High-power charging device topological structure based on three-level rectifier
阅读说明：本技术 一种基于三电平整流器的大功率充电装置拓扑结构 (High-power charging device topological structure based on three-level rectifier ) 是由 杜玖玉 刘郑心 陈天锦 边慧萍 于 2020-12-24 设计创作，主要内容包括：一种基于三电平整流器的大功率充电装置拓扑结构,属于大功率充电技术领域。解决了现有电动汽车大功率充电装置可靠性低、响应速度慢、功率等级低的问题。本发明包括前级三电平整流器和后级DC-DC变换器；前级AC-DC部分采用带中线的三电平整流结构,其三相独立的可以实现自动解耦,具有功率密度高、器件电压应力低便于实际应用中器件选型、高功率因数、控制方式简单等优点。后级的DC-DC部分采用了二次升压和改进型电压倍增单元,具有输入电流纹波低、器件电压应力低、高电压增益、宽范围运行等优点。本发明适用于大功率充电技术领域。(A high-power charging device topological structure based on a three-level rectifier belongs to the technical field of high-power charging. The problems of low reliability, low response speed and low power level of the conventional high-power charging device for the electric automobile are solved. The invention comprises a front-stage three-level rectifier and a rear-stage DC-DC converter; the front-stage AC-DC part adopts a three-level rectification structure with a neutral line, three phases of the front-stage AC-DC part are independent, automatic decoupling can be realized, and the front-stage AC-DC part has the advantages of high power density, low device voltage stress, convenience in device model selection in practical application, high power factor, simple control mode and the like. The DC-DC part of the later stage adopts a secondary boosting and improved voltage multiplication unit, and has the advantages of low input current ripple, low device voltage stress, high voltage gain, wide-range operation and the like. The invention is suitable for the technical field of high-power charging.)
1. A high-power charging device topological structure based on a three-level rectifier is characterized by comprising a front-stage three-level rectifier and a rear-stage DC-DC converter;
the front-stage three-level rectifier comprises an inductor La, an inductor Lb, an inductor Lc, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a diode D7, a diode D8, a diode D9, a diode D10, a diode D11, a diode D12, a switching tube S1, a switching tube S2, a switching tube S3, a switching tube S4, a switching tube S5, a switching tube S6, a capacitor C1 and a capacitor C2;
the post-stage DC-DC converter comprises an inductor L1, an inductor L2, an inductor L3, a switch tube S7, a diode D13, a diode D14, a diode D15, a diode D16, a diode D17, a diode D18, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8 and a switch tube S7;
one end of the inductor La is connected with a phase-a network side power supply, the other end is connected with the anode of the diode D1,
the cathode of the diode D1 is connected with the drain of the switch tube S1, the source of the switch tube S1 is connected with the drain of the switch tube S2, the source of the switch tube S2 is connected with the anode of the diode D6, and the cathode of the diode D6 is connected with the anode of the diode D1;
the cathode of the diode D1 is also connected with the anode of the diode D9, the cathode of the diode D9 is connected with the cathode of the diode D8, and the anode of the diode D8 is connected with the cathode of the diode D2;
one end of the inductor Lb is connected with a b-phase network side power supply, the other end of the inductor Lb is connected with the anode of a diode D2, the cathode of a diode D2 is connected with the drain of a switch tube S3, the source of a switch tube S3 is connected with the drain of a switch tube S4, the source of a switch tube S4 is connected with the anode of a diode D5, and the cathode of a diode D5 is connected with the anode of a diode D2;
one end of the inductor Lc is connected with the c-phase grid side power supply, the other end of the inductor Lc is connected with the anode of the diode D3, the cathode of the diode D3 is connected with the drain of the switch tube S5, the source of the switch tube S5 is connected with the drain of the switch tube S6, the source of the switch tube S6 is connected with the anode of the diode D4, and the cathode of the diode D4 is connected with the anode of the diode D3;
the cathode of the diode D3 is further connected to the anode of the diode D7, the cathode of the diode D7 is simultaneously connected to the cathode of the diode D8 and one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the anode of the diode D12, and the cathode of the diode D12 is connected to the source of the switching tube S6 and the anode of the diode D4;
the other end of the capacitor C2 is connected with the anode of the diode D11, and the cathode of the diode D11 is simultaneously connected with the source of the switch tube S4 and the anode of the diode D5;
the other end of the capacitor C2 is also connected with the anode of the diode D10, and the cathode of the diode D10 is simultaneously connected with the source of the switch tube S2 and the anode of the diode D6;
the other end of the capacitor C1 is sequentially connected with the source electrode of the switch tube S1, the source electrode of the switch tube S3, the source electrode of the switch tube S5 and a neutral point of a three-phase power supply;
one end of the inductor L1 is connected with the cathode of the diode D7, the other end of the inductor L1 is connected with the anode of the diode D13, the cathode of the diode D13 is connected with one end of the capacitor C3, and the other end of the capacitor C3 is connected with the other end of the capacitor C2;
the cathode of the diode D13 is connected with one end of the inductor L2, the other end of the inductor L2 is connected with the drain of the switch tube S7, and the source of the switch tube S7 is connected with the other end of the capacitor C3;
the drain of the switch tube S7 is connected with the cathode of the diode D14, and the anode of the diode D14 is connected with the anode of the diode D13;
the drain of the switching tube S7 is further connected to the anode of the diode D15, the cathode of the diode D15 is connected to the anode of the diode D16, the cathode of the diode D16 is connected to one end of the capacitor C4, and the other end of the capacitor C4 is connected to the anode of the diode D15;
the cathode of the diode D16 is connected with the anode of the diode D17, the cathode of the diode D17 is connected with one end of an inductor L3, the other end of the inductor L3 is connected with one end of a capacitor C5, and the other end of the capacitor C5 is connected with the anode of the diode D17;
the other end of the inductor L3 is further connected with the anode of the diode D18, the cathode of the diode D18 is connected with one end of the capacitor C8, the other end of the capacitor C8 is connected with one end of the capacitor C7, the other end of the capacitor C7 is connected with one end of the capacitor C6 and the other end of the capacitor C2, and the other end of the capacitor C6 is connected with the cathode of the diode D17;
the anode of the diode D16 is also connected to the other terminal of the capacitor C8.
2. The high-power charging device topology structure based on the three-level rectifier according to claim 1, further comprising a control circuit, wherein the control circuit comprises a switching tube driving circuit, a DSP control system, a voltage sensor and a current sensor;
the voltage sensor is used for collecting three-phase input voltage of a front-stage AC-DC structure, voltage of a capacitor C1 on an output side, voltage of a capacitor C1 and output voltage of a rear-stage DC/DC converter structure, and sending collected voltage signals to the DSP system;
the current sensor is used for collecting three-phase input current of a front-stage AC-DC structure and current of an inductor L1; sending the collected current signal to a DSP system;
the DSP control system obtains a control signal of a switching tube in the front-stage three-level rectifier and a control signal of a switching tube in the rear-stage DC-DC converter by adopting a PI algorithm according to the received voltage signal and current signal, and sends the control signal of the switching tube in the front-stage three-level rectifier and the control signal of the switching tube in the rear-stage DC-DC converter to a switching tube driving circuit, and the switching tube driving circuit respectively drives the switching tube S1, the switching tube S2, the switching tube S3, the switching tube S4, the switching tube S5, the switching tube S6 and the switching tube S7 to be switched on or switched off according to the received control signals.
3. The topological structure of the high-power charging device based on the three-level rectifier according to claim 2, wherein the specific method for obtaining the control signal of the switching tube in the preceding-stage three-level rectifier comprises the following steps:
step A1, comparing the voltage of a capacitor C1 and the voltage of a capacitor C2 at the output side of the front-stage AC-DC structure with a reference voltage; acquiring an error voltage signal of a capacitor C1 and an error voltage signal of a capacitor C2;
step A2, judging the positive and negative of the three-phase input voltage, if the input voltage is positive, executing step A3, if the input voltage is negative, executing step A4,
step A3, calculating an error voltage signal of a capacitor C1 by using a voltage ring and a PI control algorithm to obtain an input value of an inner ring of a current ring, and executing the step A5;
a4, performing PI control on the error voltage signal of the capacitor C2 by adopting a voltage loop to obtain an input value of an inner loop of a current loop; step a5 is executed;
a5, multiplying the input value of the current loop inner ring with the phase of the three-phase input voltage to obtain a current reference value;
step A6, comparing the input current with a current reference value to obtain a current error signal;
and A7, performing PI control on the current error signal by adopting a current loop to obtain a control signal of a switching tube in a preceding-stage AC-DC structure.
4. The topological structure of the high-power charging device based on the three-level rectifier according to claim 2, wherein the specific method for obtaining the control signal of the switching tube in the post-stage DC-DC converter comprises the following steps:
step B1, comparing the output voltage of the rear-stage DC-DC converter with a target reference voltage to obtain an error signal;
b2, performing voltage loop control on the error signal by adopting a PI controller to obtain an expected inductive current;
step B3, obtaining the expected inductive current and the inductive current IL1Comparing the currents to obtain a current error signal;
step B4, inputting the error current signal into a current loop PI controller to obtain the duty ratio of each switching tube;
b5, adjusting the on-off time of the switching tubes in one period of the PWM wave according to the duty ratio value of each switching tube; and obtaining a control signal for the rear-stage DC-DC converter.
Technical Field
The invention belongs to the technical field of high-power charging.
Background
With the development of electric vehicles becoming more and more rapid, the development of related supporting infrastructure of electric vehicles is also accelerating. The most important infrastructure of the electric automobile is a high-power charging device, and the performance of the charging device plays an important role in the popularization of the electric automobile. As the charging mode of the electric vehicle is developed to be high-power and rapid, a direct current charging device with a high voltage class is required to rapidly charge the battery of the electric vehicle. Therefore, the high-power charging device with high reliability, high compatibility, high response speed and high DC output voltage level is of great significance to the re-development of the whole automobile industry.
The existing high-power charging device structure generally adopts a traditional rectification mode or is additionally provided with a direct current converter which is connected with a front-stage rectification structure to jointly convert electric energy on a network side and output direct current to charge an electric automobile. The charging mode has a simple structure, but cannot meet the requirements of higher and higher voltage levels and power levels of the direct-current output end, and has the problems of low reliability and low response speed.
Disclosure of Invention
The invention aims to solve the problems of low reliability, low response speed and low power grade of the conventional high-power charging device of an electric automobile, and provides a high-power charging device topological structure based on a three-level rectifier.
The invention relates to a high-power charging device topological structure based on a three-level rectifier, which comprises a front-stage three-level rectifier and a rear-stage DC-DC converter;
the front-stage three-level rectifier comprises an inductor La, an inductor Lb, an inductor Lc, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a diode D7, a diode D8, a diode D9, a diode D10, a diode D11, a diode D12, a switching tube S1, a switching tube S2, a switching tube S3, a switching tube S4, a switching tube S5, a switching tube S6, a capacitor C1 and a capacitor C2;
the post-stage DC-DC converter comprises an inductor L1, an inductor L2, an inductor L3, a switch tube S7, a diode D13, a diode D14, a diode D15, a diode D16, a diode D17, a diode D18, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8 and a switch tube S7;
one end of the inductor La is connected with a phase-a network side power supply, the other end is connected with the anode of the diode D1,
the cathode of the diode D1 is connected with the drain of the switch tube S1, the source of the switch tube S1 is connected with the drain of the switch tube S2, the source of the switch tube S2 is connected with the anode of the diode D6, and the cathode of the diode D6 is connected with the anode of the diode D1;
the cathode of the diode D1 is also connected with the anode of the diode D9, the cathode of the diode D9 is connected with the cathode of the diode D8, and the anode of the diode D8 is connected with the cathode of the diode D2;
one end of the inductor Lb is connected with a b-phase network side power supply, the other end of the inductor Lb is connected with the anode of a diode D2, the cathode of a diode D2 is connected with the drain of a switch tube S3, the source of a switch tube S3 is connected with the drain of a switch tube S4, the source of a switch tube S4 is connected with the anode of a diode D5, and the cathode of a diode D5 is connected with the anode of a diode D2;
one end of the inductor Lc is connected with the c-phase grid side power supply, the other end of the inductor Lc is connected with the anode of the diode D3, the cathode of the diode D3 is connected with the drain of the switch tube S5, the source of the switch tube S5 is connected with the drain of the switch tube S6, the source of the switch tube S6 is connected with the anode of the diode D4, and the cathode of the diode D4 is connected with the anode of the diode D3;
the cathode of the diode D3 is further connected to the anode of the diode D7, the cathode of the diode D7 is simultaneously connected to the cathode of the diode D8 and one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the anode of the diode D12, and the cathode of the diode D12 is connected to the source of the switching tube S6 and the anode of the diode D4;
the other end of the capacitor C2 is connected with the anode of the diode D11, and the cathode of the diode D11 is simultaneously connected with the source of the switch tube S4 and the anode of the diode D5;
the other end of the capacitor C2 is also connected with the anode of the diode D10, and the cathode of the diode D10 is simultaneously connected with the source of the switch tube S2 and the anode of the diode D6;
the other end of the capacitor C1 is sequentially connected with the source electrode of the switch tube S1, the source electrode of the switch tube S3, the source electrode of the switch tube S5 and a neutral point of a three-phase power supply;
one end of the inductor L1 is connected with the cathode of the diode D7, the other end of the inductor L1 is connected with the anode of the diode D13, the cathode of the diode D13 is connected with one end of the capacitor C3, and the other end of the capacitor C3 is connected with the other end of the capacitor C2;
the cathode of the diode D13 is connected with one end of the inductor L2, the other end of the inductor L2 is connected with the drain of the switch tube S7, and the source of the switch tube S7 is connected with the other end of the capacitor C3;
the drain of the switch tube S7 is connected with the cathode of the diode D14, and the anode of the diode D14 is connected with the anode of the diode D13;
the drain of the switching tube S7 is further connected to the anode of the diode D15, the cathode of the diode D15 is connected to the anode of the diode D16, the cathode of the diode D16 is connected to one end of the capacitor C4, and the other end of the capacitor C4 is connected to the anode of the diode D15;
the cathode of the diode D16 is connected with the anode of the diode D17, the cathode of the diode D17 is connected with one end of an inductor L3, the other end of the inductor L3 is connected with one end of a capacitor C5, and the other end of the capacitor C5 is connected with the anode of the diode D17;
the other end of the inductor L3 is further connected with the anode of the diode D18, the cathode of the diode D18 is connected with one end of the capacitor C8, the other end of the capacitor C8 is connected with one end of the capacitor C7, the other end of the capacitor C7 is connected with one end of the capacitor C6 and the other end of the capacitor C2, and the other end of the capacitor C6 is connected with the cathode of the diode D17;
the anode of the diode D16 is also connected to the other terminal of the capacitor C8.
The control circuit comprises a switching tube driving circuit, a DSP control system, a voltage sensor and a current sensor;
the voltage sensor is used for collecting three-phase input voltage of a front-stage AC-DC structure, voltage of a capacitor C1 on an output side, voltage of a capacitor C1 and output voltage of a rear-stage DC/DC converter structure, and sending collected voltage signals to the DSP system;
the current sensor is used for collecting three-phase input current of a front-stage AC-DC structure and current of an inductor L1; sending the collected current signal to a DSP system;
the DSP control system obtains a control signal of a switching tube in the front-stage three-level rectifier and a control signal of a switching tube in the rear-stage DC-DC converter by adopting a PI algorithm according to the received voltage signal and current signal, and sends the control signal of the switching tube in the front-stage three-level rectifier and the control signal of the switching tube in the rear-stage DC-DC converter to a switching tube driving circuit, and the switching tube driving circuit respectively drives the switching tube S1, the switching tube S2, the switching tube S3, the switching tube S4, the switching tube S5, the switching tube S6 and the switching tube S7 to be switched on or switched off according to the received control signals.
Further, a specific method for acquiring a control signal of a switching tube in a preceding stage three-level rectifier includes:
step A1, comparing the voltage of a capacitor C1 and the voltage of a capacitor C2 at the output side of the front-stage AC-DC structure with a reference voltage; acquiring an error voltage signal of a capacitor C1 and an error voltage signal of a capacitor C2;
step A2, judging the positive and negative of the three-phase input voltage, if the input voltage is positive, executing step A3, if the input voltage is negative, executing step A4,
step A3, calculating an error voltage signal of a capacitor C1 by using a voltage ring and a PI control algorithm to obtain an input value of an inner ring of a current ring, and executing the step A5;
a4, performing PI control on the error voltage signal of the capacitor C2 by adopting a voltage loop to obtain an input value of an inner loop of a current loop; step a5 is executed;
a5, multiplying the input value of the current loop inner ring with the phase of the three-phase input voltage to obtain a current reference value;
step A6, comparing the input current with a current reference value to obtain a current error signal;
and A7, performing PI control on the current error signal by adopting a current loop to obtain a control signal of a switching tube in a preceding-stage AC-DC structure.
Further, a specific method for acquiring a control signal of a switching tube in the post-stage DC-DC converter includes:
step B1, comparing the output voltage of the rear-stage DC-DC converter with a target reference voltage to obtain an error signal;
b2, performing voltage loop control on the error signal by adopting a PI controller to obtain an expected inductive current;
step B3, obtaining the expected inductive current and the inductive current IL1Comparing the currents to obtain a current error signal;
step B4, inputting the error current signal into a current loop PI controller to obtain the duty ratio of each switching tube;
b5, adjusting the on-off time of the switching tubes in one period of the PWM wave according to the duty ratio value of each switching tube; and obtaining a control signal for the rear-stage DC-DC converter.
The front-stage AC-DC part of the structure adopts a three-level rectification structure with a neutral line, three phases of the structure are independent, automatic decoupling can be realized, and the structure has the advantages of high power density, low device voltage stress, convenience in device model selection in practical application, high power factor, simple control mode and the like. The DC-DC part of the later stage adopts a secondary boosting and improved voltage multiplication unit, and has the advantages of low input current ripple, low device voltage stress, high voltage gain, wide-range operation and the like. Therefore, the invention is suitable for the technical field of high-power charging.
Drawings
FIG. 1 is a circuit diagram of a three-level rectifier based high power charging device topology according to the present invention;
FIG. 2 is a schematic block diagram of a three-level rectifier based high power charging device topology in connection with a control circuit;
FIG. 3 is a block diagram of the control principle of the preceding stage AC-DC control circuit;
FIG. 4-a is a single phase equivalent circuit diagram of a pre-stage AC-DC rectifier;
fig. 4-b is an effective circuit diagram of the preceding stage AC-DC rectifier when the phase voltage is switched on by the positive switching tube S1;
fig. 4-c is an effective circuit diagram of the preceding stage AC-DC rectifier when the phase voltage is the positive switching tube S1 off;
fig. 4-d is an effective circuit diagram of the preceding stage AC-DC rectifier when the phase voltage is turned on by the negative switching tube S2;
4-e are effective circuit diagrams of the preceding AC-DC rectifier when the phase voltage is turned off by the negative switching tube S2;
FIG. 5 is an equivalent circuit diagram of the post-stage DC-DC circuit operating during the inductor charging period;
FIG. 6 is an equivalent circuit diagram of the post-stage DC-DC circuit operating during the inductor discharge period;
fig. 7 is a control block diagram of the post-stage DC-DC circuit.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The first embodiment is as follows: the following describes the present embodiment with reference to fig. 1, and the topology of the high-power charging device based on the three-level rectifier in the present embodiment includes a front-stage three-level rectifier and a rear-stage DC-DC converter;
the front-stage three-level rectifier comprises an inductor La, an inductor Lb, an inductor Lc, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, a diode D6, a diode D7, a diode D8, a diode D9, a diode D10, a diode D11, a diode D12, a switching tube S1, a switching tube S2, a switching tube S3, a switching tube S4, a switching tube S5, a switching tube S6, a capacitor C1 and a capacitor C2;
the post-stage DC-DC converter comprises an inductor L1, an inductor L2, an inductor L3, a switch tube S7, a diode D13, a diode D14, a diode D15, a diode D16, a diode D17, a diode D18, a capacitor C3, a capacitor C4, a capacitor C5, a capacitor C6, a capacitor C7, a capacitor C8 and a switch tube S7;
one end of the inductor La is connected with a phase-a network side power supply, the other end is connected with the anode of the diode D1,
the cathode of the diode D1 is connected with the drain of the switch tube S1, the source of the switch tube S1 is connected with the drain of the switch tube S2, the source of the switch tube S2 is connected with the anode of the diode D6, and the cathode of the diode D6 is connected with the anode of the diode D1;
the cathode of the diode D1 is also connected with the anode of the diode D9, the cathode of the diode D9 is connected with the cathode of the diode D8, and the anode of the diode D8 is connected with the cathode of the diode D2;
one end of the inductor Lb is connected with a b-phase network side power supply, the other end of the inductor Lb is connected with the anode of a diode D2, the cathode of a diode D2 is connected with the drain of a switch tube S3, the source of a switch tube S3 is connected with the drain of a switch tube S4, the source of a switch tube S4 is connected with the anode of a diode D5, and the cathode of a diode D5 is connected with the anode of a diode D2;
one end of the inductor Lc is connected with the c-phase grid side power supply, the other end of the inductor Lc is connected with the anode of the diode D3, the cathode of the diode D3 is connected with the drain of the switch tube S5, the source of the switch tube S5 is connected with the drain of the switch tube S6, the source of the switch tube S6 is connected with the anode of the diode D4, and the cathode of the diode D4 is connected with the anode of the diode D3;
the cathode of the diode D3 is further connected to the anode of the diode D7, the cathode of the diode D7 is simultaneously connected to the cathode of the diode D8 and one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the anode of the diode D12, and the cathode of the diode D12 is connected to the source of the switching tube S6 and the anode of the diode D4;
the other end of the capacitor C2 is connected with the anode of the diode D11, and the cathode of the diode D11 is simultaneously connected with the source of the switch tube S4 and the anode of the diode D5;
the other end of the capacitor C2 is also connected with the anode of the diode D10, and the cathode of the diode D10 is simultaneously connected with the source of the switch tube S2 and the anode of the diode D6;
the other end of the capacitor C1 is sequentially connected with the source electrode of the switch tube S1, the source electrode of the switch tube S3, the source electrode of the switch tube S5 and a neutral point of a three-phase power supply;
one end of the inductor L1 is connected with the cathode of the diode D7, the other end of the inductor L1 is connected with the anode of the diode D13, the cathode of the diode D13 is connected with one end of the capacitor C3, and the other end of the capacitor C3 is connected with the other end of the capacitor C2;
the cathode of the diode D13 is connected with one end of the inductor L2, the other end of the inductor L2 is connected with the drain of the switch tube S7, and the source of the switch tube S7 is connected with the other end of the capacitor C3;
the drain of the switch tube S7 is connected with the cathode of the diode D14, and the anode of the diode D14 is connected with the anode of the diode D13;
the drain of the switching tube S7 is further connected to the anode of the diode D15, the cathode of the diode D15 is connected to the anode of the diode D16, the cathode of the diode D16 is connected to one end of the capacitor C4, and the other end of the capacitor C4 is connected to the anode of the diode D15;
the cathode of the diode D16 is connected with the anode of the diode D17, the cathode of the diode D17 is connected with one end of an inductor L3, the other end of the inductor L3 is connected with one end of a capacitor C5, and the other end of the capacitor C5 is connected with the anode of the diode D17;
the other end of the inductor L3 is further connected with the anode of the diode D18, the cathode of the diode D18 is connected with one end of the capacitor C8, the other end of the capacitor C8 is connected with one end of the capacitor C7, the other end of the capacitor C7 is connected with one end of the capacitor C6 and the other end of the capacitor C2, and the other end of the capacitor C6 is connected with the cathode of the diode D17;
the anode of the diode D16 is also connected to the other terminal of the capacitor C8.
In the embodiment, the front-stage AC-DC rectification part adopts a voltage-current double closed-loop control method, and the positive voltage loop and the negative voltage loop are independently controlled. In a switching period, a required voltage error signal is selected according to the positive and negative of a three-phase input voltage, when the input voltage is positive, the voltage error signal of a capacitor C1 is selected as a control signal of a voltage ring, when the input voltage is negative, the error signal of a capacitor C2 is selected as a control signal of the voltage ring, output signals of the voltage ring under the two conditions are input signals of a current inner ring, a feed-forward voltage-current double closed-loop control system is adopted in a rear-stage DC-DC part, the influence of input voltage fluctuation on an inductive current can be counteracted after feed-forward control is added, and the robustness of the whole system can be enhanced.
The front-stage three-level AC-DC rectification part outputs a stable DC bus voltage, the rear-stage DC-DC part requires to perform boost conversion on the DC output by the rectification part according to the power requirement of an output load, and the DC output by the rectification part is quickly responded by taking the power of the output side of the load as a target, so that the level of the DC output by the rectification side is improved.
The topological structure of the invention has the advantages of high reliability and no current backflow by adopting an AC-DC structure at the front stage, adopting a three-level boost rectifying circuit and utilizing a method of independent control of a positive voltage ring and a negative voltage ring. The DC-DC converter at the later stage has higher voltage gain, lower voltage stress and quick response speed, and can track the power by controlling a switching tube of the DC-DC converter part according to the power requirement of a load so as to meet the requirement of high-power charging level of the electric automobile. Meanwhile, the advantages of small current harmonic wave, high terminal output voltage level and the like exist. The front stage of the invention adopts a three-phase three-level boost rectification structure, and the rear-end direct-current converter adopts a direct-current converter with high voltage gain, so that the output voltage grade of the system is further improved, and the power tracking is carried out on the load by adjusting the duty ratio. In addition, the voltage stress of the device in the direct current converter is low, and the device model selection in practical application is facilitated. The invention is suitable for the high-power charging device of the electric automobile.
The control circuit comprises a switching tube driving circuit, a DSP control system, a voltage sensor and a current sensor;
the voltage sensor is used for collecting three-phase input voltage of a front-stage AC-DC structure, voltage of a capacitor C1 on an output side, voltage of a capacitor C2 and output voltage of a rear-stage DC/DC converter structure, and sending collected voltage signals to the DSP system;
the current sensor is used for collecting three-phase input current of a front-stage AC-DC structure and current of an inductor L1; sending the collected current signal to a DSP system;
the DSP control system obtains a control signal of a switching tube in the front-stage three-level rectifier and a control signal of a switching tube in the rear-stage DC-DC converter by adopting a PI algorithm according to the received voltage signal and current signal, and sends the control signal of the switching tube in the front-stage three-level rectifier and the control signal of the switching tube in the rear-stage DC-DC converter to a switching tube driving circuit, and the switching tube driving circuit respectively drives the switching tube S1, the switching tube S2, the switching tube S3, the switching tube S4, the switching tube S5, the switching tube S6 and the switching tube S7 to be switched on or switched off according to the received control signals.
Further, in this embodiment, a specific method for obtaining a control signal of a switching tube in a preceding stage three-level rectifier includes:
step A1, comparing the voltage of a capacitor C1 and the voltage of a capacitor C2 at the output side of the front-stage AC-DC structure with a reference voltage; acquiring an error voltage signal of a capacitor C1 and an error voltage signal of a capacitor C2;
step A2, judging the positive and negative of the three-phase input voltage, if the input voltage is positive, executing step A3, if the input voltage is negative, executing step A4,
step A3, calculating an error voltage signal of a capacitor C1 by using a voltage ring and a PI control algorithm to obtain an input value of an inner ring of a current ring, and executing the step A5;
a4, performing PI control on the error voltage signal of the capacitor C2 by adopting a voltage loop to obtain an input value of an inner loop of a current loop; step a5 is executed;
a5, multiplying the input value of the current loop inner ring with the phase of the three-phase input voltage to obtain a current reference value;
step A6, comparing the input current with a current reference value to obtain a current error signal;
and A7, performing PI control on the current error signal by adopting a current loop to obtain a control signal of a switching tube in a preceding-stage AC-DC structure.
In this embodiment, the front-stage three-level rectifier is a three-phase boost three-level rectifier, and the center point of the dc-side capacitor is connected to the input voltage center line N, so that each phase can be equivalent to a single-phase three-level circuit. Because of the three-phase symmetry of the preceding-phase AC-DC structure, when the input voltage of one phase is positive, the duty ratio of the upper switching tube of the same bridge arm is controlled to control the input current, and further the voltage of the capacitor on the upper side of the direct current output side is controlled, and the working mode at the moment is irrelevant to the voltage of the capacitor on the lower side. Therefore, the voltage of the upper capacitor is selected as the voltage loop reference signal to obtain the reference signal of the current loop. Similarly, when the input voltage of one phase is negative, the duty ratio of the lower switching tube of the same bridge arm is controlled to control the input current, and further the voltage of the lower side capacitor of the direct current output side is controlled, and the working mode at the moment is irrelevant to the voltage of the upper capacitor. Therefore, the voltage of the lower capacitor is selected as the voltage loop reference signal to obtain the reference signal of the current loop. The control strategy realizes independent control of the voltage of the upper capacitor and the lower capacitor on the output side, does not need voltage decoupling, greatly simplifies the complexity of a control loop, can realize voltage balance without designing a voltage balance control method for the upper capacitor and the lower capacitor on the output side, and ensures the reliability and the simplicity.
Further, in this embodiment, a specific method for acquiring a control signal of a switching tube in a post-stage DC-DC converter includes:
step B1, comparing the output voltage of the rear-stage DC-DC converter with a target reference voltage to obtain an error signal;
b2, performing voltage loop control on the error signal by adopting a PI controller to obtain an expected inductive current;
step B3, obtaining the expected inductive current and the inductive current IL1Comparing the currents to obtain a current error signal;
step B4, inputting the error current signal into a current loop PI controller to obtain the duty ratio of each switching tube;
b5, adjusting the on-off time of the switching tubes in one period of the PWM wave according to the duty ratio value of each switching tube; and obtaining a control signal for the rear-stage DC-DC converter.
The specific embodiment is as follows:
the control block diagram of the front-stage AC-DC part is shown in FIG. 3, and the specific control process is described below with reference to FIG. 3:
a, collecting voltages of capacitors C1 and C2 on a rectification output side, and three-phase voltages and currents on an input side;
b, comparing the two sampled capacitor voltages with a given reference voltage to respectively obtain two voltage error signals of a capacitor C1 and a capacitor C2;
c, judging whether the input voltage is positive or negative;
d, if the input voltage is positive, selecting a voltage error signal of the capacitor C1 as a control signal of the voltage ring, controlling the voltage ring through the voltage ring PI, and outputting the voltage error signal as an input value of an inner ring of the current ring;
e, if the input voltage is negative, selecting a voltage error signal of the capacitor C2 as a control signal of the voltage ring, controlling the voltage ring through the voltage ring PI, and outputting the voltage error signal as an input value of an inner ring of the current ring;
f, multiplying the input value of the current inner loop by the phase of the input voltage to obtain a reference value of the current;
g, comparing the sampled network side current with a reference value of the current to obtain an error signal of the current;
and H, the current error signal passes through the current PI controller and then outputs a control signal to control the switch tube.
The pre-stage AC-DC structure adopted in this embodiment includes a neutral point between two capacitors C1 and C2 and a neutral point neutral line N sequentially connecting a neutral point between a switching tube S1 and a switching tube S2, a neutral point between a switching tube S3 and a switching tube S4, a neutral point between a switching tube S5 and a switching tube S6, and a three-phase power supply, where the three phases are completely independent (switching tube S1 and a switching tube S2 are one phase, switching tube S3 and a switching tube S4 are one phase, and switching tube S5 and a switching tube S6 are one phase), so that automatic decoupling can be achieved, and each phase can be controlled independently, and the working principle of the pre-stage AC-DC rectifying part is explained below with one phase as an example in conjunction with fig. 4;
when the input voltage of the phase is positive, if the upper switch tube S1 is turned on, the input voltage is all applied to the inductor, and this operation mode is executed no matter whether the lower tube S2 is turned on or not, the input voltage of the phase all drops on the inductor, the inductor current increases linearly, the output side capacitor C1C2 supplies power to the load terminal, and the equivalent circuit is as shown in fig. 4-b.
When the input voltage of the phase is positive, if the upper switching tube S1 is turned off, the inductor releases energy through the diode D9, the input side and the inductor supply power to the output end and the capacitor C1 together, the inductor current linearly decreases, and the capacitor C2 continues to supply power to the load end; as shown in fig. 4-c.
When the input voltage of the phase is negative, no matter whether the upper switch tube S1 is conducted or not, the input voltage is totally reversely applied to the inductor, and the current of the inductor reversely rises; the output side capacitors C1, C2 supply power to the load side, and the equivalent circuit is shown in fig. 4-d.
When the input voltage of the phase is negative, if the lower switching tube S2 is turned off, the inductor reversely releases energy, the energy is supplied to the output end and the capacitor C2 together with the input through the diode D10, and the capacitor C1 continues to supply power to the load end; as shown in fig. 4-e.
According to the working principle analysis, the existence of the diode can ensure that the current can only flow from the input to the output, and the backflow phenomenon can not occur. Because of the existence of the neutral line, two tubes of the same bridge arm can not be directly connected, the reliability of the circuit is greatly improved, and simultaneously, because each diode is only conducted under a specific working mode, the reverse recovery problem does not exist. In addition, because the three phases are symmetrical, as long as the control signal of one phase is correct, the normal work of the system can be ensured by adopting the same control signal for other two phases, and the reliability of the system is further improved.
The specific control process is introduced according to the control block diagram of the DC-DC part shown in fig. 7:
a. setting a reference voltage;
b. the voltage sensor acquires input voltage of a rear-stage DC-DC converter, namely output voltage of a rectifier and output voltage UO of a DC/DC converter circuit, and the current sensor acquires inductive current of a conversion unit and performs digital-to-analog conversion;
c. the voltage value UO is compared with a reference voltage UrefComparing, and sending the obtained error signal e1 to a voltage loop PI controller for processing to obtain expected inductive current;
d. comparing the expected inductive current obtained in the step c with the fed-back inductive current to obtain an error signal e2, sending the error signal e2 into a current loop PI controller to obtain a duty ratio d, and adjusting the on-off time of the switching tube in one period of the PWM wave according to different duty ratios;
e. the duty ratio d output by the current loop PI controller and the signal output by the feedforward controller are summed and then sent to a transfer function from the duty ratio d to the inductive current to obtain the adjusted IL1；
f. Subjecting the I obtained in step e toL1The adjusted output voltage UO is obtained as an input quantity of a transfer function of the inductor current to the output.
The operation of the DC-DC part is explained according to fig. 5 and 6:
when the switch tube is turned on, the inductor L1 and the inductors L2 and L3 are respectively charged, the inductor current rises linearly, and at the moment, 6 loops exist in the circuit. From the volt-second equilibrium principle, the following equation can be derived:
when the switch tube S7 is turned off, the inductor L1 and the inductors L2 and L3 discharge, and the inductor current decreases linearly. From the volt-second equilibrium principle, the following equation can be derived:
wherein, UL1onIs the current of the inductor L1 when the switch tube S7 is conducted, d is the duty ratio of the driving signal of the switch tube S7, T is a PWM period, U isL1offIs the current, U, of the inductor L1 when the switch tube S7 is turned offL2onThe inductor L2 is connected with the switch tube S7Current on, UL2offIs the current, U, of the inductor L2 when the switch tube S7 is turned offL3onIs the current, U, of the inductor L3 when the switch tube S7 is onL3offIs the current of the inductor L2 when the switch tube S7 is turned off.
The following equation can be obtained from the volt-second equilibrium principle:
wherein, UinIs the input voltage (rectified output voltage) of the back-end DC-DC section, UC1Is the voltage, U, of the capacitor C1 of the back-end DC-DC sectionC2Is the voltage of the capacitor C2 of the back-end DC-DC section, UC4Is the voltage of the capacitor C4 of the back-end DC-DC section, UC3Is the voltage of the capacitor C3 of the back-end DC-DC section, UC6Is the voltage of the capacitor C6 of the back-end DC-DC section, UoIs the output voltage of the back-end DC-DC section, UC5Is the voltage of the capacitor C5 of the back end DC-DC section.
The voltage stress of the device in the later stage DC-DC converter can be obtained according to equations 2 and 3, and the results are as follows:
the voltage gain M of the post-stage DC-DC converter and the voltage U of the rectified output end can be obtainedinWith the voltage U at the DC outputoThe relationship is as follows:
it can be seen from the above equations (5) - (9) that the voltage stress on all devices does not exceed half of the output voltage, the voltage gain can easily reach more than 15 without using the limit duty cycle, and the requirement of high voltage level can be completely met.
The following equation can be obtained for the subsequent DC-DC converter using ampere-second balance principle:
IC1oncurrent stress, I, of the capacitor C1 of the back-end DC-DC section when the switching tube is conductingC2onCurrent stress, I, of the capacitor C2 of the back-end DC-DC section when the switching tube is conductingC3onCurrent stress, I, of the capacitor C3 of the back-end DC-DC section when the switching tube is conductingC4onCurrent stress, I, of the capacitor C4 of the back-end DC-DC section when the switching tube is conductingC5onCurrent stress, I, of the capacitor C5 of the back-end DC-DC section when the switching tube is conductingC6onCurrent stress, I, of the capacitor C6 of the back-end DC-DC section when the switching tube is conductingC4offCurrent stress, I, of the capacitor C4 of the back-end DC-DC section at switching-off of the switching tubeC5offCurrent stress, I, of the capacitor C5 of the back-end DC-DC section at switching-off of the switching tubeC3offCurrent stress, I, of the capacitor C3 of the back-end DC-DC section at switching-off of the switching tubeC2offCurrent stress, I, of the capacitor C2 of the back-end DC-DC section at switching-off of the switching tubeC1offIs the current stress of the capacitor C1 of the back end DC-DC section when the switching tube is off.
Further, the following equation can be obtained:
the current stress of all devices in the later-stage DC-DC part can be obtained according to the formula
Ic3on＝Io
Ic4on＝-Io
Ic5on＝-dIo (14)
Wherein, ID1Is the current, I, of diode D1D2Is the current, I, of diode D2D3Is the current, I, of diode D3D4Is the current, I, of diode D4D5Is the current, I, of diode D5D6Is the current, I, of diode D6D7Is the current of diode D7.
By combining the above analysis, the topology of the high-power charging device based on the three-level rectifier and the high-voltage gain dc converter has lower device stress and high voltage gain. Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.
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