CN102185514B - Single-phase three-level inverter - Google Patents

Abstract

The invention discloses a single-phase three-level inverter, which includes an input capacitor, six power switches, two freewheeling diodes and a single-phase output filter. The present invention uses six power switches and freewheeling diodes to coordinate switching actions, so that when the output voltage of the inverter is at zero level, the output AC side and the input DC side of the inverter are in a decoupling state, thereby ensuring the output voltage of the inverter While realizing the three-level, its common-mode voltage is maintained as a constant, thereby completely eliminating the common-mode current; the circuit of the present invention does not have the capacitor voltage imbalance problem caused by the parasitic capacitance of the power switching device, so it will not damage the non-leakage current The working mechanism is simple, and the control method is simple; the circuit of the present invention has a reliable dead zone working mechanism and high circuit working stability. The invention adopts the unipolar pulse width modulation mode, the output current ripple of the inverter is small, the copper loss and magnetic loss generated on the filter inductance are small, and the output power quality is high.

Description

A single-phase three-level inverter

technical field

The invention relates to an inverter in the field of DC-AC converters of power electronics technology, in particular to a single-phase three-level transformerless inverter.

Background technique

As the world's energy shortage and environmental pollution become increasingly serious, energy and the environment have become one of the most important issues facing mankind in the 21st century. The development and application of clean and renewable energy has attracted more and more attention from countries all over the world. . A large number of renewable energy sources are direct current, which needs to be converted into industrial frequency alternating current through an inverter before it can be used in large quantities. Therefore, inverter technology plays a vital role in the development and utilization of renewable energy.

Inverter refers to a power electronic converter that converts DC power into AC power by turning on and off semiconductor power switching devices. The early inverter circuit was usually a square wave circuit. Due to the successful application of pulse width modulation (PWM) technology in power electronics, a PWM inverter circuit with the function of voltage regulation and frequency conversion has been developed. Common inverter circuit topologies using PWM modulation include full-bridge circuits, half-bridge circuits, half-bridge mid-point clamp circuits, and various multi-level circuits.

According to different output levels, the PWM inverter circuit system can be divided into two-level circuits, three-level circuits and multi-level circuits. The two-level circuit means that under the PWM modulation control mode, the output voltage waveform will have positive and negative polarity levels in each switching cycle of the main circuit, which is different from the traditional square wave inverter or phase-shift voltage regulation full-bridge inverter. Compared with the inverter circuit, the output voltage of the two-level inverter circuit is easy to adjust, and the output harmonic performance is better. The three-level circuit means that the output voltage of the inverter has only zero point and one positive or negative level in each switching cycle. Compared with the two-level circuit, the output voltage and current harmonic performance of the three-level inverter circuit are better. , and because the change of the inverter output voltage in each switching cycle is half of that of the two-level circuit, the parameters of the output filter will be significantly reduced, so that the volume and weight of the entire circuit device will also be significantly reduced. Multi-level circuits are mainly used in high-voltage and high-power occasions. Due to the limited voltage blocking capability and current output capability of power switching devices, multi-level circuits that use power devices in series and parallel to expand capacity and expand voltage are used in high-voltage and high-power applications. more suitable.

According to different application occasions and control methods of inverters, inverter systems can be divided into independent inverters and grid-connected inverters; according to different transformer configurations in inverters, inverter systems can be divided into belt-connected inverters. Power frequency transformer type inverter, with high frequency transformer type inverter and transformerless type inverter. Inverters with power frequency transformers or high frequency transformers can realize the functions of boosting and isolation. However, inverters with power frequency transformers are bulky, heavy, expensive, and inconvenient for system installation; Although the size and weight of the type inverter are greatly reduced, this type of inverter system is often composed of multiple stages, resulting in a complex system structure and reduced system efficiency. The non-transformer inverter has been rapidly developed in the world because of its simple system structure, high efficiency, small size, and low cost.

Contents of the invention

The invention provides a transformerless single-phase three-level inverter with simple structure, capable of eliminating common mode current and adopting unipolar pulse width modulation mode.

A single-phase three-level inverter of the present invention includes an input capacitor, a first power switch, a second power switch, a third power switch, a fourth power switch, a fifth power switch, a sixth power switch, a first A freewheeling diode, a second freewheeling diode and a filter; the drain of the first power switch, the drain of the third power switch, and the positive terminal of the input capacitor are connected to the positive terminal of the input DC terminal; the source of the first power switch, the second The drain of the second power switch, the anode of the first freewheeling diode, and the cathode of the second freewheeling diode are connected to the first input terminal of the filter; the source of the second power switch, the source of the sixth power switch, and the input capacitor The negative terminal of the input DC terminal is connected to the negative terminal; the source of the third power switch and the cathode of the first freewheeling diode are connected to the drain of the fourth power switch; the drain of the sixth power switch is connected to the anode of the second freewheeling diode It is connected with the source of the fifth power switch; the source of the fourth power switch and the drain of the fifth power switch are connected with the second input terminal of the filter.

The first power switch is composed of a first switching transistor and a first anti-parallel diode in parallel, the second power switch is composed of a second switching transistor and a second anti-parallel diode in parallel, and the third power switch is composed of a third switching transistor and a first Three anti-parallel diodes are connected in parallel, the fourth power switch is composed of the fourth switching transistor and the fourth anti-parallel diode in parallel, the fifth power switch is composed of the fifth switching transistor and the fifth anti-parallel diode in parallel, the sixth power switch is composed of the sixth The switch transistor and the sixth anti-parallel diode are connected in parallel; the parallel connection mode of the switch transistor and the anti-parallel diode is as follows: the drain or collector of the switch transistor is connected with the cathode of the anti-parallel diode to form the drain of the power switch, and the source or collector of the switch transistor The emitter is connected with the anode of the anti-parallel diode to form the source of the power switch.

The freewheeling diode is an independent diode, or a switching transistor with an antiparallel diode.

The input capacitor is a capacitor or a capacitor combination composed of multiple capacitors connected in series and parallel.

The filter is a single inductance filter, an inductance-capacitance filter or an inductance-capacitance-inductance filter.

The switch transistor is a high voltage metal oxide silicon field effect transistor or an insulated bipolar transistor.

The anti-parallel diode is an independent diode or a built-in diode inside the switching transistor.

The modulation mode of the inverter of the present invention has the following two types, unipolar pulse width modulation mode 1 and unipolar pulse width modulation mode 2 .

In the unipolar pulse width modulation method 1, the first switching transistor, the second switching transistor, the third switching transistor and the sixth switching transistor alternately perform switching operations in a power frequency cycle (for example, 50 Hz) and a high frequency cycle (for example, 20 kHz). . In the positive half cycle of power frequency, the first switching transistor and the sixth switching transistor operate at high frequency synchronously, the second switching transistor and the third switching transistor are normally closed, the fourth switching transistor is normally closed, and the fifth switching transistor is normally open; In the negative half period, the first switching transistor and the sixth switching transistor are normally closed, the second switching transistor and the third switching transistor operate at high frequency synchronously, the fourth switching transistor is normally open, and the fifth switching transistor is normally closed.

In unipolar pulse width modulation mode 2, the first switching transistor, the second switching transistor, the third switching transistor, the fourth switching transistor, the fifth switching transistor and the sixth switching transistor alternately operate at a power frequency cycle (for example, 50 Hz) and The switching operation is performed at a high frequency cycle (for example, 20kHz). In the positive half cycle of power frequency, the first switching transistor and the sixth switching transistor operate synchronously at high frequency, the second switching transistor and the third switching transistor are normally closed, the fourth switching transistor and the first switching transistor are complementary turned on, and the fifth switching transistor is normally On; in the negative half cycle of power frequency, the first switching transistor and the sixth switching transistor are normally closed, the second switching transistor and the third switching transistor operate at high frequency synchronously, the fourth switching transistor is normally open, the fifth switching transistor and the second switching transistor The transistors are complementary turned on.

When the single-phase three-level inverter of the present invention is working, six power switches with anti-parallel diodes and two freewheeling diodes are coordinated to perform switching operations, so that when the inverter output voltage is at zero level, the inverter output The AC side and the input DC side are in a decoupling state, which ensures that during the entire modulation process, while the inverter output voltage achieves three levels, the common-mode voltage at the inverter output side remains constant, thereby completely eliminating common mode current.

When the inverter of the present invention adopts the above two unipolar pulse width modulation modes, when the working mode of the circuit is switched, the parasitic junction capacitance voltage of the power switch is always balanced, so no additional pulse width modulation strategy or hardware circuit is required To compensate the voltage balance problem of parasitic junction capacitance, so its control method is relatively simple; the output voltage of the inverter of the present invention is three levels, so that the volume of the output filter can be greatly reduced, and the loss on the filter can be reduced; The invented inverter only needs to set a dead zone when the output current is near the power frequency zero crossing point, so the circuit output power quality is good and the circuit stability is high. The inverter of the present invention is applicable to independent inverters and grid-connected inverter systems, and is particularly suitable for use in distributed photovoltaic grid-connected power generation systems.

The present invention uses six power switches with anti-parallel diodes and two freewheeling diodes to coordinate the switching action, completely eliminating the common-mode current; the circuit has a simple control mode and a reliable dead-zone working mechanism under a suitable modulation mode . The invention adopts the unipolar pulse width modulation mode, and the output current ripple is reduced, thereby improving the output power quality of the inverter, reducing the volume and weight of the filter, and reducing the copper loss and magnetic flux generated on the filter inductance. damage. The invention has a simple structure and can realize a three-level output voltage while eliminating the common mode current.

Description of drawings

Fig. 1 is a schematic circuit diagram of a single-phase three-level inverter of the present invention.

FIG. 2 is a schematic diagram of waveforms using unipolar pulse width modulation mode 1 in the present invention.

FIG. 3 is a schematic diagram of waveforms using unipolar pulse width modulation mode 2 in the present invention.

4a-4j are schematic diagrams of ten working modes of the single-phase three-level inverter of the present invention.

Detailed ways

Referring to accompanying drawing 1, a single-phase three-level inverter of the present invention includes an input capacitor C _dc , a first power switch S ₁ , a second power switch S ₂ , a third power switch S ₃ , and a fourth power switch S ₄ , the fifth power switch S ₅ , the sixth power switch S ₆ , the first freewheeling diode D ₇ , the second freewheeling diode D ₈ and the filter F;

The first power switch S ₁ described in this embodiment is composed of the first switching transistor T ₁ and the first anti-parallel diode D ₁ connected in parallel, and the second power switch S ₂ is composed of the second switching transistor T ₂ and the second anti-parallel diode D ₂ in parallel, the third power switch _S3 is composed of the third switching transistor _T3 and the third anti-parallel diode _D3 in parallel, the fourth power switch _S4 is composed of the fourth switching transistor _T4 and the fourth anti-parallel diode _D4 in parallel The fifth power switch _S5 is composed of the fifth switching transistor _T5 and the fifth anti-parallel diode _D5 in parallel, and the sixth power switch _S6 is composed of the sixth switching transistor _T6 and the sixth anti-parallel diode _D6 in parallel; The parallel connection of the switching transistor and the anti-parallel diode is as follows: the drain or collector of the switching transistor is connected to the cathode of the anti-parallel diode to form the drain of the power switch, and the source or emitter of the switching transistor is connected to the anode of the anti-parallel diode to form a power switch. source of the switch.

The drain of the first power switch _S1 , the drain of the third power switch _S3 , and the positive terminal of the input capacitor C _dc are connected to the positive terminal of the input DC terminal; the source of the first power switch _S1 , the second power switch _S2 The drain of the first freewheeling diode _D7 , the cathode of the second freewheeling diode _D8 are connected to the first input terminal of the filter; the source of the second power switch _S2 , the sixth power switch _S6 The source and the negative terminal of the input capacitor C _dc are connected to the negative terminal of the input DC terminal; the source of the third power switch _S3 and the cathode of the first freewheeling diode _D7 are connected to the drain of the fourth power switch _S4 ; the sixth The drain of the power switch _S6 and the anode of the second freewheeling diode _D8 are connected to the source of the fifth power switch _S5 ; the source of the fourth power switch _S4 and the drain of the fifth power switch _S5 are connected to the filter connected to the second input of the device;

The modulation mode of the inverter of the present invention is unipolar pulse width modulation.

Accompanying drawing 2 is a schematic diagram of waveforms using unipolar pulse width modulation method 1, where _uc is a high-frequency carrier (eg 20 kHz), and _ug is a power frequency modulation wave (eg 50 Hz). The first switching transistor T ₁ , the second switching transistor T ₂ , the third switching transistor T ₃ and the sixth switching transistor T ₆ alternately perform switching operations in a power frequency cycle (for example, 50 Hz) and a high frequency cycle (for example, 20 kHz). When the modulating wave _ug is in the positive half cycle, the first switching transistor _T1 and the sixth switching transistor _T6 operate synchronously at high frequency, the second switching transistor _T2 and the third switching transistor _T3 are normally closed, and the fourth switching transistor T ₄ is normally closed, the fifth switching transistor _T5 is normally open; when the modulation wave u _g is in the negative half cycle, the first switching transistor _T1 and the sixth switching transistor _T6 are normally closed, the second switching transistor _T2 and the third switching transistor _T3 synchronously operates at high frequency, the fourth switching transistor _T4 is normally open, and the fifth switching transistor _T5 is normally closed.

Accompanying drawing 3 is the waveform schematic diagram adopting unipolar pulse width modulation mode 2, wherein _uc is a high-frequency carrier (such as 20kHz), _ug is a power frequency modulation wave (such as 50Hz), the first switch transistor T ₁ , the second The switching transistor T ₂ , the third switching transistor T ₃ , the fourth switching transistor T ₄ , the fifth switching transistor T ₅ and the sixth switching transistor T ₆ alternately operate in a power frequency cycle (for example, 50 Hz) and a high frequency cycle (for example, 20 kHz). switch action. When the modulating wave _ug is in the positive half cycle, the first switching transistor _T1 and the sixth switching transistor _T6 operate synchronously at high frequency, the second switching transistor _T2 and the third switching transistor _T3 are normally closed, and the fourth switching transistor T ₄ is complementary to the first switching transistor _T1 , and the fifth switching transistor _T5 is normally open; when the modulation wave u _g is in the negative half cycle, the first switching transistor _T1 and the sixth switching transistor _T6 are normally closed, and the second switching transistor _T2 and the third switching transistor _T3 synchronously operate at high frequency, the fourth switching transistor _T4 is always on, and the fifth switching transistor _T5 is turned on complementary to the second switching transistor _T2 .

Referring to accompanying drawings 4a-4j, the inverter of the present invention mainly has 10 working modes during the whole working process. Among them: in working mode 1, the current flows through the first switching transistor T ₁ , the fifth switching transistor T ₅ and the sixth switching transistor T ₆ , and the inverter outputs a positive voltage; in working mode 2, the current flows through the fifth switching transistor T 6 The switching transistor T ₅ , the second freewheeling diode D ₈ , and the inverter output zero level; in the working mode 3, the current flows through the sixth anti-parallel diode D ₆ , the fifth anti-parallel diode D ₅ and the first anti-parallel diode Diode D ₁ , the inverter outputs a positive voltage; in working mode 4, the current flows through the first freewheeling diode D ₇ and the fourth switching transistor T ₄ , the inverter outputs zero level; in working mode 5, the current Flowing through the third switching transistor T ₃ , the fourth switching transistor T ₄ and the second switching transistor T ₂ , the inverter outputs a negative voltage; in working mode 6, the current flows through the first freewheeling diode D ₇ and the fourth switching transistor D 7 Transistor T ₄ , the inverter outputs zero level; in working mode 7, the current flows through the second switching transistor T ₂ , the fourth anti-parallel diode D ₄ and the third anti-parallel diode D ₃ , and the inverter outputs a negative voltage ; In working mode 8, the current flows through the fifth switching transistor T ₅ and the second freewheeling diode D ₈ , and the inverter outputs zero voltage. In working mode 9, the current flows through the sixth anti-parallel diode D ₆ , the fifth anti-parallel diode D ₅ , and the first anti-parallel diode D ₁ , and the inverter outputs a positive level. In working mode 10, the current flows through the second anti-parallel diode D ₂ , the fourth anti-parallel diode D ₄ , and the third anti-parallel diode D ₃ , and the inverter outputs a negative level. In working mode 2, working mode 4, working mode 6 and working mode 8, the first switching transistor _T1 and the first inverter diode _D1 are both in the off state, and the second switching transistor _T2 and the second inverter Both the parallel diode _D2 are in the off state, the third switching transistor _T3 and the third anti-parallel diode _D3 are both in the off state, the sixth switching transistor _T6 and the sixth anti-parallel diode _D6 Both are in the off state, so that the output AC side of the inverter and the input DC side are in a decoupling state, thereby ensuring that the output of the inverter has no common-mode leakage current.

The power switch described in this embodiment can be composed of a switching transistor with an internal anti-parallel diode, or can be composed of an independent switching transistor and an independent diode in anti-parallel connection; the freewheeling diode is an independent diode, or it is an internal A switching transistor with an anti-parallel diode; the switching transistor can be a fully-controlled power semiconductor device such as a power metal oxide silicon field effect transistor or an insulated bipolar transistor; the anti-parallel diode is an independent diode or an internal self-automatic with a diode; the filter F is an inductance filter, and can also be replaced by an inductance-capacitance filter or an inductance-capacitance-inductance filter; the transformerless inverter structure described in this embodiment is suitable for both It is also suitable for grid-connected inverters and independent inverter structures or other transformerless inverters.

Claims (7)

1. A single-phase three-level inverter, comprising an input capacitor (C _dc ), a first power switch (S ₁ ), a second power switch (S ₂ ), a third power switch (S ₃ ), a fourth Power switch (S ₄ ), fifth power switch (S ₅ ), sixth power switch (S ₆ ), first freewheeling diode (D ₇ ), second freewheeling diode (D ₈ ) and filter (F) ; The drain of the first power switch (S ₁ ), the drain of the third power switch (S ₃ ), and the positive terminal of the input capacitor (C _dc ) are connected to the positive terminal of the input DC terminal; the positive terminal of the first power switch (S ₁ ) The source, the drain of the second power switch (S ₂ ), the anode of the first freewheeling diode (D ₇ ), and the cathode of the second freewheeling diode (D ₈ ) are connected to the first input terminal of the filter (F) ; The source of the second power switch (S ₂ ), the source of the sixth power switch (S ₆ ), and the negative terminal of the input capacitor (C _dc ) are connected to the negative terminal of the input DC terminal; the third power switch (S ₃ ) The source, the cathode of the first freewheeling diode (D ₇ ) are connected to the drain of the fourth power switch (S ₄ ); the drain of the sixth power switch (S ₆ ), the second freewheeling diode (D ₈ ) The anode is connected to the source of the fifth power switch (S ₅ ); the source of the fourth power switch (S ₄ ) and the drain of the fifth power switch (S ₅ ) are connected to the second input terminal of the filter (F) ; by supplying the first power switch (S ₁ ), the second power switch (S ₂ ), the third power switch (S ₃ ), the fourth power switch (S ₄ ), the fifth power switch (S ₅ ) and the sixth The control terminal of the power switch (S ₆ ) inputs a pulse width modulation signal, and the inverter converts the input DC power into AC power. 2. The single-phase three-level inverter according to claim 1, characterized in that: the power switch is composed of a switching transistor and an anti-parallel diode in anti-parallel connection, and the drain or collector of the switching transistor and the anti-parallel diode The cathode is connected to form the drain of the power switch, and the source or emitter of the switching transistor is connected to the anode of the anti-parallel diode to form the source of the power switch. 3. The single-phase three-level inverter according to claim 1, characterized in that: the first freewheeling diode (D ₇ ) and the first freewheeling diode (D ₈ ) are independent diodes, or Switching transistor with anti-parallel diode. 4. The single-phase three-level inverter according to claim 1, characterized in that: said input capacitor (C _dc ) is a capacitor or a capacitor combination composed of multiple capacitors connected in series and parallel. 5. The single-phase three-level inverter according to claim 1, characterized in that: the filter (F) is a single inductance filter, an inductance-capacitor filter or an inductance-capacitor-inductance type filter. 6 . The single-phase three-level inverter according to claim 2 , wherein the switching transistor is a high voltage metal oxide silicon field effect transistor or an insulated bipolar transistor. 7. The single-phase three-level inverter according to claim 2, wherein the anti-parallel diode is an independent diode or an internal anti-parallel diode of the switching transistor.

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