Hen-Geul Yeh

Adaptive VAR Control for Distribution Circuits With Photovoltaic Generators

We show how an adaptive control algorithm can improve the performance of distributed reactive power control in a radial distribution circuit with a high penetration of photovoltaic (PV) cells. The adaptive algorithm is designed to balance the need for power quality (voltage regulation) with the desire to minimize power loss. The adaptation law determines whether the objective function minimizes power losses or voltage regulation based on whether the voltage at each node remains close enough to the voltage at the substation. The reactive power is controlled through the inverter on the PV cells. The control signals are determined based on local instantaneous measurements of the real and reactive power at each node. We use the example of a single branch radial distribution circuit to demonstrate the ability of the adaptive scheme to effectively reduce voltage variations while simultaneously minimizing the power loss in the studied cases. Simulations verify that the adaptive schemes compares favorably with local and global schemes previously reported in the literature.

A scheme for cancelling intercarrier interference using conjugate transmission in multicarrier communication systems

To mitigate intercarrier interference (ICI), a two-path algorithm is developed for multicarrier communication systems, including orthogonal frequency division multiplexing (OFDM) systems. The first path employs the regular OFDM algorithm. The second path uses the conjugate transmission of the first path. The combination of both paths forms a conjugate ICI cancellation scheme at the receiver. This conjugate cancellation (CC) scheme provides (1) a high signal to interference power ratio (SIR) in the presence of small frequency offsets (50 dB and 33 dB higher than that of the regular OFDM and linear self-cancellation algorithms (Y. Zhao and S.-G. Haggman, 2001), (J. Armstrong, 1999), respectively, at DeltafT = 0.1% of subcarrier frequency spacing); (2) better bit error rate (BER) performance in both additive white Gaussian noise (AWGN) and fading channels; (3) backward compatibility with the existing OFDM system; (4) no channel equalization is needed for reducing ICI, a simple low cost receiver without increasing system complexity. Although the two-path transmission reduces bandwidth efficiency, the disadvantage can be balanced by increasing signal alphabet sizes

Systolic implementation on Kalman filters

Two schemes for implementing systolic and pipelined processing on Kalman filters in real time are presented. In the first, a single two-dimensional systolic processor is used to perform a Kalman filtering process. In the second scheme, the utilization of the two-dimensional systolic processor is fully expanded and improves the speed of updating estimates, Kalman filter algorithms are implemented on two concurrent, identical systolic processors. In both schemes, the mathematical formulation of the Kalman filter algorithms is rearranged to be the type of the Faddeeva algorithm for generalizing matrix/vector manipulations. The corresponding data flow is easily mapped from algorithms into the computing structure which is of nearest neighbor type. The architecture of the processor cells is regular, simple, expandable, and suitable for VLSI implementation. The computing methodology and the two-dimensional systolic arrays are useful for Kalman filter applications as well as general matrix/vector algebraic computations. >

Real-time implementation of a narrow-band Kalman filter with a floating-point processor DSP32

The author presents experimental results from two studies. First, a real-time narrowband Kalman filter is implemented with a floating-point digital processor DSP32. The real-time capability of this narrowband filter is investigated by varying parameters Q and R. The covariance matrices Q and R of the dynamic and measurement noise sequences are found to exhibit duality in the real-time tuning process and have a direct effect on system stability. If the value of Q used is smaller (with fixed R), the tracking time and the narrower tracking bandwidth of the filter will be longer. In addition, if the value of R used (with fixed Q) is smaller, the tracking time will be smaller, and the tracking bandwidth of the filter will be larger. The results are tabulated. Second, two optimal codes (in the sense of the execution speed), straight-line code and general matrix-based code, have been developed for implementing the narrowband Kalman filter. These two codes are compared in terms of program memory size, data memory size, and speed of execution. With the matrix-based code, the DSP32 performance is evaluated in terms of speed and memory size by varying the number of states of a Kalman filter. The results are also tabulated. >

New parallel algorithm for mitigating the frequency offset of OFDM systems

We study the problem of frequency offset due to the Doppler velocity of orthogonal frequency division multiplexing (OFDM) systems. A regular OFDM has an IFFT at the transmitter and an FFT at the receiver. The proposed parallel algorithm employs an FFT at the transmitter and an IFFT at the receiver. The regular OFDM samples, which are generated by the IFFT, are transmitted as the first block, and the FFT outputs are transmitted as the second block. At the receiver, the results of the first output generated by the FFT are combined with the second output generated by the IFFT. This combined operation forms a parallel intercarrier interference (ICI) cancellation scheme for mitigating frequency offsets of OFDM systems. It provides: (1) a robust OFDM system in the presence of relative velocity, also known as Doppler frequency offset; (2) high signal to ICI ratio (7 dB better than that of the linear self-cancellation algorithms at N=1024 and /spl Delta/fT/spl les/1% of subcarrier frequency spacing); (3) backward compatibility with the existing OFDM system; (4) better BER performance in both additive white Gaussian noise (AWGN) and fading channels.

A conjugate operation for mitigating intercarrier interference of OFDM systems

In order to mitigate intercarrier interference (ICI), a two-path algorithm is developed for orthogonal frequency division multiplexing (OFDM) systems. The first path is a regular OFDM system for transmitting and receiving. The second path requires a conjugate operation of the 1st block of data to form the 2nd block of data for transmission. The received 2nd block of data is conjugated at the receiver and then demodulated. The demodulated results of the 1st path are combined with that of the 2nd path with equal weights to form the final detected data symbols. This conjugate cancellation (CC) scheme provides (1) a high signal-to-ICI power ratio in the presence of small frequency offsets - 33 dB higher than that of linear self-cancellation algorithms (Zhao, Y. and Haggman, S.-G., 2001; Armstrong, J., 1999) at /spl Delta/fT = 0.1% of subcarrier frequency spacing; (2) backward compatibility with the existing OFDM system; (3) significantly better BER performance in both additive white Gaussian noise (AWGN) and frequency selective fading channels.

Kalman filtering and systolic processors

A new parallel computing structure of the systolic array type for implementing the Kalman filter for state-space estimation is presented. This corresponds to the adjustment of Kalman filter algorithms to the type of the Faddeev algorithm. The Faddeev algorithm provides a wide range of matrix computational capabilities and it maps easily into a concurrent systolic array architecture. The special arrangement for the data flow mapping from Kalman filter to Faddeev algorithm, and from Faddeev algorithm to architecture are presented.

PV ramp limiting controls with adaptive smoothing filter through a battery energy storage system

Photovoltaic (PV) variability can adversely affect system frequency and voltage stability in a high PV penetration location. High cloud cover in a short time scale can cause excessive ramp rates for large PV array installations. Smoothing is desired to limit the impact of cloud shading on the distribution circuit. Existing algorithms typically are simple moving averages that introduce time lag. The goal of this paper is to introduce a control method to smooth PV power ramp rates with a focus on reducing battery size (cost) and energy throughput (life) requirements. Simulated data from a high PV penetration multi-megawatt (MW) solar array site with large ramp rates is analyzed. Simulations verify that the control schemes work for a reduced size battery system.

Coherent power combining on spacecraft via wavefront multiplexing techniques

A novel orthogonal wavefront (WF) Multiplexing (Muxing) and De-Multiplexing (Demuxing) scheme as the pre-and post-processing method of a new WF transceiver is proposed for uplink from antenna array elements to multiple spacecraft (S/C). By using an adaptive equalizer at the receiver of S/C, the phase deviation due to different distances in the near field of the uplink from antenna array elements to S/C is compensated via the WF Demuxing method on S/C. Moreover, this feed-forward scheme allows power combining from antenna array transmitter to S/C, also this scheme can be extended and applied to multiple S/C. Simulations verify that the proposed scheme achieves the same bit error rate (BER) performance as the theoretical BER in additive white Gaussian noise (AWGN) channels. Although the radiated signals among the multiple radiating antenna array elements are non-coherent, the coherent power combining of the radiations of multiple radiating antenna array elements is accomplished on the S/C receiver.

Dynamic power allocation via wavefront multiplexing through multiple base stations

A novel orthogonal wavefront (WF) multiplexing (Muxing) and de-multiplexing (Demuxing) scheme as the pre- and post-processing method of a new WF transceiver is proposed for down links from multiple base stations (BSs) to multiple mobile units (MUs). By using an adaptive equalizer at the receiver of a MU, the phase deviation due to different distances in down links from multiple BSs to a MU is compensated via the WF Demuxing method. Moreover, this feed-forward scheme allows the dynamic power allocation from BSs to MUs. Simulations verify that the proposed scheme achieves the same bit error rate (BER) performance as the theoretical BER in an additive white Gaussian noise (AWGN) channel. Furthermore, the coherent power combining of the radiation of multiple BSs is accomplished on receivers in the proposed techniques. The radiated signals from the multiple BSs are non-coherent. Thus, due to multipath transmission, the required effective equivalent isotropically radiated power (EIRP) by sending non-coherent signals to the targeted coverage area around MUs is significantly reduced. The associated interfering power levels to other wireless systems in adjacent frequency bands for nearby users will be significantly reduced accordingly.