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Abstract It is often more complicated to measure the phase response of a large system than the magnitude. In that case, one can attempt to use the Kramers–Kronig (KK) relations for magnitude and phase, which relates magnitude and phase analytically. The advantage is that then only the magnitude of the frequency response needs to be measured. It is shown that the KK relations for magnitude and phase may yield invalid results when the transfer function has zeros located in the right half of the complex s‐plane, that is, the system is non‐minimum phase. In this paper, a method which enables to determine these zeros is proposed, by using specific excitation signals and measuring the resulting time responses of the system. The method is verified using blind tests among the authors. When the locations of the zeros in the right half of the complex s‐plane are known, modified KK relations can be successfully applied to non‐minimum phase systems. This is demonstrated by computing the phase response of the electric field, excited by a point dipole source inside a closed cavity with Perfect Electrically Conducting (PEC) walls. Also, the effects of simulated measurement noise are considered for this example.

Abstract The poor damping of bidirectional dc (bi‐dc) converter caused by constant power load makes power system prone to oscillation, and non‐minimum phase characteristic also jeopardises voltage stability. To solve these challenges, the interconnection and damping assignment passivity‐based control (IDA‐PBC) is utilised to improve transient response. The influences of the right‐half‐plane (RHP) zero on the stability margin and controller design are illustrated by zero dynamics analysis. Then the port‐controlled Hamiltonian modelling is used to obtain the IDA‐PBC control law, which is suitable to the bi‐dc converter and independent of the operation mode. The system dissipation property is modified, and thus the desired damping is injected to smooth the transient voltage. To remove the voltage error caused by RHP zero and adjust the damping ratio, an energy controller with an adjustment factor is introduced. Besides, a virtual circuit is established to explain the physical meaning of the control parameter, and the parameter design method is given. Passivity analysis assesses the controller performance. Simulation results are analysed and compared with other control strategies to test the proposed IDA‐PBC strategy.

Abstract The present work focuses on the state‐of‐charge (SOC) estimation of a lithium‐ion battery in terms of a second‐order extended Kalman filter (EKF). First, an equivalent circuit model is introduced to describe the performance of lithium‐ion batteries. The model parameters are then identified through hybrid pulse power characterization experiments conducted over a wide range of temperatures (−10 to 55°C). A two‐dimensional mathematical relationship is established with respect to the SOC and temperature based on a dual‐fifth polynomial expression. The main effects and sensitivities of the SOC and temperature on the parameters are analysed according to the principle of variance analysis and partial derivatives. An estimation algorithm is developed, which combines the two‐dimensional parameter model and second‐order EKF. Finally, the proposed approach is validated compared to other estimation schemes through discharge experiments under extreme temperatures and dynamic loading profiles, which yields experimental results that estimate the SOC with an absolute error of less than 4.5% under harsh conditions. This not only demonstrates that it can characterize dependency of the model parameters on the operating conditions and address the uncertainty of model parameters, but also verifies the advantage of present method at low temperatures especially at sub‐zero temperatures.

Abstract In this letter, a novel wideband bandstop filter with controllable equal‐ripple response is newly presented. The proposed topology consists of two cascaded transmission lines and three open‐circuited stubs, where, one two‐section OS is shunted between two transmission lines, two three‐section OSs are shunted at two output ports, respectively. By using the proposed design approach, both passband and stopband provide controllable equal‐ripple responses independently, where there are five transmission zeros and six reflection zeros in a single period of frequency domain. For demonstration, an experimental BSF centered at 2 GHz with 20‐dB FBW 129.5% and 30‐dB stopband rejection is designed and fabricated. The simulations and measurements agree with the design theory very well.

Abstract Cross‐coupled microwave filter with flexible topology is an essential component in a modern communication system. Among the various filter networks, the use of an extended box section can effectively reduce the difficulty of filter design, but the synthesis approach for this popular structure is not well developed. This paper presents the synthesis method based on the folded coupling matrix to derive the extended box sections. At the same time, an eighth‐degree filter with extended sixth‐degree box sections is synthesized to demonstrate the correctness of the approach. Finally, the new approach's feature to derive advanced circuits such as peculiar quintets is discussed, indicating that it has certain universality.