A dual passive harmonic injection 12-pulse rectifier based on average current control

Abstract

The application discloses a double-passive harmonic injection 12-pulse rectifier based on average current control, which comprises a parallel type 12-pulse rectifier, a balanced reactor with a secondary side, a sampling unit and a prediction controller. A harmonic injection system composed of an inductor and a resistor is added. The balanced reactor with the secondary side transmits the 12-pulse waveform output by the parallel type 12-pulse rectifier to the single-phase rectifier bridge connected to the secondary side through the primary side, and the 12-pulse waveform is input to the load through the modulation of the single-phase rectifier bridge. The average current prediction method is set in the load current, load voltage and line voltage prediction controller, the inductor current value at the next moment is calculated according to the load current, load voltage and line voltage collected by the sampling unit, and the inductor current value is compared with the current reference value at the next moment, so that the thyristor corresponding to the line voltage with the minimum error is triggered at the next moment. Compared with the prior art, the application can make the circuit triggering more accurate and effectively reduce the THD of the grid side.

Description

Technical Field

[0001] This invention belongs to the field of high-power rectification technology, and specifically relates to a dual passive harmonic injection 12-pulse rectifier based on average current control. Background Technology

[0002] High-power rectified power supplies have a wide range of applications and are used in numerous industrial settings, including electroplating in the chemical industry, capillary electrophoresis for cell separation in instrument manufacturing, and satellites in the aerospace industry. Therefore, obtaining high-quality, high-power power supplies is a major research focus.

[0003] In the field of new energy vehicles, by the end of 2021, my country had 7.84 million new energy vehicles (data from the Ministry of Public Security) and 2.617 million charging piles (data from the China Electric Vehicle Charging Infrastructure Promotion Alliance (EVCIPA), with a vehicle-to-pile ratio of 3:1. According to the "2021 China Electric Vehicle User Charging Behavior White Paper" released by EVCIPA, due to the current scarcity of charging piles, long and unpredictable waiting times, and the inability of fast charging piles to achieve high-power coverage throughout the charging process, the actual time to charge to 50% often far exceeds half an hour, affecting user charging efficiency. Solutions include increasing the number of charging piles and improving charging speed. High-power charging is an effective solution, and new energy vehicle manufacturers are deploying public battery swapping and high-power charging facilities to improve user experience. High-power charging often involves high voltage and high current; therefore, high-power rectification technology is a key research focus for achieving faster charging.

[0004] Multi-pulse rectification technology connects multiple rectifier circuits through phase-shifting transformers, allowing certain harmonics generated by the rectifier circuits to cancel each other out. It boasts advantages such as simple circuit topology and high stability, making multi-pulse rectifiers widely used in high-power applications. Traditional 12-pulse rectifiers have a simple structure and can eliminate lower-order 5th and 7th harmonics, but they offer no suppression of higher-order harmonics. Compared to traditional parallel-type uncontrolled 12-pulse rectifiers, semi-controlled or controlled rectifiers offer more precise conduction angles, giving thyristor-based multi-pulse controlled rectifiers the advantage of continuously adjustable output voltage. However, their higher grid-side current harmonic content and susceptibility to load current dynamic response performance due to the firing angle limit their application range. Currently, no multi-pulse controlled rectifiers simultaneously address input-side harmonic suppression and load current dynamic response. Optimizing the input current waveform without affecting the dynamic response capability of the load current of the multi-pulse controllable rectifier is a challenge for the input current harmonic suppression of the multi-pulse controllable rectifier. Summary of the Invention

[0005] Purpose of the invention: In view of the problems pointed out in the background art, the present invention proposes a dual passive harmonic injection 12-pulse rectifier based on average current control. The rectifier is composed of thyristors forming a parallel 12-pulse rectifier structure. It adopts average current prediction control. The prediction controller calculates the inductor current value at the next moment and compares it with the current reference value at the next moment. The thyristor corresponding to the input line voltage with the smallest error will be triggered at the next moment.

[0006] Technical solution: This invention proposes a dual passive harmonic injection 12-pulse rectifier based on average current control, including a parallel 12-pulse rectifier, a harmonic injection system, a balancing reactor with a secondary side, a sampling unit, and a predictive controller.

[0007] The parallel 12-pulse rectifier includes parallel rectifier bridges rec1 and rec2, each rectifier bridge including 6 thyristors. The parallel 12-pulse rectifier is connected in parallel with a harmonic injection system. The balancing reactor with secondary side transmits the waveform output by the parallel 12-pulse rectifier through the primary side to the single-phase rectifier bridge connected to the secondary side, and then modulates the single-phase rectifier bridge to input to the load. The sampling unit collects the load current, load voltage, and line voltage. The predictive controller is equipped with an average current prediction method. Based on the collected load current, load voltage, and line voltage, the inductor current value at the next moment is calculated and compared with the current reference value at the next moment. The thyristor corresponding to the input line voltage with the smallest error will be triggered at the next moment.

[0008] Furthermore, the harmonic injection system includes a resistor and an inductor connected in series, which are connected in parallel to a parallel 12-pulse rectifier.

[0009] Furthermore, the conditions required for the average current prediction method are:

[0010] 1) Set the inductor current reference value ;

[0011] 2) Sample the instantaneous value of the inductor current, load voltage, and input line voltage;

[0012] 3) Based on the current inductor current value Load voltage value and voltage vector Calculate the current value at the next moment. .

[0013] Furthermore, each of the voltage vectors participates in predicting the current value at the next moment. , to make the current reference value With instantaneous value The voltage vector with the smallest error is selected as the voltage vector for the next moment, and the thyristor corresponding to this voltage will be triggered to conduct.

[0014] By approximating the current pulse as a sine wave, average value predictive control is obtained, and the calculation expression is as follows:

[0015] .

[0016] Furthermore, the specific method for predicting the current value at the next moment is as follows:

[0017] 1) Calculate the area enclosed by the two line voltage vectors and the load voltage, which represents the maximum increment of the inductor current;

[0018] 2) Calculate the inductor current increment formed by triggering the thyristor at different times;

[0019] 3) Predict the inductor current at the next moment and compare it with the reference current. Record the inductor current with the smallest error and select the line voltage vector that induces this inductor current.

[0020] 4) Trigger the corresponding thyristor based on the line voltage vector selected in the previous step.

[0021] Beneficial effects:

[0022] This invention achieves rapid dynamic response of the rectifier output current through a current predictive control strategy. It improves the DC-side harmonic suppression strategy and topology to meet the input-side harmonic suppression requirements of multi-pulse controllable rectifiers. The current control strategy employs an average-value current predictive control approach. The harmonic suppression method introduces a balancing reactor with a secondary side, doubling the 12-pulse frequency and increasing the circuit output pulse count to 24 pulses, effectively reducing grid-side THD. An unwired harmonic injection system composed of inductors and resistors further optimizes the DC-side current waveform. Both the balancing reactor and the unwired harmonic injection system utilize simple electronic components, reducing circuit cost. The use of the current predictive control method makes circuit triggering more precise, effectively reducing grid-side THD. Attached Figure Description

[0023] Figure 1 This is a circuit diagram of the dual passive harmonic injection 12-pulse rectifier of the present invention;

[0024] Figure 2 This invention relates to a balanced reactor with a secondary side;

[0025] Figure 3 This invention uses one of the wavefronts of a parallel 12-pulse waveform for analysis of the current flow waveform.

[0026] Figure 4 This invention uses one of the wavefronts of a parallel 12-pulse waveform for analysis, which is the second current flow waveform.

[0027] Figure 5 This is an area diagram enclosed by the two line voltage vectors and the load voltage in the average current prediction method of this invention.

[0028] Figure 6 This is a schematic diagram illustrating how harmonics are injected to form a triangular wave according to the present invention. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

[0030] This invention discloses a dual passive harmonic injection 12-pulse rectifier based on average current control, including a parallel 12-pulse rectifier, a harmonic injection system, a balancing reactor with a secondary side, a sampling unit, and a predictive controller.

[0031] The parallel 12-pulse rectifier includes parallel rectifier bridges rec1 and rec2, each containing 6 thyristors. A harmonic injection system is connected in parallel to the parallel 12-pulse rectifier. A balancing reactor with a secondary side transmits the waveform output from the parallel 12-pulse rectifier through the primary side to the single-phase rectifier bridge connected to the secondary side. The waveform is then modulated by the single-phase rectifier bridge and input to the load. The sampling unit collects the load current, load voltage, and line voltage. The predictive controller is equipped with an average current prediction method. Based on the collected load current, load voltage, and line voltage, the inductor current value for the next moment is calculated and compared with the current reference value for the next moment. The thyristor corresponding to the input line voltage with the smallest error will be triggered in the next moment.

[0032] like Figure 1 As shown, the principle of the average current prediction method in the predictive controller is roughly as follows:

[0033] Conditions required for the average current prediction method:

[0034] 1) Set the inductor current reference value .

[0035] 2) Sample the instantaneous value of the inductor current, load voltage, and input line voltage.

[0036] 3) Based on the current inductor current value Load voltage value and voltage vector Calculate the current value at the next moment. .

[0037] For the structure described above, each voltage vector participates in predicting the current value at the next moment. , to make the current reference value With instantaneous value The closest voltage vector (the voltage vector with the smallest error) is selected as the voltage vector for the next moment, and the thyristor corresponding to this voltage will be triggered to conduct.

[0038] Based on the above steps, the peak current prediction can be obtained. To achieve average current prediction control, the current pulse can be approximated as a sine wave to obtain average current prediction control, expressed as:

[0039]

[0040] The steps of the average current prediction method are shown in the following figure:

[0041] 1) Calculate the area enclosed by the two line voltage vectors and the load voltage. This area represents the maximum increment of the inductor current. See [reference needed]. Figure 5 .

[0042] 2) Calculate the inductor current increment formed by triggering the thyristor at different times.

[0043] 3) Predict the inductor current at the next moment and compare it with the reference current. Record the inductor current with the smallest error and select the line voltage vector that induces this inductor current.

[0044] 4) Trigger the corresponding thyristor based on the line voltage vector selected in the previous step.

[0045] For detailed calculation methods, please refer to [link / reference]. Figure 5 :

[0046] When the thyristor is When turned on, the inductor current will be The time when the maximum value is reached is:

[0047]

[0048] Similarly, to predict the inductor current value of t3, you only need to know The volt-second integral of the inductor voltage and the instantaneous value of the inductor current at time t2:

[0049]

[0050] However, the above formula states... If it's difficult to determine precisely, then we can calculate it indirectly by assuming the output line voltages are symmetrical. , It can be calculated in real time using a microprocessor, where S is known. This can be used for S- So what you get The increment of inductor current at any given moment:

[0051]

[0052] Assuming that the reference value of the inductor current is , then the triggering mode of the thyristor is: when the instantaneous value of the inductor current and the predicted current increment sum to the reference value, the corresponding thyristor is triggered:

[0053] = +

[0054] For example, when triggering for conduction at time, the inductor current will reach the maximum value at time, at which time the instantaneous value of the inductor current is equal to the reference value:

[0055]

[0056] Also, the average value and the amplitude satisfy the following approximate relationship:

[0057]

[0058] Therefore, the corrected current prediction method is:

[0059] .

[0060] A balancing reactor with a secondary side is as Figure 2 shown. The waveforms output by rectifier bridges D1 and D2 are transmitted through the primary side of the balancing reactor with a secondary side to the single-phase rectifier bridge connected to the secondary side, and input to the load through modulation by the single-phase rectifier bridge. The general principle is:

[0061] One pulse head of the parallel 12-pulse is taken for analysis: the grid-side current is a sine wave with a phase difference of 30° input to the rectifier.

[0062] When Ua1b1>Ua2b2, where Ua1b1 represents the voltage of the previous grid-side input rectifier, and Ua2b2 represents the voltage that has a phase difference of 30° from the previous grid-side input rectifier, as shown in Figure 3 :

[0063] The current direction is: rectifier bridge rec1->upper half of balancing reactor->single-phase rectifier D3->secondary transformer->single-phase rectifier D1->load->rectifier bridge rec1.

[0064] When Ua1b1<Ua2b2, as shown in Figure 4:

[0065] The direction of the current is: rectifier bridge rec2 -> lower half of the balancing reactor -> single-phase rectifier D2 -> secondary transformer -> single-phase rectifier D4 -> load -> rectifier bridge rec2.

[0066] By modulating the single-phase rectifier, the pulse count of the rectifier can be increased from 12 pulses to 24 pulses. The optimal turns ratio of the balancing reactor can be calculated through Fourier analysis, thereby significantly reducing the THD of the rectifier.

[0067] As can be seen from the principle of DC-side harmonic injection, when a certain measure is taken to inject harmonic current into the circuit and modulate the current waveform of the DC-side output of the rectifier, the harmonic content of the grid-side current of the rectifier can be effectively reduced.

[0068] See Figure 6 The triangular wave in the figure represents the output waveform of an ideal rectifier. L1 and i L2 The actual output current of the rectifier bridge is given. If harmonics are injected into the output sections of the two rectifier bridges, making the output current approach the amplitude and phase of a triangular wave, then the harmonic content on the grid side will be further suppressed. This invention uses a resistor and an inductor connected in series to form a harmonic injection system. The principle is as follows:

[0069] i L1 with i L2 The difference between the output current and the reference triangular wave value is the amplitude of the harmonic injection. The voltage across the resistor and inductor is the voltage difference between the outputs of the two rectifiers. The voltage-to-current ratio gives the resistance of the harmonic injection system. The harmonic injection system composed of a resistor and inductor has a simple structure and a good suppression effect on grid-side harmonics.

[0070] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A dual passive harmonic injection 12-pulse rectifier based on average current control, characterized in that, It includes a parallel 12-pulse rectifier, a harmonic injection system, a balanced reactor with a secondary side, a sampling unit, and a predictive controller; The parallel 12-pulse rectifier includes parallel rectifier bridges rec1 and rec2, each rectifier bridge including 6 thyristors. The parallel 12-pulse rectifier is connected in parallel with a harmonic injection system. The balancing reactor with secondary side transmits the waveform output by the parallel 12-pulse rectifier through the primary side to the single-phase rectifier bridge connected to the secondary side, and then modulates the input to the load through the single-phase rectifier bridge. The sampling unit collects the load current, load voltage, and line voltage. The predictive controller is equipped with an average current prediction method. Based on the collected load current, load voltage, and line voltage, the inductor current value at the next moment is calculated and compared with the current reference value at the next moment. The thyristor corresponding to the input line voltage with the smallest error will be triggered at the next moment. Each voltage vector participates in predicting the current value at the next moment. , to make the current reference value With instantaneous value The voltage vector with the smallest error is selected as the voltage vector for the next moment, and the thyristor corresponding to this voltage will be triggered to conduct; the current pulse is approximated as a sine wave to obtain average value predictive control, and the calculation expression is: .

2. The dual passive harmonic injection 12-pulse rectifier based on average current control according to claim 1, characterized in that, The harmonic injection system includes a resistor and an inductor connected in series, which are connected in parallel to a parallel 12-pulse rectifier.

3. The dual passive harmonic injection 12-pulse rectifier based on average current control according to claim 1, characterized in that, The conditions required for the average current prediction method are: 1) Set the inductor current reference value ; 2) Sample the instantaneous value of the inductor current, load voltage, and input line voltage; 3) Based on the current inductor current value Load voltage value and voltage vector Calculate the current value at the next moment. .

4. The dual passive harmonic injection 12-pulse rectifier based on average current control according to claim 1, characterized in that, The specific method for predicting the current value at the next moment is as follows: 1) Calculate the area enclosed by the two line voltage vectors and the load voltage, which represents the maximum increment of the inductor current; 2) Calculate the inductor current increment formed by triggering the thyristor at different times; 3) Predict the inductor current at the next moment and compare it with the reference current. Record the inductor current with the smallest error and select the line voltage vector that induces this inductor current. 4) Trigger the corresponding thyristor based on the line voltage vector selected in the previous step.

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