Frequency multiplication string photovoltaic power converter based on tri-state switching cells

Abstract

A triac-based frequency multiplication cascaded photovoltaic power converter device is provided. The power converter device includes a plurality of cascaded triac-based switching cells arranged in two or more power units for receiving power from two or more variable DC power sources, such as a cascaded photovoltaic power source, and generating a multi-level dc link voltage. The device generates reduced amplitude ripple and multiplies the effective switching frequency in the reactive components by two, four, or more times the basic switching frequency of the triac-based switching cells. Frequency multiplication and multi-level voltage generation are assisted by cascading two triac-based switching cells that share a single transformer. The reduced voltage and current ripple amplitude and increased effective frequency result in reduced component size, resulting in a high efficiency power converter device with high power density.

Description

Technical Field

[0001] Various aspects of the embodiments of this disclosure generally relate to power conversion devices, and more particularly to power converters for photovoltaic inverter applications. Background Technology

[0002] Two-stage photovoltaic (PV) inverters consist of a front-end DC-DC converter and a back-end DC-AC inverter, and are typically used to connect solar energy to the grid. Multilevel converter topologies such as T-type, flying capacitor, midpoint clamp, cascaded multilevel converters, and modular multilevel converters have been widely used in PV applications to provide DC-AC power conversion due to their numerous advantages.

[0003] Despite its many advantages, developing multilevel converter topologies capable of achieving high efficiency and high power density remains challenging. The large volume of reactive power components used in filtering hinders the development of high-efficiency, high-power-density converters. Increasing the converter's switching frequency can reduce the size of the reactive power components; however, this leads to increased switching losses, reduced efficiency, and increased heat generation.

[0004] To avoid increased switching losses due to higher switching frequencies, converters have been developed that can multiply the effective switching frequency of reactive power components used for filtering. However, most of these topologies can only double the switching frequency and typically suffer from increased component count, more complex design and control requirements, and higher voltage levels, which negatively impact power density and efficiency.

[0005] Therefore, there is a need for improved power converters suitable for photovoltaic DC-AC inverter applications, capable of reducing the size and cost of reactive power components and improving the overall efficiency of the converter. In view of this, there is an urgent need to provide methods and apparatus that can at least solve some of the aforementioned problems. Attached Figure Description

[0006] In the following detailed description of the invention, the invention will be explained in detail with reference to exemplary embodiments shown in the accompanying drawings, wherein the same reference numerals indicate the same elements.

[0007] Figure 1 An illustration shows an exemplary single-phase power converter device based on a three-state switching unit incorporating various aspects of embodiments of the present disclosure.

[0008] Figure 2 A schematic diagram of the switching states of an exemplary three-state switching unit incorporating various aspects of embodiments of the present disclosure is shown.

[0009] Figure 3A diagram showing exemplary operating waveforms of a single-phase power inverter device based on a three-state switching unit incorporating various aspects of embodiments of the present disclosure is provided.

[0010] Figure 4 A diagram showing exemplary operating waveforms of a single-phase power inverter device based on a three-state switching unit incorporating various aspects of embodiments of the present disclosure is provided.

[0011] Figure 5 An exemplary three-phase power converter apparatus incorporating aspects of embodiments of the present disclosure is shown.

[0012] Figure 6 A diagram showing exemplary operating waveforms of a three-phase power converter device incorporating various aspects of embodiments of the present disclosure is provided.

[0013] Figure 7 A diagram showing exemplary operating waveforms of a three-phase power converter device incorporating various aspects of embodiments of the present disclosure is provided.

[0014] Figure 8 A schematic diagram of an exemplary additional cascaded power unit incorporating various aspects of embodiments of this disclosure is shown. Detailed Implementation

[0015] Figure 1 Illustrations show an exemplary power converter device 100 based on a three-state switching cell (TSSC) incorporating aspects of embodiments of this disclosure. Exemplary device 100 relates to an improved DC-AC power converter employing cascaded power cells to achieve multi-level voltages at the output terminals and frequency multiplication in the reactive power components. The TSSC-based frequency multiplication topology disclosed herein provides bidirectional multi-level power conversion suitable for use in string photovoltaic (PV) inverter applications, overcoming many drawbacks of conventional power converters.

[0016] like Figure 1 As shown, in one embodiment, the power converter device 100 based on a three-state switching unit includes a first three-state switching unit 160 having a first switching arm 102, a second switching arm 104, and a first transformer T1. The first switching arm 102 and the second switching arm 104 are coupled in parallel with a first power supply VD1. The first winding 120 of the first transformer T1 is coupled between the midpoint 124 of the first switching arm 102 and the intermediate voltage (vi). The second winding 122 of the first transformer T1 is coupled between the midpoint 126 of the second switching arm 104 and the intermediate voltage (vi).

[0017] The power converter device 100 based on the three-state switching unit further includes a second three-state switching unit 162 having a third switching arm 106, a fourth switching arm 108, and a second transformer T2. The third switching arm 106 and the fourth switching arm 108 are coupled in parallel with the first power supply VD1.

[0018] The power converter device 100 based on the three-state switching unit further includes a third three-state switching unit 164 having a fifth switching arm 110 and a sixth switching arm 112. The fifth switching arm 110 and the sixth switching arm 112 are coupled in parallel with the next power supply VD2. The first winding 136 of the second transformer T2 is coupled between the midpoint 130 of the fourth switching arm 108 and the midpoint 132 of the fifth switching arm 110. The second winding 138 of the second transformer T2 is coupled between the midpoint 128 of the third switching arm 106 and the midpoint 134 of the sixth switching arm 112.

[0019] The power converter device 100 based on the three-state switching unit further includes a fourth three-state switching unit 166 having a seventh switching arm 114, an eighth switching arm 116, and a third transformer T3. The seventh switching arm 114 and the eighth switching arm 116 are coupled in parallel with the next power supply VD2. The first winding 144 of the third transformer T3 is coupled between the midpoint 140 of the seventh switching arm 114 and the intermediate voltage (vi). The second winding 146 of the third transformer T3 is coupled between the midpoint 142 of the eighth switching arm 116 and the intermediate voltage (vi).

[0020] A filter inductor (Lf) is connected in series between the intermediate voltage (vi) and the point of common coupling (PCC), and a filter capacitor (Cf) is connected in parallel between the point of common coupling (PCC). The second power supply VD2 and the next power supply include the same power supply VD2.

[0021] In one embodiment, the effective switching frequency is multiplied by a factor equal to, for example, 8 times, the basic switching frequency of the TSSC. Reactive power components L f , C f The voltage and current ripple decreases proportionally to the increase in effective frequency caused by the frequency harmonic characteristics of device 100. The increase in effective frequency and decrease in ripple will make the reactive power components... L f , C f The size and volume are significantly reduced, thus providing a highly efficient and high-power-density converter topology.

[0022] Typically, DC-AC inverters for PV applications aim to: generate more levels in the inverter voltage to achieve a near-sinusoidal low total harmonic distortion (THD) inverter output voltage; minimize harmonics in the grid current; reduce filtering requirements; support the use of low-voltage switching devices (more voltage levels reduce the voltage handled by each device); reduce the rate of change of voltage (dv / dt) of the switching devices; have a smaller common-mode voltage and reduced leakage current, thus allowing for smaller electromagnetic interference (EMI) filters; and achieve fault-tolerant operation using redundant switching states and appropriate control schemes. As will be discussed further below, exemplary device 100 and related topologies employing more than two cascaded power units 148, 150 achieve at least some of the above objectives.

[0023] Exemplary device 100 is used to receive a first DC power V D1 Second DC power V D2 For example, the power delivered by a string photovoltaic source, and the AC output power generated at the point of common connection (PCC). v o , i o For off-grid operation, a suitable load R can be used. o Connect to PCC. For grid connection G operation, load R can be disconnected. o And can use switch S w1 S w2 (For example, a relay) via the mains inductor L g Connect the power grid G ​​to the PCC.

[0024] Power conversion in the exemplary device 100 is achieved using four coupled TSSCs 160, 162, 164, and 166, which are used to provide frequency multiplication and generate multi-level output voltages in the reactive power component. Each TSSC includes two switching arms, wherein each switching arm 102, 104, 106, 108, 110, 112, 114, and 116 includes a first switching device. S 1. S 3. S 5. S 7. S 9. S 11 , S 13 , S 15 The first switching device S1. S 3. S 5. S 7. S 9. S 11 , S 13 , S 15 With the second switching device S 2. S 4. S 6. S 8. S 10 , S 12 , S 14 , S 16 They are connected in series, forming midpoints 124, 126, 128, 130, 132, 134, 140, and 142 between the first and second switching devices, and each switching device... S 1. S 2. S 3. S 4. S 5. S 6. S 7. S 8. S 9. S 10 , S 11 , S 12 , S 13 , S 14 , S 15 , S 16 This includes one of the following: silicon-carbide metal-oxide-semiconductor field-effect transistors (SiC MOSFETs), insulated-gate bipolar transistors (IGBTs), and gallium-nitride metal-oxide-semiconductor field-effect transistors (GANMOSFETs).

[0025] As used herein, the term "switch arm" refers to a pair of switching devices connected in series, forming a circuit node between the two switching devices, referred to herein as the midpoint. For example, switch arm 102 includes two switching devices S1 and S2 connected in series, forming a midpoint 124 between the two switching devices S1 and S2.

[0026] In the illustrated embodiment, the exemplary device 100 includes a first three-state switching unit 160, which includes a first switch bridge arm 102, a second switch bridge arm 104, and a first transformer T1. The first switch bridge arm 102 and the second switch bridge arm 104 are connected to a first power supply V. D1 Parallel coupling. The first winding 120 of the first transformer T1 is coupled to the midpoint 124 of the first switch bridge arm 102 and the intermediate voltage. v i Between them, the second winding 122 of the first transformer T1 is coupled to the midpoint 126 of the second switch bridge arm 104 and the intermediate voltage. v i Between. Intermediate voltage v i It is generated at the output terminals 156 and 158 of the cascaded power units 148 and 150, and can also be referred to as the terminal voltage.

[0027] The second three-state switching unit 162 includes a third switch bridge arm 106, a fourth switch bridge arm 108, and a second transformer T2, wherein the third switch bridge arm 106 and the fourth switch bridge arm 108 are connected to the first power supply V. D1 Parallel coupling.

[0028] The third three-state switching unit 164 includes a fifth switching bridge arm 110, a sixth switching bridge arm 112, and a second transformer T2, wherein the fifth switching bridge arm 110 and the sixth switching bridge arm 112 are connected to the second power supply V. D2 Parallel coupling. The first winding 136 of the second transformer T2 is coupled between the midpoint 130 of the fourth switch arm 108 and the midpoint 132 of the fifth switch arm 110, and the second winding 138 of the second transformer T2 is coupled between the midpoint 128 of the third switch arm 106 and the midpoint 134 of the sixth switch arm 112. A cascaded configuration is provided within device 100 by coupling the second TSSC 162 and the third TSSC 164 via the shared transformer T2, creating a dependency between the two power units 148 and 150.

[0029] The fourth three-state switching unit 166 includes a seventh switch bridge arm 114, an eighth switch bridge arm 116, and a third transformer T3, wherein the seventh switch bridge arm 114 and the eighth switch bridge arm 116 are connected to the second power supply V. D2Parallel coupling. The first winding 144 of the third transformer T3 is coupled at the midpoint 140 of the seventh switch bridge arm 114 to the intermediate voltage. v i Between, the second winding 146 of the third transformer T3 is coupled at the midpoint 142 of the eighth switch bridge arm 116 with the intermediate voltage. v i between.

[0030] Controller 152 generates switching signals 154, which operate four TSSCs 160, 162, 164, and 166. These signals are used to generate signals capable of efficiently driving the switching devices. S 1. S 2. S 3. S 4. S 5. S 6. S 7. S 8. S 9. S 10 , S 11 , S 12 , S 13 , S 14 , S 15 , S 16 Any suitable digital controller for the switching signal can be advantageously used as controller 152. In some embodiments, it may be advantageous to configure controller 152 to employ pulse width modulation (PWM) when generating the switching signal 154. If desired, PWM may include sinusoidal pulse width modulation (SPWM).

[0031] exist Figure 1 In the illustrated embodiment, the switching device S 1. S 2. S 3. S 4. S 5. S 6. S 7. S 8. S 9. S 10 , S 11 , S 12 , S13 , S 14 , S 15 , S 16 The diagram shows a metal-oxide-semiconductor field-effect transistor (MOSFET). However, without departing from the spirit and scope of the invention, any suitable switching device capable of switching the required power at the desired frequency can be advantageously used as a switching device. S 1. S 2 、S 3. S 4. S 5. S 6. S 7. S 8. S 9. S 10 , S 11 , S 12 , S 13 , S 14 , S 15 , S 16 .

[0032] It is enlightening to consider the device 100 as having two cascaded power units 148 and 150. The first power unit 148 draws power from a first power source V. D1 Receive power and generate intermediate voltage v i The first terminal 156, while the second power unit 150 is powered by the second power source V. D2 Receive power and generate intermediate voltage v i The second terminal 158. The cascading of the first power unit 148 and the second power unit 150 is achieved through a second transformer T2, which is shared by the second TSSC 162 and the third TSSC 164. This coupling of the two TSSCs through a shared transformer contributes to the frequency multiplication and multilevel voltage generation characteristics of the exemplary device 100.

[0033] As will be described in more detail below, the intermediate voltage generated by the two cascaded power units 148 and 150 v i It is a sinusoidal AC voltage comprising nine voltage levels, and includes reactive power components L. f Cf The exposure is the TSSC switching frequency f s At eight times the frequency. In order to obtain from the intermediate voltage v i To remove high-frequency components, the device 100 includes an inductor L connected in series. f and the capacitor C connected in parallel f The resulting output filter. The output filter consists of components connected in series at the intermediate voltage. v i The filter inductor L between one end 156 and the point of common coupling (PCC) f and across the output voltage v o And the filter capacitor C connected in parallel with the point of common coupling (PCC) f form.

[0034] To aid understanding, this invention describes a power flow in one direction from a DC source to AC output power. This described power flow is suitable for PV inverter applications. It should be understood that the currently disclosed power converter devices and topologies (e.g., device 100) are not limited thereto and can be operated as needed by controlling switching signals 154 for operating the four TSSCs 160, 162, 164, 166 to operate from the source V D1 V D2 To PCC or from PCC to source V D1 V D2 Power is transmitted in any direction.

[0035] Maximum power point tracking (MPPT) is a technique for variable power sources, such as PV solar-based systems and wind turbine-based systems. MPPT seeks to optimize the system as load characteristics change to maximize power transfer efficiency. The flexible control scheme provided by exemplary device 100 makes the disclosed embodiments ideally suited for string photovoltaic inverter applications that use distributed MPPT to improve power transfer efficiency from the source PV panels. D1 V D2 Power extraction. In addition, the multilevel output generated by the exemplary device 100 produces very low total harmonic distortion (THD) in both the output voltage and the output current.

[0036] In the exemplary device 100, the first power unit 148 receives power from the first power source V. D1Received power, the second power unit 150 receives power from the second power source V. D2 Received power. Due to the cascading nature of the disclosed topology, the exemplary device 100 can be expanded to consume any desired number of two or more power sources by including additional cascaded power units for each additional power source. As will be further described below, additional cascaded power units can be added at the point marked by numeral 168 between the first power unit 148 and the second power unit 150.

[0037] The number of voltage levels, effective switching frequency, and peak-to-peak inductor voltage of a power converter device based on a three-state switching unit (e.g., exemplary device 100) can be calculated based on the characteristics of the converter topology disclosed herein. At intermediate voltage... v i The number of voltage levels generated is given by Equation 1:

[0038] in, N L It is the intermediate voltage v i The number of voltage levels in N i It is the number of input sources. N u This is the number of cascaded power units. The effective switching frequency experienced by the filter components is given by equation (2):

[0039] in, f e It is the effective switching frequency. N i and N u As shown above, the peak-to-peak inductor voltage ripple is given by equation (3):

[0040] in, v p-p It is a filter inductor L f Peak-to-peak voltage ripple. Peak-to-peak inductor voltage and effective switching frequency are used to select the filter inductor. L f Key design parameters. Higher frequency and lower peak-to-peak voltage reduce the filter inductor. L f The smaller size improves power density and converter efficiency.

[0041] A conventional TSSC includes two switching arms and an autotransformer. This would indicate that an exemplary device 100, comprising four TSSCs 160, 162, 164, and 166, would include four autotransformers, one for each TSSC. However, in the exemplary topology incorporated into device 100, power units 148 and 150 are cascaded in such a manner that two TSSCs 162 and 164 are coupled via a single shared transformer T2. It can be shown that even if the autotransformer is replaced by the single shared transformer T2, each of the coupled TSSCs 162 and 164 retains its basic characteristics, namely three voltage levels.

[0042] Figure 2 Schematic diagrams 202, 204, 206, and 208 illustrate the switching states of exemplary TSSCs in conjunction with various aspects of embodiments of this disclosure. Each TSSC includes four switching devices. S 1. S 2. S 3. S The two switching arms 210 and 212 are formed by 4. The transformer T is configured as an autotransformer, wherein the first end of each transformer winding 214 and 216 is coupled to a corresponding midpoint 218 and 220 of the switching arms 210 and 212, and the second end of each transformer winding 222 and 224 is coupled to the load 226. A transformer configured in this way can be called an autotransformer. When the TSSC switches through its switching states 202, 204, 206, and 208, it generates three voltage levels at its output terminals. V TO : V D , V D / 2 and 0, where, V D This indicates the input voltage.

[0043] As used in this article, a switch or switching device is referred to as "on" or "closed" when conducting current, and as "off" or "open" when not conducting current. Figure 2 In the TSSC 202, 204, 206, and 208 shown, the open switching devices are indicated by gray shading, and the closed switching devices are indicated by black lines.

[0044] In the first switching state 202, the switching device S 1 and S 3. On, switching device S 2 and S 4. Turning off causes the output voltage across load 226 to be reduced. V TO equal to input voltage VD In the next switching state 204, the switching device S 2 and S 3 is on, while the switching device is on. S 1 and S 4. Turning off causes the output voltage across load 226 to be reduced. V TO equal to half of the input voltage V TO = V D / 2. In the third switching state 206, the switching device S 1 and S 4 is on, while the switching device is on. S 2 and S 3. Turning off causes the output voltage across load 226 to be reduced. V TO equal to half of the input voltage V TO = V D / 2. In the final switching state 208, the switching device S 2 and S 4 is on, while the switching device is on. S 1 and S 3. Turning off causes the output voltage across load 226 to be reduced. V TO equal to 0 volts V TO = 0.

[0045] As described above, the topology employed in the exemplary device 100 achieves a multi-level intermediate voltage by using four TSSCs configured as two cascaded power units 148, 150. v i and reactive power components L f C f The frequency multiplication factor. Each TSSC 160, 162, 164, and 166 generates three voltage levels (V). D 0.5V D When operating as a phase-shift switch, the two power units 148 and 150 generate nine output voltage levels (2V). D 1.5V D V D 0.5V D 0, -2V D -1.5V D –V D -0.5V D Intermediate voltage generated by exemplary device 100. v iThe results can be derived based on the terminal voltages of each TSSC 160, 162, 164, and 166, as shown in Equation 4:

[0046] in, , , and These represent the terminal voltages generated by each of the four TSSCs 160, 162, 164, and 166, respectively.

[0047] Each TSSC can generate three voltage levels (V). D 0.5V D By configuring controller 152 to employ phased switching for each TSSC, device 100 can operate at intermediate voltages. v i Nine different voltage levels are generated. The voltage at each TSSC terminal in Equation 3 is... , , and The three possible output values ​​are replaced and the permutations are calculated, resulting in nine voltage levels, as shown in Equation 4:

[0048] For example, when at intermediate voltage v i Requires 2V D At that time, TSSC 160 and 164 will be operated to produce their maximum output voltage (V). D ), and TSSC 162 and 166 will be operated to produce zero (0) volts. Then, according to Equation 3, the intermediate voltage of the cascaded power units 148 and 150 is... v i This will equal 2V D .

[0049] Figure 3 Figure 300 illustrates exemplary operating waveforms of a single-phase power inverter device based on a three-state switching unit, incorporating various aspects of embodiments of this disclosure. Exemplary operating waveform 300 illustrates a DC-AC power converter (e.g., referenced above). Figure 1 The exemplary power inverter device 100 based on a three-state switching unit (hereinafter referred to as the device) demonstrates its frequency multiplication and multilevel output voltage generation capabilities. In Figure 300, time is depicted increasing to the right along the horizontal axis 302, and signal amplitude (volts or amperes) is depicted increasing upward along the vertical axis 304.

[0050] Those skilled in the art will readily recognize that the exemplary device 300 can advantageously operate in various power conversion scenarios, including bidirectional operation. However, for the purpose of understanding, the operating waveforms shown in FIG300 correspond to an exemplary operating scenario, wherein the exemplary device 100 operates at each source V D1 V D2 It receives 300 volts (300 V) DC input power and produces 500 volts (500 V) 50 Hz (50 Hz) AC output voltage. The converter switching frequency is 10 kHz.

[0051] Curve 306 shows the 10 kHz carrier signal used to generate switching signals for the four TSSCs 160, 162, 164, and 166. The filter inductor is shown in Figure 308. L f voltage at both ends v L The frequency doubling characteristics of device 100 are shown, along with the multi-level intermediate voltage. v i Figure 310 shows the output current transmitted to the load connected to the PCC. i o (in amperes) and output voltage v o (In volts) are shown in Figures 312 and 314 respectively.

[0052] As can be observed in Figure 310, the exemplary converter device 100 at the intermediate voltage v i Nine voltage levels are generated, as shown in Equation 3. The output voltage is a perfect sinusoidal voltage. v o and output current i o The results are shown in Figures 312 and 314, respectively.

[0053] Figure 4 Figure 400 illustrates exemplary operating waveforms of a single-phase power inverter device based on a three-state switching unit, incorporating various aspects of embodiments of this disclosure. Figure 400 shows time segment 316 as shown in Figure 300, with an extended time scale to better illustrate the frequency harmonic characteristics of the exemplary device 100. In Figure 400, time is depicted increasing to the right along the horizontal axis 402, and signal amplitude (volts or amperes) is depicted increasing upward along the vertical axis 404.

[0054] Figure 406 shows the 10 kHz carrier signal used to generate switching signals for the four TSSCs. (Filter inductor) L f voltage at both ends vL The corresponding intermediate voltage is shown in Figure 408. v i As shown in Figure 410. Figures 412 and 414 show the corresponding output current in amperes. i o and output voltage in volts v o .

[0055] The carrier signal 406 has a fundamental switching frequency of 10 kHz (10 kHz), which is referred to as the switching frequency in this paper. f s Equation 2 predicts that the effective frequency of the reactive component applied to the converter device 100 with two cascaded power units is eight times the switching frequency, or 80 kHz in the example shown. Figure 408 shows the inductor charging and discharging eight times in each switching cycle 408 to provide an inductor operating frequency of 80 kHz, which, as predicted by Equation 2, is eight times the 10 kHz switching frequency.

[0056] Due to the multi-level voltage generation, the inductor ripple is reduced, as shown in Equation 3. Equation 3 gives the peak-to-peak ripple as the supply voltage divided by the number of power supplies; in the example shown, it is 300 volts / 2 power supplies = 150V. The inductor voltage can be seen in Figure 408. v L The expected inductor ripple was observed.

[0057] Figure 5 An exemplary three-phase power converter device 500 incorporating various aspects of embodiments of this disclosure is shown. The device 500 of the disclosed embodiment incorporates three TSSC-based frequency multiplier power converters 100a, 100b, and 100c, which are used in reactive power components L... fa L fb L fc C fa C fb C fc Generates a multi-level intermediate voltage v ia , v ib , v ic The three-phase power of the ripple voltage and frequency multiplication. Exemplary device 500 is suitable for operation as an inverter in a PV power system, wherein device 500 receives power from a string photovoltaic source and supplies three-phase AC power to the grid.

[0058] An exemplary three-phase power converter device 500 includes: a first power converter device 100a for receiving power from a first power source 502 and a second power source 504, and generating a first intermediate voltage. v ia The second power converter device 100b is used to receive power from the third power source 506 and the fourth power source 508, and to generate a second intermediate voltage. v ib ; and a third power converter device 100c, for receiving power from the fifth power source 510 and the sixth power source 512, and generating a third intermediate voltage. v ic .

[0059] One or more of the first power converter device 100a, the second power converter device 100b, and the third power converter device 100c include TSSC-based power converter devices, such as those described above. Figure 1 The exemplary power converter device 100 described above. Any of the above embodiments of the exemplary power converter device 100 can be advantageously used as power converter devices 100a, 100b, 100c included in the three-phase power converter device 500.

[0060] In an embodiment where the exemplary device 500 operates as an inverter, it may be beneficial to filter the AC side or output of each phase to remove unwanted higher frequencies and reduce THD from the intermediate voltage. Filtering of the output voltage can be achieved by coupling a filter inductor in series between the intermediate voltage and the load. In one embodiment, the first intermediate voltage... v ia Second intermediate voltage v ib and the third intermediate voltage v ic Each through the first filter inductor L fa Second filter inductor L fb and the third filter inductor L fc One of the phases is coupled to a phase of the three-phase load 516.

[0061] Additional filtering can be provided when needed by coupling the filter capacitors in parallel with each phase of the three-phase load 516. In some embodiments, the filter capacitors may be coupled to the first filter inductor L. fa Second filter inductor L fb and the third filter inductor L fc This additional filtering is achieved using three star-connected filter capacitors 514.

[0062] As described above, the exemplary device 100 employed in each phase of the exemplary device 500 can advantageously operate by driving each TSSC based on pulse width modulation (PWM) technology. When included in a three-phase power conversion device (e.g., the exemplary three-phase power conversion device 500), PWM can be configured as one of sinusoidal PWM, space vector PWM, and discontinuous PWM. The control flexibility provided by using PWM technology to drive each TSSC-based power converter 100a, 100b, 100c supports optimization of each phase of the converter as the operating points of sources 502, 504, 506, 508, 510, 512 vary. This control flexibility and optimization are advantageous in systems that may benefit from MPPT.

[0063] Figure 6 FIG600 illustrates exemplary operating waveforms of a three-phase power converter apparatus incorporating various aspects of embodiments of the present disclosure. Exemplary operating waveform 600 illustrates a three-phase DC-AC power converter (e.g., referenced above). Figure 5 The exemplary three-phase power converter device 500 has the capability to generate frequency multiplication and multilevel output voltage.

[0064] For Figure 600, the time is depicted increasing to the right along the horizontal axis 602, and the signal amplitude (volts or amperes) is depicted increasing upward along the vertical axis 604. The waveforms shown in Figures 614, 616, and 618 include the operating waveforms of each of the three phases 100a, 100b, and 100c, and are labeled with the corresponding subscripts a, b, and c, respectively.

[0065] While the exemplary device 500 can be beneficially operated in a variety of power conversion scenarios, for the purpose of understanding, the operating waveforms shown in Figure 600 correspond to one possible scenario in which the exemplary device 500 receives 300 volts (300 V) DC input power at each of the power supplies 502, 504, 506, 508, 510, 512 and produces 500 volts (500 V) 50 Hz (50 Hz) three-phase AC output power, with the converter switching frequency at 10 kHz (10 kHz).

[0066] Figure 606 shows the 10 kHz carrier signal used to generate switching signals for three power converter devices 100a, 100b, and 100c. Three filter inductors L a L b and L c voltage at both ends v La , v Lb and v LcSee Figures 612, 610, and 608 respectively. Multilevel intermediate voltage. v ia , v ib , v ic Figure 614 shows the multi-level intermediate voltage generated by the exemplary device 500. Figures 616 and 618 show the output current in amperes transmitted to the three-phase load 516. i oa , i ob , i oc and output voltage in volts v oa , v ob , v oc It should be noted that each of the power converter devices 100a, 100b, and 100c includes a power converter device, such as the exemplary device 100 described above. Therefore, the operating waveform generated by each phase a, b, and c has the characteristics described above and in conjunction with... Figure 3 and Figure 4 The aforementioned characteristics of similar working waveforms.

[0067] Figure 7 Figure 700 illustrates exemplary operating waveforms of a three-phase power converter device (e.g., exemplary device 500) incorporating various aspects of embodiments of this disclosure. Figure 700 shows time segment 626 as shown in Figure 600, with an extended time scale to better illustrate the octave characteristics of exemplary device 500. In Figure 700, time is depicted increasing to the right along the horizontal axis 702, and signal amplitude (volts or amperes) is depicted increasing upward along the vertical axis 704. The waveforms shown in Figures 714, 716, and 718 include the operating waveforms of each of the three phases 100a, 100b, and 100c, and are labeled with corresponding subscripts a, b, and c, respectively.

[0068] Figure 706 shows the 10 kHz carrier signal used to generate switching signals for three power converter devices 100a, 100b, and 100c. Three filter inductors L a L b and L c voltage at both ends v La , v Lb and v Lc See Figures 712, 710, and 808 respectively. Multilevel intermediate voltage. v ia ,v ib , v ic Figure 714 illustrates the multi-level intermediate voltage generated by each phase of the exemplary device 500. Figures 716 and 718 show the output current in amperes delivered to the three-phase load 516. i oa , i ob , i oc and output voltage in volts v oa , v ob , v oc .

[0069] The carrier signal 706 has a fundamental switching frequency or switching frequency of 10 kHz (10 kHz). f s Equation 2 predicts that the effective switching frequency of each converter device 100a, 100b, 100c with two cascaded power units is eight times the switching frequency, which would be 80 kHz in the example shown. Figures 708, 710, and 712 show that each filter inductor L a L b and L c The inductor is charged and discharged eight times in each switching cycle of 720 to provide an inductor operating frequency of 80 kHz (80 kHz), which, as predicted by Equation 2, is eight times the 10 kHz switching frequency.

[0070] As described above, the multi-level voltages generated by each power converter 100a, 100b, and 100c reduce the inductor voltage ripple, as shown in Equation 3. The inductor voltage can be seen in Figure 708. v La , v Lb , v Lc The expected inductor voltage ripple was observed with a reduced amplitude and an increased frequency.

[0071] Figure 8 A schematic diagram of an exemplary additional cascaded power unit 800 incorporating various aspects of embodiments of the present disclosure is shown. The exemplary additional power unit 800 is adapted to supply an additional power supply V. DA Added to power converter devices based on three-state switching units, such as those mentioned above. Figure 1The exemplary device 100, as described above, can be expanded to consume any desired number of two or more power sources by including an additional cascaded power unit (e.g., exemplary cascaded power unit 800) between the first power unit 148 and the second power unit 150 at point 168.

[0072] An exemplary additional cascaded power unit 800 draws power from an additional power source V. DA Receive power, and includes power supplied by an additional power source V. DA The first additional TSSC 804 and the second additional TSSC 806 are coupled in parallel. The midpoints 812 and 814 of the first additional TSSC 804 are coupled to a shared transformer within the prior power unit 816, and the midpoints 808 and 810 of the second additional TSSC 806 are coupled through the shared transformer T. A Coupled to the next power unit 818.

[0073] For example, consider adding additional power units, such as exemplary additional power unit 800, to exemplary device 100 at point 168, for a total of three power sources. When doing so, first power unit 148 becomes prior power unit 816, and the midpoints 812, 814 of first additional TSSC 804 are coupled to a shared transformer T2 in first power unit 148. Second power unit 150 becomes next power unit 818, and the midpoints 808, 810 of second additional power unit 806 are coupled to the midpoints 132, 134 of third TSSC 164 via additional transformers. Any desired number of additional power units 800 can be added to exemplary device 100 by inserting additional power units 800 between prior power units and next power units as described above.

[0074] The inclusion of additional power units (such as exemplary additional power unit 800) increases the intermediate voltage. v i The number of voltage levels in the filter and the amount applied to the output filter L f C f The effective frequency of the reactive power components in the system.

[0075] Therefore, although the essential novel features of the invention applicable to exemplary embodiments thereof have been shown, described, and pointed out herein, it should be understood that those skilled in the art can make various omissions, substitutions, and changes to the form and details of the illustrated devices and methods, as well as their operation, without departing from the spirit and scope of the invention. Furthermore, all combinations of those elements that are explicitly desired to perform substantially the same function in substantially the same manner to achieve the same result are within the scope of the invention. Moreover, it should be recognized that structures and / or elements shown and / or described in conjunction with any form or embodiment of the disclosed invention can be incorporated as general design choices into any other form or embodiment disclosed, described, or suggested. Therefore, the invention is limited only to the scope set forth in the appended claims.

Claims

1. A power converter device (100) based on a three-state switching unit, characterized in that, include: The first three-state switching unit (160) includes a first switching bridge arm (102), a second switching bridge arm (104), and a first transformer (T1), wherein the first switching bridge arm (102) and the second switching bridge arm (104) are connected to a first power supply (V). D1 Parallel coupling, and the first winding (120) of the first transformer (T1) is coupled at the midpoint (124) of the first switch bridge arm (102) with the intermediate voltage ( v i Between the first transformer (T1) and the second winding (122), the second winding (122) of the first transformer (T1) is coupled at the midpoint (126) of the second switch bridge arm (104) to the intermediate voltage ( v i )between; The second three-state switching unit (162) includes a third switch bridge arm (106), a fourth switch bridge arm (108), and a second transformer (T2), wherein the third switch bridge arm (106) and the fourth switch bridge arm (108) are connected to the first power supply (V). D1 Parallel coupling; The third three-state switching unit (164) includes a fifth switch bridge arm (110) and a sixth switch bridge arm (112), wherein the fifth switch bridge arm (110) and the sixth switch bridge arm (112) are connected to the next power supply (V). D2 The second transformer (T2) is coupled in parallel, and the first winding (136) of the second transformer (T2) is coupled between the midpoint (130) of the fourth switch bridge arm (108) and the midpoint (132) of the fifth switch bridge arm (110), and the second winding (138) of the second transformer (T2) is coupled between the midpoint (128) of the third switch bridge arm (106) and the midpoint (134) of the sixth switch bridge arm (112). The fourth three-state switching unit (166) includes a seventh switch bridge arm (114), an eighth switch bridge arm (116), and a third transformer (T3), wherein the seventh switch bridge arm (114) and the eighth switch bridge arm (116) are connected to the next power supply (V). D2 Parallel coupling, and the first winding (144) of the third transformer (T3) is coupled at the midpoint (140) of the seventh switch arm (114) to the intermediate voltage ( v i Between the third transformer (T3) and the intermediate voltage (T3), the second winding (146) is coupled at the midpoint (142) of the eighth switch arm (116). v i )between; Filter inductor (L f ), connected in series with the intermediate voltage ( v i Between the point of common coupling (PCC) and the common coupling point; Filter capacitor (C) f ), and connected in parallel with the point of common coupling (PCC), Among them, the second power supply (V D2 The next power supply includes the same power supply (V). D2 ).

2. The apparatus (100) according to claim 1, characterized in that, Each switch bridge arm (102, 104, 106, 108, 110, 112, 114, 116) includes a first switching device ( S 1. S 3. S 5. S 7. S 9. S 11 , S 13 , S 15 ), the first switching device ( S 1. S 3. S 5. S 7. S 9. S 11 , S 13 , S 15 ) and the second switching device ( S 2. S 4. S 6. S 8. S 10 , S 12 , S 14 , S 16 The switches are connected in series, thereby forming the midpoints (124, 126, 128, 130, 132, 134, 136, 138) between the first and second switches, and each switch ( S 1. S 2. S 3. S 4. S 5. S 6. S 7. S 8. S 9. S 10 , S 11 , S 12 , S 13 , S 14 , S 15 , S 16 This includes one of silicon carbide metal-oxide-semiconductor field-effect transistors, insulated-gate bipolar transistors, and gallium nitride metal-oxide-semiconductor field-effect transistors.

3. The apparatus (100) according to any one of the preceding claims, characterized in that, It also includes an additional power unit (800), wherein the additional power unit (800) includes an additional power source (V) DA The first additional three-state switching unit (804) and the second additional three-state switching unit (806) are coupled in parallel, and the first midpoint (812) and the second midpoint (814) of the first additional three-state switching unit (804) are coupled to the shared transformer (T2) in the prior power unit (148), and the first midpoint (808) and the second midpoint (810) of the second additional three-state switching unit (806) are coupled through the additional transformer (T2). A It is coupled to the next power unit 150.

4. The apparatus (100) according to any one of the preceding claims, characterized in that, First input capacitor (C) D1 ) and the first power supply (V D1 Parallel coupling, second input capacitor (C) D2 ) and the second power supply (V D2 Parallel coupling.

5. The apparatus (100) according to any one of the preceding claims, characterized in that, The device (100) further includes a controller (154) for operating the first three-state switching unit (160), the second three-state switching unit (162), the third three-state switching unit (164), and the fourth three-state switching unit (166) based on pulse width modulation and phase shift switching to generate a sinusoidal intermediate voltage comprising nine voltage levels (310). v i ), and the voltage across the filter inductor (408), the filter inductor (408) including a ripple frequency eight times the switching frequency (406) f r ).

6. The apparatus (100) according to any one of the preceding claims, characterized in that, The pulse width modulation includes sinusoidal pulse width modulation.

7. The apparatus (100) according to any one of the preceding claims, characterized in that, The first power supply ( V D1 ) and the second power supply ( V D2 Each includes one or more photovoltaic panels.

8. The apparatus (100) according to any one of the preceding claims, characterized in that, The common connection point is coupled to the power grid.

9. A three-phase power converter device (500), characterized in that, The device (500) includes: A first power converter device (100a) is used to receive power from a first power source (502) and a second power source (504) and generate a first intermediate voltage. v ia ); The second power converter device (100b) is used to receive power from the third power source (506) and the fourth power source (508) and generate a second intermediate voltage. v ib ); A third power converter device (100c) is used to receive power from a fifth power source (510) and a sixth power source (512) and generate a third intermediate voltage ( v ic ), Wherein, one or more of the first power converter device (100a), the second power converter device (100b), and the third power converter device (100c) include a power converter device (100) based on a three-state switching unit according to any one of the preceding claims.

10. The apparatus 500 according to the preceding claims, characterized in that, The first intermediate voltage ( v ia ), the second intermediate voltage ( v ib ) and the third intermediate voltage ( v ic ) respectively through the first filter inductor (L fa ), the second filter inductor (L fb ) and the third filter inductor (L fc The corresponding one in ) is coupled to the three-phase load (516).

11. The apparatus (500) according to claim 8 or 9, characterized in that, Three star-connected filter capacitors (514) are coupled to the first filter inductor (L). fa ), the second filter inductor (L fb ) and the third filter inductor (L fc ).

12. The apparatus (500) according to any one of claims 8 to 10, characterized in that, One or more of the first power source (502), the second power source (504), the third power source (506), the fourth power source (508), the fifth power source (510), and the sixth power source (512) include photovoltaic panels.

13. The apparatus (500) according to any one of claims 8 to 11, characterized in that, The three-phase load (516) includes the power grid.

14. The apparatus (500) according to any one of the preceding claims, characterized in that, Each power converter device (100a, 100b, 100c) operates by pulse width modulation, which includes one of sinusoidal pulse width modulation, space vector pulse width modulation, and discontinuous pulse width modulation.

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