Dariusz Czarkowski

Multilevel selective harmonic elimination PWM technique in series-connected voltage inverters

The selective harmonic elimination PWM (SHEPWM) method is systematically applied for the first time to multilevel series-connected voltage source PWM inverters. The method is implemented based on optimization techniques. The optimization starting point is obtained using a phase-shift harmonic suppression approach. Another less computationally demanding harmonic suppression technique, called a mirror surplus harmonic method, is proposed for five-level (double-cell) inverters. Theoretical results of both methods are verified by experiments and simulations for a double-cell inverter. Simulation results for a five-cell (11-level) inverter are also presented for the multilevel SHEPWM method.

Optimal Distributed Voltage Regulation for Secondary Networks With DGs

An algorithm for the optimal voltage regulation of distribution secondary networks with distributed generators (DGs) is proposed in the paper. Based on the ε decomposition of the sensitivity matrix (inverse of Jacobian) obtained from the solution of the Newton-Raphson power flow problem, a large secondary network is divided into several small subnetworks. From the ε decomposition, the range of influence of each DG on the voltage of the entire network is determined. When voltage at particular nodes exceeds normal operating limits, the nearest DGs can be located and commanded to control the voltage. The control action can be coordinated using communications in a small-size subnetwork. The voltage regulation is achieved by solving a small linear programming optimization problem with an objective function that makes every DG to optimize its generation. The algorithm is tested with a model of a real heavily-meshed secondary network. The results show that the algorithm proposed in this paper can effectively control the voltage in a distributed manner. It is also discussed in the paper how to choose the value of ε for the system decomposition.

Analysis of Voltage Profile Problems Due to the Penetration of Distributed Generation in Low-Voltage Secondary Distribution Networks

This paper presents a comprehensive analysis of the possible impacts of different penetration levels of distributed generation (DG) on voltage profiles in low-voltage secondary distribution networks. Detailed models of all system components are utilized in a study that performs hundreds of time-domain simulations of large networked distribution systems using the Electromagnetic Transients Program (EMTP). DGs are allocated in a probabilistic fashion to account for the uncertainties of future installations. The main contribution of this paper is the determination of the maximum amount of DG that secondary distribution networks can withstand without exhibiting undervoltage and overvoltage problems or unexpected load disconnections. This information is important for network planning engineers to facilitate the extension of the maximum penetration limit. The results show that depending on the location, type, and size of the installed DGs, small amounts of DG may cause overvoltage problems. However, large amounts of DG may not cause any voltage problems when properly selected.

Phase-controlled series-parallel resonant converter

A constant-frequency, phase-controlled, series-parallel resonant DC-DC converter is introduced, analyzed in the frequency domain, and experimentally verified. To obtain the DC-DC converter, two identical series-parallel resonant inverters are paralleled and the resulting phase-controlled resonant inverter is loaded by a voltage-driven rectifier. The converter can regulate the output voltage at a constant switching frequency in the range of load resistance from full-load resistance to infinity while maintaining good part-load efficiency. The efficiency of the converter is almost independent of the input voltage. For switching frequencies slightly above the resonant frequency, power switches are always inductively loaded, which is very advantageous if MOSFETs are used as switches. Experimentally results are given for a converter with a center-tapped rectifier at an output power of 52 W and a switching frequency of 127 kHz. The measured current imbalance between the two inverters was as low as 1.2:1. >

Solving the optimal PWM problem for single-phase inverters

In this paper, the basic algebraic properties of the optimal PWM problem for single-phase inverters are revealed. Specifically, it is shown that the nonlinear design equations given by the standard mathematical formulation of the problem can be reformulated, and that the sought solution can be found by computing the roots of a single univariate polynomial P(x), for which algorithms are readily available. Moreover, it is shown that the polynomials P(x) associated with the optimal PWM problem are orthogonal and can therefore be obtained via simple recursions. The reformulation draws upon the Newton identities, Pade approximation theory, and properties of symmetric functions. As a result, fast O(n log/sup 2/ n) algorithms are derived that provide the exact solution to the optimal PWM problem. For the PWM harmonic elimination problem, explicit formulas are derived that further simplify the algorithm.

Experimental Determination of the ZIP Coefficients for Modern Residential, Commercial, and Industrial Loads

This paper presents the experimental determination of the ZIP coefficients model to represent (static) modern loads under varying voltage conditions. ZIP are the coefficients of a load model comprised of constant impedance Z, constant current I, and constant power P loads. A ZIP coefficient load model is used to represent power consumed by a load as a function of voltage. A series of surveys was performed on typical residential, commercial, and industrial customers in New York City. Household appliances and industrial equipment found in the different locations were tested in the laboratory by varying the voltage from 1.1-p.u. voltage to 0 and back to 1.1 pu in steps of 3 V to obtain the individual P- V, Q- V, and I- V characteristics. Customer load tables were built using seasonal factors and duty cycles to form weighted contributions for each device in every customer class. The loads found in several residential classes were assembled and tested in the lab. It was found that modern appliances behave quite differently than older appliances even from only 10 years back. Models of the different customer classes were validated against actual recordings of load variations under voltage reduction.

Modeling and Digital Control of a Phase-Controlled Series–Parallel Resonant Converter

A nonlinear model for a phase-controlled series-parallel resonant converter is developed using the extended describing function method and d-q decomposition. The model is linearized and reduced using the balanced model reduction technique. Based on the reduced model and taking into account the zero-order hold delay and the computation delay in the sampled-data system, a digital controller for the converter is designed. The controller is implemented with a digital signal processor (DSP). The closed-loop converter with the DSP controller is built and tested experimentally. Recorded transient waveforms show that the closed-loop converter is capable of not only responding to the reference input change as required by the design specifications, but also stabilizing the output effectively under disturbances from both the output and the input

Voltage flicker mitigation using PWM-based distribution STATCOM

Voltage flicker, a phenomenon of annoying fight intensity fluctuation, caused by large rapid industrial load changes, has been a major concern for both power companies and customers in the area of power quality. The fast response of the distribution static compensator (DSTATCOM) makes it the efficient solution for improving power quality in distribution systems. In this paper, a voltage flicker phenomena in a 69/13.8 kV distribution system Is modeled and simulated using MATLAB/Simulink Power System Blockset (PSB). Voltage flicker mitigation studies with a current controlled PWM-based DSTATCOM are also performed and discussed.

Multilevel space vector PWM technique based on phase-shift harmonic suppression

A new multilevel space vector PWM technique is proposed for high power applications. The technique is developed for H-bridge series-connected multilevel inverters. A phase-shift between space vectors produced by power cells is used for harmonic suppression. As a result, hardware and software implementation is greatly simplified. The phase-shift concept has been verified by simulations and experiments with a two-cell (five-level) series-connected voltage inverter with a space vector PWM. The proposed technique can be easily extended to higher level inverters.

A Novel Phase-Shift Control of Semibridgeless Active Rectifier for Wireless Power Transfer

A novel phase-shift control of a semibridgeless active rectifier (S-BAR) is investigated in order to utilize the S-BAR in wireless energy transfer applications. The standard receiver-side rectifier topology is developed by replacing rectifier lower diodes with synchronous switches controlled by a phase-shifted PWM signal. Theoretical and simulation results show that with the proposed control technique, the output quantities can be regulated without communication between the receiver and transmitter. To confirm the performance of the proposed converter and control, experimental results are provided using 8-, 15-, and 23-cm air gap coreless transformer which has dimension of 76 cm × 76 cm, with 120-V input and the output power range of 0 to 1kW with a maximum efficiency of 94.4%.