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The device switching frequency of current source converters (CSC) in high power medium voltage applications is usually several hundred hertz. Selective harmonic elimination (SHE) has been the dominant modulation scheme because of its ability to eliminate unwanted low order harmonics at low switching frequency. Conventional space vector modulation (SVM), as another CSC modulation method, provides variable...
Two techniques are presented to balance the filter capacitor voltages of a multi-pulse rectifier with active injection operating on a variable frequency supply. The active injector consists of a low-rated, bidirectional switch that modifies the behaviour of a 12-pulse rectifier at either low or high-frequency, resulting in 24-pulse or multi-level PWM operation respectively. The operation of the rectifier...
Power converters consisting of naturally commutated thyristors such as cycloconverters and current source inverters were the first used in driving electrical motors with variable speed but now due to their inferior performance compared to forced commutated converters, their use is restricted in the high voltage/high power range where the performance and cost of forced commutated switching devices...
This paper presents a new PWM method using a virtual DC-link voltage concept for reducing output current ripples. Matrix converter is interfaced with three phase AC voltage source. And the AC source makes three different level virtual DC-link voltages. In this paper, a generalized PWM method is proposed to use these three virtual DC-link voltages. In the case of using higher two line to line voltage...
Multilevel inverters have been widely used in medium and high voltage applications. Selective harmonics elimination for the staircase voltage waveform generated by multilevel inverters has been studied extensively in the last decade. Most published methods on this topic aimed at solving high-order multi-variable polynomial equation groups derived from Fourier series expansion. A totally different...
Harmonic Cancellation Technique (HCT) is a modulation technique which has been developed to reduce the output voltage THD of three phase voltage source inverters (VSI) when they are used to feed simultaneously both linear and non-liner loads. The HCT is based on the proper pre-distortion of the inverter output voltage in order to cancel out the low frequency harmonic content due to the non linear...
Exploiting the capability of an FPGA, a digital current controller of a single-phase inverter for grid interface is designed and implemented. A proportional and resonant (PR) controller realized in a parallel structure in the FPGA is used to reduce the harmonic current to AC grid. The harmonic compensators based on the PR controller are implemented up to the 19th order. The size of the LCL filter...
The reference frame theory constitutes an essential aspect of electric machine analysis and control. In this study, apart from the conventional applications, it is reported that the reference frame theory approach (RFTA) can successfully be applied to real time fault diagnosis of electric machinery systems as a powerful tool to find the magnitude and phase quantities of fault signatures with good...
This paper presents and analyzed short circuit failures for permanent magnet synchronous motor (PMSM). The study includes stated and dynamic condition for experimental and simulation test. The stator current is analyzed by means of higher order spectral analysis (HOSA). HOSA techniques are used for stator current analysis under stable conditions is power frequency spectrum density (PSD); and multiple...
When a power factor corrector (PFC) is designed with a fast output-voltage feedback loop, the study of the power stage varies in comparison with the one carried out with a slow output-voltage feedback loop. This is a consequence of the voltage ripple that appears in the control signal. The static behaviour of a PFC with a fast output-voltage feedback loop is studied in this paper using two parameters:...
The winding AC loss behaviors of push-pull transformer with four windings and two central taps are much different from that of general two winding transformer because the windings conduct currents in different time intervals. The model was introduced by the winding current FFT decomposition and magnetic motive force (MMF) analysis and discloses that the odd harmonic MMF is balanced among the all windings...
This paper presents an improved controller for parallel connected single-phase UPS inverters in distributed generation application areas. The proposed control strategy needs only locally measurable feedback signals with communicationless between each inverter. It also shows how the improved adaptive droop method can be easily adapted to account for the operation of parallel inverters, providing good...
The large capacity harmonic current generator based on three-phase-four-wire configuration uses four-leg converter as its main circuit. So it is different from the traditional small capacity linear current source. The whole equipment can output steady harmonic current include the selective order harmonic (below 25th order), reactive current and unbalanced current. Besides, dynamic change process of...
In this paper, computationally-efficient sinusoidal disturbance estimation and elimination methods are introduced into the control of an active front end (AFE) voltage-source converter (VSC) to achieve effective disturbance rejection in high-power systems with slower PWM switching frequencies (e.g., 5 kHz) and limited current controller bandwidth. Since the active rectifier is in series with the source...
Proportional Resonant (PR) controller with harmonic compensators has extremely higher gain at the desired frequencies to reduce the harmonic distortions in the alternative voltage or current waves. However, the harmonic compensators of the PR controller are limited to several low-order current harmonics, due to the system instability when the compensated frequency is out of the bandwidth of the system...
This paper proposes a group of high performance filters for fundamental positive / negative sequences and harmonics detection under varied grid conditions based on a basic filter cell. The filter cell is demonstrated to be equivalent to a band-pass filter in the stationary frame, and is easily implemented using a multi-state-variable structure. To achieve high performance in different grid conditions,...
Suitable model for the analysis and control of the Unified Power Quality Controller (UPQC) was quite difficult to obtain, which prohibited not only the analysis and comparison between existing control strategies, but also the industrial applications, as no generalized method to design the control loop for different disturbances. In this paper, a unified DC voltage compensator design is proposed for...
Due to the difficulty of handling nonlinear loads for traditional active power filter(APF) with two-level inverter in high voltage high power grid, this paper researches three-level active power filters. This paper presents an improved repetitive scheme to control the shape of output current waveform. The design process of each part in the repetitive controller is presented. Q(z) is designed as a...
In this paper we propose two three-phase series active power filters (SAPF) for voltage harmonic compensation and voltage regulation. The power filters are conceived to operate without isolation transformer and auxiliary active dc source. The topologies are adequate for applications in which the load or grid terminals are accessible. The model of the systems are derived to analyze their behavior for...
With development of sophisticated renewable energy technologies, paradigm shift of both power generation and power distribution is happening and happening fast. Compared with conventional power generation, renewable energy sources are installed to the utility grid in a distributed fashion, which may result in various power quality issues, such as unbalance voltage and harmonic voltage resonance. An...
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