A ZVS switching digital power amplifier based on H-bridge topology

Abstract

The present invention relates to a ZVS switching digital power amplifier based on H-bridge topology, comprising a DC regulated power supply module, a bridge chopper module, a transformer isolation module, an output rectifier filter module, a control module, a duty cycle loss compensation module, a switch tube drive module and an auxiliary power supply. The duty cycle loss compensation module is used to pre-distort the external input signal to be amplified to compensate for the duty cycle loss problem of the H-bridge circuit, and its output is connected to the PWM modulator of the control module; the duty cycle loss compensation module includes an addition circuit, which performs addition operation on U1 and U2, U1 is the external input signal, and U2 is a distorted voltage with the same monotonicity as the external input signal. U2, as a distorted voltage with the same monotonicity as the input signal, is superimposed on the external input signal after passing through the addition circuit. The present invention has the characteristics of high efficiency, excellent quality and low distortion.

Description

Technical Field

[0001] The present invention relates to the field of digital power amplifiers, in particular to a high-efficiency, low-distortion switching ZVS power amplifier. Background Art

[0002] Power amplifiers are categorized into analog and digital power amplifiers based on the operating region of their power devices. Analog power amplifiers are further divided into Class A, Class B, and Class AB based on their static operating point. Digital power amplifiers primarily refer to Class D, also known as switching power amplifiers. Analog power amplifiers operate in the linear amplification region of the switching device, resulting in high losses and low efficiency, which limits power level increases. With the advancement of power electronics technology, digital power amplifiers, which use fully controlled switching devices and operate in the cutoff and saturation regions, offer low losses and high efficiency, making them suitable for high-power applications and gradually replacing analog power amplifiers.

[0003] In the field of DC-DC converters, resonant soft-switching technology further reduces the switching losses of power field-effect transistors. Its principle is to use the parasitic capacitance of the switching tube and the resonant inductor to form a resonant network so that the current and voltage do not overlap when the switching tube switches. Taking the H-bridge network phase-shifted control DC-DC soft-switching converter as an example, the resonant inductor added at the midpoint of the bridge arm resonates with the parasitic capacitance of the switching tube to make the voltage across the two ends zero when the switching tube switches, that is, to achieve ZVS switching, further improving the efficiency of the converter. However, the introduction of the resonant inductor causes the duty cycle of the secondary side of the transformer to be different from the duty cycle of the switching network, resulting in duty cycle loss. If the resonant full-bridge converter topology is introduced into a digital power amplifier, the magnitude of the duty cycle loss is proportional to the output voltage, that is, related to the size of the input signal to be amplified. As a result, when used as a power amplifier, the circuit has different voltage amplification factors for different input signal levels, resulting in distortion.

[0004] Based on the advantages of digital power amplifiers, the present invention designs a ZVS switching digital power amplifier based on H-bridge topology. Compared with traditional digital power amplifiers, this design retains the soft switching technology in the DC-DC field, further improving efficiency. In addition, to address the duty cycle loss problem introduced by the resonant inductor in the soft switching technology and overcome the resulting distortion, the present invention designs a duty cycle loss compensation module to compensate for it. Summary of the Invention

[0005] The present invention designs a ZVS switching digital power amplifier based on H-bridge topology, which has the characteristics of high efficiency, excellent performance and low distortion, and can fill the gaps in related technologies. The technical solution is as follows:

[0006] A ZVS switching digital power amplifier based on an H-bridge topology includes a DC regulated power supply module, a bridge chopper module, a transformer isolation module, an output rectifier and filter module, a control module, a switch tube driver module, and an auxiliary power supply. The control module is used to generate switch tube on and off control instructions through a PWM modulator according to an external input signal; the switch tube driver module is used to drive the switch tube of the bridge chopper module to turn on and off according to the on and off instructions of the control module, and chop the voltage provided by the DC regulated power supply into positive and negative pulse voltages whose duty cycle is modulated by the input signal; the positive and negative pulse voltages generated by the bridge chopper module are isolated by a transformer and sent to the output rectifier and filter module; the output rectifier and filter module is used to rectify the positive and negative pulse voltages into square wave voltages, and the square wave voltages are filtered out by an LC low-pass filter to remove high-frequency components to become a high-power output signal. The invention is characterized in that

[0007] The system also includes a duty cycle loss compensation module. The module is used to pre-distort the external input signal to be amplified to compensate for the duty cycle loss problem of the H-bridge circuit. Its output is connected to the PWM modulator of the control module. The module includes an adding circuit that performs an addition operation on U1 and U2. U1 is the external input signal, and U2 is a distorted voltage with the same monotonicity as the external input signal. U2, as a distorted voltage with the same monotonicity as the input signal, is superimposed on the external input signal after passing through the adding circuit.

[0008] Preferably, a voltage is divided between the input terminal of the duty cycle loss compensation module and the ground terminal via a fixed resistor R4 and a variable resistor R5, the divided voltage is U2, and the magnitude of the distorted voltage is adjusted by adjusting the variable resistor R5.

[0009] Preferably, the adding circuit is composed of a resistor R1, a resistor R2, a resistor R3, a feedback resistor Rf, a resistor R and an operational amplifier. The input end of the duty cycle loss compensation module is connected to the positive input end of the operational amplifier through the resistor R2. The positive input end of the operational amplifier is grounded through the resistor R, and the negative input end of the operational amplifier is grounded through the resistor R1. The divided voltage U2 is connected to the positive input end of the operational amplifier after passing through the resistor R3.

[0010] From the above description, it can be seen that the switch tube in this solution operates in the ZVS switching state, which further reduces the loss compared with the traditional digital power amplifier. In order to solve the duty cycle loss problem introduced by the H-bridge resonant network, the compensation module is used to suppress the pre-distortion of the input signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a simplified diagram of the overall circuit in a specific embodiment of the present invention.

[0012] Figure 2This is a simplified diagram of the H-bridge circuit in the present invention.

[0013] Figure 3 This is the timing diagram of the amplitude pulse voltage generated by the H-bridge under the action of the PWM signal.

[0014] Figure 4 This is a simplified diagram of the full-wave rectifier and filter circuit on the secondary side of the transformer.

[0015] Figure 5 This is the measured duty cycle loss in the H-bridge ZVS topology.

[0016] Figure 6 It is the duty cycle loss compensation module.

[0017] Figure 7 Output results of the prototype test for this patent. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clear, the specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings:

[0019] Attachment Figure 1 This is a simplified diagram of the overall circuit in a specific embodiment of the present invention. The ZVS switching digital power amplifier based on the H-bridge topology proposed in the present invention includes a DC regulated power supply, an H-type bridge, an isolation transformer, a rectifier and filter module, a duty cycle loss compensation module, a control circuit module and an auxiliary power supply.

[0020] Attachment Figure 2 It is an H-type bridge. Q1, Q2, Q3, and Q4 are four power field-effect tubes, which are connected in the order shown in the figure. Q1 and Q2 form the left arm of the bridge, and Q3 and Q4 form the right arm of the bridge. The two switch tubes Q1 and Q3 are the first group of diagonal bridge arm switch tubes, and the two switch tubes Q2 and Q4 are the second group of diagonal bridge arm switch tubes. Under the action of the circuit control module and the switch tube drive signal, the upper and lower switch tubes in the left bridge arm are staggered and complementary in a fixed switching period T. The conduction time of each switch tube is 0.5T, and the upper and lower switch tubes in the right bridge arm are staggered and complementary. The two switching tubes are turned on in an alternating and complementary manner within a fixed switching period T, with each switching tube being turned on for 0.5T. The positive output of the DC regulated power supply is connected to the drains of the switching tubes Q1 and Q4 on the left and right bridge arms. The output voltage of the DC regulated power supply is V, and the negative output of the DC regulated power supply is connected to the sources of the switching tubes Q2 and Q3 on the left and right bridge arms. When the two switching tubes in the diagonal bridge arms are turned on at the same time, the voltage between points AB on the primary side of the transformer is +V or -V (+V when the first set of diagonal bridge arms is turned on, and -V when the second set of diagonal bridge arms is turned on).

[0021] Attachment Figure 3The diagram illustrates the operating timing of the H-bridge switches, where t represents the high-level duration of the control circuit's PWM signal. Q1, Q2, Q3, and Q4 are the drive signals for the four power field-effect transistors (MOSFETs), and the last row, AB, represents the transformer primary voltage. Based on the staggered, complementary conduction of the upper and lower switches in the left and right arms, the high-level duration t of the square wave output by the PWM modulator in the circuit control module controls the duration of simultaneous conduction of the two diagonal switches. When t = 0, the simultaneous conduction duration of the two diagonal switches is the shortest, equal to 0. When the high-level duration t equals half a switching cycle, the simultaneous conduction duration of the two diagonal switches is the longest, equal to half a switching cycle. With the cooperation of the drive and control circuits, the voltage provided by the DC regulated power supply is chopped by the H-bridge, generating positive and negative pulse voltages between the transformer primary windings AB. These pulses have a high-level duration equal to t and an amplitude equal to the input voltage V, with a period equal to the switching cycle T of the switches.

[0022] The signal input to the controller is a+x(t), which modulates the duty cycle of the square wave output by the PWM module, and the high-level time of the PWM signal is N(a+x(t)). N is a proportional coefficient, which is related to the characteristics of the PWM module used. It requires that the frequency of x(t) is much smaller than the switching frequency. The controller adjusts the opening timing of the four switch tubes Q1, Q2, Q3, and Q4 according to the high-level time of the PWM signal, so that the time when the two switch tubes in the diagonal bridge arm are turned on at the same time is equal to the high-level time of the PWM output square wave signal N(a+x(t)), generating a positive and negative pulse voltage with a period of T and an amplitude of V on the primary side of the transformer.

[0023] Attachment Figure 4 It is a rectifier and filter circuit. The positive and negative pulse voltages on the primary side of the aforementioned transformer are coupled to the secondary side through a transformer with a primary-to-secondary turns ratio of 1 / K. After rectification, a square wave voltage with a period of T / 2, an amplitude of KN, and a high-level duration of N(a+x(t)) is obtained. After LC low-pass filtering, the high-frequency components are filtered out to obtain an output high-power voltage, which can be expressed as 2KVN(a+x(t)) / T. At this time, the output voltage consists of two parts, the DC component is 2KVNa / T, and the AC component is 2KVx(t) / T. The output drive signal is an AC component superimposed on a DC bias. By changing the input signal a+x(t), adjusting the a value can adjust the DC of the output drive signal, and adjusting x(t) can adjust the AC component of the output drive signal.

[0024] Duty cycle loss is a unique phenomenon of ZVS PWM full-bridge converter, that is, the duty cycle of the secondary side of the transformer is not exactly equal to the duty cycle of the primary side, but slightly smaller. The difference is recorded as duty cycle loss D loss , attached Figure 5This is the experimental result of the duty cycle loss phenomenon. The size of the duty cycle loss increases linearly with the increase of the output current. If the load resistance of the power amplifier is constant, the duty cycle loss is proportional to the size of the output voltage. The reason for the duty cycle loss is that during the H-bridge current commutation process, although there is a positive voltage square wave (or negative voltage square wave) on the primary side, the primary side is not enough to provide the load current. The two diodes in the secondary side rectification part are turned on at the same time for the secondary side freewheeling. Since the two diodes are turned on at the same time, the secondary side voltage is clamped to zero, resulting in a time when there is voltage on the primary side but no voltage on the secondary side. The output square wave of the PWM module is inconsistent with the secondary side duty cycle, that is, the secondary side loses part of the duty cycle. The duty cycle lost on the secondary side is:

[0025]

[0026] Among them L r The resonant inductor introduced to assist ZVS, V o is the output voltage of the power amplifier, f s is the switching frequency of the H-bridge switch tube, R is the load of the power amplifier, V in is the DC regulated power supply voltage, and the transformer primary-to-secondary turns ratio is 1 / K. From the above formula, it can be seen that the duty cycle loss on the secondary side of the transformer is proportional to the output voltage of the power amplifier, while the digital power amplifier requires that the duty cycle of the square wave obtained after chopping is proportional to the input small signal voltage. If the duty cycle loss is not suppressed, the larger the input signal of the power amplifier, the more serious the duty cycle loss, that is, the amplification factor of the power amplifier for each part of the input signal is not the same. The duty cycle loss of the part with high input signal voltage is large, and the duty cycle loss of the part with low input signal voltage is small, which will introduce greater distortion.

[0027] In order to reduce the distortion introduced thereby, this patent proposes the following Figure 6 The duty cycle loss compensation module shown pre-distorts the input signal to be amplified, thereby compensating for the subsequent duty cycle loss, and the actual duty cycle finally obtained is proportional to the input signal.

[0028] R1, R2, R3, Rf, R and the operational amplifier form an adding circuit to add U1 and U2. The output voltage Uo of the module is:

[0029] U O =a(U i +bU i )

[0030] in:

[0031]

[0032]

[0033] After the duty cycle loss compensation module, the input signal is pre-distorted by U O From the expression, we can see that the output signal of this module increases based on the original signal, and the increment is the same as the input signal U i Proportional to the duty cycle loss, the opposite effect of duty cycle loss is achieved by adjusting the value of potentiometer R5 to change the magnitude of input signal distortion. The distorted signal is fed into the PWM module, and finally the duty cycle and input signal U are generated on the secondary side. i The pre-distortion module offsets the duty cycle loss of the H-bridge and reduces the distortion of the digital power amplifier.

[0034] By adjusting the value of potentiometer R5, the size of the pre-distortion variable of the input signal can be adjusted. When R5 increases, the additional increment of the input control signal becomes larger after passing through the compensation module, which can compensate for the larger duty cycle loss of the H-bridge; when R5 decreases, the additional increment of the input control signal becomes smaller after passing through the compensation module, and the compensated duty cycle loss is smaller. In practice, the value of R5 can be adjusted according to the specific situation of the circuit duty cycle loss, so that the pre-distortion module can just compensate for the duty cycle loss of the H-bridge.

[0035] The difference between the present invention and the traditional H-bridge digital power amplifier circuit lies in the added duty cycle loss compensation module. Phase shift control refers to a control method in which the control module changes the conduction overlap time of the two upper switch tubes of the H-bridge (generally referred to as the phase shift angle) to control the duty cycle of the primary side of the transformer. Duty cycle loss is an inherent defect of the phase-shifted full-bridge topology structure. It refers to the phenomenon that the duty cycle of the transformer secondary side voltage caused by the transformer leakage inductance and resonant inductance is less than the primary side duty cycle generated by the controller. The amount of duty cycle loss on the secondary side of the transformer is proportional to the magnitude of the load current. When the load resistance of the digital power amplifier is constant, the duty cycle loss is proportional to the magnitude of the output voltage, that is, proportional to the signal of the input control module. The principle of the duty cycle loss compensation module is to use this proportional relationship to pre-distort the input control signal, and use an analog adder circuit to additionally increase the input control signal. The size of the increment is proportional to the size of the input control signal to offset the duty cycle loss of the H-bridge topology.

[0036] Attachment Figure 7To test the output results, the control module of the circuit under test uses the UCC3895 chip from Texas Instruments. The chip has a built-in PWM modulation module, and the modulation signal is input from pin 2 of the chip. Pins 17 and 18 of the chip output complementary square wave signals as drive instructions for the two switching tubes of the left bridge arm, and pins 13 and 14 output complementary square wave signals as drive instructions for the two switching tubes of the right bridge arm. The time when pins 13 and 17, and pins 14 and 18 simultaneously output high levels is modulated by the modulation signal from pin 2, which can meet the requirements of the invention for the control part function. During the test, the modulation signal input from pin 2 is a triangular wave voltage with a frequency of 5Hz, a 2.65V DC bias, and a peak-to-peak value of 0.8V. The output voltage of the DC regulated power supply is 160V, the primary-to-secondary turns ratio of the transformer is 1.1, and the circuit output is a triangular wave with a 95V DC bias and a peak-to-peak value of 28V.

Claims

1. A ZVS switching digital power amplifier based on an H-bridge topology, comprising a DC regulated power supply module, a bridge chopper module, a transformer isolation module, an output rectifier and filter module, a control module, a switch driver module, an auxiliary power supply, and a duty cycle loss compensation module. The control module is configured to generate switch on / off control instructions via a PWM modulator based on an external input signal. The switch driver module is configured to drive the switch of the bridge chopper module on and off based on the on / off instructions from the control module, thereby chopping the voltage provided by the DC regulated power supply into positive and negative pulse voltages whose duty cycle is modulated by the input signal. The positive and negative pulse voltages generated by the bridge chopper module are isolated by a transformer and sent to the output rectifier and filter module; The output rectifier and filter module is used to rectify the positive and negative pulse voltages into square wave voltages. After the square wave voltage passes through the LC low-pass filter to remove the high-frequency components, it becomes a high-power output signal. The duty cycle loss compensation module is used to pre-distort the external input signal to be amplified to compensate for the duty cycle loss problem of the H-bridge circuit, and its output is connected to the PWM modulator of the control module; The duty cycle loss compensation module includes an adding circuit that performs an addition operation on U1 and U2, where U1 is an external input signal and U2 is a distorted voltage having the same monotonicity as the external input signal. U2, as a distorted voltage having the same monotonicity as the input signal, is superimposed on the external input signal after passing through the adding circuit; The input end of the duty cycle loss compensation module and the ground end are divided by a fixed resistor R4 and a variable resistor R5. The divided voltage is U2, and the size of the distorted voltage is adjusted by adjusting the variable resistor R5. The adding circuit consists of a resistor R1, a resistor R2, a resistor R3, a feedback resistor Rf, a resistor R and an operational amplifier. The input end of the duty cycle loss compensation module is connected to the positive input end of the operational amplifier through the resistor R2. The positive input end of the operational amplifier is grounded through the resistor R, and the negative input end of the operational amplifier is grounded through the resistor R1. The divided voltage U2 is connected to the positive input end of the operational amplifier after passing through the resistor R3.

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