CN112838769A - Transformer-isolation-free star-connection medium-high voltage variable frequency speed regulation system and control method - Google Patents

Transformer-isolation-free star-connection medium-high voltage variable frequency speed regulation system and control method Download PDF

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CN112838769A
CN112838769A CN202110249091.2A CN202110249091A CN112838769A CN 112838769 A CN112838769 A CN 112838769A CN 202110249091 A CN202110249091 A CN 202110249091A CN 112838769 A CN112838769 A CN 112838769A
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phase
pwm
signal
voltage
output
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王聪
程红
赵志浩
杨道宽
徐正
于龙飞
袁巍
陶艳梅
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China University of Mining and Technology Beijing CUMTB
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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
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without 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
    • H02M7/217—Conversion of ac power input into dc power output without 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
    • H02M7/219—Conversion of ac power input into dc power output without 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 in a bridge configuration
    • 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
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • 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
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/49—Combination of the output voltage waveforms of a plurality of converters
    • 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
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without 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
    • H02M7/537—Conversion of dc power input into ac power output without 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, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without 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, e.g. single switched pulse inverters in a bridge configuration
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/16—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring
    • H02P25/18—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring with arrangements for switching the windings, e.g. with mechanical switches or relays
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
    • H02P27/085—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention relates to a transformer-isolated star-connected medium-high voltage variable frequency speed control system and a control method, belonging to medium-high voltage variable frequency speed control technology and control technology thereof, the technology cancels a power frequency transformer used by the traditional medium-high voltage frequency converter and a high-frequency isolation DC/DC conversion link in a new generation of medium-high voltage frequency converter based on a non-power frequency transformer cascade multilevel converter, each phase of cascade multilevel rectifier in the scheme forms a pair of common medium-high voltage DC buses which can be directly connected with a diode clamping type or capacitance clamping type inverter circuit, and less hardware is added in a rectifier stage, so that the inverter stage and a three-phase stator winding of an alternating current motor can be directly connected in a star shape without isolation, the volume and the weight of the frequency converter are greatly reduced, the system structure and the control complexity of the medium-high voltage frequency converter and the loss in the operation process are greatly reduced, meanwhile, the system reliability and the overall efficiency are greatly improved, and the method is particularly suitable for the field of medium-high voltage high-power variable frequency speed regulation.

Description

Transformer-isolation-free star-connection medium-high voltage variable frequency speed regulation system and control method
Technical Field
The invention belongs to the technical field of medium-high voltage variable frequency speed regulation, and particularly relates to a medium-high voltage variable frequency speed regulation system formed by organically fusing a star-connected high-power cascade multilevel converter without an isolation transformer and an alternating current motor and a control method.
Background
In recent years, "Multilevel Converter" has been used more and more successfully in the fields of medium-high voltage high-power frequency conversion speed regulation, active power filtering, High Voltage Direct Current (HVDC) transmission, reactive power compensation of power systems, and the like. The basic circuit topology of the multilevel converter can be roughly divided into two types, namely a clamping type and a unit cascade type, for example, diode clamping type three-level medium-high voltage frequency converter manufactured by siemens corporation or ABB corporation, which is widely used in industry at present, and a cascade H-bridge medium-high voltage frequency converter manufactured by robinko corporation or rituximab corporation are typical representatives of the two types of products. In any of the two types of high-voltage frequency converters, in order to implement high-power conversion of high voltage by using low-voltage-resistant power electronic devices, a power frequency phase-shifting transformer with large volume, complex wiring and high price is required to be used at the input side of the rectifier to realize electrical isolation, so that the application of the high-voltage frequency converter in many industrial occasions is limited.
The cascaded multilevel converter without the power frequency transformer has attracted much attention in the power electronic technology field in recent years, and is considered as an implementation scheme of a new generation of medium-high voltage frequency converter. The converter uses a high-frequency transformer to replace a power frequency phase-shifting transformer in the traditional cascade converter to realize electrical isolation, and when the high-frequency isolation bidirectional DC/DC converter is used for bidirectional power transmission, the middle stage adopts the high-frequency isolation bidirectional DC/DC converter to bidirectionally transmit energy. And two sides or a high-voltage side adopt a cascaded fully-controlled H-bridge multi-level power converter structure. When the power converter is used for unidirectional power transmission, the middle stage adopts a high-frequency isolation unidirectional DC/DC converter to transmit energy, the rectification side adopts a unidirectional cascade type multi-level power converter structure (comprising a cascade diode + Boost rectification circuit, a cascade bridgeless rectification circuit, a cascade VIENNA rectification circuit and the like), and the inversion side adopts a cascade type multi-level power converter structure (of a clamping type or a unit cascade type). Compared with the traditional medium-high voltage frequency converter, the implementation scheme of the medium-high voltage frequency converter in the new generation can effectively reduce the volume, the weight and the manufacturing cost of the system. However, such converters also have significant drawbacks, mainly represented by: the DC/DC conversion stage formed by the high-frequency isolation transformer makes the whole system have a complex structure, increases the loss in the operation process, and the existence of the link is a key factor for preventing the whole system from further reducing the cost, improving the efficiency, reducing the volume and weight and improving the reliability. Obviously, the elimination of the high-frequency isolation DC/DC conversion link in the high-voltage inverter in the new generation will bring great benefits to the application of the inverter in the actual industry. However, the high-frequency isolation DC/DC conversion link is necessary for the high-voltage inverter in this new generation because: 1) each phase of N cascade modules can generate N groups of direct current output ends, and the N groups of direct current output ends cannot be directly connected in series to form a pair of common direct current output buses, but a clamping type inverter circuit, whether the clamping type inverter circuit is a diode clamping type or a capacitor clamping type, needs to be supplied with power by one common direct current bus, so the N groups of direct current output ends cannot be directly connected with the clamping type inverter circuit, a cascade inverter circuit formed by N H-bridge circuits needs to be supplied with power by N isolated independent direct current power supplies, the N groups of direct current output ends are not isolated independent N groups of direct current power supplies, and therefore cannot be directly connected with the cascade H-bridge inverter circuit, otherwise, a plurality of short circuits of the circuit can be caused; 2) the three-phase cascade rectifier also has no common direct current output bus, if a high-frequency isolation DC/DC conversion link is not available, the cascade three-phase inverter is directly connected with a star-connected or angle-connected alternating current motor stator winding, and a plurality of short circuits of the system can be caused, so that the whole system can not work normally.
In addition, in a clamping type inverter circuit powered by an independent direct current power supply, compared with a capacitance clamping type circuit, the diode clamping type multi-level inverter circuit is widely applied to various industrial fields due to the fact that a plurality of capacitors are not needed, the structure is simple, the reliability is high, and the control is convenient. However, the equalization control of the capacitance and voltage of the input side of the diode clamping type multi-level inverter circuit is difficult to realize by itself, and theories prove that the diode clamping type multi-level inverter circuit is finally degenerated into a three-level inverter circuit due to the unbalanced capacitance and voltage of the input side without adopting a special control strategy, which is why only the diode clamping type three-level inverter circuit is successfully applied in the industry at present.
Disclosure of Invention
In order to solve the problems, the invention provides a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system, which cancels a high-frequency isolation DC/DC conversion link in a new generation of medium-high voltage frequency converter based on a power-frequency-free transformer cascade multi-level converter, is different from the traditional high-frequency converter which uses a power-frequency transformer to realize electrical isolation, and is also different from the new generation of medium-high voltage frequency converter which uses a high-frequency transformer to realize electrical isolation; 2) the inverter stage of the star-connected medium-high voltage variable frequency speed control system can be directly connected with the three-phase stator winding of the alternating current motor in a star shape, so that the size, weight and cost of the medium-high voltage frequency converter based on the cascade multilevel converter of the non-power frequency transformer are greatly reduced, the system efficiency is greatly improved, and the direct current voltage utilization rate is also improved.
In order to achieve the above object, the transformer-free isolated satellite-based medium-high voltage variable frequency speed control system provided by the invention is characterized by comprising three high-frequency filters and a three-phase cross-direct-alternating current converter circuit, wherein the three-phase cross-direct-alternating current converter circuit comprises three single-phase cross-direct-alternating current converter circuits, each single-phase cross-direct-alternating current converter circuit comprises a single-phase rectification stage circuit, each single-phase rectification stage circuit comprises a five-level cascade rectifier unit, each single-phase rectification stage circuit provides a pair of common medium-high voltage output direct current buses, each single-phase cross-direct-alternating current converter circuit comprises a single-phase inversion stage circuit, each single-phase inversion stage circuit comprises a five-level cascade inverter unit, and the direct current input end of each five-level cascade inverter unit is directly connected with the pair of common medium-high voltage output direct current buses provided by the single-phase rectification stage circuit The single-phase rectifier stage circuit of the single-phase cross-direct-alternating current converter circuit is provided with two alternating current input ends, the three single-phase rectifier stage circuits of the single-phase cross-direct-alternating current converter circuit have six alternating current input ends, the first alternating current input ends of the single-phase rectifier stage circuits of the three single-phase cross-direct-alternating current converter circuits form a group of wiring ends, the second alternating current input ends of the single-phase rectifier stage circuits of the three single-phase cross-direct-alternating current converter circuits form another group of wiring ends, one group of wiring ends are connected to a common neutral point, and the other group of wiring ends are respectively connected with the three high-frequency filters in series to be connected into a three-phase power grid to form star connection.
In order to achieve the above object, the present invention provides a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system, wherein the single-phase rectifier circuit in the single-phase cross-dc-ac converter circuit comprises a single-phase diode rectifier bridge, two boost inductors L1、L2Four switching devices S1、S2、S3、S4Four fast recovery diodes D1、D2、D3、D4Two common inductors L3、L4Two DC capacitors C1、C2And four output DCContainer C3、C4、C5、C6Said switching device S1And said dc capacitor C1Is connected to the DC capacitor C1And the other end of the diode and the fast recovery diode D1Is connected to the anode of the fast recovery diode D1And the output DC capacitor C3Is connected to the first terminal (m), said switching device S1And said switching device S2And said fast recovery diode D2Is connected to the anode of the fast recovery diode D2And the common inductor L3And said output DC capacitor C4Is connected to the first terminal (m), the common inductance L3And the other end of the diode and the fast recovery diode D1Is connected with the anode of the output direct current capacitor C3And said output dc capacitor C4Is connected to the first terminal (m), said switching device S2And said switching device S3And said output dc capacitor C5Is connected to the first terminal (m), the output dc capacitor C4And said output dc capacitor C5Is connected to the first terminal (m), said switching device S3And said switching device S4And said fast recovery diode D3Is connected to the cathode of the fast recovery diode D3And the output direct current capacitor C5And said output dc capacitor C6Is connected to the first terminal (m), said switching device S4And said dc capacitor C2And the boost inductor L2Is connected to the other end of the voltage boosting inductor L2The other end of the DC capacitor C is connected with the negative end of the rectification output of the single-phase diode rectifier bridge, and the DC capacitor C2And the other end of the common inductor L4And the fast recovery diode D4Is connected to the cathode of the common inductor L4The other end of (2) and the fast recovery twoPolar tube D3Is connected to the anode of the fast recovery diode D4And the output direct current capacitor C6Is connected to the second terminal (n), said switching device S1With said boost inductor L1Is connected to the other end of the voltage boosting inductor L1And the other end of the single-phase diode rectifier bridge is connected with the positive end of the rectification output of the single-phase diode rectifier bridge.
In order to achieve the above object, the present invention provides a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system, wherein the single-phase rectifier circuit in the single-phase cross-dc-ac converter circuit comprises a single-phase diode rectifier bridge, two boost inductors L1、L2Four switching devices S1、S2、S3、S4Four fast recovery diodes D1、D2、D3、D4Two flying capacitors C1、C2And two output DC capacitors C3、C4Said switching device S1And the fast recovery diode D1Is connected to the anode of the fast recovery diode D1And the fast recovery diode D2Is connected to the anode of the fast recovery diode D2And the output DC capacitor C3Is connected to the first terminal (m), the output dc capacitor C3And said output dc capacitor C4Is connected to the first terminal (m), said switching device S1And said switching device S2And said flying capacitor C1Is connected to the first terminal (e), said flying capacitor C1And said fast recovery diode D2Is connected to the anode of the switching device S2And said switching device S3And said output dc capacitor C4Is connected to the first terminal (m), said switching device S3And said switching device S4And said flying capacitor C2Is connected to the first terminal (e), said flyAcross the capacitance C2And said fast recovery diode D3And the fast recovery diode D4Is connected to the cathode of the fast recovery diode D4And the output direct current capacitor C4Is connected to the second terminal (n), said switching device S4And said fast recovery diode D3And the boost inductor L2Is connected to the other end of the voltage boosting inductor L2Is connected with the negative end of the rectification output of the single-phase diode rectifier bridge, and the switching device S1With said boost inductor L1Is connected to the other end of the voltage boosting inductor L1And the other end of the single-phase diode rectifier bridge is connected with the positive end of the rectification output of the single-phase diode rectifier bridge.
In order to achieve the above object, the transformer-isolated star-connected medium-high voltage variable frequency speed control system provided by the present invention is characterized by comprising a three-phase ac motor, wherein six ac output ends are provided for the five-level cascaded inverter units in the three single-phase ac-dc converter circuits, a first ac output end of the five-level cascaded inverter units in the three single-phase ac-dc converter circuits forms a group of terminals, a second ac output end of the five-level cascaded inverter units in the three single-phase ac-dc converter circuits forms another group of terminals, one group of terminals is connected to a common neutral point, and the other group of terminals is connected to stator windings of the three-phase ac motor to form a star connection.
In order to achieve the aim, the invention provides a control method of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system, which is characterized by comprising the following control steps:
(1) sampling the total voltage of each phase of rectification stage DC side in the three-phase AC-DC-AC converter circuit to obtain 3 total voltage signals U of DC sideA、UB、UCThen, sampling N (N is 2 or 4) cascaded module voltages of each phase of rectification stage to obtain 3N module voltage signals UA1、UA2、...UAN，UB1、UB2、...UBN，UC1、UC2、...UCNCalculating 3 total voltage signals U at DC side by using the following formulaA、UB、UCAverage value of Uo：
Figure BDA0002965255760000031
(2) Mixing U in the step (1)oWith a given signal U of DC voltageo *After comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signal d3 DC side total voltage signals U in the step (1)A、UB、UCRespectively associated with a given signal U of DC voltageo *After comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldA、IdB、IdC；
(3) Calculating the module voltage signal U in step (1) by using the following formulaA1、UA2、...UANAverage value of UAeVoltage signal U of moduleB1、UB2、...UBNAverage value of UBeVoltage signal U of moduleC1、UC2、...UCNAverage value of UCe：
Figure BDA0002965255760000032
(4) The module voltage signal U in the step (1) is processedA1、UA2、...UANRespectively comparing the voltage signals with the module voltage signal U in the step (3)A1、UA2、...UANAverage value of UAeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldA1、IdA2、...IdANThe module voltage signal U in the step (1) is processedB1、UB2、...UBNRespectively comparing the voltage signals with the module voltage signal U in the step (3)B1、UB2、...UBNAverage value of UBeAfter comparison, the signals are sent to a PI voltage regulator to obtain a DC/DC converterAmplitude of the current signal IdB1、IdB2、...IdBNThe module voltage signal U in the step (1) is processedC1、UC2、...UCNRespectively comparing the voltage signals with the module voltage signal U in the step (3)C1、UC2、...UCNAverage value of UCeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldC1、IdC2、...IdCN；
(5) The amplitude I of the direct current signal in the step (2) is measureddAnd IdAAdding the added value and the amplitude I of the direct current signal in the step (4)dA1、IdA2、...IdANRespectively added to obtain the given signal amplitude I of the direct currentdA1 *、IdA2 *、...IdAN *The amplitude I of the DC current signal in the step (2)dAnd IdBAdding the added value and the amplitude I of the direct current signal in the step (4)dB1、IdB2、...IdBNRespectively added to obtain the given signal amplitude I of the direct currentdB1 *、IdB2 *、...IdBN *The amplitude I of the DC current signal in the step (2)dAnd IdCAdding the added value and the amplitude I of the direct current signal in the step (4)dC1、IdC2、...IdCNRespectively added to obtain the given signal amplitude I of the direct currentdC1 *、IdC2 *、...IdCN *；
(6) Setting the signal amplitude I to the direct current in the step (5)dA1 *、IdA2 *、...IdAN *Multiplying the sine signal with the same Phase as the A-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate an A-Phase alternating current given signal idA1 *、idA2 *、...idAN *Setting the DC current in the step (5) to be a signal amplitude IdB1 *、IdB2 *、...IdBN *And using Phase-Locked loop PLL (Phase-Locked loop)Multiplying the obtained sine signals with the same phase as the voltage of the B-phase power grid to generate a B-phase alternating current given signal idB1 *、idB2 *、...idBN *Setting the DC current in the step (5) to be a signal amplitude IdC1 *、IdC2 *、...IdCN *Multiplying the sine signal with the same Phase as the C-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate a C-Phase alternating current given signal idC1 *、idC2 *、...idCN *；
(7) Sampling three-phase actual current of a three-phase AC-DC-AC converter circuit to obtain three actual AC current signals iA、iB、iCGiving the A alternating current in the step (6) to a signal idA1 *、idA2 *、...idAN *Respectively with the actual AC current signal iAAfter comparison, sending the signal into a PI current regulator to obtain an A-phase PWM modulation wave signal gA1、gA2、...gAN(ii) a Giving a signal i to the B alternating current in the step (6)dB1 *、idB2 *、...idBN *Respectively with the actual AC current signal iBAfter comparison, sending the signals into a PI current regulator to obtain a B-phase PWM modulation wave signal gB1、gB2、...gBNGiving the C alternating current in the step (6) to a signal idC1 *、idC2 *、...idCN *Respectively with the actual AC current signal iCAfter comparison, sending the signal into a PI current regulator to obtain a C-phase PWM modulation wave signal gC1、gC2、...gCN；
(8) The A-phase PWM modulation wave signal g in the step (7) is processedA1、gA2、...gANWith N successive lags TS1The triangular carrier signals of the/N are compared to obtain PWM signals of the A-phase power switching device of the rectifier stage and B-phase PWM modulation wave signals gB1、gB2、...gBNAnd C-phase PWM modulated wave signal gC1、gC2、...gCNRespectively comparing with the triangular carrier signals same as A phase to obtain PWM signals T of B phase and C phase power switch devices of the rectifier stageS1The period of the triangular carrier signals is, the N different triangular carrier signals have the same frequency and amplitude and are symmetrically distributed on two sides of a time axis;
(9) the three-phase sinusoidal reference voltage signal of the inverter stage of the three-phase AC-DC-AC converter circuit is given by:
Figure BDA0002965255760000041
in the formula V*For pulse-width modulation of the command voltage signal amplitude, va *、vb *、vc *Is a three-phase sinusoidal reference voltage signal, omega is V*Rotational angular velocity of (a);
(10) the peak value of the sine voltage to be inverted by each phase of inverting stage circuit is set as VacLet us order
Figure BDA0002965255760000042
When g is less than or equal to 1, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure BDA0002965255760000043
(11) when g is>1 time, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Respectively as follows:
Figure BDA0002965255760000044
Figure BDA0002965255760000051
Figure BDA0002965255760000052
(12) because each phase inverter circuit adopts a five-level cascade inverter unit, four different triangular carrier signals are needed, the different triangular carrier signals have the same frequency and amplitude and are continuously and vertically distributed in space and symmetrically distributed on two sides of a time axis, the phases of the four different triangular carrier signals sequentially differ by 180 degrees, and the period of the different triangular carrier signals is Ts2Amplitude of is
Figure BDA0002965255760000053
In the formula VmPWM modulating signal v for each phase of inverse conversion stage circuit in step (10) and step (11)am *、vbm *、vcm *The amplitude of (d);
(13) PWM modulating signal v of each phase of inverse conversion stage circuit in the step (10) and the step (11)am *、vbm *、vcm *Comparing with the four triangular carrier signals in the step (12) to obtain a PWM signal of a first bridge arm of the inverter stage circuitA1、PWMA2、PWMA3、PWMA4，PWMB1、PWMB2、PWMB3、PWMB4，PWMC1、PWMC2、PWMC3、PWMC4Inverting the PWM signal to obtain PWM signalA5、PWMA6、PWMA7、PWMA8，PWMB5、PWMB6、PWMB7、PWMB8，PWMC5、PWMC6、PWMC7、PWMC8；
(14) PWM modulating signal v of each phase of inverse conversion stage circuit in the step (10) and the step (11)am *、vbm *、vcm *After 180 degrees of phase shift, comparing the phase-shifted phase-a1、PWMa2、PWMa3、PWMa4，PWMb1、PWMb2、PWMb3、PWMb4，PWMc1、PWMc2、PWMc3、PWMc4Inverting the PWM signal to obtain PWM signala5、PWMa6、PWMa7、PWMa8，PWMb5、PWMb6、PWMb7、PWMb8，PWMc5、PWMc6、PWMc7、PWMc8；
(15) And (3) sending the PWM signals in the step (13) and the step (14) to corresponding power switching devices to control power switching tubes of each phase of inverter stage circuit, wherein the control strategy improves the utilization rate of direct current voltage within a certain output voltage range, and realizes the same control effect as the traditional space vector pulse width modulation.
The invention is further described below with reference to the accompanying drawings.
Drawings
FIG. 1 is a structural diagram of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system;
FIG. 2 is a topological diagram a of a rectification stage of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system;
FIG. 3 is a topological diagram b of a rectification stage of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system;
FIG. 4 is a three-phase rectification stage control block diagram of a transformer isolation-free star-connected medium-high voltage variable frequency speed control system;
FIG. 5 is a three-phase inverter control block diagram of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system;
FIG. 6 is a three-phase DC side voltage waveform of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system;
FIG. 7 is a three-phase input current waveform of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system;
FIG. 8 is a waveform of the rotating speed, torque and stator current of an AC motor of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system;
best mode for carrying out the invention
The embodiments and the working principle of the present invention will be further described with reference to the accompanying drawings:
referring to fig. 1, a transformer-isolated star-connected medium-high voltage variable frequency speed control system comprises three high-frequency filters and three cross-dc-ac converter circuits, wherein the three cross-dc-ac converter circuits comprise three single cross-dc-ac converter circuits, the single cross-dc-ac converter circuits comprise single-phase rectifier circuits, each single-phase rectifier circuit comprises a five-level cascade rectifier unit, each single-phase rectifier circuit provides a pair of common medium-high voltage output direct current buses, each single cross-dc-ac converter circuit comprises a single-phase inverter circuit, each single-phase inverter circuit comprises a five-level cascade inverter unit, direct current input ends of the five-level cascade inverter units are directly connected with the pair of common medium-high voltage output direct current buses provided by the single-phase rectifier circuits, the single-phase rectifier stage circuit of the single-phase intersection-direct-alternating current converter circuit is provided with two alternating current input ends, the single-phase rectifier stage circuits of the three single-phase intersection-direct-alternating current converter circuits have six alternating current input ends, the first alternating current input ends of the single-phase rectifier stage circuits of the three single-phase intersection-direct-alternating current converter circuits form a group of wiring ends, the second alternating current input ends of the single-phase rectifier stage circuits of the three single-phase intersection-direct-alternating current converter circuits form another group of wiring ends, one group of the wiring ends are connected to a common neutral point, and the other group of the wiring ends are respectively connected with three high-frequency filters in series to form a three-phase power grid to form star connection.
Referring to fig. 1 and 2, a single-phase rectifier circuit in a single-phase cross-DC-AC converter circuit in a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system comprises a single-phase diode rectifier bridge and two boost inductors L1、L2Four switching devices S1、S2、S3、S4Four fast recovery diodes D1、D2、D3、D4Two common inductors L3、L4Two DC capacitors C1、C2And four output DC capacitors C3、C4、C5、C6Switching device S1First terminal (a) and direct currentCapacitor C1Is connected to a DC capacitor C1And the other end of the diode D and the fast recovery diode D1Is connected with the anode of the fast recovery diode D1Cathode and output DC capacitor C3Is connected to the first terminal (m), the switching device S1And the second terminal (b) of the switching device S2First terminal (a) and fast recovery diode D2Is connected with the anode of the fast recovery diode D2Cathode and common inductor L3And an output DC capacitor C4Is connected to the first terminal (m) of the common inductor L3And the other end of the diode D and the fast recovery diode D1Is connected with the anode of the output direct current capacitor C3And the second terminal (n) of the output DC capacitor C4Is connected to the first terminal (m), the switching device S2And the second terminal (b) of the switching device S3And an output DC capacitor C5Is connected to output a DC capacitor C4And the second terminal (n) of the output DC capacitor C5Is connected to the first terminal (m), the switching device S3And the second terminal (b) of the switching device S4First terminal (a) and fast recovery diode D3Is connected to the cathode of a fast recovery diode D3Anode and output dc capacitor C5And an output DC capacitor C6Is connected to the first terminal (m), the switching device S4Second terminal (b) of and a dc capacitor C2And a boost inductor L2Is connected to one end of a boost inductor L2The other end of the DC capacitor C is connected with the negative end of the rectification output of the single-phase diode rectifier bridge2The other end of (1) and a common inductor L4And a fast recovery diode D4Is connected to the cathode of a common inductor L4And the other end of the diode D and the fast recovery diode D3Is connected with the anode of the fast recovery diode D4Anode and output dc capacitor C6Is connected to the second terminal (n), the switching device S1First terminal (a) of and boost inductor L1Is connected to one end of a boost inductor L1The other end of the single-phase diode rectifier bridge is connected with the positive end of the rectification output of the single-phase diode rectifier bridge.
Referring to fig. 1 and 3, a single-phase rectifier circuit in a single-phase cross-direct-alternating current converter circuit in a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system comprises a single-phase diode rectifier bridge and two boost inductors L1、L2Four switching devices S1、S2、S3、S4Four fast recovery diodes D1、D2、D3、D4Two flying capacitors C1、C2And two output DC capacitors C3、C4Switching device S1First terminal (a) of and fast recovery diode D1Is connected with the anode of the fast recovery diode D1Cathode and fast recovery diode D2Is connected with the anode of the fast recovery diode D2Cathode and output DC capacitor C3Is connected to output a DC capacitor C3And the second terminal (n) of the output DC capacitor C4Is connected to the first terminal (m), the switching device S1And the second terminal (b) of the switching device S2First terminal (a) and flying capacitor C1Is connected to the first terminal (e) of the flying capacitor C1Second terminal (f) of and fast recovery diode D2Is connected to the anode of the switching device S2And the second terminal (b) of the switching device S3And an output DC capacitor C4Is connected to the first terminal (m), the switching device S3And the second terminal (b) of the switching device S4First terminal (a) and flying capacitor C2Is connected to the first terminal (e) of the flying capacitor C2Second terminal (f) of and fast recovery diode D3Anode and fast recovery diode D4Is connected to the cathode of a fast recovery diode D4Anode and output dc capacitor C4Is connected to the second terminal (n), the switching device S4Second terminal (b) of and fast recovery diode D3Cathode and boost inductor L2Is connected to one end of a boost inductor L2Is connected with the negative end of the rectification output of the single-phase diode rectifier bridge, and a switching device S1First terminal (a) of and boost inductor L1Is connected to one end of a boost inductor L1The other end of the single-phase diode rectifier bridge is connected with the positive end of the rectification output of the single-phase diode rectifier bridge.
Referring to fig. 1 and 4, a transformer-isolated star-connected medium-high voltage variable frequency speed control system comprises a three-phase alternating current motor, wherein five-level cascaded inverter units in three single-phase intersection-direct-alternating current converter circuits have six alternating current output ends, the first alternating current output ends of the five-level cascaded inverter units in the three single-phase intersection-direct-alternating current converter circuits form a group of wiring ends, the second alternating current output ends of the five-level cascaded inverter units in the three single-phase intersection-direct-alternating current converter circuits form another group of wiring ends, one group of wiring ends are connected to a common neutral point, and the other group of wiring ends are respectively connected with stator windings of the three-phase alternating current motor to form star connection.
Referring to fig. 1, fig. 2, fig. 3, fig. 4 and fig. 5, a control method of a transformer isolation-free star-connected medium-high voltage variable frequency speed control system comprises the following control steps:
(1) sampling the total voltage of each phase of rectification stage DC side in the three-phase AC-DC-AC converter circuit to obtain 3 total voltage signals U of DC sideA、UB、UCThen, sampling N (N is 2 or 4) cascaded module voltages of each phase of rectification stage to obtain 3N module voltage signals UA1、UA2、...UAN，UB1、UB2、...UBN，UC1、UC2、...UCNCalculating 3 total voltage signals U at DC side by using the following formulaA、UB、UCAverage value of Uo：
Figure BDA0002965255760000071
(2) Mixing U in the step (1)oWith a given signal U of DC voltageo *After comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signal d3 DC side total voltage signals U in the step (1)A、UB、UCRespectively connected with DC voltage supplyFixed signal Uo *After comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldA、IdB、IdC；
(3) Calculating the module voltage signal U in step (1) by using the following formulaA1、UA2、...UANAverage value of UAeVoltage signal U of moduleB1、UB2、...UBNAverage value of UBeVoltage signal U of moduleC1、UC2、...UCNAverage value of UCe：
Figure BDA0002965255760000072
(4) The module voltage signal U in the step (1) is processedA1、UA2、...UANRespectively comparing the voltage signals with the module voltage signal U in the step (3)A1、UA2、...UANAverage value of UAeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldA1、IdA2、...IdANThe module voltage signal U in the step (1) is processedB1、UB2、...UBNRespectively comparing the voltage signals with the module voltage signal U in the step (3)B1、UB2、...UBNAverage value of UBeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldB1、IdB2、...IdBNThe module voltage signal U in the step (1) is processedC1、UC2、...UCNRespectively comparing the voltage signals with the module voltage signal U in the step (3)C1、UC2、...UCNAverage value of UCeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldC1、IdC2、...IdCN；
(5) The amplitude I of the direct current signal in the step (2) is measureddAnd IdAAdding the added value and the amplitude I of the direct current signal in the step (4)dA1、IdA2、...IdANRespectively added to obtain the given signal amplitude I of the direct currentdA1 *、IdA2 *、...IdAN *The amplitude I of the DC current signal in the step (2)dAnd IdBAdding the added value and the amplitude I of the direct current signal in the step (4)dB1、IdB2、...IdBNRespectively added to obtain the given signal amplitude I of the direct currentdB1 *、IdB2 *、...IdBN *The amplitude I of the DC current signal in the step (2)dAnd IdCAdding the added value and the amplitude I of the direct current signal in the step (4)dC1、IdC2、...IdCNRespectively added to obtain the given signal amplitude I of the direct currentdC1 *、IdC2 *、...IdCN *；
(6) Setting the signal amplitude I to the direct current in the step (5)dA1 *、IdA2 *、...IdAN *Multiplying the sine signal with the same Phase as the A-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate an A-Phase alternating current given signal idA1 *、idA2 *、...idAN *Setting the DC current in the step (5) to be a signal amplitude IdB1 *、IdB2 *、...IdBN *Multiplying the sinusoidal signal with the same Phase as the B-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate a B-Phase alternating current given signal idB1 *、idB2 *、...idBN *Setting the DC current in the step (5) to be a signal amplitude IdC1 *、IdC2 *、...IdCN *Multiplying the sine signal with the same Phase as the C-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate a C-Phase alternating current given signal idC1 *、idC2 *、...idCN *；
(7) Sampling three-phase actual current of a three-phase AC-DC-AC converter circuit to obtain three actual AC current signals iA、iB、iCGiving the A alternating current in the step (6) to a signal idA1 *、idA2 *、...idAN *Respectively with the actual AC current signal iAAfter comparison, sending the signal into a PI current regulator to obtain an A-phase PWM modulation wave signal gA1、gA2、...gAN(ii) a Giving a signal i to the B alternating current in the step (6)dB1 *、idB2 *、...idBN *Respectively with the actual AC current signal iBAfter comparison, sending the signals into a PI current regulator to obtain a B-phase PWM modulation wave signal gB1、gB2、...gBNGiving the C alternating current in the step (6) to a signal idC1 *、idC2 *、...idCN *Respectively with the actual AC current signal iCAfter comparison, sending the signal into a PI current regulator to obtain a C-phase PWM modulation wave signal gC1、gC2、...gCN；
(8) The A-phase PWM modulation wave signal g in the step (7) is processedA1、gA2、...gANWith N successive lags TS1The triangular carrier signals of the/N are compared to obtain PWM signals of the A-phase power switching device of the rectifier stage and B-phase PWM modulation wave signals gB1、gB2、...gBNAnd C-phase PWM modulated wave signal gC1、gC2、...gCNRespectively comparing with the triangular carrier signals same as A phase to obtain PWM signals T of B phase and C phase power switch devices of the rectifier stageS1The period of the triangular carrier signals is, the N different triangular carrier signals have the same frequency and amplitude and are symmetrically distributed on two sides of a time axis;
(9) the three-phase sinusoidal reference voltage signal of the inverter stage of the three-phase AC-DC-AC converter circuit is given by:
Figure BDA0002965255760000081
in the formula V*For pulse-width modulation of the command voltage signal amplitude, va *、vb *、vc *Is a three-phase sinusoidal reference voltage signal, omega is V*Rotational angular velocity of (a);
(10) the peak value of the sine voltage to be inverted by each phase of inverting stage circuit is set as VacLet us order
Figure BDA0002965255760000082
When g is less than or equal to 1, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure BDA0002965255760000083
(11) when g is>1 time, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Respectively as follows:
Figure BDA0002965255760000091
Figure BDA0002965255760000092
Figure BDA0002965255760000093
(12) because each phase inverter circuit adopts a five-level cascade inverter unit, four different triangular carrier signals are needed, the different triangular carrier signals have the same frequency and amplitude and are continuously and vertically distributed in space and symmetrically distributed on two sides of a time axis, the phases of the four different triangular carrier signals sequentially differ by 180 degrees, and the period of the different triangular carrier signals is Ts2Amplitude of is
Figure BDA0002965255760000101
In the formula VmPWM modulating signal v for each phase of inverse conversion stage circuit in step (10) and step (11)am *、vbm *、vcm *The amplitude of (d);
(13) PWM modulating signal v of each phase of inverse conversion stage circuit in the step (10) and the step (11)am *、vbm *、vcm *Comparing with the four triangular carrier signals in the step (12) to obtain a PWM signal of a first bridge arm of the inverter stage circuitA1、PWMA2、PWMA3、PWMA4，PWMB1、PWMB2、PWMB3、PWMB4，PWMC1、PWMC2、PWMC3、PWMC4Inverting the PWM signal to obtain PWM signalA5、PWMA6、PWMA7、PWMA8，PWMB5、PWMB6、PWMB7、PWMB8，PWMC5、PWMC6、PWMC7、PWMC8；
(14) PWM modulating signal v of each phase of inverse conversion stage circuit in the step (10) and the step (11)am *、vbm *、vcm *After 180 degrees of phase shift, comparing the phase-shifted phase-a1、PWMa2、PWMa3、PWMa4，PWMb1、PWMb2、PWMb3、PWMb4，PWMc1、PWMc2、PWMc3、PWMc4Inverting the PWM signal to obtain PWM signala5、PWMa6、PWMa7、PWMa8，PWMb5、PWMb6、PWMb7、PWMb8，PWMc5、PWMc6、PWMc7、PWMc8；
(15) And (3) sending the PWM signals in the step (13) and the step (14) to corresponding power switching devices to control power switching tubes of each phase of inverter stage circuit, wherein the control strategy improves the utilization rate of direct current voltage within a certain output voltage range, and realizes the same control effect as the traditional space vector pulse width modulation.
Referring to fig. 6, a voltage waveform of a three-phase dc side in a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system in the embodiment of the present invention is shown, and the dc side voltage is stable and reaches balance quickly.
Referring to fig. 7, the three-phase input current waveform in the transformer-isolation-free star-connected medium-high voltage variable frequency speed control system in the embodiment of the invention has good current waveform quality and is approximate to sine.
Referring to fig. 8, it is shown that the motor operates normally in the form of the waveforms of the rotating speed, torque and stator current of the alternating current motor in the transformer-isolation-free star-connected medium-high voltage variable-frequency speed control system according to the embodiment of the present invention.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the spirit and scope of the present invention, and various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the technical solutions of the present invention fall into the protective scope of the present invention, and the technical contents of the present invention as claimed are all described in the claims.

Claims (5)

1. A transformer-free isolated satellite-connected medium-high voltage variable frequency speed control system is characterized by comprising three high-frequency filters and three intersecting-direct-alternating current converter circuits, wherein each three intersecting-direct-alternating current converter circuit comprises three single intersecting-direct-alternating current converter circuits, each single intersecting-direct-alternating current converter circuit comprises a single-phase rectifier stage circuit, each single-phase rectifier stage circuit comprises a five-level cascade rectifier unit, each single-phase rectifier stage circuit provides a pair of common medium-high voltage output direct current buses, each single intersecting-direct-alternating current converter circuit comprises a single-phase inverter stage circuit, each single-phase inverter stage circuit comprises a five-level cascade inverter unit, direct current input ends of the five-level cascade inverter units are directly connected with the pair of common medium-high voltage output direct current buses provided by the single-phase rectifier stage circuit, the single-phase rectifier stage circuit of the single-phase cross-direct-alternating current converter circuit is provided with two alternating current input ends, the three single-phase rectifier stage circuits of the single-phase cross-direct-alternating current converter circuit have six alternating current input ends, the first alternating current input ends of the single-phase rectifier stage circuits of the three single-phase cross-direct-alternating current converter circuits form a group of wiring ends, the second alternating current input ends of the single-phase rectifier stage circuits of the three single-phase cross-direct-alternating current converter circuits form another group of wiring ends, one group of wiring ends are connected to a common neutral point, and the other group of wiring ends are respectively connected with the three high-frequency filters in series to form a three-phase power grid to form star connection.
2. The transformer-less isolated star-connected medium-high voltage variable frequency speed control system according to claim 1, wherein the single-phase rectifier stage circuit in the single-phase cross-DC-AC converter circuit comprises a single-phase diode rectifier bridge, two boost inductors L1、L2Four switching devices S1、S2、S3、S4Four fast recovery diodes D1、D2、D3、D4Two common inductors L3、L4Two DC capacitors C1、C2And four output DC capacitors C3、C4、C5、C6Said switching device S1And said dc capacitor C1Is connected to the DC capacitor C1And the other end of the diode and the fast recovery diode D1Is connected to the anode of the fast recovery diode D1And the output DC capacitor C3Is connected to the first terminal (m), said switching device S1And said switching device S2And said fast recovery diode D2Is connected to the anode of the fast recovery diode D2And the common inductor L3And said output DC capacitor C4Is connected to the first terminal (m), the common inductance L3And the other end of the diode and the fast recovery diode D1Is connected with the anode of the output direct current capacitor C3And said output dc capacitor C4Is connected to the first terminal (m), said switching device S2And said switching device S3And said output dc capacitor C5Is connected to the first terminal (m), the output dc capacitor C4And said output dc capacitor C5Is connected to the first terminal (m), said switching device S3And said switching device S4And said fast recovery diode D3Is connected to the cathode of the fast recovery diode D3And the output direct current capacitor C5And said output dc capacitor C6Is connected to the first terminal (m), said switching device S4And said dc capacitor C2And the boost inductor L2Is connected to the other end of the voltage boosting inductor L2The other end of the DC capacitor C is connected with the negative end of the rectification output of the single-phase diode rectifier bridge, and the DC capacitor C2And the other end of the common inductor L4And the fast recovery diode D4Is connected to the cathode of the common inductor L4And the other end of the diode and the fast recovery diode D3Is connected to the anode of the fast recovery diode D4And the output direct current capacitor C6Is connected to the second terminal (n), said switching device S1With said boost inductor L1Is connected to the other end of the voltage boosting inductor L1And the other end of the single-phase diode rectifier bridge is connected with the positive end of the rectification output of the single-phase diode rectifier bridge.
3. The transformer-less isolated star-connected medium-high voltage variable frequency speed control system according to claim 1, wherein the single-phase rectifier stage circuit in the single-phase cross-DC-AC converter circuit comprises a single-phase diode rectifier bridge, two boost inductors L1、L2Four switching devices S1、S2、S3、S4Four fast recovery diodes D1、D2、D3、D4Two flying capacitors C1、C2And two output DC capacitors C3、C4Said switching device S1And the fast recovery diode D1Is connected to the anode of the fast recovery diode D1And the fast recovery diode D2Is connected to the anode of the fast recovery diode D2And the output DC capacitor C3Is connected to the first terminal (m), the output dc capacitor C3And said output dc capacitor C4Is connected to the first terminal (m), said switching device S1And said switching device S2And said flying capacitor C1Is connected to the first terminal (e), said flying capacitor C1And said fast recovery diode D2Is connected to the anode of the switching device S2And said switching device S3And said output dc capacitor C4Is connected to the first terminal (m), said switching device S3And said switching device S4And said flying capacitor C2Is connected to the first terminal (e), said flying capacitor C2And said fast recovery diode D3And the fast recovery diode D4Is connected to the cathode of the fast recovery diode D4And the output direct current capacitor C4Is connected to the second terminal (n), said switching device S4And said fast recovery diode D3And the boost inductor L2Is connected to the other end of the voltage boosting inductor L2Is connected with the negative end of the rectification output of the single-phase diode rectifier bridge, and the switching device S1With said boost inductor L1Is connected to the other end of the voltage boosting inductor L1And the other end of the single-phase diode rectifier bridge is connected with the positive end of the rectification output of the single-phase diode rectifier bridge.
4. A transformer-isolation-free star-connected medium-high voltage variable-frequency speed control system is characterized by comprising a three-phase alternating-current motor, wherein the five-level cascade inverter unit in the three single-phase cross-DC-AC converter circuits disclosed in claim 1 is provided with six alternating-current output ends, the first alternating-current output ends of the five-level cascade inverter unit in the three single-phase cross-DC-AC converter circuits disclosed in claim 1 form a group of terminal ends, the second alternating-current output ends of the five-level cascade inverter unit in the three single-phase cross-DC-AC converter circuits disclosed in claim 1 form another terminal end group, one of the terminals is connected to a common neutral point, and the other terminal is connected to the stator windings of the three-phase ac motor, respectively, to form a star connection.
5. A control method of a transformer-isolation-free star-connected medium-high voltage variable frequency speed control system is characterized by comprising the following control steps:
(1) sampling the total voltage of each phase of rectification stage DC side in the three-phase AC-DC-AC converter circuit to obtain 3 total voltage signals U of DC sideA、UB、UCThen, sampling N (N is 2 or 4) cascaded module voltages of each phase of rectification stage to obtain 3N module voltage signals UA1、UA2、...UAN，UB1、UB2、...UBN，UC1、UC2、...UCNCalculating 3 total voltage signals U at DC side by using the following formulaA、UB、UCAverage value of Uo：
Figure FDA0002965255750000021
(2) Mixing U in the step (1)oWith a given signal U of DC voltageo *After comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signald3 DC side total voltage signals U in the step (1)A、UB、UCRespectively associated with a given signal U of DC voltageo *After comparison, the signals are sent to a PI voltage regulator,obtaining the amplitude I of the DC current signaldA、IdB、IdC；
(3) Calculating the module voltage signal U in step (1) by using the following formulaA1、UA2、...UANAverage value of UAeVoltage signal U of moduleB1、UB2、...UBNAverage value of UBeVoltage signal U of moduleC1、UC2、...UCNAverage value of UCe：
Figure FDA0002965255750000022
(4) The module voltage signal U in the step (1) is processedA1、UA2、...UANRespectively comparing the voltage signals with the module voltage signal U in the step (3)A1、UA2、...UANAverage value of UAeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldA1、IdA2、...IdANThe module voltage signal U in the step (1) is processedB1、UB2、...UBNRespectively comparing the voltage signals with the module voltage signal U in the step (3)B1、UB2、...UBNAverage value of UBeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldB1、IdB2、...IdBNThe module voltage signal U in the step (1) is processedC1、UC2、...UCNRespectively comparing the voltage signals with the module voltage signal U in the step (3)C1、UC2、...UCNAverage value of UCeAfter comparison, sending the signal to a PI voltage regulator to obtain the amplitude I of the direct current signaldC1、IdC2、...IdCN；
(5) The amplitude I of the direct current signal in the step (2) is measureddAnd IdAAdding the added value and the amplitude I of the direct current signal in the step (4)dA1、IdA2、...IdANRespectively added to obtain the given signal amplitude I of the direct currentdA1 *、IdA2 *、...IdAN *The amplitude I of the DC current signal in the step (2)dAnd IdBAdding the added value and the amplitude I of the direct current signal in the step (4)dB1、IdB2、...IdBNRespectively added to obtain the given signal amplitude I of the direct currentdB1 *、IdB2 *、...IdBN *The amplitude I of the DC current signal in the step (2)dAnd IdCAdding the added value and the amplitude I of the direct current signal in the step (4)dC1、IdC2、...IdCNRespectively added to obtain the given signal amplitude I of the direct currentdC1 *、IdC2 *、...IdCN *；
(6) Setting the signal amplitude I to the direct current in the step (5)dA1 *、IdA2 *、...IdAN *Multiplying the sine signal with the same Phase as the A-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate an A-Phase alternating current given signal idA1 *、idA2 *、...idAN *Setting the DC current in the step (5) to be a signal amplitude IdB1 *、IdB2 *、...IdBN *Multiplying the sinusoidal signal with the same Phase as the B-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate a B-Phase alternating current given signal idB1 *、idB2 *、...idBN *Setting the DC current in the step (5) to be a signal amplitude IdC1 *、IdC2 *、...IdCN *Multiplying the sine signal with the same Phase as the C-Phase grid voltage obtained by using a Phase-Locked loop (PLL) to generate a C-Phase alternating current given signal idC1 *、idC2 *、...idCN *；
(7) Sampling three-phase actual current of a three-phase AC-DC-AC converter circuit to obtain three actual AC current signals iA、iB、iCThe A alternating current in the step (6) is converted intoGiven signal idA1 *、idA2 *、...idAN *Respectively with the actual AC current signal iAAfter comparison, sending the signal into a PI current regulator to obtain an A-phase PWM modulation wave signal gA1、gA2、...gAN(ii) a Giving a signal i to the B alternating current in the step (6)dB1 *、idB2 *、...idBN *Respectively with the actual AC current signal iBAfter comparison, sending the signals into a PI current regulator to obtain a B-phase PWM modulation wave signal gB1、gB2、...gBNGiving the C alternating current in the step (6) to a signal idC1 *、idC2 *、...idCN *Respectively with the actual AC current signal iCAfter comparison, sending the signal into a PI current regulator to obtain a C-phase PWM modulation wave signal gC1、gC2、...gCN；
(8) The A-phase PWM modulation wave signal g in the step (7) is processedA1、gA2、...gANWith N successive lags TS1The triangular carrier signals of the/N are compared to obtain PWM signals of the A-phase power switching device of the rectifier stage and B-phase PWM modulation wave signals gB1、gB2、...gBNAnd C-phase PWM modulated wave signal gC1、gC2、...gCNRespectively comparing with the triangular carrier signals same as A phase to obtain PWM signals T of B phase and C phase power switch devices of the rectifier stageS1The period of the triangular carrier signals is, the N different triangular carrier signals have the same frequency and amplitude and are symmetrically distributed on two sides of a time axis;
(9) the three-phase sinusoidal reference voltage signal of the inverter stage of the three-phase AC-DC-AC converter circuit is given by:
Figure FDA0002965255750000031
in the formula V*For pulse-width modulation of the command voltage signal amplitude, va *、vb *、vc *Is three phasesSinusoidal reference voltage signal, omega being V*Rotational angular velocity of (a);
(10) the peak value of the sine voltage to be inverted by each phase of inverting stage circuit is set as VacLet us order
Figure FDA0002965255750000032
When g is less than or equal to 1, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure FDA0002965255750000033
(11) when g is>1 time, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Respectively as follows:
Figure FDA0002965255750000034
Figure FDA0002965255750000041
(12) because each phase inverter circuit adopts a five-level cascade inverter unit, four different triangular carrier signals are needed, the different triangular carrier signals have the same frequency and amplitude and are continuously and vertically distributed in space and symmetrically distributed on two sides of a time axis, the phases of the four different triangular carrier signals sequentially differ by 180 degrees, and the period of the different triangular carrier signals is Ts2Amplitude of is
Figure FDA0002965255750000042
In the formula VmPWM modulating signal v for each phase of inverse conversion stage circuit in step (10) and step (11)am *、vbm *、vcm *The amplitude of (d);
(13) PWM modulating signal v of each phase of inverse conversion stage circuit in the step (10) and the step (11)am *、vbm *、vcm *Comparing with the four triangular carrier signals in the step (12) to obtain a PWM signal of a first bridge arm of the inverter stage circuitA1、PWMA2、PWMA3、PWMA4，PWMB1、PWMB2、PWMB3、PWMB4，PWMC1、PWMC2、PWMC3、PWMC4Inverting the PWM signal to obtain PWM signalA5、PWMA6、PWMA7、PWMA8，PWMB5、PWMB6、PWMB7、PWMB8，PWMC5、PWMC6、PWMC7、PWMC8；
(14) PWM modulating signal v of each phase of inverse conversion stage circuit in the step (10) and the step (11)am *、vbm *、vcm *After 180 degrees of phase shift, comparing the phase-shifted phase-a1、PWMa2、PWMa3、PWMa4，PWMb1、PWMb2、PWMb3、PWMb4，PWMc1、PWMc2、PWMc3、PWMc4Inverting the PWM signal to obtain PWM signala5、PWMa6、PWMa7、PWMa8，PWMb5、PWMb6、PWMb7、PWMb8，PWMc5、PWMc6、PWMc7、PWMc8；
(15) And (3) sending the PWM signals in the step (13) and the step (14) to corresponding power switching devices to control power switching tubes of each phase of inverter stage circuit, wherein the control strategy improves the utilization rate of direct current voltage within a certain output voltage range, and realizes the same control effect as the traditional space vector pulse width modulation.
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