CN106532725A - Power distribution network voltage control method based on virtual synchronous generator type distributed generation - Google Patents

Abstract

The invention discloses a distribution network voltage control method based on a virtual synchronous generator type distributed power supply. The VSG-DG control system used in the method collects the inner loop current, output current and VSG of the VSG-DG through a voltage and current acquisition module The voltage at the PCC of ‑DG connected to the grid is used to simulate the active frequency regulation and reactive voltage regulation functions of the synchronous generator through the power calculation module, active power‑frequency control module and reactive power voltage control module, and then through the voltage conversion module, voltage The compensation control module, the DC voltage control module and the current control module realize that the external characteristics of the output of the VSG-DG are consistent with the external characteristics of the synchronous generator, and the reactive power-voltage control module adaptively sets the PCC voltage compensation reference value according to the fluctuation of the PCC voltage , to effectively suppress voltage fluctuations at the PCC.

Description

Distribution network voltage control method based on virtual synchronous generator type distributed generation

technical field

The invention belongs to the field of power quality management of active distribution networks for distributed generation, and in particular relates to a distribution network voltage control method based on a virtual synchronous generator type distributed power supply.

Background technique

The traditional distribution network usually relies on a flexible network structure and a large capacity margin to cope with the uncertainty of the load, so as to ensure the safety and reliability of the power system, and its operation control method is relatively simple. In the past ten years, the rapid development of power electronics technology has solved the problem of grid-connected operation of distributed generation (DG) in the medium and low voltage distribution network, and promoted the wide application of DG at all levels of the power system. However, the traditional distribution network still has problems such as insufficient renewable energy consumption capacity, weak primary network structure, low level of automation, backward dispatching methods, and low level of electricity interaction, which seriously restrict the high penetration of DG. Conducive to the optimization and adjustment of energy structure. Faced with the current situation of slow load growth, limited space resources for distribution network development, and difficult network expansion, active distribution network technology has emerged to solve grid compatibility and apply large-scale intermittent renewable energy to improve green energy utilization. , Optimizing primary energy structure and other issues.

The traditional passive distribution network adopts the mode of absorbing intermittent energy locally. When DG is connected to the distribution network, due to the intermittent, random, and non-linear characteristics of DG, if the intermittent energy generates excess power, the distribution network itself has no adjustment ability and cannot be sent to the distribution network. Run hard. The active distribution network has the ability to accommodate intermittent energy. If the intermittent energy generates excess power, it can absorb the excess through flexible loads and the hierarchical capacity of the multi-level grid under the condition of satisfying the operating constraints of the distribution network. of energy. However, this will lead to a reverse power flow in the distribution network, voltage regulation problems may occur at any location of the active distribution network (AND) feeder, and voltage quality control faces more severe challenges.

In recent years, virtual synchronous generator-type distributed generation (VSG-DG) integrated with synchronous generator control model has received widespread attention. Because it realizes the physical and mathematical equivalence of renewable energy grid-connected units and synchronous generators, it can effectively reduce the impact of large-scale renewable energy grid-connected on the grid, and has aroused extensive research interest worldwide.

Figure 1 shows a feeder connected to the active distribution network of VSG-DG, including three common bus PCCs and three groups of loads, and each common bus PCC is connected to several DGs and VSG-DGs. DG includes DC micro-source, three-phase full-bridge inverter, LC filter circuit and DG control system, VSG-DG includes DC side capacitor, three-phase full-bridge inverter, LC filter circuit and VSG-DG control system. VSG-DG makes the output external characteristics of DG consistent with the external characteristics of synchronous generator through the control of VSG-DG control system. The VSG-DG control system mainly includes active power-frequency control module and reactive power-voltage control module. VSG-DG The control method is to collect the outlet voltage and current of the VSG-DG, pass through the active-frequency control module and the reactive-voltage control module, output the pulse width modulation signal, and input the pulse width modulation signal to the three-phase full-bridge inverter to change the inverter The output power of the generator is used to simulate the operation mechanism of the synchronous generator. At present, the function of the VSG-DG connected to the active distribution network is mainly to improve the frequency stability of the power grid. When the voltage fluctuation problem occurs in the power grid, the VSG-DG cannot respond quickly to improve the voltage control level of the active distribution network. All this is inconsistent with the requirements of the active distribution network.

Contents of the invention

The technical problem solved by the invention is: the existing VSG-DG control method cannot simulate the external characteristics of the synchronous generator well and cannot suppress the voltage fluctuation of the common busbar PCC of the active distribution network ADN.

The specific technical scheme of the present invention is as follows: a distribution network voltage control method based on a virtual synchronous generator type distributed power supply, characterized in that it includes the following steps:

S1. Construct the control system of virtual synchronous generator type distributed power supply VSG-DG, mainly including voltage and current acquisition module, power calculation module, active power-frequency control module, reactive power-voltage control module, voltage conversion module, voltage compensation control module , DC voltage control module and current control module, the voltage and current acquisition module is used to collect the inner loop current value of VSG-DG, the output current value and the voltage value at the common bus PCC of VSG-DG connected to the grid, the output terminal of the voltage and current acquisition module Connect the input terminal of the power calculation module, the input terminal of the reactive power-voltage control module and the input terminal of the current control module, and the output terminal of the power calculation module is connected with the input terminal of the active power-frequency control module and the input terminal of the reactive power-voltage control module and the input end of the voltage compensation module, the output end of the active-frequency control module and the output end of the reactive power-voltage control module are all connected to the input end of the voltage conversion module, and the output end of the voltage conversion module is connected to the input end of the voltage compensation control module, Both the output end of the voltage compensation control module and the output end of the DC voltage control module are connected to the input end of the current control module, and the output end of the current control module is connected to the three-phase full-bridge inverter of VSG-DG;

S2. The voltage and current acquisition module collects the value v _abc of the voltage at the PCC connected to the VSG-DG _i in the three-phase static abc coordinate system and the value i _abc,i of the output current of the VSG-DG _i in the three-phase static abc coordinate system, Calculate the modulus V of the voltage v _abc at the PCC, and convert it into a real-time voltage value v _αβ in the two-phase stationary αβ coordinate system, where VSG-DG _i is the ith VSG-DG connected to the PCC;

S3. The power calculation module calculates the output reactive power Q _i and the output active power P _{i of the VSG-DG i ;}

S4. The reactive power-voltage control module adaptively sets the PCC voltage compensation reference value V _ref according to the PCC voltage fluctuation;

S5. Set the output reactive power reference value Q _{ref,i and} output active power reference value Pre ref,i of VSG-DG _i , and the reactive power-voltage control module compensates the reference value V _ref , output reactive power Q _i and output reactive power according to the voltage compensation Reference value Q _ref,i , output virtual stator electromotive force of VSG-DG _i Among them, k _u and K are the droop coefficient and integral coefficient of the reactive power-voltage control module respectively; the active power-frequency control module outputs the virtual electrical angle of VSG-DG _i according to the output active power P _i and the output active power reference value _{Pre ref,i} Among them, J is the moment of inertia, D is the damping coefficient, ω is the angular frequency of the VSG rotor;

S6. The voltage conversion module calculates the control reference voltage through the electromotive force E _i in the virtual stator and the virtual electrical angle θ _1,i

in

S7. The voltage compensation module controls the reference voltage according to Real-time voltage v _αβ and output reactive power Q _i , calculate the output current reference process quantity of VSG-DG _i in n _{P, i} are active power distribution coefficients, k _{e, p} are voltage error proportional coefficients, k _{P, P} , k _{I, P} are proportional coefficients and integral coefficients of the voltage compensation module, respectively;

S8. Set the rated DC voltage of VSG-DG _i Collect the DC side voltage V _DC,i of VSG-DG _i , and the DC voltage control module calculates the active power that VSG-DG _i needs to absorb to maintain the real-time DC voltage at the rated DC voltage Among them, k _P,DC and k _I,DC are the proportional coefficient and integral coefficient of the DC voltage control module respectively, and calculate the active current to be absorbed

S9, the current control module will output the current reference value After comparing with the rated current I _N of VSG-DG _i , the pulse width modulation input signal is synthesized, and output to the three-phase full-bridge inverter of VSG-DG _i after pulse width modulation.

Further, the specific steps of S4 are: if the voltage modulus V at the PCC>1.07V _N , the voltage compensation reference value If the modulus value of the voltage at PCC is V<0.93V _N , the voltage compensation reference value If 0.93V _N <V<1.07V _N , the voltage compensation reference value V _ref =V _N ; where V _N is the rated voltage of the distribution network, H is the sampling rate, ΔV _s2 is the voltage of the second sampling cycle after the PCC voltage fluctuation The amount of change, t is the moment when the voltage fluctuation starts to count, and the adjustment time of the voltage compensation reference value is

After the PCC voltage fluctuates, the trajectory curvature of the adaptive arctangent curvature control is determined according to the PCC voltage deviation degree, and the voltage adjustment time is determined according to the PCC voltage change rate, which improves the robustness of the voltage and frequency of the active distribution network.

Further, the specific execution steps of the current control module in S9 are:

S9.1 Synthesize the output current reference value of VSG-DG _i If the output current reference value exceeds the rated current I _N of VSG-DG _i , then

S9.2 Output current reference value And the output current value i _αβ,i collected by the voltage and current acquisition module passes through the first proportional resonant controller to obtain the inner loop current reference value of VSG-DG _i

S9.3 Inner loop current reference value After subtracting the inner loop current value i _{L, αβ, i} , through the second proportional resonance controller, the PWM control input signal U _{PWM,i, αβ} under the two-phase static αβ coordinate system is obtained;

S9.4 Through the transformation from the two-phase static αβ coordinate system to the three-phase static abc coordinate system, the PWM control input signal U _PWM,i,abc in the three-phase static abc coordinate system is obtained, and input to the PWM generation unit for pulse width modulation. After modulation, it is output to the three-phase full-bridge inverter of VSG-DG _i .

In step S9.1, when the output current reference value of the VSG-DG reaches or exceeds the limit, limit the output current reference value to avoid overloading the VSG-DG.

The beneficial effects of the present invention are: (1) the VSG-DG control system that this method uses collects the inner loop current of VSG-DG, the output current and the PCC place voltage of VSG-DG grid-connected through the voltage and current acquisition module, through the power calculation module , Active power-frequency control module and reactive power-voltage control module are used to simulate the active frequency modulation and reactive power voltage regulation functions of synchronous generators, and then through the voltage conversion module, voltage compensation control module, DC voltage control module and current control module, Realize that the output external characteristics of VSG-DG are consistent with the external characteristics of synchronous generators, wherein the reactive power-voltage control module adaptively sets the PCC voltage compensation reference value according to the PCC voltage fluctuations, effectively suppressing the voltage fluctuations at the PCC; (2) PCC voltage After the fluctuation, the trajectory curvature of the adaptive arctangent curvature control is determined according to the PCC voltage deviation degree, and the voltage adjustment time is determined according to the PCC voltage change rate, which improves the robustness of the voltage and frequency of the active distribution network; (3) Adopting this control method The VSG-DG can not only operate independently, but also realize parallel operation without interconnection wires. It has high flexibility and reliability margin, and solves the power distribution problem when VSG-DGs with different capacities are operated in parallel, which is more suitable for smart grids. Plug-and-play requirements for electronic equipment; (4) When the output current of the VSG-DG reaches or exceeds the limit, limit the reference value of the output current to avoid overloading the VSG-DG. This method satisfies the actual demand of increasing DG penetration rate in the distribution network, realizes the comprehensive control of PCC power quality, makes up for the problem of voltage quality reduction caused by DG power uncertainty, and improves the local and regional voltage quality of the distribution network. , to achieve the safe and stable operation of the distribution network.

Description of drawings

Fig. 1 is a schematic diagram of a feeder structure of an active distribution network containing multiple DGs and VSG-DGs.

Fig. 2 is a schematic diagram of the primary circuit structure and control system structure of a VSG-DG.

Fig. 3 is a schematic diagram of voltage reference value changes with adaptive adjustment characteristics.

detailed description

The present invention will be described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 2, a VSG-DG of the present invention includes a primary circuit and a VSG-DG control system, and the VSG-DG control system mainly includes a voltage and current acquisition module, a power calculation module, an active power-frequency control module, and a reactive power-voltage control module , voltage conversion module, voltage compensation control module, DC voltage control module and current control module, the voltage and current acquisition module is used to collect the inner loop current value of VSG-DG, the output current value and the voltage value at the PCC of the VSG-DG connected to the grid , the output terminal of the voltage and current acquisition module is connected to the input terminal of the power calculation module, the input terminal of the reactive power-voltage control module and the input terminal of the current control module, the output terminal of the power calculation module is connected to the input terminal of the active power-frequency control module, The input terminal of the power-voltage control module and the input terminal of the voltage compensation module, the output terminal of the active power-frequency control module and the output terminal of the reactive power-voltage control module are all connected to the input terminal of the voltage conversion module, and the output terminal of the voltage conversion module is connected to The input terminal of the voltage compensation control module, the output terminal of the voltage compensation control module and the output terminal of the DC voltage control module are all connected to the input terminal of the current control module, and the output terminal of the current control module is connected to the three-phase full-bridge inverter of VSG-DG .

The following takes the i-th VSG-DG _i connected to the PCC as an example to illustrate the control method of the present invention.

A distribution network voltage control method based on a virtual synchronous generator type distributed power supply, comprising the following steps:

Step 1. Build the control system of VSG-DG _i as mentioned above.

Step 2, the current and voltage acquisition module collects the value of the voltage at the PCC in the three-phase static abc coordinate system v _abc =[v _a v _b v _c ] ^T and the value i of the output current of VSG-DG _i in the three-phase static abc coordinate system _abc,i =[i _a,i i _b,i i _c,i ] ^T , calculate the modulus V of the voltage v _abc at the PCC, and convert v _abc and i _abc,i into two-phase static The voltage value v _αβ and the output current value i _αβ,i in the αβ coordinate system,

in

Step 3. The power calculation module calculates the output reactive power Q _i and output active power P _{i of VSG-DG i :}

Step 4. The reactive power-voltage control module adaptively sets the voltage control reference value V _ref of the PCC. The specific steps are:

(1) After the PCC voltage fluctuates, calculate the voltage variation ΔV _s2 in the second sampling period after the PCC voltage fluctuates:

ΔV _s2 =V _s2 -V _s1 (3)

Wherein V _s1 and V _s2 are the voltage values of the first sampling point and the second sampling point respectively.

(2) According to the requirements of the power system for the distribution network voltage below 35kV, under normal circumstances, the deviation of the PCC voltage should be within ±7%. Considering that the voltage fluctuation is divided into two situations: swell or sag, there are three ways to set V _ref :

(a) When V>1.07V _N ,

Among them, V _N is the rated voltage of the distribution network, and H is the sampling rate (kHz). As shown by the solid line in Figure 3, the control of the voltage control reference value V _ref has the characteristic of adaptive arctangent curvature control: in the initial stage of voltage control, the change rate of the voltage control reference value V _ref is small, on the one hand, it avoids the distribution network The transient process of voltage fluctuation, on the other hand, waits for other voltage regulation equipment in the distribution network to participate in voltage control to reduce the output power pressure of VSG-DG _i ; in the final stage of voltage control, the change rate of voltage control reference value V _ref also It is very small, and the purpose is to accurately and gently restore the PCC voltage of the distribution network to the rated voltage value. Where t is the timing from the voltage fluctuation, and the voltage compensation reference value adjustment time is The adjustment time of V _ref is adaptively adjusted according to the voltage change rate of the second sampling period after the PCC voltage fluctuates. The greater the PCC voltage change rate, the longer the adjustment time.

(b) When V<0.93V _N ,

As shown by the dotted line in Figure 3, the voltage control reference value V _ref also has the characteristic of adaptive arctangent curvature control: in the initial stage of voltage control, the change rate of the voltage control reference value V _ref is small, on the one hand, it avoids voltage fluctuations in the distribution network On the other hand, it waits for other voltage regulation equipment in the distribution network to participate in voltage control to reduce the output power pressure of VSG-DG _i ; in the final stage of voltage control, the change rate of the voltage control reference value V _ref is also very small , the purpose is to accurately and gently restore the PCC voltage of the distribution network to the rated voltage value.

(c) When 0.93V _N < V < 1.07V _N , there is a slight voltage fluctuation in the distribution network at this time, and the voltage reference value can be set according to the normal operation state:

V _ref = V _N (6)

Step 5, (1) Set the output reactive power reference value Q _ref,i and the output active power reference value Pre ref _{,i of VSG-DG i .}

(2) Input V _ref , Q _ref,i and Q _i to the reactive power-voltage control module to obtain the virtual internal electromotive force E _i of the VSG-DG _i , and the control formula is as follows:

Among them, k _u and K are the droop coefficient and integral coefficient of the reactive power-voltage controller, respectively.

(3) Input Pre _ref,i and P _i to the VSG active-frequency control module to obtain the virtual electrical angle θ _1,i of VSG-DG _i , and the control formula is as follows:

Among them, J is the moment of inertia, D is the damping coefficient, and ω is the angular frequency of the VSG rotor.

Step 6. The voltage conversion module synthesizes E _i and θ _1,i into a control reference voltage with

in

Step 7. The voltage compensation module is divided into α voltage compensation module and β voltage compensation module, respectively according to the input reference value with Obtain the output current reference process quantity of VSG-DG _i It can be expressed as:

in n _P,i is the active power distribution coefficient of VSG-DG _i , k _e,p is the voltage error proportional coefficient; the voltage compensation module is designed as a PI controller, and k _P,P , k _I,P are the proportional coefficients of the PI controller and integral coefficients.

When the system enters a steady state, Since k _e,P is a fixed constant, the and v _αβ are the same, so n _P,i Q _i connected to the same PCC are equal, and n _P,i is set according to the rated capacity of VSC-DG _i , then the parallel VSC-DG will output proportionally according to their respective rated capacities reactive power.

Step 8. Set the rated value of the VSG-DG _i DC bus voltage Collect the DC side voltage V _DC,i of VSG-DG _i , and the DC voltage control module is also designed as a PI controller, then VSG-DG _i needs to absorb active power Among them, k _{P, DC} and k _{I, DC} are proportional-integral control parameters. Calculation of active current to maintain DC bus voltage stability Specifically:

Step 9. The current control module adopts a proportional resonant controller (PR), and the specific steps are:

(1) The current control module first synthesizes the output current reference value of VSG-DG _i During operation, if the output current reference value exceeds the rated current I _N of VSG-DG _i , then

(2) Output current reference value And the output current value i _αβ,i passes through the first proportional resonant controller to get the inner loop current reference value of VSG-DG _i

(3) Inner loop current reference value After subtracting the inner loop current value i _{L, αβ, i} , through the second proportional resonance controller, the PWM control input signal U _{PWM,i, αβ} under the two-phase static αβ coordinate system is obtained;

(4) After transforming the two-phase static αβ coordinate system to the three-phase static abc coordinate system, the PWM control input signal U _PWM,i,abc in the three-phase static abc coordinate system is obtained, and input to the PWM generation unit for pulse width modulation, pulse After modulation, it is output to the three-phase full-bridge inverter of VSG-DG _i .

The transfer function of the proportional resonant controller is:

Among them, k _PRp and k _PRr are the proportional coefficient and resonance gain of the proportional resonant controller respectively, and ω _c is the cut-off frequency.

Claims (3)

1. A distribution network voltage control method based on virtual synchronous generator type distributed power supply, it is characterized in that, comprises the following steps: S1. Construct the control system of virtual synchronous generator type distributed power supply VSG-DG, mainly including voltage and current acquisition module, power calculation module, active power-frequency control module, reactive power-voltage control module, voltage conversion module, voltage compensation control module , DC voltage control module and current control module, the voltage and current acquisition module is used to collect the inner loop current value of VSG-DG, the output current value and the voltage value at the common bus PCC of VSG-DG connected to the grid, the output terminal of the voltage and current acquisition module Connect the input terminal of the power calculation module, the input terminal of the reactive power-voltage control module and the input terminal of the current control module, and the output terminal of the power calculation module is connected with the input terminal of the active power-frequency control module and the input terminal of the reactive power-voltage control module and the input end of the voltage compensation module, the output end of the active-frequency control module and the output end of the reactive power-voltage control module are all connected to the input end of the voltage conversion module, and the output end of the voltage conversion module is connected to the input end of the voltage compensation control module, Both the output end of the voltage compensation control module and the output end of the DC voltage control module are connected to the input end of the current control module, and the output end of the current control module is connected to the three-phase full-bridge inverter of VSG-DG; S2. The voltage and current acquisition module collects the value v _abc of the voltage at the PCC connected to the VSG-DG _i in the three-phase static abc coordinate system and the value i _abc,i of the output current of the VSG-DG _i in the three-phase static abc coordinate system, Calculate the modulus V of the voltage v _abc at the PCC, and convert it into a real-time voltage value v _αβ in the two-phase stationary αβ coordinate system, where VSG-DG _i is the ith VSG-DG connected to the PCC; S3. The power calculation module calculates the output reactive power Q _i and the output active power P _{i of the VSG-DG i ;} S4. The reactive power-voltage control module adaptively sets the PCC voltage compensation reference value V _ref according to the PCC voltage fluctuation; S5. Set the output reactive power reference value Q _{ref,i and} output active power reference value Pre ref,i of VSG-DG _i , and the reactive power-voltage control module compensates the reference value V _ref , output reactive power Q _i and output reactive power according to the voltage compensation Reference value Q _ref,i , output virtual stator electromotive force of VSG-DG _i Among them, k _u and K are the droop coefficient and integral coefficient of the reactive power-voltage control module respectively; the active power-frequency control module outputs the virtual electrical angle of VSG-DG _i according to the output active power P _i and the output active power reference value _{Pre ref,i} Among them, J is the moment of inertia, D is the damping coefficient, ω is the angular frequency of the VSG rotor; S6. The voltage conversion module calculates the control reference voltage through the electromotive force E _i in the virtual stator and the virtual electrical angle θ _1,i in S7. The voltage compensation module controls the reference voltage according to Real-time voltage v _αβ and output reactive power Q _i , calculate the output current reference process quantity of VSG-DG _i in n _{P, i} are active power distribution coefficients, k _{e, p} are voltage error proportional coefficients, k _{P, P} , k _{I, P} are proportional coefficients and integral coefficients of the voltage compensation module, respectively; S8. Set the rated DC voltage of VSG-DG _i Collect the DC side voltage V _DC,i of VSG-DG _i , and the DC voltage control module calculates the active power that VSG-DG _i needs to absorb to maintain the real-time DC voltage at the rated DC voltage Among them, k _P,DC and k _I,DC are the proportional coefficient and integral coefficient of the DC voltage control module respectively, and calculate the active current to be absorbed S9, the current control module will output the current reference value After comparing with the rated current I _N of VSG-DG _i , the pulse width modulation input signal is synthesized, and output to the three-phase full-bridge inverter of VSG-DG _i after pulse width modulation. 2. The distribution network voltage control method based on virtual synchronous generator type distributed power supply according to claim 1, characterized in that, the specific steps of S4 are: if the voltage modulus value V at the PCC>1.07V _N , the voltage compensation Reference If the modulus value of the voltage at PCC is V<0.93V _N , the voltage compensation reference value If 0.93V _N <V<1.07V _N , the voltage compensation reference value V _ref =V _N ; where V _N is the rated voltage of the distribution network, H is the sampling rate, ΔV _s2 is the voltage of the second sampling cycle after the PCC voltage fluctuation The amount of change, t is the moment when the voltage fluctuation starts to count, and the adjustment time of the voltage compensation reference value is 3. according to the distribution network voltage control method based on the virtual synchronous generator type distributed power source described in claim 1 or 2, it is characterized in that, the specific execution steps of the current control module in S9 are: S9.1 Synthesize the output current reference value of VSG-DG _i If the output current reference value exceeds the rated current I _N of VSG-DG _i , then S9.2 Output current reference value And the output current value i _αβ,i passes through the first proportional resonant controller to get the inner loop current reference value of VSG-DG _i S9.3 Inner loop current reference value After subtracting the inner loop current value i _{L, αβ, i} , through the second proportional resonance controller, the PWM control input signal U _{PWM,i, αβ} under the two-phase static αβ coordinate system is obtained; S9.4 Through the transformation from the two-phase static αβ coordinate system to the three-phase static abc coordinate system, the PWM control input signal U _PWM,i,abc in the three-phase static abc coordinate system is obtained, and input to the PWM generation unit for pulse width modulation. After modulation, it is output to the three-phase full-bridge inverter of VSG-DG _i .