Reference Voltage Magnitude Research Articles

Overmodulation Strategy for Voltage Source Inverter With a Single DC-Link Current Sensor

With a single shunt resistor, it is possible to sense the phase currents, although some dead regions exist around vertices of the voltage hexagon. In this article, an overmodulation method is presented for such single current shunt inverters. Regions near vertices of voltage hexagon are defined as holding regions, and the rest are defined as linear regions. The overmodulation strategy is developed based on the Fourier analysis: The magnitude of reference voltage determines the arc radius in the linear region and the holding angle of the holding region. By adjusting either the arc radius or the holding angle, the desired modulation index (MI) can be output. It is particularly useful for low-cost inverters, since it is implemented with an additional look-up table for induction motor or permanent magnet synchronous motor control. The linearity is maintained between the reference MI and its output MI until it reaches to the maximum, 12-step operation. In addition, the technique provides the seamless transition from space vector modulation to 12-step operation. The effectiveness is evidenced by the experimental results.

Predictive Torque Control With Simple Duty-Ratio Regulator of PMSM for Minimizing Torque and Flux Ripples

In this paper, a new method for reducing the ripples of torque and flux is proposed for the predictive torque control (PTC) of permanent magnet synchronous motors. The conventional PTC uses equations to analyze the relationship between the electrical torque and voltage with a fixed magnitude of reference voltage. Consequently, flux and torque ripples increase significantly at low-speed operation. This paper proposes an improved PTC algorithm using a simple duty-ratio regulator. The proposed method will minimize the torque error by calculating an appropriate torque minimization function to mitigate the induced torque and flux ripple at low speed operation. This torque minimization function is synthesized into the space vector pulse-width modulation block to reduce the torque ripple induced owing to the fixed time duration. The proposed scheme considerably reduces the torque and flux ripples and establishes a fast-dynamic response of the torque in the transient state. Simulation and experimental results show that the proposed method achieves a more efficient steady-state performance and a faster step response compared with the conventional PTC.

Simple Controller Configuration for Decentralized Parallel Operation of Inverters

In this paper, a simple controller configuration for the decentralized parallel operation of single-phase inverters in stand-alone ac supply systems is proposed. The configuration is designed considering the unavailability of the filter capacitor voltage and grid current information to the controller. Due to the unavailability of voltage information, internally estimated voltage references and the measured value of the converter-side inductor current are used for the calculation of the active and reactive power. Frequency and voltage droop characteristics are used, and hence, communication is not required. The operation of the inverter at the reference voltage magnitude and frequency is achieved by the direct control of the modulating wave. Therefore, inability to implement closed loops caused by the absence of certain voltage and current information is mitigated. The proposed controller has the provision for protection of switching devices during overcurrent situation. The accuracy and feasibility of the proposed controller are validated using the simulation and experimental results.

Adaptive Virtual Impedance Droop Control Based on Consensus Control of Reactive Current

It is difficult to achieve accurate distribution of reactive power based on conventional droop control due to the line impedance mismatch in an islanded microgrid. An adaptive virtual impendence method based on consensus control of reactive current is proposed in this paper. A distributed control structure without the central controller has been established. In this structure, each distributed generation unit (DG) is an independent agent, one-way communication is used between the adjacent DGs, and the reactive power sharing is equivalent to a problem of reactive power current consensus. It has been proven that the system is asymptotically stable under the proposed control strategy. When the adjacent DG’s reactive power is not proportionally distributed, the current weight error term will generate a virtual impedance correction term through the proportional-integral controller based on the reactive current consensus control strategy, thus introducing adaptive virtual impedance to eliminate mismatches in output impedance between DGs. Reactive power auto-proportional distribution can be achieved without knowing the line impedance. At the same time, the power control loop is simplified and the virtual impedance compensation angle is employed to compensate the decreased reference voltage magnitude and varied phase angle due to the introduction of the virtual impedance, so the stability of the system can be improved. Finally, the correctness and effectiveness of the proposed strategy are verified by modeling analysis and microgrid simulations.

Simplified model predictive control with variable weighting factor for current ripple reduction

Finite control set model predictive control evaluates a predefined cost function for each switching state of power converter. In addition to reference tracking term, cost function can include a term for switching frequency reduction. Small value for the weighting factor of switching reduction term cannot reduce switching frequency effectively and the great value results in reference tracking failure and increase current ripple. In this study a variable weighting factor based on current ripple is obtained and applied to the cost function. The value of weighting factor changes with the position and magnitude of reference voltage. Simulation and experimental results verify the effectiveness of proposed method.

Optimization-based reactive power control in HVDC-connected wind power plants

One application of high–voltage dc (HVdc) systems is the connection of remotely located offshore wind power plants (WPPs). In these systems, the offshore WPP grid and the synchronous main grid operate in decoupled mode, and the onshore HVdc converter fulfills the grid code requirements of the main grid. Thus, the offshore grid can be operated independently during normal conditions by the offshore HVdc converter and the connected wind turbines. In general, it is well known that optimized reactive power allocation might lower the component loading and power losses. This paper aims to propose and assess a reactive power allocation optimization within HVdc–connected WPPs. For these systems, the offshore converter operates the adjoining grid by imposing frequency and voltage. The reference voltage magnitude is used as additional control variable for the optimization algorithm. The loss function incorporates both the collection grid and the converter losses. The use of the proposed strategy results in an effective reduction of losses compared to conventional reactive power dispatch strategies alongside with improvements of the voltage profile. A case study for a 500 MW–sized WPP demonstrates an additional annual energy production of 6819 MWh or an economical benefit of 886 k€yr−1 when using the proposed strategy.

멀티레벨 인버터를 이용한 무효전력 보상장치에서의 DC-Link 전압 불평형 보상

Recently, we use a static synchronous compensator(STATCOM) with cascaded H-bride topologies, because it is easy to increase capacity and to reduce total harmonic distortion(THD). When we use equipment for reactive power compensation, dc-link voltage unbalances occur from several reasons although loads are balanced. In the past, switching pattern change of single phase inverter and reference voltage magnitude change of inverter equipped with power sensor have been used for dc-link voltage balance. But previous methods are more complicated and expensive because of additional component costs. Therefore, this paper explains reasons of dc-link voltage unbalance and proposes solution. This solution is complex method that is composed of reference voltage magnitude change of inverter without additional hardware and shifted phase angle of inverter reference voltages change. It proves possibility through 1000[KVA] system simulation.

공간벡터 PWM을 이용한 간단한 정적 과변조기법

본 논문은 출력 전압의 선형성을 확장하기위한 정적 과변조 기법에 대한 것이다. 제안하는 방식은 기본파 전압 크기 지령에 해당하는 변조 지수로부터 직접 과변조 영역에서의 순시치 전압 크기를 얻어내는 방식을 취하며, 전압 위상 지령의 형태도 간소화시킨 간단한 정적 과변조 기법이다. 제안된 기법은 지령치 전압 크기 계산시 삼각함수의 연산이 불필요하다. 순시치 전압 크기와 유지각은 출력전압의 크기가 변조 지수에 해당하는 지령치 전압의 기본파 크기와 동일하도록 푸리에 급수 전개를 통하여 미리 계산된 근사식을 이용한다. This paper proposes a simple static overmodulation strategy that extends the linearity of the inverter output voltage. The proposed method obtains the reference vector having the instantaneous value directly from the modulation index based on the magnitude of fundamental voltage, and has a simplified form of phase command. This method does not need trigonometric functions for calculating the magnitude of the reference vector. The magnitude of reference voltage and holding angle in the overmodulation region corresponding to the modulation index are determined in advance to have the same fundamental voltage magnitude by using the result of Fourier series expansion.

A new family of multi‐output DC‐DC converter topologies to supply an asymmetrical four‐level diode‐clamped inverter

PurposeMulti‐level diode‐clamped inverters have the challenge of capacitor voltage balancing when the number of DC‐link capacitors is three or more. On the other hand, asymmetrical DC‐link voltage sources have been applied to increase the number of voltage levels without increasing the number of switches. The purpose of this paper is to show that an appropriate multi‐output DC‐DC converter can resolve the problem of capacitor voltage balancing and utilize the asymmetrical DC‐link voltages advantages.Design/methodology/approachA family of multi‐output DC‐DC converters is presented in this paper. The application of these converters is to convert the output voltage of a photovoltaic (PV) panel to regulate DC‐link voltages of an asymmetrical four‐level diode‐clamped inverter utilized for domestic applications. To verify the versatility of the presented topology, simulations have been directed for different situations and results are presented. Some related experiments have been developed to examine the capabilities of the proposed converters.FindingsThe three‐output voltage‐sharing converters presented in this paper have been mathematically analysed and proven to be appropriate to improve the quality of the residential application of PV by means of four‐level asymmetrical diode‐clamped inverter supplying highly resistive loads.Originality/valueThis paper shows that an appropriate multi‐output DC‐DC converter can resolve the problem of capacitor voltage balancing and utilize the asymmetrical DC‐link voltages advantages and that there is a possibility of operation at high‐modulation index despite reference voltage magnitude and power factor variations.

An application of a constrained adaptive lattice-structure allpass-based notch filter for advanced control of surface-mounted permanent-magnet synchronous drives

A constrained adaptive lattice-structure allpass-based notch filter provides minimal phase delay and complete attenuation of the notch frequency. The allpass sections of the filter are realized as structurally lossless bounded real functions, with a minimum number of delay elements and multipliers. The filter structure admits orthogonal tuning of the notch frequency and notch bandwidth. An improved control scheme for surface-mounted permanent-magnet synchronous (SMPMS) drives ensures stable high-performance operation in the Bur weakening region, utilizing the over-modulation and six-step modes of the space vector modulation (SVM). An automatic transition into the flux weakening region is achieved by controlling the reference voltage magnitude. The fifth and seventh stator current harmonics of the fundamental frequency, generated in the over-modulation and six-step modes, propagate through the current control loops, resulting in the sixth harmonic in the reference voltage for the flux weakening loop and deteriorating drive performance. To properly filter the sixth harmonic over the extended speed range of the drive, the constrained adaptive lattice-structure allpass-based notch filter is employed.