Common-mode Resonance Research Articles

Modeling and Attenuation of Common Mode Resonance Current for Improved LCL-Type Parallel Inverters in PV Plants

Modeling and Attenuation of Common Mode Resonance Current for Improved LCL-Type Parallel Inverters in PV Plants

A Novel Common-Mode Voltage Suppression Strategy for Current Source Converter

The problem of common-mode voltage (CMV) in current source converter (CSC) has been concerned with the development and application of CSC, such as in the transformerless motor drive system. Using a common-mode choke is a popular solution to suppressing CMV. The high-frequency harmonics of the CMV can be eliminated by the common-mode filter. However, the low-order harmonics cannot be eliminated effectively, especially at low modulation index, which may cause common-mode resonance and increase the size of the choke. In this paper, a novel virtual space vector modulation (VSVM) method is proposed, which constructs virtual space vectors by the original vectors. The average value of the CMV produced by each virtual vector is zero. The proposed method can reduce the amplitude and third-order harmonic component of the CMV. In addition, the number of switching transitions in a switching sequence of the proposed method is the same as the conventional 5-segment SVM. The suppression effects of different methods on the low-order harmonics of CMV are compared through simulation and experiments, and the effectiveness of the proposed methods is verified.

A Low-Phase-Noise VCO With Common-Mode Resonance Expansion and Intrinsic Differential 2nd-Harmonic Output Based on a Single Three-Coil Transformer

In this article, we propose a voltage-controlled oscillator (VCO) with a single three-coil transformer, featuring a common-mode (CM) resonance expansion and intrinsic differential 2nd harmonic output. In addition to a conventional transformer-based class-F resonator, an internal third coil is added to manipulate the CM response. On one hand, it expands the CM resonance bandwidth, eliminating the need for manual harmonic tuning to align the 2nd harmonic resonance. On the other hand, it creates a simultaneous wideband differential response at the 2nd harmonic frequency, therefore, the power consumption of the extra frequency doubler can be saved. Using the proposed stacked 8-shape inductor topology, the third coil can be placed inside the class-F transformer without consuming an extra chip area. Fabricated in a 65-nm CMOS process, the measured tuning range of the proposed VCO is 21.1%, from 12.3 to 15.2 GHz. The proposed VCO achieves a peak phase noise (PN) performance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 118.0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 111.9 dBc/Hz at 1 MHz offset for fundamental frequency and 2nd harmonic, respectively, the corresponding peak figure-of-merit (FoM) of which is 190.4 and 190.1 dBc/Hz, respectively. The VCO consumes a power of 8.4–9.6 mW, while occupying a small area of 0.06 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}$</tex-math> </inline-formula> thanks to the stacked 8-shape inductor topology.

A Low-Voltage Class-D VCO with Implicit Common-Mode Resonator Implemented in 55 nm CMOS Technology

This paper presents a Class-D voltage-controlled oscillator (VCO) with a hybrid switch capacitor array. In order to reduce the phase noise of the oscillator, an implicit common-mode resonance technique is used, effectively suppressing the conversion of power supply noise to VCO phase noise. At the same time, due to the use of a transformer in implicit common-mode resonance technology, the core area of the oscillator is not significantly increased compared with the traditional Class-D VCO. Based on the proposed technology, the proposed VCO exhibits lower phase noise compared to the original Class-D VCO, and also has many different advantages compared to low-voltage VCOs produced by similar technological processes. The proposed VCO was designed in a 55 nm CMOS process. Simulation results show that this VCO has an operating range from 4.36 to 6.43 GHz, resulting in the frequency tuning range (FTR) of 38.5%. In addition, its power consumption was 3.46 mW, the phase noise at 4.36 GHz was −124.2 dBc/Hz@1 MHz, and the figure of merit (FoM) was −191.6 dBc/Hz@1 MHz. The core area is 0.15 mm2.

A Multifrequency Small-Signal Model for the MLCL-Filtered Grid-Connected Inverter Considering the FCE of Nonlinear Inductors

To study the frequency coupling effect (FCE) of nonlinear inductors in frequency domain, a multifrequency small signal model is developed in this paper for the modified LCL (MLCL) filtered grid-connected inverter. This model is realized by extracting side band coupling (SBC) units out of the harmonic state-space (HSS) model and superposing them to the perturbation frequency loop. Compared with the complicated reductant HSS model, the proposed multifrequency model provides an intuitive efficient accurate way to describe the system. Besides, notions in classical control theory can be directly utilized with the multifrequency model. With this model, the current control loop of the inverter is studied. Besides, by introducing a simplified linear time invariant (LTI) small signal model (the FCE is ignored), it is found that the FCE effect is non-negligible especially in the frequency range around resonance points, which affects the stability of the differential mode resonance (DMR) and common mode resonance (CMR). The proposed multifrequency model accurately predicts the DMR and CMR stability, while the simplified LTI model fails. Furthermore, damping strategies are developed to suppress the DMR and CMR. Finally, simulations and experiments based on a 228 kW PV inverter are conducted to verify the analytical result.

An Ultrawideband Dual-Polarized Phased Array Antenna for Sub-3–GHz 5G Applications With a High Polarization Isolation

A dual-polarized ultra-wideband phased array antenna with a wide scanning range and high isolation polarization characteristics is presented in this paper. A tightly coupled dipole with an etched slot is proposed as the element antenna, which has a low active input impedance in a wideband and a wide scanning range. Thus, a simple feed strategy without requiring additional external matching networks and baluns could be adopted for the designed scheme. To obtain a large polarization isolation, a capacitively-loaded cross-shaped metallic wall is proposed. It is also helpful to improve the in-band matching by mitigating the bandwidth-limiting loop mode at lower frequencies and removing the undesirable common-mode resonance. As a demonstration, an array is designed with a 4.1:1 bandwidth (0.69-2.88 GHz) and an active VSWR < 3.4 while scanning up to ±45° in the E-, H-, and D-planes. Its polarization isolation is better than 45 dB at the broadside and 35 dB within most of the bandwidth when scanning to ±45° in the E-/H-planes. Its cross-polarization level is more than 51 dB at broadside and 40 dB in scanning up to ±45° in the E- and H- planes. A dual-polarized 8×8 array prototype (64 ports per polarization) is manufactured and evaluated. Results from the experiment demonstrate good agreement between the measurement and design. The designed antenna is scalable, has a high polarization isolation, a wide scanning range, an ultra-wide bandwidth, and a low cost.

A Tuning Range Extension Technique for Waveform-Shaping Single-Core CMOS Oscillators With No Dedicated Harmonic Tuning

This brief presents a tuning range extension technique for output voltage waveform-shaping single-core CMOS oscillators. First, the parasitic capacitors in previous waveform-shaping oscillators that limit the tuning range are analyzed. Next, a triple coupled LC resonator (TCLCR) is proposed to separate the differential-mode and common-mode (CM) resonance path which improves the tuning range significantly. The TCLCR is also able to establish the harmonically tuned impedance without using dedicated harmonic tuning both at CM 2rd harmonic and 3rd harmonic for oscillator’s implicit CM resonance or class-F23 operation to suppress the white noise and flicker noise conversion to phase noise. Finally, as a proof of concept, a 2.79-to-4.9 GHz class-F23 oscillator prototype covering a wide tuning range of 54.9% is designed and fabricated in a 130-nm CMOS technology. The oscillator achieves figure-of-merit with tuning range (FOMT) of 199.4/202.2 dBc/Hz, 196.3/200.9 dBc/Hz and 195/199.7 dBc/Hz at 100-kHz/1-MHz offset from 2.79, 3.83 and 4.9 GHz.

Suppression of Common-Mode Resonance in Multiband Base Station Antennas

5G demands a significant increment in the number of connected devices. As a result, gNodeBs are constantly pushed to serve more spectrum and smaller sectors. These increased capacity demands are met by using multiband antennas in base stations. One of the key challenges with multiband antennas is the pattern distortions due to the presence of other surrounding antenna element structures. This work provides a novel approach to address the challenge of pattern distortion in the lower frequency band 690-960 MHz due to common-mode (CM) currents in the high- frequency-band antenna element operating in the 1810-2690 MHz band. A common-mode suppression circuit is integrated with the impedance matching network of the high-band antenna element to reduce these common-mode currents. The experimental results verified that the common-mode suppression circuit reduces the common-mode currents at low-band frequencies by moving the common-mode resonance frequency outside the low frequency band, resulting in cleaner low-band patterns meeting pattern specifications.

Modeling and Control Method to Suppress Common-Mode Resonance Circulating Current for High-Power Parallel Three-Level Inverters System With Improved LCL Filter

In parallel three-level inverters, to eliminate the undesired internal common-mode (CM) resonance circulating currents (ICMRCCs) and external CM resonance circulating currents (ECMRCCs) introduced by the improved <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> , the inverter-side CM current feedback (ICMCF) control is presented. However, since the switching frequency of the inverters is generally low in high-power applications to reduce power loss, the stability of the ICMCF control will be threatened by the delays of digital controller. In this case, the existing methods are not capable of ICMRCC and ECMRCC suppression any more. To deal with the situation, an improved CM resonance circulating current control method for high-power parallel inverters is proposed. First, the model of ICMCF with control delay is established. Second, the influences of control delay with different sampling modes on the stability of CM current control are investigated. Based on this, the allowable range of control delays and sampling frequency to keep the system stable is analyzed and deduced. Third, the multisampling mode is further extended to CM current control in the parallel inverters. The analysis results show that the stability margin and control bandwidth of the ICMCF control are significantly improved. Finally, the theoretical analysis and proposed control method are verified by simulation and experiment.

A Low-Profile Ultra-Wideband and Wide-Scanning Phased Array for UHF Applications

This article presents a novel low-profile ultra-wideband and wide-scanning array antenna using the transversely connected folded tightly coupled dipoles array (TCF-TCDA). The tightly coupled folded dipole arms are used to extend the operational frequency band with a simple feed structure. The capacitively-loaded metallic walls are adopted to move the problematic common-mode resonance out of the desired band and mitigate the bandwidth-limiting loop mode at the lower frequency, as well as reducing the weight and cost. A meta-surface-based wide angle impedance matching (MS-WAIM) layer is used to improve the beam scanning ability and lower the antenna profile, which consists of the star-shaped patches loaded on the dipole element. To demonstrate the wideband and wide scanning-range capability, a prototype is designed with an 8:1 bandwidth (0.41–3.3 GHz) at broadside, a scanning range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm \mathrm{75}^{\circ }$ </tex-math></inline-formula> from 0.5 to 3.25 GHz (6.5:1 bandwidth) in the E- and D-planes and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm \mathrm{50}^{\circ }$ </tex-math></inline-formula> from 0.6 to 3.3 GHz (5.5:1 bandwidth) in the H-plane for active VSWR < 3.6. The proposed antenna has a very low profile, which is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.07\lambda _{\mathrm {low}}$ </tex-math></inline-formula> at the lowest operating frequency. A 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 16 array prototype is fabricated and measured. Experimental results show that the design and measurement results have good agreement. The proposed antenna has an ultra-wide bandwidth, a wide scanning range, a very compact size and a low cost, which is a good candidate for modern wireless system.

Novel Planar Ultra-Wideband Modular Antenna Array with Low Profile

A planar ultra-wideband modular antenna array with an ultra-low profile based on a tight coupling effect is proposed. The antenna array is composed of multi-layer printed circuit boards. Since its frequency operation can extend up to the grading lobe frequency, the number of T/R components for the antenna aperture is reduced to the greatest extent. Specifically, a horizontal “fin” structure is added on the parallel feeding lines, which assists in improving the impedance matching of the array. In order to break the bandwidth limitation of the low-frequency loop mode, a capacitive short-circuit probe is introduced to push the common-mode resonance point into the low-frequency band. Finally, subject to Active VSWR &lt; 3, the array can realize E-plane, H-plane, and D-plane ± 45° beam scan coverage across the 6:1 frequency band (3.48–20.97 GHz). A 128-element prototype was processed and tested to validate the design. This array not only has the advantages of low profile, modularity, easy assembly, and maintenance but also minimizes the number of T/R components and reduces the cost of phased array antennas.

Common-Mode Resonance Suppressing Surface for Tightly Coupled Array

Common-mode resonance in traditional tightly coupled arrays (TCAs) limits bandwidth severely. In this communication, a common-mode resonance suppressing surface (CRSS) is proposed to mitigate the common-mode resonance. The CRSS is a surface etched with slots along the polarized direction placed below the antenna array to replace the ground of traditional TCAs. The CRSS cuts off the surface current on the ground, and thus the common-mode resonance is mitigated. Furthermore, a dual-linear polarized TCA embedded with the CRSS is simulated and manufactured, and the results show that it achieves an impedance bandwidth of 9.3:1 (0.6–5.58 GHz) and more than 90% radiation efficiency for broadside with the active VSWR ≤ 3.0. Besides, such an array remains the same bandwidth while scanning up to 60° in the E- and D-planes and scanning up to 45° in the H-plane with the active VSWR ≤ 3.5. Therefore, the CRSS shows a very promising application in engineering.

A Cryo-CMOS Oscillator With an Automatic Common-Mode Resonance Calibration for Quantum Computing Applications

This article presents a 4-to-5GHz LC oscillator operating at 4.2K for quantum computing applications. The phase noise (PN) specification of the oscillator is derived based on the control fidelity for a single-qubit operation. To reveal the substantial gap between the theoretical predictions and measurement results at cryogenic temperatures, a new PN expression for an oscillator is derived by considering the shot-noise effect. To reach the optimum performance of an LC oscillator, a common-mode (CM) resonance technique is implemented. Additionally, this work presents a digital calibration loop to adjust the CM frequency automatically at 4.2K, reducing the oscillator’s PN and thus improving the control fidelity. The calibration technique reduces the flicker corner of the oscillator over a wide temperature range (10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> and 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> reduction at 300K and 4.2K, respectively). At 4.2K, our 0.15-mm2 oscillator consumes a 5-mW power and achieves a PN of −153.8dBc/Hz at a 10MHz offset, corresponding to a 200-dB FOM. The calibration circuits consume only a 0.4-mW power and 0.01-mm2 area.

A novel design and control method for improved LCL filter three-level inverter to suppress common mode resonant current and leakage current

The method of connecting the common point of the LCL filter capacitor of the three-level grid-connected inverter to the midpoint of the DC side can effectively suppress the leakage current between the DC side photovoltaic panel and the power grid. However, the improved MLCL inverter is easy to generate common mode resonance, which results in excessively increasing the midline current and affecting the efficiency and stability of the system. Aiming at the common mode resonance problem of MLCL three-level inverter, this paper expounds the generation of common mode resonance current and large neutral current by establishing the mathematical model of the improved MLCL filter. After analyzing the restraining effect and limitation of traditional passive damping control scheme on common mode resonance, a novel filtering structure is proposed in this paper, which is combined with PI+ PR double closed-loop control scheme to solve the above problems. Simulation results verify the validity of the analysis on common mode resonance and neutral current, and the effectiveness of the scheme in suppressing common mode resonance current, midline current and leakage current is also confirmed.

A wide‐angle beam scanning circularly polarized, tightly coupled dipole array based on two‐layer parasitic ring structure elements

In this paper, a wide-angle beam scanning circularly polarized (CP) phased array element, which consists of a concentric tightly coupled dipole array (TCDA) element with a two-layer parasitic ring structure and a wideband 90° phase shifter, is proposed. To solve the problem of the scanning blindness zone caused by a concentric layout, the grounded coupling patch for the traditional TCDA element is ‘split’ into a combination of a grounded parasitic ring and coupling patch. This combination structure can not only suppress the in-band common-mode resonance but also destroy the scanning blind zone mode formed by the dipole and grounded coupling patch. In addition, a two-layer parasitic ring structure is introduced to obtain a wider axial ratio (AR) beamwidth relative to a single-layer structure, so a wide-angle beam scanning AR is realized. An 8 × 8 left-handed CP planar array based on the proposed wide-angle beam scanning CP elements is designed and prototyped. Results show that the array can operate over a 3.2:1 (3.75–12.0 GHz) overlapping bandwidth, meeting an AR < 3 dB in the main beam and an active voltage standing wave ratio <2.8 within a ±60° angle scanning range.

2–18 GHz balanced antipodal Vivaldi conformal phased array antenna with resistive load and shorting posts

In this paper, a 2–18 GHz balanced antipodal Vivaldi conformal phased array antenna is proposed. Firstly, the conformal array achieves a low profile of 0.11λLow by using the tightly coupling mechanism. Here, the gap-induced element resonance (GIER) and the common mode resonance occur in the operating band, limiting the impedance bandwidth. Thus, the resistors are loaded to eliminate the GIER by suppressing the resonant current. Furthermore, the shorting posts are used to remove the common mode resonance by decreasing the resonant length. A transition structure between the stripline (SL) and the ground coplanar waveguide (GCPW) is designed to feed the antenna. The simulated results show that the array achieves a 9:1 bandwidth (2–18 GHz) for active VSWR <2.5 at broadside. Besides, the active VSWR is less than 2.5 for ±60° scanning in E-plane and 3.8 for ±45° scanning in H-plane. A 12 × 8 array prototype is fabricated and measured to validate the performance of the array. The measured results show a good agreement with the simulation.

Fully integrated wideband phased array with large scan range and 5:1 bandwidth

In this work, a fully integrated phased array using multi-layer printed circuit board (PCB) fabrication technologies is presented. This array is directly fed by 50 Ω coaxial cables, without balanced-to-unbalanced transitions. An asymmetric dipole is used to achieve stable input impedance. Furthermore, to broaden the operating bandwidth, a coupling patch is designed beneath the asymmetric dipole , which also eliminates the common-mode resonance and decreases the array profile. In addition, three wide-angle impedance matching (WAIM) layers with different structures are utilised to improve the scan range in all scanning planes. Infinite array simulations indicate that the proposed array can operate over a 5.1:1 bandwidth (2.4 ∼ 12.2 GHz) with an active voltage standing wave ratio below 3 while scanning up to ± 60° in H plane and ±75° in the E plane. Furthermore, the proposed antenna, whose cross-polarization levels remain below −35 and −7.5 dB when scanning up to 75° in the E plane and 60° in the D plane, demonstrates the merits of high polarization purity. Array simulations are verified by the measurements of a 12 × 12 prototype, and good agreement is observed.

Design of an ultra-wideband dual-polarized array antenna

In order to meet the requirements of ultra-wideband wireless communication system applications, this paper studies an ultra-wideband dual-polarization strongly-coupled array antenna. The array element is composed of two pairs of connected printed dipoles orthogonally. The feed network is constructed by the Marchand Balun and the Wilkinson power splitter and realizes the balanced feed, the impedance transformation and common mode resonance suppression. Simulated and measured results show that the proposed antenna achieves an impedance bandwidth of 1.5 GHz to 4.0 GHz, and an E-plane beam scanning range ±60°, H-plane beam scanning range ±50°, and the antenna structure is simple, and is suitable for the applications of dual-polarization wide-angle scanning phased array antenna system.

Planar Ultra-Wideband and Wide-Scanning Dual-Polarized Phased Array With Integrated Coupled-Marchand Balun for High Polarization Isolation and Low Cross-Polarization

In this article, a dual-polarized planar phased array with high polarization isolation and low cross-polarization is presented operating from 4 to 18 GHz, i.e., 4.5:1. The proposed array is comprised of tightly coupled dipoles with integrated coupled-Marchand baluns. To improve the uniformity of fields distributed on the array, the center-feeding dipole is used in this design instead of the conventional edge-feeding one at first. Then, the outer conductors of the feed are composed of a group of shorted vias with the proper number and position. Based on these methods, the output balance of the balun is significantly improved, resulting in high isolation between ports with different polarization modes. Furthermore, this feed has a natural ability to suppress the D-plane common mode resonance. The capacitive metallic annular plate over adjacent radiating elements and the thick aluminum plate with an air cavity placed under the array are employed together to suppress the in-band coupled-loop modes. The infinite array simulation indicates that the array can achieve transmit (Tx)/receive (Rx) isolation more than 48 dB at broadside. Isolation better than 32 and 30 dB can be achieved when scanning to 45° in E-/H-planes and 60° in E-plane, respectively. The cross-polarization level is below −54 dB at broadside and remains below −29 dB when scanning to 60° in E-plane as well as 45° in H-plane. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12\times12$ </tex-math></inline-formula> dual-polarized antenna array is fabricated and measured to validate the correctness of this design. This type of antenna can be applied in wideband simultaneous transmit and receive (STAR) monostatic systems.

Modeling and Resonance Damping for the CM Loop of the MLCL-Filtered Grid-Connected Inverter With Variable Inductors Under the Weak Grid Condition

The modified LCL (MLCL) is commonly applied in photovoltaic (PV) string inverters to suppress the leakage current and enhance the electromagnetic interference (EMI) performance of the grid current. However, the potential risk of resonance appears in the common mode (CM) loop, which was caused by the MLCL filter. In this article, the CM model of the inverter is first built considering the inductance saturation. It is found that the variable inductor brings phase margin decreasing problem and additional resonance points in the CM loop. To suppress the CM resonance (CMR), novel passive and active damping strategies are explored in this article. The improved passive damping (IPD) strategy is realized by introducing a paralleled <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> unit, which greatly reduces the damping resistor losses without affecting the damping performance. Besides, a novel active damping (NAD) strategy is proposed to compensate the time delay and to raise the phase margin. Moreover, considering the gradient mutation issue brought by the discontinuous pulsewidth modulation (DPWM) scheme, an antisaturation PWM (ASPWM) scheme is applied to eliminate the oscillation. Finally, experiments are conducted on an 80-kW PV string inverter. After applying the proposed CMR damping strategy with the ASPWM scheme, CMR is fully eliminated in the whole power range despite the grid condition.