Background technology
Traditional AC voltage conversion adopts the electromagnetic transformers technology, and the low frequency electromagnetic transformer is widely used in fields such as industrial and mining enterprises, scientific research institutions and laboratory in colleges and universities, has realized functions such as AC/AC transformation and electrical isolation, and power transfer efficiency is high.But traditional electromagnetic transformers volume is big and heavy, audio noise is big, no voltage stabilizing function, serious to nonlinear load (like typical diode rectification, capacitor filter) power supply time-harmonic wave pollution electrical network phenomenon, does not satisfy the needs of electric/electronic device miniaturization.
Along with the development of power electronic technology, various power conversion units are used and are given birth to.Power electronic equipment is of a great variety, and AC-AC conversion (AC/AC conversion) is a kind of usefulness power conversion unit very widely.Utilizing semiconductor switch type power transformation circuit, can be the electric energy of another kind of frequency, voltage, waveform with the transformation of electrical energy of a kind of frequency, voltage, waveform, again to electric, can improve power consumption efficiency and economic benefit greatly.The AC/AC converter mainly can be divided into the phased frequency converter of controllable silicon, have resonance exchange the AC/AC converter, matrix converter of link, based on the direct AC/AC converter of DC-DC topology and AC-AC conversion (AC-DC-AC) code converter indirectly.
The AC-DC-AC code converter is used particularly extensive by the double four quadrant photoelectric PWM converter system that two three-phase bridge PWM current transformers combine; Can realize PWM rectification and PWM invert function through three-phase six switching inverters; Guarantee that three-phase alternating current side electric current has High Power Factor, low harmonic wave characteristics, thereby guaranteed the quality of power supply of electrical network.It can be used for a plurality of links of transmission of electricity in the electric power system, distribution and electricity consumption, is a kind of basis and very important Power Electronic Circuit structure, belongs to the forward position direction of power electronics development.It some are mainly used as follows: the direct current long distance power transmission of (1) electric power system.At the power transmission line head end AC rectification is become direct current, after remote direct current transportation, direct current is transformed to the alternating current powering load at the power transmission line end; (2) main body of unified electric energy regulator UPQC of formation or online interaction formula UPS.It is stable that mains side comes compensation network voltage to keep inverter direct-flow side by 3-phase power converter of series connection, and current transformer of load side joint parallel connection comes idle, the negative phase-sequence harmonic electric current of compensating load; (3) frequency conversion and speed regulation of AC motor system.Utilize the three-phase inverter of input stage will exchange Denso and turn to direct current, utilize V/f control then, vector control, methods such as direct torque control are controlled back level inverter, realize frequency conversion and speed regulation of AC motor; (4) two current transformers are all as the operation of PWM tandem type compensating controller, and trend is controlled (IPFC) between keying line voltage, electric current, equiva lent impedance or realization line; (5) variable speed constant frequency constant voltage electricity generation system etc. is like the power conversion system of double feedback electric engine.
To low pressure middle low power occasion, this by the two indirect AC-DC-AC code converters formed of formula three-phase inverter back-to-back, it is many to have a switching device, shortcoming such as loss is big.
Summary of the invention
Technical problem to be solved by this invention is; Not enough to prior art; A kind of efficient three-phase AC-DC-AC of reduced form converter that is adapted to the middle low power occasion is provided; Reduce the loss of energy; Reduce cost; Realize the efficient conversion and the transmission of energy, reduce idle harmonic, improve the quality of power supply of electrical network.
To solve the above problems, the present invention is used in technical solutions: one adapted to small and medium-power applications of simplified and efficient three-phase AC-DC-AC converter, comprising six output filter inductor, also includes two three-phase four switching inverter and a DC-side pressure equalizing circuit, three-phase four-switch inverter consists of two switching arms and a capacitor branch composed of two three-phase four-switch inverter share a capacitor branch, two-phase four-switch inverter switching arms are parallel to the sides of the capacitor branch, the switch arm by two switches in series, the capacitor branch consisting of two capacitors in series; DC were a piezoelectric routing switch and a branch inductor branch composition, switch branch consists of two switches in series, the switch branch and three-phase four-switch inverter capacitor branch in parallel, one end of the inductor branch branch access switch the two switches , the other end to the three-phase four-switch inverter capacitor branch between two capacitors; Three-phase four-switch inverter connected to the grid through the output filter inductor or three phase load.
DC side adopts a kind of equalizer circuit; Form by two switching tubes and an inductance; The rated current of its switching tube and inductance three-phase four switch inversion device switching tube rated current 5% in, through adopting the dynamic equalization that can realize two dc bus capacitors based on the control method of current closed-loop.
Operation principle of the present invention is described in detail as follows:
The efficient three-phase AC-DC-AC of reduced form converter comprises two back-to-back three-phase four switch inversion devices, a DC side equalizer circuit and six output inductors.Described three-phase four switch inversion device is a kind of three-phase inverter of three-phase two arms; When inverter three-phase alternating current side is connected with three phase mains; The three-phase four switch inversion device of this moment can be used for doing PWM rectification stable DC side voltage, also can control the first-harmonic harmonic signal of following the tracks of or compensate expectation through current closed-loop; When inverter three-phase alternating current side is connected with three-phase equilibrium resistance, the three-phase four switch inversion device of this moment can be used for doing PWM inversion output energy, also can control the first-harmonic harmonic signal of following the tracks of or compensate expectation through current closed-loop.In order to keep the dynamic equalization of dc voltage, control the IGBT of equalizer circuit through the control method that adopts capacitance voltage difference outer shroud, current inner loop, can realize the dynamic equalization of dc bus capacitor, can improve the stability of converter like this.
The present invention proposes a kind of reduced form three-phase AC-DC-AC converter that is adapted to the middle low power occasion; Compare with the double four quadrant photoelectric pwm converter that combines by formula three-phase six switching inverters back-to-back commonly used; AC-DC-AC converter of the present invention only comprises 4 power switch pipe arms; Reduced the pair of switches arm; Reduce the loss of energy, reduced cost significantly, can realize the efficient conversion and the transmission of energy; Reduce idle harmonic, improve the quality of power supply of electrical network; In order to keep the dynamic equalization of dc voltage,, can improve the stability of converter like this through adopting the dynamic equalization that to realize dc bus capacitor based on the control method of current closed-loop.
Embodiment
Referring to Fig. 1, for existing by two AC-DC-AC converters of forming of formula three-phase inverter back-to-back.This system has two three-phase six switching inverters, a dc bus capacitor and six outputting inductances to constitute.Two three-phase six switching inverters have formed back to back structure through public dc bus capacitor; Can realize PWM rectification on one side and one side PWM invert function through three-phase six switching inverters; The High Power Factor that can realize electrical network like this moves, also can realize the dynamic transfer of meritorious energy, and dynamic compensation is idle, the negative phase-sequence harmonic.Yet to the middle low power occasion, this AC-DC-AC transformer configuration has shortcomings such as device for power switching is more, and loss is big, and efficient is low.
Referring to Fig. 2, be structure chart of the present invention.To the AC-DC-AC converter of middle low power, the present invention proposes a kind of reduced form three-phase AC-DC-AC converter, this structure comprises two back-to-back three-phase four switch inversion devices, a DC side equalizer circuit and six output inductors.Described three-phase four switch inversion device is a kind of three-phase inverter of three-phase two arms; When inverter three-phase alternating current side is connected with three phase mains; The three-phase four switch inversion device of this moment can be used for doing PWM rectification stable DC side voltage, also can control the first-harmonic harmonic signal of following the tracks of or compensate expectation through current closed-loop; When inverter three-phase alternating current side is connected with three-phase equilibrium resistance, the three-phase four switch inversion device of this moment can be used for doing PWM inversion output energy, also can control the first-harmonic harmonic signal of following the tracks of or compensate expectation through current closed-loop.
The present invention and tradition by two back-to-back the AC-DC-AC converter formed of formula three-phase inverter compare; This system has adopted two formula three-phase four switch inversion devices back-to-back; Under the prerequisite of accomplishing identical PWM rectification and PWM inverter power; Device for power switching has further reduced 4; Structure is more simplified; Reduce the cost and the complexity of hardware, improved the efficient of system.
Referring to Fig. 3, the closed-loop control block diagram when getting access to grid for three-phase four switch inversion device three-phase side proposed by the invention.
In order to realize the stable control of dc voltage, the dc voltage outer shroud has adopted a PI controller.The direct voltage tracking error multiply by synchronizing signal respectively and obtains three-phase current on line side reference instruction signal behind pi regulator.Output order through outer shroud PI controller reasonably regulates and control inverter like this, can realize the energy exchange of electrical network and dc bus capacitor.In the current inner loop tracking Control; Current on line side command signal and detected actual current on line side are poor; After utilizing PI closed-loop control and PWM modulation then; Obtain the control signal of each power switch pipe of inverter; Thereby realize the High Power Factor of system, low harmonic operation, guaranteed the quality of power supply of electrical network.Concrete steps are following:
In order to keep the loss of stablizing and remedy power switch pipe of dc voltage, adopt a pi regulator to realize the closed-loop adjustment of dc voltage outer shroud:
I
out=k
P1Δu
dc+k
I1∫Δu
dcdt (1)
Wherein, I
OutBe outer loop voltag PI controller output; k
P1And k
I1Be ratio and integral coefficient; Δ u
Dc=U
Ref-u
DcBe valtage following.Utilize I
OutCarry out the compensation of dc voltage energy, keep the stable of dc voltage, if the switching tube power loss take jointly by switch arm separately, then with I
OutMultiply by the synchronizing signal of each phase respectively, can obtain the pressure regulation command signal of inverter two phase power switch arms.Like this with the current command signal of pressure regulation command signal with the expectation compensation
Stack, then can push away the current reference signal (i of two phase switch arms of three-phase four switch inversion device
Ar, i
Br) be:
Detect the actual output current (i of two switch arms then
A1, i
B1), with the current reference signal (i of two switch arms
Ar, i
Br) subtract each other the current tracking error that can obtain two switch arms.To the closed-loop control of interior circular current, adopt the PI control method here, after the current tracking error input PI controller of two switch arms is handled, can obtain the modulation wave signal (d of two switch arms
A1, d
B1).
At last, utilize the PWM modulator approach with modulation wave signal (d
A1, d
B1) with carrier wave ratio after, can obtain the pulse drive signal of two switch arms, drive the voltage and current signal that IGBT obtains expectation.
Referring to Fig. 4, the closed-loop control block diagram during the three-phase four switch inversion device three-phase side joint balanced load that proposed.
When the load of three-phase four switch inversion device three-phase side joint, three-phase four switch inversion device mainly is used for carrying out the PWM inversion and gives loading functional or compensating reactive power, harmonic current etc.Here can realize the tracking output of system through the closed-loop control of adopting electric current.Controlled step is following:
At first pass through the output current signal (i of two switch arms of detection inverter
A2, i
B2), then with the current signal of expecting
Subtract each other, can obtain the output current tracking error of two switch arms of three-phase four switch inversion device.
To the tracking Control of electric current, adopt the PI closed loop control method here, after the current tracking error input PI controller of two switch arms is handled, can obtain the modulation wave signal (d of two switch arms
A2, d
B2).
At last, utilize the PWM modulator approach with modulation wave signal (d
A2, d
B2) with carrier wave ratio after, can obtain the pulse drive signal of two switch arms, drive the voltage and current signal that IGBT obtains expectation.
Referring to Fig. 5, Fig. 5 is the pressure equalizing control method block diagram of dc bus capacitor.
Because DC side is made up of the electric capacity of two series connection, then there is the problem of an equal equilibrium in system's DC side.If Voltage unbalance then can cause the distortion of inverter output voltage electric current, the compensation effect of influence and reliability.
In order to keep the balance of two capacitance voltages, guarantee the normal and stable operation of bucking-out system, the present invention has adopted a kind of equalizer circuit, by switch transistor T
1, T
2And balance inductance L
mForm, and come by-pass cock pipe T through closed-loop control
1And T
2Conducting realize dc-voltage balance.Poor through detecting dc capacitor voltage, utilize a low pass filter filters out alternating component, obtain the flip-flop of capacitance voltage difference.Then, through value of PI controller output, through the expectation current signal of adjusted dc capacitor voltage difference behind the amplitude limit
Afterwards with flow through inductance L
mDc current signal i
mDiffer from, through the duty cycle signals d of output DC side equalizer circuit behind adjusting of PI controller and the amplitude limit
o, obtain T through the PWM modulation at last
1And T
2Switching drive signal.Work as V
C1>V
C2The time, d
o>0.5, make T like this
1ON time is long, with capacitor C
1Energy be discharged into inductance, transfer to C afterwards
2, vice versa.During homeostasis, d is arranged then
o=0.5.Through the closed-loop control of electric current, direct current i
mCan not suddenly change, and voltage stable after, direct current i
mVery little, generally have only several amperes, so the capacity of the switching tube of equalizer circuit and balance inductance is very little, like this,, can realize the homeostasis of dc voltage through low capacity voltage-equalizing control circuit cheaply, improved the stability and the reliability of system.