CN117394708A - Current-mode PWM rectifier control system and method suitable for input unbalance - Google Patents
Current-mode PWM rectifier control system and method suitable for input unbalance Download PDFInfo
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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
- 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
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- 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
- H02J3/01—Arrangements for reducing harmonics or ripples
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- 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
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/14—Arrangements for reducing ripples from dc input or output
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K7/00—Modulating pulses with a continuously-variable modulating signal
- H03K7/08—Duration or width modulation ; Duty cycle modulation
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Abstract
The invention belongs to the technical field of PWM rectification control, and provides a current type PWM rectifier control system and method suitable for unbalanced input, which mainly comprise the following steps: firstly, acquiring the change of each equivalent input resistance when the input voltage is unbalanced; and secondly, according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, the equivalent on-time Ta, tb and Tc of each phase in one input voltage period is adjusted, and the balance of three-phase input currents ia, ib and ic under the input voltage unbalance is realized. The invention can realize the input current balance of the current type PWM rectifier under the unbalanced input voltage condition without additional hardware equipment, and simultaneously reduce the output current ripple.
Description
Technical Field
The invention relates to the technical field of PWM rectification control, in particular to a current type PWM rectifier control system and method suitable for unbalanced input.
Background
The conversion of alternating current into direct current is called rectification, also called AC-DC conversion, and the rectification circuit is a circuit that converts alternating current power supply voltage into direct current power supply voltage. The rectifying circuit is widely applied to the fields of electric automobile charging, direct current transmission systems, aerospace and the like. The PWM rectifiers can be classified into voltage-type rectifiers and current-type rectifiers according to the difference of the output-side energy storage elements. The voltage type PWM rectifier has the advantages of high energy storage efficiency, low loss, quick dynamic response and convenient control, and the technology is relatively mature. The current type PWM rectifier takes the inductance as an energy storage element, and has been well applied to the aspects of active power filtering, reactive compensation, superconducting energy storage, motor speed regulation, grid-connected power generation of renewable energy sources, induction heating power sources, electronic loads and the like.
In practical application, the three-phase current type PWM rectifier may work under unbalanced input voltage condition or have deviation of sampling proportion of the three-phase input voltage, if the traditional control scheme is adopted, the three-phase current type PWM rectifier designed by taking voltage balance as constraint condition may generate even number and odd number of non-characteristic harmonic waves on the direct current side and alternating current side, these low order non-characteristic harmonic waves may generate harmonic pollution to the power grid, so that performance of the rectifier is deteriorated, and even rectifying equipment may be burnt out in severe cases.
In the current type PWM rectifier modulation method, the existing twelve-sector space pulse width modulation method has high DC voltage or current utilization rate, flexible and various digital implementation modes and the lowest switching loss, and is always the first choice of the current type PWM rectifier modulation method. However, in the existing twelve-sector space vector modulation method, under the condition of unbalanced power grid voltage, input current is severely distorted and unbalanced, a large amount of odd harmonics are generated, and accordingly a large amount of reactive power is generated, so that serious pollution is caused to the power grid, normal operation of other equipment in the power grid is affected, and output voltage also contains a large amount of even harmonics, so that output voltage ripple is overlarge.
Disclosure of Invention
The invention aims to provide a current type PWM rectifier control system and a method suitable for input unbalance, which can restrain input current unbalance caused by power grid voltage unbalance and reduce output current ripple at a direct current side.
The invention solves the technical problems and adopts the following technical scheme:
in one aspect, the present invention provides a current-mode PWM rectifier control system adapted for input imbalance, comprising:
the three-phase input voltage equivalent resistance change acquisition unit is used for acquiring the change of each phase of equivalent input resistance when the input voltage is unbalanced;
and the three-phase input current balance control unit under the unbalance of the input voltage is used for adjusting the equivalent on time Ta, tb and Tc of each phase in one input voltage period according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, so as to realize the balance of the three-phase input currents ia, ib and ic under the unbalance of the input voltage.
On the other hand, the invention also provides a control method of the current type PWM rectifier suitable for input unbalance, which is applied to the control system of the current type PWM rectifier suitable for input unbalance, and comprises the following steps:
acquiring the change of each equivalent input resistance when the input voltage is unbalanced;
according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, the equivalent on time Ta, tb and Tc of each phase in one input voltage period is adjusted, and the balance of three-phase input currents ia, ib and ic under the input voltage unbalance is realized.
As a further optimization, the variation of the input resistance per each equivalent is represented by respective phase resistance variation coefficients Ka, kb and Kc, and the resistance variation coefficients Ka, kb and Kc for the nth input voltage period are represented by respective equivalent on-times Ta, tb and Tc for the N-1 th input voltage period;
the method for acquiring the change of the equivalent input resistance of each phase when the input voltage is unbalanced comprises the following steps:
integrating the three-phase modulated wave signals in the N-1 th input voltage period to obtain equal effective on-time Ta, tb and Tc of the N-1 th input voltage period;
the equivalent resistance of each phase of resistance of the nth input voltage period is distributed according to the equivalent on time of each phase of the (N-1) th period, namely Ka: kb: kc=ta: tb: tc;
maintaining kc=1, the respective phase resistance change coefficients ka=ta/Tc, kb=tb/Tc, kc=1 in the nth period are obtained.
As a further optimization, each of the phase resistance change coefficients Ka, kb, and Kc of the 1 st input voltage period is initialized to 1.
As a further optimization, for the resistance change coefficients Ka, kb and Kc of the nth input voltage period, represented by the respective equivalent on-times Ta, tb and Tc of the nth input voltage period, the integral calculation is performed for the respective phase on-times Ta, tb and Tc in the nth 1 period as a reference, thereby correcting the Ka, kb and Kc of the nth period.
As a further optimization, the three-phase input currents ia, ib and ic have the following calculation formula:
where Ua, ub, uc represent input phase voltages of each phase, ra, rb, rc are equal effective input resistances of each phase, R represents an average input resistance of each phase at the full balance of three-phase input, and Ka, kb, and Kc represent equal effective input resistance change coefficients of each phase.
As a further optimization, the balancing of the three-phase input currents ia, ib and ic under the imbalance of the input voltages is achieved by the following specific implementation modes:
the equal effective on-time Ta, tb and Tc in one input voltage period is in direct proportion to the input voltage Ua, ub and Uc, the equal effective on-time Ta, tb and Tc is used for calculating the equal effective input resistance change coefficient Ka, kb and Kc, the equal effective input resistance change coefficient Ka, kb and Kc changes along with the input voltage Ua, ub and Uc, and the three-phase input current ia, ib and ic are further equal in amplitude value, so that the balance of the three-phase input current ia, ib and ic is realized.
As a further optimization, the equivalent on-times Ta, tb and Tc within one input voltage period are adjusted by adjusting the space vector pulse width modulation respective vector on-times.
As a further optimization, the adjusting the equivalent on-times Ta, tb and Tc in one input voltage period by adjusting the space vector pulse width modulation respective vector on-times includes the following steps:
dividing the input side three-phase input voltage into sectors according to 30 electric angles, and dividing the period of the three-phase input voltage into 12 sectors according to the anticlockwise direction;
determining a current vector acting in a sector through the sector in which the input voltages Ua, ub and Uc are positioned;
calculating the acting time of each current vector in the sector according to the output voltage, the input voltages Ua, ub and Uc and the phase resistance change coefficients Ka, kb and Kc of the current input voltage period;
generating a three-phase modulated wave signal according to the action time of each current vector;
and comparing the three-phase modulated wave signal with the triangular carrier signal Ut, generating a driving signal corresponding to the switching tube on the bridge arm as 1 when the value of the three-phase modulated wave is larger than the triangular carrier signal Ut, and generating a driving signal corresponding to the switching tube on the bridge arm as 0 when the value of the three-phase modulated wave is smaller than or equal to the triangular carrier signal Ut.
The beneficial effects of the invention are as follows: by the control system and the method for the current-type PWM rectifier suitable for input unbalance, the equivalent on-time Ta, tb and Tc of each phase in one input voltage period can be adjusted according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, and then the balance of three-phase input currents ia, ib and ic under the input voltage unbalance is realized. In the invention, the input current can be kept balanced and has low distortion degree, a large amount of odd harmonics can not be generated, a large amount of reactive power can not be generated, serious pollution to a power grid is avoided, normal operation of other equipment in the power grid is not influenced, and output voltage ripple is effectively reduced.
Drawings
FIG. 1 is a schematic diagram of a system configuration of a control system for a PWM rectifier of the current imbalance type according to embodiment 1 of the present invention;
FIG. 2 is a flow chart of a control method for a current-type PWM rectifier suitable for input unbalance in embodiment 2 of the present invention;
FIG. 3 is a graph showing the variation of the coefficient of resistance variation of each phase with the period of the input voltage according to embodiment 2 of the present invention;
FIG. 4 is a waveform of input three-phase current according to the conventional twelve-sector space vector modulation method in embodiment 2 of the present invention;
FIG. 5 is a waveform of three-phase current input by the control method of the current-type PWM rectifier suitable for unbalanced input under the same power, load and circuit topology conditions in embodiment 2 of the present invention;
FIG. 6 is a waveform of the DC side output current under the same power, load, and circuit topology conditions in embodiment 2 of the present invention using the prior modulation method;
fig. 7 is a waveform of the output current of the dc side of embodiment 2 of the present invention under the same power, load, and circuit topology conditions, using the control method of the PWM rectifier suitable for unbalanced input.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Example 1
The present embodiment provides a current-mode PWM rectifier control system adapted for input unbalance, comprising:
the three-phase input voltage equivalent resistance change acquisition unit is used for acquiring the change of each phase of equivalent input resistance when the input voltage is unbalanced;
and the three-phase input current balance control unit under the unbalance of the input voltage is used for adjusting the equivalent on time Ta, tb and Tc of each phase in one input voltage period according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, so as to realize the balance of the three-phase input currents ia, ib and ic under the unbalance of the input voltage.
Referring to fig. 1, the topology structure of the current-type PWM rectifier includes an input (ac side) LC filter structure composed of an inductor Lin and a capacitor Cin, which functions to filter out harmonics of the switching frequency of the current on the network side of the rectifier; the three-phase rectifier bridge is composed of all-control switching tubes, wherein each switching tube is connected with a diode in series, so that the voltage reverse blocking capacity of the device can be improved; the output inductor Lo plays a role in maintaining the stability of output current; the freewheeling diode can maintain the output inductance Lo current continuous; the output capacitor Co plays a role in stabilizing the output voltage.
In this embodiment, if the equivalent voltage control is adopted, the equivalent voltages cannot be obtained directly by using the equivalent acting times Ta, tb and Tc, and the control process is relatively more complex, so that the equivalent resistance control strategy is adopted, and the ratio of the equivalent resistances is the same as the ratio of the equivalent acting times of the phases in one input voltage period, so that if the equivalent resistance control strategy is adopted, the equivalent resistance change coefficients Ka, kb and Kc of the phases can be obtained by calculating the equivalent acting times Ta, tb and Tc of the phases in each input voltage period.
Example 2
The present embodiment provides a control method for a current-type PWM rectifier suitable for unbalanced input, with a flowchart shown in fig. 2, based on embodiment 1, wherein the method includes the following steps:
s1, acquiring the change of each equivalent input resistance when input voltages are unbalanced;
s2, according to the change of each equivalent input resistance when the input voltage is unbalanced, the equivalent on time Ta, tb and Tc of each phase in one input voltage period is adjusted, and the balance of three-phase input currents ia, ib and ic under the input voltage unbalance is realized.
In this embodiment, the equivalent acting time of each phase in each input voltage period is calculated to indirectly obtain the equivalent input resistance change coefficients Ka, kb and Kc, so that the equivalent acting time of each phase in the N-1 th input voltage period needs to be calculated to obtain the equivalent resistance change coefficients Ka, kb and Kc in the N-1 th input voltage period. According to the embodiment, through a periodic equivalent resistance strategy, the resistance change coefficients Ka, kb and Kb can be continuously updated, and balanced three-phase input current can be obtained after a steady state is achieved.
In this embodiment, the change in the input resistance per equivalent is represented by the respective phase resistance change coefficients Ka, kb, and Kc, and the resistance change coefficients Ka, kb, and Kc for the nth input voltage period are represented by the respective equivalent on-times Ta, tb, and Tc for the N-1 th input voltage period;
the step of obtaining the change of the equivalent input resistance of each phase when the input voltage is unbalanced may include the following steps:
step 1, integrating the three-phase modulation wave signals in the N-1 th input voltage period to obtain equal on-time Ta, tb and Tc of each of the N-1 th input voltage period;
step 2, the equivalent resistance of each phase of resistance of the nth input voltage period is distributed according to the equivalent on time of each phase of the (N-1) th period, namely Ka: kb: kc=ta: tb: tc;
step 3, maintaining kc=1 to obtain each phase resistance change coefficient ka=ta/Tc, kb=tb/Tc, kc=1 in the nth period.
In the practical application process, the resistance change coefficients Ka, kb and Kc of each phase in the 1 st input voltage period are all initialized to 1; further, the resistance change coefficients Ka, kb and Kc of the N-th input voltage period are represented by the respective equivalent on-times Ta, tb and Tc of the N-1 th input voltage period, and the on-times Ta, tb and Tc of the respective phases in the N-1 th period are integrated as references, thereby correcting the Ka, kb and Kc of the N-th period.
It should be noted that the three-phase input currents ia, ib and ic have the following calculation formulas:
where Ua, ub, uc represent input phase voltages of each phase, ra, rb, rc are equal effective input resistances of each phase, R represents an average input resistance of each phase at the full balance of three-phase input, and Ka, kb, and Kc represent equal effective input resistance change coefficients of each phase.
The realization method for balancing the three-phase input currents ia, ib and ic under unbalanced input voltage comprises the following specific realization modes:
the equal effective on-time Ta, tb and Tc in one input voltage period is in direct proportion to the input voltage Ua, ub and Uc, the equal effective on-time Ta, tb and Tc is used for calculating the equal effective input resistance change coefficient Ka, kb and Kc, the equal effective input resistance change coefficient Ka, kb and Kc changes along with the input voltage Ua, ub and Uc, and the three-phase input current ia, ib and ic are further equal in amplitude value, so that the balance of the three-phase input current ia, ib and ic is realized.
Preferably, the equivalent on-times Ta, tb and Tc for each phase in one input voltage period can be adjusted by adjusting the space vector pulse width modulation respective vector on-times.
Specifically, the adjustment of the equivalent on-times Ta, tb and Tc in one input voltage period by adjusting the space vector pulse width modulation of the respective vector on-times may include the following steps:
a. dividing the input side three-phase input voltage into sectors according to 30 electric angles, and dividing the period of the three-phase input voltage into 12 sectors according to the anticlockwise direction;
b. determining a current vector acting in a sector through the sector in which the input voltages Ua, ub and Uc are positioned;
c. calculating the acting time of each current vector in the sector according to the output voltage, the input voltages Ua, ub and Uc and the phase resistance change coefficients Ka, kb and Kc of the current input voltage period;
d. generating a three-phase modulated wave signal according to the action time of each current vector;
e. and comparing the three-phase modulated wave signal with the triangular carrier signal Ut, generating a driving signal corresponding to the switching tube on the bridge arm as 1 when the value of the three-phase modulated wave is larger than the triangular carrier signal Ut, and generating a driving signal corresponding to the switching tube on the bridge arm as 0 when the value of the three-phase modulated wave is smaller than or equal to the triangular carrier signal Ut.
In the practical application process, the duration of each working mode of the rectifier can be calculated according to the output voltage, the input voltages Ua, ub and Uc and the phase resistance change coefficients Ka, kb and Kc of the current input voltage period, and the method specifically comprises the following steps:
the calculation formula of the action time of each current vector is as follows:
sector 12,1:
sector 2,3:
sectors 4,5:
sectors 6,7:
sectors 8,9:
sectors 10, 11:
in the formula, T1, T2, T3, T4, T5, T6 and T0 respectively represent the acting time of current vectors I1, I2, I3, I4, I5, I6 and I0, ts represents the switching period, ka, kb and Kc respectively represent the equivalent resistance change coefficients, uo represents the direct-current side output voltage, and Ua, ub and Uc respectively represent the three-phase input voltage.
Fig. 3 shows the variation of the phase resistance coefficient with the input voltage period in the present embodiment, and it can be seen from fig. 3 that, every other input voltage period, under the condition of maintaining kc=1, the values of Ka and Kb are updated with each equal action time.
Fig. 4 is a waveform of input three-phase current when input voltage is unbalanced in the conventional twelve-sector space vector modulation method, and it can be seen from the waveform of fig. 4 that the three-phase input current is asymmetric at this time, the amplitude differences among the phases are larger, and the amplitude variance of the three-phase current reaches 0.3262.
Fig. 5 shows that under the same power, load and circuit topology conditions, the method is suitable for inputting three-phase current waveforms under the control method of the current-type PWM rectifier with unbalanced input, and according to the hardware design and simulation verification of the modulation method in the specific implementation process, the symmetry of the three-phase input current is better, the variance of the three-phase current amplitude is reduced to 0.0137, the current harmonic content is small, and the harmonic pollution to the input power supply is smaller.
Fig. 6 and fig. 7 are waveforms of output current at the direct current side under the same power, load and circuit topology conditions in the present embodiment, respectively using the conventional twelve-sector space vector modulation method and the current-type PWM rectifier control method suitable for input imbalance, and comparing the waveforms in fig. 6 and fig. 7, the output current ripple is smaller and the output power quality is high when the current-type PWM rectifier control method suitable for input imbalance is provided in the present embodiment.
Therefore, the current-mode PWM rectifier control method suitable for unbalanced input is simple in algorithm and easy to realize, does not need additional hardware equipment, can realize input current balance under unbalanced input voltage of the current-mode PWM rectifier, and effectively reduces output current ripple.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A current-mode PWM rectifier control system adapted for input imbalance, comprising:
the three-phase input voltage equivalent resistance change acquisition unit is used for acquiring the change of each phase of equivalent input resistance when the input voltage is unbalanced;
and the three-phase input current balance control unit under the unbalance of the input voltage is used for adjusting the equivalent on time Ta, tb and Tc of each phase in one input voltage period according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, so as to realize the balance of the three-phase input currents ia, ib and ic under the unbalance of the input voltage.
2. A control method for a current-mode PWM rectifier suitable for input unbalance, applied to the control system for a current-mode PWM rectifier suitable for input unbalance according to claim 1, comprising the steps of:
acquiring the change of each equivalent input resistance when the input voltage is unbalanced;
according to the change of the equivalent input resistance of each phase when the input voltage is unbalanced, the equivalent on time Ta, tb and Tc of each phase in one input voltage period is adjusted, and the balance of three-phase input currents ia, ib and ic under the input voltage unbalance is realized.
3. The control method for a current-mode PWM rectifier adapted for input unbalance according to claim 2, wherein the change in the effective input resistance per time is represented by respective phase resistance change coefficients Ka, kb, and Kc, and the resistance change coefficients Ka, kb, and Kc for the nth input voltage period are represented by respective effective on-times Ta, tb, and Tc for the N-1 th input voltage period;
the method for acquiring the change of the equivalent input resistance of each phase when the input voltage is unbalanced comprises the following steps:
integrating the three-phase modulated wave signals in the N-1 th input voltage period to obtain equal effective on-time Ta, tb and Tc of the N-1 th input voltage period;
the equivalent resistance of each phase of resistance of the nth input voltage period is distributed according to the equivalent on time of each phase of the (N-1) th period, namely Ka: kb: kc=ta: tb: tc;
maintaining kc=1, the respective phase resistance change coefficients ka=ta/Tc, kb=tb/Tc, kc=1 in the nth period are obtained.
4. A control method for a current-mode PWM rectifier adapted to an input imbalance according to claim 3, wherein each of the phase resistance change coefficients Ka, kb and Kc of the 1 st input voltage period is initialized to 1.
5. A control method for a current-mode PWM rectifier adapted to an input unbalance according to claim 3, wherein the resistance change coefficients Ka, kb and Kc for the nth input voltage period are represented by respective equivalent on-times Ta, tb and Tc for the N-1 th input voltage period, and the integral calculation is performed for the respective phase on-times Ta, tb and Tc for the N-1 th period as a reference, thereby correcting the Ka, kb and Kc for the nth period.
6. The control method for a current-mode PWM rectifier adapted for input unbalance according to claim 2, wherein the three-phase input currents ia, ib and ic are calculated as:
where Ua, ub, uc represent input phase voltages of each phase, ra, rb, rc are equal effective input resistances of each phase, R represents an average input resistance of each phase at the full balance of three-phase input, and Ka, kb, and Kc represent equal effective input resistance change coefficients of each phase.
7. The method for controlling a PWM rectifier adapted for unbalanced input of claim 6, wherein the balancing of the three phase input currents ia, ib and ic under unbalanced input voltage is implemented by:
the equal effective on-time Ta, tb and Tc in one input voltage period is in direct proportion to the input voltage Ua, ub and Uc, the equal effective on-time Ta, tb and Tc is used for calculating the equal effective input resistance change coefficient Ka, kb and Kc, the equal effective input resistance change coefficient Ka, kb and Kc changes along with the input voltage Ua, ub and Uc, and the three-phase input current ia, ib and ic are further equal in amplitude value, so that the balance of the three-phase input current ia, ib and ic is realized.
8. The control method for a current-mode PWM rectifier adapted for input imbalance according to claim 2, wherein the equivalent on-times Ta, tb and Tc of each phase in one input voltage period are adjusted by adjusting the space vector pulse width modulation respective vector on-times.
9. The method for controlling a PWM rectifier adapted for input imbalance according to claim 8, wherein said adjusting the equivalent on-times Ta, tb and Tc of each phase in an input voltage cycle by adjusting the space vector pulse width modulation on-times of each vector comprises the steps of:
dividing the input side three-phase input voltage into sectors according to 30 electric angles, and dividing the period of the three-phase input voltage into 12 sectors according to the anticlockwise direction;
determining a current vector acting in a sector through the sector in which the input voltages Ua, ub and Uc are positioned;
calculating the acting time of each current vector in the sector according to the output voltage, the input voltages Ua, ub and Uc and the phase resistance change coefficients Ka, kb and Kc of the current input voltage period;
generating a three-phase modulated wave signal according to the action time of each current vector;
and comparing the three-phase modulated wave signal with the triangular carrier signal Ut, generating a driving signal corresponding to the switching tube on the bridge arm as 1 when the value of the three-phase modulated wave is larger than the triangular carrier signal Ut, and generating a driving signal corresponding to the switching tube on the bridge arm as 0 when the value of the three-phase modulated wave is smaller than or equal to the triangular carrier signal Ut.
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