Disclosure of Invention
The invention provides a control method of a bidirectional symmetrical LLC resonant converter, which can realize stable operation in a wide input range and a wide load range and realize a power modulation function.
The invention is realized by the following technical scheme:
a method of controlling a bi-directional symmetrical LLC resonant converter, comprising the steps of:
S1, judging that the working mode of the bidirectional symmetrical LLC resonant converter is a voltage gain mode or a power modulation mode, if the working mode is the power modulation mode, the modulation mode of the bidirectional symmetrical LLC resonant converter is a quasi-multiphase shift modulation mode with fixed frequency, otherwise, jumping to S2;
S2, judging that the working state of the bidirectional symmetrical LLC resonant converter is a high-gain working state or a low-gain working state, if the working state is the high-gain working state, the modulation mode of the bidirectional symmetrical LLC resonant converter is a variable frequency control mode, otherwise, the modulation mode of the bidirectional symmetrical LLC resonant converter is a quasi-multiphase shift modulation mode of fixed frequency.
In S1, as an optimization, the basis for determining the working mode of the bidirectional symmetrical LLC resonant converter is set by a user according to actual requirements.
The judgment basis of the S2 is that sampling values of the input voltage, the output voltage and the output current are used as optimization.
As an optimization, in S2, before the bidirectional symmetric LLC resonant converter is subjected to the operation mode determination, it is further required to determine whether the bidirectional symmetric LLC resonant converter is in a forward operation state or a reverse operation state.
As an optimization, the bidirectional symmetrical LLC resonant converter controls output by adjusting the magnitude of the inter-bridge phase shift angle θ of the primary side and the secondary side of the bidirectional symmetrical LLC resonant converter in a power modulation mode.
As optimization, the bidirectional symmetrical LLC resonant converter controls output by adjusting the bridge arm internal phase shift phip of the bidirectional symmetrical LLC resonant converter in a low-gain operating state of a voltage gain mode.
As an optimization, the bidirectional symmetrical LLC resonant converter controls output by adjusting the switching frequency of the bidirectional symmetrical LLC resonant converter in a high-gain operating state of a voltage gain mode.
The bidirectional symmetrical LLC resonant converter is optimized in the forward working state that the input of the bidirectional symmetrical LLC resonant converter is on the primary side and the output of the bidirectional symmetrical LLC resonant converter is on the secondary side, and in the reverse working state that the input of the bidirectional symmetrical LLC resonant converter is on the primary side and the output of the bidirectional symmetrical LLC resonant converter is on the secondary side.
The bidirectional symmetrical LLC resonant conversion circuit is optimized, two ends of the bidirectional symmetrical LLC resonant conversion circuit are respectively provided with a high-voltage direct-current bus and a low-voltage direct-current bus, the two direct-current buses are respectively connected with two full bridges in a butt joint mode, each full bridge is formed by connecting two groups of two switching tubes in series, the middle points of the two groups of switching tubes in series are led out of a lead wire to be connected with a resonant cavity, the resonant cavity is a two-port network, one port is connected with the middle point of two bridge arms on the high-voltage side, the other port is connected with the middle point of two bridge arms on the low-voltage side, a transformer is arranged in the middle of the resonant cavity, the high-voltage side of the transformer is connected with a high-voltage side inductor Lr and a high-voltage side capacitor Cr in series, the high-voltage side port is finally connected in series, one end of the high-voltage side port is not provided with a first inductor Lm and one end of a second inductor Lc, and the other end of the first inductor Lm and the other end of the second inductor Lc are respectively connected with one end far away from the high-voltage side inductor Lr and the high-voltage side capacitor Cr.
As optimization, the transformation ratio of the transformer is n, and the corresponding parameter relationship is as follows: n is an integer.
Compared with the prior art, the invention has the following advantages and beneficial effects:
The invention provides a hybrid control strategy combining a variable frequency control mode and a quasi-multi-phase shift control mode with fixed frequency, which aims at a bidirectional symmetrical LLC resonant converter, when the converter gain is larger than 1, the variable frequency control mode is adopted, the zero voltage on of a primary side switching tube and the zero current off of a secondary side switching tube can be realized by the variable frequency control in a gain range larger than 1, so that the switching loss is reduced, the working efficiency of the converter is improved, the output voltage of the variable frequency control in the range is stable, the output ripple is small, when the converter gain is smaller than 1, the quasi-multi-phase shift control mode with fixed frequency is adopted, the gain modulation with the gain smaller than 1 can be stably realized, the adjusting range is large, and meanwhile, the gain characteristic irrelevant to the load is realized, in addition, the power modulation can be realized according to the required function, and the control mode only has one control variable in each working state, and the control of the variable is convenient.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present invention and the descriptions thereof are for illustrating the present invention only and are not to be construed as limiting the present invention.
Examples
According to the control method under the bidirectional symmetrical LLC loop, the working mode and the working state of the power supply are divided according to the real-time input voltage, the output current and the voltage sampling result, and then the corresponding control mode is selected according to the working state. After selecting a corresponding control mode, changing the frequency and three phase angles of a real-time driving signal through a loop control mode (PI, 2P2Z or other high-order negative feedback control modes) of the system to adjust the gain and power of the system, and when the frequency and the phase angle of the driving signal are operated, slowly and smoothly changing the frequency and the phase angle of the driving signal according to a fixed step diameter so as to achieve the effect of stable transition, so that the system can stably work in a full voltage range and a full load range, can realize stable work in a wide input range and a wide load range, can realize a power modulation function, and specifically comprises the following steps:
Firstly, a user inputs and selects a working mode, namely a voltage gain mode and a power modulation mode, a sampling module is started, the working state of the converter is determined according to real-time input voltage, output current and voltage sampling results, and the working state of the direct current converter is judged to be a forward working state or a reverse working state;
When the bidirectional symmetrical LLC resonant converter works in a voltage gain mode, the bidirectional symmetrical LLC resonant converter is divided into a high-gain working state and a low-gain working state according to sampling values of input voltage, output voltage and output current, a corresponding modulation mode is selected according to the working state, a variable frequency control mode is adopted in the high-gain working state, a quasi-multiphase shift modulation mode with fixed frequency is adopted in the low-gain working state, and when the bidirectional symmetrical LLC resonant converter works in a power modulation mode, the bidirectional symmetrical LLC resonant converter is the same as the modulation mode in the low-gain mode, a quasi-multiphase shift modulation mode with fixed frequency is adopted, but specifically regulated phase angle variables are different.
1. Voltage gain mode
The input voltage, the output voltage and the output current of the bidirectional symmetrical LLC resonant converter are sampled in real time, the sampling values of the input voltage, the output voltage and the output current are divided into a high-gain working state (gain is larger than 1) and a low-gain working state (gain is smaller than 1), and corresponding loop control modes are selected according to the working states of the converter.
And (3) high-gain loop control, wherein in a high-gain working state, a variable frequency control mode is adopted, and LLC loop control changes the frequency of a real-time driving signal calculated by a feedback loop to control the system gain. Under variable frequency modulation, the converter gain characteristic can be expressed as:
where M represents the voltage gain, fn represents the normalized switching frequency, M represents the ratio of excitation inductance to resonance inductance, and Q represents the quality factor. The working frequency of the converter is at the low impedance resonance frequencyAnd high impedance resonant frequencyThe primary side of the converter in the range can realize zero-voltage on of a primary side switching tube and zero-current off of a secondary side switching tube, and is the optimal switching frequency range for ensuring the efficiency under the variable frequency control mode of the LLC resonant converter.
And the low-gain loop control adopts a quasi-multiphase shift modulation mode with fixed frequency in a low-gain working state, the converter works at a fixed low-impedance resonance frequency fr, meanwhile, the phase shift theta between the primary side bridge and the secondary side bridge is 0, and the gain characteristic of the converter can be expressed as:
Where φp denotes the primary side leg internal phase shift and φs denotes the secondary side leg internal phase shift. The voltage gain is controlled by adjusting phip and phis, so that the converter can work stably, and the voltage gain range is irrelevant to the load and is only relevant to the phase shifts phip and phis in the bridge arm according to the formula (2), so that the voltage modulation under a wide load range can be realized.
2. Power modulation mode
In the power modulation mode, the same control mode is adopted as the low-gain working state, at the moment, the fixed converter works at the fixed frequency of fs＝1.75fr, the phase shift phip＝φs =pi in the fixed bridge arm, and the output power of the converter is regulated by regulating the inter-bridge phase shift theta between the primary side and the secondary side.
Therefore, the operating states of the bidirectional symmetrical LLC resonant converter are divided into 6 states, which are respectively:
(1) A low gain mode is input to the positive high voltage;
(2) Inputting a high gain mode in a forward low voltage;
(3) Reverse high voltage input low gain mode;
(4) Reverse low voltage input high gain mode;
(5) Forward power modulation mode;
(6) Reverse power modulation mode.
When the bidirectional symmetrical LLC resonant converter works in a forward (reverse) high-voltage input low-gain mode, the converter control loop selects a quasi-multi-phase shift control mode with fixed frequency, the output is controlled by adjusting the phase shift phip(φs in a bridge arm, when the bidirectional symmetrical LLC resonant converter works in the forward (reverse) low-voltage input high-gain mode, the converter control loop selects a variable frequency control mode, the output is controlled by adjusting the switching frequency, and when the bidirectional symmetrical LLC resonant converter works in a forward (reverse) power modulation mode, the converter control loop selects a quasi-multi-phase shift control mode with fixed frequency, and the converter controls the output by adjusting the magnitude of the inter-bridge phase shift angle theta between the primary side and the secondary side. Through the hybrid control mode, the converter can realize stable operation under a wide input range and a wide load range, and can also realize a power modulation function.
The topological structure of the bidirectional symmetrical LLC resonant converter is shown in figure 1, the bidirectional symmetrical LLC resonant converter circuit is of a symmetrical structure, two ends of the bidirectional symmetrical LLC resonant converter circuit are respectively provided with a high-voltage direct-current bus and a low-voltage direct-current bus, the two direct-current buses are respectively connected with two full bridges in a butt joint mode, each full bridge is formed by connecting two groups of two switching tubes in parallel, the middle points of the two groups of switching tubes in series are led out of a lead wire to be connected with a resonant cavity, the resonant cavity is a two-port network, one port is connected with the middle point of two bridge arms on the high-voltage side, the other port is connected with the middle point of two bridge arms on the low-voltage side, a transformer is arranged in the middle of the resonant cavity, the high-voltage side of the transformer is connected with a high-voltage side inductor Lr and a high-voltage side capacitor Cr in series, one end of the high-voltage side inductor Lr and one end of the high-voltage side capacitor Cr are connected with one end of a first inductor Lm and one end of a second inductor Lc, and the other end of the first inductor Lm and the other end of the second inductor Lc are respectively connected with one end of the high-voltage side inductor Lr and one end of the high-voltage capacitor Cr far away from each other.
A control implementation flow chart is shown in fig. 2.
1. User input selects the operating modes, namely a voltage gain mode and a power modulation mode;
2. Starting a sampling module, and determining the working state of the converter according to the real-time input voltage, the output current and the voltage sampling result, wherein the working state is used as a basis for determining a control mode;
3. when the converter works in a forward high-voltage input low-gain mode, a control loop of the converter selects a quasi-multi-phase shift control mode with fixed frequency, at the moment, the switching frequency fs＝fr is fixed, the inter-bridge phase shift theta=0, the phase shift 0 in a bridge arm is less than or equal to phip≤π,φs =pi, the converter samples the output voltage of a secondary side and inputs the sampled value and the reference voltage into a comparator at the same time, the output end of the comparator is connected with a PI regulator, the phase shift controller is used for determining the phase shift angle phip in a primary side bridge arm after passing through the PI regulator, and a corresponding driving signal is output to control the switching tube to be conducted, so that the converter works stably in the forward high-voltage input low-gain mode;
4. when the converter works in a forward low-voltage input high-gain mode, the converter control loop selects a variable frequency control mode, the converter samples the output voltage of the secondary side and inputs the sampled value and the reference voltage into the comparator at the same time, the output end of the comparator is connected with a PI regulator, a corresponding real-time variable frequency driving signal is output through the voltage-controlled oscillator after passing through the PI regulator, and the switching tube of the converter is driven to work by the signal so that the converter stably works in the forward low-voltage input high-gain mode;
5. When the converter works in a reverse high-voltage input low-gain mode, the converter control loop selects a quasi-multi-phase shift control mode with fixed frequency, at the moment, the switching frequency fs＝fr is fixed, the inter-bridge phase shift theta=0, the phase shift in the bridge arm is 0-s≤π,φp =pi, the converter samples the primary side output voltage and inputs the sampled value and the reference voltage into the comparator, the output end of the comparator is connected with a PI regulator, the phase shift controller is used for determining the size of the phase shift angle phis in the primary side bridge arm after passing through the PI regulator, and a corresponding driving signal is output to control the switching tube to be in a conducting state, so that the converter works stably in the reverse high-voltage input low-gain mode.
6. When the converter works in a reverse low-voltage input high-gain mode, the converter control loop selects a frequency conversion control mode, the converter samples the primary side output voltage and inputs the sampled value and the reference voltage into the comparator at the same time, the output end of the comparator is connected with a PI regulator, a corresponding real-time frequency conversion driving signal is output through the voltage-controlled oscillator after passing through the PI regulator, and the switching tube of the converter is driven to work by the signal so that the converter stably works in the reverse low-voltage input high-gain mode;
7. When the converter works in the forward power modulation mode, the converter control loop selects a quasi-multi-phase shift control mode with a fixed frequency, the converter works in the fixed frequency of fs＝1.75fr, the phase shift phip＝φs =pi in the fixed bridge arm, and the output power of the converter is regulated by regulating the inter-bridge phase shift theta between the primary side and the secondary side, at the momentThe converter samples the output voltage of the secondary side and inputs the sampled value and the reference voltage into the comparator at the same time, the output end of the comparator is connected with a PI regulator, the phase shift angle theta between the primary side and the secondary side is determined through the phase shift controller after passing through the PI regulator, and a corresponding driving signal is output to control the conduction state of the switching tube, so that the converter stably works in a forward power modulation mode;
8. When the converter works in the reverse power modulation mode, the converter control loop selects a quasi-multi-phase shift control mode with a fixed frequency, the converter works at the fixed frequency of z, the phase shift phip＝φs = pi in the fixed bridge arm, the output power of the converter is regulated by regulating the inter-bridge phase shift theta between the primary side and the secondary side, and the converter is controlled by the control loopThe converter samples the primary side output voltage and inputs the sampled value and the reference voltage into the comparator at the same time, the output end of the comparator is connected with a PI regulator, the phase shift controller is used for determining the magnitude of the inter-bridge phase shift angle theta between the primary side and the secondary side after passing through the PI regulator, and a corresponding driving signal is output to control the conduction state of the switching tube, so that the converter stably works in a reverse power modulation mode, a switching tube driving waveform diagram of a quasi-multi-phase shift control mode under a fixed frequency is shown in fig. 3, and table 1 is a list of operation modes of the invention.
TABLE 1
The foregoing detailed description of the preferred embodiments has been presented for purposes of illustration and description, and it is to be understood that the invention is not limited to the particular embodiments disclosed, but is intended to cover all modifications, equivalents, alternatives, and modifications falling within the spirit and principles of the invention.