CN108023496B - Series simultaneous selection switch voltage type single-stage multi-input low-frequency link inverter - Google Patents

Abstract

The invention relates to a series simultaneous selection switch voltage type single-stage multiple-input low-frequency link inverter, which is formed by connecting a plurality of input filters which are not in common with a common output low-frequency isolation transformation filter circuit by a multiple-input single-output high-frequency inverter circuit with a series simultaneous selection power switch, wherein each input end of the multiple-input single-output high-frequency inverter circuit is correspondingly connected with the output end of each input filter one by one, and the output end of the multiple-input single-output high-frequency inverter circuit is connected with the input end of the output low-frequency isolation transformation filter circuit. The inverter has the characteristics of multiple input sources which are not in common ground, power supply at the same time or in a time-sharing manner, low-frequency isolation between output and input, shared output low-frequency voltage transformation and filtering circuit, simple circuit topology, single-stage power transformation, high transformation efficiency, small output voltage ripple, wide application prospect and the like, and lays a key technology for realizing a large-capacity distributed power supply system for jointly supplying power by multiple new energy sources.

Description

Series and simultaneous selection of switching voltage type single-stage multi-input low frequency link inverter

technical field

The invention relates to a series-connected and simultaneous selection switching voltage type single-stage multi-input low-frequency link inverter, which belongs to the power electronic conversion technology.

Background technique

The inverter is a static converter device that uses power semiconductor devices to convert an unstable and inferior DC power into stable, high-quality AC power for use by AC loads or to achieve AC grid connection. Inverters with low-frequency electrical isolation or high-frequency electrical isolation between the output AC load or the AC grid and the input DC power supply are called low-frequency link and high-frequency link inverters respectively. The electrical isolation element mainly plays the following roles in the inverter: (1) realizes the electrical isolation between the output and input of the inverter, and improves the safety, reliability and electromagnetic compatibility of the inverter operation; (2) realizes the The matching between the output voltage of the inverter and the input voltage is achieved, that is, the technical effect that the output voltage of the inverter is higher than, equal to or lower than the input voltage is realized, and its application range has been greatly expanded. Therefore, the inverter has important application value in secondary electric energy conversion occasions with DC generators, batteries, photovoltaic cells and fuel cells as the main DC power sources.

New energy (also called green energy) such as solar energy, wind energy, tidal energy and geothermal energy has the advantages of clean, non-polluting, cheap, reliable and abundant, so it has a wide range of application prospects. Due to the increasing tension of traditional fossil energy (non-renewable energy) such as oil, coal and natural gas, serious environmental pollution, global warming, and the production of nuclear energy will produce nuclear waste and pollute the environment, the development and utilization of new energy is increasingly more and more attention. New energy power generation mainly includes photovoltaics, wind power, fuel cells, hydropower, geothermal and other types, all of which have shortcomings such as unstable, discontinuous, and climatic changes in power supply.

The traditional new energy distributed power supply system is shown in Figures 1 and 2. The system usually uses multiple single-input DC converters to convert photovoltaic cells, fuel cells, wind turbines, and other new energy power generation equipment that do not require energy storage through a one-way DC converter respectively. It is then connected to the DC bus of the public inverter to ensure that various new energy sources are jointly supplied and can work in harmony. The distributed generation system realizes the simultaneous supply of power to the load and the preferential utilization of energy from multiple input sources, which improves the stability and flexibility of the system, but has the defects of two-stage power conversion, low power density, low conversion efficiency, and high cost. Its usefulness is greatly limited.

In order to simplify the circuit structure and reduce the number of power conversion stages, it is necessary to replace the two-stage cascaded circuit structure with a DC converter and an inverter shown in Figures 1 and 2 with a new multi-input inverter with a single-stage circuit structure shown in Figure 3 The traditional multi-input inverter constitutes a new single-stage new energy distributed power supply system. Single-stage multi-input inverters allow a variety of new energy inputs, and the nature, amplitude and characteristics of the input sources can be the same or very different. The new single-stage new energy distributed power supply system has the advantages of simple circuit structure, single-stage power conversion, multiple input sources supply power to the load at the same time or time-sharing within a high-frequency switching cycle, and low cost.

Therefore, it is extremely urgent to actively seek a class of single-stage multi-input inverters and their new energy distributed power supply systems that allow a variety of new energy sources to jointly supply power. Utilization will be of great significance.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a multi-input single-output high-frequency inverter circuit with multiple new energy combined power supply, no common ground for input DC power supply, multiple input and single output high-frequency inverter circuits set in series with simultaneous selection switches, low-frequency isolation between output and input, multiple input power supplies Simultaneous or time-sharing power supply to the load, simple circuit topology, shared output low-frequency transformer filter circuit, single-stage power conversion, high conversion efficiency, small output voltage ripple, large output capacity, and wide application prospects. Single-stage multi-input low-frequency link inverter.

The technical scheme of the present invention is: a series-connected and simultaneous selection switching voltage type single-stage multi-input low-frequency link inverter, which consists of a multi-input single-output high-frequency inverter circuit that connects a plurality of input filters that do not share the ground with one common ground. The output low-frequency isolation transformer filter circuit is formed by connection, each input terminal of the multi-input single-output high-frequency inverter circuit is connected with the output terminal of each input filter in one-to-one correspondence, and the output of the multi-input single-output high-frequency inverter circuit The terminal is connected with the input terminal of the low-frequency transformer or the output filter inductor of the output low-frequency isolation transformer filter circuit and the non-connected input terminal of the low-frequency transformer or the input terminal of the output filter. The multi-input single-output high-frequency inverter The circuit is composed of multi-channel series-connected power switch circuits with simultaneous selection of output terminals in series, and bidirectional power flow single-input single-output high-frequency inverter circuits are sequentially cascaded, which is equivalent to a bidirectional power flow at any time. Inverter circuit, each of the series-connected simultaneous selection power switch circuits is composed of a two-quadrant power switch and a power diode, and the source of the two-quadrant power switch is connected to the cathode of the power diode, and the drain of the two-quadrant power switch is connected. The pole and the anode of the power diode are respectively the positive and negative input terminals of the power switch circuit that are connected in series and simultaneously select the power switch circuit. , Negative output terminal, the output low-frequency isolation transformer filter circuit is composed of a low-frequency transformer, an output filter, or an output filter inductor, a low-frequency transformer, an output filter capacitor, or an output filter and a low-frequency transformer.

The invention is a multi-input inverter circuit structure formed by cascading the DC converter and the inverter of the traditional multiple new energy combined power supply system in two stages, and constructs a new single-stage multi-input inverter with simultaneous selection switches in series The circuit structure, the circuit structure and topology family and its energy management control strategy of the single-stage multi-input low-frequency link inverter with series-selective switching voltage are proposed. The single-output high-frequency inverter circuit is formed by connecting a plurality of input filters that do not share the ground and a common output low-frequency isolation transformer filter circuit.

The single-stage multi-input low-frequency link inverter of series-connected and simultaneous selection switching voltage can invert multiple non-common and unstable input DC voltages into stable and high-quality output AC power required by a load, and has multi-input The DC power supply does not share the ground, the multi-input and single-output high-frequency inverter circuits are not isolated, the output and the input low-frequency isolation, the multi-input power supply supplies power to the load at the same time or time-sharing, the circuit topology is simple, the common output low-frequency transformer filter circuit, single It has the characteristics of high power conversion, high conversion efficiency, small output voltage ripple, large output capacity, and wide application prospects. The comprehensive performance of the switching voltage type single-stage multi-input low-frequency link inverter in series and selection at the same time will be superior to the multi-input inverter formed by two-stage cascade connection of the traditional DC converter and the inverter.

Description of drawings

Figure 1, a traditional two-stage new energy distributed power supply system with parallel output terminals of multiple unidirectional DC converters.

Figure 2, a traditional two-stage new energy distributed power supply system with multiple unidirectional DC converter outputs connected in series.

Figure 3, the principle block diagram of the new single-stage multi-input inverter.

Figure 4, the block diagram of the single-stage multi-input low-frequency link inverter of the series-connected and simultaneous selection of switching voltage.

Figure 5, the circuit structure diagram of the single-stage multi-input low-frequency link inverter of the series-connected and simultaneous selection of switching voltage.

Figure 6, the steady state principle waveform diagram of the bipolar SPWM control series and simultaneous selection of switching voltage type single-stage multi-input low-frequency link inverter.

Figure 7, the steady state principle waveform diagram of the unipolar SPWM control series and simultaneous selection of switching voltage type single-stage multi-input low-frequency link inverter.

Figure 8, circuit topology example 1 of a single-stage multi-input low-frequency link inverter of series-connected and simultaneous selection of switching voltage - push-pull circuit schematic diagram.

Fig. 9, the circuit topology example 2 of the single-stage multi-input low-frequency link inverter of the series-connected and simultaneous selection of switching voltage - push-pull forward circuit schematic diagram.

Fig. 10, circuit topology example 3 of a single-stage multi-input low-frequency link inverter of series-connected and simultaneous selection of switching voltage type ---- half-bridge circuit schematic diagram I.

Fig. 11, circuit topology example 4 of a single-stage multi-input low-frequency link inverter of series-connected and simultaneous selection of switching voltage type ---- half-bridge circuit schematic diagram II.

Fig. 12, circuit topology example 5 of the single-stage multi-input low-frequency link inverter of series-connected and simultaneous selection of switching voltage ---- half-bridge circuit schematic diagram III.

Fig. 13, circuit topology example 6 of a single-stage multi-input low-frequency link inverter of series-connected and simultaneous selection of switching voltage ---- full-bridge circuit schematic diagram I.

Fig. 14, circuit topology example VII of the single-stage multi-input low-frequency link inverter of the series-connected and simultaneous selection of switching voltage ---- full-bridge circuit schematic diagram II.

Fig. 15, circuit topology example VIII of the single-stage multi-input low-frequency link inverter of the series-connected and simultaneous selection of switching voltage ---- full-bridge circuit schematic diagram III.

Figure 16, the output voltage and input current instantaneous value feedback bipolar SPWM master-slave power distribution energy management control block diagram of the switching voltage type single-stage multi-input low-frequency link inverter with simultaneous selection in series.

Figure 17 shows the waveform diagram of the output voltage and input current instantaneous value feedback bipolar SPWM master-slave power distribution energy management control principle of the switching voltage type single-stage multi-input low-frequency link inverter.

Figure 18, the output voltage and input current instantaneous value feedback unipolar SPWM master-slave power distribution energy management control block diagram of the switching voltage type single-stage multi-input low-frequency link inverter with simultaneous selection in series.

Figure 19, the waveform diagram of the output voltage and input current instantaneous value feedback unipolar SPWM master-slave power distribution energy management control principle of the switching voltage type single-stage multi-input low-frequency link inverter with simultaneous selection in series.

Figure 20, a single-stage multi-input low-frequency link independent power supply system with output terminals connected in series with a single-stage isolation bidirectional charge-discharge converter at the same time selecting a switching voltage.

Figure 21. Maximum power output energy management control strategy with a single-stage isolated bidirectional charge-discharge converter output voltage independent control loop.

Figure 22, the waveforms of the output voltage u _o and the output filter inductor currents i _Lf and i _Lf ' of the independent power supply system.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments of the specification.

The single-stage multi-input low-frequency link inverter of series connection and selection of switching voltage is composed of a multi-input single-output high-frequency inverter circuit that connects multiple input filters that do not share the ground and a common output low-frequency isolation transformer filter circuit. Each input end of the multi-input single-output high-frequency inverter circuit is connected with the output end of each input filter in a one-to-one correspondence, and the output end of the multi-input single-output high-frequency inverter circuit is isolated and transformed with the output low frequency. The low-frequency transformer input end or output filter inductance of the filter circuit is connected with the non-connected input end of the low-frequency transformer or the input end of the output filter, and the multi-input single-output high-frequency inverter circuit consists of multiple output ends connected in series in the forward direction. The power switch circuit and the bidirectional power flow single input single output high frequency inverter circuit are cascaded in sequence at the same time, which is equivalent to a bidirectional power flow single input single output high frequency inverter circuit at any time. At the same time, the selective power switch circuit is composed of a two-quadrant power switch and a power diode, and the source of the two-quadrant power switch is connected to the cathode of the power diode, and the drain of the two-quadrant power switch and the anode of the power diode are the The positive and negative input terminals of the power switch circuit are selected in series, and the source of the two-quadrant power switch and the anode of the power diode are respectively the positive and negative output terminals of the power switch circuit selected in series. The output low-frequency isolation transformer filter circuit is composed of a low-frequency transformer, an output filter, or an output filter inductor, a low-frequency transformer, an output filter capacitor, or an output filter and a low-frequency transformer in sequence.

The principle block diagram, circuit structure, and steady-state principle waveforms of bipolar SPWM control and unipolar SPWM control inverters are shown in Figures 4, 5, and 6, respectively. , 7 shown. In Figures 4, 5, 6, and 7, U _i1 , U _i2 , ..., U _in are n input DC voltage sources (n is a natural number greater than 1), Z _L is a single-phase AC load (including passive AC loads and Active AC load), u _o and i _o are the single-phase output AC voltage and AC current respectively. The n-input single-output high-frequency inverter circuit is composed of a multi-channel series-selected power switch circuit and a bi-directional power flow single-input single-output high-frequency inverter circuit in which the output terminals are connected in series in sequence. The multi-channel series simultaneous selection power switch circuit is composed of n two-quadrant high-frequency power selection switches S _s1 , S _s2 , ..., S _sn and n selection diodes D _s1 , D , which can withstand unidirectional voltage stress and bidirectional current stress. _s2 , ..., D _sn (power selection switches S _s1 , S _s2 , ..., S _sn are turned on at the same time or with a phase difference, the switching frequency is the same or different, here only the analysis of S _s1 , S _s2 , ..., S _sn uses the same The control method of switching frequency and turning on at the same time), bidirectional power flow, single input and single output high-frequency inverter circuit is composed of multiple two-quadrant high-frequency power switches that can withstand unidirectional voltage stress and bidirectional current stress. MOSFET, IGBT can be selected , GTR and other power devices; the output low-frequency isolation transformer filter circuit in the dashed box ("1" and "1'" terminals are the connection ends) is composed of low-frequency transformers and output filters cascaded in sequence, or an output filter inductor , low-frequency transformer, and output filter capacitors are cascaded in sequence (the leakage inductance of the primary side of the low-frequency transformer can be absorbed and utilized by the output filter inductance or completely used as the output filter inductance), or the output filter and the low-frequency transformer are cascaded in sequence. , due to space limitations, only the circuit diagram of the LC output filter or output filter capacitor suitable for passive AC load is drawn in the figure, and the output filter inductor is added after the LCL output filter or output filter capacitor suitable for AC grid load is not drawn. circuit diagram; the n-channel input filters are LC filters ₍ including filter _inductors L _i1 , L _i2 , _. ..., L _in ), the n-channel input DC current will be smoother when the LC filter is used. The n-input single-output high-frequency inverter circuit _modulates the n-channel input DC voltage sources U _i1 , U _i2 , . The level SPWM voltage wave u _AB is passed through the low frequency transformer T, the output filter L _f -C _f or the output filter inductor L _f , the low frequency transformer T, the output filter capacitor C _f or the output filter inductor L _f , the output filter capacitor C _f . After the low-frequency transformer T, a high-quality sinusoidal AC voltage u _o or sinusoidal AC current i _o is obtained on a single-phase AC passive load or a single-phase AC power grid, and n input pulse currents of n input single-output high-frequency inverter circuit are passed through After the input filters L _i1 -C _i1 , L _i2 -C _i2 , ..., L _in -C _in or C _i1 , C _i2 , ... , C _in n channels of input DC power supplies U _i1 , U _i2 , ..., U _in to obtain smooth input DC currents I _i1 , I _i2 , . . . , I _in . It needs to be supplemented that when the output low-frequency isolation transformer filter circuit is composed of low-frequency transformers and output filters cascaded in sequence, the bipolar two-state multi-level SPWM voltage wave u _AB outputs the +1-state amplitude of the positive half cycle. are (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ , (U _i1 +U _i2 +…+U _in-1 )N ₂ /N ₁ ,…, U _i1 N ₂ /N ₁ and - The 1-state amplitude is (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ , and the output negative half cycle -1-state amplitude is (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ , (U _i1 +U _i2 +…+U _in-1 )N ₂ /N ₁ ,…, U _i1 N ₂ /N ₁ and +1 state amplitudes are (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ ; the amplitudes of the +1 state and -1 state of the unipolar three-state multi-level SPWM voltage wave u _AB are both (U _i1 +U _i2 +...+U _in )N ₂ /N ₁ , (U _i1 +U _i2 +...+U _in-1 )N ₂ /N ₁ ,..., U _i1 N ₂ /N ₁ ; when N ₂ /N ₁ =1, the amplitude of the above-mentioned multi-level SPWM voltage wave u _AB expresses The formula is that the output low-frequency isolation transformer filter circuit is composed of an output filter inductor, a low-frequency transformer, an output filter capacitor or a bipolar two-state and unipolar three-state multi-level SPWM when the output filter and low-frequency transformer are cascaded in sequence. The corresponding amplitude of the voltage wave u _AB . For the half-bridge circuit, the +1 state amplitude and -1 state amplitude of the bipolar two-state multilevel SPWM voltage wave u _AB shown in Figure 6 should be multiplied by 1/2 during the positive and negative half cycles of the output voltage. .

The single-stage multi-input low-frequency link inverter of series connection and selection of switching voltage is a step-down inverter, and n input sources can supply power to the load at the same time. _Assume that the _amplitudes of the output _signals I _1e , _{I 2e ,} . _{-1) em} , U _em , the amplitude of the sawtooth carrier signal _uc is U _cm , then the corresponding modulation degree is m ₁ =I _1em /U _cm , m ₂ =I _2em /U _cm ,..., m _n = U _em /U _cm , and there are 0≦mn , . . . , _{m 2} , m ₁ ≦1, and m ₁ > _{m 2} >…>mn . The principle of the inverter is equivalent to the superposition of the voltages of multiple voltage-type single-input inverters at the output terminals, that is, the output voltage u _o and the input DC voltage (U _i1 , U _i2 , . . . , U _in ), the low-frequency transformer turns ratio The relationship between N ₂ /N ₁ and the degree of modulation (m ₁ , m ₂ , ..., m _n ) is u _o =[(m ₁ U _i1 +m ₂ U _i2 +...+m _n U _in )]N ₂ /N ₁ (unipolar SPWM control) or u _o =[(2m ₁ -1)U _i1 +(m ₂ +m ₁ -1)U _i2 +...+(m _n +m ₁ -1)U _in ] N ₂ /N ₁ (bipolar SPWM control). For appropriate modulation degrees m ₁ , m ₂ , ..., mn and low frequency transformer turns ratio _{N 2} /N ₁ , u _o may be greater than, equal to or less than the sum of the input DC voltages U _i1 +U _i2 +...+U _in , The low-frequency transformer in the inverter not only improves the safety, reliability and electromagnetic compatibility of the inverter operation, but also plays the role of matching the output voltage and the input voltage, that is, the output voltage of the inverter is high. The technical effect of being equal to, equal to or lower than the sum of the input DC voltages U _i1 +U _i2 +…+U _in , its application range has been greatly broadened. Since there are 0<m ₁ , m ₂ ,..., m _n < 1 (unipolar SPWM control) and (2m ₁ -1)+(m ₂ +m ₁ -1)+...+(m _n +m ₁ - 1) <1 (bipolar SPWM control), so u _o <(U _i1 +U _i2 +...+U _in )N ₂ /N ₁ , that is, the output voltage u _o is always lower than the input DC voltage (U _i1 , _{The sum of} the _{products of U i2 , .} , the operating frequency of the transformer is equal to the frequency of the output voltage, and the n-input single-output high-frequency inverter circuit is provided with a multi-channel series-connected power switch circuit with the output terminals connected in series at the same time, so this type of inverter is called a series-connected and simultaneous selection of switching voltage Type (step-down) single-stage multi-input low-frequency link inverter. The n input sources of the inverter supply power to the output AC load at the same time or time-sharing within a high-frequency switching cycle, and the modulation degree can be the same (m ₁ =m ₂ =...=m _n ) or different (m ₁ ≠ m ₂ ≠…≠m _n ).

The single-stage multi-input low-frequency link inverter of the series-connected and simultaneous selection of the present invention shares a multi-input single-output high-frequency inverter circuit and an output low-frequency isolation transformer filter circuit, which is different from the DC converter and the inverter. There are essential differences in the circuit structure of the traditional multi-input inverter composed of two-stage cascaded inverters. Therefore, the inverter of the present invention is novel and creative, and has the advantages of low frequency isolation between output and input, simultaneous or time-sharing power supply in one switching cycle of multiple input power supplies, simple circuit topology, single-stage power conversion, and high conversion efficiency (meaning that It has the advantages of small energy loss), flexible input voltage configuration, small output voltage ripple, large output capacity, low cost and wide application prospects. It is an ideal energy-saving and consumption-reducing single-stage multi-input inverter. Building an energy-saving and energy-saving society today has more important value.

The circuit topology family embodiments of the switching voltage type single-stage multi-input low-frequency link inverters with series selection at the same time are shown in Figs. In the circuit shown in Figure 8-15, the multi-channel series simultaneous selection power switch circuits whose output terminals are connected in series are composed of n two-quadrant high-frequency power switches that can withstand unidirectional voltage stress and bidirectional current stress, and n diodes. The bidirectional power flow single-input single-output high-frequency inverter circuit is composed of multiple two-quadrant high-frequency power switches that can withstand unidirectional voltage stress and bidirectional current stress (Push-pull shown in Figures 8, 9, 10, 11, and 12). Type, push-pull forward and half-bridge circuits are composed of two two-quadrant high-frequency power switches, and the full-bridge circuit shown in Figures 13, 14, and 15 is composed of four two-quadrant high-frequency power switches). It should be added that the circuits shown in Figures 8, 9, 10, 11, 12, 13, 14, and 15 show the case where the input filter is an LC filter, but the case where the input filter is a capacitor filter is not given due to space limitations. When the circuit; the push-pull forward circuit shown in Figure 9 and the half-bridge circuit shown in Figures 10, 11, and 12 are only suitable for the situation where the modulation ratios of n input power are basically equal; The output low frequency isolation transformer filter circuits of bridge circuits I, II and III are respectively cascaded in sequence by low frequency transformer and output filter, output filter inductor and low frequency transformer and output filter capacitor, output filter inductor and output filter capacitor and low frequency transformer. The output low frequency isolation transformer filter circuit of the full bridge circuit I, II and III shown in Figures 13, 14 and 15 is composed of a low frequency transformer and an output filter, an output filter inductor, a low frequency transformer, an output filter capacitor, and an output filter inductor. It is formed by cascade connection with output filter capacitor and low frequency transformer in sequence. Table 1 shows the power switch voltage stress of the four topological embodiments of the switching voltage type single-stage multi-input low-frequency link inverters connected in series at the same time. Push-pull and push-pull forward circuits are suitable for high-power low-voltage input inverter applications, half-bridge circuits are suitable for medium-power high-voltage input inverter applications, and full-bridge circuits are suitable for high-power high-voltage input inverter applications. This circuit topology family is suitable for converting multiple non-common ground and unstable input DC voltages into a stable and high-quality output AC power with the required voltage. Energy distributed power supply system, such as photovoltaic cell 40-60VDC/220V50HzAC or 115V400HzAC, 10kw proton exchange membrane fuel cell 85-120V/220V50HzAC or 115V400HzAC, small and medium-sized household wind power 24-36-48VDC/220V50HzAC or 115V400HzAC, large wind power 510VDC /220V50HzACor115V400HzAC and other multi-input sources supply power to AC loads or AC power grids.

Table 1 Power switch voltage stress of four topology embodiments of single-stage multi-input low-frequency link inverters with simultaneous selection of switching voltage in series

Energy management and control strategies are crucial for a variety of new energy combined power supply systems. Since there are multiple input sources and corresponding power switch units, multiple duty ratios need to be controlled, that is, there are multiple control degrees of freedom, which provides the possibility for energy management of multiple new energy sources. The energy management control strategy of switching voltage type single-stage multi-input low-frequency link inverters in series at the same time should be equipped with energy management of input sources, MPPT and output voltage (current) control of new energy power generation equipment such as photovoltaic cells and wind turbines. Three major functions, sometimes also need to consider the charge and discharge control of the battery and the smooth and seamless switching of the system under different power supply modes. The switching voltage type single-stage multi-input low-frequency link inverter is selected in series and adopts two different energy management modes: (1) Energy management mode I--master-slave power distribution mode, the power required by the known load is supplied by the master as much as possible Provided by the 1st, 2nd, ..., n-1 input sources of the device, given the input current of the 1st, 2, ..., n-1 input sources, it is equivalent to the given 1st, 2, ..., n-1 channels The input power of the input source, the insufficient power required by the load is provided by the nth input source from the power supply equipment, and there is no need to add battery energy storage equipment; (2) Energy management mode II - maximum power output mode, the first, second, …, n input sources are output to the load with maximum power, eliminating the need for battery energy storage equipment, and realizing the full utilization of energy by the grid-connected power generation system. The stability of the output voltage (current) of the power supply system. When the input voltages of the n new energy sources are all given, by controlling the input current of the first, second, ..., n input sources, it is equivalent to controlling the input power of the first, second, ..., n input sources.

Select the switching voltage type single-stage multi-input low-frequency link inverter in series at the same time, and adopt the output voltage, input current instantaneous value feedback bipolar SPWM, unipolar SPWM master-slave power distribution energy management control strategy to form an independent power supply system; or The input current instantaneous value feedback bipolar SPWM and unipolar SPWM maximum power output energy management control strategies are used to form a grid-connected power generation system. The output voltage and input current instantaneous value feedback bipolar SPWM, unipolar SPWM master-slave power required by the 1st, 2nd,..., n-1 input sources with fixed output power and the nth input source supplementing the load required by the load Distribution energy management control block diagram and control principle waveform, as shown in Figure 16, 17, 18, 19 respectively. The reference current signals I ^* _i1r , I ^* _i2r , ..., I ^* _i(n-1)r are obtained after the 1st, 2nd, ..., n-1 input sources are calculated by the maximum power point. The inverter's 1st, 2nd The input current feedback signals I _i1f , I _i2f , ... , I _i(n-1)f of the , ..., n-1 channels are respectively connected with the reference current signals I _i1r , I i2r , I _i2r , ..., I _i(n-1)r are amplified by the proportional-integral regulator, and the amplified error signals I _1e , I _2e , ..., I _(n-1)e are respectively multiplied with the sinusoidal synchronization signal and then passed through the absolute value circuit ︱i _1e ︳, ︳i _2e ︱, …, ︳i _(n-1)e ︱, the inverter output voltage feedback signal u _of is proportional to the reference sinusoidal voltage u _r The integral regulator is relatively amplified, and the amplified error signal ue is obtained after the absolute value circuit n to obtain _{︱u e ︳} ,︱i _1e ︳, ︳i _2e ︱, …, ︳i _(n-1)e ︱, ︱u _e ︳ The control signals _ugss1 , _ugss2 , ..., _ugssn , _ugs1 ( _ugs4 ) _{, ugs2 (} u _gs3 ). When the load power P _o is greater than the sum of the maximum powers of the 1st, 2, ..., n-1 input sources, the output voltage u _o decreases, and the effective value of the output voltage _ue of the voltage regulator is greater than the threshold comparison level U _{t And I 1e , I 2e} , . Work independently with the n-th voltage regulator, that is, I _i1r =I ^* _i1r , I _i2r =I ^* _i2r ,..., I _i(n-1)r =I ^* _i(n-1)r , the first, 2, ..., n-1 current regulators are used to achieve the maximum power output of the 1st, 2, ..., n-1 input sources, the nth voltage regulator is used to stabilize the output voltage of the inverter, and the nth input The source supplies power to the load at the same time or time-sharing; when the load power P _o is less than the sum of the maximum powers of the 1st, 2nd, ..., n-1 input sources, the output voltage u _o increases, and when the voltage regulator output voltage u _e When the rms value of t is lower than the threshold comparison level U _t , the diode D _n-1 is turned on, D ₁ , D ₂ , ..., D _n-2 are still blocked, and the hysteresis comparator circuit n+1 outputs a low level, The nth input source stops the power supply, the voltage regulator and the current regulator form a double closed-loop control system, the 1st, 2nd, ..., n-1th input sources supply power to the load at the same time or time-sharing within one switching cycle, and the current regulator The reference current I _i(n-1)r decreases, i.e. I _i(n-1)r <I ^* _i(n-1)r , the output power of the n-1th input source decreases (working at non-maximum operation) point), the output power of the nth input source drops to zero, and the output voltage u _o of the inverter tends to be stable. When the input voltage or load changes, the error voltage signal _{︱u e} ︳ and the error current signal _{︱i 1e} ︳, ︳i _2e ︱, …, ︳i _{(n-1 )} e︱, thereby changing the modulation degree m ₁ , m ₂ , ···, m _n , so the regulation and stabilization of the inverter output voltage and input current (output power) can be realized.

When the nth input source in Figure 16-19 is designed as input current feedback to control the input current, it constitutes the input current instantaneous value feedback bipolar SPWM, unipolar SPWM maximum power output energy management control strategy. The input current feedback signals I _i1f , I _i2f , ..., I _inf of the 1st, 2nd, ..., n channels of the inverter and the input sources of the 1st, 2nd, ..., n channels respectively and the reference current obtained by the calculation of the maximum power point _Signals I _i1r , _{I i2r , .} Then we get ︱i _1e ︳, ︳i _2e ︱, …, ︳i _ne ︱, ︱i _1e ︳, ︳i _2e ︱, …, ︳i _ne ︱ respectively intersect with the sawtooth carrier u _c and consider the output voltage to select communication After the signal is passed through an appropriate combinational logic circuit, the control signals _ugss1 , _ugss2 , ..., _ugssn , _ugs1 ( _ugs4 ), and _ugs2 ( _ugs3 ) of the power switch are obtained. The 1st, 2nd, ..., n-way current regulators work independently, and are used to achieve the maximum power output of their respective input sources, and the n-way input sources supply power to the load simultaneously within one switching cycle.

The bipolar and unipolar SPWM control principle waveforms shown in Figures 17 and 19 indicate a certain high-frequency switching period T _S and the on-time T _on1 and T _on2 of the 1st, 2nd, ..., n input sources. _{, . _ _ _ _ _ _} In addition, for the half-bridge circuits I, II, and III shown in Figures 10, 11, and 12, half of the input DC voltage value (U _i1 /2, U _i2 /2, . . . , U _in /2) should be substituted into the voltage Calculated in the transmission ratio formula.

In order to form an independent power supply system that can make full use of the energy of multiple input sources, multiple input sources should work in the maximum power output mode and need to be equipped with energy storage devices to stabilize the output voltage, that is, connect one in parallel at the output end of the inverter. A single-stage isolated bidirectional charge-discharge converter, as shown in Figure 20. The single-stage isolated bidirectional charge-discharge converter consists of an input filter (L _i , C _i or C _i ), a high-frequency inverter, a high-frequency transformer, a cyclic converter, and an output filter (L _f ′, C _f ′). ) are cascaded in sequence, and the cycloconverter is composed of four-quadrant high-frequency power switches that can withstand bidirectional voltage stress and bidirectional current stress. The single-stage isolated bidirectional charge-discharge converter is equivalent to a single-stage high-frequency link DC-AC converter and a single-stage high-frequency link DC-AC converter when the energy is transferred forward (discharging the energy storage device) and in the reverse direction (charging the energy storage device). A single stage high frequency link AC-DC converter.

The independent power supply system adopts a maximum power output energy management control strategy with a single-stage isolated bidirectional charge-discharge converter output voltage independent control loop, as shown in Figure 21. When the load power P _o =U _o I _o is greater than the sum of the maximum powers of multiple input sources P _1max +P _2max +...+P _nmax , the energy storage devices such as batteries and supercapacitors pass the single-stage isolation bidirectional charge-discharge converter to the The load provides the required insufficient power—power supply mode II, the energy storage device supplies power to the load alone—power supply mode III, which is an extreme case of power supply mode II; when the load power P _o =U _o I _o is less than the maximum value of multiple input sources When the sum of power is P _1max +P _2max +...+P _nmax , the residual energy output by multiple input sources charges the energy storage device through the single-stage isolated bidirectional charge-discharge converter - power supply mode I. Taking a resistive load as an example, the power flow control of a single-stage isolated bidirectional charge-discharge converter is discussed, as shown in Figure 22. For the output filter capacitors C _f , C _f ′ and the load Z _L , the parallel connection of the output terminals of the switching voltage type single-stage multi-input low-frequency link inverter and the single-stage isolated bidirectional charge-discharge converter in series is equivalent to two Parallel superposition of current sources. It can be seen from the energy management control strategy shown in Figure 21 that the output filter inductor current i _Lf of the switching voltage type single-stage multi-input low-frequency link inverter is selected in series at the same frequency and in the same phase as the output voltage u _o , and the active power is output; the charge-discharge converter It is controlled by the error amplification signal u _oe of the output voltage u _o and the reference voltage u _oref and the high frequency carrier to generate the SPWM signal for control, and there is a phase difference θ between the output filter inductor current i _Lf ' and u _o , different phase differences θ means outputting active power of different magnitudes and directions. When P _o =P _1max +P _2max +...+P _nmax , θ=90°, the active power output by the charge-discharge converter is zero, and it is in a no-load state; when P _o >P _1max +P _2max +...+P When _nmax , u _o decreases, θ<90°, the charge-discharge converter outputs active power, and the energy storage device discharges the load, that is, the energy storage device provides insufficient power required by the load; when P _o <P _1max +P _2max + When ...+P _nmax , u _o increases, θ > 90°, the charge-discharge converter outputs negative active power, and the load feeds back energy to the energy storage device, that is, the residual power output by multiple input sources charges the energy storage device, when θ When =180°, the energy returned by the load to the energy storage device is the largest. Therefore, the energy management control strategy can control the power flow size and direction of the single-stage isolated bidirectional charge-discharge converter in real time according to the relative size of P _o and P _1max +P _2max +…+P _nmax , and realize the system in three different power supply. Smooth and seamless switching between modes.

Claims (2)

1. A single-stage multi-input low-frequency link inverter of a series-connected selection of switching voltages is characterized in that: this inverter is composed of a bidirectional power flow n input and a single output in series to select a power switch circuit, a bidirectional power flow and a single input at the same time. The single-output high-frequency inverter circuit and the output low-frequency isolation transformer filter circuit are cascaded in sequence, and the two-way power flow n input and single output are connected in series at the same time. The input filters are not isolated and have no common terminal, n is the number of multiple input sources, and n is a natural number greater than 1; the bidirectional power flow n input single output series at the same time selection power switch circuit is a series of n channels at the same time. The selective power switch circuit is composed of positive and negative output terminals of each channel in series in the forward direction. Each series of the selective power switch circuit is composed of a two-quadrant power selective switch that can withstand unidirectional voltage stress and bidirectional current stress, and a power The source of the two-quadrant power selection switch is connected to the cathode of the power selection diode, and the drain of the two-quadrant power selection switch and the anode of the power selection diode are the positive and negative polarities of the power switch circuit in series, respectively. The input terminal, the source of the two-quadrant power selection switch and the anode of the power selection diode are respectively the positive and negative output terminals of the power switch circuit in series connection; The filter may be composed of an output filter inductor containing the leakage inductance of the primary side of the low-frequency transformer, a low-frequency transformer, and an output filter capacitor, or an output filter and a low-frequency transformer may be cascaded in sequence; the bidirectional power flow single-input single-output high-frequency inverter The circuits are push-pull, push-pull forward, half-bridge and full-bridge circuits. The push-pull circuit is composed of two two-quadrant high-frequency power switches that withstand unidirectional voltage stress and bidirectional current stress. The source of the high-frequency power switch is connected to the negative output terminal of the series-selective power switch circuit, the drains of the two two-quadrant high-frequency power switches are respectively connected to both ends of the primary winding of the low-frequency transformer, and the center tap of the primary winding of the low-frequency transformer is connected. Connected to the positive output terminal of the power switch circuit that selects the power in series at the same time, the push-pull forward circuit is composed of two two-quadrant high-frequency power switches that are subjected to unidirectional voltage stress and bidirectional current stress, and a clamping capacitor, and a two-quadrant high frequency power switch. The drain and source of the high-frequency power switch are respectively connected with the non-"·" terminal of one primary winding of the low-frequency transformer and the "·" terminal of the other primary winding, and the drain is connected with the positive output terminal of the series-selective power switch circuit. , The drain and source of the other two-quadrant high-frequency power switch are respectively connected with the "·" end of one primary winding of the low-frequency transformer and the non-"·" end of the other primary winding, and the source is connected to the series connection while selecting the power switch circuit. The negative output terminal is connected to each other, and the two ends of the clamping capacitor are respectively connected to the "·" terminals of the two primary windings of the low-frequency transformer. The two-quadrant high-frequency power switch of voltage stress bidirectional current stress is formed, and the positive terminal of the left upper bridge arm capacitor and the drain of the right upper bridge arm switch are connected in series to select the positive polarity of the power switch circuit at the same time. The polarity output terminal is connected, the source of the right upper bridge arm switch is connected to the drain of the right lower bridge arm switch, the negative polarity terminal of the left lower bridge arm capacitor and the source of the right lower bridge arm switch are connected in series while selecting the power switch circuit The negative output terminal of the low-frequency transformer is connected to each other, and the two ends of the primary winding of the low-frequency transformer are respectively connected to the midpoint of the left bridge arm capacitor and the right bridge arm switch. The two-quadrant high-frequency power switch composition of voltage stress and bidirectional current stress, the drains of the two upper-side switches and the sources of the two lower-side switches are respectively connected in series to select the positive output terminal and negative polarity of the power switch circuit at the same time The output terminal is connected, the source of the left upper bridge arm switch and the drain of the left lower bridge arm switch are connected to one end of the primary winding of the low frequency transformer, the source of the right upper arm switch and the drain of the right lower arm switch are connected to the original winding of the low frequency transformer. The other ends of the windings are connected with each other; the bidirectional power flow of the multi-input low-frequency link inverter n-input single-output series selects the power switch circuit and the bi-directional power flow single-input single-output high-frequency inverter circuit to input the n-channel DC voltage source at the same time. _{U i1} , U _i2 ,... To obtain high-quality sinusoidal AC voltage or grid-connected sinusoidal current on a single-phase AC load, the +1-state amplitude of the positive half cycle of the bipolar two-state multilevel SPWM voltage wave output is (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ , (U _i1 +U _i2 +…+U _in-1 )N ₂ /N ₁ ,…, U _i1 N ₂ /N ₁ or U _i1 +U _i2 +…+U _in , U _i1 +U _i2 +…+U _in-1 ,…,U _i1 , the -1 state amplitude of the positive half cycle of the output is (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ or U _i1 +U _i2 + ...+U _in , the -1 state amplitude of the output negative half cycle is (U _i1 +U _i2 +...+U _in )N ₂ /N ₁ , (U _i1 +U _i2 +…+U _in-1 )N ₂ / _{N 1 , . _ _ _ _ _ _ _} The value is (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ or U _i1 +U _i2 +…+U _in , the +1 state and -1 state of the unipolar three-state multi-level SPWM voltage wave The amplitudes are all (U _i1 +U _i2 +…+U _in )N ₂ /N ₁ , (U _i1 +U _i2 +…+U _in-1 )N ₂ /N ₁ ,…,U _i1 N ₂ /N ₁ or U _i1 +U _i2 +…+U _in , U _i1 +U _i2 +…+U _in-1 ,…,U _i1 , only the half-bridge circuit bipolar two-state multi-level SPWM voltage wave positive and negative half cycle +1 state and -1 state amplitude should be multiplied by 1/ 2. N ₁ and N ₂ are the turns of the primary and secondary windings of the low-frequency transformer, respectively; the voltage stresses of the first, second, ..., n power selection switches and power selection diodes are respectively U _i1 , U _i2 , ... , U _in , the two-quadrant power switch voltage stress of push-pull and push-pull forward, half-bridge and full-bridge high-frequency inverter circuits is 2(U _i1 +U _i2 +…+U _in ), U _i1 +U _i2 +...+U _in ; the independent power supply system formed by the multi-input low-frequency link inverter adopts the fixed output power of the 1st, 2nd, ..., n-1 input sources and the nth input source supplementary load Insufficient power output voltage and input current instantaneous value feedback bipolar SPWM or unipolar SPWM master-slave power distribution energy management control strategy, the grid-connected power generation system composed of the multi-input low-frequency link inverter adopts the first, 2, ..., n-channel input source input current instantaneous value feedback bipolar SPWM or unipolar SPWM maximum power output energy management control strategy; the multi-input low-frequency link inverter according to the size of the AC load by controlling n-channel series series at the same time Select the on and off of the power switch to determine the number of input sources that need to be put into operation. In a high frequency switching cycle, the n input sources press U _i1 +U _i2 +…+U _in , U _i1 +U _i2 +…+U _In-1 , ..., U _i1 are serially connected in series to supply power to the AC load at the same time, which realizes the stable and high-quality sinusoidal AC power required by the single-stage low-frequency isolation and high-efficiency inversion of n unstable input DC voltages with different grounds into an AC load. 2. The series-connected simultaneous selection switching voltage type single-stage multi-input low-frequency link inverter according to claim 1 is characterized in that: said series connection simultaneously selects the output ends of the switching voltage type single-stage multi-input low-frequency link inverter and A single-stage isolated bidirectional charge-discharge converter connected to an energy storage device to form an independent power supply system with stable output voltage that can fully utilize the energy of n input sources; the single-stage isolated bidirectional charge-discharge converter is composed of input DC Filter, high-frequency inverter, high-frequency transformer, cyclic converter, and output AC filter are cascaded in sequence. The cyclic converter is composed of a four-quadrant high-frequency power switch that can withstand bidirectional voltage stress and bidirectional current stress. The discharge of the energy storage device is carried out by directly inverting the DC power of the energy storage device into AC load power through a single-stage isolated bidirectional charge-discharge converter. At this time, the single-stage isolated bidirectional charge-discharge converter is equivalent to a single-stage voltage. Type high-frequency link DC-AC converter, the charging of energy storage equipment is to select the switching voltage type single-stage multi-input low-frequency link inverter in series at the same time to convert n-channel input source DC power into AC power first, and then through single-stage isolation bidirectional The charge-discharge converter rectifies and converts the AC power into the DC power of the energy storage device. At this time, the single-stage isolated bidirectional charge-discharge converter is equivalent to a single-stage current-type high-frequency link AC-DC converter; the independent The power supply system adopts the maximum power output energy management control strategy of n-channel input source with independent control loop of output voltage of single-stage isolated bidirectional charge-discharge converter. The n-channel input sources all work in the maximum power output mode. The relative size of the sum of the maximum power of the input source controls the power flow size and direction of the single-stage isolated bidirectional charge-discharge converter in real time, realizing the stability of the system output voltage and the smooth and seamless switching of the charge and discharge of the energy storage device; the AC load power is greater than n channels When the sum of the maximum power of the input source, the system works in the energy storage device. The single-stage inversion of the DC power into AC power through the single-stage isolated bidirectional charge-discharge converter provides the AC load with the required insufficient power. Mode II, the energy storage device The power supply mode III that supplies power to the AC load alone belongs to the extreme case of the power supply mode II. When the AC load power is less than the sum of the maximum powers of the n-channel input sources, the system works when the residual energy output by the n-channel input sources is connected in series and simultaneously selects the switching voltage type single source. The two-stage multi-input low-frequency link inverter and the single-stage isolated bidirectional charge-discharge converter are two-stage conversion power supply mode I for charging the energy storage device; for the output AC filter capacitor and the AC load, the switching voltage type single-stage multi-stage The output terminals of the input low-frequency link inverter and the single-stage isolated bidirectional charge-discharge converter are connected in parallel, which is equivalent to the parallel superposition of two AC current sources; 2, ..., n channels of input source maximum power point reference current for error amplification, the 1st, 2nd, ..., n channels of error amplification signals are multiplied by the sinusoidal synchronization signal and then intersected with the same high-frequency carrier signal to generate the 1st, 2nd, ..., n-channel signals control n-input inverter, n-input inverter output AC filter inductor current and output voltage at the same frequency and phase, output active power There is a phase difference θ between the output AC filter inductor current and the system output voltage of the charge-discharge converter, which is controlled by intersecting the error amplification signal of the system output voltage and the reference voltage with the high-frequency carrier signal to generate an SPWM signal. The phase difference θ means outputting active power of different sizes and directions; when the AC load power is equal to the sum of the maximum powers of the n-channel input sources, θ=90°, the active power output by the charge-discharge converter is zero, and the AC load power is greater than the n-channel output power. The output voltage decreases when the sum of the maximum powers of the input sources, θ<90°, the output active power of the charge-discharge converter is the insufficient power required by the energy storage device to provide the AC load, and the AC load power is less than the sum of the maximum powers of the n input sources. When the output voltage increases, θ>90°, the charge-discharge converter outputs negative active power, that is, the residual power output by n input sources charges the energy storage device.

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