Design Project Control Active Power and Reactive Power

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

School of Electrical Engineering

Design Project Control Active Power and Reactive Power

Teacher: PhD Vu Thi Thuy Nga

Nguyen Si Hà

Le Quoc Viet

Nguyen Hoang Dinh Duc

201738172017703220173749

Hanoi, 8/2021

1 Theory of Connecting Wind Power Systems to the Electrical Grid

1.1 Connecting Wind Power Systems to the Electrical Grid in reality

Wind power generation, just like solar is not consistent throughout the year The weather changesand alters the availability of wind and sunlight There are fluctuations in power generation on aregular basis Even though there are inverters available for power management, the inherent nature

of wind power generation is not stable with traditional grids

A wind farm is not operational on a continuous basis Hence, efficient backup power systems arerequired to make up the power supply during a shutdown The difference between the powergeneration forecast and actual power production needs to be managed and regulated

The main purpose of a power grid is to make electricity available to every consumer in acontinuous, stable and measurable fashion The customers of the grid operators are extremelyvolatile and dynamic People expect power to be available at any point of time whenever they turn

on a switch or plug-in a socket Such varying loads call for extreme applications of just-in-timemanagement

1.2 Conditions for grid connectivity

Given the context of proper grid management, the fluctuations and deviations in power generationfrom wind energy sources puts extreme pressure on grid systems The fluctuations from a singlewind farm are negligible but when combined together, the fluctuation patterns become significant.Even before connecting a wind turbine to the main grid, there are certain things that should beconsidered

• The annual average wind speeds of minimum 10 mph are mandatory for sufficient energyproduction to qualify for grid connectivity.

• The grid-supplied electricity is more expensive than renewable energy systems

There provisions made for successfully connecting wind energy generation systems to pre-existinggrids Added to this, grid connection equipment such as inverters should be readily available

• There are tax incentives and policies in place that support the use of renewable energy.1.3 Challenges in connecting wind energy sources to traditional grids

• Most of the wind turbines even today use induction generators where the rotational speed isdirected by the frequency of the grid that is connected to The blades are fixed and there is nopitching This results in a passive controlling mechanism during extremely high wind speeds Thisdesign is in widespread use due to its cost-effectiveness and ease of design However, there arespecific major concerns regarding such wind turbine designs and grid connectivity

• The loss of control and regulation of power in such wind turbines means that the frequency ofthe system cannot be controlled Connectivity to grid requires a fixed frequency of generation

• Network voltages and fluctuations in current cannot be controlled Traditional power plantshave devices in place that check such fluctuations in the system and regulate the supply of power

• Traditional grids do not provide energy independence to renewable energy users If the gridgoes down in one location, then even the renewable energy users will be affected

• Sudden faults in the system such as circuit overlap, power surges and reverse flows amongothers are made worse by the presence of wind power sources

• Energy management equipment such as inverters for wind energy are extremely expensivelyand cannot be easily integrated with local power grids

1.4 Control targets

Grid control circuits for wind turbine have several targets:

• Realize active grid power so that the power of the wind turbine is as big as possible in a normalmode

• Realize reactive grid power so that the wind turbine has the power factor given by the gridsupplier

• Limit so that the wind turbinehas the limited active power given by the grid supplier

• Increase the grid frequency, if it is too small, decrease the grid frequency, if it is too high,increase, if grid voltage is too small, decrease, if grid voltage is running too high, even if gridvoltage is too small over a long time

1 Grid-connected 3-phase inverter control

The simulation based on the control algorithm below

Where PLL model is :

Control target: Control for reactive power on grid to go to 0

The parameters in the simulation file

Simulation result

a) When =-205 and = 0

Current graph and voltage graph at grid

For a closer look, we've put each phase of the current and the voltage into a graph

Current graph and voltage graph at grid

Comment 1: From the 2 pictures above you can see that voltage and current graphs are sinusoidal The current is in phase with the voltage Where the voltage amplitude is 580 (V) approximately

(V)(The reference voltage amplitude of Three-Phase Source), the current amplitude is200(A).Therefore, the deviation compared to the value is 2.5% Also ,you can see valueand value :

Comment 2 : is very small compared to So it is possible to see Q approaching 0

2 Grid-connected 3-phase inverter control including local load

Where PLL model is

Control target: Control the reactive power and active power on the grid by the reflected power and the active power on the load and equal the set value Where, (KW)

(KVAr)

The parameters in the simulation file

QL: 100000Qc: 0

Simulation result

Fig 2:Current graph and voltage graph at grid and at load

Comment 1: The voltage graphs at the grid and at the load are sinusoidalare Also , they are almostthe same, similar to the current graph

Comment 2 :

(KW) The deviation compared to (KW) is 0.25%

(KVAr) The deviation compared to (KVAr) is 0.25%

(KW) The deviation compared to (KW) is 0.05%

(KVAr) The deviation compared to (KVAr) is 3%

IV Adaptive voltage controller for a Standalone DistributedGeneration System:

In recent years, eco-friendly distributed generation systems (DGS) such as wind turbines, solarcells, and fuel cells are dramatically growing because they can fulfill the increasing demand forelectric power due to the rapid growth of the economy and strict environmental regulationsregarding greenhouse gas emissions Generally, the DGSs are interconnected in parallel with theelectric utility grid and provide maximum electric power to the grid However, there are some areas(e.g., remote islands or villages) where the connection to the grid is expensive or impractical, andthen small-scaled standalone DSGs are the only efficient and economical options In such DGSs,depending on the power needs of the consumer, the DGSs will operate in parallel or independently.Therefore, the stable operation of a single DGS is as important as the stability of a system ofmultiple DGSs operating in parallel, where load division for each block is one of the main researchissues by voltage controllers used in a standalone DGS or multiple DGSs operating at the sametime For that reason, the design of a voltage regulator for a standalone DGS that can provide agood voltage supply for symmetric and nonlinear loads is an interesting topic in this section.The voltage controller needs to ensure the output voltage quality of the inverter in different loadcases (balanced load, unbalanced load, nonlinear load, ) On the other hand, the existence ofuncertain parameters of the system, the deviation between the output signal and the set value is one

of the major difficulties when designing a voltage controller This section proposes an adaptivevoltage controller consisting of an adaptive control part and a state feedback control part Theadaptive control part compensates for the system parameter uncertainty, while the state feedbackcontrol part forces the error to converge exponentially to zero

4.1 System model:

Fig 1 Block diagram of a standalone DGS using renewable energy sources

Fig.1 describes a block diagram of a standalone DGS using renewable energy sources which arewind turbines, solar cells, fuel cells, etc As depicted in Fig 1, the DGS is divided into six parts: anenergy source, an ac-dc power converter (wind turbines) or a dc-dc boost converter (solar cells orfuel cells), a three-phase dc–ac inverter, an LC output filter, an isolation transformer, and a localload In this section, a renewable energy source and an ac–dc power converter or a dc-dc boostconverter can be replaced by a stiff dc voltage source (Vdc) because this section focuses ondesigning an adaptive voltage controller under various types of loads such as balanced load,unbalanced load, and nonlinear load And the system model incorporating the adaptive voltagecontroller is:

Fig 2 Block diagram of adaptive voltage control system

The LC output filter shown in Fig 2 yields the following state equations by usingKirchhoff ’svoltage lawandKirchhoff ’scurrent law:

The equations of state in the abc frame of reference can be transformed into the equations in the d-qrotating frame:

Where ωi s the angular frequency (ω=2π·f), f is the fundamental frequency of output voltage orcurrent, and

In this work, the following assumptions are used to design anadaptive voltage controller:

1) The desired load d-q axis voltages (V Lqr and V Ldr) are considered as constant during a smallsampling period

2) The load d-q axis currents (I Ld and I Lq) vary slowly during a small sampling period.

The output filter capacitance C f usually satisfies 0 <C f <<1 or 1<<k1<∞ We may the assumption

1<<k1± ∨∆ k1∨¿<∞ leading to the following equations:

Where Δki denotes the imprecision of the parameter ki (i=1,2,3,4)

Four state variables are defined as follows:

With this definition, the system model can be rewritten as

4.2 Control Strategy:

The control inputs V id and V iqcan be defined as two control components, respectively:

Where V id 1 and V iq 1 are the feedback control components to stabilize the error dynamics of the

system, whereas V id 2 and V iq 2 are the nonlinear compensating control components given by:

The system model can be rearranged as the following:

(1)Thus, the model can be rewritten in the state-space formas:

Assume that there exists a positive definite matrix P ∈ R 4 × 4 satisfying the following inequality:

Where Q ∈ R 4 × 4

and R ∈ R 2×2

are positive definite matrices

The above inequality is satisfied if the following inequality holds for some positive ρ:

Assume that |Δk1|≤ζ for some known positive constant ζ; then inequality is satisfied if thefollowing Riccati-like inequality has a positive definite solution matrix P ∈ R 4 × 4:

The controllerucan make the error dynamicsxconverge to zero:

(2)

Where K=R−1B T P a gain matrix, Π is estimated value of Π¿, and the adaptive control law is givenby:

Let us choose the Lyapunov function as:

Where Π e= Π - Π¿ The time derivative is:

The Riccati-like inequality implies that:

Then, by integrating both sides, the following equationis derived:

This implies x∈L2∩L∞, Π∈L∞ Combining the previousresults and using Barbalat’s lemma, xconverges to zero as timegoes to infinity, that is,

4.3.2 Simulation model:

4.3.3 Simulation results:

In the case of a resistive load, the voltage across the load has the following figure:

In the case of a nonlinear load, the voltage across the load has the following figure:

Conclusion: In both cases, the output voltage on the load is almost sinusoidal after 0.025s timeinterval The voltage value is 223.6V, which is close to being equal to the set value is 220V