CN110920422B - High-power electric vehicle charging device based on current source and control method - Google Patents

Abstract

The invention discloses a high-power electric vehicle charging device and control method based on a current source. Topological structure, the pre-stage CSR adopts the specific harmonic elimination (SHE) modulation method with variable modulation ratio, and directly controls the output DC voltage of the post-stage (ISOP-DAB); the post-stage ISOP-DAB adopts the control method of carrier phase shift to reduce output voltage ripple. The topology and control of the new electric vehicle charging device are very simple, and compared with other existing electric vehicle charging devices, a large amount of electrolytic capacitors are saved, and the volume, weight and cost are greatly reduced.

Description

A high-power electric vehicle charging device and control method based on a current source

technical field

The invention relates to the field of high-power AC/DC conversion, in particular to a high-power electric vehicle charging device and a control method based on a current source converter.

Background technique

With the increasingly prominent problems of energy and environment and the improper development of technology, electric vehicles with the advantages of high efficiency, energy saving and environmental protection have attracted widespread attention. As the most important supporting facilities for electric vehicles, electric vehicle charging device has become a research hotspot at home and abroad.

At present, the widely used high-power electric vehicle charging device usually adopts a two-stage structure. The front stage is a three-phase diode uncontrolled rectifier circuit, and the rear stage is an isolated DC/DC conversion circuit with input series and output parallel. The structure and control of the above charging device are simple, but the power factor is uncontrollable, and a large number of harmonics are generated, which affects the safe and stable operation of the power grid. For this reason, most of the current research schemes use voltage source PWM rectifier circuits, such as cascaded H-bridges, MMCs, etc., as the pre-stage of electric vehicle charging devices. The high-power electric vehicle charging device with voltage source rectifier as the front stage has reliable structure and control, flexible operation mode, and related research and application have been relatively mature. However, this charging device also has many shortcomings. The structure of the front and rear stages requires a large number of electrolytic capacitors, which is large in size, heavy in weight, and high in cost; the cascaded H-bridge and MMC have complex structures, and the voltage and current protection is very cumbersome and requires The pressure equalization control reduces the reliability of the device to a certain extent.

On the other hand, current source converters are widely used in medium-voltage and high-power applications due to their advantages of simple control, natural short-circuit resistance, and four-quadrant operation. In order to reduce switching losses and ensure system efficiency, the switching frequency of high-power current source converters is generally set at several hundred Hz. is widely used. However, the traditional SHE modulation method has a fixed switching angle and less freedom for control, which restricts the further application of current source converters in high-power applications.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies in the prior art, and to provide a novel high-power electric vehicle charging device and control method based on a current source. The topology of the parallel resonant dual active bridge; the front stage directly controls the output DC voltage of the rear stage by using the specific harmonic elimination modulation method of the variable modulation ratio of the current source rectifier, and the rear stage shifts the carrier of the resonant dual active bridge. Phase control. Compared with the existing electric vehicle charging device, the topology and control are greatly simplified, the volume, weight and cost are greatly reduced, and the system reliability is further enhanced.

The purpose of this invention is to realize through the following technical solutions:

A high-power electric vehicle charging device based on a current source, its topology is divided into two stages, the front stage is a current source rectifier (CSR), and the rear stage is a resonant dual active bridge (ISOP) with an input in series and an output in parallel. -DAB), the CSR consists of six gate commutated thyristors to form a three-phase full bridge, the AC side of the three-phase full bridge is connected to the common connection point PCC through the CL filter and exchanges power with the three-phase power grid, and the DC side is connected in series with DC After smoothing the inductor, it is connected to the high-voltage side of ISOP-DAB; the ISOP-DAB consists of three resonant double active bridges connected in series at one end as the high-voltage input side of the post-stage, and the other end in parallel as the low-voltage output side of the post-stage. The input side is connected to the DC side of the front-stage CSR, and the low-voltage output side of the latter stage is connected in parallel with the load through a DC filter capacitor; the resonant dual active bridge is composed of two H-bridges and a high-frequency isolation transformer. The H-bridge is composed of A single-phase full-bridge structure composed of four insulated gate bipolar transistors (IGBTs), in which the H-bridge on the high-voltage input side of the rear stage is connected with a DC filter capacitor on the DC side, and the AC side passes through the first resonant capacitor and the high-frequency isolation transformer. The primary side of the high-frequency isolation transformer is connected to the leakage inductance of the high-frequency isolation transformer to form a resonance circuit; the secondary side of the high-frequency isolation transformer is connected to the AC side of the H-bridge at the output side of the low-voltage output side of the latter stage through the second resonance capacitor, which also forms a resonance circuit; The DC side of the H-bridge at the output side is directly connected in parallel with the DC side of the H-bridge at the low-voltage output side of other resonant dual active bridges.

A control method for a high-power electric vehicle charging device, the CSR directly controls the DC voltage of the output side of the low-voltage side of the rear-stage ISOP-DAB, and the ISOP-DAB uses a square wave control based on carrier phase shift to reduce the ripple of the output voltage. The specific steps are as follows:

(1) At the beginning of each sampling period, use the sampling circuit to collect the three-phase voltage V _PCC of the power grid and the low-voltage side output DC voltage V _dc of ISOP-DAB; the three-phase power grid voltage V _PCC generates the real-time phase of the power grid voltage through the phase-locked loop PLL θ _g ;

(2) After subtracting the adopted DC voltage V _dc and the DC voltage reference V _{dc_ref} as a feedback amount, obtain the modulation ratio ma required by the CSR through _a proportional integral (PI) controller;

(3) using the obtained modulation ratio ma to obtain the switching angles θ ₁ to θ ₁₀ required for the modulation ratio variable specific harmonic cancellation modulation _;

(4) Input the obtained grid voltage real-time phase θ _g and switching angles θ ₁ to θ ₁₀ into the PWM modulation of the CSR to generate corresponding gate control signals G ₁ to G ₆ , which are used to control the gate commutated thyristor of the previous stage CSR. turn on and off;

(5) The post-stage ISOP-DAB adopts square wave voltage control based on carrier phase shift.

Further, the generation of the modulation ratio variable specific harmonic cancellation modulation switching angle in step (3) includes the following steps:

(301) Adopting 9-pulse modulation ratio variable specific harmonic elimination modulation, θ ₁ to θ ₄ are free angles, θ ₆ to θ ₁₀ from θ ₁ to θ ₄ and bypass pulse width θ ₀ can pass through the free angle θ ₁ ~θ ₄ is obtained by:

(302) Substitute the modulation ratio ma obtained in step (2 ₎ and equation (1-1) into the following equation, and use iterative solution to obtain the switching angles θ ₁ to θ ₁₀ :

Wherein, θ _k represents the k-th switching angle in θ ₁ to θ ₁₀ , and k=1 to 10.

Further, the square wave voltage control based on carrier phase shifting in step (5) includes the following steps:

(501) Determine the frequency _fsw of the square wave control signal according to the used first resonant capacitor and the leakage inductance of the high-frequency isolation transformer:

The capacitance value of the first resonant capacitor is C _r1 , and the leakage inductance of the high-frequency isolation transformer is L _r1 ;

(502) The H-bridge at the input end and output end of each resonant dual active bridge of ISOP-DAB uses exactly the same square wave control signal with a duty cycle of 0.5;

(503) The square wave control signals of the two IGBTs in the upper arm of each H bridge are the same, and the square wave control signals of the two IGBTs in the lower arm are the same, but the square wave control signals of the upper arm and the lower arm are different in phase 180°, and there is a dead zone;

(504) The square wave control signals between the three resonant dual active bridges are 120° out of phase in phase.

Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are:

1. The front stage of the electric vehicle charging device in the present invention adopts a high-power current source type rectifier. Compared with the currently widely used cascaded H-bridge or MMC rectifier, a large amount of large-capacity electrolytic capacitors are saved, which means that the volume and weight of the device are and greatly reduced costs.

2. The control of the electric vehicle charging device proposed by the present invention is very simple, and the rear stage adopts a resonant dual active bridge with input in series and output in parallel, which can automatically equalize voltage without control. Therefore, the entire electric vehicle charging device only uses a DC The voltage control is sufficient, which greatly simplifies the control structure and is beneficial to improving the reliability of the device.

3. The pre-stage of the electric vehicle charging device proposed in the present invention adopts a high-power current source type converter, which has natural anti-short-circuit ability, which greatly enhances the anti-fault ability of the system. In addition, the front stage adopts a high-power current source rectifier, which also avoids the complex startup problem of cascaded H-bridges or MMCs. The entire system does not need startup control and can be started directly.

4. The front-stage high-power current source converter adopts a specific harmonic elimination modulation method with adjustable modulation ratio, which greatly reduces the switching frequency, reduces the switching loss of the switching device, and greatly improves the efficiency of the system.

5. The resonant dual active bridge with input in series and output in parallel at the rear stage works in the state of zero-current switching, and the switching loss is greatly reduced, which greatly improves the system efficiency.

6. The rear-stage input series output parallel resonant dual active bridge adopts carrier phase shifting, which greatly reduces the ripple of the output DC voltage of the electric vehicle charging device, that is, the capacitance value of the DC filter electrolytic capacitor can be reduced, thereby further reducing The size and cost of the device.

Description of drawings

FIG. 1 is a schematic diagram of a topology structure and control of an electric vehicle charging device according to the present invention.

FIG. 2 is a comparison diagram of experimental waveforms before and after the ISOP-DAB carrier phase shift of the rear stage of the electric vehicle charging device of the present invention.

FIG. 3 is an experimental waveform diagram of the electric vehicle charging device of the present invention when the load changes abruptly.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The topology of the new electric vehicle charging device proposed by the present invention is shown in the upper part of Figure 1, and its structure is as follows: the charging device is divided into two stages: the front stage is a current source rectifier (CSR), and the rear stage is input in series and output in parallel. The resonant dual active bridge (ISOP-DAB), the CSR consists of six gate commutated thyristors to form a three-phase full bridge, the AC side of the three-phase full bridge is connected to the common connection point PCC through a CL filter, and then communicates with the three-phase full bridge. The phase grid exchanges power, and the DC side is connected to the high-voltage side of the ISOP-DAB after being connected in series with a DC smoothing inductor; the ISOP-DAB consists of three resonant double active bridges connected in series at one end as the high-voltage input side of the rear stage, and the other end in parallel as the high-voltage input side of the rear stage. The post-stage low-voltage output side, the post-stage high-voltage input side is connected to the DC side of the pre-stage CSR, and the post-stage low-voltage output side is connected in parallel with the load through a DC filter capacitor; the resonant dual active bridge consists of two H bridges and high It is composed of a frequency isolation transformer, and the H bridge is a single-phase full bridge structure composed of four insulated gate bipolar transistors (IGBTs). The first resonant capacitor is connected to the primary side of the high-frequency isolation transformer, and forms a resonant circuit with the leakage inductance of the high-frequency isolation transformer; the secondary side of the high-frequency isolation transformer is connected to the AC side of the H-bridge on the low-voltage output side of the latter stage through the second resonant capacitor. , also form a resonant circuit; the DC side of the H-bridge on the low-voltage output side is directly connected in parallel with the DC side of the H-bridge on the low-voltage output side of other resonant dual active bridges.

The control method of the novel electric vehicle charging device proposed by the present invention is shown in the lower half of Figure 1, and the specific method is as follows:

(1) At the beginning of each sampling period, use the sampling circuit to collect the three-phase voltage V _PCC of the power grid and the low-voltage side output DC voltage V _dc of ISOP-DAB; the three-phase power grid voltage V _PCC generates the real-time phase of the power grid voltage through the phase-locked loop PLL θ _g ;

(2) After subtracting the adopted DC voltage V _dc and the DC voltage reference V _{dc_ref} as a feedback amount, obtain the modulation ratio ma required by the CSR through _a proportional integral (PI) controller;

(3) using the obtained modulation ratio ma to obtain the switching angles θ ₁ to θ ₂₀ required for the modulation ratio variable specific harmonic elimination modulation _;

(4) Input the obtained grid voltage real-time phase θ _g and switching angles θ ₁ to θ ₂₀ into the PWM modulation of the CSR to generate corresponding gate control signals G ₁ to G ₆ , which are used to control the gate commutated thyristor of the previous stage CSR. turn on and off;

(5) The post-stage ISOP-DAB adopts square wave voltage control based on carrier phase shift.

specific:

The generation of the modulation ratio variable specific harmonic cancellation modulation switching angle described in step (3) includes the following steps:

(301 ₎ Substitute the obtained ma into the following formula to obtain the switching angles θ ₁ to θ ₄ and the bypass pulse width:

(302 ₎ Substitute the obtained ma into the following formula to obtain the switching angles θ ₁ to θ ₄ and the bypass pulse width:

Wherein, θ _k represents the kth switching angle in θ ₁ to θ ₁₀ .

(303) Substitute ma obtained in step (2 ₎ and formula (1-1) into the following formula, and use iterative solution to obtain the switching angles θ ₁ to θ ₁₀ :

The square wave voltage control based on carrier phase shifting described in step (5) includes the following steps:

(501) Determine the frequency _fsw of the square wave control signal according to the used resonant capacitor C _r1 and the leakage inductance L _r1 of the high-frequency isolation transformer:

(502) The H-bridge at the input end and output end of each resonant dual active bridge of ISOP-DAB uses exactly the same square wave control signal with a duty cycle of 0.5;

(503) The square wave control signals of the two IGBTs in the upper arm of each H bridge are the same, and the square wave control signals of the two IGBTs in the lower arm are the same, but the square wave control signals of the upper arm and the lower arm are different in phase 180°, and there is a dead zone;

(504) The square wave control signals between the three resonant dual active bridges are 120° out of phase in phase.

Figure 2 is a comparison diagram of the experimental waveforms of the rear-stage ISOP-DAB carrier phase-shift of the novel electric vehicle charging device proposed by the present invention. In the zero-current switching mode, the line current waveform THD is within 3%, and the grid-side waveform quality is high; after the carrier phase shift, the amplitude of the DC voltage ripple is greatly reduced, from 12.5V to 2.5V.

Fig. 3 is the experimental waveform diagram of the new electric vehicle charging device proposed by the present invention when the load changes abruptly. It can be seen from the figure that when the system experiences a sudden load change, the response speed of the system is very fast, and the adjustment can be completed with only one cycle. And the ripple amplitude of the output DC voltage is only 5V.

To sum up: the new electric vehicle charging device based on the current source proposed by the present invention has the functions of electrical isolation and output voltage control, and the topology and control are very simple, and the reliability is good. The weight and cost are greatly reduced, and it is an electric vehicle charging device worthy of promotion.

The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above-mentioned specific embodiments are only illustrative and not restrictive. Without departing from the spirit of the present invention and the protection scope of the claims, those of ordinary skill in the art can also make many specific transformations under the inspiration of the present invention, which all fall within the protection scope of the present invention.

Claims (2)

1. A control method of a high-power electric vehicle charging device is based on the high-power electric vehicle charging device, the topological structure of the high-power electric vehicle charging device is divided into a front stage and a rear stage, the front stage is a current source type rectifier (CSR), the rear stage is a resonant double-active bridge (ISOP-DAB) with input, series and output connected in parallel, the CSR consists of six gate pole converter thyristors to form a three-phase full bridge, the alternating current side of the three-phase full bridge is connected to a common connection point PCC through a CL filter and then exchanges power with a three-phase power grid, and the direct current side is connected with a direct current smoothing inductor in series and then is connected with the high voltage side of the ISOP-DAB; the ISOP-DAB is characterized in that three resonant double-active bridges are connected in series at one end to serve as a rear-stage high-voltage input side, the other end of each resonant double-active bridge is connected in parallel to serve as a rear-stage low-voltage output side, the rear-stage high-voltage input side is connected with a direct-current side of a front-stage CSR, and the rear-stage low-voltage output sides are connected in parallel and then connected with a load through a direct-current filter capacitor; the resonant double-active bridge is composed of two H-bridges and a high-frequency isolation transformer, wherein the H-bridge is a single-phase full-bridge structure composed of four Insulated Gate Bipolar Transistors (IGBT), a direct-current filter capacitor is connected to the H-bridge at the rear high-voltage input side at the direct-current side, and the alternating-current side is connected with the primary side of the high-frequency isolation transformer through a first resonant capacitor and forms a resonant loop with the leakage inductance of the high-frequency isolation transformer; the secondary side of the high-frequency isolation transformer is connected with the alternating current side of the H bridge at the rear-stage low-voltage output side through a second resonant capacitor, and a resonant circuit is formed in the same way; the direct current side of the H bridge at the rear-stage low-voltage output side is directly connected in parallel with the direct current sides of the H bridges at the low-voltage output sides of other resonant dual-active bridges, and the method is characterized in that the CSR directly controls the direct current voltage at the rear-stage ISOP-DAB low-voltage side, the ISOP-DAB reduces the ripple waves of the output voltage by using carrier phase shift-based square wave control, and the method specifically comprises the following steps:

(1) At the beginning of each sampling period, the three-phase voltage V of the power grid is acquired by using a sampling circuit _PCC And ISOP-DAB low-voltage side output direct-current voltage V _dc (ii) a Three-phase network voltage V _PCC Generating a real-time phase theta of a grid voltage via a phase locked loop PLL _g ；

(2) The DC voltage V is collected _dc And a DC voltage reference V _{dc_ref} Subtracting the difference to obtain a feedback quantity, and obtaining a modulation ratio m required by CSR through a Proportional Integral (PI) controller _a ；

(3) Using the resulting modulation ratio m _a Obtaining the switching angle theta required by the modulation ratio variable specific harmonic elimination modulation ₁ ～θ ₁₀ (ii) a The method comprises the following specific steps:

(301) using a variable specific harmonic cancellation modulation of 9 pulse modulation ratios, theta ₁ ～θ ₄ Is a free angle, θ ₆ ～θ ₁₀ By theta ₁ ～θ ₄ And bypass pulse width θ ₀ Can pass through the free angle theta ₁ ～θ ₄ Obtained by the following formula:

(302) the modulation ratio m obtained in the step (2) is _a Substituting the formula (1-1) into the following formula, and obtaining the switching angle theta by iterative solution ₁ ～θ ₁₀ ：

；

Wherein, theta _k I.e. for theta ₁ ～θ ₁₀ The kth switching angle k is 1-10;

(4) real-time phase theta of the obtained power grid voltage _g And a switching angle theta ₁ ～θ ₁₀ PWM modulation of input CSR to generate corresponding gate control signal G ₁ ～G ₆ The control circuit is used for controlling the turn-on and turn-off of the front-stage CSR gate commutated thyristor;

(5) and the later-stage ISOP-DAB adopts square wave voltage control based on carrier phase shift.

2. The method as claimed in claim 1, wherein the step (5) of controlling the square wave voltage based on carrier phase shift comprises the steps of:

(501) determining the frequency f of the square wave control signal according to the first resonance capacitor and the leakage inductance of the high-frequency isolation transformer _sw ：

Wherein the capacitance value of the first resonant capacitor is C _r1 Leakage inductance of high frequency isolation transformer is L _r1 ；

(502) H bridges of the input end and the output end of each resonant double-active bridge of ISOP-DAB use the completely same square wave control signals with the duty ratio of 0.5;

(503) the square wave control signals of the two IGBTs of the upper bridge arm of each H bridge are the same, the square wave control signals of the two IGBTs of the lower bridge arm are the same, but the phase difference between the square wave control signals of the upper bridge arm and the square wave control signal of the lower bridge arm is 180 degrees, and a dead zone exists;

(504) the square wave control signals between the three resonant dual-active bridges differ in phase by 120 °.

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