CN204031005U - The T-shaped inverter of a kind of Z source three level - Google Patents

Abstract

The utility model relates to a Z-source three-level T-type inverter. The topology has the same boosting characteristics as a Z-source network three-level neutral point clamp (NPC) inverter, but the number of switching devices used is less. Higher efficiency. Compared with the three-level T-type inverter, the topology of the utility model can not only realize the step-up/down function, but also allow the upper and lower bridge arms to pass through, the reliability is obviously increased, the dead time is eliminated, and the waveform distortion is prevented; and Compared with the Z-source two-level inverter, the output voltage has a mid-point potential, so the high-frequency harmonics are small, and the required filter is small. Since the three-level is closer to the sine wave than the two-level, the switching frequency can be reduced, and the switching loss is small; it uses the same phase voltage offset (phase disposition, PD) method to control the inverter, and the same method can reduce the switching times, reduce the switching loss, and reduce the harmonic content of the output voltage.

Description

A Z-source three-level T-type inverter

technical field

The utility model relates to a Z-source three-level T-type inverter.

Background technique

With the rapid development of distributed power and the continuous improvement of efficiency requirements, improving power quality, reducing harmonic pollution, and improving the efficiency of power generation systems are key issues in the development of distributed power. Compared with the traditional two-level inverter, the three-level inverter has the advantages of less harmonics, high withstand voltage, small switch stress, and less electromagnetic interference (Electro Magnetic Interference, EMI). fields are widely used. However, the output voltage of distributed power sources such as fuel cells and photovoltaic cells is not constant, and it is impossible to realize the conversion function of a wide DC voltage range and obtain a higher AC output voltage. In order to meet the wide voltage range of the DC bus, the researchers added a DC/DC converter, that is, a two-stage structure. However, this converter not only requires more power devices, but also generates a large amount of switching loss during operation, which reduces system efficiency. In order to reduce the influence of the switching loss caused by the DC/DC converter on the system efficiency, a two-level inverter using a Z-source network is an ideal choice.

Z-source two-level inverters are widely used in new energy fields such as photovoltaic inverters, energy storage, electric vehicles, and fuel cells. However, with the rapid development of distributed power generation, the requirements for improving power quality and power level have attracted much attention. Z source multilevel inverter can solve the above problems. The Z-source three-level neutral point clamped (NPC) inverter is widely used in photovoltaic inverters, wind power generators, fuel cells and other renewable energy sources. It consists of an independent DC power supply, two It consists of a DC side voltage dividing capacitor, a Z source network and a three-level NPC inverter circuit. The introduction of the Z-source network makes the through-through a normal working state. By controlling the through-duty ratio, the Z-source three-level NPC inverter can realize the boost function, and there is no need to control the dead time to prevent inverter waveform distortion. The direct connection of the bridge arm will not cause damage to the power device, and the reliability will be significantly increased. Therefore, the Z-source three-level NPC inverter has obvious advantages over the traditional three-level NPC inverter, and has a very broad prospect. However, the Z-source three-level NPC inverter requires too many passive components, which will generate a large amount of power loss, which will result in low system efficiency. Efficiency and power quality are the guarantees for reliable, stable and economical operation of renewable energy and microgrids. Therefore, it is very important to study a topology with optimal efficiency and power quality. For three-level T-type inverters, the efficiency and power quality are better than those of Z-source three-level NPC and Z-source two-level inverters, but for the output voltage of distributed power sources such as fuel cells and photovoltaic cells The output is not constant, a wide output voltage cannot be achieved, and the harmonics are very large due to the dead zone.

Utility model content

In order to solve the above problems, the utility model proposes a Z-source three-level T-type inverter, which adopts the control mode of the same phase voltage offset (phase disposition, PD), compared with the reverse phase voltage offset modulation (alternative phase Oppositiondisposition, APOD) method, can reduce the switching times, reduce the switching loss.

In order to achieve the above object, the utility model adopts the following technical solutions:

A Z-source three-level T-type inverter, including three-phase bridge arms connected in parallel, each phase bridge arm includes two series-connected IGBT tubes, and two IGBT tubes in different directions are connected in series on one side of the midpoint of each phase bridge arm , the other side is connected to the resistor through the filter; the input terminal of each bridge arm connected in parallel is connected to the Z source network and then connected to the input voltage source; The two directions of the bridge arm are different from one end of the IGBT tube, and each IGBT tube is driven by the control circuit.

The Z source network includes two inductors and capacitors, the two inductors are respectively connected in series at the connection between the two ends of the input voltage source and the three-phase bridge arm, a diode is connected in series at the connection side of the inductor and the input voltage source, and the two diodes are reversed , one end of the two capacitors is respectively connected to the junction of the diode and the inductor, and the other end is connected to the junction of another inductor and the three-phase bridge arm.

The filter is an LC filter circuit, and the common terminal of the capacitor is grounded.

The control circuit includes a protection circuit, a drive circuit, and a sampling conditioning circuit. The sampling conditioning circuit is connected to a DSP module, and the DSP module communicates with the protection circuit bidirectionally. off.

The sampling conditioning circuit collects the DC voltage and DC current of the input voltage source, the capacitor voltage of the Z source network, and the three-phase voltage value output by the filter.

The beneficial effects of the utility model are:

1. Compared with the three-level T-type inverter, the Z-source three-level T-type inverter can not only achieve boosting, but also because the direct connection will not cause damage to the power device, the reliability is significantly increased, and the dead time is eliminated. Prevent waveform distortion;

2. Compared with the Z-source two-level inverter, the output voltage of the Z-source three-level T-type inverter has a midpoint potential, so the high-frequency harmonics are small, and the required filter is small. The level is closer to the sine wave than the two levels, so the switching frequency can be reduced and the switching loss is small;

3. Compared with the Z-source three-level NPC inverter, the Z-source three-level T-type inverter reduces the number of components, has lower conduction loss and higher efficiency;

4. It has the advantages of high power and good waveform quality, and has broad prospects in the fields of photovoltaic power generation systems, wind power generation systems, fuel cells and other renewable energy.

Description of drawings

Figure 1 is a structural diagram of a three-level T-type inverter;

Figure 2 shows the modulation wave and carrier waveform of the three-level T-type inverter;

Figure 3a is a working principle diagram of a state of the three-level T-type inverter;

Figure 3b is a working principle diagram of a state of the three-level T-type inverter;

Fig. 3c is a working schematic diagram of a state of the three-level T-type inverter;

Fig. 4 is a structural diagram of the utility model system;

Figure 5a is an equivalent circuit diagram of a Z-source three-level T-type inverter in a non-through state;

Figure 5b is an equivalent circuit diagram of the Z-source three-level T-type inverter in the upper straight-through state;

Fig. 5c is an equivalent circuit diagram of the Z-source three-level T-type inverter in the lower straight-through state;

Fig. 5d is an equivalent circuit diagram of a Z-source three-level T-type inverter in a full direct-through state.

Figure 6a shows the boost and inverter control of the Z-source three-level T-type inverter by using the alternative phase opposition disposition (APOD-SPWM) method;

Fig. 6b is a phase disposition (phase disposition, PD-SPWM) control method to realize Z-source three-level T-type inverter boost and inversion control;

Figure 7 shows the operating waveforms of the Z-source three-level T-type inverter in the case of through-through and non-through-through;

Figure 8 is the operating waveform of the Z-source three-level T-type inverter under the conditions of full direct connection and upper and lower direct connection;

Figure 9 shows the operating waveforms of the Z-source three-level T-type inverter and the Z-source three-level NPC inverter in the case of non-straight-through and upper-lower direct-through;

Figure 10 is a structural diagram of a Z-source three-level NPC inverter;

Figure 11 is a control circuit diagram of a Z-source T-type inverter.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is described further.

Figure 1 is a structural diagram of a three-level T-type inverter. The main circuit is a three-level T-type inverter, the input voltage is connected to a capacitor, the midpoint of the capacitor on the DC side is connected to the IGBT tube 3, and the filter is an LC filter. The system output is connected to the load.

For the three-level T-type inverter, the APOD-SPWM method will make the final output voltage contain a large number of harmonics, which will affect the waveform quality of the output voltage. The use of PD-SPWM to control the PWM output can improve the quality of the voltage waveform. Therefore, the utility model adopts the method of PD-SPWM to realize the control of the three-level T-type inverter.

The signal conditioning circuit conditions the relevant signals measured by the Hall sensor to obtain an analog signal that the sampling circuit can receive. The sampling and conversion of AD converter is controlled by DSP, which converts the adjusted analog signal into digital quantity. Digital signal processing, SPWM control, and PWM generation are all realized by DSP, and the finally generated PWM signal is sent to the driving circuit to control the opening and closing of the IGBT tube.

Figure 2 is the SPWM modulation wave and carrier waveform, and Figure 3 is the structure and circuit schematic diagram of the inverter part of the three-level T-type inverter. The specific control methods are as follows:

The modulating wave is a three-phase sine wave, namely

u _a = sinωt

u _b = sin(ωt-120°)

u _c = sin(ωt-240°);

The carrier wave is a triangle wave with a phase difference of 180°.

Taking phase a as an example, assuming that the current flowing to the right is positive, the switching sequence is generated as follows:

If Ua>CA1 and Ua>CA2, then the switching sequence (Ua1, Ua2, Ua3, Ua4)=(1,1,0,0)=P. It can be seen from Figure 3a that when i>0, when Ua1 is turned on, although Ua2 is turned on, no current flows through Ua2, and Ua3 and Ua4 are turned off. When i<0, Ua1, Ua2, Ua3, Ua4 are turned off. At this time Ua0=Vin/2.

If Ua<CA1 and Ua<CA2, then the switching sequence (Ua1, Ua2, Ua3, Ua4)=(0,0,1,1)=N. It can be seen from Figure 3c that when i<0, Ua4 is turned on, although Ua3 is turned on, but no current flows through Ua3, and Ua,1, Ua2 are turned off. When i>0, Ua1, Ua2, Ua3, Ua4 are turned off. So Ua0=-Vin/2.

If Ua<CA1 and Ua>CA2, then the switching sequence (Ua1, Ua2, Ua3, Ua4)=(0,1,1,0)=0. It can be seen from Figure 3b that when i>0, Ua2 is turned on, and Ua1, Ua3, and Ua4 are turned off. Therefore Ua0=0.

If Ua<CA1 and Ua>CA2, then the switching sequence (Ua1, Ua2, Ua3, Ua4)=(0,1,1,0)=0. It can be seen from Figure 3b that when i<0, Ua3 is turned on, and Ua1, Ua2, and Ua4 are turned off. Therefore Ua0=0.

As shown in Figure 4, each bridge arm includes two IGBT tubes connected in series. The left side of the midpoint of each phase bridge arm is connected to two IGBT tubes in opposite directions, and the right side of the midpoint of each phase bridge arm is connected to the corresponding IGBT tube through a filter. Resistor connection; a pair of capacitors C1 and C2 in series are connected in parallel at the input ends of each bridge arm in parallel, the left side of capacitor C1 and capacitor C2 is connected to the input voltage; the right side of capacitor C1 and capacitor C2 is connected to the Z source network, The two opposite IGBT tubes of each bridge arm are connected to the midpoint of the capacitors C1 and C2. Figure 5a is the equivalent circuit diagram of the Z-source three-level T-type inverter in the non-through state; Figure 5b is the equivalent circuit diagram of the Z-source three-level T-type inverter in the up-through state; Figure 5c is the Z-source three-level inverter The equivalent circuit diagram of the level T-type inverter in the lower through state; Figure 5d is the equivalent circuit diagram of the Z-source three-level T-type inverter in the full through state. It can be seen from the derivation of the formula that when the boost factor B=1, the Z-source three-level T-type inverter works in the traditional buck mode; when the boost factor B>1, it works in the boost mode.

Figure 6a shows the APOD-SPWM modulation method of the traditional inverter and the Z-source cascaded inverter; the boost control of the Z-source three-level T-type inverter needs to add an additional through state, and the addition of the through state cannot change the inverter The normal inversion of the inverter, so it needs to be added to the inactive state {O, O, O}, this state can increase the output voltage, but has no effect on the output load of the inverter. In order to obtain the through state of T0', it is necessary to translate T0'/T in the vertical direction of the modulating wave, and obtain the through time in the horizontal direction. At any time, increase the vertical offset of T0'/T to Umax (the maximum value among Ua, Ub, Uc) of the modulation signal, and decrease T0' to Umin (the minimum value among Ua, Ub, Uc) of the modulation signal /T vertical offset, while keeping Umid (the middle value among Ua, Ub, Uc) of the modulating signal unchanged. Thus, the direct duty cycle required by the Z-source three-level T-type inverter is obtained.

Figure 6b shows the PD-SPWM modulation method of the traditional inverter and the Z-source cascaded inverter; compared with the APOD-SPWM modulation method, the output voltage that can be obtained by the PD-SPWM modulation method. For the Z-source three-level T-type inverter, the injection of the through state cannot affect the output voltage of the bridge arm. For the same-phase voltage offset control, the {O, O, O} state cannot produce full through, so only the upper through and lower through, and the upper and lower through can only be produced in the equivalent zero vector. Wherein, the {O, O, O} state means that the IGBT tubes of the three-phase bridge arms connected in parallel are all in the {O} state. The turn-on signals of the four IGBT tubes in the state of {O} are (0,1,1,0) respectively; the turn-on signals of the four IGBT tubes in the state of {N} are respectively: (0,0,1,1); The conduction signals of the four IGBT tubes in the state of {P} are (1,1,0,0) respectively.

The up-through can only occur within the action time of the equivalent vectors of the {O} and {N} states, and the down-through can only occur within the action time of the equivalent vectors of the {O} and {P} states, and the state transition of the selection switch is the least At any time, for Umax of the modulation signal, that is, the maximum value of Ua, Ub, and Uc, the vertical offset of 0.5T0/T is added to generate an upper pass-through, and at the same time, Umin, Ua, Ub of the modulation signal , the minimum value in Uc, reduce the vertical offset of 0.5T0/T to produce a lower pass-through, keep the Umid, Ua, Ub, and Uc of the modulation signal unchanged, and obtain the Z-source three-level T-type inverter The required straight-through duty cycle, and finally the obtained PWM signal is sent to the drive circuit.

Fig. 7 is the waveform of the through time T0=0 and T0=0.2 under the control of the PD-SPWM method. When the through time T0 = 0, the modulation degree M is set to 0.8. In the figure, the phase voltage, phase current, line voltage, Z source network capacitor voltage, and Vdc voltage are output in sequence. The Z-source three-level T-type inverter has no boost, so the peak value of the line voltage is equal to 200V. When the through time T0=0.2, it can be seen from the formula that the boost factor B=1.66, so the theoretical phase voltage value is 159*1.66/1.732=151V, and the actual measured value is 140V. From the formula, the theoretical boost value Vdc is 332V, while the actual measured value is 324V. The current is not distorted by the through signal. The capacitance voltage of the Z source network can be obtained from the relevant formula as 266V, and the actual measured value is 265V. In addition, the Vdc voltage changes from 162V to 324V to realize the boost and inverter functions. The simulation results show that the Z-source three-level T-type inverter can increase the line voltage to the set value without affecting the waveform quality of the output current.

Figure 8 shows the influence of the APOD-SPWM method and the PD-SPWM method on the quality of the output voltage waveform. It is assumed that the APOD-SPWM method uses the same parameters as the PD-SPWM method. Under the APOD-SPWM method, the modulation degree M is set to 0.8, and the time T0' of the direct duty cycle is set to 0.2. In the PD-SPWM method, set the modulation degree M to 0.8, and the time T0 of the direct duty cycle to be 0.2. It can be seen from the simulation results that the PD-SPWM method has the advantages of small switching loss and harmonic distortion.

Figure 9 shows the simulation comparison of the Z-source three-level NPC inverter and the Z-source three-level T-type inverter using the PD-SPWM method. It can be seen from the figure and Table 1 that under the same modulation strategy, the Z-source three-level T-type inverter and the Z-source three-level NPC inverter have small harmonics and comparable waveform quality.

Table 1 Harmonic comparison under PD modulation strategy

Z source T-type inverter Z source NPC inverter through 0.63% 0.65% non-through 0.47% 0.49%

Fig. 10 is a structural diagram of a Z-source three-level NPC.

Figure 11 is a control circuit diagram of a Z-source T-type inverter; the control circuit includes a protection circuit, a drive circuit and a sampling conditioning circuit, and the sampling conditioning circuit includes DC voltage Vin, Z-source capacitor voltage Vzc, DC current Idc, and the output of the filter. Phase voltage Ua, Ub, Uc, signal conditioning circuit and control voltage have over/undervoltage protection and overcurrent protection; the drive circuit outputs PWM signal to drive the IGBT tube in the bridge arm to turn on and off.

Therefore, using the PD modulation strategy can realize the boost and inversion functions of the Z-source three-level T-type inverter, and compared with the Z-source three-level NPC inverter, the conduction loss is lower, the efficiency is high, and the waveform quality quite. The topology inverter has broad prospects in the fields of photovoltaic power generation systems, wind power generation systems, fuel cells and other renewable energy sources.

Although the specific implementation of the utility model has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the utility model. Those skilled in the art should understand that on the basis of the technical solution of the utility model, those skilled in the art do not need to Various modifications or deformations that can be made with creative efforts are still within the protection scope of the present utility model.

Claims (5)

1. the T-shaped inverter of Z source three level, is characterized in that: comprise three-phase brachium pontis in parallel, every phase brachium pontis comprises the IGBT pipe of two series connection, the different IGBT pipe of mid point one side series connection both direction of each phase brachium pontis, and opposite side is connected with resistance through filter; After connecting Z source network, each brachium pontis input of parallel connection accesses input voltage source; Input voltage source two ends are parallel with the electric capacity of two series connection, and two electric capacity junctions connect one end of the both direction different I GBT pipe of every brachium pontis, and each IGBT pipe drives by control circuit.

2. the T-shaped inverter of a kind of Z as claimed in claim 1 source three level, it is characterized in that: described Z source network comprises two inductance and electric capacity, two inductance are connected on respectively the junction of input voltage source two ends and three-phase brachium pontis, inductance is in series with diode with the side that is connected of input voltage source, and two diode reverse, one end of two electric capacity connects respectively the junction of diode and inductance, and the other end is connected to the junction of another road inductance and three-phase brachium pontis.

3. the T-shaped inverter of a kind of Z as claimed in claim 1 source three level, is characterized in that: described filter is LC filter circuit, and electric capacity common end grounding wherein.

4. the T-shaped inverter of a kind of Z as claimed in claim 1 source three level; it is characterized in that: described control circuit comprises protective circuit, drive circuit, sampling modulate circuit; sampling modulate circuit connects DSP module; DSP module and protective circuit two-way communication; DSP module connects drive circuit, and in drive circuit output pwm signal driving brachium pontis, IGBT pipe opening and turn-offing.

5. the T-shaped inverter of a kind of Z as claimed in claim 4 source three level, is characterized in that: the three-phase voltage value size of the direct voltage of described sampling modulate circuit Gather and input voltage source, direct current, Z source network capacitance voltage and filter output.