JP6018792B2 - Power converter control method - Google Patents

Description

  The present invention relates to a control method for controlling a power converter.

  In general, it is known to perform vector control of a power converter (see, for example, Patent Document 1). Moreover, connecting a power converter device to an alternating current system via a transformer and controlling the output current of the power converter device in a grid connection point to a desired value is performed.

  A harmonic current is superimposed on the fundamental current in the output current of a power converter such as a PWM (Pulse Width Modulation) inverter. If the harmonic current flows into the AC system, the AC system is adversely affected. For this reason, in order to suppress the outflow of the harmonic current to the AC system, an output filter may be provided between the transformer and the grid connection point.

Japanese Patent Laid-Open No. 3-256587

  However, when the power converter provided with the output filter is controlled based on the current detected at the grid connection point, it is difficult to control the current flowing through the system constituted by the output filter and the transformer. In addition, when the stability of the system is reduced due to the impedance relationship between the transformer and the output filter, a resonance current may be generated in the system. Therefore, in order to cope with the resonance current, it is necessary to increase the capacities of the power converter, the transformer, and the output filter. Furthermore, since the resonance current is shunted to the grid connection point, the accuracy of current control of the power converter is deteriorated.

  On the other hand, if a current flowing through the system is detected by the power conversion device provided with the output filter and controlled based on this, the resonance current generated in the system can be controlled. However, in the case of such control, it is difficult to control the output current at the grid connection point with high accuracy because the control is not the detection of the current at the grid connection point.

  Therefore, an object of the present invention is to improve the control accuracy of the current at the grid connection point in the power conversion device provided with the output filter between the transformer and the grid connection point, and at the same time comprises the output filter and the transformer. An object of the present invention is to provide a method for controlling a power converter capable of controlling the resonance current of a system to be controlled.

A control method for a power conversion device according to an aspect of the present invention is a system interconnection with a power system, controls a current to the system to a desired value, is connected to the power system via a transformer, and the power system A method for controlling a power conversion device that controls a power conversion device provided with a filter on the output side for suppressing a harmonic current that flows into the power system, the system connection flowing to a connection point that is connected to the power system A system point current is detected, a control amount for controlling the detected grid connection point current to be a desired current command value is calculated, and the power conversion is performed on the power conversion device side than the filter. An output current of the apparatus is detected, a compensation amount for suppressing a resonance current flowing through the filter is calculated based on the current command value and the detected output current, and the calculated control amount and the calculated compensation amount Based on the power It controls conversion device, calculation of the compensation amount, and calculates the difference between the output current detected with said current command value, on the calculated the difference, multiplied by a gain to calculate the amount of compensation for the voltage dimension including that.

  According to the present invention, in the power conversion device provided with the output filter between the transformer and the grid connection point, the current control accuracy of the grid connection point is improved, and at the same time, the output filter and the transformer are configured. It is possible to provide a method for controlling a power converter capable of performing control to suppress the resonance current of the system.

The block diagram which shows the structure of the electric power grid | system system to which the control apparatus of the power converter device which concerns on the 1st Embodiment of this invention is applied. The three-phase connection diagram which shows the circuit of the electric power grid | system system which concerns on 1st Embodiment. In the power system according to the first embodiment, the current command value for the a phase, the output current of the semiconductor power conversion device, and the case where the stability of the system composed of the output filter and the transformer is reduced, and The wave form diagram which shows the correlation of output filter electric current. The wave form diagram which shows the correlation of the electric current command value about a phase by the control of the control apparatus which concerns on 1st Embodiment, the output current of a semiconductor power converter device, and an output filter current. The block diagram which shows the structure of the electric power grid | system system to which the control apparatus of the semiconductor power converter device which concerns on the 2nd Embodiment of this invention is applied.

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

(First embodiment)
FIG. 1 is a configuration diagram illustrating a configuration of a power system 20 to which a control device 10 for a power conversion device according to a first embodiment of the present invention is applied. In addition, the same code | symbol is attached | subjected to the same part in subsequent figures, the detailed description is abbreviate | omitted, and a different part is mainly described. In the following embodiments, the same description is omitted.

  The power system system 20 includes a semiconductor power conversion device 1, a transformer 2, an output filter 3, an output current detector 4, a grid connection point current detector 5, a voltage detector 6, and an AC system 7. And a control device 10. The system 8 includes a semiconductor power conversion device 1, a transformer 2, and an output filter 3. The power conversion device includes a semiconductor power conversion device 1 and a transformer 2.

  The AC system 7 is an electric power system including an AC power source 71 that generates three-phase AC power. The AC system 7 is connected to the output side of the semiconductor power converter 1 via the transformer 2 at the system connection point Pc.

  The semiconductor power conversion device 1 is connected to the grid connection point Pc via the transformer 2. The semiconductor power converter 1 controls the grid connection point currents ia, ib, ic flowing to the grid connection point Pc. The grid connection point currents ia, ib, and ic are instantaneous values of the respective phases of the three-phase alternating current flowing through the grid connection point Pc. The semiconductor power converter 1 generates a pulsed voltage by PWM (Pulse Width Modulation) control. In principle, a harmonic current is superimposed on the fundamental current in the current output from the semiconductor power conversion device 1 by the pulse voltage.

  The transformer 2 transforms the three-phase AC voltage output from the semiconductor power converter 1 to a voltage suitable for the system voltage of the AC system 7.

  The output filter 3 is provided between the transformer 2 and the grid connection point Pc. The output filter 3 is mainly composed of a capacitor 31 and a reactor 32. The output filter 3 is provided in order to suppress the harmonic current output from the semiconductor power conversion device 1. This is because if the harmonic current flows out into the AC system 7, the AC system 7 is adversely affected. Here, the output filter 3 refers to all three sets of output filters provided in each phase.

  The output current detector 4 is provided between the transformer 2 and the output filter 3. The output current detector 4 detects the output currents iha, ihb, ihc of the semiconductor power conversion device 1 that flows between the transformer 2 and the output filter 3. The output currents iha, ihb, ihc are instantaneous values that flow in each phase of the three-phase alternating current output from the power conversion device 1. The output current detector 4 outputs the detected output currents iha, ihb, ihc to the control device 10. Here, the output current detector 4 indicates all three current detectors provided in each phase.

  The grid connection point current detector 5 is provided between the output filter 3 and the grid connection point Pc. The grid connection point current detector 5 detects grid connection point currents ia, ib, ic flowing through the grid connection point Pc. The grid connection point current detector 5 outputs the detected grid connection point currents ia, ib, ic to the control device 10. Here, the grid connection point current detector 5 refers to all three current detectors provided in each phase.

  The voltage detector 6 is provided between the output filter 3 and the grid connection point Pc. The voltage detector 6 detects system voltages va, vb, vc of the AC system 7. The system voltages va, vb, vc are instantaneous values of each phase of the three-phase AC voltage applied to the AC system 7. The voltage detector 6 outputs the detected system voltages va, vb, vc to the control device 10. Here, the voltage detector 6 refers to all three voltage detectors provided in each phase.

  The control device 10 includes output currents iha, ihb, ihc detected by the output current detector 4, grid connection point currents ia, ib, ic detected by the grid connection point current detector 5, and a voltage detector 6. Based on the system voltages va, vb, and vc detected by the above, the semiconductor power conversion device 1 is controlled so that the system connection point currents ia, ib, and ic have a desired current value.

  Next, the configuration of the control device 10 will be described.

  The control device 10 includes a phase detection unit 11, three dq rotation coordinate conversion units 12, 13, and 14, a current control unit 15, an inverse dq rotation coordinate conversion unit 16, a PWM control unit 17, and two gain devices. 18d, 18q, four subtractors 21d, 21q, 23d, 23q, and two adders 22d, 22q.

  The phase detection unit 11 performs a rotation coordinate conversion process performed by the dq rotation coordinate conversion units 12 to 14 and the inverse dq rotation coordinate conversion unit 16 based on the system voltages va, vb, and vc detected by the voltage detector 6. A reference phase ωt is generated. The phase detection unit 11 outputs the generated phase ωt to the dq rotation coordinate conversion units 12 to 14 and the inverse dq rotation coordinate conversion unit 16.

  The dq rotation coordinate conversion unit 12 converts the system voltages va, vb, vc, which are three-phase AC voltages detected by the voltage detector 6, into the dq axis coordinate system using the phase ωt, and the d axis voltages Vd and q A shaft voltage Vq is calculated. The dq coordinate system is composed of two axes, a d-axis indicating active power components and a q-axis indicating reactive power components. The dq rotation coordinate conversion unit 12 outputs the calculated d-axis voltage Vd and q-axis voltage Vq to the subtracters 21d and 21q, respectively.

  The dq rotation coordinate conversion unit 13 converts the grid connection point currents ia, ib, ic, which are three-phase alternating currents detected by the grid connection point current detector 5, into the dq axis coordinate system using the phase ωt. Then, the grid connection point d-axis current Id and the grid connection point q-axis current Iq are calculated. The dq rotation coordinate conversion unit 13 outputs the calculated grid connection point d-axis current Id and grid connection point q-axis current Iq to the current control unit 15.

  The dq rotation coordinate conversion unit 14 converts the output currents iha, ihb, ihc, which are three-phase alternating currents detected by the output current detector 4, into the dq axis coordinate system using the phase ωt, and the d axis output current Ihd. And q-axis output current Ihq. The dq rotation coordinate conversion unit 14 outputs the calculated d-axis output current Ihd and q-axis output current Ihq to the subtracters 23d and 23q, respectively.

The subtractor 23d receives the d-axis current command value Id * instructed by the host control system and the d-axis output current Ihd calculated by the dq rotation coordinate conversion unit 14. The d-axis current command value Id * may be set in the control device 10 in advance. The d-axis current command value Id * is a control command value for the d-axis component (active power component) of the current flowing through the grid connection point Pc. The subtractor 23d subtracts the d-axis output current Ihd from the d-axis current command value Id *. The subtractor 23d outputs the calculated difference between the d-axis components to the gain unit 18d.

  The subtracter 23q receives the q-axis current command value Iq * instructed from the host control system and the q-axis output current Ihq calculated by the dq rotation coordinate conversion unit 14. The q-axis current command value Iq may be set in the control device 10 in advance. The q-axis current command value Iq * is a control command value for the q-axis component (reactive power component) of the current flowing through the grid connection point Pc. The subtracter 23q subtracts the q-axis output current Ihq from the q-axis current command value Iq *. The subtractor 23q outputs the calculated difference between the q-axis components to the gain unit 18q.

  A gain is set in advance in the gain device 18d. This gain is a control gain that determines the stability of the system 8. The gain unit 18d multiplies the difference between the d-axis components calculated by the subtractor 23d and calculates a first d-axis voltage command value Vd1 *. The first d-axis voltage command value Vd1 * is a voltage command value of a d-axis component that is a compensation amount for compensating the resonance current generated in the system 8. The gain unit 18d outputs the calculated first d-axis voltage command value Vd1 * to the adder 22d.

  Similarly to the gain unit 18d, a gain is set in the gain unit 18q in advance. The gain unit 18q multiplies the difference between the q-axis components calculated by the subtracter 23q, and calculates a first q-axis voltage command value Vq1 *. The first q-axis voltage command value Vq1 * is a q-axis component voltage command value serving as a compensation amount for compensating the resonance current generated in the system 8. The gain unit 18q outputs the calculated first q-axis voltage command value Vq1 * to the adder 22q.

  The current control unit 15 receives the grid connection point dq axis currents Id and Iq and the dq axis current command values Id * and Iq * calculated by the dq rotation coordinate conversion unit 13. The current control unit 15 converts the second voltage command values Vd2 * and Vq2 * for controlling the system interconnection point dq axis currents Id and Iq to follow the dq axis current command values Id * and Iq * on the dq axis. Calculate for each component. The current control unit 15 outputs the second voltage command values Vd2 * and Vq2 * to the adders 22d and 22q for each dq axis component, respectively.

The adder 22d adds the first d-axis voltage command value Vd1 * calculated by the gain unit 18d and the second d-axis voltage command value Vd2 * calculated by the current control unit 15, and adds the third d-axis. A voltage command value Vd3 * is calculated. The adder 22d outputs the calculated third d-axis voltage command value Vd3 * to the subtractor 21d.

The adder 22q adds the first q-axis voltage command value Vq1 * calculated by the gain unit 18q and the second q-axis voltage command value Vq2 * calculated by the current control unit 15, and adds the third q-axis. Voltage command value Vq3 * is calculated. The adder 22q outputs the calculated third q-axis voltage command value Vq3 * to the subtractor 21q.

  The subtractor 21d subtracts the third d-axis voltage command value Vd3 * calculated by the adder 22d from the d-axis voltage Vd calculated by the dq rotation coordinate conversion unit 12, and the fourth d-axis voltage command value Vd4. * Is calculated. The calculated fourth d-axis voltage command value Vd4 * is generated in the system 8 while controlling the current flowing through the grid connection point Pc to a desired current value (d-axis current command value Id *). This is a d-axis component of a voltage command value for controlling to suppress the resonance current. The subtractor 21d outputs the calculated fourth d-axis voltage command value Vd4 * to the inverse dq rotation coordinate conversion unit 16.

  The subtractor 21q subtracts the third q-axis voltage command value Vq3 * calculated by the adder 22q from the q-axis voltage Vq calculated by the dq rotation coordinate conversion unit 12, and the fourth q-axis voltage command value Vq4. * Is calculated. The calculated fourth q-axis voltage command value Vq4 * is generated in the system 8 while controlling the current flowing through the grid connection point Pc to a desired current value (q-axis current command value Iq *). The q-axis component of the voltage command value for controlling the resonance current to be suppressed. The subtractor 21q outputs the calculated fourth q-axis voltage command value Vq4 * to the inverse dq rotation coordinate conversion unit 16.

  The inverse dq rotational coordinate converter 16 uses the phase ωt to convert the fourth dq-axis voltage command values Vd4 * and Vq4 * input from the two subtractors 21d and 21q into a three-phase voltage command value (three-phase amount). Convert to The inverse dq rotation coordinate conversion unit 16 outputs the calculated three-phase voltage command values va *, vb *, vc * to the PWM control unit 17.

  The PWM control unit 17 generates a gate pulse (gate pattern) GP on the basis of the three-phase voltage command values va *, vb *, and vc * calculated by the inverse dq rotation coordinate conversion unit 16, and the semiconductor power conversion device 1 is controlled. Thereby, the semiconductor power converter device 1 outputs a voltage according to the three-phase voltage command values va *, vb *, and vc *.

  Next, the theory of control by the control device 10 will be described with reference to FIG.

  FIG. 2 is a three-phase connection diagram illustrating a circuit of the power system 20 according to the present embodiment.

  Here, the output filter currents ifa, ifb, and ifc are currents flowing through the output filters 3 of the respective phases.

The following equation holds between the grid connection point currents ia, ib, ic, the output currents iha, ihb, ihc, and the output filter currents ifa, ifb, ifc.

The grid connection point d-axis current Id and the grid connection point q-axis current Iq converted by the dq rotation coordinate conversion unit 13 can be expressed by the following equations using the grid connection point currents ia, ib, ic.

Here, “T” is a conversion equation for dq rotation coordinate conversion used in the dq rotation coordinate conversion units 12, 13, and 14. That is, “T” can be expressed as the following equation.

Similarly, the d-axis voltage Vd and the q-axis voltage Vq of the system voltage converted by the dq rotation coordinate conversion unit 12 can be expressed by the following equations using the three-phase system voltages va, vb, and vc.

Similarly, the d-axis output current Ihd and the q-axis output current Ihq converted by the dq rotation coordinate conversion unit 14 can be expressed by the following equations using three-phase output currents iha, ihb, ihc.

According to the above equation, the outputs of the gain devices 18d and 18q can be expressed as the following equation when the gain set in the gain devices 18d and 18q is “K”.

Each phase va *, vb *, vc * of the three-phase voltage command values va *, vb *, vc * output from the inverse dq rotation coordinate conversion unit 16 can be expressed by the following equations.

Here, when the control is in a steady state and the current control unit 15 causes the grid interconnection point dq axis currents Id and Iq to follow the dq axis current command values Id * and Iq *, −Id + Id * = 0, −Iq + Iq * = Since it is 0, the above equation becomes the following equation.

  The first term and the second term on the right side of the above equation are current control terms for the grid connection point current. The third term is the product of the resonance current of system 8 and the control gain K. The third term has the effect of attenuating the resonance current. That is, it is possible to arbitrarily improve the stability of the system 8 by increasing the attenuation rate of the resonance current by the value of the gain K.

  According to this embodiment, the following effects can be obtained.

  FIG. 3 is a waveform diagram showing the correlation among the current command value Ia0 * for the a phase, the output current Iha0 of the semiconductor power converter 1, and the output filter current Ifa0 * when the stability of the system 8 is lowered. It is. FIG. 4 is a waveform diagram showing a correlation among the current command value Ia *, the output current Iha of the semiconductor power converter 1, and the output filter current Ifa controlled by the control device 10 according to the present embodiment. Here, both FIG. 3 and FIG. 4 show various current waveforms for one phase (typically a phase).

  In the current waveform shown in FIG. 4, it can be seen that the resonance current is suppressed compared to the current waveform shown in FIG. 3, and the output current Iha of the semiconductor power conversion device 1 follows the current command value Ia *.

  Therefore, the control device 10 detects the grid connection point currents ia, ib, ic and the output currents iha, ihb, ihc of the semiconductor power conversion device 1 and performs control based on the equation (8), whereby the system 8 Since the resonance current is suppressed by improving the stability of the power supply and the resonance current diverted to the grid connection point is reduced, the grid connection point currents Id and Iq are made to accurately follow the current command values Id * and Iq *. be able to.

  In addition, since the resonance current flowing through the semiconductor power converter 1, the transformer 2, and the output filter 3 is reduced, the margin of current capacity of the semiconductor power converter 1, the transformer 2, and the output filter 3 can be reduced. . Therefore, these devices can be miniaturized and the cost can be reduced.

(Second Embodiment)
FIG. 5: is a block diagram which shows the structure of 20 A of electric power grid systems to which the control apparatus 10 of the power converter device which concerns on the 2nd Embodiment of this invention is applied.

  The power system 20A is obtained by replacing the output current detector 4 with the output current detector 4A in the power system 20 according to the first embodiment shown in FIG. Other points are the same as in the first embodiment.

  The output current detector 4 </ b> A is provided in a DC winding between the transformer 2 and the semiconductor power conversion device 1. The output current detector 4A detects the current flowing through the DC winding as the output currents iha, ihb, ihc of the semiconductor power converter 1. Here, the output current detector 4A refers to all three current detectors provided in each phase. Other points are the same as those of the output current detector 4 according to the first embodiment.

  According to the present embodiment, by detecting the DC winding current of the transformer 2 as the output currents iha, ihb, ihc of the semiconductor power converter 1, the same effects as those of the first embodiment can be obtained. .

  In each embodiment, the dq rotation coordinate is used as the current control. However, the present invention is not limited to this. Current control may be performed by other methods.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor power converter device, 2 ... Transformer, 3 ... Output filter, 4 ... Output current detector, 5 ... Grid connection point current detector, 6 ... Voltage detector, 7 ... AC system, 8 ... System, 10 ... Control device, 11 ... Phase detector, 12, 13, 14 ... dq rotational coordinate converter, 15 ... Current controller, 16 ... Inverse dq rotational coordinate converter, 17 ... PWM controller, 18d, 18q ... Gain device, 21d, 21q, 23d, 23q ... subtractor, 22d, 22q ... adder, 20 ... power system, 31 ... capacitor, 32 ... reactor, 71 ... AC power supply, GP ... gate pulse, Pc ... grid connection point.

Claims (9)

A filter is connected to the power system, controls the current to the system to a desired value, is connected to the power system via a transformer, and suppresses harmonic current flowing out to the power system on the output side A method for controlling a power conversion device for controlling a power conversion device provided in
Detecting a grid connection point current flowing in a grid connection point with the power system,
Calculate a control amount for controlling the detected grid connection point current so as to have a desired current command value,
The output current of the power converter is detected on the power converter side of the filter,
Based on the current command value and the detected output current, a compensation amount for suppressing the resonance current flowing in the filter is calculated,
Based on the calculated control amount and the calculated compensation amount, the power converter is controlled ,
The calculation of the compensation amount is
Calculate the difference between the current command value and the detected output current,
A control method for a power converter , comprising: multiplying the calculated difference by a gain to calculate the compensation amount of the voltage dimension . Detecting the system voltage of the power system;
Calculating a voltage command value for controlling the output voltage of the power converter based on the calculated control amount and the calculated compensation amount;
Detected on the basis of the system voltage and computed the voltage command value, control method of the power converter according to claim 1, wherein the controller controls the power converter. Calculating the control amount in the dq axis coordinate system;
The method of controlling a power converter according to claim 1 or 2 , wherein the compensation amount is calculated in a dq axis coordinate system. A filter is connected to the power system, controls the current to the system to a desired value, is connected to the power system via a transformer, and suppresses harmonic current flowing out to the power system on the output side A power converter control device for controlling the power converter provided in
Grid connection point current detecting means for detecting a grid connection point current flowing in a grid connection point with the power system;
Current control means for calculating a control amount for controlling the grid connection point current detected by the grid connection point current detection means so as to have a desired current command value;
An output current detecting means provided on the power converter side of the filter and detecting an output current of the power converter;
Based on the current command value and the output current detected by the output current detection means,
Compensation amount calculating means for calculating a compensation amount for suppressing the resonance current flowing in the filter;
Power conversion control means for controlling the power converter based on the control amount calculated by the current control means and the compensation amount calculated by the compensation amount calculation means ,
The compensation amount calculating means includes:
Current difference calculation means for calculating a difference between the current command value and the output current detected by the output current detection means;
Voltage compensation amount calculating means for calculating the compensation amount of the voltage dimension by multiplying the difference calculated by the current difference calculating means by a gain.
Control system for a power converter according to claim. System voltage detection means for detecting the system voltage of the power system;
Voltage command value calculation for calculating a voltage command value for controlling the output voltage of the power converter based on the control amount calculated by the current control unit and the compensation amount calculated by the compensation amount calculation unit Means and
The power conversion control means controls the power converter based on the system voltage detected by the system voltage detection means and the voltage command value calculated by the voltage command value calculation means. The control apparatus of the power converter device of Claim 4 . The current control means calculates the control amount in a dq axis coordinate system,
The said compensation amount calculating means calculates the said compensation amount by a dq axis coordinate system, The control apparatus of the power converter device of Claim 4 or Claim 5 characterized by the above-mentioned. Power conversion means for interconnecting the power system and controlling the current to the system to a desired value;
A transformer provided between the power conversion means and the power system;
A filter for suppressing harmonic current flowing out from the power conversion means to the power system;
Grid connection point current detecting means for detecting a grid connection point current flowing in a grid connection point with the power system;
Current control means for calculating a control amount for controlling the grid connection point current detected by the grid connection point current detection means so as to have a desired current command value;
An output current detection means that is provided on the power conversion means side of the filter and detects an output current of the power conversion means;
Based on the current command value and the output current detected by the output current detection means,
Compensation amount calculating means for calculating a compensation amount for suppressing the resonance current flowing in the filter;
Power conversion control means for controlling the power conversion means based on the control amount calculated by the current control means and the compensation amount calculated by the compensation amount calculation means ,
The compensation amount calculating means includes:
Current difference calculation means for calculating a difference between the current command value and the output current detected by the output current detection means;
Voltage compensation amount calculating means for calculating the compensation amount of the voltage dimension by multiplying the difference calculated by the current difference calculating means by a gain.
Electric power system according to claim. System voltage detection means for detecting the system voltage of the power system;
Voltage command value calculation for calculating a voltage command value for controlling the output voltage of the power conversion unit based on the control amount calculated by the current control unit and the compensation amount calculated by the compensation amount calculation unit Means and
The power conversion control means controls the power conversion means based on the system voltage detected by the system voltage detection means and the voltage command value calculated by the voltage command value calculation means. The power system system according to claim 7 . The current control means calculates the control amount in a dq axis coordinate system,
The power system according to claim 7 or 8 , wherein the compensation amount calculation means calculates the compensation amount in a dq axis coordinate system.

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