Power prediction control method of doubly-fed motor converter under three-phase imbalance condition

Abstract

The invention relates to a power prediction control method of a doubly-fed motor converter under a three-phase imbalance condition. The power prediction control method comprises the following steps: step 1, constructing a power prediction model of a three-phase voltage source converter under a three-phase power grid voltage imbalance state; 2, predicting a six-power component change value of the three-phase voltage source converter in the next control period based on the power prediction model; step 3, setting a value function and calculating the action duration of the voltage vector in the next control period by minimizing the function; and 4, realizing power switch control of the three-phase voltage source converter by adopting a space vector pulse width modulation technology. The method has the advantages that the active power, the reactive power and the harmonic components of the three-phase voltage source converter with the alternating-current-to-direct-current conversion function in the doubly-fed motor speed regulation system can be controlled under the condition that the three-phase power grid voltage is unbalanced, and the purpose of improving the efficiency and the control performance of the doubly-fed motor speed regulation system is achieved.

Description

Technical Field

[0001] This invention belongs to the field of power conversion technology in new energy technology, specifically relating to a power model prediction control method for a doubly fed motor converter under three-phase unbalanced conditions. Background Technology

[0002] With the increasing proportion of new energy sources, coal-fired power has been given a new mission, becoming a ballast stone for my country's energy security and playing a crucial role in social stability. In recent years, to meet the development needs of energy-efficient and high-performance coal-fired power generation, promoting the structural adjustment of coal-fired power plants and accelerating the high-efficiency and energy-saving retrofitting of coal-fired power units has become of great significance. In coal-fired power units, more than 80% of the plant's operating load is consumed by various rotating auxiliary equipment such as fans and pumps. Improving the operating efficiency of these auxiliary equipment has become one of the important means to improve the quality and efficiency of coal-fired power units. Compared with the traditional method of changing flow by adjusting dampers and gate valves, using variable speed control technology to regulate auxiliary equipment such as fans and pumps can save more than 50% of energy consumption and significantly improve the operating efficiency of the unit, making it one of the important research directions for energy-saving retrofitting of coal-fired power units.

[0003] For fans and pumps in coal-fired power units, speed regulation typically employs a doubly-fed induction generator (DFIG) system. This DFIG speed regulation system usually requires two stages of three-phase power conversion circuits to achieve power conversion, and then uses power control to achieve the DFIG speed regulation function. However, due to the voltage imbalance in the three-phase power grid, the input current of the three-phase converter used for power conversion is distorted, causing fluctuations in the output DC voltage. This can lead to abnormal overheating or even damage to the equipment, and introduce significant harmonic interference into the power grid, resulting in degraded system performance. Therefore, researching control strategies for the three-phase converter under three-phase power grid voltage imbalance conditions is of great significance for improving the stability and control performance of the DFIG speed regulation system, reducing harmonic interference, and increasing system efficiency. Summary of the Invention

[0004] To overcome the shortcomings of existing control methods for three-phase voltage source converters commonly used in doubly-fed induction generator (DFIG) speed control systems under three-phase grid voltage imbalance conditions, this invention aims to provide a power model predictive control method based on six power component conditions. This method establishes a six-power component prediction model for the three-phase voltage source converter under three-phase grid voltage imbalance conditions, and applies model predictive control to achieve overall control of the six power components, thereby improving the control performance of the three-phase voltage source converter under grid imbalance conditions.

[0005] To achieve the above objectives, the technical approach adopted by this invention is: a power model predictive control method for a doubly-fed induction generator converter under three-phase unbalanced conditions, characterized by comprising the following steps:

[0006] Step 1: Construct a power prediction model for the three-phase voltage source converter under the condition of three-phase power grid voltage imbalance;

[0007] Step 2: Based on the power prediction model, predict the six power component transformation values ​​of the three-phase voltage source converter in the next control cycle;

[0008] Step 3: Define the value function and calculate the duration of the voltage vector action in the next control cycle by minimizing the function;

[0009] Step 4: Use space vector pulse width modulation technology to realize the power switching control of the three-phase voltage source converter.

[0010] Step 1, as described above, is specifically performed as follows:

[0011] A novel six-power-component prediction model is established for a three-phase voltage source converter under three-phase grid voltage imbalance conditions, expressed as follows: (1)

[0012] in P is the average value of the active power components of the three-phase voltage source converter. cos2 P is the second cosine component of the active power of the three-phase voltage source converter. sin2 This represents the second sinusoidal component of the active power of the three-phase voltage source converter. This represents the average value of the reactive power components of the three-phase voltage source converter. This represents the second cosine component of the reactive power of the three-phase voltage source converter. This represents the second sinusoidal component of the reactive power of the three-phase voltage source converter. , , , , , These are the power components mentioned above. , P cos2 , P sin2 , , , The derivative; , These represent the three-phase AC voltages U of the three-phase voltage source converter. a U b U c The positive-sequence components in the two-phase rotating (dq) coordinate system , These represent the three-phase AC voltages U of the three-phase voltage source converter. a U b U cThe negative order component in the two-phase rotating (dq) coordinate system , These represent the three-phase input currents I of the three-phase voltage source converter. a , I b , I c The positive-sequence components in the two-phase rotating (dq) coordinate system , These represent the three-phase input currents I of the three-phase voltage source converter. a , I b , I c The negative sequence component in the two-phase rotating (dq) coordinate system; R is the estimated equivalent resistance of the three-phase voltage source converter circuit, L is the estimated input filter inductance of the three-phase voltage source converter; ω=2πf is the angular frequency of the input three-phase AC voltage of the three-phase voltage source converter, f is the frequency of the input three-phase AC voltage; U rd =S d U dc U rq =S q U dc To control the quantity, S d S q The three-phase bridge arm switch states S of the three-phase voltage source converter are respectively. a S b S c The switching components in the two-phase rotating (dq) coordinate system define the three-phase bridge arm switching state S. a S b S c For S i When S = 1 (i = a, b, c), it means that the upper switch of bridge arm i is closed and the lower switch is open. i When =0 (i=a,b,c), it means that the upper switch of bridge arm i is open and the lower switch is closed.

[0013] Step 2, as described above, specifically involves the following operations:

[0014] Define the three-phase bridge arm switching state S of the three-phase voltage source converter. a S b S c Voltage vector V under different combinations of conditions n For V n =[S a S b S cIf n=1,2,…,8, then V1=[0 0 0], V2=[0 0 1], V3=[0 1 0], V4=[0 1 1], V5=[1 0 0], V6=[1 0 1], V7=[1 1 0], V8=[1 1 1], where V2 to V7 are defined as non-zero voltage vectors, and V1 and V8 are defined as zero voltage vectors.

[0015] One three-phase voltage cycle of the AC input of the three-phase voltage source converter is divided into six sectors at 60-degree intervals, specifically defined as follows:

[0016] 1) When the three-phase AC voltage U a >U b >0>U c At this time, it is sector 1. The voltage vector used to control the three-phase voltage source converter should be selected from voltage vectors V1, V3, and V7.

[0017] 2) When the three-phase voltage U b >U a >0>U c At this time, for sector 2, the voltage vector used to control the three-phase voltage source converter should be selected from voltage vectors V1, V5, and V6.

[0018] 3) When the three-phase voltage U b >U c >0>U a When sector 3 is defined, the voltage vector for controlling the three-phase voltage source converter should be selected from voltage vectors V1, V5, and V7.

[0019] 4) When the three-phase voltage U c >U b >0>U a At this time, it is sector 4, and the available subsystem states are V1, V2, and V4;

[0020] 5) When the three-phase voltage U c >U a >0>U b At this time, sector 5, the voltage vector for controlling the three-phase voltage source converter should be selected from voltage vectors V1, V3, and V4.

[0021] 6) When the three-phase voltage U a >U c >0>U b When sector 6 is defined, the voltage vector that enables the control of the three-phase voltage source converter should be selected from voltage vectors V1, V2, and V6.

[0022] Assuming that at the start of the k-th control cycle, the three-phase voltage source converter, under the condition of unbalanced three-phase grid voltage, has the following six power components: (k), P cos2 (k), P sin2 (k), (k), (k), (k). After the operating voltage vector U1 (selected from the two non-zero voltage vectors of the corresponding sector) acts for time T1, the operating voltage vector U2 (selected from the two non-zero voltage vectors of the corresponding sector and cannot be the same as the operating voltage vector U1) acts for time T2, and the operating voltage vector U0 (the zero voltage vector of the corresponding sector) acts for time T0, the six power component values ​​become:

[0023] (5)

[0024] In the formula, , , , , , The predicted value of the six power components of the three-phase voltage source converter for the next control cycle after the kth control cycle, i.e., the k+1 control cycle. , , , , , Each of the six power components , P cos2 ,P sin2 , , , The change in power after the operating voltage vector U0 has been applied for a time T0; , , , , , Each of the six power components , P cos2 , P sin2 , , , The change in power after the operating voltage vector U1 has been applied for a time T1; , , , , , Each of the six power components , P cos2 , Psin2 , , , The power change after the operating voltage vector U2 has been applied for a time T2; the above-mentioned power changes under different operating voltage vectors U j Changes in the six power components under the action of (j=0,1,2) , , , , , (j=0,1,2) represents the vector U applied at different operating voltages. j The changes in the six power components under the action of (j=0,1,2) can be calculated by the prediction model (1), specifically expressed as:

[0025] (6)

[0026] in , , , They represent , , , Squaring operations; , They are control quantities U rd U rq Different operating voltage vectors U j The values ​​under the influence of (j=0,1,2) are as follows:

[0027] ,in and The values ​​under different voltage vectors are:

[0028] When the operating voltage vector U j (j=0,1,2)=V2, U rα The value is -U dc / 3, U rβ The value is When the operating voltage vector U j When (j=0,1,2)=V3, U rα The value is -U dc / 3, U rβ The value is When the operating voltage vector U j (j=0,1,2)=V4, U rα The value is -2U dc / 3, U rβThe value is 0; when the operating voltage vector U j When (j=0,1,2)=V5, U rα The value is 2U dc / 3, U rβ The value is 0; when the operating voltage vector U j When (j=0,1,2)=V6, U rα The value is U dc / 3, U rβ The value is When the operating voltage vector U j When (j=0,1,2)=V7, U rα The value is U dc / 3, U rβ The value is When the operating voltage vector U j (j=0,1,2) = V1 or operating voltage vector U j When (j=0,1,2)=V8, U rα and U rβ The values ​​are all 0.

[0029] Step 3, as described above, is performed as follows:

[0030] The value function J considering the six power components is defined as follows:

[0031]

[0032] (7)

[0034] in , P cos2r , P sin2r , , , They are respectively six power components , P cos2 , P sin2 , , , The expected value.

[0035] By minimizing the value function J, i.e., by taking the derivative of the value function, we obtain the voltage vector action times T0, T1, and T2 that minimize the value function, expressed as:

[0036] (8)

[0037] in This represents taking the partial derivative with respect to the time T1 of the voltage vector's action. This represents taking the partial derivative with respect to the time T2 of the voltage vector's action.

[0038] Based on formulas (2)-(8), we get:

[0039] (9)

[0040] in:

[0041]

[0042] Step 4, as described above, is specifically performed as follows:

[0043] Based on the voltage vector action time calculation results T0, T1, and T2 in step 3, the switching states of different bridge arms of the three-phase voltage source converter are generated according to the space vector pulse width modulation (SVPWM) method.

[0044] The beneficial effects of this invention are:

[0045] This invention proposes a six-power model predictive control method for a three-phase voltage source converter. It comprehensively considers the control requirements of the six power components of the three-phase voltage source converter under unbalanced three-phase power grid conditions, successfully achieving high-efficiency control of the three-phase voltage source converter in such environments. This method offers significant advantages for improving the control performance and efficiency of doubly-fed induction generator (DFIG) speed control systems. Attached Figure Description

[0046] Figure 1 This is a circuit diagram of a three-phase voltage source converter.

[0047] Figure 2 This is a sector division diagram of a three-phase voltage source converter under the input three-phase AC voltage.

[0048] Figure 3 The simulation waveforms of the three-phase input AC voltage and three-phase input AC current of the three-phase voltage source converter using the method of this invention are shown under the condition of unbalanced three-phase power grid voltage.

[0049] Figure 4 The simulation waveform of the DC output voltage of the three-phase voltage source converter using the method of this invention is shown under the condition of unbalanced three-phase power grid voltage.

[0050] Figure 5 The simulation waveforms of the average active and reactive power of the three-phase voltage source converter using the method of this invention are shown under the condition of unbalanced three-phase power grid voltage.

[0051] Figure 6 The simulation waveforms of the sinusoidal and cosine components of active and reactive power of the three-phase voltage source converter using the method of this invention are shown under the condition of unbalanced three-phase power grid voltage. Detailed Implementation

[0052] The technical solutions of the present invention will be explained in detail and comprehensively with reference to the accompanying drawings of the embodiments of the present invention. It should be understood that the provided embodiments represent only some examples of the present invention and not all possible implementations. Other implementations that can be deduced by those skilled in the art based on these embodiments without creative work also fall within the protection scope of the present invention.

[0053] like Figure 1 The three-phase voltage source converter circuit shown has three input AC phase voltages U and U, respectively. a U b U c The three-phase AC input phase currents are respectively I a , I b , I c L is the input filter inductor; R is the equivalent resistance of the circuit; C is the DC-side filter capacitor, U dc This represents the output DC bus voltage.

[0054] Step 1: Construct a power prediction model for the three-phase voltage source converter under the condition of three-phase power grid voltage imbalance;

[0055] A novel six-power-component prediction model is established for a three-phase voltage source converter under three-phase grid voltage imbalance conditions, expressed as follows: (1)

[0056] in P is the average value of the active power components of the three-phase voltage source converter. cos2 P is the second cosine component of the active power of the three-phase voltage source converter. sin2 This represents the second sinusoidal component of the active power of the three-phase voltage source converter. This represents the average value of the reactive power components of the three-phase voltage source converter. This represents the second cosine component of the reactive power of the three-phase voltage source converter. This represents the second sinusoidal component of the reactive power of the three-phase voltage source converter. , , , , , These are the power components mentioned above. , P cos2 , Psin2 , , , The derivative; , These represent the three-phase AC voltages U of the three-phase voltage source converter. a U b U c The positive-sequence components in the two-phase rotating (dq) coordinate system , These represent the three-phase AC voltages U of the three-phase voltage source converter. a U b U c The negative order component in the two-phase rotating (dq) coordinate system , These represent the three-phase input currents I of the three-phase voltage source converter. a , I b , I c The positive-sequence components in the two-phase rotating (dq) coordinate system , These represent the three-phase input currents I of the three-phase voltage source converter. a , I b , I c The negative sequence component in the two-phase rotating (dq) coordinate system; R is the estimated equivalent resistance of the three-phase voltage source converter circuit, L is the estimated input filter inductance of the three-phase voltage source converter; ω=2πf is the angular frequency of the input three-phase AC voltage of the three-phase voltage source converter, f is the frequency of the input three-phase AC voltage; U rd =S d U dc U rq =S q U dc To control the quantity, S d S q The three-phase bridge arm switch states S of the three-phase voltage source converter are respectively. a S b S c The switching components in the two-phase rotating (dq) coordinate system define the three-phase bridge arm switching state S. a S b S c For S i When S = 1 (i = a, b, c), it means that the upper switch of bridge arm i is closed and the lower switch is open. i When =0 (i=a,b,c), it means that the upper switch of bridge arm i is open and the lower switch is closed.

[0057] Step 2: Based on the power prediction model, predict the six power component transformation values ​​of the three-phase voltage source converter in the next control cycle;

[0058] Define the three-phase bridge arm switching state S of the three-phase voltage source converter. a S b S c Voltage vector V under different combinations of conditions n For V n =[S a S b S c If n=1,2,…,8, then V1=[0 0 0], V2=[0 0 1], V3=[0 1 0], V4=[0 1 1], V5=[1 0 0], V6=[1 0 1], V7=[1 1 0], V8=[1 1 1], where V2 to V7 are defined as non-zero voltage vectors, and V1 and V8 are defined as zero voltage vectors.

[0059] One three-phase voltage cycle of the AC input of the three-phase voltage source converter is divided into six sectors at 60-degree intervals, specifically defined as follows:

[0060] 3) When the three-phase AC voltage U a >U b >0>U c At this time, it is sector 1. The voltage vector used to control the three-phase voltage source converter should be selected from voltage vectors V1, V3, and V7.

[0061] 4) When the three-phase voltage U b >U a >0>U c At this time, for sector 2, the voltage vector used to control the three-phase voltage source converter should be selected from voltage vectors V1, V5, and V6.

[0062] 3) When the three-phase voltage U b >U c >0>U a When sector 3 is defined, the voltage vector for controlling the three-phase voltage source converter should be selected from voltage vectors V1, V5, and V7.

[0063] 4) When the three-phase voltage U c >U b >0>U a At this time, it is sector 4, and the available subsystem states are V1, V2, and V4;

[0064] 5) When the three-phase voltage U c >U a >0>U b At this time, sector 5, the voltage vector for controlling the three-phase voltage source converter should be selected from voltage vectors V1, V3, and V4.

[0065] 6) When the three-phase voltage U a >U c >0>U b When sector 6 is defined, the voltage vector that enables the control of the three-phase voltage source converter should be selected from voltage vectors V1, V2, and V6.

[0066] Assuming that at the start of the k-th control cycle, the three-phase voltage source converter, under the condition of unbalanced three-phase grid voltage, has the following six power components: (k), P cos2 (k), P sin2 (k), (k), (k), (k). After the operating voltage vector U1 (selected from the two non-zero voltage vectors of the corresponding sector) acts for time T1, the operating voltage vector U2 (selected from the two non-zero voltage vectors of the corresponding sector and cannot be the same as the operating voltage vector U1) acts for time T2, and the operating voltage vector U0 (the zero voltage vector of the corresponding sector) acts for time T0, the six power component values ​​become:

[0067] (5)

[0068] In the formula, , , , , , The predicted value of the six power components of the three-phase voltage source converter for the next control cycle after the kth control cycle, i.e., the k+1 control cycle. , , , , , Each of the six power components , P cos2 ,P sin2 , , , The change in power after the operating voltage vector U0 has been applied for a time T0; , , , , , Each of the six power components , P cos2 , P sin2 , , , The change in power after the operating voltage vector U1 has been applied for a time T1; , , , , , Each of the six power components , P cos2 , P sin2 , , , The power change after the operating voltage vector U2 has been applied for a time T2; the above-mentioned power changes under different operating voltage vectors U j Changes in the six power components under the action of (j=0,1,2) , , , , , (j=0,1,2) represents the vector U applied at different operating voltages. j The changes in the six power components under the action of (j=0,1,2) can be calculated by the prediction model (1), specifically expressed as:

[0069] (6)

[0070] in , , , They represent , , , Squaring operations; , They are control quantities U rd U rq Different operating voltage vectors U j The values ​​under the influence of (j=0,1,2) are as follows:

[0071] ,in and The values ​​under different voltage vectors are:

[0072] When the operating voltage vector U j (j=0,1,2)=V2, U rα The value is -U dc / 3, U rβ The value is When the operating voltage vector U j When (j=0,1,2)=V3, Urα The value is -U dc / 3, U rβ The value is When the operating voltage vector U j (j=0,1,2)=V4, U rα The value is -2U dc / 3, U rβ The value is 0; when the operating voltage vector U j When (j=0,1,2)=V5, U rα The value is 2U dc / 3, U rβ The value is 0; when the operating voltage vector U j When (j=0,1,2)=V6, U rα The value is U dc / 3, U rβ The value is When the operating voltage vector U j When (j=0,1,2)=V7, U rα The value is U dc / 3, U rβ The value is When the operating voltage vector U j (j=0,1,2) = V1 or operating voltage vector U j When (j=0,1,2)=V8, U rα and U rβ The values ​​are all 0.

[0073] Step 3: Define the value function and calculate the duration of the voltage vector action in the next control cycle by minimizing the function;

[0074] The value function J considering the six power components is defined as follows:

[0075]

[0076] (7)

[0078] in , P cos2r , P sin2r , , , They are respectively six power components , P cos2 , P sin2 , , , The expected value.

[0079] By minimizing the value function J, i.e., by taking the derivative of the value function, we obtain the voltage vector action times T0, T1, and T2 that minimize the value function, expressed as:

[0080] (8)

[0081] in This represents taking the partial derivative with respect to the time T1 of the voltage vector's action. This represents taking the partial derivative with respect to the time T2 of the voltage vector's action.

[0082] Based on formulas (2)-(8), we get:

[0083] (9)

[0084] in:

[0085]

[0086] Step 4: Use space vector pulse width modulation technology to realize the power switching control of the three-phase voltage source converter.

[0087] Based on the voltage vector action time calculation results T0, T1, and T2 in step 3, the switching states of different bridge arms of the three-phase voltage source converter are generated according to the space vector pulse width modulation (SVPWM) method.

[0088] Simulation verification

[0089] The circuit parameters of the three-phase voltage source converter are as follows: the effective value of the three-phase input phase voltage is 220 volts, the angular frequency is ω=2πf=100π, the actual value of the input filter inductor is 50 millihenries, the equivalent resistance of the inductor and circuit is 3 ohms, the output filter capacitor is 1500 microfarads, and the load is 300 ohms. The simulation model parameters are: control period T s It is 0.0001 seconds. For 1200 watts, P cos2r , P sin2r , , , All are 0.

[0090] Figure 2 This is a schematic diagram of dividing a three-phase voltage cycle input to the AC side of a three-phase voltage source converter into six sectors at 60-degree intervals.

[0091] Figure 3The simulation waveforms of the three-phase input AC voltage and input AC current of the three-phase voltage source converter using the method of this invention are shown when they enter steady state under the condition of three-phase grid voltage imbalance. It can be seen that the three-phase input AC voltage exhibits a sinusoidal change but the amplitude is unbalanced, while the waveform of the generated input three-phase AC current exhibits a sinusoidal change and the amplitude is relatively balanced.

[0092] Figure 4 This is a simulation waveform of the DC output voltage of a three-phase voltage source converter when it enters steady state. It can be clearly seen that the waveform reaches steady state in a short time and there is no obvious oscillation. Finally, it stabilizes at 600V.

[0093] Figure 5 The waveforms of the average active power and average reactive power of the voltage source converter when entering steady state are presented, where the black line represents the average active power and the blue line represents the average reactive power. The average active power fluctuates around 1200W when entering steady state, while the average reactive power fluctuates around 0W.

[0094] Figure 6 The waveforms representing the sine and cosine components of active and reactive power show that, in steady state, the second cosine component of active power fluctuates between -2.5W and -1.3W, the second sine component fluctuates between -1.4W and -0.2W, the second cosine component of reactive power fluctuates between 1.4W and 0.2W, and the second sine component fluctuates between -2.5W and -1.3W, all fluctuating near 0W. This demonstrates that the present invention can effectively suppress the sine and cosine components of power under grid imbalance conditions.

[0095] It should be noted that the relational terms mentioned in the text, such as "first" and "second," are used only to distinguish different entities or operations and do not imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," and variations thereof are intended to cover non-exclusive content, thereby allowing a process, method, article, or apparatus that comprises multiple elements to include not only the listed elements but also other elements not expressly listed or inherent elements. An element defined by "comprising one..." does not exclude the presence of other identical elements in the said process, method, article, or apparatus.

[0096] Although embodiments of the invention have been shown and described herein, those skilled in the art will understand that these embodiments can be varied, modified, substituted, and modified without departing from the principles and spirit of the invention. The scope of protection of the invention is defined by the appended claims and their equivalents.

Claims

1. A method of power predictive control of a doubly-fed machine converter under three-phase unbalanced conditions, characterized in that, Includes the following steps: Step 1: Construct a power prediction model for the three-phase voltage source converter under the condition of three-phase power grid voltage imbalance; Step 2: Based on the power prediction model, predict the six power component transformation values ​​of the three-phase voltage source converter in the next control cycle; Step 3: Define the value function and calculate the duration of the voltage vector action in the next control cycle by minimizing the function; Step 4: Use space vector pulse width modulation technology to realize the power switching control of the three-phase voltage source converter.

2. A method of power predictive control of a double-fed machine converter under three-phase unbalanced conditions according to claim 1, characterized in that, Step 1, as described above, is specifically performed as follows: A novel six-power-component prediction model is established for a three-phase voltage source converter under three-phase grid voltage imbalance conditions, expressed as follows: Where P avg P is the average value of the active power components of the three-phase voltage source converter. cos2 P is the second cosine component of the active power of the three-phase voltage source converter. sin2 This represents the second sinusoidal component of the active power of the three-phase voltage source converter. This represents the average value of the reactive power components of the three-phase voltage source converter. This represents the second cosine component of the reactive power of the three-phase voltage source converter. This represents the second sinusoidal component of the reactive power of the three-phase voltage source converter. The above power components P are respectively avg ,P cos2 ,P sin2 , The derivative; These represent the three-phase AC voltages U of the three-phase voltage source converter. a U b U c The positive sequence components in the two-phase rotating (dq) coordinate system These represent the three-phase AC voltages U of the three-phase voltage source converter. a U b U c The negative order component in the two-phase rotating (dq) coordinate system These represent the three-phase input currents I of the three-phase voltage source converter. a ,I b ,I c The positive sequence components in the two-phase rotating (dq) coordinate system These represent the three-phase input currents I of the three-phase voltage source converter. a ,I b ,I c The negative sequence component in the two-phase rotating (dq) coordinate system; R is the estimated equivalent resistance of the three-phase voltage source converter circuit, L is the estimated input filter inductance of the three-phase voltage source converter; ω=2πf is the angular frequency of the input three-phase AC voltage of the three-phase voltage source converter, f is the frequency of the input three-phase AC voltage; U rd =S d U dc U rq =S q U dc To control the quantity, S d S q The three-phase bridge arm switch states S of the three-phase voltage source converter are respectively. a S b S c The switching components in the two-phase rotating (dq) coordinate system define the three-phase bridge arm switching state S. a S b S c For S i When S = 1 (i = a, b, c), it means that the upper switch of bridge arm i is closed and the lower switch is open. i When =0 (i=a,b,c), it means that the upper switch of the i-th bridge arm is open and the lower switch is closed.

3. A method of power predictive control of a double-fed machine converter under three-phase unbalanced conditions according to claim 1, characterized in that, Step 2, as described above, is specifically performed as follows: Define the three-phase bridge arm switching state S of the three-phase voltage source converter. a S b S c Voltage vector V under different combinations of conditions n For V n =[S a S b S c If n = 1, 2, ..., 8, then V1 = [000], V2 = [001], V3 = [010], V4 = [011], V5 = [100], V6 = [101], V7 = [110], V8 = [111], where V2 to V7 are defined as non-zero voltage vectors, and V1 and V8 are defined as zero voltage vectors. One three-phase voltage cycle of the AC input of the three-phase voltage source converter is divided into six sectors at 60-degree intervals, specifically defined as follows: 1) when three-phase alternating voltage U a >U b >0>U c , sector 1. It is defined that the voltage vector for implementing the three-phase voltage source converter control at this time should be selected from voltage vectors V1, V3, V7; 2) when three-phase voltage U b >U a >0>U c is sector 2, the voltage vector that implements the three-phase voltage source inverter control at this time should be selected from the voltage vectors V1, V5, V6; 3) when three-phase voltage U b >U c >0>U a , sector 3, the voltage vector that implements the three-phase voltage source converter control at this time should be selected from the voltage vectors V1, V5, V7; 4) when three-phase voltage U c >U b >0>U a is sector 4, the voltage vector that implements the three-phase voltage source inverter control at this time should be selected from voltage vectors V1, V2, V4; 5) when three-phase voltage U c >U a >0>U b , sector 5, define the voltage vector should be selected from the voltage vector V1, V3, V4 when the three-phase voltage source converter control is implemented; 6) When the three-phase voltage U a >U c >0>U b At this time, sector 6, the voltage vector for controlling the three-phase voltage source converter should be selected from voltage vectors V1, V2, and V6. Assuming that at the beginning of the k-th control cycle, the three-phase voltage source converter, under the condition of unbalanced three-phase grid voltage, has six power components P... avg (k),P cos2 (k),P sin2 (k), After the operating voltage vector U1 (selected from the two non-zero voltage vectors of the corresponding sector) acts for a time T1, the operating voltage vector U2 (selected from the two non-zero voltage vectors of the corresponding sector and cannot be the same as the operating voltage vector U1) acts for a time T2, and the operating voltage vector U0 (the zero voltage vector of the corresponding sector) acts for a time T0, the six power component values ​​become: In the formula, P avg (k+1), P cos2 (k+1), P sin2 (k+1), The predicted six power components of the three-phase voltage source converter for the next control cycle after the k-th control cycle, i.e., the k+1 control cycle; E pavg0 E pcos0 E psin0 E qavg0 E qcos0 E qsin0 They are six power components P avg ,P cos2 ,P sin2 , The change in power after the operating voltage vector U0 has been applied for a time T0; E pavg1 E pcos1 E psin1 E qavg1 E qcos1 E qsin1 They are six power components P avg ,P cos2 ,P sin2 , The change in power after the operating voltage vector U1 has been applied for a time T1; E pavg2 E pcos2 E psin2 E qavg2 E qcos2 E qsin2 They are six power components P avg ,P cos2 ,P sin2 , The power change after the operating voltage vector U2 has been applied for a time T2; the above-mentioned power changes under different operating voltage vectors U j The changes in the six power components E under the action of (j=0,1,2) pavgj E pcosj E psinj E qavgj E qcosj E qsinj (j = 0, 1, 2) represents the vector U applied at different operating voltages. j The changes in the six power components under the action of (j=0,1,2) can be calculated by the prediction model (1), and are specifically expressed as follows: in They represent Squaring operations; They are control quantities U rd U rq Different operating voltage vectors U j The values ​​under the influence of (j=0,1,2) are as follows: where U rα and U rβ The values at different voltage vectors are: When the operating voltage vector U j When (j=0,1,2)=V2, U rα The value is -U dc / 3, U rβ The value is When the operating voltage vector U j When (j=0,1,2)=V3, U rα The value is -U dc / 3, U rβ The value is When the operating voltage vector U j When (j=0,1,2)=V4, U rα The value is -2U dc / 3, U rβ The value is 0; when the operating voltage vector U j When (j=0,1,2)=V5, U rα The value is 2U dc / 3, U rβ The value is 0; when the operating voltage vector U j When (j=0,1,2)=V6, U rα The value is U dc / 3, U rβ The value is When the operating voltage vector U j When (j=0,1,2)=V7, U rα The value is U dc / 3, U rβ The value is When the operating voltage vector U j (j=0,1,2)=V1 or operating voltage vector U j When (j=0,1,2)=V8, U rα and U rβ The values ​​are all 0.

4. The power prediction and control method for a doubly-fed induction generator converter under three-phase unbalanced conditions according to claim 1, characterized in that, Step 3, as described above, is specifically performed as follows: The value function J considering the six power components is defined as follows: where P avgr , cos2r , sin2r , are the expected values of the six power components P avg , cos2 , sin2 , respectively. By minimizing the value function J, i.e., by taking the derivative of the value function, we obtain the voltage vector action times T0, T1, and T2 that minimize the value function, expressed as: wherein denotes the partial derivative with respect to the voltage vector application time T1, denotes the partial derivative with respect to the voltage vector application time T2, Based on formulas (2)-(8), we get: T0=T S -T1-T2 (9) in: M0=A0A1+B0B1+C0C1+D0D1+E0E1+F0F1 M1 = A1 2 + B1 2 + C1 2 + D1 2 + E1 2 + F1 2 M2=A1A2+B1B2+C1C2+D1D2+E1E2+F1F2 N0=A0A2+B0B2+C0C2+D0D2+E0E2+F0F2 N1=A1A2+B1B2+C1C2+D1D2+E1E2+F1F2 N2 = A2 2 + B2 2 + C2 2 + D2 2 + E2 2 + F2 2 .

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