CN109194135B - An adaptive efficiency optimization method for a resonant state adjustable power converter - Google Patents

Abstract

The invention relates to an adaptive efficiency optimization method for a resonant state adjustable power converter. The power converter includes a single or multiple resonant topologies, each resonant topology is controlled by a separate control signal, and the control signal is connected to an auxiliary inside the resonant topology. For circuits or original devices, the optimization method includes: after measuring N voltages and M currents in the current state, the values of N and M depend on the actual resonant circuit structure, and the frequency and resonance are performed without changing the gain. Efficiency optimization control in coordination with state, and then output control signal to power converter to achieve maximum efficiency tracking. Compared with the prior art, the present invention performs adaptive matching of the switching frequency during the dynamic adjustment of the resonance state through the coordinated control of the resonance state and the switching frequency, so that the resonant converter can obtain the compromise optimization between the switching loss and the conduction loss, and can achieve the optimal performance of the switching loss and the conduction loss. Maintain a wide range of voltage gain adjustment for a narrow range of switching frequencies.

Description

An adaptive efficiency optimization method for a resonant state adjustable power converter

technical field

The invention relates to an efficiency optimization method of a power converter, in particular to an adaptive efficiency optimization method of a resonant state adjustable power converter.

Background technique

High frequency, high power density and high efficiency are the development trends of DC/DC power converters. Traditional hard-switching converters will generate large switching losses and noise, which limit the improvement of power density and switching frequency. Soft switching power converters.

The most commonly used type is the phase-shifted full-bridge converter, which can achieve zero-voltage turn-on (ZVS) of the main switch, but it is difficult to achieve soft switching of the hysteresis bridge arm, and the secondary-side rectifier diode has a reverse recovery problem. Not conducive to the improvement of efficiency.

Another common type is the LLC resonant converter, which can realize zero-voltage turn-on and zero-current turn-off (ZCS) of the main switch in the full load range, and the secondary rectifier diode can also realize ZCS. However, the LLC converter adopts the frequency modulation control method. If the switching frequency is less than the resonant frequency and the switching frequency is too large, the circulating current will last too long, which will reduce the efficiency of the converter. The same problem exists for the phase-shift controlled resonant circuit. The large gap between the resonant period and the switching period leads to a decrease in the efficiency of the converter.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an adaptive efficiency optimization method of a resonant state adjustable power converter in order to overcome the above-mentioned defects of the prior art.

The object of the present invention can be realized through the following technical solutions:

An adaptive efficiency optimization method for a resonant state adjustable power converter, the power converter includes single or multiple resonant topologies, the input ends of each resonant topology are connected in parallel or in combination, and the output ends are connected in parallel or in combination to the load , each resonant topology is controlled by a separate control signal, and the control signal is connected to the auxiliary circuit or original device inside the resonant topology,

The optimization method includes: after measuring N voltages and M currents in the current state, the values of N and M depend on the actual resonant circuit structure, and the frequency and the resonant state are coordinated without changing the gain. efficiency optimization control, and then output a control signal to the power converter to achieve maximum efficiency tracking.

The efficiency optimization control method for the coordination of the frequency and the resonance state includes one or more of a look-up table method, an interpolation calculation method, a disturbance observation method and a closed-loop control method.

The table look-up method is: formulating an optimal point parameter table in each working condition, and determining the frequency, duty cycle and phase-shift control parameters of the resonant state adjustable power converter by looking up the table.

The interpolation calculation method is as follows: by judging the changing trend of the efficiency under three different control parameters, if there is a rising and a falling trend, the interpolation calculation is performed to find the approximate optimum point.

The perturbation observation method includes the following steps:

S1, obtain the input voltage and current and output voltage and current of the current state 1, and calculate the efficiency of state 1;

S2, under the premise of ensuring the output voltage, change the frequency and phase shift angle, or change the frequency and duty cycle to obtain state 2;

S3, obtain the input voltage and current and output voltage and current of state 2, and calculate the efficiency of state 2;

S4, judge whether the efficiency of state 2 is greater than that of state 1, if so, go to step S5, otherwise go to step S6;

S5, take the current state 2 as the new state 1, calculate the efficiency of state 1, and on the basis of state 1, continue to change the frequency and phase shift angle, or change the frequency and duty cycle in the same direction as step S2, to obtain a new state 2, return to step S3;

S6, on the basis of state 1, continue to change the frequency and phase shift angle in the opposite direction of step S2, or change the frequency and duty cycle, obtain a new state 2, and return to step S3.

The control signal is generated by the PWM module.

Compared with the prior art, the present invention has the following advantages:

(1) Through the coordinated control of the resonant state and the switching frequency, the adaptive matching of the switching frequency is carried out during the dynamic adjustment of the resonant state, so that the resonant converter can achieve the compromise optimization of switching loss and conduction loss, and can maintain a narrow range of switching frequency. Wide-range adjustment of the voltage gain under.

(2) For converters with adjustable resonant state, such as injection current resonant converters, the resonant state will change with the change of the input voltage. Once the resonant time is much smaller than the switching period, the circulating current in one switching period will change. Time will account for a large proportion, which is not conducive to the improvement of efficiency. Therefore, through the coordinated control of the resonance state and the switching frequency, the duration of the circulating current can be reduced and the efficiency of the power converter can be improved.

(3) For the traditional LLC, in order to achieve wide-range adjustment capability, the switching frequency has a wide variation range, which will generate large switching losses at high frequencies. The resonant adjustable converter with optimized efficiency can be combined with the duty cycle. Or phase-shift adjustment, in the case that the voltage gain adjustment range is unchanged, the switching frequency can be changed in a narrow range, so as to realize the compromise optimization of switching loss and conduction loss, which is beneficial to the improvement of efficiency. The control method of maximum efficiency tracking allows the converter to always work at the operating point where the efficiency is more optimized.

Description of drawings

FIG. 1 is a structural block diagram of a power converter of this embodiment;

FIG. 2 is a control route diagram of the optimization method of the present embodiment;

FIG. 3 is a circuit schematic diagram of the current injection type resonant converter of the present embodiment;

FIG. 4 is a typical waveform diagram of this embodiment;

5(a), 5(b), 5(c), 5(d), and 5(e) are the modes 1, 2, 3, 4, and 4 of the resonant converter of the present embodiment, respectively. The circuit schematic diagram of Mode 5;

Fig. 6 is the flow chart of the disturbance observation method of the present embodiment;

Figures 7(a) to 7(c) are efficiency comparison diagrams of current injection resonant current with/without efficiency optimization. The input voltages of Figures 7(a) to 7(c) are 260V, 300V, and 340V, respectively.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and provides a detailed implementation manner and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

Example

1 is a structural block diagram of a power converter of the present invention, including (N≥1) resonant topologies (resonant topologies include half-bridge/full-bridge resonant topology, phase-shifted resonant topology, asymmetric half-bridge/full-bridge resonant topology, Forward resonant topology, LLC or LCL or CL topology, compound resonant topology, multilevel topology and multiport converter). There are N auxiliary circuits or the original device is used to adjust the resonance state, and there may be a coupling relationship between the resonance topologies. For example, the nth resonance topology uses the n+1th resonance topology to adjust the resonance state. There are N control signals corresponding to N resonant topologies, which provide control signals to the switches in the resonant topology. The energy is transferred to the resonant topology through the connection or combination of the input terminals (ie, series and parallel hybrid), and multiple resonant topologies provide energy to the load through the connection or combination of the output terminals.

The present invention mainly optimizes the efficiency of such circuits. The control idea is shown in Figure 2. After measuring N voltages and M currents in the current state (the amount of N and M depends on the actual resonant circuit structure), the frequency Efficiency optimization control coordinated with parameters such as resonance state, and then output control signal to the power converter through the PWM module, so as to complete the control and achieve maximum efficiency tracking. This control idea requires the acquisition of voltage and current signals for closed-loop control to achieve efficiency optimization without changing the gain. There are four methods (only four are listed, there are other methods) for the efficiency optimization control of the coordination of parameters such as frequency and resonance state, including look-up table method, interpolation calculation method, disturbance observation method and closed-loop control method.

As shown in Figure 6, the perturbation observation method includes the following steps:

S1, obtain the input voltage and current and output voltage and current of the current state 1, and calculate the efficiency of state 1;

S2, under the premise of ensuring the output voltage, change the frequency and phase shift angle, or change the frequency and duty cycle to obtain state 2;

S3, obtain the input voltage and current and output voltage and current of state 2, and calculate the efficiency of state 2;

S4, judge whether the efficiency of state 2 is greater than that of state 1, if so, go to step S5, otherwise go to step S6;

S5, take the current state 2 as the new state 1, calculate the efficiency of state 1, and on the basis of state 1, continue to change the frequency and phase shift angle, or change the frequency and duty cycle in the same direction as step S2, to obtain a new state 2, return to step S3;

S6, on the basis of state 1, continue to change the frequency and phase shift angle in the opposite direction of step S2, or change the frequency and duty cycle, obtain a new state 2, and return to step S3.

Through the coordinated control of the resonant state and the switching frequency, the adaptive matching of the switching frequency is carried out during the dynamic adjustment of the resonant state, so that the resonant converter can achieve the compromise optimization between the switching loss and the conduction loss, and can maintain the voltage in a narrow range of the switching frequency. Gain wide range adjustment.

For converters with adjustable resonant state, such as injection current resonant converters, the resonant state will change with the change of the input voltage. Once the resonant time is much smaller than the switching period, the circulating current time in one switching period will occupy A large proportion is not conducive to the improvement of efficiency. Therefore, through the coordinated control of the resonance state and the switching frequency, the duration of the circulating current can be reduced and the efficiency of the power converter can be improved. For a traditional LLC, in order to achieve wide-range adjustment capability, the switching frequency has a wide variation range, which will result in large switching loss at high frequencies. The efficiency-optimized resonant tunable converter can be combined with duty cycle or phase shift. Adjustment, when the voltage gain adjustment range is unchanged, the switching frequency is changed in a narrow range, so as to achieve the compromise optimization of switching loss and conduction loss, which is beneficial to the improvement of efficiency. The control method of maximum efficiency tracking allows the converter to always work at the operating point where the efficiency is more optimized.

As shown in Figure 3, this embodiment is a current injection type resonant converter, which consists of two half-bridges, one is an LLC half-bridge and the other is an auxiliary half-bridge, which realizes output voltage regulation and efficiency through phase shifting and frequency fine-tuning optimization. Among them, Q ₁ to Q ₄ are switch tubes, L ₁ is the resonant inductor, L ₂ is the auxiliary inductor, C ₁ is the resonant capacitor, T ₁ is the transformer, the turns ratio is N _p : N _s : N _s , and L _M is T ₁ The excitation inductance, D ₁ and D ₂ are rectifier diodes, C _in is the input filter capacitor, and C _o is the output filter capacitor.

Fig. 4 is a typical waveform diagram of the present embodiment, wherein v _GS1 ∼ v _GS4 are the driving waveforms of Q ₁ ∼ Q ₄ respectively, v _Tp is the voltage waveform of the primary side of the transformer, i _L1 and i _L2 are the driving waveforms of L ₁ and L ₂ respectively Current waveform, _{i M} is the excitation current waveform _of T1, is the secondary current waveform.

In one switching cycle, the present invention can be divided into 10 working modes, wherein t ₂ ˜t ₅ and t ₇ ˜t ₁₀ are the phase shift angle T _FS , t ₁ ˜t ₂ , t ₄ ˜t ₅ , and t ₆ ~ t ₇ and t ₉ ~ t ₁₀ are dead time t _dead , in the case of ignoring the dead time, the duty cycle of the two half bridges is 50%, so there is no DC bias in the transformer T ₁ . The equivalent circuits of each switching mode are shown in Figure 5(a) to Figure 5(e), and the working process is as follows:

Mode 1 [t ₀ ~ t ₁ ]: As shown in Figure 5(a), at time _{t 0} , the switch Q1 is turned on. In this mode, _Q2 and _Q4 are turned off, and _Q3 is turned on. state, v _Tp is clamped by the secondary side, the LLC half-bridge starts to resonate, the secondary side D2 is turned _on , the difference between i _L1 and i _M is transferred to the secondary side, and i _L2 decreases approximately linearly.

Mode 2 [t ₁ ~ t ₂ ]: As shown in Figure 5(b), this mode is the dead time of the auxiliary half-bridge. At t ₁ , the switch _Q3 is turned off. Since i _L2 is small, it can be Considered ZCS, current i _L2 is diverted to _Q4 's body diode to achieve _Q4 's ZVS.

Mode 3 [t ₂ ~ t ₃ ]: As shown in Figure 5(c), at time t ₂ , the switch tube Q ₄ is turned on. In this mode, Q ₁ is turned on, and Q ₂ and Q ₃ are turned off. state, i _L2 begins to rise approximately linearly.

Mode 4 [t ₃ ~ t ₄ ]: As shown in Figure 5(d), at time t ₃ , i _L1 resonates to be equal to i _M , the secondary side D ₂ is both disconnected, and i _L1 and i _M begin to rise slowly.

Mode 5 [t ₄ ~ t ₅ ]: As shown in Figure 5(e), this mode is the dead time of the LLC half-bridge. At t ₅ , the switch Q1 is turned off. Since i _M is small, it can be considered that is ZCS, the current i _L1 is diverted to the body diode of _Q2 to achieve ZVS of _Q2 .

The working modes from t ₆ to t ₁₀ are similar to modes 1 to 5 , which will not be described in detail here. At time t ₁₀ , one switching cycle ends and the next switching cycle begins.

Since the gain can be reduced as the phase shift time increases, the output voltage can be adjusted, but the resonance time will be reduced, which will lead to an increase in the duration of the circulating current. Therefore, the frequency needs to be appropriately increased. In this embodiment, the resonance time is equal to The ratio of switching periods is set to 0.8 to improve the efficiency of the converter. In addition, the perturbation observation method can also be used for maximum efficiency tracking.

This embodiment is 260V-340V input (rated input is 300V) and 48V/5A output, which is compared with the injection current type resonant circuit without efficiency optimization. Table 1 is the main parameters of this embodiment.

Table 1 Main parameters of this embodiment

Switching frequency f_s/kHz 200 Resonant inductance L₁/uH 12.5 Resonant capacitance C₁/nF 30 Inductance L₂/uH 226 Transformer T₁ turns ratio N_p:N_s:N_s 20:6:6 Transformer T₁ Magnetizing Inductance L_M/uH 200

Figures 7(a) to 7(c) are the efficiency comparison diagrams of the current injection type resonant current with and without efficiency optimization. It can be seen that at 260V input, the efficiencies of the two are equivalent, and at 300V and 340V input, the efficiency optimized This embodiment has certain advantages, and the efficiency is about 1.5%-2% higher.

Claims (4)

1. An adaptive efficiency optimization method for a resonant state adjustable power converter, wherein the power converter comprises single or multiple resonant topologies, the input ends of each resonant topology are connected in parallel or in combination, and the output ends are connected in parallel or in combination To the load, each resonant topology is controlled by a separate control signal, and the control signal is connected to the auxiliary circuit or original device inside the resonant topology, It is characterized in that, the optimization method includes: after measuring N voltages and M currents in the current state, the values of N and M depend on the actual resonant circuit structure. Efficiency optimization control coordinated with resonance state, and then output control signal to power converter to achieve maximum efficiency tracking; The efficiency optimization control method for the coordination of the frequency and the resonance state includes one or more of a look-up table method, an interpolation calculation method, a disturbance observation method and a closed-loop control method; The perturbation observation method includes the following steps: S1, obtain the input voltage and current and output voltage and current of the current state 1, and calculate the efficiency of state 1; S2, under the premise of ensuring the output voltage, change the frequency and phase shift angle, or change the frequency and duty cycle to obtain state 2; S3, obtain the input voltage and current and output voltage and current of state 2, and calculate the efficiency of state 2; S4, judge whether the efficiency of state 2 is greater than that of state 1, if so, go to step S5, otherwise go to step S6; S5, take the current state 2 as the new state 1, calculate the efficiency of state 1, and on the basis of state 1, continue to change the frequency and phase shift angle, or change the frequency and duty cycle in the same direction as step S2, to obtain a new state 2, return to step S3; S6, on the basis of state 1, continue to change the frequency and phase shift angle in the opposite direction of step S2, or change the frequency and duty cycle, obtain a new state 2, and return to step S3; Through the coordinated control of the resonant state and the switching frequency, the adaptive matching of the switching frequency is carried out during the dynamic adjustment of the resonant state, so that the resonant converter can achieve the compromise optimization between the switching loss and the conduction loss, and maintain the voltage gain in the narrow range of the switching frequency. Wide range adjustment; For converters with adjustable resonant state, the resonant state will change with the change of the input voltage. Once the resonant time is much smaller than the switching period, the circulating current time in one switching period will account for a large proportion. Therefore, through the resonant state The coordinated control with the switching frequency can reduce the duration of the circulating current and improve the efficiency of the power converter; For LLC, in order to achieve wide-range adjustment capability, the switching frequency has a wide variation range, resulting in large switching losses at high frequencies. The efficiency-optimized resonant tunable converter combined with duty cycle or phase-shift adjustment, can be used in the voltage gain. Under the condition that the adjustment range remains unchanged, the switching frequency can be changed in a narrow range, so as to realize the compromise optimization of switching loss and conduction loss, which is beneficial to the improvement of efficiency; the control method of maximum efficiency tracking allows the converter to always work in the work with optimized efficiency point. 2. The adaptive efficiency optimization method of a resonant state adjustable power converter according to claim 1, wherein the table look-up method is: formulating the optimal point parameter table in each working condition, The frequency, duty cycle and phase shift control parameters of the resonant state adjustable power converter are determined by looking up the table. 3. the self-adaptive efficiency optimization method of a kind of resonance state adjustable power converter according to claim 1, is characterized in that, described interpolation calculation method is: by judging the efficiency change trend under different control parameters three times, If there is an upward and downward trend, an interpolation calculation is performed to find an approximate optimal point. 4 . The adaptive efficiency optimization method of a power converter with adjustable resonance state according to claim 1 , wherein the control signal is generated by a PWM module. 5 .

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