CN111969631A

CN111969631A - Energy storage converter and control method thereof

Info

Publication number: CN111969631A
Application number: CN202010925728.0A
Authority: CN
Inventors: 张淼; 李博然; 陈栩杰; 莫可维; 刘岩
Original assignee: Guangdong University of Technology
Current assignee: Guangdong University of Technology
Priority date: 2020-09-07
Filing date: 2020-09-07
Publication date: 2020-11-20

Abstract

The invention discloses an energy storage converter and a control method thereof, wherein the energy storage converter is a control device for connecting energy conversion between a direct current system and an alternating current system, can rectify and filter alternating current voltage to form direct current voltage to charge a storage battery, and can convert the direct current energy into the alternating current voltage through inversion to continuously supply power to a load or a power grid.

Description

Energy storage converter and control method thereof

Technical Field

The invention relates to the technical field of converters, in particular to an energy storage converter and a control method thereof.

Background

In recent years, the world has gradually paid attention to climate change and energy demand, and compared with the traditional fossil energy, wind power generation and solar photovoltaic power generation have the advantages of cleanness, safety, abundant resources and the like, are widely paid attention and paid attention to all countries in the world at present, and all countries in the world actively advocate and encourage large-scale development and utilization of renewable energy.

Because the electric energy is difficult to store, in the traditional electric power production, the electricity generation, the electricity transmission, the electricity distribution and the electricity utilization are almost simultaneously carried out, and the real-time balance of the electric energy is ensured by a power grid through a scheduling means. Under the background of large-scale access of new energy and large-scale rotation and expansion of a micro-grid in the world, the energy storage system serving as a peak regulation means increasingly highlights the important role of the new energy due to the randomness of the output power generated by the new energy and the requirement of the self composition of the micro-grid.

The Battery Energy Storage System (BESS) mainly includes two parts, namely a battery and a management System thereof and an Energy conversion System (PCS). The battery exchanges energy with the power grid through an energy conversion system, and stores energy or releases energy according to actual conditions. The energy conversion system plays a role of an interface for connection between the battery and the power grid, and bidirectional exchange of energy between the battery and the power grid is realized.

In general, a converter includes a power device, a control circuit, a driving circuit, and a filter for connecting the power device and an ac system; in the inverter control strategy, a PID control algorithm is applied, the control effect is good, and meanwhile programming and control are easy.

However, as the demand of the power grid increases, the power factor becomes an indispensable part, so that the converter with the variable power factor is provided for facilitating engineering application.

Disclosure of Invention

The present invention is directed to an energy storage converter and a control method thereof, so as to solve the problems in the background art. In order to achieve the purpose, the invention provides the following technical scheme: a control method of an energy storage converter comprises inversion control and rectification control; wherein, contravariant control includes the following step: A. firstly, sampling an alternating-current side voltage, carrying out PLL phase locking on the sampled voltage to obtain a reference phase angle, and simultaneously carrying out DQ conversion on the reference phase angle; then sampling the alternating current, carrying out DQ conversion on the alternating current, then comparing the value after the current conversion with a reference value to obtain a deviation, carrying out closed-loop PID (proportion integration differentiation) regulation on a DQ value fed back by a switching node and the reference DQ value by a PID (proportion integration differentiation) controller according to the deviation, outputting a current DQ reference value, and comparing and operating the current DQ reference value with a voltage DQ calculated value to obtain a reference value of an output DQ component; B. d, carrying out DQ-ABC transformation on the reference value of the output DQ component of the DQ in the step A to obtain the reference value of the ABC three-phase current; C. inputting the reference value of the ABC three-phase current in the step B into an SPWM controller for modulation or inputting the reference value into an SVPWM controller for modulation, so as to obtain PWM waves; D. and inputting the PWM wave obtained by modulation into a driving circuit to obtain a PWM wave signal which is enough to drive the IGBT, so that the IGBT is driven to be conducted. Preferably, the rectification control includes the steps of: A. firstly, sampling current on an alternating current side, simultaneously carrying out DQ conversion on the sampled current, obtaining related data by traditional PID regulation according to deviation, then sampling direct current voltage, inputting the deviation of the direct current voltage and given direct current voltage into a PID regulator, wherein in a control strategy, the deviation of the alternating current is used as an inner ring of PID control, the direct current voltage is used as an outer ring of the PID control, thereby obtaining DQ two-axis regulation components through control operation and obtaining a reference value of DQ; B. d, carrying out DQ-ABC conversion on the reference value of DQ in the step A to obtain a reference value of ABC three-phase voltage; C. inputting the reference value of the ABC three-phase voltage in the step B into an SPWM controller for modulation or inputting the reference value into an SVPWM controller for modulation, so as to obtain PWM waves; D. and inputting the PWM wave obtained by modulation into a driving circuit to obtain a PWM wave signal which is enough to drive the IGBT, so that the IGBT is driven to be conducted. Preferably, the energy storage converter comprises an energy storage battery, a power device and a controller, wherein the energy storage battery and the power device are respectively connected with the controller, and the energy storage battery is used for providing a direct current power supply; the power device is used for bidirectional flow of energy, and the controller is used for controlling the on and off of the power device to ensure alternating current-direct current; the dc-ac energy flows in both directions. Preferably, the controller comprises an acquisition circuit and a PLL phase-locked loop; the system comprises a PID or fuzzy PID controller, an ABC-DQ conversion calculation unit, a DQ-ABC conversion calculation unit and an SPWM generator; the acquisition circuit is used for sampling alternating current voltage, alternating current and direct current voltage. Compared with the prior art, the invention has the beneficial effects that: the invention mainly solves the problem of how to enable energy to flow in two directions in a high-power converter, and simultaneously enables the power factor to be adjustable during inversion so as to obtain better electric energy quality. The PID controlled inversion system can invert direct current into alternating current, and meanwhile, the power factor is adjustable. The structure is relatively easy, a PID control system is constructed by using a DSP or an FPGA and the like, the structure is not different from that of a common digital system, a PID algorithm is realized by software, the design is easy, and the cost is gradually reduced; the robust characteristic is good, the PID control can effectively control linear or nonlinear variables, and the robustness and the controllability are good. And the excellent static and dynamic stability of the system is ensured.

Drawings

FIG. 1 is a main topology diagram of a current transformer; FIG. 2 is a schematic diagram of a current transformer simulation primary topology; FIG. 3 is a diagram of a PLL phase lock loop control architecture; FIG. 4 is a logic diagram of inversion control; FIG. 5 is a schematic diagram of DQ set-point calculated by power factor; FIG. 6 is a SPWM modulation control map; FIG. 7 is a waveform diagram resulting from modulation; FIG. 8 is a block diagram of inverter control; FIG. 9 is a graph of the current waveform resulting from the inversion; FIG. 10 is a graph of the voltage waveform resulting from the inversion; FIG. 11 is a power factor angle diagram for a given power factor angle versus output; FIG. 12 is a schematic diagram of a control strategy for a commutating mode operation; FIG. 13 is a schematic diagram of a rectifier control strategy; FIG. 14 is a schematic diagram of a rectifier PID control loop; FIG. 15 is a schematic diagram of the output waveform of the rectifier voltage and the given amount of the DC voltage; fig. 16 is a screenshot of the value of the rectifier output voltage THD. Detailed description of the inventiontechnical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent 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. Referring to fig. 1-3, the present invention provides a technical solution: the control method of the energy storage converter comprises inversion controlControl and rectification control; wherein, contravariant control includes the following step: A. as shown in fig. 4, in the inversion control, the ac side voltage is sampled first, the sampled voltage is PLL-locked to obtain a reference phase angle, and DQ conversion is performed on the reference phase angle; then sampling the alternating current, carrying out DQ conversion on the alternating current, then comparing the value after the current conversion with a reference value to obtain a deviation, carrying out closed-loop PID (proportion integration differentiation) regulation on a DQ value fed back by a switching node and the reference DQ value by a PID (proportion integration differentiation) controller according to the deviation, outputting a current DQ reference value, and comparing and operating the current DQ reference value with a voltage DQ calculated value to obtain a reference value of an output DQ component; the DQ transformation calculation method is as follows: the Park transform dq0 coordinate system is a combined two-phase coordinate system and a zero sequence system and rotor rotation. If the rotor is salient, the D axis coincides with the center axis of the salient, and the Q axis creates an electrical angle of 90 degrees with it. Taking the stator current as an example. Setting the current in the three-phase winding of the stator as

、

The included angle between the d axis of the rotor and the axis of the a phase winding of the stator is

(electrical angle) of the dq0 components of the stator current after Park conversion

、

. On d and q axes of the rotary shaft

、

Respectively projected on three-phase axes of stators a, b and c, and added with zero sequence current

Can obtain

、

And

：

（1-1）

（1-2）

wherein

（1-3）

（1-4）

In the formula

，

Is the angular velocity of the rotor and is,

when the angle between the d axis and the a axis is 0, when the rotor rotates,

is a time varying array. If it is

I.e. the rotor is not rotating and the d-axis coincides with the a-axis, the dq0 coordinate system degenerates toα&#946, 0 coordinate system. Obviously, the above formula is not an orthogonal matrix, and the Clarke transformation is performed by converting the transformation into equal-amplitude transformation and converting the unit orthogonalization of the transformation matrix into an orthogonal matrix

（1-5）

Then

At this time, the conversion will be equal power conversion. Both Park and Clarke transforms areα-&#946, and which is still cross-current in nature, so its value varies with the three-phase value of ABC. Its main purpose is instantaneous reactive power control. The Park transformation is a transformation AC-DC coordination system coordinate system, the transformation AC current can be effectively controlled through a PI link through the transformation, the control is simple, the control is commonly used in the conversion of a general VSC (voltage source converter), and the steady state quantity under the conversion of the AC quantity DC coordinate dq can be kept constant. A. D, performing DQ-ABC conversion on the output current reference value of DQ in the step A to obtain a reference value of ABC three-phase current; the DQ inverse transformation calculation formula is as follows: if the rotating coordinate system is required to be converted to the static coordinate system, only the corresponding d-q direction is required

Projection, one can obtain:

（1-6）

in the same way, can

Projected onto A, B, C, respectively, to obtain their inverse transforms:

（1-7）

as can be seen from the above formula for DQ conversion, the D-axis component corresponds to the real component, and the Q-axis component corresponds to the reactive component, so that in step B, the given value of the DQ two-axis is calculated by the input power factor (as shown in fig. 5).

C. Inputting the reference value of the ABC three-phase current in the step B into an SPWM controller for modulation or inputting the reference value into an SVPWM controller for modulation, so as to obtain PWM waves (a modulation model is built according to the principle of PWM modulation, and a modulation block diagram and a modulation waveform are respectively shown in FIG. 6 and FIG. 7);

D. and inputting the PWM wave obtained by modulation into a driving circuit to obtain a PWM wave signal which is enough to drive the IGBT, so that the IGBT is driven to be conducted.

The three-phase alternating current component is subjected to SPWM modulation, SPWM waves are output, the IGBT is driven to be switched on and switched off by the PWM waves, and the waveform of the PWM waves is three-phase sine waves after filtering according to the PWM wave principle, so that the inversion work is finished (the general control block diagram is shown in fig. 8).

The inverter current and the inverter voltage are shown in fig. 9 and fig. 10, the given input power factor is 0.6, the output power factor is shown in fig. 11, and the value is also about 0.6, so that the control purpose of controlling the power factor is met. Meanwhile, the current and the voltage of the device do not fluctuate too much, and the stable operation condition is met.

For a high-power converter, the operation of the converter in a rectification mode is also an indispensable part, the rectification part is explained below, when the converter works in a rectification mode, a power element still uses an IGBT which is the same as the operation of the converter in an inversion mode, the converter is also in a three-phase full-bridge structure, only the control mode is different, because the rectified output is used for charging a storage battery, the converter can be controlled by a PID, the control method meets the requirement of battery charging operation, meanwhile, the control structure is relatively simple and easy to program, and the operation in the rectification mode is explained below.

The rectification control comprises the following steps:

A. firstly, sampling current at an alternating current side, simultaneously carrying out DQ conversion on the sampled current, obtaining related data by traditional PID regulation according to deviation, then sampling direct current voltage, inputting the deviation of the direct current voltage and given direct current voltage into a PID regulator, and in a control strategy, the deviation of the alternating current is used as an inner ring of PID control, and the direct current voltage is used as an outer ring of the PID control, so that DQ two-axis regulation components are obtained through control operation, and a reference value of DQ is obtained (a control general diagram of the DQ is shown in FIG. 12; a control module is shown in FIG. 13 for a control strategy);

B. d, carrying out DQ-ABC conversion on the reference value of DQ in the step A to obtain a reference value of ABC three-phase voltage;

C. inputting the reference value of the ABC three-phase voltage in the step B into an SPWM controller for modulation or inputting the reference value into an SVPWM controller for modulation, so as to obtain PWM waves;

The invention also discloses an energy storage converter, which comprises an energy storage battery, a power device and a controller, wherein the energy storage battery and the power device are respectively connected with the controller; the power device is used for bidirectional flow of energy, and the controller is used for controlling the on and off of the power device to ensure alternating current-direct current; the direct current-alternating current can flow in two directions; the controller comprises an acquisition circuit and a PLL; PID and fuzzy PID controller, ABC-DQ conversion calculating unit, DQ-ABC conversion calculating unit and SPWM generator; the acquisition circuit is used for sampling alternating current voltage, alternating current and direct current voltage.

Sampling the three-phase alternating current to obtain a reference phase angle of the alternating current and a DQ value of the alternating current, namely ID and IQ. The calculation method for the DQ conversion has already been mentioned above and is not described in detail here.

The PID control loop is shown in fig. 14, where the dc voltage is sampled and passed to the PID control module.

In the control module, the outer loop PID control of the dc voltage and the inner loop PID control of the current are mainly used to achieve the effect of outputting a controllable dc voltage, and the control logic will be described below.

Firstly, comparing a direct-current voltage sampling value with a given value to obtain deviation of the direct-current voltage sampling value, inputting the deviation into a PID (proportion integration differentiation) module to obtain a D-axis given quantity ID-ref of current, comparing the ID obtained by sampling and calculating with the D-axis given quantity ID-ref of the current, and inputting into a PID controller; and similarly, comparing the IQ obtained by sampling and calculation with the Q-axis given quantity IQ-ref of the current, inputting the IQ into a PID controller, and outputting an ID control quantity and an IQ control quantity after PID calculation.

The collected and calculated ID and IQ are multiplied by the filtered inductance value to obtain voltage quantities, namely, (2 × pi × 50) × 0.0035 × ID and (2 × pi 50) × 0.0035 × IQ, which are respectively marked as wL _ IQ and wL _ ID.

Comparing and adding the ID control quantity, wL _ ID and UD obtained by converting the alternating voltage and outputted by PID control to obtain Ud; similarly, the IQ control quantity, wL _ IQ and UQ output by PID control are compared, added and subtracted to obtain Uq to output.

And carrying out DQ- - -ABC inverse transformation on the output Ud and Uq to obtain an ABC trigonometric function expression, wherein the output component is a three-phase alternating current component.

And carrying out SPWM (sinusoidal pulse Width modulation) on the three-phase alternating current component, outputting an SPWM wave, driving the IGBT (insulated gate bipolar translator) to be switched on and off by using the PWM wave, and finishing rectification after filtering according to the PWM wave principle.

According to the above description, a rectified waveform is obtained, and the voltage is as shown in fig. 15, and it can be seen that the voltage is 640V DC and has almost the same difference with the given voltage of 640V, so that the rectification control is successful, the overshoot time is less, the waveform is smooth after being stabilized, and the control requirement is met.

For the rectifier, the THD (total harmonic distortion) is an important index for measuring the quality of the rectified waveform of the rectifier, and under the control strategy, the THD is about 0.03805, as shown in fig. 16, the THD is small, so that the rectification task is well completed.

Embodiments of a current transformer apparatus are provided herein, the apparatus comprising a processor and a memory: the memory is used for storing the program codes and transmitting the program codes to the processor; the processor is used for executing the control method of the inversion control and the rectification control according to instructions in the program codes.

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application may be substantially implemented or contributed to by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: u disk, removable hard disk, read only memory, random access memory, magnetic or optical disk, etc. for storing program codes.

In conclusion, the invention mainly solves the problem of how to enable energy to flow in two directions in a high-power converter, and meanwhile, the power factor can be adjusted during inversion, so that better electric energy quality is obtained. The PID controlled inversion system can invert direct current into alternating current, and meanwhile, the power factor is adjustable. The structure is relatively easy, a PID control system is constructed by using a DSP or an FPGA and the like, the structure is not different from that of a common digital system, a PID algorithm is realized by software, the design is easy, and the cost is gradually reduced; the robust characteristic is good, the PID control can effectively control linear or nonlinear variables, and the robustness and the controllability are good. And the excellent static and dynamic stability of the system is ensured.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A control method of an energy storage converter is characterized in that: the method comprises inversion control and rectification control; wherein, contravariant control includes the following step:

A. firstly, sampling an alternating-current side voltage, carrying out PLL phase locking on the sampled voltage to obtain a reference phase angle, and simultaneously carrying out DQ conversion on the reference phase angle; then sampling the alternating current, carrying out DQ conversion on the alternating current, then comparing the value after the current conversion with a reference value to obtain a deviation, carrying out closed-loop PID (proportion integration differentiation) regulation on a DQ value fed back by a switching node and the reference DQ value by a PID (proportion integration differentiation) controller according to the deviation, outputting a current DQ reference value, and comparing and operating the current DQ reference value with a voltage DQ calculated value to obtain a reference value of an output DQ component;

B. d, carrying out DQ-ABC transformation on the reference value of the output DQ component of the DQ in the step A to obtain the reference value of the ABC three-phase current;

C. inputting the reference value of the ABC three-phase current in the step B into an SPWM controller for modulation or inputting the reference value into an SVPWM controller for modulation, so as to obtain PWM waves;

2. The control method of an energy storage converter according to claim 1, characterized in that: the rectification control comprises the following steps:

A. firstly, sampling current on an alternating current side, simultaneously carrying out DQ conversion on the sampled current, obtaining related data by traditional PID regulation according to deviation, then sampling direct current voltage, inputting the deviation of the direct current voltage and given direct current voltage into a PID regulator, wherein in a control strategy, the deviation of the alternating current is used as an inner ring of PID control, the direct current voltage is used as an outer ring of the PID control, thereby obtaining DQ two-axis regulation components through control operation and obtaining a reference value of DQ;

3. An energy storage converter, characterized by: the energy storage battery and the power device are respectively connected with the controller, and the energy storage battery is used for providing a direct-current power supply; the power device is used for bidirectional flow of energy, and the controller is used for controlling the on and off of the power device to ensure alternating current-direct current; the dc-ac energy flows in both directions.

4. An energy storage converter according to claim 3, wherein: the controller comprises an acquisition circuit and a PLL (phase locked loop); the device comprises a PID or fuzzy PID controller, an ABC-DQ conversion calculation unit, a DQ-ABC conversion calculation unit and an SPWM generator; the acquisition circuit is used for sampling alternating current voltage, alternating current and direct current voltage.