JP2005514889A - Resonant converter with phase delay control - Google Patents

Abstract

  The phase delay control for the power converter operates in conjunction with a phase lock loop and current sensing feedback to provide improved control stability and dynamic output range. The phase locked loop includes a voltage controlled oscillator that is controlled based on an error signal derived from the phase of the power converter output. The error signal applied to the voltage controlled oscillator creates a shift in the switching frequency for the converter to drive the error to zero. The power converter includes an LCC resonant circuit for manipulating resonant electrical energy to improved switching speed and power density.

Description

  This application is based on US Provisional Application No. 60 / 339,308, filed Dec. 12, 2001, entitled "Resonant Converter with Phase Delay Control" for which priority is claimed. And claims the retrospective benefits of the filing date.

  The present invention relates generally to resonant power converters, and more particularly to a resonant power converter controlled with a phase delay control configuration.

  Many types of power converters are well known, especially pulse width modulation (PWM) converters and resonant power converters. The PWM power converter operates by providing a pulse train whose pulse width is adjusted according to the desired power to be supplied. PWM converters can typically be switched at a frequency that provides high efficiency to allow for a reduction in the magnetic component resulting in smaller packaging. However, typically, the higher the frequency switching in the PWM converter, the more switching loss and greater electromagnetic interference (EMI) will be generated. Typically, switching losses are caused by the switch being controlled to switch while current is conducting or receiving voltage, resulting in “hard switching”. Hard switching losses in typical PWN converters tend to increase with switching frequency. Furthermore, EMI generated by hard switching, particularly at high frequencies, can be a major factor affecting the efficiency of input power supply due to the small power factor.

  To overcome the difficulties associated with hard switching in a PWM converter, a resonance with an oscillating waveform that allows "soft switching" where either the current or voltage carried by the switch is close to zero Converters have been used. In particular, the switch in the resonant converter can be turned on with zero current and turned off with zero voltage. Low switching losses and implementation simplification allow the resonant converter to operate at a typically higher frequency than that implemented with a PWM converter. Thus, a typical resonant converter can provide much efficiency at high power density. In addition, the oscillating nature of the input in the resonant converter allows the control mechanism to shape the input current to match that of the voltage that results in a high power factor. The desired power output from the resonant converter is typically controlled by changing the switching frequency to adjust the output voltage. A typical series resonant inverter is shown in FIG. 1 using a half-bridge switching configuration in which the switches are operated complementarily with respect to switching on and off.

  Resonant converters can be operated in several modes, including conductivity, capacitive and resistive. FIG. 2 shows operating waveforms for the inductive mode operation of the resonant converter shown in FIG. FIG. 3 shows operating waveforms for the capacitive mode operation of the resonant converter shown in FIG. FIG. 4 shows operating waveforms for the resistive mode operation of the resonant converter shown in FIG.

  Referring to FIG. 3, capacitive mode operation exhibits a reduced switching frequency that is lower than that of the resonant frequency for the circuit. In capacitive mode, the MOSFET switch body diode recovers with considerable loss. Accordingly, the resonant converter preferably operates at a frequency greater than the resonant frequency of the circuit to minimize these losses.

  When the resonant converter is operating in resistive mode, the operating frequency is close to the resonant frequency, thus obtaining a high degree of efficiency. In this case, the voltage and current sinusoidal waveforms have almost the same phase, resulting in a high power factor, and less energy is lost when circulating the voltage and current. However, the operating frequency of the resonant converter must be maintained when exposed to changing loads to continue to obtain high efficiency and good power factor correction.

  Different phases are used in the resonant converter to obtain different desired results. For example, FIG. 5 shows a parallel resonant converter and FIG. 6 shows an LCC resonant converter. In FIG. 5, when the capacitor Cin / 2 acts as a voltage divider for the input DC voltage, the capacitor Cp is simply a resonant capacitor. In FIG. 6, both the capacitor Cp and the capacitor Cs / 2 function as resonant capacitors.

  The operating characteristics change during the phase of the resonant converter described above. For example, the series resonant converter shown in FIG. 1 may operate in the open circuit mode, but not in the short circuit mode. The parallel resonant converter shown in FIG. 5 can operate in the short circuit mode, but does not operate in the open circuit mode. The LCC resonant converter shown in FIG. 6 cannot operate in either a short circuit or open circuit mode, and therefore, in actual operation, it preferably includes open and short circuit protection. However, LCC resonant converters have increased overall efficiency and available output load range. Increased range and efficiency result from reduced circulating current at reduced load, thus maintaining the entire high efficiency range.

  In the resonant converter described above, the output voltage is typically maintained and adjusted as a function of the switching frequency. Increasing the switching frequency allows more power to be delivered to the load, thereby allowing increased power output. However, this type of control results in resonant currents and voltages with high peak values, which increase conduction losses and require higher ratings for power devices. Furthermore, variable switching frequency control typically adds to the overall complexity of the control and adds to the complexity of the converter filter design. This type of control typically relies on feedback from the output to adjust the switching frequency and maintain the desired power output level. However, the relationship between output power and switching frequency is typically highly nonlinear, increasing the difficulty of achieving robust control over the resonant power converter.

  According to the present invention, a resonant power converter is provided that is controlled using phase delay control to obtain improved feedback control while maintaining high efficiency. The resonant converter of the present invention can obtain a high switching frequency, resulting in element miniaturization while limiting the current or voltage surge encountered by the resonant converter element.

  Phase delay control incorporates a phase-locked loop to track the phase of the inductor in the resonant power converter relative to the reference phase signal. The phase delay is adjusted by obtaining an error signal representing the difference between the phase of the output stage current and the reference phase signal. The error signal is supplied to a voltage controlled oscillator (VCO) to modify the appropriate operating frequency for the transfer function of the output stage. Changes in operating frequency tend to reduce the phase delay error signal to zero, resulting in simple and robust control.

  The present invention uses an integrated circuit (IC) that can be used to control the lamp ballast circuit to obtain the desired control characteristics in a simplified manner. The operating characteristics of the IC are modified by selecting elements and IC functions to implement phase delay control. The result is a phase delay control with improved operating characteristics that can be implemented with only available elements.

  Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

  The present invention provides a resonant converter with phase delay control implemented in an IC to obtain high efficiency and a wide output range while reducing EMI. Phase delay control is implemented with a feedback arrangement that provides current sensing to determine the phase angle error measurement. The phase angle error measurement derived from comparison with the reference phase angle is used to control a VCO that can modify the switching frequency to adjust the phase angle of the resonant tank voltage and current.

  Referring to FIGS. 8-13, there are shown graphs of the relationship between switching frequency and phase angle of power output for series, parallel and LCC resonant converters. 8, 10 and 12, the relationship between output power and phase angle is substantially linear over a wide range of phase angles for each of several types of resonant converters. In contrast, FIGS. 9, 11 and 13 show that the power output relationship with the switching frequency is substantially non-linear, providing a relatively small dynamic range suitable for feedback control. Thus, a comparison between phase angle control and frequency control for a resonant converter clearly shows that phase angle control is advantageous when using a feedback configuration to control output power.

  Referring to FIG. 7, a model of a resonant circuit is shown with various derived operating parameters for the circuit. In particular, the phase angle is described as a function of frequency. This equation for obtaining the phase angle for various types of resonant converters is substantially linear over a wide range of output power to the circuit. Note that FIG. 7 shows that the output power is defined as the magnitude across the output resistance of the squared output voltage. Thus, the output power varies as a function of output voltage, and the output voltage varies as a function of switching frequency. This relationship is illustrated in FIGS.

  Referring now to FIG. 14, a block diagram of phase delay control according to the present invention is shown. The control uses a phase angle reference value that is added to the value of the feedback phase angle from the power control output. The difference between the phase angle reference value and the phase angle feedback provides an error value indicative of the difference between the desired phase and the actual phase. The summing point may alternatively be implemented as a comparison function.

  The error value for the phase delay is amplified and input to the VCO to generate an oscillating signal having a specific frequency associated with the VCO input. The oscillation output is applied to the power control stage of the power converter, and the phase of the power control output signal is adjusted accordingly. The power control output is shown connected to a resonant tank circuit, which also affects the phase angle feedback signal. Thus, the PLL described in FIG. 14 may provide a soft switching control arrangement for a resonant power converter based on phase delay control.

  Referring to FIG. 15, the open loop frequency response for a resonant converter with phase delay control and a given power output is shown. The open loop frequency response shows a 20 dB / dec decrease in gain due to the open loop integral characteristics of the system. The closed loop gain indicating the pole at the filter frequency is further reduced by 20 dB / dec.

  Referring now to FIG. 16, there is shown a block diagram of phase delay control realized by an IC. This IC block diagram is disclosed in US Pat. No. 6,008,593, the disclosure of which is hereby incorporated by reference. The IC circuit design is for lamp ballasts, but includes features and functions that can be used to implement phase delay control for a resonant converter according to the present invention. For example, the IC includes a VCO input at pin 2 along with a current sensing input at pin 10 for implementing PLL phase delay control according to the present invention.

  Referring to FIG. 17, there is shown a diagram illustrating the state operation of the IC for lamp ballast control. In the present invention, the preheat and ignition modes are unnecessary and can be selectively removed using an externally connected circuit. As shown in the state diagram, the IC provides a reduced voltage lockout (UVLO) mode to ensure proper input voltage for corrective action. In addition, the IC provides overcurrent and overtemperature protection as well as hard switching detection. If the IC detects either of these or other defects, the output to drive the two half bridge switches is forced to an OFF value or a safe value.

  Referring to FIG. 18, a selective delay circuit externally connected to the IC is shown. Inputs to the two AND gates are drive signal outputs HO and LO from the IC. The circuit shown in FIG. 18 provides a delay mechanism so that the driver output during preheat and ignition modes does not affect the operation of the resonant converter.

  FIG. 19 is a diagram illustrating how the phase delay control operates. The timing diagram shown shows the phase reference, phase feedback and phase error signal. In this illustration, the phase feedback is slightly out of alignment with the phase reference, as determined by the zero crossing of the current sense voltage Vcs. The phase difference generates a phase error signal that appears as a short spike, whose duration is indicative of the phase error. The phase error signal is input to a voltage controlled oscillator and is shown as having a slightly increasing voltage due to the phase error difference. The VCO output then adjusts the frequency of the resonant converter to drive the phase angle error to zero.

  Referring now to FIG. 20, the operating range for phase delay control is programmable through pins MIN and MAX. An external resistor on pin MAX sets the maximum output power for the resonant converter. The maximum output range corresponds to 5 volts on pin DIM. Similarly, an external resistor coupled to pin MIN sets the maximum phase shift or minimum output power for the resonant converter. The minimum output power for the resonant converter corresponds to 0.5 volts on pin DIM, as shown in FIG. These programmable ranges allow the user to set the reference phase angle in the range from 0 to -90 °, as shown in FIG. The phase angle range from 0 to -90 ° corresponds to a bounded voltage on pin MIN between 1 and 3 volts. This feature using the dimming action of the IC circuit allows the user to set the reference phase angle to achieve a specific power output.

  Now, referring to FIG. 21, a current sensing circuit using an IC is shown. The current sensing resistor RCS is used to derive a signal on pin CS that can be used to detect zero crossing and overcurrent conditions. Overcurrent detection produces a fault indication that places the half-bridge driver in safe stop mode. The safe stop (shutdown) mode persists until, for example, the overcurrent condition is removed for a specified period of time or the power to the circuit is returned. The current sense signal is compared to a common signal reference on pin COM to determine the zero crossing. It is the zero crossing that is used to determine the feedback phase angle described above as shown in FIG. As shown in FIGS. 19 and 22, the feedback phase angle is obtained during the interval when the switch on the low side of the half bridge driven by the signal LO is high. During this interval, the voltage on pin CS undergoes a zero crossing, which gives an indication of the phase angle for controlling the resonant circuit.

  Referring to FIG. 22, when the low side switch is driven ON by the signal LO becoming high, the voltage on pin CS is caused by the switching noise generated by turning on the low side switch. Transient response appears. To avoid erroneously measuring the zero crossing of voltage Vcs, a measurement delay period of 400 nanoseconds is introduced into the transient response circuit as shown in FIGS.

  Referring now to FIG. 23, an external circuit connected to an IC that performs phase delay control with the topology of an LCC resonant converter is shown. The topology of the LCC resonant converter preferably takes advantage of the associated efficiency and load range provided by this resonant circuit configuration. The circuit shown in FIG. 23 also provides overcurrent and open circuit protection to prevent the circuit from operating to the extent that damage can occur to the elements. As shown in FIG. 17, if a defect is sensed by the IC, the HO and LO drive signals are driven off or to a safe state to provide adequate protection for the elements in the resonant converter.

The circuit diagram shown in FIG. 23 provides a resonant converter having the following characteristics:
Line input voltage range: 400V ± 10%
Output power: 300W
DC output voltage: 12V
Minimum switching frequency: 60 kHz
Rfmin = 15k ohm Rmin = 9k ohm Rmax = Rfmin · Rmin / [4Rmin−Rfmin (1-Ψ / 45)]
= 7.64KΩ
Rcs = 0.14 ohm

  Referring to FIG. 24, a topological model of the LCC resonant converter circuit is shown. Switches M1 and M2 are switched by output signals HO and LO, respectively.

  Now referring to FIG. 25, there is shown a waveform showing converter gain for an LCC resonant converter. As mentioned above, the converter gain of interest can be achieved when the operating frequency of the resonant converter is greater than the resonant frequency.

  The design of the phase delay control according to the present invention was examined using the LCC resonant circuit simulation shown in FIG. The switch having inputs Q1 and Q2 is a model of a power MOSFET switch used in a resonant converter. Therefore, the switch signals Q1 and Q2 are driven by the respective output signals HO and LO of the IC. Circuit simulations show that phase delay control provides large efficiency and dynamic output range with a simplified design.

  Referring now to FIG. 27, a circuit diagram of a power stage implementation according to the present invention is shown. Note the LCC topology in the resonant stage of the converter.

  Referring now to FIG. 28, a circuit diagram for implementing the control is shown. The preheating and ignition effects provided by the IC are selectively removed from circuit operation through the use of a delay circuit incorporating two AND gates. The control signal supplied by the AND gate is provided to a MOSFET driver that provides a signal to the MOSFET switch.

  Circuit parameter measurements were obtained with a resonant converter operating at full load and 20% of full load. The measurements were taken for high side switch drain voltage, low side switch drain current, capacitor voltage, induced current, and transformer primary side voltage. It has been observed that when the MOSFET switch in the circuit is turned on, the body diode is conducting, allowing the MOSFET to be turned on at zero voltage to avoid switching losses. However, higher voltage and current peak levels have been observed in resonant converter elements that would be typical for PWM converters. Since the ratio of the switching frequency to the resonant frequency undergoes a relatively small change, the change in phase delay for the resonant converter is small even when the load changes.

  The drain voltage for the high side switch and the drain current for the low side switch were measured with output voltages of 8.4 and 12 V, resulting in the following observations. Given the same operating characteristics of the remaining resonant circuit based on the load, a change in output voltage produces a corresponding change in output power. The switching frequency is observed to change accordingly and the observed phase delay is modified according to the present invention to track the reference phase.

  Referring now to FIG. 29, a graph showing output power percentage versus input and output voltage is shown. FIG. 29 shows that the output voltage can be adjusted depending on the minimum input voltage, but cannot be adjusted if the minimum input voltage becomes smaller than a certain value depending on the output power percentage. For example, at 20% of full load, the output voltage can be adjusted when the input voltage is greater than 220V. The boundary setting for output voltage regulation varies depending on the percentage of the full load output power requested.

  The phase delay control of the present invention defines that the switching frequency of the power converter is above the resonant frequency in order to achieve high performance and system protection. Furthermore, by programming the minimum phase, hard switching in light load conditions can be limited. Phase delay control offers advantages over variable frequency controllers in general by providing limited hard switching at light loads, which is very much to achieve with conventional frequency control. Have difficulty. The phase delay control of the present invention also has improved linear output characteristics over that of frequency control. Another advantage of the present invention is that the current sensing resistor Rcs can have the dual function of both current sensing and overcurrent protection. Thus, no additional elements are required to perform both functions.

  Another advantage of the present invention is that phase delay control is independent of component tolerances and allows the stray inductance of the transformer to act as the main inductance of the LCC resonant converter phase. Many other types of topologies can be used with this control arrangement that can make the resonant circuit insensitive to element tolerances through minimal phase limiting. Thus, the resonant circuit of the present invention allows a generally higher frequency range compared to a PWM converter.

  While the invention has been described with respect to specific embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Accordingly, the invention is not limited to the specific disclosures described herein, but is preferably limited only by the scope of the appended claims.

It is a figure which shows the conventional series resonance converter. It is a figure which shows the operation | movement waveform of the circuit of FIG. 1 in an inductive mode. FIG. 2 is a diagram showing operating waveforms of the circuit of FIG. 1 operated in capacitive mode. It is a figure which shows the operation | movement waveform of the circuit of FIG. 1 operated by resistive mode. It is a figure which shows the conventional parallel resonant converter. It is a figure which shows the conventional LCC resonant converter. It is a figure which shows the circuit parameter with respect to an ideal resonant circuit. 6 is a graph showing the relationship between phase angle and output power for the circuit of FIG. 6 is a graph of switching frequency versus power output for the circuit of FIG. 2 is a graph showing phase angle versus power output for the circuit of FIG. 2 is a graph showing switching frequency versus output power for the circuit of FIG. 7 is a graph showing phase angle versus output power for the circuit of FIG. 7 is a graph showing switching frequency versus output power for the circuit of FIG. It is a block diagram of the phase delay control by this invention. 6 is a graph showing a frequency response for a phase delay control system. It is a block diagram which shows the internal circuit of IC used in order to implement the phase delay control by this invention. FIG. 17 is a state diagram showing an operation mode of the circuit of FIG. 16. FIG. 17 shows a circuit for use with the IC shown in FIG. 16 to select functions performed by the IC. It is a timing diagram which shows the operation | movement of the phase delay control by this invention. 6 is a set of graphs showing operational characteristics of phase delay control using an IC according to the present invention. It is a figure which shows the current sensing circuit implemented using IC. It is a graph which shows an electric current sensing blanking period. FIG. 3 is a circuit diagram showing connection of elements to an IC for realizing the present invention. It is a circuit diagram which shows the LCC resonant converter which has a resonant tank circuit. It is a graph which shows the relationship between the operating frequency near resonance frequency, and converter gain. FIG. 25 is a simulation circuit diagram of the circuit of FIG. 24. FIG. 3 is a circuit diagram implementing a power stage according to the present invention. It is a circuit diagram which shows the selection function control of IC with respect to the resonant converter by this invention. It is a figure which shows the graph showing the relationship between the output electric power with respect to a resonant converter, input voltage, and output voltage.

Claims (20)

A power converter controller for controlling a resonant power converter,
A current sensing circuit that detects the phase of the power converter feedback signal and outputs an associated phase angle signal; and
A phase-locked loop circuit for controlling the switching frequency of the power converter, the phase-locked loop circuit being provided with the phase angle signal at its input;
A phase angle error signal generated in the phase lock loop in relation to a reference phase angle and the phase angle signal;
A voltage controlled oscillator in the phase locked loop for adjusting the switching frequency of the resonant power converter, the voltage controlled oscillator being provided with the phase angle error signal at its input;
A switch output circuit coupled to the phase-locked loop to control switching of a power switch in the resonant power converter;
A power converter feedback signal that is affected by switching the power switch in the resonant converter such that the power output of the resonant power converter is controllable by phase adjustment provided by the phase lock loop;
Power converter controller with   The power converter controller of claim 1, wherein the power converter feedback signal includes a voltage across a resistor coupled to one of the power switches.   The power converter controller of claim 1, wherein the resonant power converter has a characteristic frequency and the switching frequency is greater than or equal to the characteristic frequency.   The power converter controller of claim 1 further comprising a fault signal provided by the current sensing circuit to declare a fault to allow the resonant power converter to be placed in safe mode operation.   The power converter controller of claim 1, wherein the controller is implemented in an IC.   The power converter controller of claim 1 further comprising a selection circuit for selectively enabling or disabling the function of the controller.   The power converter controller of claim 1, wherein the current sensing circuit provides a zero crossing indication for a switch voltage.   The power converter controller of claim 1, further comprising a blanking circuit for producing the phase angle signal for a specific period.   The power converter controller of claim 1, wherein the specific period is about 400 nanoseconds.   The power converter controller of claim 1, wherein the phase angle control is operable in a range of about 0 to about −90 °.   The power converter controller of claim 1, wherein the resonant power converter includes an LCC circuit.   A switching power converter having regulated power output through operation of a power switch in a half bridge configuration, wherein switching of the switch is controlled by a power converter controller according to claim 1.   The power converter controller of claim 1 further comprising a programmable input for determining a minimum phase shift reference and a maximum phase shift.   The power converter controller of claim 2, wherein the resistor is coupled to a low side switch of a half-bridge switching arrangement. A resonant circuit for storing electrical energy;
A half-bridge switching arrangement coupled to the resonant circuit to control transfer of the electrical energy to and from the resonant circuit;
A controller coupled to the half bridge circuit to control switching of the switches in the half bridge circuit;
A current sensing device coupled to the controller and to the half bridge circuit for providing a current sensing signal to the controller;
A current sensing signal circuit in the controller for providing a phase angle signal based on the current sensing signal;
Operable to receive the phase angle signal and provide switching control for switching the switch in the half-bridge circuit such that the phase of the electrical energy in the resonant circuit is adjusted toward a reference phase A phase-locked loop in the controller,
Power converter with   The power converter of claim 15, wherein the phase locked loop further comprises a voltage controlled oscillator for providing a variable oscillating output to adjust the phase in the resonant circuit.   The power converter of claim 15, wherein the current sensing device is a resistor and a voltage measurement can be made across the resistor to obtain a current sensing signal.   The power converter of claim 15, wherein the controller circuit is incorporated in an IC.   The power converter of claim 15 further comprising a function selection circuit coupled to the controller to selectively adjust a controller function. The power converter of claim 15, wherein the controller further comprises a current sensing blanking device for masking the current sensing signal during a specified time interval.

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