Hybrid rectifier and control method

Abstract

The application discloses a hybrid rectifier and a control method. The hybrid rectifier comprises a main circuit and a controller. The main circuit comprises a VIENNA rectifier and a flying capacitor auxiliary switch tube bridge arm. The controller comprises a voltage and current double-loop controller, a zero common-mode voltage controller and a neutral point voltage balance controller. The VIENNA rectifier comprises three phases and three groups of switching devices, and the output ends of the three groups of switching devices are used as neutral points. The flying capacitor auxiliary switch tube bridge arm comprises four switching devices and a capacitor, and the output node is connected with the neutral points. The problems of the rectifier, such as the incapability of simultaneously realizing zero common-mode voltage and neutral point voltage balance, low output power quality, system safety and system efficiency, are solved, the common-mode voltage of the rectifier is zero, the neutral point voltage is balanced, and the quality of the output waveform, the safety of the system and the economy are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power electronics, and more particularly relates to a hybrid rectifier and a control method BACKGROUND

[0002] Three-level converters have the advantages of less output harmonics, small switching voltage stress and high output waveform quality compared with traditional two-level converters, and are widely used in active power filtering and high voltage direct current (HVDC) transmission.

[0003] Compared with the traditional diode clamped three-level converter, the VIENNA rectifier has fewer power switching devices and does not need to consider the dead zone of the upper and lower switching tubes, and has better economy and safety. Therefore, it is widely used in industries such as UPS and charging piles that do not require bidirectional energy flow. The significant feature of the VIENNA circuit is that each phase bridge arm is composed of two switching tubes and two diodes, and the DC side is divided by two capacitors, and the point between them is usually called the neutral point. By controlling the turn-on and turn-off of the switching tubes, each phase can output positive, negative and zero levels relative to the center point.

[0004] Because the number of phases is odd, there will be a common-mode voltage under conventional modulation. The common-mode voltage will generate a leakage current through the stray loop to the ground, which may damage the devices in the system over a long period of time, thereby reducing the safety of the system. Therefore, it is necessary to use zero common-mode voltage vectors to actively suppress the common-mode voltage at the source. In an ideal case, the voltages of the two divided capacitors are exactly equal, and the neutral point voltage is half of the DC side voltage. However, due to the particularity of the zero common-mode voltage vector, the charging and discharging of the two capacitors in the DC side capacitor branch will be unbalanced, thereby making the neutral point voltage fluctuate greatly. This imbalance of the neutral point voltage will make the output voltage quality of the rectifier and the common-mode voltage suppression effect worse, and will introduce additional harmonics to the load side, thereby reducing the system efficiency. In addition, the voltage fluctuation of the DC side divided capacitor will shorten the service life of the capacitor. Therefore, the balance of the neutral point voltage is crucial for maintaining good output waveform and ensuring the normal operation of the rectifier. However, the common method for suppressing the imbalance of the neutral point voltage cannot achieve suppression of the common-mode voltage. SUMMARY

[0005] In view of the defects of the related art, the present application aims to provide a hybrid rectifier and a control method, which aims to solve the problems of the rectifier in the prior art that cannot simultaneously achieve zero common-mode voltage and neutral point voltage balance, and low output energy quality, system safety and system efficiency when working.

[0006] To achieve the above-mentioned purpose, in a first aspect, the present application provides a hybrid rectifier, comprising: a main circuit and a controller; the main circuit comprises: a VIENNA rectifier and a flying capacitor auxiliary switching tube bridge arm;

[0007] The VIENNA rectifier comprises three phases and three groups of switching devices; each phase is composed of two diodes, the middle nodes of the two diodes are independently connected as the interfaces of the AC side input, each phase is connected with an AC power source as the input of the AC side; each of the middle nodes is further connected with a group of switching devices in reverse series, the other sides of the three groups of switching devices are connected together, and the output ends of the three groups of switching devices are connected as the neutral point of the hybrid rectifier;

[0008] The flying capacitor type auxiliary switching tube bridge arm comprises four switching devices and a capacitor, the four switching devices are connected in series between the positive and negative poles of the DC side, and the capacitor is connected to the middle nodes of the first and second switching devices and the middle nodes of the third and fourth switching devices; the middle nodes of the second and third switching devices are connected as the output nodes of the neutral point;

[0009] The controller comprises a voltage and current double-loop controller, a zero common-mode voltage controller and a neutral point voltage balance controller;

[0010] The voltage and current double-loop controller is connected across the VIENNA rectifier, and is configured to control the states of the switching devices of each phase of the VIENNA rectifier according to the three-phase AC input of the VIENNA rectifier and the DC voltage output of the VIENNA rectifier, so as to output a target DC voltage;

[0011] The zero common-mode voltage controller is connected to the three phases of the VIENNA rectifier, and is configured to control the states of the switching devices of each phase of the VIENNA rectifier based on the modulation waves of the three phases of the VIENNA rectifier, so as to make the common-mode voltage of the hybrid rectifier zero;

[0012] The neutral point voltage balance controller is connected to the flying capacitor type auxiliary switching tube bridge arm, and is configured to control the states of the switching devices of the flying capacitor type auxiliary switching tube bridge arm based on the current direction of the neutral point and the capacitor voltage of the flying capacitor type auxiliary switching tube bridge arm, so as to make the voltage of the capacitor always half of the output voltage of the DC side, thereby controlling the neutral point voltage balance of the hybrid rectifier.

[0013] Optionally, the upper nodes of the flying capacitor type auxiliary switching tube bridge arm and the upper nodes of the three phases of the VIENNA rectifier are connected together as the positive pole of the DC side output, and the lower nodes of the flying capacitor type auxiliary switching tube bridge arm and the lower nodes of the three phases of the VIENNA rectifier are connected together as the negative pole of the DC side output;

[0014] The frequencies of the four switching devices of the flying capacitor type auxiliary switching tube bridge arm are consistent with the frequencies of the switching devices of the VIENNA rectifier.

[0015] Optionally, the hybrid rectifier further comprises a voltage stabilizing capacitor.

[0016] The voltage stabilizing capacitor is connected in parallel to the DC side of the VIENNA rectifier, and is used for voltage stabilization of the DC side output.

[0017] Optionally, the switching device is a fully controlled switching device, and the diode is an uncontrolled device.

[0018] Optionally, the controller is completely decoupled in control of the VIENNA rectifier and the flying capacitor auxiliary switching bridge arm.

[0019] In a second aspect, the application further provides a control method of a hybrid rectifier, which is suitable for the hybrid rectifier of any one of the first aspect, and comprises:

[0020] The voltage-current dual-loop controller obtains the three-phase alternating current input of the hybrid rectifier and the DC voltage of the output side, and obtains the given value of the three-phase modulation wave voltage after voltage outer loop controller processing and current inner loop controller processing

[0021] The zero common-mode voltage controller receives the given value of the three-phase modulation wave voltage output by the voltage-current dual-loop controller Based on space vector modulation or carrier phase-shifted modulation, the PWM signal is obtained by operation The switching device of the VIENNA rectifier is controlled to make the common-mode voltage of the hybrid rectifier zero;

[0022] The neutral point voltage balancing controller controls the state of the switching device of the flying capacitor auxiliary switching bridge arm according to the PWM signal, controls the driving PWM signals of the first switching device and the third switching device to be consistent, controls the driving PWM signals of the second switching device and the fourth switching device to be consistent, and the duty cycles are both 50%, so that the voltage of the capacitor of the flying capacitor auxiliary switching bridge arm is half of the output voltage of the DC side, and the neutral point voltage of the hybrid rectifier is balanced.

[0023] Optionally, the voltage-current dual-loop controller obtains the three-phase alternating current input of the VIENNA rectifier and the DC voltage of the output side, and obtains the given value of the three-phase modulation wave voltage after voltage outer loop controller processing and current inner loop controller processing Comprises:

[0024] The sampling trigger module of the voltage outer loop PI controller samples the DC output side voltage of the VIENNA rectifier to obtain the voltage given value u * ;

[0025] The voltage outer loop PI controller will give the voltage given value u * The voltage difference value signal Δu is obtained by subtracting the sampled voltage actual value u, and the voltage difference value signal Δu is obtained by the current inner loop PI controller

[0026] The sampling trigger module of the current inner loop PI controller samples the three-phase current input to the AC side of the VIENNA rectifier to obtain the three-phase current i a b c The d-axis and q-axis current actual values i d q are obtained through coordinate transformation

[0027] The inner loop PI controller will give the d-axis current given value Subtract the d-axis current actual value i d to obtain the d-axis current difference value signal Δi d Subtract the q-axis current given value 0 from the q-axis current actual value i q to obtain the q-axis current difference value signal Δi q

[0028] The d-axis and q-axis current difference value signals Δi d and Δi q are input to the decoupling module after PI controller; at the same time, the sampling trigger module of the voltage outer loop controller samples the grid voltage input to the AC side to obtain e a b c The d-axis and q-axis grid voltages e d and e q are obtained through coordinate transformation and input to the decoupling module

[0029] The decoupling module controls the d-axis and q-axis current to obtain the d-axis and q-axis given values of the modulation wave voltage and The d-axis and q-axis given values of the modulation wave voltage and are obtained through coordinate transformation to obtain the given values of the three-phase modulation wave voltage

[0030] Optionally, the three-phase modulation wave voltage given values of the VIENNA rectifier satisfy

[0031] Optionally, the zero common-mode voltage controller receives the three-phase modulation wave voltage given values output by the voltage and current double-loop controller Based on carrier phase-shifted modulation, the PWM signal is obtained by operation​​​​​​ Controlling the switching devices of the VIENNA rectifier to make the common-mode voltage of the hybrid rectifier zero includes:

[0032] Receive the given value of the three-phase modulated wave voltage output from the voltage-current dual-loop controller. The virtual voltage V is obtained by calculation. x1 V x2 V x3 ;

[0033] The virtual voltage is compared with a triangular carrier wave to generate a PWM signal v. x1 v x2 v x3 ;

[0034] The PWM signal v x1 v x2 v x3 PWM signal is obtained through calculation. V b * V c * ;

[0035] According to the PWM signal V b * V c * A switching signal is generated to drive the VIENNA rectifier, controlling the state of the VIENNA rectifier's switching devices to make the common-mode voltage of the hybrid rectifier zero; when the PWM signal... V b * V c * When the value is 0, the switching device controlling the VIENNA rectifier is turned on, and the VIENNA rectifier outputs zero voltage; when the PWM signal is 0, the switching device controlling the VIENNA rectifier is turned on, and the VIENNA rectifier outputs zero voltage; V b * V c * When the value is ±1, the switching devices of the VIENNA rectifier are turned off.

[0036] Optionally, the zero common-mode voltage controller receives a given value of the three-phase modulated wave voltage output by the voltage-current dual-loop controller. The PWM signal is obtained by performing calculations based on space vector modulation and using only the zero common-mode voltage vector. V b * V c* Controlling the switching devices of the VIENNA rectifier to make the common-mode voltage of the hybrid rectifier zero, comprising:

[0037] Receiving a given value of the three-phase modulation wave voltage output by the voltage-current double-loop controller According to the formula Synthesizing to obtain a rotating vector V r * ; the rotating vector V r * In each sector, only the middle vector and the zero vector with zero common-mode voltage are used for synthesis;

[0038] According to the principle of vector decomposition, the vector action time is calculated to generate a PWM signal to control the switching devices of the VIENNA rectifier, so that the common-mode voltage of the hybrid rectifier is zero.

[0039] Overall, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0040] 1. Based on zero common-mode voltage vector modulation, the switching devices of the VIENNA rectifier of the hybrid rectifier are controlled, which can make the common-mode voltage of the VIENNA rectifier zero, greatly reduce the leakage current, reduce the harm of the leakage current to the system, improve the safety and reliability of the system, and also improve the economy of the system.

[0041] 2. Based on the neutral point voltage control of the flying capacitor auxiliary switching bridge arm, the capacitor voltage of the flying capacitor auxiliary switching bridge arm can be maintained at half of the DC output voltage, and the neutral point voltage of the hybrid rectifier can be maintained at half of the DC output voltage, thereby realizing the balance of the neutral point voltage of the hybrid rectifier.

[0042] 3. Through the neutral point voltage control of the hybrid rectifier, the low-frequency fluctuation of the capacitor voltage is suppressed, the life of the capacitor voltage is improved, and the quality of the output waveform is improved.

[0043] 4. The hybrid rectifier control method provided by the present application is completely decoupled from the VIENNA rectifier and has higher freedom; the control method provided by the present application can theoretically completely eliminate the common-mode voltage and has better electromagnetic interference suppression effect. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a schematic block diagram of the hybrid rectifier provided by embodiment one of the present application;

[0045] Figure 2 is a main circuit topology diagram of the hybrid rectifier provided by embodiment one of the present application;

[0046] Figure 3 is a schematic block diagram of a controller of the hybrid rectifier provided in Embodiment One of the present application;

[0047] Figure 4 is a schematic diagram of common-mode voltage of a common VIENNA converter in the prior art;

[0048] Figure 5 is a schematic diagram of common-mode voltage of the hybrid rectifier provided in Embodiment One of the present application;

[0049] Figure 6 is a schematic diagram of neutral point voltage of the VIENNA rectifier without flying capacitor type auxiliary switch bridge arm provided in Embodiment One of the present application;

[0050] Figure 7 is a schematic diagram of neutral point voltage of the hybrid rectifier provided in Embodiment One of the present application. DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0052] The content involved in the above embodiments will be described below in combination with a preferred embodiment.

[0053] In combination with Figure 1 and Figure 3 , the present application provides a hybrid rectifier, comprising: a main circuit and a controller; the controller is used to control common-mode voltage of the main circuit to be zero and neutral point voltage to be balanced; the main circuit comprises: a VIENNA rectifier 11 and a flying capacitor type auxiliary switch bridge arm 12; the controller comprises: a voltage and current double-loop controller 21, a zero common-mode voltage controller 22 and a neutral point voltage balancing controller 23;

[0054] As shown in Figure 2 , the VIENNA rectifier 11 comprises three phases (a, b, c) and three groups of switching devices (S a , S b , S c);Each phase is composed of two diodes, and the middle node of the two diodes is independently connected as the interface of the alternating side input, and each phase is connected to an alternating power supply as the input of the alternating side; Each of the middle nodes is also connected to a group of two switch devices in reverse series, and the other side of the three groups of switch devices is connected together, and the output end of the three groups of switch devices is the neutral point O of the hybrid rectifier;

[0055] The flying capacitor auxiliary switch tube bridge arm 12 comprises four switch devices and a capacitor C F The four switch devices are connected in series between the positive and negative poles of the direct current side, and the two ends of the capacitor C F are connected to the middle nodes of the first and second switch devices and the third and fourth switch devices, respectively; The middle node of the second and third switch devices is connected to the neutral point O as the output node;

[0056] As shown in Figure 1 and Figure 3 , the voltage and current double-loop controller 21 is connected across the VIENNA rectifier, and is used to control the state of each switch device of the three phases of the VIENNA rectifier according to the three-phase alternating current input by the VIENNA rectifier and the direct current voltage output by the VIENNA rectifier, so as to output a target direct current voltage;

[0057] The zero common-mode voltage controller 22 is connected to the three phases of the VIENNA rectifier, and is used to control the state of each switch device of the three phases of the VIENNA rectifier based on the three-phase modulation wave of the VIENNA rectifier, so as to make the common-mode voltage of the hybrid rectifier zero;

[0058] The neutral point voltage balancing controller 23 is connected to the flying capacitor auxiliary switch tube bridge arm 12, and is used to control the state of each switch device of the flying capacitor auxiliary switch tube bridge arm 12 based on the current direction of the neutral point O and the capacitor C F voltage of the flying capacitor auxiliary switch tube bridge arm 12, so as to make the voltage of the capacitor C F always half of the output voltage of the direct current side, thereby controlling the neutral point voltage balancing of the hybrid rectifier.

[0059] As shown in Figure 1 and Figure 2As shown, the three phases (a, b, c) of the VIENNA rectifier 11 each consist of two diodes. Each phase has one diode in the upper bridge arm and one diode in the lower bridge arm, with the two diodes connected in the same direction. The two diodes in each phase are connected in series, with their ends serving as the positive and negative terminals of the DC output. The switching transistors of the upper bridge arm of each phase are connected together, forming the positive terminal of the DC output side of the VIENNA rectifier, and the switching transistors of the lower bridge arm of each phase are connected together, forming the negative terminal of the DC output side of the VIENNA rectifier. Further, the upper nodes of the a-phase, b-phase, and c-phase bridge arms of the VIENNA rectifier are called the P-terminal of the VIENNA rectifier; the lower nodes of the a-phase, b-phase, and c-phase bridge arms are called the N-terminal of the VIENNA rectifier. The middle nodes of the two diodes are independently connected as AC input interfaces, each connected to the AC power supply through an inductor L. The input nodes of each phase are independently connected, collectively forming the AC electrical interface O'. Each intermediate node is also connected to a set of switching devices, and the other sides of the three sets of switching devices are connected together as the neutral point O of the hybrid rectifier; wherein, each set of switching devices consists of two anti-tandem switching transistors, for example, a corresponds to a set of switching devices S. a Including two S-types connected in opposite directions a1 Switching transistor and S a2 Switching transistor.

[0060] like Figure 2 As shown, the flying capacitor-type auxiliary switching bridge arm 12 includes: four switching devices and a capacitor C. F Four switching devices are connected in series between the positive and negative terminals of the DC side. The direction from the P-terminal to the N-terminal of the VIENNA rectifier is denoted as VT1, VT2, VT3, and VT4, respectively. The upper node of switch VT1 is connected to the P-terminal of the VIENNA rectifier, and the lower node of switch VT4 is connected to the N-terminal of the VIENNA rectifier. The midpoint of switches VT2 and VT3 is connected to the neutral point O of the hybrid rectifier. The neutral point voltage of the hybrid rectifier is controlled through the flying capacitor auxiliary switch arm. The midpoint of VT1 and VT2 is connected to capacitor C. F The positive terminal of VT3 and the midpoint of VT4 are connected to capacitor C. F The negative terminal of the capacitor C is controlled by switching transistors VT1, VT2, VT3, and VT4. F The voltage is controlled, thereby controlling the voltage at the neutral point of the hybrid rectifier.

[0061] The frequencies of the four switching devices are the same as those of the switching devices in the VIENNA rectifier.

[0062] The VIENNA rectifier realizes zero common-mode voltage modulation, and first needs to ensure normal operation of the VIENNA rectifier, because the VIENNA rectifier needs to use double-loop control; the double-loop control includes: one voltage outer loop control based on a direct current side output voltage; and one current inner loop control based on an alternating current side input current.

[0063] A sampling trigger module of the voltage outer loop controller samples the direct current side output voltage and the alternating current side input current of the VIENNA rectifier, and after controller operation, obtains control signals corresponding to three-phase switching devices of the VIENNA rectifier, controls states of the three-phase switching devices of the VIENNA rectifier, so that the VIENNA rectifier outputs a target direct current voltage.

[0064] The zero common-mode voltage controller 22 is connected to three phases of the VIENNA rectifier, analyzes a working state of the VIENNA rectifier, and the output voltage of each phase of the VIENNA rectifier is determined by switching tubes thereof; taking the a phase as an example, when two switching tubes of the a phase are turned on, the alternating current output of the a phase is clamped to a midpoint of the flying capacitor auxiliary switching bridge arm, and the output voltage of the a phase is zero; by controlling states of the switching tubes of each phase, the three-phase output voltage of the VIENNA rectifier is: ±V / 2, 0, so that the common-mode voltage of the hybrid rectifier is zero. dc

[0065] The neutral point voltage balance controller 23 controls a voltage of the capacitor C F of the flying capacitor auxiliary switching bridge arm 12; when VT1 and VT3 are turned on, the charging voltage of the capacitor C F of the flying capacitor auxiliary switching bridge arm 12 rises, and when VT2 and VT4 are turned on, the discharging voltage of the capacitor C F of the flying capacitor auxiliary switching bridge arm 12 falls; the states of the switching devices of the flying capacitor auxiliary switching bridge arm 12 are controlled, so that the voltage of the capacitor C F is always half of the direct current side output voltage, thereby controlling the neutral point voltage balance of the hybrid rectifier.

[0066] Optionally, the hybrid rectifier further includes: a voltage stabilizing capacitor C;

[0067] The voltage stabilizing capacitor C is connected in parallel to the direct current side of the VIENNA rectifier, two ends of the voltage stabilizing capacitor C are connected to the P pole and the N pole respectively, and is used for voltage stabilization of the direct current side output.

[0068] Optionally, the switching device is a full-controlled switching device, and the diode is a non-controlled device, thereby saving cost.

[0069] ​Optionally, the controller controls the VIENNA rectifier and the flying capacitor auxiliary switching bridge arm completely decoupled. VIENNA rectifier and flying capacitor auxiliary switching bridge arm do not affect each other.

[0070] The technical scheme of the embodiment adds a flying capacitor type auxiliary switching tube bridge arm to the VIENNA rectifier to form a new hybrid rectifier. The voltage and current double-loop controller and the zero common-mode voltage controller control the switching devices of the VIENNA rectifier to output a target DC voltage of the VIENNA rectifier and make the common-mode voltage of the hybrid rectifier zero. The neutral point voltage balancing controller controls the voltage of the capacitor of the flying capacitor type auxiliary switching bridge arm to always be half of the output voltage of the DC side, thereby controlling the neutral point voltage balancing of the hybrid rectifier. The technical scheme solves the technical problems that the rectifier cannot simultaneously realize zero common-mode voltage and neutral point voltage balancing when working, resulting in low output power quality, system safety and system efficiency, realizes zero common-mode voltage of the rectifier and balancing of the neutral point voltage of the hybrid rectifier, improves the quality of the output waveform, and improves the safety and economy of the system.

[0071] Embodiment two

[0072] In a second aspect, the application further provides a control method of a hybrid rectifier, which is suitable for the hybrid rectifier of any one of the first aspect, and comprises the following steps:

[0073] S1, the voltage and current double-loop controller obtains the input three-phase alternating current of the hybrid rectifier and the DC voltage of the output side, and obtains the given value of the three-phase modulation wave voltage after processing by the voltage outer loop controller and the current inner loop controller

[0074] S2, the zero common-mode voltage controller receives the given value of the three-phase modulation wave voltage output by the voltage and current double-loop controller Based on space vector modulation or carrier phase-shifted modulation, the PWM signal is obtained by operation V b * , V c * The switching devices of the VIENNA rectifier are controlled to make the common-mode voltage of the hybrid rectifier zero.

[0075] S3. The neutral point voltage balance controller controls the state of the switching devices of the flying capacitor type auxiliary switch bridge arm according to the PWM signal, controls the driving PWM signals of the first and third switching devices to be consistent, controls the driving PWM signals of the second and fourth switching devices to be consistent, and the duty cycle of each is 50%, so that the voltage of the capacitor of the flying capacitor type auxiliary switch bridge arm is half of the DC side output voltage, and the neutral point voltage of the hybrid rectifier is balanced.

[0076] The controller is designed based on the common-mode voltage and neutral point voltage of the hybrid rectifier. It controls the switching of each switching device on the three-phase bridge arm and the flying capacitor auxiliary switching bridge arm of the VIENNA rectifier to achieve zero common-mode voltage of the hybrid rectifier, while simultaneously ensuring that the neutral point voltage of the three-phase bridge arm structure of the hybrid rectifier is half of the DC output voltage. This control method achieves the goal of stabilizing the neutral point potential of the bridge arm of the novel hybrid rectifier, realizing zero common-mode voltage of the hybrid rectifier, and improving the safety and economy of the system.

[0077] Optionally, step S1 specifically includes:

[0078] The sampling trigger module of the voltage outer loop PI controller samples the DC output voltage of the VIENNA rectifier to obtain the voltage setpoint u. * ;

[0079] The voltage outer loop PI controller will set the voltage setpoint u * The voltage difference signal Δu is obtained by subtracting the actual voltage value u from the sampled voltage value. The voltage difference signal Δu is then processed by the inner current loop PI controller to obtain the d-axis current setpoint.

[0080] The sampling trigger module of the inner current loop PI controller samples the three-phase current input to the AC side of the VIENNA rectifier to obtain the three-phase current i. a i b i c The actual current values ​​i along the d-axis and q-axis are obtained through coordinate transformation. d i q ;

[0081] The inner loop PI controller sets the d-axis current value. Actual current value i along the d-axis d The difference is used to obtain the d-axis current difference signal Δi. d The q-axis current setpoint 0 and the actual q-axis current value i are compared. q The difference is used to obtain the q-axis current difference signal Δi. q ;

[0082] The current difference signal Δi between the d-axis and q-axisd and Δi q After passing through the PI controller, the input is sent to the decoupling module; simultaneously, the sampling trigger module of the voltage outer loop controller samples the AC-side grid voltage input to obtain e. a e b e c After coordinate transformation, the grid voltage e on the d-axis and q-axis is obtained. d and e q The input is sent to the decoupling module;

[0083] The decoupling module obtains the d-axis and q-axis setpoints of the modulated wave voltage by decoupling the d-axis and q-axis currents. and The modulated wave voltage is given values ​​on the d-axis and q-axis. and The given value of the three-phase modulated wave voltage obtained after coordinate transformation

[0084] like Figure 3 As shown, specifically, the sampling trigger module (not shown) of the voltage outer loop controller samples the DC-side output voltage of the VIENNA rectifier and sets the DC-side voltage setpoint u. * The voltage difference signal Δu is obtained by subtracting the actual DC-side voltage value u from the sampled value. This voltage difference signal is then passed through the outer-loop PI controller to obtain the d-axis current command signal.

[0085] Furthermore, the inner current PI controller includes a d-axis inner current PI controller 32 and a q-axis inner current PI controller 33; the outer voltage PI controller 31 receives the d-axis current command signal. The current is sent to the d-axis inner loop PI controller 32. The sampling trigger module of the current inner loop controller samples the AC side input current of the VIENNA rectifier and sends the sampled three-phase current i to the d-axis inner loop PI controller 32. a i b i c The actual value of the dq-axis current, i, is obtained after coordinate transformation. d i q Set the d-axis current value The actual d-axis current value i obtained after coordinate transformation d The difference is used to obtain the d-axis current difference signal Δi. d The difference signal of the d-axis is input to the decoupling module after passing through the d-axis current inner loop PI controller 32.

[0086] At the same time, the given q-axis current value 0 and the actual q-axis current value i obtained after coordinate transformation are compared. q The difference is used to obtain the q-axis current difference signal Δi.q The difference signal of the q-axis is input to the decoupling module after being input to the q-axis current inner loop PI controller 33.

[0087] Further, at the same time, the sampling trigger module of the voltage outer loop controller samples the grid voltage input on the alternating current side, and obtains the dq-axis grid voltage e d , e q , after coordinate transformation, and then inputs the same to the decoupling module. and The decoupling module obtains the given values of the d-axis and q-axis of the modulation wave voltage through decoupling control of the d-axis and q-axis currents and , and the given values of the three-phase modulation wave voltage obtained after coordinate transformation are used for modulation to realize voltage and current double-loop control, and the proportional coefficient and integral coefficient of each PI controller are adjusted to realize fast following.

[0088] Specifically, the principle of the decoupling module is as follows:

[0089]

[0090] Optionally, the given value of the three-phase modulation wave voltage of the VIENNA rectifier satisfies

[0091] Optionally, step S2 specifically comprises:

[0092] receiving the given value of the three-phase modulation wave voltage output by the voltage and current double-loop controller performing calculation to obtain virtual voltages V x1 , V x2 , V x3 ;

[0093] comparing the virtual voltages with triangular carriers respectively to generate PWM signals v x1 , v x2 , v x3 ;

[0094] performing calculation on the PWM signals v x1 , v x2 , v x3 to obtain a PWM signal V b * , V c * ;

[0095] According to the PWM signal V b* 、V c * The switching signal driving the VIENNA rectifier is generated to control the state of the switching device of the VIENNA rectifier, so that the common-mode voltage of the hybrid rectifier is zero; when the PWM signal V b * 、V c * is 0, the switching device of the VIENNA rectifier is turned on, and the VIENNA rectifier outputs zero voltage; when the PWM signal V b * 、V c * is ±1, the switching device of the VIENNA rectifier is turned off.

[0096] In order to realize zero common-mode voltage modulation, the working state of the VIENNA rectifier is analyzed, and the output voltage of each phase of the VIENNA rectifier is determined by the switching tube. Taking the a phase as an example, when the two switching tubes of the a phase are turned on, the AC output of the a phase is clamped to the midpoint of the flying capacitor type auxiliary switching bridge arm, and the output voltage of the a phase is zero, which is defined as O. When the two switching tubes of the a phase of the VIENNA rectifier are turned off, when the current flows from the AC side, the output voltage of the a phase is V dc / 2, which is defined as P; when the current flows from the AC side, the output voltage of the a phase is-V dc / 2, which is defined as N; zero common-mode vector, by controlling each power switching tube of the VIENNA rectifier, the three-phase output voltage is: ±V dc / 2, 0, so that the common-mode voltage is zero.

[0097] There are two methods for realizing zero common-mode voltage modulation of the technical scheme of the application, the first method is based on carrier comparison modulation, and the other method is based on space vector modulation.

[0098] (1) The method for realizing zero common-mode voltage modulation based on carrier comparison is as follows:

[0099] The three-phase voltage command output by the voltage-current double-loop controller is calculated to obtain a virtual voltage V x1 , V x2 , V x3 , the virtual voltage calculation formula is as follows, then the virtual voltage is compared with the triangular carrier respectively, and the PWM signal V x1 , V x2 , V x3 is generated, then the PWM signal V x1 , Vx2 , V x3 Operation to obtain PWM signal V b * , V c * ; wherein, three-phase voltage instruction is the unit value, the amplitude of the triangular carrier is 1, and the frequency is the switching frequency. Because Therefore, the zero common-mode voltage modulation can realize the common-mode voltage of the VIENNA rectifier to be zero;

[0100]

[0101] According to the characteristics of the VIENNA rectifier, the PWM signal V b * , V c * is used to generate a switching signal for driving the VIENNA rectifier; when the PWM signal V b * , V c * is 0, the corresponding phase of the VIENNA rectifier outputs zero voltage, that is, the switch tube is turned on; when the PWM signal V b * , V c * is ±1, the corresponding phase of the VIENNA rectifier outputs ±V dc / 2, that is, the switch tube is turned off.

[0102] Optionally, step S3 specifically comprises:

[0103] receiving a given value of the three-phase modulation wave voltage output by the voltage and current double-loop controller According to the formula , the rotating vector V r * is obtained by synthesis; the rotating vector V r * In each sector, only the middle vector and the zero vector with zero common-mode voltage are used for synthesis;

[0104] According to the principle of vector decomposition, the vector action time is calculated to generate a PWM signal to control the switching device of the VIENNA rectifier, so that the common-mode voltage of the hybrid rectifier is zero.

[0105] (2) The specific implementation method of the space vector modulation is:

[0106] The three-phase modulation wave obtained through the coordinate transformation The synthesis is performed to obtain a rotating vector In each sector, only the middle vector and the zero vector with a common-mode voltage of zero are used for synthesis.

[0107] The a-phase voltage of the three-phase stationary coordinate system is taken as a phase reference point, when the angle θ of the rotating vector is in [-30°, 30°], the rotating vector is in the first sector; when the angle θ of the rotating vector is in [30°, 90°], the rotating vector is in the second sector; when the angle θ of the rotating vector is in [90°, 150°], the rotating vector is in the third sector; when the angle θ of the rotating vector is in [150°, 210°], the rotating vector is in the fourth sector; when the angle θ of the rotating vector is in [210°, 270°], the rotating vector is in the fifth sector; and when the angle θ of the rotating vector is in [270°, 330°], the rotating vector is in the sixth sector.

[0108] The zero common-mode voltage vectors, the zero common-mode voltage vectors V1 and V2 in the first sector are [PON] and [PNO] respectively; the zero common-mode voltage vectors V1 and V2 in the second sector are [OPN] and [PON] respectively; the zero common-mode voltage vectors V1 and V2 in the third sector are [NPO] and [OPN] respectively; the zero common-mode voltage vectors V1 and V2 in the fourth sector are [NOP] and [NPO] respectively; the zero common-mode voltage vectors V1 and V2 in the fifth sector are [ONP] and [NOP] respectively; and the zero common-mode voltage vectors V1 and V2 in the sixth sector are [PNO] and [ONP] respectively. The zero vector V0 is always [OOO].

[0109] The sector judgment and the angle calculation are completed by a vector calculation module, and the sector judgment formula and the sector angle formula are respectively:

[0110]

[0111]

[0112] The calculation formula of the action time t1 of the zero common-mode voltage vector V1 is:

[0113] t1 = m sin (θ') T s

[0114] The calculation formula of the action time t2 of the zero common-mode voltage vector V2 is:

[0115]

[0116] The calculation formula of the action time t0 of the zero vector V0 is:

[0117] t0 = T s-t1-t2

[0118] When the vector acts, when the phase is O, it is equivalent to the phase output of the VIENNA rectifier zero voltage, that is, the switch tube is turned on; when the phase is P or N, it is equivalent to the phase output of the VIENNA rectifier ±V dc / 2, that is, the switch tube is turned off.

[0119] In this embodiment, only zero common-mode voltage vectors are used for modulation, so that the common-mode voltage of the VIENNA rectifier is zero. Since the calculation amount of the space vector modulation is large, in actual work, the carrier modulation is used preferentially for simplicity.

[0120] The zero common-mode voltage modulation of the hybrid rectifier provided by the application is compared with the simulation experiment of the ordinary VIENNA rectifier. The working condition of the simulation experiment is that the effective value of the AC side power grid voltage is 220V, the given voltage of the DC side load is 800V, the fundamental frequency is 50Hz, the carrier frequency is 20kHz, the input filter inductance is 3mH, the DC side steady voltage capacitor is 0.44mF, and the DC side load is 100Ω.

[0121] The common-mode voltage of the ordinary VIENNA rectifier is as shown in Figure 4 , and there is a low-frequency component with an amplitude of 2V dc / 3; the common-mode voltage of the zero common-mode voltage modulation system of the hybrid rectifier provided by the application is as shown in Figure 5 , and the common-mode voltage is almost zero, which is fully suppressed, and the common-mode voltage is reduced by about 98.5%. Figure 4 Figure 6 is a neutral point voltage schematic diagram of the VIENNA rectifier zero common-mode voltage modulation system without flying auxiliary switch tube bridge arm provided by the application, Figure 7 The neutral point voltage schematic diagram of the hybrid rectifier zero common-mode modulation system provided by the application is provided, and it can be found by comparison that the amplitude of the midpoint voltage fluctuation of the hybrid rectifier is reduced by about 98.1%. The common-mode voltage of the hybrid rectifier provided by the application is almost zero, the harm of the leakage current is reduced, the neutral point voltage fluctuation is small, and the stability and economy of the system are improved.

[0122] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the application and is not used to limit the application, and any modification, equivalent replacement and improvement made within the spirit and principle of the application shall be included in the protection scope of the application.​

Claims

1. A hybrid rectifier characterized by, include: The main circuit and controller; the main circuit includes: a VIENNA rectifier and a flying capacitor-type auxiliary switching bridge arm; The VIENNA rectifier includes three phases and three sets of switching devices; each phase consists of two diodes, and the middle node of the two diodes is independently connected as an interface for AC side input. Each phase is connected to an AC power supply as an input for AC side connection; each middle node is also connected to a set of switching devices consisting of two reverse series connections. The other sides of the three sets of switching devices are connected together, and the output terminals of the three sets of switching devices serve as the neutral point of the hybrid rectifier. The flying capacitor type auxiliary switching bridge arm includes: four switching devices and one capacitor. The four switching devices are connected in series between the positive and negative terminals of the DC side. The two ends of the capacitor are respectively connected to the intermediate node between the first and second switching devices and the intermediate node between the third and fourth switching devices. The intermediate node between the second and third switching devices serves as the output node and is connected to the neutral point. The controller includes: a voltage and current dual-loop controller, a zero common-mode voltage controller, and a neutral point voltage balance controller; The voltage and current dual-loop controller is connected to both ends of the VIENNA rectifier and is used to control the state of each switching device of the three phases of the VIENNA rectifier according to the three-phase AC power input and the DC voltage output of the VIENNA rectifier, so as to output the target DC voltage. The zero common-mode voltage controller is connected to the three phases of the VIENNA rectifier and is used to control the state of each switching device of the three phases of the VIENNA rectifier based on the three-phase modulation wave of the VIENNA rectifier, so as to make the common-mode voltage of the hybrid rectifier zero. The neutral point voltage balance controller is connected to the flying capacitor type auxiliary switch bridge arm and is used to control the state of each switching device of the flying capacitor type auxiliary switch bridge arm based on the current direction of the neutral point and the capacitor voltage of the flying capacitor type auxiliary switch bridge arm, so that the voltage of the capacitor is always half of the DC side output voltage, thereby controlling the neutral point voltage balance of the hybrid rectifier.

2. The hybrid rectifier of claim 1, wherein, The upper node of the flying capacitor type auxiliary switch bridge arm is connected to the upper node of the three phases of the VIENNA rectifier as the positive terminal of the DC output, and the lower node is connected to the lower node of the three phases of the VIENNA rectifier as the negative terminal of the DC output. The frequencies of the four switching devices in the flying capacitor auxiliary switching bridge arm are the same as the frequencies of the switching devices in the VIENNA rectifier.

3. The hybrid rectifier of claim 2, wherein, The hybrid rectifier also includes: a voltage stabilizing capacitor; The voltage-regulating capacitor is connected in parallel to the DC side of the VIENNA rectifier for voltage regulation of the DC output.

4. The hybrid rectifier of claim 2, wherein, The switching device is a fully controlled switching device, while the diode is an uncontrolled device.

5. The hybrid rectifier of claim 1, wherein, The controller is completely decoupled from the control of the VIENNA rectifier and the flying capacitor auxiliary switch arm.

6. A control method of a hybrid rectifier, applicable to a hybrid rectifier as claimed in any one of claims 1-5, characterized in that, include: The voltage and current double-loop controller acquires the three-phase alternating current of the input of the hybrid rectifier and the direct current voltage of the output side, and after processing by a voltage outer loop controller and a current inner loop controller, obtains the given value of the three-phase modulation wave voltage The zero common-mode voltage controller receives a given value of a three-phase modulation wave voltage output by the voltage-current dual-loop controller Based on space vector modulation or based on carrier phase-shifted modulation, operation is performed to obtain PWM signals Switching devices of the VIENNA rectifier are controlled to make the common-mode voltage of the hybrid rectifier zero. The neutral point voltage balance controller controls the state of the switching devices of the flying capacitor auxiliary switch bridge arm according to the PWM signal, controls the driving PWM signals of the first and third switching devices to be consistent, and controls the driving PWM signals of the second and fourth switching devices to be consistent, with a duty cycle of 50% for each device, so that the voltage of the capacitor of the flying capacitor auxiliary switch bridge arm is half of the DC side output voltage, and the neutral point voltage of the hybrid rectifier is balanced.

7. The control method according to claim 6, characterized by, The voltage current double loop controller acquires the three-phase alternating current of the input of the VIENNA rectifier and the direct current voltage of the output side, and after processing by a voltage outer loop controller and a current inner loop controller, obtains the given value of the three-phase modulation wave voltage comprises: The sampling trigger module of the voltage outer loop PI controller samples the DC output side voltage of the VIENNA rectifier to obtain a voltage given value u * ; The voltage outer loop PI controller obtains a voltage given value u * The voltage difference value signal Δu is obtained by subtracting the sampled voltage actual value u from the voltage given value u, and the voltage difference value signal Δu is input into the current inner loop PI controller to obtain a d-axis current given value id* The sampling trigger module of the current inner loop PI controller samples three-phase current inputted to the AC side of the VIENNA rectifier to obtain three-phase current i a 、 b 、 c , and actual values of d-axis and q-axis currents i d 、 q are obtained through coordinate transformation. The inner loop PI controller gives a d-axis current given value The d-axis current actual value i d The difference gives a d-axis current difference signal Δi d The q-axis current actual value i q The difference gives a q-axis current difference signal Δi q ; The current difference signal Δi of the d-axis and the q-axis d and Δi q is input to the decoupling module after passing through a PI controller; meanwhile, the sampling trigger module of the voltage outer loop controller samples the grid voltage input on the alternating current side to obtain e a , e b , e c After coordinate transformation, the d-axis and the q-axis grid voltages e d and e q are input to the decoupling module; The decoupling module obtains given values of d-axis and q-axis of the modulation wave voltage by decoupling control of d-axis and q-axis currents and The given values of d-axis and q-axis of the modulation wave voltage are obtained by coordinate transformation and The given values of three-phase modulation wave voltage are obtained by coordinate transformation 8. The control method as described in claim 7, characterized in that, The three-phase modulation wave voltage given value of the VIENNA rectifier satisfies 9. The control method as described in claim 6, characterized in that, The zero common-mode voltage controller receives a given value of a three-phase modulation wave voltage output by the voltage-current dual-loop controller Based on the carrier phase shift modulation, operation is carried out to obtain a PWM signal The switch device of the VIENNA rectifier is controlled to make the common-mode voltage of the hybrid rectifier zero, comprising: receiving a given value of a three-phase modulated wave voltage output from the voltage current dual loop controller carrying out an operation to obtain a virtual voltage V x1 , V x2 , V x3 ; The virtual voltage is compared with a triangular carrier, respectively, to generate PWM signals v x1 、 x2 、 x3 ; The PWM signal v x1 is obtained by performing operation on the voltage signal v x2 , the current signal i x3 and the voltage signal v According to the PWM signal v , a switching signal for driving the VIENNA rectifier is generated, so as to control the state of the switching device of the VIENNA rectifier, so that the common-mode voltage of the hybrid rectifier is zero; when the PWM signal v is 0, the switching device of the VIENNA rectifier is turned on, and the VIENNA rectifier outputs zero voltage; when the PWM signal v is ±1, the switching device of the VIENNA rectifier is turned off.

10. The control method as described in claim 6, characterized in that, The zero common-mode voltage controller receives a given value of a three-phase modulation wave voltage output by the voltage-current dual-loop controller Based on space vector modulation, operation is performed to obtain PWM signals using only zero common-mode voltage vectors The switch devices of the VIENNA rectifier are controlled to make the common-mode voltage of the hybrid rectifier zero, comprising: receiving a given value of a three-phase modulated wave voltage output from the voltage current dual loop controller according to the formula synthesizing to obtain a rotation vector the rotation vector In each sector, only the middle vector and zero vector with zero common-mode voltage are used for synthesis. Based on the principle of vector decomposition, the vector action time is calculated, and a PWM signal is generated to control the switching devices of the VIENNA rectifier so that the common-mode voltage of the hybrid rectifier is zero.

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