CN111864776B - Charging device of super-capacitor energy storage station and control method - Google Patents

Abstract

The invention provides a charging device and a control method for a super-capacitor energy storage station, wherein the device comprises a three-phase four-wire PWM rectifier, an isolated three-level DC/DC converter, a first bus capacitor subunit and a second bus capacitor subunit; an alternating current input port of the three-phase four-wire PWM rectifier is connected with a power grid system in parallel, a high-voltage input port of the isolation three-level DC/DC converter is connected with a direct current output port of the three-phase four-wire PWM rectifier, and a low-voltage output port of the isolation three-level DC/DC converter is connected with a super capacitor bank; and the first bus capacitor subunit and the second bus capacitor subunit are connected in series and then connected in parallel to a direct current output port of the three-phase four-wire PWM rectifier. The charging device for the super-capacitor energy storage station can realize isolated charging with small volume and high efficiency. The device adopts the maximum power charge control strategy, can reduce the charge time to shorten the preparation time in earlier stage.

Description

A supercapacitor energy storage station charging device and control method

technical field

The invention relates to the technical field of power system control, in particular to a charging device and a control method for a supercapacitor energy storage station.

Background technique

One of the key technologies supporting electromagnetic launch technology is pulsed power technology. The pulsed power supply based on supercapacitor energy storage has the characteristics of long service life, large instantaneous power and wide operating temperature range, and can be used as a pulsed power supply for electromagnetic emission. The supercapacitor energy storage station should be charged to a fully charged state prior to electromagnetic emission. Considering that electromagnetic launchers are generally installed on mobile carriers such as launch vehicles or ships, high-quality power grids cannot be provided, and the installation space is limited, so the charging devices of supercapacitor energy storage stations have strong adaptability to the power grid and have a small size. . Considering safety, a transformer should be used to electrically isolate the supercapacitor energy storage station from the power grid. The traditional energy storage device charging topology is shown in Figure 1.

Referring to Figure 1, it can be seen that the traditional charging topology of the energy storage device adopts a two-stage structure, and the front stage adopts a three-phase three-wire PWM rectifier device to convert alternating current into direct current to realize unity power factor rectification. The latter stage uses a phase-shifted full-bridge DC/DC converter to charge the supercapacitor bank to achieve isolated charging.

The voltage stress of the switch tube of the phase-shifted full-bridge converter used in the traditional energy storage device charging topology is the DC bus voltage. Since the PWM rectifier has a boost function, the DC bus voltage is higher. As a result, the voltage level of the switch tube used in the phase-shifted full-bridge converter is higher, and the switch tube of the high voltage level tends to have a lower switching frequency. The lower switching frequency brings larger high frequency transformer volume and larger ripple current.

SUMMARY OF THE INVENTION

In view of solving the problems of low switching frequency of the DC/DC converter of the traditional charging device, resulting in large volume of the high-frequency transformer and large output current ripple, the present invention provides a charging device and a control method for a supercapacitor energy storage station.

In one aspect of the present invention, a supercapacitor energy storage station charging device is provided, the device includes a three-phase four-wire PWM rectifier, an isolated three-level DC/DC converter, a first bus capacitor subunit and a second bus capacitor subunit;

The AC input port of the three-phase four-wire PWM rectifier is connected to the power grid system in parallel, the high-voltage input port of the isolated three-level DC/DC converter is connected to the DC output port of the three-phase four-wire PWM rectifier, and the The low-voltage output port of the isolated three-level DC/DC converter is connected to the supercapacitor bank;

The first bus capacitor sub-unit and the second bus capacitor sub-unit are connected in series and then connected in parallel to the DC output port of the three-phase four-wire PWM rectifier.

Wherein, the isolated three-level DC/DC converter includes an upper half-bridge sub-module, a lower half-bridge sub-module, a first capacitor unit and a first transformer unit;

The DC input end of the upper half-bridge sub-module is connected in parallel to the first bus capacitor sub-unit, the DC input end of the lower half-bridge sub-module is connected in parallel to the second bus capacitor sub-unit, the upper half The bridge submodule and the lower half bridge submodule respectively include a bridge arm midpoint, and the first capacitor unit connects the bridge arm midpoints of the upper half bridge submodule and the lower half bridge submodule in series to the primary winding of the first transformer.

Wherein, the isolated three-level DC/DC converter further includes a first commutation auxiliary circuit and a second commutation auxiliary circuit;

The first commutation auxiliary circuit includes a first auxiliary inductance and a first auxiliary capacitor, one end of the first auxiliary inductance is connected to the midpoint of the bridge arm of the upper half-bridge sub-module, and the other end is connected to the first auxiliary capacitor The positive electrode of the first auxiliary capacitor is connected to the negative electrode of the first bus capacitor sub-unit;

The second commutation auxiliary circuit includes a second auxiliary inductance and a second auxiliary capacitor, one end of the second auxiliary inductance is connected to the midpoint of the bridge arm of the lower half-bridge sub-module, and the other end is connected to the second auxiliary capacitor The anode of the second auxiliary capacitor is connected to the cathode of the second bus capacitor subunit.

Wherein, the isolated three-level DC/DC converter further includes an AC/DC conversion unit connected to the secondary winding of the first transformer, and the AC port of the AC/DC conversion unit is connected to the first transformer the secondary winding.

Wherein, the supercapacitor energy storage station charging device further includes a control circuit;

The control circuit is respectively connected with the three-phase four-wire PWM rectifier and the isolated three-level DC/DC converter, and is used to control the working parameters of the three-phase four-wire PWM rectifier and the isolated three-level DC/DC converter .

Another aspect of the present invention also provides a control method applied to the above-mentioned supercapacitor energy storage station charging device, the method comprising:

Calculate the positive and negative sequence dq axis voltage control signals according to the DC voltage given signal u _DC * and the collected DC side voltage u _DC ;

transforming the positive and negative sequence dq axis voltage control signals into positive and negative sequence αβ axis voltage control signals;

Calculate the zero-sequence voltage control signal according to the voltage u _DC1 of the first bus capacitor sub-unit and the voltage u _DC2 of the second bus capacitor sub-unit;

generating a three-phase PWM drive signal of the three-phase four-wire PWM rectifier according to the positive- and negative-sequence αβ-axis voltage control signals and the zero-sequence voltage control signal;

The output control of the isolated three-level DC/DC converter is realized by adopting the output current closed-loop control.

The calculation of the positive and negative sequence dq-axis voltage control signals according to the DC voltage given signal u _DC * and the collected DC side voltage u _DC includes:

Compare the DC voltage given signal u _DC * with the collected DC side voltage u _DC to obtain the DC voltage deviation signal;

Inputting the direct voltage deviation signal into the first PI controller, and using the output signal of the first PI controller as the current given current signal i _DC * of the current loop;

Calculate the active power given signal according to the current given signal i _DC * and the DC voltage given signal u _DC *;

Calculate the positive and negative sequence dq axis components of the grid current according to the grid voltage dq axis component signal and the active power given signal;

inputting the positive-sequence d-axis component of the grid current into the second PI controller, and using the output signal of the second PI controller as the positive-sequence d-axis voltage control signal;

inputting the positive-sequence q-axis component of the grid current into a third PI controller, and using the output signal of the third PI controller as a positive-sequence q-axis voltage control signal;

inputting the negative-sequence d-axis component of the grid current into a fourth PI controller, and using the output signal of the fourth PI controller as a negative-sequence d-axis voltage control signal;

The negative-sequence q-axis component of the grid current is input into the fifth PI controller, and the output signal of the fifth PI controller is used as the negative-sequence q-axis voltage control signal.

The calculation of the zero-sequence voltage control signal v ₀ * according to the voltage u _DC1 of the first bus capacitor sub-unit and the voltage u _DC2 of the second bus capacitor sub-unit includes:

Comparing the voltage u _DC1 of the first bus capacitor sub-unit with the voltage u _DC2 of the second bus capacitor sub-unit to obtain an output capacitor voltage difference signal;

Inputting the output capacitor voltage difference signal into the sixth PI controller, and taking the output signal of the sixth PI controller as the zero-sequence current given signal i ₀ *;

Compare the zero-sequence current given signal i ₀ * with the collected zero-sequence current i ₀ to obtain the zero-sequence current difference signal;

The zero-sequence current difference signal is input into the seventh PI controller, and the output signal of the seventh PI controller is used as the zero-sequence voltage control signal v ₀ *.

The supercapacitor energy storage station charging device provided by the embodiment of the present invention has a two-stage structure. The front stage adopts a three-phase four-wire PWM rectifier to convert alternating current into direct current, realizes unity power factor rectification, and isolates three-level DC/DC for the latter stage. The DC converter provides two series voltages, and the back stage uses an isolated three-level DC/DC converter to charge the supercapacitor bank to achieve small volume and high-efficiency isolated charging.

The control method of the supercapacitor energy storage station charging device provided by the embodiment of the present invention adopts the maximum power charging strategy to reduce the charging time, thereby shortening the early preparation time of the equipment.

The above description is only an overview of the technical solutions of the present invention, in order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the description, and in order to make the above and other objects, features and advantages of the present invention more obvious and easy to understand , the following specific embodiments of the present invention are given.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are for the purpose of illustrating preferred embodiments only and are not to be considered limiting of the invention. Also, the same components are denoted by the same reference numerals throughout the drawings. In the attached image:

Fig. 1 is a circuit schematic diagram of a conventional supercapacitor energy storage station charging device in the prior art;

2 is a schematic circuit diagram of a charging device for a supercapacitor energy storage station provided by an embodiment of the present invention;

3 is a schematic circuit diagram of another supercapacitor energy storage station charging device provided by an embodiment of the present invention;

4 is a schematic diagram of a waveform diagram of an isolated three-level DC/DC converter in an embodiment of the present invention;

5 is a schematic diagram 1 of a current flow of an isolated three-level DC/DC converter in an embodiment of the present invention;

6 is a schematic diagram 2 of a current flow of an isolated three-level DC/DC converter in an embodiment of the present invention;

7 is a schematic diagram 3 of a current flow of an isolated three-level DC/DC converter in an embodiment of the present invention;

8 is a schematic diagram 4 of the current flow of the isolated three-level DC/DC converter in the embodiment of the present invention;

9 is a schematic diagram 5 of the current flow of the isolated three-level DC/DC converter in the embodiment of the present invention;

10 is a schematic diagram 6 of the current flow of the isolated three-level DC/DC converter in the embodiment of the present invention;

11 is a schematic diagram 7 of the current flow of the isolated three-level DC/DC converter in the embodiment of the present invention;

12 is a schematic diagram 8 of the current flow of the isolated three-level DC/DC converter in the embodiment of the present invention;

13 is a schematic diagram 9 of the current flow of the isolated three-level DC/DC converter in the embodiment of the present invention;

14 is a schematic diagram ten of the current flow of the isolated three-level DC/DC converter in the embodiment of the present invention;

15 is a flowchart of a control method of a charging device for a supercapacitor energy storage station according to an embodiment of the present invention;

16 is an overall control block diagram of a charging device for a supercapacitor energy storage station according to an embodiment of the present invention;

17 is a control block diagram of a three-phase four-wire PWM rectifier according to an embodiment of the present invention;

FIG. 18 is a block diagram of the detection and control of the positive and negative sequence dq-axis component voltage of the grid voltage according to an embodiment of the present invention;

FIG. 19 is a control block diagram of an isolated three-level DC/DC converter according to an embodiment of the present invention.

Detailed ways

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be more thoroughly understood, and will fully convey the scope of the present disclosure to those skilled in the art.

It will be understood by those skilled in the art that the singular forms "a", "an", "the" and "the" as used herein can include the plural forms as well, unless expressly stated otherwise. It should be further understood that the word "comprising" used in the description of the present invention refers to the presence of stated features, integers, steps, operations, elements and/or components, but does not exclude the presence or addition of one or more other features, Integers, steps, operations, elements, components and/or groups thereof.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and not to be taken in idealized or overly formal meanings unless specifically defined to explain.

FIG. 2 schematically shows a circuit block diagram of a charging device for a supercapacitor energy storage station provided by an embodiment of the present invention. 2 , the supercapacitor energy storage station charging device provided by the embodiment of the present invention includes a three-phase four-wire PWM rectifier 10, an isolated three-level DC/DC converter 20, a first bus capacitor subunit 30 and a second bus capacitor Subunit 40. in:

The AC input port of the three-phase four-wire PWM rectifier 10 is connected to the power grid system in parallel, and the high-voltage input port of the isolated three-level DC/DC converter 20 is connected to the DC output port of the three-phase four-wire PWM rectifier 10 , the low-voltage output port of the isolated three-level DC/DC converter 20 is connected to the supercapacitor bank;

The first bus capacitor sub-unit 10 and the second bus capacitor sub-unit 20 are connected in series and then connected in parallel to the DC output port of the three-phase four-wire PWM rectifier.

In a specific embodiment, as shown in FIG. 3 , the isolated three-level DC/DC converter 20 includes an upper half-bridge sub-module 201 , a lower half-bridge sub-module 202 , a first capacitor unit C _b and a first transformer unit 203, the transformer leakage inductance of the first transformer unit 203 is L _r ;

The DC input terminal of the upper half-bridge sub-module 201 is connected in parallel to the first bus capacitor sub-unit 30, and the DC input terminal of the lower half-bridge sub-module 202 is connected in parallel to the second bus capacitor sub-unit 40, The upper half bridge submodule 201 and the lower half bridge submodule 202 respectively include a bridge arm midpoint, and the first capacitor unit _Cb connects the upper half bridge submodule 201 and the lower half bridge submodule. The midpoint of the bridge arm of 202 is connected to the primary winding of the first transformer 203 in series.

Further, as shown in FIG. 3 , the isolated three-level DC/DC converter 20 further includes a first commutation auxiliary circuit 204 and a second commutation auxiliary circuit 205 , wherein the first commutation auxiliary circuit 204 It includes a first auxiliary inductance L _A1 and a first auxiliary capacitor C _A1 , one end of the first auxiliary inductance L _A1 is connected to the midpoint of the bridge arm of the upper half-bridge sub-module 201 , and the other end is connected to the first auxiliary capacitor C The positive pole of _A1 , the negative pole of the first auxiliary capacitor C _A1 is connected to the negative pole of the first bus capacitor sub-unit 30;

The second commutation auxiliary circuit 205 includes a second auxiliary inductance L _A2 and a second auxiliary capacitor C _A2 . One end of the second auxiliary inductance L _A2 is connected to the midpoint of the bridge arm of the lower half-bridge sub-module 202 , and the other One end is connected to the positive electrode of the second auxiliary capacitor C _A2 , and the negative electrode of the second auxiliary capacitor C _A2 is connected to the negative electrode of the second bus capacitor sub-unit 40 .

In this embodiment, the isolated three-level DC/DC converter 20 further includes an AC/DC conversion unit connected to the secondary winding of the first transformer, and an AC port of the AC/DC conversion unit is connected to the first transformer. A secondary winding of a transformer.

In this embodiment, the supercapacitor energy storage station charging device further includes a control circuit; the control circuit is respectively connected with the three-phase four-wire PWM rectifier and the isolated three-level DC/DC converter for controlling the Operating parameters of three-phase four-wire PWM rectifiers and isolated three-level DC/DC converters.

The present invention will be described in detail below through a specific embodiment.

As shown in Figure 3, the three-phase four-wire PWM rectifier outputs two voltages u _DC1 and u _DC2 to supply power for the isolated three-level DC/DC converter. Switch tubes S ₁ and S ₂ form the upper half bridge of the isolated three-level DC/DC converter, S ₃ and S ₄ form the lower half bridge, L _r is the leakage inductance of the transformer, and C _b is the DC blocking capacitor. C ₁ to C ₄ are the equivalent parallel capacitances of the main switch tubes, including the parasitic capacitance of the switch tubes and a parallel buffer capacitor. The equivalent parallel capacitors will realize the zero-voltage turn-off of the switch tubes. The voltages of C ₁ to C ₄ are respectively V _S1 ~ _VS4 . Switch tubes S ₂ and S ₄ are easier to realize ZVS, because the energy to realize ZVS comes from the output filter inductance and the leakage inductance of the transformer. However, S ₁ and S ₃ are not easy to realize ZVS, because the energy to realize ZVS only comes from the leakage inductance of the transformer. The proposed isolated three-level DC/DC converter adopts a commutation auxiliary circuit, and the switches S ₁ to S ₄ can realize ZVS in the full load range. The commutation auxiliary circuit is composed of a small auxiliary inductor L _A and a capacitor C _A . The auxiliary inductance L _A is a small resonant inductance, and the capacitance C _A is large enough that the voltage across the capacitor can be considered constant within one cycle. FIG. 4 is a schematic diagram of a waveform diagram of an isolated three-level DC/DC converter including a commutation auxiliary circuit according to an embodiment of the present invention, and the positive direction of the voltage and current is shown in FIG. 3 . A switching cycle is divided into 10 stages, and the current flow diagrams in each stage are shown in Figures 5 to 14. Before the analysis, it is assumed that the capacitor C _d1 , the C _d2 voltage u _DC1 =u _DC2 =V _in /2, the DC blocking capacitor C _b voltage V _b =V _in /2, and the output inductance is sufficient enough that the output current I _o can be assumed to be in one cycle The capacitors C _A1 , C _A2 are large enough to assume that the voltages V _CA1 , V _CA2 are held constant for one cycle. The analysis of each stage is as follows:

Stage 1 (t ₀ to t ₁ ): Referring to FIG. 5 , the switches S1 and S4 are turned on, and the capacitors C _d1 and C _d2 supply power to the load and the DC blocking capacitor C _b . The capacitor C _d1 charges C _A1 through the switch tube S1, resulting in a linear decrease in the current i _A1 . The capacitor C _A2 is discharged through the switch S4, resulting in a linear increase in the current i _A2 . The changes of current i _A1 and i _A2 at this stage can be expressed as equations (1), (2).

Stage 2 (t ₁ to t ₂ ): Referring to FIG. 6 , at time t ₁ , the switch S1 is turned off, and due to the clamping action of the buffer capacitor C1 , S1 realizes zero-voltage turn-off. Current i _A1 and i _Lr charge C1 and discharge C2. When the voltage of C2 is discharged to zero, the switch S2 reaches the zero-voltage turn-on condition, and at time _t2 , the switch S2 realizes the zero-voltage turn-on. Due to the large output filter inductance, it can provide enough energy for the soft switching of S2. Even if the output current is small, due to the discharge effect of the current i _A1 on C2, S2 can smoothly achieve soft switching.

Stage 3 (t ₂ to t ₃ ): Referring to FIG. 7 , at time t ₂ , the switch tube S2 is turned on at zero voltage. The current i _Lr will flow through the freewheeling diode D2. Since u _DC2 =V _b =V _in /2, the transformer winding voltage V _m =0, and the converter enters the freewheeling stage. The current i _A1 increases linearly, as shown in equation (3).

in the formula

Stage 4 (t ₃ to t ₄ ): Referring to FIG. 8 , at time t ₃ , the switch S4 is turned off, and due to the clamping effect of the buffer capacitor C4 , S4 realizes zero-voltage turn-off. Current i _A2 and i _Lr charge C4 and discharge C3. When the voltage of C3 is discharged to zero, the switch S3 reaches the zero-voltage turn- _on condition, and at time t4, the switch S3 realizes the zero-voltage turn-on. This stage is in the freewheeling stage, and the energy to achieve soft switching comes from the transformer leakage inductance and i _A2 . Due to the discharge effect of auxiliary current i _A2 on C3, S3 can smoothly realize soft switching.

Stage 5 (t ₄ to t ₅ ): Referring to FIG. 9 , the switches S2 and S3 are turned on, and the capacitor C _b supplies power to the load. The capacitor C _d2 charges C _A2 through the switch tube S3, resulting in a linear decrease in the current i _A2 . The capacitor C _A1 is discharged through the switch tube S2, resulting in a linear increase in the current i _A1 . The change of current i _A2 at this stage can be expressed as Equation (4).

in the formula

Stage 6 (t ₅ to t ₆ ): Referring to FIG. 10 , at t5, the current i _A2 decreases to zero and starts to reverse, while the current i _A1 increases to zero and starts to reverse. The current i _A2 continues to decrease, and i _A1 continues to increase, as shown in equations (5) and (6).

Stage 7 (t ₆ to t ₇ ): Referring to FIG. 11 , at time t ₆ , the switch S3 is turned off, and due to the clamping effect of the buffer capacitor C3 , S3 realizes zero-voltage turn-off. Current i _A2 and i _Lr charge C3 and discharge C4. When the voltage of C4 is discharged to zero, the switch S4 reaches the zero-voltage turn- _on condition, and at time t7, the switch S4 realizes the zero-voltage turn-on. Due to the large output filter inductance, it can provide enough energy for S4 soft switching. Even if the output current is small, due to the discharge effect of the current i _A2 on C4, S4 can smoothly achieve soft switching.

Stage 8 (t ₇ to t ₈ ): Referring to FIG. 12 , at time t ₇ , the switch tube S4 is turned on at zero voltage. The current i _Lr will flow through the freewheeling diode D4. Since u _DC2 =V _b =V _in /2, the transformer winding voltage V _m =0, and the converter enters the freewheeling stage again. The current i _A2 increases linearly, as shown in equation (7).

in the formula

Stage 9 (t ₈ to t ₉ ): Referring to FIG. 13 , at time t ₈ , the switch S2 is turned off, and due to the clamping effect of the buffer capacitor C2 , S2 realizes zero-voltage turn-off. Current i _A1 and i _Lr charge C2 and discharge C1. When the voltage of C1 is discharged to zero, the switch S1 reaches the zero-voltage turn-on condition, and at the time of _t9 , the switch S1 realizes the zero-voltage turn-on. This stage is in the freewheeling stage, and the energy to achieve soft switching comes from the transformer leakage inductance and i _A1 . Due to the discharge effect of auxiliary current i _A1 on C1, S1 can successfully realize soft switching.

Stage 10 (t ₉ to t ₁₀ ): Referring to FIG. 14 , the switches S1 and S4 are turned on, and the capacitors C _d1 and C _d2 supply power to the load and the DC blocking capacitor C _b . The capacitor C _d1 charges C _A1 through the switch tube S1, resulting in a linear decrease in the current i _A1 . The capacitor C _A2 is discharged through the switch S4, resulting in a linear increase in the current i _A2 . At t ₁₀ , the current i _A1 decreases to zero, the current i _A2 increases to zero, the cycle ends, and a new cycle begins.

According to the above analysis, the voltage stress of the switch tube of the proposed isolated three-level DC/DC converter is V _in /2, and a low voltage level switch tube can be selected to achieve a higher switching frequency. Moreover, the adopted commutation auxiliary circuit can realize soft switching within the full load range, thereby further increasing the switching frequency and improving the efficiency of the converter.

FIG. 15 is a flowchart of a control method applied to the above-mentioned supercapacitor energy storage station charging device according to an embodiment of the present invention. Referring to FIG. 15 , a method for controlling a charging device for a supercapacitor energy storage station provided by an embodiment of the present invention specifically includes the following steps:

S101. Calculate the positive and negative sequence dq axis voltage control signals according to the DC voltage given signal u _DC * and the collected DC side voltage u _DC ;

S102, converting the positive and negative sequence dq axis voltage control signals into positive and negative sequence αβ axis voltage control signals;

S103, calculating the zero-sequence voltage control signal according to the voltage u _DC1 of the first bus capacitor sub-unit and the voltage u _DC2 of the second bus capacitor sub-unit;

S104, generating a three-phase PWM drive signal of the three-phase four-wire PWM rectifier according to the positive- and negative-sequence αβ-axis voltage control signals and the zero-sequence voltage control signal;

S105 , implementing output control of the isolated three-level DC/DC converter by adopting an output current closed-loop control.

Considering that electromagnetic launchers are generally installed on mobile carriers such as launch vehicles or ships, and cannot provide high-quality power grids, the PWM rectifier should be able to work normally under unbalanced power grids and achieve unity power factor rectification. The three-phase four-wire PWM rectification also provides two-way voltages with stable and equal voltages for the latter-stage isolated three-level DC/DC converter. The isolated three-level DC/DC converter realizes the charging current control, so the output current closed-loop control is adopted. The overall control strategy of the proposed supercapacitor energy storage station charging device is shown in Figure 16.

In a specific embodiment, the calculation of the positive and negative sequence dq-axis voltage control signals according to the given DC voltage signal u _DC * and the collected DC side voltage u _DC specifically includes: calculating the given DC voltage signal u _DC * Compared with the collected DC side voltage u _DC , a direct voltage deviation signal is obtained; the direct voltage deviation signal is input into the first PI controller, and the output signal of the first PI controller is used as the current of the current loop Given signal i _DC *; calculate active power given signal according to the current given signal i _DC * and DC voltage given signal u _DC *; negative-sequence dq-axis component; input the grid current positive-sequence d-axis component into the second PI controller, and use the output signal of the second PI controller as a positive-sequence d-axis voltage control signal; use the grid current The positive-sequence q-axis component is input into the third PI controller, and the output signal of the third PI controller is used as the positive-sequence q-axis voltage control signal; the negative-sequence d-axis component of the grid current is input into the fourth PI controller In the controller, the output signal of the fourth PI controller is used as the negative-sequence d-axis voltage control signal; the negative-sequence q-axis component of the grid current is input into the fifth PI controller, and the fifth PI controller The output signal is used as the negative sequence q-axis voltage control signal.

In the embodiment of the present invention, the three-phase four-wire PWM rectifier realizes the output voltage closed-loop control, the output capacitor voltage difference balance control, and the DC/DC converter realizes the output current closed-loop control.

Under the unbalanced power grid, the PWM output voltage will produce double frequency fluctuations. The positive and negative sequence separation method can be used to control the positive and negative sequence dq-axis components respectively to suppress the output voltage fluctuations. At the same time, the zero-sequence component is controlled by the output capacitor voltage difference. The control block diagram of the three-phase four-wire PWM rectifier is shown in Figure 17.

As shown in Figure 17, the output capacitor voltage difference control loop is independent of the power control loop, and the given value of the output capacitor voltage difference control system is zero. After the PI closed-loop control, the zero-sequence current given signal is generated. Generate zero sequence voltage given signal. After the DC voltage u _DC is closed by the PI, a current given signal is generated, and then multiplied with the voltage given signal to obtain the active power given signal. Under the unbalanced grid, the power generated by the positive and negative sequence voltage and current is shown in equation (8).

为电网电压dq轴正序分量，

为电网电压dq轴负序分量，

为并网电流dq轴正序分量，

为并网电流dq轴负序分量，P₀有功功率直流分量，P_c2有功功率2倍频余弦振荡分量，P_s2有功功率2倍频正弦振荡分量，Q₀无功功率直流分量，Q_c2无功功率2倍频余弦振荡分量，Q_s2无功功率2倍频正弦振荡分量。in the formula

is the positive sequence component of the grid voltage dq axis,

is the negative sequence component of the grid voltage dq axis,

is the positive sequence component of the grid-connected current dq axis,

It is the negative sequence component of grid-connected current dq axis, P ₀ active power DC component, P _c2 active power 2 times frequency cosine oscillation component, P _s2 active power 2 times frequency sine oscillation component, Q ₀ reactive power DC component, Q _c2 no Cosine oscillation component of double frequency of active power, Q _s2 sine oscillation component of double frequency of reactive power.

四个自由度，而功率有P₀,P_c2,P_s2,Q₀,Q_c2,Q_s2六个自由度，只能选其中的四个功率进行控制。有功P₀必须被控制，其次为了避免直流母线产生二倍频波动，有功功率二倍频分量P_c2＝0，P_s2＝0。为了实现单位功率因数并网，无功功率Q₀＝0。因此P₀,P_c2,P_s2,Q₀被选择，其表达式如式(9)所示。有功功率直流分量给定

由输出直流电压闭环得到，

已知功率给定，对矩阵M_4×4求逆，可以得到dq轴电流给定表达式如式(10)所示。The control volume of the controller has

Four degrees of freedom, and power has six degrees of freedom P ₀ , P _c2 , P _s2 , Q ₀ , Q _c2 , Q _s2 , and only four of them can be selected for control. The active power P ₀ must be controlled, and secondly, in order to avoid the double-frequency fluctuation of the DC bus, the double-frequency components of the active power P _c2 =0, P _s2 =0. In order to achieve unity power factor grid connection, reactive power Q ₀ =0. Therefore, P ₀ , P _c2 , P _s2 , and Q ₀ are selected, and their expressions are shown in equation (9). Active power DC component given

Obtained from the closed-loop output DC voltage,

Given the given power, by inverting the matrix M _4×4 , the given expression of the dq-axis current can be obtained as shown in formula (10).

in the formula

才能得到电流dq轴给定值。在电压检测过程中，dq轴分量互相影响，含有2倍频震荡。一种简单的方法是通过添加陷波器消除2倍频震荡。但是陷波器减小了系统相角裕度，使系统稳定性变差。本文采用正负序解耦合电压检测方法。电网电压的dq轴分量可以表示为式(11)所示。It can be seen from equation (10) that in addition to the given power, the dq axis component of the grid voltage needs to be obtained

Only then can the given value of the current dq axis be obtained. In the process of voltage detection, the dq-axis components influence each other and contain double-frequency oscillation. An easy way to do this is to remove the 2-octave oscillation by adding a notch filter. But the notch filter reduces the system phase angle margin and makes the system stability worse. This paper adopts the positive and negative sequence decoupling voltage detection method. The dq-axis component of the grid voltage can be expressed as equation (11).

为正序，负序分量平均值，为有用信息，

为变换矩阵，如式(12)所示。in the formula

is the average value of positive sequence and negative sequence components, which is useful information,

is the transformation matrix, as shown in equation (12).

where ω is the grid voltage vector angular frequency obtained by the phase-locked loop.

其中ω为电网角频率。电网电流正负序dq轴分量检测方法同电压检测方法。According to the formula (11), the detection control of the positive and negative sequence dq-axis components of the grid voltage is obtained as shown in Figure 18. The average value of the dq-axis components is obtained by low-pass filter (LPF) filtering, and then the average value is used to decouple the AC quantity, thereby effectively reducing the output average value oscillation. From the comprehensive consideration of attenuating the AC signal and rapidity, the LPF cutoff frequency can be selected as

where ω is the grid angular frequency. The detection method of the positive and negative sequence dq-axis components of the grid current is the same as the voltage detection method.

As shown in Figure 17, after the positive and negative sequence currents are decoupled by the dq axis, they are closed-loop controlled by the PI regulator, and the PI regulator can be designed according to the engineering design method. After the current closed-loop control, the dq axis voltage control signal is obtained, and then the dq axis control voltage is transformed to the αβ axis through the transformation shown in equation (13). The zero-sequence voltage control signal is obtained by the output capacitor voltage difference control loop. The three-phase PWM drive signal S _abc is generated according to the αβ0 axis voltage given.

The above is the control method of three-phase four-wire PWM rectification.

In a specific embodiment, calculating the zero-sequence voltage control signal v ₀ * according to the voltage u _DC1 of the first bus capacitor sub-unit and the voltage u _DC2 of the second bus capacitor sub-unit specifically includes: The voltage u _DC1 of the unit is compared with the voltage u _DC2 of the second bus capacitor sub-unit to obtain an output capacitor voltage difference signal; the output capacitor voltage difference signal is input into the sixth PI controller, and the sixth PI control The output signal of the device is taken as the zero-sequence current given signal i ₀ *; the zero-sequence current given signal i ₀ * is compared with the collected zero-sequence current i ₀ to obtain the zero-sequence current difference signal; the zero-sequence current difference signal is obtained; The difference signal is input into the seventh PI controller, and the output signal of the seventh PI controller is used as the zero-sequence voltage control signal v ₀ *.

In the embodiment of the present invention, the isolated three-level DC/DC converter charges the supercapacitor bank, so an output current closed-loop control strategy is adopted for the converter. Using the state space averaging method to model the isolated three-level DC/DC converter, the steady-state operating point of the converter is obtained as V _SC =Du _DC /2n, and the transfer function from duty cycle to output current is shown in equation (14) .

In the formula, n is the transformer ratio, u _DC input DC bus voltage, L _o output filter inductance.

The block diagram of the output current closed-loop control is shown in Figure 19, where G _fi (s) is the transfer function of the current sampling link, and T _s is the PWM period. The PI regulator can be designed by the engineering design method, and the system is designed as a typical type II system.

In order to realize the fast charging of the supercapacitor group and reduce the launch preparation time, a maximum power charging strategy is adopted for the supercapacitor group. If the designed maximum charging power is P _max , the current given of the isolated three-level DC/DC converter can be expressed as formula (15).

where V _SC is the terminal voltage of the super capacitor group.

It should be noted that, in addition to the implementation circuit exemplified in the embodiments of the present invention, a more complex wide-load range soft-switch isolation three-level DC/DC converter can be used to accomplish some of the objectives of the present invention. However, the soft-switching auxiliary circuit adopted in the present invention only adopts smaller inductance and capacitance, and realizes the soft-switching in the whole load range, which is simpler than any other soft-switching method, uses the fewest devices and does not require additional control. Moreover, since there is no energy-consuming device in the switching process, the soft-switching auxiliary circuit consumes almost no energy.

It should be noted that, in addition to the implementation circuit exemplified in the embodiments of the present invention, other rectifier methods may be used to supply power to the isolated three-level DC/DC converter. But the use of three-phase four-wire PWM rectifier is the simplest and most optimal way of power supply. Mainly reflected in: 1. The structure is simple, a three-phase four-wire PWM rectifier can output two equal voltages, and can keep the two voltages equal through control. 2. It can realize unity power factor rectification. 3. Able to adapt to unbalanced power grid.

In the supercapacitor energy storage station charging device provided by the present invention, the voltage stress of the switch tube in the isolated three-level DC/DC converter is reduced by half, and a switch tube with a lower voltage level can be selected, thereby increasing the switching frequency and reducing the Transformer volume.

The supercapacitor energy storage station charging device provided by the invention adopts an auxiliary commutation circuit composed of an inductance and a capacitor to realize the soft switching of the DC/DC converter, thereby broadening the soft switching range. The converter can realize soft switching in the full load range or even under no-load condition, which effectively improves the efficiency of the converter.

The supercapacitor energy storage station charging device provided by the invention adopts a three-phase four-wire PWM rectifier to provide power for the isolated three-level DC/DC converter, which can realize unit power rectification on the AC side and reduce harmonic pollution. And through the positive and negative sequence separation and decoupling control algorithm, the converter can still work normally under the unbalanced grid.

The supercapacitor energy storage station charging device provided by the embodiment of the present invention has a two-stage structure. The front stage adopts a three-phase four-wire PWM rectifier to convert alternating current into direct current, realizes unity power factor rectification, and isolates three-level DC/DC for the latter stage. The DC converter provides two series voltages, and the back stage uses an isolated three-level DC/DC converter to charge the supercapacitor bank to achieve small volume and high-efficiency isolated charging.

The control method of the supercapacitor energy storage station charging device provided by the embodiment of the present invention adopts the maximum power charging strategy to reduce the charging time, thereby shortening the early preparation time of the equipment.

It will be understood by those skilled in the art that although some of the embodiments herein include certain features included in other embodiments and not others, combinations of features of the different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the following claims, any of the claimed embodiments may be used in any combination.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (6)

1. A charging device for a super-capacitor energy storage station is characterized by comprising a three-phase four-wire PWM rectifier, an isolated three-level DC/DC converter, a first bus capacitor subunit and a second bus capacitor subunit;

an alternating current input port of the three-phase four-wire PWM rectifier is connected with a power grid system in parallel, a high-voltage input port of the isolation three-level DC/DC converter is connected with a direct current output port of the three-phase four-wire PWM rectifier, and a low-voltage output port of the isolation three-level DC/DC converter is connected with a super capacitor bank;

the first bus capacitor subunit and the second bus capacitor subunit are connected in series and then connected in parallel to a direct current output port of the three-phase four-wire PWM rectifier;

the isolation three-level DC/DC converter comprises an upper half-bridge submodule, a lower half-bridge submodule, a first capacitor unit and a first transformer unit; the direct current input end of the upper half-bridge submodule is connected to a first bus capacitor subunit in parallel, the direct current input end of the lower half-bridge submodule is connected to a second bus capacitor subunit in parallel, the upper half-bridge submodule and the lower half-bridge submodule respectively comprise a bridge arm midpoint, and the bridge arm midpoints of the upper half-bridge submodule and the lower half-bridge submodule are connected to a primary winding of a first transformer in series through the first capacitor unit;

the isolated three-level DC/DC converter further comprises a first commutation auxiliary circuit and a second commutation auxiliary circuit;

the first commutation auxiliary circuit comprises a first auxiliary inductor and a first auxiliary capacitor, one end of the first auxiliary inductor is connected with the middle point of a bridge arm of the upper half-bridge sub-module, the other end of the first auxiliary inductor is connected with the anode of the first auxiliary capacitor, and the cathode of the first auxiliary capacitor is connected with the cathode of the first bus capacitor sub-unit;

the second commutation auxiliary circuit comprises a second auxiliary inductor and a second auxiliary capacitor, one end of the second auxiliary inductor is connected with the middle point of a bridge arm of the lower half-bridge sub-module, the other end of the second auxiliary inductor is connected with the anode of the second auxiliary capacitor, and the cathode of the second auxiliary capacitor is connected with the cathode of the second bus capacitor sub-unit.

2. The supercapacitor energy storage station charging device according to claim 1, wherein the isolated three-level DC/DC converter further comprises an AC/DC conversion unit connected to the secondary winding of the first transformer, an AC port of the AC/DC conversion unit being connected to the secondary winding of the first transformer.

3. The supercapacitor energy storage station charging device according to claim 1, further comprising a control circuit;

and the control circuit is respectively connected with the three-phase four-wire PWM rectifier and the isolated three-level DC/DC converter and is used for controlling the working parameters of the three-phase four-wire PWM rectifier and the isolated three-level DC/DC converter.

4. A control method applied to the charging device of the super capacitor energy storage station as claimed in any one of claims 1 to 3, wherein the method comprises the following steps:

setting a signal according to a DC voltage

With the collected DC side voltage u_DCCalculating positive and negative sequence dq axis voltage control signals;

converting the positive and negative sequence dq axis voltage control signals into positive and negative sequence alpha beta axis voltage control signals;

according to the voltage u of the first bus capacitor subunit_DC1And the voltage u of the second bus capacitor subunit_DC2Calculating a zero sequence voltage control signal;

generating three-phase PWM driving signals of the three-phase four-wire PWM rectifier according to the positive and negative sequence alpha beta shaft voltage control signals and the zero sequence voltage control signal;

and realizing output control of the isolated three-level DC/DC converter by adopting output current closed-loop control.

5. Method according to claim 4, characterized in that the signal is given as a function of a direct voltage

With the collected DC side voltage u_DCCalculating positive and negative sequence dq axis voltage control signals, comprising:

giving a DC voltage to a signal

With the collected DC side voltage u_DCComparing to obtain a direct voltage deviation signal;

inputting the direct voltage deviation signal into a first PI controller, and using the output signal of the first PI controller as a current setting signal of a current loop

Setting a signal according to the current

And a given signal of DC voltage

Calculating an active power given signal;

calculating a grid current positive and negative sequence dq axis component according to the grid voltage dq axis component signal and the active power given signal;

inputting the grid current positive sequence d-axis component into a second PI controller, and taking an output signal of the second PI controller as a positive sequence d-axis voltage control signal;

inputting the grid current positive sequence q-axis component into a third PI controller, and taking an output signal of the third PI controller as a positive sequence q-axis voltage control signal;

inputting the grid current negative sequence d-axis component into a fourth PI controller, and taking an output signal of the fourth PI controller as a negative sequence d-axis voltage control signal;

and inputting the grid current negative sequence q-axis component into a fifth PI controller, and taking an output signal of the fifth PI controller as a negative sequence q-axis voltage control signal.

6. Method according to claim 4, characterized in that the voltage u according to the first bus capacitor subunit_DC1And the voltage u of the second bus capacitor subunit_DC2Calculating zero sequence voltage control signals

The method comprises the following steps:

converting the voltage u of the first bus capacitor subunit_DC1And the voltage u of the second bus capacitor subunit_DC2Comparing to obtain an output capacitance voltage difference signal;

inputting the output capacitance voltage difference signal into a sixth PI controller, wherein the output signal of the sixth PI controller is used as a zero-sequence current given signal

Giving a zero sequence current to a signal

And the collected zero sequence current i₀Comparing to obtain a zero sequence current difference signal;

inputting the zero sequence current difference signal into a seventh PI controller, and using the output signal of the seventh PI controller as a zero sequence voltage control signal

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