CN104184149B - Voltage fluctuation stabilizing method based on sliding mode control and super-capacitor - Google Patents

Abstract

The invention relates to a method for suppressing voltage fluctuations based on sliding mode control and a supercapacitor. The supercapacitor is connected in parallel to the output end of a bidirectional DC-DC converter as an energy storage device, and the supercapacitor is connected to a DC bus through the bidirectional DC-DC converter. above, a bidirectional energy transmission loop is formed; the inductive current of the bidirectional DC‑DC converter and the capacitor voltage on the DC bus are used as the control parameters of the internal sliding mode variable structure controller of the bidirectional DC‑DC converter, and are input to the sliding mode variable structure control In the device; processed by the sliding mode variable structure controller, a control signal is generated to control the working mode of the bidirectional DC-DC converter and the conduction duty cycle of the power switch tube, so as to control the charging and discharging of the supercapacitor; form a DC dynamic The voltage restorer system stabilizes the voltage fluctuation on the DC bus. The invention simplifies the control algorithm, enhances the robustness of the system, suppresses the voltage fluctuation on the direct current bus, and provides stable and reliable voltage for the load.

Description

A Method of Suppressing Voltage Fluctuation Based on Sliding Mode Control and Supercapacitor

technical field

The invention relates to a technology for adjusting power voltage fluctuations, in particular to a method for suppressing voltage fluctuations based on sliding mode control and supercapacitors.

Background technique

With the development of social economy, the demand for electric power in human life and production is getting higher and higher. At the same time, with the wide application of high-tech precision electronic equipment in life and production, power users have higher and higher requirements for power quality. . If the power quality is damaged, it will seriously threaten the safe operation of the power system, disrupt the normal life and production of power users, and even cause immeasurable economic losses and social impacts.

At present, the main method to prevent and control the voltage fluctuation of the power grid in China is to install UPS power supply. However, the UPS power supply has disadvantages such as short service life and small discharge current, which reduce the cost performance of the system. The present invention proposes a DC DVR system based on the combination of a super capacitor energy storage device and a sliding mode variable structure controller. The system not only combines many advantages of supercapacitors in energy storage, but also has the control advantages of sliding mode variable structure control for nonlinear systems. The system provides high-quality, high-stability voltage for the load by adjusting the DC bus voltage.

As a new type of electric energy storage element, supercapacitor has the characteristics of high power density, short charging time, long service life and high charging and discharging efficiency; therefore, it has been widely researched and applied in energy storage. The DC DVR device based on the supercapacitor can effectively protect the sensitive load from the harm caused by the voltage fluctuation. The sliding mode variable structure control can overcome the uncertainty of the system. The algorithm is simple and the response speed is fast. Modular dynamics have strong robustness. Especially for the control of nonlinear systems, it has a good control effect. Therefore, sliding mode variable structure control, as an important method of nonlinear control, has been extensively and deeply studied in recent years.

Contents of the invention

The present invention aims at the problems of short service life and small discharge current of the UPS power supply currently used for overcoming grid voltage fluctuations, and proposes a method for suppressing voltage fluctuations based on sliding mode control and supercapacitors to solve the problem of grid voltage fluctuations.

The technical solution of the present invention is: a method for suppressing voltage fluctuations based on sliding mode control and a supercapacitor, the supercapacitor is connected in parallel to the output end of the bidirectional DC-DC converter as an energy storage device, and the supercapacitor passes through the bidirectional DC-DC converter Connected to the DC bus to form a bidirectional energy transmission loop; the inductance current of the bidirectional DC-DC converter and the capacitor voltage on the DC bus are used as the control parameters of the sliding mode variable structure controller inside the bidirectional DC-DC converter, and input to the sliding In the modulus variable structure controller, after processing by the sliding mode variable structure controller, a control signal is generated to control the working mode of the bidirectional DC-DC converter and the conduction duty cycle of the power switch tube, so as to control the charge and discharge of the supercapacitor ; Supercapacitors and bidirectional DC-DC converters form a DC dynamic voltage restorer system to stabilize voltage fluctuations on the DC bus.

The bidirectional DC-DC converter adopts a bidirectional half-bridge converter topology. Two power switch tubes in series are connected in parallel at both ends of the capacitor on the DC bus, and the middle point of the two series power switch tubes is connected to a super capacitor through an inductor. The position tracking sliding mode variable structure controller of the law outputs control signals to the control terminals of the two power switch tubes. The sliding mode variable structure controller adopts double-loop control, the inner loop tracking controls the inductance current of the bidirectional DC-DC converter, and the outer loop tracking control Capacitive voltage on the DC bus.

The sliding mode variable structure controller includes an outer loop voltage sliding mode controller and an inner loop current sliding mode controller,

The difference between the reference voltage signal v _ref and the DC bus capacitor voltage v _c is used as an input, which is supplied to the outer loop voltage sliding mode controller. After calculation by the sliding mode controller, the inductor current reference signal i _ref is output; the inductor current reference signal i _ref and The difference value of the inductance current i _L of the bidirectional DC-DC converter is used as an input, which is provided to the inner loop current sliding mode controller, and is calculated by the sliding mode controller to output the duty ratio control signal u of the power switch tube; the duty ratio control The signal u controls the turn-on and turn-off of the two power switches of the bidirectional DC-DC converter, thereby adjusting the inductor current i _L to make it track a given reference current signal; the outer loop voltage sliding mode controller outputs the inductor current reference signal i _ref controls the working mode of the bidirectional DC-DC converter through the hysteresis control link, and adjusts the capacitor voltage on the DC bus.

The beneficial effects of the present invention are: the present invention is based on the sliding mode control and supercapacitor voltage fluctuation method, the method is to use the sliding mode variable structure controller and the supercapacitor energy storage system to realize the DC DVR system, and suppress the voltage fluctuation on the DC bus , to provide a stable and reliable voltage for the load. The sliding mode variable structure control method is adopted, which simplifies the control algorithm and enhances the robustness of the system. At the same time, a supercapacitor is used as an energy storage element, and many advantages of the supercapacitor and sliding mode variable structure control are combined, so that the present invention has wide applicability.

Description of drawings

Fig. 1 is the block diagram of DC VAR system of the present invention;

Fig. 2 is the block diagram of the present invention's smooth voltage fluctuation system based on sliding mode control and supercapacitor;

Fig. 3 is a schematic diagram of energy transmission of the bidirectional DC-DC converter of the present invention.

detailed description

As shown in Figure 1, the block diagram of the DC VAR system of the present invention uses a supercapacitor as the energy storage device, and the supercapacitor is connected to the DC bus through a bidirectional DC-DC converter to form a bidirectional energy transmission circuit. The inductance current of the bidirectional DC-DC converter and the capacitor voltage on the DC bus are used as the control parameters of the sliding mode variable structure controller and input into the sliding mode variable structure controller. After being processed by the sliding mode variable structure controller, a control signal is generated to control the working mode of the bidirectional DC-DC converter and the conduction duty cycle of the power switch tube, so as to control the charging and discharging of the supercapacitor; form a DC dynamic voltage restorer system to stabilize the voltage fluctuation on the DC bus.

Utilizing the energy storage characteristics of the supercapacitor and the energy bidirectional flow characteristics of the bidirectional DC-DC converter, the sliding mode control is adopted to control the charging and discharging of the supercapacitor according to the value of the DC bus voltage to achieve the purpose of stabilizing the fluctuation of the DC bus voltage.

The bidirectional DC-DC converter adopts a bidirectional half-bridge converter topology. Energy can be transmitted bidirectionally between the input end and the output end, and power can flow not only from the input end to the output end, but also from the output end to the input end. The DC bus is connected to the input end of the bidirectional DC-DC converter; the supercapacitor is connected to the output end of the bidirectional DC-DC converter. The connection relationship between the bidirectional DC-DC converter, the DC bus and the supercapacitor is shown in Figure 2 as a system structure diagram.

The supercapacitor is connected to the output end of the bidirectional DC-DC converter as an energy storage device. When the bidirectional DC-DC converter works in buck mode, the supercapacitor acts as a load, absorbing abundant electric energy from the DC bus for charging and storing the abundant electric energy. When the bidirectional DC-DC converter works in boost (Boost) mode, the supercapacitor acts as a power source to provide power to the DC bus to stabilize the voltage on the DC bus.

The position tracking sliding mode variable structure controller based on reaching law adopts double-loop control; the inner loop tracks and controls the inductor current of the bidirectional DC-DC converter, and the outer loop tracks and controls the capacitor voltage on the DC bus.

Among them, the difference between the reference voltage signal v _ref and the DC bus capacitor voltage v _c is used as an input, which is supplied to the outer loop voltage sliding mode controller. After calculation by the sliding mode controller, the inductor current reference signal i _ref is output.

The difference between the inductance current reference signal i _ref and the inductance current i _L of the bidirectional DC-DC converter is used as an input, which is provided to the inner loop current sliding mode controller, and is calculated by the sliding mode controller to output the duty of the power switch tube of the main circuit than the control signal u .

The duty cycle control signal u controls the turn-on and turn-off of the power switch of the bidirectional DC-DC converter, thereby adjusting the inductor current i _L to make it track a given reference current signal, forming a current inner loop controller. On this basis, the outer loop voltage controller adjusts the capacitor voltage on the DC bus to make it equal to the reference voltage signal, forming a voltage outer loop controller.

At the same time, the reference current signal i _ref passes through the hysteresis control link to control the working mode of the bidirectional DC-DC converter: Buck working mode (reference current i _ref > 0) and Boost working mode (reference current i _ref < 0). The working mode and energy transmission direction of the bidirectional DC-DC converter are shown in Figure 3.

The concrete implementation of the present invention is as follows:

1. Modeling analysis of bidirectional DC-DC converter

According to the state space averaging method, the main circuit of the power stage is modeled, and the state space equations of the bidirectional DC-DC converter in Buck and Boost working modes are respectively established.

2. When charging the supercapacitor, the bidirectional DC-DC converter works in Buck mode. Let the on-duty ratio of the power switch VT1 be D ₁ , and the duty ratio D ₂ of the power switch VT2 is 0 at this time. At the same time, the inductor current and DC bus capacitor terminal voltage are taken as state variables, and the direction of current and voltage is set as the associated reference direction. According to the state space averaging method, the state space equation of the Buck circuit is established as:

(1-1)

v _uc is the voltage across the super capacitor, i _bus is the DC bus current, L is the inductance of the bidirectional DC-DC converter, and C is the value of the super capacitor.

3. When the supercapacitor is discharging, the bidirectional DC-DC converter works in Boost mode. At this time, it is assumed that the conduction duty cycle D ₂ of the power switch tube VT2 and the duty cycle D ₁ of the power switch tube VT1 are 0. According to the state space averaging method, the established Boost circuit state space equation is:

(1-2)

4. Combining formula (1-1) and formula (1-2), the unified state space equation of bidirectional DC-DC can be obtained:

(1-3)

in: (1-4)

5. Design of sliding mode controller

The reaching law of the sliding mode controller is:

(1-5)

Among them: sgn(s) is a symbolic function.

6. Design of sliding mode variable structure controller for DC bus capacitor voltage outer loop

On the basis of the inner loop control of the inductor current, a bidirectional DC-DC DC bus capacitor voltage outer loop sliding mode variable structure controller is designed. Assume . According to formula (1-3), we can get:

(1-6)

According to the design method of the current controller, the control law of the voltage controller can be deduced similarly. Let the reference voltage be v _ref . Take the error as: , the first derivative of the voltage error is:

.

Take the voltage error vector:

7. Take the voltage switching function as:

(1-7)

Then there are:

(1-8)

in: is the coefficient.

Bringing the state equation (1-3) into S1 , the control law of θ can be calculated. which is:

(1-9)

8. Determine the parameters in the control law value. The inductor current reference value i _ref can be deduced from the control law of θ : . Thus, the voltage outer loop control can generate the reference signal i _ref for the current inner loop control.

9. Design of sliding mode variable structure controller for inner loop of inductor current

Assuming the reference current is i _ref , the current error is: ; The first derivative of the error is: .

Take the error vector as: , then the switching function of the inductor current is:

(1-10)

but:

(1-11)

in: is the coefficient.

10. Bring the state equation (1-3) into , the control law of the duty cycle u can be calculated as:

(1-12)

Determining the parameters in the control law value. Realize inner loop sliding mode control.

The sliding mode controller set according to the above is used as a compensation loop, connected with the bidirectional DC-DC converter to form a closed-loop system, and controls the charging and discharging of the supercapacitor energy storage device to form a DC dynamic voltage restorer (VAR) system, thereby Smooth voltage fluctuations on the DC bus.

Claims (1)

1. a kind of to stabilize voltage pulsation method based on sliding formwork control and super capacitor, super capacitor is in parallel even as energy storage device The output end of bidirectional DC-DC converter is connected on, super capacitor is connected on dc bus by bidirectional DC-DC converter, is formed Energy two-way transmission loop；Bidirectional DC-DC converter uses bi-directional half bridge converter topology structure, by bidirectional DC-DC converter Inductive current and dc bus on capacitance voltage as bidirectional DC-DC converter inside Sliding Mode Controller control Parameter, is input in Sliding Mode Controller；Processed through Sliding Mode Controller, produce control signal, control two-way DC- The mode of operation of DC converters and its conducting dutycycle of power switch pipe, you can the discharge and recharge of control super capacitor；Super electricity Hold and bidirectional DC-DC converter forms direct current dynamic electric voltage recovery device system, the voltage pulsation on dc bus is stabilized in realization；

The bidirectional DC-DC converter, the power switch pipe of electric capacity two ends two series connection in parallel on dc bus, two series connection Power switch pipe intermediate point connects super capacitor by inductance, the position tracking Sliding Mode Controller output control based on Reaching Law To two power switch pipe control ends, Sliding Mode Controller uses double -loop control, the two-way DC- of inner ring tracing control to signal processed The inductive current of DC converters, the capacitance voltage on outer shroud tracing control dc bus；

The Sliding Mode Controller includes outer loop voltag sliding mode controller and interior circular current sliding mode controller,

Reference voltage signal v_refWith dc-link capacitance voltage v_cDifference as input, supply outer loop voltag sliding mode controller, By the calculating of sliding mode controller, outputting inductance current reference signal i_ref；Inductive current reference signal i_refBecome with bi-directional DC-DC The inductive current i of parallel operation_LDifference as input, there is provided to interior circular current sliding mode controller, calculated through sliding mode controller, output The duty cycle control signal u of power switch pipe；Duty cycle control signal u control two power switch of bidirectional DC-DC converter Turn-on and turn-off, so as to adjust inductive current i_L, the reference current signal for making its tracking given；Outer loop voltag sliding mode controller is defeated Go out inductive current reference signal i_refBy Hysteresis control link, the working method of bidirectional DC-DC converter is controlled, adjust direct current Capacitance voltage on bus；

Characterized in that, designing the dc-link capacitance outer voltage of bi-directional DC-DC on the basis of the control of inductive current inner ring Sliding Mode Controller, if θ=ui_L, outer voltage choose switching function be：s₁=c₁(v_ref-v_c)+v′_ref-v′_c, by referring to Number Reaching LawRelease control law：

Current inner loop choose switching function be：

s₂=c₂(i_ref-i_L)+i′_ref-i′_L, byReleasing converter switches control law is：

$u=-\frac{L}{c_2*v_C}\&lsqb;c_2*{i^{\&prime;}}_{ref}+{i^{\&prime;\&prime;}}_{ref}+c_2*\frac{v_{uc}}{L}+{\mathrm{\&epsiv;}}_2\mathrm{sgn}\left(S_2\right)+k_2{s}_2\&rsqb;$

Wherein, v_ucIt is super capacitor both end voltage, i_busIt is DC bus current, C is super capacitor output capacitance value, and L is conversion Device inductance value；v′_cIt is output voltage v_cDerivative；i′_LIt is inductive current i_LDerivative；WithRespectively switching function s₁With s₂Derivative；v_refIt is busbar voltage reference value, i_refIt is converter inductive current reference value；v′_refWith v "_refRespectively bus is joined Examine voltage v_refFirst derivative and second dervative；i′_refWith i "_refThe respectively first derivative of converter inductive current reference value And second dervative；Outer voltage controlled output θ and inductive current reference value i_refRelation is：k₁、k₂、ε₁、ε₂、 c₁、c₂It is sliding mode controller parameter, sgn () is sign function.