CN115622376B - Cascade type energy storage converter system capable of inhibiting leakage current and control method - Google Patents

Cascade type energy storage converter system capable of inhibiting leakage current and control method Download PDF

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Publication number
CN115622376B
CN115622376B CN202211432187.3A CN202211432187A CN115622376B CN 115622376 B CN115622376 B CN 115622376B CN 202211432187 A CN202211432187 A CN 202211432187A CN 115622376 B CN115622376 B CN 115622376B
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switching tube
type
module
switching
bridge circuit
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CN115622376A (en
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刘亚涛
刘永奎
廖正军
曹立航
李江江
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Xi'an Singularity Energy Co ltd
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Xi'an Singularity Energy Co ltd
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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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/123—Suppression of common mode voltage or current
    • 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
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/79—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal 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
    • H02M7/797—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal 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
    • 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
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention discloses a cascade energy storage converter system capable of inhibiting leakage current and a control method thereof, belonging to the technical field of new energy storage, and comprising the following steps: the system comprises a type I DC/AC module topological system, a type II DC/AC module topological system and a type III DC/AC module topological system which are sequentially connected in series; the type I DC/AC module topology system comprises: a plurality of series connected type I DC/AC modules; the type II DC/AC module topology system comprises: a plurality of series connected type II DC/AC modules; the type III DC/AC module topology system comprises: a plurality of series connected type III DC/AC modules. According to the invention, under the traditional H-bridge topological structure, an additional switching tube and a matched inductance and capacitance are added, and the common-mode voltage change of a battery and a direct-current bus to the ground and the flow path of partial common-mode current are cut off through the cooperation of the tube with the S1 switching tube, the S2 switching tube, the S3 switching tube and the S4 switching tube, so that the overall leakage current level of the system is reduced.

Description

Cascade type energy storage converter system capable of inhibiting leakage current and control method
Technical Field
The invention relates to the technical field of new energy storage, in particular to a cascade energy storage converter system capable of inhibiting leakage current.
Background
The cascade energy storage PCS has the characteristic of high efficiency, but all power sub-modules must be insulated, and because of the large volume of the battery module, the battery module and a connecting cable thereof can introduce larger parasitic capacitance, so that common mode current paths exist among all power sub-modules of the PCS, and challenges are brought to practical engineering due to the requirement of the battery unit on ground insulation and the existence of common mode current in the system.
At present, the suppression of leakage current is carried out through HERIC topology, NPC topology and H6 topology in the traditional photovoltaic inverter industry, but the technical scheme cannot be applied to a cascade energy storage converter system due to the three-phase and non-cascade structural characteristics of the photovoltaic inverter. In addition, as the application time of the medium-high voltage cascade energy storage topology is short, no technical discussion on the aspect of targeted leakage current inhibition is currently seen. In recent two years, the medium-high voltage cascade energy storage system is applied on test points, but the problem is weakened by adopting the traditional optimized battery arrangement and structural design in specific product design, but the effect is limited in the mode, the occupied area is greatly increased, and the power density is reduced.
Disclosure of Invention
In one aspect, the present invention addresses the above-mentioned problems by providing a cascaded energy storage converter system with suppressed leakage current.
The invention adopts the technical scheme that: a cascaded energy storage converter system with suppressed leakage current, comprising: the system comprises a type I DC/AC module topological system, a type II DC/AC module topological system and a type III DC/AC module topological system which are sequentially connected in series;
the type I DC/AC module topology system comprises: a plurality of series connected type I DC/AC modules;
the type I DC/AC module comprises: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switch tube is connected between the positive electrode of the supporting capacitor and the positive direct current bus of the H bridge circuit of the H bridge, and the S6 switch tube is connected between the negative electrode of the supporting capacitor and the negative direct current bus of the H bridge circuit;
the type II DC/AC module topology system comprises: a plurality of series connected type II DC/AC modules;
the type II DC/AC module comprises: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switching tube and the S6 switching tube are connected between the positive electrode of the supporting capacitor and the positive direct current bus of the H bridge circuit, and the S5 switching tube and the S6 switching tube are connected in reverse series;
the type III DC/AC module topology system comprises: a plurality of series connected type III DC/AC modules;
the type III DC/AC module includes: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switching tube and the S6 switching tube are connected between the negative electrode of the supporting capacitor and the negative direct current bus of the H bridge circuit, and the S5 switching tube and the S6 switching tube are connected in reverse series.
Further, in the I-type DC/AC module, a collector electrode or an anti-parallel diode cathode of the S5 switching tube is connected with a positive output port of a battery pack and a positive electrode of a supporting capacitor, and an emitter electrode or an anode electrode of the anti-parallel diode of the S5 switching tube is connected with a positive direct current bus of an H bridge circuit;
the collector electrode or the cathode of the anti-parallel diode of the S6 switch tube is connected with the negative output port of the battery pack and the negative electrode of the supporting capacitor, and the emitter electrode or the anode of the anti-parallel diode of the S6 switch tube is connected with the negative direct current bus of the H bridge circuit.
Further, in the type ii DC/AC module, a collector or an anti-parallel diode cathode of the S5 switching tube is connected to an output port of the positive electrode of the battery pack, an emitter or an anti-parallel diode anode of the S5 switching tube is connected to an emitter or an anti-parallel diode anode of the S6 switching tube, and a collector or an anti-parallel diode cathode of the S6 switching tube is connected to a positive DC bus of the H bridge circuit.
Further, in the type iii DC/AC module, a collector or an anti-parallel diode cathode of the S5 switching tube is connected to a capacitance negative output port, and an emitter or an anti-parallel diode anode of the S5 switching tube is connected to an emitter or an anti-parallel diode anode of the S6 switching tube;
and the collector electrode of the S6 switching tube or the cathode of the anti-parallel diode is connected with a negative direct current bus of the H bridge circuit.
On the other hand, the scheme provides a method for inhibiting leakage current of a cascade energy storage converter system, wherein the method adopts a unipolar sectional control strategy:
in the H bridge circuit, two upper bridge arms are respectively an S1 switching tube and an S3 switching tube, and two lower bridge arms are respectively an S2 switching tube and an S4 switching tube; the alternating current positive electrode extraction point is positioned between the S1 switching tube and the S2 switching tube, and the alternating current negative electrode extraction point is positioned between the S3 switching tube and the S4 switching tube;
the connection relation of the I-type DC/AC module topology in the H bridge circuit is as follows:
the S5 switching tube is connected in series to the positive direct current bus, the collector electrode of the S5 switching tube is connected with the positive electrode of the battery, and the emitter electrode of the S5 switching tube is connected with the emitters of the S1 switching tube and the S3 switching tube;
the S6 switching tube is connected in series to the negative direct current bus, the collector of the S6 switching tube is connected with the negative electrode of the battery, and the emitter of the S6 switching tube is connected with the emitters of the S2 switching tube and the S4 switching tube;
in the discharging stage, the S6 switching tube is kept to be turned off, and the S1 switching tube, the S2 switching tube, the S3 switching tube, the S4 switching tube and the S5 switching tube are modulated;
and in the charging stage, the S5 switching tube is kept to be turned off, and the S1 switching tube, the S2 switching tube, the S3 switching tube, the S4 switching tube and the S6 switching tube are modulated.
Further, the following is described in terms of the type II DC/AC module topology:
the connection relation of the II type DC/AC module topology in the H bridge circuit is as follows:
the S5 switching tube and the S6 switching tube are connected in series on the positive direct current bus, and the S5 switching tube and the S6 switching tube are in a reverse connection mode;
specifically, a collector of an S5 switching tube is connected with a battery anode, an emitter of the S5 switching tube is connected with an emitter of an S6 switching tube, and a collector of the S6 switching tube is connected with emitters of an S1 switching tube and an S3 switching tube of the full-bridge module;
in the discharging stage, under the positive polarity of the modulated wave, the S1 switching tube is continuously conducted, the S4 switching tube and the S5 switching tube are kept on and off synchronously, and the on actions of the S4 switching tube and the S5 switching tube are judged by comparing the modulated wave with a carrier wave; specifically, a high level is output when the amplitude of the modulated wave is greater than the carrier wave, or a low level is output when the amplitude of the modulated wave is less than the carrier wave;
and under the negative polarity of the modulation wave, the S3 switching tube is continuously conducted, the S2 switching tube and the S5 switching tube are kept on and off synchronously, and the actions of the S2 switching tube and the S5 switching tube are judged by comparing the modulation wave with a carrier wave.
Furthermore, the connection relation of the III type DC/AC module topology in the H bridge circuit is as follows:
the S5 switching tube and the S6 switching tube are connected in series on the negative direct current bus, and the S5 switching tube and the S6 switching tube are in a reverse connection mode;
specifically, an emitter of an S5 switching tube is connected with a negative electrode of a battery, a collector of the S5 switching tube is connected with a collector of an S6 switching tube, and an emitter of the S6 switching tube is connected with collectors of an S2 switching tube and an S4 switching tube of the full-bridge module;
in the charging stage, under the positive polarity of the modulation wave, the S1 switching tube is continuously conducted, the S4 switching tube and the S6 switching tube are kept on and off synchronously, and the on actions of the S4 switching tube and the S6 switching tube are judged by comparing the modulation wave with a carrier wave;
and under the negative polarity of the modulation wave, the S3 switching tube is continuously conducted, the S2 switching tube and the S6 switching tube are kept on and off synchronously, and the switching actions of the S2 switching tube and the S6 switching tube are judged by comparing the modulation wave with a carrier wave.
The invention has the beneficial effects that:
under the traditional H bridge topological structure, an additional switching tube and a matched inductance and capacitance are added, the common mode voltage change of a battery and a direct current bus to the ground is reduced through the cooperation of the tube with an S1 switching tube, an S2 switching tube, an S3 switching tube and an S4 switching tube, and the circulation path of partial common mode current is cut off, so that the overall leakage current level of the system is reduced, and an energy storage system control and leakage current suppression modulation strategy matched with the optimized system structure and suitable for multi-level cascading is provided for the optimized system structure, so that the field operation index of equipment is integrally improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1a is a schematic diagram of a type I modified cascaded PCS control process in accordance with an embodiment of the present invention;
FIG. 1b is a schematic diagram of a type II modified cascaded PCS control process in accordance with an embodiment of the present invention;
FIG. 1c is a schematic diagram of a type III modified cascaded PCS control process in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of leakage current of a dual-sided arrangement of single-phase H-bridge inductors according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an S5 pulse blocking leakage circuit according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a type I DC/AC module system in accordance with an embodiment of the invention;
FIG. 5 is a schematic diagram of a type II DC/AC modular system in accordance with an embodiment of the present invention;
FIG. 6 is a schematic diagram of a type III DC/AC module system in accordance with an embodiment of the present invention;
FIG. 7 is a schematic diagram of carrier distribution of a two-module cascade system according to an embodiment of the invention;
FIG. 8 is a schematic diagram of a switch state of a modular cascading discharge process in accordance with an embodiment of the present invention;
FIG. 9 is a schematic diagram of the H-bridge port voltage and common and differential mode voltages for two modules according to an embodiment of the present invention;
fig. 10 is a schematic diagram of a single-phase full-bridge inverter topology with single-inductance filtering according to an embodiment of the invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
Referring to fig. 1a to 1c, a cascaded energy storage converter system with suppressed leakage current, comprising: the system comprises a type I DC/AC module topological system, a type II DC/AC module topological system and a type III DC/AC module topological system which are sequentially connected in series;
the type I DC/AC module topology system comprises: a plurality of series connected type I DC/AC modules;
the type I DC/AC module comprises: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switch tube is connected between the positive electrode of the supporting capacitor and the positive direct current bus of the H bridge circuit of the H bridge, and the S6 switch tube is connected between the negative electrode of the supporting capacitor and the negative direct current bus of the H bridge circuit;
the type II DC/AC module topology system comprises: a plurality of series connected type II DC/AC modules;
the type II DC/AC module comprises: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switching tube and the S6 switching tube are connected between the positive electrode of the supporting capacitor and the positive direct current bus of the H bridge circuit, and the S5 switching tube and the S6 switching tube are connected in reverse series;
the type III DC/AC module topology system comprises: a plurality of series connected type III DC/AC modules;
the type III DC/AC module includes: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switching tube and the S6 switching tube are connected between the negative electrode of the supporting capacitor and the negative direct current bus of the H bridge circuit, and the S5 switching tube and the S6 switching tube are connected in reverse series.
It should be noted that, under the existing control system and architecture, the invention aims to evolve 3 different DC/AC module topologies on the basic topology by slightly increasing the number of switches, and connect the evolved DC/AC modules in series to form a cascade energy storage converter system with leakage current inhibition capability, thereby reducing the problem of exceeding common mode leakage current of the system under the existing H-bridge cascade energy storage scheme and improving the field operation index of the equipment.
Referring to fig. 4, in an embodiment of the present invention, in the type i DC/AC module, a collector electrode or an anti-parallel diode cathode of the S5 switching tube is connected to a positive output port of a battery pack and a positive electrode of a supporting capacitor, and an emitter electrode or an anode electrode of the anti-parallel diode of the S5 switching tube is connected to a positive DC bus of an H bridge circuit;
the collector electrode or the cathode of the anti-parallel diode of the S6 switch tube is connected with the negative output port of the battery pack and the negative electrode of the supporting capacitor, and the emitter electrode or the anode of the anti-parallel diode of the S6 switch tube is connected with the negative direct current bus of the H bridge circuit.
Referring to fig. 5, in an embodiment of the present invention, in the type ii DC/AC module, a collector or an anti-parallel diode cathode of the S5 switching tube is connected to a positive output port of a battery pack, an emitter or an anti-parallel diode anode of the S5 switching tube is connected to an emitter or an anti-parallel diode anode of the S6 switching tube, and a collector or an anti-parallel diode cathode of the S6 switching tube is connected to a positive DC bus of an H bridge circuit.
Referring to fig. 6, in an embodiment of the present invention, in the type iii DC/AC module, a collector or an anti-parallel diode cathode of the S5 switching tube is connected to a negative output port of a capacitor, and an emitter or an anti-parallel diode anode of the S5 switching tube is connected to an emitter or an anti-parallel diode anode of the S6 switching tube;
and the collector electrode of the S6 switching tube or the cathode of the anti-parallel diode is connected with a negative direct current bus of the H bridge circuit.
Example two
It should be noted that, referring to fig. 10, the reason for affecting the leakage current is as follows;
in order to analyze the leakage current problem in the full-bridge cascade system, firstly, the common-mode voltage condition of the single-phase full-bridge inverter is analyzed:
Figure GDA0004150004450000071
from the above, u cm ＝u bn So that it has a common mode current I cm The method comprises the following steps:
Figure GDA0004150004450000072
wherein U is an Is the voltage at two ends of the left bridge arm S2 tube, U bn Is the voltage at two ends of the S4 tube of the right bridge arm, U L And U g U is inductance voltage and grid phase voltage cm Is common-mode voltage in the converter, C p Is equivalent parasitic capacitance.
In the above structure, u is due to the high frequency operation of the switching tube bn Will frequency hop between 0 and the battery voltage, thereby generating a larger common mode current.
How to eliminate leakage current:
the thought of this patent suppression leakage current is: the common-mode voltage of the common-mode voltage at different working conditions is ensured to be unchanged. In order to ensure that the common-mode voltage is unchanged in the follow current stage, the constructed combined switch tube is operated so as to cut off a charge-discharge loop of a common-mode capacitor.
According to the characteristics of the full-bridge module and the cascade system, the method is improved on the basis of the existing basic topology, a double-Buck-like circuit structure is constructed by adding 2 switching tubes on an H-bridge direct-current bus, and a pulse modulation mode is further expanded aiming at the structure.
Referring to fig. 2, an h-bridge module inductance bilateral arrangement
Voltage loop equation:
Figure GDA0004150004450000081
the method comprises the following steps:
Figure GDA0004150004450000082
consider u g For the power grid voltage, the frequency is relatively low, the influence of the power grid voltage on the common mode voltage is ignored, and the common mode voltage can be ensured to be:
Figure GDA0004150004450000083
the AC capacitance mainly solves EMC problem and is an optional configuration. The high-frequency electromagnetic interference problem can be ignored when the number of the cascade modules is large, the capacitor is not needed to be arranged at the moment, and the cascade modules are assembled according to the requirement of product specifications when the number of the cascade modules is small.
Additional switching devices are arranged on the direct current bus:
the switch with the increased part can cut off a common mode current loop under partial working conditions, and can solve the problem of overhigh switching frequency of the S2 switching tube and the S4 switching tube. After a new switching tube is introduced, the S2 switching tube and the S4 switching tube work in a power frequency state, thereby ensuring u an And u bn Is less frequent. The dual configuration of the newly added switching tube ensures the power bidirectional flow requirement.
The detailed analysis procedure was as follows:
referring to FIG. 3, for example, the common mode voltage is 0.5u in the S1, S4, S5 switching tube operating conditions bat The method comprises the steps of carrying out a first treatment on the surface of the When the S1 switching tube and the S3 switching tube are connected in parallel with the diode in working state, the common mode loop between the direct current bus and the battery/capacitor is ensured to be turned off by blocking the pulse of the S5 switching tube.
In order to adapt to the module cascade energy storage system, the improved design adopts a conventional cascade PCS control architecture, combines the leakage current suppression idea on the basis of carrier phase shift control, and optimally designs a module modulation link.
The control mode adopts the basic thought of unipolar modulation, and in the realization: the S1 switching tube and the S3 switching tube are ensured to operate at the power frequency switching frequency, the S2 switching tube, the S4 switching tube, the S5 switching tube and the S6 switching tube are ensured to alternately operate at the carrier switching frequency, and the switching frequency is basically equal to the switching frequency in the conventional multi-module cascading design. Compared with bipolar modulation and unipolar modulation applied to cascade topology, the switching efficiency is higher in the modulation mode.
The method adopts unipolar sectional control in control realization, for example, an S1 switching tube is continuously conducted under the positive polarity of a modulation wave, and an S4 switching tube and an S5 switching tube are kept on and off synchronously; under the negative polarity of the modulation wave, the S3 switching tube is continuously conducted, and the S2 switching tube and the S5 switching tube are kept on and off synchronously.
In the discharging stage, the S6 switching tube is kept to be turned off, and the S1 switching tube, the S2 switching tube, the S3 switching tube, the S4 switching tube and the S5 switching tube are modulated;
under the positive polarity of the modulated wave, the S1 switching tube is continuously conducted, the S4 switching tube and the S5 switching tube are kept on and off synchronously, and the on-state actions of the S4 switching tube and the S5 switching tube are judged by comparing the modulated wave with a carrier wave; specifically, a high level is output when the amplitude of the modulated wave is greater than the carrier wave, or a low level is output when the amplitude of the modulated wave is less than the carrier wave;
and under the negative polarity of the modulation wave, the S3 switching tube is continuously conducted, the S2 switching tube and the S5 switching tube are kept on and off synchronously, and the actions of the S2 switching tube and the S5 switching tube are judged by comparing the modulation wave with a carrier wave.
And in the charging stage, the S5 switching tube is kept to be turned off, and the S1 switching tube, the S2 switching tube, the S3 switching tube, the S4 switching tube and the S6 switching tube are modulated.
Under the positive polarity of the modulated wave, the S1 switching tube is continuously conducted, the S4 switching tube and the S6 switching tube are kept on and off synchronously, and the on actions of the S4 switching tube and the S6 switching tube are judged by comparing the modulated wave with a carrier wave;
and under the negative polarity of the modulation wave, the S3 switching tube is continuously conducted, the S2 switching tube and the S6 switching tube are kept on and off synchronously, and the switching actions of the S2 switching tube and the S6 switching tube are judged by comparing the modulation wave with a carrier wave.
Referring to fig. 7, (1) when unipolar modulation is used, it is assumed that the equivalent switching frequency requirement of the cascaded PCS system is f ceq Setting the triangular carrier frequency as f if the number of single-phase cascade modules is N c ＝f ceq The carrier lag time between adjacent modules is: Δt=1/(f×n);
(2) When unipolar frequency doubling modulation is adopted, the equivalent switching frequency requirement of the cascaded PCS system is assumed to be f ceq Setting the triangular carrier frequency as f if the number of single-phase cascade modules is N c ＝f ceq The carrier lag time between adjacent modules is: Δt=1/(2×f×n).
The method for generating the triangular carrier wave specifically comprises the following steps:
each phase of N modules generates 2N triangular carriers, wherein the 2N triangular carriers comprise N positive triangular carriers and N negative triangular carriers, and the carrier amplitude is 1. Each module corresponds to a positive carrier and a negative carrier, which are 180 ° different and symmetrically distributed on two sides of the X-axis, for example, unipolar modulation, and the carrier distribution of the two-module system is shown in fig. 7:
after the triangular carrier is realized, amplitude comparison is carried out on the modulated wave and the triangular wave, and control pulses are generated according to the magnitude relation of the modulated wave and the triangular wave. Wherein the modulated wave is generated for upper layer control.
To further illustrate the common mode current suppression and pulse modulation process, the modulation and pulse generation process (where the S1 and S6 switching transistors are turned off) is described with a 2-module cascade system discharge as an example.
Referring to fig. 8-9, S11, S12, S13, S14, S15, and S16 (s16=s26=0) respectively correspond to the S1 switching tube, the S2 switching tube, the S3 switching tube, the S4 switching tube, the S5 switching tube, and the S6 switching tube of the 1 st module in the cascade system. Wherein V is cr1+ And V cr2+ Is a forward modulation wave of the modules 1, 2, V cr1- And V cr2- Is a reverse modulated wave of modules 1, 2, where V cr1+ And V is equal to cr1- The phase difference is 180 degrees and symmetrically distributed at two sides of the X axis, V cr2+ And V is equal to cr2- 180 DEG different, symmetrically distributed on two sides of X axis, V cr1+ And V is equal to cr2+ The lateral phase difference is 180 deg. on the X-axis (carrier delay Δt under multiple modules). Modulated wave V m And triangular carrier V cr1+ And V cr1- Comparing the modulated pulse signals of S11 to S15 to generate a modulated wave V m And triangular carrier V cr2+ And V cr2- Comparing and generating the modulation pulse signals of S21 to S25, wherein the pulse generation process of S11 to S15 is as follows:
the positive half cycle S11 of the modulated wave remains on and S12 remains off. At the same time when V m ＞V cr1+ When the method is used, S14 and S15 are switched on, and S13 is switched off; when modulating wave V m ＜V cr1+ At this time, S14 and S15 are turned off, and S13 is turned on.
The negative half cycle S13 of the modulated wave remains on and S14 remains off. At the same time when V m ＜V cr1- When the method is used, S12 and S15 are switched on, and S11 is switched off; when Vm > V cr1- When the method is used, S12 and S15 are turned off, and S11 is turned on;
in the charging process, the S5 switching tube is kept off, and similar logic judgment is adopted to calculate the switching actions of S11, S12, S13, S14 and S16.
When n unit modules are cascaded, the voltages at two ends of the parasitic capacitance are the same as those of the single module during operation, and are the sum of the voltages at two ends of the parasitic capacitance in the high-frequency equivalent model and the voltages at two ends of the parasitic capacitance in the low-frequency equivalent model. By optimizing the modulation scheme, the voltage across the parasitic capacitor is constant at-u bat /2。
In order to meet the charging condition of the energy storage system, the method constructs an additional S6 switching tube, the working process and the common mode voltage analysis process of the additional S6 switching tube are similar to those described above, and the single-module structure is shown in fig. 4.
Analyzing the operation mode of the S6 switch tube, the II type and III type DC/AC module structures can be evolved, see fig. 5 and 6.
The added S6 switching tube action logic is determined by the power direction, when the power direction is the charging direction, the S6 switching tube carries out switching action, and the switching tube keeps an off state in the discharging process; and when the discharging direction is the discharging direction, the S5 switching tube performs switching action, and the off state is kept in the charging process. The S5 switching tube and the S6 switching tube have the same operation logic in the I, II and III type DC/AC module systems.
Example III
The reverse push procedure of the method is used for supporting the conclusion of the method of the invention:
the recursion process realized by the method comprises the following steps:
according to the column write voltage loop equation of fig. 10:
Figure GDA0004150004450000121
obtaining:
Figure GDA0004150004450000122
when single-inductance filtering is adopted, the common-mode voltage cannot be ensured to be constant due to the limitation of a topological structure, and the single-polarity modulation or the bipolar modulation cannot be ensured;
and carrying out bilateral symmetrical distribution on the inductors to construct a second inductor loop, wherein the unilateral inductor is set to be L/2.
According to the column write voltage loop equation of fig. 4:
Figure GDA0004150004450000123
the method comprises the following steps:
Figure GDA0004150004450000124
consider u g The frequency is relatively low for the grid voltage, so its effect on the common mode voltage is ignored:
Figure GDA0004150004450000125
Figure GDA0004150004450000126
in a conventional H-bridge topology, when unipolar modulation is employed, there are 3 modes in the positive half-cycle of the grid voltage: (common mode voltage condition under conventional topology)
When S1 is on and S4 is off, and current flows through S3 parallel diodes, u cm ＝0.5(u an +u bn )＝u bat Wherein u is bat Is the battery voltage;
when S1, S4 are on, the common mode voltage u cm ＝0.5(u an +u bn )＝0.5u bat ；
When S4 is on, current flows through S2 parallel diodes, u cm ＝0.5(u an +u bn )＝0；
Common-mode voltage is 0, 0.5u bat 、u bat And the excitation generates a common mode current.
In a conventional H-bridge topology, when bipolar modulation is employed, there are 2 modes:
when S1 and S4 are on and S2 and S3 are off, u cm ＝0.5u bat ；
When S1 and S4 are turned off and S2 and S3 are turned on, u cm ＝0.5u bat ；
It can be seen that by adding inductance to the original circuit (fig. 3) and matching the proper modulation scheme, the common mode voltage remains unchanged, and the common mode current can be effectively suppressed. However, the bipolar modulation mode requires that 4 switching tubes all operate under high switching frequency, so that switching loss is large, the invention further evolves and optimizes a circuit structure and a control mode, and designs a 1-type cascade system topology by adding matched port inductance and capacitance to a mature topology structure and assisting in a proper modulation mode, and a single-phase system connection diagram is shown in fig. 5.
Under the topology and unipolar control modes mentioned in the scheme, taking discharging as an example, 4 working modes exist, and the common mode voltages corresponding to the modules are respectively:
working mode 1, switching tubes 1, 4, 5 are turned on 2, 3 are turned off, u cm ＝0.5u bat ；
The working mode 2, the switching tube 1 is conducted, the switching tubes 2, 3, 4 and 5 are turned off, the current flows through the 3-tube freewheeling diode, at the moment, the parasitic capacitor cannot form a charge-discharge loop, the capacitor voltage is approximately considered to keep the previous mode unchanged, and u cm ＝0.5u bat ；
Working mode 3, switching tubes 2, 3, 5 are on, 1, 4 are off, u cm ＝0.5u bat ；
In the working mode 4, the switching tube 3 is continuously turned on, the 1, 2, 4 and 5 are turned off, the current flows through the 1-tube parallel diode, at the moment, the parasitic capacitor cannot form a charge-discharge loop, the capacitor voltage is approximately considered to keep the previous mode unchanged, and u cm ＝0.5u bat ；
By comparing the above, the topology and control method described in the patent can inhibit common-mode voltage and further reduce common-mode current.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims (7)

1. A cascaded energy storage converter system with suppressed leakage current, comprising: the system comprises a type I DC/AC module topological system, a type II DC/AC module topological system and a type III DC/AC module topological system which are sequentially connected in series;
the type I DC/AC module topology system comprises: a plurality of series connected type I DC/AC modules;
the type I DC/AC module comprises: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switching tube is connected between the positive electrode of the supporting capacitor and the positive direct current bus of the H bridge circuit, and the S6 switching tube is connected between the negative electrode of the supporting capacitor and the negative direct current bus of the H bridge circuit;
the type II DC/AC module topology system comprises: a plurality of series connected type II DC/AC modules;
the type II DC/AC module comprises: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switching tube and the S6 switching tube are connected between the positive electrode of the supporting capacitor and the positive direct current bus of the H bridge circuit, and the S5 switching tube and the S6 switching tube are connected in reverse series;
the type III DC/AC module topology system comprises: a plurality of series connected type III DC/AC modules;
the type III DC/AC module includes: the switching circuit comprises an H bridge circuit, an S5 switching tube and an S6 switching tube;
the S5 switching tube and the S6 switching tube are connected between the negative electrode of the supporting capacitor and the negative direct current bus of the H bridge circuit, and the S5 switching tube and the S6 switching tube are connected in reverse series.
2. The cascading energy-storage converter system with suppressed leakage current according to claim 1, wherein in the type i DC/AC module, the collector or anti-parallel diode cathode of the S5 switching tube is connected with the battery pack positive output port, the support capacitor positive electrode, and the emitter or anti-parallel diode anode of the S5 switching tube is connected with the positive DC bus of the H-bridge circuit;
the collector electrode or the cathode of the anti-parallel diode of the S6 switch tube is connected with the negative output port of the battery pack and the negative electrode of the supporting capacitor, and the emitter electrode or the anode of the anti-parallel diode of the S6 switch tube is connected with the negative direct current bus of the H bridge circuit.
3. The cascading energy-storage converter system with suppressed leakage current according to claim 1, wherein in the type ii DC/AC module, the collector or anti-parallel diode cathode of the S5 switching tube is connected to the battery pack positive output port, the emitter or anti-parallel diode anode of the S5 switching tube is connected to the emitter or anti-parallel diode anode of the S6 switching tube, and the collector or anti-parallel diode cathode of the S6 switching tube is connected to the positive DC bus of the H bridge circuit.
4. The cascading energy-storage converter system with suppressed leakage current according to claim 1, wherein in the type iii DC/AC module, the collector or anti-parallel diode cathode of the S5 switching tube is connected with a capacitive negative output port, and the emitter or anti-parallel diode anode of the S5 switching tube is connected with the emitter or anti-parallel diode anode of the S6 switching tube;
and the collector electrode of the S6 switching tube or the cathode of the anti-parallel diode is connected with a negative direct current bus of the H bridge circuit.
5. A method for suppressing leakage current of a cascaded energy storage converter system, characterized in that the system of any one of claims 1-4 is adopted to suppress leakage current of the cascaded energy storage converter system, and a unipolar sectional control strategy is adopted in the method:
in the H bridge circuit, two upper bridge arms are respectively an S1 switching tube and an S3 switching tube, and two lower bridge arms are respectively an S2 switching tube and an S4 switching tube; the alternating current positive electrode extraction point is positioned between the S1 switching tube and the S2 switching tube, and the alternating current negative electrode extraction point is positioned between the S3 switching tube and the S4 switching tube;
in the discharging stage, the S6 switching tube is kept to be turned off, and the S1 switching tube, the S2 switching tube, the S3 switching tube, the S4 switching tube and the S5 switching tube are modulated;
and in the charging stage, the S5 switching tube is kept to be turned off, and the S1 switching tube, the S2 switching tube, the S3 switching tube, the S4 switching tube and the S6 switching tube are modulated.
6. A method of suppressing leakage current in a cascaded energy storage converter system as defined in claim 5, wherein,
in the discharging stage, under the positive polarity of the modulated wave, the S1 switching tube is continuously conducted, the S4 switching tube and the S5 switching tube are kept on and off synchronously, and the on actions of the S4 switching tube and the S5 switching tube are judged by comparing the modulated wave with a carrier wave; specifically, a high level is output when the amplitude of the modulated wave is greater than the carrier wave, or a low level is output when the amplitude of the modulated wave is less than the carrier wave;
and under the negative polarity of the modulation wave, the S3 switching tube is continuously conducted, the S2 switching tube and the S5 switching tube are kept on and off synchronously, and the actions of the S2 switching tube and the S5 switching tube are judged by comparing the modulation wave with a carrier wave.
7. A method of suppressing leakage current in a cascaded energy storage converter system as defined in claim 5, wherein,
in the charging stage, under the positive polarity of the modulation wave, the S1 switching tube is continuously conducted, the S4 switching tube and the S6 switching tube are kept on and off synchronously, and the on actions of the S4 switching tube and the S6 switching tube are judged by comparing the modulation wave with a carrier wave;
and under the negative polarity of the modulation wave, the S3 switching tube is continuously conducted, the S2 switching tube and the S6 switching tube are kept on and off synchronously, and the switching actions of the S2 switching tube and the S6 switching tube are judged by comparing the modulation wave with a carrier wave.
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