A control system for a bidirectional power converter

Abstract

A control system for a bidirectional power converter includes a control circuit for controlling a bidirectional DC-DC converter, a circuit for providing an auxiliary supply voltage for one or more limiting operational amplifiers, and a circuit for generating an adjusted reference voltage for forward or reverse current limit in the control circuit. The control system is particularly suitable for use in a bidirectional programmable power supply with bidirectional precisely adjustable current limit in addition to voltage regulation, bidirectional precisely adjustable power limit, and parallel precisely adjustable constant resistance control for reverse control and forward series constant resistance control. The control system allows control to quickly transfer from one mode to another and allows the converter output current direction to change seamlessly when load conditions or program mode values change, and eliminates the tendency of the control circuit to oscillate at the boundaries of various control modes. The invention also enables a control deadband for current limit or power limit at very low output current to be minimized or eliminated.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of high frequency switching power converter technology, including AC-DC, DC-DC or DC-AC power electronic converters, and in particular to AC-DC switching mode programmable power supplies. BACKGROUND

[0002] Programmable power supplies (PPS) were originally known as laboratory power supplies, with precise, adjustable voltage output and current limit programmed through front panel potentiometers. Until the introduction of the Anatek Electronics Lab 3000 series in 1980, these power supplies were low efficiency linear regulators. Switching mode types, such as the Lab 3000 series, are now increasingly popular due to their high efficiency and compact size. In recent years, the advent of battery electric vehicles and the need to test batteries has increased the demand for bidirectional switching mode programmable power supplies that can provide (forward) as well as sink (reverse) load current, inverters, converters and chargers. In both directions of these bidirectional programmable power supplies, there is an increasing need for a wide range of precise programmable output voltages, precise and adjustable current limits and power limits. Precise and adjustable shunt constant current control in reverse and series constant current control in forward are also usually required. These different control modes should exist simultaneously, but ideally only one mode should regulate the load current at any time. Furthermore, it is desirable that the control mode can change seamlessly from one mode to another with minimal delay time and without oscillation at the boundary of the control modes. Traditionally, the control system of these laboratory or programmable power supplies used analog circuits of operational amplifiers or dedicated pulse width modulation (PWM) control ICs, however, the delay problem of transferring control modes and oscillation has plagued this analog control. Recently, digital control systems have been proposed because they are more flexible and less prone to oscillation. However, digital control is inherently slower than analog control because there is an unavoidable time delay in sensing voltage and current sampling and computation, which further slows down the response speed.

[0003] Silicon General (now manufactured by Microchip) SG1524 is one of the earliest dedicated pulse width modulation (PWM) control ICs designed to control switching mode power converters, the schematic diagram of which is shown in Figure 2 The voltage error operational amplifier is a transconductance operational amplifier. The current error operational amplifier is a low bandwidth, low gain differential operational amplifier with an input offset voltage of 200 mV. Therefore, the transition to current limit mode is slow and imprecise. A later dedicated PWM control IC is Texas Instruments (TI) TL494, the schematic diagram of which is shown inFigure 3 As shown. They are connected together and pulled down by a 0.7mA constant current sink. This allows selection of constant voltage mode or constant current mode. This configuration provides more precise control and faster switching between voltage control mode and current limiting mode, but may cause oscillations at the crossover point between the two modes because one control loop route is loaded with a compensation network of the other control loop.

[0004] The control method used by the TL494 can be extended to more modes, such as power limiting or constant resistance limiting, but the crossover oscillation problem will be more serious, and the method cannot be extended to bidirectional control.

[0005] Two digital control methods have recently been proposed to implement multi-loop control of bidirectional converters. The first method is as follows: Figure 4 As shown, this involves the main voltage control loop, where the measured output voltage Vs is subtracted from the desired voltage setpoint input Vset to establish a voltage error value. This voltage error value is amplified by the transfer function Gv and then input to the pulse width modulator Kpwm. Various other control loops (e.g., a positive current loop) function to reduce the voltage setpoint input Vset of the voltage loop to limit the positive or negative load current. Therefore, at least two of these loops—the voltage loop and one of the current or power limiting loops—operate simultaneously, which makes the response time even slower. The second method is as follows... Figure 5 As shown, a loop selection modulation block is involved, which selects which of the loops will control the modulation block according to a digital algorithm.

[0006] A first objective of this invention is to provide an analog control method for bidirectional converters or programmable power supplies that allows for seamless switching of converter current direction from forward to reverse. Another objective is to provide an improved analog control method for bidirectional converters or programmable power supplies, featuring rapid and seamless transitions from one control mode to another, such as from voltage control to current limiting and reverse control. A further objective is to eliminate the tendency for boundary point oscillations between different control modes. A further objective is to eliminate or minimize the possibility of control dead zones in the forward or reverse directions at very low converter currents. Summary of the Invention

[0007] The present invention includes the configuration and connection of multiple Operational Amplifiers (Op Amps) to create a high performance analog control circuit that can be used as part of the control system of a bi-directional converter or a bi-directional programmable controller. This circuit allows multiple control loops to exist simultaneously, while only one control loop is active at any particular time to control the converter. It overcomes the limitations of the prior art TL494 configuration in eliminating oscillations at the crossover point between two control loops and allowing a bi-directional converter to have minimal control deadband between the two directions of the converter. Like the TL494 circuit, it allows fast and seamless transfer between control loops, much faster than possible with digital control methods such as the prior art digital control methods discussed. The controlled converter can be a non-isolated bi-directional converter (e.g. a buck or boost converter as shown Figure 8 ) or an isolated converter (e.g. a bi-directional phase-shifted full-bridge converter).

[0008] The present invention is particularly suitable for use with a single or multiple parallel converters, each using an internal control loop such as the average current control described by Lloyd Dixon in his article "Average Current Mode Control of Switching Power Supplies" Figure 6 , or a charge control loop as described in the ON Semiconductor NCP4390D IC data sheet. Multiple parallel converters are commonly used in programmable power supplies of high power or current, and can be operated at the same frequency but at different phases from each other to increase the power capability of the programmable power supply and reduce input and output ripple current and voltage. These individual converters can be well controlled through average current mode control Figure 7 as described in the LM5170 data sheet. This control method ensures that the parallel converters share the load current equally and prevents current recirculation between the converters. It should be noted that the circuit disclosed in the NCP4390D IC data sheet is only suitable for unidirectional converters, while the circuit disclosed in the LM5170 does not allow seamless control between the two directions of the converter control, as is necessary in a programmable power supply as a current direction control input is necessary.

[0009] One aspect of the invention is a voltage error operational amplifier (Op Amp) with a series resistor connected to its output. A low value capacitor is connected to the output of the operational amplifier just enough to prevent high frequency oscillation of the voltage error operational amplifier that can occur due to the presence of the series resistor. A second aspect of the invention is a buffer operational amplifier with its positive input connected to one end of the series resistor and its output connected to its negative input to create a unity gain non-inverting buffer. Connected between the buffer operational amplifier output and the negative input of the voltage error operational amplifier. For better understanding we will refer to the output of the buffer operational amplifier as the buffer bus and its negative input as the loop bus. Both the voltage error operational amplifier and the buffer operational amplifier are powered by a positive auxiliary supply and a negative auxiliary supply, in this case +5V and -5V respectively, to allow both the operational amplifier inputs and outputs to have a bipolar range and to facilitate the circuit signal common (signal ground) to be connected to ground, i.e. to have a bipolar range with respect to the positive and negative of a common voltage point. The buffer bus is also the output signal of the converter current or charge control input, and it can also be said that a signal conversion circuit with the required voltage scaling and offset adjustment can be added between the buffer bus and the converter control input.

[0010] A third aspect of the invention is a number of other operational amplifiers that we will call limiting operational amplifiers whose outputs are connected to the loop bus through a diode connected in series with its output. These series connected diodes are polarized, so the role of a particular limiting operational amplifier is to reduce the converter control voltage to zero volts. The forward voltage of a diode is typically 0.35V. The feedback network of these limiting operational amplifiers is connected from the buffer bus to the negative input of the corresponding operational amplifier. Each of these operational amplifiers performs a unipolar limiting function such as forward current limiting, reverse current limiting, forward power limiting, reverse power limiting or reverse parallel resistance limiting. The current limiting operational amplifier can be equivalent to a gain operational amplifier with no capacitor used in its feedback network, only a resistor, because when used with an average current control converter the circuit control output essentially determines the output current. The positive input of these limiting operational amplifiers is connected to the appropriate reference voltage for the particular control loop, in this case the forward limiting operational amplifiers are connected to a positive polarity reference voltage and the reverse operational amplifiers are connected to a negative polarity reference voltage.

[0011] It is convenient to use a positive control voltage range for the forward direction of the converter and a negative control voltage range for the reverse direction, but it is also easy to use the opposite direction. It is also desirable to use rail-to-rail input and output op-amps so that their outputs can accurately reach either power supply rail. In this case, the forward limiting op-amp should be powered by a positive auxiliary supply and a negative voltage (e.g. -0.6V) that is slightly negative of the forward conduction voltage of the series diode. Similarly, in this case, the reverse limiting op-amp should be powered by a negative auxiliary supply and a positive voltage (e.g. +0.6V) that is slightly higher than the forward conduction voltage of the series diode.

[0012] A fourth aspect of the present invention is that simple circuits can be employed to generate these low voltage auxiliary supplies that are temperature compensated to match the temperature dependence of the forward conduction voltage of the series connected diode. Thus, at low converter current or power limit reference voltages, the ability of the forward limiting op-amp to oppose the reverse limiting op-amp is limited by the resistance of the op-amp output stage and the series diode.

[0013] A fifth aspect of the present invention is a circuit for precisely adjusting the reference input of a current limited unity gain op-amp to address the inaccuracy of the average control loop of each average current mode or charge mode controlled converter and to implement the current limit. A summing op-amp allows the error op-amp to adjust the current limit reference voltage to improve the accuracy of the programmable power current limit. A soft start circuit establishes a symmetrical ramp of the current limit as the on / off input goes low to implement the soft start function of the converter.

[0014] Adding an inverting configured op-amp circuit can be used to generate a negative polarity reference for the control mode from a positive polarity reference source, these can be differential op-amps to improve accuracy and reject noise and offset voltage between the reference source (typically a precision digital to analog converter) and the control circuit. Likewise, a non-inverting differential op-amp can be added to improve accuracy and reject noise and offset voltage of the positive reference input. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort based on these drawings.

[0016] Figure 1 is a circuit structure schematic diagram of a control circuit of a bidirectional power converter disclosed by the first aspect, the second aspect and the third aspect of the embodiment of the present application.

[0017] Figure 2is a simplified circuit diagram of a prior art analog PWM control IC Silicon General (now Microchip) SG1524. The circuit diagram discloses two error amplifiers connected directly together. The left error amplifier is an output voltage error amplifier, which is a trans-impedance amplifier. The current error amplifier is a low bandwidth, low gain differential amplifier with an input offset voltage of 200mV.

[0018] Figure 3 is a simplified circuit diagram of a prior art analog PWM control IC TL494. This IC uses two conventional operational amplifiers as voltage and current error amplifiers, with the anodes of diodes connected in series with their outputs, and the cathodes connected together and pulled down by a constant current sink of 0.7mA.

[0019] Figure 4 is a logic block diagram of a prior art digital control method involving a main voltage control loop, which measures the output voltage Vs from the desired voltage set input Vset to produce a voltage error value, which is amplified by a transfer function Gv and then input to a pulse width modulator Kpwm. Other various control loops, such as a positive current loop with gain Gc+, act to reduce the voltage set input Vset of the voltage loop to limit the load current in the positive or negative direction. As a result, the voltage control loop and another control loop tend to be active at the same time.

[0020] Figure 5 is a loop selection block diagram of a prior art digital control method involving a loop selection block, which selects which loop controls the modulation block according to an algorithm. If this is to be implemented in a physical circuit rather than a digital processor, then comparators, logic and switches are required to create the algorithm.

[0021] Figure 6 is a simplified schematic diagram of an average current mode controlled converter from Lloyd Dixon’s article “Average current mode control of switching power supplies”.

[0022] Figure 7 is a simplified diagram of the control method of the LM5170 average current control IC for a 2 Phase interleaved bi-directional Buck or Boost converter.

[0023] Figure 8is a system block diagram of a bidirectional power converter disclosed by the embodiment of the present application, which is composed of several DC-DC converters connected in parallel, each of which has its own average current controller. The output current of the power supply is detected by a current shunt, and the output voltage thereof is detected by a voltage detection lead. The signal conditioning and calculation circuit processes these inputs as well as various reference voltage inputs to provide appropriate scaling and polarized reference input voltages for the analog control system.

[0024] Figure 9 is a voltage and current diagram for illustrating the working mode of the bidirectional programmable power supply disclosed by the embodiment of the present application.

[0025] Figure 10 is a circuit structure schematic diagram of an auxiliary power supply circuit disclosed by the fourth aspect of the embodiment of the present application.

[0026] Figure 11 is a circuit structure schematic diagram of a fine tuning circuit disclosed by the fifth aspect of the embodiment of the present application. DETAILED DESCRIPTION

[0027] In order to make the person skilled in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor shall fall within the protection scope of the present application.

[0028] Embodiment one

[0029] The embodiment of the present application discloses a control circuit of a bidirectional power converter, which comprises a first aspect, a second aspect and a third aspect, and the basic schematic diagram is as shown in Figure 1 .

[0030] The first aspect of the present application is a voltage error operational amplifier (Op Amp) 101, which has a series-connected resistor 103 and a capacitor 104, the first terminal of the resistor 103 is connected to the output of the voltage error operational amplifier, the first terminal of the capacitor 104 is also connected to the output of the voltage error operational amplifier, and its second terminal is connected to the negative input pin of the operational amplifier, and has sufficient capacitance to prevent high-frequency oscillation of the operational amplifier that may occur due to the presence of the series resistor. The first terminal of the voltage loop gain determining resistor 106 is connected to the negative input of the voltage error operational amplifier 101, and the second terminal thereof is connected to the output of the voltage sensing circuit, which scales and buffers the output voltage of the converter for the control circuit. The voltage reference input 102 is connected to the positive input pin of the voltage error operational amplifier 101.

[0031] A second aspect of the invention is a buffer operational amplifier 107 whose positive input is connected to the second terminal of the series resistor 103 and whose output is connected to its negative input to create a unity gain non-inverting voltage buffer. The first terminal of the resistors and capacitors of the voltage loop feedback compensation network of the voltage error operational amplifier 105 is connected to the output of the buffer operational amplifier while its second terminal is connected to the negative input of the voltage error operational amplifier. For better understanding we will call the output of the buffer operational amplifier the buffer bus 115 while its negative input will be called the loop bus 114. Both the voltage error operational amplifier operational amplifier 101 and the buffer error operational amplifier operational amplifier 107 are powered by a positive and negative auxiliary power supply, in this example +5V and -5V respectively, to allow both the operational amplifier inputs and outputs to have a bipolar range, which can be positive or negative with respect to a common voltage point which is most conveniently the circuit signal common or signal ground. The voltage of the buffer bus 115 is also the output signal of the converter current or charge control input, although a separate buffer operational amplifier could be used, it should be said that a voltage scaling and offset adjustment operational amplifier could be added between the buffer bus and the converter control input.

[0032] A third aspect of the invention is a plurality of other limiting operational amplifiers 108 whose outputs are connected to the loop bus 115 via series diodes 109, one terminal of each diode 109 is connected to one of the limiting operational amplifier outputs and their second terminal is connected to the loop bus. These diodes are unipolar, so the role of a particular limiting operational amplifier is to reduce the control voltage of the loop bus to zero volts. Ideally these diodes will have a small forward voltage, so small signal Schottky diodes with a forward voltage of typically 0.35 volts are preferred. The compensation feedback network 111 of these operational amplifiers must have some series resistance, the first terminal of each compensation feedback network 111 is connected to the buffer bus and their second terminal is connected to the negative input of the corresponding operational amplifier. Each of these operational amplifiers performs a unipolar limiting function such as forward current limiting, reverse current limiting, forward power limiting, reverse power limiting or reverse parallel resistance limiting. The current limiting operational amplifiers can be configured as unity gain operational amplifiers with no capacitor in their feedback compensation network, like the average current control converter, whose output current is proportional to the control circuit control voltage. For limiting operational amplifiers 108 that are not unity gain, the first terminal of the gain control resistor 113 is connected to the negative input of the operational amplifier 108 and its second terminal is connected to the appropriate output sampling circuit, such as an output power sampling circuit, or a current sampling circuit.

[0033] It is convenient to use the positive control voltage range as the forward direction of operation of the converter, although the opposite voltage range can be used just as easily, and rail-to-rail input and output op-amps are preferred so that their outputs can go accurately to either supply voltage. In this case, the forward limiting op-amps should be powered by a substantially positive auxiliary supply and a negative voltage that is substantially no more positive than the forward conduction voltage of a series-connected diode (e.g. -0.6V). Similarly, the reverse limiting op-amps should be powered by a substantially negative auxiliary supply and a positive voltage that is substantially no more negative than the forward conduction voltage of a series-connected diode (e.g. +0.6V). Input clamping diodes 112 of the appropriate polarity are also connected to the negative input of each limiting op-amp 108, so that these inputs do not exceed the common-mode range of the op-amps during transient conditions. The positive input of each of these limiting op-amps is connected to the appropriate reference voltage 110 for the particular control loop, and in this case the forward limiting op-amps are connected to a positive polarity reference voltage, while the reverse op-amps are connected to a negative polarity reference voltage.

[0034] Figure 8 A block diagram of a partially programmable power supply consisting of multiple DC-DC converters 1 connected in parallel, each containing its own average current controller is shown. The DC-DC converters have a supply input 2 and a load output 3 across an output capacitor 4. A signal conditioning and calculation circuit block 7 processes these inputs as well as various reference voltage inputs 9 to provide appropriately scaled and polarized reference input voltages to the analog control system 10 that is the subject of this invention. The negative polarity reference for the reverse limiting op-amps is generated from a positive polarity reference source, and these op-amps can be differential op-amps to improve accuracy and suppress noise and offset voltages between the reference sources, which are typically precision digital-to-analog converters. Similarly, in-phase differential op-amps can be added to the circuit block 7 to improve accuracy and suppress noise and offset voltages as references for the forward limiting op-amps. This block should also include a multiplier to calculate the output power of the programmable power supply, and in the case of reverse constant resistance limiting op-amp usage of reference inputs; a circuit that multiplies the output voltage by the constant resistance reference voltage. A signal conversion circuit block 11 scales and levels the current control signals to the requirements of the control inputs of the converter average current control circuits.

[0035] The novelty of this circuit and the explanation of its operation are as follows: Figure 9A diagram showing the operating modes of a bidirectional DC programmable power supply (PPS) is shown. The primary operating mode is constant voltage mode (CV), in which the control circuit maintains the output voltage constant, regardless of whether the load current is sourced from the PPS (forward) or sunk by the PPS (reverse). The PPS will have a maximum output voltage Vmax and a CV set point Vset that can be adjusted from zero volts to Vmax. The PPS will also have maximum forward and reverse current limits +Imax and -Imax, power limits +Pmax and -Pmax, and adjustable set points +Iset, -Iset, +Pset, and -Pset that can also be adjusted from near zero to the maximum values to implement forward and reverse constant current (CC) and constant power (CP) modes. In addition, the DC PPS will typically have a parallel reverse constant resistance mode (CR) mode that can be adjusted from a minimum value Rmin to infinity. There can also be a series forward CR mode, which is not the subject of this document. The output operation of the PPS requires regulation through the control circuit to be accurately at one of the adjustable set points of one of the modes at any time and to transition from one mode to another mode quickly and seamlessly without oscillating at the boundaries between the various modes. Figure 1The described analog control circuit achieves this with an output voltage error operational amplifier (OpAmp) having a first terminal of resistor 103 connected to its output terminal and a second terminal of the resistor connected to the Oring bus 114. The voltage of the loop bus is used to control the output current of the PPS converter, which is directly proportional to the output current value if all the controlled converters use an average current control loop. The output of the other control mode limiting OpAmps is connected to this second terminal of resistor 103 via series and properly polarized diodes 109, so that they can bring the control voltage close to zero volts to adjust the output current set point of each of the other control modes. The second novelty of the invention is that a buffer OpAmp 107 is placed between the loop bus 114 and the buffer bus 115, and all the compensation feedback networks 105 and 111 of all the control mode OpAmps, including the voltage error OpAmp, are connected to the buffer OpAmp 107. This prevents the compensation feedback networks 105 and 111 from affecting the voltage of the loop bus, and the low output impedance of the buffer OpAmp 107 also effectively decouples the compensation feedback networks from each other. When one of the limiting error OpAmps 108 other than the voltage error OpAmp 101 is controlling the converter current, the error voltage OpAmp 101 outputs a voltage that reaches one of its auxiliary supply voltage rails, so it is no longer controlling the converter output current. Since the compensation feedback networks 105 and 111 are not driven by the error OpAmps, the output voltage of all the error OpAmps can change very quickly and is only limited by their specified slew rate, so that the control circuit can change from one control mode to another control mode. This greatly reduces the overshoot of the converter output voltage and current when the control mode is switched from one mode to another. Since the loop bus 114 is not loaded by the various compensation feedback networks, and since the low output impedance of the buffer OpAmp effectively isolates the networks from each other, oscillations at the boundaries between modes are eliminated. The third novelty of the invention is that the opposite auxiliary supply voltage of the forward and reverse limiting error OpAmps (CC, CP, and CR) is adjusted to be only slightly greater than the forward conduction voltage of the series diode connected in series with it. This prevents conflicts between the forward and reverse limiting OpAmps when the mode setting value is close to zero volts. The series connected diode and the resistance of the OpAmp output stage will be sufficient to limit the conflict current to less than the current that the control error OpAmp can source or sink. For example, when the converter is operating forward and one of the limiting OpAmps is controlling the output current of the converter, the error OpAmp output will be at its forward auxiliary supply voltage, and only the forward limiting OpAmp can limit the control voltage of the loop bus and the buffer bus.

[0036] Embodiment Two

[0037] A fourth aspect of the present invention is a circuit that can be used to generate small value auxiliary supply voltages for positive and negative limiting operational amplifiers as shown in Figure 10 Bias diodes 201. The value of the resistors must be low enough so that the current flowing through them is greater than the current required by all of the connected operational amplifier auxiliary supply pins. The diodes must have a slightly higher forward conduction voltage than the series connected diodes 109, so it is preferable to use silicon diodes. The type of diode can be chosen to achieve the desired auxiliary supply voltage, for example 0.6V. Capacitors 203 act as filtering and energy storage components for the auxiliary supplies to ensure that their voltages have minimal ripple and noise. One advantage of this type of low voltage auxiliary supply circuit is that these auxiliary supply voltages will vary with temperature to match the temperature dependent forward voltage of the series connected diodes 109, as these auxiliary voltages are determined by the temperature dependent forward conduction voltage of the diodes 109.

[0038] Example Three

[0039] A fifth aspect of the invention is a circuit for fine tuning the reference input of a current limit unity gain operational amplifier to address the inaccuracy of the average control loop of individual average current mode or charge mode controlled converters and for implementing current limit. Two current limit regulating operational amplifiers 301 compare the actual sensed output current signal to a current limit reference voltage. The first terminal of a feedback compensation network 302 is connected to the respective output pin of these operational amplifiers and its second terminal is connected to the negative input pin. The first terminal of gain resistors 303 is connected to the respective regulating operational amplifier negative input pin and their second terminal is connected to the low impedance signal of the sensed output current. The first terminal of a voltage divider network 304 is connected to the corresponding current limit reference signal, the second terminal is connected to the positive input of the corresponding current limit regulating operational amplifier and the third terminal is connected to the signal common reference point. The output of the current limit regulating operational amplifiers is connected to the first input of the appropriate summing operational amplifier 305. The second input of each summing operational amplifier 305 is connected to the respective current limit reference voltage input of the circuit. The input gain from the error operational amplifier to the summing operational amplifier should be low, for example -5%, so the operational amplifier can only fine tune the current reference voltage, while the input gain from the current reference voltage is typically -1. The first terminal of resistor 306 is connected to the output of the summing operational amplifier and the second terminal of resistor 306 is connected to the respective adjusted current limit reference output of the circuit. A soft start capacitor 307 is initially discharged by a switching device 309 upon receiving a low switch on input signal and is charged by a first terminal of a small current source 308, which can be a high value resistor, and a second terminal connected to a higher value auxiliary supply voltage, for example 15V. The positive input pin of a unity gain non-inverting operational amplifier 310 is also connected to the soft start capacitor 307 and its output pin is connected through a first terminal of a low forward voltage diode 311 and a second terminal to the output pin of the non-inverting unity gain operational amplifier 310, which diode is polarized to pull down the adjusted forward current limit reference output to zero volts when the soft start capacitor is discharged. The negative input of a unity gain inverting operational amplifier 312 is also connected through a series resistor to the output pin of the buffer operational amplifier 310. The second terminal is connected to the reverse current limit adjusted reference output and the diode is polarized to pull up the reverse current limit adjusted reference output to zero volts when the soft start capacitor is discharged. In this way, a current limit symmetric slope can be achieved after the switch on / off input goes low, thus enabling the soft start function of the converter. It should be noted that due to the nature of the summing operational amplifier being an inverting configuration, opposite polarity current reference signals are required to be input to the circuit.Preferably differential inverting operational amplifier type, can be part of the signal conditioning and computation circuit block 7, and used to generate from a single positive reference source a negative polarized current reference signal for the positive current limit reference adjustment circuit, while the negative current limit reference input can be handled by a non-inverting operational amplifier, also preferably a differential type operational amplifier.

[0040] Embodiment four

[0041] The embodiment of the present application discloses a control system of a bidirectional power converter, comprising a control circuit of a bidirectional power converter as described in embodiment one, a circuit for generating a small auxiliary power voltage for positive and negative limit operational amplifiers as described in embodiment two, and a circuit for accurately adjusting the reference input of the current limit unit gain operational amplifier as described in embodiment three.

[0042] The embodiment of the present application discloses the content disclosed only for the preferred embodiment of the present application, only for the description of the technical solutions of the present application, and not for the limitation; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand; the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced; and the modification or replacement does not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A control system of a bidirectional power converter comprising a control circuit for controlling a bidirectional DC-DC converter, characterized in that, The control circuit comprises a voltage error operational amplifier, a resistor, a first capacitor, a plurality of series diodes and a plurality of limiting operational amplifiers; The voltage error operational amplifier is configured to compare an output voltage of the converter with a reference voltage; A first end of the resistor is connected to an output of the voltage error operational amplifier; The first capacitor is connected between the output of the voltage error operational amplifier and a negative input of the voltage error operational amplifier; Each of the limiting operational amplifiers is associated with a respective feedback compensation network, and further comprises a unity-gain non-inverting buffer operational amplifier, a positive input of the buffer operational amplifier is connected to a second end of the resistor, and an output of the buffer operational amplifier is connected to a negative input of the buffer operational amplifier and to a terminal of at least one of the feedback compensation networks, wherein the output of the buffer operational amplifier provides an output signal to control current in the converter; The plurality of series diodes are divided into two groups, a negative pole of series diodes in one group is connected to an output of a first type of limiting operational amplifier for limiting forward output current, and a positive pole of the series diodes in the one group is commonly connected to a positive input of the buffer operational amplifier; a positive pole of series diodes in the other group is connected to an output of a second type of limiting operational amplifier for limiting reverse output current, and a negative pole of the series diodes in the other group is commonly connected to the positive input of the buffer operational amplifier; so that at least one series diode is in series with an output of a corresponding limiting operational amplifier, and is polarized according to a function of the corresponding limiting operational amplifier, the function limiting the output of the limiting operational amplifier to control a forward direction or a reverse direction of the converter output current; The output of the buffer operational amplifier is also connected to a terminal of a voltage error operational amplifier feedback compensation network; An auxiliary power supply pin of each of the limiting operational amplifiers is connected to an auxiliary power supply, a value of the auxiliary power supply is selected so that each of the limiting operational amplifiers can only limit the converter output in one direction, and so that the converter output current is controlled to a value close to zero by each of the limiting operational amplifiers; The first type of limiting operational amplifier in the limiting operational amplifiers is configured to limit forward output current, and is powered by a positive auxiliary power supply and a negative auxiliary power supply slightly higher than a forward conduction voltage of the series diodes as auxiliary power supplies; the second type of limiting operational amplifier in the limiting operational amplifiers is configured to limit reverse output current, and is powered by a negative auxiliary power supply and a positive auxiliary power supply slightly higher than the forward conduction voltage of the series diodes as auxiliary power supplies.

2. The control system of claim 1, wherein, At least one of the limiting operational amplifiers has a first positive input connected to a voltage reference, and a second negative input connected to another terminal of the feedback compensation network, the feedback compensation network comprises a feedback resistor, another terminal of the feedback resistor is connected to a negative input of the limiting operational amplifier.

3. The control system of claim 1, wherein, Wherein at least one of the negative inputs of the limiting operational amplifiers is connected to a signal representing the converter output through a gain resistor, such that the control circuit implements at least one selected from the group of functions: forward current limit, reverse current limit, forward power limit, reverse power limit and reverse constant resistance limit; the signal is selected from the group of output current sample signal, output power sample signal of the converter.

4. The control system of claim 1, wherein, Wherein the operational amplifier is a rail-to-rail input and output type operational amplifier.

5. The control system of claim 1, wherein, Wherein the series diode is a small signal Schottky diode.

6. The control system of claim 1, wherein, Wherein the auxiliary power supply pins of the voltage error operational amplifier and the buffer operational amplifier are connected to an auxiliary power supply, the value of the auxiliary power supply enables the input and output voltages of the voltage error operational amplifier and the buffer operational amplifier to cover the bipolar range, in turn allowing control of the forward direction of the converter output current and the reverse direction of the converter output current in the DC-DC converter.

7. The control system of claim 1, wherein, Wherein the negative input pins of the limiting operational amplifiers are protected from the voltage applied thereto exceeding its common mode range by a properly polarized forward or reverse clamping diode connected to the negative input pins of the limiting operational amplifiers, one terminal of the clamping diode is connected to the negative input pin of the limiting operational amplifier, and the other terminal of the clamping diode is connected to the signal ground or signal common.

8. The control system of claim 7, wherein, Wherein the feedback compensation network has a selectable resistance value such that the current capability of the clamping diode and the output of the buffer operational amplifier is not exceeded.

9. The control system of any one of claims 1-8, wherein, Also included is a circuit for providing an auxiliary power supply for one or more of the limiting operational amplifiers, which includes a bias diode with a forward conduction voltage greater than the forward conduction voltage of the series diode, one terminal of the bias diode is connected to the signal common, and the other terminal of the bias diode is connected to the first terminal of the feedback compensation resistor in the circuit of the auxiliary power supply, the feedback compensation resistor acts as a current source for forward biasing the bias diode, the second terminal of the feedback compensation resistor is connected to the auxiliary power supply, and a second capacitor connected in parallel with the bias diode is also included, the second capacitor is used to filter and store energy for the auxiliary power supply.

10. The control system of any one of claims 1-8, wherein, Also included is a circuit for generating an adjusted reference voltage for forward or reverse current limit in the control circuit, which includes first and second operational amplifiers and two inverting adder operational amplifiers, the first operational amplifier generates an output proportional to the difference between the forward current reference, the first inverting adder operational amplifier adds the forward current limit reference input and the output of the first operational amplifier, and the second inverting adder operational amplifier adds the reverse current limit reference input and the output of the second operational amplifier.

11. The control system of claim 10, wherein, The circuit for adjusting the reference voltage also has a bidirectional current soft start function: further comprising a third capacitor, one terminal of the third capacitor is connected to a signal ground or a signal common end, and a second terminal of the third capacitor is connected to a first terminal of a current source, a second terminal of the current source is connected to a main auxiliary power supply with a higher voltage than the auxiliary power supply, and the third capacitor is connected in parallel with a switching device configured to selectively discharge the third capacitor; a non-inverting operational amplifier has its negative input connected to its output and its positive input connected to the third capacitor; an inverting operational amplifier has its negative input connected to the output of the non-inverting operational amplifier and its positive input connected to the signal ground or the signal common end. A first diode has a terminal connected to the output of the non-inverting operational amplifier and is polarized to pull the value of the adjusted current reference voltage towards zero, and a second diode has a terminal connected to the output of the inverting operational amplifier and is polarized to pull the value of the adjusted current reference voltage towards zero.

12. The control system of claim 1, wherein, Each of the feedback compensation networks comprises at least one resistor, or at least one resistor and at least one capacitor.

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