JP5678844B2 - Control device for power converter - Google Patents

Description

  The present invention relates to a control device for a power converter that is connected to an AC system, converts a DC voltage into an AC voltage, and supplies a current to the AC system.

  In a conventional power converter control device introduced in, for example, Patent Document 1, an impedance element is provided between an AC system and a power converter, and a power converter that converts a DC voltage into an AC voltage is an impedance element. A current control circuit for controlling the current flowing through the power supply, a system voltage compensation circuit, and a PWM circuit. The current control circuit amplifies the deviation between the current command value and the current detection value, and the system voltage compensation circuit detects the system voltage and corrects the output signal of the current control circuit. Then, the output of the current control circuit and the correction signal of the system voltage compensation circuit are added to give an AC voltage command to be generated by the power converter, and in accordance with the voltage command value, the PWM circuit determines the switching element of the power converter. An ignition signal is generated, and the power converter is configured to generate an AC voltage corresponding to the voltage command value.

  The current flowing through the impedance element depends on the potential difference between the system voltage and the AC voltage generated by the power converter. By detecting the current flowing through the impedance element and amplifying the deviation from the desired current command value to make the AC voltage command of the power converter, a current feedback control loop is formed, and the current that matches the current command value Can flow. On the other hand, there is a system voltage fluctuation as an element that generates a potential difference in the impedance element. For this reason, the system voltage is detected and the AC voltage command is corrected with a signal corresponding to the system voltage. The fluctuations in the system voltage correspond to disturbances from the viewpoint of the current control feedback loop. Therefore, the system voltage compensation circuit can be regarded as a disturbance feedforward compensation loop, and suppresses current fluctuations due to voltage fluctuations (disturbance fluctuations). Can do. Therefore, according to this configuration, when a fluctuation in the system voltage occurs, the system voltage compensation circuit corrects the AC voltage to be generated by the power converter so that it substantially matches the system voltage, thereby allowing the system voltage and the power conversion. The AC voltage of the capacitor is balanced to reduce the potential difference of the impedance element, thereby operating the current flowing through the impedance element to be suppressed.

JP-A-4-289728

  In such a power converter control device, the voltage command of the power converter is corrected based on the detected value of the system voltage. However, when control for compensating for fluctuations in the system voltage is performed, the system voltage is constantly It operates to correct the voltage of the power converter in a state in which the harmonic component present in is also detected. For this reason, there is a problem that harmonic distortion is increased due to detection delay, an error between the voltage command and the AC voltage of the power converter, and voltage distortion may increase.

  The present invention has been made to solve the above-described problems, and controls a power converter that can stably suppress current fluctuations without amplifying harmonics that exist constantly. The purpose is to obtain a device.

A control device for a power converter according to the present invention converts a DC voltage into an AC voltage and outputs the AC voltage to an AC system via an impedance element. The current detector detects the current flowing through the impedance element. Voltage detector for detecting voltage, current control means for generating a voltage command signal so that the current detection value from the current detector follows the current command value, voltage fluctuations in the AC system based on the voltage detection value from the voltage detector Voltage correction means for generating a voltage correction signal for compensating the accompanying current fluctuation, and converter control means for controlling the power converter based on a signal obtained by adding the voltage command signal and the voltage correction signal are provided. The voltage correction means outputs the first correction signal based on the voltage detection signal taken out from the output of the voltage detector through the first filter that removes higher harmonic components whose frequency is higher than the fundamental wave component of the AC system. A first correction circuit that generates a second correction signal based on a voltage detection signal that is extracted from the output of the first voltage corrector and the voltage detector that is extracted through the second filter whose cutoff frequency is higher than the cutoff frequency of the first filter. When the voltage detection value of 2 and the voltage detection value from the voltage detector are within a predetermined setting range, the first correction signal is output as a voltage correction signal, and when the voltage correction value exceeds the predetermined setting range, the second correction signal is output. comprises a voltage correction signal switching means for switching the correction signal to output a correction signal as a voltage correction signal, the voltage correction signal switching means, after switching from the first correction signal to the second correction signal, electrostatic That the voltage detection value from the detector is comprised within a predetermined set range, and was the first correction signal so as to return to the first correction signal from the second correction signal when it becomes within a predetermined range It is.

As described above, the voltage correction means of the control device for the power converter according to the present invention uses the first voltage corrector when the AC system is in a steady state or the like and the detected voltage value is within a predetermined setting range. The current fluctuation is calculated based on the first correction signal generated based on the voltage detection signal extracted through the first filter that removes the harmonic component having a frequency higher than the fundamental wave component of the AC system from the output of the voltage detector. Since the compensating operation is performed, the current fluctuation can be stably suppressed without amplifying the harmonics that exist constantly. Also, when the voltage detection value exceeds a predetermined setting range due to an AC system failure or the like, the second voltage corrector passes the second filter through a second filter whose cutoff frequency is higher than the cutoff frequency of the first filter. Since the operation for compensating for the current fluctuation is performed based on the second correction signal generated based on the extracted voltage detection signal, the current fluctuation accompanying the voltage fluctuation due to a failure or the like can be reliably suppressed.
Furthermore, it can be determined that the AC system has been reliably restored to the steady state, and based on this determination result, switching to return to the first voltage corrector can be performed, and the correction signal can be switched stably. be able to.

It is a block diagram which shows the control apparatus of the power converter by Embodiment 1 of this invention. It is an equivalent circuit diagram for demonstrating operation | movement of this invention. It is a block diagram which shows the control apparatus of the power converter by Embodiment 2 of this invention. It is a block diagram which shows the control apparatus of the power converter by Embodiment 3 of this invention.

Embodiment 1 FIG.
1 is a configuration diagram of a power converter control device according to Embodiment 1 of the present invention. The power converter 1 and the AC system 4 are connected via the impedance element 2, and the capacitor 3 and the DC system 5 are connected to the DC side of the power converter 1. The current flowing through the impedance element 2 is detected by the current detector 6, and the voltage of the AC system 4 is detected by the voltage detector 7 and sent to the control device 8. The control device 8 includes a subtractor 801 for obtaining a deviation between the current I detected by the current detector 6 and its command value I *, a current controller 802 as current control means for amplifying the deviation, and voltage detection. The first voltage corrector 805a that generates the first correction signal from the voltage of the AC system 4 detected by the voltage detector 7 and the second correction signal are generated from the voltage of the AC system 4 that is also detected by the voltage detector 7. A second voltage corrector 805b, a correction signal determination unit 806 that generates a switching signal from the voltage of the AC system 4 that is also detected by the voltage detector 7, and a first voltage correction unit 805a and a second voltage correction unit 805a according to the switching signal A correction signal switch 807 for switching to the voltage corrector 805b.

  Here, the correction signal determination unit 806 and the correction signal switching unit 807 constitute a voltage correction signal switching unit, and the voltage correction unit includes the first voltage correction unit 805a and the second voltage correction unit 805b including them. Configure.

  An adder 803 that adds the output of the current controller 802 and the output of the correction signal switch 807 outputs an AC voltage command to be generated by the power converter 1, and a pulse width controller 804 as a converter control means. Outputs an ignition signal for igniting the switching element of the power converter 1 in accordance with the output of the adder 803.

  The configuration for feedback control of the current flowing through the impedance element 2 is the same as in the prior art, and the current controller 802 amplifies the current deviation obtained by the subtractor 801 and gives a voltage command to the pulse width controller 804, so that the pulse The switching element is fired by the width controller 804, and the power converter 1 converts the DC voltage into an AC voltage corresponding to the voltage command. As a result, feedback control is performed so that the current deviation decreases, and the current detection value detected by the current detector 6 operates so as to follow the current command value. As a result, the current flowing through the impedance element 2 is the current command value. It is controlled according to.

  Next, the operation of the voltage correction means will be described. The first voltage corrector 805a receives the output detected by the voltage detector 7, and a voltage detection signal from which higher harmonic components than the fundamental component of the AC system 4 are removed by passing through the built-in first filter. The first correction signal is generated and output based on the above. The second voltage corrector 805b incorporates a second filter having a cutoff frequency higher than the cutoff frequency of the first filter of the first voltage corrector 805a, and the voltage detection taken out through the second filter A second correction signal is output based on the signal. Note that the band of the first voltage corrector 805a is included in the band of the second voltage corrector 805b.

  The first voltage corrector 805a and the second voltage corrector 805b are configured by first and second filters having low-pass characteristics, respectively, but the second voltage corrector 805b passes higher frequencies. Become a characteristic. For example, when the cut-off frequency when the first voltage corrector 805a (first filter) is a primary delay filter is 250 to 500 rad / s, the second voltage corrector 805b (second filter) The cutoff frequency of the first-order lag is set to 500 to 2000 rad / s or the like (the cutoff frequency of the first filter <the cutoff frequency of the second filter).

  The correction signal determination unit 806 detects the fluctuation of the voltage from the voltage detector 7, selects the second correction signal when the fluctuation exceeds a predetermined setting range, and selects the second correction signal when the fluctuation is within the setting range. A selection signal is output so as to select one correction signal, and the correction signal switch 807 switches between the output of the first voltage corrector 805a and the output of the second voltage corrector 805b in accordance with the selection signal. To work.

  Specifically, the predetermined setting range is, for example, a range of about 10 to 20% in terms of voltage fluctuation. As a result, when the AC system 4 is in a steady state, the correction signal determination unit 806 selects the first voltage correction unit 805a, and in a transient state in which a failure or the like occurs in the AC system 4, the correction signal determination unit 806 Operates to select the second voltage corrector 805b.

  By adopting the above configuration, for the voltage distortion included in the AC system 4 in the steady state, the adder 803 outputs the current controller 802 with the first correction signal output from the first voltage corrector 805a. By correcting the output to be a voltage command, the harmonic component in the steady state operates so as not to be output from the power converter 1.

On the other hand, when the voltage fluctuation of the AC system 4 is large, for example, when an instantaneous voltage drop or voltage rise occurs due to an AC system failure or a lightning strike, the voltage fluctuation becomes large, and the correction signal determination unit 806 performs the second voltage correction. A signal is sent to the correction signal switch 807 so as to select the second correction signal output from the adjuster 805b, the second correction signal from the second voltage corrector 805b is output, and a voltage command is issued by the adder 803. to correct.
By this operation, in response to the system voltage fluctuation, for example, when the voltage suddenly drops, the voltage of the power converter 1 can also be sharply reduced similarly, suppressing the increase of the potential difference of the impedance element 2 Current fluctuation can be reliably suppressed.

  With respect to voltage distortion in the steady state of the AC system 4, the current fluctuation generated by the potential difference applied to the impedance element 2 is suppressed to be small by the characteristics of the impedance element 2. For example, the impedance element 2 may be constituted by a reactor or a transformer having an inductance component.

Note that the cutoff frequency of the second filter built in the second voltage corrector 805b is set to a sufficiently high value so that an instantaneous voltage drop or voltage rise due to an AC system failure or a lightning strike can be detected quickly. From this point, the cut-off frequency can be infinite, that is, the second filter can be practically just a conductor.
However, in actual system operation, it is necessary to consider the influence of the power converter 1 itself as well as the influence of the AC system 4. That is, the detection output from the voltage detector 7 includes a harmonic component generated by the power converter 1, and this harmonic component may be fed back and amplified to cause a harmful effect.
Therefore, by adopting a second filter having a cutoff frequency that removes higher-order harmonic components generated from the power converter 1 due to its pulse width control, the above-described adverse effects can be prevented. can do.

As in the conventional case, the following is the result of examining the phenomenon in the case where the compensation operation for the voltage fluctuation of the AC system 4 is always performed by the correction signal from the second voltage corrector 805b from the transfer characteristics of the circuit. Explained. That is, when the voltage command is corrected by the correction signal of the second voltage corrector 805b in a state where voltage distortion is occurring in the AC system 4 in the steady state, the following increase in voltage harmonics may occur. There is.
The AC system 4 is not a simple power supply but includes an inductance component, a resistance component, a capacitance component, and the like, and its impedance characteristics are not uniform and change depending on the operating state of the AC system 4. For this reason, the voltage distortion detected by the voltage detector 7 is a result of reflecting the impedance characteristics of the AC system 4.

  FIG. 2 shows an example of an equivalent circuit assuming this case. When the power converter 1 is a controllable voltage source, the impedance element 2 is Zc, and the voltage source Vs, impedance Zs, and admittance Ys are elements constituting the AC system 4, the AC system voltage Vo from the voltage Vc generated by the power converter 1 is used. The transfer characteristics up to are as shown in equation (1).

  Vo / Vc = Zs / (Zc (1 + Ys · Zs) + Zs) (1)

  When the transfer characteristic Gout of the power converter 1 is taken into consideration from the transfer characteristic Gin of the voltage detector 7 and the voltage command, and the transfer characteristic of the second voltage corrector 805b is corrected to 1, the output Vi of the current controller 802 The transfer characteristic up to Vo is expressed by equation (2) from Vc = Gout (Vi + Gin · Vo).

Vo / Vi = Gout · Zs /
(Zc (1 + Ys · Zs) + Zs−Gin · Gout · Zs) (2)

  If the relationship of Gin · Gout = 1 is satisfied, the expression (2) becomes the expression (3), which is stable when the AC system 4 is composed of passive elements.

  Vo / Vi = Gout · Zs / (Zc (1 + Ys · Zs)) (3)

However, Gin includes a detection delay, Gout includes a control delay and a conversion error, and Gin · Gout = 1 cannot be satisfied. For this reason, depending on the impedance Zs and the admittance Ys of the AC system 4, there is a possibility that a positive feedback is formed at a certain frequency in Vo / Vi and voltage distortion is increased.
As described above, considering that the AC system 4 has complicated characteristics, there is a possibility of increasing voltage distortion even when the transfer characteristic of the second voltage corrector 805b is 1.

  As described above, in the control apparatus for the power converter according to the first embodiment of the present invention, when the AC distortion occurs in the AC system 4 in the steady state, the first transfer characteristic has such a transfer characteristic that the voltage distortion does not increase. By using the first voltage corrector 805a composed of one filter and at the time of sudden voltage fluctuation, the second voltage corrector 805b is used to suppress the expansion of the potential difference of the impedance element 2 with a quick response. Current fluctuation can be reliably suppressed. As a result, it is possible to achieve both stable operation during steady state and reliable current fluctuation suppression during transition such as failure.

  The power converter 1 is disconnected from the DC system 5 and does not allow active power to be accommodated, and an operation for outputting reactive power to the AC system 4 or a device for the purpose has the same effect. Further, when the voltage of the DC system 5 is stable, the same effect can be obtained without the capacitor 3.

Embodiment 2. FIG.
FIG. 3 is a configuration diagram of a control device for a power converter according to the second embodiment of the present invention. In FIG. 3, the output of the first voltage corrector 805 a is also input to the correction signal determiner 806. Then, the switching from the first voltage corrector 805a to the second voltage corrector 805b is performed according to a signal from the voltage detector 7 according to the predetermined setting range described above (specifically, the voltage fluctuation is 10 This is performed when it is determined that it has exceeded approximately 20%), and when returning from the second voltage corrector 805b to the first voltage corrector 805a, it is performed according to the output of the first voltage corrector 805a. .

For example, by detecting that the amplitude of the correction signal (first correction signal) output from the first voltage corrector 805a is within a predetermined range, the first voltage corrector 805b can detect the first amplitude. The operation of returning to the voltage corrector 805a is performed.
Here, the predetermined range is, for example, a range of about 105 to 110%. This corresponds to 5 to 10% when converted to the voltage fluctuation of the AC system 4, and therefore the operation of returning from the second voltage corrector 805b to the first voltage corrector 805a is the voltage from the voltage detector 7. The detected value is within a predetermined setting range (for example, a range of 10 to 20% for voltage fluctuation), and the first correction signal is within a predetermined range (for example, a range of 5 to 10% for voltage fluctuation). When it comes to.

  As described above, the power converter control device according to Embodiment 2 of the present invention can determine that the AC system 4 has reliably returned to the steady state, and based on this determination result, the first voltage Switching back to the corrector 805a can be performed, and the correction signal can be switched stably.

Embodiment 3 FIG.
FIG. 4 is a configuration diagram of a control device for a power converter according to the third embodiment of the present invention. In addition to the configuration of the first embodiment, when a signal for selecting the output of the second voltage corrector 805b is input to the output of the correction signal determiner 806, the signal holder that continues the state for a predetermined time 808 is provided. As a result, for a predetermined period after the voltage fluctuation occurs, the second voltage correction device 805b can operate to suppress the current fluctuation by the second correction signal, and stable operation characteristics even with an instantaneous voltage fluctuation. Is obtained.

Here, as the above-mentioned predetermined time, about 1 to 2 times the power cycle of the AC system 4 is considered appropriate, which corresponds to 20 to 40 ms in the 50 Hz system and 16.7 to 33 ms in the 60 Hz system. To do.
It is to be noted that the same effect can be obtained when the correction signal determiner 806 itself of the second embodiment shown in FIG. 3 has the function of the signal holder 808.

Embodiment 4 FIG.
Note that the current controller 802, the first voltage corrector 805a, the second voltage corrector 805b, the correction signal determiner 806, and the correction signal switch 807 are not necessarily configured to be a three-phase alternating current. The present invention can be similarly applied to a control device that is controlled on a rotating coordinate synchronized with the frequency of the AC system 4 such as a reactive current component.

When the voltage detection of the AC system 4 is rotated and biaxially converted, the fundamental component is a direct current component, and the harmonic component is a harmonic of each order ± 1 (for example, the fourth and sixth orders if the fifth order harmonic). It is separated into wave components and remains as a harmonic component in the signal after biaxial conversion.
Both the first voltage corrector 805a and the second voltage corrector 805b function as a low-pass filter, and pass the DC component, and thus the fundamental wave component before biaxial conversion, and the harmonic component has its cutoff frequency. By removing the harmonic component corresponding to the above, the same operation as described above is performed.

Embodiment 5 FIG.
In each of the previous embodiments, the correction signal determination unit 806 performs the determination operation based on whether or not the voltage instantaneous value of the voltage detection value from the voltage detector 7 is within a predetermined range. The same effect can be obtained even if the determination operation is performed based on the voltage distortion of the detected value.
Since the voltage causing the voltage variation includes many frequency components, it can be treated as an increase in voltage distortion and can be used for determination of the correction signal.

  As a method for detecting voltage distortion, for example, a fundamental wave component is obtained by removing a harmonic component of a voltage detection value with a filter, and an effective value of a component obtained by subtracting the fundamental wave component from the voltage detection value is obtained as voltage distortion. There is a way. This method has a disadvantage that a time delay occurs in the calculation of the effective value, and the operation is delayed as compared with the case where the switching timing is determined by the instantaneous voltage value. On the other hand, it is less susceptible to relatively low-order harmonics and measurement noise, and an advantage is obtained that unnecessary operations can be avoided as compared with the case where determination is made based on instantaneous voltage values.

1 power converter, 2 impedance element, 3 capacitor, 4 AC system,
5 DC system, 6 Current detector, 7 Voltage detector, 8 Control device, 801 Subtractor,
802 current controller, 803 adder, 804 pulse width controller,
805a First voltage corrector, 805b Second voltage corrector, 806 correction signal determiner, 807 correction signal switch, 808 signal holder.

Claims (5)

A control device for a power converter that converts a DC voltage into an AC voltage and outputs it to an AC system via an impedance element,
A current detector for detecting a current flowing through the impedance element, a voltage detector for detecting a voltage of the AC system, and a current control for generating a voltage command signal so that a current detection value from the current detector follows a current command value Means, a voltage correction means for generating a voltage correction signal for compensating for a current fluctuation accompanying a voltage fluctuation of the AC system based on the voltage detection value from the voltage detector, and the voltage command signal and the voltage correction signal. In a power converter control device comprising converter control means for controlling the power converter based on the added signal,
The voltage correction means outputs a first correction signal based on a voltage detection signal extracted through a first filter that removes a higher harmonic component having a frequency higher than the fundamental wave component of the AC system from the output of the voltage detector. A first voltage corrector to be generated, and a second correction signal is generated based on a voltage detection signal extracted from the output of the voltage detector through a second filter having a cutoff frequency higher than the cutoff frequency of the first filter When the voltage detection value from the second voltage corrector and the voltage detector is within a predetermined setting range, the first correction signal is output as the voltage correction signal, and exceeds the predetermined setting range. Voltage correction signal switching means for switching the correction signal to output the second correction signal as the voltage correction signal when
After the voltage correction signal switching means switches from the first correction signal to the second correction signal, the voltage detection value from the voltage detector is within the predetermined set range, and the first correction signal is switched to the first correction signal. A control device for a power converter, wherein the second correction signal is returned to the first correction signal when the correction signal is within a predetermined range . 2. The control apparatus for a power converter according to claim 1, wherein the second filter has a cutoff frequency for removing higher-order harmonic components generated from the power converter. 3. The voltage correction signal switching means is configured to hold the state for a predetermined time after switching from the first correction signal to the second correction signal. controller of the power converter. 4. The voltage correction signal switching unit sets the predetermined setting range based on a voltage instantaneous value of a voltage detection value from the voltage detector, according to any one of claims 1 to 3. The control apparatus of the power converter as described . The voltage correction signal switching means sets the predetermined setting range based on voltage distortion of a voltage detection value from the voltage detector. controller of the power converter.

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