Three-phase buck-boost type PWM rectifier and control method thereof

Abstract

This invention discloses a three-phase Buck-Boost PWM rectifier and its control method. The rectifier includes a Buck rectifier unit, a first Boost boost unit, a second Boost boost unit, and a common-mode current suppression unit. The positive output terminal of the Buck rectifier unit is connected to the load via the first Boost boost unit, and the negative output terminal of the Buck rectifier unit is connected to the load via the second Boost boost unit. The common-mode current suppression unit is a capacitor C. mn Capacitor C mn One end of the capacitor is connected to the neutral point of the three-phase input filter capacitor, and capacitor C... mn The other end is connected to the intermediate connection node between the first Boost unit and the second Boost unit, as well as the intermediate connection node between the positive and negative output terminals of the Buck rectifier unit. The advantage of this invention is that it avoids the influence of parasitic capacitance on the quality of its input current and improves the quality of the input current.

Description

Technical Field

[0001] This invention relates to the field of power circuit design, specifically to a three-phase Buck-Boost PWM rectifier and its control method. Background Technology

[0002] Three-phase Buck-Boost PWM rectifiers can achieve balanced and highly sinusoidal three-phase input current. They not only possess the high reliability of three-phase Buck rectifiers but also feature step-up / step-down characteristics, allowing them to adapt to a wide input voltage range. Therefore, three-phase Buck-Boost PWM rectifiers are widely used in fields such as communication and data center power supply, new energy vehicle charging systems, aviation power supplies, and static synchronous compensators.

[0003] Figure 1 This is a commonly used three-phase Buck-Boost PWM rectifier, mainly composed of two units: a Buck rectifier unit and a Boost converter unit. The input filter of the Buck rectifier unit consists of a three-phase LC filter to suppress high-order current harmonics flowing into the AC power supply. The Buck rectifier bridge contains three pairs of arms, each pair consisting of upper and lower arms. Each arm is composed of a switching transistor and a diode connected in series. This unit transfers energy from the AC side to the DC side, ensuring that the three-phase input current is highly sinusoidal and has the same frequency and phase as the input voltage. The Boost converter unit consists of an inductor, switching transistor, diode, and capacitor to achieve the boost function, while the inductor performs filtering and energy storage.

[0004] As the switching frequency and power density of three-phase Buck-Boost PWM rectifiers continue to increase, their limitations become increasingly apparent. First, the rectifier switches in existing three-phase Buck-Boost PWM rectifiers withstand input line voltage; with a current 380V utility grid input, the maximum voltage stress on the switches is approximately 540V. Considering the typical margin in switch selection (approximately 50%), the rated voltage of the switches must be at least 900V or higher. This leads to equipment selection issues. Silicon (Si) MOSFETs offer good performance, but their rated voltage is typically below 650V. IGBTs can easily achieve higher rated voltages (over 1200V), but their switching performance is poor, and the devices cannot be paralleled to improve efficiency. SiC MOSFETs can achieve even higher rated voltages and have excellent switching performance, but they remain expensive compared to comparable Si devices, ultimately resulting in high cost and low efficiency for existing topologies. Second, with increasing power density, parasitic capacitance increases; the higher switching frequency exacerbates the parasitic capacitance effect, and its impact on input current quality becomes increasingly severe. Poor input current quality often leads to wasted power supply capacity, while the amplitude of higher harmonics represents the intensity of electromagnetic interference.

[0005] In three-phase Buck-Boost PWM rectifiers, the presence of common-mode voltage and parasitic capacitance leads to significant high-frequency noise and low-frequency distortion in the input current. Chinese Patent Publication No. CN116505785A discloses a current-mode PWM rectifier and its control strategy. By controlling the on / off states of the switching transistors in the rectifier bridge and the freewheeling path, the inductor current can be kept in a quasi-continuous mode, thereby reducing the load dynamic response time and significantly improving load dynamic response performance. However, this patent application does not address how to solve the switching losses caused by high voltage stress, nor does it consider how to address the impact of parasitic capacitance on the input current quality.

[0006] Chinese Patent Publication No. CN116054609A discloses a control method and system for a three-phase current-mode PWM rectifier. By connecting the midpoint of the diode, the midpoint of the output capacitor, and one end of the common-mode filter capacitor, it addresses the switching losses caused by high voltage stress and the impact of parasitic capacitance on the input current quality. However, the topology in this patent application is a buck topology, which can only perform voltage reduction and cannot perform voltage boost. For buck-boost topologies, the method described in the aforementioned patent application cannot reduce the voltage stress of the switching transistors to the phase voltage; furthermore, for a three-phase Buck-Boost PWM rectifier topology, an effective low-resistance path cannot be formed in some modes (modes 3 and 4), causing parasitic capacitance to still affect the input current quality. Summary of the Invention

[0007] The technical problem to be solved by this invention is that the existing three-phase Buck-Boost PWM rectifier cannot avoid the influence of parasitic capacitance on the quality of its input current.

[0008] This invention solves the above-mentioned technical problems through the following technical means: A three-phase Buck-Boost PWM rectifier, comprising a Buck rectifier unit, a first Boost boost unit, a second Boost boost unit, and a common-mode current suppression unit. The input terminal of the Buck rectifier unit is connected to a three-phase AC power supply. The positive terminal of the DC bus containing the positive output terminal of the Buck rectifier unit is connected to the load via the first Boost boost unit. The negative terminal of the DC bus containing the negative output terminal of the Buck rectifier unit is connected to the load via the second Boost boost unit. The first Boost boost unit and the second Boost boost unit are connected. The common-mode current suppression unit is a capacitor C. mn Capacitor C mn One end of the capacitor is connected to the neutral point of the three-phase input filter capacitor, and capacitor C... mnThe other end is connected to the intermediate connection node between the first Boost converter and the second Boost converter, as well as the intermediate connection node between the positive and negative output terminals of the Buck rectifier unit.

[0009] Furthermore, the Buck rectifier unit includes a three-phase LC filter, three pairs of bridge arms, and two diodes D. FP D Fn Each phase LC filter's filter inductor is connected to the corresponding AC power supply and bridge arm, respectively. Each phase LC filter's filter capacitor is located between the filter inductor and the bridge arm. The three-phase input filter capacitors are star-connected, with their neutral point at m. Each pair of bridge arms consists of upper and lower arms, for a total of six arms, designated as bridge arms S1 to S6. Each upper and lower bridge arm is controlled by a switching transistor Q. i and a diode D i Composition, i = 1, 2, ..., 6, switching transistor Q i The source and diode D i The anode of the diode is connected, the drain of the upper arm switching transistor is connected to the cathode of the corresponding lower arm diode, the cathodes of the three upper arm diodes are connected and connected to the positive terminal of the DC bus, and the drains of the three lower arm switching transistors are connected and connected to the negative terminal of the DC bus. Diode D... FP anode and diode D Fn The cathode is connected at point n, which is the intermediate connection node between the positive and negative output terminals of the Buck rectifier unit. Diode D FP The cathode of diode D is connected to the positive terminal of the DC bus. Fn The anode is connected to the negative terminal of the DC bus.

[0010] Furthermore, the first Boost converter includes an inductor L p Switching transistor Q Bp diode Q Bp and capacitor C p Inductor L p One end is connected to the positive terminal of the DC bus, and the inductor L p The other end, the switching transistor Q Bp Drain and diode D BP Anode connection, diode D BP Cathode and capacitor C p One end is connected to capacitor C p The other end, the switching transistor Q Bp The source and diode D FP D Fn Connect n points between them.

[0011] Furthermore, the second Boost converter includes an inductor L nSwitching transistor Q Bn Diode D Bn and capacitor C n Inductor L n One end is connected to the negative terminal of the DC bus, and the inductor L n The other end, the switching transistor Q Bn The source and diode D Bn Cathode connection, diode D Bn anode and capacitor C n One end is connected to capacitor C n The other end, the switching transistor Q Bn Drain and diode D FP D Fn Connect n points between them.

[0012] Furthermore, the capacitor C mn One end of the capacitor is connected to the neutral point m of the three-phase input filter capacitor, and the capacitor C... mn The other end is connected to diode D FP D Fn The connection points between n points are connected; the load R L One end is connected to capacitor C p One end is connected, and the load R L The other end is connected to capacitor C n One end is connected.

[0013] This invention also provides a control method for a three-phase Buck-Boost PWM rectifier. Based on the relative relationship of the three-phase input voltages, one input voltage cycle is divided into several sectors. Within each sector, the rectifier operates in sequentially numbered modes one through four. The Buck rectifier unit has three pairs of bridge arms, each pair consisting of upper and lower arms, for a total of six arms. The first Boost unit includes a switching transistor Q. Bp The second Boost converter includes the switching transistor Q. Bn Switch Q Bp The drain of the transistor is connected to the positive terminal of the DC bus, and the switching transistor Q... Bp The source and switch Q Bn The drain connection, the switching transistor Q Bn The source of the transistor is connected to the negative terminal of the DC bus. In the first to third modes, two bridge arms are conducting. In the fourth mode, all bridge arms are de-conducting. The switching transistor Q... Bp and switching transistor Q Bn All are conducting; the rectifier forms at least three current paths, and the common-mode current of the rectifier flows in the current paths.

[0014] Furthermore, the division of one input voltage cycle into several sectors based on the relative relationship of the three-phase input voltages includes:

[0015] Based on the relative relationship of the three-phase input voltages, one input voltage cycle is divided into 12 sectors. When the three-phase input voltages satisfy v a >0>v b >v c This region is defined as the first sector when the three-phase input voltage satisfies v a >v b >0>v c This region is defined as the second sector when the three-phase input voltage satisfies v b >v a >0>v c This region is defined as the third sector when the three-phase input voltage satisfies v b >0>v a >v c This region is defined as the fourth sector when the three-phase input voltage satisfies v b >0>v c >v a This region is defined as the fifth sector when the three-phase input voltage satisfies v b >v c >0>v a This region is defined as the sixth sector when the three-phase input voltage satisfies v c >v b >0>v a This region is defined as the seventh sector when the three-phase input voltage satisfies v c >0>v b >v a This region is defined as the eighth sector when the three-phase input voltage satisfies v c >0>v a >v b This region is defined as the ninth sector when the three-phase input voltage satisfies v c >v a >0>v b This region is defined as the tenth sector when the three-phase input voltage satisfies v a >v c >0>v b This region is defined as the eleventh sector when the three-phase input voltage satisfies v a >0>v c >v b This area is then defined as the twelfth sector.

[0016] In each mode of control cycle within each sector, the voltage stress on the switching transistor is less than the peak phase voltage.

[0017] When a three-phase Buck-Boost PWM rectifier is running, the inductor current cannot change suddenly due to the energy storage inductor on the DC side. Simultaneously, to control the AC input current, the rectifier must ensure that at any given time, only one switch in each of the upper and lower bridge arms is conducting. Therefore, a three-valued logic function can be defined:

[0018]

[0019] The boost-side switch has only two switching modes, and it is simultaneously on and off, so a binary logic function can be defined:

[0020]

[0021] Based on the above logic functions, a total of 18 operating vector states can be formed. To simplify the expression of the turn-on and turn-off of the bridge arms and switching transistors, the logic functions can be... σ b =β,σ c =χ,σ B =δ represents the vector σ, which can be further simplified. αβχδ Representation. For example, vector σ 0000 σ a =0, σ b =0, σ c =0, σ B =0. That is, all switches Q1 through Q6 are off, and switch Q... Bp and switching transistor Q Bn All are off. This invention provides the switching states of the proposed topology arms during each switching cycle for each sector. Within each switching cycle, the arms exist in four different operating modes: mode one, mode two, mode three, and mode four. In modes one, two arms of the rectifier switching unit are each conducting, while in mode four, all three pairs of rectifier arms are off. In modes one and two, the switching transistor Q... Bp and switching transistor Q Bn Both are turned off; in the third and fourth modes, the switching transistor Q... Bp and switching transistor Q Bn All are on. In each mode within the control cycle of each sector, the voltage stress on the switching transistor is less than the peak phase voltage.

[0022] In the fourth mode, all switches Q1 through Q6 in each sector are turned off, and switch Q... Bp and switching transistor Q Bn All are conducting; in the first sector, each bridge arm and the switching transistor operate at vector σ in the first mode. 10-10 In this state; in the second mode, each bridge arm and switching transistor of the first sector operates at vector σ. 1-100In this state; in the third mode, each bridge arm and switching transistor of the first sector operates at vector σ. 1-101 In this state; in the fourth mode, each bridge arm and switching transistor of the first sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor of the second sector operates at vector σ. 10-10 In this state; in the second mode, each bridge arm and switching transistor of the second sector operates at vector σ. 01-10 In this state; in the third mode, each bridge arm and switching transistor of the second sector operates at vector σ. 01-11 In this state; in the fourth mode, each bridge arm and switching transistor of the second sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the third sector operates at vector σ 01-10 In this state; in the second mode, each bridge arm and switching transistor in the third sector operates at vector σ 10-10 In this state; in the third sector, each bridge arm and switching transistor in the third mode operate at vector σ 10-11 In this state; in the fourth mode, each bridge arm and switching transistor of the third sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor of the fourth sector operates at vector σ. 01-10 In this state; in the second mode, each bridge arm and switch in the fourth sector operates at vector σ. -1100 In this state; in the third mode, each bridge arm and switching transistor of the fourth sector operates at vector σ. -1101 In this state; in the fourth mode, each bridge arm and switching transistor of the fourth sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the fifth sector operates at vector σ -1100 In this state; in the second mode, each bridge arm and switch in the fifth sector operates at vector σ. 01-10 In this state; in the third mode, each bridge arm and switching transistor of the fifth sector operates at vector σ. 01-11 In this state; in the fourth mode, the fifth sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the sixth sector operates at vector σ. -1100 In this state; in the second mode, the sixth sector's bridge arms and switching transistors operate at vector σ. -1010 In this state; in the third mode, the sixth sector's bridge arms and switching transistors operate at vector σ. -1011 In this state; in the fourth mode, the sixth sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the seventh sector operates at vector σ. -1010 In this state; in the second mode, the seventh sector's bridge arms and switching transistors operate at vector σ. -1100 In this state; in the third mode, the seventh sector's bridge arms and switching transistors operate at vector σ. -1101In this state; in the fourth mode, the seventh sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the eighth sector operates at vector σ -1010 In this state; in the second mode, each bridge arm and switching transistor of the eighth sector operates at vector σ. 0-110 In this state; in the third mode, each bridge arm and switching transistor of the eighth sector operates at vector σ. 0-111 In this state; the eighth sector operates in the fourth mode with each bridge arm and switch transistor operating at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the ninth sector operates at vector σ 0-110 In this state; in the second mode, each bridge arm and switching transistor in the ninth sector operates at vector σ. -1010 In this state; in the third mode, the bridge arms and switching transistors of the ninth sector operate at vector σ. -1011 In this state; in the fourth mode, the bridge arms and switching transistors of the ninth sector operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the tenth sector operates at vector σ. 0-110 In this state; in the second mode, the bridge arms and switching transistors of the tenth sector operate at vector σ. 1-100 In this state; in the third mode, the bridge arms and switching transistors of the tenth sector operate at vector σ. 1-101 In this state; the tenth sector operates in the fourth mode with each bridge arm and switch transistor operating at vector σ. 0001 In this state; under the first mode, each bridge arm and switching transistor in the eleventh sector operates at vector σ. 1-100 In this state; under the second mode, each bridge arm and switching transistor in the eleventh sector operates at vector σ. 0-110 In this state; under the third mode, each bridge arm and switching transistor in the eleventh sector operates at vector σ. 0-111 In this state; under the fourth mode, the eleventh sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the twelfth sector operates at vector σ. 1-100 In this state; in the second mode, each bridge arm and switching transistor of the twelfth sector operates at vector σ. 10-10 In this state; in the third mode, each bridge arm and switching transistor of the twelfth sector operates at vector σ. 10-11 In this state; in the fourth mode, each bridge arm and switch in the twelfth sector operates at vector σ. 0001 In the current state.

[0023] The advantages of this invention are:

[0024] (1) This invention adds a common-mode current suppression unit to capacitor C mnBy connecting the input and output to form a low-resistance path, and with capacitors in place, the common-mode current will flow through the low-resistance path. Therefore, by setting up the above, the common-mode current is reduced, the significant high-frequency noise and low-frequency distortion of the input current are avoided, the input current quality is improved, and the influence of parasitic capacitance on the input current quality is avoided.

[0025] (2) The voltage stress of the switching transistor is the maximum value of the switching transistor voltage. Experimental verification shows that the maximum value is in the fourth mode. Therefore, this invention controls different modes so that switching transistors Q1 to Q6 in each sector are all turned off in the fourth mode. Bp and switching transistor Q Bn All modes are on, reducing the voltage of the fourth mode, lowering voltage stress, improving system efficiency, and reducing system cost; simultaneously, through capacitor C... mn The connection with the three-phase input filter capacitor reduces interference, further reduces the voltage stress on the switching transistors, and further improves the performance of the three-phase Buck-Boost PWM rectifier in high-frequency, high-power-density applications. Attached Figure Description

[0026] Figure 1 The circuit diagram for an existing three-phase Buck-Boost PWM rectifier;

[0027] Figure 2 This is a schematic diagram of a three-phase Buck-Boost PWM rectifier disclosed in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of a three-phase input voltage sector division method in a three-phase Buck-Boost PWM rectifier disclosed in an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the bridge arm switching state of a three-phase Buck-Boost PWM rectifier disclosed in an embodiment of the present invention;

[0030] Figure 5 This is the i1 path of each mode of power current in sector twelve of a three-phase Buck-Boost PWM rectifier disclosed in an embodiment of the present invention;

[0031] Figure 6 The high-frequency current i in each mode of sector twelve of a three-phase Buck-Boost PWM rectifier disclosed in this embodiment of the invention. cp path;

[0032] Figure 7 The high-frequency current i in each mode of sector twelve of a three-phase Buck-Boost PWM rectifier disclosed in this embodiment of the invention. cnpath;

[0033] Figure 8 The switching transistor Q in a three-phase Buck-Boost PWM rectifier disclosed in this embodiment of the invention i (i=1~6) Voltage stress curves. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Currently, existing three-phase Buck-Boost PWM rectifiers suffer from significant issues in high-frequency, high-power-density applications, including high bridge arm voltage stress and a substantial impact of common-mode current on input current quality. Existing improvement strategies cannot simultaneously address these problems. To address these issues, such as... Figure 2 As shown, this invention provides a three-phase Buck-Boost PWM rectifier, including a Buck rectifier unit 100, a first Boost converter unit 200, a second Boost converter unit 300, and a common-mode current suppression unit 400. The input terminal of the Buck rectifier unit 100 is connected to the power supply. The positive output terminal of the Buck rectifier unit 100 is connected to the first Boost converter unit 200 between itself and the load. The negative output terminal of the Buck rectifier unit 100 is connected to the second Boost converter unit 300 between itself and the load. The common-mode current suppression unit 400 is a capacitor C. mn Capacitor C mn One end of the capacitor is connected to the neutral point of the three-phase input filter capacitor, and capacitor C... mn The other end is connected to the intermediate connection node between the first Boost converter 200 and the second Boost converter 300, as well as the intermediate connection node between the positive and negative output terminals of the Buck rectifier unit 100. The circuit principles and connection relationships of each part are described in detail below.

[0036] Continue reading Figure 2 The Buck rectifier unit 100 includes a three-phase LC filter, three pairs of bridge arms, and two diodes D. FP D FnEach phase LC filter's filter inductor is connected to the corresponding AC power supply and bridge arm, respectively. Each phase LC filter's filter capacitor is located between the filter inductor and the bridge arm. The three-phase input filter capacitors are connected in a star (Y) configuration, with a neutral point at m. Each pair of bridge arms consists of upper and lower arms, for a total of six arms, designated as bridge arms S1 to S6. Each upper and lower bridge arm is controlled by a switching transistor Q. i and a diode D i Composition, i = 1, 2, ..., 6, switching transistor Q i The source and diode D i The anode of the diode is connected, the drain of the upper arm switching transistor is connected to the cathode of the corresponding lower arm diode, the cathodes of the three upper arm diodes are connected and connected to the positive terminal of the DC bus, and the drains of the three lower arm switching transistors are connected and connected to the negative terminal of the DC bus. Diode D... FP anode and diode D Fn The cathode is connected, and the connection point is point n. Diode D FP The cathode of diode D is connected to the positive terminal of the DC bus. Fn The anode is connected to the negative terminal of the DC bus.

[0037] Continue reading Figure 2 The first Boost converter 200 includes an inductor L p Switching transistor Q Bp Diode D BP and capacitor C p Inductor L p One end is connected to the positive terminal of the DC bus, and the inductor L p The other end, the switching transistor Q Bp Drain and diode D BP Anode connection, diode D BP Cathode and capacitor C p One end is connected to capacitor C p The other end, the switching transistor Q Bp The source and diode D FP D Fn Connect n points between them.

[0038] Continue reading Figure 2 The second Boost unit 300 includes an inductor L n Switching transistor Q Bn Diode D Bn and capacitor C n Inductor L n One end is connected to the negative terminal of the DC bus, and the inductor L n The other end, the switching transistor Q Bn The source and diode D Bn Cathode connection, diode DBn anode and capacitor C n One end is connected to capacitor C n The other end, the switching transistor Q Bn Drain and diode D FP D Fn Connect n points between them.

[0039] Continue reading Figure 2 The capacitor C mn One end of the capacitor is connected to the neutral point m of the three-phase input filter capacitor, and the capacitor C... mn The other end is connected to diode D FP D Fn The connection points between n points are connected; the load R L One end is connected to capacitor C p One end is connected, and the load R L The other end is connected to capacitor C n One end is connected. A common-mode current suppression unit 400 is added to the three-phase Buck-Boost PWM rectifier topology. This unit can reduce the voltage stress on the rectifier switching transistors and provide a low-impedance internal path for common-mode current, preventing common-mode current from flowing to the input terminal.

[0040] like Figure 3 and Figure 4 As shown, this invention also provides a control method matching the topology of the aforementioned three-phase Buck-Boost PWM rectifier. Based on the relative relationship of the three-phase input voltages, one input voltage cycle is divided into 12 sectors. Within each sector, the rectifier operates in four modes: a first mode, a second mode, a third mode, and a fourth mode. In the first, second, and third modes, two bridge arms are conducting, while in the fourth mode, all bridge arms are de-conducting. In the first and second modes, the switching transistor Q... Bp Q Bn Both are turned off; in the third and fourth modes, the switching transistor Q... Bp Q Bn All are conducting. In each mode of each sector, the rectifier forms at least two high-frequency current paths, which are common-mode current circulation paths within the rectifier. The specific process is as follows:

[0041] When the three-phase input voltage satisfies v a >0>v b >v c This region is defined as the first sector when the three-phase input voltage satisfies v a >v b >0>v c This region is defined as the second sector when the three-phase input voltage satisfies v b >va >0>v c This region is defined as the third sector when the three-phase input voltage satisfies v b >0>v a >v c This region is defined as the fourth sector when the three-phase input voltage satisfies v b >0>v c >v a This region is defined as the fifth sector when the three-phase input voltage satisfies v b >v c >0>v a This region is defined as the sixth sector when the three-phase input voltage satisfies v c >v b >0>v a This region is defined as the seventh sector when the three-phase input voltage satisfies v c >0>v b >v a This region is defined as the eighth sector when the three-phase input voltage satisfies v c >0>v a >v b This region is defined as the ninth sector when the three-phase input voltage satisfies v c >v a >0>v b This region is defined as the tenth sector when the three-phase input voltage satisfies v a >v c >0>v b This region is defined as the eleventh sector when the three-phase input voltage satisfies v a >0>v c >v b This area is then defined as the twelfth sector.

[0042] When a three-phase Buck-Boost PWM rectifier is running, the inductor current cannot change suddenly due to the energy storage inductor on the DC side. Simultaneously, to control the AC input current, the rectifier must ensure that at any given time, only one switch in each of the upper and lower bridge arms is conducting. Therefore, a three-valued logic function can be defined:

[0043]

[0044] The boost-side switch has only two switching modes, and it is simultaneously on and off, so a binary logic function can be defined:

[0045]

[0046] Based on the above logic functions, a total of 18 operating vector states can be formed. To simplify the expression of the turn-on and turn-off of the bridge arms and switching transistors, the logic functions can be... σ b =β,σ c =χ,σ B =δ represents the vector σ, which can be further simplified. αβχδ Representation. For example, vector σ 0000 σ a =0, σ b =0, σ c =0, σ B =0. That is, all switches Q1 through Q6 are off, and switch Q... Bp and switching transistor Q Bn All are turned off. For example... Figure 4 As shown, this invention provides the switching states of the proposed topology bridge arms during each switching cycle for each sector. Within each switching cycle, the bridge arms exist in four different operating modes: a first mode, a second mode, a third mode, and a fourth mode. In the first, second, and third modes, two bridge arms of the rectifier switching unit are each conducting, while in the fourth mode, all three pairs of bridge arms of the rectifier are turned off. In the first and second modes, the switching transistor Q... Bp and switching transistor Q Bn Both are turned off; in the third and fourth modes, the switching transistor Q... Bp and switching transistor Q Bn All are on. In each mode within the control cycle of each sector, the voltage stress on the switching transistor is less than the peak phase voltage.

[0047] Continue reading Figure 4 In each sector, switching transistors Q1 through Q6 are all turned off in the fourth mode, and switching transistor Q... Bp and switching transistor Q Bn All are conducting; in the first sector, each bridge arm and the switching transistor operate at vector σ in the first mode. 10-10 In this state; in the second mode, each bridge arm and switching transistor of the first sector operates at vector σ. 1-100 In this state; in the third mode, each bridge arm and switching transistor of the first sector operates at vector σ. 1-101 In this state; in the fourth mode, each bridge arm and switching transistor of the first sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor of the second sector operates at vector σ. 10-10 In this state; in the second mode, each bridge arm and switching transistor of the second sector operates at vector σ. 01-10 In this state; in the third mode, each bridge arm and switching transistor of the second sector operates at vector σ. 01-11 In this state; in the fourth mode, each bridge arm and switching transistor of the second sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the third sector operates at vector σ 01-10 In this state; in the second mode, each bridge arm and switching transistor in the third sector operates at vector σ10-10 In this state; in the third sector, each bridge arm and switching transistor in the third mode operate at vector σ 10-11 In this state; in the fourth mode, each bridge arm and switching transistor of the third sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor of the fourth sector operates at vector σ. 01-10 In this state; in the second mode, each bridge arm and switch in the fourth sector operates at vector σ. -1100 In this state; in the third mode, each bridge arm and switching transistor of the fourth sector operates at vector σ. -1101 In this state; in the fourth mode, each bridge arm and switching transistor of the fourth sector operates at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the fifth sector operates at vector σ -1100 In this state; in the second mode, each bridge arm and switch in the fifth sector operates at vector σ. 01-10 In this state; in the third mode, each bridge arm and switching transistor of the fifth sector operates at vector σ. 01-11 In this state; in the fourth mode, the fifth sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the sixth sector operates at vector σ. -1100 In this state; in the second mode, the sixth sector's bridge arms and switching transistors operate at vector σ. -1010 In this state; in the third mode, the sixth sector's bridge arms and switching transistors operate at vector σ. -1011 In this state; in the fourth mode, the sixth sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the seventh sector operates at vector σ. -1010 In this state; in the second mode, the seventh sector's bridge arms and switching transistors operate at vector σ. -1100 In this state; in the third mode, the seventh sector's bridge arms and switching transistors operate at vector σ. -1101 In this state; in the fourth mode, the seventh sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the eighth sector operates at vector σ -1010 In this state; in the second mode, each bridge arm and switching transistor of the eighth sector operates at vector σ. 0-110 In this state; in the third mode, each bridge arm and switching transistor of the eighth sector operates at vector σ. 0-111 In this state; the eighth sector operates in the fourth mode with each bridge arm and switch transistor operating at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the ninth sector operates at vector σ 0-110 In this state; in the second mode, each bridge arm and switching transistor in the ninth sector operates at vector σ. -1010 In this state; in the third mode, the bridge arms and switching transistors of the ninth sector operate at vector σ.-1011 In this state; in the fourth mode, the bridge arms and switching transistors of the ninth sector operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the tenth sector operates at vector σ. 0-110 In this state; in the second mode, the bridge arms and switching transistors of the tenth sector operate at vector σ. 1-100 In this state; in the third mode, the bridge arms and switching transistors of the tenth sector operate at vector σ. 1-101 In this state; the tenth sector operates in the fourth mode with each bridge arm and switch transistor operating at vector σ. 0001 In this state; under the first mode, each bridge arm and switching transistor in the eleventh sector operates at vector σ. 1-100 In this state; under the second mode, each bridge arm and switching transistor in the eleventh sector operates at vector σ. 0-110 In this state; under the third mode, each bridge arm and switching transistor in the eleventh sector operates at vector σ. 0-111 In this state; under the fourth mode, the eleventh sector's bridge arms and switching transistors operate at vector σ. 0001 In this state; in the first mode, each bridge arm and switching transistor in the twelfth sector operates at vector σ. 1-100 In this state; in the second mode, each bridge arm and switching transistor of the twelfth sector operates at vector σ. 10-10 In this state; in the third mode, each bridge arm and switching transistor of the twelfth sector operates at vector σ. 10-11 In this state; in the fourth mode, each bridge arm and switch in the twelfth sector operates at vector σ. 0001 In the state; Figure 4 For the sake of brevity, sectors 1 to 12 are directly written as sector 1 to sector 12, and modes 1 to 4 are directly written as mode 1 to mode 4.

[0048] The working principle of the topology of this invention is explained below in conjunction with the switching state of the twelfth sector:

[0049] During the first mode, bridge arm S1 (composed of switch Q1 in series with diode D1) and bridge arm S6 (composed of switch Q6 in series with diode D6) are turned on, while the other bridge arms are turned off. Freewheeling diode D... p With D n It is cut off when subjected to reverse voltage. Switch Q Bp Q Bn Turn off, diode D Bp D Bn During the second mode, bridge arm S1 (composed of switch Q1 in series with diode D1) and bridge arm S2 (composed of switch Q2 in series with diode D2) are turned on, while the other bridge arms are turned off. Freewheeling diode D... p With D n It is cut off when subjected to reverse voltage. Switch Q Bp Q BnTurn off, diode D Bp D Bn During the third mode, bridge arm S1 (composed of switch Q1 in series with diode D1) and bridge arm S2 (composed of switch Q2 in series with diode D2) are turned on, while the other bridge arms are turned off. Freewheeling diode D... p With D n It is cut off when subjected to reverse voltage. Switch Q Bp Q Bn Conduction, diode D Bp D Bn It is cut off when subjected to reverse voltage; during the fourth mode, all bridge arms are turned off. Freewheeling diode D p With D n On. Switch Q Bp Q Bn Conduction, diode D Bp D Bn It is cut off when subjected to reverse voltage.

[0050] Figure 5 This indicates the power current path i1 in each mode of the twelfth sector. During mode one, the input voltages of phase A and phase B pass through bridge arm S1, bridge arm S6, and inductor L. p L n Two diodes D Bp D Bn This forms the current path i1, providing energy to the load. During mode two, the input voltages of phase A and phase B pass through bridge arm S1, bridge arm S2, and inductor L. p L n Two diodes D Bp D Bn The current path i1 is formed, providing energy to the load; during mode three, the input voltages of phase A and phase B pass through bridge arm S1, bridge arm S2, and inductor L. p L n Two switching transistors Q Bp Q Bn This forms a current path i1, charging the inductor; during mode four, the DC-side inductor L... p With L n Through the freewheeling diode D p D n With the switching transistor Q Bp Q Bn It forms a current path.

[0051] Figure 6 Indicates the high-frequency current i in each mode of the twelfth sector. cp Path. High-frequency current i cp The internal loop of the rectifier is the current path i2. During mode one, the capacitor C... a Bridge arm S1, inductor Lp Diode D Bp Capacitor C p and capacitor C mn This forms the current path i2; during mode two, the high-frequency current i cp The internal circuit of the rectifier is the current path i2, i.e., capacitor C. a Bridge arm S1, inductor L p Diode D Bp Capacitor C p and capacitor C mn Composition; During mode three, capacitance C a Bridge arm S1, energy storage inductor L p Switching transistor Q Bp and capacitor C mn Forming the current path i2; during mode four, diode D p and the switching transistor Q Bp This forms the current path i2.

[0052] Figure 7 Indicates the high-frequency current i in each mode of the twelfth sector. cn Path. High-frequency current i cn The internal loop of the rectifier is the current path i3. During mode one, the capacitor C... b Bridge arm S6, inductor L n Diode D Bn Capacitor C n and capacitor C mn Forming current path i3; during mode two, capacitor C c Bridge arm S2, inductor L n Diode D Bn Capacitor C n and capacitor C mn Forming current path i3; during mode three, capacitor C c Bridge arm S2, inductor L n Switching transistor Q Bn and capacitor C mn Forming current path i3; during mode four, diode D n and the switching transistor Q Bn This forms the current path i3.

[0053] like Figure 8 As shown, during the first mode in the twelfth sector, the voltage v at point p is... p =v A Voltage at point n, v n =v B The voltage across the switching transistor is v. Q1 =v Q2 =v Q3 =vQ4 =v Q5 =v Q6 =0V. During the second and third modes, the voltage at point p is v. p =v A Voltage at point n, v n =v C The voltage across the switching transistor Q6 is v. Q6 =v C -v B The voltage across the other switching transistors is V. Q1 =v Q2 =v Q3 =v Q4 =v Q5 =0V. During the fourth mode, the voltage at point p is v. p =v Cmn Voltage at point n, v n =v Cmn The voltage stress that the switching transistor Q1 withstands is v Q1 =v A -v Cmn The voltage stress that the switching transistor Q6 withstands is v Q6 =v Cmn -v B The voltage stress that the switching transistor Q2 withstands is v Q2 =v Cmn -v C The voltage across the other switching transistors is v. Q3 =v Q4 =v Q5 =0V. Where v A v B v C This represents the instantaneous value of the phase voltage. Following this pattern, the voltage stress over 12 sectors can be obtained. In the twelfth sector, the voltage across the switching transistor is v. C -v B v A -v Cmn v Cmn -v B v Cmn -v C Because it operates in sector 12, v C -v B The maximum value is 0.87V. l-gmax V l-g max This represents the peak value of the phase voltage. Therefore, we conclude that v... C -v B ≤V l-g max .

[0054] Capacitor C mn The voltage is:

[0055]

[0056]

[0057] Where, d A d is the duty cycle of the switching transistor Q1. B d is the duty cycle of the switching transistor Q6. C M represents the duty cycle of the switching transistor Q2, and M represents the modulation index.

[0058] For v A -v Cmn To put it another way, substituting formula (2) into formula (1) and eliminating v B v C We can obtain:

[0059]

[0060] 0.87V in sector 12 l-g max ≤v A ≤V l-g max Then there is Conclusion

[0061] For v Cmn -v B To put it another way, substituting formula (2) into formula (1) and eliminating v A We can obtain:

[0062]

[0063] When M is 1, capacitor C mn Voltage v Cmn The largest, has

[0064]

[0065]

[0066] Since the minimum value of the squared term is 0, it is easy to conclude that...

[0067] For v Cmn -v C Similarly, from formulas (4) and (5) above, we can obtain formula (7):

[0068]

[0069] Since the minimum value of the squared term is 0, it is easy to conclude that...

[0070] In summary, in sector 12, the voltage stress on the switching transistor is less than the peak phase voltage V in each mode within a control cycle. l-g max The same principle applies to other sectors.

[0071] Through the above technical solutions, this invention addresses the problems of high switching voltage stress and poor current quality in existing three-phase Buck-Boost PWM rectifiers. Based on the existing three-phase Buck-Boost PWM rectifier topology, it proposes a novel topology with low voltage stress and high input current quality. This not only reduces the voltage stress on the bridge arm switches, improving system efficiency and reducing system cost, but also suppresses the influence of parasitic capacitance on the input current, improving input current quality. This invention can further enhance the performance of three-phase Buck-Boost PWM rectifiers in high-frequency, high-power-density applications.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase Buck-Boost PWM rectifier, characterized in that, The system includes a Buck rectifier unit, a first Boost converter unit, a second Boost converter unit, and a common-mode current suppression unit. The input terminal of the Buck rectifier unit is connected to the power supply. The positive terminal of the DC bus containing the positive output terminal of the Buck rectifier unit is connected to the load via the first Boost converter unit. The negative terminal of the DC bus containing the negative output terminal of the Buck rectifier unit is connected to the load via the second Boost converter unit. The first Boost converter unit and the second Boost converter unit are connected together. The common-mode current suppression unit is a capacitor. ,capacitance One end of the capacitor is connected to the neutral point of the three-phase input filter capacitor. The other end is connected to the intermediate connection node between the first Boost converter and the second Boost converter, and to the intermediate connection node between the positive and negative output terminals of the Buck rectifier unit; the first Boost converter includes an inductor. Switching transistor ,diode and capacitors ,inductance One end is connected to the positive terminal of the DC bus, and the inductor The other end, the switching transistor drain and diode Anode connection, diode Cathode and capacitor One end is connected to the capacitor. The other end, the switching transistor source and diode , The connection points between n points are connected; the second Boost unit includes an inductor. Switching transistor ,diode and capacitors ,inductance One end is connected to the negative terminal of the DC bus, and the inductor The other end, the switching transistor source and diode Cathode connection, diode anode and capacitor One end is connected to the capacitor. The other end, the switching transistor drain and diode , Connect n points between them.

2. A three-phase Buck-Boost PWM rectifier according to claim 1, characterized in that, The Buck rectifier unit includes a three-phase LC filter, three pairs of bridge arms, and two diodes. , Each phase LC filter's filter inductor is connected to the corresponding AC power supply and bridge arm, respectively. Each phase LC filter's filter capacitor is located between the filter inductor and the bridge arm. The three-phase input filter capacitors are star-connected, with their neutral point at m. Each pair of bridge arms consists of upper and lower arms, for a total of six arms, which are designated as bridge arms. To the bridge arm Each upper arm and each lower arm is controlled by a switch. and a diode constitute, i =1, 2, ..., 6, Switching transistors source and diode The anode of the diode is connected, the drain of the upper arm switching transistor is connected to the cathode of the corresponding lower arm diode, the cathodes of the three upper arm diodes are connected and connected to the positive terminal of the DC bus, and the drains of the three lower arm switching transistors are connected and connected to the negative terminal of the DC bus. anode and diode The cathode is connected at point n, which is the intermediate connection node between the positive and negative output terminals of the Buck rectifier unit. The diode... The cathode of the diode is connected to the positive terminal of the DC bus. The anode is connected to the negative terminal of the DC bus.

3. A three-phase Buck-Boost PWM rectifier according to claim 1, characterized in that, The capacitor One end of the capacitor is connected to the neutral point m of the three-phase input filter capacitor. The other end is connected to the diode , The connection points between n points; load One end is connected to the capacitor One end is connected, load The other end is connected to the capacitor One end is connected.

4. A control method for a three-phase Buck-Boost PWM rectifier according to any one of claims 1-3, characterized in that, Based on the relative relationship of the three-phase input voltages, one input voltage cycle is divided into several sectors. Within each sector, the rectifier operates in sequentially numbered modes one through four. The Buck rectifier unit has three pairs of bridge arms, each pair consisting of upper and lower arms, for a total of six arms. The first Boost converter unit includes a switching transistor. The second Boost converter includes a switching transistor. Switching transistor The drain of the switching transistor is connected to the positive terminal of the DC bus. Source and switch Drain connection, switching transistor The source is connected to the negative terminal of the DC bus. In the first to third modes, two bridge arms are conducting. In the fourth mode, all bridge arms are de-conducting. The switching transistor... and switching transistors All are conducting; the rectifier forms at least three current paths, and the common-mode current of the rectifier flows in the current paths.

5. The control method for a three-phase Buck-Boost PWM rectifier according to claim 4, characterized in that, Based on the relative relationship of the three-phase input voltages, one input voltage cycle is divided into 12 sectors. In each mode of the control cycle of each sector, the voltage stress on the switching transistor is less than the peak phase voltage.

6. The control method for a three-phase Buck-Boost PWM rectifier according to claim 5, characterized in that, To prevent abrupt changes in inductor current and control the AC input current, the Buck rectifier unit must ensure that at any given time, only one switch in each bridge arm is turned on. The operating state of the Buck rectifier unit is defined as a ternary logic function: The switching transistor of the first Boost converter The switching transistor of the second Boost boost unit The working state is defined as a binary logic function: 。 7. The control method for a three-phase Buck-Boost PWM rectifier according to claim 6, characterized in that, Using vector Simplified representation of the turn-on and turn-off of bridge arms and switching transistors, vector The meaning is logical function Vector express That is, the upper and lower arms of the three phases a, b, and c of the Buck rectifier unit are all turned off, and the switching transistors are... and switching transistors All are turned off.

8. The control method for a three-phase Buck-Boost PWM rectifier according to claim 7, characterized in that, The rectifier operates in the following manner: The first sector operates in vector mode from the first to the fourth modes, respectively. Vector Vector and vector Under the state; the second sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the third sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the fourth sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the fifth sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the sixth sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the seventh sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the eighth sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the ninth sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the tenth sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the eleventh sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector Under the state; the twelfth sector operates in vector mode from the first mode to the fourth mode respectively. Vector Vector and vector In the current state.

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