CN111934558A - Implementation scheme of novel medium-high voltage variable frequency speed control system without transformer isolation - Google Patents

Implementation scheme of novel medium-high voltage variable frequency speed control system without transformer isolation Download PDF

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CN111934558A
CN111934558A CN202010810648.0A CN202010810648A CN111934558A CN 111934558 A CN111934558 A CN 111934558A CN 202010810648 A CN202010810648 A CN 202010810648A CN 111934558 A CN111934558 A CN 111934558A
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phase
circuit
high voltage
inverter
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王聪
程红
赵志浩
李瑶璞
陶艳梅
于龙飞
袁巍
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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
    • 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
    • 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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Abstract

The invention relates to a novel middle-high voltage variable frequency speed control system implementation scheme without transformer isolation, which belongs to a middle-high voltage variable frequency speed control technology and a control technology implementation scheme thereof, and the scheme cancels a power frequency transformer used by the traditional middle-high voltage frequency converter and a high-frequency isolation DC/DC conversion link in a new generation of middle-high voltage frequency converter based on a non-power frequency transformer cascade multilevel converter, and each phase of cascade rectifier in the scheme forms a pair of common middle-high voltage direct current buses which can be directly connected with a diode clamping type or capacitor clamping type inverter circuit; and the frequency converter does not need electrical isolation, and the electrical isolation between three-phase inverters is realized by using a three-phase stator winding of the alternating current motor, so that the size and the weight of the frequency converter are greatly reduced, the system structure and the control complexity of the medium-high voltage frequency converter are greatly reduced, the loss in the operation process and the hardware cost are greatly reduced, the system reliability and the overall efficiency are also greatly improved, and the frequency converter is particularly suitable for the field of medium-high voltage high-power variable frequency speed regulation.

Description

Implementation scheme of novel medium-high voltage variable frequency speed control system without transformer isolation
Technical Field
The invention belongs to the technical field of medium-high voltage variable frequency speed regulation, and particularly relates to a novel medium-high voltage variable frequency speed regulation system implementation scheme formed by organically integrating a high-power cascade multilevel converter without an isolation transformer and an alternating current motor.
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 medium-high voltage frequency converters, in order to implement high-voltage power conversion 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 on 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 (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, and 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. 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 novel implementation scheme of a medium-high voltage variable frequency speed control system, which can cancel the high-frequency isolation DC/DC conversion link in the new generation of medium-high voltage frequency converter based on the non-power frequency transformer cascade multilevel converter. Different from the traditional power frequency transformer for the middle-high voltage frequency converter to realize electrical isolation, and different from the high-frequency transformer for the middle-high voltage frequency converter of the new generation to realize electrical isolation, the invention provides a novel middle-high voltage variable frequency speed control system implementation scheme with unidirectional energy transmission, 1) each phase of cascade rectifier can form a common direct current bus, so that the cascade rectifier can be directly connected with a clamping type inverter circuit (a diode clamping type or a capacitor clamping type); 2) the frequency converter does not need electrical isolation, and the electrical isolation between each phase of the three-phase inverter is realized by using a three-phase stator winding of the alternating current motor. Therefore, the size, the weight and the cost of the medium and high voltage frequency converter based on the cascading multi-level converter without the power frequency transformer can be greatly reduced, and the system efficiency is greatly improved.
The invention aims to realize the technical scheme, and the scheme is characterized in that:
in order to achieve the purpose, the implementation scheme of the novel medium-high voltage variable frequency speed control system without transformer isolation is characterized in that: the three-phase inverter comprises three high-frequency filters and three-phase cross-DC-AC converter circuits, wherein the three-phase cross-DC-AC converter circuits comprise three single-phase cross-DC-AC converter circuits, each single-phase cross-DC-AC converter circuit comprises a single-phase rectifier and N cascaded control module units, N is a positive integer and is more than or equal to 1, the single-phase rectifier circuit provides a pair of public high-voltage output direct-current buses, each single-phase cross-DC-AC converter circuit comprises a single-phase inverter circuit, each single-phase inverter circuit comprises an N +1 level cascaded inverter unit, the direct-current input end of each N +1 level cascaded inverter unit is directly connected with the pair of public high-voltage output direct-current buses provided by the corresponding single-phase rectifier 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.
In order to achieve the purpose, the implementation scheme of the novel medium-high voltage variable frequency speed control system without transformer isolation is characterized in that: each phase of stator winding of the three-phase alternating current motor is respectively connected with the alternating current output ends of the N +1 level cascade type inverter units in the three single-phase intersection-direct-alternating current converter circuits to form open winding connection, so that the electrical isolation among three-phase power flows is realized.
In order to achieve the purpose, the implementation scheme of the novel medium-high voltage variable frequency speed control system without transformer isolation is characterized in that: the control strategy comprises the control strategy of the novel medium-high voltage variable frequency speed control system implementation scheme without transformer isolation, and the control strategy of the novel medium-high voltage variable frequency speed control system implementation scheme without transformer isolation comprises the following steps:
(1) in order to improve the utilization rate of the direct-current voltage of the inverter stage circuit and obtain the same control effect as the traditional space vector pulse width modulation, a three-phase sinusoidal reference voltage signal of each phase of the inverter stage circuit is assumed to be given by the following formula:
Figure BDA0002630852250000021
in the formula V*For conventional space vector pulse width modulation of the command voltage signal, va *、vb *、vc *Is a three-phase sinusoidal reference voltage signal, and ω t is V*The angle of rotation of (a);
(2) according to the traditional space vector pulse width modulation waveform and area equivalence principle, obtaining the pulse width modulation voltage waveform v of each phase inverter circuit in each sectora *、vb *、vc *Are respectively:
Figure BDA0002630852250000022
Figure BDA0002630852250000023
Figure BDA0002630852250000031
TS＝2(T0+Ta+Tb)
in the formula, T0Zero vector action time, TsFor a switching period, VdIs the DC side voltage, T, of each phase invertera、TbRespectively, lag command voltage signal V*Of the vector action time and the advanced command voltage signal V*The vector action time of (a);
(3) assume a command voltage signal V in step (1)*In the fifth sector:
Figure BDA0002630852250000032
above formula alpha is V*At each sector angle, the above formula Ta、Tbω t into v of the fifth sector in step (2)ao *、vbo *、vco *To obtain the following formula:
Figure BDA0002630852250000033
when the command voltage signal V in step (1)*When the upper surface T is positioned in the first, second, third, fourth and sixth sectors, the upper surface T is positioned in the same waya、TbSubstituting the expression of ω t into the first, second, third, fourth and sixth sectors in step (2) to obtain vao *、vbo *、vco *The expressions in the first, second, third, fourth, and sixth sectors are as follows:
Figure BDA0002630852250000034
Figure BDA0002630852250000035
Figure BDA0002630852250000041
Figure BDA0002630852250000042
Figure BDA0002630852250000043
(4) synthesizing v of each sector in step (3)ao *、vbo *、vco *To obtain the following formula:
Figure BDA0002630852250000044
Figure BDA0002630852250000051
Figure BDA0002630852250000052
(5) the three-phase pulse width modulation waveform v in the range of not less than 0 and not more than ω t and not more than 2 pi in the step (4)ao *、vbo *、vco *The period extension is carried out for one period to obtain a three-phase pulse width modulation waveform v within the range of not less than 0 and not more than ω t and not more than 2k piao *、vbo *、vco *K is a positive integer greater than or equal to 1;
(6) the peak value of the sine voltage to be inverted by each phase of inverting stage circuit is set as VacThe signal participating in PWM modulation of each phase inverter circuit is vam *、vbm *、vcm *Let us order
Figure BDA0002630852250000053
In the formula VdThe voltage of the direct current side of each phase of inverter in the step (2);
(7) when g in step (6)<1 time, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure BDA0002630852250000054
when g in the step (6) is more than or equal to 1, participating in the PWM signal v of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure BDA0002630852250000061
v of the above formulaao *、vbo *、vco *The three-phase pulse width modulation waveform v in the range of not less than 0 and not more than ω t and not more than 2k pi in the step (5)ao *、vbo *、vco *；
(8) Because each phase inverter circuit adopts an N +1 level cascade inverter unit, N is more than or equal to 1 and is a positive integer, N different triangular carrier signals are needed, the N different triangular carrier signals have the same frequency and amplitude and are continuously and vertically distributed in space and symmetrically distributed at two sides of a time axis, the phases of the N different triangular carrier signals sequentially differ by 180 degrees, and the period of the N different triangular carrier signals is the switching period T in the step (2)sAmplitude of is
Figure BDA0002630852250000062
In the formula VmPWM modulated signal v for each phase inverter stage circuit in step (7)am *、vbm *、vcm *The amplitude of (d);
(9) PWM modulating signal v of each phase of inverse conversion stage circuit in step (7)am *、vbm *、vcm *And (4) comparing the PWM signals with the N triangular carrier signals in the step (8) to obtain the PWM signal of each phase of inverse-conversion stage circuit, and further controlling a power switch tube of each phase of inverse-conversion stage circuit.
The following detailed description is made with reference to the accompanying drawings in conjunction with the embodiments.
Drawings
FIG. 1 is a structural diagram of an implementation scheme of a novel medium-high voltage variable frequency speed control system without transformer isolation;
FIG. 2 is a diagram of a conventional space vector pulse width modulation sector;
FIG. 3 is a pulse width modulation waveform of a command voltage signal in a fifth sector of a conventional space vector control;
FIG. 4 is a control block diagram of an implementation scheme of a novel medium-high voltage variable frequency speed control system without transformer isolation;
FIG. 5 is a reference diagram of one cycle PWM modulation for each phase inverter stage circuit;
Detailed Description
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 novel implementation scheme of a transformer-isolated medium-high voltage variable frequency speed control system includes three high-frequency filters and three-phase cross-dc-ac converter circuits, each three-phase cross-dc-ac converter circuit includes three single-phase cross-dc-ac converter circuits, each single-phase cross-dc-ac converter circuit includes a single-phase rectifier circuit and a single-phase inverter circuit, each single-phase rectifier circuit includes a single-phase rectifier and N cascaded control module units, wherein N is greater than or equal to 1 and is a positive integer, each single-phase rectifier circuit provides a pair of common high-voltage output dc buses, each inverter single-phase circuit includes an N +1 level cascaded inverter unit, the dc input end of each N +1 level cascaded inverter unit is directly connected with one pair of common high-voltage output dc buses provided by the single-phase rectifier circuit, 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 circuit of the three single-phase intersection-direct-alternating current converter circuits has 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 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.
Referring to fig. 1, a novel medium-high voltage variable frequency speed control system implementation scheme without transformer isolation comprises a three-phase alternating current motor, wherein each phase of stator winding of the three-phase alternating current motor is respectively connected with alternating current output ends of N +1 level cascade type inverter units in three single-phase intersection-direct-alternating current converter circuits to form open winding connection, so that electrical isolation among three-phase power flows is realized.
Referring to fig. 1, fig. 2, fig. 3, fig. 4 and fig. 5, a novel implementation scheme of a medium-high voltage variable frequency speed control system without transformer isolation includes a control strategy of the implementation scheme of the novel medium-high voltage variable frequency speed control system without transformer isolation, and includes the following steps:
(1) in order to improve the utilization rate of the direct-current voltage of the inverter stage circuit and obtain the same control effect as the traditional space vector pulse width modulation, a three-phase sinusoidal reference voltage signal of each phase of the inverter stage circuit is assumed to be given by the following formula:
Figure BDA0002630852250000071
in the formula V*For conventional space vector pulse width modulation of the command voltage signal, va *、vb *、vc *Is a three-phase sinusoidal reference voltage signal, and ω t is V*The angle of rotation of (a);
(2) according to the traditional space vector pulse width modulation waveform and area equivalence principle, obtaining the pulse width modulation voltage waveform v of each phase inverter circuit in each sectorao *、vbo *、vco *The expressions are respectively:
Figure BDA0002630852250000072
Figure BDA0002630852250000073
Figure BDA0002630852250000074
TS＝2(T0+Ta+Tb)
in the formula, T0Zero vector action time, TsFor a switching period, VdIs the DC side voltage, T, of each phase invertera、TbRespectively, lag command voltage signal V*Of the vector action time and the advanced command voltage signal V*The vector action time of (a);
(3) assume a command voltage signal V in step (1)*In the fifth sector:
Figure BDA0002630852250000075
above formula alpha is V*At each sector angle, the above formula Ta、Tbω t into v of the fifth sector in step (2)ao *、vbo *、vco *To obtain the following formula:
Figure BDA0002630852250000081
when the command voltage signal V in step (1)*In the same manner, the upper side T can be positioned in the first, second, third, fourth and sixth sectorsa、TbSubstituting the expression of ω t into the first, second, third, fourth and sixth sectors in step (2) to obtain vao *、vbo *、vco *The expressions in the first, second, third, fourth, and sixth sectors are as follows:
Figure BDA0002630852250000082
Figure BDA0002630852250000083
Figure BDA0002630852250000084
Figure BDA0002630852250000085
Figure BDA0002630852250000091
synthesizing v of each sector in step (3)ao *、vbo *、vco *To obtain the following formula:
Figure BDA0002630852250000092
Figure BDA0002630852250000093
Figure BDA0002630852250000101
(5) the three-phase pulse width modulation waveform v in the range of not less than 0 and not more than ω t and not more than 2 pi in the step (4)ao *、vbo *、vco *Extending for one period to obtain a three-phase pulse width modulation waveform v within the range of not less than 0 and not more than ω t and not more than 2k piao *、vbo *、vco *K is a positive integer greater than or equal to 1;
(6) the peak value of the sine voltage to be inverted by each phase of inverting stage circuit is set as VacThe signal participating in PWM modulation of each phase inverter circuit is vam *、vbm *、vcm *Let us order
Figure BDA0002630852250000102
In the formula VdThe voltage of the direct current side of each phase of inverter in the step (2);
(7) when g in step (6)<1 time, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure BDA0002630852250000103
when g in the step (6) is more than or equal to 1, participating in the PWM signal v of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure BDA0002630852250000104
v of the above formulaao *、vbo *、vco *The three-phase pulse width modulation waveform v in the range of not less than 0 and not more than ω t and not more than 2k pi in the step (5)ao *、vbo *、vco *；
(8) Because each phase inverter circuit adopts an N +1 level cascade inverter unit, N is more than or equal to 1 and is a positive integer, N different triangular carrier signals are needed, the N different triangular carrier signals have the same frequency and amplitude and are continuously and vertically distributed in space and symmetrically distributed at two sides of a time axis, the phases of the N different triangular carrier signals sequentially differ by 180 degrees, and the period of the N different triangular carrier signals is the switching period T in the step (2)sAmplitude of is
Figure BDA0002630852250000105
In the formula VmPWM modulated signal v for each phase inverter stage circuit in step (7)am *、vbm *、vcm *The amplitude of (d);
(9) PWM modulating signal v of each phase of inverse conversion stage circuit in step (7)am *、vbm *、vcm *Comparing the N triangular carrier signals in the step (8) to obtain a PWM signal of each phase of inverter stage circuit, and further controlling a power switch tube of each phase of inverter stage circuitThe 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 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 design solutions of the present invention shall fall within the protection scope of the present invention, and the technical contents of the present invention as claimed are all described in the claims.

Claims (3)

1. The utility model provides a novel well high voltage variable frequency speed control system implementation scheme of no transformer isolation which characterized in that: the three-phase inverter comprises three high-frequency filters and three-phase cross-DC-AC converter circuits, wherein the three-phase cross-DC-AC converter circuits comprise three single-phase cross-DC-AC converter circuits, each single-phase cross-DC-AC converter circuit comprises a single-phase rectifier and N cascaded control module units, N is a positive integer and is more than or equal to 1, the single-phase rectifier circuit provides a pair of public high-voltage output direct-current buses, each single-phase cross-DC-AC converter circuit comprises a single-phase inverter circuit, each single-phase inverter circuit comprises an N +1 level cascaded inverter unit, the direct-current input end of each N +1 level cascaded inverter unit is directly connected with the pair of public high-voltage output direct-current buses provided by the corresponding single-phase rectifier 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 utility model provides a novel well high voltage variable frequency speed control system implementation scheme of no transformer isolation which characterized in that: the three-phase AC motor comprises a three-phase AC motor, wherein each phase of stator winding of the three-phase AC motor is respectively connected with the AC output ends of the N +1 level cascade type inverter units in the single-phase intersection-DC-AC converter circuit of claim 1 to form open winding connection, so that the electrical isolation among three-phase power flows is realized.
3. The utility model provides a novel well high voltage variable frequency speed control system implementation scheme of no transformer isolation which characterized in that: the control strategy comprises the control strategy of the novel medium-high voltage variable frequency speed control system implementation scheme without transformer isolation, and the control strategy of the novel medium-high voltage variable frequency speed control system implementation scheme without transformer isolation comprises the following steps:
(1) in order to improve the utilization rate of the direct-current voltage of the inverter stage circuit and obtain the same control effect as the traditional space vector pulse width modulation, a three-phase sinusoidal reference voltage signal of each phase of the inverter stage circuit is assumed to be given by the following formula:
Figure FDA0002630852240000011
in the formula V*For conventional space vector pulse width modulation of the command voltage signal, va *、vb *、vc *Is a three-phase sinusoidal reference voltage signal, and ω t is V*The angle of rotation of (a);
(2) according to the traditional space vector pulse width modulation waveform and area equivalence principle, obtaining the pulse width modulation voltage waveform v of each phase inverter circuit in each sectora *、vb *、vc *Are respectively:
Figure FDA0002630852240000012
(first sector)
Figure FDA0002630852240000013
(second sector)
Figure FDA0002630852240000014
(third sector)
Figure FDA0002630852240000015
(fourth sector)
Figure FDA0002630852240000025
(fifth sector)
Figure FDA0002630852240000026
(sixth sector)
TS＝2(T0+Ta+Tb)
In the formula, T0Zero vector action time, TsFor a switching period, VdIs the DC side voltage, T, of each phase invertera、TbRespectively, lag command voltage signal V*Of the vector action time and the advanced command voltage signal V*The vector action time of (a);
(3) assume a command voltage signal V in step (1)*In the fifth sector:
Figure FDA0002630852240000021
above formula alpha is V*At each sector angle, the above formula Ta、Tbω t into v of the fifth sector in step (2)ao *、vbo *、vco *To obtain the following formula:
Figure FDA0002630852240000022
when the command voltage signal V in step (1)*When the upper surface T is positioned in the first, second, third, fourth and sixth sectors, the upper surface T is positioned in the same waya、TbSubstituting the expression of ω t into the first, second, third, fourth and sixth sectors in step (2) to obtain vao *、vbo *、vco *The expressions in the first, second, third, fourth, and sixth sectors are as follows:
Figure FDA0002630852240000023
Figure FDA0002630852240000024
Figure FDA0002630852240000031
Figure FDA0002630852240000032
Figure FDA0002630852240000033
(4) synthesizing v of each sector in step (3)ao *、vbo *、vco *To obtain the following formula:
Figure FDA0002630852240000034
Figure FDA0002630852240000041
Figure FDA0002630852240000042
(5) the three-phase pulse width modulation waveform v in the range of not less than 0 and not more than ω t and not more than 2 pi in the step (4)ao *、vbo *、vco *The period extension is carried out for one period to obtain a three-phase pulse width modulation waveform v within the range of not less than 0 and not more than ω t and not more than 2k piao *、vbo *、vco *K is a positive integer greater than or equal to 1;
(6) the peak value of the sine voltage to be inverted by each phase of inverting stage circuit is set as VacThe signal participating in PWM modulation of each phase inverter circuit is vam *、vbm *、vcm *Let us order
Figure FDA0002630852240000043
In the formula VdThe voltage of the direct current side of each phase of inverter in the step (2);
(7) when g in step (6)<1 time, participating in PWM modulation of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure FDA0002630852240000044
when g in the step (6) is more than or equal to 1, participating in the PWM signal v of each phase inverter circuitam *、vbm *、vcm *Comprises the following steps:
Figure FDA0002630852240000051
v of the above formulaao *、vbo *、vco *The three-phase pulse width modulation waveform v in the range of not less than 0 and not more than ω t and not more than 2k pi in the step (5)ao *、vbo *、vco *；
(8) Because each phase inverter circuit adopts an N +1 level cascade inverter unit, N is more than or equal to 1 and is a positive integer, N different triangular carrier signals are needed, the N different triangular carrier signals have the same frequency and amplitude and are continuously and vertically distributed in space and symmetrically distributed at two sides of a time axis, the phases of the N different triangular carrier signals sequentially differ by 180 degrees, and the period of the N different triangular carrier signals is the switching period T in the step (2)sAmplitude of is
Figure FDA0002630852240000052
In the formula VmPWM modulated signal v for each phase inverter stage circuit in step (7)am *、vbm *、vcm *The amplitude of (d);
(9) PWM modulating signal v of each phase of inverse conversion stage circuit in step (7)am *、vbm *、vcm *And (4) comparing the PWM signals with the N triangular carrier signals in the step (8) to obtain the PWM signal of each phase of inverse-conversion stage circuit, and further controlling a power switch tube of each phase of inverse-conversion stage circuit.
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CN112838769A (en) * 2021-03-08 2021-05-25 中国矿业大学(北京) Transformer-isolation-free star-connection medium-high voltage variable frequency speed regulation system and control method
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