CN101741235B - Buck three-phase power factor corrector with controlled output voltage - Google Patents

Abstract

The step-down three-phase power factor corrector with controllable output voltage introduces the generalized active power filter into the three-phase uncontrollable rectifier unit, and introduces the output DC voltage feedback of the three-phase uncontrollable rectifier unit into the energy bidirectional In the control of the flowing three-phase voltage-type inverter, the control of the output DC voltage of the three-phase uncontrollable rectifier unit is realized by amplitude phase control or dq axis component control (vector control). Among them, the three-phase uncontrollable rectifier unit can be 6-pulse uncontrollable rectifier, or 12, 18-pulse and other three-phase uncontrollable rectifier units; any three-phase voltage inverter with bidirectional energy flow can be applied to In the present invention, the three-phase voltage type inverter only needs to deal with harmonic waves and part of reactive power. The invention has the advantages of excellent harmonic suppression performance, high efficiency, step-down type and controllable output voltage. It is especially suitable for aviation three-phase power factor correction in future "more electric aircraft".

Description

Step-down three-phase power factor corrector with controllable output voltage

technical field

The invention relates to power factor correction technology, in particular to a step-down three-phase power factor corrector.

Background technique

The three-phase uncontrolled rectifier bridge used in the power system is the main source of harmonics. In order to suppress such harmonics, the methods commonly used at present are mainly three-phase power factor correction (PFC) and three-phase active power filter (APF). Three-phase PFC is an active harmonic control scheme, which controls harmonic pollution from the perspective of eliminating harmonic sources. Its structure mainly includes: three-phase single-switch structure, three single-phase PFC structures, three-phase series/parallel dual Boost structure, Vienna structure, three-phase two-level and three-level PWM rectifiers, and step-down Buck type, etc. Among them, the three-phase single-switch structure has been widely used in small and medium power, but the scheme works in discontinuous conduction mode, and its harmonic suppression effect is not ideal. In addition, the power capacity of the single-switch structure is limited; three single-phase PFC phase combination structure, the structure of this scheme is complex, in the three-phase three-wire system, the phase-to-phase coupling degree is high, the conduction loss is large, and the efficiency is low; the three-phase series/parallel dual Boost structure, Vienna and two-level and three-level PWM rectifiers, Although good harmonic control performance can be achieved, the high-frequency switches in all structures need to handle all load power, which has no advantages in cost and efficiency. Moreover, this type of power factor correction circuit adopts a Boost structure, which belongs to the boost Buck type, its output requires an additional step-down circuit to match with the subsequent stage, which will increase the complexity of the system; although the step-down Buck structure can realize the function of output step-down, but because it works in the intermittent conduction mode, the harmonic control effect Not ideal, it is difficult to achieve high performance power factor correction.

The three-phase active power filter (APF) does not need to change the structure of the original uncontrolled rectifier bridge step-down type, and at the same time, the high-frequency switching part only needs to process part of the power, which has high efficiency. However, no matter it is series type, parallel type or hybrid type, it is necessary to detect the load harmonic voltage or current to achieve harmonic control, which puts forward very high requirements on the voltage or current loop bandwidth of APF, and requires a higher switching frequency In order to achieve a better harmonic control effect, it is difficult to achieve harmonic compensation with superior performance at the level of existing power devices. Another reported generalized active power filter can achieve a better harmonic control effect at a lower switching frequency, but like other APF solutions with other structures, the output DC voltage of the rectifier bridge is uncontrollable. When the power supply voltage fluctuates When , there will be large fluctuations in the DC side voltage, which cannot meet the requirements in most applications (such as "more electric aircraft").

To sum up, the existing three-phase power factor corrector has the defects of poor harmonic control performance, low efficiency and uncontrollable output voltage.

Contents of the invention

The object of the present invention is to provide a step-down three-phase power factor corrector with good harmonic control performance, high efficiency and controllable output voltage.

The technical solution of the present invention is such a step-down three-phase power factor corrector with controllable output voltage, which has the same part as the prior art: the power factor corrector is composed of a main circuit, a sampling circuit and a control circuit; Its main circuit includes a three-phase voltage-type inverter with bidirectional energy flow, a three-phase uncontrolled rectification unit, a low-pass filter after the three-phase uncontrolled rectification unit, three power supply side inductors and three three-phase uncontrolled rectification units. Unit front inductance; among them, the three power supply side inductances are connected in series between the three-phase power supply and the three three-phase uncontrollable rectification unit front inductances, and the other ends of the three three-phase uncontrollable rectification unit front inductances are respectively connected to The three AC input terminals of the three-phase uncontrolled rectification unit; the low-pass filter after the three-phase uncontrolled rectification unit is a second-order low-pass filter composed of an inductor and a capacitor, or a first-order low-pass filter composed of only one capacitor device. The three-phase voltage-type inverter with bidirectional flow of energy is composed of a three-phase inverter bridge and a capacitor connected in parallel on the DC side of the three-phase inverter bridge. The AC terminal of the three-phase voltage-type inverter with bidirectional energy flow corresponds to It is connected in parallel at the connection node of the three power supply side inductors and the front inductors of the three three-phase uncontrollable rectification units; the sampling circuit includes a voltage sensor unit connected in parallel at the input end of the three-phase power supply to sample the three-phase input voltage, and connected in series with the three-phase Any two phases of the input terminal of the power supply are used to sample two current sensors of the two-phase input current of the three-phase input current, and they are connected in parallel on the DC side of the three-phase voltage inverter whose energy can flow bidirectionally to sample the three-phase inverter that can flow bidirectionally. The voltage sensor I of the DC side voltage of the phase-voltage inverter; the voltage sensor unit, the two current sensors and the signal output terminals of the voltage sensor I are all correspondingly connected to the connection terminals of the control operation unit. The improvement of the present invention is that a voltage sensor II is connected in parallel to the DC output terminal of the three-phase uncontrollable rectifier unit to sample the DC output voltage of the three-phase uncontrollable rectifier unit, and the signal output terminal of the voltage sensor II is also connected to the corresponding On one connection end of the control operation unit to form a control circuit.

In the above-mentioned improved step-down three-phase power factor corrector with controllable output voltage, the control operation unit in the control circuit is also improved. Improved structure of dq-axis component control operation.

In the improved structure through amplitude and phase control operations, its control operation unit includes a switch drive generation unit I, a regulator I, a regulator II, a subtractor I and a subtractor II; wherein, the subtractor I receives The DC output voltage of the three-phase uncontrollable rectifier unit and the DC output reference voltage of the three-phase uncontrollable rectifier unit are subtracted, and then the error signal of the DC output voltage of the three-phase uncontrollable rectifier unit is generated and input to the regulator I; the subtractor II receives The DC side voltage of the three-phase voltage type inverter with bidirectional flow of energy obtained by the sampling circuit is subtracted from the reference voltage of the DC side of the three-phase voltage type inverter with bidirectional energy flow, and then generated and input to the regulator II The DC side voltage error signal of the three-phase voltage type inverter with bidirectional energy flow; the regulator I generates the input current phase reference signal after receiving the DC output voltage error signal of the three-phase uncontrollable rectifier unit, and then sends the signal to the switch drive Generation unit I; Regulator II receives the DC side voltage error signal of the three-phase voltage type inverter with bidirectional flow of energy, generates an input current amplitude reference signal, and then sends the signal to the switch drive generation unit I; switch drive The generation unit I simultaneously receives any two input current signals and input voltage signals in the input current signal obtained by the sampling circuit, and the switch drive generation unit I obtains any two of the input current phase reference signal, the input current amplitude reference signal, and the input current signal. After an input current signal and an input voltage signal, a drive signal for a three-phase voltage-type inverter with drive energy that can flow bidirectionally is generated.

In the improved structure of control operation through dq axis components, its control operation unit includes switch drive generation unit II, regulator III, regulator IV, phase-locked loop, and conversion unit from three-phase stationary coordinate system to two-phase rotating coordinate system I. Subtractor III and subtractor IV; wherein, subtractor III receives the DC output voltage of the three-phase uncontrollable rectifier unit obtained by the sampling circuit and the DC output reference voltage of the three-phase uncontrollable rectifier unit and performs subtraction, and then generates and sends to The regulator III inputs the DC output voltage error signal of the three-phase uncontrollable rectification unit; the subtractor IV receives the energy obtained from the sampling circuit, and the three-phase voltage type inverter has a two-way flow of DC side voltage and energy. The reference voltage on the DC side of the inverter is subtracted, and then the voltage error signal on the DC side of the three-phase voltage-type inverter with bidirectional flow of energy is generated and input to the regulator IV; the regulator III receives the DC output of the three-phase uncontrollable rectifier unit After the voltage error signal, generate the reference signal of the quadrature axis component of the input current, and then send the signal to the switch drive generation unit II; after the regulator IV receives the DC side voltage error signal of the three-phase voltage type inverter whose energy can flow bidirectionally, Generate the reference signal of the direct-axis component of the input current, and then send the signal to the switch drive generation unit II; the phase-locked loop receives the input voltage signal obtained from the sampling circuit, and then generates and sends the signal to the three-phase stationary coordinate system to the two-phase rotating coordinate system The transformation unit I inputs the sine and cosine signals representing the frequency and phase of the input voltage; the transformation unit I from the three-phase stationary coordinate system to the two-phase rotating coordinate system simultaneously receives any two input current signals from the input current signals obtained from the sampling circuit Finally, the input current direct-axis component and the input current quadrature-axis component are generated, and then the input current direct-axis component and the input current quadrature-axis component signal are sent to the switch drive generation unit II; the switch drive generation unit II obtains the input current quadrature-axis component reference signal After inputting the reference signal of the direct-axis component of the current, the direct-axis component of the input current and the quadrature-axis component signal of the input current, a driving signal of the three-phase voltage-type inverter whose driving energy can flow bidirectionally is generated.

It can be seen from the scheme that the present invention introduces the generalized active power filter (that is, the same part as the prior art) into the circuit of the present invention, and introduces the DC output voltage feedback of the three-phase uncontrollable rectification unit into the energy-controlled In the control of the three-phase voltage inverter with bidirectional flow, the problem of uncontrollable output voltage is solved. The advantages of the present invention are as follows:

1. High performance. Under the condition of the same switching frequency, the harmonic suppression performance of the present invention is similar to that of the existing three-phase PWM rectifier, and is better than the three-phase active power filter and the like.

2. High efficiency. The three-phase voltage-type inverter with bi-directional flow of energy only needs to deal with harmonics and part of reactive power, effectively reducing the capacity of the inverter, which can reduce the capacity of the device and improve efficiency.

3. Step-down type. The step-down is realized through the three-phase uncontrollable rectification unit, and a step-down DC bus bar lower than the amplitude of the input AC power voltage can be obtained.

4. The DC output voltage is controllable. Under the condition of the AC side power supply voltage fluctuates, the stability of the DC output voltage can still be well maintained.

In short, the present invention is a step-down three-phase power factor corrector with good harmonic control performance, high efficiency and controllable output voltage; it is especially suitable for aviation three-phase Phase power factor correction.

The present invention will be further described below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 - circuit structure diagram of the present invention

Figure 2a - Amplitude phase control block diagram of the present invention

Fig. 2b - dq axis component control block diagram of the present invention

Figure 3a - A-phase input voltage and current waveforms when the input voltage is 400Hz and 115V

Figure 3b - DC output voltage waveform diagram when the input voltage is 400Hz and 115V

Figure 4a——A phase input voltage and current waveform diagram when the input voltage is 400Hz and 100V

Figure 4b - DC output voltage waveform when the input voltage is 400Hz and 100V

Figure 5a - A-phase input voltage and current waveforms when the input voltage is 400Hz and 122V

Figure 5b - DC output voltage waveform when the input voltage is 400Hz and 122V

Figure 6a - A-phase input voltage and current waveforms when the input voltage is 50Hz and 220V

Figure 6b - DC output voltage waveform diagram when the input voltage is 50Hz and 220V

Detailed ways

The present invention has two solutions with the same specific technical features. In order to save space, firstly, the specific structure of the step-down three-phase power factor corrector with controllable output voltage is disclosed collectively in the form of a general scheme; Improved different structures. In order to maintain the necessary continuity, when disclosing the different structures of the control operation unit CONU, the same specific technical features will not be omitted.

The general scheme is as follows:

A step-down three-phase power factor corrector with controllable output voltage (refer to Figure 1). The power factor corrector is composed of a main circuit, a sampling circuit and a control circuit. The main circuit includes a three-phase voltage inverter with bidirectional energy flow, a three-phase uncontrollable rectifier unit, a low-pass filter (L ₁ , C ₁ ) after the three-phase uncontrollable rectifier unit, and three power supply side inductors ( L _sa , L _sb , L _sc ) and three three-phase uncontrollable rectifier unit front inductances (L _da , L _db , L _dc ); among them, the three power supply side inductances (L _sa , L _sb , L _sc ) correspond to _It is connected in series between the _three -phase power supply and three three _- phase uncontrollable rectifier front inductors (L _da , L _db , L _dc ). ) are respectively connected to the three AC input terminals of the three-phase uncontrolled rectification unit; the low-pass filter behind the three-phase uncontrolled rectification unit is a second-order low-pass filter composed of an inductor _L1 and a capacitor _C1 , or The first-order low-pass filter that only is made of a capacitor C ₁ ---the rear stage DC bus bar after this low-pass filter is the output of the step-down type three-phase power factor corrector with controllable output voltage of the present invention (Fig. 1 What is drawn in is the "second-order low-pass filter composed of inductor L ₁ and filter capacitor C ₁ ", and the "first-order low-pass filter" is obtained after removing the inductor L _1. Therefore, the latter is not separately Draw.In addition, under the premise of reaching the object of the present invention, also can replace above-mentioned second-order low-pass filter or first-order low-pass filter with the low-pass filter of other forms.R _L among Fig. 1 is this invention The output is connected to the load equivalent resistance). The three-phase voltage-type inverter whose energy can flow bidirectionally is composed of a three-phase inverter bridge BDPIB and a capacitor _C2 connected in parallel on the DC side of the three-phase inverter bridge BDPIB. The three-phase voltage-type inverter whose energy can flow bidirectionally The AC terminals of the corresponding three power supply side inductors (L _sa , L _sb , L _sc ) and three three-phase uncontrollable rectifier front inductors (L _da , L _db , L _dc ) are connected in parallel. The sampling circuit includes a voltage sensor unit VT connected in parallel to the input terminal of the three-phase power supply to sample the three-phase input voltage (va, v _b , v _c ), and connected in series to any two phases _of the input terminal of the three-phase power supply to sample the three-phase input current Two _{current sensors} ( _{CT 1 , CT 2} )(Note: The three-phase input current (i _a , i _b , i _c ) can be calculated by collecting the two-phase input current according to Kirchhoff's current law in the circuit principle, so the three-phase current sensor is used here to directly measure Three-phase input current is also possible), connected in parallel on the DC side of the three-phase voltage inverter with bidirectional energy flow to sample the voltage sensor I VT of the DC side voltage v _dc of the three-phase voltage inverter with bidirectional energy flow ₁ ; the signal output terminals of voltage sensor unit VT, two current sensors (CT ₁ , CT ₂ ) and voltage sensor I VT ₁ are all correspondingly connected on the connection terminal of control arithmetic unit CONU; in the present invention, in three-phase The DC output terminal of the controlled rectification unit is connected in parallel with a voltage sensor II VT ₂ to sample the DC output voltage v _{out of} the three-phase uncontrollable rectifier unit, and the signal output terminal of the voltage sensor II VT ₂ is also connected to a connection terminal of the control operation unit CONU correspondingly Above, to form a control circuit—that is, the control operation unit CONU, according to the signal input by the sampling circuit, through the corresponding amplitude phase control or dq axis component control operation to obtain the drive of the three-phase voltage inverter with bidirectional energy flow The signal is used to drive the three-phase voltage-type inverter with bidirectional flow of energy to work (the specific implementation method of the above-mentioned control circuit will be described in detail later in conjunction with FIG. 2 ).

The different structures of the control operation unit CONU in the general scheme are as follows.

One, through the improved structure of the amplitude phase control operation (refer to Figure 2a):

In the above overall scheme, the control operation unit CONU includes a switch drive generating unit IGDU I, a regulator I, a regulator II, a subtractor I S ₁ and a subtractor II S ₂ ; wherein, the subtractor I S ₁ receives the The DC output voltage v _out of the three-phase uncontrollable rectifier unit is subtracted from the reference voltage v _{out_ref} of the three-phase uncontrollable rectifier unit DC output, and then the error signal Δv _{out of} the DC output voltage of the three-phase uncontrollable rectifier unit is generated and input to the regulator I Subtractor II S ₂ receives and subtracts the DC side voltage v _dc of the three-phase voltage type inverter with bidirectional energy flow and the reference voltage v _{dc_ref} of the three-phase voltage type inverter with bidirectional energy flow obtained from the sampling circuit operation, and then generate and input to the regulator II a three-phase voltage-type inverter DC side voltage error signal Δv _dc that can flow bidirectionally. After the regulator I receives the three-phase uncontrollable rectifier unit DC output voltage error signal Δv _out , it generates an input Current phase reference signal θ ^* , and then send the signal to the switch drive generation unit I GDU I; after the regulator II receives the DC side voltage error signal Δv _dc of the three-phase voltage type inverter with bidirectional energy flow, it generates the input current Amplitude reference signal I _s ^* , and then send the signal to the switch drive generation unit I GDU I; the switch drive generation unit I GDU I simultaneously receives the input current signal ( _ia , _ib , _ic ) obtained by the sampling circuit Any two input current signals and input voltage signals (va _a , v _b , v _c ), the switch drive generation unit I GDU I obtains the input current phase reference signal θ ^* , the input current amplitude reference signal I _s ^* , the input current signal After any two input current signals (i _a , _ib , _ic ) and input voltage signals ( _va , v _b , v _c ), the driving signals of the three-phase voltage-type inverter with driving energy flowing bidirectionally are generated (S ₁ , S ₂ . . . S _n ).

Two, through the improved structure of the dq axis component control operation (refer to Figure 2b, except for the part drawn by the dotted line):

In the above general scheme, the control operation unit CONU includes the switch drive generation unit II GDU II, the regulator III, the regulator IV, the phase-locked loop PLL, and the conversion unit I from the three-phase stationary coordinate system to the two-phase rotating coordinate system (C _{3s /2r} I), subtractor IIIS ₃ and subtractor IVS ₄ ; wherein, subtractor IIIS ₃ receives the three-phase uncontrollable rectifier DC output voltage v _out obtained by the sampling circuit and the three-phase uncontrollable rectifier DC output reference voltage v _{out_ref} and perform subtraction, and then generate and input the three-phase uncontrollable rectification unit DC output voltage error signal Δv _out to the regulator III; the subtractor IVS ₄ receives the energy obtained by the sampling circuit and can flow bidirectionally. Three-phase voltage type inverter DC side voltage v _dc and three-phase voltage inverter with bidirectional flow of energy The DC side reference voltage v _{dc_ref} is subtracted, and then generated and input to the regulator IV Three-phase voltage inverter DC with bidirectional flow of energy side voltage error signal Δv _dc ; after the regulator III receives the DC output voltage error signal Δv _{out of} the three-phase uncontrollable rectification unit, it generates the input current quadrature axis component reference signal I _q ^* , and then sends the signal to the switch drive generation unit II GDU II; after the regulator IV receives the DC-side voltage error signal Δv _dc of the three-phase voltage-type inverter with bidirectional energy flow, it generates the reference signal I _d ^* of the direct-axis component of the input current, and then sends the signal to the switch drive generation unit II GDU II; phase-locked loop PLL receives the input voltage signal ( _va , v _b , v _c ) obtained from the sampling circuit, and then generates and converts the three-phase stationary coordinate system to the two-phase rotating coordinate system I (C _{3s /2r} I) Input the sine and cosine signals (sinωt, cosωt) representing the frequency and phase of the input voltage; the conversion unit I (C _3s/2r I) from the three-phase stationary coordinate system to the two-phase rotating coordinate system receives the slave sampling circuit at the same time After any two input current signals among the obtained input current signals (i _a , i _b , i _c ), generate the input current direct-axis component i _d and the input current quadrature-axis component i _q , and then convert the input current direct-axis component i _d and the input current quadrature axis component i _q signal are sent to the switch drive generation unit II GDU II; the switch drive generation unit II GDU II obtains the input current quadrature axis component reference signal I _q ^* , the input current direct axis component reference signal I _d ^* , After inputting the current direct-axis component _id and the input current quadrature-axis component i _q signals, the drive signals (S ₁ , S ₂ ...S _n ) of the three-phase voltage-type inverter that drive energy can flow bidirectionally are generated.

Furthermore, in the above-mentioned improved structure of the control operation through the dq axis components (refer to Figure 2b, especially the dotted line drawing part), the dotted line part is the input voltage feedforward introduction part, through the introduction of voltage feedforward, to realize the input current direct axis The decoupling control of component and quadrature axis can get better dynamic performance. In the control operation unit CONU, there is also a conversion unit II (C _3s/2r II) from the three-phase stationary coordinate system to the two-phase rotating coordinate system; the phase-locked loop PLL receives the input voltage signal (v _a , v _b , v _c ), simultaneously input the sine and cosine signals (sinωt, cosωt) representing the frequency and phase of the input voltage to the transformation unit II (C _3s/2r II) from the three-phase stationary coordinate system to the two-phase rotating coordinate system; The transformation unit II (C _3s/2r II) from the three-phase stationary coordinate system to the two-phase rotating coordinate system generates the input voltage direct axis after simultaneously receiving the input voltage signals ( _va , v _b , v _c ) obtained from the sampling circuit Component v _d and input voltage quadrature axis component v _q , and then send the signal to switch drive generation unit II GDU II.

In the above specific implementation manner, the three-phase uncontrollable rectification unit is an uncontrollable rectification bridge composed of six diodes (D ₁ -D ₆ ) (drawn accordingly in FIG. 1 ). Certainly, the three-phase uncontrollable rectification unit in the present invention may also be a 12-pulse or 18-pulse or other three-phase uncontrollable rectification unit. Among them, the 6-pulse three-phase uncontrollable rectifier unit composed of 6 diodes has the simplest and most economical structure.

The present invention has passed the verification of the simulation test, and the working characteristics of the present invention will be described below in conjunction with the simulation results. For the aviation power supply system with a rated input voltage of 115V and a DC bus voltage of 270V, the following will illustrate that the present invention has better harmonic suppression performance and step-down function from different input voltage situations, and can stabilize the DC voltage 270V output at the same time. Figure 3a shows the input voltage and current waveform of phase A when the input voltage is 400Hz and 115V; Figure 4a shows the input voltage and current waveform of phase A when the input voltage is 400Hz and 110V; Figure 5a shows the input voltage and current waveform of phase A when the input voltage is 400Hz and 122V Comparing the current waveforms under different input voltage conditions, it can be concluded that the present invention has better harmonic suppression performance; Figure 3b is the DC output voltage waveform of the three-phase uncontrollable rectifier unit when the input voltage is 400Hz and 115V, and Figure 4b is the input voltage The DC output voltage waveform of the three-phase uncontrollable rectifier unit at 400Hz and 110V, Figure 5b shows the DC output voltage waveform of the three-phase uncontrollable rectifier unit at an input voltage of 400Hz and 122V, comparing the DC output voltage of the three-phase uncontrollable rectifier unit under different input voltage conditions It can be concluded from the waveforms that the present invention can realize the step-down output function, and at the same time, under the condition of input voltage fluctuation, the present invention can control the DC output voltage to stabilize to a set value of 270V.

In a 50Hz industrial power supply system, the step-down three-phase power factor corrector with controllable output voltage of the present invention also has good harmonic suppression performance and step-down function with controllable output voltage. Taking a typical 220V, 50Hz industrial power supply system as an example, set the DC output voltage of the three-phase uncontrolled rectifier unit to 515V. Figure 6a shows the input voltage and current waveforms of phase A when the input voltage is 50Hz and 220V, and Figure 6b shows the DC output voltage waveform of the three-phase uncontrollable rectifier unit when the input voltage is 50Hz and 220V. It can be explained from this that the invention is applied in the three-phase PFC of the industrial 50Hz power supply system, it also has good harmonic suppression performance, can realize the step-down function, and can stabilize the three-phase uncontrollable rectification under the condition of input voltage fluctuation Unit DC output voltage.

Claims (4)

1. A step-down three-phase power factor corrector with controllable output voltage, the power factor corrector is composed of a main circuit, a sampling circuit and a control circuit; the main circuit includes a three-phase voltage type inverter with bidirectional energy flow device, three-phase uncontrolled rectifier unit, low-pass filter after the three-phase uncontrolled rectifier unit, three power supply side inductors and three three-phase uncontrollable rectifier unit front inductors; among them, the three power supply side inductors (L _sa , L _sb , L _sc ) are respectively connected in series between the three-phase power supply and three three-phase uncontrollable rectifier unit front inductors (L _da , L _db , L _dc ), these three three-phase uncontrollable rectifier unit front inductors (L _da , L _db , L _dc ) are respectively connected to the three AC input terminals of the three-phase uncontrollable rectification unit; the low-pass filter after the three-phase uncontrollable rectification unit is composed of an inductor (L ₁ ) and A second-order low-pass filter composed of a capacitor (C ₁ ), or a first-order low-pass filter composed of only one capacitor (C ₁ ); The transformer bridge (BDPIB) and the capacitor (C ₂ ) connected in parallel on the DC side of the three-phase inverter bridge (BDPIB) are composed of three-phase voltage-type inverters whose energy can flow bidirectionally. side inductance (L _sa , L _sb , L _sc ) and three three-phase uncontrollable rectifier unit front inductance (L _da , L _db , L _dc ); the sampling circuit includes The voltage sensor unit (VT) for sampling the three-phase input voltage ( _va , v _b , v _c ) is connected in series with any two phases of the three-phase power input terminal to sample the three-phase output current ( _ia , i _b , i The two current sensors (CT ₁ , CT ₂ ) of the two-phase input current in _c ) are connected in parallel on the DC side of the three-phase voltage inverter with bidirectional energy flow to sample the three-phase voltage inverter with bidirectional energy flow. The voltage sensor I (VT ₁ ) of the DC side voltage (v _dc ) of the transformer; the voltage sensor unit (VT), the two current sensors (CT ₁ , CT ₂ ) and the signal output terminals of the voltage sensor I (VT ₁ ) They are all correspondingly connected to the connection terminal of the control operation unit (CONU); the feature of the present invention is that a voltage sensor II (VT ₂ ) is connected in parallel with the DC output terminal of the three-phase uncontrollable rectifier unit to sample the three-phase uncontrollable The DC output voltage (v _out ) of the rectification unit, the signal output terminal of the voltage sensor II (VT ₂ ) is also correspondingly connected to a connection terminal of the control operation unit (CONU) to form the control circuit; The control operation unit (CONU) includes a switch drive generating unit I (GDU I), a regulator I, a regulator II, a subtractor I (S ₁ ) and a subtractor II (S ₂ ); wherein, the subtractor I (S ₁ ) receiving and subtracting the DC output voltage (v _out ) of the three-phase uncontrollable rectification unit obtained from the sampling circuit and the DC output reference voltage (v _{out_ref} ) of the three-phase uncontrollable rectification unit, and then generating and sending to the The regulator I inputs the DC output voltage error signal (Δv _out ) of the three-phase uncontrollable rectification unit; the subtractor II (S ₂ ) receives the energy obtained by the sampling circuit and can flow bidirectionally into the three-phase voltage inverter The DC side voltage (v _dc ) is subtracted from the DC side reference voltage (v _{dc_ref} ) of the three-phase voltage inverter with bidirectional energy flow, and then the three-phase bidirectional energy flow bidirectional energy flow is generated and input to the regulator II The DC side voltage error signal (Δv _dc ) of the voltage source inverter; the regulator I generates an input current phase reference signal (θ ^* ) after receiving the DC output voltage error signal (Δv _out ) of the three-phase uncontrollable rectification unit , and then send the signal to the switch drive generating unit I (GDU I); after the regulator II receives the DC side voltage error signal (Δv _dc ) of the three-phase voltage-type inverter whose energy can flow bidirectionally , to generate the input current amplitude reference signal (I _s ^* ), and then send the signal to the switch drive generation unit I (GDU I); the switch drive generation unit I (GDU I) simultaneously receives the obtained by the sampling circuit Any two input current signals and input voltage signals (v _a , v _b , v _c ) in the input current signals ( _ia , _ib , _ic ), the switch drives the generation unit I (GDU I) to obtain the input current phase _Any two input _current signals and _input ^{voltage signals} (v _a , v _{b ,} After v _c ), drive signals (S ₁ , _{S 2} . 2. A step-down three-phase power factor corrector with controllable output voltage, the power factor corrector is composed of a main circuit, a sampling circuit and a control circuit; the main circuit includes a three-phase voltage type inverter with bidirectional energy flow device, three-phase uncontrolled rectifier unit, low-pass filter after the three-phase uncontrolled rectifier unit, three power supply side inductors and three three-phase uncontrollable rectifier unit front inductors; among them, the three power supply side inductors (L _sa , L _sb , L _sc ) are respectively connected in series between the three-phase power supply and three three-phase uncontrollable rectifier unit front inductors (L _da , L _db , L _dc ), these three three-phase uncontrollable rectifier unit front inductors (L _da , L _db , L _dc ) are respectively connected to the three AC input terminals of the three-phase uncontrollable rectification unit; the low-pass filter after the three-phase uncontrollable rectification unit is composed of an inductor (L ₁ ) and A second-order low-pass filter composed of a capacitor (C ₁ ), or a first-order low-pass filter composed of only one capacitor (C ₁ ); The transformer bridge (BDPIB) and the capacitor (C ₂ ) connected in parallel on the DC side of the three-phase inverter bridge (BDPIB) are composed of three-phase voltage-type inverters whose energy can flow bidirectionally. side inductance (L _sa , L _sb , L _sc ) and three three-phase uncontrollable rectifier unit front inductance (L _da , L _db , L _dc ); the sampling circuit includes The voltage sensor unit (VT) for sampling the three-phase input voltage ( _va , v _b , v _c ) is connected in series with any two phases of the three-phase power input terminal to sample the three-phase output current ( _ia , i _b , i The two current sensors (CT ₁ , CT ₂ ) of the two-phase input current in _c ) are connected in parallel on the DC side of the three-phase voltage inverter with bidirectional energy flow to sample the three-phase voltage inverter with bidirectional energy flow. The voltage sensor I (VT ₁ ) of the DC side voltage (v _dc ) of the transformer; the voltage sensor unit (VT), the two current sensors (CT ₁ , CT ₂ ) and the signal output terminals of the voltage sensor I (VT ₁ ) They are all correspondingly connected to the connection terminal of the control operation unit (CONU); the feature of the present invention is that a voltage sensor II (VT ₂ ) is connected in parallel with the DC output terminal of the three-phase uncontrollable rectifier unit to sample the three-phase uncontrollable The DC output voltage (v _out ) of the rectification unit, the signal output terminal of the voltage sensor II (VT ₂ ) is also correspondingly connected to a connection terminal of the control operation unit (CONU) to form the control circuit; The control operation unit (CONU) includes a switch drive generation unit II (GDUII), a regulator III, a regulator IV, a phase-locked loop (PLL), and a transformation unit I (C _3s/2r I), subtractor III (S ₃ ) and subtractor IV (S ₄ ); wherein, the subtractor III (S ₃ ) receives the DC output voltage of the three-phase uncontrollable rectification unit obtained by the sampling circuit (v _out ) and the three-phase uncontrollable rectification unit DC output reference voltage (v _{out_ref} ) are subtracted, and then a three-phase uncontrollable rectification unit DC output voltage error signal (Δv _out ) is generated and input to the regulator III; The subtracter IV (S ₄ ) receives the DC side voltage (v dc ) of the three-phase voltage type inverter with bidirectional energy flow and the DC side voltage (v _dc ) of the three-phase voltage type inverter with bidirectional energy flow obtained by the sampling circuit. side reference voltage (v _{dc_ref} ) and perform subtraction, and then generate and input to the regulator IV a three-phase voltage-type inverter DC side voltage error signal (Δv _dc ) where energy can flow bidirectionally; the regulator III receives After the DC output voltage error signal (Δv _out ) of the three-phase uncontrollable rectification unit, an input current quadrature-axis component reference signal (I _q ^* ) is generated, and then the signal is sent to the switch drive generation unit II (GDUII); After the regulator IV receives the DC-side voltage error signal (Δv _dc ) of the three-phase voltage-type inverter whose energy can flow bidirectionally, it generates a reference signal of the direct-axis component of the input current (I _d ^* ), and then the signal Send it to the switch drive generation unit II (GDUII); the phase-locked loop (PLL) receives the input voltage signal ( _va , v _b , v _c ) obtained from the sampling circuit, and then generates and sends to the three The transformation unit I (C _3s/2r I) of the phase stationary coordinate system to the two-phase rotating coordinate system inputs the sine and cosine signals (sinωt, cosωt) representing the input voltage frequency and phase; the three-phase stationary coordinate system transforms to the two-phase rotating The transformation unit I (C _3s/2r I) of the coordinate system generates the direct-axis component of the input current after receiving any two input current signals ( _ia , i _b , _ic ) obtained from the sampling circuit at the same time (i _d ) and the quadrature-axis component of the input current (i _q ), and then send the signals of the direct-axis component of the input current ( _id ) and the quadrature-axis component of the input current (i _q ) to the switch drive generating unit II (GDUII); The switch drive generation unit II (GDU II) obtains the input current quadrature-axis component reference signal (I _q ^* ), the input current direct-axis component reference signal (I _d ^* ), the input current direct-axis component (i _d ) and the input current After the quadrature-axis component (i _q ) signal, generate the drive signal that drives the three-phase voltage-type inverter that the energy can flow bidirectionally (S ₁ , S ₂ . . . S _n ). 3. The step-down type three-phase power factor corrector with controllable output voltage according to claim 2, characterized in that, in the control operation unit (CONU), there are also three-phase stationary coordinate system to two-phase rotating coordinate system The conversion unit II (C _3s/2r II); the phase-locked loop (PLL) receives the input voltage signal ( _va , v _b , v _c ) from the sampling circuit, and simultaneously sends The transformation unit II (C _3s/2r II) to the two-phase rotating coordinate system inputs the sine and cosine signals (sinωt, cosωt) representing the frequency and phase of the input voltage; the transformation unit from the three-phase stationary coordinate system to the two-phase rotating coordinate system _II (C _3s/2r II) generates input voltage direct-axis component ₍ v _d ) and input _voltage quadrature-axis component (v _q ), and then send the signal to the switch drive generating unit II (GDU II). 4. The step-down three-phase power factor corrector with controllable output voltage according to claim 1, 2 or 3, characterized in that the three-phase uncontrollable rectifier unit is composed of six diodes (D ₁ -D ₆ ) composed of a 6-pulse uncontrolled rectifier unit, or a 12-pulse or 18-pulse or 24-pulse or 36-pulse three-phase uncontrollable rectifier unit.

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