A droop control method for resonant converter with adaptive voltage reference adjustment

Abstract

The present invention discloses a droop control method for a resonant converter with adaptive voltage reference adjustment, which is suitable for current sharing control of IPOP type DC converters and other DC converter parallel control systems. The output voltage loop is introduced before the droop control loop, the voltage reference of the droop control is improved, and the consistent droop characteristics between the power modules are used to achieve power sharing, which solves the problem that the output voltage is less than the reference value in the traditional droop control, while retaining the advantages of no interconnection between the modules and current sharing output between the modules under the droop control method, and at the same time introducing a voltage reference adaptive adjustment loop to eliminate the drop in the system output voltage caused by the droop characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of resonant converters, and in particular to a droop control method for a resonant converter with adaptive voltage reference adjustment. Background Art

[0002] In recent years, with the development of data centers and electric vehicle technology, the demand for high-power DC power supplies is increasing. Small-capacity power supplies can no longer meet the needs of large power supply systems, and multiple power supplies need to be combined to improve power supply capacity. With the development of power electronics technology, modular power supply technology can better solve this problem and is increasingly used. Multiple power modules in parallel are the key technology to solve high-power power supply systems. Its advantages are that it can be flexibly combined into power supply systems of various power levels, improve system reliability, obtain fault-tolerant redundant power through N+1 redundancy, can achieve hot replacement, and is easy to maintain.

[0003] However, when the power modules are connected in parallel, due to the difference in output voltages between the power modules, a circulating current will be generated between the modules with high output voltage and the modules with low output voltage, resulting in oscillation. In this way, the module with low output voltage not only does not provide current to the outside, but also absorbs the current of the module with high output voltage; the module with high output voltage not only provides load current, but also provides current to other modules. Therefore, the module with high output voltage will be impacted by large current; oscillation will produce large voltage impact; several modules interfere with each other, and the module with high output voltage will suppress the module with low output voltage. Especially for the IPOP type DC converter parallel control system, due to the differences in device parameters between modules, in the direct voltage or current control mode, the output power of each module is not evenly distributed, resulting in module overload and affecting system stability.

[0004] There are two main means of parallel connection for DC converters: master-slave control and droop control. Master-slave control is the most common parallel control method. In the master-slave control mode, a power module connected in parallel acts as the master power module to provide the system voltage reference, and other slave power modules perform current closed-loop control to follow the power of the master power module to achieve current sharing control between modules. This method is easy to implement, but for PFM-controlled resonant converters such as LLC resonant converters, due to the delay in communication between the master power module and the slave power module, the noise caused by the communication will be introduced into the control loop, making the design of the compensator control more difficult. Due to the different dynamic performance of the master and slave modules, it is easy to cause the system to oscillate when disturbed. And due to the reliance on the current sharing reference provided by the master power module, the dependence on the master power module is relatively large, and the overall reliability of the system is low.

[0005] Droop control uses the consistency of the output droop characteristics in the parallel system to connect the converters in parallel. In this method, the modules do not need to communicate with each other, the dynamic characteristics of the modules in the system are relatively consistent, and it is easy to switch in and out of the faulty modules, which improves the reliability of the system. Although the droop system is easy to implement parallel control of the converters, the negative feedback of the output current will cause the output voltage of the system to drop as the load increases. Reducing the droop coefficient can reduce this drop, so the droop coefficient cannot be too large, which causes the current sharing accuracy of the system to vary greatly under different loads. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] In view of the deficiencies of the prior art, the present invention discloses a droop control method for a resonant converter with adaptive adjustment of a voltage reference to solve the problems raised in the above background technology.

[0008] (II) Technical solution

[0009] To achieve the above objectives, the present invention is implemented through the following technical solutions: In view of the problem of output voltage drop caused by droop control, the present invention proposes a resonant converter droop control method with adaptive voltage reference adjustment, by introducing the output voltage loop before the droop control loop, increasing the voltage reference of the droop control, and using the consistent droop characteristics between the power modules to achieve power sharing, thereby solving the problem of the output voltage being less than the reference value in the traditional droop control, while retaining the advantages of no interconnection between the modules and equal current output between the modules under the droop control method, and introducing a voltage reference adaptive adjustment loop to eliminate the drop in the system output voltage caused by the droop characteristics, and being suitable for IPOP type DC converters and other DC converter parallel control systems.

[0010] The present invention is designed for an IPOP type DC converter parallel control system. In the IPOP type DC converter parallel control system, each LLC resonant converter module is connected in parallel input and output, and the IPOP type DC converter parallel control system is controlled to share current by using a frequency modulation control method. A suitable frequency modulation interval is set so that each LLC resonant converter works in the state of a primary switch tube and a complex rectifier diode, thereby improving the operating efficiency of the system.

[0011] The present invention adopts a droop control method for controlling each power module, and the specific steps are as follows:

[0012] S1: Soft start all LLC resonant converters in parallel to stabilize the output voltage of the entire LLC resonant converter

[0013] Due to the frequency-voltage (fV) gain characteristics of the LLC resonant converter itself, the phase shift angle between the bridge arms of each LLC resonant converter is gradually adjusted from 180° to 0°, and at the same time, the resonant frequency is slowly reduced from 2-3 times the resonant frequency to the resonant frequency to reduce the resonant current overshoot and make the output voltage of all LLC resonant converters reach a stable value.

[0014] S2: Introduce a droop control loop to achieve module output current balancing

[0015] Set the initial reference value V of the outer loop output voltage of all LLC resonant converters ref * With the current IPOP system output voltage V o and the droop coefficient k and the output current I of the current LLC resonant converter n on (n=1,2,3......n) to obtain the difference of the inner loop of droop control, and send this difference to the inner control loop to obtain the switching frequency of LLC converter. o have:

[0016]

[0017] Among them G D (s) is the transfer function of droop control, G fV (s) is the transfer function of the LLC converter frequency to the output voltage. The voltage drop ΔV of all LLC resonant converters caused by droop control is recorded as:

[0018] ΔV=V ref -V o (2)

[0019] When the voltage outer loop is not introduced,

[0020]

[0021] So at this time, the voltage drop of all LLC resonant converters is:

[0022]

[0023] S3: Introduce the output voltage loop to stabilize the voltage drop of all LLC resonant converters

[0024] All LLC resonant converter output voltages are introduced before the droop control loop to form a reference voltage outer loop for droop control, and the droop characteristic curve is shifted to eliminate the drop in the output voltage of all LLC resonant converters caused by droop control.

[0025] Set the reference value V of the output voltage of all LLC resonant converters refAnd all LLC resonant converter voltage output values ​​after droop control V o The difference is sent to the voltage outer loop. The output of the voltage outer loop is used as the voltage reference value of the droop control inner loop. The inner loop voltage reference is shifted to obtain the output of the voltage outer loop:

[0026]

[0027] Among them G V (s) is the transfer function of the voltage outer loop control. The voltage outer loop output V ref * The droop control inner loop acts on the controller. At this time, the complex frequency domain expression of the output voltage of all LLC resonant converters is:

[0028]

[0029] At this time, the voltage drop of all LLC resonant converters is:

[0030]

[0031] From the voltage drop expression of all LLC resonant converters, it can be seen that after the voltage outer loop is introduced, when all LLC resonant converters are stable, the voltage drop of all LLC resonant converters is 0;

[0032] The complex frequency domain expression of the output current of each LLC resonant converter is:

[0033]

[0034] So when all LLC resonant converters are stable,

[0035]

[0036] Among them, K VI is the integral constant of the voltage outer loop, and M is the gain of each LLC resonant converter when it is stable.

[0037] The present invention discloses a droop control method for a resonant converter with adaptive voltage reference adjustment, which has the following beneficial effects:

[0038] (1) The parallel current sharing control without interconnection between converter units of the LLC resonant converter system is realized, which reduces the impact of system instability caused by communication and the accumulation of output errors between converters caused by communication bandwidth; through parallel current sharing control, the stress of current devices within a single module is reduced. The method is simple and easy to implement, shortening the development cycle of high-power power supplies.

[0039] (2) The introduction of an output voltage feedforward outer loop control solves the problem of the system output voltage being less than the preset value caused by droop control.

[0040] (3) The output of the outer loop control increases with the load, which weakens the error change rate introduced into the system each time a disturbance occurs, making it easier to design compensation and increasing the stability of the control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A structural diagram of an IPOP type DC converter parallel control system of a voltage reference adaptively adjusted resonant converter droop control method of the present invention;

[0042] Figure 2 A control block diagram of a voltage reference adaptively adjusted resonant converter droop control method according to the present invention;

[0043] Figure 3 A diagram showing changes in a droop curve and a steady-state operating point when a load changes in a droop control method for a resonant converter with adaptive voltage reference adjustment according to the present invention;

[0044] Figure 4 A comparison diagram of the system voltage external characteristics and the output current balancing degree of each module under three control modes in a voltage reference adaptively adjusted resonant converter droop control method of the present invention under full load range;

[0045] Figure 5 A comparison of the output currents of the LLC resonant converters after the voltage reference adaptively adjusted resonant converter droop control method of the present invention is introduced;

[0046] Figure 6 A comparison diagram of the current sharing effect and output voltage change of a resonant converter droop control method with adaptive voltage reference adjustment of a resonant converter droop control method with adaptive voltage reference adjustment of two LLC resonant converters in parallel when the output load jumps in the present invention and the droop control;

[0047] Figure 7 This is a comparison diagram of the current sharing effect and output voltage change of the resonant converter droop control method with adaptive adjustment of the voltage reference of the present invention, in which two LLC resonant converters are connected in parallel and the traditional droop control when the input voltage suddenly changes. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

[0049] See also Figures 1 to 7The figure shows a droop control method of a resonant converter with adaptive adjustment of voltage reference in the present invention.

[0050] like Figure 1 The structure diagram of the IPOP type DC converter parallel control system is shown. In the IPOP type DC converter parallel control system, each LLC resonant converter module is connected in parallel input and output. For the IPOP type DC converter parallel control system, the phase shift and frequency modulation control methods can be used for current sharing control. However, the reflux power of the phase shift control is large, and the zero current switch of the secondary side rectifier unit cannot be realized, resulting in low conversion efficiency of each module. Therefore, the frequency modulation control method is used to control the current sharing of the IPOP type DC converter parallel control system, and a suitable frequency modulation range is set so that each LLC resonant converter works on the primary switch tube (the first switch tube Q 11 , the second switch tube Q 12 , the third switch tube Q 13 , the fourth switch tube Q 14 )Zero voltage turn-on and compound rectifier diode (first rectifier diode D 11 , the second rectifier diode D 12 , the third rectifier diode D 13 , the fourth rectifier diode D 14 )Zero current shutdown state, improving the operating efficiency of the system.

[0051] The LLC resonant converter includes a full-bridge switching circuit, a resonant capacitor C r1 , resonant inductor L r1 , Excitation inductance L rm1 , transformer T1, rectifier, full-bridge switch circuit consists of the first switch tube Q 11 , the second switch tube Q 12 , the third switch tube Q 13 , the fourth switch tube Q 14 The first switch tube Q 11 With the third switch tube Q 13 In series, the second switch tube Q 12 With the fourth switch tube Q 14 series, and then with the first capacitor C 11 Connected in parallel at the power input, the excitation inductance L rm1 In parallel with transformer T1, resonant inductor L r1 In series with the excitation inductor L rm1 With the first switch tube Q 11 Between, the resonant capacitor C r1 In series with the excitation inductor L rm1 With the fourth switch tube Q 14 The rectifier consists of a first rectifier diode D 11 , the second rectifier diode D12 , the third rectifier diode D 13 , the fourth rectifier diode D 14 The first rectifier diode D 11 With the third rectifier diode D 13 In series, the second rectifier diode D 12 With the fourth rectifier diode D 14 series, and then with the second capacitor C 01 Connect in parallel to the power supply output, and connect the output to the load R L .

[0052] The present invention adopts a droop control method for controlling each power module, and the specific steps are as follows:

[0053] S1: Soft start all LLC resonant converters in parallel to stabilize the output voltage of the entire LLC resonant converter

[0054] Due to the frequency-voltage (fV) gain characteristics of the LLC resonant converter itself, the phase shift angle between the bridge arms of each LLC resonant converter is gradually adjusted from 180° to 0°, and at the same time, the resonant frequency is slowly reduced from 2-3 times the resonant frequency to the resonant frequency to reduce the resonant current overshoot and make the output voltage of all LLC resonant converters reach a stable value.

[0055] S2: Introduce a droop control loop to achieve module output current balancing

[0056] Set the initial reference value V of the outer loop output voltage of all LLC resonant converters ref * With the current IPOP system output voltage V o and the droop coefficient k and the output current I of the current LLC resonant converter n on (n=1,2,3......n) to obtain the difference of the inner loop of droop control, and send this difference to the inner control loop to obtain the switching frequency of LLC converter. o have:

[0057]

[0058] Among them G D (s) is the transfer function of droop control, G fV (s) is the transfer function of the LLC converter frequency to the output voltage. The voltage drop ΔV of all LLC resonant converters caused by droop control is recorded as:

[0059] ΔV=V ref -V o (2)

[0060] When the voltage outer loop is not introduced,

[0061]

[0062] So at this time, the voltage drop of all LLC resonant converters is:

[0063]

[0064] S3: Introduce the output voltage loop to stabilize the voltage drop of all LLC resonant converters

[0065] All LLC resonant converter output voltages are introduced before the droop control loop to form a reference voltage outer loop for droop control, and the droop characteristic curve is shifted to eliminate the drop in the output voltage of all LLC resonant converters caused by droop control.

[0066] Set the reference value V of the output voltage of all LLC resonant converters ref And all LLC resonant converter voltage output values ​​after droop control V o The difference is sent to the voltage outer loop. The output of the voltage outer loop is used as the voltage reference value of the droop control inner loop. The inner loop voltage reference is shifted to obtain the output of the voltage outer loop:

[0067]

[0068] Among them G V (s) is the transfer function of the voltage outer loop control. The voltage outer loop output V ref * The droop control inner loop acts on the controller. At this time, the complex frequency domain expression of the output voltage of all LLC resonant converters is:

[0069]

[0070] At this time, the voltage drop of all LLC resonant converters is:

[0071]

[0072] From the voltage drop expression of all LLC resonant converters, it can be seen that after the voltage outer loop is introduced, when all LLC resonant converters are stable, the voltage drop of all LLC resonant converters is 0;

[0073] The complex frequency domain expression of the output current of each LLC resonant converter is:

[0074]

[0075] So when all LLC resonant converters are stable,

[0076]

[0077] Among them, K VI is the integral constant of the voltage outer loop, and M is the gain of each LLC resonant converter when it is stable. It can be seen that after the introduction of the output voltage outer loop, there is no effect on the current sharing degree of the system in the steady-state characteristics, that is, this method retains the advantage of droop control for power sharing between modules, while also eliminating the voltage drop caused by droop control.

[0078] like Figure 3 The figure shows the changes of the droop curve and steady-state operating point when the system increases the load. Point P is the LLC resonant converter when the output current is I o1 The steady-state operating point is when the voltage outer loop increases the output reference of the LLC resonant converter's droop control inner loop to V * ref1 , so that the output voltage of all LLC resonant converters is stable at the set value V ref When the load increases, the output current of the LLC resonant converter increases to I o2 Due to the droop characteristic, the output voltage of all LLC resonant converters will drop to less than V ref At this time, the error between the output voltage and the voltage setting value is sent to the voltage outer loop. Under the action of the voltage outer loop, the droop curve is shifted upward, and the voltage reference is increased by V * ref2 , at this time the output voltage of the curve will rise again to V ref , until it stabilizes at point Q.

[0079] like Figure 4 The figure shows a comparison of the external characteristics of the system output voltage and the imbalance of the module output current under different loads under three control modes: direct voltage closed-loop control with introduction of current sharing control, droop control, and droop control with output voltage feedforward. It can be seen that the droop control with introduction of voltage feedforward takes into account the advantages of better external characteristics under direct frequency control and higher current sharing degree of the LLC resonant converter with droop control.

[0080] like Figure 5The figure shows the comparison of the output current of each LLC resonant converter before and after the introduction of the resonant converter droop control method with adaptive voltage reference adjustment. It can be seen that before the introduction of the resonant converter droop control method with output voltage feedforward, the output voltage of the system is 24V, but there is an imbalance in the output current of each LLC resonant converter. As the load increases, this imbalance will increase, and eventually cause a certain LLC resonant converter to be overloaded, affecting the stability of all LLC resonant converters. After the introduction of the resonant converter droop control method with output voltage feedforward, each LLC resonant converter achieves balanced output current, and the output voltage of all LLC resonant converters is still stabilized at 24V, that is, the power of each module is evenly distributed.

[0081] like Figure 6 The figure shows a comparison of the effects of the resonant converter droop control method that introduces output voltage feedforward and the traditional droop method on the output voltage and current sharing characteristics of all LLC resonant converters. Due to the droop characteristics, the traditional droop control will cause the output voltage to be less than the preset value of 24V when the load jumps, and because the droop coefficient cannot be too large, the current sharing of all LLC resonant converters will change when the load is different. After introducing the voltage feedforward outer loop, not only is it guaranteed that the output voltage of all LLC resonant converters can be stabilized at 24V after the load increases, but also because the droop coefficient can be as large as possible, it can be ensured that the current sharing of all LLC resonant converters in each load range changes very little.

[0082] like Figure 7 The figure shows the influence of the resonant converter droop control method introducing output voltage feedforward and the traditional droop method on the output voltage and current sharing characteristics of all LLC resonant converters when the input voltage suddenly changes from 150V to 100V. Due to the droop characteristics, when the input voltage fluctuates, it is equivalent to an increase in load. The traditional droop control cannot select a larger droop coefficient and cannot stabilize the output voltage at the preset value of 24V. The introduction of the output voltage outer loop solves this problem and the problem of decreased current sharing after the input fluctuates.

[0083] The working principle and working process of the present invention are as follows:

[0084] By introducing the output voltage loop before the droop control loop, the voltage reference of the droop control is increased, and the consistent droop characteristics between the power modules are used to achieve power sharing, which solves the problem of the output voltage being less than the reference value in traditional droop control. At the same time, the advantages of no interconnection between modules and equal current output between modules under the droop control method are retained. At the same time, a voltage reference adaptive adjustment loop is introduced to eliminate the drop in system output voltage caused by the droop characteristics.

Claims

1. A droop control method for a resonant converter with adaptive voltage reference adjustment, characterized in that: Before the output voltage loop is introduced into the droop control loop, the voltage reference of the droop control is increased, and the consistent droop characteristics between the power modules are used to achieve power sharing. At the same time, a voltage reference adaptive adjustment loop is introduced, which is suitable for the IPOP type DC converter parallel control system. The droop control method is used to control each power module. The specific steps are as follows: S1: Soft start all LLC resonant converters in parallel to stabilize the output voltage of the entire LLC resonant converter: Due to the frequency-voltage (fV) gain characteristics of the LLC resonant converter itself, the phase shift angle between the bridge arms of each LLC resonant converter is gradually adjusted from 180° to 0°, and the resonant frequency is gradually reduced from 2-3 times the resonant frequency to the resonant frequency to reduce the resonant current overshoot, so that the output voltage of all LLC resonant converters reaches a stable value; S2: Introduce a droop control loop to achieve equal distribution of module output current: Set the initial reference value V of the outer loop output voltage of all LLC resonant converters * refn With the current IPOP system output voltage V o and the droop coefficient k and the output current I of the current LLC resonant converter n on (n=1,2,3......n) to obtain the difference of the inner loop of droop control, and send this difference to the inner control loop to obtain the switching frequency of LLC converter. o have: Among them G D (s) is the transfer function of droop control, G fV (s) is the transfer function of the LLC converter frequency to the output voltage. The voltage drop ΔV of all LLC resonant converters caused by droop control is recorded as: ΔV=V ref -V o (2) When the voltage outer loop is not introduced, there are: So at this time, the voltage drop of all LLC resonant converters is: S3: Introduce the output voltage loop to stabilize the voltage drop of all LLC resonant converters: All LLC resonant converter output voltages are introduced before the droop control loop to form a reference voltage outer loop for droop control, and the droop characteristic curve is shifted to eliminate the drop in the output voltage of all LLC resonant converters caused by droop control. Set the reference value V of the output voltage of all LLC resonant converters ref And all LLC resonant converter voltage output values ​​after droop control V o The difference is sent to the voltage outer loop. The output of the voltage outer loop is used as the voltage reference value of the droop control inner loop. The inner loop voltage reference is shifted to obtain the output of the voltage outer loop: Among them G V (s) is the transfer function of the voltage outer loop control. The voltage outer loop output V * refn The droop control inner loop acts on the controller. At this time, the complex frequency domain expression of the output voltage of all LLC resonant converters is: At this time, the voltage drop of all LLC resonant converters is: From the voltage drop expression of all LLC resonant converters, it can be seen that after the voltage outer loop is introduced, when all LLC resonant converters are stable, the voltage drop of all LLC resonant converters is 0; The complex frequency domain expression of the output current of each LLC resonant converter is: So when all LLC resonant converters are stable, we have: Among them, K VI is the integral constant of the voltage outer loop, and M is the gain of each LLC resonant converter when it is stable.

2. The voltage reference adaptively adjusted resonant converter droop control method according to claim 1, characterized in that: In the IPOP type DC converter parallel control system, each LLC resonant converter module is connected in parallel input and output, and the IPOP type DC converter parallel control system is controlled by frequency modulation. A suitable frequency modulation range is set so that each LLC resonant converter works in the state of primary switch tube and complex rectifier diode, thereby improving the operation efficiency of the system.

Images