A control method for eliminating DC bias of transformer in dual active bridge converter
Through the two-sided single-phase shift modulation method, the DC biased magnetic flux of the transformer during the load angle change is offset, and the magnetic saturation problem caused by single-phase shift modulation in the bidirectional active bridge converter is solved, thereby realizing the stable control of the transformer in a transient state.
Patent Information
- Application Number
- CN202111417335.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-11-25
- Publication Date
- 2025-08-22
- Estimated Expiration
- 2041-11-25
AI Technical Summary
When the bidirectional active bridge converter suddenly changes the load angle under single phase shift modulation, the transformer winding generates overshoot current and DC bias, resulting in magnetic saturation and affecting dynamic control performance.
The double-sided single-phase shift modulation method is adopted to switch to the reference point by switching to the primary and secondary sides of the transformer with relatively delayed switching operations respectively, so as to keep the total load angle unchanged to offset the DC biased magnetic flux and avoid magnetic saturation.
Effectively eliminate DC bias of the transformer during load angle changes, avoid magnetic saturation, ensure that the current and magnetic flux reach steady state in transient state, and improve dynamic control performance.
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Figure CN114123792B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of transformers, and in particular to a control method for eliminating a DC bias of a transformer in a dual active bridge converter. Background Art
[0002] In a traditional single-phase-shifted modulation dual-active bridge (DAB) converter, when the load angle of the single-phase-shifted modulation is suddenly changed, the transformer winding generates a large overshoot current and DC bias. This can put pressure on the power semiconductor devices and cause magnetic saturation of the series inductor, thereby affecting the dynamic control performance. However, existing methods for controlling the DC bias of the transformer in a DAB converter tend to address the overshoot problem of the transformer winding current. By introducing an intermediate load angle during the transient process and actively controlling the trajectory of the transformer current, using a transient current control method, the transformer winding current can reach a new stable state within half a switching cycle, thereby achieving high dynamic control of the DAB converter. However, in addition to the overshoot problem of the transformer winding current, the sudden change in the load angle of the single-phase-shifted modulation can also induce a DC bias in the transformer magnetic flux. If this is not considered in the transformer design, it may lead to magnetic saturation. Therefore, it is necessary to provide a DC bias control method that considers the DC bias and magnetic saturation of the transformer caused by the sudden change in the load angle of the single-phase-shifted modulation. Summary of the Invention
[0003] The present invention provides a control method for removing DC bias of a transformer in a dual active bridge converter, which is used to solve the technical problem that a DC bias of the transformer occurs due to a sudden change in the load angle caused by single phase shift modulation, leading to magnetic saturation.
[0004] In view of this, the present invention provides a control method for eliminating DC bias of a transformer in a dual active bridge converter, comprising:
[0005] Establish the transformer equivalent circuit under single phase shift modulation;
[0006] Obtain transformer winding current trajectory and flux linkage trajectory of the transformer equivalent circuit;
[0007] When the load angle between the primary and secondary sides of the transformer changes, the primary side is The switching operation is switched to the reference point with a relative delay, and the secondary side is switched to the reference point with a relative delay. The relative delay of the switching operation to the reference point is, where p is the distribution factor, is the load angle.
[0008] Optionally, the distribution factor p is calculated as:
[0009]
[0010] Among them, L p is the primary side leakage inductance, N tr is the transformer turns ratio, U s is the secondary DC voltage, U p is the primary DC voltage, L' s is the secondary side leakage inductance equivalent to the primary side.
[0011] Optionally, it also includes:
[0012] Obtain the transformer current and flux simulation results, and determine whether the transformer DC bias is eliminated based on the simulation results.
[0013] Optionally, the transformer equivalent circuit under single phase shift modulation includes: a primary leakage inductance, a secondary leakage inductance equivalent to the primary side, and an excitation inductance, and the primary leakage inductance, the secondary leakage inductance equivalent to the primary side, and the excitation inductance form a T-type network.
[0014] From the above technical solutions, it can be seen that the method for assessing the probability of insulation damage of low-voltage DC system equipment provided by the present invention has the following advantages:
[0015] The control method for eliminating DC bias of the transformer in the dual active bridge converter provided by the present invention divides the load angle between the primary side and the secondary side of the transformer into two parts, adopts a double-side single phase shift modulation method, and the primary side is The switching operation is switched to the reference point with a relative delay, and the secondary side is switched to the reference point with a relative delay. The switching operation is switched to the reference point with a relative delay, so that the total load angle remains unchanged. The DC bias flux component induced on the primary side offsets the component induced on the secondary side. Therefore, the DC bias flux is offset in the transient state of the load angle change of single-phase-shift modulation, and the flux can instantly reach a new steady state, solving the technical problem of DC bias in the transformer and magnetic saturation caused by the sudden change of the load angle due to single-phase-shift modulation. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.
[0017] Figure 1 A schematic flow chart of a control method for eliminating DC bias of a transformer in a dual active bridge converter provided by the present invention;
[0018] Figure 2A schematic diagram of the structure of a transformer equivalent circuit under single phase shift modulation provided by the present invention;
[0019] Figure 3 The transformer winding current trajectory diagram in the αβ coordinates provided by the present invention;
[0020] Figure 4 The magnetization flux linkage trajectory diagram of the transformer winding in the αβ coordinates provided by the present invention;
[0021] Figure 5 A schematic diagram of a switching sequence for bilateral single phase shift modulation provided by the present invention;
[0022] Figure 6 The current and flux simulation results in the Abc stationary coordinate system of the traditional control method are shown in the figure;
[0023] Figure 7 The magnetic flux simulation result diagram in the αβ stationary coordinate system of the traditional control method;
[0024] Figure 8 This is a diagram showing the simulation results of current and flux linkage in the Abc stationary coordinate system of the control method provided by the present invention;
[0025] Figure 9 This is a diagram of the magnetic flux simulation results in the αβ stationary coordinate system of the control method provided by the present invention. DETAILED DESCRIPTION
[0026] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.
[0027] For easier understanding, see Figure 1 The present invention provides an embodiment of a control method for eliminating DC bias of a transformer in a dual active bridge converter, comprising:
[0028] Step 101: Establish a transformer equivalent circuit under single phase shift modulation.
[0029] Use circuit simulation software (such as PLECS) to build the transformer equivalent circuit under single phase shift modulation, such as Figure 2 As shown in the figure, the primary leakage inductance, the secondary leakage inductance equivalent to the primary side and the excitation inductance form a T-type network. p is the primary leakage inductance, L' sis the secondary leakage inductance equivalent to the primary side, L M is the magnetizing inductance, is the equivalent primary DC voltage, is the equivalent secondary DC voltage, is the equivalent excitation inductance DC voltage, is the equivalent primary current.
[0030] Step 102: Obtain the transformer winding current trajectory and flux linkage trajectory of the transformer equivalent circuit.
[0031] In SPS modulation, within a given primary bridge switching state n, the secondary bridge switches from state m to n with a delay angle of Depending on the direction of energy flow on the primary side, m is equal to n-1 or n+1. Therefore, in the αβ coordinate system, the current at each switching state end of the main bridge forms a regular hexagon in the αβ coordinate system. In the stable state, the center of this hexagon is located at the origin of the αβ coordinate system, as shown in the figure below: Figure 3 The transformer magnetization flux trajectory is also a hexagon, with its center located at the origin of the αβ coordinate system in the steady state, as shown in Figure 4 shown.
[0032] Step 103: When the load angle between the primary and secondary sides of the transformer changes, the primary side is set to The switching operation is switched to the reference point with a relative delay, and the secondary side is switched to the reference point with a relative delay. The relative delay of the switching operation to the reference point is, where p is the distribution factor, is the load angle.
[0033] Based on the transient current control method, when the load angle changes from becomes hour( and is the load angle corresponding to any two states), the drift of the obtained magnetic flux trajectory and the initial trajectory is:
[0034]
[0035] Where f is the switching frequency, and For two switching sequences, The load angle is The magnetic link when The load angle is Magnetic link at the time.
[0036] It can be seen that the transient DC bias flux is only caused by the load angle change on the secondary side. In the traditional single phase shift modulation, the switching time of the primary side is fixed at 1 / 6 of each switching cycle, while the switching time of the secondary side is variable. Delayed to the primary side.
[0037] In order to avoid transient DC bias flux linkage during load angle change, the present invention proposes bilateral single phase shift modulation. It is divided into two parts, the primary side is The secondary side is like Figure 5 As shown, Figure 5 In the figure, Sp represents the switching state of the phase branch, Ss represents the switching state of the primary and secondary bridges, and the primary side is based on each 1 / 6 of the switching cycle. The switching operation is switched to the reference point with a relative delay, and the secondary side is switched to the reference point with a relative delay. The switching operation is performed with a relative delay to the reference point, where p is the distribution factor. The total load angle between the primary and secondary remains unchanged, and the double-sided load angle has no effect on the steady-state trajectory of the primary current and flux.
[0038] Since the primary current is determined by the total load angle between the primary and secondary sides, the bilateral single phase shift can be applied to the transient current control method. becomes When , the difference in primary current between the transient flux and current control method and the transient current control method is:
[0039]
[0040] in, The load angle is The transient flux and current vectors of 5 to 6 when controlling the current are The load angle is When the transient current is controlled, the current vector is 5 to 6, and p is the distribution factor. is the derivative of the phase branch current when the switching state changes from 6 to 6.
[0041] When the load angle changes from becomes When , the difference in primary current between the transient flux and current control method and the transient current control method is:
[0042]
[0043] in,, The load angle is The transient flux and current vectors from 2 to 3 when controlling the current are The load angle is When the transient current is controlled from 2 to 3, the current vector is the derivative of the phase branch current when the switching state changes from 3 to 3.
[0044] It can be seen that the differences in primary currents completely cancel each other out, thus proving that the primary current and flux can be controlled instantaneously and simultaneously without causing overshoot current and transient DC bias flux during load angle changes.
[0045] The control method for eliminating DC bias of the transformer in the dual active bridge converter provided by the present invention divides the load angle between the primary side and the secondary side of the transformer into two parts, adopts a double-side single phase shift modulation method, and the primary side is The switching operation is switched to the reference point with a relative delay, and the secondary side is switched to the reference point with a relative delay. The switching operation is switched to the reference point with a relative delay, so that the total load angle remains unchanged. The DC bias flux component induced on the primary side offsets the component induced on the secondary side. Therefore, the DC bias flux is offset in the transient state of the load angle change of single-phase-shift modulation, and the flux can instantly reach a new steady state, solving the technical problem of DC bias in the transformer and magnetic saturation caused by the sudden change of the load angle due to single-phase-shift modulation.
[0046] When the load angle changes from becomes When , for bilateral single phase shift modulation, the flux linkage difference in the switching state should be 0:
[0047]
[0048] in, is the switching state of the primary side, is the switching state of the secondary side.
[0049] Assume L M >>L p , L M >>L' s ,have to:
[0050]
[0051] Among them, L p is the primary side leakage inductance, N tr is the transformer turns ratio, U s is the secondary DC voltage, U p is the primary DC voltage, L' s is the secondary side leakage inductance equivalent to the primary side.
[0052] To better compare the effect of the control method for eliminating the DC bias of the transformer in the dual active bridge converter provided by the present invention, the present invention provides a comparison of the effect with the traditional control method as follows:
[0053] Dual active bridge converter with load angle At startup, the first step of the load angle change is from arrive t=5ms. Then, the load angle changes from arrive t=20ms,from arrive t = 35ms. The converter finally powers down at t = 38ms.
[0054] like Figure 6 and Figure 7 As shown, Figure 6 The current and flux simulation results in the Abc stationary coordinate system of the traditional control method are shown in the figure. Figure 7 The figure shows the magnetic flux simulation results in the αβ stationary coordinate system of the traditional control method. Figure 6 and Figure 7 It can be seen that during the load angle change, a large overshoot current is induced in the primary current, where the damping effect of the winding resistance can be observed. On the other hand, an initial DC bias component is induced in the flux immediately after startup, and the DC bias component changes instantaneously with the load angle. The flux between the three phases is unbalanced, with a peak value almost twice the nominal value. Due to the large time constant of the transformer flux, the DC bias component does not significantly decay. The startup and power flow are obtained from arrive The corresponding flux linkage trajectory in the reversed αβ coordinates. Due to the hard magnetization, an initial flux linkage is generated, and the flux linkage trajectory drifts significantly after the power flow is reversed, resulting in a significant DC bias.
[0055] like Figure 8 and Figure 9 As shown, Figure 8 This is a diagram showing the simulation results of current and flux linkage in the Abc stationary coordinate system of the control method provided by the present invention. Figure 9 This is a diagram of the magnetic flux simulation results in the αβ stationary coordinate system of the control method provided by the present invention. Figure 8 and Figure 9 As can be seen, the primary current is well controlled, with virtually no overshoot during load angle changes. Compared to conventional transient current control methods, no additional DC bias flux is generated during load angle changes, and the initial DC bias and flux transient overshoot are completely eliminated. As a result, even in transient conditions, the flux trajectory is regulated within maximum limits.
[0056] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A control method for eliminating DC bias of a transformer in a dual active bridge converter, characterized in that: include: Establish the transformer equivalent circuit under single phase shift modulation; Obtain transformer winding current trajectory and flux linkage trajectory of the transformer equivalent circuit; When the load angle between the primary and secondary sides of the transformer changes, the primary side is The switching operation is switched to the reference point with a relative delay, and the secondary side is switched to the reference point with a relative delay. The relative delay of the switching operation to the reference point is, where p is the distribution factor, is the load angle; The calculation formula of the distribution factor p is: Among them, L p is the primary side leakage inductance, N tr is the transformer turns ratio, U s is the secondary DC voltage, U p is the primary DC voltage, L' s is the secondary side leakage inductance equivalent to the primary side.
2. The control method for eliminating DC bias of a transformer in a dual active bridge converter according to claim 1, characterized in that: Also includes: Obtain the transformer current and flux simulation results, and determine whether the transformer DC bias is eliminated based on the simulation results.
3. The control method for eliminating DC bias of a transformer in a dual active bridge converter according to claim 1, characterized in that: The transformer equivalent circuit under single phase-shift modulation includes: primary leakage inductance, secondary leakage inductance equivalent to the primary side, and excitation inductance. The primary leakage inductance, secondary leakage inductance equivalent to the primary side, and excitation inductance form a T-type network.