GB2590693A

GB2590693A - A resonant current control system

Info

Publication number: GB2590693A
Application number: GB1919288.9A
Authority: GB
Inventors: John Peto Raymond
Original assignee: Quepal Ltd
Current assignee: Quepal Ltd
Priority date: 2019-12-24
Filing date: 2019-12-24
Publication date: 2021-07-07
Anticipated expiration: 2039-12-24
Also published as: GB201919288D0; GB2590693B

Abstract

A resonant current controller 10 provides first soft I1S and second soft I2S and first hard I1H and second hard I2H input signals to respective current drivers 12, 14. The current drivers generate current pulses in response to the input signals and as prescribed by a sequence driver 16. Current pulses supplied from current drivers are output as a continuous train of pulses (Fig. 8) of energy to an operational circuit 18 which includes an L-C circuit 20 which is maintained in a resonant state. The controller provides at least first and second soft and hard input signals in order to remove situations where stalling of the resonant current control system can occur. The resonant current control system may include a step down or buck converter so as to enable voltage to be varied over an optimum range input range thereby reducing losses.

Description

A Resonant Current Control System

Field

The present invention relates to a resonant current control system and more particularly, but not exclusively, the invention relates to a resonant control system for example for use with electric power conversion.

Background

Resonant power conversion techniques are very efficient when compared with existing power control systems. However, reliability of resonant power conversion systems, due to problems encountered when attempting to maintain continuous operation of the resonant circuit, is very difficult to achieve under all conditions that can arise due to variations occurring in resonant operation.

Another advantage of resonant power conversion systems is that they capable of almost instantaneously adjusting feedback times in the time domain for almost all types of switching transients. From an implementation point of view, timers that are utilised in resonant power conversion systems, may be implemented in hardware, software or a combination of these.

Prior Art

Our granted European patent EP 2 641 321 (Quepal limited) describes a voltage regulator for regulation both of AC and DC voltages which uses a repetitive switching signal to control a switch that allows current to be supplied to a reservoir capacitor. A module contains a dual inductor which includes first and second windings around a common core. A switching signal can be suitably voltage restored to provide a signal suitable for controlling and operating the switches.

However, despite being successful there are occasionally transient conditions that are encountered that can lead to instability or systems stalling.

An aim of the invention is to provide a resonant current control system that is able to operate across all types of switching and transient conditions.

Another aim of the invention is to provide a resonant current control system that is capable of providing at least first and second soft and hard input signals in order to remove situations where stalling of the resonant current control system can occur.

Summary of the invention

According to a first aspect of the invention there is provided a resonant current control system provides at least first and second soft and hard input signals to respective current drivers, each of the current drivers generate current pulses in response to the input signals and as prescribed by a respective sequence driver; the current pulses are supplied as a continuous train of pulses of energy to an operational circuit which includes an L-C circuit in resonance, the pulses ensuring that a continuous reserve of energy is available for commutation to the operational circuit at instants when resonance in the L-C circuit is compromised, so that energy is transferred from the reserve to the L-C circuit when required to maintain continuous resonance.

In some embodiments the sequence drivers control the phase and/or magnitude and/or frequency of input signal pulses so as to initiate a soft transition for the remainder.

Ideally a plurality of timers is operative to synchronise pulses so that the resonant L-C circuit continues to operate in a resonance mode in response to a disturbance that interferes with commutation.

Even when the disturbance is a current or a voltage transition event the timers ensure generation of pulses which provide a supply of energy that ensures any shortfall arising as a result of transients or other forms of interference which may lead to loss of commutation.

Optionally a current optimiser is operative to switch a negative current supply at a desired instant when energy is required. Ideally the current optimiser operates as a tolerance controller within a predefined optimum electromagnetic compatibility (EMC) emissions range.

In some embodiments a detector senses an error in an input voltage or input current and applies a correction factor to at least one pulse at an instant when additional energy is required, thereby maintaining continuous resonance.

Optionally a means is provided for transmitting a warning signal when an error is detected. In some embodiments a self-tuning circuit is provided to oversee a timing instant of a voltage and/or current input and operative to maintain continuous resonance.

Preferably the self-tuning circuit includes a look-up table to update a timing instant of a voltage and/or current input and operative to maintain continuous resonance.

Optionally the look up table may be compared with previous versions and operate in conjunction with software configured as an algorithm to record and predict changes in operating characteristics and/or conditions that may be monitored to indicate a risk of imminent, gradual or sudden system changes. Variables may be recorded, saved and reported to alert onset of maintenance requirement or failure issues.

Optionally a sensor is provided to detect wear and supplies a feedback alert signal which signal is capable of being used to modify an input to the self-tuning circuit.

A switching device may be deployed for modifying soft voltage input. However, the system in a preferred embodiment is adapted to monitor conditions, such as current, and to input soft pulses in order to maintain resonance.

In some embodiments of the resonant components in the control system there is provided a step down or Buck converter so as to enable voltage to be varied over an optimum input range hereby reducing losses.

In some embodiments of the resonant current control system there is a step up or boost converters which may also include a Buck converter.

A transformer is ideally provided to isolate the system. An advantage of this is that the transformer is able to offer more energy as a reservoir when switched to supply additional energy.

In some embodiments control circuits ensure the resonant circuits remain naturally resonant.

In some embodiments of the resonant current control the resonant components are forced to operate in a state of resonance.

Ideally at least one synchronous rectifier is operative to improve efficiency of rectification when the system is used with transformers as part of a power conversion system.

The system is ideally suited for use in four quadrant systems and is particularly well suited for use with electric motors which operate in all forward braking, forward motoring, reverse motoring and reverse braking modes.

In some embodiments the resonant current control system includes at least one timing means or timer which is implemented as a hardware device. Ideally the at least one timer is implemented partly in hardware operating under control of a microprocessor in accordance with software.

When implemented the resonant current control system is operative in all four quadrants and it also applies to synchronous rectification and four quadrant operation.

Preferably the resonant current control system has a timing adjustment feedback that takes account of variations in tolerances in order to reduce electromagnetic interference (EMI).

The control system provides a method that guarantees operation of a resonant system under all conditions.

A step down or Buck converter is considered useful in the understanding of operation. However, the method also applies to step up or boost converters as well as transformer isolated systems. The invention may also be deployed in resonant circuits that are naturally resonant or are forced to be resonant.

Preferred embodiments of the invention will now be described with reference to the following Figures in which:

Brief Description of the drawings

Figure 1 shows an example of a typical step down converter circuit; Figure 2 shows examples of voltage and current waveform for nett positive output current from D; Figure 3 shows an example of a voltage transition at B for different turn off currents ILI in inductor L1 where Vout > 1/2 Vin; Figure 4 shows the voltage transition for different turn off currents IL1 in inductor L1 where Vout = 1⁄2 yin; Figure 5 shows the voltage transition for different turn off currents IL1 in inductor L1 where Vout <1/2 yin, Figure 6 shows the voltage conditions of a potential fail at resonance transition from low to high; Figure 7 shows a block diagram representation of the hardware implementation of the Resonant Current synchroniser; Figure 8 shows the waveforms present in correct operation of the resonant circuit; and Figure 9 shows examples of waveforms present in recovered operation of the resonant circuit.

Detailed Description of preferred embodiments of the invention Referring to Figure 1 there is shown an example of a step down converter circuit 100 which includes a resonant current controller 10 which provides first soft (I1S) and second soft (125) and first hard (I1H) and second hard (I2H) input signals to respective current drivers 12 and 14. The current drivers 12 and 14 generate current pulses in response to the input signals (I15, I25, I1H, I2H) and as prescribed by a sequence driver 16. Current pulses supplied from current drivers 12 and 14 are output as a continuous train of pulses (Figure 8) of energy to an operational circuit 18 which includes an L-C circuit 20 which is maintained in a resonant state.

The current pulses from current drivers 12 and 14 ensure that a continuous reservoir of energy is available for commutation to the operational circuit 18 and in particular at an instant when resonance in the L-C circuit 20 is compromised.

Resonance in the operational circuit 18 can become compromised, for example when resonance becomes destabilised which can occur in response to a variation in load or problems in supplying current to one or more components in the circuit in Figure 7 resonant energy reduces in amplitude thereby risking dissipation of resonant energy. Destabilisation may occur due to a transient in a load or a variation in input current or input voltage.

Such transients can result in a sudden loss of energy being transferred and are overcome by the invention by providing a constantly available supply of energy in the form of a reservoir from which energy can be drawn when required by the L-C circuit 20 so as to maintain its continuous operation at resonance. The gate drivers 12 and 14 implement when to apply a hard or soft input signal in order to switch respective first and second transistors 01 and 02. 01 and 02 are shown as bipolar but these may be based on any suitable switching technology.

Figure 2 shows current and voltage waveforms that correspond to output commands from timer sequencer 58 shown in Figure 7 In this sense it is useful to analyse low to high' voltage transitions at point B in Figure 1 and by inference when the same conditions apply to the 'high to low' transition at point B in Figure 1.

Figures 3 to 6 show graphs of voltage transitions at point B, in Figure 1 for different turn off currents IL1 in inductor L1 and show a curve indicative of a system in natural resonance. Figure 3 is for a step down ratio where Vout is greater than 50% of Vin.

Figure 4 is where Vout is approximately the same as Vin. Figure 5 is where Vout is less than 50% of Vin.

Inspection of Figures 3, 4 and 5 show how the optimum resonance point varies with coil current and voltage transformation ratios. For minimum EMC generation and lowest switching losses it is desirable for the voltage transient at B to be as long as possible while at the same time meeting the top rail A so as to ensure lossless commutation of energy to/from Ql.

A resonance fail prevention timer 61 has a pre-set time period that is set to a value or a value slightly longer than a maximum permitted value to allow for tolerance issues. An advantage of this is that the system regains resonance of its own accord. However, if it fails to return to resonance then energy is supplied in a manner and an amount in order to enable commutation to take place in order that the system can again operate in a resonant state.

Figure 3 shows an example of waveforms with different inductance current IL1 at the instant of turn off. The higher the current the more rapid is the transition and the greater is a back EMF transient from low to high. As the current IL1 that is flowing at the instant of turn off decreases, the slope dV/dt becomes shallower, as can be seen in transient B in Figure 3.

At the optimum turn off instant of Q2 there is no current IL1 flowing in inductor L1, the voltage transition between bottom rail (VC) and top rail (VA) is dictated by the values of resonant components (L1, Cl, C2 and C3) that form the L-C circuit 20. The ratio of voltage out (Vout) to the voltage in (Vin) is: Vout >1/2 Vin.

Figure 4 shows an example of waveforms with different inductance current IL1 at the instant of turn off. The higher the current the more rapid is the transition, the greater is a back EMF transient from low to high. As the current IL1 that is flowing at the instant of turn off decreases, the slope dV/dt becomes shallower, as can be seen in transient B in Figure 4.

At the optimum turn off instant of 02 there is no current IL1 flows in inductor L1, the voltage transition between bottom rail (VC) and top rail (VA) is dictated by the values of resonant components (L1, C1, C2 and C3) that form the L-C circuit 20. The ratio of voltage out (Vout) to the voltage in (Vin) is: Vout =1/2 Vin.

The operation with switch off of 02 at zero IL1 is marginal due to losses in the resonant components. A small inductor current IL1 ensures reliable commutation.

Figure 5 shows an example of waveforms with different inductance currents IL1 at turn off. This is for a step down ratio where Vout is less than 50% of Vin. The higher the current IL1 in inductor L1 at the point of turn off, the quicker is the transition from low to high. As the current IL1 that flows at the point of turn off decreases, the slope becomes shallower as a result of the system losing energy and becoming less resonant.

At the instant when there is no current IL1 flows in the inductor Li, at the moment of turn off, the time of voltage transition is dictated by the values of the resonant components (in Figure 1) and stray capacitances and inductances and the ratio of the output voltage Vout to the input voltage Vin. The resonance fail prevention timer time period is set to this value, or a value slightly longer than this, to allow for tolerance issues and natural recovery.

From the waveforms shown in Figure 5 it is clear that resonance will fail to commutate correctly unless a certain amount of current IL1 is flowing in the inductor. The value set into the bottom on timer 64 enables this.

Figure 6 illustrates the voltage conditions of a potential failure to achieve a resonance transition from low to high. This occurs, for example due to a turn off decision of bottom transistor 02, being incorrectly determined from an instantaneous operating state of the resonant circuitry, for example as shown in Figure 1.

It can be seen in Figure 6 the resonant voltage is not quite sufficient to reach low or zero point across the top of transistor Q1, at which instant lossless switching would occur. However, as a result the transistor Q1 not being switched to a conductive state resonance is not achieved and the operation of the circuit in Figure 1 fails, with the resulting energy in the L-C circuit dissipating.

When the resonance fails the resonance fail prevention timer 61 in Figure 7 time period is exceeded, a soft drive of 01 is initiated to assist it to return to a resonant state. When this occurs the voltage difference (VA-VB) is reduced below the voltage threshold of lossless commutation for 01 and hard switching circuits in current driver P1, 12, take over and disable the previous switching regime.

The condition of such instability is detected by the occurrence of a soft switching event, 22, and the timing regime of switching transistors 01 and 02 are altered to ensure subsequent switching results in a correction to the transient voltages, currents and zero volt commutation operation of the resonant circuit in Figure 1.

Normal resonant operation requires there to be always sufficient current available within the resonant circuit Cl, C2 and L1 for a given ratio of Vout to Vin. The maximum time possible (the natural resonant time) for a low to high transition occurs when the switching occurs at the zero point of the inductor current IL1.

The actual time of the low to high transition. TL-H (shown in Figure 3 to 6), is the value of the natural resonant time less a factor related to the actual coil current at the point of turn off of 02 The function of ratio of Vout to Vin on optimum IL1inductor current levels are affected by actual values of L1, Cl and C2 as well as any other parasitic and secondary order effects, such as switching device capacitances, component and circuitry resistances and substrate diode reverse recovery times.

The variables that dictate the natural resonant time are also influenced by value of the inductor current IL1 that flows at the instant of switching of 02. The current time reduction value is zero when there is no inductor current IL1 flowing at point B in the circuit of Figure 1 which is also referred to as the initiation of the voltage transition point.

Figure 7 shows a block diagram of an embodiment of a resonant current synchroniser 50. This can be implemented in a microprocessor 56 or in hardware as described below or a combination of hardware and software. For the sake of convenience Figure 7 is described using hardware and comprises a resonant circuit 52 and is described below.

A resonant circuit 52 provides a driver signal to a resonant circuit monitor 54. A microprocessor 56 oversees collective control of a timing sequencer 58, a series of timers 61, 62. 63 and 64, collectively referred to as a timing block 60; and an output sequence logic driver 66. The timing block 60 includes a low to high fail prevention timer 61, a top on timer 62, a high to low fail prevention timer 63 and a bottom on timer 64. These separate timers are operative to supply the driver signals output sequence logic driver 66.

Figure 8 shows waveforms present in normal (Figure 8) and corrected (Figure 9) operation of waveforms of the resonant circuit. It can be seen that in Figure 8 the shape and amplitude of the resonant voltage cause the voltage to attempt to exceed more positive than the positive rail A permits and to go more negative with respect to the negative rail. Drive circuitry (Figure 7) interprets this as the correct conditions of a zero switching device voltage state and thereby turns on the switching devices (Figure 1) in a lossless turn on operation.

Figure 9 shows the waveforms present in the corrected or recovered operation of the resonant circuit in Figure 1. Referring again to Figure 5, the waveform that fails to ensure continued resonant operation is reviewed. The waveform illustrates the natural resonant time is not quite contacting the positive rail and so continues to decrease in voltage as the resonant energy shuttles between inductive and capacitive elements of the L-C resonant circuit 20.

Without the detection and correction that are applied by the present invention such a condition would result in cessation of the resonant operation of the circuitry. However the timer 61 that is initiated at the beginning of a low to high transition, reaches the end of its operational period and initiates a soft turn on of top switching device Q1. As a result of this, the voltage is switched towards the positive rail A at which instant the zero voltage switching conditions are met and the switching device 01 is able to be switched on as if it were operating in a normal lossless switching operation.

The invention has been described by way of example only and it will be appreciated that variation may be made to the aforementioned embodiments without departing from the scope of protection as defined by the claims.

Parts List resonant current controller 12 first current driver 14 second current driver 11 S first soft input signal second soft input signal 11 H first hard input signal I2H second hard input signal 16 current sequence driver 18 operational circuit L-C circuit 22 resonance fail detector 01 first switching transistor 02 second switching transistor resonant current synchroniser 52 resonant circuit 54 resonant circuit monitor 56 microprocessor 58 timing sequencer timing block 61 low to high fail prevention timer 62 top on timer 63 high to low fail prevention timer 64 bottom on timer 66 output sequence logic driver converter circuit 102 self-tuning circuit

Claims

Claims 1. A resonant current control system provides at least first and second soft and hard input signals to respective current drivers, each of the current drivers generate current pulses in response to the input signals and as prescribed by a respective sequence driver; the current pulses are supplied as a continuous train of pulses of energy to an operational circuit which includes an L-C circuit in resonance, the pulses ensuring that a continuous reserve of energy is available for commutation to the operational circuit at instants when resonance in the L-C circuit is compromised, so that energy is transferred from the reserve to the L-C circuit when required to maintain continuous resonance.
2. A resonant current control system according to claim 1 wherein the sequence drivers control the phase and/or magnitude and/or frequency of input signal pulses so as to initiate a soft transition for the remainder.
3. A resonant current control system according to claim 1 or 2 includes a plurality of timers which are operative to synchronise pulses so that the resonant L-C circuit continues to operate in a resonance mode in response to a disturbance that interferes with commutation.
4. A resonant current control system according to any preceding claim wherein the disturbance is a current or a voltage transition event.
5. A resonant current control system according to any preceding claim includes a current optimiser which switches a negative current supply at an instant of switching.
6. A resonant current control system according to claim 5 wherein a current optimiser which operates as a tolerance controller within a predefined optimum EMC emissions range.
7. A resonant current control system according to any preceding claim includes a detector which senses an error and applies a correction factor to at least one pulse at an instant when additional energy is required to maintain continuous resonance.
8. A resonant current control system according to any preceding claim wherein a warning signal is transmitted when an error is detected.
9. A resonant current control system according to any preceding claim includes a self-tuning circuit connected to update a timing instant of a voltage and/or current input and operative to maintain continuous resonance.
10. A resonant current control system according to any preceding claim wherein the self-tuning circuit includes a look-up table to update a timing instant of a voltage and/or current input and operative to maintain continuous resonance.
11. A resonant current control system according to claim 9 or 10 includes a sensor is provided for detecting wear which supplies a feedback alert signal which signal is used to modify and input to the self-tuning circuit.
12. A resonant current control system according to any preceding claim has a switching device for soft voltage modification.
13. A resonant current control system according to any preceding claim includes a step down or Buck converter so as to enable voltage to be varied over an optimum range input range thereby reducing losses.
14. A resonant current control system according to any preceding claim has a step up or boost converters.
15. A resonant current control system according to any preceding claim has at least one transformer isolated systems.
16. A resonant current control system according to any preceding claim wherein circuits wherein the resonant circuits are naturally resonant.
17. A resonant current control system according to any preceding claim wherein circuits where the resonant circuits are forced to be resonant.
18. A resonant current control system according to any preceding claim has at least one synchronous rectifier operative to improve efficiency of rectification and thereby allowing four quadrant operation.
19. A resonant current control system according to any preceding claim wherein at least one timer is implemented as a hardware device.
20. A resonant current control system according to any preceding claim wherein at least one timer is implemented as a microcontroller operating in accordance with software.
21. A resonant current control system according to any preceding claim is operative in all four quadrants thereby enabling forward and reverse operation.
22. A resonant current control system according to any preceding claim has a timing adjustment feedback takes variations of tolerances into account in order to reduce electromagnetic interference (EMI).
23 A resonant circuit control system according to any preceding claim wherein the rate of change of the resonant switching transient (dV/dt) at point B in the circuit of Figure 1, is used to modify one or more timing predictions.
24. A monitoring system includes the resonant current control system according to any preceding claim and a database for storing data derived from at least one variable in the system; a processor for processing the data and comparing data with a set of stored criteria in order to determine whether to issue an alert signal.
25. A monitoring system according to claim 24 wherein the data is stored on a database.