Design of Custom Power Devices for Power Quality Improvement using Fractional order PID Controller
Description for Complete Filing Field of the Invention:
The present invention generally relates to the field of electrical power quality and Flexible AC Transmission (FACTS) in a power system, and in particularly to the design of Unified Power Quality Conditioner (UPQC) for Power Quality Improvement using Fractional order PID Controller.
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Back ground of the invention:
With the interconnection of large scale power systems with the application of various novel equipments in power generation, power transmission and distribution become more economic and more efficient. It increases the scale and complexity of the power systems. In addition, large quantity of renewable energy based power generation systems are connected to a power grid, this reverses the traditional direction of the power flow from a transmission grid to a distribution grid. Due to utilization of nonlinear loads in end user, which creates spurious noise signals, including harmonic currents, background noise and spike impulse noise are developed on AC power distribution lines. Such noise signals can originate from the power source, the distribution network, local and remote loads coupled to the network, lightning strikes and distribution equipment malfunction.
The AC supply current delivered from a public utility is not a pure sine wave and contains harmonics that interfere with proper operation of connected equipment. Additionally, noise and switching transients may be introduced from active loads. By way of example, if a branch is loaded by an electronic dimmer and lamp, the dimmer will "chop" the 50 Hz AC power waveform at a high frequency to reduce the lighting intensity. This will introduce harmonics and high frequency noise on the power distribution conductors. Such noise is not constant with respect to time, and it also varies from place to place in the power distribution network.
Moreover, a typical AC power line network distributes power to a variety of electrical load devices. Each load can conduct a significant level of noise and harmonic currents back onto the power line, causing distortion of the power waveform. Different loads and control devices produce different types and degrees of distortion that may interfere with the operation of the equipment and machines that are being supplied by the distribution network.

The amount of electric power used by machinery and the machinery itself can be affected by waveform distortions present in a power distribution system. Elimination or control of the distortions may provide a substantial cost savings with respect to electrical energy consumption. and a cost savings with respect to machinery failure and repair or replacement. Thus, mitigation and reduction of power quality issues in AC power distribution systems can result in a substantial energy cost savings for industrial customers.
In the context of AC power distribution systems, linear electrical loads are load devices which, in steady state operation, present essentially constant impedance to the power source throughout the cycle of the applied voltage. An example of a linear load is an AC induction motor that applies torque to a constant (time invariant) mechanical load. Non-linear loads are loads that draw current discontinuously or whose impedance varies throughout the cycle of the input AC sine wave. Examples of nonlinear loads in an industrial distribution system include arc lighting, welding machines, variable frequency drive converter power supplies, switched mode power supplies and induction tpotors that are applying torque to time-varying mechanical loads.
Harmonic currents produced by non-linear loads in an electrical distribution system flow away from the non-linear source and toward the distribution system power supply. The injection of harmonic currents into the power distribution system can cause overheating of transformers and high neutral currents in three phase, grounded four wire systems. As harmonic currents flow through the distribution system, voltage drops are produced for each individual harmonic, causing distortion of the applied voltage waveform, which is applied to all loads connected to the distribution bus.
Harmonic distortion of the voltage waveform affects AC induction motor performance by inducing harmonic fluxes in the motor magnetic circuit. These harmonic fluxes cause heat buildup and additional losses in the motor magnetic core, which reduce power transfer efficiency. Inductive heating effects increase generally in proportion to the square of the harmonic current. Induction motors can be damaged or degraded by harmonic current heating if the supply voltage is distorted. Negative sequence harmonic currents operate to reduce motor torque output. The combination of these effects reduces power transfer efficiency and can cause
motors to overheat and burn out.
* Harmonic fluxes in the motor windings are either positive, negative or zero sequence depending on the number or order of the harmonic distortion that created them. Positive sequence harmonic magnetic fields (flux) will rotate in the direction of the synchronous field. Negative sequence harmonic flux will rotate in opposition to the synchronous field, thereby reducing torque and increasing overall current demand. Zero sequence harmonic flux will not produce a rotating field, but still will induce additional heat in the stator windings as it flows through the motor magnetic circuit.
Industrial power distribution systems supply AC operating power to connected machinery and devices that produce some harmonic distortion of the AC voltage waveform. Each harmonic of the fundamental frequency, depending on whether it is a positive, negative, or zero sequence,

and its percentage of the fundamental, can have an adverse effect on motor performance and temperature rise, as well as increase the energy costs of electrical service that is charged by the utility service provider.
Electric utilities must generate service capacity adequate to meet the expected peak demand, kVA (kilovolt amps apparent power), whether or not the customer is using that current efficiently. The ratio of kW (real active power) to kVA (apparent power) is called the load power factor. Most utilities charge a penalty when the customer's total load power factor is low. Apparent power can be larger than real power when non-linear loads are present. Non-linear loads produce harmonic currents that circulate back through the branch distribution transformer and into the distribution network. Harmonic current adds to the RMS value of the fundamental current supplied to the load, but does not provide any useful power. Using the definition for total power factor, the real active power kW is essentially that of the fundamental (50Hz) AC waveform only, while the RMS value of the apparent active power kVA is greater because of the presence of the harmonic current components.
A low kW/kVA power factor rating can be the result of either a significant phase difference between-the. voltage and current at the motor load terminals, or it can be due to a high harmonic content or a distorted/discontinuous current waveform. An unacceptable load current phase angle difference can be expected because of the high inductive impedance presented by the stator windings of an induction motor. A distorted current waveform will also be the result of an induction motor that is applying torque to a non-linear load. When the induction motor is operating under discontinuous load conditions, or when the load is non-linear, high harmonic currents will result, degrading motor performance and reducing power factor.
Unified Power Quality Conditioner (UPQC) is a custom power device which is currently the most universal power flow control device. It consists of two identical voltage source converters that are connected by using a common DC port, and can be considered as being formed by one static synchronous compensator (STATCOM) connected in parallel and one Dynamic voltage restorer (DVR) connected in series. Different control functions such as parallel compensation, series compensation and phase shift can be rapidly implemented separately or simultaneously by simply changing the control strategy, thereby inrmroving the performance of the power system.
Currently, thyristor switches are used in conventional controllers for controlling the AC power supplied to the load. Because of the fast on-off switching action (fast dv/dt) of the thyristors, high peak voltage and high switching frequency, the input current on the supply side of the power controller becomes distorted with high frequency switching transients, which cause an increase of harmonic components in the AC power delivered to the load.
Moreover, spurious noise and harmonic currents from remote sources that are conducted down the branch distribution circuit can interfere with the proper switching operation of the controller itself, resulting in loss of power control. These factors not only reduce the power factor of the branch load, but also interfere with motor operation and inject harmonic currents

back through the power distribution branch and into the distribution network. Moreover. controller-generated harmonic distortion increases the RMS value of the load current in the power distribution branch, on which the utility service fees are based, thus increasing the customer's energy costs.
Conventional power quality mitigation equipment is proving to be inadequate for an increasing number of applications, and this fact has attracted the attention of power engineers to develop dynamic and adjustable solutions to power quality problems. This has led to the development of Custom Power Devices (CPD).One modem and very promising CPD that deals with both load current and supply voltage imperfections is the Unified Power Quality Conditioner (UPQC) such a solution can compensate for different power quality phenomena, such as voltage sag, voltage swell, voltage imbalance, harmonics and reactive currents.
Disclosure of the invention:
An improved power controller system is provided for increasing the operating efficiency and performance of conventional AC induction motors that receive operating power from an electronic controller that employs fast switching circuits to control the application of AC power to the stator windings of the motor. The improved controller system operates efficiently to drive a non-linear mechanical load under light torque loading as welt as full-rated torque loading conditions, mitigates harmonic currents from remote sources, mitigates controller-induced harmonic currents and mitigates load-induced harmonic currents.
A primary low pass filter is connected in series between the branch phase conductors and the power controller. kVAR (kilovolt ampere reactive) capacitors are connected across the output terminals of the power controller in shunt to neutral relation. The kVAR capacitor values are coordinated with the inductive reactance values of the STATCOM to form a secondary low pass filter across the controller output terminals. The primary and secondary low pass filters isolate the power controller and induction motor with respect to spurious noise and harmonics generated ■ by local as well as remote sources, and also improves real power transfer efficiency from the power generating source to the induction motor.
This invention will now be described with reference to tlte accompanying drawings, wherein:
Figure 1. Block diagram of UPQC
Figure 2. Power supply circuit to the power converter module
Figure 3. Power supply circuit to the gate pulse driver module
Figure 4. Three phase power converter switching circuit
Figure 5. Gate pulse generator circuit
Figure 6. Power converter module'

Figure 7. From view of'DVR Figure 8. Front view of STATCOM Figure 9. Top view of D^VR & STATCOM Figure 10. Side view of switching module

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Design of Custom Power Devices for Power Quality Improvement using Fractional order PID Controller
CLAIMS:
Wc Claim that:
.A custom power device represented in figure 1 is called as unified power Quality Conditioner (UPQC) for a real time power quality improvement using fractional order PID controller comprising:
1. A series connected custom power device (8) claimed as Dynamic Voltage Restorer (DVR) for the mitigation of voltage sag, voltage swell in the power distribution side end user loads.
2. A shunt connected custom power device (9) claimed as Static synchronous compensator (STATCOM) for the mitigation of harmonics present in the power system and to compensate the reactive power requirement of the system to improve the power factor.
3. For the operation of STATCOM a Control logic having relays and contactors for sequencing and interlocking of all the commands, required for the proper operation of the compensator and as received from control electronics.
4. Said control electronics consist of a 16 bit micro-controller based digital card (with necessary set of software instructions written in assembly language and residing in EPROMs) wherein the controller works a* 12 MHz, said digital card comprising means microcontroller intelligence used for interlocking and sequencing the compensator operation through control logic, outputting the necessary modulating signals, updating of all parameters i.e. voltage, current, dc link voltage, frequency, and sequencing the operation once again at the start of every cycles, checking for the receipt of any faults in the compensator, giving output command for maintaining ON and OFF control of MOSFET gate pulse and also checking and maintaining the health of its own hardware. The said control electronics also having other control cards such as:

i. A relay card for receiving and relaying of various controls and used for interfacing the control electronics with control logic and to deliver the regulated power supplies to the control electronics.
ii. A filler card to receive the input voltage from the potential transformer, filter the same using capacitor and relay it to the relay card as inputs.
iii. A clamp card to receive the three phase current inputs form a current transformer, rectify the same and then pass the output signal as an over current signal to a protection card through the said relay card.
iv. An analog card having necessary circuits for processing the load current feedback, input voltage obtained through step down potential transformer, dc voltage feedback from the converter dc voltage sensor, dc voltage referencing. the dc voltage loop FPID amplifier, to be delivered as the processed inputs to the digital card and also having triangular waveform generator as shown in figure 5 gate pulse generator circuit and processing for the modulating signal received from the digital card to deliver appropriate PWM signals for the MOSFET.
v. A protection card for generating the fault output commends in response to the AC overcurrent based on the input received from clamp card, AC overvoltage and under voltage based on the input received from filter card through analog card and dc voltage based on the input received from DC sensor card and processed through analog card, door interlock, fuse failure and heat sink temperature excess based on the inputs received through relay card and also generating the final gate pulse and delivering it to the gate drive cards through the analog card, to stop the MOSFET pulses and enter the stop sequence mode.
vi. Gate driver cards for accepting the MOSFET gate triggering pulses from the analog card, isolating these signals and delivering them to the MOSFET gates, generating the signal for over current / short circuit current flowing in the MOSFET converter stack, isolating this signal and delivering it to analog card for further processing as a fault input from gate driver.
vii. A dc voltage sensor card for sensing the dc voltage of the MOSFET converter stack through a sensor for required closed loop operation of the said stack and the voltage source converter as its respective dc voltage.

The control system as claimed in claim 4. wherein ihc microcontroller based cligiuil card includes EPROM bank of 64 K space, RAM of 16K space, NVRAM space of 8k, programmable peripheral interface, programmable timer, high speed D/A converters, buffers as input signals and control regulators to reference the analog section of the circuit.
The control system as claimed in claim 4, except for the microcontroller based digital card, uses only one type of a quad operational amplifier for implementing all functions tike comparator, gain amplifier, differentiator, zero cross detector and others.
The control system as claimed in claim 4, wherein the relay card is designed to receive all the power supplies necessary for the analog card, protection card, digital card, gate driver card and also gives out power supply required for clamp card and dc voltage sensor card.
The control system as claimed in claim 4, wherein the real time control logic is feed from a separate isolation transformer, consisting of start push button which delivers the start command through a start contactor to the digital card and microcontroller in response delivers command to operate a start contactor and a bypass contactor, a stop push button, which delivers the stop command through stop contactor in a similar way as the start command and stop trie MOSFET pulse and withdraw bypass contactor.
Design of Custom Power Devices for Power Quality Improvement using Fractional order PID Controller, as claimed in 4, utilizing a three phase power circuit/ power supply and comprising:
i. An MCB, HRC fuses and a smoothening reactor in the incoming power supply line
ii. An incoming surge energy absorbing rectifier
iii. An incoming surge suppressor network *
iv. Means for incoming AC voltage and the dc capacitor for voltage sensing
v. A transformer for the supplies to relay and contactor based control electronics and a microcontroller based digital card assembly
vi. A main contactor
vii. A bypsss contactor
viii. A pre charging resistor

:. A switching current ripple filler capacitor for each phase
;. Protection CTs for each phase
i. Three phase boost inductor/reactor
i. Metal Oxide Semiconductor Field Effect Transistor (MOSFET) power device based converters also having snubber. additional snubber capacitor for each MOSFET module (two MOSFETs in series in' one leg of the converter) connected directly across the dc bus, suitable heatsink to accommodate the MOSFET modules and snubber resistors and a blower for the force cooling the heatsink to deliver the required power.
i. A dc capacitor bank and discharge resistors for the said power switch / MOSFET stack
y. The control system as claimed in 5 to 8, to execute necessary number of analog and digital functions
v. Control logic as claimed in 5 and 6, which provides sequencing the interlocking of the entire compensator based on the commands received from a microcontroller based digital card.
For the operation of DVR as claimed in 3 to 9, to execute necessary functions are repeated to improve the power quality of the system.