A high-performance digital control method and system for grid-connected converters

Abstract

The application belongs to the field of grid-connected converter control, and discloses a grid-connected converter high-performance digital control system and method. First, grid voltage and grid-connected current of the grid-connected converter are collected, and then a modulation wave is generated according to actual grid voltage and actual grid-connected current sampling values, vertical crossover of the modulation wave is eliminated, and a PWM control signal is generated together with a triangular carrier wave to control on-off of a switching tube of the grid-connected converter. The application can inhibit vertical crossover caused by switching frequency components, reduce grid-connected current distortion caused by vertical crossover, and ensure current THD treatment performance under the premise of maintaining dynamic performance of a multiple sampling method.

Description

Technical Field

[0001] This invention belongs to the field of grid-connected converter control, specifically relating to a high-performance digital control method and system for grid-connected converters. Background Technology

[0002] Grid-tied converters are fundamental units in AC microgrid systems for renewable energy generation and energy storage, and have a wide range of industrial applications. In a power grid, grid-tied converters maintain voltage stability for equipment and can adjust active and reactive power output according to the grid's needs. High-power grid-tied converters typically have low switching frequencies. When using traditional single-sampling or double-sampling digital control methods, the control frequency is 1-2 times the switching frequency, resulting in significant digital delays. This limits the performance in mitigating total harmonic distortion (THD) and the fast, error-free tracking of the grid current.

[0003] Multi-sampling (MS) refers to sampling and controlling multiple times within a switching cycle, increasing the control frequency and effectively reducing digital control delay. However, this method introduces switching frequency components into the modulation wave, causing the carrier wave and modulation wave to cross vertically during PWM modulation. This results in the converter losing closed-loop control at a specific duty cycle, introducing additional grid-connected current distortion.

[0004] Currently, suppressing this phenomenon mainly relies on switching frequency notch filters. These filters reduce components in the modulation wave that are integer multiples of the switching frequency, as well as sideband components that are integer multiples of the switching frequency plus or minus the power frequency, thus preventing vertical crossing and ensuring the THD control performance of the grid-connected current. However, the trade-off is that the added filter introduces additional phase lag, which reduces the fast performance of error-free tracking.

[0005] In summary, suppressing the vertical ride-through phenomenon caused by switching frequency components in multi-sample digitally controlled grid-connected converters is a valuable research question. Improvements to the control methods are needed to simultaneously ensure THD control of the grid-connected current and fast, error-free tracking. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a high-performance digital control method and system for grid-connected converters. The implementation process of this invention does not require a filter, can improve the system control frequency, and reduce grid-connected current distortion.

[0007] To achieve the above objectives, a high-performance digital control method for grid-connected converters includes the following steps:

[0008] The system generates a timing control pulse CTRLCLK to control the grid voltage u of the grid-connected converter. gand grid-connected current i g Perform sampling;

[0009] According to the grid voltage u g and grid-connected current i L Obtain the actual grid voltage u gs and the actual grid-connected current sampling value i gs The grid-connected current sampling value can come from either the left or right side of the output filter;

[0010] Based on the actual grid voltage u gs and the actual grid-connected current sampling value i gs Generate modulated wave v m ;

[0011] The modulation wave v is updated according to the system timing control pulse CTRLCLK. m Eliminate the modulated wave v m Vertical crossing;

[0012] Generate a triangular carrier wave v based on the system clock SYSCLK. ca ;

[0013] According to the triangular carrier v ca and the modulated wave v after eliminating vertical crossing m Generate PWM control signals to control the switching transistors of the grid-connected converter.

[0014] The frequency of the system timing control pulse CTRLCLK is the switching frequency f. s It is N times the multisampling coefficient, where N is the multisampling coefficient.

[0015] Generate modulated wave v m The specific methods are as follows:

[0016] Based on the actual grid voltage u gs Obtain the grid phase θ as the phase of the grid-connected current command;

[0017] Design grid-connected current amplitude instruction I according to power requirements. ref Grid-connected current amplitude command I ref Multiplying the current by the grid phase θ yields the grid-connected current command i. ref , will connect the grid current command i ref and the actual grid-connected current sampling value i gs The error input current regulator between them calculates the modulation wave v. m The value;

[0018] The modulation wave v is updated according to the system timing control pulse CTRLCLK. m And output it.

[0019] Demodulation wave v mVertical crossing, and generating triangular carriers v according to the system clock SYSCLK. ca The specific methods are as follows:

[0020] The values ​​of the modulated wave before and after the update are compared with the values ​​of the triangular carrier wave at the time of the update, and the vertical crossing is determined based on the comparison results.

[0021] If no vertical crossing occurs, a triangular carrier wave v is generated. ca ;

[0022] If a vertical crossing occurs, the phase of the triangular carrier wave is adjusted to suppress the vertical crossing phenomenon.

[0023] The specific method for determining whether a vertical crossing has occurred based on the comparison results is as follows:

[0024] If the comparison result indicates that vertical crossing detection did not occur, the counter increments or decrements by one in each system clock cycle (SYSCLK) until it reaches a preset upper limit or decrements to 0. Then, it increments or decrements by one in each cycle accordingly, generating a triangular carrier wave v. ca ;

[0025] If the comparison result indicates that vertical crossing detection has occurred, the counter loads the updated value of the modulation wave on the edge of the system clock SYSCLK to complete the carrier phase adjustment.

[0026] In (k+l / N)T s At all times, the grid voltage u g and grid-connected current i g Sampling is performed, where k and l are positive integers, N is the multisampling coefficient, and T s The switching cycle.

[0027] A high-performance digital control system for a grid-connected converter includes:

[0028] The system timing control module receives the pulse signal of the system clock and generates the system timing control pulse CTRLCLK, which is sent to the carrier phase control module and the multi-sampling current regulator.

[0029] A multi-sampling current regulator is used to regulate the grid voltage u of the grid-connected converter. g and grid-connected current i g Sampling is performed based on the actual grid voltage u gs and the actual grid-connected current sampling value i gs Update modulated wave v m ;

[0030] The carrier phase control module is used to update the modulated wave v according to the system timing control pulse CTRLCLK. m Eliminate the modulated wave v mVertical crossing, and generating triangular carriers v according to the system clock SYSCLK. ca Simultaneously, it is sent to the PWM modulation module;

[0031] The PWM modulation module is used to modulate the waveform based on the modulation wave v. m and triangular carrier v ca A PWM control signal is generated and sent to the corresponding switching transistor of the grid-connected converter.

[0032] The multi-sample current regulator includes:

[0033] The multiple sampling module is used to collect the actual grid voltage u. gs Send to the phase-locked loop to collect the actual grid-connected current sampling value i gs Send to the current control module;

[0034] Phase-locked loop (PLL) is used to adjust the voltage based on the actual grid voltage u. gs Obtain the grid phase θ and send it to the current control module;

[0035] The current control module is used to combine the grid phase θ and the grid-connected current amplitude command I. ref The actual grid-connected current sample value i is obtained by the system timing control pulse CTRLCLK. gs After processing, the modulated wave v is obtained. m It is sent to the carrier phase control module.

[0036] The carrier phase control module includes a vertical cross-travel detection module and a triangular carrier generation module;

[0037] The vertical crossing detection module includes:

[0038] Register, used to store the modulated wave v before updating m The value;

[0039] The first comparator is used to compare the previously updated modulated wave v. m The value of the value is compared with the value of the triangular carrier wave at the time of update, and the comparison result is sent into an XOR logic gate;

[0040] The second comparator is used to compare the updated modulated wave v. m The value of the value is compared with the value of the triangular carrier wave at the time of update, and the comparison result is sent into an XOR logic gate;

[0041] The XOR logic gate is used to output a high or low level to the triangular carrier generation module based on the result of the comparison between two comparators.

[0042] The triangular carrier generation module is used to generate a triangular carrier phase or a triangular carrier v based on the received level signal and the system clock SYSCLK. ca .

[0043] The triangular carrier generation module is used to increment or decrement a counter by one in each system clock cycle when the received level signal remains unchanged, until it reaches a preset upper limit or decrements to 0, and then decrements or increments by one in each cycle accordingly to generate a triangular carrier.

[0044] The received level signal is detected on the rising edge of each system clock SYSCLK. When the received level signal changes from low to high, the counter is loaded with the updated value of the modulation wave to complete the carrier phase adjustment.

[0045] Compared with existing technologies, this invention first collects the grid voltage and grid-connected current of the grid-connected converter. Then, based on the sampled values ​​of the actual grid voltage and grid-connected current, it generates a modulation wave. After eliminating vertical crossover of the modulation wave, it is used in conjunction with a triangular carrier wave to generate a PWM control signal to control the switching of the grid-connected converter's transistors. This invention can suppress vertical crossover caused by switching frequency components while maintaining the dynamic performance of the multi-sampling method, reducing grid-connected current distortion caused by vertical crossover, and ensuring current THD mitigation performance. Attached Figure Description

[0046] Figure 1 This is the main circuit topology and control block diagram of the system of the present invention;

[0047] Figure 2 This is a control flowchart of the carrier phase control module in this invention;

[0048] Figure 3 In the example, the grid-connected current i is obtained through double sampling and 16-times multiple sampling. g Comparison chart of instruction step response;

[0049] Figure 4 In the example, the grid-connected current i is obtained through double sampling and 16-times multiple sampling. g Fourier analysis comparison chart;

[0050] Figure 5 In this embodiment, the grid-connected current i is obtained through double sampling and carrier phase control with 16 multiple samplings. g Comparison chart of instruction step response;

[0051] Figure 6 In this embodiment, the grid-connected current i is obtained through double sampling and carrier phase control with 16 multiple samplings. g Fourier analysis comparison chart. Detailed Implementation

[0052] The invention will now be further described with reference to the accompanying drawings.

[0053] See Figure 1 and Figure 2 A high-performance digital control method for grid-connected converters includes the following steps:

[0054] S1 generates the system timing control pulse CTRLCLK, which controls the grid voltage u of the grid-connected converter. g and grid-connected current i g Sampling is performed; the frequency of the system timing control pulse CTRLCLK is the switching frequency f. s It is N times the multisampling coefficient, where N is the multisampling coefficient.

[0055] S2, based on the grid voltage u g and grid-connected current i g Obtain the actual grid voltage u gs and the actual grid-connected current sampling value i gs According to the actual grid voltage u gs and the actual grid-connected current sampling value i gs Generate modulated wave v m ; in (k+l / N)T s At all times, the grid voltage u g and grid-connected current i g Sampling is performed, where k and l are positive integers, N is the multisampling coefficient, and T s The switching cycle.

[0056] S3, update the modulated wave v according to the system timing control pulse CTRLCLK. m Eliminate the modulated wave v m Vertical crossing, and generating triangular carriers v according to the system clock SYSCLK. ca ;

[0057] S4, according to the triangular carrier v ca and the modulated wave v after eliminating vertical crossing m Generate a PWM control signal to control the switching of the transistors in the grid-connected converter. Modulated wave v m Greater than or equal to triangular carrier v ca At this time, switches S1 and S4 are turned on, while switches S2 and S3 are turned off; the modulated wave v m Less than the triangular carrier wave v ca When switching transistors S1 and S4 are turned off, switching transistors S2 and S3 are turned on.

[0058] Generate modulated wave v m The specific methods are as follows:

[0059] S21, based on the actual grid voltage u gs Obtain the grid phase θ as the phase of the current command;

[0060] S22, Design grid-connected current amplitude command I according to power requirements ref Grid-connected current amplitude command I refMultiplying the current by the grid phase θ yields the grid-connected current command i. ref , will connect the grid current command i ref and the actual grid-connected current sampling value i gs The error input current regulator between them calculates the modulation wave v. m The value;

[0061] S23, Update the modulated wave v according to the system timing control pulse CTRLCLK. m And output it.

[0062] Demodulation wave v m Vertical crossing, and generating triangular carriers v according to the system clock SYSCLK. ca The specific methods are as follows:

[0063] S31, compare the values ​​of the modulated wave before and after the update with the values ​​of the triangular carrier wave during the update, and determine whether vertical crossing has occurred based on the comparison results;

[0064] S32, if no vertical crossing occurs, then a triangular carrier wave v is generated. ca ;

[0065] If a vertical crossing occurs, the phase of the triangular carrier wave is adjusted to suppress the vertical crossing phenomenon.

[0066] The specific method for determining whether a vertical crossing has occurred based on the comparison results is as follows:

[0067] S321, if the comparison result indicates that vertical crossing detection did not occur, the counter increments or decrements by one in each system clock cycle until it reaches a preset upper limit or decrements to 0. Then, it decrements or increments by one in each cycle accordingly, generating a triangular carrier wave v. ca ;

[0068] If the comparison result indicates that vertical crossing detection has occurred, the counter is loaded with the updated value of the modulated wave to complete carrier phase adjustment.

[0069] See Figure 1 A high-performance digital control system for a grid-connected converter, comprising:

[0070] The system timing control module receives the pulse signal of the system clock and generates the system timing control pulse CTRLCLK, which is sent to the carrier phase control module and the multi-sampling current regulator.

[0071] A multi-sampling current regulator is used to regulate the grid voltage u of the grid-connected converter. g and grid-connected current i g Sampling is performed based on the actual grid voltage u gs and the actual grid-connected current sampling value i gs Update modulated wave vm ;

[0072] The carrier phase control module is used to update the modulated wave v according to the system timing control pulse CTRLCLK. m Eliminate the modulated wave v m Vertical crossing, and generating triangular carriers v according to the system clock SYSCLK. ca Simultaneously, it is sent to the PWM modulation module;

[0073] The PWM modulation module is used to modulate the waveform based on the modulation wave v. m and triangular carrier v ca A PWM control signal is generated and sent to the corresponding switching transistor in the grid-connected converter. The PWM modulation module uses an SPWM module.

[0074] The multi-sample current regulator includes:

[0075] The multiple sampling module is used to collect the actual grid voltage u. gs Send to the phase-locked loop to collect the actual grid-connected current sampling value i gs Send to the current control module;

[0076] Phase-locked loop (PLL) is used to adjust the voltage based on the actual grid voltage u. gs Obtain the grid phase θ and send it to the current control module;

[0077] The current control module is used to combine the grid phase θ and the grid-connected current amplitude command I. ref The actual grid-connected current sample value i is obtained by the system timing control pulse CTRLCLK. gs After processing, the modulated wave v is obtained. m It is sent to the carrier phase control module.

[0078] See Figure 2 The carrier phase control module includes a vertical cross-travel detection module and a triangular carrier generation module;

[0079] The vertical crossing detection module includes:

[0080] Register, used to store the modulated wave v before updating m The value;

[0081] The first comparator is used to compare the previously updated modulated wave v. m The value of the value is compared with the value of the triangular carrier wave at the time of update, and the comparison result is sent into an XOR logic gate;

[0082] The second comparator is used to compare the updated modulated wave v. m The value of the value is compared with the value of the triangular carrier wave at the time of update, and the comparison result is sent into an XOR logic gate;

[0083] The XOR logic gate is used to output a high or low level to the triangular carrier generation module based on the result of the comparison between two comparators.

[0084] The triangular carrier generation module is used to generate a triangular carrier phase or a triangular carrier v based on the received level signal and the system clock SYSCLK. ca When the received signal level is low, the counter increments or decrements by one in each system clock cycle (SYSCLK) until it reaches a preset upper limit or decrements to 0. Then, it increments or decrements by one in each cycle to generate a triangular carrier wave. The received signal level is detected at the rising edge of each system clock cycle (SYSCLK). When the received signal level changes from low to high, the counter loads the updated value of the modulation wave to complete the carrier phase adjustment.

[0085] Example:

[0086] The switching network uses a single-phase full-bridge design, the output filter uses a single inductor, and the grid current sampling is located to the left of the output filter. Tests were conducted on the PSIM simulation platform based on the parameters shown in Table 1.

[0087] Table 1 Test Platform Parameters

[0088]

[0089]

[0090] First, a comparison is made between the multisampling control method before the addition of carrier phase control and the traditional double-sampling control method. Because the multisampling method reduces digital control delay, the current loop proportional coefficient can be higher than that in the double-sampling method, thereby increasing the system control bandwidth. This characteristic is... Figure 3 The simulation results clearly demonstrate that for a step current command of 20A→10A→20A, the multisampling method can achieve error-free tracking faster. However, Figure 4 The results of Fourier analysis on the grid-connected current show that the multiple sampling method leads to an increase in harmonic components below 500Hz in the grid-connected current, which is detrimental to the power quality of the converter.

[0091] After adding carrier control, the multiple sampling control method is compared with the traditional double sampling control method again. Figure 5 Simulation results show that carrier phase control does not affect the speed of the multiple sampling method. The Fourier analysis results of the grid-connected current under the three methods are as follows: Figure 6 As shown, the harmonic components of the grid-connected current are lowest below 500Hz under the carrier phase control method proposed in this invention.

Claims

1. A digital control method for a grid-connected converter, characterized in that, Includes the following steps: The system generates the timing control pulse CTRLCLK, which controls the grid voltage of the grid-connected converter. u g and grid-connected current i g Perform sampling; According to the grid voltage u g and grid-connected current i g Obtain the actual grid voltage sample value u gs and actual grid-connected current sampling value i gs Based on the actual grid voltage sampling value u gs and actual grid-connected current sampling value i gs Generate modulated wave v m ; The modulation wave is updated according to the system timing control pulse CTRLCLK. v m Eliminate modulated waves v m Vertical crossing; Generate a triangular carrier wave based on the system clock SYSCLK. v ca The specific method is as follows: The values ​​of the modulated wave before and after the update are compared with the values ​​of the triangular carrier wave at the same update time. Based on the comparison results, it is determined whether a vertical crossover has occurred. If no vertical crossover has occurred, a triangular carrier wave is generated. v ca If vertical crossing occurs, the phase of the triangular carrier wave is adjusted to suppress the vertical crossing phenomenon. The specific method for determining whether vertical crossing has occurred based on the comparison results is as follows: If the comparison result indicates that vertical crossing detection did not occur, the counter increments or decrements by one in each system clock cycle until it reaches a preset upper limit or decrements to 0. Then, it decrements or increments by one in each cycle accordingly, and the counter generates a triangular carrier wave. v ca If the comparison results are opposite, it indicates that vertical crossing detection has occurred. In this case, the counter is loaded with the updated value of the modulated wave, and carrier phase adjustment is completed. According to triangular carrier v ca and modulated waves after vertical crossing v m Generate PWM control signals to control the switching transistors of the grid-connected converter.

2. The digital control method for a grid-connected converter according to claim 1, characterized in that, The frequency of the system timing control pulse CTRLCLK is the switching frequency. f s It is N times the multisampling coefficient, where N is the multisampling coefficient.

3. The digital control method for a grid-connected converter according to claim 1, characterized in that, Generate modulated wave v m The specific methods are as follows: Based on actual grid voltage sampling values u gs Obtaining grid phase As the phase of the current command; Design grid-connected current amplitude instructions based on power requirements. I ref Grid-connected current amplitude command I ref Phase with the power grid Multiplication yields the current command i ref , will connect the grid current command i ref and actual grid-connected current sampling value i gs The error input current regulator between them calculates the modulated wave. v m The value; The modulation wave is updated according to the system timing control pulse CTRLCLK. v m And output it.

4. The digital control method for a grid-connected converter according to claim 1, characterized in that, exist( k + l / N ) T s Constantly monitor the grid voltage u g and grid-connected current i g Sampling was performed, among which, k and l It is a positive integer. N For multiple sampling coefficients, T s The switching cycle.

5. A digital control system for a grid-connected converter, characterized in that, A digital control method for a grid-connected converter according to claim 1 includes: The system timing control module is used to receive the pulse signal of the system clock and generate the system timing control pulse CTRLCLK to send to the carrier phase control module and the multi-sampling current regulator; Multiple sampling current regulators are used to regulate the grid voltage of grid-connected converters. u g and grid-connected current i g Sampling is performed based on the actual grid voltage sampling value. u gs and actual grid-connected current sampling value i gs Update modulated wave v m ; The carrier phase control module is used to update the modulated wave according to the system timing control pulse CTRLCLK. v m Eliminate modulated waves v m Vertical crossing, and generating triangular carriers based on the system clock SYSCLK. v ca Simultaneously, it is sent to the PWM modulation module; PWM modulation module, used to modulate the waveform v m and triangular carrier v ca A PWM control signal is generated and sent to the corresponding switching transistor of the grid-connected converter.

6. A digital control system for a grid-connected converter according to claim 5, characterized in that, The multi-sample current regulator includes: The multiple sampling module is used to collect actual grid voltage sample values. u gs Send to the phase-locked loop to collect the actual grid-connected current sampling value. i gs Send to the current control module; Phase-locked loop (PLL) is used to sample actual grid voltage values. u gs Obtaining grid phase Send to the current control module; Current control module, used to combine grid phase Grid-connected current amplitude command I ref The actual grid-connected current sampled by the system timing control pulse CTRLCLK. i gs The modulated wave is obtained through processing. v m It is sent to the carrier phase control module.

7. A digital control system for a grid-connected converter according to claim 5, characterized in that, The carrier phase control module includes a vertical cross-travel detection module and a triangular carrier generation module; The vertical crossing detection module includes: Registers are used to store the modulated wave before updating. v m The value; The first comparator is used to compare the previously updated modulated wave. v m The value of the value is compared with the value of the triangular carrier wave at the time of update, and the comparison result is sent into an XOR logic gate; The second comparator is used to compare the updated modulated wave. v m The value of the value is compared with the value of the triangular carrier wave at the time of update, and the comparison result is sent into an XOR logic gate; The XOR logic gate is used to output a high or low level to the triangular carrier generation module based on the result of the comparison between two comparators. The triangular carrier generation module is used to generate a triangular carrier with adjustable phase or triangular carrier frequency based on the received level signal and the system clock SYSCLK. v ca .

8. A digital control system for a grid-connected converter according to claim 7, characterized in that, The triangular carrier generation module is used to increment or decrement the counter by one in each system clock cycle SYSCLK when the received level signal remains unchanged, until it reaches a preset upper limit or decrements to 0, and then decrements or increments by one in each cycle accordingly, thereby generating a triangular carrier. The received level signal is detected on the rising edge of each system clock SYSCLK. When the received level signal changes from low to high, the counter is loaded with the updated value of the modulation wave to complete the carrier phase adjustment.

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