Advanced control of PWM converter with variable-speed induction generator
TL;DR: Different control principles, indirect vector control and deadbeat current control, are developed for a voltage source pulsewidth-modulation (PWM) converter and the three-phase variable-speed squirrel-cage IG to regulate dc link and generator voltages with the newly designed phase-locked loop circuit.
Abstract: This paper describes simple control structures for the vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Different control principles, indirect vector control and deadbeat current control, are developed for a voltage source pulsewidth-modulation (PWM) converter and the three-phase variable-speed squirrel-cage IG to regulate dc link and generator voltages with the newly designed phase-locked loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to buildup the voltage of the IG without the need for a battery, to reduce the rating of the PWM converter with the need for only three sensors, and to eliminate the harmonics generated by the PWM converter. These proposed schemes can be used efficiently for variable-speed wind energy conversion systems. The measurements of the IG systems at various speeds and loads are given and show that these systems are capable of good ac and dc voltage regulations
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TL;DR: In this article, the authors investigated a permanent-magnet wind generator with a full power voltage-source converter in weak-grid mode, where the DC-link voltage needs to be controlled from the generator side instead of the grid side.
Abstract: When the wind power accounts for a large portion of the grid power, it may need to help the grid voltage and frequency regulation. This paper investigates a permanent-magnet wind generator with a full power voltage-source converter in weak-grid mode, where the DC-link voltage needs to be controlled from the generator side instead of the grid side. The energy relationship of the wind generator, DC-link energy storage, and load is established. An intrinsic right-half-plane zero, together with the wind power characteristics, the mechanical system inertia, and the DC-link energy storage, is identified as the physical limitations for the control. With the understanding of the system energy relationship and limitations, a hybrid adaptive control algorithm is proposed that searches for the optimal generator acceleration to achieve the maximum wind generator power change rate to match the load power variation. The proposed control scheme is verified through simulation of a 1.5-MW wind system as well as through the experiment of a scaled 1-kW, DSP-/field-programmable-gate-array-controlled, permanent-magnet-generator-based test bed. The results show that it is feasible to regulate DC link by the generator-side converter through the generator speed control. Some important applications issues are also investigated, including the DC-link energy storage requirement, wind speed change impact, and control transition between the weak-grid and strong-grid modes.
205 citations
TL;DR: In this article, a novel maximum power point (MPP) tracking (MPPT) algorithm for grid-connected wind energy generation systems (WEGS) is presented, which is a rapid tracking algorithm that uses the fact that the value of?s,? an intermediate variable, especially defined for the purpose, remains constant ( =sMPP ) for a given WEGS at the MPP irrespective of the wind velocity.
Abstract: This paper presents a novel maximum power point (MPP) tracking (MPPT) algorithm for grid-connected wind energy generation systems (WEGS). This is a rapid tracking algorithm that uses the fact that the value of ?s,? an intermediate variable, especially defined for the purpose, remains constant ( =sMPP ) for a given WEGS at the MPP irrespective of the wind velocity. The value of sMPP is known in advance. The algorithm works in two stages. In the first stage, it uses large steps to quickly drive the operating point to lie within a narrow band with limits smax and smin. In the second stage, exact MPP is tracked using the ?perturb and observe? method. No extra hardware or measurements (sensors) are required compared to the existing algorithms. Hence, the cost is not increased. Application of the proposed algorithm to an example WEGS shows that the time taken by the system to reach MPP is much smaller compared to most of the existing algorithms. A prototype matrix converter has been developed for grid interfacing and the proposed MPPT scheme has been implemented in conjunction with Venturini and space-vector-modulation-based switching schemes. All the results of this study are presented.
189 citations
Cites methods from "Advanced control of PWM converter w..."
...When an SCIG with power converter [12]–[14] or DFIG with rotor side control is used, the speed of the IG can be varied over a wide range by changing the frequency at the generator terminals [15]....
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16 May 2008
TL;DR: In this article, a variable step search algorithm based on the derivation of the electro-mechanical dynamic model describing the wind turbine is proposed, which enables the wind generator output power to match the load power, thus keeping the dc-link voltage regulated.
Abstract: In this paper, permanent magnet wind generator with full power converter is investigated in weak grid systems, where the dc-link voltage needs to be controlled from the generator side instead of grid side. When wind power takes a large portion of grid power, it needs to help grid to regulate the voltage and frequency. To achieve this, a variable step search algorithm based on the derivation of the electro-mechanical dynamic model describing the wind turbine is proposed, which enables the wind generator output power to match the load power, thus keeping the dc-link voltage regulated. Based on the non-linearity and different slopes of wind power curve, the controller is designed specifically for different sectors. A back-EMF observer based sensor-less generator control is adopted here to regulate the generator speed. Simulation is built up with a 10 kW wind power generator system and a reduced-scale 1.5 kW system experiment is also carried out in the condition of load power step change and wind speed change. Both simulation and experimental results validate the effectiveness of the proposed control scheme, where the dc-link voltage can be kept stable by adjusting the wind generator speed.
91 citations
TL;DR: In this article, a new offline identification scheme is presented based on the vector constructing method, which is applied to the continuous-time model of the squirrel-cage induction machine at standstill.
Abstract: The squirrel-cage induction machine (IM) has been widely employed in microgrid. Accurate electrical parameters are necessary for the field-oriented control of the IM to achieve excellent performance. In this paper, a new offline identification scheme is presented based on the vector constructing method. The IM parameters are estimated using the recursive least squares (RLS) algorithm, which is applied to the continuous-time model of the IM at standstill. A single-phase ac test is used to make the machine standstill. The main feature of the proposed scheme is that the stator voltage, stator current and their derivatives, which are normally needed for the RLS algorithm, are constructed by the vector constructing method. The constructing rules are elaborated, which indicate that the phase shift and the amplitude ratio between the fundamental components of the voltage and the current have to be unchanged. This feature can avoid the analog or digital differentiators and greatly increase the noise immunity. Furthermore, the digital low-pass filter is not required for the proposed scheme, which can reduce the complexity of the identification scheme. Simulation and experimental results have been presented to demonstrate the validity and the feasibility of the proposed scheme.
86 citations
Cites methods from "Advanced control of PWM converter w..."
...In order to track the maximum power point during wind velocity changes, the field-oriented control of the IM is often employed to obtain fast dynamic response and accurate torque control both in grid-connected [5], [6] and standalone mode [7], [8]....
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TL;DR: In this article, a maximum power point tracking control (MPPTC) is used to maximize the captured energy when the wind speeds are below the rated speed. But, the proposed strategy is to utilize a modified perturb and observe (P&O) algorithm for MPPT control, where the dc side current is used as a perturbation variable and the dc-link voltage slope information was used to enhance the tracking speed and stability.
Abstract: This paper presents a new overall control strategy for small-scale wind energy conversion systems (WECS). The purpose of the proposed strategy is to utilize a maximum power point tracking control (MPPT) to maximize the captured energy when the wind speeds are below the rated speed. For high wind speed region; two stall controllers are developed: The constant speed stall controller which will limit the rotational speed of the generator to its rated value, and the constant power stall controller, which will regulate the captured power to be within the system rating. For the MPPT control, a modified perturb and observe (P&O) algorithm is utilized, where the dc side current is used as a perturbation variable and the dc-link voltage slope information is used to enhance the tracking speed and stability of the algorithm. For the speed and power regulation operation during high wind speeds, the system is controlled in the stall region to limit the rotational speed and the power of the generator. A stabilizing control loop is proposed to compensate for the stall region instability. A new mode transfer control strategy is developed to effectively control the transition between different modes of operation while ensuring the system stability without using any preknowledge of the system parameters. A 1 kW hardware prototype is developed and tested to validate the proposed new control strategy.
85 citations
References
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03 Oct 1999
TL;DR: This paper presents a novel usage of a dual stator winding, three-phase induction machine as a stand-alone generator with both controlled output load voltage magnitude and frequency and a detailed mathematical model of the system is confirmed to accurately predict dynamic and steady-state performance characteristics.
Abstract: This paper presents a novel usage of a dual stator winding, three-phase induction machine as a stand-alone generator with both controlled output load voltage magnitude and frequency. This generator, with both three-phase power and control windings housed in the stator structure, has the load connected to the power winding and a three-phase PWM voltage source inverter sourcing the control winding. The input to the PWM inverter is either a battery source or a charged DC capacitor. The operational characteristics of these generator schemes with either of the two inverter sources is investigated and shown to have desirable performance. How the load voltage magnitude depends on the various control and design parameters such as rotor speed, compensating capacitance and load impedance are determined using a detailed mathematical model of the system which is confirmed to accurately predict dynamic and steady-state performance characteristics.
193 citations
TL;DR: In this paper, a three-phase self-excited induction generator (SEIG) with squirrel-cage rotor is presented along with its operating performance evaluations for small-scale clean renewable and alternative energy utilizations.
Abstract: In this paper, the practical impedance approach steady-state analysis in the frequency domain for the three-phase self-excited induction generator (SEIG) with squirrel-cage rotor is presented along with its operating performance evaluations. The three-phase SEIG is driven by a variable-speed prime mover(VSPM) in addition to a constant-speed prime mover (CSPM) such as a wind turbine and a micro gas turbine for clean alternative renewable energy in rural areas. The basic steady-state characteristics of the VSPM are considered in the three-phase SEIG approximate equivalent circuit and the operating performance of the three-phase SEIG coupled with a VSPM and/or a CSPM are evaluated and discussed online under the conditions related to the speed changes of the prime mover and the electrical inductive load power variations with simple computation processing procedures. A three-phase SEIG prototype setup with a VSPM is implemented for small-scale clean renewable and alternative energy utilizations. The experimental performance results give good agreement with those obtained from the simulation results. Furthermore, a proportional-integral (PI) closed-loop feedback voltage regulation of the three-phase SEIG driven by the VSPM on the basis of the static var compensator (SVC) composed of the thyristor phase-controlled reactor in parallel with the thyristor switched capacitor and the fixed-excitation capacitor bank is designed and considered for the wind generation as a renewable power conditioner. The simulation analysis and experimental results obtained from the three-phase SEIG with SVC for its voltage regulation prove the practical effectiveness of the additional SVC with the PI-controller-based feedback loop in steady-state operation in terms of high performance with low cost.
160 citations
TL;DR: In this article, a new strategy for controlling voltage and frequency of a self-excited induction generator (SEIG) is presented, which operates in the linear region of the core magnetizing curve, so that efficiency and performance are upgraded.
Abstract: A new strategy for controlling voltage and frequency of a self excited induction generator (SEIG) is presented. The SEIG operates in the linear region of the core magnetizing curve, so that efficiency and performance are upgraded. An external excitation circuit, comprising permanently connected capacitors and electronically switched inductances is used. The external circuit allows to compensate for the generator reactive demand. A detailed analysis is performed, showing some salient aspects related to the connection of the external excitation circuit on the control performance. Asynchronous switching is used, but some important considerations must be taken into account related to the instantaneous phase angle between stator voltage and external inductor current at the switching instant, if good transient response is desired. Sliding mode controllers are proposed, showing good dynamic response and robust behavior upon changes in load and generator parameters. Computer simulations are used to demonstrate the validity of the proposed scheme.
141 citations
19 Feb 2003
TL;DR: In this paper, the voltage build up process and terminal voltage control in an isolated wind powered induction generator driven by a variable speed wind turbine using stator flux oriented vector control is presented.
Abstract: This paper presents the voltage build up process and terminal voltage control in an isolated wind powered induction generator driven by a variable speed wind turbine using stator flux oriented vector control. Here three-phase induction generator is excited using a PWM inverter/rectifier connected to a single capacitor on the DC side. Wind powered isolated induction generators have an input, wind, which is not controllable, but they can be set to operate within a given variation of speed. Unlike a grid connected induction generator, in an isolated induction generator there should be a control system that keeps the DC bus voltage at a constant value when the speed of the rotor is varied. This paper present the control system to maintain the DC bus voltage at a constant value by varying the flux in the induction generator when the rotor speed is varied. During voltage build up the variation of magnetizing inductance is taken into consideration.
139 citations
TL;DR: In this paper, a three-phase cage induction machine (IM) was used as a self-excited generator connected to the AC side of a voltage-source PWM bidirectional inverter.
Abstract: This paper concerns an application of a three-phase cage induction machine (IM) as a self-excited generator connected to the AC side of a voltage-source PWM bidirectional inverter. The generator is supposed to be driven by a low-head unregulated shaft hydraulic turbine. The proposed system is intended to be applied in rural plants as a low-cost source of high-quality AC sinusoidal regulated voltage with constant frequency. Simulation results are obtained based on the /spl alpha//spl beta//spl gamma/ stationary reference frame model of the IM. The experimental results demonstrated that the system presents satisfactory behavior when feeding AC loads and during the startup of induction motors.
130 citations