CN117155117A - High-voltage high-capacity direct-current transformer regulation and control method and system - Google Patents
High-voltage high-capacity direct-current transformer regulation and control method and system Download PDFInfo
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- CN117155117A CN117155117A CN202311428751.9A CN202311428751A CN117155117A CN 117155117 A CN117155117 A CN 117155117A CN 202311428751 A CN202311428751 A CN 202311428751A CN 117155117 A CN117155117 A CN 117155117A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The invention discloses a regulation and control method and a regulation and control system for a high-voltage high-capacity direct-current transformer. The existing direct current transformer regulation and control method needs to order the capacitance voltage of the sub-module twice in one switching period, and adopts current detection to use a current sensor, so that the difficulty of an algorithm is increased, and the volume and the cost of a direct current system are increased. The invention relates to a regulating and controlling method of a high-voltage high-capacity direct-current transformer, which adopts the following technical scheme: based on the quasi-two-level modulation of the ladder wave in light load, the bridge arm current waveform is changed by adjusting the duty ratio of the bridge arm submodule of the direct-current transformer, so that the voltage equalizing control of the bridge arm submodule is realized, and the charge quantity absorbed by the submodule in one switching period in light load is restored to monotonicity. The invention realizes that the capacitor voltage of the submodule is ordered once in one switching period, and the current sensor is not required to be used for detecting the current direction of the bridge arm.
Description
Technical Field
The invention relates to control of a direct current transformer, in particular to a method and a system for regulating and controlling a high-voltage high-capacity direct current transformer.
Background
The modular multilevel direct current transformer (Modular Multilevel Direct Current Transformer, MMDCT) combines the advantages of a modular multilevel converter (Modular Multilevel Converter, MMC) and a buck type bidirectional DC-DC converter, can bear high voltage, avoids complex series technology of power devices, and can realize soft switching. Typical non-isolated MMDCT is Buck-MMDCT. When the Buck-MMDCT operates under the rated load working condition, the upper bridge arm and the lower bridge arm adopt a stepped wave quasi-two-level modulation method with complementary phase shifting, and the charge quantity absorbed by the sub-module capacitor in the bridge arm in one switching period is monotonic, so that the sub-module capacitor voltage sequencing can be adopted to realize the sub-module energy balance.
However, the bridge arm current is affected by the working condition, and when the Buck-MMDCT operates in the light load working condition, the bridge arm current changes, so that the charge quantity absorbed by the capacitance of the sub-module in the bridge arm in one switching period no longer meets monotonicity, and the capacitance and voltage sequencing strategy of the sub-module is not applicable. In order to solve the above problems, it is necessary to propose a sub-module capacitor voltage balance control strategy of Buck-MMDCT under the light load condition.
When the step wave quasi-two-level modulation is adopted, the pulse sequence of the submodules is obtained through carrier phase-shift modulation, at the moment, the duty ratio of each submodule is consistent, and the charge quantity absorbed by the submodule capacitor is determined by bridge arm current. The basic waveforms of the single-phase Buck-MMDCT and the quasi-two-level modulation based on the step wave are shown in FIGS. 1 and 2, respectively. SM (Submodule) in fig. 1 is a Submodule, the topology employs a half-bridge Submodule, i.e. HBSM is a half-bridge Submodule,C sm for submodule capacitance, FIG. 2d s Is a shift in contrast to this, the method comprises,d 1 is the duty cycle of the upper bridge arm,Tis the switching period.
One of the sub-module capacitor voltage equalizing strategies combines current detection and capacitor voltage sequencing. In the rising and falling process of the bridge arm ladder wave voltage, the direct current transformer determines the submodule capacitor which is put into and cut off according to the direction of the bridge arm submodule string current and the submodule capacitor voltage sequencing result, so that the submodule capacitor voltage equalizing is realized. In order to prevent the sub-module capacitors from being switched repeatedly, each sub-module capacitor is only switched on or off once in the voltage conversion process. The sequence of submodule throw-in and cut-out during the voltage rise and fall in steady state is shown in figures 3 and 4, wherein the interval between triggering of two adjacent submodules in throw-in and cut-out is defined as the step wave jump timeT d . The method needs to sort the capacitance voltage of the sub-module twice in one switching period, and adopts current detection to use a current sensor, so that the difficulty of an algorithm is increased, and the volume and the cost of a direct current system are increased.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a method and a system for regulating and controlling a high-voltage high-capacity direct-current transformer so as to realize voltage equalizing control of bridge arm submodules, wherein the capacitor voltage of the submodules is sequenced once in one switching period, and a current sensor is not required to be used for detecting the current direction of the bridge arm.
Therefore, the invention adopts the following technical scheme: a regulation and control method of a high-voltage high-capacity direct current transformer is based on the quasi-two-level modulation of a ladder wave in light load, and changes bridge arm current waveforms by a method of adjusting the duty ratio of bridge arm submodules of the direct current transformer, so that voltage equalizing control of the bridge arm submodules is realized, and the charge quantity absorbed by the submodules in one switching period in light load is restored to monotonicity; obtaining the change rate of the bridge arm inductance current in light load according to the bridge arm inductance voltage equation of four modes and the low-voltage side filtering inductance voltage equation in one switching period of the direct-current transformer; and finally obtaining a basic current waveform diagram of the direct-current transformer based on the step wave quasi-two-level modulation in light load according to the change rate of the bridge arm inductance current.
The invention only needs to sort the capacitance voltage of the sub-module once in one switching period, and does not need to use a current sensor to detect the current direction of the bridge arm.
Further, the contents of the step wave quasi-two-level modulation during light load are as follows:
the duty ratio of the output voltage of the upper bridge arm and the lower bridge arm is respectively as follows when the direct current transformer is in heavy loadd 1 Andd 2 the duty ratios of the output voltages of the upper bridge arm and the lower bridge arm are adjusted during light load, respectivelyd 1 ’ Andd 2 ’ the relation is satisfied:
，
in the method, in the process of the invention,the ratio of the output duty ratio of the upper bridge arm and the lower bridge arm in heavy load to the light load is shown;
thus, when the output voltages of the upper bridge arm and the lower bridge arm are all at a high level, the following are:
，
in the method, in the process of the invention,、/>respectively representing the highest voltage output by the upper bridge arm and the lower bridge arm during light load>Representing the high-side dc bus voltage;
in combination with the topological structure of the direct-current transformer, the direct-current transformer has four working modes according to kirchhoff voltage law:
1) The first mode of operation [0 ],d 1 ’T)
in the mode, the output voltage of the upper bridge arm is in a high level, and the output voltage of the lower bridge arm is in a low level 0, so that the voltage values of the bridge arm inductance and the filter inductance are obtained:
，
，
in the method, in the process of the invention,、/>respectively representing the bridge arm inductance voltage value and the filter inductance voltage value; />、/>Respectively representing the output voltage values of the upper bridge arm and the lower bridge arm; />Representing the low-side direct current bus voltage;
2) Second modality [d 1 ’T,d s T)
The output voltages of the upper bridge arm and the lower bridge arm of the mode are all in a low level, and all the submodule capacitors are all in a cut-off state, and the following steps are obtained:
，
，
d s representing the phase shift ratio between the output voltages of the upper bridge arm and the lower bridge arm;
3) Third modality [d s T, (d 2 ’+d s )T)
The mode is opposite to the first mode, the output voltage of the lower bridge arm is in a high level, the output voltage of the upper bridge arm is in a low level, and the following steps are obtained:
，
，
4) Fourth mode [ (]d 2 ’+d s )T,T]
The mode is the same as the second mode, the output voltages of the upper bridge arm and the lower bridge arm are all in low level, and the following steps are obtained:
，
。
further, since the alternating current component of the output voltage of the lower bridge arm is applied to the low-voltage side filter inductor to form an alternating current component, the current of the lower bridge armi 3 The fluctuation is slightly larger than the current of the upper bridge armi 1 。
Further, in the first mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is +.>。
Further, in the second mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is。
Further, in the third mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is +.>。
Further, in the fourth mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is。
Further, when the dc transformer adopts the quasi-two-level modulation based on the step wave at the time of light load, the output side voltage is closed-loop controlled, and the difference value is used as the duty ratio by comparing the output side voltage value with a given reference value through the PI controllerd 1 Andd 2 is a given value, phase shift ratiod s Has a coupling relation with the duty ratio, and when all the submodules in a certain bridge arm are subjected to capacitance-voltage balance control, the phase shift ratio also needs to be adjustedd s The bridge arm energy balance is ensured, and the average value of the capacitance voltage of all the submodules is ensured to be kept constant; in order to perform energy balance control on the upper bridge arm and the lower bridge arm, the difference between the capacitance voltage average value of all the sub-modules of the upper bridge arm and the capacitance voltage average value of all the sub-modules of the lower bridge arm is selected to be used as a phase shift ratio through a low-pass filter and a PI regulatord s And sub-module energy balance control is implemented using capacitor voltage sequencing.
Further, the direct-current transformer is a Buck type modularized multi-level direct-current transformer.
The invention also provides a regulating and controlling system of the high-voltage high-capacity direct-current transformer, which is used for realizing the regulating and controlling method of the high-voltage high-capacity direct-current transformer.
The invention has the following beneficial effects: according to the invention, the bridge arm current waveform is changed by a method of adjusting the duty ratio of the bridge arm submodule of the direct-current transformer, so that the voltage equalizing control of the bridge arm submodule is realized, the capacitor voltage of the submodule is ordered once in one switching period, and the bridge arm current direction detection is not required to be carried out by using a current sensor.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.
FIG. 1 is a topology block diagram of a unidirectional Buck-MMDCT;
FIG. 2 is a basic waveform diagram of Buck-MMDCT based on step wave quasi-two level modulation;
FIG. 3 is a chart showing the sequence of voltage rise sub-module inputs and cuts at steady state;
FIG. 4 is a chart showing a voltage drop process sub-module input and cut-out sequence at steady state;
FIG. 5 is a basic waveform diagram of Buck-MMDCT based on quasi-two-level modulation of step wave during light load in an embodiment of the present invention;
FIG. 6 is a block diagram of the overall control of the Buck-MMDCT in accordance with one embodiment of the present invention;
FIG. 7 is a steady-state waveform diagram of the upper arm voltage during light load of the Buck-MMDCT in an embodiment of the invention;
FIG. 8 is a steady-state waveform diagram of the current of the lower arm during light load of the Buck-MMDCT in an embodiment of the invention;
FIG. 9 is a steady-state waveform of the low-side current during light load of the Buck-MMDCT according to one embodiment of the present invention;
FIG. 10 is a waveform diagram of the steady state capacitance and voltage of the upper arm submodule during light load of the Buck-MMDCT in an embodiment of the present invention;
FIG. 11 is a waveform diagram of a steady state capacitor voltage of a lower bridge arm submodule during light load of the Buck-MMDCT in an embodiment of the present invention;
FIG. 12 is a graph showing waveforms of capacitance and voltage of the upper arm submodule of the Buck-MMDCT under different working conditions in an embodiment of the present invention;
FIG. 13 is a graph showing the capacitance and voltage waveforms of the lower arm submodule of the Buck-MMDCT under different operating conditions in accordance with an embodiment of the present invention.
Detailed Description
The technical solutions of the present embodiment will be clearly and systematically described below with reference to the accompanying drawings of the present invention, however, the described embodiment of the present invention is only a better example of the implementation of the present invention, and all the related embodiments obtained by those skilled in the art without any inventive effort are within the scope of the present invention.
The embodiment provides a method for controlling the starting of a direct current transformer of an all-direct current system. The direct-current transformer is a Buck-type modularized multi-level direct-current transformer, namely Buck-MMDCT.
The invention changes the bridge arm current waveform by adjusting the duty ratio of the bridge arm submodule of the direct-current transformer on the basis of the quasi-two-level modulation of the ladder wave in light load, so that the charge quantity absorbed by the submodule in one switching period in light load is restored to monotonicity. The capacitor voltages of the submodules need to be sequenced only once in one switching period, and a current sensor does not need to be used for detecting the current direction of the bridge arm.
The contents of the quasi-two-level modulation of the ladder wave in light load are as follows:
the duty ratio of the output voltage of the upper bridge arm and the lower bridge arm is respectively as follows when the direct current transformer is in heavy loadd 1 Andd 2 the duty ratios of the output voltages of the upper bridge arm and the lower bridge arm are adjusted during light load, respectivelyd 1 ’ Andd 2 ’ the relation is satisfied:
in the method, in the process of the invention,the ratio of the output duty ratio of the upper bridge arm and the lower bridge arm is shown in heavy load and light load.
Thus, when the output voltages of the upper bridge arm and the lower bridge arm are all at a high level, the following are:
in the method, in the process of the invention,、/>respectively representing the highest voltage output by the upper bridge arm and the lower bridge arm during light load>The high-side dc bus voltage is shown.
In combination with the topological structure of the direct-current transformer, the direct-current transformer has four working modes according to kirchhoff voltage law:
1) The first mode of operation [0 ],d 1 ’T)
in the mode, the output voltage of the upper bridge arm is in a high level, and the output voltage of the lower bridge arm is in a low level 0, so that the voltage values of the bridge arm inductance and the filter inductance are obtained:
，
，
in the method, in the process of the invention,、/>respectively representing the bridge arm inductance voltage value and the filter inductance voltage value; />、/>Respectively representing the output voltage values of the upper bridge arm and the lower bridge arm; />Indicating the low side dc bus voltage.
2) Second modality [d 1 ’T,d s T)
The output voltages of the upper bridge arm and the lower bridge arm of the mode are all in a low level, and all the submodule capacitors are all in a cut-off state, and the following steps are obtained:
，
，
d s representing the phase shift ratio between the output voltages of the upper bridge arm and the lower bridge arm;
3) Third modality [d s T, (d 2 ’+d s )T)
The mode is opposite to the first mode, the output voltage of the lower bridge arm is in a high level, the output voltage of the upper bridge arm is in a low level, and the following steps are obtained:
，
，
4) Fourth mode [ (]d 2 ’+d s )T,T]
The mode is the same as the second mode, the output voltages of the upper bridge arm and the lower bridge arm are all in low level, and the following steps are obtained:
，
，
and obtaining the inductance current change rate of the direct current transformer in light load according to bridge arm inductance voltage equations of four modes and a low-voltage side filtering inductance voltage equation in one switching period of the direct current transformer, wherein the inductance current change rate is shown in table 1.
TABLE 1 inductor current change rate at light load
And finally obtaining a basic current waveform diagram of the direct-current transformer based on the quasi-two-level modulation of the step wave in light load according to the change rate of the inductance current of the bridge arm, as shown in fig. 5. The alternating current component of the output voltage of the lower bridge arm is applied to the low-voltage side filter inductor to form an alternating current component, so that the current of the lower bridge armi 3 The fluctuation is slightly larger than the current of the upper bridge armi 1 。
When the direct-current transformer adopts the step wave quasi-two-level modulation, the basic working principle is similar to that of the traditional Buck DC-DC converter, and the duty ratio is consistent, so that the control strategy of the Buck converter can be consulted when closed-loop control is carried out, the output side voltage is subjected to closed-loop control, the output side voltage value is compared with a given reference value, and the difference value is taken as the duty ratio through a PI controllerd 1 Andd 2 is a given value, phase shift ratiod s Has a coupling relation with the duty ratio, and when all the submodules in a certain bridge arm are subjected to capacitance-voltage balance control, the phase shift ratio also needs to be adjustedd s The bridge arm energy balance is ensured, and the average value of the capacitance voltage of all the submodules is ensured to be kept constant; in order to perform energy balance control on the upper bridge arm and the lower bridge arm, the average value of capacitance and voltage of all submodules of the upper bridge arm is selectedu p_avg And the average value of capacitance and voltage of all submodules of lower bridge armu n_avg The difference is used as the phase shift ratio through a low-pass filter and a PI regulatord s And sub-module energy balance control is implemented using capacitor voltage sequencing.
The overall control block diagram of the dc transformer is shown in fig. 6. Wherein,
the PI controller transfer functions of the output voltage closed loop control and the phase shift control are represented respectively.K P1 、K P2 Are all proportional coefficients of the PI controller,K I1 、K I2 are the integral coefficients of the PI controller.
Representing the transfer function of the low-pass filter,T f representing the filter time constant.
In combination with the above embodiment, MATLAB/Simulink software is used to perform simulation verification on the system, and simulation parameters are shown in table 2.
Table 2 buck_mmdct simulation parameters
When the transmission power of the Buck-MMDCT is 5MW, the Buck-MMDCT is in a light load working condition, and according to the figures 7-11, the voltages and the currents of the upper bridge arm and the lower bridge arm can be seen to accord with theoretical analysis, and the capacitance voltage of the sub-module can be balanced in a steady state. In fig. 10, the ordinate indicates the output voltage values of the 1 st to 8 th sub-modules of the upper arm. In fig. 11, the ordinate indicates the output voltage values of the 1 st to 8 th sub-modules of the lower bridge arm. In the figures 12-13 of the drawings,u SM_upper representing the voltage of the capacitors of each sub-module of the upper bridge arm,u SM_lower representing the voltage of the capacitors of each sub-module of the lower bridge arm. When t=1s, the Buck-MMDCT transmission power is reduced from 20MW to 5MW, at the moment, the Buck-MMDCT working condition is considered to be changed from heavy load to light load, and when the modulation and control strategy still adopts the strategy under the heavy load, the capacitor voltage of the upper bridge arm submodule is found to be rapidly diverged; by adopting the regulation and control method of the high-voltage high-capacity direct-current transformer provided by the invention at t=1.2s, the capacitor voltage of the inner submodule of the upper bridge arm is found to be re-converged, so that verification is carried outThe effectiveness of the method of the invention is demonstrated.
The embodiment also provides a high-voltage high-capacity direct-current transformer regulation and control system which is used for realizing the high-voltage high-capacity direct-current transformer regulation and control method.
While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the invention, such changes and modifications are also intended to be within the scope of the invention.
Claims (10)
1. The regulation and control method of the high-voltage high-capacity direct-current transformer is characterized in that on the basis of the quasi-two-level modulation of the ladder wave in light load, the bridge arm current waveform is changed by a method of adjusting the duty ratio of a bridge arm submodule of the direct-current transformer, so that the voltage equalizing control of the bridge arm submodule is realized, and the charge quantity absorbed by the submodule in one switching period in light load is restored to monotonicity; obtaining the change rate of the bridge arm inductance current in light load according to the bridge arm inductance voltage equation of four modes and the low-voltage side filtering inductance voltage equation in one switching period of the direct-current transformer; and finally obtaining a basic current waveform diagram of the direct-current transformer based on the step wave quasi-two-level modulation in light load according to the change rate of the bridge arm inductance current.
2. The method for regulating and controlling a high-voltage high-capacity direct current transformer according to claim 1, wherein the content of the step wave quasi-two-level modulation during light load is as follows:
the duty ratio of the output voltage of the upper bridge arm and the lower bridge arm is respectively as follows when the direct current transformer is in heavy loadd 1 Andd 2 the duty ratios of the output voltages of the upper bridge arm and the lower bridge arm are adjusted during light load, respectivelyd 1 ’ Andd 2 ’ the relation is satisfied:
，
in the method, in the process of the invention,the ratio of the output duty ratio of the upper bridge arm and the lower bridge arm in heavy load to the light load is shown;
thus, when the output voltages of the upper bridge arm and the lower bridge arm are all at a high level, the following are:
，
in the method, in the process of the invention,、/>respectively representing the highest voltage output by the upper bridge arm and the lower bridge arm during light load>Representing the high-side dc bus voltage;
in combination with the topological structure of the direct-current transformer, the direct-current transformer has four working modes according to kirchhoff voltage law:
1) The first mode of operation [0 ],d 1 ’T)
in the mode, the output voltage of the upper bridge arm is in a high level, and the output voltage of the lower bridge arm is in a low level 0, so that the voltage values of the bridge arm inductance and the filter inductance are obtained:
，
，
in the method, in the process of the invention,、/>respectively represent bridge arm electricityA voltage sensing value and a filter inductance voltage value; />、/>Respectively representing the output voltage values of the upper bridge arm and the lower bridge arm; />Representing the low-side direct current bus voltage;Trepresenting a switching period;
2) Second modality [d 1 ’T, d s T)
The output voltages of the upper bridge arm and the lower bridge arm of the mode are all in a low level, and all the submodule capacitors are all in a cut-off state, and the following steps are obtained:
，
，
d s representing the phase shift ratio between the output voltages of the upper bridge arm and the lower bridge arm;
3) Third modality [d s T, (d 2 ’+d s )T)
The mode is opposite to the first mode, the output voltage of the lower bridge arm is in a high level, the output voltage of the upper bridge arm is in a low level, and the following steps are obtained:
，
，
4) Fourth mode [ (]d 2 ’+d s )T, T]
The mode is the same as the second mode, the output voltages of the upper bridge arm and the lower bridge arm are all in low level, and the following steps are obtained:
，
。
3. the method of claim 2, wherein the ac component of the output voltage of the lower arm is applied to the low-side filter inductor to form an ac component, thereby the current of the lower armi 3 The fluctuation is slightly larger than the current of the upper bridge armi 1 。
4. The method for regulating and controlling a high-voltage high-capacity direct current transformer according to claim 2, wherein in the first mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is +.>。
5. The method for regulating and controlling a high-voltage high-capacity direct current transformer according to claim 2, wherein in the second mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is +.>。
6. According toThe method for regulating and controlling a high-voltage high-capacity direct-current transformer as claimed in claim 2, wherein in the third mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is +.>。
7. The method for regulating and controlling a high-voltage high-capacity direct current transformer according to claim 2, wherein in the fourth mode, the change rate of the inductance current of the bridge arm isThe change rate of the filter inductance current is +.>。
8. The method for regulating and controlling a high-voltage high-capacity direct-current transformer according to claim 2, wherein when the direct-current transformer adopts a quasi-two-level modulation based on a step wave in light load, the output side voltage is subjected to closed-loop control, and the difference value is used as a duty ratio by comparing the output side voltage value with a given reference value through a PI controllerd 1 Andd 2 is a given value, phase shift ratiod s Has a coupling relation with the duty ratio, and when all the submodules in a certain bridge arm are subjected to capacitance-voltage balance control, the phase shift ratio also needs to be adjustedd s The bridge arm energy balance is ensured, and the average value of the capacitance voltage of all the submodules is ensured to be kept constant; in order to perform energy balance control on the upper bridge arm and the lower bridge arm, the difference between the capacitance voltage average value of all the sub-modules of the upper bridge arm and the capacitance voltage average value of all the sub-modules of the lower bridge arm is selected to be used as a phase shift ratio through a low-pass filter and a PI regulatord s And sub-module energy balance control is implemented using capacitor voltage sequencing.
9. The method for regulating and controlling a high-voltage high-capacity direct current transformer according to claim 1, wherein the direct current transformer is a Buck type modularized multi-level direct current transformer.
10. A high voltage high capacity dc transformer regulation system for implementing the high voltage high capacity dc transformer regulation method of any one of claims 1 to 9.
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