Constant Power Factor Control Research Articles

Power factor control for inverters under high penetration of distributed generation

AbstractThe paper proposes a method to select a power factor for an inverter of distributed power generation systems to keep appropriate voltage of a power system with the high penetration of inverter‐interfaced generation. The increase of inverter‐interfaced power sources, such as wind and photovoltaic power generation, arouses concerns on the voltage fluctuations in a power system. While constant power factor control of an inverter has been studied as a means to stabilize the voltage of a power system, there still remains room to improve the control. The proposed method in the paper selects the power factor based on the R/X ratio of the looking‐back impedance into the interconnected power system. By normalizing the related variables, a general formula is derived for the power factor, and the resultant relationship between the apparent power and voltage of an inverter becomes identical irrespective of the R/X ratio with the control. Sample studies show that, by operating an inverter with the power factor, voltage fluctuations are effectively suppressed even for a power system with the high penetration of inverter‐interfaced generation.

A sensorless stable V/f control of SPMSM based on constant power factor control with a novel MTPA tracking

The paper presents a sensorless stable V/f control strategy of surface permanent magnet synchronous motor (SPMSM), where the maximum torque per ampere (MTPA) condition is satisfied by controlling the d-axis current to zero. However, to directly control the d-axis current, it is necessary to know the exact rotor position, which is not possible in sensorless V/f control. Based on this fact, a constant power factor (CPF) control loop in voltage vector reference frame dvqv with a novel MTPA tracking according to a look-up table (LUT) was developed. The LUT was created based on a set of experimental measurements to store the motor power factor where MTPA is reached. The proposed stable V/f control strategy shows an accurate MTPA tracking of SPMSM in the entire operational range verified by experiments.

Research on novel var compensator based on dual-rotary phase-shifting transformers and its control strategy

With the continuous increase in the penetration of distributed power with random output, the acceleration of the urban cableization rate and the rapid development of supergrid, the active distribution network puts forward higher requirements for the performance of dynamic reactive power compensation. A topology of novel rotary VAR compensator (NRVC) is proposed by integrating the current source static synchronous compensator with the continuous regulation characteristics of dual rotary phase-shifting transformers. The NRVC compensation principle is analyzed by establishing the steady-state mathematical model of dual rotary phase-shifting transformers and NRVC. The dynamic response performance and universal applicability are improved by considering its compensation capacity constraints, applying the instantaneous reactive power theory, and constant power factor control. A dual closed-loop decoupling control strategy of power outer-loop and current inner-loop is also presented to prevent internal overcurrent. Finally, the simulation and experimental results are performed to verify the effectiveness of the proposed system and control strategy, which realized bidirectional and continuous regulation of compensated reactive power, and has manifold advantages: low cost, strong shock resistance, large heat capacity, simple control, and no harmonic pollution.

Voltage Reduction in Medium Voltage Distribution Systems Using Constant Power Factor Control of PV PCS

Reverse power flow from a photovoltaic (PV) system in a distribution system causes a voltage rise. A relative study regarding the reduction in the distribution feeder voltage depending on system conditions and the magnitude of reverse power flow has been conducted. Several methods for mitigating voltage rise have been proposed; however, the influence of these methods on the voltage in the distribution system, where the voltage is reduced due to reverse power flow, remains to be determined. In this study, the effect of constant power factor control in low-voltage PV systems, which are widely used as voltage rise countermeasures in distribution systems, was analyzed under the condition that the distribution line voltage decreases due to reverse power flow. Consequently, the constant power factor control of the low-voltage distribution system was found to adversely reduce voltage in the medium voltage distribution system due to the consumption of lagging reactive power by the PV systems.

High-Efficiency Operation of an Open-Ended Winding Induction Motor Using Constant Power Factor Control

A controller is presented for an open-ended winding motor dual-inverter drive (DID), where main and floating inverters are supplied from a dc power source and a floating dc capacitor, respectively. The controller utilizes the efficiency characteristic of induction machines, where high power conversion efficiencies are obtained when operating the machine with a constant fundamental power factor, typically around 0.70–0.75, over a wide load range and under variable frequency. The controller uses the drive's topology to maintain the motor's desired power factor. In essence, the main inverter's output voltage is used to control the floating inverter's dc capacitor voltage to keep the injected fundamental voltages of both inverters at a desired ratio. The floating inverter's voltage is operated with a 90° lead relative to the main inverter and uses a constant maximum amplitude modulation depth to minimize the capacitor's operating voltage. This approach updates the motor's voltage automatically to ensure constant power factor operation and improves the floating capacitor's voltage stability during transient conditions. The inherent voltage-boosting capability of this topology is especially beneficial in extending the constant torque region of the motor and improving performance in the speed range extension region. Simulation and experimental results verify the predicted motor efficiency gains and stability under speed and load transients.

Reactive Power Control of Mega‐Solar System for Voltage Regulation with Long Distribution Line

SUMMARYConstant power factor control of a power conditioning system in a large‐scale photovoltaic generation system (PV system) such as a mega‐solar system is introduced to mitigate voltage variations on a distribution line. However, it is difficult for the control to mitigate the voltage variation on a long distribution line because of the changes in the loss on the distribution line. This paper proposes an advanced reactive power control in which the power factor of the PV system is adjusted using both the output power of the PV system and the apparent power of loads not to minimize the voltage variation at the interconnecting point but to minimize the voltage variation over the whole distribution line. We report on the results based on numerical analysis on mitigating the voltage variation by applying this control. This paper shows that the proposed control can mitigate the voltage variation better than constant power factor control can. The proposed control has the potential to be used as a measure for suppressing voltage variations on a long distribution line.

An Analytical Solution for Voltage Stability Studies Incorporating Wind Power

Voltage stability is one of the most critical security issues which has not yet been well resolved to date. In this paper, an analytical method called PQ plane analysis with consideration of the reactive power capability of wind turbine generator and the wake effect of wind farm is proposed for voltage stability study. Two voltage stability indices based on the proposed PQ plane analysis method incorporating the uncertainties of load-increasing direction and wind generation are designed and implemented. Cases studies are conducted to investigate the impacts of wind power incorporation with different control modes. Simulation results demonstrate that the constant voltage control based on reactive power capability significantly enhances voltage stability in comparison of the conventional constant power factor control. Some meaningful conclusions are obtained.

長距離配電線に対応したメガソーラー発電システムの無効電力制御による電圧変動抑制

Constant power factor control of a power conditioning system in a large-scale photovoltaic generation system (PV system), such as a mega-solar system, is introduced to mitigate voltage variations on a distribution line. However, it is difficult for the control to mitigate the voltage variation on a long distribution line because of the loss change on the distribution line. This paper proposes an advanced reactive power control, in which the power factor of the PV system is adjusted both by output power of the PV system and by apparent power of loads not to minimize the voltage variation at the interconnecting point but to minimize the voltage variation over the whole distribution line, and reports the result examined by numerical analysis about mitigating the voltage variation by applying the control. This paper shows that the proposed control can mitigate the voltage variation more than constant power factor control and there is a probability that it will be applied as a measure of suppressing the voltage variation on the long distribution line.

PV出力に応じた無効電力制御によるSVC容量低減効果と配電線路損失への影響評価

When a large number of photovoltaic (PV) power generations are installed in the distribution system, it is expected that distribution line voltage will fluctuate by the PV output. Then, the large capacity of SVC may be required because the distribution line voltage cannot be controlled by only SVR operation. In this paper, a reactive power control method in proportion to the PV output change is proposed to reduce the capacity of SVC by complementing SVR operation. By the simulation analyses, it was shown that the capacity of the SVC was reduced by the proposed reactive power control. In addition the distribution line loss of the proposed method was smaller than that of the constant power factor control.

Dynamic Mathematical Model of Variable Pitch Double-Fed Wind Power Generator

Based on the variable speed constant frequency doubly-fed wind turbine model, this paper increased the power factor control link for the wind farm to apply two kinds of constant voltage and constant power factor control mode of the simulation needs, and build a suitable for our country to contain a mathematical model of wind power system stability analysis.

A Novel High-Power-Density Three-Level LCC Resonant Converter With Constant-Power-Factor-Control for Charging Applications

This paper proposes a variable-frequency zero-voltage-switching (ZVS) three-level LCC resonant converter that is able to utilize the parasitic components of the high turns-ratio transformer. By applying a three-level structure to the primary side, the voltage stress of the primary switches is half of the input voltage. Low-voltage MOSFETs with better performance can be used in this converter, and zero-current-switching (ZCS) is achieved for rectifier diodes. By applying a magnetic integration technique, only one magnetic component is required in this converter. The power factor concept of resonant converters is proposed and analyzed, and a novel constant power-factor control scheme is proposed. Based on this control strategy, the circulating energy of resonant converters is considerably reduced. High efficiency can be obtained for high-voltage high-power charging applications. The operation principle of the converter is analyzed and verified on a 700-kHz, 3.7-kW prototype, with which a power density of 72 W/inch3 is achieved.

Measured Effects of Wind Turbine Reactive Power Control on an Isolated Utility

One phase of an overall effort in evaluating performance of a 150 kW MOD-OA wind turbine connected to the Block Island Power Company (BIPCO) system consisted in analyzing three methods of excitation (reactive power) control. These are identified as: 1) constant var (reactive), 2) constant voltage, and 3) constant power factor (PF) control. The power system environment in which the wind turbine generator (WTG) exists ultimately determines which method of control is the most suitable. In the case of the BIPCO installation, the major emphasis was to insure sufficient WTG electrical torque during wind gusts in low power output periods. Subsequent use of constant PF control demonstrated an adequacy of performance equivalent to that of constant var control while constant voltage control indicated a diminished capacity to maintain synchronism with the utility, when compared to constant var or PF control. A mathematical model which incorporates the detailed excitation system transfer functions is used to compare the results indicated by the measurements produced during a three-month data acquisition effort.

Measured Effects of Wind Turbine Reactive Power Control on an Isolated Utility

One phase of an overall effort in evaluating performance of a 150 kW MOD-OA wind turbine connected to the Block Island Power Company (BIPCO) system consisted in analyzing three methods of excitation (reactive power) control. These are identified as 1) constant var (reactive), 2) constant voltage, and 3) constant power factor (PF) control. The power system environment in which the wind turbine generator (WTG) exists ultimately determines which method of control is the most suitable. In the case of the BIPCO installation, the major emphasis was to insure sufficient WTG electrical torque during wind gusts in low power output periods. Subsequent use of constant PF control demonstrated an adequacy of performance equivalent to that of constant var control while constant voltage control indicated a diminished capacity to maintain synchronism with the utility, when compared to constant var or PF control. A mathematical model which incorporates the detailed excitation system transfer functions is used to compare the results indicated by the measurements produced during a three-month data acquisition effort.

Constant power factor control system for HVDC transmission

In inverter operation of a converter for h.v.d.c. transmission, commutation failure is inevitable in such a case that a.c. voltage suddenly drops due to occurrence of a fault in the a.c. system. In this paper, the region of inevitable commutation failure is first discussed and then the constant power factor control system is proposed to squeeze the region. By using this control system, the extinction angle is kept larger in partial load than in full load. Also, the proposed control system makes it possible to rapidly increase d.c. transmission power from the minimum to full loads without controlling transformer taps.