unit generates a voltage command based on the current command. A DC voltage control device of a power conversion device that generates a value and controls the output voltage of the converter by a PWM control unit according to the voltage command value, the low-pass filter that pseudo-differentiates the current command, and the DC circuit The voltage detection value obtained by averaging the voltage values output from the two voltage detectors provided is multiplied by the combined capacitance of the two capacitors and differentiated. A current estimator that performs differentiation to estimate a current estimation value, and superimposes a deviation between an output of the low-pass filter and an output of the current estimation unit as a disturbance estimation value on the current command in a reverse polarity. .

  Further, as one aspect thereof, a limit circuit is provided on the input side of the current control unit, and a value obtained by multiplying the input / output difference signal of the limit circuit by a gain is fed back to the PI calculation unit, and the voltage command and the voltage An integral operation is performed based on a deviation between a deviation from the detected value and a value obtained by multiplying the difference signal by a gain.

  According to the present invention, in the DC voltage control device of the power converter, it is possible to suppress the fluctuation of the DC voltage even when there is a load current fluctuation while reducing the deviation dv.

Schematic which shows an example of the main circuit of a power converter device. Schematic which shows the DC voltage control apparatus in Embodiment 1. FIG. Schematic which shows the DC voltage control apparatus in Embodiment 2. FIG.

  Hereinafter, Embodiments 1 and 2 of a DC voltage control device in a power converter according to the present invention will be described in detail with reference to FIGS.

[Embodiment 1]
The main circuit of the power conversion device according to the first embodiment is the same as that shown in FIG. Note that voltage detectors (not shown) are provided at the positions of the capacitors C1 and C2, respectively, and detect the terminal voltages Vdc1 and Vdc2 of the capacitors C1 and C2.

  FIG. 2 shows a DC voltage control unit of the power conversion device according to the first embodiment. For simplification of description, FIG. 2 shows the s region after Laplace transform.

  First, voltage control is performed as follows. The voltage command Vdc_cmd (s) for the converter CV is subjected to a difference calculation with the voltage detection value Vdc_det (s) in the subtraction unit, and the difference is input to the PI calculation unit 2. The PI calculation unit 2 includes a proportional calculation unit 21 having a proportional gain of Kp and an integration unit 22 having an integration time constant Ti, and calculates a current command Icmd (s). Based on the calculated current command Icmd (s), a voltage command value Vcmd (s) is calculated in a current controller ACR (Automatic Current Regulator). Based on the voltage command value Vcmd (s), the PWM control unit PWM controls the converter CV, outputs an output current Io (s) from the converter CV, and charges the capacitors C1 and C2.

  Capacitors C1 and C2 are charged with a current obtained by adding disturbance D (s) to output current Io (s). When the current obtained by adding the disturbance D (s) to the output current Io is divided by the capacitances C1 (s) and C2 (s) of the capacitors C1 and C2, the voltage Vdc1 (s) charged in the capacitors C1 and C2 is obtained. ), Vdc2 (s). In the first embodiment, the terminal voltages Vdc1 (s) and Vdc2 (s) of the capacitors C1 and C2 are detected and added by the voltage detector, respectively, and divided by 2 in the divider 4 and averaged. The value is Vdc_det (s). This voltage detection value Vdc_det (s) is fed back to the input side of the PI calculation unit 2 and used for a difference calculation with the voltage command Vdc_cmd (s).

  Reference numeral 3 denotes a current estimation unit that inputs the voltage detection value Vdc_det (s) and estimates a current estimation value.

  Reference numeral 5 denotes a low-pass filter that receives the current command Icmd (s). The deviation between the output of the low-pass filter 5 and the current estimated value is added to the current command Icmd (s) as a disturbance estimated value −D ^ (s).

  Considering the disturbance D (s) when the power conversion device performs a regenerative operation with the above configuration, since the energy flowing in the capacitors C1 and C2 is a current, the disturbance D (s) is also a current. Therefore, it can be assumed that the disturbance D (s) is superimposed on the output current Io (s). Here, in consideration of the following equation (1), when the capacitance of the combined capacitor of the capacitors C1 and C2 is C [F], the DC voltage Vdc (s) is approximately expressed by the following equation (2). Is done.

  Here, when the DC voltage detection value is Vdc_det (s), the following equation (3) is obtained.

  In the first embodiment, by providing two voltage detectors in the DC circuit, the deviation dv caused by the characteristic impedance Z (s) of the wiring is halved.

  In the first embodiment, the detected voltage Vdc_det (s) in the DC circuit is first converted into a DC current, and the disturbance (current) D (s) is estimated from the state before and after the occurrence of the disturbance.

  In order to convert the voltage detection value Vdc_det (s) into the output current Io, it is only necessary to multiply and differentiate the combined capacitance C of the two capacitors C1 and C2. However, since the disturbance D (s) may be amplified if differentiated as it is, the current estimation unit 3 performs pseudo differentiation that suppresses higher harmonics with a low-pass filter LPF (Low Pass Filter) after differentiation. The following formula (4) shows an estimation formula of the direct current.

  If the converter CV outputs the output current Io based on the current command Icmd (s), the disturbance D (s) should be zero. Therefore, as shown in the following equation (5), since the current command Icmd (s) substantially coincides with the output current Io, the disturbance D (s) is estimated by taking a deviation between the current command Icmd (s) and the current estimated value. can do.

  Before taking the deviation, it is necessary to add a low-pass filter 5 for pseudo differentiation to the current command Icmd (s). If the current command Icmd (s) is also subjected to the low-pass filter 5 to obtain a deviation from the estimated current value, only the disturbance D (s) can be estimated. The estimated disturbance estimated value -D ^ (s) is shown in the following equation (6).

  That is, since the current estimation unit 3 applies the voltage detection value Vdc_det (s) to the low-pass filter for the pseudo differentiation to obtain the current estimation value, the current command Icmd (s) is also applied to the low-pass filter 5 and the deviation is taken to obtain the disturbance D. Only (s) is estimated.

  Since the disturbance D (s) can be estimated from this, the disturbance can be suppressed by performing correction control to cancel the disturbance D (s). Assume that the estimated disturbance estimated value is -D ^ (s). The obtained disturbance estimated value −D ^ (s) is added to the current command Icmd (s) calculated by the PI calculation unit 2 so as to cancel the disturbance, and is input to the current control unit ACR.

  Next, the time constant of the low-pass filter used when the current estimation unit 3 performs pseudo differentiation will be examined.

  The voltage command value Vcmd (s) calculated by the current control unit ACR is PWM-modulated by the PWM control unit PWM. For this reason, a current pulsation with a carrier frequency Fc [Hz] is superimposed on the DC voltage Vdc. When the PWM control method is adopted, this frequency cannot be controlled, but is not necessary for the above-described current estimation. Therefore, it is assumed that the carrier frequency band or higher is attenuated as a time constant determination criterion in the current estimation unit 3. Therefore, the time constant of the low-pass filter used for the pseudo-differentiation may be set to be twice or more the carrier period as shown by the equation (7) based on the sampling theorem.

  According to the first embodiment, in the power conversion device that performs AC-DC conversion and further DC-AC conversion, the disturbance estimated value D ^ (s) is estimated even when there is a load current fluctuation, and the disturbance D (s). Since the correction control is performed to cancel out DC, fluctuations in the DC voltage can be suppressed. In addition, since no current detector is used, the cost can be reduced and the apparatus can be downsized.

  Even if the DC circuit wiring has characteristic impedance Z (s), the characteristic impedance Z (s) can be halved by providing two voltage detectors in the DC circuit.

  Further, since the fluctuation of the direct current can be suppressed, it is possible to prevent the power conversion apparatus from stopping the load due to the operation of the protection function due to overvoltage or overcurrent.

  Further, when estimating the current estimated value from the voltage detection value Vdc_det (s), the calculation is performed so as not to superimpose the pulsation due to the carrier frequency, so that the gain of the voltage control mechanism can be increased and the target value response is improved. Can be planned.

[Embodiment 2]
FIG. 3 shows a DC voltage control device for a power conversion device according to the second embodiment. The same reference numerals are assigned to the same or corresponding portions as those in FIG.

  In the power conversion device according to the first embodiment, when the estimated disturbance estimated value −D ^ (s) is superimposed on the current command Icmd (s), the control amount may increase. In general, a limit circuit is provided to limit the control amount assuming that the control amount becomes large. When the control amount is limited by the limit circuit, a windup phenomenon that fluctuates in the opposite direction of the limit occurs.

  Therefore, the second embodiment is different from the first embodiment in that a limit circuit 6 and a feedback unit 7 having a gain Kfb are provided in order to avoid a windup phenomenon.

  Hereinafter, based on FIG. 3, the DC voltage control apparatus of the power converter device of this Embodiment 2 is demonstrated.

  The difference between the input and output of the limit circuit 6 is detected from the signal on the input side and the output side of the limit circuit 6, and the estimated disturbance value D ^ (s) is subtracted, and the feedback unit 7 multiplies the gain Kfb. The multiplication value is fed back to the PI calculation unit 2. In the PI calculation unit 2, the output of the feedback unit 7 is further subtracted from the deviation between the voltage command Vdc_cmd (s) and the voltage detection value Vdc_det (s), and the integration unit 22 performs integration calculation based on the difference. That is, the PI calculation unit 2 is configured as an automatic matching PI control system, and automatically adjusts to suppress the I operation, thereby suppressing a reset windup operation that occurs when the I operation becomes too large. Thereby, current disturbance compensation considering the limit circuit 6 can be realized.

  Therefore, according to the second embodiment, in addition to the effects of the first embodiment, the windup operation when the limit circuit 7 is further provided is suppressed.

  Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

CV ... Converter IV ... Inverter C1, C2 ... Capacitor Vdc_cmd (s) ... Voltage command Vdc_det (s) ... Voltage detection value Icmd (s) ... Current command Vcmd (s) ... Voltage command value PWM ... PWM control unit 2 ... PI calculation Section ACR ... Current control section 3 ... Current estimation section 5 ... Low pass filter C (s) ... Synthetic capacitance D ^ (s) ... Disturbance estimated value

Claims (2)

In a power converter in which two capacitors are connected to a DC circuit that connects a converter that converts AC to DC and an inverter that converts DC to AC and supplies power to a load, a voltage command and voltage detection of the DC circuit A current command is generated by the PI calculation unit based on the deviation from the value, a voltage command value is generated by the current control unit based on the current command, and the output voltage of the converter is controlled by the PWM control unit according to the voltage command value A DC voltage control device for a power converter,
A low-pass filter that pseudo-differentiates the current command;
A pseudo differential that suppresses harmonics after differentiation by multiplying the voltage detection value obtained by averaging the voltage values output from the two voltage detectors provided in the DC circuit by the combined capacitance of the two capacitors. And a current estimation unit for estimating the current estimated value,
A DC voltage control device for a power converter, wherein a deviation between an output of the low-pass filter and an output of a current estimation unit is superimposed on the current command as a disturbance estimated value with a reverse polarity.   A limit circuit is provided on the input side of the current control unit, and a value obtained by multiplying a difference signal between the input and output of the limit circuit by a gain is fed back to the PI calculation unit, and a deviation between the voltage command and the voltage detection value, 2. The DC voltage control device for a power conversion device according to claim 1, wherein an integral operation is performed based on a deviation between a value obtained by multiplying the difference signal by a gain.

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