CN102510064B - Improved droop control method in micro electric network detached island operation control system - Google Patents

Abstract

The invention discloses an improved droop control method in an improved micro electric network detached island operation control system. The automatic adjustment of the droop coefficient and the rated output power at the direct-current side is added in the traditional droop control, so as to reduce the fluctuation in voltage amplitude and frequency due to load change is reduced. In case that k groups of inverters are connected in parallel in the micro electric network, the active power and the reactive power output by the k-th inverter are respectively Pk and Qk. In the traditional droop control, the control equation of the output voltage amplitude of the inverter and the frequency droop is represented in the description: the droop coefficients kP Omega and kQU are replaced by simple functions correlative with the active power and the reactive power, represented in the description: the rated output powers on the direct current side of a drawing-in system are Pn and Qn, the rated output voltage angle frequency and amplitude of the micro electric network system are Omega n and Un, the load power is detected at the real time, the Pn and Qn are automatically adjusted, thus the Pn and Qn gradually reach Pk and Qk in delta T time, at the same time, the system droop control equation is represented in the description: the detached island operation of the micro electric network is controlled using the droop control equation.

Description

Improvement droop control method in micro-capacitance sensor islet operation control system

Technical field

The present invention relates to a kind of progress control method of micro-capacitance sensor, particularly relate to the improvement droop control method in a kind of micro-capacitance sensor islet operation control system.

Background technology

From systematic point of view, micro-capacitance sensor, by combinations such as generator, load, energy storage device and control device, forms a single controlled unit, can simultaneously to user's supply of electrical energy and heat energy.Include multiple distributed power source (DistributedGeneration, DG) and energy storage device in micro-capacitance sensor, combine and power to load, whole micro-capacitance sensor is externally an entirety, is connected with higher level's electricity grid substation by a main isolating switch.The basic structure of micro-capacitance sensor as shown in Figure 1.

Micro-capacitance sensor is incorporated into the power networks and islet operation two kinds of operational modes, because a lot of DG is by inverter access micro-capacitance sensor, during micro-capacitance sensor islet operation, is just equivalent to multiple inverter parallel.Suppose there is k (k >=2) individual inverter parallel, its simplified pinciple figure as shown in Figure 2.Wherein, the output voltage of each DG is respectively U ₁∠ δ ₁, U ₂∠ δ ₂u _k∠ δ _k, load voltage is U _l∠ 0, and the parameter of each shunt chopper module is identical, i.e. r ₁=r ₂=r ₃=...=r _k=r, X ₁=X ₂=X ₃=...=X _k=X.

As shown in Figure 2, in the power of load consumption, the active-power P provided by inverter k (k>=2) _kand reactive power Q _kcan be expressed as:

$\left\{\begin{array}{c}{P}_k=\frac{U_L}{{r_k}^2+{X_k}^2}[r_k(U_k\cos {\mathrm{\δ}}_k-U_L)+X_k{U}_k\sin {\mathrm{\δ}}_k]\\ Q_k=\frac{U_L}{{r_k}^2+{X_k}^2}[X_k(U_k\cos {\mathrm{\δ}}_k-U_L)-r_k{U}_k\sin {\mathrm{\δ}}_k]\end{array}\right.---\left(1\right)$

If the induction reactance between AO, between BO, between CO and between DO is much larger than resistance (i.e. X _k> > r _k), when power angle is less, can be similar to and thinks sin δ _k=δ k, cos δ _k=1, then formula (1) can be written as:

$\left\{\begin{array}{c}{P}_k=\frac{U_L{U}_k}{X_k}{\mathrm{\δ}}_k\\ Q_k=\frac{U_L{U}_k-U_L^2}{X_k}\end{array}\right.---\left(2\right)$

Can be found out by above formula, active power depends mainly on merit angle, and reactive power depends mainly on the amplitude of inversion unit output voltage.The amplitude of inversion unit output voltage can directly control, and its merit angle controls to be then by regulating inversion unit output angle frequencies omega _kor frequency f _krealize, that is:

$f_k=\frac{{\mathrm{\ω}}_k}{2\mathrm{\π}}=\frac{d{\mathrm{\δ}}_k}{\mathrm{dt}}---\left(3\right)$

Now, the droop control of inverter parallel system comprises output voltage amplitude U _kand angular frequency _ksagging, droop control equation is:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_0-k_{\mathrm{P\ω}}{P}_k\\ U_k=U_0-k_{\mathrm{QU}}{Q}_k\end{array}\right.---\left(4\right)$

In formula, ω ₀for angular frequency during system zero load; U ₀for the amplitude of output voltage during system zero load; k _{p ω}for system meritorious-the characteristic sagging coefficient of frequency droop; k _qUfor the sagging coefficient of System Reactive Power-voltage droop characteristic.

If the resistance between AO, between BO, between CO and between DO is much larger than induction reactance (i.e. r _k> > X _k), when power angle is less, formula (1) can be rewritten as:

$\left\{\begin{array}{c}{P}_k=\frac{U_L{U}_k-U_L^2}{r_k}\\ Q_k=-\frac{U_L{U}_k}{r_k}{\mathrm{\δ}}_k\end{array}\right.---\left(5\right)$

As can be seen from the above equation, active power depends mainly on voltage magnitude, and reactive power depends mainly on merit angle.

Now, the droop control equation of inverter parallel system is:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_0+k_{\mathrm{Q\ω}}{Q}_k\\ U_k=U_0-k_{\mathrm{PU}}{P}_k\end{array}\right.---\left(6\right)$

In formula, k _{q ω}for the characteristic sagging coefficient of System Reactive Power-frequency droop; k _pUfor system is gained merit the-sagging coefficient of voltage droop characteristic.

In like manner, if the resistance between AO, between BO, between CO and between DO and induction reactance close to time, system droop control equation is:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_0-k_{\mathrm{P\ω}}{P}_k+k_{\mathrm{Q\ω}}{Q}_k\\ U_k=U_0-k_{\mathrm{QU}}{Q}_k-k_{\mathrm{PU}}{P}_k\end{array}\right.---\left(7\right)$

In traditional droop control mode, the automatically adjustable of system output power can be realized, but sacrifice the stability index of system output voltage amplitude and frequency.Although sagging coefficient in theory can be arbitrarily small, in actual applications owing to being subject to the impact of hardware error and control precision, often have to get a compromise value.In traditional droop control, under different system loadings, sagging coefficient is constant, thus may cause the excessive sag of output voltage and frequency, affects the stability of micro-capacitance sensor voltage magnitude and frequency.

Summary of the invention

Object of the present invention is exactly to solve the problem, and adopts the improvement droop control method in a kind of micro-capacitance sensor islet operation control system, can effectively reduce the fluctuation of voltage magnitude and frequency in droop control, and be applicable to the situation of multiple DG parallel connection.

For realizing above-mentioned target, the present invention adopts following technical scheme:

For the improvement droop control method in micro-capacitance sensor islet operation control system, its step is:

Step 1, gets in micro-capacitance sensor and has k group DG, and output impedance and the line impedance sum of kth group inverter are r _k+ jX _k, it is main for supposing that shunt chopper output impedance and line impedance sum present perception, i.e. X _k> > r _k;

Step 2, gets ω _k, U _kbe respectively angular frequency and the amplitude of kth group inverter output voltage, ω ₀, U ₀be respectively angular frequency and the amplitude of output voltage during micro-grid system zero load, k _{p ω}, k _qUthe system of being respectively gains merit-the sagging coefficient of frequency droop characteristic curve and idle-voltage droop characteristic, and P _k, Q _kbe respectively active power and the reactive power of the output of kth group inverter;

Step 3, in traditional droop control, inverter output voltage amplitude and frequency droop governing equation are:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_0-k_{\mathrm{P\ω}}{P}_k\\ U_k=U_0-k_{\mathrm{QU}}{Q}_k\end{array}\right.---\left(8\right)$

Step 4, by the sagging coefficient k in traditional droop control _{p ω}and k _qUsubstitute to meritorious, idle relevant simple function with one, k _{p ω 2}, k _qU2be respectively k _{p ω}and k _qUthe coefficient of simple function, k _{p ω 1}, k _qU1be respectively k _{p ω}and k _qUconstant in simple function, that is:

$\left\{\begin{array}{c}{k}_{\mathrm{P\ω}}=k_{\mathrm{P\ω}1}+k_{\mathrm{P\ω}2}{P}_k\\ k_{\mathrm{QU}}=k_{\mathrm{QU}1}+k_{\mathrm{QU}2}{Q}_k\end{array}\right.---\left(9\right)$

Step 5, drawing-in system DC side rated output power P _nand Q _n, and the rated output voltage angular frequency of micro-grid system and amplitude ω _n, U _n;

Step 6, real-time detection load power P _kand Q _k, during load power change, within the scope of the peak power output of DG, to P _nand Q _nautomatic adjustment, makes it within the Δ t time, level off to P gradually _kand Q _k, now, system droop control equation is:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_n-(k_{\mathrm{P\ω}1}+k_{\mathrm{P\ω}2}{P}_k)(P_n-P_k)\\ U_k=U_n-(k_{\mathrm{QU}1}+k_{\mathrm{QU}2}{Q}_k)(Q_n-Q_k)\end{array}\right.---\left(10\right)$

, and then micro-grid system is controlled.

Described system dc side rated output power P _nand Q _n, their initial value is the rated output power of DG in micro-capacitance sensor.The rated output voltage angular frequency of described micro-grid system _n=2 π f=100 π, rated output voltage amplitude U _n=311V.

The invention relates to during micro-capacitance sensor islet operation control system is run the invention improving droop control.In traditional droop control, drawing-in system DC side rated output power, and the rated output voltage angular frequency of micro-grid system and amplitude, increase the automatic adjustment of sagging coefficient, and the automatic adjustment of DC side rated output power, reduce the fluctuation of voltage magnitude that load variations causes and frequency.

The invention has the beneficial effects as follows: method is simple, can effectively reduce and eliminate the fluctuation of micro-capacitance sensor output voltage amplitude that load variations causes and frequency.

Accompanying drawing explanation

Fig. 1 is the basic block diagram of micro-capacitance sensor;

Fig. 2 is inverter parallel simplified pinciple figure;

Output voltage frequency waveform during Fig. 3 micro-capacitance sensor islet operation;

Phase voltage amplitude waveform is exported during Fig. 4 micro-capacitance sensor islet operation;

Embodiment

Below in conjunction with accompanying drawing and example, the present invention will be further described.

For the improvement droop control method in micro-capacitance sensor islet operation control system, its step is:

Step 1, gets in micro-capacitance sensor and has k group DG, and output impedance and the line impedance sum of kth group inverter are r _k+ jX _k, it is main for supposing that shunt chopper output impedance and line impedance sum present perception, i.e. X _k> > r _k;

Step 2, gets ω _k, U _kbe respectively angular frequency and the amplitude of kth group inverter output voltage, ω ₀, U ₀be respectively angular frequency and the amplitude of output voltage during micro-grid system zero load, k _{p ω}, k _qUthe system of being respectively gains merit-the sagging coefficient of frequency droop characteristic curve and idle-voltage droop characteristic, and P _k, Q _kbe respectively active power and the reactive power of the output of kth group inverter;

Step 3, in traditional droop control, inverter output voltage amplitude and frequency droop governing equation are:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_0-k_{\mathrm{P\ω}}{P}_k\\ U_k=U_0-k_{\mathrm{QU}}{Q}_k\end{array}\right.---\left(8\right)$

Step 4, by the sagging coefficient k in traditional droop control _{p ω}and k _qUsubstitute to meritorious, idle relevant simple function with one, k _{p ω 2}, k _qU2be respectively k _{p ω}and k _qUthe coefficient of simple function, k _{p ω 1}, k _qU1be respectively k _{p ω}and k _qUconstant in simple function, that is:

$\left\{\begin{array}{c}{k}_{\mathrm{P\ω}}=k_{\mathrm{P\ω}1}+k_{\mathrm{P\ω}2}{P}_k\\ K_{\mathrm{QU}}=k_{\mathrm{QU}1}+k_{\mathrm{QU}2}{Q}_k\end{array}\right.---\left(9\right)$

Step 5, drawing-in system DC side rated output power P _nand Q _n, and the rated output voltage angular frequency of micro-grid system and amplitude ω _n, U _n;

Step 6, real-time detection load power P _kand Q _k, during load power change, within the scope of the peak power output of DG, to P _nand Q _nautomatic adjustment, makes it within the Δ t time, level off to P gradually _kand Q _k, now, system droop control equation is:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_n-(k_{\mathrm{P\ω}1}+k_{\mathrm{P\ω}2}{P}_k)(P_n-P_k)\\ U_k=U_n-(k_{\mathrm{QU}1}+k_{\mathrm{QU}2}{Q}_k)(Q_n-Q_k)\end{array}\right.---\left(10\right)$

The inventive method principle is as follows:

Get in micro-capacitance sensor and have k group DG, in traditional droop control, it is main for supposing that shunt chopper output impedance and line impedance sum present perception, namely to kth group inverter, and X _k> > r _k, the droop control of inverter parallel system comprises the sagging of output voltage amplitude and angular frequency, and droop control equation is:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_0-k_{\mathrm{P\ω}}{P}_k\\ U_k=U_0-k_{\mathrm{QU}}{Q}_k\end{array}\right.---\left(11\right)$

In formula, ω _kfor the command value of kth group inverter output angle frequency; ω ₀for angular frequency during system zero load; k _{p ω}for system meritorious-the characteristic sagging coefficient of frequency droop; U _kfor kth group inverter output voltage amplitude command value; U ₀for the amplitude of output voltage during system zero load; k _qUfor the sagging coefficient of System Reactive Power-voltage droop characteristic.

Now, under different system loadings, sagging coefficient is constant, thus may cause the excessive sag of output voltage and frequency, affects the stability of micro-capacitance sensor voltage magnitude and frequency.For solving this problem, the present invention proposes a kind of droop control method of improvement.

First, by increasing the adjustment of sagging coefficient, the micro-capacitance sensor voltage magnitude caused by inverter sharing control when can reduce load variations and the excessive sag of frequency, thus avoid ac bus voltage magnitude and frequency in micro-capacitance sensor to occur larger fluctuation, increase stability and the reliability of microgrid inverter parallel system.The present invention is by sagging coefficient k _{p ω}and k _qUsubstituting to meritorious, idle relevant simple function with one, when changed power being detected, dynamically can regulate sag of chain according to real output size.

Secondly, present invention further introduces system dc side rated output power P _nand Q _n, and the rated output voltage angular frequency of micro-grid system and amplitude ω _n, U _n, real-time detection load power P _kand Q _k, during load power change, within the scope of the peak power output of DG, to P _nand Q _nautomatic adjustment, makes it within the Δ t time, level off to P gradually _kand Q _k, be main when shunt chopper output impedance and line impedance sum present perception, and when load power is less than system peak power output, the droop control equation of system is as follows:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_n-(k_{\mathrm{P\ω}1}+k_{\mathrm{P\ω}2}{P}_k)(P_n-P_k)\\ U_k=U_n-(k_{\mathrm{QU}1}+k_{\mathrm{QU}2}{Q}_k)(Q_n-Q_k)\end{array}\right.---\left(12\right)$

In formula, k _{p ω 1}and k _{p ω 2}for sagging coefficient k _{p ω}-P _kthe constant of linear function and coefficient; k _qU1and k _qU2for sagging coefficient k _qU-Q _kthe constant of linear function and coefficient.

Wherein, system dc side rated output power P _nand Q _ninitial value be the rated output power of DG in micro-capacitance sensor, the rated output voltage angular frequency of micro-grid system _n=2 π f=100 π, rated output voltage amplitude U _n=311V.

According to method of the present invention, micro-capacitance sensor islet operation is emulated, adopt traditional droop control and improve droop control simulation result more as shown in Figure 3 and Figure 4.Simulation model is made up of k DG, and each DG AC is jointly for load is powered after filter, and the optimum configurations in model is as follows: the parameter of each DG module is consistent, the wherein filter inductance L of inverter ac side _k=2.2mH, resistance r _k=0.1 Ω, filter capacitor C _k=500 μ F; In tradition droop control, P-f sagging curve slope is-1 × 10 ^-5, Q-U sagging curve slope is-1 × 10 ^-3; Initial time, load is P=20kW, Q=0Var; During t=0.8s, load becomes P=40kW, Q=5kVar; During t=1.2s, load reverts to P=20kW again, Q=0Var; The system emulation time is 2s.Can find out according to simulation result, when load variations, adopt the improvement droop control in the present invention that the output voltage amplitude of system and frequency retrieval can be made to rated value, the stability of increase microgrid inverter parallel system and reliability.

Claims (1)

1. the improvement droop control method in a micro-capacitance sensor islet operation control system, it is characterized in that, in traditional droop control, increase the automatic adjustment of sagging coefficient, and the automatic adjustment of DC side rated output power, thus effectively reduce the fluctuation of voltage magnitude that load variations causes and frequency; Concrete steps are:

Step 1, gets in micro-capacitance sensor and has k group DG, and output impedance and the line impedance sum of kth group inverter are r _k+ jX _k, it is main for supposing that shunt chopper output impedance and line impedance sum present perception, i.e. X _k>>r _k;

Step 2, gets ω _k, U _kbe respectively angular frequency and the amplitude of kth group inverter output voltage, ω ₀, U ₀be respectively angular frequency and the amplitude of output voltage during micro-grid system zero load, k _{p ω}, k _qUthe system of being respectively gains merit-the sagging coefficient of frequency droop characteristic curve and idle-voltage droop characteristic, and P _k, Q _kbe respectively active power and the reactive power of the output of kth group inverter;

Step 3, in traditional droop control, inverter output voltage amplitude and frequency droop governing equation are:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_0-k_{\mathrm{P\ω}}{P}_k\\ U_k=U_0-k_{\mathrm{QU}}{Q}_k\end{array}\right.---\left(8\right)$

By the sagging coefficient k in traditional droop control _{p ω}and k _qUsubstitute to meritorious, idle relevant simple function with one, k _pw2, k _qU2be respectively k _{p ω}and k _qUthe coefficient of simple function, k _pw1, k _qU1be respectively k _{p ω}and k _qUconstant in simple function, that is:

$\left\{\begin{array}{c}{k}_{\mathrm{P\ω}}=k_{\mathrm{P\ω}1}+k_{\mathrm{P\ω}2}{P}_k\\ k_{\mathrm{QU}}=k_{\mathrm{QU}1}+k_{\mathrm{QU}2}{Q}_k\end{array}\right.---\left(9\right)$

Step 4, drawing-in system DC side rated output power P _nand Q _n, and the rated output voltage angular frequency of micro-grid system and amplitude ω _n, U _n;

Step 5, real-time detection load power P _kand Q _k, during load power change, within the scope of the peak power output of DG,

To P _nand Q _nautomatic adjustment, makes it within the Δ t time, level off to P gradually _kand Q _k, now, system droop control equation is:

$\left\{\begin{array}{c}{\mathrm{\ω}}_k={\mathrm{\ω}}_n-(k_{\mathrm{P\ω}1}+k_{\mathrm{P\ω}2}{P}_k)(P_n-P_k)\\ U_k=U_n-(k_{\mathrm{QU}1}+k_{\mathrm{QU}2}{Q}_k)(Q_n-Q_k)\end{array}\right.---\left(10\right)$

Utilize the droop control equation of this improvement, the operation of micro-capacitance sensor is controlled;

Described system dc side rated output power Pn and Qn, their initial value is the rated output power of DG in micro-capacitance sensor; The rated output voltage angular frequency of micro-grid system _n=2 π f=100 π, rated output voltage amplitude U _n=311V;

Emulate micro-capacitance sensor islet operation, simulation model is made up of k DG, and each DG AC is jointly for load is powered after filter, and the optimum configurations in model is as follows: the parameter of DG1 with DG2 is consistent, wherein the filter inductance L of inverter ac side _k=2.2mH, resistance r _k=0.1 Ω, filter capacitor C _k=500 μ F; In tradition droop control, P-f sagging curve slope is-1 × 10 ^-5, Q-U sagging curve slope is-1 × 10 ^-3; Initial time, load is P=20kW, Q=0Var; During t=0.8s, load becomes P=40kW, Q=5kVar; During t=1.2s, load reverts to P=20kW again, Q=0Var; The system emulation time is 2s; When load variations, adopt and improve droop control the output voltage amplitude of system and frequency retrieval can be made to rated value, the stability of increase microgrid inverter parallel system and reliability.