CN115940185B - A series-parallel side coordinated control method for UPQC topology - Google Patents
A series-parallel side coordinated control method for UPQC topology Download PDFInfo
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Abstract
The invention discloses a UPQC topological structure and a serial-parallel connection side cooperative control method thereof, which comprises a serial connection side unit, a direct current capacitor and a parallel connection side unit, wherein the serial connection side unit comprises a serial transformer, a serial connection coupling capacitor, a first filter and a serial connection converter which are sequentially connected in series, the parallel connection side unit comprises a parallel connection converter, a second filter and a parallel connection transformer which are sequentially connected in series, the serial connection converter, the direct current capacitor and the parallel connection converter are mutually connected in parallel, the first filter comprises a first inductor and a first capacitor which are serially connected, the second filter comprises a second inductor, the serial connection converter comprises four insulated gate bipolar transistors, and the parallel connection converter comprises four insulated gate bipolar transistors. The invention can effectively improve the utilization rate of the series-side device, and can reduce the rated capacity of the parallel-side converter by utilizing the series-side converter, thereby further reducing the active capacity of the device.
Description
Technical Field
The invention relates to the technical field of electronic power control, in particular to a UPQC topological structure and a serial-parallel side cooperative control method thereof.
Background
With the massive access of renewable energy sources and nonlinear loads, the power quality problem of a power distribution network is increasingly serious, such as voltage sag, voltage flicker, harmonic waves and the like. However, precision instruments and sensitive equipment, such as computers, medical equipment, high-precision production equipment, and the like, have extremely high requirements on the quality of electric energy. The unified power quality controller (unified power quality conditioner, UPQC) is used as a typical comprehensive power quality control device, and can solve the problems of voltage and current quality at the same time.
At present, a typical UPQC topological structure is that a series-side converter is connected with a series transformer in series into a power grid through an LC filter, a parallel-side converter is connected with the power grid in a hanging manner through an L-shaped filter and a parallel transformer, and the series-parallel converters are connected through a direct current capacitor. However, the traditional UPQC device has large active capacity and high cost, and severely restricts the application and popularization of the device in a power distribution network. In addition, because the voltage fluctuation frequency of the power distribution network is low and the time is short, the series-side converter is usually in an idle state, and the utilization rate of the device is greatly reduced.
Disclosure of Invention
In order to solve the technical problems, the invention provides a UPQC topological structure and a serial-parallel connection side cooperative control method thereof, which can effectively improve the utilization rate of a serial-connection side device and reduce the active capacity of the UPQC device.
In a first aspect, an embodiment of the present invention provides a UPQC topology, the UPQC being connected between a power grid and a load, including:
A series side unit, a direct current capacitor and a parallel side unit;
the series side unit comprises a series transformer, a series coupling capacitor, a first filter and a series converter which are sequentially connected in series;
The parallel side unit comprises a parallel converter, a second filter and a parallel transformer which are sequentially connected in series;
the series converter, the direct current capacitor and the parallel converter are connected in parallel;
the first filter comprises a first inductor and a first capacitor which are connected in series, and the second filter comprises a second inductor;
the series converter comprises four insulated gate bipolar transistors, namely a first transistor, a second transistor, a third transistor and a fourth transistor, wherein the first transistor and the third transistor are connected in series, the second transistor and the fourth transistor are connected in series, and the first transistor and the third transistor which are connected in series, the second transistor and the fourth transistor which are connected in series are connected in parallel;
The parallel converter comprises four insulated gate bipolar transistors, namely a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor, wherein the fifth transistor and the seventh transistor are connected in series, the sixth transistor and the eighth transistor are connected in series, and the fifth transistor and the seventh transistor which are connected in series, and the sixth transistor and the eighth transistor which are connected in series are connected in parallel.
Further, the collector of the first transistor and the collector of the second transistor are connected together and are connected to the positive electrode of the dc capacitor, the emitter of the first transistor and the collector of the third transistor are connected together and are connected to the positive electrode of the first inductor, the emitter of the second transistor and the collector of the fourth transistor are connected together and are connected to the negative electrode of the first capacitor, and the emitter of the third transistor and the emitter of the fourth transistor are connected together and are connected to the negative electrode of the dc capacitor.
Further, the negative electrode of the first inductor is connected with the series coupling capacitor and is connected to one end of the primary side of the series transformer together, the negative electrode of the first capacitor is connected to the other end of the primary side of the series transformer, and the secondary side of the series transformer is connected in series to a power grid.
Further, the collector of the fifth transistor and the collector of the sixth transistor are connected together and are connected to the positive electrode of the dc capacitor, the emitter of the fifth transistor and the collector of the seventh transistor are connected together and are connected to the positive electrode of the second inductor, the negative electrode of the second inductor is connected to one end of the primary side of the shunt transformer, the emitter of the sixth transistor and the collector of the eighth transistor are connected together and are connected to the other end of the primary side of the shunt transformer, and the emitter of the seventh transistor and the emitter of the eighth transistor are connected together and are connected to the negative electrode of the dc capacitor.
Further, one end of the secondary side of the parallel transformer is connected to the power grid, and the other end of the secondary side of the parallel transformer is grounded.
In a second aspect, an embodiment of the present invention provides a method for controlling co-operation of serial and parallel sides of a UPQC topology, where the method is applied to the above-mentioned UPQC topology, and includes:
Judging power grid working conditions according to the voltage value of the power grid, wherein the power grid working conditions comprise a voltage normal working condition and a voltage drop working condition;
If the power grid working condition is the voltage normal working condition, controlling the series side units of the UPQC to work in a reactive power regulation mode, and jointly compensating load reactive power through the series side units and the parallel side units so as to enable the power grid to be maintained to operate in a unit power factor;
And if the power grid working condition is the voltage drop working condition, controlling the series side units to work in a voltage compensation mode, performing voltage compensation through the series side units so as to ensure that the load voltage is unchanged, and jointly compensating the load reactive power through the series side units and the parallel side units.
Further, if the power grid working condition is the voltage normal working condition, the step of controlling the series side unit of the UPQC to work in the reactive power regulation mode includes:
Setting the phase of the series coupling capacitor voltage and the phase of the grid voltage vertically, and setting the phase of the series converter output voltage and the phase of the grid voltage in opposite phase;
Injecting a preset first series side compensation voltage through a series transformer so that the compensated load voltage leads the power grid voltage by a phase angle difference, and taking the current output by the parallel transformer as a first parallel side compensation current;
and taking the reactive power output by the series coupling capacitor as first series side compensation power, and taking the reactive power output by the parallel converter as first parallel side compensation power, wherein the first series side compensation power and the first parallel side compensation power jointly compensate the reactive power of the load.
Further, according to the vector principle of the normal voltage working condition, the first series side compensation voltage and the first parallel side compensation current are calculated;
the amplitude and phase angle of the first series side compensation voltage are calculated respectively using the following formula:
In the formula, In order to compensate for the load voltage after the compensation,To compensate for the phase angle of the load voltage;
The amplitude and phase angle of the first parallel side compensation current are calculated respectively using the following formula:
In the formula, In order to compensate for the load current after the compensation,Is the load power factor angle.
Further, if the grid condition is the voltage drop condition, the step of controlling the series side unit to operate in the voltage compensation mode includes:
Setting the phase of the series coupling capacitor voltage and the phase of the dropped power grid voltage vertically, and setting the phase of the output voltage of the series converter and the phase of the series coupling capacitor voltage in phase;
Injecting a preset second series side compensation voltage through a series transformer so that the compensated load voltage leads the dropped power grid voltage by a phase angle difference, and taking the current output by the parallel transformer as a second parallel side compensation current;
And taking the reactive power output by the series coupling capacitor and the reactive power output by the series converter as second series side compensation power, and taking the reactive power output by the parallel converter as second parallel side compensation power, wherein the second series side compensation power and the second parallel side compensation power jointly compensate the load reactive power.
Further, according to the vector principle of the voltage drop working condition, the second series side compensation voltage and the second parallel side compensation current are calculated;
The amplitude and phase angle of the second series side compensation voltage are calculated respectively using the following formulas:
In the formula, In order to compensate for the load voltage after the compensation,To compensate for the phase angle of the load voltage;
the amplitude and phase angle of the second parallel side compensation current are calculated respectively using the following formula:
In the formula, In order to compensate for the load current after the compensation,In order to load the power factor angle,Is the voltage drop coefficient of the power grid.
Compared with the prior art, the UPQC provided by the invention not only can improve the utilization rate of the series-connection side device, but also can reduce the rated capacity of the parallel-connection side converter by utilizing the series-connection side converter, so that the UPQC has smaller overall active capacity and higher utilization rate than the traditional UPQC device.
Drawings
FIG. 1 is a schematic diagram of a UPQC topology in an embodiment of the present invention;
FIG. 2 is a schematic flow chart of a method for controlling the cooperation of serial and parallel sides of a UPQC topology in an embodiment of the invention;
FIG. 3 is a vector schematic diagram of the grid voltage under normal conditions;
FIG. 4 is a power flow diagram for a grid voltage normal condition;
FIG. 5 is a vector schematic diagram of a grid voltage sag condition;
FIG. 6 is a power flow diagram for grid voltage sag conditions;
FIG. 7 is a simulated waveform of grid voltage and load voltage in a simulation experiment of an embodiment of the present invention;
FIG. 8 is a simulated waveform of grid voltage and grid current in a simulation experiment of an embodiment of the present invention;
FIG. 9 is a simulated waveform of load current and parallel side output current in a simulation experiment of an embodiment of the present invention;
FIG. 10 is a simulation waveform of the series side compensation voltage and the series converter output voltage in a simulation experiment of an embodiment of the present invention;
FIG. 11 is a simulation waveform of the active power of the system in a simulation experiment according to an embodiment of the present invention;
fig. 12 is a simulation waveform of reactive power of the system in a simulation experiment of an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1, a UPQC topology according to a first embodiment of the present invention is provided, where the UPQC topology 1 includes a series side unit, a dc capacitor C dc, and a parallel side unit, the series side unit includes a series transformer T 1, a series coupling capacitor C S, a first filter, and a series converter 11 sequentially connected in series, and the parallel side unit includes a parallel converter 12, a second filter L 2, and a parallel transformer T 2 sequentially connected in series, and the series converter 11, the dc capacitor C dc, and the parallel converter 12 are connected in parallel. In the invention, the first filter is an LC filter, that is, the first filter includes a first capacitor C 1 and a first inductor L 1, and the second filter is an L filter, that is, only a second inductor L 2.
In order to better explain the topology of the UPQC, parameter values such as current and voltage generated by each device are explained first, in fig. 1, U S represents a power grid voltage, U L represents a load voltage, U SC represents a series side compensation voltage, U CS represents a series coupling capacitor voltage, U conv represents a series converter output voltage, U dc represents a direct current side voltage, I s represents a power grid current, I pc represents a parallel side compensation current, and I L represents a load current.
The serial converter 11 and the parallel converter 12 in the invention have the same structure and are all composed of four Insulated Gate Bipolar Transistors (IGBT), namely, the serial converter 11 comprises 4 IGBTs from S 1 to S 4, and the parallel converter 12 comprises 4 IGBTs from S 5 to S 8.
The series converter 11 is specifically connected in such a manner that a collector of the first transistor S 1 is connected to a collector of the second transistor S 2 and is connected to an anode of the dc capacitor C dc, an emitter of the first transistor S 1 is connected to a collector of the third transistor S 3 and is connected to an anode of the first inductor L 1, an emitter of the second transistor S 2 is connected to a collector of the fourth transistor S 4 and is connected to a cathode of the first capacitor C 1, that is, one end of a primary side of the series transformer T 1, an emitter of the third transistor S 3 is connected to an emitter of the fourth transistor S 4 and is connected to a cathode of the dc capacitor C dc, a cathode of the first inductor L 1 (that is, an anode of the first capacitor C 1) is connected to a primary side of the series transformer T 1 and the other end of the series capacitor C S in series, and a secondary side of the series transformer T 1 is connected to a power grid in series.
The parallel converter 12 is specifically connected in such a way that the collector of the fifth transistor S 5 and the collector of the sixth transistor S 6 are connected and connected to the positive electrode of the dc capacitor C dc, the emitter of the fifth transistor S 5 and the collector of the seventh transistor S 7 are connected and connected to the positive electrode of the second inductor L 2, the negative electrode of the second inductor L 2 is connected to one end of the primary side of the parallel transformer T 2, the emitter of the sixth transistor S 6 and the collector of the eighth transistor S 8 are connected and connected to the other end of the primary side of the parallel transformer T 2, the emitter of the seventh transistor S 7 and the emitter of the eighth transistor S 8 are connected and connected to the negative electrode of the dc capacitor C dc, one end of the secondary side of the parallel transformer T 2 is connected to the power grid, and the other end of the secondary side of the parallel transformer T 2 is grounded. The working model of the UPQC topology of the present invention is described in detail below with reference to fig. 2.
Referring to fig. 2, based on the same inventive concept, a series-parallel side cooperative control method of a UPQC topology according to a second embodiment of the present invention includes steps S10 to S30:
And step S10, judging the working conditions of the power grid according to the voltage value of the power grid, wherein the working conditions of the power grid comprise a normal voltage working condition and a voltage drop working condition.
And step S20, if the power grid working condition is the voltage normal working condition, controlling the series side units of the UPQC to work in a reactive power regulation mode, and compensating the reactive power of the load through the series side units and the parallel side units so as to enable the power grid to maintain to operate in a unit power factor.
And step S30, if the power grid working condition is the voltage drop working condition, controlling the series side units to work in a voltage compensation mode, performing voltage compensation through the series side units so as to ensure that the load voltage is unchanged, and jointly compensating the load reactive power through the series side units and the parallel side units.
In summary, the UPQC of the present invention mainly has two operation modes according to different power grid conditions, in which, under the condition that the power grid voltage is normal, the UPQC works in a reactive regulation mode, the series-parallel side compensates the reactive power of the load together to maintain the unit power factor operation of the power grid side, and when the power grid voltage fluctuates, the UPQC works in a voltage compensation mode, in which, the series side supplements the load voltage to maintain the load voltage unchanged, and the series-parallel side supplements the reactive power of the load together to maintain the unit power factor operation of the power grid side. The following describes in detail two modes of operation of UPQC under different grid conditions, in combination with the topology of fig. 1:
① Normal working condition of grid voltage
In order to increase the utilization rate of the series converter 11 and reduce the rated capacity of the parallel converter 12, under the working condition, the series side of the UPQC is set to work in the reactive regulation mode, please refer to the vector schematic diagram of fig. 3, a compensation voltage U sc with proper amplitude and phase angle is injected into the series side of the UPQC through a series transformer T 1, and the compensated load voltage is made on the premise of ensuring that the amplitude of the load voltage U L is unchangedLeading grid voltage U s by a phase angle differenceBy controlling the phase angle differenceThe UPQC system can adjust the magnitude of the series side injection reactive power Q SC, and control the series and parallel sides to jointly complete the reactive power compensation of the load, thereby achieving the effect of reducing the UPQC active capacity.
In order to fully utilize the reactive compensation capability of the series capacitor C S and reduce the power transmission of the series converter 11, the phase of the series coupling capacitor voltage U CS may be set perpendicular to the phase of the grid voltage U S, and the phase of the series converter output voltage U conv may be set opposite to the phase of the grid voltage U S, i.e. the reactive power Q conv output by the series converter is set to 0, and the amplitude and phase angle of the series side compensation voltage under this condition may be calculated according to fig. 3:
In the formula, In order to compensate for the load voltage after the compensation,To compensate for the phase angle of the load voltage;
since the series capacitor C S can withstand most of the compensation voltage, the series converter output voltage amplitude U conv is much smaller than the series side compensation voltage U SC, namely:
Similarly, from the current vector portion in fig. 3, the magnitude and phase angle of the parallel side compensation current I PC can be calculated:
In the formula, In order to compensate for the load current after the compensation,Is the load power factor angle.
The system power flow diagram under this condition is shown in fig. 4, where the reactive Q SC of the series side compensation is provided by the series capacitor C S, i.e. Q SC=QCS. The remaining reactive power of the load is then provided by the parallel side, i.e. Q PC=QL-QCS. However, since the series converter output voltage U conv is inverted from I S, the series converter will absorb a small amount of active P SC and the active component will be output through the parallel side, i.e., P PC=PSC. That is, under the normal working condition of the power grid voltage, the series-parallel connection sides of the UPQC compensate the reactive power of the load together so as to maintain the power grid to run at the unit power factor.
② Grid voltage sag condition
When the power grid voltage drops, the series side of the UPQC works in a voltage compensation mode, and the phase of the series coupling capacitor voltage U CS and the dropped power grid voltage can be adjusted by adopting a pure reactive compensation strategyThe phase of the output voltage U conv of the series converter is set in phase with the phase of the voltage U CS of the series coupling capacitor, please refer to the vector schematic diagram shown in fig. 5, and the compensation voltage U sc with proper amplitude and phase angle is injected into the series side of the UPQC through the series transformer T 1, so that the compensated load voltage is obtained on the premise of ensuring that the amplitude of the load voltage U L is unchanged, as in the normal working condition of the grid voltageGrid voltage after leading dropPhase angle differenceCan see the voltage of the power grid after fallingLess than the compensated load voltageI.e. the vector radii are different, whereas the missing part of the voltage is in this mode compensated by the series side, so that the load voltage is unchanged. In the working mode, not only the minimization of active injection can be realized, but also the active exchange of the serial-parallel connection side of the system can be reduced.
As can be calculated from fig. 5, the amplitude and phase angle of the series-side compensation voltage in this operation mode are:
In the formula, In order to compensate for the load voltage after the compensation,To compensate for the phase angle of the load voltage, wherein:
and:
In the formula, Is the voltage drop coefficient of the power grid.
Similarly, the magnitude and phase angle of the parallel side compensation current can also be calculated from fig. 5:
referring to the system power flow diagram shown in fig. 6, the load reactive compensation tasks are commonly borne by the serial and parallel sides of the system, and the reactive outputs of the serial and parallel sides are Q SC and Q PC respectively. Wherein, a large part of Q SC is provided by a series coupling capacitor C S, and the rest is output by a series converter.
Therefore, under the normal working condition of the power grid voltage, the UPQC provided by the invention can utilize the serial side to compensate the reactive power of the load part, effectively reduce the capacity of the parallel converter, and under the dropping working condition of the power grid voltage, the output voltage amplitude of the serial converter can be greatly reduced by utilizing the serial coupling capacitor, so that the capacity of the serial converter is reduced. Therefore, compared with the traditional UPQC device, the UPQC topological structure and the cooperative control method thereof provided by the invention have the advantages that the whole active capacity of the device is smaller, and the utilization rate of the device is higher.
In order to better prove the effectiveness of the cooperative control method provided by the invention, the following verification is carried out by combining a simulation example, firstly, a simulation platform is built in MATLAB/Simulink, and simulation parameters are shown in the following table 1.
Table 1 simulation parameters
As shown in fig. 7 and 8, it is assumed that the grid voltage drops by 20% during 0.35-0.45s, and the grid operates normally for the rest of the time. During the period of 0.3-0.35s and 0.45-0.5s, the UPQC works in a power regulation mode, the amplitudes of U L and U S are the same, the phase difference is 30.67 degrees, and the power grid voltage U S and the power grid current I S are always kept in phase. As shown in fig. 9, the parallel side output current I PC decreases from 20.2A to 10.29A, since the series side compensates a portion of the load reactive power. As shown in fig. 10, although the series side offset voltage U SC is very large (164.5V), the series converter output voltage U conv is very small (49.7V).
Similarly, as shown in fig. 7 and 8, the UPQC operates in the voltage compensation mode during 0.35s-0.45s, the U L and U S have the same amplitude, the phase difference is 36.87 degrees, and the grid voltage U S and the grid current I S are always in phase. As can be seen from I PC shown in fig. 9, the reactive current provided by the parallel section is required to drop to a smaller value (5.4A) due to the increase in the magnitude of I S resulting in an increase in the output reactive power of the coupling capacitor. As shown in fig. 10, although U SC is very large (186.4V), the magnitude of U conv remains at a small value (28.3V) due to the presence of the coupling capacitance sharing most of the compensation voltage. Furthermore, it is also clear from fig. 11 and 12 that P S is equal to P L,QL is equal to the sum of Q SC and Q PC, i.e. the reactive compensation capability of UPQC and the effectiveness of the series side and parallel side coordination are verified.
In summary, the embodiment of the invention provides a UPQC topological structure and a serial-parallel side cooperative control method thereof, which comprises a serial side unit, a direct current capacitor and a parallel side unit, wherein the serial side unit comprises a serial transformer, a serial coupling capacitor, a first filter and a serial converter which are sequentially connected in series, the parallel side unit comprises a parallel converter, a second filter and a parallel transformer which are sequentially connected in series, the serial converter, the direct current capacitor and the parallel converter are mutually connected in parallel, the first filter comprises a first inductor and a first capacitor which are connected in series, the second filter comprises a second inductor, the serial converter comprises four insulated gate bipolar transistors which are respectively a first transistor, a second transistor, a third transistor and a fourth transistor, wherein the first transistor and the third transistor are connected in series, the third transistor and the fourth transistor are connected in series, the serial connection, the first transistor and the third transistor are connected in series, the serial connection, the second transistor and the third transistor are connected in parallel, the second transistor and the second transistor are connected in parallel, the second inductor and the second filter comprises a second inductor, the serial bipolar transistor comprises a fourth insulated gate bipolar transistor, the serial transistor comprises a fourth transistor, the serial transistor and the serial transistor comprises a seventh transistor and a serial transistor, the serial transistor and the serial transistor, and the serial transistor are connected between the seventh transistor and the serial transistor, and the serial transistor are connected between the serial transistor and the serial transistor, and the serial transistor are respectively, and the fifth transistor and the serial transistor are connected. The invention can effectively improve the utilization rate of the series-connection side device, and can reduce the rated capacity of the parallel-connection side converter by utilizing the series-connection side converter, thereby further reducing the active capacity of the UPQC device.
In this specification, each embodiment is described in a progressive manner, and all the embodiments are directly the same or similar parts referring to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments. It should be noted that, any combination of the technical features of the foregoing embodiments may be used, and for brevity, all of the possible combinations of the technical features of the foregoing embodiments are not described, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing examples represent only a few preferred embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the application. It should be noted that modifications and substitutions can be made by those skilled in the art without departing from the technical principles of the present application, and such modifications and substitutions should also be considered to be within the scope of the present application. Therefore, the protection scope of the patent of the application is subject to the protection scope of the claims.
Claims (8)
1. The serial-parallel side cooperative control method of the UPQC topological structure, wherein the UPQC is connected between a power grid and a load, is characterized in that the UPQC topological structure comprises the following steps:
A series side unit, a direct current capacitor and a parallel side unit;
the series side unit comprises a series transformer, a series coupling capacitor, a first filter and a series converter which are sequentially connected in series;
The parallel side unit comprises a parallel converter, a second filter and a parallel transformer which are sequentially connected in series;
the series converter, the direct current capacitor and the parallel converter are connected in parallel;
the first filter comprises a first inductor and a first capacitor which are connected in series, and the second filter comprises a second inductor;
the series converter comprises four insulated gate bipolar transistors, namely a first transistor, a second transistor, a third transistor and a fourth transistor, wherein the first transistor and the third transistor are connected in series, the second transistor and the fourth transistor are connected in series, and the first transistor and the third transistor which are connected in series, the second transistor and the fourth transistor which are connected in series are connected in parallel;
The parallel converter comprises four insulated gate bipolar transistors, namely a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor, wherein the fifth transistor and the seventh transistor are connected in series, the sixth transistor and the eighth transistor are connected in series, and the fifth transistor and the seventh transistor which are connected in series, the sixth transistor and the eighth transistor which are connected in series are connected in parallel;
The serial-parallel side cooperative control method comprises the following steps:
Judging power grid working conditions according to the voltage value of the power grid, wherein the power grid working conditions comprise a voltage normal working condition and a voltage drop working condition;
If the power grid working condition is the voltage normal working condition, controlling the series side units of the UPQC to work in a reactive power regulation mode, and jointly compensating load reactive power through the series side units and the parallel side units so as to enable the power grid to be maintained to operate in a unit power factor;
If the power grid working condition is the voltage drop working condition, controlling the series side units to work in a voltage compensation mode, performing voltage compensation through the series side units so as to ensure that the load voltage is unchanged, and jointly compensating the load reactive power through the series side units and the parallel side units;
and if the power grid working condition is the voltage normal working condition, controlling the series side unit of the UPQC to work in a reactive power regulation mode comprises the following steps:
Setting the phase of the series coupling capacitor voltage and the phase of the grid voltage vertically, and setting the phase of the series converter output voltage and the phase of the grid voltage in opposite phase;
Injecting a preset first series side compensation voltage through a series transformer so that the compensated load voltage leads the power grid voltage by a phase angle difference, and taking the current output by the parallel transformer as a first parallel side compensation current;
and taking the reactive power output by the series coupling capacitor as first series side compensation power, and taking the reactive power output by the parallel converter as first parallel side compensation power, wherein the first series side compensation power and the first parallel side compensation power jointly compensate the reactive power of the load.
2. The method according to claim 1, wherein the collector of the first transistor and the collector of the second transistor are connected together and are connected to the positive electrode of the dc capacitor, the emitter of the first transistor and the collector of the third transistor are connected together and are connected to the positive electrode of the first inductor, the emitter of the second transistor and the collector of the fourth transistor are connected together and are connected to the negative electrode of the first capacitor, and the emitter of the third transistor and the emitter of the fourth transistor are connected together and are connected to the negative electrode of the dc capacitor.
3. The method for cooperatively controlling the serial-parallel sides of the UPQC topology according to claim 2, wherein the negative electrode of the first inductor is connected with the serial coupling capacitor and is connected to one end of the primary side of the serial transformer together, the negative electrode of the first capacitor is connected to the other end of the primary side of the serial transformer, and the secondary side of the serial transformer is connected in series to the power grid.
4. The method according to claim 1, wherein a collector of the fifth transistor and a collector of the sixth transistor are connected together and are connected to an anode of the dc capacitor, an emitter of the fifth transistor and a collector of the seventh transistor are connected together and are connected to an anode of the second inductor, a cathode of the second inductor is connected to one end of a primary side of the shunt transformer, an emitter of the sixth transistor and a collector of the eighth transistor are connected together and are connected to the other end of the primary side of the shunt transformer, and an emitter of the seventh transistor and an emitter of the eighth transistor are connected together and are connected to a cathode of the dc capacitor.
5. The method for cooperative control of series and parallel sides of a UPQC topology as in claim 4 wherein one end of the secondary side of the shunt transformer is connected to the grid and the other end of the secondary side of the shunt transformer is grounded.
6. The method for cooperatively controlling the serial and parallel sides of the UPQC topological structure according to claim 1, wherein the first serial side compensation voltage and the first parallel side compensation current are calculated according to the vector principle of the normal voltage working condition;
the amplitude and phase angle of the first series side compensation voltage are calculated respectively using the following formula:
In the formula, In order to compensate for the load voltage after the compensation,To compensate for the phase angle of the load voltage;
The amplitude and phase angle of the first parallel side compensation current are calculated respectively using the following formula:
In the formula, In order to compensate for the load current after the compensation,Is the load power factor angle.
7. The method for controlling the series-parallel connection side cooperative control of the UPQC topology according to claim 1, wherein the step of controlling the series-connection side unit to operate in the voltage compensation mode if the grid condition is the voltage drop condition includes:
Setting the phase of the series coupling capacitor voltage and the phase of the dropped power grid voltage vertically, and setting the phase of the output voltage of the series converter and the phase of the series coupling capacitor voltage in phase;
Injecting a preset second series side compensation voltage through a series transformer so that the compensated load voltage leads the dropped power grid voltage by a phase angle difference, and taking the current output by the parallel transformer as a second parallel side compensation current;
And taking the reactive power output by the series coupling capacitor and the reactive power output by the series converter as second series side compensation power, and taking the reactive power output by the parallel converter as second parallel side compensation power, wherein the second series side compensation power and the second parallel side compensation power jointly compensate the load reactive power.
8. The method for cooperatively controlling the series-parallel side of the UPQC topological structure according to claim 7, wherein the second series-side compensation voltage and the second parallel-side compensation current are calculated according to the vector principle of the voltage drop working condition;
The amplitude and phase angle of the second series side compensation voltage are calculated respectively using the following formulas:
In the formula, In order to compensate for the load voltage after the compensation,To compensate for the phase angle of the load voltage;
the amplitude and phase angle of the second parallel side compensation current are calculated respectively using the following formula:
In the formula, In order to compensate for the load current after the compensation,In order to load the power factor angle,Is the voltage drop coefficient of the power grid.
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