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In this paper, a new single-stage half-bridge (HB) resonant $LLC$ converter additionally employing one resonant capacitor and two relays with one package is proposed, compared with a single-stage HB $LLC$ converter. Moreover, a center-tapped transformer is replaced with a coupled transformer. Since the proposed converter changes the turns ratio of the coupled transformer using a relay according to low- or high-input-voltage range, it can decrease the range of its needed voltage gain. It means that the proposed converter can be designed with large transformer magnetizing inductance compared with the conventional single-stage HB $LLC$ converter. As a result, the primary conduction and turn-off losses are reduced. Moreover, in low input voltage range, it has smaller total primary wire resistance of the transformer due to parallel connection of the coupled transformer, which decreases its conduction loss. In addition, additionally employed small-sized components can be inserted to the conventional system. To confirm the operation, features, and validity of the proposed converter, universal input with low line and high line and 16.5 V/60 W output laboratory prototype targeting laptop adapters with wide-input-voltage range is built and tested. [ABSTRACT FROM AUTHOR]

Many publications have been presented on the modulation and control of the modular multilevel converter, some of which are based on phase-shifted carrier modulation. This paper presents an analysis of how the switching frequency affects the capacitor voltages, circulating currents, and alternating voltages using phase-shifted carrier modulation. It is found that switching frequencies that are integer multiples of the fundamental frequency should be avoided as they can cause the capacitor voltages to diverge. Suitable switching frequencies are derived for which the arm and line quantities will be periodic with symmetric operating conditions in the upper and lower arms. Thus, the practical outcome of this paper is a detailed description of how the switching frequency should be chosen in order to achieve advantageous operating conditions. The theoretical results from the analysis are validated by both simulations and experimental results. [ABSTRACT FROM AUTHOR]

A new zero-sequence circulating current (ZSCC) reduction method for multimodule voltage source inverters (MVSIs) consisting of P three-phase inverters that are connected in parallel is proposed in this paper. Four-switch inverter modules are used instead of the conventional six-switch modules to reduce the cost. In this paper, the effectiveness of the proposed ZSCC reduction method is studied using selective harmonic elimination pulse width modulation. The proposed ZSCC reduction method can remove about P times the number of harmonics using the same switching frequency as compared to more conventional methods, as explained later in this paper. The concepts discussed in the paper are confirmed with results obtained from an MVSI experimental prototype. [ABSTRACT FROM AUTHOR]

Interleaving of voltage-source converter (VSC) legs enables higher output currents per phase, effectively increasing the power rating without increasing semiconductor ratings. However, the interleaved operation results in circulating currents between each phase converter legs as well as a zero-sequence circulating current (ZSCC), which become quite prominent when the converters operate with low switching frequencies. This paper demonstrates the interleaved operation of three-level converters under selective harmonic elimination pulsewidth modulation (SHE-PWM). A controller for the circulating current within the legs of each phase is also proposed. The controller is used in combination with optimally selected SHE-PWM patterns to generate the maximum number of voltage levels and minimize the peak value of the circulating current. Simulation and experimental results show the interleaved operation and the effect of SHE-PWM pattern selection in the overall system. [ABSTRACT FROM PUBLISHER]

Efficiency in a light load dc–dc converter is improved by reducing the switching frequency with the load current. Further, a bifrequency operation (BFO) using pulse train (PT) control can achieve spread spectrum. Using discrete-time models, this paper shows that a stable periodic BFO is generally not achievable in existing PT control methods. Thereafter, a unified multimode digital control technique is proposed, in which a voltage-mode digital pulse-width-modulator (DPWM) is used to control a predefined periodic BFO. Beside the fixed-frequency DPWM, an extra multiplexer is considered for real-time configuration to: 1) bifrequency pulse frequency modulation; 2) PT control; or 3) pulse regulation control; or 4) pulse skipping control with smooth transition. Analysis and design methods are discussed to ensure periodic BFO and to customize the power spectrum with predictable ripple parameters. A buck converter prototype is made, and the proposed control is implemented using an FPGA device. [ABSTRACT FROM PUBLISHER]

This paper proposes a bidirectional three-level LLC resonant converter with a new pulse width and amplitude modulation control method. With different control signals, it has three different operation modes with different voltage gains. Therefore, it can achieve wide voltage gain range by switching among these three modes, which is attractive for energy storage system applications needing wide voltage variation. The proposed topology operates with constant switching frequency, which is easy to implement with digital control, and it can achieve soft switching for all the switches and diodes in the circuit as a conventional LLC resonant converter. The performance of the proposed converter is validated by the experimental results from a 1-kW prototype with 20 A maximum output current. [ABSTRACT FROM PUBLISHER]

A novel complementary phase disposition pulsewidth modulation method for the modular multilevel converter (MMC) with a limited number of submodules is proposed in this paper. Compared with the previous works, more practical issues have been considered, and the corresponding solutions have been provided. First, a new preset PWM signal mapping sequence and an improved virtual loop mapping (VLM) are used in the modulation. This method not only achieves a favorable capacitor voltage balance in the symmetry system but lowers the switching frequency of MMC's devices. Second, to further reduce the switching frequency, the unbalance margin of capacitor voltages is adopted to achieve the switching between the VLM and the selective VLM (SVLM). Moreover, the system robustness has been improved by considering the situation of symmetry losing, like cell fails; in these cases, the capacitor voltages of the upper and lower arms are balanced through the collaboration of the SVLM and the reconfigurable VLM. Finally, the effectiveness of the proposed method has been verified with simulation and experimental studies. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage balancing method for a flying capacitor multilevel converter based on the phase-disposition sinusoidal pulsewidth modulation (PD-SPWM). This voltage balancing method uses redundant switching states, which are determined by the minimization of a cost function. The implementation of the PD-SPWM using standard triangular carriers leads to additional switching events that are due to the transitions within the same voltage level, thus increasing the switching frequency of the power devices. Such drawback can be avoided by using sawtooth carrier waveforms. Another characteristic of the proposed voltage balancing method is that it does not require the tuning of parameters to achieve optimal performance. Simulation and experimental results confirm the robustness of the proposed method operating with different loads and transient conditions. [ABSTRACT FROM PUBLISHER]

A new zero-voltage switching (ZVS) dc converter for high input voltage and high output current applications is presented in this paper. Two three-level pulse-width modulation (PWM) circuits with the same active switches connected in parallel at the output side are adopted to achieve load current sharing and to decrease current stress of rectifier diodes. The center-tapped rectifiers are adopted at the secondary side to have only one diode conduction loss in the forward current path. The series resonant tank of three-level converter is used to achieve ZVS turn-on for all power switches and zero-current switching for all rectifier diodes within nearly entire load range. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. In order to overcome the drawback of a wide range of switching frequency in conventional series resonant converters, the fixed frequency pulse-width modulation is adopted to regulate the output voltage. The series-connected transformers are used in the primary and secondary sides to share and balance the load current. Finally, experiments based on a laboratory prototype are provided to verify the operation principle and demonstrate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

This paper presents a unique modulation method for extending the input range of pulse-width modulation (PWM)-integrated resonant converters, such as the isolated boost resonant converter, while maintaining high conversion efficiency. The technique includes primarily the hybridizing of constant-on, constant-off, and fixed-frequency control depending only on the required duty cycle. The modulation scheme reduces core loss and conduction loss dramatically by decreasing the applied volt-seconds at the transformer and improving the switching period utilization. With hybrid-frequency control, the circuit also maintains zero current switching for the output diodes, minimizes switching loss, and eliminates circulating energy at the transformer across the entire operating range. It also allows for a predictable voltage gain, dependent only on duty cycle and transformer turns ratio. A detailed loss analysis is provided and verified against a 180 W experimental prototype, with an input range of 12–48 V and a switching frequency range of 30–70 kHz. Implementation issues are also handled with a variety of solutions for realizing the modulation scheme. Experimental results show greater than 4% weighted efficiency improvement in the prototype using the proposed method. [ABSTRACT FROM AUTHOR]

The maximum closed-loop bandwidth of a dc-dc converter is restricted to a fraction of its switching frequency when governed by a conventional average-based pulsewidth modulation (PWM) controller. Even an advanced geometric control is limited by internal slew rates. The bandwidth can reach or exceed the switching frequency through converter augmentation; however, this requires a nonlinear control algorithm and circuit arrangements. This paper considers methods of augmentation and control for a fast buck converter. Conditions for time-optimal transient recovery are obtained for both instantaneous and delayed transient disturbance detection. Design tradeoffs and control issues related to augmentation are considered here. The main switch is controlled using a fixed frequency PWM current-mode control with load current feedforward, and augmented switches are controlled using frequency-limited bang-bang control based on a geometric approach. A small-signal model is obtained and extended control bandwidth is demonstrated. Fast transient recovery is achieved for both single- and two-resistance augmentation. A prototype augmented buck converter is tested. Output voltage and inductor current overshoot and undershoot can be lowered more than with previous methods. It is possible to achieve near-null response in the sense of ripple band to a large-signal transient. [ABSTRACT FROM AUTHOR]

This paper presents a flyback switch-mode rectifier (SMR) with spread harmonic spectrum. The SMR switching control is conducted by a charge-regulated pulsewidth modulation (PWM) scheme with constant turn-on period. The inherently stable discontinuous conduction mode operation is preserved to yield good line drawn power quality. In voltage loop, a quantitatively designed PI feedback controller is augmented with a robust error cancellation control scheme. Further improved dc output voltage regulation and input power quality performances are achieved under varied operating conditions. In spread harmonic spectrum control, the harmonic spectral properties of the developed flyback SMR are first analyzed. Then, the dedicated random switching scheme is developed to let its switch current harmonic spectrum be dispersedly distributed. In the proposed random switching scheme, the PWM turn-off period is modulated using 1-b binary sequence, pseudo random binary sequence, and 4-b binary sequences. Under randomized harmonic spectrum, the SMR control performances are not sacrificed. [ABSTRACT FROM PUBLISHER]

Multilevel cascaded H-bridge converters have found industrial application in the medium-voltage high-power range. In this paper, a generalized modulation technique for this type of converter based on a multidimensional control region is presented. Using the multidimensional control region, it is shown that all previous modulation techniques are particularized versions of the proposed method. Several possible solutions to develop a specific implementation of the modulation method are addressed in order to show the potential possibilities and the flexibility of the proposed technique. In addition, a feedforward version of this technique is also introduced to determine the switching sequence and the switching times, avoiding low harmonic distortion with unbalanced dc voltages. Experimental results are shown in order to validate the proposed concepts. [ABSTRACT FROM AUTHOR]