CN113659629B - Synchronous computerized power electronic grid-connected device and control method thereof - Google Patents
Synchronous computerized power electronic grid-connected device and control method thereof Download PDFInfo
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- CN113659629B CN113659629B CN202111224748.6A CN202111224748A CN113659629B CN 113659629 B CN113659629 B CN 113659629B CN 202111224748 A CN202111224748 A CN 202111224748A CN 113659629 B CN113659629 B CN 113659629B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/40—Synchronising a generator for connection to a network or to another generator
- H02J3/42—Synchronising a generator for connection to a network or to another generator with automatic parallel connection when synchronisation is achieved
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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Abstract
The invention provides a synchronous computerized power electronic grid-connected device and a control method thereof, wherein the synchronous computerized power electronic grid-connected device comprises the following steps: the converter bridge, the energy consumption switching device, the open winding motor and the excitation control assembly; the open-winding motor comprises a three-phase stator winding and a rotor; a damping winding is arranged on the rotor; the direct current side of the converter bridge is connected with a direct current power supply, and the output side of the converter bridge is connected with the input end of the three-phase stator winding; one end of the energy consumption switching device is connected with the output side of the converter bridge, and the other end of the energy consumption switching device is connected with the input end of the three-phase stator winding; the output end of the three-phase stator winding is connected with an alternating current power grid; the rotor is connected with the excitation control assembly, and the active supporting capacity of the new energy source unit is improved by introducing the energy consumption switching device and the excitation control assembly.
Description
Technical Field
The invention relates to the technical field of new energy power generation, in particular to a synchronous computerized power electronic grid-connected device and a control method thereof.
Background
The characteristic that renewable resources and power load demands are reversely distributed determines that large-base and long-distance extra-high voltage alternating current/direct current transmission is one of the leading forms of new energy development and utilization.
With the transformation of energy structures, the structure of a power supply matched with an extra-high voltage direct current transmission end is changing deeply, an early transmission end power supply is gradually replaced by a wind power generation station taking a power electronic device as a main body by using thermal power/water power mainly comprising a synchronous generator, a transmission end grid frame is further weak due to high proportion of new energy, and the short circuit ratio of a grid connection point of a new energy station is gradually reduced. On one hand, the problem of frequent broadband oscillation off-network during steady-state operation of the system is solved, and on the other hand, transient overvoltage generated at the new energy machine end by alternating current/direct current faults of the system causes large-scale new energy off-network, so that the extra-high voltage alternating current/direct current sending capacity is seriously restricted.
In the prior art, the control characteristics of the new energy device body are optimized, the networking performance of the new energy unit is improved, broadband oscillation and transient overvoltage suppression under a fault working condition can be realized in a power grid environment with a lower short-circuit ratio, and finally, safe grid connection is realized. The disadvantage of this approach is that there is a margin limit in the control design versatility, i.e. when the short circuit ratio is low to a certain extent, the approach has a failure problem.
Most new energy stations are provided with a dynamic reactive power compensation device with a certain capacity (20% of station rated capacity) at a grid-connected point, and the transient overvoltage suppression under broadband oscillation and fault working conditions is realized by further excavating the control performance of the device. The disadvantage of this method is that there is inherent delay of signal sampling in the control, the response characteristic of the transient voltage of ms level lags seriously, and the control effect of the transient voltage can not be realized.
The phase modulator device with a certain capacity is configured at the grid-connected point of the new energy station, the mode fully utilizes the large short-circuit current of the traditional synchronizer device, and the short-circuit ratio of the station is improved to realize broadband oscillation suppression; and the flux linkage keeps the unchanged basic characteristic in the transient process, so that the transient overvoltage suppression effect is realized. The disadvantage of this method is that it needs to add extra investment cost and the operation and maintenance workload is large.
At present, a new energy grid-connected power generation device based on power electronic current converter is strong in dependence control technology, weak in overvoltage capacity, and free of the advantages of inertia, magnetic linkage and the like of a traditional synchronous generator, when various temporary and steady faults occur in a power grid, the frequency and voltage of the system cannot be effectively controlled, large-scale new energy interlocking disconnection is easily caused, and large-scale new energy safety grid connection is seriously influenced.
Disclosure of Invention
In order to solve the problems that the system frequency and voltage cannot be effectively controlled when various temporary and steady faults occur in a power grid, large-scale new energy interlocking and off-grid are easily caused, and the large-scale new energy safety grid connection is seriously influenced, the invention provides a synchronous computerized power electronic grid connection device, which comprises: the energy-saving control system comprises a converter bridge, an energy-consuming switching device, a winding-opening motor and an excitation control assembly;
the open-winding motor comprises a three-phase stator winding and a rotor;
a damping winding is arranged on the rotor;
the direct current side of the converter bridge is connected with a direct current power supply, and the output side of the converter bridge is connected with the input end of the three-phase stator winding;
one end of the energy consumption switching device is connected with the output side of the converter bridge, and the other end of the energy consumption switching device is connected with the input end of the three-phase stator winding; the output end of the three-phase stator winding is connected with an alternating current power grid;
the rotor is connected with the excitation control assembly.
Preferably, the converter bridge comprises 6 full-control devices;
each two full-control devices are connected in series to form an upper bridge arm and a lower bridge arm of one phase;
the end points of the upper and lower bridge arms of each phase are connected with the two ends of the direct-current power supply, and the middle points are respectively connected with the input end of the energy consumption switching device and the input end of the stator winding of the open-winding motor.
Preferably, the energy consumption switching device comprises: three on/off switches and three energy dissipation resistors;
each on-off switch is connected in series with an energy consumption resistor;
the three on-off switches are respectively connected to the middle positions of upper and lower bridge arms of three phases of the converter bridge;
and the three energy dissipation resistors are respectively connected to the three phases of the stator winding.
Preferably, the excitation control assembly comprises a selection contactor control switch, a direct-current excitation power supply and an additional resistor;
one end of the selection contactor control switch is connected with the rotor of the open winding motor, and the other end of the selection contactor control switch is connected with the direct-current excitation power supply or the additional resistor.
Preferably, the additional resistance is 10 times the resistance value of the damping winding.
Preferably, the synchronous-motorized power electronic grid-connection device further includes: two control switches;
and the two control switches are respectively connected between two adjacent output ends of the three-phase stator winding.
Preferably, the synchronous-motorized power electronic grid-connection device further includes: a grid-connected circuit breaker;
and one end of the grid-connected breaker is connected with the three-phase output end of the three-phase stator winding of the open winding motor, and the other end of the grid-connected breaker is connected with an alternating current power grid.
The invention also provides a control method of the synchronous computerized power electronic grid-connected device based on the same invention concept, which comprises the following steps:
when the power electronic grid-connected device is in a starting stage:
short-circuiting the output end of an open-winding motor, inverting direct current provided by a direct current power supply into three-phase alternating current by using a converter bridge, generating a rotating magnetic field by a three-phase stator winding of the open-winding motor, generating asynchronous starting torque by interaction with induced current in a damping winding arranged on a rotor of the open-winding motor to drive the rotor to rotate, and opening the circuit of the output end of the three-phase stator winding when the difference value of the rotor rotating speed and the synchronous rotating speed is within a set range; closing an excitation control assembly connected with the rotor to apply direct-current excitation to the rotor;
when the amplitude, frequency, phase sequence and phase of the output voltage of the open-winding motor are consistent with those of an alternating current power grid, connecting the output end of the three-phase stator winding into the alternating current power grid, and entering a steady-state operation stage;
when the power electronic grid-connected device is in a transient state stage and the output current of the converter bridge is detected to be larger than a set safety threshold value:
putting the energy consumption switching device between the output end of the converter bridge and the input end of the three-phase stator winding into operation, so that alternating current generated by inverting direct current flowing through the converter bridge is reduced, active power transmitted by the three-phase stator winding is reduced, a generated rotating magnetic field and a rotor move relatively, induction current is generated in a damping winding arranged on the rotor, the induction current and the rotating magnetic field interact to generate torque for preventing the rotor from operating relative to the rotating magnetic field, excitation current is adjusted, and output reactive power is adjusted;
and when the output current of the converter bridge is recovered to be within the set safety threshold value or meets the duration, the energy consumption switching device is switched off, and the steady-state operation stage is started after the disappearance of the power grid fault is detected.
Preferably, the short-circuiting the output end of the open-winding motor, inverting the direct current provided by the direct current power supply into a three-phase alternating current by using the converter bridge, and generating a rotating magnetic field by a three-phase stator winding of the open-winding motor includes:
closing two control switches positioned between the output ends of the three-phase stator windings to enable the three-phase stator windings to be in short circuit to form a star-shaped midpoint;
inverting the direct current into three-phase alternating current by a converter bridge to provide input voltage for the three-phase stator winding;
the three-phase stator winding generates a rotating magnetic field based on an input voltage provided by the converter bridge.
Preferably, the putting into operation the energy consumption switching device between the output end of the converter bridge and the input end of the three-phase stator winding includes:
and connecting an energy consumption resistor connected with each on-off switch between the output end of the converter bridge and the input end of the three-phase stator winding by closing the three on-off switches of the energy consumption on-off device connected with the output end of the converter bridge.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention provides a synchronous computerized power electronic grid-connected device, comprising: the converter bridge, the energy consumption switching device, the open winding motor and the excitation control assembly; the open-winding motor comprises a three-phase stator winding and a rotor; a damping winding is installed on the rotor, the direct current side of the converter bridge is connected with a direct current power supply, and the output side of the converter bridge is connected with the input end of the three-phase stator winding; one end of the energy consumption switching device is connected with the output side of the converter bridge, and the other end of the energy consumption switching device is connected with the input end of the three-phase stator winding; the output end of the three-phase stator winding is connected with an alternating current power grid; the rotor is connected with the excitation control assembly, and the grid-connected supporting capability of the new energy source unit is improved by introducing the energy consumption switching device and the excitation control assembly.
2. The invention can realize the control of the direct current voltage converted by the converter bridge through the input of the energy consumption switching device in the transient state stage, avoid damaging the power electronic device, and adjust the reactive power of the power electronic grid-connected device by changing the exciting current after the open winding motor responds, thereby avoiding the new energy off-grid.
3. The invention can form a star-shaped midpoint by short-circuiting the three-phase winding output side of the open winding motor at the starting stage, reconstruct the traditional synchronous motor, control the excitation control assembly to enable the rotor of the open winding motor to synchronously operate when the difference value of the rotor rotating speed and the synchronous rotating speed is in a set range, and access an alternating current power grid when the voltage output by the open winding motor is consistent with the power grid, thereby ensuring that the voltage accessed to the alternating current power grid is stably dropped.
Drawings
Fig. 1 is a schematic structural view of a synchronous-motorized power electronic grid-connection device according to the present invention;
FIG. 2 is a phasor diagram of an over-excited state when the open winding motor of the present invention is operating in a synchronous compensator mode;
fig. 3 is a phasor diagram of an under-excited state when the open-winding motor of the present invention operates in a synchronous compensator mode.
Detailed Description
The invention provides a synchronous motor-based power electronic grid-connected device and a control method thereof from a new energy power generation device, wherein the device comprises a converter bridge, an energy consumption switching device and a winding-opening motor, not only can the characteristics of high control speed, multiple control functions and the like of the power electronic device be kept, the characteristics of fluctuation of new energy power generation and the like are fully exploited, but also the advantages of large inertia, strong overcurrent capacity and obvious transient magnetic linkage characteristics of the traditional synchronous generator can be inherited, and therefore, the friendly grid-connection of large-scale new energy is realized, and stronger support is provided for a high-proportion new energy power system.
Example 1: a synchronous-motorized power electronic grid-connection device, as shown in fig. 1, comprises: the converter bridge, the energy consumption switching device, the open winding motor and the excitation control assembly;
the open-winding motor comprises a three-phase stator winding and a rotor;
the rotor is provided with a damping winding;
the direct current side of the converter bridge is connected with a direct current power supply, and the output side of the converter bridge is connected with the input end of a three-phase stator winding of the open winding motor;
one end of the energy consumption switching device is connected with the output side of the converter bridge, and the other end of the energy consumption switching device is connected with a three-phase stator winding of the open winding motor;
the output end of a three-phase stator winding of the open winding motor is connected with an alternating current power grid;
the rotor of the open-winding motor is connected with the excitation control assembly.
The concrete contents of each part are as follows:
(1) a converter bridge:
the converter bridge is also called a three-phase converter bridge, and a direct current side of the three-phase converter bridge is connected with a direct current power supply, which can be a power generation device, such as a direct current power supply rectified by a power generation unit of wind power, photovoltaic and the like, or an energy storage device, such as a storage battery. The three-phase converter bridge is composed of 6 full-control devices, respectively S1、S2、S3、S4、S5、S6In which S is1，S4Respectively represent A phase upper and lower bridges, S3，S6Respectively represent a B-phase upper and lower bridge, S5，S2Respectively represent a C-phase upper bridge and a C-phase lower bridge.
(2) The energy consumption is thrown and is moved back the device:
the input end of the three-phase energy consumption switching device is connected with A, B, C three phases of a three-phase converter bridge, and the output end of the three-phase energy consumption switching device is connected with A, B, C three phases of a three-phase open winding motor. Three-phase energy-consumption switching device A-phase circuit passing on-off switchKaConnecting energy consumption resistorRaThe B-phase circuit being switched on or off by means of a switchKbConnecting energy consumption resistorRbThe C-phase circuit is switched on or off by switching on or offKcConnecting energy consumption resistorRc。
(3) An open winding motor:
the open winding motor is also called as a three-phase open winding motor, the three-phase open winding motor consists of a three-phase stator winding and a rotor, a damping winding is arranged on the rotor, the input of the A-phase stator winding is the A-phase output of a converter bridge, and the output is a; the input of the B-phase stator winding is the B-phase output of the converter bridge, and the output is B; the input of the C-phase stator winding is the output of the converter bridge C phase, and the output is C. The three-phase open winding motor rotor is connected with the positive pole + and the negative pole of a direct-current excitation power supply of the excitation control assembly, and the three-phase open winding motor rotor is provided with a damping winding.
The damping winding is similar to the cage-type winding structure of the cage-type asynchronous motor rotor, and the whole damping winding is formed by welding a copper bar inserted into a pole shoe hole and a short-circuit-terminated copper ring.
(4) Excitation control assembly:
the excitation control component comprises a selection contactor control switch K0A direct current excitation power supply and an additional resistor; one end of a control switch of the selection contactor is connected with the rotor of the open-winding motor, the other end of the control switch of the selection contactor is connected with the direct-current excitation power supply or an additional resistor, and the additional resistor is 10 times of the resistance value of the excitation winding, such as 10r in figure 1.
(5) Controlling a switch:
the output end of the three-phase stator winding of the open winding motor is also provided with a control switch K1、K2The two switches are closed in the starting stage of the power electronic grid-connected device, so that the output end of the three-phase stator winding is short-circuited, the generated rotating magnetic field interacts with the induced current in the damping winding to generate asynchronous starting torque to start the rotor of the open-winding motor to rotate, and when the rotating speed of the rotor is close to the speed generated by the rotating magnetic field, the control switch K is opened1、K2Then selecting the contactor control switch K0And a direct-current excitation power supply is connected.
(6) Grid-connected circuit breaker:
when the frequency, the phase sequence and the phase of the voltage output by the open winding motor are detected to be consistent with the power grid and the amplitude of the voltage is within an allowable error range, a grid-connected breaker between the output end of the three-phase stator winding of the open winding motor and the alternating current power grid is closed, and the three-phase stator winding is connected to the alternating current power grid.
Example 2:
the invention also provides a control method of the synchronous computerized power electronic grid-connected device, which comprises the following steps: from the start-up phase to the steady-state operation phase, and from the transient operation phase to the steady-state operation phase, each phase is specifically described as follows:
first, start stage
Because the synchronous motor structure can not realize self-starting, a three-phase synchronous motor asynchronous starting method is generally adopted, most of modern synchronous motors are provided with a starting winding (namely a damping winding) similar to a cage winding of the asynchronous motor on a rotor, and the synchronous motor can be started by adopting a method similar to that of starting the cage type asynchronous motor.
Based on the asynchronous starting idea of a synchronous motor, the output end of an open-winding motor is in short circuit, after direct current provided by a direct current power supply is inverted into three-phase alternating current by a converter bridge, a rotating magnetic field is generated by a three-phase stator winding of the open-winding motor, asynchronous starting torque is generated by the interaction of induced current in a damping winding and the rotating magnetic field to drive a rotor to rotate, and when the rotating speed of the rotor is a set multiple of synchronous rotating speed, the output end of the three-phase stator winding is opened; closing an excitation control assembly connected with the rotor to apply direct-current excitation to the rotor; the synchronous revolution speed of the multiple set here may be a nearly synchronous revolution speed.
When the amplitude, frequency, phase sequence and phase of the output voltage of the open-winding motor are consistent with those of the alternating current power grid, the output end of the three-phase electronic winding is connected to the alternating current power grid, and the steady-state operation stage is started.
The rotor of the three-phase open-winding motor is provided with a damping winding, an excitation loop is connected in series with an additional resistor which is about 10 times of the resistance value of the damping winding, as shown in 10r in figure 1, the three-phase stator winding of the three-phase open-winding motor is directly put into a power grid to start the three-phase stator winding according to an asynchronous motor, when the rotating speed reaches a sub-synchronous rotating speed (about 95 percent of synchronous rotating speed), the additional resistor is cut off, and meanwhile, proper excitation current is introduced. The method comprises the following specific steps:
1) checking to confirm that the entire device is functioning properly and checking all control switches: (Ka、Kb、Kc、K0、K1、K2) And whether the grid-connected breaker QF is in a disconnected state;
2) closing control switch K1、K2The three-phase output end of the three-phase stator winding of the open winding motor is short-circuited to form a star-shaped midpoint, namely, the open winding motor is reconstructed into a traditional synchronous motor, and meanwhile, a selection contactor controls a switch K0Closed at one side of the additional resistor;
3) starting a three-phase converter bridge, inverting the direct-current voltage into three-phase alternating-current voltage for output, and providing input voltage for a three-phase stator winding of the open-winding motor;
4) when the rotor speed of the open-winding motor is close to the synchronous speed, K is firstly added1、K2Opening, then controlling switch K with selective contactor0Rapidly switching from the left side to the right side to force the rotor of the open-winding motor to be pulled in for synchronous operation by adding a direct-current excitation power supply;
5) detecting whether the amplitude, frequency, phase sequence and phase of the output voltage of a three-phase stator winding of the open-winding motor are consistent with those of a power grid or not, wherein the maximum error of the voltage amplitude is within 5%;
6) when the conditions are met, the grid-connected breaker QF is closed, so that the open winding motor is connected into an alternating current power grid for operation.
In the starting stage of the device, the second part (the three-phase energy consumption switching device) is always in a switching-out state, and the first part (the three-phase converter bridge) and the third part (the three-phase open winding motor) are sequentially executed according to the steps to complete the starting of the whole device.
Second, steady state operation stage
When the whole device is in a steady state operation state, the invention can realize pure converter grid-connected mode operation by stopping rotor excitation, and can also realize synchronous machine/phase modulator mode operation by rotor excitation control, and the device can be divided into the following 2 working conditions according to the working state of the open-winding motor:
(1) the open-winding motor does not work, namely, the rotor is not excited;
(2) and (3) excitation of the rotor of the open winding motor, namely, grid connection of the open winding motor as a synchronous machine interface.
These two parts are described in detail below:
(1) open-winding motor rotor is not excited:
when the power grid is in a normal operation state and the output power of the three-phase converter bridge meets the load requirement, the open-winding motor is in an inoperative state, namely the rotating speed of the rotor is 0, and the rotor is not excited. At this time, the three-phase stator windings of the open-winding motor serve as output filter inductors of a three-phase converter bridge to reduce output current ripples of inverter Pulse Width Modulation (PWM).
According to the instantaneous power theory, the output power of the device under steady state operation is as follows:
wherein the content of the first and second substances,U abc andI abc respectively phase voltage vector and phase current vector of converter bridge outlet in three-phase static coordinate system, and corresponding instantaneous values are respectivelyU abc =[ia ib ic]；
As a vector of voltageU abc Sum current vectorI abc Of a power factor ofλ= cos ϕ; in the formula
Satisfies the following conditions:
in this operating state, the performance of the power electronic grid-connected device is completely determined by the first part (three-phase converter bridge) and the control system thereof, and the four-quadrant operation is realized by controlling the three-phase converter bridge as the same as the operating principle of a normal grid-connected inverter.
(2) The open winding motor is connected to the grid as a synchronous machine interface:
when the power grid is in a normal state, the power grid is opened and woundThe rotation speed of the rotor of the group motor is synchronous with the frequency of the voltage of the power grid, and when no mechanical load is arranged on the shaft, the principle that the power factor can be adjusted by changing the exciting current of the synchronous motor is utilized, and the exciting current I of the open-winding motor is adjustedfThe output reactive power of the synchronous machine can be controlled, at the moment, the open winding motor is used as a synchronous machine interface for grid connection, works in a synchronous compensator mode, and is specially used for adjusting the reactive power and improving the power factor of a power grid.
Mechanical power P output by open-winding motor2=0, so that in normal operation, the open-winding motor inputs active power P from the converter bridge side1Only to overcome the copper loss p of the stator (armature)CuaIron loss pFeAnd mechanical loss pΩIf the loss is not counted, the input power P of the open-winding motor can be considered1Approximately zero. Open-winding machines therefore always operate close to zero electromagnetic power and zero power factor. According to the V-shaped curve of the synchronous motor, when the excitation is normal excitation, the armature current of the open-winding motor is close to zero; during over-excitation, the open winding motor can draw advanced reactive current from the power grid; under excitation, a lagging reactive current is drawn from the grid. Therefore, an open-winding motor acts as a set of variable capacitors connected in parallel when excited excessively, and acts as a variable reactor when excited insufficiently.
If the total losses of an open-winding machine are neglected, the armature current is all the reactive component (I)d=I，Iq= 0), the voltage equation for an open-winding motor can be simplified as:
in the formula (I), the compound is shown in the specification,
in order to open the voltage of the winding motor,
to excite the electromotive force (i.e. commonly referred to as the unloaded potential),jis an imaginary numberThe number of bits is,
in order to output current for an open-winding motor,Xsthe synchronous reactance of an open-winding motor is shown, so that phasor diagrams of the open-winding motor in over-excitation and under-excitation can be drawn, as shown in fig. 2 and 3. As can be seen from the figure, when over-excited, the current flows
Leading voltage
90 DEG under excitation, current
Hysteresis voltage
At 90 deg.. Therefore, the nature and the magnitude of the reactive power can be flexibly adjusted only by adjusting the exciting current.
The output voltages of the three-phase converter bridge are respectivelyU a 、U b 、U c The phase winding counter electromotive force of the stator of the open winding motor isE a 、E b 、E c The stator flux linkage of the open-winding motor is
The port voltages of the grid-connected devices are respectivelyv a 、v b 、v c The system output current isi a 、i b 、i c The voltage relationship is as follows:
in the formula (I), the compound is shown in the specification,R a、R b 、R crespectively the phase resistance of the stator winding,L a 、L b 、L c respectively, the phase inductances of the stator windings,pin order to be a differential operator, the system is,θis the output voltage phase.
Selecting coordinate transformation with invariable magnetic potential, transforming the formula (4) to a two-phase synchronous rotation dq coordinate system, orienting the d axis according to the synchronous rotor flux linkage, leading the q axis by 90 degrees ahead of the d axis to obtain:
in the formulav d 、v q Respectively are the direct-axis component and the alternating-axis component of the port voltage of the grid-connected device;u d 、u q the direct-axis component and the alternating-axis component of the output voltage of the three-phase converter bridge are respectively;i d 、i q the direct and alternating components of the output current are respectively; omega is synchronous rotating speed;Ris the equivalent resistance value under the dq coordinate system;Lis the equivalent inductance value under dq coordinate system;pis a differential operator.
At this time, the active power P transmitted to the power grid by the power electronic grid-connected device is:
the formula (5) may be substituted for the formula (6):
according to the theory of electromechanics, the voltage equation and the flux linkage equation of the synchronous motor under the dq coordinate system are obtained by adopting a practical forward direction:
in the formula (I), the compound is shown in the specification,e d 、e q respectively are the direct-current component and the alternating-current component of the counter electromotive force of the stator phase winding of the open winding motor,Ψd、Ψqrespectively are the direct-axis component and the alternating-axis component of the stator flux linkage of the open-winding motor,i f in order to be the exciting current,i D andi Q respectively the direct and alternating components of the equivalent damping winding current,
respectively, the direct and alternating components of the synchronous reactance,
is a direct axis armature reactive reactance.
When the open-winding motor is in steady-state operation, the rotating speed is constant at synchronous speed, and the exciting currenti f Is constant, the current of the equivalent damping winding is zero, thenpΨd =pΨq =0, and furthermore the stator resistance R is omitted and the open-winding machine is considered to output zero active power and electromagnetic power, i.e. the power angleδAlso zero. Therefore, from equations (8) and (9), the potential equation in the dq coordinate system of the open-winding motor in the steady-state condition is:
in the formula (I), the compound is shown in the specification,E 0 =Ψ fd =Xadi f ，Ψ fd andE 0 respectively representing the mutual inductance flux linkage and the corresponding induced potential generated by the excitation current to the stator windings.
From equation (10), the direct current flowing through the system in the dq coordinate systemi d Current of sum and quadrature axisi q Respectively as follows:
the reactive power Q delivered by the device to the grid is then:
in the working state, the active power sent by the hybrid power generation device is mainly determined by the three-phase converter bridge, the reactive power sent by the hybrid power generation device is determined by the open-winding motor, at the moment, the active power output by the system is adjusted by controlling the three-phase converter bridge, and the exciting current of the open-winding motor is controlledi f To regulate the reactive power output by the system.
Third, transient operation phase
When the power grid has a short-circuit fault, the whole device acts according to the following reaction sequence:
1) when the short-circuit fault of the power grid is detected, the control strategy of the three-phase converter bridge is quickly switched to a fault ride-through mode, the active power transmitted to a backward-stage system is temporarily reduced, and certain reactive power is sent to the power grid according to the fault depth of the power grid;
2) after the excitation system of the open-winding motor responds, the excitation current is adjustedi f The open-winding motor provides reactive power required during the fault period, and simultaneously the three-phase converter bridge is switched to an active priority mode, so that the active power sent by the new energy source unit is transmitted to the power grid as much as possible;
3) during the fault period, if the output current of the three-phase converter bridge is detected to be larger than the preset safety threshold value, the three-phase converter bridge is closed rapidlyK a 、K b 、K c So that the three-phase energy consumption device is put into operation;
4) when the output current of the three-phase converter bridge is recovered to be within the preset safety threshold or meets the duration time, the three-phase converter bridge is quickly disconnectedK a 、K b 、K c So that the three-phase energy consumption device is out of operation;
5) and when the grid fault disappears, switching the whole device to a steady-state operation mode.
In the transient operation stage of the device, the whole device is prevented from being disconnected and even damaged by controlling the switching of the second part (the three-phase energy consumption switching device), and simultaneously, the active power and the reactive power sent by the first part (the three-phase converter bridge) and the third part (the three-phase open winding motor) are coordinately controlled, so that the safe and stable operation of the whole device during the fault period is ensured.
The rotor and the converter bridge of the open-winding motor share the same group of reactance, so that grid-connected operation is realized, and active power and reactive power are output to a power grid;
the invention can realize the decoupling control of the converter bridge outlet and the grid-connected interface current during the fault period, wherein the grid-connected interface refers to the connection position of the open winding motor output and the power grid.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention which are filed as the application.
Claims (8)
1. A synchronous-motorized power electronics grid connection, comprising: the energy-saving control system comprises a converter bridge, an energy-consuming switching device, a winding-opening motor and an excitation control assembly;
the open-winding motor comprises a three-phase stator winding and a rotor;
a damping winding is arranged on the rotor;
the direct current side of the converter bridge is connected with a direct current power supply, and the output side of the converter bridge is connected with the input end of the three-phase stator winding;
one end of the energy consumption switching device is connected with the output side of the converter bridge, and the other end of the energy consumption switching device is connected with the input end of the three-phase stator winding; the output end of the three-phase stator winding is connected with an alternating current power grid;
the rotor is connected with the excitation control assembly;
the converter bridge comprises 6 full-control devices;
each two full-control devices are connected in series to form an upper bridge arm and a lower bridge arm of one phase;
the end points of the upper and lower bridge arms of each phase are connected with the two ends of a direct-current power supply, and the middle points of the upper and lower bridge arms of each phase are respectively connected with the input end of the energy consumption switching device and the input end of a three-phase stator winding of the open-winding motor;
the excitation control assembly comprises a selection contactor control switch, a direct-current excitation power supply and an additional resistor;
one end of the selection contactor control switch is connected with the rotor of the open winding motor, and the other end of the selection contactor control switch is connected with the direct-current excitation power supply or the additional resistor.
2. The apparatus of claim 1, wherein the energy consuming commissioning device comprises: three on/off switches and three energy dissipation resistors;
each on-off switch is connected in series with an energy consumption resistor;
the three on-off switches are respectively connected to the middle positions of upper and lower bridge arms of three phases of the converter bridge;
and the three energy dissipation resistors are respectively connected to three phases of the three-phase stator winding.
3. The apparatus of claim 1, wherein the additional resistance is 10 times the damping winding resistance value.
4. The apparatus of claim 1, wherein the synchronous, motorized power electronics grid tie apparatus further comprises: two control switches;
and the two control switches are respectively connected between two adjacent output ends of the three-phase stator winding.
5. The apparatus of claim 1, wherein the synchronous, motorized power electronics grid tie apparatus further comprises: a grid-connected circuit breaker;
and one end of the grid-connected breaker is connected with the three-phase output end of the three-phase stator winding of the open winding motor, and the other end of the grid-connected breaker is connected with an alternating current power grid.
6. A method for controlling a synchronous-motorized power electronic grid-connected device, comprising:
when the power electronic grid-connected device is in a starting stage:
short-circuiting the output end of an open-winding motor, inverting direct current provided by a direct current power supply into three-phase alternating current by using a converter bridge, generating a rotating magnetic field by a three-phase stator winding of the open-winding motor, generating asynchronous starting torque by interaction with induced current in a damping winding arranged on a rotor of the open-winding motor to drive the rotor to rotate, and opening the output end of the three-phase stator winding when the difference value of the rotor rotating speed and the synchronous rotating speed is within a certain range; closing an excitation control assembly connected with the rotor to apply direct-current excitation to the rotor;
when the amplitude, frequency, phase sequence and phase of the output voltage of the open-winding motor are consistent with those of an alternating current power grid, connecting the output end of the three-phase stator winding into the alternating current power grid, and entering a steady-state operation stage;
when the power electronic grid-connected device is in a transient state stage and the output current of the converter bridge is detected to be larger than a set safety threshold value:
putting the energy consumption switching device between the output end of the converter bridge and the input end of the three-phase stator winding into operation, reducing alternating current flowing through the converter bridge, reducing active power transmitted by the three-phase stator winding, enabling a generated rotating magnetic field to move relative to the rotor, generating induction current in a damping winding arranged on the rotor, enabling the induction current to interact with the rotating magnetic field to generate torque for preventing the rotor from running relative to the rotating magnetic field, adjusting exciting current and further adjusting output reactive power;
and when the output current of the converter bridge is recovered to be within the set safety threshold value or meets the duration, the energy consumption switching device is switched off, and the steady-state operation stage is started after the disappearance of the power grid fault is detected.
7. The method of claim 6, wherein the step of short-circuiting the output of the open-winding motor and inverting the dc power from the dc power source into three-phase ac power using the converter bridge to generate a rotating magnetic field through the three-phase stator windings of the open-winding motor comprises:
closing two control switches positioned between the output ends of the three-phase stator windings to enable the three-phase stator windings to be in short circuit to form a star-shaped midpoint;
inverting the direct current into alternating current by a converter bridge to provide input voltage for the three-phase stator winding;
the three-phase stator winding generates a rotating magnetic field based on an input voltage provided by the converter bridge.
8. The method of claim 6, wherein said operating the energy consuming switching devices between the output of the converter bridge and the input of the three-phase stator windings comprises:
and connecting an energy consumption resistor connected with each on-off switch between the output end of the converter bridge and the input end of the three-phase stator winding by closing the three on-off switches of the energy consumption on-off device connected with the output end of the converter bridge.
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| CN109494799B (en) * | 2018-12-14 | 2021-10-08 | 浙江大学 | Permanent magnet synchronous generator direct grid-connected system based on open winding structure and control method thereof |
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