CN112350590A - Uncontrolled rectifier harmonic compensation circuit and control method - Google Patents
Uncontrolled rectifier harmonic compensation circuit and control method Download PDFInfo
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- CN112350590A CN112350590A CN202110010258.XA CN202110010258A CN112350590A CN 112350590 A CN112350590 A CN 112350590A CN 202110010258 A CN202110010258 A CN 202110010258A CN 112350590 A CN112350590 A CN 112350590A
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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
- H02M7/06—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
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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
- H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
- H02M1/4208—Arrangements for improving power factor of AC input
- H02M1/4216—Arrangements for improving power factor of AC input operating from a three-phase input voltage
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- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The invention discloses an uncontrolled rectifier harmonic compensation circuit and a control method, wherein a three-phase uncontrolled rectifier is used as a compensation object, the three-phase uncontrolled rectifier is compensated through a three-phase harmonic compensation circuit, the PFC function of the whole circuit is realized, and then direct current is output after parallel connection through DC-DC conversion. The invention has the characteristics of rapid dynamic compensation, high precision, good reliability and the like, can also greatly reduce the capacity of the active filter, and is a power quality solution with low cost, high reliability and large capacity.
Description
Technical Field
The invention belongs to the technical field of harmonic compensation of power equipment, and particularly relates to a harmonic compensation circuit of an uncontrolled rectifier and a control method.
Background
With the continuous development of society, electric energy is widely applied as a clean and efficient energy form, and is an important guarantee for maintaining the normal operation of contemporary society. With the use of a large number of power electronic devices, the problems of harmonic pollution, low power factor and other electric energy quality in the power grid are more and more serious. On the other hand, with the demand of power users on the quality of electric energy becoming higher and higher, a safe and reliable power grid environment is built, and providing high-quality and clean electric energy for the power users is a primary task, wherein harmonic wave and reactive power management become research hotspots. In the wide application of power electronic technology, a great deal of power electronic equipment such as various high-power rectifying, inverting and frequency conversion devices and the like are put into industrial production and use, and meanwhile, the specific gravity of various nonlinear loads on a user side is increased continuously, such as a frequency converter, an electric arc furnace and the like, and a great deal of harmonic components are generated during working.
At present, harmonic wave treatment modes mainly comprise two types, one is active treatment, harmonic wave sources are taken as research objects, so that the harmonic wave sources do not generate harmonic waves, the power factor is controlled to be 1, and the harmonic wave treatment method is suitable for power electronic devices serving as main harmonic wave sources in a power grid, can reduce the generation of the harmonic waves to a certain extent, but cannot completely eliminate the harmonic waves.
The active treatment method mainly comprises the following steps
(1) Multi-pulse rectification technology: theoretical analysis shows that the harmonic frequency generated on the alternating current side is nk +/-1 (n is a pulse number, and k is a positive integer), and the higher the pulse number is, the lower the low-frequency subharmonic content is. However, as the pulse number increases, the size of the rectifier transformer increases, and the wiring is more complicated.
(2) Multilevel conversion technology: by superimposing the square wave voltage waveforms, the output current is approximated to a sine wave and in phase with the grid side voltage.
(3) Pulse Width Modulation (PWM) technique: and a high-frequency pulse width modulation technology is adopted, so that the harmonic current at the side of a power grid is reduced, and the power factor is controlled. When the technology is applied to the rectifier, the current on the network side can be sinusoidal, and the harmonic pollution is reduced.
The other is passive treatment, which is to install a harmonic compensation device near a harmonic source to compensate harmonic in the system and prevent harmonic current from flowing into a power grid by mainly including passive filters, active filters (APF), hybrid filters and the like.
The passive filter provides a low-impedance loop for harmonic waves through inductance-capacitance (LC) series resonance, avoids the influence of the harmonic waves on a power grid, and can be mainly divided into a single-tuning filter, a double-tuning filter, a high-pass filter and the like. The method can compensate certain reactive power while inhibiting harmonic waves, has simple structure and low manufacturing cost, and is widely applied to electric power systems. However, the passive filter also has inevitable disadvantages: the compensation frequency band is narrow, only fixed subharmonics can be compensated, the compensation frequency depends on element parameters seriously, the compensation effect is unstable when LC parameters drift, and the compensation frequency is easily influenced by power grid fluctuation and generates harmonic amplification and circuit heating and the like due to parallel resonance with a system. The APF makes up the deficiency of the passive filter, can detect the harmonic component in the system in real time, controls the converter circuit to generate the compensation current to filter the harmonic component, and has high compensation precision and flexible control mode. Compared with a passive filter, the APF can be regarded as a programmable variable impedance loop, and can be regarded as a parallel equivalent network with infinite low-impedance resonant frequency points theoretically, so that real-time tracking compensation can be performed on harmonic current, a resonance phenomenon with system impedance can be avoided, better dynamic performance and compensation effect are achieved, and the APF gradually becomes a harmonic wave treatment research hotspot.
The APF may be classified into a series type, a parallel type, and a series-parallel type structure according to a connection method with a power grid.
(1) The series APF structure is shown in figure 1, the APF is connected between a power grid and a harmonic source in series through a reactor L and a transformer T, harmonic components in the voltage on the load side are detected, compensation voltage is injected into the power grid, the influence of the voltage source type harmonic source on the power grid can be restrained, and the voltage of the power grid is improved. Under the structure, load current can flow through the coupling transformer, so that large loss is brought, and the load current is less in practical application.
(2) The parallel APF structure is shown in fig. 2, the APF is connected to a power grid in a parallel mode through a reactor L, and compensation current is injected into the power grid after detecting harmonic components in current on a load side for filtering the harmonic components in the current and compensating reactive power. The structure is simple and easy to expand, and is one of the most widely applied structures at present.
(3) Series-parallel APF. As shown in fig. 3, two APF devices are respectively connected to the power grid in series and parallel, in the topology, the series APF is used as a voltage source to compensate the fundamental voltage and harmonic voltage of the power grid, the parallel APF is used as a current source to absorb the load harmonic current and adjust the dc-side bus voltage, and functions such as reactive compensation and voltage control (fluctuation and unbalance) can be realized while harmonic control is performed, so the topology is called a Unified Power Quality Conditioner (UPQC), but the topology is complex in structure and difficult to control, and thus the topology is not yet popularized and applied.
The prior art scheme is as follows:
a three-phase rectification circuit is taken as a representative harmonic source, an APF is connected into a power grid in a parallel mode, a direct-current side element is a capacitor and can be equivalent to a controlled current source, and the three-phase rectification circuit is suitable for compensating current type loads. The main circuit structure of the three-phase three-wire system voltage parallel type APF is shown in figure 4,U a、U b、U cis the voltage on the side of the power grid,i Sa、i Sb、i Scis the current on the side of the power grid,i Xa、i Xb、i Xcis the current on the load side and is,i Ca、i Cb、i Ccfor APF to generate compensating current, APF mainThe topology adopts a three-phase voltage type bridge converter structure and three switching tubesVT 1、VT 3、VT 5Three switch tubes connected in common anodeVT 2、VT 4、VT 6The common cathode is connected with the anode,VT 1、VT 2、VT 3、VT 4、VT 5、VT 6a diode is reversely connected in parallel on the switch tubeVD 1、VD 2、VD 3、VD 4、VD 5、VD 6The upper and lower bridge arms are connected with the power grid through the reactor, the direct current side is a capacitance element, and a resistance R for slow electrification is added on the direct current side for ensuring the work safety0Can avoid overlarge current flowing through the capacitor when the APF is put into operation and avoid R in a normal working state0Is short-circuited. After the current harmonic wave generated by the nonlinear load is compensated, the current on the side of the power grid is not basically influenced by the nonlinear load, and the sine of the waveform is kept.
In order to solve the harmonic problem caused by a harmonic source, a scheme of harmonic compensation is generally a topology combining a multi-level PWM circuit and a Power Factor Correction (PFC), which can meet the requirements of high voltage and large capacity, further reduce the Total Harmonic Distortion (THD) of input current, compensate corresponding harmonics, reduce system loss, and improve system efficiency.
Currently, for the current research situation of three-phase PWM rectifier, a three-phase single-switch topology and a three-phase six-switch topology are typical topologies, such as those shown in fig. 5 and fig. 6, whereinQ、Q 1 、Q 2 、Q 3 、Q 4 、Q 5 、Q 6 Is a Metal Oxide Semiconductor (MOS) tube,VDthe two topologies are diodes, and can obviously improve the power factor of the circuit compared with uncontrolled rectification. Although the two circuit structures can effectively improve the power factor of the system, when the state of the switching tube is switched from on to off, the voltage borne by the two ends is the voltage of the whole direct current bus, and the voltage stress borne by the voltage is largerThus limiting its application in high power, high voltage applications.
What is used for harmonic compensation in this invention is a new three-phase harmonic compensation circuit topology, which is shown in fig. 7.
Disclosure of Invention
The invention provides an uncontrolled rectifier harmonic compensation circuit and a control method thereof, aiming at solving the problems of harmonic waves caused by the introduction of a large amount of power electronic equipment, nonlinear loads and the like in a power grid and the problems of high APF (active power filter) cost and the like.
According to the uncontrolled rectifier harmonic compensation circuit, a three-phase uncontrolled rectifier is used as a compensation object, harmonic characteristics of the three-phase uncontrolled rectifier are analyzed, the three-phase uncontrolled rectifier is compensated through the three-phase harmonic compensation circuit, a PFC function of the whole circuit is achieved, and then direct current is output after the three-phase uncontrolled rectifier is connected in parallel through DC-DC conversion. The specific circuit is as follows:
inductanceL 1And diodeD A+、D a+Anode, diodeD A-、D a-The negative electrode is connected with the MOS tubeQ 1The drain of (a) the gate of (b),Q 1andQ 2the two-stage power supply is connected with the same source stage,Q 2is connected to neutral point M; inductanceL 2And diodeD B+、D b+Anode, diodeD B-、D b-The negative electrode is connected with the MOS tubeQ 3The drain of (a) the gate of (b),Q 3andQ 4the two-stage power supply is connected with the same source stage,Q 4is connected to neutral point M; inductanceL 3And diodeD C+、D c+Anode, diodeD C-、D c-The negative electrode is connected with the MOS tubeQ 5The drain of (a) the gate of (b),Q 5andQ 6the two-stage power supply is connected with the same source stage,Q 6is connected to neutral point M;D A+ 、D B+ 、D C+is connected to the positive pole P of the output terminal,D A- 、D B- 、D C-is connected to the negative pole N of the output end, and outputs a voltage stabilizing capacitorC 1The anode is connected to the output end anode P, the cathode is connected to the neutral point M,C 2the anode is connected to the neutral point M, and the cathode is connected to the cathode N of the output end; the harmonic wave circuit part is provided with a harmonic wave circuit part,D a+ 、D b+ 、D c+is connected to the positive pole p of the output terminal,D a- 、D b- 、D c-is connected to the negative pole n of the output end; the output end PN of the three-phase uncontrolled rectifying part is connected with a DC-DC converter, and the output end PN of the three-phase harmonic compensation circuit is connected with the DC-DC converter in parallel to output direct current. The structure is different from APF, when the three-phase rectifier carries out harmonic compensation, the compensation current is not input in an externally-hung mode any more, but the three-phase rectifier is integrated with a harmonic source and a DC-DC converter and participates in energy transfer together, the power factor correction of the total input current is realized, and the advantages of high power density of the three-phase uncontrolled rectifier and active controllability of the three-phase rectifier are considered.
The invention discloses a control method of an uncontrolled rectifier harmonic compensation circuit, which outputs feedback voltageU outAnd a reference voltageU refAfter difference is made, a reference current value is obtained through a Proportional Integral (PI) linkI refThen will beI refThe sine half-wave signal and the three-phase compensating current are obtained by transmitting the sine half-wave signal into the current inner loop and multiplying the sine half-wave signal by the absolute value of each phase voltageiL A 、iL B 、iL CAnd three-phase harmonic currentiL a、iL b 、iL cAnd after the sum is subjected to difference, obtaining a modulation wave through a PI link, comparing the modulation wave with a triangular carrier wave, and finally outputting three paths of PWM.
The beneficial technical effects of the invention are as follows:
1. the traditional APF harmonic detection and compensation method adopts a three-phase six-switch topology, for example, in a three-phase three-wire system voltage parallel APF circuit, when a switch tube is switched from on to off, the voltage borne by two ends of the switch tube is the voltage of the whole direct-current bus, and the voltage stress borne by the switch tube is large, so that the application of the switch tube in high-power and high-voltage occasions is limited. According to the three-phase harmonic compensation circuit topology, each phase of bridge arm adopts a fast recovery power MOS tube, the voltage stress of the MOS tube is only half of the output voltage on a direct current bus, each phase of bridge arm consists of a driving circuit formed by two power switching devices, the control is simple, and the stable control of the midpoint voltage is easy to realize; when one phase is conducted up and down simultaneously, the short circuit of the circuit can not be caused, the direct-current bus direct connection condition does not exist, and the structure is safe and reliable; small volume and high power density. High power density, easy integration and suitability for high-voltage and high-power occasions.
2. Compared with other control schemes, the precision of single closed loop PI control depends on a proportional term and an integral term, the control effect is difficult to realize for systems with higher requirements on dynamic performance and stable precision, meanwhile, a PI controller cannot realize non-static tracking adjustment of sine instructions, and the application has certain limitation; hysteresis control has the defects of random operation, unstable influence on switching frequency, frequent change, high requirement on the rapid dynamic response performance of a filter, certain difficulty in design and less adoption; the repeated control method can effectively control the harmonic content to obtain a stable output waveform, and has the defect of poor dynamic performance; in the harmonic current compensation control scheme, a compensation current command signal is compared with an actual compensation signal, the difference value of the two signals is amplified by a PI link to form a modulation signal, and then the modulation signal is compared with a high-frequency triangular wave to obtain corresponding PWM, so that the actual compensation current can realize real-time tracking of the harmonic current. This harmonic compensation control strategy switching frequency is fixed, dynamic response is fast, easily realize control simply, in addition output voltage stabilization control, utilize output capacitor charge-discharge balance to realize output voltage's balanced control, make neutral point voltage keep about 0V, this kind of scheme is more simple easily to be controlled, has reduced the influence of electric capacity ripple for electric capacity appearance value in the driver can effectually reduce, and the cost is lower, thereby has improved the reliability and the life of converter.
3. In the harmonic compensation circuit, the whole three-phase harmonic compensation circuit packComprising 12 uncontrollable diodesD A+ 、D B+ 、 D C+、D A- 、D B- 、D C-、D a+ 、D b+ 、D c+、D a- 、D b- 、D c-3 power inductorsL 1、L 2、L 33 output capacitorsC 1、C 2、C 3And 3 groups of MOS tubes with same source levelQ 1、Q 2、Q 3、Q 4、Q 5、Q 6Bidirectional flow of energy can be achieved. Taking phase A as an example, an inductorL 1And diodeD A+、D a+Anode, diodeD A-、D a-The negative electrode is connected with the MOS tubeQ 1The drain of (a) the gate of (b),Q 1andQ 2the two-stage power supply is connected with the same source stage,Q 2is connected to the neutral point M,D A+ 、D B+ 、D C+is connected to the positive pole P of the output terminal,D A- 、D B- 、D C-is connected to the negative pole N of the output end, and outputs a voltage stabilizing capacitorC 1The anode is connected to the output end anode P, the cathode is connected to the neutral point M,C 2the anode is connected to the neutral point M, and the cathode is connected to the cathode N of the output end. The harmonic wave circuit part is provided with a harmonic wave circuit part,D a+ 、D b+ 、D c+is connected to the positive pole p of the output terminal,D a- 、D b- 、 D c-is connected to the negative pole n of the output terminal. The output pn of the harmonic part is connected with a DC-DC converter, and the compensation circuit is connected with the DC-DC converter and then outputs direct current in parallel. The structure has the characteristics of rapid dynamic compensation, high precision, good reliability and the like, can also greatly reduce the capacity of the APF, and is a power quality solution with low cost, high reliability and large capacity.
Drawings
Fig. 1 is a tandem APF.
Fig. 2 is a parallel APF.
Fig. 3 is a series-parallel type APF.
Fig. 4 is a main circuit structure of a three-phase three-wire system voltage parallel type APF.
Fig. 5 is a three-phase single switch topology.
Fig. 6 is a three-phase six-switch topology.
Fig. 7 is a three-phase harmonic compensation circuit topology.
FIG. 8 is a circuit for compensating harmonics of an uncontrolled rectifier according to the present invention.
FIG. 9 is a harmonic compensation topology for a three-phase uncontrolled rectifier of the present invention.
Fig. 10 is a schematic view showing a forward current flow and a reverse current flow.
Fig. 11 is a simplified topology of a three-phase harmonic compensation circuit.
Fig. 12 shows the positive half Sa cut-off.
Fig. 13 shows the positive half cycle Sa on.
Fig. 14 shows the negative half cycle Sa.
Fig. 15 shows the negative half cycle Sa on.
Fig. 16 is a harmonic compensation control scheme.
FIG. 17 shows harmonic currentsiL aThe PSIM of (1) simulates a waveform.
FIG. 18 shows the compensation currentiL AThe PSIM of (1) simulates a waveform.
Fig. 19 is a simulation waveform of the compensated a-phase current PSIM.
Fig. 20 shows simulation waveforms of input voltage and input current PSIM.
Fig. 21 is a simulation waveform of the output voltage PSIM of the upper and lower capacitors.
Detailed Description
The invention is described in further detail below with reference to the figures and the detailed description.
The widely applied power electronic device introduces harmonic waves into a power system and consumes a large amount of reactive power. Before the harmonic and reactive problems brought by the power electronic device are treated, the compensation object is firstly analyzed, so that the selection of a compensation mode is facilitated, and meanwhile, the specific design of the compensation device is facilitated. Among them, the three-phase uncontrolled rectifying circuit has been used as the most widely applied power electronic device for a long time, and will bring about the lag of harmonic current and power factor, and a lot of attention and research are paid. As a current mode harmonic source, harmonic compensation can be studied.
Fig. 8 shows a harmonic compensation circuit of an uncontrolled rectifier according to the present invention, which inputs three-phase power from a power gridU a、U b、U c、iL 1、iL 2 、iL 3WhereiniL a、iL b 、iL cIn order to generate a current of a harmonic wave,iL A 、iL B 、iL Ccompensating the harmonic source for the compensation current generated by the compensation circuit by means of a three-phase compensation circuitiL 1、iL 2 、iL 3The input current waveform is compensated into sine wave to realize the PFC function, and then the circuit outputs direct current after being connected in parallel through DC-DC conversion.
In the three-phase uncontrollable rectification harmonic compensation circuit, as shown in fig. 9, the topological structure is composed of 12 uncontrollable diodesD A+ 、D B+ 、D C+、D A- 、D B- 、D C-、D a+ 、D b+ 、D c+、D a- 、D b- 、D c-3 power inductorsL 1、L 2、L 33 output capacitorsC 1、C 2、C 3And 3 groups of MOS tubes with same source levelQ 1、Q 2、Q 3、Q 4、Q 5、Q 6And the bidirectional flow of energy can be realized. InductanceL 1And diodeD A+、D a+Anode, diodeD A-、D a-The negative electrode is connected with the MOS tubeQ 1The drain of (a) the gate of (b),Q 1andQ 2the two-stage power supply is connected with the same source stage,Q 2is connected to neutral point M; inductanceL 2And diodeD B+、D b+Anode, diodeD B-、D b-The negative electrode is connected with the MOS tubeQ 3The drain of (a) the gate of (b),Q 3andQ 4the two-stage power supply is connected with the same source stage,Q 4is connected to neutral point M; inductanceL 3And diodeD C+、D c+Anode, diodeD C-、D c-The negative electrode is connected with the MOS tubeQ 5The drain of (a) the gate of (b),Q 5andQ 6the two-stage power supply is connected with the same source stage,Q 6is connected to neutral point M;D A+ 、D B+ 、D C+is connected to the positive pole P of the output terminal,D A- 、D B- 、D C-is connected to the negative pole N of the output end, and outputs a voltage stabilizing capacitorC 1The anode is connected to the output end anode P, the cathode is connected to the neutral point M,C 2the anode is connected to the neutral point M, and the cathode is connected to the cathode N of the output end; the harmonic wave circuit part is provided with a harmonic wave circuit part,D a+ 、D b+ 、D c+is connected to the positive pole p of the output terminal,D a- 、D b- 、D c-is connected to the negative pole n of the output end; the output end PN of the three-phase uncontrolled rectifying part is connected with a DC-DC converter, and the output end PN of the three-phase harmonic compensation circuit is connected with the DC-DC converter in parallel to output direct current.
The bidirectional power switch is composed of two MOS tubes connected in series in reverse direction, arrows in the figure are a forward current flowing route and a reverse current flowing route, and when a current flows in the forward direction, the current passes through the two MOS tubesQ 1AndVD 2when the current flows in the reverse direction, byQ 2AndVD 1as shown in fig. 10.
Available ideal switch Sa、Sb、ScInstead, the three-phase harmonic compensation circuit topology can be simplified as shown in fig. 11.
Taking the A-phase bridge arm as an example, the working principle of the harmonic compensation circuit is analyzed independently, and the arrow direction is currentiIn the positive half period, when Sa is off, the input end of phase A of the rectifier is connected with the positive electrode of the direct current bus through a DA + diode, and the output voltage isU dc (ii)/2, as shown in FIG. 12; when Sa is turned on, the voltage at the phase a input terminal is clamped to the neutral point M, and the voltage at the input terminal is 0 at this time, as shown in fig. 13. In the negative half period, when Sa is disconnected, the input end of phase A is connected with the negative pole of the DC bus through DA-, and the output voltage is-U dc (ii)/2, as shown in FIG. 14; when Sa is turned on, the voltage at the phase a input terminal is clamped to the neutral point M, and the voltage at the input terminal is 0 at this time, as shown in fig. 15.
The harmonic current detection link is the basis for realizing harmonic compensation, and the tracking control method of the compensation current is another key for influencing the compensation effect. According to the APF working principle, the harmonic current obtained by the harmonic detection algorithm is inverted and used as the instruction current to obtain the PWM signal for controlling the power device, and the switching-on and switching-off of the switching device are controlled by the driving circuit to realize the compensation of the harmonic current. Due to the complexity of a power grid, the harmonic environment is often accompanied by uncontrollable factors such as fluctuation, flicker and the like, so that the compensation current is required to change along with the command current in real time, and the requirements on instantaneity and dynamic performance are high.
The compensation current tracking control methods are various, and the commonly used control methods include hysteresis comparison control, triangular carrier comparison control, space voltage vector control, single-cycle control, dead-beat control, repetitive control, prediction control and the like.
In the compensation circuit, a novel harmonic current compensation control strategy is provided, which mainly comprises a voltage outer ring and a current inner ring, and outputs feedback voltageU outAnd a reference voltageU efAfter difference is made, a reference current value is obtained through a PI linkI refThe voltage of each phase is transmitted into the current inner loopUa、Ub、Uc taking absolute value firstUa|、|Ub|、|Uc | is multiplied by a scaling factor K and then summedI refMake an product to obtain a positiveHalf-wave sinusoidal signals, respectively associated with currents of three-phase Vienna (VIENNA)iL A、iL B、iL CAnd current of three-phase uncontrolled rectifieriL a、iL b、iL cAbsolute value of sum ofi a |、|i b |、|i c |After the difference is made, a modulation wave is obtained through a PI link, and is compared with a triangular carrier wave, and PWM is finally output, as shown in figure 16, compared with other schemes, the hysteresis control method has the problems of unfixed switching frequency, the effect of single-period control is easy to interfere, the tracking effect is influenced, the algorithms of predictive control and artificial neural network control are too complex, in practical application, in the algorithm of space voltage vector modulation (SVPWM), when the current sector is switched during VIENNA simulation, A, B, C three-phase currents are all distorted greatly, the reason for this is that, at the time of sector switching, the manner in which each sector synthesizes the pulse vector of the PWM wave is different, therefore, A, B, C three-phase current generates larger distortion, and in conclusion, the novel harmonic current compensation control scheme is simpler and more reliable and is easy to expand research, such as three-phase imbalance and the like.
A corresponding simulation model is set up in electrical simulation software (PSIM), and the simulation parameters are as follows in the following table 1:
TABLE 1 PISM simulation parameters for harmonic compensation circuits of three-phase uncontrolled rectifiers
FIG. 17 shows phase A current flowing into a three-phase uncontrolled rectifying circuitiL aWith larger harmonics, fig. 18 shows the output current when compensated by a three-phase harmonic compensation circuitiL AAfter compensation, the current waveform approaches a sine wave as shown in fig. 19.
FIG. 20 is an input voltageUa, input currentIa PSIM simulation oscillogram can show that the input voltage and the input current are in the same phase, and the harmonic compensation circuit is completedResulting in power factor correction of the input total current.
FIG. 21 shows the output upper and lower capacitors of the three-phase harmonic compensation circuitC 1、C 2Voltage ofU PM、U MNThe PSIM simulation waveform is shown in the figure, the upper voltage amplitude and the lower voltage amplitude are stabilized at about 400V, the circuit can well realize output balance, and the circuit has good voltage-sharing characteristic.
According to the analysis, the three-phase uncontrolled rectifier harmonic compensation circuit provided by the invention integrates the three-phase harmonic compensation circuit, the three-phase uncontrolled rectifier and the DC-DC converter together to participate in energy transfer, so that the power factor correction of the total input current is realized, and the advantages of high power density of the three-phase uncontrolled rectifier and active controllability of the three-phase rectifier are taken into consideration.
Claims (2)
1. A harmonic compensation circuit of an uncontrolled rectifier is characterized in that a three-phase uncontrolled rectifier is used as a compensation object, the three-phase uncontrolled rectifier is compensated through a three-phase harmonic compensation circuit, the PFC function of the whole circuit is realized, and then direct current is output after parallel connection through DC-DC conversion; the specific circuit is as follows:
inductanceL 1And diodeD A+、D a+Anode, diodeD A-、D a-The negative electrode is connected with the MOS tubeQ 1The drain of (a) the gate of (b),Q 1andQ 2the two-stage power supply is connected with the same source stage,Q 2is connected to neutral point M; inductanceL 2And diodeD B+、D b+Anode, diodeD B-、D b-The negative electrode is connected with the MOS tubeQ 3The drain of (a) the gate of (b),Q 3andQ 4the two-stage power supply is connected with the same source stage,Q 4is connected to neutral point M; inductanceL 3And diodeD C+、D c+Anode, diodeD C-、D c-The negative electrode is connected with the MOS tubeQ 5OfThe number of stages is such that,Q 5andQ 6the two-stage power supply is connected with the same source stage,Q 6is connected to neutral point M;D A+ 、D B+ 、D C+is connected to the positive pole P of the output terminal,D A- 、D B- 、D C-is connected to the negative pole N of the output end, and outputs a voltage stabilizing capacitorC 1The anode is connected to the output end anode P, the cathode is connected to the neutral point M,C 2the anode is connected to the neutral point M, and the cathode is connected to the cathode N of the output end; the harmonic wave circuit part is provided with a harmonic wave circuit part,D a+ 、D b+ 、D c+is connected to the positive pole p of the output terminal,D a- 、D b- 、D c-is connected to the negative pole n of the output end; the output end PN of the three-phase uncontrolled rectifying part is connected with a DC-DC converter, and the output end PN of the three-phase harmonic compensation circuit is connected with the DC-DC converter in parallel to output direct current.
2. The method of claim 1, wherein the output feedback voltage is a feedback voltageU outAnd a reference voltageU refAfter difference is made, a reference current value is obtained through a PI linkI refThen will beI refThe sine half-wave signal and the three-phase compensating current are obtained by transmitting the sine half-wave signal into the current inner loop and multiplying the sine half-wave signal by the absolute value of each phase voltageiL A 、iL B 、iL C And three-phase harmonic currentiL a、iL b 、iL c And after the sum is subjected to difference, obtaining a modulation wave through a PI link, comparing the modulation wave with a triangular carrier wave, and finally outputting three paths of PWM.
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