Electromagnetic and electronic hybrid on-load capacity-regulating and voltage-regulating transformer and control method

Abstract

The invention provides an electromagnetic and electronic hybrid on-load capacity-regulating and voltage-regulating transformer and a control method, the hybrid on-load capacity-regulating and voltage-regulating transformer comprises a three-phase circuit topological structure, and the three-phase circuit topological structure comprises a three-phase electromagnetic transformer and three single-phase power electronic converters; wherein each phase winding on the low-voltage side of the electromagnetic transformer comprises a section I wire turn and a section II wire turn; the I-section wire turn and the II-section wire turn of the electromagnetic transformer are isolated from each other; the input of the power electronic converter is connected in parallel with the output of the section II wire turn of the electromagnetic transformer; and the output of the power electronic converter and the output of the I-section wire turn of the electromagnetic transformer are connected in series to supply power to a load. According to the invention, a complex switching link can be directly omitted, and the capacity and the voltage are dynamically adjusted from the perspective of the output voltage of the low-voltage side of the transformer.

Description

Technical Field

[0001] The invention belongs to the technical field of AC voltage regulators, and in particular relates to an electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer and a control method thereof. Background Art

[0002] With the implementation of the national energy conservation and emission reduction policy, reducing the loss of each link in the power grid has always been a problem studied by power workers; transformers, as an important part of the power supply and distribution system, play a vital role in the power supply and distribution system of the power grid. At present, resources are unevenly distributed. The load in developed areas and industrial parks is high and the load changes little; while the load in residential areas and rural areas is low, and the daily load changes greatly, resulting in different losses of transformers when running at different capacities. When the daily load is at a low point, the transformer is almost close to no-load operation, resulting in transformer losses that are almost equal to no-load losses. Considering that it does not affect the daily life of residents, the capacity of distribution transformers in general residential areas and rural areas is relatively large; therefore, there will be a situation where a big horse pulls a small cart, and the performance of the transformer cannot be fully utilized; therefore, it is urgent to reduce the loss of distribution transformers in residential areas and rural areas.

[0003] Based on the above situation, many scholars have designed and modified the distribution transformer, using the capacity-adjusting transformer to achieve the purpose of reducing no-load voltage and load loss. Up to now, the capacity-adjusting transformer has been upgraded four times; the first upgraded capacity-adjusting transformer is: no-excitation capacity-adjusting and voltage-adjusting, the characteristics are: the equipment needs to be powered off, and the disadvantage is: it greatly affects the reliability of power supply. The second upgraded capacity-adjusting transformer is: on-load capacity-adjusting and no-excitation voltage-adjusting, the characteristics are: the voltage-adjusting process requires power outage and manual operation, the disadvantage is: it can only be applied to seasonal adjustment, it cannot meet the situation of large voltage fluctuations, and it will also affect the reliability of power supply. The third upgraded capacity-adjusting transformer is: automatic capacity-adjusting and automatic voltage-adjusting, the characteristics are: it can automatically detect and track the voltage offset and the size of the load, and automatically adjust the capacity and voltage. The disadvantage is: the number of taps for voltage regulation is small, and because of the need for short-term load shedding, it has a great impact on sensitive loads. The fourth upgraded capacity-adjusting transformer is: adaptive composite type, which has the following characteristics: the winding can change the connection method according to the change of voltage, and can track the change of load to change the connection method of the winding to automatically adjust the capacity, and also has the functions of load phase change and phase reactive power compensation. Currently, the most commonly used is the adaptive load type after the fourth upgrade. Although the adaptive load type capacity-adjusting transformer after the fourth upgrade can well achieve the purpose of capacity and voltage regulation; however, the design has a special design on the low-voltage side, which requires the introduction of data information acquisition system, comprehensive analysis and judgment system, output control system and other systems, which is costly and not suitable for full promotion.

[0004] If the fourth upgrade of the complex control system can be omitted, the cost can be reduced, and the automatic capacity and voltage regulation of the capacity-regulating transformer can be achieved, a capacity-regulating transformer with superior performance will be obtained.

[0005] Therefore, it is necessary to design an electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer and a control method to solve the above-mentioned technical problems. Summary of the invention

[0006] In view of the above problems, the present invention provides an electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer and a control method, comprising:

[0007] An electromagnetic-electronic hybrid on-load capacity-adjusting and voltage-regulating transformer, the hybrid on-load capacity-adjusting and voltage-regulating transformer comprising a three-phase circuit topology structure, the three-phase circuit topology structure comprising a three-phase electromagnetic transformer and three single-phase power electronic converters;

[0008] Each phase winding of the low-voltage side of the electromagnetic transformer includes a section I wire turn and a section II wire turn; the section I wire turn and the section II wire turn of the electromagnetic transformer are isolated from each other, wherein the number of the section I wire turns is greater than the number of the section II wire turns;

[0009] The input of the power electronic converter is connected in parallel with the output of the electromagnetic transformer section II turn; the output of the power electronic converter is connected in series with the output of the electromagnetic transformer section I turn to supply power to the load;

[0010] The total output voltage of the hybrid on-load capacity-regulating and voltage-regulating transformer is the sum of the output voltage of the power electronic converter and the output voltage of the turns of section I of the electromagnetic transformer.

[0011] Furthermore, the high-voltage side of the electromagnetic transformer is connected in a triangle at the first rated capacity, and in a star at the second rated capacity; the low-voltage side of the electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer can be connected in a star or a triangle, wherein the value of the first rated capacity is three times that of the second rated capacity.

[0012] Further, the power electronic converter includes a rectifier and an inverter;

[0013] Wherein, the rectifier includes inductors L1, L2, L3, power semiconductors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 and a DC capacitor C1;

[0014] The inverter includes power semiconductors Q9, Q 10 , Q 11 , Q 12 , filter inductor L f And filter capacitor C f ;

[0015] Specific connection method: L1, Q1 and Q2 form an interlaced phase, L2, Q3 and Q4, and L3, Q5 and Q6 all form an interlaced phase; Q1 and Q2, Q3 and Q4, Q5 and Q6 respectively form a pair of bridge arms with three interlaced phases, the midpoints of the corresponding upper and lower bridge arms are connected to the first stage of the corresponding inductor, the other pole of the corresponding inductor is connected to the positive pole of the input power supply, and the negative pole of the input power supply is connected to a bridge arm formed by Q7 and Q8; power semiconductors Q9, Q 10 , Q 11 , Q 12 The inverter bridge consists of power semiconductors Q9 and Q 11 The drain is connected to the positive electrode of the DC capacitor C1, and the power semiconductor Q 10 , Q 12 The source is connected to the negative electrode of the DC capacitor C1; the source of the power semiconductor Q9 is connected to the filter inductor L f , followed by a filter capacitor C f One pole of the filter capacitor C f The other pole is connected to the power semiconductor Q 12 Drain; filter capacitor C f Connected in parallel with the power electronic converter output.

[0016] On the other hand, the present invention also provides a control method for an electromagnetic electronic hybrid on-load capacity-adjusting and voltage-regulating transformer, wherein the hybrid on-load capacity-adjusting and voltage-regulating transformer adopts the above-mentioned hybrid on-load capacity-adjusting and voltage-regulating transformer, and the method is performed based on the system parameters of the hybrid on-load capacity-adjusting transformer, wherein the method includes a rectifier control method of a power electronic converter, specifically including:

[0017] DC bus reference voltage V bus_ref The DC bus voltage V on the DC capacitor C1 bus Subtract and use it as the input of the voltage outer loop proportional integral controller PI;

[0018] The output value of the PI controller is related to the rectified AC input voltage V s Multiplying them together can get the reference current I of the boost link pfc_ref The reference current is the reference value of the current inner loop, which is different from the AC input current I pfc After subtraction, it is used as the input of the current inner loop proportional resonant controller PR;

[0019] The output value of the PR controller is the reference voltage V of the rectifier link. pfc , the reference voltage is modulated by PWM to generate drive signals S1 to S6 of six power semiconductor devices Q1 to Q6;

[0020] The driving signals S7 and S8 of the power semiconductor devices Q7 and Q8 are turned on alternately according to whether the input voltage is in the positive half-wave or the negative half-wave.

[0021] On the other hand, the present invention also provides a control method for an electromagnetic-electronic hybrid on-load capacity-adjusting and voltage-regulating transformer, wherein the hybrid on-load capacity-adjusting and voltage-regulating transformer adopts the above-mentioned hybrid on-load capacity-adjusting and voltage-regulating transformer, and the method is performed based on the system parameters of the hybrid on-load capacity-adjusting transformer, wherein the method includes a control method for an inverter link of an inverter of a power electronic converter, specifically including:

[0022] Reference value of output voltage of hybrid on-load capacity and voltage regulating transformer V out_ref The output voltage V of the actual power electronic converter out The difference is used as the input of the voltage outer loop proportional resonant controller PR;

[0023] The output value of the PR controller is I Lf_ref As the reference value of the current inner loop controller; this current reference value I Lf_ref and filter inductor L f Current actual value I Lf Subtracting, and then passing through a current inner loop controller PR, the reference voltage V of the inverter link can be obtained. inv ;

[0024] V inv After PWM modulation, four power semiconductor devices Q9, Q 10 , Q 11 , Q 12 The driving signals S9 and S 10 , S 11 , S 12 .

[0025] On the other hand, the present invention also provides a control method for an electromagnetic-electronic hybrid on-load capacity-adjusting and voltage-regulating transformer, wherein the hybrid on-load capacity-adjusting and voltage-regulating transformer adopts the above-mentioned hybrid on-load capacity-adjusting and voltage-regulating transformer, and the method is performed based on the system parameters of the hybrid on-load capacity-adjusting transformer, wherein the method includes a phase-locked loop control method for a power electronic converter, specifically including:

[0026] Phase-lock the grid voltage to obtain the phase information of the input grid through phase-locking, including:

[0027] The second-order generalized integrator generates a voltage sine wave V in phase with the input voltage V α and a sine wave V with a phase difference of 90° β , as the phase detection link of the input voltage; the input voltage of the integrator is the output of the electromagnetic transformer II section turns;

[0028] The output of the phase detection link is linearized by Park transform to obtain the d-axis component and the q-axis component V d and V q ; V q As the input of the loop filter, it is used to convert the q-axis component V q Lock to zero to achieve phase tracking;

[0029] The output of the loop filter should be proportional to the feedforward quantity ω n The phases are superimposed and the phase tracking of the input voltage V can be obtained through the integration link. At the same time, the phase is fed back to the aforementioned Park transformation to form negative feedback.

[0030] Furthermore, when the electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer operates at a first rated capacity, the output voltage of the power electronic converter is 0V; when operating at a second rated capacity, the output voltage of the power electronic converter compensates for the voltage drop of the electromagnetic transformer to stabilize the output voltage of the on-load capacity-regulating and voltage-regulating transformer.

[0031] The beneficial effects of the present invention are:

[0032] The electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer and control method provided by the present invention have the following beneficial effects:

[0033] The present invention uses the voltage regulation function of the power electronic converter to automatically regulate the voltage according to the voltage deviation during the capacity regulation process of the hybrid on-load capacity and voltage regulating transformer, and automatically maintain the voltage output on the low voltage side.

[0034] Compared with the traditional method of using mechanical switches and power electronic switches to adjust capacity and voltage, the present invention directly eliminates the complex switch link and dynamically adjusts the capacity and voltage from the perspective of the output voltage on the low-voltage side of the transformer. Since the voltage regulation process of the power electronic converter is smooth and controllable, the impact on the power grid is small and the service life is longer.

[0035] Compared with the prior art, the present invention has the advantages of no arc, fast switching action and short response time due to the absence of mechanical switches. At the same time, compared with power electronic capacity adjustment switches, it has the characteristics of simple structure and high reliability, and does not require complex voltage and current balancing.

[0036] The rectification, boosting and inversion links of the present invention all adopt voltage and current dual closed-loop control, and an interleaved power factor correction circuit is adopted in the rectification and boosting links, taking into account both the boosting of the DC bus voltage and the input end power factor correction. The interleaved totem pole bridgeless power factor correction circuit has a smaller requirement for the inductor current, is more suitable for use in the case of large current, and has higher power, higher efficiency and higher power density.

[0037] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 The present invention is a schematic structural diagram of a hybrid on-load capacity-regulating and voltage-regulating transformer to which an embodiment of the present invention is applied.

[0040] Figure 2 A schematic diagram of a topological structure of a power electronic converter according to an embodiment of the present invention;

[0041] Figure 3 This is a flow chart of a control method for a rectifier in a power electronic converter according to an embodiment of the present invention;

[0042] Figure 4 is a flow chart of a control method for an inverter in a power electronic converter according to an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of the basic structure of a single-phase phase-locked loop technology based on a second-order generalized integrator according to an embodiment of the present invention;

[0044] Figure 6 It is a simulation waveform diagram of the low-voltage side voltage of the electromagnetic transformer before and after capacity adjustment according to an embodiment of the present invention;

[0045] Figure 7 It is a simulation waveform diagram of the DC bus capacitor voltage of the power electronic converter according to an embodiment of the present invention;

[0046] Figure 8 It is a simulation waveform diagram of the output voltage of each phase of the hybrid capacity and voltage regulating transformer and the output voltage of the power electronic converter according to the embodiment of the present invention;

[0047] Fig. 9 The figure is a simulation waveform diagram of the current at the input end of the power electronic converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] like Figure 1 As shown, the present invention provides an electromagnetic-electronic hybrid on-load capacity-adjusting and voltage-regulating transformer, wherein the hybrid on-load capacity-adjusting and voltage-regulating transformer includes a three-phase circuit topology structure, and the three-phase circuit topology structure includes a three-phase electromagnetic transformer and three single-phase power electronic converters.

[0050] The hybrid on-load capacity-adjusting and voltage-adjusting transformer of the present invention is applied as follows Figure 1 As shown. The high-voltage side of the electromagnetic transformer is connected to the three-phase high-voltage AC power grid A, B, and C. Each phase winding on the low-voltage side includes two sections of wire turns, Ⅰ and Ⅱ. The number of wire turns in section Ⅰ is greater than the number of wire turns in section Ⅱ, and the wire turns in section Ⅰ and section Ⅱ are isolated from each other. Section Ⅰ is the majority of wire turns, which serves as the main output voltage on the low-voltage side of the electromagnetic transformer. Section Ⅱ is a minority of wire turns, which is connected to the input end of the power electronic converter. The output end of the power electronic converter is connected in series with the wire turns in section Ⅰ to compensate for the voltage change after the electromagnetic transformer is adjusted. The low-voltage side of the series-connected on-load capacity-adjusting and voltage-regulating transformer is externally connected to the three-phase low-voltage AC distribution network a, b, and c.

[0051] The input of the power electronic converter is connected in parallel with the output of the electromagnetic transformer section II turn; the output of the power electronic converter is connected in series with the output of the electromagnetic transformer section I turn to supply power to the load;

[0052] The total output voltage of the hybrid on-load capacity-regulating and voltage-regulating transformer is the sum of the output voltage of the power electronic converter and the output voltage of the turns of section I of the electromagnetic transformer.

[0053] In addition, in some embodiments of the present invention, the high-voltage side is connected to a 10kV high-voltage power grid, and the two sections of turns I and II on the low-voltage side output 220V and 60V respectively, and are connected to a three-phase 220V AC distribution network. The high-voltage winding of the electromagnetic transformer is connected in a triangle when the capacity is large (i.e., the first rated capacity), and in a star when the capacity is small (i.e., the second rated capacity, where the value of the first rated capacity is approximately 3 times the second rated capacity). The low-voltage side of the hybrid on-load capacity-regulating and voltage-regulating transformer can be connected in a star or triangle. When the high-voltage winding is changed from a triangle connection to a star connection, the phase voltage will be reduced to the original value. The corresponding transformer no-load reactive loss and active loss also decrease accordingly. In the small capacity state, the active loss is reduced to about 1 / 3 of the original. Among them, it is necessary to understand that the capacity-adjusting transformer generally has two rated capacities, large and small, which can be automatically adjusted in real time according to the power consumption situation, that is, it is adjusted to large capacity operation during less peak power consumption periods, and automatically adjusted to small capacity operation during periods of relatively less power consumption, thereby greatly reducing the power loss of the transformer during operation. The high-voltage side winding of the conventional capacity-adjusting transformer is star-delta transformation, and the low-voltage side winding is series-parallel transformation (referred to as DY capacity-adjusting). The reasonable value of the ratio of large and small capacities of the capacity-adjusting transformer is about 3:1. And the size of the capacity is relative, depending on the rated capacity of the transformer. If it is a transformer of 100 kVA level, it is considered that the rated capacity is the maximum capacity of the transformer. When the load is less than 1 / 3 of the rated capacity, the transformer is adjusted to operate in a small capacity state. When the load is greater than 1 / 3 of the rated capacity, the transformer is adjusted to operate in a small capacity state. The purpose is to reduce the power loss of the transformer during operation.

[0054] The topological structure of the power electronic converter using the present invention is as follows: Figure 2 As shown, it includes rectification and inversion. Rectification and boost are realized by rectifier, and inversion is realized by inverter. Power electronic converter includes rectifier and inverter;

[0055] The rectifier includes inductors L1, L2, L3, power semiconductors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 and DC capacitor C1, which together constitute a bidirectional staggered totem-pole bridgeless power factor correction circuit (Totem-Pole Power Factor Correction, TTPL-PFC); the inverter includes power semiconductors Q9, Q 10 , Q 11 , Q 12 , filter inductor L f And filter capacitor C f Specific connection method: L1, Q1 and Q2 form an interlaced phase, L2, Q3 and Q4, and L3, Q5 and Q6 all form an interlaced phase; Q1 and Q2, Q3 and Q4, Q5 and Q6 respectively form a pair of bridge arms with three interlaced phases, the midpoints of the corresponding upper and lower bridge arms are connected to the first stage of the corresponding inductor, the other pole of the corresponding inductor is connected to the positive pole of the input power supply, and the negative pole of the input power supply is connected to a bridge arm formed by Q7 and Q8; power semiconductors Q9, Q 10 , Q 11 , Q 12 The inverter bridge consists of power semiconductors Q9 and Q 11 The drain is connected to the positive electrode of the DC capacitor C1, and the power semiconductor Q 10 , Q 12The source is connected to the negative electrode of the DC capacitor C1; the source of the power semiconductor Q9 is connected to the filter inductor L f , followed by a filter capacitor C f One pole of the filter capacitor C f The other pole is connected to the power semiconductor Q 12 Drain; filter capacitor C f Connected in parallel with the output of the power electronic converter, the AC power supply voltage can be converted into a stable DC bus voltage based on the boost principle.

[0056] When the PFC inductor current of the rectifier circuit of the rectifier operates in a continuous conduction mode (CCM), the CCM mode is usually suitable for high-power converters and can adopt a fixed frequency control.

[0057] In some embodiments of the present invention, it also includes determining the system parameters of the hybrid on-load capacity and voltage regulating transformer. The purpose of determining these parameters is to determine the selection of devices in the power electronic converter. Figure 2 The selection of the inductance and capacitance of the inductor and capacitor, as well as the selection of the switch tube, rated current, withstand voltage, etc. can be carried out through the following formulas (1)-(9):

[0058] According to the power conservation law, the average inductor current effective value I can be calculated L(rms ) and the average inductor current peak value I L(max) for:

[0059]

[0060] V s is the input voltage of the power electronic converter. When the electromagnetic transformer is in a large-capacity connection mode, its value is 60VAC. However, when the capacity is small, the corresponding input voltage should be reduced to the original P o is the output power, which depends on the load end; η is the efficiency of the PFC converter.

[0061] ΔI L =0.2I L(max) (3)

[0062]

[0063] Since the key to PFC inductor design depends on the size of the inductor current ripple, consider the inductor current ripple ΔI L is 20% of the average inductor current peak value, that is, the inductor current ripple ΔI calculated by equation (3) L Then, when the input voltage reaches its peak value, the corresponding maximum duty cycle D max can be obtained by (4), where V ois the output voltage after rectifier rectification. Combining the above equations (3), (4) and the switching frequency f of the power semiconductor s , the minimum value of PFC inductance L can be calculated min for:

[0064]

[0065] The output capacitor C1 is used as an AC / DC converter to convert the AC power supply voltage into a stable DC bus voltage. Its actual capacity needs to meet the output capacity requirements and minimize the ripple on the output capacitor to create a good DC bus voltage for the subsequent inverter link. The output capacitor is designed to meet the 2 times power frequency ripple ΔV caused by the instantaneous input and output power imbalance. o , the corresponding capacitor output peak voltage ripple V can be calculated by (6) ripple , and then the minimum value of the DC bus capacitance C can be calculated min It is formula (7).

[0066]

[0067] By considering the current and ripple of inductors L1, L2, and L3, and the voltage and ripple of capacitor C1, appropriate inductance and capacitance values ​​are selected to meet the requirements of power, size, and loss, which is particularly important for the subsequent inverter process and loss.

[0068] The DC bus voltage is passed through the power semiconductor devices Q9, Q 10 , Q 11 and Q 12 The inverter bridge is inverted into AC power, and then connected to the inductor L f and C f The LC filter circuit composed of the filter will filter it into a standard sine wave current. The inverter works in high-frequency PWM (Pulse width modulation). Considering the fundamental frequency f1 of the inverter output voltage, the cutoff frequency of the LC filter must be much smaller than the lowest harmonic frequency f contained in the PWM voltage. har(min) , and at the same time it must be much larger than the fundamental frequency. Calculate the cutoff angular frequency ω of the LC filter as:

[0069]

[0070] The size and weight of the filter are mainly determined by the inductor, and due to the changes in the winding method, number of turns and core material, the inductor often needs to be customized, and its inductance value is not as standard as that of the capacitor. Therefore, the main consideration of the LC filter is the impact of the selection of the inductance value on the LC reactive characteristics. According to formula (9), the inductance value L can be approximately selected, where ω1 is the fundamental angular frequency of the inverter output voltage:

[0071]

[0072] In view of the requirements of the present invention for the power electronic converter, combined with the above-mentioned electromagnetic electronic hybrid on-load capacity and voltage regulating transformer system parameters, the corresponding control method includes the following:

[0073] (1) Rectifier control method of power electronic converter:

[0074] The rectifier adopts a voltage and current double closed-loop control strategy. The control method flow chart is as follows: Figure 3 As shown. DC bus reference voltage V bus_ref The actual DC bus voltage V bus Subtract and use it as the input of the voltage outer loop proportional integral controller PI. After adjusting the capacitance, the voltage to be compensated is ΔV, where V bus_ref Formula (10) needs to be satisfied to leave enough margin.

[0075]

[0076] The output value of the PI controller is related to the rectified AC input voltage V s Multiplying them together can get the reference current I of the boost link pfc_ref The reference current is the reference value of the current inner loop, which is different from the AC input current I pfc After subtraction, it is used as the input of the current inner loop proportional resonant controller PR. The PR controller as the current inner loop has a larger bandwidth and faster response speed than the PI controller as the voltage outer loop to ensure the stability of the control system.

[0077] The output value of the PR controller is the reference voltage V of the rectifier link. pfc The reference voltage is modulated by PWM to generate drive signals S1 to S6 for the six power semiconductor devices Q1 to Q6 in the TTPL PFC. The drive signals S7 and S8 for the power semiconductor devices Q7 and Q8 depend on the input voltage on the AC side. The input voltage obtains the phase through the phase-locked loop, and the corresponding power semiconductors are triggered alternately in sequence according to the phase of the input voltage.

[0078] (2) Inverter control method of power electronic converter:

[0079] The inverter in the inverter link adopts a voltage and current double closed-loop control strategy. The control method flow chart is as follows: Figure 4 The reference value of the output voltage of the on-load capacity and voltage regulating transformer is V out_ref The output voltage V of the actual power electronic converter out The difference is used as the input of the voltage outer loop proportional resonant controller PR. When the capacity is large, since the effective value of the voltage of the I-stage wire turn is 220V, V out_ref The setting should be 0. The inverter tries to maintain the converter output voltage at zero under the control strategy. When the capacity is small, since the effective value of the voltage of the I-stage line turn is 127V, V out_ref The setting should be ΔV to compensate for the voltage drop at this time.

[0080] The output value of the PR controller is I Lf_ref As the reference value of the current inner loop controller, the current inner loop controller still uses the PR controller. This current reference value I Lf_ref With L f Actual value of filter inductor current I Lf Subtracting, the reference voltage V of the inverter link can be obtained through the current inner loop controller inp The PR controller as the current inner loop has a larger bandwidth and faster response speed than the PR controller as the voltage outer loop to ensure the stability of the control system.

[0081] V inv After PWM modulation, four power semiconductor devices Q9, Q 10 , Q 11 , Q 12 The driving signals S9 and S 10 , S 11 , S 12 PWM uses bipolar modulation, and the power semiconductors between the same bridge arms are turned on alternately.

[0082] (3) Phase-locked loop control method of power electronic converter:

[0083] In order to ensure the phase synchronization between the input voltage and output voltage of the power electronic converter, the grid voltage is phase-locked, and the phase information of the input side grid is obtained through phase locking. The single-phase phase-locked loop (PLL) technology based on the second-order generalized integrator (SOGI) has a basic structure diagram as shown in the figure. Figure 5 shown.

[0084] The second-order generalized integrator (SOGI) generates a voltage sine wave V in phase with the input voltage V α and a sine wave V with a phase difference of 90° β, which is not affected by the frequency, serves as the phase detection link for the input voltage. Here, the input voltage of the integrator is the output of the turns of the electromagnetic transformer II.

[0085] The output of the phase detection link is linearized by Park transform to obtain the d-axis component and the q-axis component V d and V q . V q As the input of the loop filter, the loop filter uses a PI controller to convert the q-axis component V q The phase is tracked by locking it to zero. Since the loop filter has a low-pass filter characteristic, the high-frequency components can be ignored.

[0086] Feedforward ω n It is related to the frequency of the input voltage V being tracked. Since the grid frequency is basically stable around 50Hz, the feedforward value ω n It can be 100π, and it does not need to be completely consistent with the input voltage frequency. The output of PI control should be consistent with the feedforward quantity ω n Phase superposition (ω n The angular frequency of the input voltage of the 50Hz grid is 100π). After the integration link, the phase of the input voltage V can be obtained, and the phase is fed back to the aforementioned Park transformation to form negative feedback. The single-phase PLL technology based on the second-order generalized integrator (SOGI) is more suitable for realizing phase tracking of the grid with small frequency changes.

[0087] Figure 6 The following is a simulated waveform diagram of the low-voltage side voltage of the electromagnetic transformer before and after capacity adjustment. It can be seen from the waveform that in the case of large capacity, the output voltage of each phase of the low-voltage side of the electromagnetic transformer is 220V (I section wire turns) and 60V (II section wire turns). After 3s, the capacity adjustment is performed, the capacity adjustment transformer switches from large capacity to small capacity, and the high-voltage side winding switches from triangle connection to star connection. The corresponding output voltage of each phase winding on the low-voltage side is reduced to the original That is, 127V (line turns of segment I) and 34.6V (line turns of segment II) in the simulation waveform.

[0088] Figure 7The simulation waveform of the DC bus capacitor voltage of the power electronic converter. Within 0 to 3 seconds, the DC bus voltage on capacitor C1 rises from zero to 180V, slightly higher than the set value of the rectifier controller, and then gradually stabilizes near the set value. After 3 seconds, as the capacity adjustment process proceeds, the power electronic converter automatically adjusts the voltage. It can be seen from the simulation waveform that the DC bus voltage fluctuates and then gradually adjusts to the set value of the DC bus voltage. In addition to being related to the performance of the controller, the fluctuation of the DC bus capacitor voltage is also closely related to the capacitance value of the capacitor. Especially in the case of large output current, too small a capacitance value may cause the bus voltage ripple to be too large, which in turn affects the total harmonic distortion of the output voltage.

[0089] Figure 8 The following is a simulation waveform diagram of the output voltage of each phase of the hybrid on-load capacity-adjusting and voltage-regulating transformer and the output voltage of the power electronic converter. It can be seen from the simulation waveform diagram that in the case of large capacity, the output voltage of the power electronic converter is almost zero, and has little effect on the turns superimposed on 220V. This is actually also closely related to the filter capacitor, because the output end of the converter is connected in parallel with the capacitor of the LC filter, which has a smaller capacitive reactance. The voltage division of the series 220V turns on the capacitor will be smaller, and the output current of the converter will be closer to zero. After 3s, the transformer begins to adjust the capacity, and the output voltage of the converter is continuously adjusted to compensate for the voltage drop of the 220V turns, and finally the output voltage of the hybrid on-load capacity-adjusting and voltage-regulating transformer is stabilized at 220V. Figure 8 It can also be seen that the control strategy has a faster response speed and lower harmonic content.

[0090] Fig. 9 This is a simulation waveform of the current at the input end of the power electronic converter. In general, the input current approaches zero before 3s, at which time the converter output voltage is 0v. After 3s, the input current also basically presents a sine wave, at which time the output voltage is a compensation for the voltage drop. However, it can also be seen from the waveform that after switching from a large capacity to a small capacity, since the converter output voltage needs to be boosted while the input voltage is decreasing, more current needs to be provided at the input end of the converter to maintain power balance. Therefore, the inductance in the II-stage turns and rectifier requires a larger current carrying value.

[0091] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An electromagnetic and electronic hybrid on-load capacity and voltage regulating transformer, characterized in that: The hybrid on-load capacity and voltage regulating transformer comprises a three-phase circuit topology structure, which comprises a three-phase electromagnetic transformer and three single-phase power electronic converters; Each phase winding of the low-voltage side of the electromagnetic transformer includes a section I wire turn and a section II wire turn; the section I wire turn and the section II wire turn of the electromagnetic transformer are isolated from each other, wherein the number of the section I wire turns is greater than the number of the section II wire turns; The input of the power electronic converter is connected in parallel with the output of the electromagnetic transformer section II turn; the output of the power electronic converter is connected in series with the output of the electromagnetic transformer section I turn to supply power to the load; The total output voltage of the hybrid on-load capacity-regulating and voltage-regulating transformer is the sum of the output voltage of the power electronic converter and the output voltage of the turns of section I of the electromagnetic transformer.

2. The electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer according to claim 1, characterized in that: The high-voltage side of the electromagnetic transformer is connected in a triangle at the first rated capacity, and in a star at the second rated capacity; the low-voltage side of the electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer can be connected in a star or a triangle, wherein the value of the first rated capacity is three times that of the second rated capacity.

3. The electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer according to claim 2, characterized in that: The power electronic converter includes a rectifier and an inverter; Wherein, the rectifier includes inductors L1, L2, L3, power semiconductors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 and a DC capacitor C1; The inverter includes power semiconductors Q9, Q 10 , Q 11 , Q 12 , filter inductor L f And filter capacitor C f ; Specific connection method: L1, Q1 and Q2 form an interlaced phase, L2, Q3 and Q4, and L3, Q5 and Q6 all form an interlaced phase; Q1 and Q2, Q3 and Q4, Q5 and Q6 respectively form a pair of bridge arms with three interlaced phases, the midpoints of the corresponding upper and lower bridge arms are connected to the first stage of the corresponding inductor, the other pole of the corresponding inductor is connected to the positive pole of the input power supply, and the negative pole of the input power supply is connected to a bridge arm formed by Q7 and Q8; power semiconductors Q9, Q 10 , Q 11 , Q 12 The inverter bridge consists of power semiconductors Q9 and Q 11 The drain is connected to the positive electrode of the DC capacitor C1, and the power semiconductor Q 10 , Q 12 The source is connected to the negative electrode of the DC capacitor C1; the source of the power semiconductor Q9 is connected to the filter inductor L f , followed by a filter capacitor C f One pole of the filter capacitor C f The other pole is connected to the power semiconductor Q 12 Drain; filter capacitor C f Connected in parallel with the power electronic converter output.

4. A control method for an electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer, characterized in that: The hybrid on-load capacity-adjusting and voltage-regulating transformer adopts the hybrid on-load capacity-adjusting and voltage-regulating transformer according to claim 3, and the method is performed based on the system parameters of the hybrid on-load capacity-adjusting and voltage-regulating transformer, wherein the method includes a rectifier control method of a power electronic converter, specifically including: DC bus reference voltage V bus_ref The DC bus voltage V on the DC capacitor C1 bus Subtract and use it as the input of the voltage outer loop proportional integral controller PI; The output value of the PI controller is related to the rectified AC input voltage V s Multiplying them together can get the reference current I of the boost link pfc_ref The reference current is the reference value of the current inner loop, which is different from the AC input current I pfc After subtraction, it is used as the input of the current inner loop proportional resonant controller PR; The output value of the PR controller is the reference voltage V of the rectifier link. pfc , the reference voltage is modulated by PWM to generate drive signals S1 to S6 of six power semiconductor devices Q1 to Q6; The driving signals S7 and S8 of the power semiconductor devices Q7 and Q8 are turned on alternately according to whether the input voltage is in the positive half-wave or the negative half-wave.

5. A control method for an electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer, characterized in that: The hybrid on-load capacity-adjusting and voltage-regulating transformer adopts the hybrid on-load capacity-adjusting and voltage-regulating transformer according to claim 3, and the method is performed based on the system parameters of the hybrid on-load capacity-adjusting and voltage-regulating transformer, wherein the method includes a control method for the inverter link of the power electronic converter, specifically including: Reference value of output voltage of hybrid on-load capacity and voltage regulating transformer V out_ref The output voltage V of the actual power electronic converter out The difference is used as the input of the voltage outer loop proportional resonant controller PR; The output value of the PR controller is I Lf_ref As the reference value of the current inner loop controller; this current reference value I Lf_ref and filter inductor L f Current actual value I Lf Subtracting, and then passing through a current inner loop controller PR, the reference voltage V of the inverter link can be obtained. inv ; V inv After PWM modulation, four power semiconductor devices Q9, Q 10 , Q 11 , Q 12 The driving signals S9 and S 10 , S 11 , S 12 .

6. A control method for an electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer, characterized in that: The hybrid on-load capacity-adjusting and voltage-regulating transformer adopts the hybrid on-load capacity-adjusting and voltage-regulating transformer according to claim 3, and the method is performed based on the system parameters of the hybrid on-load capacity-adjusting and voltage-regulating transformer, wherein the method includes a phase-locked loop control method of a power electronic converter, specifically including: Phase-lock the grid voltage to obtain the phase information of the input grid through phase-locking, including: The second-order generalized integrator generates a voltage sine wave V in phase with the input voltage V α and a sine wave V with a phase difference of 90° β , as the phase detection link of the input voltage; the input voltage of the integrator is the output of the electromagnetic transformer II turn; The output of the phase detection link is linearized by Park transform to obtain the d-axis component and the q-axis component V d and V q ; V q As the input of the loop filter, it is used to convert the q-axis component V q Lock to zero to achieve phase tracking; The output of the loop filter should be proportional to the feedforward quantity ω n The phases are superimposed and the phase tracking of the input voltage V can be obtained through the integration link. At the same time, the phase is fed back to the aforementioned Park transformation to form negative feedback.

7. The control method of the electromagnetic-electronic hybrid on-load capacity-regulating and voltage-regulating transformer according to claim 5, characterized in that: When the electromagnetic-electronic hybrid on-load capacity-adjusting and voltage-regulating transformer operates at the first rated capacity, the output voltage of the power electronic converter is 0V; when operating at the second rated capacity, the output voltage of the power electronic converter compensates for the voltage drop of the electromagnetic transformer to stabilize the output voltage of the on-load capacity-adjusting and voltage-regulating transformer.

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