JP2012175845A - Controller of parallel multiplex power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller of a parallel multiplex power conversion device that continues to stably operate even when receiving a disturbance such as an AC power system accident.SOLUTION: The controller of the parallel multiplex power conversion device is provided with a plurality of power converters each having one end connected to a bus of an AC power system through a transformer, and has a capacitor in a DC circuit at the other end of the power converters. The controller of the parallel multiplex power conversion device includes a current detection part which detects a composite current flowing to the bus and a branch current flowing to each power converter; a signal selection part which selects the composite current when the AC power system is normal or the branch current when the AC power system is in a disturbance state; and a current control part which controls a current command signal using output of the signal selection part as a current feedback signal.

Description

  The present invention relates to a control device for a parallel multiplex power conversion device that can safely continue operation even when an accident occurs in an AC power system in a voltage type power conversion device having a parallel multiplex configuration.

  For example, Japanese Patent Application Laid-Open No. H10-228561 is known as a device that performs power conversion between alternating current and direct current by installing a voltage type power conversion device having a parallel multiplex configuration in an alternating current power system.

  The power conversion device disclosed in Patent Document 1 is connected to the power converter in a parallel multiplex configuration by shifting the pulse generation phase of each power converter even if the number of pulses of one power converter is small. Since the point seems to be controlled by multiple times of pulses, there is an advantage that the current / voltage distortion at the connection point is reduced.

  Moreover, in this power converter, when it is set as the parallel multiplex structure which connects a power converter in parallel, in the steady state, the current control system is a connection point of the power converter (system side of the transformer for conversion) Is controlled as a feedback amount. As a result, the combined current at the interconnection point has a smaller ripple due to the converter and is suitable as a feedback value.

Japanese Patent Laid-Open No. 10-127065

  The power conversion device of Patent Document 1 is a so-called voltage type power conversion device provided with a capacitor on the DC side circuit. In this type of power conversion device, when the voltage drops due to an accident in the AC power system, An accident current is supplied toward the accident point, causing an overcurrent.

  In this case, the control device operates to feed back the connection point current and suppress it, but does not control the current flowing through the individual power converters. Even if it is suppressed within the limit value, some of the power converters have their current values instantaneously exceeding the limit value. As a result, when the limit current of the elements constituting the power converter is exceeded, the elements are destroyed.

  One of the reasons why the currents of the plurality of power converters are unbalanced is a delay in current control. This can be dealt with by using an IGBT element capable of high-speed switching.

  Another reason is that the phase of the carrier frequency for creating the PWM gate signal of each power converter is shifted for the purpose of suppressing the generation of harmonic current as a parallel multiplex configuration. The output current of each power converter differs instantaneously due to the phase shift of the carrier frequency. If the output changes suddenly due to an accident in the AC power system, the output balance of each power converter Tends to collapse, and tends to be an imbalance of current.

  In order to prevent the destruction of the element, it is necessary to stop the power converter from the viewpoint of equipment protection, but on the other hand, the demand for ride-through operation due to disturbances such as AC power system accidents has been expanded, Even in the event of a disturbance due to an accident or the like, it has become necessary to develop technology that allows the power converter to continue operation without stopping.

  In view of the above, an object of the present invention is to provide a control device for a parallel multiple power conversion device that can continue operation stably even when subjected to disturbance such as an AC power system failure.

  In a control device for a parallel multiple power conversion apparatus, in which a plurality of power converters, one end of which is connected to a bus of an AC power system through a transformer, and a capacitor is provided in a DC circuit of the other end of the power converter, Current detector for detecting the combined current flowing through the power converter and the branch current flowing through each power converter, the signal selecting section for selecting the combined current when the AC power system is normal, and the signal selecting section for selecting the branch current when the AC power system is disturbed A current control unit is provided that controls the output to be a current command signal as a current feedback signal.

  Further, the current feedback signal and the current command signal are obtained as a P-axis component and a Q-axis component.

  In addition, in order to obtain a current feedback signal as a P-axis component and a Q-axis component by rotating coordinate conversion, a reference phase is calculated from the AC system voltage, and the reference phase for the branch current is transformed with respect to the reference phase for the combined current. Taking into account the phase change in the vessel.

  Further, the reference phase for the branch current is used as the reference phase obtained from the AC system voltage when obtaining the three-phase signal from the output of the current control unit by reverse rotation coordinate transformation.

  In addition, the signal selection unit and the current control unit are configured for each power converter.

  Even when a disturbance such as an AC power system accident occurs, the operation can be continued stably.

The figure which shows the specific circuit structure of a control apparatus. The figure which shows the structure of a parallel multiple power converter device and its control apparatus. The figure which shows the circuit structure around the PQ-axis calculating part of a control apparatus. The figure which shows the circuit structure around the electric current control part of a control apparatus. The figure which shows an alternating current system event and each part waveform at the time of not employ | adopting this invention. The figure which shows the alternating current system event at the time of employ | adopting this invention, and each part waveform.

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

  FIG. 2 is a diagram illustrating a parallel multiple power conversion device to which the present invention is applied and a control device thereof. In this figure, the bus B is an interconnection point between the AC power system G and the parallel multiple power converter. The parallel multiple power conversion apparatus includes a plurality of transformers Tr (Tr1, Tr2, Tr3, Tr4) (four examples are shown in FIG. 2) connected to the bus B, and a plurality of transformers provided for each transformer Tr. Power converter C (C1, C2, C3, C4) and a DC circuit D common to the plurality of power converters C. The plurality of power converters C are connected in series or in parallel on the DC circuit D side, and a DC capacitor, for example, is installed in the DC circuit D to form a so-called voltage-type parallel multiple power converter.

  The control device 1 of the parallel multiple power conversion device finally gives a firing angle control pulse P (P1, P2, P3, P4) to each of the plurality of power converters C, but AC power is used for firing control. A current (hereinafter referred to as a combined current) I1 and a voltage V of the system G are obtained from the current transformer CT and the voltage transformer PT. In the present invention, the current I2 (I21, I22, I23, I24: hereinafter referred to as a branch current) flowing through each power converter C (C1, C2, C3, C4) is converted into a branch current transformer CTB (CTB1, CTB2, CTB3). , CTB4) to detect and input. The control device 1 uses an analog-digital converter AD when inputting current and voltage signals in order to determine the ignition signal by digital processing.

  As is apparent from the above description of the control device 1 of the parallel multiple power conversion device, the control device 1 includes a control unit 1A common to the power converters and an individual control unit 1B installed for each power converter C. And have. In the illustrated example, since four power converters C are provided, the individual control unit 1B installed for each power converter has individual control for each of these power converters C1, C2, C3, and C4. 1B1, 1B2, 1B3, 1B4 are provided.

  FIG. 1 shows the processing contents of the control device 1. This control device 1 controls the P-axis current component IP and the Q-axis current component IQ to be constant to their target values IPr and IQr for each power converter, and the current of each of the four individual control units 1B. The controller A performs this PQ axis current control process. The target values IPr and IQr have the same value for the current control units A of the four individual control units 1B from the P-axis current setting unit PS and the Q-axis current setting unit QS in the common control unit 1A. Given.

  In addition, in the current control unit A of the individual control unit 1B, the P-axis current component IP and the Q-axis current component IQ are used as feedback signals from the parallel multiple power conversion device side to be controlled. The PQ axis current calculation unit PQI is provided for each input current. Specifically, a PQ axis current calculation unit PQI is provided for the input current (combined current) I1 of the common control unit 1A and the input currents (branch currents) I21, I22, I23, and I24 of the individual control unit 1B. Since the PQ axis current calculation unit PQI uses currents having a phase difference of 90 degrees as its input, the three-phase current is converted into the two-phase currents Iα and β components of the α component and the β component that are 90 degrees different in phase. A three-phase to two-phase converter (not shown in FIG. 1) for converting to Iβ is provided. These three-phase to two-phase conversion units and the PQ axis current calculation unit PQI constitute a so-called rotational coordinate conversion unit. Note that the P-axis current component IP and the Q-axis current component IQ obtained by the PQ-axis current calculation unit PQI are direct-current signals having only magnitudes.

  Further, since the reference phase is required in the process of converting the two-phase currents Iα and Iβ into the PQ axis current components IP and IQ in the PQ axis current calculation unit PQI, the voltage phase calculation unit 33 that calculates the reference phase for the voltage V. Are provided in the common control unit 1A.

  Further, the PQ and Q axis components output from the current control unit A are added with the PQ axis components VP and VQ of the voltage obtained from the voltage V of the AC power system G, respectively, and the voltages of the P axis and Q axis components are added. The set values VPr and VQr are used. For this purpose, the PQ axis components VP and VQ of the voltage used here are calculated in the PQ axis voltage calculation unit PQV of the common control unit 1A. The PQ-axis voltage calculation unit PQV also has a three-phase two-phase conversion unit (not shown in FIG. 1) that converts the three-phase voltage into α-phase and β-component two-phase voltages Vα and Vβ that are 90 degrees different in phase. Prepared).

  On the other hand, the processing result of the current control unit A is two sets of signals related to the PQ axis current components IP and IQ, but the signals finally given by each pulse control circuit PWM are AC three-phase signals. In the reverse rotation coordinate conversion unit 5, the PQ axis current component is converted into the αβ component, and the reverse rotation coordinate conversion is further performed as a three-phase component.

  The control device 1 of the parallel multiple power conversion device operates as described above. In the present invention, when an accident occurs in the AC power system G, the PQ axis current calculation unit PQI to be supplied to the current control unit A The output is switched from the combined current side to the branch current side using the feedback current changeover switch SW.

  Hereinafter, the operation of the control device 1 of the parallel multiple power conversion device will be described with reference to detailed circuits of main components. First, FIG. 3 shows a PQ axis calculation unit PQ used in the common control unit 1A and the individual control unit 1B and its peripheral circuit configuration. In this figure, the main circuit configuration of the common control unit 1A is shown on the lower side, and the main circuit configuration of 1B1 is shown on the upper side to represent the plurality of individual control units 1B. In addition, since the same input as 1B1 is given also to individual control parts other than 1B1, and it functions similarly, 1B1 is described and demonstrated here as a representative.

  The common control unit 1A in FIG. 3 is provided with two sets of PQ axis calculation units (PQI1 and PQV) that receive the current I1 and the voltage V, and the individual control unit 1B receives the PQ axis that receives the current I21. A calculation unit PQI21 is installed. Further, a three-phase / two-phase converter 32 (32I1, 32V, 32I21) is provided in the preceding stage of these PQ axis calculation units PQ, and a rotational coordinate conversion circuit is configured by a combination thereof.

  According to this circuit configuration, first, the three-phase two-phase converters 32I1, 32V, 32I2 are obtained from the three-phase detection signals (digital values) of the current (synthetic current) I1 and voltage V of the AC power system G and the branch current I21. Are converted into two-phase signals (I1α and I1β, Vα and Vβ, I21α and I21β) of α and β components.

  Next, using the combined current I1 and voltage V of the AC power system G and the two-phase signals (I1α and I1β, Vα and Vβ, I21α and I21β) of the branch current I21, the P-axis component ( IP1, VP, IP21) and Q-axis components (IQ1, VQ, IQ21) are calculated. In this calculation, since the two-phase signals of the α component and the β component of the voltage V of the AC power system G are used as a reference, the phase deriving unit 33 derives the reference phase signal.

  In FIG. 3, the phase deriving unit 33 includes a reference phase detecting unit 33A and a phase correcting unit 33B. The reference phase detecting unit 33A calculates a reference phase signal cos ωt and sin ωt, and generates a PQ of the combined current I1 and the voltage V. This is applied as a reference phase to the axis calculation unit (PQI1 and PQV). The phase detection method may be a phase locked loop (PLL) method or a discrete Fourier transform (DFT).

  The reference phase signal needs to be given to the PQ axis calculation unit PQI21 of the branch current I21, but the detection location is different between the combined current I1 and the voltage V and the branch current I21. Exists. From this, the reference phase signal (phase signal on the converter side) cos (ωt + θ) and sin (ωt + θ) obtained by further correcting the phase θ of the transformer connection by the phase correction unit 33B is calculated, and the branch current I21 is calculated. This is applied to the PQ axis calculation unit PQI21 as a reference phase.

  The PQ axis calculation unit calculates the P axis component and the Q axis component by executing the following equation (1). In the equation (1), Vre and Vim mean a two-phase signal of an α component and a β component, and VP and VQ mean a P-axis component and a Q-axis component. The P-axis component obtained in this way is the amplitude of the real-axis component, and the Q-axis component is a DC amount having a magnitude corresponding to the amplitude of the imaginary-axis component.

  The output of the PQ axis calculation unit PQI1 obtained as described above is the combined current P-axis component IP1 and the combined current Q-axis component IQ1 converted into a direct current amount, and the P-axis component IP1 is an effective current and a Q-axis component. IQ1 corresponds to a reactive current. Similarly, the outputs of the PQ-axis calculation unit PQI21 are a branch current P-axis component IP21 and a branch current Q-axis component IQ21 converted into a direct current amount. The P-axis component IP21 corresponds to an effective current, and the Q-axis component IQ21 corresponds to a reactive current. To do. Further, the output of the PQ axis calculation unit PQV is a linkage point voltage P-axis component VP and a linkage point voltage Q-axis component VQ converted into a direct current amount, the P-axis component VO is an effective voltage, and the Q-axis component VQ is Corresponds to reactive voltage.

  In FIG. 1 and FIG. 3, 6 is an accident detector. For example, from the connection point voltage P-axis component VP and the connection point voltage Q-axis component VQ converted into a DC amount that is the output of the PQ axis calculation unit PQV, Detects that the connection point voltage has dropped due to a power system accident. The accident detector 6 only needs to be able to detect that the interconnection point voltage has dropped, and does not necessarily have to detect the voltage after conversion to the PQ axis component.

  In the converter individual control unit 1B of FIG. 1, the feedback current changeover switch SW normally supplies the outputs IP1 and IQ1 of the PQ axis calculation unit PQI1 to the current control unit A as feedback values. On the other hand, when the accident detector 6 detects that the interconnection point voltage V has dropped, the feedback current changeover switch SW uses the outputs IP2 and IQ2 of the PQ axis calculation unit PQI2 as feedback values to the current control unit A. give. In other words, the composite current I1 is used as a feedback value when normal, but the control is switched to current control using the branch current I2 as a feedback value when the connection point voltage drops. The control feedback value change control by the current controller A is simultaneously switched for each power converter.

  FIG. 4 shows a specific circuit configuration of the current control unit A. The current control unit A is composed of a P-axis current control unit AP and a Q-axis current control unit AQ, and sets current setting values IPr and IQr from the P-axis current setting unit PS and the Q-axis current setting unit PQ of the common control unit 1A, respectively. Get as input. On the other hand, the P-axis current and the current feedback values IP and IQ of the Q-axis current are input via the feedback current changeover switch SW, respectively.

  The P-axis current IP and Q-axis current IQ that are the outputs of the feedback current changeover switch SW are negatively fed back to the subtracters SP and SQ, respectively, and the P-axis current command value IPr and Q-axis current command value that are target signals for this control. Subtracted from IQr. The outputs of the two sets of subtracters SP and SQ are supplied to current regulators ACR-P and ACR-Q, respectively, to obtain control signals IPh and IQh. In the current regulator ACR, proportional-integral control or the like for eliminating the input deviation is performed.

  Thereafter, the outputs APh and IQh of the two sets of current regulators ACR-P and ACR-Q are added to the adders AP. In AQ, two sets of DC components VP and VQ of the PQ axis converter PQV obtained from the system voltage are added.

  Further, the correction circuit FP calculates the correction signal IPm by using the Q-axis current command value IQr as an input, and provides the correction circuit IPm as a negative signal. On the other hand, the correction circuit FQ receives the P-axis current command value IPr as an input, calculates the correction signal IQm, and provides it to the adder circuit AQ as a negative signal. This addition / subtraction operation serves to cancel the interference between the P-axis and the Q-axis.

  In FIG. 4, the corrected signals VPr and VQr obtained in this way are input to the reverse rotation coordinate conversion circuit 5 of FIG. In the reverse rotation coordinate conversion circuit 5, the corrected signals VPr and VQr and the reference phase signal (phase signal on the converter side) derived from the voltage phase calculation unit 33 of the common control unit 1A, cos (ωt + θ) and sin (ωt + θ) ) To perform reverse rotation coordinate transformation.

  By this reverse rotation coordinate transformation, two-phase signals Vα and Vβ having a phase difference of 90 degrees are derived from the corrected signals VPr and VQr, which are PQ axis component signals, and the reference phase signal. A command signal 90 is obtained. A gate signal P is obtained by PWM using the three-phase current command value 90 as a signal wave.

  When the current set value is given from the PQ axis current setting units PS and PQ of the common control unit 1A in FIG. 1, the current command value IPr of the actual axis component is used as an active power control system or a DC voltage as a host control system. A control system may be provided and its output may be used. Further, a reactive power control system or an AC voltage control system may be provided as a higher-order control system for the current command value IQr of the imaginary axis component, and the output thereof may be used.

  The controller 1 of the parallel multiple power converter of the present invention is configured as described above. In short, during normal operation, the PQ axis current obtained from the AC system side current (synthetic current) matches the target values IPr and IQr. Each converter is controlled so that the PQ axis current obtained from the current (branch current) of each converter matches the target values IPr and IQr when an accident occurs on the AC system side. The ignition control of the vessel is implemented. In other words, the combined current is controlled during normal operation, and the branch current is controlled when an accident on the AC system side occurs.

  Here, the waveform of each part when the present invention is not employed is shown in FIG. 5, and the waveform of each part when the present invention is employed is shown in FIG. In these figures, the horizontal axis represents time, and the period from the occurrence of an accident (t1), the detection of an accident (t2), the removal of the accident (t3), and the return to normal (t4) in normal operation Is shown.

  On the vertical axis, the connection point voltage V, the positive phase voltage at the connection point, and the connection point current I1 are shown from the top. As is apparent from this figure, when an accident occurs in the power system to which the parallel multiple power converter is applied and the system voltage V decreases, the fault point is detected from the parallel multiple power converter during the accident duration (t1-t3). A large current flows toward. This is because the capacitor is provided in the DC circuit D of the parallel multiplex power conversion apparatus to constitute a so-called voltage type parallel multiplex power conversion apparatus, and the capacitor serves as a power source to supply power.

  In the middle of the figure, branch currents I21, I22, I23, and I24 flowing through the power converters C (C1, C2, C3, and C4) are shown. Since the combined current is controlled to a predetermined value during normal operation (before t1), each branch current is also within the limit value range, but immediately after the occurrence of the accident (t1), the DC circuit of the parallel multiple power converter An excessive current flows from the capacitor of D. In other words, when a disturbance such as a system fault occurs, the current value (branch current value) is instantaneous in each power converter even if the total connection point current is suppressed within the current limit value. Some will exceed the limit. In the example of FIG. 5, the branch current flowing through the power converter C1 deviates from the limit value. By removing the accident at time t3, the excessive current can be resolved and normal operation can be restored. However, from the viewpoint of equipment protection, it is necessary to stop the power converter C1.

  FIG. 5 shows a waveform when the operation is continued without stopping the power converter. Further, as shown in the lowermost stage of FIG. 5, the conventional control apparatus performs control using the combined current as a feedback value.

  FIG. 6 shows the events in the present invention and the signals of the respective parts. The current and voltage trends in the upper part are the same as in the past, but the current feedback value of the constant current control unit A branches from the combined currents IP1 and IQ1 in the control of each power converter on the condition that an accident is detected at time t2. The current is switched to IP2 and IQ2. As a result, each branch current is directly subjected to suppression control. In the example of FIG. 5, the branch current I21 is an excessive current exceeding the limit value, but in FIG. 6, such an excessive current is not generated. As a result, the operation can be continued without stopping the power converter. The return to the composite current control may be performed at an appropriate timing t5 after the steady return detection t4.

  In this way, by switching the feedback of the current control system from the connection point currents IP1 and IQ1 to the respective power converter currents IP2 and IQ2 during the accident, the output current of each power converter is generated due to the occurrence of a disturbance such as a system fault. Even when variations occur, by using the power converter currents IP2 and IQ2 as feedback amounts, the overcurrent of the power converter and the power converter elements can be suppressed within the limit value, and even if a disturbance occurs The operation of the power converter can be continued.

B: Bus G: AC power system Tr: Transformer C: Power converter D: DC circuit CT: Current transformer PT: Voltage transformer CTB: Branch current transformer 1: Controller AD: Analog to digital converter 1B: Individual Control unit 1A peculiar to the power converters: control unit common to power converters IP: P-axis current component IQ: Q-axis current component IPr, IQr: target value A of P-axis current component, Q-axis current component A: current Control unit 32: three-phase to two-phase conversion unit PQ: PQ axis calculation unit 33: phase derivation unit 5: reverse rotation coordinate unit SW: feedback current changeover switch 33A: reference phase detection unit 33B: phase correction unit 6: accident detector ACR : Current control unit

Claims (5)

In a control device for a parallel multiple power conversion apparatus, in which a plurality of power converters having one end connected to a bus of an AC power system via a transformer are provided, and a capacitor is provided in a DC circuit on the other end of the power converter,
A current detection unit that detects a combined current flowing through the bus and a branch current flowing through each power converter, a signal selection unit that selects a combined current when the AC power system is normal, and a branch current when the AC power system is disturbed, the signal selection A control device for a parallel multiple power converter, comprising: a current control unit that controls the output of the unit as a current feedback signal to a current command signal. In the control apparatus of the parallel multiple power conversion device according to claim 1,
The control apparatus for a parallel multiple power converter, wherein the current feedback signal and the current command signal are obtained as a P-axis component and a Q-axis component. In the control apparatus of the parallel multiple power conversion device according to claim 2,
In order to obtain a current feedback signal as a P-axis component and a Q-axis component by rotational coordinate conversion, a reference phase is calculated from the voltage of the AC system, and the reference phase for the branch current is the same as the reference phase for the combined current. A control device for a parallel multiple power conversion device, which takes into account a phase change in a transformer. In the control apparatus of the parallel multiple power converter according to claim 3,
A parallel multiple power conversion device using a reference phase for the branch current as a reference phase obtained from an AC system voltage when obtaining a three-phase signal from an output of the current control unit by reverse rotation coordinate transformation Control device. In the control apparatus of the parallel multiple power converter according to any one of claims 1 to 4,
The control apparatus for a parallel multiple power converter, wherein the signal selector and the current controller are configured for each power converter.

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