JP6601668B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a plurality of power converters operated in parallel, for example, a power conversion for wind power generation including a master power converter and a slave power converter that link a wind power generator to a power system. The present invention relates to a technique for synchronizing PWM carriers between power converters in an apparatus.

  In recent years, wind power generation has become widespread, and the capacity of wind power generation power converters has been increasing in order to improve power generation efficiency. In this wind power generator, the power converter installed between the wind power generator and the power system includes a generator-side converter and a system-side inverter, and an AC voltage output from the wind power generator is obtained. It is converted into a DC voltage by a generator-side converter, and further converted into an AC voltage having a predetermined magnitude and frequency by a system-side inverter and supplied to the power system.

As is well known, in the interconnected operation of the system-side inverter, a harmonic current is generated when the switching frequency of the system-side inverter and the system frequency are asynchronous. Since this harmonic current distorts the system voltage and causes harmonic disturbances in the electrical equipment, the switching frequency of the system-side inverter must be synchronized with the system frequency.
Since the system-side inverter is normally controlled by PWM (pulse width modulation), synchronizing the switching frequency of the system-side inverter with the system frequency is also referred to as PWM synchronization. Synchronizing the switching frequency (carrier frequency) of inverters, converters, etc. that are PWM controlled is also referred to as PWM synchronization.

On the other hand, in order to increase the capacity of facilities, when a plurality of, for example, two power converters are operated in parallel, it is necessary to synchronize the system-side inverters of each power converter. In addition, when power converters are multiplexed, a method is adopted in which the wind power generators are in a multi-winding structure and each power converter is insulated, but the power converters interfere with each other in the generator due to the influence of impedance coupling. As a result, current control of the wind power generator may become impossible.
For this reason, it is conceivable to reduce the interference by inserting a reactor between the generator and the power converter or by synchronizing the two generator-side converters with PWM, but from the viewpoint of reducing the cost, the PWM synchronization method Is desirable. Therefore, as a result, it is necessary to PWM-synchronize the generator-side converters and the system-side inverters that constitute the two power converters.

Here, what was described in patent document 1 is known as a prior art regarding the PWM synchronization in a power converter device.
This prior art is a variable speed drive system that supplies a drive current from a PWM inverter for each winding of a multi-winding motor that is operated in tandem. One inverter that takes in a motor speed detection signal is a master inverter, All inverters are slave inverters, and the master inverter performs speed control, current control, and PWM control according to the speed command and speed detection signal, and the speed signal or phase signal, current control signal, and PWM synchronization reference in these controls. The slave inverter performs serial PWM transmission to all the slave inverters, and the slave inverter performs its own PWM control using a PLL (phase looked loop) circuit that controls the oscillation frequency according to the received PWM synchronization reference signal, and PWM Phase control and current control at timing synchronized with control And performs.

JP 2007-295647 A (paragraphs [0023] to [0052] FIG. 1)

  In this type of wind power converter, two converters (generator-side converter and system-side inverter) are controlled by a single processing unit (microcomputer) while sharing sampling frequencies such as voltage and current. In addition, as described above, it is required that the generator-side converters and the system-side inverters of the two power converters operated in parallel are PWM-synchronized.

  As a method for synchronizing a plurality of converters with PWM, as described in Patent Document 1, it is effective to control the switching frequency using a PLL circuit. However, when two system-side inverters are PWM-synchronized by PLL control, PWM synchronization between two generator-side converters having different switching frequencies from the system-side inverter may not be realized.

  Therefore, the problem to be solved by the present invention is that the generator-side converter does not affect the PWM synchronization between the system-side inverters by PLL control in a plurality of power converters, and also maintains the synchronization relationship with the system-side inverter. An object of the present invention is to provide a power conversion device that enables PWM synchronization between generator-side converters by changing only the carrier for generator.

In order to achieve the above object, the invention according to claim 1 is directed to a generator-side converter that converts an AC voltage output from a generator into a DC voltage, and a DC voltage output from the generator-side converter into an AC voltage. A system-side inverter that converts and interconnects to the power system, a control device that PWM-controls the generator-side converter and the system-side inverter, means for sampling input voltage / input current of the generator-side converter, and In the power conversion device comprising a plurality of power converters having a means for sampling the output voltage and output current of the system-side inverter, and the plurality of power converters being operated in parallel,
The controller is
A single arithmetic processing unit for performing PWM control by matching the phase of the generator-side converter carrier and the phase of the system-side inverter carrier;
The arithmetic processing unit includes:
Sharing the sampling frequency for the generator-side converter and the sampling frequency for the system-side inverter,
By changing its own generator-side converter carrier, the frequency and phase of the generator-side converter carriers of all power converters operated in parallel are matched,
The frequency and phase of its own system-side inverter carrier are matched with the frequency and phase of the system-side inverter carrier of another power converter by PLL control, and the phase of its own generator-side converter carrier is While maintaining a state in which the phase of the sampling signal having the sampling frequency is matched, the phase is matched with the phase of the generator-side converter carrier of another power converter.

  According to the present invention, the system-side inverter carrier and the generator-side converter carrier of a plurality of power converters operated in parallel can all be PWM-synchronized. Thereby, the harmonic current of the power system can be suppressed, the distortion of the system voltage can be reduced, and the harmonic disturbance to the electric equipment can be suppressed. In addition, the impedance coupling in the generator having multiple windings is suppressed, and the mutual interference between the power converters is reduced, so that the desired current control of the generator can be achieved.

It is a lineblock diagram of a power converter for wind power generation concerning an embodiment of the present invention. It is a figure which shows the relationship between the operation | movement of a sampling counter, the carrier for generator side converters, and the carrier for system side inverters. It is a figure which shows the pattern of the synchronization loss of the carrier for generator side converters. It is operation | movement explanatory drawing at the time of performing PWM synchronization in embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of a wind power generation power converter according to this embodiment. This power converter for wind power generation comprises a master power converter 30 and a slave power converter 31 connected in parallel between the wind power generator 1 and the power system 20. The power converters 30 and 31 have the same configuration.

  In FIG. 1, a generator-side converter 2 of a master power converter 30 is connected to a wind power generator 1 that outputs a three-phase AC voltage, and a DC intermediate capacitor 3 is connected to the output side thereof. Both ends of the DC intermediate capacitor 3 are connected to the DC input side of the system side inverter 4, and the power system 10 is connected to the AC output side of the system side inverter 4 via the filter reactor 5 and the filter capacitor 6.

  The wind power generator 1 is a multi-winding synchronous generator in which windings are insulated from each other. The master power converter 30 is connected to one winding, and a slave power converter 31 is connected to the other winding. It is connected. Furthermore, the output side of the master power converter 30 and the slave power converter 31 is connected to the power system 10 in a lump without being insulated.

  The generator-side converter 2 and the system-side inverter 4 in both the power converters 30 and 31 are both PWM-controlled, and the converter 2 and the inverter 4 are, for example, IGBTs in which freewheeling diodes are connected in antiparallel. These semiconductor switching elements are configured by three-phase bridge connection. Here, the system-side inverter 4 operates so as to convert the DC voltage of the DC intermediate circuit into a three-phase AC voltage and connect it to the power system 10.

  The control device 20 that performs PWM control of the generator-side converter 2 and the system-side inverter 4 includes a generator-side voltage detection value a by the voltage detector 21, a generator-side current detection value b by the current detector 22, and voltage detection. DC voltage detection value c by the detector 23, system side current detection value d by the current detector 24, and system side voltage detection value e by the voltage detector 25 are input, and based on these, the control device 20 A generator-side converter voltage command f generated by an arithmetic processing unit (not shown) is given to the generator-side converter 2, and a system-side inverter voltage command g is given to the system-side inverter 4.

In this embodiment, in each of the master power converter 30 and the slave power converter 31, the generator side converter 2 and the system side inverter 4 are controlled by one microcomputer in the control device 20, and the voltage, current, etc. The generator-side converter 2 and the system-side inverter 4 share the same sampling frequency. For this reason, the carrier frequency of the generator side converter 2 and the carrier frequency of the system side inverter 4 are in a synchronous relationship with respect to the sampling frequency.
Note that the control devices 20 and 20 of the power converters 30 and 31 can communicate with each other by the master-slave communication means 32.

Hereinafter, the operation of this embodiment will be described in detail with reference to FIGS.
FIG. 2 is a diagram illustrating the relationship between the operation of the sampling counter that generates the sampling signal, the generator-side converter carrier for PWM control, and the system-side inverter carrier. Here, the system-side inverter carrier has a double cycle and the generator-side converter carrier has a quadruple cycle with respect to the sampling signal.

  As shown in the figure, the sampling counter and the system-side inverter carrier have a vertically symmetrical waveform centered on zero, whereas the generator-side converter carrier is a carrier only in the upward direction with respect to zero. . Therefore, the peak value of the system-side inverter carrier generated based on the sampling counter is doubled and the peak value of the generator-side converter carrier is eight times the peak value of the sampling counter.

Now, as shown in FIG. 2, between the master power converter 30 and the slave power converter 31, the system-side inverter carriers are synchronized by PLL control, but the generator-side converter carriers are Consider the case of being asynchronous.
Since the sampling counter is in synchronization with the system-side inverter carrier and the generator-side converter carrier, changing the sampling counter affects both the system-side inverter carrier and the generator-side converter carrier. Therefore, when the peak value of the sampling counter is changed in order to synchronize the generator-side converter carriers of both power converters 30 and 31, synchronization between the system-side inverter carriers of both power converters 30 and 31 is achieved. It will come off.

That is, the peak value of the sampling counter cannot be changed in order to synchronize the generator-side converter carriers of both power converters 30 and 31 (to synchronize the generator-side converters with each other by PWM synchronization).
Therefore, in this embodiment, the generator-side converter carrier of the slave power converter 31 is changed by an integer multiple of the peak value of the sampling counter, whereby the generator-side converter carrier of both the power converters 30 and 31 is changed. Synchronize each other.

  In the slave power converter 31, since the bottom point of the generator-side converter carrier coincides with the zero-cross point of the system-side inverter carrier, the out-of-synchronization patterns can be limited to all six patterns. The pattern can be divided into three patterns according to the counting direction (up-count or down-count) of the system-side inverter carrier when the generator-side converter carrier is the bottom.

FIG. 3 is a pattern diagram when the generator-side converter carriers of both power converters 30 and 31 are asynchronous. In the following description and FIG. 3, the generator-side converter carrier of the master power converter 30 is referred to as the master generator-side converter carrier, and the generator-side converter carrier of the slave power converter 31 is the slave generator. This is called a side converter carrier.
(1) When the master generator-side converter carrier is at the bottom and the system-side inverter carrier is “down-counting” (FIG. 3A)
Pattern 1: The phase of the slave generator-side converter carrier is delayed by 90 degrees with respect to the master generator-side converter carrier (when the slave generator-side converter carrier is at the bottom, the system-side inverter carrier is “up-counting” )) Pattern 2: The phase of the slave generator side converter carrier is 180 degrees behind the master generator side converter carrier (when the slave generator side converter carrier is at the bottom, the system side inverter carrier is Pattern 3: When the slave generator side converter carrier phase is 270 degrees behind the master generator side converter carrier (when the slave generator side converter carrier is at the bottom) The inverter carrier is “up counting”) If

(2) When the master generator-side converter carrier is at the bottom and the system-side inverter carrier is “up counting” (FIG. 3B)
Pattern 4: The phase of the slave generator-side converter carrier is delayed by 90 degrees with respect to the master generator-side converter carrier (when the slave generator-side converter carrier is at the bottom, the system-side inverter carrier is “down-counting” )) Pattern 5: The phase of the slave generator side converter carrier is 180 degrees behind the master generator side converter carrier (when the slave generator side converter carrier is at the bottom, the system side inverter carrier is Pattern 6: The phase of the slave generator side converter carrier is 270 degrees behind the master generator side converter carrier (the system side when the slave generator side converter carrier bottom is at the bottom) The inverter carrier is “counting down”) If

In this embodiment, when the count direction (up count or down count) of the system side inverter carrier at each bottom of the master generator side converter carrier and the slave generator side converter carrier is the same, the slave generator side The peak value of the converter carrier is changed from two times the peak value of the sampling counter to six times for two cycles.
Further, when the count direction of the system-side inverter carrier at each bottom of the master and slave generator-side converter carriers is different, the peak value of the slave generator-side converter carrier is set to 8 times the peak value of the sampling counter. The state is changed from 7 to 7 times for 2 cycles.

  FIG. 4 shows a waveform when the peak value of the slave generator-side converter carrier is changed for two cycles by the above method, and FIG. 4 (A) shows that the master generator-side converter carrier is at the bottom. When the system-side inverter carrier is “down-counting” at times, FIG. 4B shows the case where the system-side inverter carrier is “up-counting” when the master generator-side converter carrier is at the bottom.

  For example, in FIG. 4A, the count direction of the system-side inverter carrier at the bottom of the slave generator-side converter carrier (pattern 2) is down-count, and the system-side inverter at the bottom of the master generator-side converter carrier Since it coincides with the counting direction of the carrier for carrier, the peak value of the carrier for the slave generator side converter is changed from 8 times the peak value of the sampling counter to 6 times for 2 cycles. This completes the synchronization of the master generator side converter carrier and the slave generator side converter carrier at time Ta.

  Similarly, in FIG. 4B, the count direction of the system-side inverter carrier at the bottom of the slave generator-side converter carrier (pattern 5) is up-count, and the system side at the bottom of the master generator-side converter carrier Since it coincides with the counting direction of the inverter carrier, the peak value of the slave generator-side converter carrier is changed from 8 times the peak value of the sampling counter to 6 times for 2 cycles. This completes the synchronization of the master generator side converter carrier and the slave generator side converter carrier at time Tb.

  In FIG. 4A, the count direction of the system-side inverter carrier at the bottom of the slave generator-side converter carrier (pattern 1) is up-count, and the system-side inverter at the bottom of the master generator-side converter carrier. Since it is different from the counting direction of the carrier for carrier, the peak value of the carrier for the slave generator side converter is changed for two periods from the state of 8 times the peak value of the sampling counter to the state of 7 times. This completes the synchronization of the master generator side converter carrier and the slave generator side converter carrier at time Ta.

  Similarly, in FIG. 4B, the count direction of the system-side inverter carrier at the bottom of the slave generator-side converter carrier (pattern 4) is down-count, and the system side at the bottom of the master generator-side converter carrier Since it differs from the counting direction of the inverter carrier, the peak value of the slave generator-side converter carrier is changed for two cycles from the state of 8 times the peak value of the sampling counter to the state of 7 times. This completes the synchronization of the master generator side converter carrier and the slave generator side converter carrier at time Tb.

  By changing the peak value of the slave generator-side converter carrier as described above, for the out-of-synchronization patterns 1, 2, 4, and 5, the master generator-side converter carrier and the slave generator-side converter carrier Can be synchronized.

  For pattern 3, once the same carrier pattern as pattern 1 in FIG. 4A was executed, the phase was originally 180 degrees behind the master generator-side converter carrier at time Ta ′. Same as pattern 2. For this reason, if the carrier pattern similar to the pattern 2 of FIG. 4A is executed after the time Ta ′, it can be synchronized with the master generator side converter carrier thereafter.

  Similarly, for pattern 6, once the same carrier pattern as pattern 4 in FIG. 4B is executed, the phase is delayed by 180 degrees from the master generator side converter carrier at time Tb ′. It becomes the same as the pattern 5 which has been. Therefore, if a carrier pattern similar to the pattern 5 in FIG. 4B is executed after the time Tb ′, it can be synchronized with the master generator-side converter carrier thereafter.

  As described above, according to the present embodiment, the system-side inverter carrier and the generator-side converter carrier of the master power converter 30 and the slave power converter 31 that are operated in parallel can be PWM-synchronized. Ten harmonic currents and system voltage distortion can be reduced.

  The present invention is not limited to the above embodiment, and can also be applied to a power converter that operates a master power converter and a plurality of slave power converters in parallel. In other words, there is no restriction on the number of power converters operated in parallel. Moreover, the use of the power converter is not limited to wind power generation.

DESCRIPTION OF SYMBOLS 1 Wind power generator 2 Generator side converter 3 DC intermediate capacitor 4 System side inverter 5 Filter reactor 6 Filter capacitor 10 Electric power system 20 Controller 21,23,25 Voltage detector 22,24 Current detector 30 Master power converter 31 Slave Power converter 32 Master-slave communication means a Generator side voltage detection value b Generator side current detection value c DC voltage detection value d System side current detection value e System side voltage detection value f Generator side converter voltage command g System side Inverter voltage command

Claims (1)

A generator-side converter that converts an AC voltage output from the generator into a DC voltage; a system-side inverter that converts the DC voltage output from the generator-side converter into an AC voltage and connects to an electric power system; and A control device that PWM-controls the generator-side converter and the system-side inverter; means for sampling the input voltage / input current of the generator-side converter; and means for sampling the output voltage / output current of the system-side inverter; In a power conversion device comprising a plurality of power converters having a plurality of power converters operated in parallel,
The controller is
A single arithmetic processing unit for performing PWM control by matching the phase of the generator-side converter carrier and the phase of the system-side inverter carrier;
The arithmetic processing unit includes:
Sharing the sampling frequency for the generator-side converter and the sampling frequency for the system-side inverter,
By changing its own generator-side converter carrier, the frequency and phase of the generator-side converter carriers of all power converters operated in parallel are matched,
The frequency and phase of its own system-side inverter carrier are matched with the frequency and phase of the system-side inverter carrier of another power converter by PLL control, and the phase of its own generator-side converter carrier is A power conversion device, wherein a phase of a sampling signal having a sampling frequency is matched with a phase of a generator-side converter carrier of another power converter while maintaining a state of matching with a phase of a sampling signal having a sampling frequency .

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