A low-leakage current photovoltaic inverter

Abstract

The application provides a low leakage current photovoltaic inverter, which is mainly composed of a direct current-alternating current inversion circuit and a controller. The direct current input positive pole or negative pole is directly connected with the alternating current output or the live line or the zero line of the public power grid, so as to reduce or even eliminate the leakage current of the inverter and relieve the PID effect of the components. The power frequency bridge arm in the direct current-alternating current inversion circuit can use a low-cost low-speed power switch tube, the high-frequency bridge arm can use a fast power switch tube, and the commutation inductance is used between the high-frequency bridge arms to avoid the risk of bridge arm through. The controller samples the alternating current and direct current voltage and current signals, adjusts the input voltage and output current accordingly, realizes the balance of the charging and discharging of the switch capacitor, and reduces the direct current component of the alternating current output. The single polarity modulation strategy is adopted, the inverter midpoint output voltage is three-level, and the output can be in the form of reactive power. The inverter has the unique advantages of high efficiency, high reliability, low / zero leakage current and the ability to output reactive power, and can be widely applied to various unidirectional and bidirectional direct current-alternating current power converters.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photovoltaic technology, and in particular to a low leakage current photovoltaic inverter. BACKGROUND

[0002] Photovoltaic modules are generally grounded through aluminum frames to improve safety, but in rainy days or humid environments, the parasitic capacitance to ground will reach 50nF-1uF / kWp. In transformerless non-isolated photovoltaic power generation systems, the inverter connects the photovoltaic module and the AC power grid, and the parasitic capacitance to ground, the output filter and the AC power grid line impedance produce common-mode resonance, and the leakage current is generated by the excitation of the resonance circuit at both ends of the parasitic capacitance. The voltage at both ends of the parasitic capacitance is derived from the high-frequency voltage dynamic change between the AC output zero line or neutral line (N) of the inverter and the negative electrode of the photovoltaic module, and the amplitude is proportional to the parasitic capacitance and the voltage change rate. When the leakage current is too large, the inverter will trigger the protection shutdown to reduce the photovoltaic power generation, and generate a large harmonic to affect the quality of the grid-connected current, at the same time, there is a circulating current in the inverter, which causes additional circulating current loss, and generates a large electromagnetic interference, on the other hand, the excessive leakage current also threatens the personal safety of end users and maintenance personnel.

[0003] In order to reduce the leakage current, single-phase photovoltaic inverters usually adopt half-bridge or bipolar sine wave pulse width modulation (SPWM) full-bridge topology (H4), but the half-bridge inverter requires a higher DC bus voltage, which is less used in industry, and the main drawback of H4 topology is that the output is two-level, which increases the switching loss, causes larger current ripple and filter inductance, and thus reduces the conversion efficiency. In order to solve the common-mode leakage current problem of transformerless non-isolated photovoltaic inverters and improve the conversion efficiency, some new topologies have been proposed in recent years at home and abroad, unipolar modulation five-tube full-bridge (H5) or high efficiency and high reliability inverter concept (HERIC) are shown in Figure 1 、 Figure 2 Similar to full-bridge inverters, these topologies do not require higher DC input voltage, can achieve three-level output by unipolar modulation, thereby reducing leakage current, improving conversion efficiency, and reducing the volume and weight of internal output filter inductors.

[0004] Transformerless non-isolated photovoltaic inverter not only needs to solve the problem of leakage current, but also needs to improve the universality of various components. Photovoltaic components are divided into two major technologies of crystalline silicon and thin film, and have two positive and negative electrodes. In order to prevent the surface oxide layer of silicon-based and copper indium gallium selenide thin film components from being corroded, and to prevent the polarity induced power decay (PID) effect of crystalline silicon components in a humid environment, the negative electrode of the component must be grounded. The positive electrode of the high-efficiency back gate crystalline silicon component also needs to be grounded, and the negative electrode of the conventional crystalline silicon component can also alleviate the PID effect. Grounding the positive or negative electrode of the component can basically eliminate the leakage current of the inverter and alleviate the PID effect of the component, but the half-bridge, full-bridge, H5, HERIC and other inverters cannot work normally, and need to add an isolation transformer or a new virtual ground PID suppression device, thereby increasing the cost of the system and the improvement effect is limited. Figure 3 、 Figure 4 The inverter shown in the figure does not need to add components, but the positive or negative electrode of the component is directly connected to the AC output live wire (L) or N wire, that is, directly or indirectly grounded, wherein Figure 3 Karschny is a switched inductor inverter (Karschny), which is essentially a Buck-Boost converter, and has lower conversion efficiency and a greater risk of injecting DC components into the grid; Figure 4 The virtual DC bus inverter (Chinese patent number: CN102088252B) uses more power devices, and the charging time of the switch capacitor in the control strategy is short and there is additional discharge for a short time, so the switch capacitor needs a larger capacity. The improved type (Common-Ground-Type Transformerless Inverters for Single-Phase Solar Photovoltaic Systems, IEEE Industry Electronics 2018, Vol. 65, No. 3) uses sine wave positive half cycle freewheeling additional charging, which causes the voltage across the switch capacitor to change too much, and there are actual problems such as charge-discharge imbalance.

[0005] Metal oxide semiconductor field effect transistor (MOSFET) has faster switching speed and can further improve switching frequency, but due to its poor reverse recovery characteristics of body diode, there is a risk of bridge arm shoot-through, which reduces the reliability of the inverter. Therefore, when the above inverters generate power in the form of reactive power, insulated gate bipolar transistors (IGBT) must be used. High-efficiency topologies such as H5, HERIC, Karschny, etc. are all European and American patents, which has caused serious technical barriers to the promotion and application of new energy power generation in China. In order to improve the many shortcomings of the existing technology and further improve the safety and reliability of photovoltaic power generation systems, a new type of transformerless non-isolated low-leakage-current photovoltaic inverter has become one of the research focuses in the field of new energy power electronics. SUMMARY

[0006] In order to overcome the deficiencies of the prior art, the purpose of the present application is to provide a low leakage current photovoltaic inverter, the positive or negative of the DC input is directly connected with the AC output or the live or neutral of the public grid, which reduces or even eliminates the leakage current of the inverter and relieves the PID effect of the components.

[0007] The present application provides a low leakage current photovoltaic inverter, which comprises a DC-AC inverter circuit and a controller, the DC-AC inverter circuit comprises a DC bus capacitor, a first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube, a body diode of the first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube, a switching capacitor, a first power diode, an AC output filter inductor, an AC output filter capacitor, the positive of the DC input voltage output by the photovoltaic component or the front-stage DC converter is connected to the positive of the DC bus capacitor, the negative of the DC input voltage is connected to the negative of the DC bus capacitor, the DC input voltage is connected with the one end of the AC output filter capacitor and the one end of the AC output, the first power diode, the second power switch tube and the first power switch tube, the other end of the AC output filter capacitor and the other end of the AC output are connected to the one end of the AC output filter inductor, the other end of the AC output filter inductor is connected to the fourth power switch tube, the third power switch tube is connected with the fourth power switch tube, the first power diode is connected to the switching capacitor and the fourth power switch tube, the first power switch tube is connected to the second power switch tube, the switching capacitor and the third power switch tube.

[0008] The controller comprises a DC bus voltage sampling module, an AC output voltage sampling module, an AC output filter inductor current sampling module, a sinusoidal wave modulation module, a voltage compensator, a current compensator, a phase-locked loop module and an AC peak value calculation module, the DC bus voltage sampling module detects the sampling DC bus voltage, the AC output voltage sampling module detects the sampling AC output amplitude and is connected to the input end of the phase-locked loop module and the AC peak value calculation module, the AC output filter inductor current sampling module detects the sampling AC output filter inductor current amplitude, the sinusoidal wave modulation module is used for generating the driving signal of each power switch tube, the voltage compensator adjusts the amplitude of the DC bus voltage based on the voltage reference signal, the phase-locked loop module generates the AC frequency and phase signal, which is multiplied with the output signal of the voltage compensator to generate the current reference signal, the current compensator controls the AC output filter inductor current waveform to change with the change of the AC output, the AC peak value calculation module is used for calculating the peak value of the AC output or the public grid voltage, which is multiplied with the output signal of the phase-locked loop module and then divided by the output signal of the DC bus voltage sampling module to serve as the feedforward signal of the output of the current compensator for output power limitation.

[0009] Further, the controller further comprises a first adder, a second adder, a third adder, a first multiplier, a second multiplier and a divider, the direct current bus voltage sampling module detects the sampling direct current input voltage amplitude and is connected to the negative terminal of the first adder and the input terminal of the divider, the positive terminal of the first adder is connected with a voltage reference signal, the voltage error signal of the output terminal of the first adder is connected to the input terminal of the voltage compensator, the output terminal of the voltage compensator is connected to the input terminal of the multiplier, the alternating current output voltage sampling module detects the sampling alternating current output amplitude and is connected to the input terminal of the phase-locked loop module and the alternating current peak value calculation module, the output terminal of the phase-locked loop module is connected to the other input terminal of the first multiplier and the input terminal of the second multiplier, the current reference signal of the output terminal of the first multiplier is connected to the positive terminal of the second adder, the alternating current output filter inductance current sampling module detects the sampling alternating current output filter inductance current amplitude and is connected to the negative terminal of the second adder, the current error signal of the output terminal of the second adder is connected to the input terminal of the current compensator, the output terminal of the alternating current peak value calculation module is connected to the other input terminal of the second multiplier, the output terminal of the second multiplier is connected to the other input terminal of the divider, the output terminal of the divider is connected to one positive input terminal of the third adder, the output terminal is connected to the other positive input terminal of the third adder, and the output terminal of the third adder is connected to the input control terminal of the sine wave modulation module to generate the driving signals of the power switches.

[0010] Further, the positive pole of the direct current input voltage in the direct current-alternating current inversion circuit is connected to one end of the alternating current output filter capacitor and the live wire of the alternating current output, and is simultaneously connected to the anode of the first power diode and the drain of the second power switch, the negative pole of the direct current input voltage is connected to the source of the first power switch, the other end of the alternating current output filter capacitor and the zero line or neutral line of the alternating current output are connected to one end of the alternating current output filter inductance, the other end of the alternating current output filter inductance is connected to the drain of the third power switch and the source of the fourth power switch, the cathode of the first power diode is connected to the positive pole of the switch capacitor and the drain of the fourth power switch, and the drain of the first power switch is connected to the source of the second power switch, the negative pole of the switch capacitor and the source of the third power switch.

[0011] Further, the negative pole of the direct current input voltage in the direct current-alternating current inversion circuit is connected to one end of the alternating current output filter capacitor and the zero line or neutral line of the alternating current output, and is simultaneously connected to the cathode of the first power diode and the source of the second power switch, the positive pole of the direct current input voltage is connected to the drain of the first power switch, the other end of the alternating current output filter capacitor and the live wire of the alternating current output are connected to one end of the alternating current output filter inductance, the other end of the alternating current output filter inductance is connected to the source of the third power switch and the drain of the fourth power switch, the anode of the first power diode is connected to the negative pole of the switch capacitor and the source of the fourth power switch, and the source of the first power switch is connected to the drain of the second power switch, the positive pole of the switch capacitor and the drain of the third power switch.

[0012] Further, the direct-current alternating-current inversion circuit further comprises a commutation inductor, a second power diode, and a third power diode, one end of the commutation inductor is connected to the anode of the second power diode and the other end of the commutation inductor is connected to the cathode of the third power diode, the anode of the second power diode is connected to the source of the fourth power switch tube, and the cathode of the third power diode is connected to the source of the third power switch tube.

[0013] Further, the direct-current alternating-current inversion circuit further comprises a commutation inductor, a second power diode, and a third power diode, one end of the commutation inductor is connected to the anode of the second power diode and the other end of the commutation inductor is connected to the cathode of the third power diode, the anode of the second power diode is connected to the source of the fourth power switch tube, and the cathode of the third power diode is connected to the source of the third power switch tube.

[0014] Further, the direct-current alternating-current inversion circuit comprises an A-phase direct-current alternating-current inversion circuit, a B-phase direct-current alternating-current inversion circuit, and a C-phase direct-current alternating-current inversion circuit, and the A-phase direct-current alternating-current inversion circuit, the B-phase direct-current alternating-current inversion circuit, and the C-phase direct-current alternating-current inversion circuit are connected to the direct-current input voltage.

[0015] Further, the three-phase inverter uses three independent controllers or shares one controller, and the sinusoidal wave modulation module and the internal carrier circuit in the controller are phase-shifted and staggered by 120 degrees.

[0016] Further, all the power switch tubes use basic power devices or are mixed with low-speed power switch tubes and fast power switch tubes.

[0017] Further, the direct-current alternating-current inversion circuit and the controller adopt a discrete semiconductor device mode or are integrated, mixedly integrated, or integrated into a power semiconductor to form a large-scale mixed power semiconductor integrated circuit.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] The application provides a low leakage current photovoltaic inverter, whose direct current input positive pole or negative pole is directly connected with alternating current output or public grid firewire or zero line, so as to reduce or even eliminate leakage current and relieve component PID effect; the direct current-alternating current inverter circuit can output in the form of active power and reactive power, and can be applied to unidirectional and bidirectional direct current-alternating current power converter; the power frequency bridge arm can use low-cost low-speed power switch tube, and the high-frequency bridge arm can use fast power switch tube, so as to reduce inverter component cost; the commutation inductance is used between the high-frequency bridge arms to avoid the risk of bridge arm through, and improve inverter working reliability; the single polarity modulation mode can improve conversion efficiency, and reduce internal output filter inductance volume and weight, so as to further reduce component cost; the advanced control strategy is more easy to realize switch capacitor charging and discharging balance, reduce alternating current output direct current component, so as to improve output power quality; the power loop of positive and negative half cycles of the sine wave has only two power tubes turned on, so as to reduce power loss and further improve conversion efficiency.

[0020] The above description is only a summary of the technical scheme of the application, in order to more clearly understand the technical means of the application, and the application can be implemented according to the content of the description, as follows. The preferred embodiments of the application are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings described herein are used to provide further understanding of the application, and form a part of the application. The schematic embodiments of the application and their descriptions are used to explain the application, and do not constitute an improper limitation on the application. In the drawings:

[0022] Figure 1 H5 inverter schematic diagram for background art of the application;

[0023] Figure 2 HERIC inverter schematic diagram for background art of the application;

[0024] Figure 3 Switching inductance inverter schematic diagram for background art of the application;

[0025] Figure 4 Virtual direct current bus inverter schematic diagram for background art of the application;

[0026] Figure 5 Component positive pole and alternating current firewire direct connection high reliability and safety type photovoltaic inverter and controller of embodiment one of the application;

[0027] Figure 6 Main working waveform of embodiment one of the application;

[0028] Figure 7 Component positive pole and alternating current firewire direct connection safety type photovoltaic inverter of embodiment two of the application;

[0029] Figure 8 The assembly negative pole of the embodiment three of the present application is directly connected with the AC zero line, and the high-reliability and safe photovoltaic inverter is obtained.

[0030] Figure 9 The assembly negative pole of the embodiment four of the present application is directly connected with the AC zero line, and the safe photovoltaic inverter is obtained.

[0031] Figure 10 The assembly positive pole of the embodiment five of the present application is directly connected with the AC live line, and the high-reliability and safe three-phase photovoltaic inverter is obtained. DETAILED DESCRIPTION

[0032] Hereinafter, the present application is further described in combination with the drawings and specific embodiments, and it should be noted that the following described embodiments or technical features can be combined to form new embodiments without conflict.

[0033] In the embodiment one, the assembly positive pole is directly connected with the AC live line, and the high-reliability and safe photovoltaic inverter is obtained as shown in the figure. Figure 5 The high-reliability and safe photovoltaic inverter is mainly composed of a direct current-alternating current inverter circuit and a controller, and adopts the switching capacitor technology and the modified full-bridge inverter circuit and its dead-zone-free control. Wherein, Vdc is the direct current input voltage, Vac is the alternating current output or the public power grid, Cb is the direct current bus capacitor, S1, S2, S3 and S4 are power switching tubes, Ds1, Ds2, Ds3 and Ds4 are body diodes of the power switching tubes S1, S2, S3 and S4 respectively, C FC is the switching capacitor, D1, D3 and D4 are power diodes, Lp is the bridge arm commutation inductance, Lf is the alternating current output filter inductance, and Cf is the alternating current output filter capacitor. Vdc comes from the photovoltaic assembly or the output of the previous direct current converter, the positive pole of which is connected to the positive pole of Cb, one end of Cf and one end of the live line (L) of the alternating current output Vac, and at the same time is connected to the anode of D1 and the drain (D) of S2, the negative pole of which is connected to the negative pole of Cb and the source (S) of S1, the other end of Cf and the other end of the zero line or neutral line (N) of the alternating current output are connected to one end of Lf. The other end of Lf is connected to the anode of D3, the drain (D) of S3 and one end of Lp, the other end of Lp is connected to the cathode of D4 and the source (S) of S4. The cathode of D1 is connected to the positive pole of Cb, the drain (D) of S4 and the cathode of D3, and the drain (D) of S1 is connected to the source (S) of S2, C FC and the drain (D) of S3, and the other end of Lf is connected to the anode of D3, the drain (D) of S3 and one end of Lp, the other end of Lp is connected to the cathode of D4 and the source (S) of S4. The cathode of D1 is connected to the positive pole of Cb, the drain (D) of S4 and the cathode of D3, and the drain (D) of S1 is connected to the source (S) of S2, C FCThe negative electrode, the D4 anode and the S3 source electrode (S). The controller comprises several key modules, wherein Hvb is a DC bus voltage sampling module, Hvac is an AC output voltage sampling module, Iiac is an Lf current sampling module, SPWM is a sine wave modulation module, Gcv is a voltage compensator, Gci is a current compensator, PLL is a phase-locked loop module, Vacm is an AC peak value calculation module, Vref is a voltage reference signal, and the controller also comprises adder 1, adder 2, adder 3, multiplier 1, multiplier 2 and divider. Hvb detects the amplitude of the sampled Vdc and is connected to the negative end of adder 1 and one input end of the divider, and the positive end of adder 1 is connected to Vref, and the voltage error signal at the output end thereof is connected to the input end of Gcv, and the output end of Gcv is connected to one input end of multiplier 1. Hvac detects the amplitude of the sampled Vac and is connected to the input end of PLL and Vacm, and the output end of PLL is connected to another input end of multiplier 1 and one input end of multiplier 2, and the current reference signal Iref at the output end thereof is connected to the positive end of adder 2, and Iiac detects the amplitude of the sampled Lf current and is connected to the negative end of adder 2, and the current error signal at the output end thereof is connected to the input end of Gci. The output end of Vacm is connected to another input end of multiplier 2, and the output end thereof is connected to another input end of the divider, and the output end of the divider is connected to one positive input end of adder 3, and the output end of Gci is connected to another positive input end of adder 3, and the output end of adder 3 is connected to the input control end of SPWM to generate the driving signals of the power switches. The AC output uses an inductor-capacitor type (LC) filter, and when the photovoltaic grid-connected inverter is used, an inductor-capacitor-inductor type (LCL) filter can also be used to further reduce the output filter inductance and its volume. Hvb detects the DC bus voltage Vdc, and Gcv adjusts the amplitude of the DC bus voltage based on the voltage reference signal Vref. PLL generates an AC frequency and phase signal and multiplies the output signal of Gcv to generate the current reference signal Iref. Gci is a current compensator to control the Lf current waveform to change with Vac. Vacm is used to calculate the peak value of the AC output or the public grid voltage, and after multiplying the output signal of PLL and dividing the output signal of Hvb, it is used as the feedforward signal of the output of Gci to achieve the output power limiting function.

[0034] The main working waveform is shown in Figure 6 The single-polarity modulation mode is adopted, and thus the inverter midpoint output voltage is three-level. The DC-AC inverter circuit can realize bidirectional energy flow, so that the inverter has active power and reactive power output capability, and the specific working process is described as follows:

[0035] (t0~t1): AC output sine wave voltage is positive, AC output sine wave current is also positive, that is, active inverter state 1: S1, S3 open, S2, S4 off, Vdc and Cb through Lf, Cf filtering to achieve AC inverter output to Vac, at the same time D1 forward conduction, Vdc and Cb through S1, D1 to C FC charge, at this time the AC output voltage value and Cb voltage is equal potential and with "+1" to designate, this is called the positive inverter state; S1 continues to conduct, S3 off, D3 clamp S3 off the moment of the peak voltage, Vdc and Cb continue through S1, D1 to C FC charge, at the same time the energy stored in Lf through S1, D3, C FC to achieve freewheeling, steady state C FC and Cb voltage is equal, so the AC output voltage value is zero and with "0" to designate, this is called the positive freewheeling state. S1, D1 conduction, Cb and C FC Essentially in parallel, so you can reduce the DC bus current ripple.

[0036] (t1~t2): AC output sine wave voltage is negative, AC output sine wave current is positive, that is, the active rectifier state 1: S3 open, Vac through S2 body diode Ds2 to Lf energy storage charging, this is called the negative energy storage state; S3 off, D3 clamp S3 off the moment of the peak voltage, the energy stored in Lf through Ds2, D3, Vac freewheeling discharge to C FC , this is called the negative release state.

[0037] (t2~t3): AC output sine wave voltage is negative, AC output sine wave current is also negative, that is, active inverter state 2: S1, S3 off, S2, S4 open, C FC stored energy through Lp and through Lf, Cf filtering to achieve AC inverter output, at this time the output voltage value and C FC voltage is opposite and with "-1" to designate, this is called the negative inverter state; S2 continues to conduct, S4 off, D4 clamp S4 off the moment of the peak voltage, the energy stored in Lp, Lf through S2, D4 to achieve freewheeling, at this time the output voltage value is zero and with "0" to designate, this is called the negative freewheeling state.

[0038] (t3~t4): AC output sine wave voltage is positive, AC output sine wave current is negative, that is, the active rectifier state 2: S4 open, Vac through D1 to commutating inductor Lp, output filter inductor Lf energy storage charging, this is called the positive energy storage state; S4 off, D4 clamp S4 off the moment of the peak voltage, the energy stored in Lf through D1, D4, Vac and Ds1, D4, Vac respectively freewheeling discharge to CFC , Cb, this is called the forward release state.

[0039] During the forward freewheeling period, Vdc and Lf store energy to charge C FC , so the switched capacitor can charge more, and in the negative half cycle, C FC continues to discharge, so the switched capacitor is easier to achieve charge and discharge balance, so the AC output DC component can be reduced, thereby improving the output power quality. The inverter does not need to add new components, and the AC output Vac fire line is directly connected to the positive of the component, thereby reducing or even eliminating the inverter leakage current and relieving the component PID effect.

[0040] As can be seen from the above, S3 and D3, or S4 and D4 respectively constitute two inverter bridge arms, which are only connected in series by power switches and power diodes inside, without direct series connection of switches, also known as bridge arm commutation dead zone-free technology. The commutation inductance Lp can avoid the risk of shoot-through of S3 and S4, thereby improving the reliability of the inverter. Using unipolar SPWM modulation mode can realize the inverter midpoint output as "+1", "0", "-1" three levels, thereby improving the conversion efficiency and reducing the internal output filter inductance volume and weight. The inverter does not need to add new components, and the AC output fire line is directly connected to the positive of the component, thereby reducing or even eliminating the inverter leakage current and relieving the component PID effect, greatly improving the safety of the photovoltaic power generation system. In addition, the power loop of the positive and negative half cycles of the sine wave only has two power tubes conducting, thereby reducing power loss and further improving conversion efficiency, while reducing the thermal stress of power devices and further improving the working reliability. The inverter can realize the output of reactive power in a smooth control mode, thereby providing flexible compensation to the AC power grid. Through this control mode, the inverter can also work in AC-DC rectification mode, so the inverter and its control strategy can be widely applied to various types of unidirectional and bidirectional DC-AC power converters.

[0041] Four power switch tubes and two power diodes are half of the work of the power frequency cycle, two of which are high-frequency switch work in half of the work of the power frequency cycle. When the positive half cycle of the AC output sine wave is positive, the power switch tube S1 is the power frequency switch work and can use low-speed power switch tubes such as IGBT, power triode (GTR), or triode thyristor (TRIAC), silicon controlled rectifier (SCR), etc. The power switch tube S3 is high-frequency work during this period and can use fast power switch tubes such as MOSFET, wide bandgap power switch tube gallium nitride (GaN), silicon carbide (SiC), etc. When the switching frequency is low, IGBT, GRT can also be used. The power diode D3 is also high-frequency work during this period and can use super-fast recovery or SiC diodes, etc. Similarly, when the negative half cycle of the AC output sine wave is positive, the power switch tube S2 is also the power frequency switch work and can use low-speed power switch tubes such as IGBT, GTR or TRIAC, SCR, etc. The power switch tube S4 is high-frequency work during this period and can use fast power switch tubes such as MOSFET, GaN, SiC, etc. When the switching frequency is low, IGBT can also be used. The power diode D4 is also high-frequency work during this period and can use super-fast recovery or SiC diodes, etc. The power diode D1 may work in a high-frequency switch state during the positive half cycle, so super-fast recovery or SiC diodes, etc. are used. The inverter bridge arm high-frequency tube uses MOSFET, and the power frequency tube uses IGBT, which can reduce the cost of inverter components to a certain extent. When applied to a photovoltaic power generation system, multiple inverter parallel technology, multiple maximum power point tracking technology (MPPT), and interleaved parallel technology and coupled inductor structure, etc. can be easily used. The controller can be built with discrete electronic components, or it can be designed and used with special integrated circuits such as analog control chips, single-chip microcomputers (MCU) programmed through software, digital signal processors (DSP), or programmable logic devices (FPGA / CPLD), etc. The DC-AC inverter circuit and the controller can use discrete semiconductor devices or integrated, hybrid integrated, or unified integrated into power semiconductors to form a large-scale hybrid power semiconductor integrated circuit. This high-integration design can further reduce the size of the photovoltaic inverter.

[0042] In Example Two, the positive electrode of the assembly is directly connected to the AC live line Figure 7As shown. The output voltage of the photovoltaic module or the front-end DC-DC converter is Vdc. Its positive terminal is connected to the positive terminal of the DC bus capacitor Cb, one end of the AC output filter capacitor Cf, and the live wire (L) of the AC output Vac terminal. It is also connected to the anode of power diode D1 and the drain (D) of power switch S2. The negative terminal is connected to the negative terminal of Cb and the source (S) of power switch S1. The other end of Cf and the neutral wire (N) of the other end of the AC output are connected to one end of the AC output filter inductor Lf. The other end of Lf is connected to the drain (D) of power switch S3 and the source (S) of power switch S4. The cathode of D1 is connected to the switching capacitor C. FC The positive electrode and drain (D) of S4 are connected, and the drain (D) of S1 is connected to the source (S) of S2 and the collector (C). FC Negative electrode and S3 source electrode (S). Therefore, it can be seen that... Figure 5 Compared to other systems, only the commutation inductor Lp is omitted. The operating principle of the other parts is the same. Figures 4-5 They are basically the same, so I won't repeat the explanation here.

[0043] In Example 3, a high-reliability and safe photovoltaic inverter is directly connected to the negative terminal of the component and the AC neutral line, such as... Figure 8 As shown. The output voltage of the photovoltaic module or the front-end DC converter is Vdc. Its positive terminal is connected to the positive terminal of the DC bus capacitor Cb and the drain (D) of the power switch S1. Its negative terminal is connected to the negative terminal of Cb, the cathode of the power diode D1, the source (S) of the power switch S2, one end of the AC output filter capacitor Cf, and the neutral line (N) of the AC output. The other end of Cf and the live wire (L) of the other end of the AC output Vac are connected to one end of the AC output filter inductor Lf. The other end of Lf is connected to the anode of the power diode D4, the drain (D) of the power switch S4, and one end of the commutation inductor Lp. The other end of Lp is connected to the cathode of the power diode D3 and the source (S) of the power switch S3. The source (S) of S1 is connected to the drain (D) of S2 and the switching capacitor C. FC Positive electrode, cathode D4, and drain S3 (D), with anode D1 connected to cathode C. FC The cathode is composed of a negative electrode, a source (S4), and a cathode (D3). Therefore, it can be seen that... Figure 5 Compared to simply connecting the positive terminal of Vdc directly to the AC output L line, this method directly connects the negative terminal of Vdc to the AC output N line. The other working principles are the same. Figures 4-5 They are basically the same, so I won't repeat the explanation here.

[0044] In Example 4, a safety-type photovoltaic inverter with the negative terminal of the component directly connected to the AC neutral line is shown. Figure 9As shown. The output voltage of the photovoltaic module or the front-end DC converter is Vdc. Its positive terminal is connected to the positive terminal of the DC bus capacitor Cb and the drain (D) of the power switch S1. Its negative terminal is connected to the negative terminal of Cb, the cathode of the power diode D1, the source (S) of the power switch S2, one end of the AC output filter capacitor Cf, and the neutral line (N) of the AC output terminal. The other end of Cf and the live wire (L) of the other end of the AC output Vac are connected to one end of the AC output filter inductor Lf. The other end of Lf is connected to the drain (D) of the power switch S4 and the source (S) of the power switch S3. The source (S) of S1 is connected to the drain (D) of S2, the positive terminal of the switching capacitor CFC, and the drain (D) of S3. The anode of D1 is connected to the negative terminal of CFC and the source (S) of S4. Therefore, it can be seen that... Figure 8 Compared to other systems, only the commutation inductor Lp is omitted. The operating principle of the other parts is the same. Figures 4-5 They are basically the same, so I won't repeat the explanation here.

[0045] In Example 5, a high-reliability and safe three-phase photovoltaic inverter is directly connected to the positive terminal of the component and the AC live wire, such as... Figure 10 As shown. The output voltage of the photovoltaic module or the front-end DC converter is Vdc. Its positive terminal is connected to the positive terminal of the DC bus capacitor Cba, one end of the AC output filter capacitor Cfa, and the live wire (L) of the AC output Va. It is also connected to the anode of the power diode D1a and the drain (D) of the power switch S2a. The negative terminal is connected to the negative terminal of Cba and the source (S) of the power switch S1a. The other end of Cfa and the neutral wire (N) of the other AC output terminal are connected to one end of the AC output filter inductor Lfa. The other end of Lfa is connected to the anode of the power diode D3a, the drain (D) of the power switch S3a, and one end of the commutation inductor Lpa. The other end of Lpa is connected to the cathode of the power diode D4a and the source (S) of the power switch S4a. The cathode of D1a is connected to Cba. FCa Positive electrode, drain (D) of S4a, and cathode of D3a; drain (D) of S1a is connected to source (S) of S2a, and cathode of C. FCa The cathode, anode (D4a), and source (S3a) are formed. The above process constitutes the AC output phase A, and phases B and C are constructed similarly. Therefore, it can be seen that... Figure 5 Compared to converting a single-phase inverter to a three-phase inverter, only the B-phase and C-phase DC-AC inverter circuits are added. A three-phase inverter can use three independent controllers or share a single controller. The SPWM module and its internal carrier circuit in the controller need to be phase-shifted by 120 degrees. Its operating principle is similar to... Figures 4-5 Basically the same, in addition Figures 7-9 All of these can be used to construct similar three-phase photovoltaic inverters, which will not be explained again here.

[0046] The application provides a low leakage current photovoltaic inverter, which is mainly composed of a direct current-alternating current inverter circuit and a controller. The direct current input positive pole or negative pole is directly connected with the alternating current output or the public power grid live line or zero line, so as to reduce or even eliminate the leakage current of the inverter and relieve the PID effect of components. The power frequency bridge arm in the direct current-alternating current inverter circuit can use low-cost low-speed power switch tubes, the high-frequency bridge arm can use fast power switch tubes, and the commutation inductors are used between the high-frequency bridge arms to avoid the risk of bridge arm through. The controller samples alternating current and direct current voltage and current signals, adjusts the input voltage and output current accordingly, and realizes the balance of the charging and discharging of the switch capacitor, so as to reduce the direct current component of the alternating current output. The single polarity modulation strategy is adopted, the inverter midpoint output voltage is three-level, and the inverter can output in the form of reactive power. The inverter has the unique advantages of high efficiency, high reliability, low / zero leakage current and the ability to output reactive power, and can be widely applied to various unidirectional and bidirectional direct current-alternating current power converters.

[0047] The application is a high-performance safe photovoltaic inverter, which can be applied to photovoltaic grid-connected, photovoltaic off-grid and photovoltaic energy storage inverters, converters, uninterruptible power supplies (UPS), active filters (APF), frequency converters, motor drivers and various unidirectional and bidirectional direct current-alternating current power converters.

[0048] The above is only the preferred embodiment of the application, and does not limit the application in any form; any ordinary technical personnel in the industry can implement the application according to the above and the drawings; however, any equivalent changes, modifications and evolutions made by those skilled in the art within the scope of the technical solutions of the application, using the disclosed technical content, are equivalent embodiments of the application; at the same time, any equivalent changes, modifications and evolutions of the above embodiments according to the essence of the application are still within the protection scope of the technical solutions of the application.

Claims

1. A low leakage current photovoltaic inverter, characterized by: including direct current an alternating current inverter circuit and a controller, the direct current The alternating current inverter circuit includes a direct current bus capacitor, a first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube, a body diode of the first power switch tube, the second power switch tube, the third power switch tube, the fourth power switch tube, a switching capacitor, a first power diode, an alternating current output filter inductor, an alternating current output filter capacitor, a positive electrode of a direct current input voltage output by a photovoltaic module or a front-stage direct current converter is connected to a positive electrode of the direct current bus capacitor, a negative electrode of the direct current input voltage is connected to a negative electrode of the direct current bus capacitor, the direct current input voltage is connected with one end of the alternating current output filter capacitor and one end of the alternating current output, the first power diode, the second power switch tube and the first power switch tube, the other end of the alternating current output filter capacitor and the other end of the alternating current output are connected to one end of the alternating current output filter inductor, the other end of the alternating current output filter inductor is connected to the fourth power switch tube, the third power switch tube is connected with the fourth power switch tube, the first power diode is connected to the switching capacitor and the fourth power switch tube, and the first power switch tube is connected to the second power switch tube, the switching capacitor and the third power switch tube. The controller further comprises a first adder, a second adder, a third adder, a first multiplier, a second multiplier and a divider, the DC bus voltage sampling module is connected to the negative terminal of the first adder and the input terminal of the divider after detecting the DC input voltage amplitude, the positive terminal of the first adder is connected with a voltage reference signal, the voltage error signal of the output terminal of the first adder is connected to the input terminal of the voltage compensator, the output terminal of the voltage compensator is connected to the input terminal of the first multiplier, the AC output voltage sampling module is connected to the input terminal of the phase-locked loop module and the AC peak value calculation module after detecting the AC output amplitude, the output terminal of the phase-locked loop module is connected to the other input terminal of the first multiplier and the input terminal of the second multiplier, the current reference signal of the output terminal of the first multiplier is connected to the positive terminal of the second adder, the AC output filter inductor current sampling module is connected to the negative terminal of the second adder after detecting the AC output filter inductor current amplitude, the current error signal of the output terminal of the second adder is connected to the input terminal of the current compensator, the output terminal of the AC peak value calculation module is connected to the other input terminal of the second multiplier, the output terminal of the second multiplier is connected to the other input terminal of the divider, the output terminal of the divider is connected to one positive input terminal of the third adder, the output terminal of the current compensator is connected to the other positive input terminal of the third adder, and the output terminal of the third adder is connected to the input control terminal of the sine wave modulation module to generate the driving signals of the power switches.

2. A low leakage current photovoltaic inverter as claimed in claim 1, characterized in that: The direct current The positive pole of the direct current input voltage in the alternating current inversion circuit is connected to one end of the alternating current output filter capacitor and the live wire of the alternating current output, and is connected to the anode of the first power diode and the drain of the second power switch tube at the same time. The negative pole of the direct current input voltage is connected to the source of the first power switch tube. The other end of the alternating current output filter capacitor and the neutral wire or the neutral line of the alternating current output are connected to one end of the alternating current output filter inductor. The other end of the alternating current output filter inductor is connected to the drain of the third power switch tube and the source of the fourth power switch tube. The cathode of the first power diode is connected to the positive pole of the switch capacitor and the drain of the fourth power switch tube. The drain of the first power switch tube is connected to the source of the second power switch tube, the negative pole of the switch capacitor and the source of the third power switch tube.

3. A low leakage current photovoltaic inverter as in claim 1, wherein: The direct current The negative pole of the direct current input voltage in the alternating current inversion circuit is connected to one end of the alternating current output filter capacitor, the zero line or neutral line of the alternating current output, the cathode of the first power diode and the source of the second power switch tube, the positive pole of the direct current input voltage is connected to the drain of the first power switch tube, the other end of the alternating current output filter capacitor and the other end of the alternating current output are connected to one end of the alternating current output filter inductor, the other end of the alternating current output filter inductor is connected to the source of the third power switch tube and the drain of the fourth power switch tube, the anode of the first power diode is connected to the negative pole of the switch capacitor and the source of the fourth power switch tube, the source of the first power switch tube is connected to the drain of the second power switch tube, the positive pole of the switch capacitor and the drain of the third power switch tube.

4. A low-leakage current photovoltaic inverter as claimed in claim 1, characterized in that: the direct current The AC inverter circuit comprises an A-phase direct current The AC inverter circuit, a B-phase direct current The AC inverter circuit, a C-phase direct current The AC inverter circuit, the A-phase direct current The AC inverter circuit, the B-phase direct current The AC inverter circuit, the C-phase direct current The input of the AC inverter circuit is connected with the direct current input voltage.

5. A low-leakage current photovoltaic inverter as claimed in claim 4, characterized in that: The three-phase inverter uses three independent controllers or shares one controller, and the sine wave modulation module and the internal carrier circuit thereof in the controller are shifted by 120 degrees.

6. A low leakage current photovoltaic inverter as in claim 1, wherein: All the power switches use basic power devices or mix low-speed power switches and fast power switches.

7. A low leakage current photovoltaic inverter as in claim 1, wherein: The direct current The AC inverter circuit and the controller are constructed in a discrete semiconductor device manner or in a respective integrated, hybrid integrated manner, or are integrated into a power semiconductor in unison to form a large-scale hybrid power semiconductor integrated circuit.

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