CN114079392B - AC-DC converter based on constant power load and control method thereof - Google Patents

Abstract

The present disclosure provides an AC-DC converter based on a constant power load and a control method thereof. The method includes: based on the output current i _odc and the DC side voltage v _dc of the switching unit in the AC-DC converter, obtain the power observation value P _CPL of the constant power load. *; Calculate the predicted value i _od1 of the output active current of the AC-DC converter based on the power observation value P _CPL *; Perform nonlinear proportional and integral adjustment based on the output DC voltage v _dc and the reference voltage v _dc * to obtain the reference current correction value △i _od *; based on the reference current correction value △i _od * and predicted value i _od1 *, the reference active component i _od * of the AC output current is obtained; based on the reference active component i _od * of the AC output current and the active component i _od of the AC side line current , the reactive component i _oq of the AC side line current and the reference reactive component i _oq * of the AC output current, the active component v _od and the reactive component v _oq of the AC-DC converter output line voltage are obtained; based on the active component v _od and the reactive power The component v _oq controls the switching unit of the AC-DC converter.

Description

An AC-DC converter based on constant power load and its control method

Technical field

The present disclosure relates to the field of electric power technology, and in particular to an AC-DC converter based on a constant power load and a control method thereof.

Background technique

With the development of distributed new energy, DC microgrids have been increasingly used. Connecting the AC distribution network through an AC-DC converter can greatly improve the power supply reliability of the DC microgrid. When the load converter is connected to a constant resistance, its output power is constant and exhibits constant power characteristics. However, in practical applications, constant power loads may exhibit negative impedance characteristics, which reduces the stability and reliability of the entire power grid system.

Contents of the invention

In view of this, the purpose of this disclosure is to propose an AC-DC converter based on a constant power load and a control method thereof.

Based on the above purpose, the present disclosure provides a control method for an AC-DC converter based on a constant power load, including: based on the output current i _odc and the DC side voltage v _dc of the switching unit in the AC-DC converter, obtaining the constant power load Power observation value P _CPL *;

Calculate the predicted value i _od1 * of the output active current of the AC-DC converter based on the power observation value P _CPL *;

Based on the output DC voltage v _dc and the reference voltage v _dc *, nonlinear proportional integral adjustment is performed to obtain the adjusted output △i _od *; by adding i _od1 * and △i _od *, the reference active component i of the AC output current is obtained _od *.

Based on the reference active component i _od * of the AC output current, the active component i _od of the AC side line current, the reactive component i _oq of the AC side line current, and the reference reactive component i _oq * of the AC output current, the AC-DC transformation is obtained The active component v _od and the reactive component v _oq of the device output line voltage;

The switching unit of the AC-DC converter is controlled based on the active component v _od and the reactive component v _oq .

On the other hand, the present disclosure provides an AC-DC converter, which is controlled using the method according to the first aspect.

It can be seen from the above that the AC-DC converter control method for constant power load provided by the present disclosure uses nonlinear proportional integral and passive control to control the AC-DC converter by observing the constant power load, achieving rapid It tracks load changes, has good dynamic performance, quickly eliminates static errors, and improves the stability and reliability of the power grid system.

Description of the drawings

In order to more clearly illustrate the technical solutions in the present disclosure or related technologies, the drawings needed to be used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings in the following description are only for illustration of the present disclosure. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic main circuit diagram of an AC-to-DC converter according to an embodiment of the present disclosure;

Figure 2 is a schematic schematic diagram of an AC-DC converter control method for a constant power load according to an embodiment of the present disclosure;

Figure 3 is a schematic diagram of AC voltage and current waveforms of an AC-DC converter according to an embodiment of the present disclosure;

Figure 4 is a schematic diagram of the reference value and output value of the active current of the AC-DC converter according to an embodiment of the present disclosure;

Figure 5 is a schematic diagram of a DC voltage reference value and an output value of an AC-DC converter according to an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of constant power load values and observation values of an AC-DC converter according to an embodiment of the present disclosure.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present disclosure more clear, the present disclosure will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of this disclosure should have the usual meanings understood by those with ordinary skills in the field to which this disclosure belongs. The "first", "second" and similar words used in the embodiments of the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprising" mean that the elements or things appearing before the word include the elements or things listed after the word and their equivalents, without excluding other elements or things. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

Constant power load can refer to a load that exhibits constant load power characteristics. The negative impedance characteristic can refer to the characteristic that a circuit or electronic component exhibits an increase in current and a decrease in voltage within a specific voltage range or current range. In a DC microgrid, when the constant power load of the AC-DC converter connected to the AC distribution network exhibits negative impedance characteristics, the stability and reliability of the system will be endangered. Therefore, how to improve the stability and reliability of the system when the constant power load exhibits negative impedance characteristics has become an urgent technical issue that needs to be solved.

In view of this, embodiments of the present disclosure provide a control method for an AC-DC converter for a constant power load. By observing the constant power load, changes in the load can be quickly tracked, static errors can be quickly eliminated, and the stability of the system is improved.

Referring to FIG. 1 , FIG. 1 shows a schematic main circuit diagram of an AC-to-DC converter according to an embodiment of the present disclosure. In Figure 1, the AC-DC converter includes a first inductor L _a1 , a second inductor L _b1 and a third inductor L _c1 . The first ends of the first inductor L _a1 , the second inductor L _b1 and the third inductor L _c1 are respectively connected to AC power grid N, the second end of the first inductor L _a1 is connected to the first end of the first capacitor C _a , the second end of the second inductor L _b1 is connected to the first end of the second capacitor C _b , and the third inductor L The second end of _c1 is connected to the first end of the third capacitor C _c ; the second ends of the first capacitor C _a , the second capacitor C _b and the third capacitor C _c are connected to each other. The first resistor G _fa is connected in parallel with the first capacitor C _a , the second resistor G _fb is connected in parallel with the second capacitor C _b , and the third resistor G _fc is connected in parallel with the first capacitor C _c . The first end of the fourth inductor L _a2 is connected to the connection point of the first inductor L _a1 and the first capacitor C _a , and the second end of the fourth inductor L _a2 is connected to the first end of the fourth resistor R _a1 ; the fifth inductor The first end of L _b2 is connected to the connection point of the second inductor L _b1 and the second capacitor C _b , the second end of the fifth inductor L _b2 is connected to the first end of the fifth resistor R _b1 ; the sixth inductor L _c2 The first terminal is connected to the connection point of the third inductor L _c1 and the third capacitor C _c , and the second terminal of the sixth inductor L _c2 is connected to the first terminal of the sixth resistor R _c1 .

The second end of the fourth resistor R _a1 is connected to the connection point of the first switch S _a1 and the second switch S _a2 , and the second end of the fifth resistor R _b1 is connected to the connection point of the third switch S _b1 and the fourth switch S _b2 point, the second end of the sixth resistor R _c1 is connected to the connection point of the fifth switch _Sc1 and the sixth switch _Sc2 .

The first terminal of the first switch S _a1 , the first terminal of the third switch S _b1 and the first terminal of the fifth switch S _c1 are connected to each other and are recorded as the first connection point; the second terminal of the first switch S a1 and the first terminal of the fifth switch S _c1 are connected to each other. The first end of the second switch S _a2 is connected, the second end of the third switch S _b1 is connected to the first end of the fourth switch S _b2 , the second end of the fifth switch S _c1 is connected to the first end of the sixth switch _Sc connection; and the second terminal of the second switch _Sa2 , the second terminal of the fourth switch _Sb2 and the second terminal of the sixth switch _Sc2 are connected to each other, which is recorded as the second connection point.

The DC capacitor C, the DC side equivalent resistance R ₂ and the constant power load P _CPL are connected between the first connection point and the second connection point.

Referring to FIG. 2 , FIG. 2 shows a schematic schematic diagram of an AC-DC converter control method for a constant power load according to an embodiment of the present disclosure. As shown in Figure 2, the AC-DC converter control method for constant power load can include:

Step S210: Based on the output current i _odc and the DC side voltage v _dc of the switching unit in the AC-DC converter, the power observation value P _CPL * of the constant power load is obtained.

Specifically, the power observation value P _CPL * can be expressed as,

In the formula, P _A is the intermediate variable value, γ is the observer coefficient; R ₂ is the equivalent resistance value of the DC side, C is the DC capacitance, v _dc is the DC side voltage, and _{i odc} is the output current of the switching unit.

The switch unit may include the first switch _Sa1 to the sixth switch S _c2 in Figure 1 , and the output current i _odc of the switch unit is the sum of the currents of the upper bridge arm, that is, the first switch _Sa1 , the third switch S _b1 and The current sum of the fifth switch S _c1 .

Step S220: Calculate the predicted value i _od1 * of the output active current of the AC-DC converter based on the power observation value P _CPL *.

In specific implementation, the predicted value i _od1 * of the output active current can be expressed as:

In the formula, v _d and v _q are the active and reactive components of the AC side line voltage, and i _oq is the reactive component of the AC output current.

In some embodiments, the active component v _d of the AC side line voltage and the reactive component v _q of the AC side line voltage can be calculated based on the dq transformation of the AC side line voltages v _ab , v _bc , and v _ca in the abc coordinate system. For example, the AC side phase voltages v _oa , v _ob , and v _oc can be respectively the sum of the connection points of the first switch S _a1 and the second switch S _a2 , the connection point of the third switch S _b1 and the fourth switch S _b2 in Figure 1 The voltage at the connection point of the fifth switch S _c1 and the sixth switch S _c2 is: AC side line voltage v _{ab =} v _oa - v _ob , AC side line voltage v _{bc =} v _ob - v _oc , AC side line voltage v _{ca =} v _oc - _voa .

In some embodiments, the active component i _od of the AC side line current and the reactive component i _oq of the AC side line current can be calculated by performing dq transformation based on the AC side phase currents i _oa , i _ob , and i _oc . For example, the AC side phase currents i _oa , i _ob , and i _oc may be the output currents of the fourth resistor R _a1 , the fifth resistor R _b1 , and the sixth resistor R _c1 in FIG. 1 respectively.

Step S230: Perform nonlinear proportional and integral adjustment based on the output DC voltage v _dc and the reference voltage v _dc * to obtain the reference current correction value Δi _od *.

In some embodiments, step S230 may further include:

The input deviation e is obtained based on the output DC voltage v _dc and the reference voltage v _dc *;

Nonlinear proportional integral adjustment is performed based on the input deviation e to obtain the reference current correction value Δi _od *.

In specific implementation, as shown in Figure 2, the reference current correction value Δi _od * can be expressed as:

In the formula, k _p and k _i are the proportional coefficient and the integral coefficient respectively, fal is the nonlinear function, e=v _dc *-v _dc is the input deviation, α is the coefficient between 0 and 1, the smaller α, the faster the tracking speed. Fast, but the filtering effect becomes worse. δ is the filter coefficient. The larger the δ, the better the filtering effect.

Step S240: Obtain the reference active component _i od * of the AC output current based on the reference current correction value Δi _od * and the predicted value i _od1 *. In specific implementation, as shown in Figure 2, by adding i _od1 * and △i _od *, the reference active component i _od * of the AC output current can be obtained.

Step S250, based on the reference active component i _od * of the AC output current, the active component i _{od of} the AC side line current, the reactive component i _oq of the AC side line current, and the reference reactive component i _oq * of the AC output current, obtain Describe the active component v _od and the reactive component v _oq of the AC-DC converter output line voltage.

In specific implementation, the active component v _od and the reactive component v _oq can be expressed as:

Among them, L is the equivalent reactance, that is, L = L _a1 + L _a2 = L _b1 + L _b2 = L _c1 + L _c2 , R is the equivalent resistance, that is, R = Ra1 = Rb1 = Rc1, and r ₁₁ is the passive control damping coefficient. .

In some embodiments, the reference reactive component i _oq * of the AC output current may be zero.

Step S260: Control the switching unit of the AC-DC converter based on the active component v _od and the reactive component v _oq .

In some embodiments, step S260 may further include:

Perform dq inverse transformation on the active component v _od and the reactive component v _oq to obtain the output voltage value of the abc coordinate system;

Perform pulse modulation based on the output voltage value of the abc coordinate system to obtain the driving signal of the switch unit;

The switching unit of the AC-DC converter is driven based on the drive signal.

It should be noted that Figure 2 is only an example and is not intended to set the number of AC-DC converters. It can include one or more AC-DC converters. These AC-DC converters can be connected in parallel. When multiple converters are connected in parallel, can be controlled independently, further improving the stability of the system.

Referring to Figures 3 to 6, the initial state output is no-load. At time t4, a 5kW constant power load is put in. At time t5, the constant power load suddenly changes from 5kW to -5kW. Figure 3 shows an AC-DC converter according to an embodiment of the present disclosure. AC voltage and current waveforms of the converter. Figure 4 shows the reference value and output value of the active current of the AC-DC converter according to an embodiment of the present disclosure. Figure 5 shows the DC voltage of the AC-DC converter according to an embodiment of the present disclosure. Reference values and output values, FIG. 6 shows constant power load values and observed values of the AC-DC converter according to embodiments of the present disclosure. As shown in Figures 3 to 6, based on the method of the embodiment of the present disclosure, by observing the constant power load, power changes can be quickly detected without overshoot and oscillation phenomena, and a steady state is reached in about 15 ms. Using nonlinear proportional integral to adjust the input deviation can eliminate the DC voltage error. The DC voltage overshoot and drop are very small, and there is no oscillation. The static error can be eliminated in about 5-10ms. Fast tracking of current instructions is achieved through passive control, so that whether it is an active power step or an active power reverse, it can be quickly tracked and has good dynamic and static characteristics, thus improving the reliability and stability of the power system.

Those of ordinary skill in the art should understand that the discussion of any above embodiments is only illustrative, and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples; under the spirit of the present disclosure, the above embodiments or Technical features in different embodiments may also be combined, steps may be implemented in any order, and there are many other variations of different aspects of the disclosed embodiments as described above, which are not provided in detail for the sake of brevity.

Additionally, to simplify illustration and discussion, and so as not to obscure embodiments of the present disclosure, well-known power supplies/components with integrated circuit (IC) chips and other components may or may not be shown in the provided figures. Ground connection. Furthermore, devices may be shown in block diagram form in order to avoid obscuring the embodiments of the present disclosure, and this also takes into account the fact that details regarding the implementation of these block diagram devices are highly dependent on the implementation of the disclosed embodiments. platform (i.e., these details should be well within the understanding of those skilled in the art). Where specific details (eg, circuits) are set forth to describe exemplary embodiments of the present disclosure, it will be apparent to those skilled in the art that systems may be constructed without these specific details or with changes in these specific details. The embodiments of the present disclosure are implemented below. Accordingly, these descriptions should be considered illustrative rather than restrictive.

The disclosed embodiments are intended to embrace all such alternatives, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present disclosure shall be included in the protection scope of the present disclosure.

Claims (6)

1. A control method for an AC-DC converter based on constant power load, which is characterized by including: Based on the output current i _odc and the DC side voltage v _dc of the switching unit in the AC-DC converter, the power observation value P _CPL * of the constant power load is obtained; Calculate the predicted value i _od1 * of the output active current of the AC-DC converter based on the power observation value P _CPL *; Based on the DC side voltage v _dc and the reference voltage v _dc *, nonlinear proportional integral adjustment is performed to obtain the reference current correction value Δi _od *; Based on the reference current correction value Δi _od * and the predicted value i _od1 *, the reference active component i _od * of the AC output current is obtained; Based on the reference active component i _od * of the AC output current, the active component i _od of the AC side line current, the reactive component i _oq of the AC side line current, and the reference reactive component i _oq * of the AC output current, the AC-DC transformation is obtained The active component v _od and the reactive component v _oq of the device output line voltage; Control the switching unit of the AC-DC converter based on the active component v _od and the reactive component v _oq ; Wherein, the power observation value P _CPL * is: Among them, P _A is the intermediate variable value, γ is the observer coefficient; R ₂ is the equivalent resistance value of the DC side, C is the DC capacitance, v _dc is the DC side voltage, and _{i odc} is the output current of the switching unit; The active component v _od and the reactive component v _oq are: Among them, L is the equivalent reactance value, R is the equivalent resistance value, and r ₁₁ is the passive control damping coefficient; v _d and v _q are the active and reactive components of the AC side line voltage, and i _oq is the reactive component of the AC output current. 2. The method according to claim 1, characterized in that the predicted value i _od1 * of the output active current is 3. The method according to claim 1, characterized in that nonlinear proportional integral adjustment is performed based on the DC side voltage v _dc and the reference voltage v _dc * to obtain the reference current correction value Δi _od *, including: The input deviation e is obtained based on the DC side voltage v _dc and the reference voltage v _dc *; Nonlinear proportional integral adjustment is performed based on the input deviation e to obtain the reference current correction value Δi _od *. 4. The method according to claim 1, characterized in that the reference current correction value Δi _od * is: In the formula, k _p and k _i are the proportional coefficient and the integral coefficient respectively, fal is the nonlinear function, e=v _dc *-v _dc is the input deviation, α is the coefficient between 0 and 1, and δ is the filter coefficient. 5. The method according to claim 1, characterized in that controlling the switching unit of the AC-DC converter based on the active component _vod and the reactive component _voq includes: Perform dq inverse transformation on the active component v _od and the reactive component v _oq to obtain the output voltage value of the abc coordinate system; Perform pulse modulation based on the output voltage value of the abc coordinate system to obtain the driving signal of the switch unit; The switching unit of the AC-DC converter is driven based on the drive signal. 6. An AC-DC converter, characterized in that the method according to any one of claims 1-5 is used for control.