CN104300589A - Hierarchical control method for ad/dc microgrid with direct voltage recovery character - Google Patents

Abstract

The invention relates to a hierarchical control method for an ad/dc microgrid with the direct voltage recovery character. The method comprises two layers of control, wherein in the first layer of control, a direct voltage-active power droop control method is adopted, and even load allocation is achieved; in the second layer of control, a method for compensating for the direct current bus voltage reference value is adopted for the direct current bus voltage drop caused by the droop control, the recovery of the bus voltage is achieved, and the quality of the direct current bus voltage is guaranteed. According to the method, the even power distribution during load changing of a local power source is achieved while the quality of the direct current bus voltage is guaranteed.

Description

A kind of alternating current-direct current micro-capacitance sensor hierarchical control method possessing direct voltage recovery characteristics

Technical field

The present invention relates to the control method in a kind of micro-capacitance sensor, specifically relate to a kind of alternating current-direct current micro-capacitance sensor hierarchical control method possessing direct voltage recovery characteristics.

Background technology

Micro-capacitance sensor refers to the small-sized electric system of being transported to be made up of distributed power source, energy storage device, energy conversion device, load, monitoring and protective device etc., be one can teaching display stand control, the autonomous system of protect and manage.Adopt the form of alternating current-direct current mixing micro-capacitance sensor, eliminate many transform parts and converting means, make microgrid structure simple, control more flexible, loss reduces, and improves economy and the reliability of whole system.In order to realize the connection between power supply and load, generally adopting the multiple methods such as the control of centralized control, master & slave control, electric current chain and Average Current Control, by controlling power electronic equipment, realizing the uniform distribution of load power between each parallel connection converter.But these control methods are only for pure interchange micro-capacitance sensor and direct-current grid, mostly need to rely on the transmission that HF communication line realizes current command signal.HF communication line can reduce the reliability of system, elevator system maintenance cost.Adopt droop control means in addition, also can cause Voltage Drop, reduce the stability of voltage.Therefore a kind of control method is provided, with while the uniform distribution realizing DC load, can quality of voltage be improved.

Summary of the invention

For the deficiencies in the prior art, the object of this invention is to provide a kind of alternating current-direct current micro-capacitance sensor hierarchical control method possessing direct voltage recovery characteristics, the method meets distributed frame requirement in micro-capacitance sensor, devise control strategy, while guarantee DC bus-bar voltage quality, realize the power uniform distribution of local power supply when load change.

The object of the invention is to adopt following technical proposals to realize:

The invention provides a kind of alternating current-direct current micro-capacitance sensor hierarchical control method possessing direct voltage recovery characteristics, described method is applicable to there is two or more AC converter connection between alternating current-direct current bus, and described alternating current-direct current micro-capacitance sensor comprises the interchange micro-grid system and DC micro power grid system that are connected by AC/DC current transformer; The interchange interface of described interchange micro-grid system is connected on micro-capacitance sensor ac bus; The DC interface of described DC micro power grid system is connected on micro-capacitance sensor DC bus;

Its improvements are, described method is by the second layer control realization that the ground floor of power-direct voltage droop control controls and common electric voltage recovery controls.

Further, described ground floor control in power-direct voltage droop control comprise the power output of AC converter (AC converter refers to the DC-AC two way convertor between DC bus and ac bus) and the direct voltage of output controlled; Calculate input power error delta P, obtain direct voltage reference value U according to the sagging relation of P-V _dcref', the voltage modulation signal P of AC converter is produced through electric current and voltage dicyclo _m; The controller that ground floor controls to adopt comprises: current inner loop controller and direct voltage ring controller.

Further, the quality of power supply that described current inner loop controller exports for improving AC converter, dynamic response is fast;

Described current inner loop controller adopts the dq0 rotating coordinate system based on park transforms thought, under three-phase instantaneous value signal is transformed to dq0 rotating coordinate system, three phase controls is converted into two phase controls; Three-phase instantaneous value current i _abcdq axle component i is become through park transforms _dq, the reference signal i exported with direct voltage ring controller _dqrefcompare, and PI control output voltage control signal P is carried out to error _m;

Ring controller in the decoupling zero that current inner loop controller adopts uncompensated link, comprising: alternating current pi controller G _pI, AC converter transfer function G _pWM, the inertial element G of AC converter _delay, the transfer function G of inductance filter and circuit _f; Expression formula is respectively as shown in the formula 1) ~ 4) shown in:

$G_{\mathrm{PI}}=k_1(1+\frac{1}{T_{1}s})---1);$

In formula, k ₁and T ₁be respectively proportionality coefficient and the integration time constant of current inner loop controller;

G _PWM＝K _PWM 2)；

In formula, K _pWMfor the gain of inverter;

$G_{\mathrm{Delay}}=\frac{1}{1+T_{D}s}---3);$

In formula, T _dfor time constant;

$G_F=\frac{1}{\mathrm{Ls}+R}---4);$

In formula, L and R is respectively equivalent inductance and the resistance of filter and circuit.

Electric current loop closed loop transfer function, is as shown in the formula 5) shown in:

$G_{\mathrm{Current}}\left(s\right)=\frac{G_{\mathrm{PI}}{G}_{\mathrm{PWM}}{G}_{\mathrm{Delay}}{G}_F}{1+G_{\mathrm{PI}}{G}_{\mathrm{PWM}}{G}_{\mathrm{Delay}}{G}_F}---5).$

Further, described direct voltage ring controller is used for the control to direct voltage and reactive power, simultaneously the reference signal I of ring controller in generation current _ref, dynamic response is slow;

Direct voltage ring controller adoption rate-integral controller, measures the direct voltage obtained and compares with reference voltage, controls to obtain inner ring current i through PI _dreference signal, AC side of converter electric current q axle component i _q; Reference value is set as 0; Direct voltage ring controller comprises: direct voltage PI controller G _pI, electric current loop transfer function G _current, for connecting the transfer function G of AC converter alternating current and direct voltage _udc-I, its expression formula is drawn by power conservation;

When not relating to AC converter loss, AC converter alternating current-direct current both sides meet power conservation relation, as shown in the formula 6) shown in:

e _di _d+e _qi _q＝i _Lu _dc 6)；

In formula, e _dand e _qbe respectively d, q axle component of AC voltage; u _dcfor DC bus-bar voltage; i _lfor AC converter DC side flows to the electric current in DC micro power grid system direction;

By formula 6) carry out small-signal analysis, and by results conversion to s territory:

e _dΔi _d+i _dΔe _d+e _qΔi _q+i _qΔe _q＝i _LΔu _dc+u _dcΔi _L 7)；

If AC voltage three-phase symmetrical, and meeting unity power factor, when only relating to the interference of d shaft current, solving:

$\frac{{\mathrm{\ΔU}}_{\mathrm{dc}}}{{\mathrm{\Δi}}_d}=\frac{e_d}{i_L}---8);$

Transform to s territory, namely

$G_{\mathrm{Udc}-i}=\frac{{\mathrm{\ΔU}}_{\mathrm{dc}}}{{\mathrm{\Δi}}_d}=\frac{E_d\left(s\right)}{I_L\left(s\right)}---9);$

Direct current pressure ring closed loop transfer function, is as shown in the formula 10):

$G_{\mathrm{voltage}}\left(s\right)=\frac{U_{\mathrm{dc}}\left(s\right)}{U_{\mathrm{dcref}}\left(s\right)}=\frac{G_{\mathrm{PI}}{G}_{\mathrm{Current}}{G}_{\mathrm{Udc}-I}}{1+G_{\mathrm{PI}}{G}_{\mathrm{Current}}{G}_{\mathrm{udc}-I}}---10).$

Further, the common electric voltage during the described second layer controls recovers to control for compensating the Voltage Drop that droop control causes, and improves the quality of voltage of DC bus; The controller that the second layer controls to adopt comprises droop control device and secondary controller.

Further, described droop control operation principle is: the initial launch point of AC converter is A, the rated power P of output ₀, DC side bus rated voltage is U ₀; When DC micro power grid system internal loading increases suddenly or distributed power source power output reduces, AC converter power output increases, and cause voltage drop, system operating point becomes B;

The pass of active-power P and direct voltage U is:

U＝U ₀+(P ₀-P)K 11)；

In formula, K is sagging coefficient;

Droop control device adoption rate controller, measures the active power obtained and compares with the reference active power of P-V droop control, obtain the compensation rate of voltage reference value through droop control; Droop control device comprises: Voltage loop transfer function G _voltage, for connecting the transfer function G of converter active power and direct voltage _udc-P;

The relation of current transformer active power of output and voltage is as shown in the formula 12) shown in, carry out small-signal analysis, and by results conversion to s territory, obtain as shown in the formula 13):

$P=\frac{U^2}{R_L}---12);$

$\frac{\mathrm{\ΔP}}{\mathrm{\ΔU}}=\frac{2}{R_L}---13);$

In formula, R _lfor load resistance; for being that independent variable is differentiated to P with U, Δ P represents active power increment, and Δ U represents voltage increment.

Further, described secondary controller is used for controlling the recovery of DC side busbar voltage, described secondary controller adoption rate-integral controller, measures the direct voltage obtained and compares with reference voltage, control through PI the compensation rate obtaining voltage reference value; G _pIfor linear quadratic control PI controller, G _voltagefor direct current pressure ring transfer function.

Compared with the prior art, the beneficial effect that the present invention reaches is:

The invention provides a kind of voltage resume control method based on direct voltage-active power droop control, the operation being applicable to alternating current-direct current mixing micro-capacitance sensor controls; Realize the load uniform distribution between local different converter, carry out linear quadratic control simultaneously, busbar voltage reference value is compensated, thus reach the object of voltage resume.Method provided by the invention not only can ensure the quality of voltage of DC bus, the uniform distribution of load can also be realized simultaneously, improve the reliability of micro-capacitance sensor, tool is controlled to safe, stable, the reliability service of alternating current-direct current mixing micro-capacitance sensor and is of great significance.

Accompanying drawing explanation

Fig. 1 is alternating current-direct current mixing micro-capacitance sensor structure chart provided by the invention;

Fig. 2 is voltage resume control structure figure provided by the invention;

Fig. 3 is current inner loop controller architecture figure provided by the invention;

Fig. 4 is direct voltage ring structure block diagram provided by the invention;

Fig. 5 is droop control schematic diagram provided by the invention;

Fig. 6 is droop control structured flowchart provided by the invention;

Fig. 7 is linear quadratic control structured flowchart provided by the invention.

Fig. 8 is the grid-connected schematic diagram of current transformer provided by the invention;

Fig. 9 is two inverter parallel structural topology figure provided by the invention;

Figure 10 is direct voltage amplitude waveform when the invention provides voltage resume effect;

Figure 11 the invention provides voltage resume used time power waveform;

Figure 12 is direct voltage amplitude waveform when the invention provides load fluctuation;

Figure 13 is power waveform when the invention provides load variations.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.

The present invention propose a kind of newly can improve the control method of DC bus quality to the load uniform distribution of alternating current-direct current power distribution network.Control method of the present invention, ground floor controls the droop control method adopting direct voltage-active power, achieves load uniform distribution; The DC bus-bar voltage that the second layer controls to cause for droop control is fallen, and adopts the method for compensating direct current busbar voltage reference value, realizes the recovery of busbar voltage, ensure that the quality of DC bus-bar voltage.

Typical alternating current-direct current mixing micro-capacitance sensor structure as shown in Figure 1.Adopt the form of alternating current-direct current mixing micro-capacitance sensor, eliminate many transform parts and converting means, make microgrid structure simple, control more flexible, loss reduces, and improves economy and the reliability of whole system.

Alternating current-direct current micro-capacitance sensor comprises the interchange micro-grid system and DC micro power grid system that are connected by AC/DC current transformer; The interchange interface of described interchange micro-grid system is connected on micro-capacitance sensor ac bus; The DC interface of described DC micro power grid system is connected on micro-capacitance sensor DC bus;

Described interchange micro-grid system comprises at least one AC/DC current transformer, DC/AC current transformer, photovoltaic DC-to-AC converter, energy storage inverter, AC blower fan, alternating current generator and AC load; Described AC/DC current transformer, alternating current generator and AC load all access on the ac bus of micro-capacitance sensor; Photovoltaic DC-to-AC converter is connected with one of them AC/DC current transformer; Energy storage inverter is connected with one of them AC/DC current transformer; One of them AC/DC current transformer, DC/AC current transformer are connected successively with AC blower fan;

Described DC micro power grid system comprises at least one DC/DC rectifier, DC/AC current transformer, photovoltaic DC-to-AC converter, energy storage inverter, DC fan and DC load; Described DC/DC rectifier and DC/AC current transformer all access on the DC bus of micro-capacitance sensor; Photovoltaic DC-to-AC converter is connected with one of them DC/DC rectifier; Energy storage inverter is connected with one of them DC/DC rectifier; DC load is connected with one of them DC/DC rectifier.

The voltage resume of the present invention's design controls to comprise two-layer, and as indicated with 2, ground floor controls as power-direct voltage droop control its structure chart, controls the power output of every platform AC converter and direct voltage output.Calculate input power error delta P and obtain direct voltage reference value U _dcref, the modulation signal Pm of AC converter is produced through electric current and voltage dicyclo.Wherein direct voltage ring controller is mainly used in ensureing the control to direct voltage and reactive power, simultaneously the reference signal Iref of generation current inner ring, and common dynamic response is slower.Current inner loop mainly carries out meticulous control, and for improving the quality of power supply that AC converter exports, common dynamic response is very fast.The second layer controls, for public voltage resume controls, in order to compensate the Voltage Drop that droop control causes, to improve the quality of voltage of bus.Whole control strategy links Controller gain variations is as follows.

(1) current loop controller

Inner ring current controller adopts and controls based under the dq0 rotating coordinate system of park transforms thought, under three-phase instantaneous value signal is transformed to dq0 rotating coordinate system, thus three-phase control problem is converted into two-phase control problem.Three-phase instantaneous value current i _abcdq axle component i is become through park transforms _dq, the reference signal i exported with direct voltage ring controller _dqrefcompare, and PI control output voltage control signal P is carried out to error _m.

Ring controller in the decoupling zero that the present invention adopts uncompensated link, its structure as shown in Figure 3.Wherein, G _pIfor alternating current pi controller, G _pWMfor converter transfer function, G _delayfor the inertial element of converter, G _ffor the transfer function of inductance filter and circuit.The expression formula of above-mentioned three is shown in formula 1) ~ 4) formula.

$G_{\mathrm{PI}}=k_1(1+\frac{1}{T_{1}s})---1);$

In formula, k1 and T1 is respectively proportionality coefficient and the integration time constant of current controller.

G _PWM＝K _PWM 2)

In formula, k _pWMfor the gain of inverter.

$G_{\mathrm{Delay}}=\frac{1}{1+T_{D}s}---3);$

In formula, TD is time constant.

$G_F=\frac{1}{\mathrm{Ls}+R}---4);$

In formula, L and R is respectively equivalent inductance and the resistance of filter and circuit.Inverter outlet filter and the line impedance lump between inverter with bus are become LR cascade, and because circuit is shorter, have ignored line capacitance impact herein, schematic diagram as grid-connected in current transformer provided by the invention as shown in Figure 8.

To sum up, electric current loop closed loop transfer function, is:

$G_{\mathrm{Current}}\left(s\right)=\frac{G_{\mathrm{PI}}{G}_{\mathrm{PWM}}{G}_{\mathrm{Delay}}{G}_F}{1+G_{\mathrm{PI}}{G}_{\mathrm{PWM}}{G}_{\mathrm{Delay}}{G}_F}---5);$

(2) direct voltage ring controller:

Direct current pressure ring controls adoption rate-integral controller, and measurement obtains direct voltage and will compare with reference voltage, and control through PI the reference signal obtaining inner ring current i d, iq reference value is set as 0.The control structure of direct current pressure ring as shown in Figure 4.Wherein, G _pIfor direct voltage PI controller, G _currentfor electric current loop transfer function, G _udc-Ifor the transfer function for connecting converter alternating current and direct voltage, its expression formula is drawn by power conservation.

Specifically, when not considering transducer loose, converter alternating current-direct current both sides meet power conservation relation, such as formula 6):

e _di _d+e _qi _q＝i _Lu _dc 6)；

In formula, e _d, e _qbe respectively d, q axle component of AC voltage; Udc is DC bus-bar voltage; i _lbe respectively the electric current that converter DC side flows to direct-current grid direction.

Formula (6) is carried out small-signal analysis, and by results conversion to s territory, can obtain

e _dΔi _d+i _dΔe _d+e _qΔi _q+i _qΔe _q＝i _LΔu _dc+u _dcΔi _L 7)；

If AC voltage three-phase symmetrical, and meeting unity power factor, when only considering that d shaft current is disturbed, solving

$\frac{{\mathrm{\ΔU}}_{\mathrm{dc}}}{{\mathrm{\Δi}}_d}=\frac{e_d}{i_L}---8);$

Transform to s territory, namely

$G_{\mathrm{Udc}-i}=\frac{{\mathrm{\ΔU}}_{\mathrm{dc}}}{{\mathrm{\Δi}}_d}=\frac{E_d\left(s\right)}{I_L\left(s\right)}---9);$

To sum up, direct current pressure ring closed loop transfer function, is:

$G_{\mathrm{voltage}}\left(s\right)=\frac{U_{\mathrm{dc}}\left(s\right)}{U_{\mathrm{dcref}}\left(s\right)}=\frac{G_{\mathrm{PI}}{G}_{\mathrm{Current}}{G}_{\mathrm{Udc}-I}}{1+G_{\mathrm{PI}}{G}_{\mathrm{Current}}{G}_{\mathrm{udc}-I}}---10);$

(3) droop control device

Droop control device is a kind of control method of imitating generating set power frequency static characteristic, and its control principle as shown in Figure 5.

In Fig. 5, the initial launch point of converter is A, the rated power P0 of output, and DC side bus rated voltage is V0.When direct-current grid internal loading increases suddenly or distributed power source power output reduces, converter power output increases, and cause voltage drop, system operating point becomes B.

The pass that can be provided active-power P and direct voltage U by Fig. 5 is

U＝U ₀+(P ₀-P)K 11)；

In formula, K is sagging coefficient;

Droop control device adoption rate controller, control structure figure as shown in Figure 6.Measurement obtains active power and will compare with reference power, obtains the compensation rate of voltage reference value through droop control.Wherein, G _voltagefor Voltage loop transfer function, G _udc-Pfor the transfer function for connecting converter active power and direct voltage.

The relation of power and voltage is such as formula 12) shown in, carry out small-signal analysis, and by results conversion to s territory, formula 13 can be obtained).

$P=\frac{U^2}{R_L}---12);$

$\frac{\mathrm{\ΔP}}{\mathrm{\ΔU}}=\frac{2}{R_L}---13);$

In formula, R _lfor load resistance; for being that independent variable is differentiated to P with U, Δ P represents active power increment, and Δ U represents voltage increment.

(4) secondary controller:

Linear quadratic control adoption rate-integral controller, measurement obtains direct voltage and will compare with reference voltage, controls through PI the compensation rate obtaining voltage reference value.The control structure of direct current pressure ring as shown in Figure 7.Wherein, G _pIfor linear quadratic control PI controller, G _voltagefor Voltage loop transfer function.

Embodiment

Below adopt Digsilent software to be described control strategy of the present invention and Steady state and transient state control effects thereof under two converter paired running modes, network topological diagram as shown in Figure 9.

Two converters all adopt voltage resume to control, but reference voltage U0 is 0.7kV parameter difference, and other network parameters are as shown in table 1.DC side is connected to two direct current constant-resistance loads and a distributed DC power.Voltage reference value 1kV.

Table 1 simulation example optimum configurations table

When emulation starts, two converters are according to droop control uniform power distribution, and during t=0.5s, voltage resume controls to start effect, and as shown in Figure 10, the power output waveform of two converters as indicated at 11 for DC voltage waveform now.As can be seen from Figure 10 and Figure 11, before voltage resume effect, busbar voltage is stabilized in 0.69kV, and the power output of two converters is stabilized in 0.48MW and 0.36MW respectively, achieve load all with distribution.Linear quadratic control puts into operation, and through about 0.1s, system reaches new steady s tate, and busbar voltage is stabilized in 0.70kV, illustrates that the voltage resume of secondary controls well to ensure that the quality of DC bus-bar voltage, demonstrates the validity of voltage resume control method; The power output of two converters is stabilized in 0.50MW and 0.37MW respectively, and under demonstrating the acting in conjunction controlled at droop control and voltage resume, two converters, according to respective reference power and sagging coefficient, have carried out uniform distribution to load power.

During t=1s, excised by load Load1, as shown in figure 12, the power output waveform of two converters as shown in figure 13 for DC voltage waveform.As can be seen from Figure 12 and Figure 13, after load variations, system is through the transient process of about 0.02s, reach new steady operational status, busbar voltage is still stabilized in 0.70kV, illustrate that the voltage resume of secondary controls well to ensure that the quality of DC bus-bar voltage, the antijamming capability that voltage resume controls meets the demands; The power output of two converters drops to 0.32MW and 0.24MW respectively, demonstrates under the effect of load fluctuation, and two converters, according to respective reference power and sagging coefficient, achieve the uniform distribution to local load.

To sum up, the present invention can realize the uniform distribution that AC converter is meritorious under alternating current-direct current mixing micro-capacitance sensor stable state and transient condition, ensure that DC bus-bar voltage is stablized simultaneously.

Finally should be noted that: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit; although with reference to above-described embodiment to invention has been detailed description; those of ordinary skill in the field still can modify to the specific embodiment of the present invention or equivalent replacement; these do not depart from any amendment of spirit and scope of the invention or equivalent replacement, are all applying within the claims of the present invention awaited the reply.

Claims (7)

1. possess an alternating current-direct current micro-capacitance sensor hierarchical control method for direct voltage recovery characteristics, the described method alternating current-direct current bus that therebetween there is multiple AC Substation, described alternating current-direct current micro-capacitance sensor comprises the AC and DC micro-grid system connected with current transformer; The interchange interface of described interchange micro-grid system is connected on micro-capacitance sensor ac bus; The DC interface of described DC micro power grid system is connected on micro-capacitance sensor DC bus;

It is characterized in that, described method adopts the second layer that the ground floor of power-direct voltage droop control controls and common electric voltage recovers to control to control.

2. alternating current-direct current micro-capacitance sensor hierarchical control method as claimed in claim 1, is characterized in that, the power-direct voltage droop control during described ground floor controls comprises and controlling the power output of AC converter and the direct voltage of output; Calculate input power error delta P, obtain direct voltage reference value U according to the sagging relation of P-V _dcref', the voltage modulation signal P of AC converter is produced through electric current and voltage dicyclo _m; The controller that ground floor controls comprises: current inner loop controller and direct voltage ring controller.

3. alternating current-direct current micro-capacitance sensor hierarchical control method as claimed in claim 2, is characterized in that, the quality of power supply that described current inner loop controller exports for improving AC converter, and dynamic response is fast;

Described current inner loop controller adopts the dq0 rotating coordinate system based on park transforms thought, under three-phase instantaneous value signal is transformed to dq0 rotating coordinate system, three phase controls is converted into two phase controls; By three-phase instantaneous value current i _abcdq axle component i is become through park transforms _dq, the reference signal i exported with direct voltage ring controller _dqrefcompare, and PI control is carried out with output voltage control signal P to error _m;

Current inner loop controller be uncompensated link decoupling zero in ring controller, comprising: alternating current pi controller G _pI, AC converter transfer function G _pWM, the inertial element G of AC converter _delay, the transfer function G of inductance filter and circuit _f; Expression formula is respectively as shown in the formula 1) ~ 4) shown in:

$G_{\mathrm{PI}}=k_1(1+\frac{1}{T_{1}s})---1);$

In formula, k ₁and T ₁be respectively proportionality coefficient and the integration time constant of current inner loop controller;

G _PWM＝K _PWM 2)；

In formula, K _pWMfor the gain of inverter;

$G_{\mathrm{Delay}}=\frac{1}{1+T_{D}s}---3);$

In formula, T _dfor time constant;

$G_F=\frac{1}{\mathrm{Ls}+R}---4);$

In formula, L and R is respectively equivalent inductance and the resistance of filter and circuit.

Electric current loop closed loop transfer function, is as shown in the formula 5) shown in:

$G_{\mathrm{Current}}\left(s\right)=\frac{G_{\mathrm{PI}}{G}_{\mathrm{PWM}}{G}_{\mathrm{Delay}}{G}_F}{1+G_{\mathrm{PI}}{G}_{\mathrm{PWM}}{G}_{\mathrm{Delay}}{G}_F}---5).$

4. alternating current-direct current micro-capacitance sensor hierarchical control method as claimed in claim 2, is characterized in that, described direct voltage ring controller is used for the control to direct voltage and reactive power, simultaneously the reference signal I of ring controller in generation current _ref, dynamic response is slow;

Described direct voltage ring controller proportional-plus-integral controller, compares the direct voltage measured with it with reference voltage, controls to obtain inner ring current i through PI _dreference signal, AC side of converter electric current q axle component i _q; Reference value is set as 0; Direct voltage ring controller comprises: direct voltage PI controller G _pI, electric current loop transfer function G _current, for connecting the transfer function G of AC converter alternating current and direct voltage _udc-I, its expression formula is drawn by power conservation;

When not relating to AC converter loss, AC converter alternating current-direct current both sides meet power conservation relation, as shown in the formula 6) shown in:

e _di _d+e _qi _q＝i _Lu _dc 6)；

In formula, e _dand e _qbe respectively d, q axle component of AC voltage; u _dcfor DC bus-bar voltage; i _lfor AC converter DC side flows to the electric current in DC micro power grid system direction;

By formula 6) carry out small-signal analysis, and by results conversion to s territory:

e _dΔi _d+i _dΔe _d+e _qΔi _q+i _qΔe _q＝i _LΔu _dc+u _dcΔi _L 7)；

If AC voltage three-phase symmetrical, and meeting unity power factor, when only relating to the interference of d shaft current, solving:

$\frac{\mathrm{\Δ}{U}_{\mathrm{dc}}}{{\mathrm{\Δi}}_d}=\frac{e_d}{i_L}---8);$

Transform to s territory, namely

$G_{\mathrm{Udc}-i}=\frac{{\mathrm{\ΔU}}_{\mathrm{dc}}}{\mathrm{\Δid}}=\frac{E_d\left(s\right)}{I_L\left(s\right)}---9);$

Direct current pressure ring closed loop transfer function, is as shown in the formula 10):

$G_{\mathrm{voltage}}\left(s\right)=\frac{U_{\mathrm{dc}}\left(s\right)}{U_{\mathrm{dcref}}\left(s\right)}=\frac{G_{\mathrm{PI}}{G}_{\mathrm{Current}}{G}_{\mathrm{Udc}-I}}{1+G_{\mathrm{PI}}{G}_{\mathrm{Current}}{G}_{\mathrm{Udc}-I}}---10).$

5. alternating current-direct current micro-capacitance sensor hierarchical control method as claimed in claim 1, is characterized in that, the common electric voltage during the described second layer controls recovers to control for compensating the Voltage Drop that droop control causes, and improves the quality of voltage of DC bus; The controller that the second layer controls to adopt comprises droop control device and secondary controller.

6. alternating current-direct current micro-capacitance sensor hierarchical control method as claimed in claim 5, it is characterized in that, described droop control operation principle is: the initial launch point of AC converter is A, the rated power P of output ₀, DC side bus rated voltage is U ₀; When DC micro power grid system internal loading increases suddenly or distributed power source power output reduces, AC converter power output increases, and cause voltage drop, system operating point becomes B;

The pass of active-power P and direct voltage U is:

U＝U ₀+(P ₀-P)K 11)；

In formula, K is sagging coefficient;

Droop control device adoption rate controller, measures the active power obtained and compares with the reference active power of P-V droop control, obtain the compensation rate of voltage reference value through droop control; Droop control device comprises: Voltage loop transfer function G _voltage, for connecting the transfer function G of converter active power and direct voltage _udc-P;

The relation of current transformer active power of output and voltage is as shown in the formula 12) shown in, carry out small-signal analysis, and by results conversion to s territory, obtain as shown in the formula 13):

$P=\frac{U^2}{R_L}---12);$

$\frac{\mathrm{\ΔP}}{\mathrm{\ΔU}}=\frac{2}{R_L}---13);$

In formula, R _lfor load resistance; for being that independent variable is differentiated to P with U, Δ P represents active power increment, and Δ U represents voltage increment.

7. alternating current-direct current micro-capacitance sensor hierarchical control method as claimed in claim 5, it is characterized in that, described secondary controller is used for controlling the recovery of DC side busbar voltage, described secondary controller adoption rate-integral controller, the direct voltage measured compares with reference voltage, controls through PI the compensation rate obtaining voltage reference value; G _pIfor linear quadratic control PI controller, G _voltagefor direct current pressure ring transfer function.