DAB magnetic bias suppression method fusing power angle dynamic interpolation and current closed loop
By integrating dynamic power angle interpolation with current closed-loop, the problem of transformer bias in DAB converters was solved, achieving effective suppression during power step changes and zero bias operation under all operating conditions, thus improving the stability and efficiency of the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING SIFANG JIBAO AUTOMATION
- Filing Date
- 2022-10-19
- Publication Date
- 2026-06-05
AI Technical Summary
In DAB converters, due to inconsistent characteristics of switching devices and asymmetry of circuit parameters, transformer bias occurs, affecting system efficiency and stability, especially during power step changes where bias cannot be effectively suppressed.
A method combining dynamic power angle interpolation and current closed-loop control is adopted. The modulated wave is generated by current closed-loop control and compared with the carrier wave. Combined with the dynamic power angle interpolation algorithm, the phase shift angle of the bridge arm is dynamically adjusted to suppress transformer bias.
This enables the suppression of bias magnetization during power step changes, ensuring zero bias magnetization operation of the transformer under all operating conditions and improving the dynamic and steady-state characteristics of the system.
Smart Images
Figure CN115664214B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of DC bias suppression technology in power systems, and more specifically, relates to a DAB bias suppression method that integrates dynamic power angle interpolation and current closed-loop. Background Technology
[0002] Dual Active Bridge (DAB) converters are widely used in DC power transmission and distribution systems, new energy power generation, and electric vehicles due to their advantages such as low loss, flexible control, and bidirectional power transmission. However, due to inconsistencies in the characteristics of switching devices, asymmetrical circuit parameters, and differences in the delay of control trigger pulses between bridge arms, the current flowing through the transformer during the positive and negative half-cycles is asymmetrical, leading to transformer magnetization. If the transformer magnetization is significant, the transformer core is prone to saturation, increasing transformer losses and temperature rise, thus affecting system efficiency and stability. Therefore, reducing or eliminating transformer DC magnetization is a crucial problem that needs to be solved for the safe and efficient operation of DC-DC converters.
[0003] In DAB converters, phase-shift control is primarily used. Without considering dead time, the signals from the two switches in the same bridge arm are 50% duty cycle square waves with complementary waveforms. The phase angle difference between different arms of the same H-bridge is defined as the inner phase shift angle, and the phase angle difference between the primary and secondary H-bridges is defined as the outer phase shift angle. Ideally, this phase shift is symmetrical with respect to the positive and negative half-cycles of the transformer current. If the circuit parameters are asymmetrical, the positive and negative half-cycles of the transformer primary and secondary voltages will be asymmetrical, leading to asymmetrical transformer current waveforms and thus magnetization. Furthermore, during a reverse power step, the power angle (phase shift angle) changes abruptly with the power, causing asymmetrical transformer current half-cycles and magnetization. In phase-shift control without considering DC magnetization suppression, the drive waveform is symmetrical in both positive and negative half-cycles. If a certain half-cycle drive waveform simultaneously uses PWM, changing the waveform duty cycle, the voltage acting on the transformer becomes asymmetrical, thus counteracting the magnetization caused by the asymmetrical transformer current.
[0004] Traditional DC bias suppression methods utilize primary and secondary current sampling for control, which can suppress DC bias caused by circuit parameter asymmetry and deviations in positive and negative half-cycle control. However, when a power step occurs, the power angle changes abruptly with the power, failing to match the current state and generating a DC bias current in the power step direction. This current cannot be suppressed in the initial control phase, and its increase can cause transformer bias and potentially lead to device overcurrent. Therefore, considering the power step process and achieving zero bias operation under all operating conditions is a pressing issue. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a DAB bias suppression method that integrates dynamic power angle interpolation and current closed-loop control. The method uses current closed-loop control to suppress DC bias and simultaneously employs a power angle current interpolation algorithm to eliminate bias generated during power step changes. This method is suitable for suppressing transformer bias caused by power step changes in DAB power units in DC transmission and distribution networks, preventing transformer bias saturation, and reducing transformer losses.
[0006] The present invention adopts the following technical solution.
[0007] This invention proposes a DAB bias suppression method that integrates dynamic power angle interpolation with current closed-loop, comprising:
[0008] Step 1: Obtain the primary-side DC modulation wave and secondary-side DC modulation wave of the transformer based on current closed-loop control;
[0009] Step 2: Determine the phase shift angle based on the power transmission principle of the DAB converter. The phase shift angle includes: the phase difference of the drive signal between the first and second bridge arms of the DAB converter, the phase difference of the drive signal between the first and third bridge arms of the DAB converter, and the phase difference of the drive signal between the third and fourth bridge arms of the DAB converter; use the phase shift angle to generate the phase-shifted carriers of the first, second, third, and fourth bridge arms of the DAB converter.
[0010] Step 3: Detect whether a power step occurs in the DAB converter; if no power step occurs, proceed directly to step 4; if a power step occurs, based on the power angle dynamic interpolation method, use the current cycle power angle setpoint and the previous cycle power angle setpoint of each bridge arm to obtain the output power angle value of each bridge arm in the current carrier cycle; in each carrier cycle, after updating the phase shift angle with the output power angle value of each bridge arm, repeat step 2 to update the phase shift carrier of the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm of the DAB converter;
[0011] Step 4: Compare the primary-side DC modulation wave with the phase-shifted carrier waves of the first and second bridge arms to obtain the driving pulses of the first and second bridge arms; compare the secondary-side DC modulation wave with the phase-shifted carrier waves of the third and fourth bridge arms to obtain the driving pulses of the third and fourth bridge arms.
[0012] Step 5: Use the drive pulses of each bridge arm to suppress the bias magnetization of the DAB converter.
[0013] Preferably, step 1 includes:
[0014] Step 1.1: Collect the first primary current flowing into the primary side of the transformer and the first secondary current flowing out of the secondary side of the transformer;
[0015] Step 1.2: The first primary current and the first secondary current are filtered by hardware to obtain the first primary DC current and the first secondary DC current.
[0016] Step 1.3: Convert the first primary DC current to the secondary side to obtain the second secondary DC current;
[0017] Step 1.4: The sum of the first secondary side DC current and the second secondary side DC current is used as the first input signal, and the difference between the first secondary side DC current and the second secondary side DC current is used as the second input signal.
[0018] Step 1.5: The first input signal and the second input signal are passed through a PI circuit and then subtracted to obtain the primary-side DC modulated wave; the first input signal and the second input signal are passed through a PI circuit and then summed to obtain the secondary-side DC modulated wave.
[0019] Preferably, step 2 includes:
[0020] Step 2.1: Based on the given transmission power and the transmission power principle of the DAB converter, determine the phase shift angle; the phase shift angle includes: the phase difference of the drive signal between the first and second bridge arms of the DAB converter, the phase difference of the drive signal between the first and third bridge arms of the DAB converter, and the phase difference of the drive signal between the third and fourth bridge arms of the DAB converter.
[0021] Step 2.2, the phase-shifted carriers of each bridge arm of the DAB converter satisfy the following relationship:
[0022] cnt_basic=cnt_main+cnt_shift;
[0023] cnt_1 = cnt_basic + d12out;
[0024] cnt_2 = cnt_basic - d12out;
[0025] cnt_basic_2=cnt_basic-d13out;
[0026] cnt_3 = cnt_basic_2 + d34out;
[0027] cnt_4 = cnt_basic_2 - d34out;
[0028] In the formula,
[0029] cnt_1 is the phase-shifted carrier of the first bridge arm;
[0030] cnt_2 is the phase-shifted carrier of the second bridge arm;
[0031] cnt_3 is the phase-shifted carrier of the third bridge arm;
[0032] cnt_4 is the phase-shifted carrier of the fourth bridge arm;
[0033] cnt_basic is the flag carrier for updating the phase shift angle of the primary side bridge arm during bias suppression.
[0034] cnt_basic_2 is an intermediate variable for updating the phase shift angle of the secondary bridge arm during bias suppression.
[0035] cnt_main is a time-synchronized triangular wave generated by controlling the increment / decrement mode of a counter.
[0036] cnt_shift is the phase shift of the first bridge arm carrier.
[0037] d12out is the phase angle difference between the carrier waves of the first and second bridge arms when no bias suppression is applied.
[0038] d13out is the phase angle difference between the carrier waves of the first and third bridge arms when no bias suppression is applied.
[0039] d34out is the phase angle difference between the carrier waves of the third and fourth bridge arms when no bias suppression is applied.
[0040] Preferably, in step 3, when a power step occurs, each bridge arm performs the following steps within each carrier cycle to obtain the output power angle value of the bridge arm within this carrier cycle:
[0041] Step 3.1: Set the first control flag and the second control flag; wherein, the first control flag is used to indicate that the input data reception is complete; the second control flag is used to indicate whether new input data has been received within one carrier cycle;
[0042] Step 3.2: When the input data reception is completed, that is, when the first control flag is set to 1, and it is determined that new input data has been received in the current carrier cycle, that is, when the second control flag is set to 1, the average of the current cycle power angle given value and the previous cycle power angle given value is used as the output power angle value of the bridge arm in the current carrier cycle.
[0043] Step 3.3: When the input data reception is completed, i.e. the first control flag is set to 1, and it is determined that no new input data has been received in the current carrier cycle, i.e. the second control flag is set to 0, the average of the current cycle power angle setpoint and the previous cycle output power angle value is used as the output power angle value of the bridge arm in the current carrier cycle.
[0044] Step 3.4: When the input data has not been received completely, i.e. the first control flag is set to 0, and it is determined that new input data has been received in the current carrier cycle, i.e. the second control flag is set to 1, the power angle given value of the previous cycle is used as the output power angle value of the bridge arm in the current carrier cycle.
[0045] Step 3.5: When the input data has not been received completely, i.e. the first control flag is set to 0, and it is determined that no new input data has been received in the current carrier cycle, i.e. the second control flag is set to 0, the current cycle power angle setpoint is used as the output power angle value of the bridge arm in the current carrier cycle.
[0046] Furthermore, in step 3.2, the output power angle value of the bridge arm within this carrier cycle satisfies the following relationship:
[0047] r_cnt_shift(n) = cnt_shift(n)
[0048] r_cnt12(n) = cnt12(n)
[0049] r_cnt13(n)=cnt13(n) / 2+cnt13(n-1) / 2
[0050] r_cnt34(n) = cnt34(n)
[0051] change2_flag = 1
[0052] In the formula,
[0053] cnt_shift(n) is the current phase shift setpoint for the first bridge arm carrier.
[0054] r_cnt_shift(n) is the phase-shift output value of the first bridge arm carrier.
[0055] r_cnt12(n) is the current phase shift angle output value between the first and second bridge arms.
[0056] r_cnt13(n) is the current phase shift angle output value between the first and third bridge arms.
[0057] r_cnt34(n) is the current phase shift angle output value between the third and fourth bridge arms.
[0058] cnt12(n) represents the phase shift angle between the first and second bridge arms given at the moment.
[0059] cnt34(n) represents the phase shift angle between the current third and fourth bridge arms.
[0060] cnt13(n) represents the phase shift angle between the first and third bridge arms given at the moment.
[0061] cnt13(n-1) is the phase shift angle between the first and third bridge arms given in the previous iteration.
[0062] change2_flag is the second control flag.
[0063] Furthermore, in step 3.3, the output power angle value of the bridge arm within this carrier cycle satisfies the following relationship:
[0064] r_cnt_shift(n) = cnt_shift(n)
[0065] r_cnt12(n) = cnt12(n)
[0066] r_cnt13(n)=cnt13(n) / 2+r_cnt13(n-1) / 2
[0067] r_cnt34(n) = cnt34(n)
[0068] change2_flag = 1
[0069] In the formula,
[0070] cnt_shift(n) is the current phase shift setpoint for the first bridge arm carrier.
[0071] r_cnt_shift(n) is the phase-shift output value of the first bridge arm carrier.
[0072] r_cnt12(n) is the current phase shift angle output value between the first and second bridge arms.
[0073] r_cnt13(n) is the current phase shift angle output value between the first and third bridge arms.
[0074] r_cnt13(n-1) is the output value of the phase shift angle between the first and third bridge arms in the previous iteration.
[0075] r_cnt34(n) is the current phase shift angle output value between the third and fourth bridge arms.
[0076] cnt12(n) represents the phase shift angle between the first and second bridge arms given at the moment.
[0077] cnt34(n) represents the phase shift angle between the current third and fourth bridge arms.
[0078] cnt13(n) represents the phase shift angle between the first and third bridge arms given at the moment.
[0079] change2_flag is the second control flag.
[0080] Furthermore, in step 3.4, the output power angle value of the bridge arm within this carrier cycle satisfies the following relationship:
[0081] r_cnt_shift(n) = cnt_shift(n)
[0082] r_cnt12(n) = cnt12(n)
[0083] r_cnt13(n) = cnt13(n-1)
[0084] r_cnt34(n) = cnt34(n)
[0085] change2_flag = 0
[0086] In the formula,
[0087] cnt_shift(n) is the current phase shift setpoint for the first bridge arm carrier.
[0088] r_cnt_shift(n) is the phase-shift output value of the first bridge arm carrier.
[0089] r_cnt12(n) is the current phase shift angle output value between the first and second bridge arms.
[0090] r_cnt13(n) is the current phase shift angle output value between the first and third bridge arms.
[0091] r_cnt34(n) is the current phase shift angle output value between the third and fourth bridge arms.
[0092] cnt12(n) represents the phase shift angle between the first and second bridge arms given at the moment.
[0093] cnt34(n) represents the phase shift angle between the current third and fourth bridge arms.
[0094] cnt13(n-1) is the phase shift angle between the first and third bridge arms given in the previous iteration.
[0095] change2_flag is the second control flag.
[0096] Furthermore, in step 3.5, the output power angle value of the bridge arm within this carrier cycle satisfies the following relationship:
[0097] r_cnt_shift(n) = cnt_shift(n)
[0098] r_cnt12(n) = cnt12(n)
[0099] r_cnt13(n) = cnt13(n)
[0100] r_cnt34(n) = cnt34(n)
[0101] change2_flag = 0
[0102] In the formula,
[0103] cnt_shift(n) is the current phase shift setpoint for the first bridge arm carrier.
[0104] r_cnt_shift(n) is the phase-shift output value of the first bridge arm carrier.
[0105] r_cnt12(n) is the current phase shift angle output value between the first and second bridge arms.
[0106] r_cnt13(n) is the current phase shift angle output value between the first and third bridge arms.
[0107] r_cnt34(n) is the current phase shift angle output value between the third and fourth bridge arms.
[0108] cnt12(n) represents the phase shift angle between the first and second bridge arms given at the moment.
[0109] cnt34(n) represents the phase shift angle between the current third and fourth bridge arms.
[0110] cnt13(n) represents the phase shift angle between the first and third bridge arms given at the moment.
[0111] change2_flag is the second control flag.
[0112] Preferably, in step 3, the phase angle is updated twice within each carrier cycle. The first update is at the peak of the triangular wave carrier, and the second update is at the trough of the triangular wave carrier. The triangular wave carrier is obtained by incrementing or decrementing the value of the counter register in the controller.
[0113] Preferably, step 4 includes:
[0114] Step 4.1: Compare the primary side DC modulation wave with the first bridge arm phase shift carrier wave. When the first bridge arm phase shift carrier wave is higher than the primary side DC modulation wave, output a high-level signal; otherwise, output a low-level signal.
[0115] Step 4.2: Compare the primary-side DC modulation wave with the second-arm phase-shift carrier wave. When the second-arm phase-shift carrier wave is higher than the primary-side DC modulation wave, output a high-level signal; otherwise, output a low-level signal.
[0116] Step 4.3: Compare the secondary-side DC modulation wave with the third-arm phase-shift carrier wave. When the third-arm phase-shift carrier wave is higher than the secondary-side DC modulation wave, output a high-level signal; otherwise, output a low-level signal.
[0117] Step 4.4: Compare the secondary-side DC modulation wave with the fourth-arm phase-shift carrier wave. When the fourth-arm phase-shift carrier wave is higher than the secondary-side DC modulation wave, output a high-level signal; otherwise, output a low-level signal.
[0118] The beneficial effect of the present invention is that, compared with the prior art, the present invention simultaneously adopts current closed-loop control technology and power angle dynamic interpolation technology to suppress transformer bias caused by inconsistent characteristics of switching devices and asymmetric circuit parameters in DAB converters.
[0119] In this invention, the current closed-loop control method uses the primary and secondary currents of the transformer to generate a modulation wave through the control loop, which is then compared with the carrier wave to generate a drive signal waveform with asymmetrical positive and negative half-cycles. The power angle dynamic interpolation method averages the given power angle value with the previous power angle value, avoiding the magnetization caused by the asymmetry of the current waveform during power step changes in traditional control. By combining the current closed-loop control with the power angle dynamic interpolation method, the magnetization current of the high-frequency transformer is suppressed.
[0120] Compared with traditional bias suppression technology, the dynamic power angle interpolation and current closed-loop fusion bias suppression technology proposed in this invention can suppress bias current in the early stage of power step when a power step occurs through dynamic power angle interpolation control, thereby realizing zero bias operation of DAB-DCT (DC transformer) isolation transformer under all operating conditions and obtaining good dynamic and steady-state characteristics. Attached Figure Description
[0121] Figure 1 This is a circuit topology diagram of DAB in an embodiment of the present invention;
[0122] Figure 1 The annotations in the accompanying drawings are explained as follows:
[0123] S1, S2, S3, and S4 are all switching transistors; 1-first bridge arm, 2-second bridge arm, 3-third bridge arm, 4-fourth bridge arm; C1-primary side support capacitor, C2-secondary side support capacitor, L-current limiting inductor, T-transformer, I1-primary side current, I2-secondary side current, i H -The first primary current flowing into the primary side of the transformer, i L -The first secondary current flowing out of the transformer secondary side;
[0124] Figure 2 This is the current closed-loop control diagram in an embodiment of the present invention;
[0125] Figure 3 This is a flowchart of the dynamic interpolation algorithm for power angle in an embodiment of the present invention;
[0126] Figure 4 This is a diagram of the square wave generation method in the DAB bias suppression method that integrates dynamic power angle interpolation and current closed-loop proposed in this invention; the dashed line in the diagram represents the PWM waveform, the double-dotted line represents the modulation waveform, and the solid line represents the carrier waveform.
[0127] Figure 5This is a comparison waveform of using only the current closed-loop algorithm and using both dynamic power angle interpolation and the current closed-loop algorithm in an embodiment of the present invention. Figure 1 ;
[0128] Figure 6 This is a comparison waveform of using only the current closed-loop algorithm and using both dynamic power angle interpolation and the current closed-loop algorithm in an embodiment of the present invention. Figure 2 . Detailed Implementation
[0129] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.
[0130] The circuit topology of the DAB converter is as follows: Figure 1 As shown in the diagram. In the DAB converter circuit, switches S1 and S2 form the first bridge arm 1, S3 and S4 form the second bridge arm 2, and the first bridge arm 1 and the second bridge arm 2 constitute the primary-side H-bridge; S5 and S6 form the third bridge arm 3, S7 and S8 form the fourth bridge arm 4, and the third bridge arm 3 and the fourth bridge arm 4 constitute the secondary-side H-bridge. C1 is the primary-side supporting capacitor, C2 is the secondary-side supporting capacitor, L is the current-limiting inductor, and T is the transformer with a turns ratio of n:1. U1 and U2 are the primary-side voltage and secondary-side voltage, respectively, and I1 and I2 are the primary-side current and secondary-side current, respectively. H i L These are the first primary current flowing into the primary side of the transformer and the first secondary current flowing out of the secondary side of the transformer, respectively.
[0131] This invention proposes a DAB bias suppression method that integrates dynamic power angle interpolation with current closed-loop, comprising:
[0132] Step 1: Obtain the primary-side DC modulation wave and the secondary-side DC modulation wave of the transformer based on current closed-loop control.
[0133] Specifically, such as Figure 2 Step 1 includes:
[0134] Step 1.1: Collect the first primary current i flowing into the primary side of the transformer. H and the first secondary current i flowing out of the transformer secondary side L ;
[0135] Step 1.2, the first primary current i H and the first secondary current i L After hardware filtering, the first primary DC current i is obtained.H_DC and the first secondary side DC current i L_DC ;
[0136] Step 1.3, the first primary-side DC current i H_DC The second secondary DC current ni is obtained by referring to the secondary side. H_DC ;
[0137] Step 1.4, using the first secondary side DC current i L_DC With the second secondary side DC current ni H_DC The sum of these is used as the first input signal i m_dc With the first secondary side DC current i L_DC With the second secondary side DC current ni H_DC The difference is used as the second input signal i bias ;
[0138] In this embodiment, the first input signal i m_dc The bias current within the transformer is characterized, thus enabling closed-loop control of the bias current; the second input signal i bias This characterizes the bias current within the transformer, thus enabling closed-loop control of the bias current.
[0139] Step 1.5: The first input signal and the second input signal are passed through a PI circuit and then subtracted to obtain the primary-side DC modulated wave D. H The first and second input signals are passed through a PI controller and then summed to obtain the secondary DC modulated wave D. L .
[0140] In this embodiment, the first input signal i m_dc The first signal ΔD is obtained after PI control and filtering. m The second input signal i bias The second signal ΔD is obtained after PI control and filtering. bias First signal ΔD m Second signal ΔD bias The difference is the primary side DC modulation wave D H The first signal ΔD m Second signal ΔD bias The sum of is the secondary-side DC modulation wave D L Primary-side DC modulation wave D H and secondary side DC modulation wave D L Together they serve as the input signals for the DAB bias suppression modulation wave generation step.
[0141] If the primary and secondary sides of the DAB converter are unbiased in steady state, then the DC modulation wave D on the primary side... H and secondary side DC modulation wave D LThe amplitudes are all 0, indicating that steady-state, non-biased control of the primary and secondary sides can be achieved through current closed-loop control; if the transformer has DC bias, then the primary side DC modulation wave D H and secondary side DC modulation wave D L The amplitude is not zero. Current closed-loop control eliminates magnetization by changing the duty cycle of the positive and negative half-cycle drive signals of the PWM waveform, making the voltage of the transformer asymmetrical during the positive and negative half-cycles. It can be seen that current closed-loop control can regulate the current and thus suppress magnetization. However, if the power angle changes too quickly during a power step change, causing the current to not change in time, it will be impossible to regulate the current and thus suppress magnetization through current closed-loop control.
[0142] Step 2: Determine the phase shift angle based on the power transmission principle of the DAB converter. The phase shift angle includes: the phase difference of the drive signal between the first and second bridge arms of the DAB converter, the phase difference of the drive signal between the first and third bridge arms of the DAB converter, and the phase difference of the drive signal between the third and fourth bridge arms of the DAB converter. Use the phase shift angle to generate the phase shift carriers of the first, second, third, and fourth bridge arms of the DAB converter.
[0143] Specifically, step 2 includes:
[0144] Step 2.1: Based on the given transmission power and the transmission power principle of the DAB converter, determine the phase shift angle; the phase shift angle includes: the phase difference of the drive signal between the first and second bridge arms of the DAB converter, the phase difference of the drive signal between the first and third bridge arms of the DAB converter, and the phase difference of the drive signal between the third and fourth bridge arms of the DAB converter.
[0145] Optionally, the phase difference of the driving signal between the first bridge arm 1 and the second bridge arm 2 is the first power angle, the phase difference of the driving signal between the first bridge arm 1 and the third bridge arm 3 is the second power angle, and the phase difference of the driving signal between the third bridge arm 3 and the fourth bridge arm 4 is the third power angle.
[0146] Step 2.2, the phase-shifted carriers of each bridge arm of the DAB converter satisfy the following relationship:
[0147] cnt_basic=cnt_main+cnt_shift;
[0148] cnt_1 = cnt_basic + d12out;
[0149] cnt_2 = cnt_basic - d12out;
[0150] cnt_basic_2=cnt_basic-d13out;
[0151] cnt_3 = cnt_basic_2 + d34out;
[0152] cnt_4=cnt_basic_2-d34out;......(1)
[0153] In the formula,
[0154] cnt_1 is the phase-shifted carrier of the first bridge arm;
[0155] cnt_2 is the phase-shifted carrier of the second bridge arm;
[0156] cnt_3 is the phase-shifted carrier of the third bridge arm;
[0157] cnt_4 is the phase-shifted carrier of the fourth bridge arm;
[0158] cnt_basic is the flag carrier for updating the phase shift angle of the primary side bridge arm during bias suppression.
[0159] cnt_basic_2 is an intermediate variable for updating the phase shift angle of the secondary bridge arm during bias suppression.
[0160] cnt_main is a time-synchronized triangular wave generated by controlling the increment / decrement mode of a counter.
[0161] cnt_shift is the phase shift of the first bridge arm carrier. This parameter is set to control the initial phase of different modules. The default initial phase angle of a module is 0, so this parameter is 0.
[0162] d12out is the phase angle difference between the carrier waves of the first and second bridge arms when no bias suppression is applied.
[0163] d13out is the phase angle difference between the carrier waves of the first and third bridge arms when no bias suppression is applied.
[0164] d34out is the phase angle difference between the carrier waves of the third and fourth bridge arms when no bias suppression is applied.
[0165] The three parameters d12out, d13out, and d34ou are the phase shift angles given without any bias suppression algorithm.
[0166] Equation (1) illustrates the generation process of phase-shifted carriers for each arm of the DAB converter. The basic time-synchronized triangular wave cnt_main is generally generated by controlling the increment / decrement mode of the counter. Before generating the carriers, the input data can be determined according to the basic theory of DAB transmission power, that is, given known quantities. The input data includes: the phase shift of the first arm carrier cnt_shift, the phase angle difference d12out between the first and second arm carriers without bias suppression, the phase angle difference d13out between the first and third arm carriers without bias suppression, and the phase angle difference d34out between the third and fourth arm carriers without bias suppression. Four sets of phase-shifted triangular wave carriers for the arms can be obtained through the generation process given by Equation (1).
[0167] Step 3: Detect whether a power step occurs in the DAB converter; if no power step occurs, proceed directly to step 4; if a power step occurs, use the current cycle power angle setpoint and the previous cycle power angle setpoint of each bridge arm to obtain the output power angle value of each bridge arm in the current carrier cycle based on the power angle dynamic interpolation method; in each carrier cycle, update the phase shift angle with the output power angle value of each bridge arm, and repeat step 2 to update the phase shift carrier of the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm of the DAB converter.
[0168] Specifically, such as Figure 3 In step 3, when a power step occurs, each bridge arm performs the following steps within each carrier cycle to obtain the output power angle value of the bridge arm within this carrier cycle:
[0169] Step 3.1: Set the first control flag bit change_flag and the second control flag bit change2_flag; wherein, the first control flag bit is used to indicate that the input data reception is complete; the second control flag bit is used to indicate whether new input data has been received within one carrier cycle.
[0170] In this embodiment, when the secondary side completes receiving input data, the first control flag bit change_flag is set to 1. The input data includes: the phase shift angle cnt12 between the first and second bridge arms, the phase shift angle cnt13 between the first and third bridge arms, the phase shift angle cnt34 between the third and fourth bridge arms, and the carrier phase shift cnt_shift of the first bridge arm.
[0171] Step 3.2: When the input data reception is completed, that is, when the first control flag change_flag is set to 1, and when it is determined that new input data has been received in the current carrier cycle, that is, when the second control flag change2_flag is set to 1, the average of the current cycle power angle given value and the previous cycle power angle given value is used as the output power angle value of the bridge arm in the current carrier cycle.
[0172] Specifically, when the first control flag change_flag = 1 and the second control flag change2_flag = 1, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship:
[0173] r_cnt_shift(n) = cnt_shift(n)
[0174] r_cnt12(n) = cnt12(n)
[0175] r_cnt13(n)=cnt13(n) / 2+cnt13(n-1) / 2
[0176] r_cnt34(n) = cnt34(n)
[0177] change2_flag = 1
[0178] In the formula,
[0179] cnt_shift(n) is the current phase shift setpoint for the first bridge arm carrier.
[0180] r_cnt_shift(n) is the phase-shift output value of the first bridge arm carrier.
[0181] r_cnt12(n) is the current phase shift angle output value between the first and second bridge arms.
[0182] r_cnt13(n) is the current phase shift angle output value between the first and third bridge arms.
[0183] r_cnt34(n) is the current phase shift angle output value between the third and fourth bridge arms.
[0184] cnt12(n) represents the phase shift angle between the first and second bridge arms given at the moment.
[0185] cnt34(n) represents the phase shift angle between the current third and fourth bridge arms.
[0186] cnt13(n) represents the phase shift angle between the first and third bridge arms given at the moment.
[0187] cnt13(n-1) is the phase shift angle between the first and third bridge arms given in the previous iteration.
[0188] change2_flag is the second control flag.
[0189] It is worth noting that the phase angles of any two bridge arms can be updated using the above formula. In this embodiment, for the sake of simplifying the actual control system, a single-phase modulation method is used to verify the method proposed in this invention, that is, a single phase shift is used to update the corresponding first and third bridge arms. Therefore, only the phase angles of the first and third bridge arms are updated, while the other two phase angles remain unchanged. Theoretically, the optimal effect is to optimize any two bridge arms. In practical applications, to save the controller's computing power and improve the computing speed, only the phase angles of the first and third bridge arms are updated.
[0190] Step 3.3: When the input data reception is completed, that is, when the first control flag bit change_flag is set to 1, and it is determined that no new input data has been received in the current carrier cycle, that is, when the second control flag bit change2_flag is set to 0, the average of the current cycle power angle given value and the previous cycle output power angle value is used as the output power angle value of the bridge arm in the current carrier cycle.
[0191] In this embodiment, when the first control flag change_flag = 1 and the second control flag change2_flag = 0, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship:
[0192] r_cnt_shift(n) = cnt_shift(n)
[0193] r_cnt12(n) = cnt12(n)
[0194] r_cnt13(n)=cnt13(n) / 2+r_cnt13(n-1) / 2
[0195] r_cnt34(n) = cnt34(n)
[0196] change2_flag = 1
[0197] Step 3.4: When the input data has not been received completely, i.e., the first control flag change_flag is set to 0, and it is determined that new input data has been received in the current carrier cycle, i.e., the second control flag change2_flag is set to 1, the power angle given value of the previous cycle is used as the output power angle value of the bridge arm in the current carrier cycle.
[0198] In this embodiment, when the first control flag change_flag = 0 and the second control flag change2_flag = 1, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship:
[0199] r_cnt_shift(n) = cnt_shift(n)
[0200] r_cnt12(n) = cnt12(n)
[0201] r_cnt13(n) = cnt13(n-1)
[0202] r_cnt34(n) = cnt34(n)
[0203] change2_flag = 0
[0204] Step 3.5: When the input data has not been received completely, i.e., the first control flag change_flag is set to 0, and it is determined that no new input data has been received in the current carrier cycle, i.e., the second control flag change2_flag is set to 0, the current cycle power angle given value is used as the output power angle value of the bridge arm in the current carrier cycle.
[0205] In this embodiment, when the first control flag change_flag = 0 and the second control flag change2_flag = 0, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship:
[0206] r_cnt_shift = cnt_shift
[0207] r_cnt12=cnt12
[0208] r_cnt13=cnt13
[0209] r_cnt34=cnt34
[0210] cnt13_reg = cnt13
[0211] change2_flag = 0
[0212] In step 3, the phase angle is updated twice within each carrier cycle. The first update is at the peak of the triangular wave carrier, and the second update is at the trough of the triangular wave carrier. The triangular wave carrier is obtained by incrementing or decrementing the counter register value in the controller.
[0213] Set cnt to the value of the increment / decrement counter register in the controller. The phase shift angle is updated twice per control cycle. Data is updated when the cnt count reaches the peak or trough of the triangular wave carrier wave. The first update occurs when cnt = -cnt_max, and the second update occurs when cnt = cnt_max. Alternating enable means that if an update is triggered when cnt = -cnt_max, the next update is triggered when cnt = cnt_max, forming an alternating cycle.
[0214] As can be seen, when a power step occurs, after updating the phase shift angle with the output power angle value of each bridge arm, step 2 is repeated to update the phase shift carriers of the first, second, third, and fourth bridge arms of the DAB converter. The resulting phase shift carriers of each bridge arm are all high-frequency carriers.
[0215] Step 4, modulate the primary-side DC-DC wave D H The phase-shifted carrier waves of the first and second bridge arms are compared to obtain the driving pulses of the first and second bridge arms; the secondary-side DC modulation wave D... L The driving pulses of the third and fourth bridge arms are compared with the phase-shifted carriers of the third and fourth bridge arms to obtain the driving pulses of the third and fourth bridge arms.
[0216] Specifically, step 4 includes:
[0217] Step 4.1, modulate the primary-side DC-DC wave D HCompared with the phase-shifted carrier wave of the first bridge arm, when the phase-shifted carrier wave of the first bridge arm is higher than the DC modulation wave D of the primary side... H When the signal is high, a high-level signal is output; otherwise, a low-level signal is output.
[0218] Step 4.2, modulate the primary-side DC-DC wave D H Compared with the phase-shifted carrier of the second bridge arm, when the phase-shifted carrier of the second bridge arm is higher than the DC modulation wave D of the primary side... H When the signal is high, a high-level signal is output; otherwise, a low-level signal is output.
[0219] Step 4.3, modulate the secondary-side DC-DC wave D L The signal is compared with the phase-shifted carrier wave of the third bridge arm. When the phase-shifted carrier wave of the third bridge arm is higher than the DC modulation wave of the secondary side, a high-level signal is output; otherwise, a low-level signal is output.
[0220] Step 4.4, modulate the secondary-side DC modulation wave D L The signal is compared with the phase-shifted carrier wave of the fourth bridge arm. When the phase-shifted carrier wave of the fourth bridge arm is higher than the DC modulation wave of the secondary side, a high-level signal is output; otherwise, a low-level signal is output.
[0221] like Figure 4 As shown, if the transformer has no bias magnetism, the modulation amplitude is 0, and the drive signal waveform is a square wave with symmetrical positive and negative half-cycles. If the transformer has bias magnetism, the modulation amplitude is not 0, and the drive signal waveform is asymmetrical with positive and negative half-cycles. This asymmetry cancels out the asymmetry of the transformer's positive and negative half-cycle voltage waveforms caused by inconsistent characteristics of switching devices, asymmetric circuit parameters, etc., in order to suppress transformer bias magnetism.
[0222] Figure 5 and Figure 6 The figures show the AC current waveforms of a transformer using only current closed-loop control and simultaneously using dynamic power angle interpolation and current closed-loop control. Both control methods can suppress transformer magnetization after a period of time. While the traditional current closed-loop control can suppress transformer magnetization, in the initial stage of a power step change, the angle changes abruptly with the power output and cannot match the current current state, still resulting in magnetization.
[0223] The beneficial effect of the present invention is that, compared with the prior art, the present invention simultaneously adopts current closed-loop control technology and power angle dynamic interpolation technology to suppress transformer bias caused by inconsistent characteristics of switching devices and asymmetric circuit parameters in DAB converters.
[0224] In this invention, the current closed-loop control method uses the primary and secondary currents of the transformer to generate a modulation wave through the control loop, which is then compared with the carrier wave to generate a drive signal waveform with asymmetrical positive and negative half-cycles. The power angle dynamic interpolation method averages the given power angle value with the previous power angle value, avoiding the magnetization caused by the asymmetry of the current waveform during power step changes in traditional control. By combining the current closed-loop control with the power angle dynamic interpolation method, the magnetization current of the high-frequency transformer is suppressed.
[0225] Compared with traditional bias suppression technology, the dynamic power angle interpolation and current closed-loop fusion bias suppression technology proposed in this invention can suppress bias current in the early stage of power step when a power step occurs through dynamic power angle interpolation control, thereby realizing zero bias operation of DAB-DCT (DC transformer) isolation transformer under all operating conditions and obtaining good dynamic and steady-state characteristics.
[0226] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.
Claims
1. A DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop, characterized in that, The method includes: Step 1: Obtain the primary-side DC modulation wave and secondary-side DC modulation wave of the transformer based on current closed-loop control; Step 2: Determine the phase shift angle based on the power transmission principle of the DAB converter. The phase shift angle includes: the phase difference of the drive signal between the first and second bridge arms of the DAB converter, the phase difference of the drive signal between the first and third bridge arms of the DAB converter, and the phase difference of the drive signal between the third and fourth bridge arms of the DAB converter. Use the phase shift angle to generate the phase-shifted carriers of the first, second, third, and fourth bridge arms of the DAB converter. The phase-shifted carriers of each bridge arm of the DAB converter satisfy the following relationship: In the formula, cnt _1 represents the phase-shifted carrier of the first bridge arm. cnt _2 represents the phase-shifted carrier of the second bridge arm. cnt _3 represents the phase-shifted carrier of the third bridge arm. cnt _4 represents the phase-shifted carrier of the fourth bridge arm. cnt_basic The carrier wave is the indicator carrier for updating the phase shift angle of the primary side bridge arm during bias suppression. cnt_basic _2 is an intermediate variable for updating the phase shift angle of the secondary bridge arm during bias suppression. cnt_main It is generated based on a time-synchronized triangular wave by controlling the increment / decrement mode of a counter. cnt_shift Phase shift for the first bridge arm carrier. d 12 out This represents the carrier phase angle difference between the first and second bridge arms without bias suppression. d 13 out This represents the carrier phase angle difference between the first and third bridge arms without bias suppression. d 34 out This represents the carrier phase angle difference between the third and fourth bridge arms without bias suppression. Step 3: Detect whether a power step occurs in the DAB converter; if no power step occurs, proceed directly to step 4; if a power step occurs, based on the power angle dynamic interpolation method, use the current cycle power angle setpoint and the previous cycle power angle setpoint of each bridge arm to obtain the output power angle value of each bridge arm in the current carrier cycle; in each carrier cycle, after updating the phase shift angle with the output power angle value of each bridge arm, repeat step 2 to update the phase shift carrier of the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm of the DAB converter; Step 4: Compare the primary-side DC modulation wave with the phase-shifted carrier waves of the first and second bridge arms to obtain the driving pulses of the first and second bridge arms; compare the secondary-side DC modulation wave with the phase-shifted carrier waves of the third and fourth bridge arms to obtain the driving pulses of the third and fourth bridge arms. Step 5: Use the drive pulses of each bridge arm to suppress the bias magnetization of the DAB converter.
2. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 1, characterized in that, Step 1 includes: Step 1.1: Collect the first primary current flowing into the primary side of the transformer and the first secondary current flowing out of the secondary side of the transformer; Step 1.2: The first primary current and the first secondary current are filtered by hardware to obtain the first primary DC current and the first secondary DC current. Step 1.3: Convert the first primary DC current to the secondary side to obtain the second secondary DC current; Step 1.4: The sum of the first secondary side DC current and the second secondary side DC current is used as the first input signal, and the difference between the first secondary side DC current and the second secondary side DC current is used as the second input signal. Step 1.5: The first input signal and the second input signal are passed through a PI circuit and then subtracted to obtain the primary-side DC modulated wave; the first input signal and the second input signal are passed through a PI circuit and then summed to obtain the secondary-side DC modulated wave.
3. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 1, characterized in that, Step 2 includes: Step 2.1: Based on the given transmission power and the transmission power principle of the DAB converter, determine the phase shift angle; the phase shift angle includes: the phase difference of the drive signal between the first and second bridge arms of the DAB converter, the phase difference of the drive signal between the first and third bridge arms of the DAB converter, and the phase difference of the drive signal between the third and fourth bridge arms of the DAB converter.
4. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 1, characterized in that, In step 3, when a power step occurs, each bridge arm performs the following steps within each carrier cycle to obtain the output power angle value of the bridge arm within this carrier cycle: Step 3.1: Set the first control flag and the second control flag; wherein, the first control flag is used to indicate that the input data reception is complete; the second control flag is used to indicate whether new input data has been received within one carrier cycle; Step 3.2: When the input data reception is completed, that is, when the first control flag is set to 1, and it is determined that new input data has been received in the current carrier cycle, that is, when the second control flag is set to 1, the average of the current cycle power angle given value and the previous cycle power angle given value is used as the output power angle value of the bridge arm in the current carrier cycle. Step 3.3: When the input data reception is completed, i.e. the first control flag is set to 1, and it is determined that no new input data has been received in the current carrier cycle, i.e. the second control flag is set to 0, the average of the current cycle power angle setpoint and the previous cycle output power angle value is used as the output power angle value of the bridge arm in the current carrier cycle. Step 3.4: When the input data has not been received completely, i.e. the first control flag is set to 0, and it is determined that new input data has been received in the current carrier cycle, i.e. the second control flag is set to 1, the power angle given value of the previous cycle is used as the output power angle value of the bridge arm in the current carrier cycle. Step 3.5: When the input data has not been received completely, i.e. the first control flag is set to 0, and it is determined that no new input data has been received in the current carrier cycle, i.e. the second control flag is set to 0, the current cycle power angle setpoint is used as the output power angle value of the bridge arm in the current carrier cycle.
5. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 4, characterized in that, In step 3.2, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship: In the formula, cnt_shift(n) The current phase shift value for the first bridge arm carrier. r_cnt_shift(n) This is the phase-shifted output value of the first bridge arm carrier. r_cnt12(n) This is the current phase shift angle output value between the first and second bridge arms. r_cnt13(n) This is the current phase shift angle output value between the first and third bridge arms. r_cnt34(n) This is the current phase shift angle output value between the third and fourth bridge arms. cnt12(n) Given the phase shift angles of the first and second bridge arms, cnt34(n) Given the phase shift angles of the third and fourth bridge arms, cnt13(n) Given the phase shift angles of the first and third bridge arms, cnt13(n-1) Given the phase shift angles of the first and third bridge arms in the previous iteration, change2_flag This is the second control flag.
6. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 4, characterized in that, In step 3.3, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship: In the formula, cnt_shift(n) The current phase shift value for the first bridge arm carrier. r_cnt_shift(n) This is the phase-shifted output value of the first bridge arm carrier. r_cnt12(n) This is the current phase shift angle output value between the first and second bridge arms. r_cnt13(n) This is the current phase shift angle output value between the first and third bridge arms. r_cnt13(n-1) This is the output value of the phase shift angle between the first and third bridge arms in the previous iteration. r_cnt34(n) This is the current phase shift angle output value between the third and fourth bridge arms. cnt12(n) Given the phase shift angles of the first and second bridge arms, cnt34(n) Given the phase shift angles of the third and fourth bridge arms, cnt13(n) Given the phase shift angles of the first and third bridge arms, change2_flag This is the second control flag.
7. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 4, characterized in that, In step 3.4, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship: In the formula, cnt_shift(n) The current phase shift value for the first bridge arm carrier. r_cnt_shift(n) This is the phase-shifted output value of the first bridge arm carrier. r_cnt12(n) This is the current phase shift angle output value between the first and second bridge arms. r_cnt13(n) This is the current phase shift angle output value between the first and third bridge arms. r_cnt34(n) This is the current phase shift angle output value between the third and fourth bridge arms. cnt12(n) Given the phase shift angles of the first and second bridge arms, cnt34(n) Given the phase shift angles of the third and fourth bridge arms, cnt13(n-1) Given the phase shift angles of the first and third bridge arms in the previous iteration, change2_flag This is the second control flag.
8. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 4, characterized in that, In step 3.5, the output power angle value of the bridge arm during this carrier cycle satisfies the following relationship: In the formula, cnt_shift(n) The current phase shift value for the first bridge arm carrier. r_cnt_shift(n) This is the phase-shifted output value of the first bridge arm carrier. r_cnt12(n) This is the current phase shift angle output value between the first and second bridge arms. r_cnt13(n) This is the current phase shift angle output value between the first and third bridge arms. r_cnt34(n) This is the current phase shift angle output value between the third and fourth bridge arms. cnt12(n) Given the phase shift angles of the first and second bridge arms, cnt34(n) Given the phase shift angles of the third and fourth bridge arms, cnt13(n) Given the phase shift angles of the first and third bridge arms, change2_flag This is the second control flag.
9. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 1, characterized in that, In step 3, the phase angle is updated twice within each carrier cycle. The first update is at the peak of the triangular wave carrier, and the second update is at the trough of the triangular wave carrier. The triangular wave carrier is obtained by incrementing or decrementing the counter register value in the controller.
10. The DAB bias suppression method integrating dynamic power angle interpolation and current closed-loop as described in claim 1, characterized in that, Step 4 includes: Step 4.1: Compare the primary side DC modulation wave with the first bridge arm phase shift carrier wave. When the first bridge arm phase shift carrier wave is higher than the primary side DC modulation wave, output a high-level signal; otherwise, output a low-level signal. Step 4.2: Compare the primary-side DC modulation wave with the second-arm phase-shift carrier wave. When the second-arm phase-shift carrier wave is higher than the primary-side DC modulation wave, output a high-level signal; otherwise, output a low-level signal. Step 4.3: Compare the secondary-side DC modulation wave with the third-arm phase-shift carrier wave. When the third-arm phase-shift carrier wave is higher than the secondary-side DC modulation wave, output a high-level signal; otherwise, output a low-level signal. Step 4.4: Compare the secondary-side DC modulation wave with the fourth-arm phase-shift carrier wave. When the fourth-arm phase-shift carrier wave is higher than the secondary-side DC modulation wave, output a high-level signal; otherwise, output a low-level signal.