Search

This article presents two unique common-ground high-reliability dual-buck single-phase inverters suitable for photovoltaic applications. The proposed inverters directly connect the source and load, excluding the inverters from leakage current. The first proposed inverter works only for unity power factor operation. In its operation, the inverter employs only one high-frequency switching device, thus presenting low switching losses and improving overall efficiency. The second proposed inverter works for any power factor. In its operation, the inverter utilizes two high-frequency switching devices, resulting in minimal switching losses. The proposed inverters have no reverse recovery loss and related issues since the body diodes of the power metal–oxide–semiconductor field-effect transistors are disabled. The proposed inverters are devoid of short-circuit issues, resulting in high reliability. The detailed modes and operating principles together with the pulsewidth-modulated strategy for the proposed inverters are described. Experiments were carried out on 0.6-kW laboratory prototypes, operating at a switching frequency of 50 kHz and an output voltage of 110 Vrms. The experimental results verified the robustness of the proposed inverters.

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.

The direct pulsewidth modulation (PWM) ac-ac converters are seeing rapid development due to their single-stage power conversion with reduced footprints, due to the elimination of intermediate dc-link capacitor. However, they only provide unipolar voltage gain and fixed frequency operation and use the bidirectional voltage-blocking devices without natural inductor current free-wheeling path, restricting their practical applications. This article proposes a direct PWM bipolar and step-variable frequency buck-boost ac-ac converter. The proposed converter is fabricated by connecting input-output $LC$ filters and a small value film capacitor to six unidirectional voltage-blocking devices, which are arranged as a three-leg inverter module. It can provide noninverting and inverting buck-boost voltage operations with a symmetric bipolar voltage gain of ${\pm }d/(1-d)$ and can also change the frequency of output voltage in discrete steps, same as that of single-phase matrix converters (MCs). It has no open-circuit risk of inductor due to the presence of natural current free-wheeling path during PWM dead time. Therefore, it is unaffected by the commutation problem of conventional direct ac-ac converters. The proposed converter can realize high-quality input and output due to the presence of second-order input-output filters with continuous input-output currents. A detailed analysis is provided based on proposed switch modulation strategies and confirmed through extensive experimental tests on a laboratory-fabricated hardware.

In this article, a new coupled-inductor-based modular multilevel cascaded inverter using a new phase shift control is presented. The proposed inverter can generate a high output ac voltage using standard low-voltage-rating devices. The number of levels in the output pulsewidth modulation (PWM) voltage and the effective switching frequency of the output filter are increased using coupled inductors and phase shift control. The switching signals of the cascaded units in the proposed inverter are phase-shifted by ${\mathbf {360}}{\mathbf {^{\circ }}}{/4n}$ , where ${n}$ is the number of cascaded units. The proposed phase shift control results in ( $4{n}$ + 1) levels in the output PWM voltage of the proposed inverter and increases the effective switching frequency of the output filter by 4n times the actual switching frequency ${f}_{\mathbf {sw}}$ . As a result, the output waveforms can be generated with better quality and less distortion. In addition, the output filter can be decreased dramatically in size. Besides, fewer coupled inductors are used to reduce the footprints, the number of inductors, and magnetic volume. Moreover, the proposed inverter is exceptionally reliable due to no short-circuit risk in the 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.