Distribution systems are undergoing many enhancements and developments to enable the future smart grid, and distribution system state estimation (DSSE) provides the control centers with the information necessary for several of its applications and operational functions. However, the quality of DSSE typically suffers from a lack of adequate/accurate measurements. Recently, many electric utilities have started to install fairly accurate smart meters throughout their distribution networks, which create an opportunity to achieve higher quality DSSE. However, the signals provided by smart meters are generally not synchronized and the difference between the measurement times of smart meters can be significant. Therefore, a complete snapshot of the entire distribution system may not be available. This paper proposes a method to deal with the issue of nonsynchronized measurements coming from smart meters based on the credibility of each available measurement and appropriately adjusting the variance of the measurement devices. To illustrate the effectiveness of the proposed method, two IEEE benchmark systems are used. The results show that the proposed method is robust and improves the accuracy of DSSE compared with the traditional DSSE approach.

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Representation of synchronous machines using constant-parameter voltage-behind-reactance (VBR) formulations improves accuracy and numerical efficiency of power systems transient simulation programs. This paper extends the VBR representation to the rotor circuit and presents two new formulations that achieve direct constant-parameter interfacing of the rotor and stator terminals with arbitrary external networks. In the first model, the entire machine is represented by constant RL branches that have algebraic coupling among the circuit variables. In the second model, all damper windings are implemented in state-space form to increase the numerical efficiency, while the stator and field windings are provided as constant-parameter circuits. The proposed models are validated against the commonly used and some state-of-the-art alternative models using a single machine with a simplified ac excitation system. Computer studies demonstrate the improved accuracy and efficiency of the proposed models when external rotor circuitry is considered.Index Terms-AC machines, interfacing circuit, power system modeling, power system simulation, synchronous machine, voltage-behind-reactance model. NOMENCLATUREThroughout this paper, matrix and vector quantities are represented by boldface characters (e.g., v abcs ), and scalar quantities are in italics (e.g., i f d ). All variables are assumed to be referred to the stator side using the appropriate turns ratio. The q-axis is 90°ahead of the d-axis [1]. Similar naming convention for the machine variables as in [1] is used here. The rotor reference frame is assumed, but the superscript "r" is omitted. The main machine quantities are listed as follows. L lf d Field winding leakage inductance. L lk dj , j = 1 . . . N Direct-axis rotor damper winding leakage inductances. L lk q j , j = 1 . . . M Quadrature-axis rotor damper winding leakage inductances. L lsStator winding leakage inductance. L m q , L m d Quadrature-and direct-axis magnetizing inductances. pHeaviside's operator (differentiation with respect to time or d/dt when t is time).

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Interfacing of electrical machine models with ac power networks has a significant impact on numerical accuracy and efficiency in state-variable-based transient simulation programs. This paper continues the recent work in this area by proposing a new explicit constant-parameter voltage-behind-reactance (VBR) induction machine model that includes main flux saturation and allows a direct interface to any external network. The proposed model uses numerical approximations to achieve a decoupled interfacing circuit with constant RL branches that is easy to use in many simulation programs. Computer studies demonstrate that the proposed model provides high numerical accuracy for machines with a diverse range of parameters, even at fairly large integration step sizes.