Balance reactor optimization and 24-pulse output design method of transformer rectifier
Technical Field
The invention belongs to the technical field of electric energy conversion, and particularly relates to a balance reactor optimization and 24-pulse output design method of a voltage transformation rectifier.
Background
The test standard RTCA DO-160E/F/G of the airborne equipment clearly specifies the current harmonic limit value of the three-phase balanced airborne electrical equipment, and the total harmonic distortion rate of the three-phase input current should not exceed 10%. The uncontrolled multi-pulse-wave voltage transformation rectifier has the advantages of simple structure and strong robustness, and the uncontrolled multi-pulse-wave voltage transformation rectifier is mostly adopted to inhibit the harmonic content of input current and the ripple content of output voltage in an airborne power supply rectification system at present, so that the electric energy quality of an aircraft power supply system is ensured, and the reliability of the airborne power supply system is improved. The pulse number of the multi-pulse transformer rectifier is increased, so that the harmonic content of the input current and the ripple content of the output voltage of the transformer rectifier can be effectively inhibited. The theoretical value of the harmonic distortion of the input current of the traditional 12-pulse transformer rectifier is 15.2%, and the harmonic distortion of the current can meet the aviation standard only by combining a passive filter circuit on the alternating current side. However, the passive filter circuit has a large volume and a large weight, can only filter characteristic subharmonics, has a certain amplification effect on non-characteristic subharmonics, and has a limited harmonic suppression effect. The research on the novel phase-shifting transformer structure can increase the pulse number of the transformer rectifier, and the method has the defect that the harmonic suppression level and the complexity of the phase-shifting transformer are mutually contradictory. The more the output phase number of the phase-shifting transformer is, the more obvious the harmonic suppression effect is, but the more complex the structure is, the difficulty in manufacturing is caused, and the utilization rate of the coil is reduced; the design and selection of the number of turns of the coil of the phase-shifting transformer are difficult, the phase symmetry of the output multi-phase voltage is poor, and the power supply system is polluted by the introduced non-characteristic subharmonic while the characteristic subharmonic is eliminated. The pulse number of the transformer rectifier can be increased by increasing the number of taps of the balance reactor, but the tap diodes are directly connected with the load, so that the loss of the diodes is large, and the application of aerospace is not facilitated.
Disclosure of Invention
The invention aims to solve the technical problems in the prior art, and aims to provide a balance reactor optimization and 24-pulse output design method for a transformer rectifier, which does not need to greatly increase the volume and weight of the transformer rectifier, has a simple structure, does not need an additional control circuit, has high reliability, improves the nonlinear characteristics of the rectifier from the source, further increases the pulse wave number of a multi-pulse-wave transformer finisher, reduces the harmonic content of input current, is not connected with a filter device, enables the working characteristics of the transformer rectifier to directly meet the aerospace standard, and is suitable for large-load working occasions.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a balance reactor optimization and 24-pulse output design of a transformer rectifier comprises 1 balance reactor with a secondary winding and two voltage-sharing capacitors (C)1、C2) And two voltage equalizing resistors (R)1、R2) The half-bridge voltage-sharing circuit is composed of 1 diode (D)1、D2) An auxiliary bridge arm formed by connecting in series; the primary winding of the balance reactor has a middle tapThe secondary side has only one winding; voltage-sharing capacitor C1And voltage-sharing capacitor C2Series voltage-sharing capacitor C1And a voltage equalizing resistor R1Parallel voltage-sharing capacitor C2And a voltage equalizing resistor R2Parallel connection; the middle point of the half-bridge voltage-sharing circuit and the middle point of the auxiliary bridge arm are respectively connected with two output ends of the secondary winding of the balance reactor; voltage-sharing capacitor C1The positive end of the voltage-sharing capacitor C is connected with the positive output end of the voltage-sharing rectifier2The negative end of the transformer rectifier is connected with the negative output end of the transformer rectifier; diode D1The anode of the diode D is connected with the positive output end of the voltage transformation rectifier2The cathode of the transformer rectifier is connected with the negative output end of the transformer rectifier.
Furthermore, the primary winding of the balance reactor is provided with an intermediate tap, and the total number of turns N of the primary winding of the balance reactorpNumber of turns N of secondary windingsThe ratio of (a) to (b) is 0.136.
The instantaneous values of the output voltages of two three-phase rectifier bridges of the front-end 12-pulse voltage transformation rectifier are unequal and are 6-pulse voltage with the phase difference of 30 degrees, alternating voltage which is 6 times of the frequency of a three-phase power supply and is generated on a secondary winding of a balance reactor forces upper and lower diodes of an auxiliary bridge arm to be alternately conducted, and the harmonic content is modulated, so that the circuit has the 24-pulse characteristic; and the turn ratio of the winding of the balance reactor is reasonably designed, and the harmonic distortion rate is reduced.
Adopt the beneficial effect that above-mentioned technical scheme brought:
compared with the existing transformer rectifier adopting the balance reactor with the secondary winding, the invention has the advantages of simple structure, small system volume, no need of an additional control circuit and high system reliability; an auxiliary circuit is adopted to modulate harmonic waves to be injected into two ends of a load, so that loss is reduced, the transformer rectifier has 24-pulse wave characteristics, harmonic wave and ripple wave contents in a rectification system are simultaneously inhibited, an additional filtering device is not connected, the transformer rectifier directly meets the aviation and aerospace standards, and the transformer rectifier is suitable for large-load working occasions of airplanes; the three-phase input current of the transformer rectifier is close to a sine wave, the theoretical value of the total harmonic content is 7.73%, and the aviation standard requirement is met.
Drawings
FIG. 1 is a schematic diagram of a 24-pulse transformer rectifier circuit;
FIG. 2 is a diagram of a balance reactor winding structure;
fig. 3 is a schematic view of the working mode 1;
fig. 4 is a schematic view of the working mode 2;
fig. 5 is a schematic view of the working mode 3;
FIG. 6 is a diagram of the theoretical relationship between the harmonic content of the input current and the turn ratio beta of the primary and secondary windings of the balance reactor;
FIG. 7 shows the A-phase input current iaSimulating a waveform;
FIG. 8 shows the A-phase input current iaSimulating a spectrum analysis chart;
the main symbolic illustrations of the above figures: u. ofa、ub、ucFor a three-phase input voltage on the network side, ia、ib、icFor three-phase input current on the network side, C1、C2As a voltage-sharing capacitor, R1、R2Being a voltage-sharing resistor, D1、D2To assist the upper and lower diodes of the bridge arm, up1For balancing the voltage of the first winding section of the primary side of the reactorp2For balancing the voltage of the second winding of the primary side of the reactor usFor balancing the secondary winding voltage of the reactor, ip1For balancing the current of the first winding section of the primary side of the reactor ip2For balancing the current of the second winding of the primary side of the reactor isFor balancing the secondary winding current of the reactor, Np1The number of turns of a primary first section winding of a balance reactor is Np2The number of turns of a primary side second-stage winding of the balance reactor is NsFor balancing the number of turns of the secondary winding of the reactor, id1、id2Respectively output currents u for two groups of three-phase rectifier bridgesd1、ud2Respectively two groups of three-phase rectifier bridge output voltages uc1Is a voltage-sharing capacitor C1The voltage across; u. ofc2Is a voltage-sharing capacitor C2Voltage across udIs the load voltage, and t is the system simulation time.
Detailed Description
The technical scheme of the invention is explained in detail in the following with the accompanying drawings.
As shown in figure 1, a balance reactor optimization and 24-pulse output design of a transformer rectifier comprises 1 balance reactor with a secondary winding and two voltage-sharing capacitors (C)1、C2) And two voltage equalizing resistors (R)1、R2) The half-bridge voltage-sharing circuit is composed of 1 diode (D)1、D2) An auxiliary bridge arm formed by connecting in series; the primary side winding of the balance reactor is provided with a middle tap, and the secondary side of the balance reactor is provided with only one winding; voltage-sharing capacitor C1And voltage-sharing capacitor C2Series voltage-sharing capacitor C1And a voltage equalizing resistor R1Parallel voltage-sharing capacitor C2And a voltage equalizing resistor R2Parallel connection; the middle point of the half-bridge voltage-sharing circuit and the middle point of the auxiliary bridge arm are respectively connected with two output ends of the secondary winding of the balance reactor; voltage-sharing capacitor C1The positive end of the voltage-sharing capacitor C is connected with the positive output end of the voltage-sharing rectifier2The negative end of the transformer rectifier is connected with the negative output end of the transformer rectifier; diode D1The anode of the diode D is connected with the positive output end of the voltage transformation rectifier2The cathode of the transformer rectifier is connected with the negative output end of the transformer rectifier.
The transformation ratio of a front-end transformer of the transformer rectifier is K; the primary winding of the balance reactor is provided with only one center tap, the winding structure is shown in fig. 2, the turn ratio of the primary winding and the secondary winding of the balance reactor is beta, and beta is equal to (N)p1+Np2)/Ns(ii) a And (3) making the effective value of the three-phase input phase voltage of the transformer rectifier be U, and then making the three-phase power supply input voltage be:
output voltage u of three-phase rectifier bridge group Id1Comprises the following steps:
output voltage u of three-phase rectifier bridge group IId2Comprises the following steps:
secondary winding voltage u of balance reactorsComprises the following steps:
when the auxiliary circuit is in operating mode 1, u is shown in FIG. 3d1>ud2,us<uC1Or ud1<ud2,|us|<uC2Auxiliary bridge arm diode D1、D2Is not conducted and the load voltage udComprises the following steps: u. ofd=0.5(ud1+ud2) Primary winding voltage u of balance reactorpComprises the following steps: u. ofp=ud1-ud2The voltage of the two primary-side windings of the balance reactor is obtained as follows:
then the current of the two sections of primary windings of the balance reactor is as follows:
the secondary winding current of the balance reactor is as follows: i.e. is=0
When the auxiliary circuit is in operating mode 2, u is shown in FIG. 4d1>ud2,us>uC1Auxiliary bridge arm diode D1On, D2And cutting off. Secondary winding voltage u of balance reactorsComprises the following steps: u. ofs=uc1=0.5udAccording to the load voltage column equation:
rectifier load voltage udComprises the following steps:
the primary and secondary winding currents of the balance reactor are as follows:
when the auxiliary circuit is in operating mode 3, u is shown in FIG. 5d1<ud2,|us|>uC2Auxiliary bridge arm diode D2On, D1And cutting off. Secondary winding voltage u of balance reactorsComprises the following steps: u. ofs=-uc1=-0.5udAccording to the load voltage column equation:
rectifier load voltage udComprises the following steps:
the primary and secondary winding currents of the balance reactor are as follows:
the obtained load voltage udThe expression of (a) is:
the load voltage exhibits 24 pulses in one cycle, when k is 0 and ω t is θ:
obtaining by solution:
in which theta is a diode D1Half the conduction angle each time.
The A-phase input current i of the transformer rectifier can be obtained according to the magnetomotive force balance principle and the kirchhoff current lawaComprises the following steps:
the a-phase input current i is in a quarter cycleaThe functional relationship of (a) is:
the input current waveform is 24 step waves, and the effective value I of the A-phase input current can be obtainedaComprises the following steps:
fundamental current effective value I of A-phase input current1Comprises the following steps:
the input current Total Harmonic Distortion (THD) is calculated by the following formula:
known phase AInput current effective value IaAnd the effective value I of the fundamental current of the A-phase input current1The total harmonic distortion of the input current of the transformer rectifier can be directly calculated by a formula. The harmonic distortion rate is a function related to the turn ratio beta of the primary winding and the secondary winding of the balance reactor. Drawing a function curve by using matlab, as shown in FIG. 6; from fig. 6, it can be known that the optimal turn ratio of the primary winding and the secondary winding of the balance reactor is 0.136, and the theoretical value of the total harmonic content of the input current at this time is 7.73%.
In order to verify the effectiveness of the invention, a simulation experiment is carried out by building a model in Matlab/Simulink, 115V/400Hz three-phase alternating current is input into the system, and the load is a 10 omega pure resistor. Input current i of phase AaThe simulation waveform diagram is shown in fig. 7, the input current is 24 step waves, the sine is good, and the theoretical correctness is verified. Input current i of phase AaThe frequency spectrum analysis chart is shown in fig. 8, the main harmonics are 23 and 25 harmonics, the total harmonic content is low and is only 5.62%, the harmonic standard of the input current in the aviation field is met, and the designed 24-pulse transformer rectifier has a good input current harmonic suppression effect.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.