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This article introduces a novel buck-boost ac–ac converter with identical bipolar operation and high-frequency voltage isolation. The proposed converter offers several distinguishing features compared to existing isolated converters: First, it provides a significant reduction in the number of active and passive components. Second, it supplies continuous input and output currents with low harmonic contents. Third, it provides bipolar output with a two-winding transformer (instead of a three-winding transformer) with enhanced magnetic utilization and reduced cost and footprint. Finally, it can operate with different winding coefficients without compromising buck-boost functionality or limiting its magnitude coverage. Additionally, the converter facilitates buck-boost operation for all transformer winding ratio values, making it suitable for shallow and deep voltage sag/swell mitigation. The integration of a high-frequency transformer eliminates the need for a low-frequency coupling transformer. The proposed converter can provide a step control of output voltage frequency and performs normally under inductive and nonlinear loads. This article provides a detailed description of the proposed topology operation and its analysis, succeeded by experimental validations conducted on a laboratory-built converter, showcasing a peak efficiency of 93.3%. Extensive comparisons affirm that the proposed converter exhibits reduced input/output total harmonic distortion, broader voltage gain coverage, and superior efficiency compared to recently developed converters.

In this article, a single-phase Z-source ac–ac converter with continuous input current and without commutation issue is proposed. The proposed converter has the ability to provide boost in-phase and buck-boost out-of-phase modes. This operation is achieved using four switches, with only one high-frequency switch being switched in each half cycle of the input voltage. In this converter, the commutation problem has been inherently solved. As a result, the converter is protected from voltage and current spikes on the switches without requiring snubber circuits or safe commutation methods. Also, a simple switching and control pattern is implemented in the proposed converter. By studying the switching device power index and comparing it with other converters, it can be claimed that the proposed converter is cost-effective. The operating principles of the proposed converter in different modes are examined in detail. Eventually, the experimental results of a 70 Vrms/50 Hz laboratory prototype are presented to confirm the validity of the theoretical relationships and the correctness of the proposed converter.

Dual-buck (DB) structured ac–ac converters are becoming advanced due to their inherent protection from open- and short-circuit risks, and elimination of commutation issue. However, the existing DB ac–ac converters provide restricted bipolar voltage operations with a large semiconductor device count and underutilized inductors. This article proposed a new reduced switch DB ac–ac converter without commutation issue. The propose converter provides multiple buck–boost voltage operations with noninverting and inverting outputs, making it a flexible topology for various ac voltage applications. The propose converter exhibits the continuous input and output currents irrespective of operation mode, and performs well with nonunity power factor loads. The positive and negative voltage gains of the proposed converter can address the grid voltage sag and swell issues, respectively, making it right candidate for application as dynamic voltage restorer. A detailed comparative evaluation is carried out with existing DB converters, which validated the effectiveness of the proposed converter, including; reduced semiconductor device count and their power ratings, reduced inductor sizes with improved magnetic utilization, enhanced voltage compensation ranges, and better efficiency. A laboratory scale hardware prototype of the proposed converter is built and thoroughly tested to validate its operation.

This article proposes a new topology of a three-phase high-frequency transformer (HFT) isolated bipolar ac–ac converter. It has a simple circuit topology consisting of nine active switches, three HFTs with primary and secondary series capacitors, and output LC filters. It can generate both noninverting and inverting outputs with a symmetric bipolar voltage gain of $ \pm nd$, where n is the turns ratio of the transformer and d is the switch duty cycle. The proposed converter can provide step-down output by setting the turns ratio to unity; however, step-up output operation can also be achieved by increasing n beyond one when required by a particular application. The proposed converter integrates HFT-based isolation and, therefore, can eliminate the sizeable low-frequency transformer for applications requiring grid interface. Owing to the use of series-blocking capacitors, the HFT is devoid of any line-frequency component. A safe-commutation-based switch modulation strategy is developed to avoid switch current and voltage overshoots. The proposed converter is well suitable for application as a three-phase dynamic voltage restorer. The inverting and noninverting operations can inject the antiphase and same-phase series voltages to mitigate grid voltage swell and sag, respectively. Moreover, the additional line-frequency isolation and voltage injection transformers can be saved. In-depth circuit analysis and operation are provided with proposed switch modulation strategies together with component design guidelines. Finally, the hardware measurements are taken on a laboratory-built circuit to confirm the operation of the proposed converter.

In this article, a new coupled-inductors based three-level bipolar buck–boost ac–ac converter is proposed. The proposed converter can produce highly efficient and symmetric in-phase and antiphase buck and boost modes of operation with much lower component voltage and current stresses. This reduces the operation and design complexity, and helps to achieve a high-efficiency operation. The high-frequency modulating switches of the proposed converter are implemented with coupled-inductor-based dual-buck phase leg, producing three-level input and output voltages, and providing inherent protection from voltage-source short-circuit issue during switch transitions. The other salient features of the proposed converter are no-commutation issue, no need for RC snubbers or dedicated safe-commutation algorithms, provision of high-quality and continuous input/output currents, and support for nonresistive loads. An in-depth circuit analysis of the proposed converter is provided based on the proposed switch modulation strategies. The guidelines for component design/selection are discussed, followed by the comparisons with state-of-the-art three-level ac–ac converters. Finally, practical circuit verifications are performed on a laboratory-assembled prototype.

This article proposes a new single-stage three-phase buck-boost inverter and control scheme, which remarkably reduces both the low and high-frequency ripple components in the input current. The low-frequency ripple component is eliminated by phase-shifting the output three-phase voltages by 120°. The high-frequency ripple component is decreased by doubling the effective switching frequencies and lowering the voltages of the input inductors. The proposed inverter has buck-boost dc-ac conversion ability and contains only six active switches. It is short-circuiting free and can avoid the reverse recovery losses of the body diodes of the mosfets. The proposed inverter has better spectral performance and has a lower distortion in the output waveforms due to no delays (equivalent to dead-time in the traditional three-phase inverter) in the switching signals. To validate the performance and advantages of the proposed inverter, detailed analytical, simulation, and experimental results are reported. Experiments have been conducted with a 1.5-kW laboratory prototype at a 50 kHz switching frequency for the line-line output voltage of 110–220 Vrms/60. At the end, integration of inductors is also suggested to decrease the magnetic volume.

In this article, we propose an improved high-boost-gain split-source inverter (SSI) for renewable energy generation. The proposed inverter retains the features of the existing SSIs, such as single-stage boost inversion with a reduced number of passive components and elimination of the inverse modulation–duty relationship constraint of the impedance-source inverters. It also provides additional features that include higher boost inversion ability than existing SSIs to connect low-voltage renewable energy sources to the grid, no voltage-source short-circuit issue, which increases the robustness of the proposed inverter and pulsewidth modulation dead times can be relieved, and the negative input dc-terminal and ac-neutral are electrically connected in the proposed inverter, resulting in a constant common-mode voltage and elimination of leakage ground currents for grid-interfaced PV power systems. A detailed circuit operation and analysis is provided, and experiments are performed on a 400-VA prototype inverter to confirm the working of the proposed topology.

Single-phase dual-buck ac–ac (DBAC) converters are gaining attention due to their intrinsic protection from shoot-through and open-circuit problems of conventional ac–ac converters. However, research works on DBAC converters are mainly concentrated around unipolar topologies. In a few developed bipolar topologies to date, the inverting buck–boost operations (for series voltage injection and step-variable frequency outputs) are inefficient and burdened by large voltage and current stresses (${v}_{\text{in}} + {v}_o\ \text{and}\ {i}_{\text{in}} + {i}_o$) of switching devices and ripples of passive elements. In this article, an efficient dual-buck structured buck–boost ac–ac converter is proposed, with the following features: no voltage source shoot-through and inductor open-circuit problems, natural attainment of safe commutation without additional protection circuitry or complex control, no need for pulsewidth modulation dead times, and elimination of high-frequency conduction of mosfet’s body diodes and related slow reverse recovery issues. The proposed converter provides distinct types of efficient inverting and noninverting buck and boost operations, with smaller switch voltage/current stresses (${v}_{\text{in}}/{v}_o$ and $\ {i}_{\text{in}}/{i}_o$) and passive component ripples. Combined inverting and noninverting buck–boost operations are also proposed with separate tuning of buck and boost voltage transfer ratios. A simple adaptable switching strategy provides the switch control pulses for all circuit operations by modulating the buck and boost control reference signals. The proposed converter provides sustained input/output currents and performs well with nonresistive loads. Extensive theoretical analysis is presented followed by practical verifications on a 400-VA laboratory circuit.

An improved dual winding magnetically coupled-inductors inverter based on a Cockcroft-Walton multiplier voltage cell is proposed in this brief. Compared with the conventional generalized Cockcroft-Walton multiplier voltage Z-source inverters, the proposed inverter attains higher voltage gain by decreasing the transformer’s turns number. As a result, lower cost, higher efficiency, larger voltage boost factor, and higher density can be realized in the proposed inverter. Furthermore, unlike conventional magnetically coupled impedance source inverters, the proposed topology offers a larger voltage boost factor for small shoot-through duty ratios with a smoother slope, which enhances the practical controllability of the inverter. Hence, a higher modulation ratio can be applied, which results in a better quality of the inverter’s waveforms. A clamping circuit is used to reduce the leakage inductance effects of the coupled inductors. As a result, the huge voltage spikes across the inverter bridge are eliminated. In addition, the proposed inverter draws a smooth and continuous input current from the input dc source, which is suitable for renewable energy sources. Detailed, theoretical analysis, simulation and experimental results are provided.

This article proposes a new H-bridge structured bipolar pulsewidth modulation (PWM) buck–boost ac–ac converter based on the nondifferential ac choppers. The proposed converter can generate simple identical noninverting and inverting buck–boost voltage outputs by modulating one phase leg with single control duty ratio (${d}_1$ or ${d}_2$). It can also provide flexible identical noninverting and inverting buck–boost operations by modulating both phase legs with two control duty ratios (${d}_1$ and ${d}_2$). In the proposed topology, the use of nondifferential ac choppers eliminates the complementary switching of ac switches and related inductor open-circuit issue. Moreover, half the switching devices are configured as switching-cell units to avoid shoot-through occurrence due to accidental turn-on of complementary switches. Therefore, the proposed topology is free from commutation issue and can abolish PWM deadtimes to produce high-quality output with improved utilization of switch duty ratios. It also provides continuous input current and can perform normally with reactive loads. It has the potential to mitigate both voltage sags and swells (due to bipolar operation) when used as series voltage compensator; and unlike the existing nondifferential bipolar ac–ac converters, it can provide compensation for more intense voltage sags (of above 50%) as well. In-depth analysis of the proposed topology and hardware verifications are provided in this article.