CN104578859B - Voltage-sharing controlling method for direct current bus voltage of single-phase power electronic transformer - Google Patents

Abstract

The invention discloses a single-phase power electronic transformer DC bus voltage equalization control method. The power main circuit of the single-phase DC-AC power electronic transformer is composed of an isolation stage and an inverter stage, wherein the isolation stage is a high-frequency isolation type DC-DC converter, the inverter stage is a DC-AC inverter; the input terminals of all DC-DC converters in the isolation stage are connected in series with medium-voltage or high-voltage DC voltage sources, and the output terminals are connected with the corresponding inverter stage DC-AC inverter The DC input terminal of the transformer; the AC side of all DC-AC inverters of the inverter stage is connected to the output filter in series; the control method includes the following steps: Step 1, the DC source side bus voltage equalization control of the power electronic transformer; Step 2, power electronic transformer isolation stage output side bus voltage equalization control. The control method of the invention can realize the voltage equalization control among the cascaded modules of the cascaded single-phase power electronic transformer, and the method is simple. The simulation results verify the correctness and reliability of the method, which provides a good reference value for engineering applications.

Description

A single-phase power electronic transformer DC bus voltage equalization control method

Technical field:

The invention relates to the application of power electronics technology in power systems, in particular to a voltage equalization control method for DC bus bars of single-phase power electronic transformers.

Background technique:

Traditional power transformers are simple in structure, high in efficiency and high in reliability, and are widely used in power systems. However, the low operating frequency makes the traditional transformer bulky and heavy, and the use of mineral oil, epoxy resin, and flame retardant oil as insulation or cooling medium has potential hidden dangers of fire and environmental pollution. In addition, it can usually only achieve relatively single functions such as electrical isolation, voltage level conversion, and bidirectional power transfer, but has no functions such as grid-side power quality adjustment, harmonic transfer isolation, overload and fault protection, and load voltage regulation. These weaknesses of traditional transformers make it unable to meet the functional requirements of some new applications such as smart grid. In view of the above-mentioned weaknesses of traditional transformers, researchers and engineers have proposed power electronic transformers (Power Electronic Transformers) or solid-state transformers (Solid-State Transformers) to solve them.

In the past few decades, power electronics technology has developed rapidly and comprehensively, and more and more power electronic devices have been applied in power systems. However, the voltage level of the single transistor or power module of the current commercialized power electronic power device cannot meet the application of the medium and high voltage level, and the module cascading of the low voltage level is usually used to solve the problem. Because there are problems such as parameter mismatch and different losses among the cascaded modules, the entire cascaded system cannot work normally. Therefore, the cascaded structure needs to use a certain control strategy to realize the voltage equalization control between the DC bus voltages.

Invention content:

The object of the present invention is to provide a DC bus voltage equalization control method for a single-phase power electronic transformer to solve the problem of unbalanced DC bus voltage in the existing cascaded modules.

In order to achieve the above object, the present invention adopts following technical scheme to realize:

A single-phase power electronic transformer DC bus voltage equalization control method, the power main circuit of the single-phase DC-AC power electronic transformer is composed of an isolation stage and an inverter stage, wherein the isolation stage is a high-frequency isolation type DC-DC conversion The inverter, the inverter stage is a DC-AC inverter; the input terminals of all DC-DC converters in the isolation stage are connected in series with medium-voltage or high-voltage DC voltage sources, and the output terminals are connected with the DC voltage of the corresponding inverter stage DC-AC inverter. The input terminal; all DC-AC inverter AC sides of the inverter stage are connected in series with the output filter; the control method includes the following steps: power electronic transformer DC source side bus voltage equalization control and power electronic transformer isolation stage output side Bus voltage equalization control.

The further improvement of the present invention is that: the DC source side bus voltage equalization control of the power electronic transformer specifically includes the following implementation steps:

Step 1.1, detect the DC side voltage V _{dc_11} , V _{dc_12} , ..., V _{dc_1i} of each DC-DC converter on the input side of the isolation stage of the power electronic transformer, and calculate the average value V _1ave of the n DC side voltages as step 1.2 The reference value of voltage equalization on the DC side, where, i=1,2,…,n;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; ave</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; i</span>}}$

In step 1.2, compare the DC side voltage value V _{dc_1i} of each module measured in step 1.1 with the average value V _1ave of the DC side voltage obtained in step 1.1, and obtain each DC- Instructions for DC side voltage equalization of DC converters

Step 1.3, detecting the DC side voltages V _{dc_21} , V _{dc_22} , ..., V _{dc_2i} on the output side of the isolation stage of the power electronic transformer, and calculating the average value V _2ave of the n DC side voltages;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; ave</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; i</span>}}$

Step 1.4, compare the average value V _2ave of the DC voltage on the output side of the isolation stage obtained in step 1.3 with the reference value V ^* _{dc_2ref} of the DC voltage on the output side of the isolation stage, and obtain the DC voltage on the output side of the isolation stage after the output passes through the proportional integral regulator mean command

In step 1.5, the instruction for equalizing the DC voltage on the input side of each isolation stage DC-DC converter obtained in step 1.2 Add the instruction of the average value of DC voltage on the output side of the isolation stage obtained in step 1.4 to synthesize the final instructions for each isolated DC-DC converter

The further improvement of the present invention is that: the bus voltage equalization control on the output side of the power electronic transformer isolation stage specifically includes the following implementation steps:

Step 2.1, regardless of whether the power electronic transformer is connected to the load or the power grid, the current loop output of the conventional double-loop control is the general control command u ^* _m of the inverter stage, and the system output current i _L is also detected;

Step 2.2, compare the DC voltage value V _{dc_1i} at the output side of each module of the isolation level measured in step 1.3 with the obtained DC voltage average value V _2ave , and its output is the same as the system output current in step 2.1 after passing through the proportional regulator i _L is multiplied by the total control command u ^* _m of the inverter stage to obtain the command Δu _{m_1} , Δu _{m_2} , ..., Δu _{m_i} of each DC side voltage equalization;

In step 2.3, add the instruction _{Δum_1} , _{Δum_2} , ..., _{Δum_i} obtained in step 2.2 to the total control instruction u ^* _m of the inverter stage in step 2.1 to obtain each inverter stage Instruction values u _{m_1} , u _{m_2} , . . . , u _{m_i} of the module.

Compared with the prior art, the beneficial technical effect of the present invention is:

The present invention utilizes the control system of the isolation level DC-DC converter to realize the control of DC voltage equalization control on the input side of the isolation level and the average value tracking reference voltage of the DC voltage on the output side of the isolation level, and realizes the control system by using the control system of the inverter level DC-AC converter DC voltage equalization control on the output side of the isolation stage.

The control method of the invention can realize the voltage equalization control among the cascaded modules of the cascaded single-phase power electronic transformer, and the method is simple. The simulation results verify the correctness and reliability of the method, which provides a good reference value for engineering applications.

Description of drawings:

Figure 1 is a topology diagram of the main circuit of a single-phase multi-module cascaded DC-AC power electronic transformer;

Fig. 2 is a control block diagram of the DC voltage equalization control part on the input side of the isolation stage;

Fig. 3 is a control block diagram of the overall control of the isolation stage combined with DC voltage equalization control on the input side and DC voltage average control on the output side of the isolation stage;

Fig. 4 is a control block diagram for the inverter stage to realize DC voltage equalization control on the output side of the isolation stage.

Figure 5 is a simulation waveform diagram of the DC voltage at the input side of the isolation stage.

Fig. 6 is a simulation waveform diagram of the DC voltage at the output side of the isolation stage.

detailed description:

Referring to Fig. 1, the power main circuit of the single-phase power electronic transformer system applied in the present invention is composed of an isolation stage and an inverter stage: the isolation stage is a high-frequency isolated DC-DC converter, and the inverter stage is a DC-AC inverter device. In order to meet the requirements of the medium voltage or high voltage level, the input terminals of all DC-DC converters of the isolation stage are connected in series with the medium voltage or high voltage DC voltage source V _dc , and the output terminals are connected to the DC input of the corresponding inverter stage DC-AC inverter end. All the AC sides of the DC-AC inverters in the inverter stage are connected to the output filter in series.

The realization process of a single-phase power electronic transformer DC bus voltage equalization control method of the present invention includes the following steps: power electronic transformer DC source side bus voltage equalization control and power electronic transformer isolation stage output side bus voltage equalization control.

Among them, the power electronic transformer DC source side bus voltage equalization control specifically includes the following implementation steps:

Step 1.1, referring to Figure 1, detect the DC side voltage V _{dc_11} , V _{dc_12} , ..., V _{dc_1i} (i=1,2,..., n), and obtain the average value _V1ave of these n dc side voltages as the dc side voltage equalization reference value in step 1.2;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; ave</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; i</span>}}$

Step 1.2, compare the DC side voltage value V _{dc_1i} (i=1,2,…,n) of each module measured in step 1.1 with the obtained DC side voltage average value V _1ave , and the output is proportionally integrated After the regulator, obtain the instruction of DC side voltage equalization of each DC-DC converter (i=1,2,...,n). The control block diagram of the DC voltage equalization control part on the input side of the isolation stage is shown in Figure 2;

Step 1.3, detect the DC side voltage V _{dc_21} , V _{dc_22} , ..., V _{dc_2i} (i=1,2,...,n) of the output side of the isolation stage of the power electronic transformer, and calculate the average value V of the n DC side voltages _2ave ;

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; ave</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; i</span>}}$

Step 1.4, compare the average value V _2ave of the DC voltage on the output side of the isolation stage obtained in step 1.3 with the reference value V ^* _{dc_2ref} of the DC voltage on the output side of the isolation stage, and obtain the DC voltage on the output side of the isolation stage after the output passes through the proportional integral regulator mean command ;

In step 1.5, the instruction for equalizing the DC voltage on the input side of each isolation stage DC-DC converter obtained in step 1.2 (i=1,2,...,n) plus the instruction of the average value of DC voltage on the output side of the isolation stage obtained in step 1.4 to synthesize the final instructions for each isolated DC-DC converter (i=1,2,...,n); the control block diagram of the overall control of the isolation stage combined with the DC voltage equalization control on the input side of the isolation stage and the average value control of the DC voltage on the output side is shown in Figure 3 .

The bus voltage equalization control on the output side of the power electronic transformer isolation stage specifically includes the following implementation steps:

Step 2.1, regardless of whether the power electronic transformer is connected to the load or the grid, the current loop output of the conventional double-loop control is the general control command u ^* _m of the inverter stage, and the system output current i _L is also detected (see Figure 1);

Step 2.2, compare the DC voltage value V _{dc_1i} (i=1,2,…,n) of the output side of each module of the isolation stage measured in step 1.3 with the calculated DC voltage average value V _2ave , and its output is passed through After the proportional regulator is multiplied with the system output current i _L in step 2.1 and the total control command u ^* _m of the inverter stage to obtain the command Δu _{m_1} , Δu _{m_2} , ..., Δu _{m_i} (i=1 ,2,...,n);

Step 2.3, combine the instruction _{Δum_1} , _{Δum_2} , _{Δum_i} (i=1,2,…,n) obtained in step 2.2 for each DC side voltage equalization with the total control instruction u of the inverter stage in step 2.1 ^* _{Add m} to get the instruction value u _{m_1} , u _{m_2} ,..., u _{m_i} (i=1,2,...,n) of each module of the inverter stage. The control block diagram of the inverter stage to realize the DC voltage equalization control on the output side of the isolation stage is shown in Fig. 4 .

In order to verify the effect of the present invention, we have set up a model with 9 H-bridge converters according to the circuit shown in Figure 1 through Matlab/Simulink, wherein the leakage inductance value of each DAB in the middle has a difference of 10%, and each DC side There is a 50% difference in equivalent loss resistance values for parallel connections. As shown in Figure 5 and Figure 6, Figure 5 is a simulation waveform diagram of the DC voltage at the input side of the isolation stage, and Figure 6 is a simulation waveform diagram of the DC voltage at the output side of the isolation stage. At 0.25s, when the control method of the present invention is cut off, the DC side voltage of the system immediately begins to be unbalanced. At 0.28s, the control method of the present invention is re-introduced, and after a certain period of dynamic adjustment, the DC voltage of the system The final balance has verified the effectiveness of the present invention.

Claims (2)

1. a kind of Monophase electric power electronic transformer DC bus-bar voltage pressure equalizing control method it is characterised in that: this Monophase electric power electricity The power main circuit of sub- transformator is made up of isolation level and inverse cascade, and wherein, isolation level is high-frequency isolation type dc-dc changer, Inverse cascade is dc-ac inverter；The input series connection medium-pressure or high pressure DC voltage of all dc-dc changers of isolation level Source, the direct-flow input end of the corresponding inverse cascade dc-ac inverter of output termination；All dc-ac inverter ac sides of inverse cascade are adopted Connect output filter with series system；This control method comprises the following steps: Monophase electric power electronic transformer DC source side bus Voltage Pressure and Control and the output side bus voltage Pressure and Control of Monophase electric power electronic transformer isolation level；

Wherein, Monophase electric power electronic transformer DC source side bus voltage Pressure and Control specifically include following step of realizing:

Step 1.1, detects each dc-dc changer DC voltage v of Monophase electric power electronic transformer isolation level input side_{dc_11}、 v_{dc_12}、…、v_{dc_1i}, and obtain meansigma methodss v of this n DC voltage_1aveReference is all pressed using the DC side as in step 1.2 Value, wherein, i=1,2 ..., n；

$v_{1ave}=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\&sigma;}}}{v}_{dc\_1i}$

Step 1.2, by each module DC voltage value v in step 1.1 measured_{dc_1i}With the direct current obtained in step 1.1 Side average voltage v_1aveCompare, its output obtains each dc-dc changer DC side electricity after proportional and integral controller The instruction of pressure all pressures

Step 1.3, the DC voltage v of detection Monophase electric power electronic transformer isolation level outlet side_{dc_21}、v_{dc_22}、…、v_{dc_2i}, And obtain meansigma methodss v of this n DC voltage_2ave；

$v_{2ave}=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\&sigma;}}}{v}_{dc\_2i}$

Step 1.4, meansigma methodss v of the isolation level outlet side DC voltage that step 1.3 is tried to achieve_2aveWith isolation level outlet side direct current Voltage reference value v^* _{dc_2ref}Compare, it is average that its output obtains isolation level outlet side DC voltage after proportional and integral controller The instruction of value

Step 1.5, by the instruction of each isolation level obtaining in step 1.2 dc-dc changer input side DC voltage all pressuresInstruction plus the isolation level outlet side DC voltage average value obtaining in step 1.4Thus Synthesize the final instruction of each isolation level dc-dc changer

2. a kind of Monophase electric power electronic transformer DC bus-bar voltage pressure equalizing control method according to claim 1, it is special Levy and be: the output side bus voltage Pressure and Control of Monophase electric power electronic transformer isolation level specifically include following step of realizing:

Step 2.1, no matter the connection of Monophase electric power electronic transformer is load or electrical network, using its electricity of conventional double -loop control Stream ring is output as total control instruction u of inverse cascade^* _m, in addition detect and obtain system output current i_l；

Step 2.2, by each module outlet side DC voltage value v of measured isolation level in step 1.3_{dc_1i}With the direct current obtained Average voltage v_2aveCompare, its output is after proportional controller with system output current i in step 2.1_lTotal with inverse cascade Control instruction u^* _mIt is multiplied and obtain the instruction δ u of each DC voltage all pressures_{m_1}、δu_{m_2}、…、δu_{m_i}；

Step 2.3, by the instruction δ u of each DC voltage all pressures obtaining in step 2.2_{m_1}、δu_{m_2}、…、δu_{m_i}Synchronous Total control instruction u of inverse cascade in rapid 2.1^* _mIt is added command value u obtaining each module of inverse cascade_{m_1}、u_{m_2}、…、u_{m_i}.