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A new control strategy for three-phase four-wire UPQC with zero steady-state error
Abstract
For UPQC, when source voltage or load current are unbalance or distort, conventional proportional-integral controller on the p-q-r axis can not eliminate steady-state error. To solve this question, an AC equivalent proportional-integral controller in p-q-r axis was proposed. Its principle of eliminating steady-state error to zero was analyzed and a new control strategy by using of it was presented. A principle analysis of the proposed control strategy is described in particular. Meanwhile the control formulas on the improved p-q-r coordinate are deduced in detail. The control schematic diagram based on these formulas is presented. Experiment result shows that UPQC efficiently carry out its compensation function while adopting the proposed control strategy.
... In distribution system various power quality problems like unbalance voltage mitigation, power flow control, flicker reduction and sag compensation compensates by UPQC explained in [110][111][112][113][114][115][116][117][118][119][120]. In [113][114][115][116][117] for avoiding problem of stability, UPQC with nonlinear strategy of control, UPQC different strategies of control at load side, UPQC with novel method of control and UPS systems are presented. ...
... In [113][114][115][116][117] for avoiding problem of stability, UPQC with nonlinear strategy of control, UPQC different strategies of control at load side, UPQC with novel method of control and UPS systems are presented. For injecting voltage in quadrature advance to the supply current control of SERC of UPQC is proposed in [112][113][114][115][116][117][118]. The schematic diagram of UPQC is presented in Figure 4 which shows UPQC unit, transformer, series inductors, parallel capacitors, loads etc. ...
... Fig. 1 shows the general power circuit configuration of the USPAF system. The USPAF structures are used in the literature such as two three-phase three-leg (3P3L) voltage source inverter (VSI) with split capacitor [7,[10][11][12][13][14], a 3P3L VSI for the series AF and a three-phase four-leg (3P4L) VSI for the parallel AF [15,16] and two 3P4L VSI topology [17] for solving power quality disturbances at the point of common coupling (PCC). ...
... By this transform, fundamental positive sequence component, which is transformed into dc quantities in d and q axes, can be extracted by Eq. (14) and then transformed back into the abc reference frame using Eq. (15). ...
The building of harmonic voltage source is the one of key issues in harmonic characteristic measurement of voltage transformer. It is required to output large capacity and controllable harmonic components, but the existing harmonic sources cannot satisfy these requirements. To solve the problem, this paper refers the scheme of IGBT single-phase inverter as the core to build the controllable harmonic voltage source. The working principle of the controllable harmonic voltage source is introduced, the system parameters are designed and simulated and the characteristics of the controller are analyzed. The simulation results show the feasibility of the proposed scheme. On this basis, the VT harmonic characteristic measurement platform is built. The output results further verify the effectiveness of the scheme, which lay the foundation for harmonic characteristic measurement and test study of the voltage transformer. ©, 2015, Power System Protection and Control Press. All right reserved.
This paper applies the topology of modular multilevel converter (MMC) to the unified power quality conditioner (UPQC). In order to improve the comprehensive compensation functions of MMC-UPQC at the high voltage, large capacity power quality environment, the paper analyzes the voltage sag compensation capability of UPQC's series MMC theoretically in detail. The topology mechanism of MMC-UPQC is given; the time domain expressions are calculated with the voltage sag value, the compensation duration, the main circuit and MMC parameters and so on, a coordinated control design method for UPQC is proposed, which is the fixed active current limit value control allowing the reduction of the common DC link voltage based on the traditional fixed DC voltage control. Define and calculate two voltage thresholds dividing the MMC-UPQC operation into the aforementioned states. The MMC-UPQC system simulation results under PSCAD/EMTDC indicate that the theoretical analysis is effective and correct. The simulation results also illustrates that the proposed coordinated control could improve voltage sag compensation time and amplitude supplied by UPQC.
To solve the control problem of DC link voltage stability for unified power quality conditioner (UPQC), a novel control strategy is presented using brain emotional learning based intelligent controller (BELBIC). The parallel compensation and series compensation converter mathematical models are established by switching function description method for UPQC system that consists of two pulse width modulation (PWM) converters connected back-to-back on the DC side. According to the structure and emotion-processing mechanism of brain emotional learning (BEL) computational model, a multi-objective control block diagram is proposed for UPQC device based on intelligent controller BELBIC. The simulation and experimental results indicate the UPQC system achieves the DC link voltage stabilization and output compensation for reactive current and active voltage. The UPQC has good dynamic and static performance. The results verify the correctness and effectiveness of this method.
In recent years, the research on control strategy of three-phase grid-connected inverter has attracted significant attention. Proportion integration (PI) control method is widely utilized to control the grid-connected inverter. However, coordinate transformation is an essential and complex step during the design process of the conventional PI controller. It is difficult to implement in practice due to the complex coordinate transformation. The proportional-resonant (PR) control method of the three-phase grid-connected inverter is proposed, where the conventional PI controller is replaced by PR controller. PR controller has a simple structure as the complex coordinate transformation can be neglected. In order to improve the power factor and the stability of the system, double closed loop structure is also introduced in the proposed control strategy. In the end, simulation software is developed, and the simulation results confirm the effectiveness of the proposed control method.
This paper presents a new configuration of Unified Power Quality Conditioner (UPQC) which is connected to a two feeder distribution system to improve the power quality. The advantage of the proposed design is the flexibility to use it as Interline Unified Power Quality Conditioner (IUPQC) or a combination of shunt/series active power filters. The shunt active power filter is used for mitigation of current harmonics and reactive power compensation, while the series active filter is to maintain the load voltage as sinusoidal at the required level. Simulation of the distribution system model by using PSCAD/ EMTDC and MATLAB/SIMULINK show the capability of the proposed UPQC to minimize the major power quality problems in a two feeder distribution system.
The operation principle of a three-phase series-parallel compensated line-interactive UPS system is presented and its merits different from the traditional double conversion on-line UPS are pointed out, and then, a kind of control manner using Synchronous Reference Frame (SRF) is proposed. By controlling the series converter as a fundamental sine current source and the parallel converter as a fundamental sine voltage source, the proposed control tactics can make this kind of UPS carry out all of the control goals: sinusoidal input current with φ=1 and sinusoidal output voltage with normal value in the case of non-sinusoidal, abnormal supply voltage and non-linear load with reactive power. The simulation results of system performance under continuous domain verify that the strategy is feasible.
This paper presents a novel Control Algorithm for Unified Power Quality Conditioner. The proposed algorithm treats the series inverter and the parallel inverter of UPQC as a unified unit, the reference of both part are simultaneously computed. To be digitalized and compensate the delay caused by a great deal of computation, deadbeat control and SVM (Space Vector Modulation) are employed to control the switch of UPQC so that the compensated current and the compensated voltage of UPQC are been exactly equal to its reference. A reduced order predictive state observer is used to reduce the number of sensors. The robustness of the deadbeat control algorithm is also discussed in this paper. The simulation results verify the viability and effectiveness of the control algorithm.
A Unified Power Quality Conditioner (UPQC) is presented in this paper. The active power balance of this UPQC is analyzed. Based on the analysis a novel control scheme is established in 2-phase synchronous rotating d-q frame (SRF). In this control scheme the series AF is controlled as a current source and makes the input current sinusoidal, while the shunt AF is controlled as a voltage source and keep the load voltage in the normal value. Simulation and experimental works are done to verify the effectiveness of applying such control strategy in UPQC.
In this paper, simulation and experimental based evaluation of novel lowpass to bandpass transformed PI control strategy for series hybrid active power filter is presented. In the series hybrid topology, the active filter is in series with a capacitor and this whole arrangement comes in parallel with an inductor. This hybrid setup is introduced in series between the source and load. The control structure is derived in the stationary reference frame through lowpass to bandpass transformation of ordinary PI controller transfer function. The effect of controller on system performance as well as its selective harmonic elimination is illustrated. The modelling, simulation and experimental results are presented.
A cascaded H-bridge multilevel inverter based active power filter with a novel direct power control is proposed in this paper. It can be directly connected to medium/high voltage power line without using the bulky transformer or passive filter. Due to the limited switching frequency (typically below 1 kHz) of high-power solid-state devices (GTO/IGCT), multiple synchronous/stationary reference frame current controllers are reviewed and derived. Based on this, a novel current controller is proposed for harmonic current elimination and system power factor compensation. Furthermore, a synchronous/stationary hybrid structure can be derived with fundamental de-coupling control. The instantaneous reactive power theory and synchronous reference frame based control are compared based on mathematical models. A direct power control concept is then derived and proposed. It is equivalent as the hybrid synchronous/stationary frame current controller, but has a simpler implementation. It has clear physical meaning and can be considered as a simplified version of the hybrid frame current controller. Simulations on a 4160 V/1.2 MVA system and experimental results on a 208 V/6 kVA laboratory prototype are presented to validate the proposed active power filter design.
Current regulators for AC inverters are commonly categorised as
hysteresis, linear PI or deadbeat predictive, with a further
subclassification into stationary ABC frame and synchronous DQ frame
implementations. Synchronous frame controllers are generally accepted to
have a better performance than stationary frame controllers do, as they
operate on DC quantities and hence can eliminate steady state errors.
This paper establishes a theoretical connection between these two
classes of regulators and proposes a new type of stationary frame
controller, which achieves the same steady state performance as a
synchronous frame controller. The new controller is applicable to both
single phase and three phase inverters
This paper deals with “unified power quality
conditioners” (UPQCs) which aim to integrate series active and
shunt active filters. The main purpose of a UPQC is to compensate for
voltage flicker/imbalance, reactive power, negative sequence current and
harmonics. In other words, the UPQC has the capability of improving
power quality at the point of installation on power distribution systems
or industrial power systems. This paper discusses the control strategy
of the UPQC, with the focus on the flow of instantaneous active and
reactive power inside the UPQC. Some interesting experimental results
obtained from a laboratory model of 20 kVA, along with theoretical
analyses, are shown to verify the viability and effectiveness of the
UPQC
Three linearly independent instantaneous powers have been defined in the time domain in three-phase four-wire systems with the use of p-q-r theory. Any three-phase circuit can be transformed into three single-phase circuits by the p-q-r transformation. Thus the instantaneous powers in any three-phase systems can be analyzed as the same way of instantaneous power in single-phase systems. This paper analyzes the instantaneous powers spectrally in the frequency domain for single-phase systems and three-phase systems. Each instantaneous power in three-phase systems has its own spectral pattern that is characterized by the spectral distribution of the system voltages and currents. The instantaneous power in single-phase systems has its own spectral pattern different from that of three-phase systems. From the spectral analysis of the instantaneous powers, powers are newly defined in the frequency domain. The definition of the powers is consistent through single-phase systems and three-phase systems and agrees well with the traditional definition of powers in sinusoidal single-phase systems. Based on the defined powers, some useful power quality factors are defined to evaluate power qualities for various circuit conditions.