CN109617075A - A control method of a multifunctional bidirectional power converter - Google Patents

Abstract

The invention discloses a kind of control methods of multi-function double-way power inverter, the described method comprises the following steps: obtaining operating instruction current value through normalized, the sagging control of active reactive according to voltage and current value, active reactive power；According to voltage and current value, the Harmonic currents detection based on FBD Power Theory, detects ac bus harmonic current and obtain harmonic wave command current value；When falling with voltage on line side or when imbalance fault, transformer be added in bidirectional power converter exchange side, is controlled by Voltage Feedback, obtains the command voltage value that control bidirectional power converter is run；According to alternating current-direct current mixing micro-capacitance sensor load, power distribution network real-time condition, in conjunction with operation, harmonic wave command current value, and command voltage value, control bidirectional power converter run on different mode, make bidirectional power converter have the function of administering harmonic wave and stablize ac bus voltage.The present invention achievees the purpose that administer ac bus harmonic current by bidirectional power converter.

Description

A control method of a multifunctional bidirectional power converter

technical field

The invention relates to the field of bidirectional power converters, in particular to a control method of a multifunctional bidirectional power converter.

Background technique

With the increasing number of distributed energy sources, AC-DC hybrid microgrids have attracted more and more attention as an effective means to efficiently utilize distributed energy sources. The AC-DC hybrid microgrid has the characteristics of both the AC microgrid and the DC microgrid, and is an important part of the future smart grid. A typical AC-DC hybrid microgrid consists of an AC sub-network, a DC sub-network, and a bidirectional power converter connected between the AC and DC sub-networks and the interface of the large grid. The bidirectional power converter is the core of energy control in the AC-DC hybrid microgrid and has been widely studied and used. However, when the AC-DC hybrid microgrid is connected to distributed energy and nonlinear loads through the power electronic interface, the The bus current is distorted. In addition, when the voltage on the distribution network side drops, swells or changes unbalanced, the AC bus voltage will also change accordingly. The above factors will inevitably affect the normal operation of the sensitive load of the AC sub-network. operation and threaten the safety of power electronic devices. Therefore, it is particularly important to ensure the power quality of the AC-DC hybrid microgrid through the bidirectional power converter.

At present, the traditional control strategies of AC/DC bidirectional power converters include voltage and current double closed-loop control, PQ (active and reactive) control, and V-F (voltage-frequency) control. The voltage and current double closed-loop control strategy has a simple structure and good robustness, but it aims at stabilizing the DC side voltage, but cannot control the transmission power of the AC and DC sub-networks. PQ and V-F control strategies can achieve seamless switching from power control mode to voltage and frequency control mode, but PQ and V-F control require a dedicated communication network and cannot make real-time adjustments according to changes in microgrid load.

In addition, some scholars have proposed a bidirectional power converter control strategy suitable for grid-connected and islanded modes. This strategy introduces active power control terms on the basis of voltage control, and solves the problem of power balance between AC and DC sub-grids when grid-connected. On this basis, another scholar proposed an improved droop control strategy for bidirectional power converters, which not only ensures the power balance between AC and DC sub-grids, but also adds a shutdown mode to avoid frequent actions of power electronic devices.

Although the above two control strategies achieve power balance between AC and DC sub-networks and further solve the problem of frequent operation of power electronic devices, they both regard the AC sub-network as an ideal situation, and do not consider the AC bus current distortion and the voltage on the distribution network side. When changing, the operating state of the sensitive load connected to the AC bus. Therefore, it is urgent to propose a control strategy for a multifunctional bidirectional power converter, which can control the harmonic current of the AC bus on the basis of ensuring the power balance of the AC and DC sub-networks, and when the voltage on the distribution network side changes, it can be adjusted. The voltage of the AC bus ensures the normal operation of sensitive loads.

SUMMARY OF THE INVENTION

The invention provides a control method of a multifunctional bidirectional power converter. On the basis of ensuring the power balance of the AC and DC sub-networks, the invention can achieve the purpose of controlling the harmonic current of the AC bus through the bidirectional power converter, and make the AC The busbar voltage is maintained in a normal operating state and is not affected by voltage fluctuations in the distribution network to ensure the normal operation of sensitive loads. See the description below for details:

A control method of a multifunctional bidirectional power converter, the method comprises the following steps:

According to the voltage and current value, active and reactive power, after normalization, active and reactive droop control, the running command current value is obtained;

According to the voltage and current value and the harmonic current detection based on FBD power theory, detect the harmonic current of the AC bus to obtain the harmonic command current value;

When the voltage on the distribution network side drops or an unbalanced fault occurs, a transformer is added to the AC side of the bidirectional power converter, and through voltage feedback control, the command voltage value for controlling the operation of the bidirectional power converter is obtained;

According to the load of the AC-DC hybrid microgrid and the real-time situation of the distribution network, combined with the operation, harmonic command current value, and command voltage value, the bidirectional power converter is controlled to operate in different modes, so that the bidirectional power converter can control harmonics and stabilize AC. function of the bus voltage.

Wherein, the active and reactive power droop control is specifically:

U _m =U _r -k _pi (P _ac -P ₁ )

δ _ac =δ _ac ^* +k _qi (Q _ac -Q ₁ )

In the formula: k _pi and k _qi are the droop coefficients of active power and reactive power, respectively; U _r and δ _ac ^* are the voltage amplitude and phase angle reference value of phase A on the AC side, respectively; P ₁ and Q ₁ are the AC side, respectively Active power and reactive power reference values; U _m , δ _ac are the actual values of the AC side A-phase voltage amplitude and voltage corresponding phase angle; P _ac , Q _ac are the actual values of the AC side active power and reactive power respectively;

U _dc =U _dc ^* -k _dc (P _dc -P _dc ^* )

In the formula: k _dc is the active power droop coefficient; U _dc ^* and P _dc ^* are the DC bus voltage reference value and active power reference respectively; U _dc , P _dc are the actual values.

Further, the running command current value is specifically:

I _dref =2P _tref /(3U _d )

In the formula, U _d , U _q , I _d , and I _q are the d-axis and q-axis components of the actual output voltage of the bidirectional power converter, and the d-axis and q-axis components of the actual output current;

I _qref =2Q _ref /(3U _d )

In the formula, S _rate is the rated apparent power of the bidirectional power converter, Q _ref is the reference value of the reactive transmission power of the bidirectional power converter, U _d , U _q , I _d , and I _q are the actual output voltage of the bidirectional power converter, respectively d-axis, q-axis components, actual output current d-axis, q-axis components.

Wherein, the harmonic command current value is specifically obtained by inputting the three-phase harmonic currents i _ah , _ibh , and i _ch into the abc/dq module;

Among them, i _al+ , i _bl+ and i _cl+ are the three-phase fundamental currents; i _a , i _b and _ic are the three-phase currents of the microgrid; I ₁₊ is the fundamental current amplitude; is the initial phase angle of the A-phase fundamental current; w is the angular velocity.

The method further includes obtaining the command voltage value through coordinate transformation according to the voltage value to be compensated.

Further, the control of the bidirectional power converter to operate in different modes according to the real-time conditions of the AC-DC hybrid microgrid load and the distribution network in combination with the operation, the harmonic command current value, and the command voltage value is as follows:

When the AC bus has no nonlinear load and the microgrid voltage conditions are good, the bidirectional power converter operates in the rectification or inverter mode;

When it is detected that the AC bus has a non-linear load, the bidirectional power converter works in the harmonic control mode;

When the distribution network voltage fluctuates within 2% of the rated value, it does not affect the normal operation of the AC bus load, and the harmonic detection based on the FBD power theory is carried out normally.

The beneficial effects of the technical scheme provided by the present invention are:

1. When the load of the AC/DC sub-network changes, the control strategy can control the AC/DC bidirectional power converter to work in different modes according to the actual situation, and the control strategy only needs to collect the voltage and current information of the AC and DC sub-network, and does not need to pass additional communication network and upper-level scheduling;

2. When the voltage of the distribution network fluctuates within 2% of the rated value, it will not affect the normal operation of the AC bus load, and the harmonic detection based on the FBD power theory can also be carried out normally, so that the bidirectional power converter can operate in more Multiple working conditions.

Description of drawings

Figure 1 is a topology diagram of an AC-DC hybrid microgrid;

Figure 2 is a flowchart of the harmonic current detection method based on FBD (Fryze-Buchholz-Depenbrock) power theory ^[1] ;

Fig. 3 is the change diagram of the voltage and current of AC bus A-phase when the bidirectional power converter operates in rectification and inversion;

Fig. 4 is the change diagram of the active power output by the AC/DC sub-network and the active power output by the bidirectional power converter;

Fig. 5 is the change diagram of the DC bus voltage;

Fig. 6 is the change diagram of the voltage and current of phase A of the AC bus when the bidirectional power converter performs harmonic current control;

Figure 7a shows the AC bus current distortion rate when the bidirectional power converter does not perform harmonic control;

Fig. 7b shows the current distortion rate of the AC bus when the rectification mode of the bidirectional power converter is used for harmonic control;

Figure 7c shows the current distortion rate of the AC bus when the bidirectional power converter inverter mode performs harmonic control;

Figure 8 is a change diagram of the three-phase voltage of the distribution network when the voltage drops and is unbalanced;

Fig. 9 is a three-phase voltage change diagram of an AC bus load;

Figure 10 is a three-phase current change diagram of the AC bus load;

FIG. 11 is a three-phase compensation current conversion diagram output by a bidirectional power converter.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention are further described in detail below.

Example 1

The embodiment of the present invention provides a control method for a multifunctional bidirectional power converter, the method controls the bidirectional power converter to work in different operation modes, so that the bidirectional power converter has the functions of controlling harmonics and stabilizing the AC bus voltage, including: The following steps:

101: Detect the voltage and current values of the system according to the selected AC-DC hybrid microgrid, and simultaneously calculate the active and reactive power of the AC-DC hybrid microgrid;

102: According to the voltage and current values, active and reactive power obtained in step 101, through normalization processing and active and reactive power droop control, the command current value I dref for controlling the operation of the bidirectional power converter and the state of good power quality is obtained, I _dref , I _qref ;

103: According to the voltage and current values obtained in step 101, the harmonic current of the AC bus is detected by the harmonic current detection method based on the FBD power theory, and the harmonic command current values I _1dref and I _{1qref are obtained} ;

104: According to the voltage and current values obtained in step 101, when the voltage on the distribution network side drops or an unbalanced fault occurs, the topology of the AC-DC hybrid microgrid changes, and a transformer needs to be added to the AC side of the bidirectional power converter to feedback the voltage through the voltage feedback. control to obtain command voltage values U _dref and U _qref for controlling the operation of the bidirectional power converter;

105: Control the bidirectional power converter according to the real-time conditions of the AC/DC hybrid microgrid load and distribution network, in combination with the above-mentioned command current values I _dref , I _qref , I _1dref , I _1qref , and command voltage values U _dref , U _qref run in different modes.

To sum up, the embodiment of the present invention achieves the purpose of controlling the harmonic current of the AC bus through the bidirectional power converter on the basis of ensuring the power balance of the AC and DC sub-networks through the above steps 101 to 105, and makes the AC The busbar voltage is maintained in a normal operating state and is not affected by voltage fluctuations in the distribution network, ensuring the normal operation of sensitive loads.

Example 2

The scheme in Embodiment 1 is further introduced below in conjunction with specific calculation formulas and examples, and is described in detail below:

201: According to the selected AC-DC hybrid microgrid, detect and calculate the system parameters of the AC-DC hybrid microgrid;

Wherein, the detected AC-DC hybrid microgrid system parameters in step 201 are:

1) Three-phase voltage U _a , U _b , U _c of distribution network point, three-phase current I _a , I _b , I _c of distribution network point, frequency f of grid-connected point;

2) The three-phase voltages U _ac , U _bc , U _cc of the AC bus, the three-phase currents I _ac , I _bc , and I _cc of the AC bus, and the phase-locked loop is used to detect the amplitudes corresponding to the three-phase voltages U _ac , U _bc , and U _cc . the value U _m and the phase angles δ _ac , δ _bc , δ _cc ;

3) DC bus voltage U _dc , DC bus current I _dc .

Wherein, the calculated AC-DC hybrid microgrid system parameters in step 201 are:

(1) Calculate the active power of the AC bus: P _ac =U _ac *I _ac +U _bc *I _bc +U _cc *I _cc (1)

(2) Calculate the reactive power of the AC bus:

(3) Calculate the active power of the DC bus: P _dc =U _dc *I _dc (3)

(4) Calculate the active power of the distribution network: P ₂ =U _a *I _a +U _b *I _b +U _c *I _c (4)

(5) Calculate the reactive power of the distribution network:

(6) Input the three-phase voltages U _ac , U _bc and U _cc of the AC bus into the coordinate transformation module abc/dq0 to obtain the AC bus voltage d and the q-axis components U _d and U _q ;

(7) Input the three-phase currents I _ac , I _bc and I _cc of the AC bus into the abc/dq0 module to obtain the AC bus current d and the q-axis components I _d and I _q .

202: According to the voltage and current, active and reactive power of the AC-DC hybrid microgrid system provided in step 201, through normalization processing and active and reactive power droop control, the command current value for controlling the operation of the bidirectional power converter and the state of good power quality is obtained I _dref , I _qref ;

Wherein, this step 202 includes:

(1) Determine the active and reactive droop characteristics of the AC side of the bidirectional power converter:

U _m =U _r -k _pi (P _ac -P ₁ ) (6)

δ _ac = δ _ac ^* +k _qi (Q _ac -Q ₁ ) (7)

In the formula: k _pi and k _qi are the droop coefficients of active power and reactive power, respectively; U _r and δ _ac ^* are the voltage amplitude and phase angle reference value of phase A on the AC side, respectively; P ₁ and Q ₁ are the AC side, respectively Active power and reactive power reference values; U _m , δ _ac are the actual values of the AC side A-phase voltage amplitude and voltage corresponding phase angle; P _ac , Q _ac are the actual values of the AC side active power and reactive power, respectively.

(2) Determine the droop characteristics of the DC side of the bidirectional power converter:

U _dc =U _dc ^* -k _dc (P _dc -P _dc ^* ) (8)

In the formula: k _dc is the active power droop coefficient; U _dc ^* and P _dc ^* are the DC bus voltage reference value and active power reference respectively; U _dc , P _dc are the actual values.

(3) Calculate the reference coefficient of power transmission of the AC-DC hybrid microgrid, and the reference value of active transmission power P _tref through normalization processing.

λ=(U _ac.norm -U _dc.norm ) (11)

P _tref = (P _tmax ×λ)/2 (12)

In the formula, U _ac.norm and U _dc.norm are the normalized values of the AC and DC bus voltages; U _ac and U _dc are the actual values of the AC and DC sub-network bus voltages; U _ac.max , U _ac.min are the AC voltages The maximum and minimum values of the sub-network bus voltage; U _dc.max and U _dc.min are the maximum and minimum values of the DC sub-network bus voltage.

The rated value of the DC bus voltage is 750V, and the fluctuation range of the actual value is within 2% of the rated value. According to the voltage tolerance regulation, let: U _ac.max = 230V, U _ac.min = 210V, U _dc.max = 760V, U _dc.min = 740V. P _tmax is the maximum value of active power transmitted by the bidirectional power converter.

(4) Calculate the d-axis current reference value I _dref of the bidirectional power converter.

I _dref = 2P _tref /(3U _d ) (14)

In the formula, U _d , U _q , I _d , and I _q are the d-axis and q-axis components of the actual output voltage of the bidirectional power converter, and the d-axis and q-axis components of the actual output current. When the grid voltage is balanced, U _q is zero. , and after calculating P _tref , the d-axis current reference value I _dref of the bidirectional power converter can be obtained.

(5) Calculate the q-axis current reference value I _qref of the bidirectional power converter.

I _qref = 2Q _ref /(3U _d ) (17)

In the formula, S _rate is the rated apparent power of the bidirectional power converter, Q _ref is the reference value of the reactive transmission power of the bidirectional power converter, U _d , U _q , I _d , and I _q are the actual output voltage of the bidirectional power converter, respectively The d-axis and q-axis components, the d-axis and q-axis components of the actual output current, when the grid voltage is balanced, U _q is zero. According to this, after calculating Q _ref , the q-axis current reference value I of the bidirectional power converter can be obtained. _qref .

203 : According to the voltage and current parameters of the AC/DC hybrid microgrid system provided in step 201, detect the harmonic current of the AC bus by the harmonic current detection method based on the FBD power theory, and obtain the harmonic command current values I _1dref and I _1qref , based on the FBD power The flow chart of the theoretical harmonic current detection method is shown in Figure 2.

Wherein, this step 203 includes:

(1) In order to reduce the influence of the distortion asymmetric voltage on the current measurement result, the three-phase voltage can be replaced by the voltage phase-locked loop signals u _pa , u _pb , and u _pc . When the voltage of the distribution network drops or the three phases are unbalanced, it does not affect the detection of harmonic currents. Harmonic current detection only uses load voltage phase information, independent of its magnitude.

(2) The load in the actual circuit is equivalent to an ideal conductance element, and it is considered that the power in the circuit is consumed on these equivalent conductances.

In the formula, U _m is the grid voltage amplitude, I _n+ and I _n- are the amplitudes corresponding to the positive sequence current and the negative sequence current, is the initial phase angle corresponding to the positive sequence current and the negative sequence current.

(3) The AC components in conductance and susceptance are filtered out by a low-pass filter, and the remaining part is the fundamental active conductance G ₁ and reactive susceptance B ₁ .

in, It is the remaining conductance and susceptance after filtering out the AC components in conductance G and susceptance B through a low-pass filter.

(4) The three-phase fundamental current i _al+ , i _bl+ and i _cl+ can be expressed as:

(5) The three-phase harmonic currents i _ah , i _bh and i _ch can be expressed as:

(6) Input the three-phase harmonic currents I _ah , I _bh , and I _ch into the abc/dq module, and calculate the harmonic command current values I _1dref and I _1qref .

204: According to the voltage and current parameters of the AC/DC hybrid microgrid system provided in step 201, when the voltage on the distribution grid side drops or an unbalanced fault occurs, the AC/DC hybrid microgrid topology changes, and a transformer needs to be added to the AC side of the bidirectional power converter. Through the voltage feedback control, the commanded voltage values U _dref and U _qref to control the operation of the bidirectional power converter are obtained. The AC-DC hybrid microgrid topology is shown in Figure 1.

Wherein, this step 204 includes:

(1) The three-phase voltage of the AC bus load can be expressed as:

In the formula, the first item on the right side is the fundamental voltage component, U is the fundamental voltage RMS value, the second item is the sum of the harmonic voltage components of each order, and U _i is the harmonic voltage RMS value of each order harmonic.

(2) Applying the instantaneous power theory to the three-phase system, the three-phase voltage can be expressed as:

(3) Filter out all harmonic components through the low-pass filter LPF to obtain the DC component Then, the three-phase fundamental voltages u _ar , u _br , and u _cr are obtained by inverse coordinate transformation.

(4) Calculate the voltage that the bidirectional power converter needs to compensate:

In the formula, u _ref is the reference voltage of the distribution network. Obtain the voltage values u _a1 , u _b1 , and u _c1 that need to be compensated. After coordinate transformation, the command voltage values U _derf and U _qerf for controlling the operation of the bidirectional power converter can be obtained.

205: According to the detection results of steps 202-204, obtain the command current or command voltage value of the bidirectional power converter, and determine that the bidirectional power converter operates in different modes.

That is, when the AC bus has no nonlinear load and the microgrid voltage conditions are good, the bidirectional power converter operates in the rectification or inverter mode.

When it is detected that the AC bus has a non-linear load, the bidirectional power converter works in a harmonic control mode (a professional term in this field, which will not be repeated here).

When the distribution network voltage fluctuates within 2% of the rated value, it will not affect the normal operation of the AC bus load, and the harmonic detection based on FBD power theory can also be performed normally.

When the voltage of the distribution network fluctuates greatly, the topology of the AC-DC hybrid microgrid will change. In this case, a transformer needs to be added to the AC side of the bidirectional power converter for voltage compensation.

To sum up, the embodiment of the present invention achieves the purpose of controlling the harmonic current of the AC bus through the bidirectional power converter on the basis of ensuring the power balance of the AC and DC sub-networks through the above steps 201 to 205, and makes the AC The busbar voltage is maintained in a normal operating state and is not affected by voltage fluctuations in the distribution network, ensuring the normal operation of sensitive loads.

Example 3

Below in conjunction with Fig. 3-Fig. 11, feasibility verification is carried out to the scheme in embodiment 1 and 2, see the following description for details:

Based on the control of the multifunctional bidirectional power converter, the embodiment of the present invention realizes the current, voltage and power quality control of the AC-DC hybrid microgrid. For the example of the present invention can be simulated with MATLAB, the bidirectional power converter can be operated in three modes.

(1) Mode 1: The bidirectional power converter operates in rectification or inverter mode

Fig. 3 is the change diagram of the voltage and current of the AC bus A phase when the bidirectional power converter is running in rectification and inversion; Fig. 4 is the change diagram of the active power output by the AC and DC sub-network and the active power output by the bidirectional power converter; Fig. 5 is the DC Graph of bus voltage change. It can be seen from Figure 3 and Figure 5 that the bidirectional power converter works in _{rectification} or inverter mode, and the DC bus voltage can be kept stable. The active power P _dc waveform changes are basically the same, which can verify the power balance from the AC and DC sub-networks.

(2) Mode 2: The bidirectional power converter operates in the harmonic control mode

Fig. 6 is the change diagram of the voltage and current of AC bus A phase when the bidirectional power converter is performing harmonic current control; Fig. 7a is the current distortion rate of the AC bus when the bidirectional power converter is not performing harmonic current control; Fig. 7b is the rectification mode of the bidirectional power converter The current distortion rate of the AC bus during harmonic control. Figure 7c shows the current distortion rate of the AC bus when the bidirectional power converter is in the inverter mode for harmonic control. It can be seen from Figure 6 that the two-way power converter can perform harmonic current control whether it is working in the rectification or inversion state. In the process of changing from rectification to inverter state, the harmonic current management is carried out synchronously. It can be seen from Figure 7b and Figure 7c that the bidirectional power converter has a good effect on the control of harmonic current. The ratio of each harmonic to the fundamental current is less than 1.1%. The harmonic current is controlled and the power quality of the microgrid is improved. .

(3) Mode 3: The bidirectional power converter operates in the voltage compensation mode

Figure 8 is the change diagram of the three-phase voltage of the distribution network when the voltage drops and unbalanced; Figure 9 is the change diagram of the three-phase voltage of the AC bus load; Figure 10 is the change diagram of the three-phase current of the AC bus load; Figure 11 is the output of the bidirectional power converter The three-phase compensation current change diagram. It can be seen from the above figure that when the three-phase voltage of the distribution network drops and is unbalanced, the bidirectional power converter can output the compensation current, so that the AC bus load can run normally and stably.

references

[1] Shi Ye, Wu Zaijun, Dou Xiaobo, et al. Improved FBD harmonic current detection algorithm based on adaptive principle [J]. Power Grid Technology, 2014, 38(04): 1051-1058.

Shi Ye, Wu Zaijun, Dou Xiaobo et al. Adaptive Theory Based Improved FBDAlgorithm for Harmonic Current Detection[J]. Power System Technology, 2014, 38(04): 1051-1058.

Those skilled in the art can understand that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the above-mentioned serial numbers of the embodiments of the present invention are only for description, and do not represent the advantages or disadvantages of the embodiments.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (6)

1. A method of controlling a multifunctional bidirectional power converter, the method comprising the steps of:

obtaining an operation instruction current value through normalization processing and active and reactive droop control according to the voltage current value and the active and reactive power;

detecting the harmonic current of the alternating current bus according to the voltage current value and the harmonic current detection based on the FBD power theory to obtain a harmonic instruction current value;

when the voltage of the distribution network side has a drop or unbalance fault, a transformer is added at the alternating current side of the bidirectional power converter, and a command voltage value for controlling the operation of the bidirectional power converter is obtained through voltage feedback control;

according to the real-time conditions of the load and the power distribution network of the alternating-current and direct-current hybrid micro-grid, the operation, harmonic command current values and command voltage values are combined to control the bidirectional power converter to operate in different modes, so that the bidirectional power converter has the functions of controlling harmonic waves and stabilizing alternating-current bus voltage.

2. The control method of the multifunctional bidirectional power converter according to claim 1, wherein the active and reactive droop control is specifically:

U_m＝U_r-k_pi(P_ac-P₁)

δ_ac＝δ_ac ^*+k_qi(Q_ac-Q₁)

in the formula: k is a radical of_pi、k_qiDroop coefficients of active power and reactive power respectively; u shape_r、δ_ac ^*Respectively is an amplitude value and a phase angle reference value of the A phase voltage at the alternating current side; p₁、Q₁Respectively taking active power reference values and reactive power reference values at an alternating current side; u shape_m、δ_acThe actual values of the amplitude value and the corresponding phase angle of the voltage of the A-phase voltage at the alternating current side are obtained; p_ac、Q_acActual values of active power and reactive power at the alternating current side are respectively;

U_dc＝U_dc ^*-k_dc(P_dc-P_dc ^*)

in the formula: k is a radical of_dcThe active power droop coefficient; u shape_dc ^*、P_dc ^*Respectively representing a direct current bus voltage reference value and an active power reference; u shape_dc、P_dcIs the actual value.

3. The method according to claim 1, wherein the operation command current value is specifically:

I_dref＝2P_tref/(3U_d)

in the formula of U_d、U_q、I_d、I_qThe method comprises the steps that d-axis and q-axis components of actual output voltage of a bidirectional power converter and d-axis and q-axis components of actual output current are respectively obtained;

I_qref＝2Q_ref/(3U_d)

in the formula, S_rateRated apparent power, Q, for a bidirectional power converter_refFor reactive transmission of a reference value of power, U, for a bidirectional power converter_d、U_q、I_d、I_qThe two-way power converter outputs d-axis and q-axis components of voltage actually and d-axis and q-axis components of current actually respectively.

4. The method according to claim 1, wherein the harmonic command current value is specifically: three-phase harmonic current i_ah、i_bh、i_chInputting an abc/dq module, and calculating to obtain the Ab/dq module;

wherein i_al+、i_bl+And i_cl+Is three-phase fundamental current; i.e. i_a、i_bAnd i_cThree-phase current of the micro-grid; i is₁₊Is the fundamental current amplitude;is the initial phase angle of A-phase fundamental wave current; w is the angular velocity.

5. The control method of a multifunctional bidirectional power converter as recited in claim 1, wherein the command voltage value is obtained by coordinate transformation according to the voltage value to be compensated.

6. The method for controlling the multifunctional bidirectional power converter according to claim 1, wherein the controlling the bidirectional power converter to operate in different modes according to real-time conditions of loads of the alternating current/direct current hybrid micro-grid and a power distribution network, and by combining operation, harmonic command current values and command voltage values specifically comprises:

when the alternating current bus has no nonlinear load and the voltage working condition of the microgrid is good, the bidirectional power converter operates in a rectification or inversion mode;

when the alternating current bus is detected to have the nonlinear load, the bidirectional power converter works in a harmonic suppression mode;

when the voltage of the power distribution network fluctuates within 2% of the rated value, the normal operation of the alternating current bus load is not influenced, and the harmonic detection based on the FBD power theory is normally carried out.